Abstract 30 - Exploration in a Changing Environment ASEG GSA Conf Sydney 1991 by GSAustralia

T H E A U S T R A L I A N S O C I E T Y OF EXPLORATION GEOPHYSICISTS 8th. C O N F E R E N C E A N D E X H I B I T I O N and

T H E GEOLOGICAL SOCIETY OF AUSTRALIA EXPLORATION SYMPOSIUM

ABSTRACTS Number 30

(Geological Society of Australia)

"Exploration in a Changing Environment" Sydney 1991

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T H E AUSTRALIAN SOCIETY OF EXPLORATION GEOPHYSICISTS 8th. CONFERENCE AND EXHIBITION and

T H E GEOLOGICAL SOCIETY OF AUSTRALIA EXPLORATION SYMPOSIUM

ABSTRACTS Number 30 (Geological Society of Australia)

Sponsored by Chamber of Mines & Energy of W.A. (Inc.)

"Exploration in a Changing Environment'

February 17-21, 1991 SyfJncy ( C o n v e n t i o n a n d K x h i b l t i o n ( a M i t r c I )a I 11 nv; 11 a i l>oin\ S> <lni >.

ASEG GSA 1991 CONFERENCE COMMITTEE

Back Row (left to right): Rex Hoare, Graham Butt, John Mulready, Ted Tyne, Dave Kirkham, Andrew Sutherland, Nigel Brown, Pat Hillsdon, Barry Smith. Front Row (left to right): Nicola Stewart, Keeva Vozoff, Tim Pippett, Wes Jamieson, Dave Pratt. CO-CHAIRMEN Wes Jamieson Tim Pippett

GSA CONVENOR Graham Taylor

SECRETARY Nigel Brown

CONFERENCE ORGANISER Conference Action Pty Ltd John Mulready Nicola Stewart

SUB COMMITTEES & CO-CHAIRMEN TECHNICAL Ted Tyne Keeva Vozoff Ken Glasson

PUBLICITY Graham Butt Ian Criss

EXHIBITIONS Pat Hillsdon Peter Brazier

TREASURER Laurel Tuckwell Derecke Palmer

SPONSORSHIP Dave Pratt Barry Smith

WORKSHOPS Andrew Sutherland Mike Smith

ACCOM/SOCIAL Rex Hoare

Technical Sub Committee Topic Organizers Petroleum Exploration

Minerals Exploration

Coal/Groundwater/Eng

Regional/Crustal/Geothermal

Andrew Nelson

Mike Smith

Peter Hatherly

Ted Lilley

Geoscience Education

Finance & Management

Computer Applications

Theoretical/Research

Malcolm Buck

Keith Skipper

Dave Pratt

Keeva Vozoff

Publications Co-ordinator Dave Kirkham

CONTENTS Page Abstract Summary Oral Papers (in program order) Plenary Session II

1(a) 1(b) 2(a) 2(b)

14 18 23

Advances in Petroleum Exploration Advances in Coal, Groundwater and Engineering Advances in Mineral Exploration Advances in Regional, Crustal and Geothermal

Plenary Session III

3(a) 3(b) 3(c) 3(d) 3(e) 4(a) 4(b) 4(c) 4(d)

31 36 41 45 49 52 56

4(e): 4(f) 5(a) 5(b) 5(c) 5(d) 5(e) 5(f):

Petroleum Exploration I - Seismic Data Processing Mineral Exploration I - Regional/Aeromagnetics Computer Applications I Petroleum Exploration II - Non-Seismic Methods Geoscience Education I Petroleum Exploration III - Seismic Data Processing Mineral Exploration II - Mineral Deposit Settings Computer Applications II Petroleum Exploration IV - Organic Petrology and Geochemistry Regional, Crustal and Geothermal I - Gravity, Magnetic and Geothermal Studies Geoscience Education II Petroleum Exploration V - Environmental Mineral Exploration III - Gravity/Borehole Studies Computer Applications III Petroleum Exploration VI - VSP and Tomography Regional, Cmstal and Geothermal II - West Australian Basins Geoscience Education III

59 67 70 74 77 79 84 86 89

Plenary Session IV

6(a) 6(b) 6(c) 6(d) 6(e)

97 100 106 109

6(f): 7(a): 7(b) 7(c) 7(d) 7(e) 7(f) 8(a) 8(b) 8(c) 8(d) 8(e)

Petroleum Exploration VII - Interpretation Methods Mineral Exploration IV - Geochemistry Computer Applications IV Exploration Management I - General Regional, Crustal and Geothermal III - Australian Basins: West, Central and East Geoscience Education IV Petroleum Exploration VIII - Reservoir and Source Rocl< Geochemistry Mineral Exploration V - Electromagnetic Interpretation Coal, Groundwater and Engineering I - Coal Exploration Management II - Legal Aspects Petroleum Exploration IX - Cretaceous to Recent Tectonics Theoretical Research Petroleum Exploration X - Seismic Data Processing Mineral Exploration VI - Airborne Resistivity Mapping Coal, Groundwater and Engineering II - Coal Petroleum Exploration XI - Cretaceous to Recent Tectonics Regional, Cmstal and Geothermal IV - Electrical Conductivity, Temperature and Petrology

112

115 118 123 125 129 132 135 137 139 146 152 154

Plenary Session V

157

9(a) 9(b) 9(c) 9(d)

160 163 167

9(e): 10(a) 10(b) 10(c) 10(d)

Petroleum Exploration XII - Interpretation Methods Mineral Exploration VII - Case Studies Coal, Groundwater and Engineering III - Groundwater Petroleum Exploration XIII - Seismic Data Acquisition and Case Histories Regional, Crustal and Geothermal V - Seismic Studies, Worldwide Petroleum Exploration XIV - Case Histories Mineral Exploration VIII - Case Studies Coal, Groundwater and Engineering IV - Engineering Regional, Crustal and Geothermal VI - Sediments and Stojcture of Basins and Rifts

171 173 178 181 191 194

Poster Papers (alphabetically by author) Petroleum Exploration Mineral Exploration Coal, Groundwater and Engineering Regional, Crustal and Geothermal Computer Applications

202 215 229 231 237

Standby Papers

239

Corporate Sponsors

242

Authors index

264

ABSTRACT SUMMARY Plenary Session II MINERAL AND PETROLEUM EXPLORATION AND ENVIRONMENTAL CO-EXISTENCE Reg C. Spngg ENVIRONMENTAL GEOSCIENCE Stanley H. Ward

Technical Session 1(a) Advances in Petroleum Exploration IMAGE PROCESSING OF INTERPRETED 3D SEISMIC DATA TO ENHANCE SUBTLE STRUCTURAL FEATURES/LINEATIONS Larry A. Tilbury and David Bush PALAEOGEOGRAPHIC, DEPOSITIONAL AND AGE CONTROLS ON THE COMPOSITION OF PETROLEUM SOURCE ROCKS AND THEIR DERIVED OILS: BASIS FOR A PREDICTIVE MODEL Trevor G. Powell and Roger E. Summons SANDBOX MODELS IN AIDING SEISMIC INTERPRETATION OF FAULT PATTERNS A. McCoss

12 13

Technical Session 1(b) Advances in Coal, Groundwater and Engineering ^ ^ ^ SALINITY MANAGEMENT IN NEW SOUTH WALES" AN UVbRVIEW T.J. Verhoeven I I A M S I N A^^^A^IE " EXAMINATION OF COAL MINE Joseph L Condon and George Schneider PO^R^^ DIRECT NON-INVASIVE GROUND WATER DETECTION TECHNOLOGY • ^r* /MJo I itALIA M. Shirov, A. Legchenko and G. Creer

Technical Session Advances in Mineral Exploration MAPPING WITH THE G E R I S AND G E O S C A N A I R C R A F T SCANNERS FOR MINERAL EXPLORATION AND MAPPING J.F.Huntington, M.D.Craig, J.N.Churchill, A.A.Green MASSIVE SULPHIDE EXPLORATION CASE HISTORIES MT. WINDSOR VOLCANIC BELT, NORTH QUEENSLAND Simon D. Beams C A I E HISTORY

SULPHIDE DISCOVERY: AN EXPLORATION

Stuart H. Robinson and Susan M. Belford

Technical Session 2(b) Advances in Regional, Crustal and Geothermal RIFTINT^^"^^'^^^'®'^ STRUCTURE OF MANTLE PLUMES AND CONTINENTAL Gregory A. Houseman PLUME TECTONICS AND THE DEVELOPMENT OF STABLE CONTINENTAL CRUST Robert I. Hill, Ian H. Campbell and Ross W. Griffiths ^ ^ ^ ^ SEISMIC REFLECTION/REFRACTION GRID P.E. Williamson, J.B. Willcox, J.B. Colwell and C.D.N. Collins

23 23 23

Plenary Session III AFIID^CREATTW^^^^^ M.J. Smith

MANAGING TO SURVIVE. SUCCEED, 25

CHAOS THEORY AND OPERATION: TERTIARY EDUCATION IN A POLITICISED, POLARISED ENVIRONMENT Ian Pllmer

Technical 3(a) I - Seismic Data Processing PetroieumSession Exploration THE ZERO VELOCITY LAYER: MIGRATION FROM IRREGULAR SURFACES Craig J. Beasley and Walt Lynn E.T. - A SLANT-STACK TRANSFORM OF THREE DIMENSIONAL DATA Brian Evans ACCURATE AMPLITUDE CALCULATIONS FOR TIME DOMAIN DM0 John C. Bancroft ANISOTROPIC WAVE PROPAGATION AND ZERO-OFFSET MIGRATION N.F. Uren, G.H.F. Gardner and JA. McDonald

28 29 29 30

Teclinicai Session 3(b) Mineral Exploration I - Regional/Aeromagnetics INTERPRETATION AND EXPLORATION SIGNIFICANCE OF THE 1988 EYRE PENINSULA AIRBORNE MAGNETIC SURVEY, SOUTH AUSTRALIA D.H. Tucker and R.G. Nelson REGIONAL AIRBORNE GEOPHYSICS, GEOLOGY AND INTERPRETED STRUCTURAL TRENDS, WESTERN VICTORIA R. Dalgarno, G. Pettifer and M. Bacchin NEW DEVELOPMENTS IN RESOLVING DETAIL IN AEROMAGNETIC DATA ST. Mudge A PRACTICAL APPROACH TO THE FILTERING OF AIRBORNE MAGNETIC DATA IN THE COBAR REGION OF NSW S.N. Sheard, J.R. Bishop and R.V. Kissitch

31 33 34 35

Technical Session 3(c) Computer Applications I APPLICATION OF FIELD COMPUTERS IN EXPLORATION PROGRAMS Andrew M. Foley, Robert M.S. White and Reginald J. Court MULTI-SENSOR MARINE GEOPHYSICAL PROFILING AND DIGITAL ACQUISITION USING SAS1 J. Lean and D.A. Pratt TRENDS IN DEVELOPMENT OF IMAGE PROCESSING SOFTWARE FOR PROCESSING OF GEOPHYSICS AND OTHER DATA Stuart Nixon SUPERCOMPUTERS IN SEISMIC DATA PROCESSING M. Stanley and R. Singh

36 37 38 40

Technical Session 3(d) Petroleum Exploration 11 - Non-Seismic Methods INTEGRATED ELECTROMAGNETIC AND SEISMIC METHODS FOR PETROLEUM EXPLORATION K.-M. Strack, A. Hoerdt, K. Vozoff, P.A. Wolfgram MAGNETOTELLURIC SOUNDINGS AND THE LEVY ALGORITHM J.P. Cull A COMPARISON OF FOURIER AND WIGNER-VILLE SIGNAL PROCESSING METHODS APPLIED TO A MAGNETOTELLURIC SURVEY OF THE KENMORE OIL FIELD I.J. Chant and L.M. Hastie IMAGE PROCESSED, HIGH RESOLUTION AIRBORNE MAGNETICS - A NEW TOOL FOR MAPPING STRUCTURE IN SEDIMENTARY BASINS Mike Etheridge, Don Pridmore, David Bush and Alasdair Cooke

41 41

42 44

Technical Session 3(e) Geoscience Education i EDUCATING FOR THE 21st CENTURY - THE IMPORTANCE OF EARTH SCIENCE R. Stutchbury

VII

A NEW APPROACH TO THE TEACHING OF GEOLOGY IN SCHOOLS W. Roberts GEOLOGY IN A SECONDARY COLLEGE AND ITS ASSOCIATION WITH THE PRIVATE SECTOR A. Perrin UNDERGRADUATE FIELD TRAINING AND REGIONAL GEOLOGICAL MAPPING: PUTTING THE TWO TOGETHER K.G. McQueen, W. Mayer, G. Taylor and M.C. Brown

46 47

Technical 4(a) lil - Seismic Data Processing PetroleumSession Exploration OFFSET DEPENDENT STATIC CORRECTIONS ON A CONTINENTAL SHELF EDGE 3D SEISMIC SURVEY M.G. Cousins, P.M. Whiting and T.J. Allen TRANSFORM TECHNIQUES APPLIED TO THE ATTENUATION OF LONG PERIOD MULTIPLES Paul Haskey and Jon Ashdown MULTIPLE SUPPRESSION BY A WAVE-EQUATION-EXTRAPOLATION METHOD B. Zhou and S.A. Greenhaigh QUANTITATIVE EVALUATION OF DYNAMIC TIME-SHIFTS FOR CORRECTING SEISMIC DATA Greg Beresford and Dylan Mair

49 49 50

Technical Session 4(b) Mineral Exploration 11 • Mineral Deposit Settings SINTERS AND THEIR GOLD CONTENTS NGAWHA GEOTHERMAL FIELD, NORTHLAND, NEW ZEALAND Malcolm E. Cox and Patrick R.L. Browne MINERAL EXPLORATION IN SUMATRA S. Johari, and C.C. Johnson FORMATION OF UNCONFORMITY-STYLE URANIUM DEPOSITS IN THE ALLIGATOR RIVERS AND WESTMORELAND PROVINCES OF NORTHERN AUSTRALIA: A MORE UPDATED OUTLOOK N.F. Rutherford THE USE OF ELECTRON PARAMAGNETISM AND TRACE ELEMENTS CONTENT OF VEIN QUARTZ IN MINERAL EXPLORATION J.C. van Moort, A.S. Nand and A. Pwa

52 53

54 55

Technical Session 4(c) Computer Applications II ASEG GRID DATA EXCHANGE FORMAT (ASEG-GXF) - A STANDARD FORMAT FOR THE TRANSMISSION OF GRIDDED DATA Steve Collins AN IDEAL EARTH SCIENCE IMAGE INTERPRETATION AND MAPPING SYSTEM G.R. Pettifer and R.G. Paterson ANALYTICAL TECHNIQUES IN INTERPRETATION OF REGIONAL AEROMAGNETIC DATA Duncan R. Cowan and Sheila Cowan MODELLING COMPLEX AND FAULTED SURFACES FROM RANDOMLY SAMPLED CONTROL POINTS USING A LEAST SQUARES LINEAR INVERSE METHOD Carl E. Youngmann and Jeffrey W. Given

56 56 57 57

Technical Session 4(d) Petroleum Exploration IV - Organic Petrology and Geochemistry THE WALLOON COAL MEASURES: INTEGRATION OF CLASTIC AND ORGANIC FACIES AS A GUIDE TO OIL POTENTIAL M. Smyth and C.R. Fielding THE SUPPRESSION OF VITRINITE REFLECTANCE - AN IMPORTANT CONSIDERATION IN THE DETERMINATION OF THERMAL MATURITY OF ORGANIC MATTER FOR PETROLEUM EXPLORATION IN AUSTRALIA Ronald W.T. Wilkins, Nigel J. Russell and Zhong Ningning

VIII

CAMBRIAN PETROLEUM AND SOURCE ROCK GEOCHEMISTRY OF SOUTH AUSTRALIA D.M. McKirdy, D.I. Gravestock and C.G. Gatehouse EVALUATION OF LOWER PALAEOZOIC AND PRECAMBRIAN PETROLEUM SOURCE ROCKS AND THEIR HYDROCARBON GENERATION POTENTIAL BY ALGINITE REFLECTANCE Miryam Glikson, Dennis Taylor and Douglas Morris

Technical Session 4(e) Regional, Crustal and Geothermal I Gravity, Magnetic and Geothermal Studies ELECTRICAL CONDUCTIVITY ANOMALIES IN THE AUSTRALIAN LITHOSPHERE: EFFECTS ON MAGNETIC GRADIOMETER SURVEYS F.E.M. Lilley GEOPHYSICAL ANOMALIES CAUSED BY ROCK-HOT FLUID INTERACTIONS M.P. Hochstein STRUCTURAL FABRIC AND TECTONICS ASSOCIATED WITH THE POLDA LINEAMENT, SOUTH AUSTRALIA - A GEOPHYSICAL AND MORPHOTECTONIC ASSESSMENT D.H. Tucker, R.G. Nelson and J.C. Pitt GRAVITY DATA OVER THE LOLWORTH-RAVENSWOOD PROVINCE - GEOLOGICAL AND STRUCTURAL IMPLICATIONS B.D. Stockill and LJ. Hutton

67 67

68 68

Technical Session 4(f) Geoscience Education li SELLING EARTH SCIENCES P.G.L Harlow TEACHING SENIOR SECONDARY SCHOOL GEOLOGY IN THE ALICE SPRINGS REGION D.H. Morton GEOPHYSICS ON A SHOE-STRING N.F. Uren and B.J. Evans STYLES IN GEOPHYSICAL EDUCATION K. Vozoff

70 y-j 72 73

Technical Session 5(a) Petroleum Exploration V - Environmental ENVIRONMENTAL GUIDELINES FOR ONSHORE SEISMIC OPERATIONS IN WESTERN AUSTRALIA I. Fraser and A. Ryall ENVIRONMENTAL AND OPERATIONAL CHALLENGES OF A SEISMIC SURVEY ON AND AROUND THE MUIRON ISLANDS, WESTERN AUSTRALIA Jenny Bauer and Brett Kelsall ENVIRONMENTAL IMPACT OF SEISMIC EXPLORATION ACTIVITIES IN PELS 5 & 6, SOUTH AUSTRALIA - A DEPARTMENT OF MINES AND ENERGY PERSPECTIVE T.N. Crabb and P.R. Dunne SOUND ENVIRONMENTAL PRACTICE IN ONSHORE SEISMIC ACQUISITION A FIELD PERSPECTIVE M.K. Walcott

74 74 75

Technical Session 5(b) Mineral Exploration ni - Gravity/Borehole Studies UNDERGROUND DHEM SURVEYS AT ROSEBERY, TASMANIA J.R. Bishop and C.H. Lutherborrow UNDERGROUND DOWNHOLE GEOPHYSICS AT CSA MINE, COBAR A.R.D. Doe, J.T. Carswell, C.K. Smith and M.E. Erickson EXPLORATION SIGNIFICANCE OF GRAVITY SURVEYS, ROSEBERY MINE TASMANIA D.E. Leaman

77 77 78

GRAVITY GRADIOMETRY FOR GEOPHYSICAL PROSPECTING M.H. Dransfield, M J. Buckingham, C. Edwards, F.J. van Kann, A.G. Mann, R. Matthews and P.J. Turner

Technical Session 5(c) Computer Applications III DESKTOP GEOLOGICAL MODELLING Anthony A. Cram and John H. Duke BRINGING ROCKS INTO A HARD PUVCE. THE COLLECTION OF GEOLOGICAL INFORMATION FOR COMPUTER DATA BASES AND COMPUTER ASSISTED ORE RESERVE STUDIES Russell J. Fountain GIS IN THE MINERALS AND OIL EXPORATiON INDUSTRY R.F. Moore COMPUTING IN THE EXPLORATION OFFICE Ian Lilly

80 81 82

Technical 5(d) VI - VSP and Tomography PetroleumSession Exploration A PARAMETRIC STUDY OF BOREHOLE INFLUENCE IN RESOLVING SEISMIC VELOCITY IN WELL-TO-WELL TOMOGRAMS A.D. Watkins IMAGING OF SUBSURFACE FAULTS BY WALKAWAY VSP WAVEGUIDING D.R. Pant, I.M. Mason and S.A. GreenhaIgh ERROR IN ESTIMATION OF ARRIVAL DIRECTION ON OFFSET VSP DATA Marianne Windhofer and Roger Young SEPARATION OF P-WAVE AND S-WAVE IN VSP WAVEFIELD ON THE BASIS OF A FORWARD MODELLING TECHNIQUE Hiroshi Amano and Yoichi Ohta

84 84 85

Technical Sessionand 5(e)Geothermal II • West Australian Basins Regional, Crustal STRUCTURAL STUDY OF THE SOUTHERN PERTH BASIN BY GEOPHYSICAL METHODS Robert P. lasky, Roger A. Young and Mike F. Middleton STRUCTURAL AND SOURCE ROCK ANALYSIS OF THE VLAMING SUB-BASIN OFFSHORE SOUTH PERTH BASIN J.F. Marshall, D.C. Ramsay, A.M.G. Moore, T.G. Graham & I. Lavering VULCAN GRABEN, TIMOR SEA; REGIONAL STRUCTURE FROM A MAGNETIC SURVEY P. Wellman and G.W. O'Brien AUSTRALIA-BANDA ARC COLLISON AND IN SITU STRESS IN THE VULCAN SUB-BASIN (TIMOR SEA) AS REVEALED BY BOREHOLE BREAKOUT DATA R. Hillis

86 86 87 88

Technical Session 5(f) Geoscience Education III THE WORK OF THE KEY CENTRE FOR MINES (KCM): UNIVERSITIES OF NEW SOUTH WALES AND WOLLONGONG C. Gerrard, M. Katz and R. Stutchbury KEY FOR STRATEGIC MINERAL DEPOSITS, UWA: TEACHING AND RESEARCH FOR "EXPLORATION IN A CHANGING ENVIRONMENT" D.I. Groves and N.M.S. Rock UNIVERSITY-INDUSTRY INTERACTION AT THE CENTRE FOR ORE DEPOSIT AND EXPLORATION STUDIES Ross R. Large NATIONAL CENTRE FOR PETROLEUM GEOLOGY AND GEOPHYSICS (NCPGG) W.J. Stuart

89 90 91 93

Plenary Session IV OIL EXPLORATION IN A CHANGING ENVIRONMENT - A PERSONAL PERSPECTIVE P.E. Power FINANCIALLY SUSTAINABLE MINERAL EXPLORATION Ian G. Gould VISUAL PROCESSING IN EXPLORATION AND PRODUCTION APPLICATIONS: UPDATE AND TRENDS John Flynn

94 95 96

Technical Session 6(a) Petroleum Exploration VII - Interpretation Methods LOW STAND SEISMIC FACIES - A CARNARVON-BROWSE BASIN COMPARISON Robert B. Kirk A SEQUENCE STRATIGRAPHIC INTERPRETATION OF THE EASTERN GIPPSLAND BASIN A.M. Fittall, M.R. Cvetanovic APPLICATION OF NORMALIZED VELOCITIES FOR DEPTH CONVERSION OF THE BOOKABOURDIE FIELD, COOPER BASIN, S.A. Joseph Chiupka, Greg Beresford and Ed Tadlar EOCENE SEISMIC VELOCITY ANOMALIES FROM THE TIMOR SEA E.P. Woods

97 97 98 98

Technical Session 6 P) Mineral Exploration IV - Geochemistry SAMPLING: THE CINDERELLA OF EXPLORATION Rob Ryan THE ASSOCIATION OF GOLD WITH PEDOGENIC CARBONATE: IMPLICATIONS FOR EXPLORATION IN SEMI-ARID AND ARID TERRAINS M.J. Lintern THE DISPERSION OF GOLD WITHIN THE WEATHERING PROFILE AT HANNAN SOUTH GOLD MINE, WESTERN AUSTRALIA L.M. Lawrance and C.R.M. Butt QUANTITATIVE MICROANALYSIS AT TRACE LEVELS USING THE PROTON MICROPROBE C.G. Ryan, S.H. Sie, W.L Griffin, T.T. Win and G.F. Suter

100 101 102 104

Technical Session 6(c) Computer Applications IV WAVE-EQUATION DATUMING ON A MICRO-COMPUTER Greg Beresford and Clayton Hurst COMPUTER-ASSISTED LEARNING (CAL) FOR THE RESOURCE INDUSTRIES N.C. Higglns, M.A. Etheridge, R.W. Henley and A. Robey AN APPLICATION OF REGRESSION M-ESTIMATION WITH THE HILBERT TRANSFORM TO MAGNETOTELLURIC DATA PROCESSING D. Sutarno and K. Vozoff

106 106 108

Technical Session 6(d) Exploration Management I - General SAFETY CONSIDERATIONS IN GEOPHYSICAL FIELD OPERATIONS Thomas J. Dujmovich THE NATIONAL RESOURCE INFORMATION CENTRE (NRIC) - ITS ROLE IN THE IDENTIFICATION, ACCESS AND INTEGRATION OF RESOURCE INFORMATION IN SUPPORT OF GOVERNMENT DECISION MAKING PROCESSES AND IN GEOSCIENCE RESEARCH B. David Johnson and Roger Bradbury THE IMPORTANCE OF THE AUSTRALIAN CODE FOR REPORTING OF IDENTIFIED MINERAL RESOURCES AND ORE RESERVES AS A GUIDE FOR INVESTMENT K.R. Glasson

109

109 110

Technical Session 6(e) Regional, Crustal and Geothermal III Australian Basins: West, Central and East THE NATURE OF FAULTING ALONG THE MARGINS OF THE FiTZROY TROUGH, CANNING BASIN, AND IMPLICATIONS FOR THE TECTONIC DEVELOPMENT OF THE TROUGH BJ. Drummond, M.J. Sexton, T.J. Barton and R.D. Shaw A FRESH LOOK AT THE LATER PALAEOZOIC TECTONIC HISTORY OF WESTERN-CENTRAL AUSTRALIA Jean Braun, Herbert McQueen and Mike Etheridge THE BMR REGIONAL SEISMIC LINE ACROSS THE AMADEUS BASIN, CENTRAL AUSTRALIA: IMPLICATIONS FOR THE TECTONICS OF THE BASIN AND FOR HYDROCARBON EXPLORATION R.D. Shaw, R.J. Korsch, B.R. Goleby and C. Wright STRUCTURE OF THE PERMIAN-MESOZOIC EASTERN AUSTRALIAN BASINS COMPLEX, WITH EMPHASIS ON THE BMR BOWEN BASIN DEEP SEISMIC PROFILES R.J. Korsch, K.D. Wake-Dyster and D.W. Johnstone

112 112

113

114

Technical Session 6(f) Geosclence Education IV SYDNEY UNIVERSITIES' CONSORTIUM OF GEOLOGY AND GEOPHYSICS John Roberts AUSTRALIAN INSTITUTE OF GEOSCIENTISTS (AIG) AND TERTIARY EDUCATION J.Thomson EDUCATION AND ENVIRONMENTAL GEOLOGY B. Nicholls MINING OR THE ENVIRONMENT - GEOLOGY'S DILEMMA! R. Stutchbury

115 116 116 117

Technical 7(a) Vlll - Reservoir and Source Rock Geochemistry PetroleumSession Exploration THERMAL HISTORIES AND ILLITE GROWTH IN SEDIMENTARY BASINS P.J. Hamilton and M. Giles INTEGRATING TIME SPECIFIC AND TIME DEPENDENT TEMPERATURE INDICATORS FOR THERMAL HISTORIES OF SEDIMENTARY BASINS P.J. Eadington and P.J. Hamilton SEDIMENTARY PROVENANCE USING Nd ISOTOPES: APPLICATION TO PETROLEUM EXPLORATION IN THE EROMANGA BASIN D.J. Whitford and P.J. Hamilton FLUID FLOW HISTORY OF E. TRIASSIC NARRABEEN GROUP SANDSTONES OF THE SOUTHERN SYDNEY BASIN G. Bai, J. Keene, P.J. Eadington, P.J. Hamilton and I. Macdougall

118 119 120

122

Technical Session 7(b) Mineral Exploration V - Electromagnetic Interpretation INTERPRETATION OF POLARISATION EFFECTS OBSERVED IN TEM FIELD DATA Peter Elliott EXAMPLES OF DATA PROCESSED USING A NEW TECHNIQUE FOR PRESENTATION OF COINCIDENT AND IN-LOOP IMPULSE-RESPONSE TRANSIENT ELECTROMAGNETIC DATA R. Smith and G. Buselli A STUDY OF GALVANIC RESPONSE IN THE TEM RESPONSE OF CONDUCTIVE ORE BODIES Michael W. Asten QUANTITATIVE RESISTANCE AND CAPACITIVE ELECTRODES: NEW DEVELOPMENTS IN INDUCTIVE SOURCE RESISTIVITY James Macnae and Patrick McGowan

123

123 124 124

XII

Technical Session 7(c) Coal, Groundwater and Engineering I - Coal PLIO-PLEISTOCENE COAL RESOURCES IN A FOREARC BASIN SETTING MEUUBOH, WEST ACEH, SUMATRA Hadiyanto and A.C. Cook COAL POTENTIAL AND RESOURCES IN THE SOUTH SUMATRA BASIN INDONESIA Rubianto Amier A COMPARISON OF EXPLORATION METHODS OF TWO INDONESIAN TERTIARY COAL DEPOSITS David J. Mason TRANSMISSION CHARACTERISTICS OF IN-SEAM SEISMIC WAVES THROUGH DYKES AT GERMAN CREEK CENTRAL COLLIERY, OLD L.A. Drake and R.D. Hewson

105 ^ 25 ^26 ^27

Technical Session 7(d) Exploration Management 11 - Legal Aspects PERSONAL LEGAL LIABILITY OF CONSULTANTS Michael Sharwood RECENT^DEVELOPMENTS IN ENVIRONMENTAL LAW AS THEY RELATE TO D. Maloney THE CHANGING LEGISLATIVE ENVIRONMENT FOR EXPLORATION Peter J. Rose

^29 . 3q ^

Technical Session 7(e) Petroleum Exploration IX • Cretaceous to Recent Tectonics THE CRUSTAL STRESS PATTERN IN THE AUSTRALIAN CONTINENT David Denham and Christopher R. Windsor THE ROLE OF INTRAPLATE STRESS IN TERTIARY (AND MESOZOIC) DEFORMATION OF THE AUSTRALIAN CONTINENT AND ITS MARGINS" A KEY FACTOR IN PETROLEUM TRAP FORMATION Mike Etheridge, Herb McQueen and Kurt Lambeck TECTONIC EVOLUTION OF THE DURROON BASIN. TASMANIA Peter Baillie and Robert Pickering TERTIARY UPLIFT ESTIMATION FROM VELOCITY DATA IN THE EROMANGA BASIN Jane Rodgers, Fred L. Wehr and John W. Hunt

100

100 . 00 134

Technical Session 7(f) Theoretical Research SEISMIC MIGRATION AND MATHEMATICAL MAPPING Peter W. Buchen HIERARCHICAL DECOMPOSITION AND INVERSION Jacob Tjeerd Fokkema SOURCE SCALING AND THE DYNAMITE SIGNATURE A.M. Ziolkowski

. oc

Technical Session 8(a) Petroleum Exploration X - Seismic Data Processing MAXIMUM ENTROPY REFLECTION TOMOGRAPHY Peter Whiting MODEL BASED INTERVAL VELOCITY ANALYSIS Shannon Maher, George Mellman and David Hadley A NEW CMP STACK CONCEPT BASED ON THE BORN APPROXIMATION Fnedemann Wenzel A HIGHER ORDER APPROXIMATION FORMULA FOR TRAVEL TIME OF AND^^'^S™"!^^^^ APPLICATION TO NMO CORRECTION Yuzuru Ashida, Norio Tenma and Koichi Sassa

107

^ 33

XIII

Technical Session 8(b) Mineral Exploration VI - Airborne Resistivity Mapping PROCESSING OF AIRBORNE TEM DATA TO ALLOW ACCURATE CONDUCTIVITY MAPPING Andrew C. Duncan SIGNAL PROCESSING CONCEPTS FOR AIRBORNE SiROTEM DATA J.P. Cull AN APPLICATION OF AIRBORNE GEOTEM* IN AUSTRALIAN CONDITIONS A.P. Annan and R. Lockwood GEOLOGIC-GEOPHYSICAL MODELS OF KIMBERLITE PIPES V.A. Erkhov

-139 140 140 141

Technical Session 8(c) Coal, Groundwater and Engineering II - Coal HIGH RESOLUTION SEISMIC FOR RESOLVING COAL SEAM STRUCTURE IN DIFFICULT TERRAIN J. Saunders, P. Lamb and D. Sweeney A NUMERICAL STUDY OF ELECTROMAGNETIC WAVE PROPAGATION (RIM) IN DISRUPTED COAL SEAMS G. Liu, G. Smith, S. Thomson, K. Vozoff and P. Hatherly 3D SEISMIC REFLECTION: EXAMPLES OF ITS APPLICATION TO MINE PLANNING AND SAFETY IN AUSTRALIAN COALFIELDS A.N. Lamboume, P.J. Hatherly and B.J. Evans SEISMIC MODELLING - AN AID TO SHALLOW REFLECTION SEISMIC ACOUISITION AND INTERPRETATION

146

O. Dixon and S. Heam

147

146

I47

Technical 8(d) XI - Cretaceous to Recent Tectonics Petroleum Session Exploration TERTIARY STRUCTURING IN SOUTHWEST QUEENSLAND: IMPLICATIONS FOR PETROLEUM EXPLORATION R.D.Shaw STRUCTURAL STYLES, CEPU OIL FIELDS, JAVA, INDONESIA N. Soeparyono and P. Lennox TECTONIC EVOLUTION OF BASS STRAIT - ORIGINS OF TERTIARY INVERSION Ian M. Young, Mark A. Trupp and Michael J. Gldding

152 153 153

Technical Session 8(e) Regional, Crustal and Geothermal IV Electrical Conductivity, Temperature and Petrology THE ELECTRICAL CONDUCTIVITY STRUCTURE OF THE OCEANIC LITHOSPHERE BENEATH THE TASMAN SEA G.S. Heinson and F.E.M. Lilley HETEROGENEITY IN THE THERMAL STATE OF THE LOWER CRUST AND UPPER MANTLE BENEATH EASTERN AUSTRALIA N.J. Pearson, S.Y. O'Reilly and W . L Griffin IMPLICATIONS FOR GEOTHERMAL PROFILING FROM MAGNETOTELLURIC DATA J.D. Gray and J.P. Cull IMPORTANT PETROLOGICAL EVIDENCE FOR THE EROMANGA-BRISBANE TRANSECT Y.D. Chen, S.Y. O'Reilly and W . L Griffin

154 154 155

155

Plenary Session V A CASE HISTORY OF GEOSCIENTISTS K.R. Glasson

157

XIV

THE TALE OF THE BIG OCKER AND THE FINK: The Evolution of Geophysics in BHP Phillip G. Harman THE CASE FOR EXPLORATIONISTS J.P. Froning

158 159

Technical 9(a) XII - Interpretation Methods PetroleumSession Exploration SEISMIC AVO ANALYSIS OF A PERMIAN GAS SAND AT KERNA FIELD, COOPER BASIN, SOUTH AUSTRALIA J. Pinchin and A.B. Mitchell HARRIET FIELD TWO DIMENSIONAL MODELLING STUDY Mark W. Ballesteros COASTAL EOLIAN DEPOSITS AND OIL PRODUCTION: MODERN AND ANCIENT EXAMPLES Steven G. Fryberger THE SEARCH FOR SUBTLE STRATIGRAPHIC TRAPS WITH HIGH RESOLUTION SEISMIC DATA: EXAMPLES FROM THE POWDER RIVER BASIN, NE WYOMING, USA John B. Frederick

160 160 161

162

Technical Session 9(b) l\1ineral Exploration VII - Case Studies PROTEROZOIC DYKES AS AN INDICATOR OF STRUCTURAL CONTROLS ON GOLD DEPOSITS IN THE YILGARN BLOCK, WA D.J. Isles and A.C. Cooke AIRBORNE, GROUND AND BOREHOLE ELECTRICAL SURVEYS - A CASE HISTORY OF THE FLYING DOCTOR DEPOSIT, BROKEN HILL E.D. Tyne and S.S. Webster THE APPLICATION OF DRILLHOLE MAGNETOMETRY AND MISE-A-LA-MASSE IN THE EXPLORATION FOR NICKEL SULPHIDES, FINLAND - DISCOVERY OF THE TELKKALA OREBODY R. Pietila FREQUENCY ELECTROMAGNETIC SOUNDINGS FOR DEEP MASSIVE SULPHIDE OREBODY DETECTION J. Bernard, B. Bourgeois and P. Valla

163 164

165

166

Technical Session 9(c) Coal, Groundwater and Engineering III - Groundwater THE USE OF ELECTRO-GEOPHYSICAL METHODS FOR GROUNDWATER POLLUTION AND SOIL SALINITY PROBLEMS G. Buselli, C. Barber, G.B. Davis and D.R. Williamson RECHARGE, SALINITY AND LAND-USE CHANGE IN NORTH-EASTERN NSW S.J. Lawson, R.M. Williams, G.W. Gates and J.A. Odins THE USE OF ELECTRICAL IMAGING TECHNIQUES FOR THE INVESTIGATION OF DRYLAND SALINITY R.I. Acworth and D. Scott PRE-TERTIARY BASEMENT STRUCTURE OF THE CENTRAL MURRAY BASIN, AND ITS EFFECT ON GROUNDWATER FLOW PATTERNS J.A. Odins, R.M. Williams, D.J. O'Neill and S.J. Lawson

167 167 169

170

Technical 9(d) Xlil - Seismic Data Acquisition and Case Histories PetroleumSession Exploration THREE-COMPONENT SEISMIC: FIELD IMPLEMENTATION AND OPERATIONS WITH OMNIPHONE D.R. Miles, G.S. Gassaway and J.E. DeBoer THE 'OCEAN'S OVERTURE' ON THE NORTH WEST SHELF OF AUSTRALIA Charles Ramsden

171 171

Technical Session 9(e) Regional, Crustal and Geothermal V - Seismic Studies, Worldwide DEEP CRUSTAL STRUCTURE IN THE GULF OF ST LAWRENCE FROM COINCIDENT SEISMIC REFLECTION AND REFRACTION SURVEYS M.C. Dentith, J. Hall, F. Marillier, K. Michel, I. Reid and B. Roberts

^^ EGMONT FAULT ZONE, TARANAKI BASIN NEW ZEALAND Glenn P. Thrasher GEOPHYSICAL DATA PROCESSING AND INTERPRETATION IN AN AREA OF OF COMPLEX STRUCTURE - THE SOUTHERN TARANAKI FAULT ZONE J.F. Montalbetti and D.J. Norrls DEEP STRUCTURE OF BAIKAL RIFT ZONE - THE BIGGEST ASIAN CONTINENTAL STRUCTURE M. Mandelbaum

. 1 /b

Technical Session 10(a) Petroleum Exploration XIV - Case Histories NORTHERN^m^n'sA^^^

'N REDUCING EXPLORATION RISK IN THE

R.LNeale EROMANGA BASIN SEISMIC STRATIGRAPHY AND TECTONIC MODELLING KEYS TO EXPLORATION SUCCESS IN ATP 299P B. Edwards THE CHALLIS AND CASSINI OILFIELDS TIMOR SEA, AUSTRALIA T. Slate and G. Grubitz DIAGENETIC RESERVOIR EVALUATION, SOUTHERN COOPER BASIN J.P. Schultz-Rojahn, A Alsop, J..EIeftheriou, A. Thomas, B.B. Farrow N. Lemon, S.E. Phillips and W.J. Stuart '

178 179 QQ

Technical Session 10(b) Mineral Exploration Vlll - Case Studies ^ f o n AO?'^^"- "METHODS FOR MINERAL EXPLORATION IN THE SOVIET lAH tAoT V.N. Gagaev and N.K. Zhdan ^ ^ ^ DETRITAL HEAVY MINERALS ON EAST ASIAN SHELF AREAS AND THEIR GEOPHYSICAL EXPLORATION John Ringis THE ROLE OF GEOPHYSICS IN EXPLORATION AT JUNCTION REEFS AND THE SHEAHAN-GRANTS GOLD MINE, CENTRAL N S W Steve Collins SPLORATION^'^^^^^

181 189

DEPOSIT: IMPLICATIONS FOR REGIONAL

I. Hodkinson and B.D. Kay

Technical Session 10(c) Coal, Groundwater and Engineering IV - Engineering GROUND PENETRATING RADAR RESPONSE TO BOUNDING SURFACES AND^LITHOFACIES VARIATIONS IN SAND BARRIER SEQUENCES AQUIFER^"^® GEOPHYSICAL TECHNIQUES TO STUDY A SMALL CONFINED

^ ^^

Paul J. Wolfe and Benjamin H. Richard

o p p ^ I S m ^^ SOURCES FOR SHALLOW SEISMIC HtFLtCTION S.J. Hearn, M.H. Kay and O. Dixon

. a,

i x P w S J I l O N S ^ T E G ? ^ ^ " ' ^ ' - ' ' ' ^ GROUNDWATERS AS AN Angela Giblin

192

XVI

Technical Session 10(d) Regional, Crustal and Geothermal VI Sediments and Structure of Basins and Rifts MODELLING THE FILL OF SEDIMENTARY BASINS J.C. Tipper STRUCTURE AND STRATIGRAPHY OF THE NEW CALEDONIA BASIN Chris Uruski and Ray Wood DEEP SEISMIC REFLECTION LINES ACROSS THE RHINE GRABEN Friedemann Wenzel and the ECORS/DEKORP Working Group RIFTING AND PETROLEUM POTENTIAL OF SIBERIAN SEDIMENTARY BASINS V.S. Surkov and V.I. Lotyshev

^94 194 195 195

Poster Session - Petroleum Exploration PAUVEOGEOGRAPHY AND SEQUENCE STRATIGRAPHY John Bradshaw, Marita Bradshaw, Robert Langford and Gerry Wilford NON-DESTRUCTIVE CORE ANALYSIS USING X-RAY COMPUTED TOMOGRAPHY L. Coshell, J. Scott, A.M. Knights, B.J. Evans and M.W. Hill SOURCE OF METALS IN THE MISSISSIPPI VALLEY-TYPE DEPOSITS IN THE CANNING BASIN, NORTHWESTERN AUSTRALIA B . L Gulson, H. Etminan and K.J. Mizon THE NUMERICAL MODELLING OF SANDSTONE PINCH-OUTS AND DRAPES IN THE BOWEN BASIN, QUEENSLAND Brian Evans, Paul Carter and David Khoo TECTONOSTRATIGRAPHIC EVOLUTION OF THE VULCAN SUB-BASIN R.R. Hillis, J. Lorenzo and C.C. von der Borch GEOLOGICAL DEVELOPMENT AND HYDROCARBON POTENTIAL OF THE OFFSHORE NORTH PERTH BASIN J.F. Marshall, C.-S. Lee, D.C. Ramsay, G.W. O'Brien and A.M.G. Moore INTERPRETATION OF THREE-COMPONENT SEISMIC DATA D.R. Miles, G.S. Gassaway, L E . Bennett and R.A. Brown ADVANCES IN TECHNIQUES OF SURFACE GEOCHEMICAL EXPLORATION FOR HYDROCARBONS IN AUSTRALIA Don Rigby and Rob Pallaser RECENT ADVANCES IN SEISMIC IMAGING Karl L. Schleicher and Matthew A. Brzostowski THE CHARACTERIZATION AND EVALUATION OF CRUDE OILS AND SOURCE ROCKS - THE ALKANE APPROACH John W. Smith, Don Rigby, Luo Binjie, Song Zhiguang and Wanq Yuxiao A MULTI-DISCIPLINARY APPROACH T O AVO ANALYSIS J.A. Ward, M.A. Hall, and T.C. Southren APPLICATION OF THE LASER RAMAN MICROPROBE IN PETROLEUM EXPLORATION John R. Wilmshurst, George HIadky, Michael V. Ellacott and Carol P. Buckingham USING SEISMIC WAVETESTS TO DETERMINE VELOCITY STRUCTURE Roger A. Young

202 202

203

203 205

206 208

poo 209 21 n 210

214

Poster Session - Mineral Exploration NORTHEASTERN NEW SOUTH WALES - CAN RADIOMETRIC DATA MAP DIFFERENT GRANITOIDS? A. Agostini, E.D. Tyne, P . L Kennedy and W. Worakanok HUMINEX SYSTEM OF GEOCHEMICAL EXPLORATION W.E.Baker QUANTITATIVE DESCRIPTION OF SHAPE IN PETROGRAPHIC IMAGE ANALYSIS M. Benhamou, A.R. Ramsden, D.H. French INVESTIGATION OF TAILINGS DAMS RESERVES, EMPEROR GOLD MINE FIJI Malcolm E. Cox and Andrew M. Foley ' A COMPARISON OF TEM (TRANSIENT ELECTROMAGNETIC) SYSTEMS CURRENTLY AND MOST WIDELY USED IN AUSTRALIA P.J.Eiliott

01 c

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xvii GEOCHEMISTRY AND MORPHOLOGY OF GOLD IN UVTERITIC PROFILES IN SAVANNA AND SEMI-ARID CLIMATES P. Freyssinet, L.M. Lawrance and C.R.M. Butt NEUTRON ACTIVATION ANALYSIS IN THE 1990s - UNIQUE SOLUTIONS TO MINERAL EXPLORATION PROBLEMS David L. Garnett and Helen M. Waldron THE GENESIS AND SEDIMENTATION OF SAPPHIRES FOUND AT WELLINGROVE Phillip G.L. Harlow APPLICATION OF PHYSICAL PROPERTY MEASUREMENTS IN BASE METAL EXPLORATION: SHEEP CREEK DEPOSIT, MONTANA, U.S.A. Gregory M. Hollyer THE APPLICATION OF A NEW FIELD-PORTABLE REFLECTANCE SPECTROMETER (PIMA) FOR IN-SITU MINERAL IDENTIFICATION IN EXPLORATION J.F. Huntington and T.D. Cocks THE SPECTREM AIRBORNE ELECTROMAGNETIC SYSTEM P.S. Kllnkert NORTHWESTERN NEW SOUTH WALES CAN REGIONAL GEOPHYSICS LEAD TO MORE EXPLORATION? J.I. Mclntyre USE OF ZIRCONS TO RESOLVE ORIGINS OF SAPPHIRES IN EAST AUSTRALIAN GEM FIELDS - THE MYSTERIOUS CASE OF THE SHUFFLING SAPPHIRE VOLCANOES F.L. Sutherland, P.D. Kinny and J.D. Hollis

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Poster Session - Coal, Groundwater and Engineering MICROGEOMETRICAL MODELS OF THE ELECTROMAGNETIC PROPERTIES OF GRANULAR GEOLOGICAL MATERIALS P.L. Baker EFFECT OF PORE PRESSURE ON COMPRESSIONAL WAVE VELOCITY IN COALS G. Yu, K. Vozoff and D.W. Durney

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Poster Session - Regional, Crustal and Geothermal APPLICATION OF SECTION BALANCING TECHNIQUES TO DEEP SEISMIC REFLECTION DATA FROM OFFSHORE EASTERN CANADA M.C. Dentith and J. Hall TECTONOSTRATIGRAPHIC EVOLUTION OF THE VULCAN SUB-BASIN R.R. Hlllls, J. Lorenzo and C.C. von der Borch IMPROVED ESTIMATION OF LATERAL VELOCITY INHOMOGENEITY FOR USE IN SEISMIC MIGRATION Beverley Moore APPLICATION OF DYNAMIC PROGRAMMING TO THE PROCESSING OF STnONG MOTION ACCELEROGRAMS Ivan A. Mumme TOWARDS ACTUALISTIC MODELS Suzanne Y. O'Reilly and W.L. Griffin AU-PGE IN LAYERED MAFIC INTRUSIONS OF THE PINE CREEK GEOSYNCLINE R.G. Warren THE HANMER BASIN. NEW ZEALAND Ray Wood

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Poster Session - Computer Applications FAST, VERY ACCURATE POSITIONING WITH GPS Erwin Frei, Rod Eckels and Chris Rizos DC RESISTIVITY INVERSION USING GENERAL-PURPOSE OPTIMISATION SOFTWARE N.P. Men-ick AN IMPROVED NAUDY BASED TECHNIQUE FOR ESTIMATING DEPTH FROM MAGNETIC PROFILES Zhiqun Shi

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ENGINEERING SEISMIC REFRACTION: AN IMPROVED FIELD PRACTICE AND A NEW INTERPRETATION PROGRAM, REFRACT Chris Walker, Tak Ming Leung, Maung Aung Win, and Robert J. Whiteley

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Standby Papers RARE EARTH ELEMENT EXPLORATION IN AUSTRALIA Bernd G. Lottermoser DRYLAND SALINITY AND RECLAMATION N. Mattocks

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Corporate Sponsors AERODATA HOLDINGS LIMITED AGL PETROLEUM AMPOL EXPLORATION LIMITED ASHTON MINING LIMITED BHP PETROLEUM BLIGH OIL AND MINERALS N.L BMR GEOLOGY AND GEOPHYSICS BP IN AUSTRALIA - A BRIEF OVERVIEW BRIDGE OIL - "THE ENERGETIC AUSTRALIAN" CARPENTARIA EXPLORATION COMPANY PTY LTD (C.E.C.) THE CHAMBER OF MINES AND ENERGY OF WA INC. CLASSIC LABORATORIES LIMITED CRA EXPLORATION PTY LTD. CRUSADER DIGICON GEOPHYSICAL CORPORATION ENCOM TECHNOLOGY PTY LIMITED ENCOR TCPL RESOURCES LTD EARTH RESOURCE MAPPING GEOTERREX PTY LTD GEOVISION HALLIBURTON GEOPHYSICAL SERVICES INC KEVRON GEOPHYSICS LANDMARK GRAPHICS CORPORATION NORCEN IN AUSTRALIA OIL ON FILM PTY LTD. PEKO OIL LIMITED PLACER PACIFIC LIMITED SAGASCO RESOURCES LTD SHELL DEVELOPMENT (AUSTRALIA) LTD SIMON-HORIZON AUSTRALIA SOUTH AUSTRALIAN DEPARTMENT OF MINES AND ENERGY SURTEC GEOSURVEYS PTY LIMITED TENSOR PACIFIC PTY LTD. VELSEIS PTY LTD WAPET WESTERN GEOPHYSICAL WESTERN MINING CORPORATION LIMITED PETROLEUM DIVISION (AUSTRALASIA)

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Plenary Session II

MINERAL AND PETROLEUM EXPLORATION AND ENVIRONMENTAL CO-EXISTENCE Reg C. Sprigg Arkaroola Pty Ltd, Flinders Ranges, SA ABSTRACT Successful mining and petroleum exploration and extractive industries are vital to Australia's future security, welfare, wealth and prosperity. It is these industries that are mainstays of decentralization in a "lucky country" of basically fringe-dwellers, and one otherwise renowned for its deserts and great open spaces. Despite some notable exceptions in the past, our industries have much to be proud of. Still, the need to be wary of often destructive, irrational and emotional criticism, particularly emanating from the no-growth environmentalists, remains. Greatly improved communication with the public is essential, with the industry taking on ever more extensive leadership roles in practical conservation of the environment. In the foregoing context our industries must effectively foster educated understanding of the evolution of life on Planet Earth, the ecological hazards facing humanity, the potentially frail nature of the biosphere, and the effects of man's often polluting activities upon it. These aspects, including the real possibility of further mass extinctions including that of man, are canvassed widely in this presentation. Policies of "multiple land use" and "sustainable development" are vital to healthy exploration and mining activity, and essential to human survival and continuing prosperity. Nor can the oceans, lakes and rivers continue to be treated as bottomlesswaste pits or open sewers. Careless releases of poisonous chemicals, excess fertilizers and greenhouse gases cannot be tolerated. Our industries must provide responsible example and play a major role in ongoing public education. INTRODUCTION Conservation of the environment and economic development are interdependent, and their implementation must go hand-in-hand. Economic growth is essential if the needs and aspirations of present and future generations are to be realised. It is only through economic growth that the potential exists to narrow the gap between the affluent and the under-developed or deprived nations. To achieve continued growth the world must pursue a programme of sustainable development. Sustainable development is defined by the World Commission on Environment and Development as choosing "new paths of progress which meet the needs and aspirations of the present generation without compromising the ability of future generations to meet their own needs". Such sustainable development will require great sensitivity in the continued search for, development of, and exploration of, the Earth's mineral and oil resources. Accordingly, Australia's exploration industry must continue to demonstrate: 1. That resource development can proceed in environmentally sensitive areas without adversely affecting natural conservation values, and:

2. That application of adequate environmental safeguards and controls under a multipurpose land use system is an essential prerequisite for sustainable development. To achieve progress and survive, then, Australia's mineral and oil exploration industries must continue to have responsible access to the major proportion of its land areas and surrounding continental shelves. The Australian Mining Industry Council has shown, however, that Government decisions have already restricted or denied access of our industry's operations to roughly 1.5 million square kilometres of prospective land area, or the equivalent of about five times the area of the British Isles. Out of arguments expressing the varying, and often conflicting, views of Australian society including government, conservation groups, industry and the general public, has evolved the best blue print yet for the process of conservation on a national scale and in harmony with exploration and development. This is entitled the "National Conservation Strategy for Australia". In it, conservation is defined as "the management and human use of the biosphere so that it may yield the greatest sustainable benefit to the present generations while maintaining its potential to meet the needs and aspirations of future generations". It proceeds also to explain the role of development as being to provide the essential needs of the individual and those of society, to generate economic wealth, and to provide the economic capacity which assists society to practise resource conservation which in turn enables sustainable development. Overall the World Conservation Strategy from which the foregoing N.C.S.A. derives, clearly recognises that both conservation and development are for the people. Too, it is clear that people are human. That humans will cause a degree of pollution whether innocently or carelessly. Rules are already well established for such developments, and increasingly the principle is being accepted that the polluter should, and must be required to pay - but according to local circumstance - and not be defined to unnecessarily restrict industry. International standards should be accepted that are adequate to protect particular fauna and flora unique to our continent. Unnecessarily onerous pollution control measures should not be designed to restrict the capacity of Australian exploration, mining and petroleum industries to compete on international markets. This is particularly so where comparable commodities are readily available to consumers from elsewhere, but not loaded with added costs of potentially punitive pollution control measures. Australia is basically a primary producer. Its population will not be willing to have its standards of living undermined by leaving its minerals in the ground, or being forced to become uncompetitive in its all-important world markets. With these concepts in mind let us go back to the beginning. We must also perceive that mankind is basically an ephemeral part of the environment, not an unchallenged master. Civilized man's span on earth has been a mere ten or so thousand years against a life-supporting span of our planet measured in billions of years. MAN'S PLACE IN SPACE Man's ability to look at planet Earth from Outer Space has demonstrated that we do live in one world. Astrophysics has shown us that, of all the inner rocky planets, ours is the only one that supports a system of moving continents or "plate tectonics" - a phenomenon greatly important in recycling vast quantities in particular of the greenhouse gas carbon dioxide, via sea floor limestones. Astrophysics has also

emphasized that along with our closest "sister planets", each continues to have atmospheres either dominated by carbon dioxide or ones in which CO2 has played an important role in past climate control. Venus, closer to the sun, exhibits a torridly hot (c. 480^^0) turbulent atmosphere in which the CO2 "greenhouse" effect is operating completely out of control. Mars, further out than Earth, is a "dead" planet. It has polar ice caps of frozen carbon dioxide, but bears evidence of a past hydrosphere now dissipated into space. Only planet Earth apparently, has a fluid iron core and viscous circulation in its mantle. This combination generates also a magnetosphere that deflects solar winds and protects life from destructive U.V. and other radiation. Geological history, on the other hand, reveals that organic life arose on earth probably 3.6 billion years ago, and that despite great changes in the composition and the nature of its biosphere since then, "something" has maintained it in the temperature range comfortable to organic life of 0-45+''C. Homo sapiens has inherited all this, and by its technology and science, sets out to make planet Earth still more congenial to life. This it has accomplished largely by developing Earth's mineral resources and harvesting the products of its lands and seas, ever more extensively and efficiently, but often at some price to the environment. Only in the 20th century has the often transcending importance of CO2 in the earth's biosphere been adequately appreciated. Significant proportions of CO2 (now 350+ppm) lead to heating of the atmosphere, to the melting of ice-caps and to rising sea level. Plants, as important recyclers of CO2, extract carbon for their tissues and transpire back oxygen that is basic to animal life. Buried organic matter, however, ties up carbon in coals and oils for geologically prolonged periods, as do limestones and related carbonaceous sediments on the sea-floor. These are only released by uplift and erosion, mining, or more significantly, via vulcanism over "subduction" zones as occur adjacent to ocean trenches. These occur around the Pacific Ocean, and in other "collision" zones as involved in sea-floor spreading. AUSTRALIA AS IS: Australia has only 17 million residents. It could support probably 100 million or more out of a world population of over 5 billion. Its continental area represents one twentieth of the total global land area. It has the longest coastline of any nation, lays claim to the largest area of continental shelves of any sovereign nation, and also claims the largest segment of Antarctica. Its combined mineral resources are as diverse and rich as those of any other continent on earth. In an already overcrowded world, but with a local population density representing but a mere fraction of our neighbours, can we justify our current "keep out" notices? World history is notable for its disregard of national boundaries. This belie'^ our comfortable belief that Australia has no enemies and faces no prospects of hostile invasion in the foreseeable future. The fact that we all but lost our sovereignty in the 1940's Pacific War was solely at the discretion of the U.S. war strategy. The U.S. understandably saw our country as a convenient platform for launching retaliatory action against an Asian enemy. Have circumstances changed that much since? Australia can claim no god-given rights to its territories. 17 million residents is small by world standards. To much of the world we appear as a relatively un-industrious people. Our economy is in decline, despite a background of plenty. A lowering of living standards is in progress that is decidedly unhealthy. Potential population decline by emigration in a population that is also aging seriously is reprehensible, but bound to

follow. That is, If impoverishment is not arrested, and immigration not accelerated significantly. Australia luxuriates in having extensive mineral, agricultural and forestry resources, and a benign climate. Australians did not put the resources there, but they cry out for continued responsible development in a world often hungry for basic necessities. If Australia ignores its responsibilities, then some other power will eventually take charge. Certainly our deserts can be forbidding and increasing in spread, thanks extensively also to the feral rabbit. Much of the agricultural land is in decline, too, due to soil erosion and salination. Its forests are receding, and at the mercy of bushfires spurred on by changing farming and some National Parks practices and policies. "Prosperity and beauty, natural beauty, go hand in hand" claims Hugh Morgan, Managing Director of Western Mining Corporation Ltd: (Aust. I.M.M. Bulletin No. 5, Aug. 1990) "Poor countries don't (i.e. can't afford to ... R.C.S.) care about the environment. Survival is much more important to them ... Poverty and socialism have been devastating for the environment..." in eastern Europe and beyond. That puts it bluntly. "SUSTAINABLE DEVELOPMENT"

The new B.M.R. strategy entitled "Geoscience for Australia's Future" as enunciated by the Minister for Resources in Canberra recently is prefaced by the following statement taken from the "Brutland" report of the 1987 U.N. Commission on the Environment and Development - as follows: "Humanity has the ability to make development sustainable - to ensure that it meets the needs of the present without compromising the ability of future generations to meet their own needs". The B.M.R. strategy takes it a step further: "Australia's future well-being requires the development of our natural resources in a sustainable and environmentally responsible way" (Aust. N. Geologist" newsletter No. 7b, p3, 26/9/90). "Sustainable development", then, is the current catch-phrase. If indeed this genuinely means to maintain "gradual growth or advancement through progressive changes" (Webster Dictionary definition), then I am all for it. To me this clearly indicates that environmentally sound exploration, and wise exploitation of the nation's resources, both mineralogical and biological, must be encouraged and supported seriously. New technology will need to be continually developed, refined and exploited to the benefit of our country and future generations. We must be able to develop, share and sell our wealth with others, and in particular with those people less fortunate than ourselves. It is well for us here also to remember: "Ore bodies are only discovered when people go looking for them".. and that "The discovery of petroleum first of all is in the minds of men" (Wallace Pratt, 1940) Exploration, then, is clearly a prerequisite for mineral and petroleum discovery and development. Earth resources are not in imminent danger of exhaustion, but as the more readily located ores are committed to exploitation then the more difficult and/or

costly it is to find replacements. The ingenuity of man and his advancing technologies, unless artificially or politically restrained, will however assure success far into the future. With the foregoing sentiments go increasing responsibilities. Tendencies to pollute the environment still further must be resisted, arrested, or where possible, reversed. The oceans are not bottomless sewers, the atmosphere is unquestionably being poisoned by industry in particular, and the land and its vegetation are broadly in serious decline. Despite the "green revolution" of recent decades, involving the high application of chemical fertilizers and chemicals in weed control, that have brought vastly improved food production in developed countries, there are more hungry people in the world today than ever before. Potable water supplies and woodfuel resources for underdeveloped countries are diminishing alarmingly. Soil erosion is accelerating, desertification is spreading, and the gap between rich and poor nations is widening. Acid rains devastate forests, lakes, fish stocks, and the world's architectural heritage alike. Soil and ground water salination is intensifying, greenhouse atmospheric warming is slowly increasing, the protective ozone layer is being depleted, and food chains are being disrupted. A frightening scenario, involving such a brief time span! ON AUSTRALIA'S RECORD IN MINING Much of Australia's heritage and prosperity is based on mining. Economic depressions in the past have been arrested by timely new mineral discoveries, and major and stable population centres have been established across the arid inland. A major proportion of our country's annual export income continues to be earned through mineral sales. One only has to visit any of the country's inland mining centres or those of northern or north western Australia, to observe this fact. Broken Hill, Mt. Isa, Kalgoorlie, Roxby Downs and others are veritable oases in deserts or semi-deserts. These virtual garden cities clearly reflect the aims, projections and aspirations of a far too often maligned mining industry, one that has striven and succeeded in creating new wealth and opportunities for populations now othen^^ise comfortably and extensively concentrated at the coast - the most affluent beneficiaries of the "lucky country". Australia needs still more long term, inland, mineral projects, and the related prospects for more decentralization. Australians who care are a resourceful people. Big and still bigger thinking, also expanding mental horizons, freedom for responsible action, reduction of red tape and of bureaucratic frustration, must continue and be the propellers of future action. Australia is undoubtedly extremely well endowed for minerals but these cannot be simply left in the ground. The discovery of the one opens up prospects for another. New geological concepts and bolder ideas flow on naturally. Remote sensing from orbitting satellites adds new dimensions and lays new foundations to supplement still more varied geophysical exploration and testing. Australia can boast some of the larger base metal mines in the world; rich gold and diamond mines, much of the world's proven uranium, enormous black and brown coal deposits, the largest coastal heavy mineral beach sand accumulations, with significant inland fossil reserves still to be fully assessed as in the Murray River Basin, and added. Platinoid metal deposits in the South Alligator Gorge may also be in world class, and there are major deposits of many other ores and minerals being assessed. The scope for new finds is extensive, that is, depending on favourable government policy and public appreciation.

EXPLORATION THEN AND NOW Between the two World Wars, mineral exploration was left largely to prospectors. Their numbers and wanderings were such that few of the more obvious outcrops of ore, often in unusual eye-catching colours or formations, rarely escaped their picks and hammers. Costeans and shafts were put down and if the prospect looked promising, there was always the company promoter or larger established company interested to buy them out. The history of such successes is too well known to be repeated here. World War II interrupted most serious prospecting and exploration and saw principally uranium and other strategic minerals being sought after vigorously - uranium search being aided by newly developed Geiger Mueller radioactivity counters and finally scintillometers. Aerial techniques came later. Post World War II witnessed the introduction of the magnetometer and its airborne equivalents out of submarine and ship detection techniques. Refined gravimetry followed, and then electromagnetism (refined extensively in Canada) and finally a number of electro-conductivity and resistivity techniques. Remote sensing via orbitting satellites is the latest innovation. Each has investigated new parameters and led to new ore discoveries in many situations. Bulldozers often moved in, removed shallow soil and other - masking cover, speeded up exploration but often gave exploration a bad name. Man's puny pick and shovel image was magnified a thousand fold. A new opposition developed, labelling such exploration effort as destructive. Hill-sides were scarred, new erosion initiated, and trees and lesser vegetation were destroyed, leading to ugly scars. Then followed new prohibitions, new rules and regulations and finally with the industry itself assuming new leadership and setting its own operational standards. A new generation of city-dwellers basking in the richnesses of these successes, has callously labelled mining "a robber" industry. New confrontations developed and a host of new Reserves, National Parks and other restrictions, whether justified or not, have been erected to limit, control, hamper and/or even halt the exploration industry in its tracks. A host of non-destructive, new or modified techniques has developed out of these potential new impediments. Much needless damage came to be avoided, but old impressions still die hard, or linger on. In the petroleum exploration industry much the same has applied. Survey and seismic lines were originally bulldozed straight and clear whatever the vegetation or physical cover. Explosive cratering and drill holes were left unprotected, and here too, accidents and public concern were left to devise penalties and force the more careless elements of industry to change their ways, and change for the better most now have. As a person once vitally implicated and eventually deeply concerned, I witnessed closely the great changes for the better that have emerged. New environmental awareness did develop significantly in the 1960's and 1970's in particular, so that many of we early culprits soon were writing articles warning of the dangers to the environment and eventually taking progressive steps in designing practical safeguards. Government and private industry became united in setting up new standards. Neither previously had had scrupulously clear consciences. Still, it was in the course of offshore scuba diving that I witnessed the worst examples of pollution involving significant sea floor, marine-life destruction. Quarrying of coastal cliffs in particular, revealed the worst examples, and local beach destruction or overextension by waste gave warning of what could be happening offshore. Still, I was never prepared for the turbidity and destruction that I witnessed in one instance at mere 10 fathom depths and several kilometers out to sea. The destruction in the French

battle fields of World War I could never have appeared more extreme. Large areas of dead hammer oysters, and of razor fish and sponges, lay covered in fine ooze and were devastated. Shoreward, wide increments of coarser white sediment waste glistened almost pristinely and failed to alert to deeper water destruction off-shore. Fortunately most of us learn from experience and the foregoing era of thoughtless damage is being buried in more ways than one. Now it is chemical toxins and residues, also raw sewerage and river-borne erosion products that are of greatest concern. The miners are now far more cautious, and now provide many of the leading personalities and influences in the continuing fight against further damage and pollution. EXPLORATION INDUSTRY SENSITIVITIES The Mining and Oil exploration industries have come a long way in recent decades. In the process they have developed sound environmental protection field guides and codes of practice. Relevant Federal, State and Local Government laws and regulations are carefully listed, and the rights of other land users are recognised and emphasized. Safety and occupational health requirements are also carefully enunciated and every attempt is made to minimise impacts on the environment. Their actions are now mostly exemplary. Companies are encouraged, where possible, to employ their own environmental officers or advisers and consult with various relevant government mining and/or petroleum authorities and land holders prior to and during all field programmes. Field teams are advised to use existing access ways and facilities wherever practicable, to minimise disturbance to vegetation and to avoid disturbing the natural drainage. Great care is to be exercised at all times in disposing of wastes and litter. Introduction of domestic or feral animals, noxious weeds and all exotic species must be strictly avoided as a matter of priority. Employers and contractors are being trained to understand the environmental implications and potential impacts of their activities. The uniqueness and potential fragility of much of Australia's arid lands is being emphasized as is also protection of its native plants and animals. Wind rows must be eliminated from newly constructed tracks and where possible rolling or slashing instituted instead of grading and bulldozing. Erosion control in relation to new works needs to be planned carefully and where excavations are required, top soil is to be carefully removed and stored in accordance with the depth of the local soil profile. Upon completion of operations involving excavations, fill is to be replaced carefully and sown with grasses or planted with tree seedlings. Environmentally sensitive areas such as parks, wildlife sanctuaries and scenic reserves require special degrees of protection. Animal breeding areas should be avoided, or entry delayed. Wetlands require particularly careful treatment, as also all coastal situations. The seismic industry in particular, has carefully moved to less harmful methods of imparting energy into the ground or into the sea. Use of chemical explosives has been extensively superceded by Vibroseis and similar techniques, and to sea, air guns and other less destructive methods are constantly being improved.

8 Specialised ground vehicles with wider, less sculptured, tyres and also helicopters are in wider use to provide further protection. Good public relations and preliminary reconnaissances that forewarn land holders, pay dividends. Maintaining these relationships throughout operations is equally essential, as is also the need to consult with such land holders during clean up and eventual withdrawal. Gates must be left as they were found. Interference with water supplies or risk of fire must be avoided assiduously. All constructions must be removed except with the approval of the land holder, and all survey markers removed except essential datum references. Special effort should go into avoiding unnecessary destruction of trees or lesser vegetation, and particularly in the approach to public roads and drainage lines. Where possible disturbance to drainage channels should be affected by provision of culverts or diversion drains. In the case of seismic shot holes or test drilling for cores and sampling, all such openings should be back filled as quickly as possible. Camp sites should be chosen in consultation with land holders to cause minimum disturbance to local constructions (including roads, drains and watering points). Rubbish and sewerage pits must be carefully sited, and subsequently covered over with carefully chosen fill or top-soil. Protection from burrowing animals needs to be carefully considered. Where deeper drilling operations are planned, drill pad clearance is to be limited to only that necessary for safe operation. Sumps must be of adequate capacity to avoid spills and topsoil retained handily for efficient reclamation. Flare pits are to be designed well clear of access tracks and vegetation. Fire fighting equipment is to be kept on site at all times and must be maintained in efficient working order. All such wells upon completion must be cased, plugged and marked in accordance with statutory requirements as "suspended" or "abandoned". Where drying out of drilling muds is not practical, off-site disposal or mechanical dewatering must be provided for. Oil-based muds are to be re-used or re-sold where practicable, or if to be disposed of, then incinerated or dealt with as otherwise approved or directed by the local authorities. Disposal of hazardous chemicals must be in accordance with the requirements of the Health Department or other relevant authority. Where significant bulldozer cuts are required for the exposure of ore bodies or coal seams or for bulk sampling, such excavations will require extensive refill, also reforming to near original surface, and top soil replacement. A degree of reseeding may be necessary, or where more extensive restitution is required, also tree planting with native or other approved tree types. The industry has indeed come a long way since the 1970's and has become an example to many others.

WHAT OF THE FUTURE? The exploration industry will never be perfect. Its leaders and operators have, however, genuine reason to be pleased with progress so far, yet we must all remain ever watchful. Despite such claimed successes, we are all participants in a much broader global scenario. Heavy reliance has still to be placed on oil or coal burning transporters and field equipment. A major proportion of electricity generation also is from such CO2 producing sources, all of which pollute the biosphere to a greater or lesser extent. In contemplating the longer term future of earth-bound civilizations it is difficult not to be somewhat pessimistic. Carbon dioxide and other "greenhouse" effects, the continued depletion of the protective ozone layer, also industrial, agricultural and urban pollution, rising sea levels, melting ice caps, mutating diseases, plagues, acid rain and the possibility of nuclear and/or poison gas warfare and many other threats, are almost too horrendous to contemplate. Can man's ingenuity and technology slow, or more desirably, turn, such tides? Western civilizations hunger for more oil out of the turbulent Middle East in particular, the widening gulfs between the "haves" of the affluent West, and the poverty of the "have nots" of the under-developed countries, plus fundamental religious differences, may be insurmountable in the brief span of the next few decades. A "nuclear winter" brought on by dust clouds raised in a prolonged nuclear interchange, could conceivably devastate the world's food bowls and the oxygen-regenerating tropical forests. The earth's powers of rehabilitation may be insufficient to counter such catastrophies. The geological record warns us that mass extinctions do occur from time to time. That 90% of the biota appeared to have been wiped out at the end of Permian times 250 million years ago, and that the whole kingdom of the Dinosaurs ended catastrophically at the end of Cretaceous time possibly as the result of some lesser disaster - comet strike, massive vulcanism or other, only 65 million years ago. Some lesser polluting technique of economically converting coal or liquid petroleum energy into electricity as via fuel cells or other, may yet be possible. Greater energy efficiency in the automotive transport industry is overdue. Solar energy photo voltaics demands far greater investigation and application. Also wind, wave and tidal energy, atomic power generation, or better still, nuclear fusion, offer the best long term options in these fields. Here the extreme "green" movement has to be convinced by practical and safe demonstration that nuclear power can be virtually non-polluting and safe, providing however that wastes can eventually be transported and stored more safely and securely for incredibly long periods. It is my personal belief that giant stopes resulting from mammoth mining operations such as at Roxby Downs and possibly Mt. Isa, could offer long term safe storage for even the most dangerous wastes. At Roxby Downs, for example, radioactive ores were previously safely contained in place there for more than one billion years. This was at kilometer depths, safely out of reach of circulating ground waters and in one of the more stable pieces of earth crust in existence. There is no doubt in my mind that the mining industry, in particular, can keep the world supplied efficiently and economically in metals, materials and energy for centuries to come. More of its profits must be re-invested in new technology relating to non-polluting energy needs, including the search for possible abiogenic hydrogen and methane from deep in the earth's crust. Continued self and governmental regulation will be tightened wherever necessary to assure environmental protection and industrial co-existence.

still more industry-based effort will be required to provide leadership in converting world action to far stricter environmental conservation, and in further reducing mining and industrial pollution, and in the development of more non-polluting power producing devices.

Ultimately power production must convert extensively to atomic energy, solar power or nuclear fusion and finally to a hydrogen-based economy. Increasingly the exploration, mining and petroleum producing industries will employ more environmental scientists on their normal staff, and such expertise will be employed at every stage in company operations. Our extractive industries must provide new leadership, set new standards and be prepared to stand up vociferously against any and all poorly informed criticism.

ENVIRONMENTAL GEOSCIENCE Stanley H. Ward Anacortes, Washington, USA Problems arising with protection and cleanup of our environment include and impact on groundwater, surface water, oceans, ocean bottoms, coastal erosion, waste disposal, waste cleanup, cropland sallnlzatlon, desertification, earth movements, nuclear accidents, radon emanation, archaeological site preservation, foundations, dams, and atmospheric pollution. There are many subdivisions under each of the topics listed above. For example, under waste disposal one may include residential garbage, industrial garbage, chemical waste containment, nuclear waste containment, underground vaults for nuclear waste containment, landfills for garbage containment, tailings ponds for mining waste, and reinjection reservoirs for petroleum extraction residues. New chemical ponds, underground vaults, landfills, tailings ponds, and reinjection reservoirs require careful design for prevention of leakage and monitoring should leakage occur. Old ponds, vaults, landfills and reinjection reservoirs require delineation, determination of contents, delineation of contaminant plumes, and cleanup if the environment is materially affected. Thus the scope of problems to be studied is enormous and requires carefully considered and integrated use of geology, geophysics, geochemistry, geography, hydrology, engineering, oceanography, well logging, and remote sensing. While I have illustrated above the depth of the problem only for waste disposal, I shall provide in my presentation elaboration of the depth of the other problems listed in the first paragraph of this abstract. Wherever practical I shall illustrate the problems by examples taken from throughout the world.

Technical Session 1(a) Advances In Petroleum Exploration IMAGE PROCESSING OF INTERPRETED 3D SEISMIC DATA TO ENHANCE SUBTLE STRUCTURAL FEATURES/LINEATIONS Larry A. Tilbury^ * and David Bush^ % o o d s l d e Offshore Petroleum Pty Ltd, Perth, WA ^Aerodata, West Perth, WA With the ever increasing number of 3D surveys being acquired, it is essential that 3D interpretation be both effective and efficient to ensure that maximum information is derived from the data. In this context, Woodside has put considerable effort into the development and application of novel techniques in seismic interpretation over recent years to assist in the optimal interpretation of its existing and planned 3D seismic data sets. These studies have included comprehensive analysis of seismic horizon attributes, coupled with the application of image processing techniques, to enhance subtle features not readily discernible by other means. Image processing, commonly applied in mineral exploration to enhance landsat images and potential field data, has been applied to interpreted seismic horizons from 3D data sets with outstanding results. Two aspects of image processing which have been utilised with good effect are data illumination and combined displays. The illumination technique involves artificially illuminating the horizon by a "sun" and varying the "sun" angle (azimuth and elevation). This tends to enhance features normal to the "sun" direction. Combined displays have allowed the Integration of different attributes onto one map using both a black/white scale and an overlay colour scale. Application of these techniques in the Goodwyn South/Tidepole area has provided new insights into the nature of subtle features of the seismic data. For example small faults, barely discernible using conventional mapping techniques, are clearly revealed and can be traced with confidence along their strike. Moreover, the dip direction of these faults is readily apparent. In particular, the illumination and dip displays enhance the fault trends, while azimuth displays combined with other attributes highlight the interrelationship of faults and direction of fault throw. Integration of all these attributes/displays during interpretation has allowed a clearer understanding of this structurally complex region. Potential also exists to highlight even more subtle features such as cuestas associated with the subcrop of resistant beds. This response was utilised recently to assist in targetting development wells in the North Rankin Field. Further development and application of these image processing techniques, coupled with horizon attribute mapping (dip and azimuth) will result in more confident and better interpretations, and hence will assist the orderly and optimum development of Goodwyn and other fields during the 1990's.

PALAEOGEOGRAPHIC, DEPOSITIONAL AND AGE CONTROLS ON THE COMPOSITION OF PETROLEUM SOURCE ROCKS AND THEIR DERIVED OILS: BASIS FOR A PREDICTIVE MODEL Trevor G. Powell and Roger E. Summons* Bureau of Mineral Resources, Geology and Geophysics, Canberra An important control on the composition of crude oils is the depositional environment of the source bed. This is related both to the nature of the primary source material (algal, bacterial and higher plant) and to the depositional conditions which control the extent and nature of bacterial reworking prior to burial. Advances in geochemical awareness, molecular palaeontology and analytical capability have recently contributed to dramatic improvements in our appreciation of the origins of specific chemical fossils found in crude oils and source rocks. These comprise both isotopic anomalies and molecular fossils such as hydrocarbons. For example, if a fossil hydrocarbon can be accurately traced to its precursor lipid, and thence to a designated organism or class of organisms, it may also be a useful marker for the special environmental conditions favoured by those organisms. In combination with depositional and palaeogeographic models of source bed distribution this information aids in the prediction and assessment of the likely source beds for petroleum and may be used to trace the origins of oils. Chemical fossils, including fossil hydrocarbons, can be roughly discerned as having origins from eubacteria, archaebacteria or eukaryotes. Those that derive from eubacteria and archaebacteria generally indicate past activity of some particular biogeochemical process such as methanogenesis or sulfate-based metabolism. These can be particularly useful as palaeoenvironmental indicators. Molecules which originate from eukaryotes, specifically planktonic algae and vascular plants, can sometimes be traced to a very select group and thus potential environment and age mariners. Our studies of Australian oils and petroleum seeps have revealed some unusual features of hydrocarbon composition that can be related to specific biological inputs. Knowledge of their preferred habitats allows us to identify particular features of their source beds. For example, there are distinct patterns of steroid hydrocarbons which arise from marine and non-marine dinoflagellates. These are found in Mesozoic and Cainozoic oils and are absent from those of Palaeozoic age. Certain vascular plant and algal and bacterial markers are diagnostic for lacustrine deposition while other hydrocarbon types correlate highly with the presence of clays or specify carbonate deposition. It is thus possible to establish an inventory of biomari^er occurrence against depositional setting of the source bed which can be used to make firm assessments about the nature of depositional environments of source beds and to exclude possible source rock types for the origin of particular oils. In conjunction with sequence concepts it may be possible to use this information to predict the likely stratigraphic and geographic distribution of source rocks and their hydrocarbon composition.

13 ROLE OF SANDBOX MODELS IN AIDING SEISMIC INTERPRETATION OF FAULT PATTERNS A. McCoss Shell Research, Rljswljk, The Netherlands Despite the widespread success of 3-D seismic in resolving complex fault geometries, many interpreters are still faced with mapping faults from inadequate grids of 2-D seismic, or in areas of poor data quality. To help constrain interpretations, conceptual geometric and kinematic models are useful, based on experiments in which the boundary conditions are well-defined. For scaled modelling of fault geometries we have found sand a convenient model material, and we have been applying sandbox techniques for some 15 years. Recent developments in X-ray tomography allow us to follow the evolution through time of the 3D shape of faults in densely packed sand, since the dilated sand along the shear zones has a lower density than the undisturbed material. Some examples show how seismic interpretation has been directly influenced by sandbox models: 1)

Experiments simulating inversion of an existing graben led to recognition of a twophase history for a foreland fault zone.

The simultaneous activity of intersecting conjugate faults was examined, and allowed recognition on seismic sections of contemporaneously active (rather than sequentially forming) conjugate fault sets.

The along-strike transition between domains of oppositely dipping, parallel normal faults was shown to be possible without the presence of perpendicular transfer faults. Examples were later confirmed from 3-D seismic based fault maps.

Sandbox experiments have also been used to observe the growth of fault arrays and fault coalescence phenomena, and to study the differences in fault styles above and below a viscous layer.

Technical Session 1(b) Advances In Coal, Groundwater and Engineering

GROUNDWATER AND SALINITY MANAGEMENT IN NEW SOUTH WALES: AN OVERVIEW TJ. Verhoeven Department of Water Resources, Parramatta, NSW Groundwater is one of the most important natural resources for NSW, supplying in excess of 350,000 megalitres (ML) per annum for agriculture and grazing, 10,000 ML for industrial, commercial and mining purposes, and 60,000 ML for 160 city and town water supplies. The resource also has a high economic value for new developments, as surface water resources in parts of the State are already fully committed to existing developments. Groundwater is also a source of some of this State's most serious environmental problems, as shown in coastal aquifers such as the Botany Basin, and in the MurrayDarling Basin with its increasing problems of salinisation and rising water tables. Problems are being tackled within a hierarchy of human resources and programs. Investigations and management of groundwater systems range in scale from local (irrigator, town) to regional (shire council, Total Catchment Management Committee) to basin-wide and State-wide (government agencies, national resource programs). The magnitude of potential environmental degradation and impact on beneficial uses are reflected in the number and range of agencies co-ordinating their efforts to address the problems, with actions and decision-making being taken at the most appropriate level. The Department of Water Resources is applying the different activities of groundwater management - assessment, planning, development, regulation and policy - in an interrelated, multldlsciplinary series of wori< programs including: Regional field investigations (surface and down-hole geophysics, drilling, testing, monitoring, assessment) of major alluvial valleys and the Murray Geological Basin. Hydrogeological mapping of the Murray Basin and Darting River Drainage Basin at 1:1000000 scale, and of alluvial valleys and the Murray Basin at 1:250000 scale. These maps, highlighting salinity and yield, are prepared from a computer data base as part of an interstate program. Regional and local scale groundwater modelling to estimate the effects of longer term issues, and to more efficiently allocate resources to the management of water and salinity problems. Studies of point sources of pollution of groundwater, maintenance of the State's groundwater pollution register, and the development of guidelines for the prevention of groundwater pollution. Studies and remediation of irrigation salinisation, including methods to manage land salinisation and waterlogging, as well as measures to reduce groundwater

15 induced river salinity. Groundwater quality deterioration by pesticides, fertilisers and nutrients is also under examination. •

Identification of recharge areas to help target vegetation programs, including the use of remote sensing techniques.

•

Studies of dryland salinisation, including eight regional reconnaissance surveys, and process studies of nine small representative catchments. The aim is to provide a system of analysis to determine technically and economically the most appropriate scenarios to recharge/discharge control for various rock types, land use types and time frames.

•

Preparation and implementation of groundwater management plans. Developed in consultation with local groundwater users, these plans provide details of the way in which groundwater is to be accessed and the conditions under which it may be used.

The issues of groundwater and salinity management are complex and changing. Broad findings from investigations include: •

The "do nothing" option will result in significantly degraded environments and agricultural industries, in both dryland and irrigated areas of the State.

•

Solutions must be site specific; there are no general Basin-wide or regional solutions.

•

Most solutions are centred on groundwater, its quality and depth. Solutions consist of one or a combination of options including changed land management practices, surface drainage and subsurface drainage. These require a multidisciplinary approach.

•

Solutions include the conjunctive use of surface water and groundwater resources.

GEOPHYSICAL TECHNIQUES FOR DETAILED EXAMINATION OF COAL MINE SEAMS IN ADVANCE OF MINING Joseph L. Condon^ and George Schneider^ ''Geophysicist, DOI, Bureau of Mines, Denver Research Center ^Geologist, DOI, Bureau of Mines, Denver Research Center The Denver Research Center of the United States Bureau of Mines is developing geophysical technology to provide a highly detailed picture of what lies in the path of advancing coal faces. Safety and economic considerations make it desirable to accurately locate natural phenomena such as, faults and sand channels before mining reaches them. Also it is necessary to map man-caused hazards such as abandoned mines and oil wells that penetrate the seam. Two geophysical tools are being developed, to locate those hazards. First, cross-borehole acoustic technique using multiple source and receiver locations. Boreholes are drilled vertically from the surface or horizontally from the mine face. Second, an electromagnetic system applied from the

16 working face underground. Both systems employ geotomographic algorithms for data analysis. Two different cross borehole systems have been developed. The first uses a "sparker" for the acoustic source. The source consists of 1) a capacitor to store electrical energy, in the case of the prototype system 500 joules, and power supplies to recharge the capacitor, 2) a rectifier switch to rapidly discharge the capacitor, and 3) a spark chamber filled with an electrolyte solution, salt water, and divided by a nonconducting partition with a small orifice connecting the 2 halves of the spark chamber. The second acoustic cross borehole system uses a driven cylindrical bender transducer as an acoustic source. A cylindrical bender transducer consists of an array of coaxial piezeoelectric elements arranged to form a cylinder. The elements are formed to flex or bend when voltage is applied so significant displacement is achieved. The advantages of a bender transducer for an acoustic source are 1) the acoustic signal produced can be any arbitrarily shaped waveform within the bandwidth of the device and 2) the device can operate as an acoustic monopole, dipole, or quadrapole to enhance the generation of specific modes of propagation. Cross borehole measurements from the systems are processed with a computer program developed from a curved ray path tomographic image reconstruction algorithm. The application for the system has been to locate old underground mine openings and any failure in the rock mass above the openings before subsidence is apparent at the surface. The purpose is to direct subsidence prevention programs because of the high costs associated with the repair or replacement of subsidence damaged structures in the older coal mining regions of the United States. The bender system will also be developed to image stress transport in coal seams and the rock mass above the coal seam, and the transfer of stress to the gob, during longwall mining. Both tomographic and holographic algorithms will be used to describe the changes in acoustic propagation associated with changes in stress and brittle failure in a rock mass during the operation of a longwall panel. The electromagnetic system is a prototype synthetic pulsed radar. The discrete frequencies of the Fourier transform of an arbitrarily centered broadband pulse are transmitted individually by the system, so that the total power coupled into the ground is significantly increased. The system has been used directly from the face in underground coal mines to image the interior of coal panels and support pillars. Both iterative and direct inversion algorithms have been used to calculate tomograms of the coal seam from measurements taken with the system. Direct inversion methods are faster than iterative algorithms for tomographic image reconstruction and applicable where noise in the image from refraction is not a significant problem.

17 A NEW DIRECT NON-INVASIVE GROUND WATER DETECTION TECHNOLOGY FOR AUSTRALIA M. Shirov^, A. Legchenko^ and G. Creer^* ''institute of Chemical Kinetics and Combustion of the Siberian Division of the USSR Academy of Sciences 2 B H P Company Ltd Recently, novel geophysical technology has been developed which is capable of determining groundwater content at various depths without drilling wells. The instrument is the Hydroscope and relies on the principles of Nuclear Magnetic Resonance (NMR) tomography. Using the Hydroscope, it is now possible to undertake a regional hydrogeological survey to map the distribution of groundwater reserves both in plan and in depth with high efficiency, thus ensuring a reliable choice of the most productive areas for water supply bores. Some results of Hydroscope tests on sedimentary, watercontaining rocks in South-Eastern Australia, undertaken during February and March 1990, together with several theoretical and experimental results obtained previously by the developers of the NMR water prospecting technology are presented.

Technical Session 2(a) Advances In Mineral Exploration AIRBORNE MINERAL MAPPING WITH THE GERIS AND GEOSCAN AIRCRAFT SCANNERS FOR MINERAL EXPLORATION AND MAPPING J.F.Huntington*, M.D.Craig, J.N.Churchill, A.A.Green CSIRO Division of Exploration Geosclence, North Ryde A major goal for geological remote sensing in the 1990s is the development of quantitative and semi-quantitative techniques for the operational sensing and identification of physically-based geological properties of the land surface. Chief amongst these is the mineralogical composition of the exposed residual or transported surface layer. Airborne sensors are now becoming available that allow much more precise identification of mineral groups and species based on optical spectrometry using visible and infrared reflectance characteristics. Amongst these airborne mineral identifications that have been achieved are the iron oxides, haematite and goethite; the sulphates, alunite and jarosite; the AL(OH) clays species, pyrophyllite, kaolinite, illite, sericite; the Mg(OH) minerals chlorite, talc, epidote and hornblende; as well as calcite. That this is technically possible has been demonstrated in Australia since the early 1980s. Only recently has the possibility of doing this routinely, as part of exploration or mapping programmes, become more feasible. Strategies and actual techniques for processing and analysis, as well as case histories of the types of mineralogical mapping that can be achieved with two such instruments, the GER 63-channel imaging spectrometer and the Geoscan 24-channel scanner, have been developed. Case histories that have been developed include both exploration applications over alteration systems, such as at Oatman, Arizona, and mapping applications, such as at Coppin Gap, in the Pilbara, WA. Mineral mapping, when it can be implemented operationally, should be considered as a potentially significant new technology that could ease the costly task of mapping and exploring this country in the decade to come. For both applications, new digitally based maps could be developed that could far better indicate the actual mineral composition (both primary and secondary) of the exposed surface and hence guide and reduce the cost of expensive field surveys. More precise lithological mapping, understanding of facies changes, metamorphic grades, weathering and alteration should be achievable with these techniques. As with any geophysical technique, consideration must be given to calibrating the airborne data for instrument and atmospheric effects, and to noise removal. Both considerations will determine the quality of the final mineral identification. Another essential requirement is the production of mineral and rock reference libraries of actual geological materials and mixtures, as seen by (convolved with) the various instrument sensor functions. When the calibration and the noise removal is successful, then it has been found that the airborne spectral data do indeed correspond well to the instrumentconvolved reference spectra. This then permits improved identification (not just discrimination) of the mineral content of the scene. Surprisingly we are also finding that spectra sampled with a relatively small number of bands, such as Geoscan's eight

2.0

Wavelength (nil Figure 1

2.2

MICROMETRES Figure 2

2.4

2.0

2.2

MICROMETRES Figure 3

2.4

20 Shortwave-infrared bands, can still permit mineral identification, at least in arid terrains. In Australia one of the major'tasks now being addressed in mineral mapping is the unmixing of scene components, or end-members, so that the end result of the remote sensing process can be expressed in geological terms, such as percentage mineral abundance, rather than the non-geological properties of radiance, reflectance or digital number. The foremost unmixing challenge in Australia is the separation of vegetation and mineralogy within scene pixels. Subsequently unmixing of individual mineral components can provide maps, as indicated above, of the abundance of different mineral and mineral groups. When both the abundances and the actual mineral groups and species present are interpreted in their full geological and geomorphological context, against some particular geological or mineralization model, then these new data become significant pointers to new exploration target areas. Figure 1 illustrates five high resolution mineral spectra (for 3 kaolinites, alunite and buddingtonite) and the same minerals as "seen" by the eight shortwave infrared bands of the Geoscan IVIark II scanner. The alunite spectrum is the second from the bottom. Figure 2 illustrates how well the actual airborne spectra for alunite extracted from 40 adjacent image pixels (the upper twenty-two spectra are alunite) correspond to the laboratory spectra in Figure 1 (after calibration and noise removal); they indeed permit an identification of the likely terrain composition, with little or no "a priori" knowledge of the area. Mineral mapping is not universally applicable, depending on the types of minerals p r e s e n t , the e x p o s u r e and w e a t h e r i n g h i s t o r y . H o w e v e r , a g e n e r i c , felslc/mafic/ultramafic Identification Is possible even if the specific minerals cannot be resolved. Future versions of these systems need to provide more precise digital landform information (digital elevation models) so that we can understand the setting of a particular mineralogy In its true unweathered or weathered geomorphological and structural context.

POLYMETALLIC MASSIVE SULPHIDE EXPLORATION CASE HISTORIES MT. WINDSOR VOLCANIC BELT, NORTH QUEENSLAND Simon D. Beams Terra Search Pty Ltd, Townsvllle, Old The Cambro-Ordovician Mt. Windsor Volcanic Belt, south of Charters Towers, is the most prospective geological province for volcanic-hosted massive sulphide mineralisation in North Queensland. In a little over fifteen years, explorationists have discovered several major ore bodies within the belt, using a combination of geological, geophysical and geochemical techniques. Cu-Pb-Zn-Ag-(Au)-Ba mineralisation is hosted within a 150km long submarine volcanic package which consists of rhyolite to andesite composition lavas and fragmentals interlayered with volcaniclastic and epiclastic sediments. The succession generally strikes east-west and youngs to the south. It is characterised by low grade slate belt style deformation of lower greenschist fades, with simple open folding about a subvertical slaty cleavage trending east-west. Structural complications occur locally.

21 notably in the Highway Synclinorial Zone located in the central part of the belt. Fluviatile deposits of Tertiary Campaspe Beds cover large sections of the stratigraphy. The history of nfiassive sulphide exploration has evolved to accommodate the different styles of mineralisation and varying degrees of concealment by cover rocks. The first deposits discovered had outcropping gossans which produced strong base metal stream sediment and soil anomalies. The initial discoveries can be divided into two separate classes on the basis of their sulphide content. There is a concomitant range of responses to different geophysical techniques. The high sulphide deposits (Thalanga 7 mt and Magpie approximately 0.5 mt) are good conductors and produce prominent ground and downhole EM anomalies. On the other hand, IP has been an effective exploration tool in delineating the low sulphide deposits (Liontown, approximately 2 mt; Handcuff, approximately 1 mt) which contain minor massive pyrite and are characterised by fine grained iron-poor sphalerite. Aeromagnetics has outlined the regional stratigraphy and structure; however, as there is little magnetic contrast within the deposits, detailed ground magnetics is not an orefinder at the prospect scale. The mineralisation at Thalanga, Liontown and Handcuff is mostly in stratiform lenses of banded sulphides with barite, fine grained silica and carbonate, interlayered with siliceous volcanic sediments and rare Fe/Mg rich chemical sediments. The massive sulphide lenses and associated sediments occur at breaks within the predominantly rhyolitic volcanic pile. The current interpretation is that the banded massive sulphides are volcanic exhalative in origin, formed contemporaneously with the host volcanic sequence. This has allowed the utilisation of conceptual geological models centred on the identification of key stratigraphic units/packages and key (primarily feldspar destructive) alteration features. Extending these geological concepts into areas of cover, coupled with bedrock and Campaspe Beds RAB geochemistry, led to the discovery of concealed deposits: for example Thalanga East and Waterloo. RAB drilling also led to the discovery of the large pipe-like massive pyrite-chalcopyrite body at Reward which is transgressive to the stratigraphy and is interpreted as being emplaced syn- or post-cleavage development at the time of peak metamorphism. Electrical geophysical methods (ground EM, downhole EM, Mise a la masse) successfully delineated the massive sulphide mineralisation (approximately 5 mt of pyrite), although the deposit has a short strike length (200m), and is blind (occurring under 100m combined thickness of Campaspe Beds overlying deeply weathered gossanous volcanics). Detailed surface geochemical surveys, geological mapping and airborne EM has effectively screened the Mt Windsor Volcanic Belt for large scale outcropping massive sulphide deposits. Future discoveries of blind or concealed deposits in this highly mineralised belt are likely to involve extensive bedrock drilling under cover, geological or structural targeting of extensions to previously recognized mineralised zones or geophysical techniques which can "see under" deep, oxidized, conductive overburden.

THE SCUDDLES MASSIVE SULPHIDE DISCOVERY: AN EXPLORATION CASE HISTORY Stuart H. Robinson^* and Susan M. Belford^ Carpentaria Exploration Company Pty Ltd, West Perth, WA ^Aztec Mining Company Ltd, Victoria Park, WA The discovery of the Scuddles volcanogenic massive zinc-copper sulphide deposit (400l<m NNE of Perth) in 1979 was the result of an integrated exploration programme. The initial diamond drill hole was proposed on the basis of anomalous copper and lead geochemistry in chloritised tuff and chert in RAB drilling across a 120 nanotesia aeromagnetic anomaly. The first 3 holes intersected interesting but sub-economic grades of copper, lead, zinc and silver mineralisation. A Pulse EM survey was then completed and identified a moderate conductor associated with the mineralised horizon. Diamond drill hole 80-4 was drilled benearth SC-3 and intersected massive sulphide which included a section of 25.5% zinc over a true width of 6 metres. Although the next 2 holes were unmlneralised, subsequent drilling quicl<ly established that a discovery of economic significance had been made. The discovery was made by the application of a well planned and carefully executed exploration programme with an emphasis on direct field geological input. It emphasises the need for flexibility in an exploration programme so that encouragement in one area can be followed up while continuing to generate and evaluate new targets.

23 Technical Session 2(b) Advances In Regional, Crustal and Geothermal

THE TRIPLE-JUNCTION STRUCTURE OF MANTLE PLUMES AND CONTINENTAL RIFTING Gregory A. Houseman Department of Earth Sciences, Monash University Numerical experiments show that the hot thermal plumes in a convecting mantle have a complex 3-dimensional structure that is approximately axisymmetric near the top of the convecting layer, but followed down towards the base of the layer evolves into a branched structure formed by the bifurcation of a hot sheet. The uplift above a thermal plume is thus characterised by a dominant axisymmetric component, to which a small, irregular, but characteristically triple-armed, perturbation is added. An explanation for the characteristic triple-junction geometry of continental rifts has long been sought in terms of the mechanical properties of the lithosphere, but these experiments suggest that the rift may inherit its basic geometry from the underlying thermal plume.

PLUME TECTONICS AND THE DEVELOPMENT OF STABLE CONTINENTAL CRUST Robert 1. Hiir, Ian H. Campbell and Ross W. Griffiths Research School of Earth Sciences, The Australian National University The early phase of a new mantle plume may result in areas of basaltic volcanism and crustal reworking 1000-2000 km across. Uplift of pre-existing continental crust by up to 800 metres may be sufficient to initiate large-scale tectonic processes, particularly extension. Conduction of heat from a hot plume layer emplaced into the uppermost mantle can result in large scale anatexis of pre-existing continental crust, and in the formation of a granitic upper crust; the Late Archaean reworking of the eastern Yilgarn Block of Western Australia provides a possible example. The magmatic development, and time and length scales inherent in plume initiated continental reworking are similar for postulated ancient and modern examples, and it is inferred that plume-initiated magmatism and tectonics may play an important role in the development of internally differentiated continental crust.

THE GIPPSLAND BASIN DEEP SEISMIC REFLECTION/REFRACTION GRID P.E. Williamson*, J.B. Willcox, J.B. Colwell and C.D.N. Collins Bureau of Mineral Resources, Canberra City, ACT Deep crustal seismic studies carried out in the Gippsland Basin, under the auspices of the Continental Margins Program of the Bureau of Mineral Resources, represent a unique evolution of the method in response to the requirements of petroleum exploration. The study was designed, inter alia, to define the three dimensional basinal

architecture in sufficient detail to be an aid to understanding the structural controls on basin development, sedimentation, trap formation and migration of hydrocarbons. This contrasts with deep-crustal seismic studies worldwide that are dominantly two dimensional in nature. The study utilised an approximate 1650 km grid of seismic reflection data designed to image the crust and upper mantle. The data were also collected so as to provide regional stratigraphic ties between exploration wells. Seismic refraction data at onshore stations were collected by BMR and Monash University, utilising shots fired during the seismic reflection survey, to provide velocity control to facilitate interpretation of the reflection data, as well as to provide an independent gross estimate of the configuration of crustal units. Deep crustal seismic reflection data within the Gippsland Basin proper show little development of highly rotated fault blocks characteristic of rift basins; such features are restricted to the margins of the basin. This suggests a low level of extension within the basin proper, perpendicular to the basin axis, since the formation of basin beginning probably in the Lake Jurassic/Early Cretaceous. Consequently, the main movements along faults in forming the basin depocentre could have been transverse. The margins of the basin proper are associated with major normal fault systems which displace the lower crust. Structures from the formation of the basin to Tertiary time show multiple periods of extension and compression probably relating to periods of movement transverse to the major sinuous bounding fault systems. The interaction between the major Tertiary compressional pulse and the prior architecture of the Gippsland Basin was probably fundamental in providing trapping structures at top Latrobe Group and migration paths for hydrocarbons. The deep-crustal data set may thus provide a predictive tool in the search for further petroleum accumulations.

25 Plenary Session III (Note: No abstract available for 2ncl paper: "Exploration Management: Petroleum" J. Armstrong Santos Ltd., Adelaide, S.A.)

MINERAL EXPLORATION IN THE 1990's: MANAGING TO SURVIVE, SUCCEED, AND CREATE WEALTH M.J. Smith Austpac Gold N.L., Sydney, N.S.W. Exploration management concerns people, property and money. People come first because the effectiveness of an exploration company depends on the motivation, commitment and ability of its front line personnel. Selecting, rewarding and training staff, recognising their accomplishments, ensuring their safety, providing necessary support, expanding their experience and sustaining their employment are the manager's tasks. Property determines the value of the company. Acquisition, farm-in-, farm-out, trade, sale and relinquishment are the tools of portfolio enhancement. Mining law, resource development history, local infrastructure, environmental expectations, tax rates and tax deductions, landowner participation, language and culture influence the manager to prioritize opportunities around the world. Geological prospectivity and commodity values are very significant but not always dominant criteria for target selection. Money is the life breath of exploration. Profit generating projects are the most stable source of funds, but major discoveries may also be achieved using funds raised through public subscription, rights issues and share placements. Income and expenditure are often controlled through Joint Ventures. Sharing the risk, combining assets, reducing exposure, relieving outlay and retaining equity are goals of joint ventures. The joint venture manager must fulfil his obligations to plan, forecast, budget and report to ensure continued funding of the Joint Venture. Fluctuating exchange rates can upset the most carefully planned budget. Legislative changes to taxes or royalties can destroy the bottom line profits of existing or planned operations. The ultimate exploration objective is not just to find a resource but to prove its viability, commence exploitation and generate wealth for the company, the community and the country. The most difficult task of the manager concerns risk - specifically, the very high risk of the job we undertake. The potential rewards are high but the probability of failure is similarly high. Despite the diversity of modern technology at hand, today's geoscientists face the same daunting inevitability as the prospector of years past. We will fail more often than we succeed. The manager must sustain morale, motivation and money until the big strike comes in. He must improve his luck and reduce the risk by persevering, by testing a large number of prospects and by keeping his team intact and funded.

26 CHAOS THEORY AND OPERATION: TERTIARY EDUCATION IN A POLITICISED, POLARISED ENVIRONMENT Ian Plimer Professor and Head, Department of Geology, University of Newcastle The Tertiary education system was once for the elite. Upon matriculation, entry was via a scholarship or by paying fees. Graduates expected higher earnings and higher taxation thereby supporting the Tertiary education system. The philosophy for experimentation was initially based on the premise that society is egalitarian. More recently, the philosophy has been to keep young people off the streets, solve youth unemployment and to postpone the structural problems of society. There is no denying that society needs to keep some tally on the cost of providing certain facilities and services, including teaching and research as well as to incorporate some feedback mechanism to respond to informal public demand. On the other hand, there is justification for a reasonable level of nervousness when the cost of tallying begins to compete with that of the actual productive work being surveyed. However, monitoring, accounting and directing have for the last two decades been real growth areas and are continuing as such while in university science and engineering courses, demand is static or falling. In many universities, growth has been prescribed as essential to survival and the consequences are alarming. For example, HSC entry marks into science and engineering are now as low as 253/500 and it is these graduates who will create the productive new wealth of the nation. The HSC entry marks for those who count this wealth is about 350/500. The great imbalance between the social and real sciences has been almost entirely moulded by the enrolment choices of 16 and 17 year old school children over a 25 year period. Although most of these do not learn much about science and even less about mathematics in their high schools, this does not mean that they are fools, because their choices echo the general perception that careers in science and technology are fraught with uncertainty and are financially relatively unrewarding compared to those involved with pestering people, manipulating money and gathering garbage. A recent analysis of all grades of engineers and scientists was inescapably monotonic with all these professionals at all levels becoming almost identical and falling below the projected mean Australian wage in 2015AD. With writing on the wall like this, it is no wonder that today's teenagers are deserting science and engineering in droves and opting for accountancy and management studies. Management is essential but it is equally essential for managers to learn something about which they are trying to manage. If this statement were an accepted truth in government and industry, then science and technology courses at tertiary institutions would be booming. There is an alarming lack of Australian graduate students in the sciences and engineering. The recent bout of restructuring has exacerbated the situation. Recent innovations in the field of taxation might also be expected to influence young people cautiously considering the future of Australian science and technology. Until about 3 years ago, most universities offered some graduate research scholarships to international competition. Ever increasing visa taxes and now $16,000 annual fees have wiped out this source of intellectual strength and Australian graduate students, the few that are left, will be the losers. Scholarship-holding foreign graduate students could well also have been regarded as probationary immigrants, with 3 or 4 years available to adapt to language and culture but in most instances, following successful completion of Australian PhD's, they are deported.

27 Australian undergraduates are now subject to the High Education Contribution Scheme or "degree tax". They do not need to pay this tax until they start earning. On the other hand, many of the better graduates find that they can still obtain offers of scholarships for post-graduate degrees abroad. These are amongst Australia's brightest young people and they are asking themselves why they should return home not only to receive lower salaries, but to be taxed for their initiative in obtaining a primary university degree in the first instance. Although some members of the community believe that it is correct for students to pay something towards the cost of their education, the response is that they already do. It takes them years to catch up with those from their school who have opted for the "dole" instead. It is in the long term interest of all Australians to live in a more educated, critically constnjctive community. We live in an age where even fewer people are engaged in the direct production of material or intellectual wealth but more and more are engaging in counting, preventing, managing or dreaming about it. For too long my discipline has been regarded as the recruiting grounds for industry with pressures to close earth science departments on the grounds of over production of graduates. We do not hear the same argument for history which is regarded as part of culture. Because the general community does not have even a basic understanding of our planet as part of our culture, the environmental movement has been able to flourish on ignorance, dogma and focussed political campaigns. Furthermore, both the US and UK mining industries have become increasingly alert to the implications of dwindling numbers of graduates because the industry has failed to convince society that they are wealth creators and not callous despoilers of the environment. This problem is exacerbated by the growing demand for natural science and engineering higher degrees which cannot be met by demand because our tertiary institutions are structurally unable to meet the demands of the 21 st century. I believe this sad scenario results from egalitarianism, the lack of long term planning by industry, the belief by successive governments that they can invent a better system, the abrogation of all responsibility by senior civil servants and governments, the inability of academics to participate in the real world, the increase in the standard of living and the decrease in the quality of life.

28 Technical Session 3(a) Petroleum Exploration I - Seismic Data Processing

THE ZERO VELOCITY LAYER: MIGRATION FROM IRREGULAR SURFACES Craig J. Beasley^* and Walt Lynn^ ^Western Geophysical, Singapore ^Western Geophysical, Houston, USA Seismic data acquired in areas with irregular topography are usually corrected to a flat datum before migration. A time-honored technique for handling elevation changes is to time shift the data before application of migration. This simple time shift, or elevationstatic correction, cannot properly represent wide-angle or dipping reflections as they would have been recorded at the datum. As a result, when elevation varies significantly, accuracy in event positioning may be compromised for migration and other waveequation processes, such as DMO. Although computationally intensive, wave-equation datuming can be-used to accurately extrapolate the data recorded over an irregular surface to a flat datum. Here, we propose an efficient technique for doing migration from irregular surfaces using almost any migration algorithm. As in elevation-static corrections, surface-recorded data are time-shifted to a horizontal datum; for our process, however, we choose that datum elevation to lie at or above the highest elevation in the survey. The choice of this datum elevation does not compromise final results because the datum elevation can always be adjusted to any other level after migration. In the migration step, the velocity is set to zero in the layer between the surface and the datum; below the original surface, the interval velocity represents the best estimate of the subsurface geology. By adding a zero-velocity layer, the migration algorithm is applied to the data from the flat datum and no lateral propagation is allowed until nonzero velocity is encountered at the recording surface. Synthetic and field data examples demonstrate that use of the "zero-velocity layer" significantly improves imaging accuracy relative to conventional migration from a flat datum. Moreover, the geologically derived migration-velocity field need not be adjusted to compensate for shortcomings in the datum-static procedure. Furthermore, the scheme can employ the same efficient finite-difference migration algorithms used in conventional processing. The technique can be extended to prestack processes such as DMO, shot- and receiver-gather downward extrapolation and migration and thus suggests a unified approach to processing data from irregular surfaces.

29 ET. - A SLANT-STACK TRANSFORM OF THREE DIMENSIONAL DATA Brian Evans Curtin University, Perth, WA The application of the discrete Radon transfornfi for plane wave decomposition by the method of slant-stacking or Tau-p transformation, is well researched for in-line two dimensional (2D) seismic data recording, and is frequently used to filter events which mask useful seismic data. In three dimensional (3D) land seismic recording, the swath recording technique causes direct arrivals to be recorded at similar, if not identical times to the desired reflections, and if such arrivals are of identical frequency, the recorded data cannot be separated. This results in data which cannot be used in further processing. This paper introduces a transformation approach to 3D data. The transform is an extension of the 2D slant-stack approach and is the correct application for stacking three dimensionally recorded data since it sums along radial trajectories. The transform allows further processing of seismic data in the conventional Tau-p domain, as well as offset dependent filtering of individual swath records. Offset dependent filtering offers a new dimension in Tau-p domain filtering.

ACCURATE AMPLITUDE CALCULATIONS FOR TIME DOMAIN DM0 John 0. Bancroft Veritas Seismic, Canada The application of prestack partial migration or dip moveout to seismic data requires a very fast algorithm to provide an economical product. The time domain method offers the greatest speed, but must address the problems of aliasing, interpolation, and amplitude-phase distortions. The amplitude and phase corrections usually require some form of special processing such as Weiner-Levinson trace matching, or the Trajectory method developed by Hale. The proposed algorithm computes the amplitude in the time domain by a simple method that is based on the Trajectory algorithm. When care is taken to accurately treat interpolation, aliasing, and phase shift, results may be obtained that match the quality of transform methods, and without the need of matching filters.

30 ANISOTROPIC WAVE PROPAGATION AND ZERO-OFFSET MIGRATION

N.F. Uren"'*, G.H.F. Gardner^ and J.A. McDonald^ ^Curtln University of Technology, WA ^University of Houston, USA

In reflection seismology, migration may be defined as the transformation of apparent reflector positions to their true positions. In practice this usually means that diffractions are collapsed, and reflector dip angles are changed. When a medium is anisotropic, and the axes of velocity symmetry are tilted with respect to the horizontal, horizontal reflection events migrate laterally as well. The lateral migration of reflections from horizontal layers was studied by constnjcting an anisotropic scale model representing a medium in which the bedding is inclined to the surface. This situation may be classified as one of transverse isotropy with a tilted axis of symmetry. The elastic parameters of the anisotropic model were recovered by P- and SH-wave transmission measurements carried out to simulate a walk-away VSP. Numerical modelling of a P-wave CMP gather above a horizontal reflector in such a medium indicated that there would be an asymmetrical distribution of reflection points. The zerooffset reflection point was displaced laterally by a distance equal to more than 20% of the depth, and the spread of reflection points was 15% of the depth. The NMD velocity was found to be a function of offset. A zero-offset reflection survey was carried out on the model. The P-wave data were migrated with an anisotropic migration algorithm which may be applied to waves of any shape. On the resulting section, the horizontal reflection features are moved laterally by a distance equal to 20% of the depth back to their correct positions. The lateral displacement of reflections from a horizontal reflector beneath a medium with tilted anisotropic velocity characteristics has significance for the selection of drill locations when such a situation is encountered in the field.

31 Technical Session 3(b) Mineral Exploration 1 - Reglonal/Aeromagnetlcs

INTERPRETATION AND EXPLORATION SIGNIFICANCE OF THE 1988 EYRE PENINSULA AIRBORNE MAGNETIC SURVEY, SOUTH AUSTRALIA D.H. Tucker''* and R.G. Nelson^ ^Preview Resources Pty Ltd, Eastwood, SA ^South Australian Department of Mines and Energy, Eastwood, SA Over the Proterozoic and Archaean rocks of the Eyre Peninsula there is an extensive cover of calcrete and transported sands and clays, and this is indicated by exploration and water bore drilling to be 10-100 metres thick. Areas of thicker cover are relatively unexplored. To promote exploration in the area, and improve knowledge of the basement and the overburden, a fixed wing airborne magnetic, gamma spectrometric and very low frequency (VLF) electromagnetic survey was conducted in the Eyre Peninsula by contract during 1988. The survey planning was initiated by SADME and was undertaken as a cooperative project between SADME, the Bureau of Mineral Resources (BMR), and exploration companies. The new survey replaced relatively low quality 1600 metre line space, 150 metre ground clearance analogue data from airborne surveys dating from the 1950's. with 1000 and 500 metre line space, 100 metre ground clearance high quality digital data in the STREAKY BAY, YARDEA, ELLISTON, KIMBA and LINCOLN 1:250,000 map sheets. Geophysical data are available from SADME. The survey area is one of high magnetic gradients and high amplitude range in some parts (commonly 500-1 OOOnT or more), and low magnetic gradients and low amplitude range in other parts (commonly 10-50nT). Induced magnetisation appears to be the predominant influence in producing magnetic anomalies in the area (ie. magnetic high to the north and low to the south of an anomaly source). Accordingly the magnetic data can be useful in estimating dip of magnetic bodies. In general, the magnetic responses observed by this survey are caused by bedrock sources and not by the flat lying Tertiary cover. Depth to magnetic basement estimates made on several hundred anomalies over the area commonly indicate a range of 20-100 metres below surface, and this is consistent with the results of drilling. Because of the scarcity of outcrop and the paucity of anomaly target drilling, the correlation of magnetic anomalies with lithologies is at an early stage in the Eyre Peninsula. The magnetic anomalies seen in the new survey contour maps, pixel maps (imagery) and profiles can be classified in terms of approximately eight 'magnetic textures' as tabulated below. The textures can give a guide to inference of the likely subsurface lithologies and structures. Lithologies are inferred by correlation of anomalies with SADME 1:250,000 geological maps and SADME mapping at 1:5,000 and 1:10,000 scale along the coast near Cape Carnot and Sleaford Bay.

32 Texture Interpretation of Magnetic Anomalies in Eyre Peninsula No. & sign

Anomaly texture in contours & imagery (amplitude range) *** - textures with known mineralisation associations

Interpreted source

Mapped formation or lithology specific examples

Flat-smooth pattern

zero

(0-50nT very long wavelength)

Thick non-magnetic sediments or granite

Proterozoic & Paleozoic sediments in Polda Trough. ?Archean granitoid basement in KIMBA

Long wavelength high or low background (+/-200nT)

Regionally high or low magnetised terrain

Generally higher over Hiltaba Suite and lower over ?Archean terrain & Proterozoic seds

Mottled &/or granular pattern (+/-50 tolOOnT)

?Gneissic terrain ?Granitoid terrain ?Acid vole terrain

?Archean - STREAKY Some Hiltaba Suite Gawler Range Voles

4. +ve. rare -ve

Circular/elliptical highs, lows or annular 5-30km wide

Plutons, plugs and stocks (acid &/or mafics). Long wavelength = deep

Mostly Hiltaba Suite granitoids. Long wavelength in Polda Trough

5. H-ve or -ve

Bullseye/circular (can be on a single flight line 5-500)

Small plugs and short strike length dykes (dolerite & ?kimberlite)

Gabbroic plugs eg Inkster Quartz magnetite

6. +ve

Narrow curvilinear (very large range at least 5-1000nT) ***

Thin steep dipping magnetic beds approx. 100-200m thick mostly. Rarer - fault zones

Hutchison metaseds Lincoln granitoids Sleaford metaseds ?Arehean metaseds

7. +ve

Broad curvilinear can be 2-5 km or more wide (200-500)

Thick and/or multilayered magnetic beds, acid voles.

Gawler Range Voles Warramboo Fe Fmn Middlebaek Ranges Fe Fmns

Linear crosscutting. Pattern breaks & lineaments (5-200nT)

Dykes, faults and fault zones, mylonite zones

Gairdner Dykes (striking NW) Polda basement NE striking faults

+&-

* * *

8. +ve -ve zero

33 The new survey has revealed numerous single line and bullseye/circular anomalies of the kind expected over small Intrusives, including kimberlites. With kimberlites known near Port Augusta, the potential is high for diamond discoveries in the area. The known large metallic mineral deposits in Eyre Peninsula have impressive size and include the iron ore deposits in the Middleback Ranges and Olympic Dam (Cu, U, Au). These deposits both have associated magnetic anomalies. We can speculate that if an Olympic Dam type deposit subcropped, a gamma spectrometric anomaly might be detectable. Across Spencer Gulf, but within the same geological province lie the copper deposits of Wallaroo and Moonta. These also lie in a magnetically anomalous area. Within the new survey area, the known base metals deposits (Pb, Zn, Cu, Ag) appear to be small stratabound, stratiform and vein types and are not incipiently magnetic. However, they mostly occur adjacent to magnetic anomalies in structurally complex zones and an association may be important. The aeromagnetic data give the Eyre Peninsula a powerful basement mapping guide and a useful guide to ore location. This abstract is published with permission of the Director General of the South Australian Department of Mines and Energy.

REGIONAL AIRBORNE GEOPHYSICS, GEOLOGY AND INTERPRETED STRUCTURAL TRENDS, WESTERN VICTORIA R. Dalgarno"'*, G. Pettifer"" and M. Bacchin^ ^Geological Survey of Victoria ^Bureau of Mineral Resources An airborne geophysical program carried out by Kevron Pty Ltd jointly for the Bureau of Mineral Resources and the Geological Survey of Victoria has provided quality data over the Gleneig River province of Western Victoria. This is a region of some 2400 square kilometres comprising metamorphic sediments of presumed Cambrian age, referred to as the Gleneig Metamorphics and related to the Kanmantoo Trough sediments of South Australia. There are minor serpentinite and syn- and post-tectonic granites related to the Delamerian intrusives of South Australia. Similarities between this region and far western New South Wales (Wonaminta Block) and the Kanmantoo Belt in South Australia suggest possibilities of base metal and copper mineralization. The mafic associations offer the prospect of multimetal deposits for which the magnetic trends in the airborne data offer exploration targeting guides. Prospective targets may be identified by intersecting linear trends in the magnetic data. These trends are enhanced by simulated sun illumination methods with the ERMAPPER imaging system.

NEW DEVELOPMENTS IN RESOLVING DETAIL IN AEROMAGNETIC DATA S.T. Mudge RGC Exploration Pty Limited, Canberra, ACT Stacked profiles of aeromagnetic data often fail to resolve and display detail as this can be obliterated by larger amplitude features on adjacent flight lines. Contours and images of interpolated data can also obscure detail because they are sensitive to survey levelling errors and can show erroneous distortions caused by the interpolation method. Mclntyre (1981) showed that shaded stacked profiles of the second horizontal differences of flight-line data are effective in detecting and displaying detail in aeromagnetic data. Mclntyre used a square-root function to control the dynamic range of the computed difference so that both small and large amplitude features could be displayed without being obliterated by larger amplitude features on adjacent flight-lines. The shaded profile preferentially enhances positive values. Improvements on Mclntyre's shaded stacked profiles of horizontal differences form the basis of a new method of presenting horizontal differences of aeromagnetic data: the bipole map. This is a series of stacked flight-line profiles of bar-graphs of the horizontal difference values. The heights of the bar-graphs are controlled by the amplitude of the difference values whilst polarity is depicted with colour: red for positive values and blue for negative values. The bar-graphs are centred and located precisely on the curve flight-line; the flight-line forming the centre-line of the profile. Wavelength dependent automatic gain control (AGC) filters are used to modify the dynamic range of the horizontal differences so that both small and large amplitude anomalies can be displayed. The bipoie map visually enhances both negative and positive values, more precisely positions the data and does not depend upon dubious magnetic values interpolated between the flight-lines. Bipole maps of the first, third and fourth horizontal differences are effective in resolving detail in other parts of the frequency spectrum. They supplement contours and images of longer wavelength features. Magnetic models show the responses of the horizontal differences for various inclinations of the Earth's magnetic field and different widths of the magnetic source. In areas of steep inclination, the horizontal differences delineate the strike axis of thin bodies and the edges of thick bodies. Bipole maps of horizontal differences may find useful application in displaying other types of geophysical data such as VLF-EM and aeromagnetic gradiometer data. Bipole maps of higher order differences are an effective means of resolving high frequency (instrument) noise in geophysical data. For aeromagnetic data from the Mt Magnet goldfield, located in the Archean greenstone belt of Western Australia, bipole maps of the second horizontal differences revealed that an anomaly from a banded iron formation might be caused by several close-spaced banded iron bodies rather than a single body, as might first be interpreted from the contours and images of the gridded data. Bipole maps of the fourth horizontal differences revealed a series of NNE striking magnetic lineaments which are not apparent in the contours and images of the gridded data.

35 A PRACTICAL APPROACH TO THE FILTERING OF AIRBORNE MAGNETIC DATA IN THE COBAR REGION OF NSW S.N. Sheard^*, J.R. Bishop^ and R.V. Kissitch^ ^CRA Exploration, Broken Hill, NSW ^Mitre Geophysics, Elliott, Tas. ^CRA Exploration, Brisbane, Old Since 1981 CRAE has flown in excess of 43,000 line l<ms of airborne magnetics in the Cobar district. The data, which were acquired from a number of surveys, are being used to assist in the exploration for base metals and gold. Examples of the targets sought are the Elura lead-zinc-silver deposit, the CSA copper deposit and the Cobar gold deposits which all have associated magnetic features. A 1974 aeromagnetic survey flown at 90 m terrain clearance gave a discrete 40 n l response over the Elura orebody. Such an anomaly could be detected in areas of low magnetic relief within the detailed surveys. Unfortunately significant parts of these surveys are affected by the variable responses of maghemite concentrations in shallow channels prevalent in the Cobar district which could mask small discrete anomalies. To test this, a process of upward and downward continuation was applied to the original 90 m data set. These data sets were added to a grid containing a maghemite channel response. The resulting grids were then filtered in an attempt to extract the original data. The results suggest that even without filtering an Elura anomaly could be detected under a maghemite channel to a depth of about 200 m. Using a Butterworth low pass filter it was considered that at depths to 400 m below a channel, an Elura anomaly could be recognised. This practical approach is applicable to other data sets that may require filtering.

36 Technical Session 3(c) Computer Applications I

APPLICATION OF FIELD COMPUTERS IN EXPLORATION PROGRAMS Andrew M. Foley*, Robert M.S. White and Reginald J. Court Surtec Geosurveys Pty Ltd, Sydney, NSW As the task of finding economic mineral deposits becomes increasingly difficult there is a requirement to collect and evaluate larger and more complex data sets. There is also a corresponding increase in the cost of conducting field programs due to rising operating costs and the necessity of making more thorough observations, both qualitative and quantitative. It is therefore critical for explorationists to make maximum use of their presence in the field by acquiring and storing as many relevant observations as possible. These observations may range from geological and drainage features at sample sites, to complex geophysical data sets. Such data collection and storage can be facilitated by the use of field portable computer technology such as electronic notepads, digital-memory instruments and PC's. Associated with this hardware is a range of appropriate software that enables data handling such as downloading to a PC, processing, statistical assessment, graphical presentation, modelling and interpretation. To maximise the effectiveness of this approach we have emphasised the digitising of data at the point of collection, where feasible. Over the past eight years we have incorporated this in the development of an integrated approach to the application of computer technology. An important part of this has been developed around the use of hand held electronic notebooks as well as memory recording instruments. These can be used for either direct entry of numerical data (e.g. sample or grid numbers, radiometric data) or alpha-numeric codes for specific parameters (e.g. stream width, lithology, alteration, overburden type). A number of such notebooks were evaluated and the Psion as having the best combination of field reliability and ease of programming was selected. This instrument has two solid-state data packs, each with a capacity for storing up to 128 Kbytes of data or program, as well as 8 Kbytes of internal memory. The small data packs are plug-in and each is backed up by an internal battery (5 year life). The Psions are programmed in pseudo-basic either from the keypad or via a PC. They have a small LCD screen, alpha-numeric keypad, built in clock and run for about a week on a 9 volt battery. The units can fit into a large pocket and for protection they are housed in a polycarbonate case with a membrane over the keypad. They can be pre-programmed to provide operators with a series of prompts relevant to the field task and are also programmed to be menu driven, allowing the collection of a variety of data within one instrument. At the end of each day the data packs can be removed and replaced with empty ones; the full ones being then or later downloaded to a computer. To cope with a wide variety of data input formats, highly flexible data base software has been written. Since the majority of exploration data are coordinate oriented, a geographic rather than relational data base was developed. The downloaded data is normally checked, then merged to the data base. The data base is designed to

37 interface with a range of commercially available software pacl<ages that allows field operators to compile and edit their field data, then to either process it to maps on site, or image process it. Field personnel can, as a result, assess and interpret data in many cases on a daily basis. This ability enables the geoscientist to mal<e informed decisions on site. In a major application of this technology a detailed exploration program was conducted over an area of 560 km^ in western Arnhem Land during 1988 and 1989. Some 1700 l<m of AMG coordinated grid were established. By use of Psions, 19 numeric and 4 alpha-numeric variables at over 180,000 primary sample locations, and 4 variables at approximately 500,000 intermediate locations were collected. By the end of the field work the project data base size was 45 Mbytes. During the entire period no field data was lost or cormpted. This approach significantly reduced the period between the collection of field data to drill site selection and testing.

MULTI-SENSOR MARINE GEOPHYSICAL PROFILING AND DIGITAL ACQUISITION USING SAS1 J. Lean^* and D.A. Pratt^ •"HydroSets Pty Ltd ^Encom Technology Pty Limited A digital seismic acquisition and processing system (SAS1) has been developed for high resolution, multi-sensor, marine geophysical surveys to replace conventional analogue methods of recording. This system has achieved vertical resolutions of better than 1 metre, with trace separations as close as 0.25 metres. As well as mapping reflections It is an ideal tool for detecting subtle changes in seismic stratigraphy. Seismic traces, high resolution magnetics, bathymetry and electronic navigation data are stored on Exabyte Video 8 cartridges with storage capacities up to 2.2 Gbytes. With data rates between 50 and 150 Mbytes/hour, this storage capacity is essential for the implementation of a practical, low cost system. A complete mapping and seismic processing system has been developed to complement this new high resolution acquisition system. Unsealed and hand annotated analogue field plots have been replaced by edited, scaled and enhanced seismic sections merged with high resolution magnetics and bathymetry. Maps of the magnetic and bathymetric data can be produced with little delay on completion of the survey. Significant improvements have been achieved with the seismic presentation by careful attention to swell filtering, trace stacking, time variant gain, variable density display and wavelet compression by deconvolution.

38 TRENDS IN DEVELOPMENT OF IMAGE PROCESSING SOFTWARE FOR PROCESSING OF GEOPHYSICS AND OTHER DATA Stuart Nixon Earth Resource Mapping (ERM), Perth Image Processing is becoming an integral part of evaluating and enhancing geophysical data. New advances in computer hardware, graphics standards and user interfaces have had an impact on how image processing software operates. Combining a new technique known as Dynamic Algorithm Compilation with the latest generation of high performance workstations allows integration of very complex processing and mosaicing of data in an interactive fashion. Geophysical images are characterised by large floating point datasets which need multi stage image processing techniques applied in order to maximise information extraction. It is also desirable to combine geophysical datasets with other sources of data, such as geochemical and remote sensed satellite data. Required processing to enhance these datasets include: • • • • • • • • •

spatial and frequency domain processing large convolutions and filters automatic mosaicing of spatially separate datasets automatic merging of multiple datasets based on priority combining of datasets with different cell dimensions balancing of dynamic range between datasets spreadsheet like "what-if" formulae display of both raster and vector datasets multiple display formats, such as Real Time Sun Angle

Common to all the Earth Sciences is the problem of having much more data available for interpretation than can be easily displayed and assimilated. The reduction of data into simple images that can be readily interpreted forms an integral part of image processing and interpretation. Combining multiple stages of processing with display techniques such as Real Time Sun Angle Shading allows maximum structural information to be extracted from available datasets. Recent attempts at mosaicing magnetic surveys covering wide regions have shown that some structures only become apparent once very large regions are considered. This indicates that it is desirable to be able to mosaic all available data for an area before carrying out combined processing. Regional datasets of coarse resolution are generally available, such as the gravity map of Australia at 11 Km grid spacing. It is desirable to use these low resolution regional datasets wherever local, more accurate datasets are not available. To implement this a priority needs to be assigned to datasets, with the system automatically choosing higher quality data where it is available. It is not practical to regrid a regional dataset to a mesh size consistent with local datasets, as the dataset storage requirements could easily exceed several gigabytes. Therefore, an ideal solution is to automatically mosaic, combine and resample datasets in real time as processing and display are carried out.

39 For each dataset being processed the following criteria can differ: • • • • • • •

null or invalid cell constants cell dimensions and cell overlap/underlap data types (integer, floating point and so on) spatial boundaries for the dataset dynamic range for data value coordinate spaces origins will differ for each dataset

These differences add complexity when integrating multiple datasets. One specific difficulty that must be catered for is the consideration that cells from different datasets will not exactly overlap due to different origins and cell sizes. Our research shows that generic software solutions are quickly overwhelmed by the complexity and variability of the problem. Any workable solution must address all of the above issues in order to mosaic, integrate, process and display the data. As performance is sacrificed in general purpose software, this solution is clearly not acceptable. While slow software is not an issue in some applications, it is of paramount concern in Image Processing. The amount of information extracted from a given dataset is almost directly related to how much processing we can carry out in a reasonable amount of time. The "what-if" nature of the problem means that processing and display needs to be interactive, so batch processing is at best a poor solution. The issue of interactive performance is the reason hand-coded machine language and dedicated array processors have been developed in the past, in an effort to boost performance. However, such specialised approaches also have limitations. For example, few hardware based array processors designed for image processing can handle a 31 by 31 or larger floating point convolution, and are often limited to the processing of byte integer data only. Such convolutions are routinely used in geophysical data processing. As a result of considerable research, specification and development, a commercial product based on Dynamic Algorithm Compilation has been implemented. This technique takes a complete description of the required processing and transforms it into computer code which is specific to the algorithm. That code is then executed. By leaving the compilation of the algorithm until the final instant prior to displaying the image, most of the image processing variables become constants. This simplification of the imaging problem in turn allows shorter and tighter code to be created, which in turn improves performance. Instead of storing output datasets, the algorithm used to create these datasets is stored. One benefit of this is consistent hardcopy output, as this technique allows the hardcopy generation program to request output at the resolution of the device. The same algorithm is used to display data and generate output. This allows many of the inconsistencies between screen dumps, colour printers, electrostatic plotters and film writers to be overcome, as the algorithm is recompiled to take into account attributes of the specific output device. In summary. Dynamic Algorithm Compilation offers benefits in a number of areas: • •

high performance flexible "what-if" integration of datasets

40 • • • • •

automatic mosaicing and merging of datasets elimination of temporary processed datasets creation of algorithm files which describe processing preservation of data dynamic range machine independent

These improvements translate into better interpretation of geophysical data.

SUPERCOMPUTERS IN SEISMIC DATA PROCESSING M. Stanley and R. Singh* Tensor Pacific Pty Limited, Port Meibourne Today's computers span a wide range of computing capability from desktop personal computers, through minicomputers and mainframes to the fastest, most powerful machines designed to the limit of existing electronics engineering technology. It is the last category, those that perform millions of floating point operations per second (megaflops) at the peak of current technology that are termed supercomputers. In seismic data processing extremely large volumes of numbers are processed through many stages, most of which involve complex mathematical operations. A typical seismic survey today is acquired with 300 recording channels to 6 s. at a 2 ms. sample rate. This recording configuration means that one kilometre of data produces 36 million samples (floating point numbers) for processing. Many seismic surveys today involve the recording of up to 10,000 kilometres of data, particularly 3D surveys. Processing techniques currently performed have evolved over past decades in accordance with the available electronic hardware of the time. The latest supercomputing technology allows more complex processing algorithms to be tested on data in realistic time, as well as the increased throughput capacity needed to accommodate today's large multichannel 2D and 3D seismic surveys.

41 Technical Session 3(d) Petroleum Exploration II - Non-SeismIc Methods

INTEGRATED ELECTROMAGNETIC AND SEISMIC METHODS FOR PETROLEUM EXPLORATION K.-M. Strack•'^ A. Hoerdt*', K. Vozoff^, P.A. Wolfgram'' ^University of Cologne, Germany ^Macquarle University, NSW During the past decade several deep electromagnetic techniques have been successfully applied to hydrocarbon exploration problems. Case histories for magnetotellurics (MT) and long offset transient electromagnetics (LOTEM) have shown both the strengths and the limitations of the individual techniques when applied in a production mode under real field conditions. When exploring for hydrocarbons it is essential that the resistive units are as well resolved as the conductive ones. This means that one must use an electric dipole transmitter and an electric field receiver because this is the most direct way to measure vertical current systems in a layered earth. Furthermore, to extend the LOTEM results to greater depth and to improve the resolution of MT at shallower depth, a combination of both techniques is required. When using MT and LOTEM together for mapping of lateral changes in resistivities, a priori information such as the interfaces from reflection seismics is needed. This type of integration of the different techniques significantly increases the reliability of the interpretation because the strengths of the different methods compensate for each other's weaknesses. This concept is underlined using field data from different case histories around the globe. A typical petroleum exploration problem is a resistive unit at great depth which simulates porosity variations within carbonates. This kind of earth model is investigated using a synthetic data set. The joint interpretation of LOTEM-MT does not yield sufficient resolution. When adding seismic information to the EM interpretation the resolution becomes significantly better and the porosity changes can be resolved.

MAGNETOTELLURIC SOUNDINGS AND THE LEVY ALGORITHM J.P. Cull Department of Earth Sciences, Monash University, Victoria Standard band-averaging techniques used for representing magnetotelluric data are subject to bias from spurious estimates identified as 'outliers'. Complex curve fitting techniques have been suggested to provide an alternative representation. Suspect bands can be eliminated and representative data can be obtained by interpolation using complex polynomials. The Levy algorithm has the additional benefit that it can be used for interpolation to approximate band averages obtained using existing software.

42 A COMPARISON OF FOURIER AND WIGNER-VILLE SIGNAL PROCESSING METHODS APPLIED TO A MAGNETOTELLURIC SURVEY OF THE KENMORE OIL FIELD I.J. Chant* and LM. Hastie Physics Department, University of Queensland, Brisbane A Magnetotelluric (MT) survey was conducted over the Kenmore oil field in south-east Queensland. Time series MT data was taken at 20, 50 and 100 ms sample rates in conjunction with a Controlled Source Audio-magnetotelluric (CSAMT) survey. Sites included a number of producing and non-producing wells. Conventional methods of MT analysis using Fourier-Transforms (FT) to obtain signal power spectra were found to have much higher errors and biases in the apparent resistivity profiles thatn the CSAMT. Non-stationarities in the MT signals have since been shown to be a major factor contributing to these biases. Time varying spectral analysis methods such as those using the Wigner-Ville Distribution (WVD) are known to be much less susceptible to this form of bias and a re-analysis of the MT survey data with WVD methods has produced results that are in better agreement with the CSAMT results than the conventional FT method. Comparisons are made using single sets of 1024 time series samples analyzed with both the FT and WVD methods. To facilitate the comparison, the FT power spectral data are band averaged to the frequencies at which the WVD power spectral estimates are calculated. The WVD impedance estimate at each frequency is produced by taking the median of the log impedance as it varies with time. The log impedance is used because the impedance distribution has been shown to be log-normal. Both methods are subjected to polynomial trend removal and tapering to reduce low frequency bias and sampling end effects in the transformations. The resulting apparent resistivity vs frequency curves are compared with the CSAMT data, which were chosen as the benchmark for comparison because inversion models using these data have been found to compare well to lithography and resistivity profiles available from well logs. Apparent resistivity vs frequency curves derived by the two MT methods and CSAMT are given in Figures 1 and 2. Figure 1 shows apparent resistivities below 25 Hz with the electric field aligned north-south, which is approximately the direction of geological strike in the area, and Figure 2 shows the apparent resistivities below 5 Hz with the electric field aligned perpendicular to the geological strike direction. The WVD method exhibits significant advantages in the reduction of MT data in that the curves are smoother and show more correct structural character than that displayed by the FT methods, however, neither processing technique is immune to coherent noise sources. More sophisticated filtering processes may be applied in the time-frequency space to eliminate non-stationary signals, but the possible gains from these improved filtering methods have to be weighed against the computational costs.

43 100.0 75.0

50.0

25.0

10.0 7.5

5.0

E a

2.5

X CL

1.0 - 1 0.8

-I

i \ 1 1

0.5 - 1

0.2

0.1

WIGNER VILLE METHOD BAND AVERAGED FT CSAMT

0.00

2.50

5.00

7.50

10.00

12.50

15.00

17.50

20.00

22.50

25.00

Frequency (Hz)

Figure 1: Apparent resistivity vs frequency plot of FT and WVD processed MT data and CSAMT data at a site approxinfiately 50m east-north-east of well Kenmore No. 1. The electric field component was measured approximately parallel to the direction of geological strike.

WIGNER VILLE METHOD BAND AVERAGED FT CSAMT

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

5.00

Frequency (Hz)

Figure 2: Apparent resistivity vs frequency plot of FT and WVD processed MT data and CSAMT data at a site approximately 50m east-north-east of well Kenmore No. 1. The electric field component was measured approximately perpendicular to the direction of geological strike.

44 IMAGE PROCESSED, HIGH RESOLUTION AIRBORNE MAGNETICS A NEW TOOL FOR MAPPING STRUCTURE IN SEDIMENTARY BASINS Mike Etheridge^ , Don Pridmore^, David Bush^ and Alasdair Cooke^ Vectonex Geoconsultants Pty Ltd, Canberra ^Questor Surveys Ltd, Toronto, Canada ^World Qeoscience Corporation, Perth Recent advances in the acquisition, processing and display of airborne magnetic data have revolutionised its application to mapping and exploration in 'hard rock' or minerals environments. These advances are currently being successfully applied to the much more subtle magnetic variations within sedimentary basin sequences, and offer an exciting new tool to aid structural mapping in petroleum exploration. The traditional role of airborne magnetics in petroleum exploration has been in the broad definition of basin shape and approximation of basement depth. Recent improvements in the depth resolution and availability of multichannel seismic (MCS) data has largely obviated the need for such information. However, parallel advances in airborne magnetics technology have raised it to the level of a potentially powerful partner for MCS in conventional structural mapping in petroleum exploration, especially at the more regional scales. The advances in airborne technology have come from a number of separate sources •

Improved acquisition systems, particularly in navigation and the removal of aircraft 'noise'; noise levels have been reduced to below 0.1 nT, allowing resolution of magnetic anomalies with amplitudes as low as 0.5 nT.

•

Data processing and display, particularly the development of sophisticated image processing techniques; a wide range of images are possible from a single dataset, enabling selective imaging and mapping of magnetic features with a wide range of amplitudes and wavelengths.

It is now possible to image structure at depths from about 100 to several thousand metres, providing a complementary and indeed synergistic mapping tool for MCS. For example, faults may be imaged because they offset weakly magnetic sedimentary horizons (e.g., heavy mineral sands, volcanics/volcaniclastics, Fe-enriched sediments), are zones of alteration involving redox reactions leading to precipitation of low temperature Fe-oxides that may be weakly magnetic, or are intaided by igneous dykes. Examples of high resolution airborne magnetic imagery from a number of onshore and offshore sedimentary basins in a range of structural and tectonic settings demonstrate the complementary nature of airborne magnetics and MCS in structural mapping. Examples will be shown of structures imaged in section by MCS and in plan by high resolution airborne magnetics. Case studies involving structures that proved difficult to resolve and/or map from MCS but were readily imaged from magnetic data will also be illustrated. Examples will be drawn from the Northwest Shelf and a number of onshore and offshore basins in other countries.

45 Technical Session 3(e) Qeosclence Education I

EDUCATING FOR THE 21st CENTURY - THE IIWIPORTANCE OF EARTH SCIENCE R. Stutchbury University of New Soutli Wales It Is essential for the future generations to have an understanding of the global changes associated with increasing human population in order to establish the technological solutions needed to sustain a civilised future for humanity. Earth Science will play a critical role in developing that understanding, but before it does so, there must be a review of the approaches used in teaching the Earth Sciences with a complete revision of the curricula. By turning to the notion of Earth System Science adopted by the United States, geology 'akes its place with all other sciences in developing an understanding and knowledge of he dynamic systems of the planet Earth. The necessary knowledge will come through he following concepts: The Earth System is a small part of a Solar System within a vast Universe. Earth System is comprised of interacting subsystems (the hydrosphere - water; the lithosphere - sediments and rocks; the atmosphere - air; the biosphere - life; the cryosphere - ice). The Earth's subsystems are continually changing, evolving the interacting through natural processes and cycles. The Earth's natural processes take place over periods of time from fractions of seconds to billions of years. Many of the resources of the Earth's subsystems are limited and vulnerable to overuse, misuse or change resulting from human activity. A better understanding of the Earth System and its subsystems stimulates greater aesthetic appreciation. The development of technology has increased and will continue to increase our ability to understand the Earth. Earth Scientists are people who study the origin, materials, history, structure, processes, and evolution of Earth's subsystems. They use their specialised knowledge to describe subsystems, identify and evaluate resources and predict the likelihood and impact of future events. These eight basic concepts will become the turning point for Geoscience Education in the United States. Their planning, which commenced in 1983, is based on the long-term strategic plan explained in the text of the paper.

A NEW APPROACH TO THE TEACHING OF GEOLOGY IN SCHOOLS W. Roberts Cranbrook School The present 2 unit Geology course in the N.S.W. Higher School Certificate is beset by many problems which see it fast approahing extinction or, at best, amalgamation with either 3/4 unit Science or Geography. The candidature in HSG Geology has never been high but there has been a general decline since the early 80's from over 1000 to about 700 students in 1989. The problems fall into three main categories which are outlined below: 1. 2. 3.

The course is perceived as irrelevant by an increasing number of students, and by the educators who see it as lacking direction and having an outmoded curriculum. It suffers from a lack of properly trained geoscience teachers. In the past Physics and Chemistry were promoted as the only "real" sciences so that students with an interest in Geoscience still felt compelled to study Physics and Chemistry at Tertiary level as with any other option they would be severely disadvantaged.

This paper will concentrate on addressing the first point. Geoscience in the integrated junior secondary science course can be used as a basic framework about which the other sciences fit. Emphasis should be on the systems and cycles that serve to unify the subjects such as the carbon cycle or hydrosphere, as well as using topical resources like media reports of geological events to introduce other science topics. The two years of senior Geoscience could be employed developing an appreciation for the subject through acquiring skills in areas like field studies, mapping, laboratory investigations and literature research. These skills can then be communicated verbally or in writing and used in problem solving applications. The HSC examination would contain a skills component and test the application of the student's knowledge. It is anticipated that students would participate in at least one extended field trip and a number of shorter ones during these two years. The proposed senior curriculum has three compulsory core units with four electives, which expand on topics in the core, attached to each. The core units are: Coal 1 - THE EARTH Time 18 weeks An examination of the surface and crust of the Earth while developing geological mapping skills. Core 2 - PLATE TECTONICS Time 12 weeks A study of the Plate Tectonic Theory and how it explains many of the large scale geological phenomena around the world. Core 3 - GEOLOGY AND MAN Time 12 weeks A study of man's exploitation of the Earth's resources (energy, mineral, soil and water) and the effects of man's activities on the natural environment. The intention of this course is to unify the different strands of geology and make it more relevant in our present society. It does not aim to produce specialist geologists but impart a broad understanding and appreciation of the importance and the significance of geology in our world today.

47 GEOLOGY IN A SECONDARY COLLEGE AND ITS ASSOCIATION WITH THE PRIVATE SECTOR A. Perrin Casuarlna Secondary College, Darwin NT Modern Science education is faced with ever increasing pressure from the private sector to ensure that curriculum and teaching practices enable students to be readily incorporated into their work force. This pressure is widespread and certainly not restricted to Tertiary Institutions, and is increasingly being brought to bear on Senior Secondary College courses. Geology at Casuarlna College experienced low student interest primarily because (1) Science engenders, in many students, a fear and apprehension, and (2) the science students, especially the better ones, opt for the physics and/or chemistry strand, in preference to geology. To address the decline in numbers in geology it was proposed that the normal Secondary School practice of work experience be expanded in respect of geology so as to give students more meaningful work, by them actually being employed on mine sites. The Chamber of Mines (N.T.) gave hesitant approval for our proposal but since gaining their support a number of students have been offered short-term positions at a number of mine sites. All students, especially the 17 and 18 year olds, have an insatiable need for money and with the prospect of (1) actual employment by a reputable company, (2) earning a wage, and (3) working on a mine site, has lead to an overwhelming reaction by the students towards the geology course. There is a continually increasing number of students enrolling in geology and there have been many more enquiries from them about possible future vocations in the mining industry. Since the student response has been so great the industry has responded in kind so that now the number of students employed and sites of their employment has increased significantly.

UNDERGRADUATE FIELD TRAINING AND REGIONAL GEOLOGICAL MAPPING: PUTTING THE TWO TOGETHER K.G. McQueen*, W. Mayer, G. Taylor and M.C. Brown Faculty of Applied Science, University of Canberra, ACT Senior Undergraduate students and staff in geology departments at Australian tertiary institutions represent a valuable human resource which could be systematically directed towards the National Mapping Accord. The result of student field work, particularly at honours and postgraduate level, have already contributed to the geological data base over many years. However, this has mostly been done in an ad hoc fashion with very little direct benefit to the students or to the educational process. The non-systematic approach has also meant that much data generated by undergraduate work has been lost or is inaccessible. Students and staff at the University of Canberra are involved in a regional geological mapping project in southwestern NSW. The aim of this project is to use the Bombala

48 1:100,000 sheet area as a training ground for our 3rd and 4tli year students and at the same time complete the geological map for final publication by the New South Wales Geological Survey. We have shown that with proper supervision students can be productively involved in regional geological mapping and that this can be a highly motivating exercise. Enthusiasm, motivation and educational benefits are maximised by involving the students in all aspects of the work within a department wide project. Students realise from the start that they are involved in a real mapping project of a poorly known area with a published map as a final goal. Much of the work is done at our 3rd year mapping camps and in individual student mapping projects. Field activities in other existing units are also directed towards the project area. Staff have the responsibility for project co-ordination, quality control, fill-in mapping and collation. New areas are investigated each year, which means that we avoid the old "stamping ground" syndrome; neither staff nor students know what to expect. The overall "team approach" and the use of small groups for some of the mapping helps students develop techniques for effective group participation and organisation. Involvement of staff from the New South Wales Geological Survey and visits from industry personnel give our students the opportunity to meet and discuss aspects of the work with other geologists. We have also been able to integrate student and staff research into the project by following up in detail, discoveries made during the regional mapping. This technique of combining student geological field training and systematic regional mapping has proved successful and we intend to continue the exercise. Other groups may also find educational advantages in this approach. Our National geological data base can only benefit from having more keen observers in the field.

49 Technical Session 4(a) Petroleum Exploration ill - Seismic Data Processing OFFSET DEPENDENT STATIC CORRECTIONS ON A CONTINENTAL SHELF EDGE 3D SEISMIC SURVEY M.G. Cousins''*, P.M. Whiting^ and T.J. Allen^ Esso Australia Limited, Sydney ^Halliburton Geophysical Services, North Ryde The problems associated with rapidly varying sea floor topography are well documented. Numerous two-dimensional procedures are available for approaching these problems, ranging in complexity from simple replacement statics to full wave equation datuming. Any application to a 3D survey must produce significant benefits in a cost effective manner. Our search for such a procedure has resulted in the development of Modelled Offset Dependent Statics (MODS), which we will show exists at the lower end of the cost scale but at the higher end of the benefit scale. Many special problems are introduced by the three-dimensional nature of our data set, in particular, the need to accurately map the sea floor and any interpreted horizons as a three-dimensional surface. These problems and their solutions are reviewed. Simple replacement statics are theoretically only correct for a flat reflector at infinite depth. MODS relocates this reflector to a realistic three dimensional shape in the zone of interest, thus optimising the accuracy of the statics over this zone. The relocation of the hypothetical object reflector is achieved by modelling the reflector and the sea floor and by tracing offset rays. MODS has been successfully applied to a continental shelf edge 3D survey. The data quality improvement demonstrates the appropriateness and the value of the technique.

TRANSFORM TECHNIQUES APPLIED TO THE ATTENUATION OF LONG PERIOD MULTIPLES Paul Haskey* and Jon Ashdown SImon-Horlzon Limited, England In deep water areas, the interference at important target levels due to water layer multiples can be extremely troublesome. Conventional deconvolution approaches are ineffective, due to variation of the multiple period with time (non-stationarity) and poor statistical estimation due to the limited number of multiple contributions within the autocorrelation window. Weighted stacking improves the attenuation of long period multiples, and in recent times the demultiple process based on the f-k transform has been routinely applied to supplement the response of CMP stack. A serious weakness of the f-k technique is that the removal of multiple energy from the record is strongly dependent on offset, the slopes of primary and multiple events

50 converging towards the near offsets, where the process if thus relatively ineffective. More recently, there has been increasing interest in applications of the general class of decompositions known as the Radon transform, which model the data as a set of projections on the zero offset axis along a number of possible geometrical trajectories. A well known example is the linear Radon transform, commonly known as slant stack or the tau-p transform. Although, like the f-k transform, slant-stack results in a plane wave decomposition of the record, the representation in terms of zero offset intercept versus ray parameter is such that each trace in the transformed record is associated with a constant angle of emergence. Water layer multiples are then represented with constant reverberation periods within each trace, and may then be treated by a conventional statistical deconvolution. A further example of the general class is the parabolic Radon transform, which models the record as a set of parabolic alignments. With prior application of approximate NMO correction, this transformation can provide a well focused mapping of multiple reflections, enabling them to be identified and isolated for inverse transformation. The predicted multiple is then removed by subtraction from the original record. This method is not dependent on the accuracy of a statistical model and provides effective demultiple on near as well as far offsets. Merits and disadvantages of these methods are discussed and performances are compared on data from a typical deep water area. Results show that the parabolic Radon transform enables a far more accurate modelling of long period multiples than the other methods considered, thus achieving a more effective demultiple process.

MULTIPLE SUPPRESSION BY A WAVE-EQUATION-EXTRAPOLATION METHOD B. Zhou and S.A. Greenhaigh* School of Earth Sciences, The Flinders University of South Australia The wave-equation-based multiple suppression method, unlike predictive deconvolution and stacking, makes no assumptions on periodicity or moveout patterns of multiples, and can cope with complex sea-bottom and sea-surface variations. It entails multiple prediction by wave equation extrapolation of the seismic data and then multiple subtraction from the recorded seismograms. In general, the multiple subtraction method requires the calculation of a subtraction scalar (a reflection coefficient function), which is a function of the ratio of the original data to the extrapolated multiple model traces. The success of the method depends on establishing the correct scalar. However, it is difficult to get a good subtraction scalar when the wavelet of the original data is different from that of the multiple model traces. This occurs for the long offset traces because of geophone ghosting, and changes of amplitude and phase in the reflection waveform beyond the critical angle. In this paper, we develop a superior alternative scheme, based on a simple 2-D Butterworth-type gain function, calculated from the original data and the (extrapolated) multiple model data. This gain function will attenuate the multiples and preserve the primaries. A simple synthetic example is used to demonstrate the efficacy of the method in multiple suppression.

51 QUANTITATIVE EVALUATION OF DYNAMIC TIME-SHIFTS FOR CORRECTING SEISMIC DATA Greg Beresford* and Dylan Mair Department of Geology, University of Melbourne Large lateral velocity changes, particularly those associated with sea-floor topography, can severely distort seismic stack sections; for example, the submarine canyons in the Gippsland Basin in Bass Strait. Conventional replacement statics partially correct these problems but are usually inadequate in situations where the sea-floor variation is severe or the water is deep. Dynamic corrections calculated by ray-tracing through the region of strong lateral velocity variation give improved results. Dynamic corrections derived by ray-tracing can be evaluated by analyzing t^-y^ plots where t is time and y is offset within CMP gathers. This facilitates the following comparisons to be made: (1) the zero-offset time before and after dynamic correction; (2) the RMS velocities (calculated using zero-offset rays traced in the model) with normalized stacking velocities after dynamics; (3) hyperbolic moveout before and after dynamics. A similar evaluation of conventional replacement statics provides a reference for evaluating the ray-tracing derived "replacement dynamics". Ray-tracing requires a subsurface model which can be difficult to construct in areas of structural complexity. This is often the case near submarine canyons. A simple model using water depth and a single marker horizon or datum when ray-traced to derive replacement dynamics gives significant improvement with respect to the conventional statics solution in submarine canyon areas. Erros in velocity can be reduced by as much as 50% and errors in hyperbolic moveout reduced by about 70%.

52 Technical Session 4(b) Mineral Exploration II - Mineral Deposit Settings

SINTERS AND THEIR GOLD CONTENTS NGAWHA QEOTHERMAL FIELD, NORTHLAND, NEW ZEALAND Malcolm E. Cox^* and Patrick R.L Browne^ ''Surtec Geosurveys Pty Ltd, Brisbane, Australia ^Geothermal Institute, University of Auckland, New Zealand The Ngawha geothermal system is a reservoir consisting of Permian-Jurassic greywackes and argillites of unknown thickness formed by structural permeability (largely joints). It is overlain by a 500-600 m thick sequence of Cretaceous-Tertiary sediments, mostly marine. Drillholes (to 2300 m depth) tapped dilute alkali chloride water in the greywackes, with high dissolved CO2 contents, at about 230^^0. Present day springs in the main thermal area discharge low volumes of chloridebicarbonate water at temperatures of up to 46'^C, and gas seeps are numerous. Within this area are three parallel zones of surface activity. Several isolated gas seeps and small sinters also occur in the surrounding area. The spring waters are dilute compared with fluids tapped by the drillholes and none presently deposit silica. Table 1: Composition of thermal waters (mg/kg)

Typical spring Reservoir drillhole fluid

Mg SIO2

480 881

40 69

11 3.3

2.2 0.15

97 405

CI SO4

HCO3

154 145

572 393

628 1257

(Higher concentrations of SO4 and HCO3 in springs are due to oxidation of H2S and CO2 respectively, and Ca and Mg to reaction with shallow sedimentary rocks.) Superficial silica sinter deposits occur in at least four areas at Ngawha but are not now forming. The largest covers an area of only 2 Ha. However, two were previously mined so their original volumes are unknown. The ones at the main springs were mined along with surface sediments in the early 1900's for mercury, and one to the north quarried for road gravel. Typical assays of the sinter are: Table 2: Composition of silica deposits (ppm)

Central thermal zone North thermal zone Area to north Well Ng9 discharge deposit

0.03 0.25 0.006 0.273

0.46 1.20 0.18 13.93

1020 100 0.01 0.49

2230 360 below 10 15

In an epithermal gold exploration programme, these sinters would usually be assumed to have deposited from a boiling alkali chloride water deriving from the reservoir. If so, their interpretation as indicating a non-mineralised deep system would be misleading. A likely explanation for the presence of the sinters is that they deposited from shallow

53 groundwater circulating only within the Cretaceous-Tertiary cover rocks, although in the main thermal zone there apparently was some leakage of deeper water. The sinter-depositing waters are believed to have been local meteoric groundwater and condensate heated (to about 180X) in the shallow subsurface (300-400 m). This water extracted an appropriate amount of S i 0 2 for this temperature by dissolving aluminosilicates in their hosts. The water ascended in permeable zones and discharged. With rapid cooling, it became saturated with respect to amorphous silica, which deposited, but then slowly crystallised. The Ngawha sinters, therefore, do not reflect the deeper reservoir conditions and have no direct bearing on epithermal gold deposition. By contrast, the deep fluid is capable of depositing silica with a significantly higher content of precious metals (Table 2).

MINERAL EXPLORATION IN SUMATRA S. Johari''*, and C.C. Johnson^ ^Directorate of Mineral Resources, Bandung, Indonesia ^British Geological Survey, Keyworth, UK The Directorate of Mineral Resources has been engaged in geological investigations in Sumatra with the British Geological Survey since 1975. The initial project, the North Sumatra Project, was a regional mapping and a geochemlcal reconnaissance survey covering Sumatra north of the equator. Geologically, Northern Sumatra Is now the most comprehensively mapped and systematically documented part of Indonesia. Several of the geochemlcal anomalies found by this project have led to the discovery of several new areas of mineralisation. The Northern Sumatra Mineral Exploration Project (1984-1988) was specifically involved in metalliferous mineral exploration in Sumatra north of the equator. This project adopted a multi-disciplinary approach with a team of geologists, geochemists, and geophysicists. Its aim was two-fold; to stimulate mineral exploration in Sumatra and to train personnel from the Directorate of Mineral Resources in the methods of mineral exploration. The project has built up valuable databases including bibliographic and mineral occurrence information. The Southern Sumatra Mineral Exploration Project, which has just started, will continue mineral exploration work in Southern Sumatra. This project will be able to assimilate all the data that is now available in order to better understand the metallogenic province in Sumatra. One of the functions of the Directorate of Mineral Resources is to maintain a mineral inventory for Indonesia. It is not therefore solely interested in gold and has to assess the full range of mineral resources - an essential requirement for future development of the country.

54 FORMATION OF UNCONFORMITY-STYLE URANIUM DEPOSITS IN THE ALLIGATOR RIVERS AND WESTMORELAND PROVINCES OF NORTHERN AUSTRALIA: A MORE UPDATED OUTLOOK N.F. Rutherford Surtec Geosurveys Pty Ltd, Sydney, NSW Misconceptions exist about the formation of the unconformity-style uranium deposits in northern Australia stemming largely from a lack of understanding of the relationships between geology (lithology) and structure. Detailed exploration for uranium in Canada has highlighted many aspects of geology, stnjcture and alteration associated with such deposits which can be applied in northern Australia. There are however physical differences between the two regions which are not fully appreciated. Implicit in modelling the formation of these major resources of uranium are factors such as source rocks, generation of low temperature hydrothermal fluids, processes of uranium and other element transport and deposition, and alteration of country rocks. Most recent ideas favour uranium being derived from source 'beds' located at the unconformity and this is well illustrated at Westmoreland. Uranium occurs coincident with a number of stratigraphic horizons each essentially at an unconformity on which has been deposited a fine grained often tuffaceous sedimentary unit. Where cut by faults, groundwater has leached uranium from the fractured siltstones and concentrated it within or adjacent to the fault and other permeable structures or against hydrological barriers such as intrusive dykes. Continuous solution and precipitation of uranium by groundwater accounts for the extensive radiogenic disequilibrium within these deposits. Translation of this simple model to the Alligator Rivers Region to account for the large higher grade deposits requires little variation. Source rocks for these larger deposits are likely to be a combination of weathered basement rocks (regollth) and sequences of shales or tuffs enriched in uranium deposited on the unconformity as valley or lake fill sediments (Yeelirrie-style). Edith River Volcanics and equivalents erupted on to the basement unconformity prior to the deposition of the Kombolgie Formation are also regarded as important sources. The second requirement is the generation of a hydrothermal system capable of leaching and transporting uranium and producing extensive host rock alteration. Regionally, igneous activity which is temporally associated with mineralisation is lacking, so an alternate heat source is required. The Alligator Rivers Province deposits have intense deformation of host rocks within and in proximity to the mineralisation, and the Athabasca Province deposits occur along zones of intense strike slip or wrench faulting. The Alligator Rivers deposits all occur in zones of moderate, low angle (Ranger) to intense, high angle (Jabiluka, Nabariek, Koongarra) reverse thrusting characterised by formation of mylonitic and cataclastic textures including brecciation of the mineralisation. Frictional energy from deformation appears to provide the required heat and seismic activity pumps the fluids. This tectonic event has been not widely recognised but is very important regionally. Circulation of oxidised tectonically-heated waters through a suitable 'active' structure which intersects with a source bed and along the unconformity initiates leaching and concentration of uranium, iron, silica, magnesium and other elements, subsequently redistributing them. The Alligator Rivers deposits have been preserved by a cap of

55 Kombolgie Formation sandstone in an essentially sealed system and are in radiogenic equilibrium. Evidence of hydrothermal fluid activity as reflected by rock alteration is well developed but its expression is often subtle being restricted to joint, shear and fault surfaces in outcrops of units such as the capping sandstones. Alteration occurs as quartz-hematite coatings on fracture surfaces. More peripherally it occurs as quartz crystal lined vughs or fractures. Towards the unconformity and the controlling structures there is an increase in fracture density and hematite, chlorite and clay content. The site of formation of a deposit is thus not directly dependent upon basement lithology, say the Cahill Formation, but on coincidence of reverse basement faults with strong deformation and overlying source beds.

THE USE OF ELECTRON PARAMAGNETISM AND TRACE ELEMENTS CONTENT OF VEIN QUARTZ IN MINERAL EXPLORATION J.C. van Moort*, A.S. Nand and A. Rwa Geology Department, University of Tasmania, Hobart Two and a half thousand microcrystalline vein quartz samples from various types of ore deposits were analysed by electron paramagnetic resonance (ERR) spectroscopy and two hundred and fifty of these were analysed for twelve trace elements by atomic absorption spectroscopy. All quartzes were selected on purity, pulverised and treated with acid in order to remove possible carbonate and sulphide inclusions. The practical outcome of this investigation is that the ERR powder spectra of auriferous and argentiferous quartz show in most cases a pronounced electron paramagnetic resonance peak at the spectroscopic splitting factor g 2.0025. Barren quartz rarely shows this paramagnetism. This relation was worked out in detail for the Devonian Beaconsfield reef in Tasmania: the Devonian shear zones at Fosterville, Victoria and at Rosebery, Tasmania; in the Tertiary gold deposits in Waihi and Karangahake in New Zealand and Rodalquilar in Spain. The intensity of the paramagnetic signal however varies between geological areas. All auriferous and argentiferous quartz studied contained submicroscopic sericite. This leads to a positive correlation of the Au content and the intensity of the ERR signal with the concentration of Al, K, Rb, Mg and, to a lesser extent of Li. Na, thought to be present as a compensating element in the quartz is a very good indicator for the presence of gold.

Technical Session 4(c) Computer Applications ii ASEG GRID DATA EXCHANGE FORMAT (ASEG-GXF) - A STANDARD FORIWIAT FOR THE TRANSMISSION OF GRIDDED DATA Steve Collins Arctan Services P/L, NSW A format has been created to facilitate the transfer of gridded data between different computers. The format has been approved by the ASEG Grid Format Standards Subcommittee and is submitted as a standard for data interchange. The format relies on a coding process which produces only printable ASCII output, thus greatly facilitating data transfer between dissimilar machines. The coding process uses a base 90 integer arithmetic where each of the first 90 printable ASCII characters are used as the 90 integer characters. The format has the following properties. It is very general and highly transportable. It is compact yet the data structure is readily checked by simple observation. The format is simple and is easily coded and decoded.

AN IDEAL EARTH SCIENCE IMAGE INTERPRETATION AND MAPPING SYSTEM G.R. Pettifer""* and R.G. Paterson^ ^Geological Survey of Victoria ^Aberfoyie Resources Limited In producing earth science maps, geologists and geophysicists use laborious manual methods to integrate and interpret the vast amounts of disparate geological, borehole, geophysical, geochemical, satellite, cartographic, topographic and environmental data generally available for study of an area. Often the difficulty of integrating a data source can lead to its under-utilization and a compromised final map. With digital image and mapping software and hardware technology, traditional data sources can be converted to digital grids/images. If this technology was more userfriendly, traditional interpretation could be done on a colour screen by superimposing various datasets and annotating an overlay. This would replace the old "light-table" approach, allowing interpreters to integrate data sources more easily. Most image processing systems were developed for satellite data and have limited capability when manipulating geophysical or other gridded data (e.g. real-time sunangle). Most available systems also have difficulty producing large maps at userspecified scales and cannot easily handle the disparate raster and vector data formats, cell sizes and coordinate systems common in earth science and environmental data bases.

57 Geographic Information Systems (GiS) are now evolving to meet the needs of mining and petroleum explorationists, but their ability to interact with databases and image processing systems and to perform intelligent graphical layer analyses is varied. The ideal system closely integrates image processing and geophysical grid filtering and fourier analysis techniques with GIS and Computer-Aided Mapping (CAM) technologies. It would condense the multitude of data formats into one internal format for each data type (3D vector, polygon, line, point, raster), and use one universal coordinate system allowing direct access by one module. Various software/hardware systems are available, incorporating some of the above features. An overview of the ideal features is illustrated in Figure 1. Experiences with existing, new and evolving mapping/image processing systems illustrate the modern trends in computer-aided image interpretation. It is hoped this knowledge will stimulate industry discussion and user-driven software development of the ideal earth science mapping system.

ANALYTICAL TECHNIQUES IN INTERPRETATION OF REGIONAL AEROMAGNETIC DATA Duncan R. Cowan* and Sheila Cowan Cowan Geodata Services Regional aeromagnetic interpretation includes an important mapping component as well as the location of possible economic targets. Given these varied requirements, objective Interpretation techniques based on spectral analysis and the application of specialised filters play a major role. Recent improvements in computer hardware, particularly in microcomputers, have made it practical to analyse more data and it is now feasible to perform quantitative analysis on complete blocks of aeromagnetic data. Quantitative analysis may be applied to profile or grid data or both, depending on the interpretation objectives and the data quality. Results are presented for two analytical interpretation techniques, namely location of the maxima of the pseudo-gravity gradient and 3D Euler deconvolution. These techniques, together with apparent susceptibility mapping, provide objective information on geological boundaries, depths and lithologies.

MODELLING COMPLEX AND FAULTED SURFACES FROM RANDOMLY SAMPLED CONTROL POINTS USING A LEAST SQUARES LINEAR INVERSE METHOD Carl E. Youngmann''* and Jeffrey W. Given^ ^Sierra Geophysics, ^Science Appilcatlons International Corporation Interpretation and modelling of complex geologic structures requires the capability to quickly generate maps and gridded surfaces from large quantities of irregular data of varying reliability. The problem of determining a complex, faulted surface from a set of randomly sampled data is ideally suited to a generalized linear inverse formulation. The surface control data are expressed as linear functions of the nearby unknown values of a regularly sampled grid. The linear functions are local operators derived using finite

58 difference approximations to the derivatives at each grid node. The surface control can include prior information, such as the location of faults, and can be easily extended to incorporate several additional types of data, such as slope information and fault offset constraints. The inverse calculations become completely determined by requiring that the surface minimize a measure of the roughness that can be selected depending on the reliability of the control data. The method is completely analogous to a finite element model of a thin elastic plate. The resulting system of equations is solved using a combination of grid resampling and iterative methods. The method can be efficiently implemented to handle complex surfaces and has been developed into an effective, interactive interpretation tool.

59 Technical Session 4(d) Petroieum Exploration IV - Organic Petrology and Geochemistry

THE WALLOON COAL MEASURES: INTEGRATION OF CLASTIC AND ORGANIC FACIES AS A GUIDE TO OIL POTENTIAL M. Smyth''* and C.R. Fielding^ JCSIRO Division of Exploration Geoscience, North Ryde, NSW ^Dept of Geology & Mineralogy, The University of Queensland This paper describes results from an interdisciplinary project aimed at assessing the hydrocarbon potential of the Jurassic Walloon Coal Measures in the Great Artesian Basin. Organic petrological and clastic sedimentological techniques have been combined to determine relationships between organic matter facies and lithofacies, in order to establish possible spatial and other trends in hydrocarbon potential. The present study has concentrated on the type area for the Walloon Goal Measures, the Rosewood-Walloon Coalfield in S.E. Queensland which is part of the ClarenceMoreton Basin. The Walloon Coal Measures were deposited on a vast alluvial plain crossed by large meandering river channels which were separated by extensive floodbasin and mire environments. The following lithofacies have been recognised: A1 B1 B2 B3 B4 C1 C2

thick sandstone bodies - active fill of meandering river channels laminated claystones - quiet-water lake deposits oolitic ironstone - lake deposits thin sandstone bodies - crevasse splays thinly interbedded sandstone and siltstone - levee coal, carbonaceous shale - alluvial swamp bentonite - volcanic ash fall

Representatives of these facies have been assessed in terms of their organic matter content. Coals have an alluvial plain origin with maceral compositions (mineral-matterfree) concentrated around 60% vitrlnite, 40% liptinite, most of which is suberinite. The Vitrinlte Coal Eromanga Basin (above Cooper Basin) (above Pedlrka Basin) Clarence-Moreton Basin Surat Basin

Liptinite

Inertinite

DOM

levee environment is ttie only other one sufficiently represented for some concentration of its dispersed organic matter (DOM), around a maceral composition of 60% vitrinite, 30% liptinite, (most of which is cutinite) and 10% inertinite. Walloon Coal Measures organic matter to the west in the Surat Basin has concentration centres of 50% vitrinite 50% liptinite

35% vitrinite 60% liptinite (DOM) 5% inertinite

Further to the west, the Birkhead Formation, equivalent of the Walloon Coal Measures in the Eromanga Basin, has concentration centres of: 90% vitrinite 10% lipti nite

(coal)

65% vitrinite 30% liptinite 5% inertinite

60% vitrinite 30% lipti nite 10% inertinite (DOM) 40% vitrinite 50% liptinite 10% inertinite

where it overlies the Cooper Basin and 70% vitrinite 10% liptinite (coal) 20% inertinite

35% vitrinite 20% liptinite (DOM) 45% inertinite

overlying the Peditl^a Basin. The highest proportion of liptinite in the Jurassic organic matter is in the Surat Basin, both coals and DOM; and in DOM of the Eromanga Basin overlying the Cooper Basin. The deposltional environments of these sediments become progressively more influenced by lacustrine conditions westwards from the Clarence-Moreton Basin through the Surat into the Eromanga Basin. Higher liptinite concentrations and hence higher source potential appear to be associated with more lake-dominated facies. Further detailed work is required to test this hypothesis and generate a regional understanding of source potential in the Walloon Coal Measures.

THE SUPPRESSION OF VITRINITE REFLECTANCE - AN IMPORTANT CONSIDERATION IN THE DETERMINATION OF THERMAL MATURITY OF ORGANIC MATTER FOR PETROLEUM EXPLORATION IN AUSTRALIA Ronald W.T. Wilkins^*, Nigel J. Russell^ and Zhong Ningning^ ''CSIRO Division of Exploration Geoscience, North Ryde ^Jiangiian Petroleum Institute, Ciiina Vitrinite reflectance (VR) is unique amongst the thermal maturity techniques used for oil exploration. In thermal maturity modelling, comparison of predicted and observed VR values provides an important test for acceptable models. With the recent increase in interest in such models, it is timely to review some major problems of the VR technique. Hutton and Cook (1980) were the first to point out that in the presence of alginite, the measured reflectance of associated vitrinite in an oil shale was suppressed; the extent of suppression being proportional to the content of alginite. Newman and Newman (1982) showed that an initial VR increase was followed by a VR decrease with depth in a Pike River (N.Z.) coal seam sequence. In this instance, there was no associated alginite, but an inverse relationship was noted between the volatile matter content and vitrinite (telocollinite) reflectance. In both studies, identification of the vitrinite was unequivocal. The different associations of anomalous vitrinites emphasizes the need for a simple microscope technique to directly determine the magnitude of suppression from vitrinite itself. Combined reflectance and fluorescence intensity measurements do not aid in evaluating suppression effects because these parameters are not independent, and lead to the same conclusions. The alteration of fluorescence with time, however, appears to be independent of reflectance and it is known that the form of the fluorescence alteration curve in liptinites is, in its own right, qualitatively useful for thermal maturity estimation (Ottenjann, 1988). Although the fluorescence alteration of vitrinites has also been studied using conventional light sources (Quick et al., 1988; Quick, 1989), such measurements are not in common use. There are many advantages in carrying out fluorescence alteration experiments with a laser Raman microprobe. By combining fluorescence intensity and alteration data, reflectance suppression in vitrinites can be readily identified and quantitative corrections can be made. The Greta and Pelton coals (Sydney Basin, NSW) provide a good example of this approach to reflectance suppression evaluation. Samples collected from an 11 metre vertical section are essentially iso-metamorphic. Vitrinite (telocollinite) reflectance vanes from 0.68% near the bottom of the Greta seam to 0.43% near the top of the overlying Pelton seam (Diessel, 1991). In Fig. 1, fluorescence alteration data for Greta and Pelton coal samples, collected under standard conditions of laser irradiation (Wilkins et al., 1990), are compared with data from vitrinites from a set of "normal" Australian coals. All Greta and Pelton samples are anomalous, with the Pelton samples plotting furthest from the "normal" coal line. Diessel (1990) has noted the strong association of marineinfluenced coals, such as the Pelton seam, with perhydrous vitrinites that have an anomalously high fluorescence. This raises the question of suppression of VR in dispersed organic matter in marine sediments in general.

The application of this technique can be demonstrated by reference to some North-West Shelf wells. Results on some Chinese and New Zealand coals suggest the approach described may have wide geographical applicability.

o H < cc z o ^ cc lU

Normal Vltrinitt

LU O 2 LU O CO LU CC

? Greta Seam

Pelton Scam

FINAL FLUORESCENCE counts/1000

FINAL FLUORESCENCE counts / 1 0 0 0

Fig. 1. (a) Comparison of fluorescence parameters between Greta-Pelton vitrinites and reference vitrinites. (b) Suppression of VR vs. final fluorescence for Greta-Pelton vitrinites. References Diessel, C.F.K. 1990 Proceedings of the 24th Newcastle Symposium pp. 33-40. Diessel, C.F.K. 1991 Coal-Bearing Depositional Systems. Springer Verlag. Berlin Heidelberg, New York, (In print). Hutton, A.C. and Cook, A.C. 1980 Fuel 59, 711-714. Newman, J. and Newman, N.A. 1982 New Zealand Joumal of Geology and Geophysics 25, 233-243. Ottenjann, K. 1988 Organic Geochemistry 12, 309-321. Quick, J. 1989 Proceedings 3rd Coal Research Conference, Wellington, New Zealand pp. 1-12. Quick, J.C., Davis, A. and Lin, R. 1988 Ironmaking Conference Proceedings pp. 331337. Wilkins, R.W.T., Wilmshurst, J.R., HIadky, G. Ellacott, M.V. and Buckingham, C P 1990 Final Report NERDDP Project 981 pp. 1-87.

63 CAMBRIAN PETROLEUM AND SOURCE ROCK GEOCHEMISTRY OF SOUTH AUSTRALIA D.M. McKirdy^*, D.l. G r a v e s t o c k ^ and C . G . Gatehouse^ ''Department of Geology and Geophysics, University of Adelaide, S.A. ^South Australian Department of Mines and Energy, Parkslde, S.A. Oil shows and moderately organic-rich sedinfients (TOC up to 1.6%) occur widely throughout the Cambrian sequences of the Officer, Warburton, Arrowie and Stansbury Basins in South Australia. With the exception of the deep-water shales and lime mudstones of the Middle-Late Cambrian Kalladeina Formation (Warburton Basin), potential source beds and their derived hydrocarbons are located in two Early Cambrian 'sequence sets' (C1 and C2). In most cases the source rocks were deposited in marine transgressive systems tracts, although a hinterland tract in the Officer Basin includes the extensive oil-prone playa lacustrine mudstones of the Observatory Hill Formation. Suboxic to anoxic bottom conditions ensured the preservation of lipid-rich microbial organic matter (kerogen Types I, II & ll-lll; principal macerals, lamalginite & bituminite; pristane/phytane < 2) in a variety of fine-grained siliciclastic and carbonate-evaporite sedimnents. Despite their petroliferous odour, marine shelf limestones and dolostones of the Arrowie Basin contain only very low concentrations of gas-prone Type III kerogen of probable cyanobacterial origin. Kerogen 5"'^CppB values are in the range -28 to -32% for both oil-prone and gas-probe organic matter. Maturity measurements based on triaromatic hydrocarbons (e.g. methylphenanthrene index, MPI), in places constrained by kerogen H/C and OC atomic ratios and organic petrological data, indicate that much of the Cambrian section in these basins is still within the oil generation and preservation window. In the Stansbury Basin maturation level appears to be controlled by proximity to Proterozoic basement and the richest potential source rocks (Parara Limestone, Heatherdale Shale) are now largely overmature. Cambrian sediments are also overmature at depths >3km in the Warburton Basin, although structural complexity due to thrust faulting has given rise to anomalously low maturities (MPI-1 = 0.6-1.5) in the Kalladeina Formation along the Gidgealpa-Merrimelia Trend. Residual oils from Cambrian reservoirs in the Officer, Warburton and Arrowie Basins range in composition from highly paraffinic to aromatic-asphaltic. Sulphur contents are low (S <0.3%), even in carbonate-sourced oils. The sterane, terpane and acyclic isoprenoid alkane biomarker geochemistries of the oils reflect differences in the microbiota (eukaryotes, eubacteria, archaebacteria) that inhabited the depositional environments of their respective source rocks. C27-C29 sterane distributions are of two main types. A predominance of 24-methylcholestane (C28). usually considered to be diagnostic of a bacillariophyceaen (diatom) input, is characteristic of oils generated from evaporitic sediments (marine and non-marine) in the Officer Basin. These particular oWf^ also contain unusually high concentrations of isoprenoid alkanes (C-15-C26 regular; ^30'^40 irregular, including squalane) which are chemical fossils of methanogenic and/or halophilic archaebacteria. In contrast, cholestane (C27) and 24-ethylcholestane (C29) are co-dominant and (?)24-n-propylcholestane (C30) is a minor component in two marine oils, one from the Relief Sandstone in the Officer Basin and the other from the Wilkawillina Limestone in the Arrowie Basin. Abundant tricyclic terpanes (C20-C30), attributable to primitive anaerobic bacteria, are another feature of these marine oils. The sterane pattern common to the latter two Cambrian marine oils differs markedly from the ethycholestane-dominant signature reported for certain latest Proterozoic marine sediments (e.g. Rodda Beds, Officer Basin) and the Bendian-sourced cnjde oils from the Siberian Platform and Oman. This is consistent with the transition from a

chlorophyte-dominated Ediacaran marine microbiota (cf. large spinose acritarchs in the Rodda Beds) to a more diverse eukaryotic biota in the Early and Middle Cambrian oceans.

EVALUATION OF LOWER PALAEOZOIC AND PRECAMBRIAN PETROLEUM SOURCE ROCKS AND THEIR HYDROCARBON GENERATION POTENTIAL BY ALGINITE REFLECTANCE Miryam Glikson^*, Dennis Taylor^ and Douglas Morris^ Department of Geology, The University of Queensland, Old ^Pacific Oil & Gas, Vic ^Pacific Oil & Gas, NT Four hundred samples from 19 drillholes in the Georgina and McArthur basins provided material for this study. The most continuous vertical profile of organic-rich rocks was provided by the continuously cored Lady Penrhyn no. 1 drillhole located in the McArthur basin. Reflectance histograms of alglnlte from 80m (TOO = 4.2%), 290m (TOO = 2.15%), 440m (TOO = 4.85%), 640m (TOO = 0.72%) show increase in reflectance with depth (Fig. 1). A distinct mode apparent in these histograms can be plotted against depth to provide a simple measure of increasing rank. This profile indicated the following important features: 1. An upper zone from 40-140m with uniformally low reflectance, and bright yellow fluorescence of alginite. 2. A zone ranging from 170 to 440m where reflectance increases somewhat erratically from 0.3 to 0.9%. Fluorescence changes to dull orange-brown over the interval 170-21 Om. 3. A zone of no change in reflectance from 440-720m. 4. A sharp increase to 1.3% Ro occurs in the interval 720740m. The three samples from the Upper Velkerri low-TOC interval (210-260) show an anomalously high reflectance for their depth in the profile. These samples are also characterised by low hydrogen content implying oxidised or degraded organic matter, comparable to recycled vitrinite. If the reflectances of these samples are plotted separately from the rest of the samples two separate burial histories are evident. Pacific Oil & Gas Hacking no. 1 from the southern part of the Georgina Basin was continuously cored through the mainly carbonate section of Cambrian age to basement. Reflectance histograms were obtained over a depth range from 258-121 Om. However only samples between 1183 and 1210m could be considered truly organic-rich. Mt. Whelan No. 1 (GSQ) in the eastern part of the basin provided a cored section with organic-rich zones between 34 and 368m. Downhole plots of alginite reflectance mode for these two holes show an increase resembling that of L. Penrhyn-1 (Fig. 1). Once again many of the low TOC samples yield erratically high reflectances and must be plotted separately from the 'main stream' samples. The three boreholes provide the basis for a six-stage maturation scale (Table 1) from immature (no significant oil generation) to overmature (gas generation only). In pyrolysis terms this corresponds to HI of over 500 to one below 100. This indicates a very narrow oil window for alginite. When comparing the vitrinite reflectance and pyrolysis data an inverse correlation between HI and reflectance and a positive correlation between Tmax and reflectance are apparent. This is expected from material which in itself is oil generating. However, where high concentrations of pyrobitumen occur and little or no alginite is present Tmax displays suppressed values, and can produce inverted profiles with Tmax declining downhole as maturation is increasing, and that is where the reflectance data are of importance in the evaluation of the real rank of the organic matter.

Transmission electron nfiicroscopy (TEM) has been used to identify different types of organic matter wliicli are indistinguishable and unrecognisable when viewed in light microscopy alone. It appears that alginite at the onset of oil generation acquires a spongy character in contrast with its previous homogenous electron-transparent appearance. The spongy appearance becomes a fine mesh at the gas generation stage. It is also evident from TEM observations that several stages co-exist in the same sample, which explains the range in reflectance as expressed in histograms. Algal matrix material usually present, considered to be rich in exopolysaccharides and non oil generating becomes harder with rank, acquiring high electron density and capacity for metal adsorption, which the lipidic residue lacks. Both, algal matrix and pyrobitumens when observed in TEM show a close resemblance to the maceral inertinite, reflecting on their thermal history. Summary and conclusions: A reliable maturation scale for alginite has been developed which can be applied to any algal-dominated, type 1 kerogen. Six zones have been recognized in the coalification path of alginite: An undermature zone I, the mature zones II and III comprising the oil window, and a fourth stable zone, where temperatures required for condensate/gas generation have not been reached, zone V where oil is still preserved and zone VI where gas only is generated. Comparison of reflectance values with geochemical and experimental pyrolysis data has confirmed a narrow oil window, and high activation energies for alginite hydrocarbon generation, and therefore a later onset of oil generation than other macerals (i.e. cutinite, exinite, resinite, vitrinite B). TEM used in the study of alginite and bitumens elucidates the changes occurring to the organic matter as maturation proceeds. Alginite is not seen to go through a distinct intermediate stage, but it is more a matter of decrease in unreacted material which marks the different maturation zones.

r n b l e I: A l g i n i t e

% Ro Alg. Alteration

ranK ^ o p a t l o n

Stage

Hydrocarbon

Fmai

5 Ro V

generation

zone <0.1 0.1

undermature

<0.5

03 0.4

438

0.6

peak oiJ generation

445

1.0

end oil generation-

450

0.6 07

start oil generation 11

III

0.8

1.3 0.9 l.O 1.1

v e t gas/condensate

IV 3

1 2-l.b

>2.0

mature U stable

end oil preservation 470

--1.3-1.6 —

gas generation onl;f

>2.0 semianthraciie

a> a>

Depth

200

Her.th

Ro R i g . ( m o H « ) :

I hi ox

a.'g.(Bode) -6 .8 1.0 1.2

R ? J ! 9 ;

5 1.C 1.2

00' 00c 00',: OOf 00S 009 OOL

350 350 400 400 450

POO FOG HRCK1HG-1

q hiHi UHELRH-1 • nrjc Fiii.i

ISC'

nr-tnur Ck.Fiii.

I GO

700

'jQ

250 250 300 300

150 I 200 200

140 100 SO

20-

vtikdii r«i» ->l«k IMIli

HI 460

400

100 100

440

Zone

110 J

so j

50 j

100 <;

70)

42 J

oo'; c . I 440 43Cij

4 tol I '«00j

500

3yO(

400 500 .

Depth

Tm ox

- oo i

300

1.0 Tmax

100 200

(mode)

-ilcta •••ica

67 Technical Session 4(e) Regional, Crustal and Geothermal I Gravity, iVIagnetic and Geothermal Studies ELECTRICAL CONDUCTIVITY ANOMALIES IN THE AUSTRALIAN LITHOSPHERE: EFFECTS ON MAGNETIC GRADIOMETER SURVEYS F.E.M. Lilley Research School of Earth Sciences, Australian National University The use of recording magnetometers to observe natural magnetic fluctuations across different parts of Australia is delineating areas where the fluctuations are anomalous. These areas are termed "conductivity anomalies", as the fluctuation patterns must be due to regions in the lithosphere of high electrical conductivity, where the naturallyinduced electric currents are concentrated. The main causes of such enhanced lithospheric conductivity are thought to be (i) water, with impurities (especially salt), and perhaps with well-connected paths of conduction due to fracturing of rock; (ii) highly conducting minerals such as graphite, and (ill) heat (which may cause partial melting at the lithosphere base). The fluctuating magnetic fields near a conductivity anomaly may cause difficulty for the data-reduction of a high-resolution aeromagnetic survey which is carried out during magnetic activity. Making gradiometer survey measurements avoids such effects, to the extent that the magnetic fluctuations are spatially uniform. This paper examines the maximum spatial magnetic gradients likely to be associated with a strong (and shallow) continental conductivity anomaly, and determines values in the range 1 to 10 nT.km""". Such gradients in the static magnetic field are typical of a sedimentary basin, but are mufh less than those which occui where the magnetic relief is strong. While the magnetic fluctuation fields of conductivity anomalies should be kept in mind during magnetic surveying, gradiometer measurements should generally be effective in minimizing their influence.

GEOPHYSICAL ANOMALIES CAUSED BY ROCK-HOT FLUID INTERACTIONS M.P. Hochstein Geothermal Institute, University of Auckland, NZ Several types of geophysical anomalies caused by rock-hot fluid interaction can be observed over geothermal prospects. Some of these anomalies persist after a geothermal system has cooled, and are targets for epithermal exploration. At high temperatures, various minerals are altered; an increase in clay minerals increases charge separation in thermally altered rocks where the matrix conductivity becomes dominant. Thermal reservoirs can exhibit extremely low resistivities (<3 Ohm m). Empirical formulas which describe resistivity as a function of clay concentration, dominant clay mineral, porosity, fluid resistivity and temperature will be presented.

Whereas the density of replacement minerals is close to that of the original minerals, the bulk density of thermal reservoir rocks can increase by mineral deposition (quartz, calcite), causing typical small gravity highs over highly porous reservoirs. If the reservoir rocks consist of volcanics, the dominant magnetic mineral 'titanomagnetite' is altered to almost non-magnetic pyrite. Many reservoirs are therefore associated with a characteristic demagnetization anomaly. The change in elastic parameters caused by thermal alteration is complex. In unaltered rock Dp decreases slightly, remains constant. In highly altered rocks both and 1)5 decrease. If two-phase fluids or vapour are dominant, x>p is reduced, whereas \)p and 1)3 increase if mineral deposition is significant. As a result, Poisson's ratio of the same reservoir rock can vary between the extreme range of 0.15 and 0.4. Examples are presented which show the effect of fluids and alteration on seismic velocities.

STRUCTURAL FABRIC AND TECTONICS ASSOCIATED WITH THE POLDA LINEAMENT, SOUTH AUSTRALIA - A GEOPHYSICAL AND MORPHOTECTONIC ASSESSMENT D.H. Tucker^*, R.G. Nelson^ and J.C. Pitt^ ^ Preview Resources Pty Ltd, Eastwood, SA ^South Australian Department of Mines and Energy, Eastwood, SA 3pitt Research Pty Ltd, Henley Beach, SA A knowledge of the structural and tectonic processes which have controlled the evolution of the Archaean/Proterozoic Gawler Craton in South Australia is crucial to an understanding of the geology of the southern central Australian continent. A particular feature transecting the southern portion of the Craton is the Polda Lineament, which extends east-west for possibly up to 1600 km. Both vertical and lateral movements have been prevalent within this zone of crustal yielding from Lower Proterozoic? to Cenozoic times. The most obvious indication of the lineament is the Polda Trough, an area of deep sedimentary section. However, extensions to the lineament are now recognised eastwards across lead-zinc mineral fields in the eastern Gawler Craton, and, albeit less prominently, cutting the Adelaidean? to Cambrian? basement of the Murray Basin. The Polda Lineament is now seen as a major zone of crustal yielding, with important connotations for mineral and petroleum exploration.

GRAVITY DATA OVER THE LOLWORTH-RAVENSWOOD PROVINCE GEOLOGICAL AND STRUCTURAL IMPLICATIONS B.D. Stockiir and L.J. Hutton Gravity data collected over the Charters Towers 1:250 000 sheet at a 4 kilometre spacing has identified several features of geological interest in the province. Structural elements covered by the gravity survey include the Lolworth-Ravenswood Province, and

69 the northern extent of the Drumnfiond Basin. This paper discusses some of the features in the Lolworth-Ravenswood Province. The most prominent gravity feature outlined in the region is a broad east-west gravity ridge coinciding with the Seventy IVIile Range Group, a sequence of Late Cambrian to Early Ordovician sediments and rhyolitic to intermediate volcanics. We interpret this high to be of more dense gabbroic or basic material at moderately shallow crustal levels. Another major feature is a large gravity low coincident with the Lolworth Granite. This contrasts strongly with the generally higher and more variable gravity response over the Ravenswood Batholith. The varied response over the Ravenswood Batholith is interpreted as reflecting the stnjcture of the individual plutons within the batholith. Areas of relative high gravity are interpreted to correspond to sheetlike granite pluton forms contrasting with a well-defined gravity low to the south of Charters Towers which is interpreted as being a diapiric pluton. The gravity data have helped recognise features of the Province that have not been previously identified.

70 Technical Session 4(f) Geoscience Education II

SELLING EARTH SCIENCES P.G.L. Harlow Ipswich Grammar School, Ipswich, Queensland Earth Science education In Australian schools, and indeed throughout the world, has grown continually weaker for decades. The result of which is that there has seldom been sufficient Australian-trained scientists to satisfy total domestic needs. In the three years prior to 1982-1983 about 40% of geoscience recruits came from overseas, and even in the good year, 1985-1986, the proportion was only about 30%. Since then, of the estimated 400 geoscientists who leave the profession each year, the Australian universities are only producing about 200 geoscience graduates, leaving a shortfall of around 200 each year. The lack of interest in studying geology at a tertiary level in Australia has been 1.

laid squarely on the teaching of Geoscience in Secondary Schools.

accredited to the perceived status of the mining industry in the community and schools which is poor due to adverse environmental publicity.

due to school curriculums which prevent the best students from taking Earth Sciences e.g. in New South Wales students cannot do more than three science subjects and in Queensland students are actively discouraged from taking Geosciences as its ranking is low.

due to the Tertiary Geoscience departments being locked into servicing the mining and petroleum industries, for at least the past 25 years, while at the same time ignoring the position of Geoscience in the schools and the general community. Up until this time student intakes into tertiary Geoscience courses have largely reflected the ups and downs of the mining industry. This has tended to give the Geosciences poor status and resulted in a lack of resources to expand into other areas, and a continual flight to retain staff numbers in the Universities.

a result of the entry policies on university Geoscience departments which literally discourage the taking of Geoscience in Secondary schools by not having Secondary level Geoscience as a requirement for entry or even seeing that Geoscience is more desirable, than physics or chemistry, for entry.

the shortage of Australian graduates has lead to a self perpetuating problem where there are insufficient graduates to provide teachers to produce further graduates.

This paper provides ideas that can be implemented to improve the status of the Geosciences in the general community and in particular to improve the number and quality of students in studying Geoscience. I will present to you, the teachers and the professional geoscientists, a model of education as an industry with Geoscience education as a product. How this product is

71 currently perceived by the consumers (students and public) will be considered in view of how the product can be designed and advertised to be more successful in the current market place.

TEACHING SENIOR SECONDARY SCHOOL GEOLOGY IN THE ALICE SPRINGS REGION D.H. Morton Sadadeen Secondary College, Alice Springs, NT Central Australia provides one of the best natural laboratories for the study of Earth Sciences and Geology in Australia and with the fact that $9.5 M was paid to Territorians in mining royalties in 1988/89, the importance of teaching geology in the Northern Territory becomes apparent. Students at senior Secondary level, in the Territory, have the option to study Year 11 Earth Science for either one or two 20 week semesters and then, if they choose, proceed on to take PES Geology as a university entrance subject at Year 12 level for a full year. 50% of the total assessment of the Year 12 course is school-based and 40% of this consists of a field work component. Within the Alice Springs town boundaries it is possible to view excellent exposures of dolerite and pegmatite intrusions in the Arunta Complex. At Heavytree Gap are exposures of two unconformities and a variety of sedimentary structures, including ripple marks, mud cracks, scour and fill, and leisegang rings. The Early Proterozoic rocks (schists, gneisses and amphibolites) of the Strangeways Metamorphic Complex and the Hartz Ranges provide excellent study opportunities. High quality minerals that are easily located in the Complex include apatite, chlorite, epidote, garnet, kyanite, magnetite, sillimanite, and zircon. In the area adjacent to Wigley's Waterhole, located 7 km north of Alice Springs, the Charles Creek Fault is observable, as is a cutting through mylonite. This area also has excellent outcrops of ultrabasic rocks, including norite (some with spheroidal weathering), dolerite dykes and migmatites, which are all exposed in a small creek traverse. 90 km west of Alice Springs are the world famous exposures of the Amadeus Basin. Here sediments, ranging in age from late Proterozoic to Devonian, are exposed in a continuous section over a distance of 6700m. Tillites, limestones, conglomerates, sandstones and shales are exposed with conspicuous massive cross-bedding and slump structures. Both trace- and other fossils, including stromatalites, Ordovician shallow marine fauna (trilobita, brachiopoda, cephalopoda, nautiloidea) and scolithus, rusophycus and cruziana, are observable. Opportunities for structural measurements abound and the area is good for photo interpretation. Other potential locations close to Alice Springs include: (1) Maloney Creek (2) Ross Highway (3) Ross River Homestead (4) White range

shallow marine fossils Tertiary land surfaces folds and stromatalites gold mine

Students are required to maintain a field note book and record all details of locations, draw sketches, and note samples collected. On return from excursions, reports have to be prepared which include maps, photos and samples. The field note book is also presented for assessment. Many student groups travel through the Alice Springs Region and the potential for these groups to observe some of the excellent geological resources available, in their one-off excursion to the area, would provide real benefit to any prospective geoscience student in the group.

GEOPHYSICS ON A SHOE-STRING N.F. Uren* and B.J. Evans Department of Exploration Geophysics, Curtin University of Technology, Perth, WA A University Department has a two-fold duty. This may be simply stated as teaching and research in its subject area. Geophysics covers a spectrum of activities. At one end, we have general exploration, and the use of geophysical data. Integration with Geology is most important at this end. The centre of the spectrum is characterised by the conduct of geophysical surveys, data reduction and interpretation. The other end may be described as the development of geophysics, the invention of new techniques, processing algorithms and the advancement of the science. University income to support its obligations comes from Federal funds based on student enrolments, State and Federal Government funding sources, public and private sector research contracts and Industry sponsorship. However, tenured (permanent) staffing is controlled basically by the number of enrolled students, and it is well recognised by Universities that these fluctuate with economic conditions. It is possible to support additional staff on research money, but a more stable base is required to build up and maintain a body of lasting expertise in a Department. Larger, more permanent staffing groups are required if the full geophysical spectrum is to be covered, to enable the education sector to fulfil its obligations to industry and the nation. In Western Australia, because of the geographical situation, there is an excellent chance to create a larger grouping of geophysicists at Curtin University of Technology. It is proposed that an Institute for Geophysics be created to carry out the State functions of governmental agencies such as the Bureau of Mineral Resources and the Geological Survey of Western Australia, as well as to support the normal education and research functions of the University. This Institute for Geophysics would also take on industrial partners and would function as a Co-operative Research Centre, attracting additional Federal funds. Situated on the Bentley Campus, it would be closely linked with the Western Australian Centre for Petroleum Exploration, the Key Centre for Resource Exploration and other research departments. Such University and Governmental groupings exist in the United States and have been remarkably productive. A business-like approach, sustaining geophysics education and research with full professional activities, not normally related to Australian educational institutions, will mean the end of geophysics on a shoe-string budget. It is probably the only financially plausible way to advance and extend the science of geophysics beyond its present level in Australia.

STYLES IN GEOPHYSICAL EDUCATION K. Vozoff Centre for Geophysical Education Research, Macquarle University, NSW It seems to be largely taken for granted in some educational systems that a geophysicist is a slightly more technologically-orientated kind of geologist. The result tends to be self-fulfilling. However, the jobs done by geophysics graduates in general are often very different from those of geologists, having little or nothing to do with the solid earth or with exploration. This poses the difficult questions of philosophy and content of geophysical education, both undergraduate and postgraduate. I will discuss aspects of these questions.

74 Technical Session 5(a) Petroleum Exploration V - Environmental

ENVIRONMENTAL GUIDELINES FOR ONSHORE SEISMIC OPERATIONS IN WESTERN AUSTRALIA 1. Fraser and A. Ryall* Petroleum Division, Department of Mines A new set of minimum environmental standards to be med by all companies undertaking onshore seismic operations in Western Australia has been issued. These "Guidelines for Onshore Petroleum Geophysical Surveying" recognise the experience gained over 45 years of operations in Western Australian lands; meet current community expectations using today's methods and technology; and allow for change to acknowledge new information, priorities and technology. Meeting the Guidelines is a condition of undertaking a seismic survey in the state. While the majority of survey practices to date have been appropriate in environmentally robust areas the Guidelines seek consistently high standards, particularly in more fragile environments. It addresses the issues of line constoiction and rehabilitation techniques, and the planning and consultation necessary to enable environmentally sound exploration to be undertaken. The Department of Mines will implement the Guidelines by informing relevant parties of their existence, by providing survey planning information and by measuring success through discussion and inspection of sites.

ENVIRONMENTAL AND OPERATIONAL CHALLENGES OF A SEISMIC SURVEY ON AND AROUND THE MUIRON ISLANDS, WESTERN AUSTRALIA Jenny Bauer* and Brett Kelsall Lasmo Oil (Australia) Limited In early 1990 the EP 342 and TP/9 joint venture conducted a seismic survey on an around the Muiron Islands in the Carnarvon Basin. Its objective was to infill the gap in existing marine seismic data coverage resulting from the presence of the islands, which are believed to overlie a prospective trend. Work on the Muiron Islands was done in conjunction with a shallow-water marine seismic survey conducted over the remainder of the permit areas. Because the Muiron Islands are a nature reserve and a significant nesting site for Wedge-tailed Shearwaters and turtles, environmental assessment of the project was required. Approval to conduct the survey was subject to stringent conditions, including: the avoidance of Shearwater nesting areas, prohibition of the use of vehicles and the clearing of vegetation, prohibition of camping on the islands, and a requirement to use environmental consultants to monitor the survey. A fully portable operation was conducted on the islands. A recording spread was laid across the islands and extended into the surrounding waters to record shots fired from both onshore in drilled or augered shotholes and offshore from the seismic vessel. On the more protected eastern side of the islands a bay cable transition zone spread was

75 extended from the islands to provide a tie with the marine data. However, the exposed western side generally proved too rough for the bay cable operation, and a shallow-draft seismic vessel was used in 'rollout mode' to obtain a tie between the onshore and offshore data. The geophysical objectives of the survey were achieved with negligible impact on the environment. There was no known mortality to wildlife and only minor and impermanent disturbance to vegetation.

ENVIRONMENTAL IMPACT OF SEISMIC EXPLORATION ACTIVITIES IN PELS 5 & 6, SOUTH AUSTRALIA A DEPARTMENT OF MINES AND ENERGY PERSPECTIVE T.N. Crabb* and P.R. Dunne South Australian Department of Mines and Energy The Department of Mines and Energy and the operators of PELs 5 and 6, Delhi Petroleum and more recently SANTOS, adopted a Joint Operations Management Group (JOMG) approach to the consideration of seismic operations in the Cooper Basin as part of a managed self regulatory environmental control process. JOMG has developed codes of environmental practice that have been field tested, modified and updated to suit conditions in PELs 5 and 6. JOMG has also reviewed programs and monitored effectiveness of these codes. Recent changes to the Petroleum Act Regulations in SA have introduced a requirement for a code of environmental practice and a declaration of environmental factors to be submitted for approval before the commencement of any geophysical programme. The joint code of environmental practice developed by JOMG over the years will form the basis of a new code produced solely by Santos which will now be legally enforcible in PELs 5 and 6. A late 1989 through early 1990 review of exploration activities in PELs 5 and 6 by the CSIRO Division of Wildlife and Rangelands Research, involving Landsat TM imagery, indicated that the JOMG has been singularly successful in minimising environmental impact of seismic operations in the Cooper Basin.

SOUND ENVIRONMENTAL PRACTICE IN ONSHORE SEISMIC ACQUISITION - A FIELD PERSPECTIVE M.K. Walcott Walcott & Associates Pty Ltd, Bombala, N.S.W. Due to the growing interest of community and government in conserving natural areas, together with the more general growth in environmental and conservation awareness, environmental management has become an important factor in seismic acquisition.

Public perception of the environmental effect of onshore petroleum exploration mainly relates to seismic activities. It is these techniques which have been, historically, the most visibly destructive to the landscape. Modified acquisition methods are being implemented, particularly in line preparation procedures. These are now vastly different to those which were employed ten years ago. This paper compares the past and present methods of seismic acquisition and discusses the techniques currently being introduced by operating oil companies and geophysical contractors to obtain high quality data with minimal impact on the environment. The introduction of environmentally sound seismic has been gradual, however, companies have reported that, with proper supervision, there has been minimal impact on the cost of operations resulting from adoption of more stringent codes of environmental practice.

77 Technical Session 5(b) Mineral Exploration III - Gravity/Borehioie Studies

UNDERGROUND DHEM SURVEYS AT ROSEBERY, TASMANIA J.R. Bishop"'* and C.H. Lutherborrow^ ^Mltre Geopiiysics, Tasmania ^Pasminco Mining, Tasmania Underground drill-hole electromagnetic (DHEM) surveys have been carried out in three adjacent holes which intersect an ore lens at the Rosebery mine. The results were disappointing. The data was either dominated by a response from black shales or only very weak anomalies were obtained. Interpretation, using simple filament modelling, was not able to successfully match the observed data, but did indicate that quite small current loops had been induced in the ore. It also demonstrated the effect of the overlying black shales. The poor responses have been attributed to an electrically discontinuous zinc-rich ore, shielded from the transmitter by conductive black shales.

UNDERGROUND DOWNHOLE GEOPHYSICS AT CSA MINE, COBAR A.R.D. Doe^*, J.T. Carswell^, C.K. Smith^ and M.E. Erickson^ "•CRA Exploration, Sydney, N.S.W. ^Cobar Mines Pty Ltd, Cobar, N.S.W. Thirteen holes totalling 3200 m were surveyed using a downhole time domain Geonics EM37 system at the 830 metre level within the CSA Mine, Cobar, New South Wales, in order to search for blind, electrically conductive sulphides at some distance from exploration drillholes. A significant off-hole conductor was detected in only one drillhole. Geophysical modelling and interpretation of the survey results indicated that this off-hole conductor was caused by a sulphide lens 30 metres from the drillhole at a hole depth of 220 metres. This interpretation was confirmed by subsequent drilling which intersected a copper-zinc lens at the predicted location. The electromagnetic survey was completed in July 1989 and is one of the first successful attempts to use downhole EM in an underground mine in Australia.

EXPLORATION SIGNIFICANCE OF GRAVITY SURVEYS, ROSEBERY MINE, TASMANIA D.E. Leaman Leaman Geophysics, Hobart, Tas. Gravity surveys of semi-regional specification around, and within, Rosebery Mine in the IVIt. Read Volcanics of western Tasmania have demonstrated that shallowly dipping base metal ore systems may generate significant perturbations in the gravity field. The effect reflects the entire ore-gangue-alteration association and not simply the proportion of ore of economic grade or density. High relief terrain, complex near surface geology and concealed granite stock do not obscure the correlation with mineralisation. Analysis shows that much of the mine lies within the metamorphic aureole of the granite and the confusing mix of isotope and mineral indicators is fully explained. Comparative analysis of the observed field and that calculated from the rock and density distribution in the mine area has revealed several local anomalous masses. The largest of these, offset from a large barren volume in the mine, has now been shown to be due to a large, previously unsuspected and detached volume of mineralised host sequence.

GRAVITY GRADIOMETRY FOR GEOPHYSICAL PROSPECTING M.H. Dransfield*, M.J. Buckingham, 0. Edwards, F.J. van Kann, A.G. Mann, R. Matthews and P.J. Turner Physics Department, The University of Western Australia Gravity gradiometers have the potential to provide gravity measurements from a moving vehicle, thus allowing airborne gravity surveys. In order to achieve this potential, exacting sensitivity and bandwidth requirements must be met by the Instrument and accuracy demands in navigation and terrain surveying must be satisfied. A gravity gradlometer for geophysical prospecting has been under development at the University of Western Australia for ten years. It is an advanced instrument using cryogenic technology and superconducting electronics and is the only gradlometer developed explicitly for prospecting use, although others elsewhere are being developed for geodetic and space applications. Appropriate sensitivity and bandwidth have been demonstrated in tests of a laboratory prototype. We briefly compare gradiometry with gravimetry and show that gravity gradiometers are better suited than gravimeters to the measurement scales of interest in geophysical prospecting. This is illustrated with the results of a modelling study of the Teutonic Bore orebody.

79 Technical Session 5(c) Computer Applications III

DESKTOP GEOLOGICAL MODELLING Anthony A. Cram and John H. Duke* Exploration Computer Services, Bowral, NSW Evaluation of a mineral deposit at the exploration stage always involves formulating a geological model which combines lode structure and grade distribution. Many exploration geologists find great difficulty in both arriving at and presenting to management a clear estimate of the resource of an exploration-stage mineral deposit. The reasons for this are varied, but often stem not only from a paucity of sub-surface data, but from an inability to both present and fully comprehend all the subtleties and complexities of the available data. Even geologists with a real 'insight' into the nature of the deposit find problems in communicating their 'mental model'. With recent developments in low cost colour workstations and geological modelling techniques, a whole new approach to resource evaluation is emerging. This approach is characterised by an ability to arrive quickly at the "best" geological interpretation and then use this to control the grade modelling process. Like the phenomenon of WYSIWYG (what you see is what you get) 'desktop publishing', the new 'desktop geological modelling' provides not only the specialist tools to carry out the task of modelling, but also the display facilities to validate it. The software package MINEX-3D, used by the author for many resource evaluation projects, provides all the elements of the new desktop geological modelling. The software tools provided by MINEX-3D for the geological modelling of mineral deposits are discussed within four main functions: statistical analysis, data display, geological interpretation and grade estimation. Interactive statistical and geostatistical analysis of databased exploration data provide the first step in coming to an understanding of grade distribution. Real benefits of application software lie in the ability to interactively display exploration data in ways which elucidate. Drillholes can easily be displayed on section or in 3D. Data imaging techniques allow multiple data types to be displayed simultaneously in graphic ways which enhance rock/assay relationships and assay populations. Many prospects show little or no lode structure when the preliminary assay and geology sections are first drawn. However, as statistical and data imaging proceed, often a tentative interpretation emerges. The main techniques used to capture structural interpretations are open surface modelling and 3D wireframing. A whole 'toolbox' of modelling techniques have been developed to provide an accurate representation of grade, density and other sampled qualities. Different prospects pose different problems for the geologist to solve. In some, sparse drillhole data and complex structure make it difficult to arrive at any more than a generalised model with no real lode definition or resolution on local grade distribution. In others, both lode structure and grade distribution can be modelled in true 3D with some degree of confidence.

80 The modelling methods described have been used successfully by the author to evaluate a host of mineral deposits over the last few years. The geological modelling approach and techniques have been developed and refined in response to solve all the problems that arise in resource evaluation projects.

BRINGING ROCKS INTO A HARD PLACE. THE COLLECTION OF GEOLOGICAL INFORMATION FOR COMPUTER DATA BASES AND COMPUTER ASSISTED ORE RESERVE STUDIES Russell J. Fountain Nord Resources (Pacific) Pty Ltd., Camperdown, NSW Advances in micro and hand-held computers offer real advantages in the acquisition, reporting and manipulation of geological data, especially in the area of project evaluation and ore reserve estimation. The geological profession has been generally slow to accept the disciplines inherent in data collection which are required to make effective use of computers in using the data. In a typical project drill logging situation, information falls into routine (basic information recorded systematically for all or almost all of the intervals logged) and non-routine (not recorded or used systematically) classes. Routinely collected information can be classified into quantitative (e.g. recovery, percentage sulphides, RQD), semi-quantitative (degree of weathering) to purely qualitative data (lithology, alteration type) together with more interpretative information (stratigraphic unit, mapping unit) which may not always be obvious at the time of logging. Non-routine information includes the whole bulk of geological information which is not judged to be significant with respect to the project in hand, or which occurs only rarely. These data types require corresponding computing field types: numeric, alpha-numeric using pre-defined codes, and free form alpha or comment fields. For effective computer manipulation, quantitative or semi-quantitative data types require a separate field for each specific item. For qualitative data, a wide range of alternatives can be covered by a single field. Numeric fields can be very space consuming when dealing with trace quantities, and are often best replaced during logging by simple alpha codes covering key ranges at appropriate precision levels, which are then translated to the appropriate numeric values at the data base stage. Experience has shown that project specific logging forms are far more readily accepted by geologists than generalised systems. This requires decision making at the project outset as to which data needs to be included for routine recording (e.g. which sulphide mineral species are significant to the project). The process of resource estimation and evaluation can be greatly assisted by the ability to interact between interpreted 3 dimensional geology and the data base. In particular, the ability to re-classify raw data on the basis of changing geological interpretation is a feature which could be advantageously added to many existing ore reserve modelling packages.

81 Available computer technology gives us a powerful tool to better understand and evaluate ore deposits. It does not on its own solve any problems, or absolve the geologist from thorough checking of his/her raw data and understanding of the detailed processes inherent in building a computerised ore reserve model.

GIS IN THE MINERALS AND OIL EXPORATION INDUSTRY R.F. Moore National Resource Infoimatlon Centre Today more than ever it can be said "information is power" and this is especially true for companies involved in the exploration and development of Australia's mineral and petroleum resources. Often information or technology that gives an exploration company an economic or competitive advantage is valued far in excess of the cost of collecting the information or purchasing the technology. The exploration industry needs access to a wide variety of data stored in a form that is readily accessible and which allows rapid integration with other data sets. The explorationist needs to generate both conventional and specialist thematic maps (e.g. maps describing resource potential). Geographic Information Systems (GIS) can provide the much needed vehicle for the integrated storage and analysis of spatial data. GIS technology offers a more objective and efficient way of doing what the explorationist has traditionally done for many years using analogue and digital mapping techniques. The geoscientist is constantly attempting to integrate many types of data (eg. geological, geochemical, geophysical, topographic) to define anomalous correlations and thus better define areas of economic potential. GIS has considerable potential to assist this process in a more rigorous and convenient manner. Not only can a GIS quickly produce working maps for use by the project team, but given a database of thematic layers stored in a GIS, it is relatively simple to derive and depict new thematic layers which can then be used by the explorationist to better define prospective areas. The presumption of course is that the data layers are spatially co-located and that it is meaningful to relate and integrate these data. For example, it is probably not appropriate to correlate deep source magnetics and surface geochemical data but it is probably appropriate to correlate gamma-spectrometer data with alteration data derived from airborne visibleinfrared spectrometer data. Having collected and stored the data, the added bonus with GIS however is its ability to allow modelling using complex analytical relationships between thematic layers. Using this technology, you might, for example, use a predictive model that uses data in the GIS database to generate a map depicting the likelihood of occurrence of the commodity being sought. The application of this technology in the exploration industry however has been slower than might have been expected for a number of reasons. As well, the technology still has some significant shortcomings for geoscience-related applications, in particular geological symbology and geological topology. The fact that the explorationist is dealing with a three-dimensional problem, however, is the biggest shortcoming and remains largely unaddressed by the commercial GIS software vendors. It is also still difficult to handle spatially-related raster and vector data in the same environment. Despite these criticisms, however, the application potential for GIS in the expoloration industry is considerable because, having collected and stored the data in a consistent

82 way, it is possible at any time to generate new maps tliat define relationsliips between the data layers in ways not easily done before. The explorationist has for years been doing this, but now he can do this and more in a more consistent, accurate and flexible manner.

COMPUTING IN THE EXPLORATION OFFICE Ian Lilly Burraneer Geosclences Pty Limited, Sydney The advent of the personal computer (PC) has seen the use of computers in the exploration environment extend from the field camp to corporate headquarters. In most organisations there exists a hierarchy of computer equipment ranging from ruggedised data collection systems in the field through battery and mains powered laptops in the project office to desktop PCs, workstations and minicomputers in regional and corporate offices. The optimum exploitation of these systems requires careful choice of hardware, communications equipment and software. Much of the data gathered by these systems is not used to its best advantage because of the lack of standardisation of data recording and encoding within and between organisations. Several attempts have been made by industry to address these issues by defining standards. One of the more successful standards is the ASEG GDF which is a selfdefining format for the interchange of geophysical data. This standard grew out of a proposed USA standard which was singularly unsuccessful in gaining acceptance in the US geophysical community. Standardisation within an organisation usually starts with the lowest "layer", the physical medium. Once it was 0.5" magnetic tape. These days it is more usually a floppy diskette. The next logical layer involves the coding of the data itself. ASCII is the norm and the ASEG GDF represents a sophisticated use of metadata such that printed documentation describing the contents of a tape or disk can be omitted and the data still be retrieved. I contend that a more important issue to be resolved early in the data collection phase of any project is the type and coding of data to be collected. It is important that within an organisation consistent and flexible methodologies exist for this coding so that general purpose software may be developed to collect and analyse the data. Companies involved in exploration must also be certain to standardise on the coding methodology and data logging procedures before commencing any sampling program. Inconsistent and incomplete logs cause significant problems in the later stages of a project. As an example, simple empirical procedures such as recording hardness of drill core via a numerical code can significantly extend the usefulness of geotechnical data collected later in a project.

83 Careful thought needs to be given to the ultimate use to which ancillary data may be put. The codes used to represent numerical and descriptive information must be succinct, extensible and readily understood by man and machine. The use of official and de-facto internal and public standards can significantly speed up the transfer of data between regional offices and headquarters; between contractors and clients; between joint venture partners and between statutory authorities and the industry. The use of standardised codes at the project and company wide levels can significantly reduce the re-keying, reformatting and mis-interpretation that occurs as a prospect matures into a project and the volume of data multiplies by an order of magnitude.

Technical Session 5(d) Petroi^um Exploration Vi - VSP and Tomograpliy A PARAMETRIC STUDY OF BOREHOLE INFLUENCE IN RESOLVING SEISMIC VELOCITY IN WELL-TO-WELL TOMOGRAMS A.D. Watkins Department of Earth Sciences, Monash University The data collected In a we 11-to-we 11 tomography experiment is inherently incomplete even when augmented by VSP data. The nature of the experiment suggests a geometric limitation to the resolution of any central structure. In particular the BackusGilbert method shows that only poor horizontal resolution can be expected (Menke, 1984). Another major constraint can now be Identified within the experiment, namely the borehole itself. A parametric model has now been developed in which the borehole

Size, transducer standoff, damage-zones, and the degree of velocity attenuation, were examined using a range of host velocities and hole separations. It was found that there are significant velocity variations caused by random perturbations in borehole size. These errors are particularly significant for boreholes with large diameters and small transducer offsets. For an altered zone, errors in both the dimensions and the degree of velocity alteration, gave measureable velocity variance, particularly with large boreholes. In all cases it is observed that the variance in velocities increased as hole separation is decreased.

IMAGING OF SUBSURFACE FAULTS BY WALKAWAY VSP WAVEGUIDING D.R. Pant^ I.M. Mason^ and S.A. Greenhalgh"'* "" School of Earth Sciences, Flinders University of South Australia ^Department of Engineering Science, University of Oxford Hydrocarbon reservoirs sometimes occur within low velocity channels, thus forming potential seismic waveguides. The waveguide might be excited at its discontinuities (faults) by seismic waves travelling downward from a surface source. Given that a waveguide would confine scattered energy to the horizontal plane, it should be possible to map fault scatterers at large range by means of a downhole triaxial geophone placed within the reservoir. A simple laboratory scale seismic model of a Southern North Sea gas reservoir was constructed to study the problem. Multicomponent seismic measurements were taken in both walkaway VSP and offset VSP shooting geometries. The results validate the presence of strong waveguiding in a low velocity layer disrupted by faulting. The diffracted arrivals can be imaged to locate the fault 'source'. The model results, when scaled to the field situation, suggest that faults within a reservoir can be detected at horizontal distances greater than several kilometers from the drill hole.

85 ERROR IN ESTIMATION OF ARRIVAL DIRECTION ON OFFSET VSP DATA Marianne Windhofer* and Roger Young Curtin University of Technology Recent advances in high resolution velocity estimation using first-arrivals on multicomponent offset VSP data are crucially dependent upon accurate determination of arrival direction. Such methods require post-acquisition orientation of 3-component data by coordinate rotation. Rotation into the direction of maximum P-wave energy in the horizontal plane at each depth of a VSP survey reorients the coordinate system. A second rotation in the vertical plane towards the source establishes the arrival direction and, in addition, separates the P-, SV-, and SH-transmitted waves. An error in the first rotation influences strongly a separation of the wavemodes. The desired rotation angles can be found from an expression which involves crossproducts between measured components. The expression assumes there is no phase difference between these components. This will certainly be the case for an isolated Pwave arrival measured on a recording system with identical impulse responses for all three channels. However, non-identical channel responses or overlapping P-wave arrivals introduce, in turn, erroneous estimates of P-wave arrival direction. The present study quantifies the error in arrival direction as a function of phase difference between components and looks closer into the difference between an instantaneous and an average estimate when calculating the rotation angle.

SEPARATION OF P-WAVE AND S-WAVE IN VSP WAVEFIELD ON THE BASIS OF A FORWARD MODELLING TECHNIQUE Hiroshi Amano* and Yoichi Ohta JAPEX Geosclence Institute Inc. A method to separate P-wave and S-wave in VSP wavefield is proposed on the basis of a synthetic forward modelling technique. The weak wavefield masked by dominant wave trains can be extracted with this method. The decomposed wavefield is expressed in frequency-depth (f-z) domain as a linear combination of up to third order differentials of traces, which is approximated by trace differences in the practical separation process. In general, five traces with single-component data are required in this process, but the same process is implemented with only three traces in the acoustic case. A two-trace extrapolation is applied to each edge of the data gather in order to enhance the accuracy of the trace difference. Since the formula is developed in f-z domain, the influence of anelasticity is taken into account easily and the speed of calculation is increased due to the use of the Fast Fourier Transform (FFT).

86 Technical Session 5(e) Regional, Crustal and Geothermal II - West Australian Basins

STRUCTURAL STUDY OF THE SOUTHERN PERTH BASIN BY GEOPHYSICAL METHODS Robert P. lasky""*, Roger A. Young^ and Mike F. Middleton^ ^W.A. Geological Survey ^Curtln University of Technology ^West Australian Geophysics & Environmental Research Seismic, gravity and geothermal data were interpreted to examine the structure and the evolution of the southern Perth Basin. Seismic data show that the principal fault trend is north-south and that strike-slip faulting is of major importance in the formation of the basin. Gravity modelling shows that: (a) crustal thickness of the basin is approximately 30 km; (b) greater crustal thickness beneath the basin than on either side implies isostatic imbalance; (c) the Darling and Busselton Faults are steeply dipping faults which extend into the lower crust and control the structure of the southern Perth Basin. Analysis of these data show that the evolution of the basin has had three major periods of tectonism which reactivated major faults: (a) a right-lateral strike-slip motion along the Darling Fault in the Late Permian-Early Triassic; (b) a phase of tectonism with associated left-lateral motion along the Dunsborough Fault in the Jurassic; (c) the separation of Australia from India in the Early Cretaceous which produced a predominantly tensional, and some oblique-transcurrent, style of faulting.

STRUCTURAL AND SOURCE ROCK ANALYSIS OF THE VLAMING SUB-BASIN - OFFSHORE SOUTH PERTH BASIN J.F. Marshall*, D.C. Ramsay, A.M.G. Moore, T.G. Graham & I. Lavering Bureau of Mineral Resources Some 3000 km of multichannel and high-resolution seismic reflection profiles, plus an extensive suite of geological samples, were acquired by the BMR's research vessel Rig Seismic from the Vlaming Sub-basin in the latter part of 1988. This data, coupled with results from previous company data in the South Perth Basin, forms the basis for this interpretation of the structure and source rock potential of the sub-basin. Interpretation of both industry and BMR seismic data suggests that most of the faulting in the Vlaming Sub-basin is transtensional in nature. Although the sub-basin displays many of the features of a classical extensional basin, geometric considerations point to a significant strike-slip component. Offsets of the bounding faults and frequent reversals in fault plane orientation indicate that the sub-basin is cut by a series of NW-SE trending transfer faults. These transfer faults have resulted in the compartmentalisation of many structures within the basin, although major structures, despite being significantly offset, do persist throughout the sub-basin. North of Rottnest Island, collapse of the eastern arch system, by an as yet undetermined mechanism at the time of breakup, resulted in the formation of the Rottnest Trough and Roe High. This event in the north does not

87 appear to have extended south of about Rottnest Island, possibly terminating at a major transfer fault at this location. The Vlaming Sub-basin contains an anomalously thick sedimentary sequence, variably estimated between 11,000 and 15,000 metres. Both the depth of the sub-basin and the style of structuring suggests that it is a detached strike-slip basin. Because of the large thickness of sediment, the timing of the initiation of the sub-basin is unknown, the only major rifting event in the Perth Basin prior to the Early Cretaceous being during the Permian. The seismic reflection profiles indicate that the sub-basin thins to the south and progressively thickens and widens to the north. This style of extension has resulted in a variety of structural plays within the sub-basin, most of which are untested. A relatively short, but intense, period of tectonism in the Valanginian, at the time of breakup, resulted in the formation of the Rottnest Trough and Roe High, as well as faulting of the arches to the south and reactivation of the transfer faults. Active extension ceased at this time, but the sub-basin underwent continuing subsidence as a result of formation of the continental margin. Results from dredging the flanks of the Fremantle Canyon have helped to refine the Tertiary stratigraphy of the Perth Basin, and have indicated the presence of Permian and Triassic rocks on the western margin of the Vlaming Sub-basin. Source rock analysis of relatively organic-rich dredge samples shows that Late Jurassic - Early Cretaceous and Permian rocks are immature in the vicinity of the canyon. The results of geohistory modelling of the thirteen wells in the Vlaming Sub-basin indicates that the sub-basin was subsiding rapidly during the Late Jurassic/Early Cretaceous. Sedimentation rates suggest that the sub-basin was also filling at a rapid rate. The subsidence/fill characteristics of the basin, which accord with a transtensional origin for the sub-basin, suggest that pre-Late Jurassic sediments have been rapidly buried and are now overmature. The pre-breakup Late Jurassic Yarragadee Formation and the Early Cretaceous Parmelia Formation are considered to be mature for hydrocarbon generation, particularly in the northern part of the Vlaming Sub-basin. Adequate source material is present, mainly in the form of exinite and subinertinite, and the sequence could source both oil and gas. the shale-rich Otorowiri and Carnac Members of the Parmelia Formation are potentially the best source rocks in the sub-basin. These units are relatively deep in the Bathurst Syncline and are likely to be oil-mature. Migration pathways exist for oil generated in the syncline to be delivered and trapped at higher levels in the Roe High region and in structures on the western margin of the sub-basin, to the north of the syncline.

VULCAN GRABEN, TIMOR SEA; REGIONAL STRUCTURE FROM A MAGNETIC SURVEY P. Wellman* and G.W. O'Brien Bureau of Mineral Resources In late 1989 the Australian Bureau of Mineral Resources (BMR) carried out a regional aeromagnetic survey by contract over the Vulcan Graben region. Elongate shortwavelength anomalies, with wavelengths of 3 to 12 km, amplitudes of 0.2 to 2.0 nT, and with generally northeast strikes, can be correlated for distances of up to 100 km on the basis of their shape and amplitude. Their source appears to be principally at depths of between 0.7 and 3.0 km. Some of the relatively larger amplitude and wavelength anomalies overlie major northwest-dipping normal faults which have been mapped by

88 seismic surveys. All of the elongate anomalies are thought to be due to structures or magnetic deposits associated either directly with NE-trending normal rift faults, or with faults in the post-rift sediments which are related to rift fault reactivation. ENE fault trends, which developed in the Neogene as a result of the collision with Timor, do not appear on the aeromagnetic data. We have mapped numerous northwest-trending faults. These have a spacing of approximately 10 to 25 km. They are thought to be strike-slip because some offset the major northeast-trending normal faults. The northwest trending faults may be due to the reactivation of Palaeozoic trends, the reactivation of Mesozoic transfer faults, or possibly some may be younger and independent of the earlier faults. Some of these faults have previously been mapped on seismic sections and correspond to seismic 'bad data' areas. These faults may have a major role in the entrapment of hydrocarbon accumulations in the Timor Sea, with most of the significant fields being close to a northwest-trending fault or its extension. In the Timor Sea, high resolution aeromagnetics has proven to be a relatively cheap and cost-effective tool which both complements and supplements the existing seismic data. It should prove equally useful in other areas with extensive seismic coverage. In frontier areas, it should rapidly define the geometry of the major tectonic elements of the basin, allowing for better positioning of seismic programs.

AUSTRALIA-BANDA ARC COLLISON AND /WS/TU STRESS IN THE VULCAN SUB-BASIN (TIMOR SEA) AS REVEALED BY BOREHOLE BREAKOUT DATA R. Hillis School of Earth Sciences, The Flinders University of South Australia Boreholes drilled in the search for oil in the Vulcan Sub-basin (Timor Sea, North West Shelf) commonly exhibit an elliptical cross-section believed to be the result of wellbore failure known as borehole breakout. Breakouts form by compressional shear failure in response to stress concentration around the borehole due to the prevailing in situ stress. The bore wall becomes elongated in the direction of least horizontal compressive stress. The orientation and shape of the breakouts are measured by the four-arm dipmeter tool. The azimuths of the long axes of breakouts in the Vulcan Sub-basin show a reasonably consistent ^30-^70''H trend implying that maximum horizontal compressive stress (SHmax) is oriented 040-080°N. This NE-ENE SHmax orientation in the Vulcan Sub-basin is not controlled by compression transmitted from the nearby Australia/Banda Arc collision zone. However, it is consistent with theoretical models of stress distribution in the Indo-Australian plate based on plate-driving forces at all of its boundaries. The present SHmax orientation is consistent with either strike-slip or normal movement on the pre-existing NE-trending faults in the basin.

89 Technical Session 5(f) Geoscience Education III

THE WORK OF THE KEY CENTRE FOR MINES (KCM): UNIVERSITIES OF NEW SOUTH WALES AND WOLLONGONG C. Garrard*, M. Katz and R. Stutchbury University of New Soutli Wales The Key Centre for Mines was established by the federal government in 1988 as a joint initiative between the Departments of Applied Geology, Mineral Processing and Extractive Metallurgy, and Mining Engineering of the School of Mines at the University of New South Wales and the Departments of Geology, and Civil Engineering at the University of Wollongong. The KCM's many services to the mineral industries are in the fields of research, education, including award courses and short course seminars, and consulting. The services are offered both nationally and internationally, and particularly in remote mining localities. An exciting initiative of the KCM is the implementation of postgraduate courses in mining management, a Graduate Diploma and Masters of Mining Management. It was perceived there was a need for a more formal managerial training program specifically geared to the minerals industries with sufficient flexibility to meet the requirements of both companies and candidates. The courses are made available to professionals who are non-graduates, provided they can demonstrate recognition of their status. The initiative involves many other new approaches to professional training including the recognition of industry-based courses and the presentation of courses in one-week, short-course format in residential blocks with assignment work especially designed for those in remote localities. The course work will be delivered either by course leaders going to mining centres or by the use of electronic communications techniques. The courses are to be part-time and will take a minimum of 2 years to complete, with an option of a longer period if required. Other features of the courses include a Science and Technology stream, a Business and Administration stream and an Industry-based Research Project. The Key Centre for Mines has an international arm, formed in 1989, to promote, market and develop activities over the full spectrum of Applied Geology, Mining Engineering, and Mineral Processing and Extraction in response to the mineral and other Earth Science-based development needs of the region and beyond. The Key Centre for Mines International (KCMI) is a co-operating organisation of the Circum-Pacific Council for Energy and Mineral Resources, and through its personnel and activities, it has established working and collaborating relations with a number of international organisations.

90 KEY FOR STRATEGIC MINERAL DEPOSITS, UWA: TEACHING AND RESEARCH FOR "EXPLORATION IN A CHANGING ENVIRONMENT" D.I. Groves* and N.M.S. Rock University of Western Australia The Key Centre was set up in mid-1988 within the geoiogy department of the University of Western Australia and was the first of three Australian Key Centres devoted to ore deposit geology. Its stated aims were to play a role in increasing Australia's competitiveness in exploration by improving undergraduate training in economic geology, numerical geology and fieldwork, setting up an M.Sc. by coursework for industry-based geoscientists, and carrying out high quality, integrated ore deposit research programs based largely on postgraduate student research. The Centre grew out of an informal research group, the Archaean Gold Group, and a further aim was to diverify research interests into base- and rare-metal deposits and mineralisation associated with alkaline rocks. Two years on, the Centre has 6 lecturing staff, 5 postdoctoral fellows or associates, 27 full-time Ph.D. students, 6 part-time Ph.D. or M.Sc. students, 9 M.Sc. and 6 M.Sc. Preliminary candidates in the M.Sc. by Coursework program, and 12 B.Sc. Honours students, and represents the largest postgraduate study group at the University of Western Australia. As well as postgraduate students from Australia, the Centre has attracted graduates from Austria, Canada, China, Ethiopia, Finland, Germany, Sri Lanka, South Africa, The Netherlands, U.S.A., and U.K. In addition, several industrybased geoscientists are Honorary Research Associates of the Centre. Research projects include integrated field- and laboratory-based studies of Archaean and Proterozoic gold deposits, Mississippi Valley-type and volcanogenic base-metal deposits, nickel and PGE deposits, a variety of mineralisation styles related to alkaline rocks (e.g. Au, REE, diamonds), and pegmatite-related deposits. Of particular interest to the theme of this conference "Exploration in a Changing Environment" are teaching and research programs initiated since the creation of the Key Centre. On the teaching front, in our Honours classes we now have the first graduates to have completed the numerical and computer geology training courses in the Geology Department. 1990 also marked the first year of an expanded field training course for 3rd year B.Sc. students in which, thanks to the cooperation of Aerodata, CSIRO, and WMC and the appointment of a new geophysicist to the Geology Department, we were able to map an area for which we had high-resolution aeromagnetic and thematic mapper data, as well as high-quality colour photography, and were able to carry out integrated geophysical and geological ground studies. With the imminent introduction of GIS training in our undergraduate course (see below), we believe our graduates will have the necessary training to face future challenges in the mining and exploration industry. We will continue to supplement this with our M.Sc. and postgraduate programs, our active professional extension courses and seminars, and timely Geology Department (Key Centre) and University Extension, UWA, publications. On the research front, the Key Centre is developing interactive systems based on computer databases and a GIS system (Arc/Info). Large databases on gold deposits (MERIGOLD), alkaline rocks and diamond indicator minerals are already in place and constantly upgraded. The Centre is experimenting in the production of gold productivity maps of the Yilgarn Craton using parameters defined by the MERIGOLD database, in co-ordination with standardised digital map data in the GIS. This should allow semiquantitative assessment of the potential prospectivity of terranes within this highly

91 mineralised craton, as well as the training of geoscientists in the use of databases and GIS systems. In summary, the Key Centre is now truly that - a centre that has attracted a large number of dedicated researchers carrying out scientific programs that are key to the training of explorationists who must succeed in "Exploration in a Changing Environment".

UNIVERSITY-INDUSTRY INTERACTION AT THE CENTRE FOR ORE DEPOSIT AND EXPLORATION STUDIES Ross R. Large University of Tasmania The Centre for Ore Deposit and Exploration Studies (CODES) is a National Key Centre established in 1989 to build on the teaching and research excellence developed in the Geology Department at the University of Tasmania. The Key Centre is jointly funded by the Federal Government, Tasmanian Government and a select number of Australian mining companies, including Aberfoyie, Pasminco, RGC, BHP-Utah, Geopeko, Pancontinental and WMC. The major objectives of CODES are: •

to undertake an inter-disciplinary approach to teaching and research across the spectrum of economic geology, with strong emphasis on the training of Honours, Masters and PhD graduates to meet the demands of the exploration and mining industry.

•

to conduct leading-edge research in close collaboration with the mining industry for the purpose of developing exploration models and improved exploration techniques.

One year after commencement the Key Centre has built-up a team of four lecturing staff and five Research Fellows with nine Honours students, eight iVIaster of Economic Geology students and eight PhD/MSc research students. Research - Our current research is focussed on understanding the geological and geochemicai controls on base metal and gold mineralisation within volcanic and sedimentary provinces in Tasmania, Queensland, South Australia and the Northern Territory. The program involves a series of collaborative projects with industry, AMIRA, State Government surveys, CSIRO and BMR, with major emphasis on the application of our results to the development of improved ore genesis models and exploration techniques which can be directly applied to on-going exploration programs. Fifty percent of our research effort is directed toward improving mineral exploration discovery rates in Tasmania. Teaching - The Key Centre offers graduate courses at the honours, masters and PhD level in Economic Geology. Honours field thesis topics are selected in consultation with the Tasmanian mining industry so that the projects are both a training/research exercise for the students and of benefit to the relevant mining company, in 1989/90 our Honours

students were supported by the following companies: Aberfoyle Resources, Cyprus Minerals, Billiton, Geopeko, Cominex, Pancontinental, Pasminco, Noranda and Renison Goldfields Exploration. An increasing number of our honours students are selecting interdisciplinary field projects in geology-geophysics or geology-geochemistry. The nucleus of the post-graduate training program at the Key Centre, the Master of Economic Geology, was introduced in 1990 and is a combination of course work (60%) with research thesis (40%) designed to bring industry and government geologists up-todate with recent advances in economic geology, ore deposit modelling and field mapping procedures, with special emphasis on applications to mineral exploration and mine geology. The course-work units are taught in an extended short course format by a panel of specialists from the Key Centre, other Universities, CSIRO, BMR and industry. Technology Transfer - Major emphasis is placed on the transfer of on-going research results to our industry sponsors. This is achieved through regular research meetings, seminars and field workshops where research staff and students present progress reports to company geoscientists. The CODES-lndustry short course program which runs in parallel with the Masters Course has also proved to be a very effective medium for technology transfer and ideas exchange.

Some major research projects at the CODES Key Centre during 1989-91PROJECT

SPONSORS

Controls on gold and silver grades in volcanogenic sulphide systems

AMIRA/ARC

Genesis of Proterozoic gold-copper deposits in Northern Australia

Formation of the Hellyar stringer zone, western Tasmania

Controls on base metal ore deposition in the Mt Windsor Volcanics, Old.

Application of ore genesis research to development of improved exploration techniques

Relationship of faulting to mineralisation in western Tasmania

AMIRA/ARC

Oak Dam deposit Stuart Shelf, SA

WMC/PNC

Gold mineralisation in NE Tasmania

Billiton/Aureole

Mineral cheistry of basemetal and gold ores

CSIRO/ARC

11 mining companies and NTGS Aberfoyle

Pancontinental & Outokumpu ARC

93 NATIONAL CENTRE FOR PETROLEUM GEOLOGY AND GEOPHYSICS (NCPGG) W.J. Stuart National Centre for Petroleum Geology and Geophysics, Adelaide The NCPGG is a Key Centre established by the Commonwealth Government at the University of Adelaide in mid-1985. The University of Adelaide provides the administrative umbrella and facilities for the Centre; three South Australian institutions (The University of Adelaide, The Flinders University of South Australia and the South Australian Institute of Technology) are involved in with the Centre in student training and specific research projects. The main objectives of the Centre are to train students for a career in petroleum exploration, to perform research relevant to the industry, and to foster co-operation between industry, academia and government. The Centre is committed to the concept of the explorationist, and adopts a multidisciplinary approach throughout its operations. The curriculum includes six months of course worl<, six weeks of industrial experience and a minimum of three months research work for students seeking either a B.Sc. (Hons) or a graduate diploma. Students who are pursuing a IVIasters degree take the same course and industrial program and their research work can vary from 6 to 16 months. The course and industrial program were set up following extensive communication with the petroleum industry and academia. As a result of the creation of the centre, Ph.D. students have been attracted in petroleum studies. Courses are run by Centre staff, experts from industry, and academics from the three participating institutions. They provide a comprehensive grounding in the many facets of petroleum exploration, including the commercial, strategic and operational aspects. There are a range of optional courses for those specialising in geophysics; however, students take all the other courses offered. Because industry personnel may attend specific courses, topics are generally presented in concentrated one or two week blocks. The NCPGG now has a reputation as a pre-eminent Centre for the training of students for the petroleum industry, and a major research establishment within that industry. To date, more than 40 students having passed through the Centre have been employed by industry.

94 Plenary Session IV

OIL EXPLORATION IN A CHANGING ENVIRONMENT A PERSONAL PERSPECTIVE P.E. Power Ampol Exploration Ltd, Sydney, NSW In the last forty years the environment in which exploration is conducted has changed in many ways, technological, political and financial. No place on earth can escape the prying geophysical eye and production is following. Whereas it was practically confined to areas of outcrop, now the monumental advances in exploration and production technology have brought the whole world Into focus. Just as a unifying theory has rationalised much geological thinking so petroleum geology has sorted out the mystifying variability or occurrence by advances in geochemistry and sedimentary geology. These are cumulative and inevitable changes. Some things have remained constant in the industry's environment. Oil supply has always been greater than demand except for temporary or local interruptions to this caused by war, politics or disaster. Oil price has generally reflected oversupply and the world's dependence on it has increased accordingly. Forty years ago coal was still king. Post-war, the end of the colonial era and the rise of nationalism saw increasing politicisation of the commodity, accompanied by rising numbers of national oil companies on one hand, and the proliferation of international independents eager to exploit new opportunity and technology on the other. What followed was the greatest transfer of wealth since the Spanish plate fleets left Peai. However, attempts to control supply and hence price caused the greatest upheavals and the biggest shift in the financial environment. A combination of Arab nationalism and opportunism by independent companies saw in 1973 the control of supply shift from a cartel of seven companies to one of eleven countries, and a big rise in prices. Proving that the market works, the exploration industry took up the challenge and in time moved the world from artificial limits to over production and low prices again. The sudden imbalance in the financial environment caused by high prices has left worldwide ripples contributing to greater poverty in Latin America and the crumbling of the Russian empire. The current situation is a re-run of the past and a pre-view of the future.

95 FINANCIALLY SUSTAINABLE MINERAL EXPLORATION Ian G. Gould CRA Limited, Melbourne, Vic. 'Ecologically sustainable development' has become a key issue for the Australian and other governments, as they strive to integrate the need to generate wealth to satisfy economic requirements with the community's rising concern for protection of the environment. Mining is In the forefront of the debate; undeservedly so because it generates the single largest component of Australia's export income from temporary use of only 0.02% of the land surface. If this contribution is to be maintained or to grow, it must be underwritten by exploration for minerals and petroleum, which is financially sustainable in the long term. Mineral exploration is an appropriate form of R&D for the mineral-based Australian economy, although it is not recognised as such amid the cries to increase our technological sophistication In areas where we lack Inherent competitive advantage. Government, industry and explorationists must increasingly consider exploration as a business like any other, with a role not unlike new product development in the manufacturing industries. On the asset side of our exploration business balance sheet are the large area and prospectivity of the Australian landmass and the flair and competence of our geoscientists. On the liability side we find an increasingly uninformed and suspicious community attitude, based on incorrect impressions of poor environmental and ethical behaviour. Our access to prospective land is being eroded as these often imaginary liabilities overshadow our genuine assets. The cash flow of our exploration business takes the form of economic discoveries of minerals, which may be substantial but are sporadic. Our business needs a sustained line of financial credit to overcome the ephemeral nature of our cash flow. This is going to be much harder to achieve in the 1990s than in the boom and bust 1980s, which were characterised by easy loans and by incomprehensible corporate structures and financial systems. Success in the 1990s requires us to strengthen our balance sheet by improving community perception of the industry and to increase our cash flow by a higher rate of worthwhile discoveries. If sustained financial support is to be forthcoming - and it will come mainly from the companies already established in the minerals industry explorationists must be able to engender confidence, by demonstrating high levels of business skills as they compete for the scarce capital available. Strategies must be based more on worthwhile and achievable discovery objectives and risk spreading, rather than geoscientific predilections and picking winners. Professional business systems will be required even more to monitor performance against these objectives and maintain financial control. There is no way out in elastic budgets and target hurdles which are continually lowered. Success will come to those whose systems facilitate better tenement selection, encourage development of human resources, focus research where it counts and engender confidence in those with control of the purse.

96 In this more focused corporate environment, with the concommitant risk of greater government regulation, the challenge will be to ensure that the flair which is so essential to exploration will not be submerged in a rising sea of bureaucratic controls. Only those exploration businesses which can achieve the balance are likely to see out the 1990s.

VISUAL PROCESSING IN EXPLORATION AND PRODUCTION APPLICATIONS: UPDATE AND TRENDS John Flynn Silicon Graphics Computer Systems, Inc. Industry Need The energy and minerals industries need to apply advanced computer technology to the exploration and development of resources; well executed data visualization and modelling can substantially reduce the cost of developing a resource and greatly reduce the risk of losing money. Quite literally in regions of high geologic complexity an oil well misplaced by several tens of feet may leave millions of dollars of oil in the ground. Accurate models depend, of course, on good data and lots of it. They also depend on proper interpretation of the data and integration of it into a model. The value of data is determined by the ability of the scientist to test different interpretations and then, once a conclusion is reached, build new information into the model. Application Trends In his interpretation the scientist/engineer considers data attributes such as patterns, surface trends, correlations with other data, and spatial characteristics. He uses his understanding of structures and properties to construct a realistic model of the geological region of interest. In response to the need for more highly resolved models, new applications are being developed which provide the following capabilities: • • • • • • • •

increased model size and complexity, volumetric representations of data, visualization and 3D interpretation of 3D seismic data, use of 3D interpretive and descriptive models, higher levels of realism or use of visual aids for interpretive assistance, animation to comprehend time varying phenomena, real time exploration of the model, and powerful graphics tools to assist in model development.

This paper will discuss how advanced workstations have enabled these visual processing techniques, how visual processing is being applied, and the benefits to the mining and oil industry through case studies. New developments in visual processing technology of interest to the exploration and production community will be discussed.

97 Technical Session 6(a) Petroleum Exploration VII - Interpretation Methods LOW STAND SEISMIC FACIES - A CARNARVON-BROWSE BASIN COMPARISON Robert B. Kirk BHP Petroleum Similarities between eleven l\/lesozoic and Cainozoic supercycles in the Carnarvon and Browse Basins of Western Australia may be exploited in exploring for low stand turbidites, located just above sequence boundaries. Seismic and well sequence analyses are the tools used. Local well calibration is vital as geometrically similar units are being tested which are lithologically dissimilar, namely slumped shale slope units versus low stand clastic fans. Most low stand fans are associated with tectonicaliy influenced base level drops, especially in the late Jurassic and Neocomian - supercycles 3 and 4. These packages are the synrift phases of two major rift periods on the west coast. A particular boundary may have a low stand unit but its details can be quite different between basins.

A SEQUENCE STRATIGRAPHIC INTERPRETATION OF THE EASTERN GIPPSLAND BASIN A.M. Fittair, M.R. Cvetanovic BHP Petroleum Pty Ltd The Latrobe stratigraphic section subcropping the Top Coarse Clastics Unconformity' in the eastern Gippsland Basin consists of three depositional sequences of Maastrichtian to Palaeocene age. A Lower Palaeocene sequence illustrates the sedimentological and seismic relationships typical of these sequences. It has been further subdivided into three seismically mappable depositional units. Unit C is a 40 m basal sandstone section characterised seismically by high frequency sigmoidal clinoforms. It is interpreted to represent iowstand fan deposition prior to a marine transgression. Unit B consists of a 50 m argillaceous siltstone overlain by a 70 m coarsening upward sandstone section, characterised seismically by high frequency and high amplitude sigmoidal reflections. It is the product of marine transgression and subsequent highstand progradation. Unit A consists of a thin argillaceous siltstone overlain by a coarsening upwards sandstone deposited during a minor transgression and continued progradation. Unit A also consists of interbedded sands, shales and coals producing parallel, often high amplitude reflections. Deposition of this fades occurred in a coastal plain environment behind the prograding shoreline.

98 The mapping of these seismic fades allows prediction of stratigraphy and reservoir and seal quality in an area of little well control, the deep water part of the Gippsland Basin. Stratigraphic pinchout plays of Unit B shoreface sandstones prograding into offshore siltstones and claystones and Unit C lowstand fan sandstones into Unit B offshore siltstones and claystones are also identified.

APPLICATION OF NORMALIZED VELOCITIES FOR DEPTH CONVERSION OF THE BOOKABOURDIE FIELD, COOPER BASIN, S.A. Joseph Chiupka^*, Greg Beresford^ and Ed Tadiar^ ^Department of Geology, University of i\/ieibourne ^Santos Limited, Adelaide Depth conversion based on velocity data from wells is commonly carried out either by using an average velocity to the target horizon or by the layer method, using interval velocities. For the latter, a proper velocity function must be used which accurately accommodates all variables affecting velocity within a given layer laterally across the study area. An exponential velocity function is used which accounts for lateral velocity variations in a layer due to changes in its depth, compaction and lithology. In this function the interval velocities are depth-normalized to isolate the effect of lithology changes from changes in the layer's depth, as pioneered by G.H. Acheson in 1963. The technique employs an iterative depth algorithm of the form proposed by M.D. Carter in 1989 which uses mapped values of normalized velocity and seismic times to estimate depth at each shotpoint. The interval velocities calculated are then tested by comparing the travel time derived from them with the actual time from seismic. The process is iterated with increasingly refined estimates of velocity and depth until acceptable convergence is obtained between the derived time and the actual travel time. The Bookabourdie Field with its geologic complexities, provides a rigorous test of the method. Effectiveness is tested by restricting the data base to that available at an early point in the field's development and comparing the resulting depth map with the current interpretation which incorporates the data of all infill seismic and present wells. The effectiveness of the exponential velocity function and iterative depth algorithm are confirmed with the method successfully predicting the present general field outline.

EOCENE SEISMIC VELOCITY ANOMALIES FROM THE TIMOR SEA E.P. Woods Norcen International Limited, Nortli Sydney NSW Several wells in the Timor Sea have encountered Eocene sections with anomalously high velocities. This paper presents case history examples of wells drilled for field appraisal or for up-dip exploration tests. Quantitative analysis of the seismic anomalies

99 and the velocity effects on the time images of deeper targets are presented for each example. The seismic anomalies observed in the Timor Sea region range in width from 200 m to 600 m and occur over strike lengths of up to 3000 m. The degree of seismic two-way time 'pull-up' on deeper seismic events is proportional to the width of the anomaly, to the relative depths of the anomaly and the underlying events. At Jabiru-2 the time image of the Jurassic reservoir zone is unaffected by the anomaly which is undershot by most of the CDP ray paths. Other wells, such as Avocet-2, exhibit considerable time pull-up due to broader high velocity zones. At Keeling-1 the target horizon was only partially affected by the overlying velocity anomaly. The seismic anomalies can be recognised by a narrow zone of noise below the Base Miocene seismic marker, varying degrees of time pull-up below the high velocity limit, and local thinning of the Eocene time interval. A common attribute of the anomalies is the confinement of the high velocity sediments to the Pre-Miocene section. This suggests that the anomalies are not due to diagenetic changes associated with fluids moving along fault planes. If this were the case, then the Lower Miocene section would be similarly affected. It is proposed that the anomalies are caused by diagenetic changes related to sub-aerial exposure of topographic highs during the Oligocene.

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Technical Session 6(b) Mineral Exploration IV - Geochemistry SAMPLING: THE CINDERELLA OF EXPLORATION Rob Ryan G.R. Ryan and Associates Sampling is the very foundation stone of mineral exploration. Whether sampling an outcrop for petrographic study, a laterite for trace element analysis, or drill cuttings for assay, how the sample is taken and dealt with will, more than any other action, determine the outcome of the exploration programme. In its broadest sense, 'sampling' includes the planning of the programme, the collection, preparation, and analysis of the sample, and the evaluation of the result. In the narrower sense it means the collection of the sample, and it is this aspect that is considered here. Anything from 50% to 95% of the potential error in a sample result lies in the processes that apply prior to the actual analysis - i.e. in planning, collection, and sample preparation. Planning is usually done by qualified professionals, and most preparation is carried out in laboratories under the supervision of qualified chemists. When it comes to sample collection however, it is not uncommonly left to totally untrained and commonly unsupervised assistants, or even to driller's offsiders who are not employed by the investigating company, and yet it is in this area that the greatest potential for error, particularly unforeseen error, exists. In a geochemical programme the principal objective is to locate departures from the geochemical norm. Thus, so far as possible, a standard sampling medium must be identified, and samplers trained to identify it in the field correctly. The analysis will demand precision rather than correctness or exactness. For ore drilling, correctness and, so far as possible, exactness, are paramount, and since they are, to a greater or lesser extent, unachievable, rigorous quality control procedures must be introduced that permit the quantification of potential error and the detection of any spurious results. The objective in sampling is to select from the medium to be sampled (rock, eluvium, alluvium, water, gas, plant) a portion that is representative of the whole, and to deliver it, still representative, for analysis. The supervisor must ensure: that the portion being collected is naturally representative of the whole; that no bias or contamination is introduced during collection; that any preparation (e.g. splitting) that is undertaken prior to delivery does not introduce bias or contamination; that adequate quality control procedures are specified and rigorously applied; that the entire procedure is properly and comprehensively recorded; and that the entire process is made safe from adulteration by human error or design. Bias may be introduced by such things as selecting an incorrect drilling design; by partition of components during sample collection; by using incorrect splitting procedures; by sampling during a particular season of the year or time of day; or by loss of part of the sample in transit. The most common cause of sample contamination is collapse of the wall of the hole during drilling or the use of an incorrect drilling technique, but in other media contamination may arise from reaction between bore casing and groundwater, from cultural activities, from unclean containers, etc. There is no such

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thing as a perfect sampling programme, so both bias and contamination must be anticipated, and procedures put in place that will detect, and quantify, not only such bias and contamination as may be foreseen, but those that may not be. The failure to detect a geochemically anomalous zone or the follow up of one that does not exist is serious. The failure to develop an orebody because the assays are biassed low, or the development of a subeconomic deposit, is even more so. But the most serious professional failure of all is to produce a set of results on which no reliability can be placed because the sampling has been inadequate; and not to realise that you have done so!

THE ASSOCIATION OF GOLD WITH PEDOGENIC CARBONATE: IMPLICATIONS FOR EXPLORATION IN SEMI-ARID AND ARID TERRAINS M.J. Lintern CSIRO, Division of Expioration Geoscience, Perth, WA The distribution of Au and other elements in soil profiles and vegetation has been studied in the Mt Hope area (now the Bounty Mine), Western Australia. Mt. Hope is about 230 km SW of Kalgoorlie within the relatively poorly explored southern extension of the Southern Cross-Forrestania Greenstone Belt. The area is deeply weathered and is covered by two major soil types: (1) Fe-rich, carbonate-poor gravelly lateritic soils mantling higher areas of the landscape, and (2) homogeneous red clay-rich soils containing variable amounts of carbonate, occurring within broad undulating valleys and flanking slopes. Both soil types are underlain by deep clay-rich saprolites. After an initial orientation survey using samples from rotary air blast and reverse circulation percussion drilling, several small pits (3 x 10 x 2 m deep) were excavated over, adjacent to and distant from mineralization in order to examine and sample the soil profiles to determine their geochemistry and mineralogy. For the gravelly soils, the results show only a weak association between Au and Fe (and no other element) in one of the profiles. However, in the calcareous clay-rich soils there is a strong and highly significant association between Au, and Ca and Mg which occur principally as pedogenic carbonate (calcrete). It appears that plants, particularly trees, are playing a role in the mechanism of mobilization, accumulation and recycling of Au, Ca and Mg. Ashed vegetation and leaf litter contain Au at concentrations that, in general, reflect the trends found in the soils. The mechanism may involve, directly and/or indirectly, the processes of evapotranspiration and evaporation: (i) xerophytic (deep rooted) trees draw solutes (including Au, Ca and Mg) from depth, accumulate and shed them in leaves; (ii) meteoric water and micro-organisms decompose the litter and mobilize the Au, Ca and Mg; (iii) the Au, Ca and Mg are deposited at variable depths that reflect the average depth of rainfall penetration before the moisture (and some Au, Ca and Mg) is removed by either phreatophytic (shallow rooted) plants or evaporation. In semi-arid and arid climates, in which evaporation exceeds precipitation, the Ca and Mg gradually accumulate in the soils, together with associated Au.

102 The association between Au, Ca and Mg tias been observed elsewhere in the southern Yilgarn Blocl< and is a significant feature of gold dispersion in this region. This hitherto unreported phenomenon has considerable importance for Au exploration in semi-arid and arid terrains characterized by calcrete development. Because (i) not all soils contains calcrete and (ii) the depths at which the Au, Ca and Mg concentrate vary, the presence of carbonate in soil samples should be recorded to assist in interpretation of near-surface Au anomalies.

THE DISPERSION OF GOLD WITHIN THE WEATHERING PROFILE AT HANNAN SOUTH GOLD MINE, WESTERN AUSTRALIA LM. Lawrance and C.R.M. Butt* CSIRO Division of Exploration Geoscience Western Australia The Hannan South gold deposit is 15 km SSE of Kalgoorlie, in the Norseman-Wiluna belt of the Archaean Yilgarn Block, Western Australia. The deposit is beneath a playa that forms part of an ephemeral lake system. The original lateritic weathering profile has been partially truncated by the migration of this system and ferruginous gypsiferous lacustrine sediments have been deposited, leaving no outcrop. In winter, water temporarily accumulates in the lake. The upper 30 m of the profile is strongly oxidized and consists of highly leached white clay, locally stained by red-brown iron oxyhydroxides. This is in sharp contact with an underlying more reducing environment characterized by grey-green saprolitic rock. The whole regolith is saturated by hypersaline water. The mineralization is hosted by a highly altered basaltic unit, now a granular and semimassive siliceous epidote-ankerite rock. A tuffaceous sediment and an andesite porphyry bound this unit. These rocks have been dissected by numerous faults which have promoted weathering to a depth of 65-75 m, where major faulting has truncated the host unit. Between this weathering front and the redox interface, gold is confined to the host unit, associated with sulphides, dominantly pyrite; it has an average grade of 17 ppm Au, with local concentrations of up to 180 ppm. Cobaltite, galenobismuthite, bismuthinite and wittichenite occur within pyrite and as free gains. Primary gold is mainly associated with the bismuth sulphide minerals and rarely as inclusions in pyrite. Higher in this zone, as weathering increases, the pyrite becomes increasingly porous and finely fractured. Groundwater flow is limited and the weathering of pyrite produces pH values of 4.0-5.5 in the host unit, in contrast with the wall rocks which produce a pH environment of 7.5-8.5. Micron-sized secondary gold begins to occur as isolated grains and clusters within the kaolinite matrix and as fine fracture fillings in epidote surrounding the semi-weathered sulphides, but remains confined to the host unit. At the redox interface, the pyrite is completely oxidized and replaced by iron oxyhydroxide pseudomorphs. Just above the interface, in a moderately acid environment (pH 5.5-6.5), a flat-lying zone of secondary gold enrichment has formed, which spreads into the adjacent weathered country rocks, resulting in a "mushroomshaped" gold distribution. The zone has an average grade of 20 ppm Au, with localized areas having grades of 50-110 ppm. The supergene gold in this zone occurs predominantly as octahedral and hexagonal crystals of high fineness, deposited in voids within iron-rich clay. Secondary gold also occurs in iron oxide veins within the host unit and along faults in the adjacent country rocks. Above this zone of secondary

103 enrichment, the upper highly leached saprolite is strongly depleted in gold and as a result the mineralization cannot be detected by surface soil sampling or shallow drilling.

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Figure Caption: Cross-section through the Hannan South gold deposit, Western Australia, illustrating leaching of gold from the upper saprolite and concentration and lateral dispersion below. The deposit is now situated beneath a playa and saturated by hypersaline groundwater.

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QUANTITATIVE MICROANALYSIS AT TRACE LEVELS USING THE PROTON MICROPROBE C.G. Ryan*, S.H. Sie, W.L. Griffin, T.T. Win and G.F. Suter CSIRO, Division of Exploration Geoscience, Nortli Ryde, NSW In-situ microanalysis of trace elements in minerals is carried out using tlie proton microprobe at the Heavy Ion Analytical Facility (HIAF) of the CSIRO. Proton Induced X-ray Emission (PIXE), following the impact of 3 MeV protons, produces an X-ray spectrum with a low continuum background enabling simultaneous multi-element analysis at the ppm level. The predictable trajectory of the protons also permits theoretical yields to be calculated resulting in a standardless quantitative method. Finally, the CSIRO electrostatic quadrupole lens permits high beam currents (-15 nA) to be focussed into individual mineral grains (-20 ^m) for rapid in-situ analyses (-5 min.). To provide reliable determination of traces, such as Ni (-10 ppm), in the presence of major Fe (-10 wt%) a statistics-sensitive background estimation algorithm has been developed and incorporated in a modified least-squares fitting procedure to optimize the determination of peak areas near the detection limit. The procedure uses relativeintensities and yields calculated including secondary-fluorescence. Both uniform and layered targets can be treated enabling, for example, the in-situ analysis of fluid inclusions in minerals. The accuracy of the method has been tested using USGS standard rocks and glasses. These tests show that standardless PIXE analysis can be performed to better than 10%, using beam current integration. Using a beam chopper, or normalization to ElVlP Fe, reduces the random error to -3%. Furthermore, Monte Carlo tests have demonstrated that analyses are reliable down to the limits of detection. Detection limits range from - 2 ppm in silicates and -0.1 ppm in diamond up to -10 ppm in some sulfides. A number of minerals are being studied in HIAF as indicators for diamond exploration. Multivariate analysis of major and trace elements in chromites has lead to a classification procedure which discriminates chromite suites from barren and kimberlitic/lamproitic sources. Trace elements in micro-diamonds help to distinguish the number of sources feeding a drainage. Ilmenites also show potential in this regard. Together, these indicators represent a powerful diamond exploration toolkit. Cr-pyrope garnets, and especially high-Cr low-Ca harzburgitic "G10" garnets, are widely used as an indicator mineral in diamond exploration. However, Argyle contains no G10 garnets and barren pipes such as Skerring, Western Australia contain abundant G10 garnets. The presence of G10 garnets alone does not mean that conditions were appropriate for diamond growth; the garnets must also have been sampled from the diamond stability field. The Cr-pyrope garnets are derived largely from the disaggregation of garnet peridotite mantle wall rock. The distribution of Ni between Cr-pyrope garnets and olivine in such xenoliths is strongly T dependent, as measured by two-pyroxene thermometry. The Ni content of the olivine in these rocks is essentially constant (2900 ± 200 ppm), while the Ni content of the garnet varies from <10 ppm to >140 ppm over the temperature range 600 - 1600°C. Hence, it is possible to estimate the equilibration temperature of single garnets by analyzing their Ni content.

105 In cratonic regions, the geotherm intercepts the diamond-graphite line at around lOOO^C. Hence, for a given kimberlite or lamproite, the occurrence of garnets with temperatures immediately above 1000^0 is a direct indication that the magma sampled material in the diamond stability field, and is therefore potentially diamond bearing. Figure 1 contrasts a high grade kimberlite (Star, South Africa) and a barren pipe (Skerring, Western Australia). From the analysis of material from --20 pipes worldwide, we have found that these T patterns correlate well with diamond grade. Consequently, combined with major and further trace element data, Ni temperatures are used routinely at HIAF in diamond exploration. The sensitivity of PIXE also makes the proton microprobe a natural choice to study the residence of precious metals in the coexisting phases of ore or exploration samples. Analyses of refractory gold ore from Lancefield revealed 150 ppm of Au in the arsenopyrite. Similarly, a HIAF study of PGE distribution in Kambalda nickel ore revealed a significant reverse of Pd in nickeline. Hence, proton microprobe analyses reveal the mineralogical sites of potentially valuable byproducts and provide essential information for the design of efficient extraction processes. 15|

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Figure 1. Ni temperature distributions for concentrate garnets from the high grade pipe Star, South Africa and the barren pipe Skerring, Western Australia.

106 Technical Session 6(c) Computer Applications IV WAVE-EQUATION DATUMING ON A MICRO-COMPUTER Greg Beresford* and Clayton Hurst Department of Geology, University of Melbourne Wave-equation datuming is a simple concept which can be used to correct seismic data recorded in areas where there are strong near-surface lateral velocity contrasts. In particular, the idea lends itself to correcting marine data recorded over near-surface limestone reefs which give rise to rapid changes in the sea-floor profile. A post-stack two-dimensional (2D) Kirchoff implementation has been designed to run efficiently on an 80386-based micro-computer with or without an attached array processor (AP). It can be generalised readily to pre-stacl< application or to threedimensional (3D) application and serves to demonstrate many of the features of these more numerically intensive implementations. The data flow is based on the semi-circle superposition rather than the hyperbola-sum approach to Kirchoff summation. This is a single trace input, multiple trace output design which has the main advantages: (1) relaxed requirements on input data organisation; (2) streamlined trace interpolation for time-shifting. In this 2D implementation, a spatially variant convolution in time serves to perform the off-line (y-direction) summation under the assumption of an earth model which is constant in y. The length of this convolver is the most critical parameter affecting performance. For reef structures which are not strictly 2D, convolver lengths can be set so that the resulting accuracy is commensurate with the limitation of the 2D assumption. Seismic data acquired in areas in the Timor Sea where reefs are a problem are ideal for demonstrating the applicability of this 2D post-stacl< datuming algorithm. A model consisting of point diffractors under a typical reef profile can be processed with waveequation datuming so that migrated images of these diffractors are equally well resolved at different horizontal positions along the profile.

COMPUTER-ASSISTED LEARNING (CAL) FOR THE RESOURCE INDUSTRIES N.C. Higgins*, M.A. Etheridge, R.W. Henley and A. Robey Learning Curve Pty Limited There is an increased recognition that sl<ills development in the workforce leads to job satisfaction, increased productivity and profits for the industry. However, the resource industries lack a coherent formal framework of professional training and career development. Skills development is traditionally via a mixture of: ad hoc and variably efficient on-the-job training in specific tasks (e.g. drilling and logging practices), commonly by osmosis occasional short courses provided by a variety of organisations

107 formal postgraduate training, usually at the Masters level involving a range of coursework and research options. Training difficulties which affect technical staff (geologists, engineers, surveyors, assistants, etc.) in the resource industries include: the highly mobile nature of personnel the commonly remote location of their workplace the empirical nature of much of their technical base (encourages a traditional reliance on experience rather than formal upgrading of skills) career paths in the Industry which lead towards management and administrative responsibility rather than to technical positions investment in skills development discouraged by the highly cyclical nature of the industries. Despite these problems, there is widespread recognition and concern throughout these industries about erosion of their technical skills base, and a number of important initiatives have been taken recently to enhance educational and training opportunities. To tackle the enhancement of skills and career opportunities, the mineral exploration sector, through The Australian Minerals Industries Research Association (AMIRA), commenced a joint venture with Learning Curve Pty Limited to develop a series of Computer-Assisted Learning (CAL) modules to bridge the gap between traditional tertiary training courses and the applied needs of the industry. Modules are also being developed at the sub-professional level in the mineral processing sector. This year the Commonwealth Government implemented a Training Guarantee Charge, through a levy on payroll, to foster a national training effort. The definition of training is broad, aimed at encouraging structured training which has identified objectives (including competencies to be achieved) and the means of achieving and assessing these objectives. This initiative places the responsibility of formulation, implementation and evaluation of the training programs with the industries concerned, thus providing a unique opportunity to tailor training to meet specific industry needs. The mineral exploration sector is doing this through their sponsorship and active participation in the AMIRA-CAL program. Computer-Assisted Learning is an interactive computer-based system which is capable of providing instruction, feedback, assessment and reporting of faults. CAL has, after a decade of largely unfulfilled promise, finally come of age with the availability of multimedia technology, inexpensive data storage and sophisticated course-building software that is graphically based and cost effective. CAL programs achieve greater retention rates than traditional teaching methods through: increased stimulation and motivation provided by the multimedia platform the ability to simulate a process rather than merely providing a description involvement of the student through course interactions the self-paced non-intimidating nature of the learning environment. Combined with the latest in multimedia technology, CAL provides management with a new educational and training medium which is: available on call to every employee in the organisation at a fraction of the cost of conventional training methods; learning is not limited to the few who are chosen to attend a course or workshop

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motivating, self-paced and designedlo improve learning and retention, with inbuilt monitoring of progress and achievement capable of being updated to incorporate the latest advances, and of being customised to the organisation's particular goals and practices portable throughout an organisation, even to remote and scattered locations, requiring only the individual and a PC to accomplish the training. The current AMIRA-CAL project entails developing modules for the mineral exploration sector. Curricula are designed in consultation with the sponsors over choice of topic and specialist course providers. Each course will provide approximately the same amount of material as a conventional 3 to 5 day intensive workshop. However, the efficiency of the CAL course structure and the self-paced learning environment will enable most geoscientists to complete a course in about half the time. This project offers a solution to the training problem of a scattered and remote workforce, will provide a cost-effective and successful training platform for professionals and sub-professionals in the resource industries, and may ultimately provide a framework for an enhanced career stnjcture for professional geoscientists.

AN APPLICATION OF REGRESSION M-ESTIMATION WITH THE HILBERT TRANSFORM TO MAGNETOTELLURIC DATA PROCESSING D. Sutarno and K. Vozoff* Centre for Geophysical Exploration Research Macquarle University An accurate estimate of impedance functions is essential for the correct interpretation of a magnetotelluric (MT) sounding. Unfortunately, noise is inevitably encountered when the MT observation is conducted. In effect this can strongly influence the results given by the MT process and result in a distortion of the estimate. This paper proposes an alternative method for making unbiased robust estimates of MT impedance functions. The means for accomplishing this is based on the regression Mestimation and the Hilbert Transform operating on minimum phase MT impedance functions. Using MT data from the Columbia River Plateau and the EMSLAB Lincoln line, it is shown that the method can produce usable MT impedance functions even under conditions of severe noise contamination and in the absence of remote reference data.

109 Technical Session 6(d) Exploration Management I - General

SAFETY CONSIDERATIONS IN GEOPHYSICAL FIELD OPERATIONS Thomas J. Dujmovich lAGC, Houston, Texas Significant progress in safety were made within the geophysical industry during 1990. Efforts have been directed at unifying the focus of safety by both seismic contractors and oil companies. In September, 1990, the United Kingdom-based E&P Forum - with the support of the International Association of Geophysical Contractors (lAGC) completed texts on minimum guidelines to be used as safety exhibits in contracts between oil and seismic companies. This initiative was a major step forward in progressing toward improved safety performance. Another important inititiative was the internationalization of the lAGC safety manual. This document, to be issued very shortly, is a cooperative effort between oil and sesimic companies worldwide. Representatives from Canada, Europe, the Pacific Rim and the United States contributed to its completion. Collection of industry injury data also was initiated last year. This will enable companies to compare their performance to the industry average and enable attention to be focused on improvement by measuring where our performance lies. The quarterly accident information exchange was also re-initiated in 1990. This process enables companies to share information on incidents and accidents in a pro-active way, treating them as events from which we can learn a lesson, thus preventing reoccurrence. Training efforts have been very active in both the Canadian and Europen Chapters of lAGC. Topics addressed have included chain saw safety, survival at sea, boat safety, tree felling, first-aid capabilities in isolated environments, and driving safety in unfamiliar surroundings. As identified in all these initiatives, the most important progress made, however, was the cooperative spirit and synergy observed within the industry during the past year. It is this type of effort which can only have a positive effect on the entire industry as it strives for safety excellence.

THE NATIONAL RESOURCE INFORMATION CENTRE (NRIC) - ITS ROLE IN THE IDENTIFICATION, ACCESS AND INTEGRATION OF RESOURCE INFORMATION IN SUPPORT OF GOVERNMENT DECISION MAKING PROCESSES AND IN GEOSCIENCE RESEARCH B. David Johnson* and Roger Bradbury National Resource Information Centre, Canberra In May 1988, Minister John Kerin announced the establishment of the National Resource Information Centre (NRIC) within the Commonwealth Department of Primary

110 Industries and Energy (QPIE). The principal aim of NRIC is to enable the rapid identification, access and integration of available resource data to support policy framework and decision making processes relating to natural resource management. NRIC is a joint facility of the Bureau of Mineral Resources (BMR) and the Bureau of Rural Resources (BRR) and therefore encompasses the whole range of natural resources including minerals, petroleum, coal, water, agriculture (plants and animals), forests and fisheries. NRIC will also be involved in obtaining information for resource management problems, such as soil degradation, and for the resolution of competing land-use issues, such as forest production versus preservation. The facilities provided by NRIC, which build upon and complement the facilities and expertise in BMR and BRR, can be classified into four areas of information management: I a) identification - a computer-based directory of resource information; b) transfer - communication facilities together with translation procedures; c) integration - compilation and rationalisation of disparate data types; and d) presentation - a range of image processing and geographic information systems. The directory development is nearing completion and descriptions of a range of resource information (mainly geoscientific) have been entered thus allowing the user community to start to use the system. At the time of writing, a number of States and Territories are in the process of adopting the FINDAR (a Facility for Interrogating the NRIC Directory of Australian resources) software to run their State/Territory level directories. FINDAR has already been installed to run the West Australian Land Information Directory a subset of which will be used to maintain the West Australian portion of the National Directory at NRIC. NRIC has initiated a number of projects with client groups, most of whom are located in the DPIE portfolio. The largest current project is the development of a regional scale Geographic Information System to support the management requires of the MurrayDarling Basin Commission. One of the important lessons to be learned from the client information requirements, is that there is a wide base of demand for digital geological information (for example, to assist in the assessment of soil-type distribution - a major requirement in tackling soil degradation issues).

THE IMPORTANCE OF THE AUSTRALIAN CODE FOR REPORTING OF IDENTIFIED MINERAL RESOURCES AND ORE RESERVES AS A GUIDE FOR INVESTMENT K.R. Glasson Consulting Geologist - Mlnnamurra Prior to the acceptance of the above "Code" in 1989 by the Councils of the AusIMM and AMIC and which the ASX incorporated into its listing rules without amendment as an appendix effective July 1, 1989, there was no way for exploration companies to report their exploration results on their prospects except as "Ore Reserves", into which category their results did not fit. Exploration companies which undertook major exploration programmes, usually associated with a "new" mineral boom such as uranium, nickel, gold, etc, relied heavily

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on the "Investing Public" and banks for their finance and tried very hard to indicate that they had "Ore Reserves" in terms of the Guidelines supplied by the AusIMM for reporting Ore Reserves (1972, 1981). Basically, these Guidelines only applied to Operating Mines and/or Mines about to go into production. This was a source of confusion for the Stock Exchange and all the financing groups. With the "Code" of 1989, there is a set of rules clearly defined and meaningful for companies seeking finance for exploration and for banks ready to finance such exploration, which clearly establish the size and potential of an Identified Mineral Resource and to what extent the Competent Person preparing the report is responsible. Thus when exploration has reached a stage when an Identified Resource can be reported as "Indicated" or "Measured", which corresponds to the geological information previously associated with "Probable" or "Proved" "ore reserves", investors will understand that an assessment for financial gain can be made prior to all the feasibility studies required to convert the "Resources" into "Ore Reserves", and hopefully by understanding the potential not only realise that their investment is "safe" but by being in it at an early stage may stand to gain a bigger profit. Attention is drawn to the follow up report by the Joint AuslMM/AMIC Committee called "Guidelines to Assist in the Use and Understanding of the Australasian Code for Reporting of Identified Mineral Resources and Ore Reserves, May 1990", which indicates the reliance that can be placed by investors in dealing with the terms of "Indicated" and "Measured" resources. Since there are three distinctly separate categories for reporting, i.e. 1. 2. 3.

Pre Resource Mineralisation Identified Mineral Resources Ore Reserves

there is much more flexibility in reporting the various stages of exploration and both companies and those competent persons preparing the reports can be held responsible for their statements. The Code is designed to provide for disclosure of sufficient information so that an intelligent laymen is able to make a reasonable and balanced assessment of the mineralisation being reported. Finally the code allows for a much closer presentation of our mineral resources by Government and companies, and government departments should seek to follow these guidelines.

112 Technical Session 6(e) Regional, Crustal and Geothermal III Australian Basins: West, Central and East

THE NATURE OF FAULTING ALONG THE MARGINS OF THE FITZROY TROUGH, CANNING BASIN, AND IMPLICATIONS FOR THE TECTONIC DEVELOPMENT OF THE TROUGH B.J. Drummond*, M.J. Sexton, T.J. Barton and R.D. Shaw Bureau of Mineral Resources, Geology and Geophysics The Fitzroy Trough is a northwest/southeast trending series of half graben which formed along the northeast margin of the Canning Basin. New deep seismic reflection data are used to revise the tectonic model of the trough. The trough formed by periods of cnjstal extension In the latest Middle to Late Devonian, the Carboniferous and the Permian. Estimates of crustal extension based on a structural analysis of the sedimentary strata are 20-25 km, 10 and 5 km in each of these periods, respectively. This represents an extension of approximately 50%, broadly consistent with the amount of crustal thinning beneath the trough. The crust may also have extended during the Ordovician. Where the deep seismic line crossed the trough, extension occurred on two half graben - one under the anticline at Mt Wynne and the other on the Fenton Fault. A third half graben began to form by backstepping of the Fenton Fault, but failed to evolve as a major structure before extension ceased. The half graben are bounded on their southwest sides by listric normal faults which sole onto a sub-horizontal detachment surface at about 7 s two-way time (15-17 km). The Pinnacle Fault, previously though to be a major bounding fault on the northeast margin of the trough, now appears to be antithetic to the major listric normal faults bounding the southwest sides of the half graben. It detached into the top of the Ordovician/Silurian sequence. Transpression during the Jurassic warped the sediments in the trough into a series of broad synclines and anticlines. The anticlines were focussed on and accentuated pre-existing local highs. Mounding of the basal sediments in the trough, possibly accentuated by slip along salt layers, deformed younger overlying sediments along the northeast side of the trough. It produced movement of the basal sediments up dip out of the trough towards the northeast margin, and possibly also into the core of the Mt Wynne Anticline.

A FRESH LOOK AT THE LATER PALAEOZOIC TECTONIC HISTORY OF WESTERN-CENTRAL AUSTRALIA Jean Braun*, Herbert McQueen and Mike Etheridge Research School of Earth Sciences Australian National University We investigate a simple model for the evolution of the central Australian (Amadeus, Officer and Ngalia) basins and the adjacent Canning and Bonaparte Gulf basins at the time of the Alice Springs orogeny. Supported by evidence from surface geology, stratigraphic correlations, structural geology, recent deep seismic and gravity anomaly data, our model suggests a genetic link between the two groups of basins. The model calls for a crustal scale shear zone, which we name the Lasseter Shear Zone, running through the Halls Creek Province and continuing south between the Canning and

113

Amadeus basins and beneath the Western Officer Basin. This shear zone would have been active during the iVIiddle Devonian to early Carboniferous, separating crustal blocks in connpression to the east from crustal blocks in extension to the west. Several driving mechanisms acting along the margins of the Australian plate can be called upon to account for the contrasting yet contemporary, types of deformation on either side of the shear zone.

THE BMR REGIONAL SEISMIC LINE ACROSS THE AMADEUS BASIN, CENTRAL AUSTRALIA: IMPLICATIONS FOR THE TECTONICS OF THE BASIN AND FOR HYDROCARBON EXPLORATION R.D. Shaw*, R.J. Korsch, B.R. Goleby and 0. Wright Bureau of Mineral Resources In 1985 the Bureau of Mineral Resources undertook deep seismic reflection and refraction profiling experiments across the Early Proterozoic to Late Palaeozoic Amadeus Basin and Arunta Block in central Australia. The experiments were designed to test various models of intracratonic basin formation which involved tectonic interaction with the surrounding basement. The seismic reflection results show the thrust belt at the northern margin of the Amadeus Basin to be dominated by a major, south-directed, basement thrust feature, the Redbank Thrust Zone, which was imaged to mantle depths. Other, more southerly, basement-cored thrusts appear to splay southwards from the Redbank Thrust Zone towards the Amadeus Basin. The seismic reflection results support a 'thick-skinned' Laramide or Wind River style of overthrusting for the final compressive Late DevonianCarboniferous event, the Alice Springs Orogeny. It was the accumulation of thick, synorogenic conglomeratic sediments in a foreland-like setting at the time of thrusting that appears to have been the dominant control on maturation of the underlying Early Ordovician source rocks. In contrast to the northern margin, in the central and southern parts of the Amadeus Basin, the seismic reflection results indicate north-directed, 'thin-skinned' overthrusting on shallow detachments that were accompanied by Jura-style box folding. The detachments sole out in a salt horizon near the base of the succession. Major repetition of part of the succession has occurred, particularly at the leading northern edge of the overthrust region. Basement involvement at the southern basin margin is enigmatic, but appears to involve both Late Proterozoic and Devonian-Carboniferous tectonism.

114 STRUCTURE OF THE PERMIAN-MESOZOIC EASTERN AUSTRALIAN BASINS COMPLEX, WITH EMPHASIS ON THE BMR BOWEN BASIN DEEP SEISMIC PROFILES R.J. Korsch*, K.D. Wake-Dyster and D.W. Johnstone Onshore Sedimentary & Petroleum Geology Branch Bureau of Mineral Resources The geometries of sedimentary basins in eastern Australia, observed in BIVIR seismic data, place constraints on models for their development. The Permian Taroom Trough (southern, subsurface extension of the Bowen Basin) is interpreted as a transtensional basin associated with strike-slip faulting. Small flower structures in overlying Jurassic sediments are interpreted as transpressional features due to reactivation of the faults. To the north, the BMR Bowen Basin deep seismic data show a Late Permian-Early Triassic sedimentary wedge that appears to thicken to the east, suggesting a similar geometry to that seen in the Taroom Trough. The sedimentary section is deformed by a series of listric thrust faults that root in a major east-dipping detachment which appears to flatten In the middle crust. Thus, the exposed part of the Bowen Basin possibly initiated during a period of extension oriented ENE-WSW in the latest Carboniferous or earliest Permian, whereas to the south, the subsurface part of the basin was dominated by oblique extension and strike-slip (transtension).

115 Technical Session 6(f) Geosclence Education IV

SYDNEY UNIVERSITIES' CONSORTIUM OF GEOLOGY AND GEOPHYSICS John Roberts University of New South Wales The Sydney Universities' Consortium of Geology and Geophysics is an umbrella organisation encompassing the Department of Applied Geology, University of New South Wales, the Department of Geology and Geophysics, University of Sydney, Geology and Geophysics disciplines in the School of Earth Sciences, Macquarie University and the Department of Applied Geology, University of Technology, Sydney. The Consortium will promote co-operation in undergraduate and postgraduate teaching, research, the purchase, housing and maintenance of large items of equipment, and will undertake joint approaches to government and industry for the funding of collaborative research projects and selected academic appointments. The aim of the Consortium is to raise the overall level of activity within the departments and to expand teaching and research to encompass new developments within geoscience, all of which are of considerable importance to the Australian economy. Each Consortium member has its own distinctive specialisation and approach to teaching, providing the community with a diversity of skills. It is essential for the present and future needs of the country that the departments have adequate support to continue In this manner so that sufficient graduates with diverse geosclentific knowledge are available to allow constructive Input Into policies concerning earth resources and management of the environment, areas of vital importance to our country's economy. It is also important to recognise that new developments within geoscience require an increased level of postgraduate training for professional earth scientists within industry and government. The close integration of teaching and research within the Sydney region will safeguard the supply of such highly trained personnel. Each of the Consortium departments will attempt to ensure that: a) a suitable core of staff is available to teach basic geology and geophysics and additional service teaching requirements; b) fields of specialisation are enhanced by the appointment of high quality staff to boost research, modernise teaching and provide the capacity for expansion into new areas of scientific or economic significance; c) staffing policies are sufficiently flexible to meet new demands within the discipline; d) the age structure of academic staff is balanced to ensure that there are young energetic workers in addition to more experienced academics; e) sufficient staff are available to teach laboratory and field classes; and f) more students are exposed to earth sciences than at present so that there is an increased level of knowledge of earth sciences within the community.

116

AUSTRALIAN INSTITUTE OF GEOSCIENTISTS (AIG) AND TERTIARY EDUCATION J. Thomson Australian Institute of Geosclentlsts, NSW The Australian Institute of Geoscientists (AIG) has sought to establish, by questionnaires on accreditation, how geoscience courses offered by Tertiary institutions vary from institution to institution and draw conclusions as to the standards achieved. This study was designed to examine how graduates were academically trained to take their place in industry and to enable a comparison to be made with overseas courses. It was also hoped that if Tertiary institutions could be accredited it would enable prospective students to choose the Tertiary institution that would best prepare them for their careers and enable both government and industry employers to evaluate the courses. AIG does not wish to interfere with any Geoscience Department's right to conduct its own curriculum bit it wants to advance three important aims of the Institute: 1. 2. 3.

To enhance the Geoscience profession in every possible way. Make sure that Geoscientists are seen as professionals. Try to attract the highest quality students into entering and graduating in Geosciences at Tertiary Institutions.

In this paper it is hoped to enlarge upon the Tertiary courses and requirements that AIG believes are needed. AIG believes that Geoscience should be a part of the curriculum at Secondary School level so that students are able to form a balanced judgement on the world where they live in, the contribution that the mineral Industry makes to their living standards, and how it forms an important part of their environment.

EDUCATION AND ENVIRONMENTAL GEOLOGY B. Nicholls Giles Road, Wlllunga SA 5172 In the past few years much public attention has been focused on environmental issues such as wastage of resources and the pollution of ground water, streams, oceans and the atmosphere. Furthermore, interest in the more theoretical fields of ozone depletion and the "greenhouse effect" continues to gain impetus in step with current research. Geoscientists have a very important role to play in both defining and solving these environmental problems. In particular, Geoscientists from all backgrounds can be called upon to work under the one banner of Environmental Geology. It is through geological education that the links between the Environment and Natural Resource Management can be strengthened. A general knowledge of geology provides

117 an understanding of the structure, history and processes of the earth, which in turn is central to any insight into environmental systems. Human exploitation of the planet's natural resources is inevitable but the impact of such endeavour can be minimised if knowledge of working systems is applied. Geology is the key to answering many of the questionsi

MINING OR THE ENVIRONMENT - GEOLOGY'S DILEMMAI R. Stutchbury Key Centre for Mines, University of New South Wales, NSW Geology is considered by some, the tool of the mining industry although to many in the community it is the tool the mining industry uses to "rape the environment". A national survey of 1st year tertiary geology students, conducted through the Geoscience Awareness Programme (GAP), has shown that students consider geology of great importance to a career in mining, but not so important to a career connected with environmental studies. In the United States over 60% of geology graduates are employed in research into the problem of toxicity in groundwater; of the remainder surprisingly few are directly employed in the mining industry. When asked if their children study geology at school many parents, when responding negatively, say that their offspring are not interested in a career in mining. Lessons in environmental "science" invariably turn to mining operations for examples of land abuse and disruption, and rarely do they look at regulations which control these problems or at successful examples of rehabilitation. Geology is one of the four major scientific "tools" used not only by the mining industry, but also for collecting the data which indicate many of the global problems currently confronting humanity. Geology should not be torn apart by forces generated by the misconception of mining and environment being opposing extremes. Through sensible teaching from an early age, geology should be used to show that the two are strongly linked and to do this there will need to be many changes to geological education. This includes a review of its purpose and direction and a revision of obsolete curricula. These changes should ensure that more gifted students are eventually attracted to geology. To implement such changes, careful strategic planning is required. The Geoscience Awareness Programme, after some years of investigation, has proposed a number of recommendations that could result in an entirely new direction for geological education. Many of these are based on the American Geological Institute's programme, for all from kindergarten to year 12 (K-12), Earth Science Education for the 21 st Century. Geology, as part of a curriculum in Earth Science, shares equal importance with the other three major sciences, in developing an understanding of the dynamic systems of the Earth and humanity's relationship to them.

118

Technical Session 7(a) Petroleum Exploration Viii Reservoir and Source Rock Geochemistry THERMAL HISTORIES AND ILLITE GROWTH IN SEDIMENTARY BASINS P.J. Hamilton"' * and M. Giles^ ^CSIRO Division of Exploration Geosclence ^Shell UK, Shell Mex House, England K-Ar dating is used extensively to assess timing of illite diagenesis relative to the time of hydrocarbon charge to petroleum reservoirs. The manner in which this geochronological tool is used involves several assumptions which can now be critically assessed by integration of age data with burial history curves, quartz overgrowth fluid inclusion temperature and petrographic observations. 1.

The youngest obtainable illite ages from sandstones with detrltal clay matrix ("dirty" sandstones) are generally older than those from nearby "clean" sandstones. This reflects either contamination with older detrltal illite or bias towards earlier illite diagenesis as a result of easier nucleation on pre-existing clay in the "dirty" samples.

"Clean" sandstones from within oil legs have illite ages for finest size fractions that generally match calculated times of oil migration and approximate the cessation of illite formation.

Neoformed illite is observed to first appear at ca. 2300 m depth, corresponding to a palaeotemperature of about 80°C. The corresponding time is tens Ma greater than the youngest illite ages - a time span significantly greater than the measured age difference between coarsest and finest fractions of an illite separate.

Illite, and by inference quartz, diagenesis can persist at reduced rates in water wet portions of oil zones after oil accumulation. High fluid inclusion temperatures that have been suggested to record the action of abnormally hot fluids prior to oil migration may be more appropriately interpreted as reflecting maximum burial conditions of the reservoir or as being artificially high as a result of inclusion leakage.

A model for illite growth is proposed that explains some of the above observations together with the fact that none of the K-Ar data provides evidence of recent diagenesis (< 15 Ma). An understanding of the importance of fluid flow rates in competition with illite forming reaction rates suggests that the aggregate nature of size fractions is always biased towards sampling of grains formed at the maximum rate of growth.

119 INTEGRATING TIME SPECIFIC AND TIME DEPENDENT TEMPERATURE INDICATORS FOR THERMAL HISTORIES OF SEDIMENTARY BASINS PJ. Eadington* and PJ. Hamilton CSIRO Division of Exploration Geoscience Fluid inclusion and stable isotope measurements provide temperatures that are specific to the time of crystallization of the diagenetic minerals that are measured. This provides a datum point for temperature, depth and heat flow during basin formation which can be used with the current heat flow and with maturity measurements to determine the intervening heat flow history in greater detail than when using the current heat flow datum alone. Indicators of thermal maturity are measures of time integrated thermal stress exerted on specific components of sedimentary organic matter during burial. Examples are vitrinite reflectance, thermal alteration index, temperature of maximum pyrolysis yield, and isomerisation of hopanes. Accurate reconstruction of thermal histories of sedimentary basins is a crucial prerequisite for valid kinetic modelling of oil generation which is becoming commonly used in petroleum exploration. A wide variety of techniques have been used to determine thermal histories and have been summarised in recent monographs (e.g. Naeser and McCulloh, 1989). Limitations in using maturity with one datum point for heat flow to determine heat flow history are demonstrated by Lerche et al. (1984). Using mean square residuals to measure the closeness of fit between measured and computed vitrinite reflectance yields a linear approximation for heat flow history (palaeo heat flux). An additional datum for heat flow enables a non linear approximation of heat flow history to be determined. The ability to identify maxima and minima in palaeo heat flux is a significant improvement that enables realistic comparison of thermal history predicted from mineralogical and geochemical measurements with that predicted from tectonic reconstnjctions. Palaeo temperature determination using fluid inclusions is from a measured homogenisation temperature and the phase relations and compressibility of the fluid within the inclusion. These are used to define an isochore (pressure temperature relation at constant density). Fluid inclusions are pressure sensitive thermal indicators because of the compressibility of fluids. This limits the certainty in estimating palaeo temperature but has the advantage that the pressure and depth of formation of the host minerals (e.g. quartz overgrowths) as well as the temperature are obtained from the interpretation procedures. A unique determination of the pressure, depth and temperature of trapping is possible if immiscible fluids of two different compressibilities (e.g. pore water and oil) have been simultaneously trapped in different inclusions. Isotope measurements together with the sequence of crystallization of diagenetic minerals constrain the timing of the heat flow datum obtained from fluid inclusions. K-Ar dating of illite or reconstruction of trends in the isotopic composition of pore water are used.

120

Consistency between the thermal regimes during diagenesis and at the present day is indicated on a graph of temperature versus depth by intersection of the isochore, sample depth marker and current temperature profile at the one point (Fig. 1 A). Where the sample depth marker and current temperature profile intersect the isochore at different points (Fig. 1B) it indicates that the thermal regime has changed and the difference may be used to evaluate the change in heat flow and, or, the amount of eroded section. The Tintaburra field in the Eromanga Basin is an example where the thermal regime during quartz cementation appears to be similar to the present day (Fig. 1 A). Using a constant heat flow history and a vitrinite reflectance model based on the kinetics of the reactions of vitrinite (Burnham and Sweeney, 1989) gives a good fit between calculated and measured reflectances. In the southern Sydney Basin near Campbelltown there is an 80 degree difference between fluid inclusion homogenisation temperatures and current temperatures in the sample horizons (Fig. 1B). Obtaining a fit between calculated and measured vitrinite reflectances while honouring the fluid inclusion data requires restoration of about 2000 m of eroded section and a heat flow maximum at about 100 Ma. The heat flow maximum corresponds to the time of commencement of rifting and sea floor spreading in the Tasman Sea.

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120

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Flg.1 References Burnham, A.K., and Sweeney, J.J., 1989. Geochimica et Cosmochinica Acta, V.53, p.2649 - 2657. Lerche, I., Yarzab, R.F. and Kendall, C.G. St. C., 1984. Bull. American Assoc. of Petroleum Geologists, V.68, p. 1704-1717. Naeser, N.D., and McCulloh, T.H., 1989. Thermal History of Sedimentary Basins. Springer - Verlag, New York.

SEDIMENTARY PROVENANCE USING Nd ISOTOPES: APPLICATION TO PETROLEUM EXPLORATION IN THE EROMANGA BASIN D.J. Whitford* and P.J. Hamilton CSIRO Division of Exploration Geosclence The Sm-Nd geochronometer, based on the radioactive decay of ^^^Sm to ^^^ Nd with a half-life of about lO"" years, is widely used for determining the "average" age of continental crust and for the related problem of determining sedimentary provenance.

121 The derivation of provenance information from Sm-Nd isotopic analyses of a sediment involves estimating when its crustal precursors were fractionated from the earth's mantle. Because the Sm/Nd ratio of crustal rocks is largely unaffected by intracrustal processes such as weathering, erosion and diagenesis, present-day Sm-Nd isotope measurements can be used to calculate an "age" when the Nd departed from a mantle source. Although the calculated age may not have direct time significance and will to some extent reflect crustal reworking and mixing, it can be used to make inferences about sediment sources. Furthermore, within a sedimentary sequence, changes in provenance over time can be detected. One of the most petroleum-productive sandstones of onshore Australia is the Hutton Sandstone of the Eromanga Basin. The play concept of a lithic sand seal of the Birkhead Formation to quartzose reservoir sandstones of the Hutton on structural closures, is relatively simple. However, it needs to be refined in order to assess the possibility of stratigraphic traps developed at the Hutton-Birkhead transition. Two depositional models have been proposed to explain the distinct lithologic change across the Hutton-Birkhead transition. These include changes in depositional style from low- to high-sinuousity channel deposits (Hill, 1985), to the introduction of volcaniclastic sediments from an active arc off the Queensland coast (Watts, 1987). Resolution between the models clearly has important implications for play concepts that invoke stratigraphic traps formed in response to changes in drainage basin geometry. Neodymium model ages with respect to a depleted mantle model have been calculated from Sm-Nd isotopic measurements on rocks spanning the transition from several wells in the basin. There is a marked decrease in ages from as high as 1.7 Ga in the Hutton Sandstone to 0.88 Ga in a sample of the Birkhead Formation. The Hutton Sandstone is characterized by model ages within the range 1.2-1.7 Ga, with most values between 1.3-1.5 Ga, whereas samples of the Birkhead Formation range from 0.88-0.96 Ga. Samples of Hutton Sandstone from individual wells show a smaller range of model ages. Preliminary Rb/Sr isotopic results also indicate a significant change in provenance across the transition. Because the Rb/Sr isotopic system is often perturbed during weathering, erosion and diagenesis, model ages are often unreliable. Nevertheless, the Hutton Sandstone has higher initial ®^Sr/^®Sr ratios than the overlying Birkhead Formation, indicative of younger source material, on average, for the latter. The old model ages for the Hutton Sandstone are consistent with their derivation from old cratonic rocks to the west and south whereas the younger ages from the Birkhead Formation imply a fundamental change in provenance. The results are consistent with, but not diagnostic of the Birkhead Formation being derived from an admixture of cratonically-derived sediments similar to the Hutton source, with younger crustal material, possibly derived from a volcanic arc to the north or east. Determination of sedimentary provenance in the Eromanga Basin using Nd isotopes in conjunction with other geological and geochemical techniques has the potential for use as a stratigraphic correlation tool and for location of possible trap structures. References Hill, L , 1985. Unpubl. B.Sc. Hons. Thesis, University of Adelaide. Watts, K., 1987. AREA Journal 27: 215-228

122

FLUID FLOW HISTORY OF E. TRIASSIC NARRABEEN GROUP SANDSTONES OF THE SOUTHERN SYDNEY BASIN G. Bai^ J. Keene"', P.J. Eadington^, P.J. Hamilton^* and I. Macdougall^ ^ Department of Geology, Sydney University ^CSIRO Division of Exploration Geoscience ^Research School of Earth Sciences, ANU Petrographic observations of fluid inclusions and diagenetic cements together with stable isotope and thermometric measurements on samples of Narrabeen Group sandstones have been obtained in order to document the thermal and chemical evolution of pore fluids during burial. Extensive carbonate cementation is common with precipitation of grain coating morphologies (calcite and siderite) followed by pore fills of calcite, siderite and ankerite. Subsequently stacks of pseudohexagonal kaolin platelets were formed and later overgrown by diagenetic quartz. The latest cements to form were calcite, ankerite and filamentous pore bridging illite. Oil migration was coincident with, and subsequent to, quartz diagenesis. Theoretical calculations of the timing of oil migration are consistent with these observations. K-Ar ages for illites approximate the cessation of illite diagenesis at between 146 and 91 Ma. Formation of illite appears to have persisted for longer and to greater depth in the eastern onshore part of the basin than in the west. This trend is paralleled by increasing maturity of organic matter in a west-to-east direction in the southern part of the Sydney Basin. Oxygen isotope compositions of various cements are used together with fluid inclusion temperatures and observations on the relative timing of diagenetic events to constrain the evolution and source(s) of pore waters during burial. Such data indicate that pore water oxygen isotope composition remained similar through the burial interval characterised by early clay and pore fill carbonate. Temperature is calculated to have increased from about 10° to about 80°C during this interval. The calculated pore water oxygen isotope composition at - 1 5 7 o o , expressed as ®0, is as would be expected for connate waters of Triassic meteoric origin. This period of diagenesis was dominated by an open fluid flow regime with a sustained meteoric water recharge. Subsequently pore waters became enriched in ""^O by about 1 2 ° / o o by the time of quartz and illite diagenesis, estimated from fluid inclusion data to have occurred at temperatures of 110° to 135°C. This latter part of diagenetic history occurred in a closed/restricted system with respect to fluid flow regime. The thermometric fluid inclusion data from quartz overgrowths indicate 45-55°C higher temperatures than currently prevail at the sampled depths of ca. 0.5 km. Modelling of vitrinite reflectance values and these fluid inclusion data suggest that the higher temperatures resulted from a combination of a maximum heat flow of 2.1 HFU, somewhat higher than the present value of 1.7-1.9 HFU, together with loss of ca. 18002100 m of section consequent to Tertiary uplift and erosion.

123

Technical Session 7(b) Mineral Exploration V - Electromagnetic Interpretation

INTERPRETATION OF POLARISATION EFFECTS OBSERVED IN TEM FIELD DATA Peter Elliott Elliott Geophysics P/L, Adelaide, SA Research has demonstrated that negative TEM voltages observed in coincident loop or in-loop survey data are due to induced polarisation effects. These effects have approximate negative exponential decays which are observed in late time data. By removing the inductive half-space response and then matching and removing the negative exponential due to polarisation effects from affected readings, it is possible to provide a better presentation of data and unveil anomalous conductive responses which would othenwise have been overlooked.

EXAMPLES OF DATA PROCESSED USING A NEW TECHNIQUE FOR PRESENTATION OF COINCIDENT AND IN-LOOP IMPULSE-RESPONSE TRANSIENT ELECTROMAGNETIC DATA R. Smith"'* and G. Buselli^ •"centre for Geophysical Exploration Research, Sydney ^CSIRO Exploration Geosclence, Sydney Coincident- and in-loop transient electromagnetic (TEM) methods measure the response as a function of time after the current in a transmitter is switched off suddenly. Voltage measurements at each delay time are often normalized to an apparent conductivity so as to provide a crude indication of the subsurface conductivity structure. The first stage of the new processing technique is to employ a sensitivity analysis to associate each apparent conductivity with a depth. In cases when the actual conductivity structure varies rapidly with depth, the apparent conductivity curves tend to vary slowly as a function of depth. This slowly varying curve appears to be a smoothed version of the actual conductivity structure. The second stage of the processing algorithm is to calculate an approximate operator which is the inverse of the smoothing operator. Applying this inverse operator to the apparent conductivity curve yields a sharper, more rapidly varying estimate of the conductivity, termed the 'spiked conductivity'. The technique has been applied to field data in an area where the conductivity staicture is essentially horizontally layered. The spiked conductivity shows greater contrast and resolution than the apparent-conductivity depth curve and the results are consistent with those from a more sophisticated three-layer parametric inversion routine. The spiked conductivities are obtained easily and quickly and, unlike the inversion routine, do not require a priori knowledge. The processing technique can be installed on small computers, so results can be generated in the field and a first-order indication of the conductivity structure can be obtained quickly.

124

A STUDY OF GALVANIC RESPONSE IN THE TEM RESPONSE OF CONDUCTIVE ORE BODIES Michael W. Asten BHP-Utah Minerals International, Hawthorn, Vic.

When the transient EM method is used to energise a conducting target, the galvanic (or current channelling) response may dominate over the more common inductive response when any or all of the following factors are present: a) b) c)

the target is moderately or poorly conducting, the target is in a conductive host rock, or in contact with a conductive overburden, the transmitter loop is laterally at a large distance from the target.

Numerical modelling studies using a conductive disc in a conducting host allow inductive and galvanic responses to be calculated separately. Comparison of the two responses over a range of targets show that the galvanic response is distinguishable from induction by its broader (unipolar) profile shape, its power-law time decay (t"^'^^ for impulse systems) and its anomaly sign. For realistic models, late-time response is always dominated by background plus inductive response, and the transition from early-time galvanic response to late-time inductive response may produce complex sign changes which defy analysis by freespace modelling. Correct identification of early-time galvanic response can assist in resolving directional ambiguities of downhole EM target location which often arise from interpretation of inductive response alone. Identification of galvanic response is demonstrated in field data from volcanogenic base metal targets at Thalanga and Dreghorn in Queensland.

QUANTITATIVE RESISTANCE AND CAPACITIVE ELECTRODES: NEW DEVELOPMENTS IN INDUCTIVE SOURCE RESISTIVITY James Macnae* and Patrick McGowan Lamontagne Geophysics Ltd, Canada The results presented in this paper show that in the Inductive Source Resistivity (ISR) technique, the transient decay of E field data can be used to calculate an apparent background resistivity (or, in the case of conductive overburden, an apparent background resistance); which can then be used to estimate an apparent transverse resistivity (apparent transverse resistance) from the late-time measured electric field data. This estimate thus makes the presentation of ISR data more meaningful in terms of modelling or interpretation with quantitative physical properties. The development of capacitive electrodes allows for measurement of the ISR, a direct current electric field response of the ground, without the need for ground contact of either the transmitter or receiver electrodes.

125 Technical Session 7(c) Coal, Groundwater and Engineering I - Coal

PLIO-PLEISTOCENE COAL RESOURCES IN A FOREARC BASIN SETTING MEULABOH, WEST ACER, SUMATRA Hadiyanto* and A.C. Cook Department of Geology, The University of Wollongong Tertiary coal measure sequences were deposited from the Oligocene to the PiioPieistocene in the Tertiary forearc basin of the l\/leuiaboh area. Although the PlioPleistocene coals are lower in rank, they have the most widespread distribution and therefore have better economic prospects than those of the Oligocene and Miocene coals. The Plio-Pleistocene contains a total resource of more than 1000 million tonnes of coal of soft brown coal/lignite rank. The coal occurs in three main series of seams with individual seams ranging from 2-10 metres in thickness. The overburden varies from 3 to 80 metres depending on the topography. The Plio-Pleistocene coals are low in rank, ash and sulphur. Ash content is fairly uniform and averages 4.00% (a.d.b) while sulphur is variable between 0.1-1.00% (a.d.b). The sodium content ranges between 0.5-1% of the ash. The volatile matter is in the range of 30-43% and fixed carbon ranges from 30-40%. Heating value is fairly uniform and averages 4900 Kcal/kg on a bed moist basis. Petrographic studies show that the Plio-Pleistocene coals are rich in vitrlnite with vitrinite content generally being within the range of 65-90% whereas liptinite content is variable ranging from 10-35%. Inertinite is usually present but seldom comprises more than 5% of coal. The most common minerals occurring in these coals are clay and to a lesser extent quartz. However, they generally occurred on cleats and fissures not exceeding more than 1 %. The vitrinite reflectance varies from 0.20-0.40%.

COAL POTENTIAL AND RESOURCES IN THE SOUTH SUMATRA BASIN, INDONESIA Rubianto Amier University of Wollongong South Sumatra Basin is one of the Sumatran back-arc basins located along the island of Sumatra. This basin plays an important role in relation to oil and coal production in Indonesia. The South Sumatra Basin occupies an area of roughly 100,000 sq km. Extensive exploration for coal has been conducted by several companies and government institutions within the South Sumatra Basin. The biggest exploration program was done by Shell Mijnbouw from 1973 to 1977 and covered an area of about 71,450 sq km. The investigation was focused on the Muara Enim Formation. The principal coal potential of the South Sumatra Basin is concentrated in the Muara Enim Formation of Upper Miocene to Lower Pliocene age and the coals are associated

126 with the regressive phase. Based on the presence of coal seams, the Muara Enim Formation is subdivided into four units, i.e. the m, M2, M3 and m. The thicl<ness of Muara Enim coals ranges from 2 meters up to 20 meters. While the thickness of Talang Akar coals varies from strings up to 3 meters. About 5 billion tonnes of coals in term of geological reserves, have been proven by Shell Mijnbouw. The coal reserves consist mainly of hard brown coal, but in the immediate vicinity of andesite intrusions, they locally reach anthracitic quality. Resources are significantly greater than 5 billion tonnes, but are almost of hard brown coal rank. Coals from the M2 subdivision of the Muara Enim Formation have been mined by the state owned Indonesia Company, PT. Bukit Asam, since 1919 in the Air Laya Deposit, Tanjung Enim. Petrographically, the South Sumatran coals consist mainly of vitrinite and liptinite groups of maceral. Inertinite is rarely present. Mineral matter occurs as pyrite and clay. Vitrinite reflectance of the Muara Enim coals ranges from 0.3% to 0.53%, while that for coals thermally affected by andesite intrusion ranges from 0.69% to 2.60%. Talang Akar coals have vitrinite reflectance ranging from 0.5% to 0.7%. Bitumens are mostly rick in both coals indicating oil generation has already taken place. In the South Sumatra Basin, Talang Akar coals have been postulated to be a source for oil.

A COMPARISON OF EXPLORATION METHODS OF TWO INDONESIAN TERTIARY COAL DEPOSITS David J. Mason PT. Asmlnco Bara Utama, Jakarta, Indonesia The PT Multi Harapan Busang and PT Adaro Indonesia Paringin coal deposits lie within the Tertiary Kutai Basin of Eastern Kalimantan. Coal bearing formations are of Middle to Upper Miocene age: Busang in the Balikpapan Formation and Paringin in the Warukin Formation. The Busang deposit contains multiple thin seams, is shallow dipping within a broad, gently plunging syncline and has variable coal quality. In contrast, the Paringin deposit consists of a single very thick, moderately to steep dipping, homogeneous coal lying in an asymmetric anticline. Exploration objectives in each case were to define a marketable coal resource to sustain a medium sized, long term mining operation. Exploration techniques were similar and included: geological mapping, stratigraphic and resource definition drilling, downhole geophysical logging, topographic mapping, trenching, augering, large diameter coring, bulk sampling and analytical testing. Commercial aspects associated with the exploitation of the coal imposed certain mining criteria on the resources. These were considered when designing the exploration programmes and, in conjunction with the contrasting geological nature of the two deposits, the methods of exploration differed. The Busang programme commenced with geological mapping and widely spaced deep drilling along the syncline axis to establish stratigraphy and stnjcture. The resource was

127 then defined by drilling on a regular polygonal grid, initially wide spaced though subsequently reduced. Paringin stratigraphy was determined by mapping and trenching perpendicular to the stril^e of the sequence. The extent of the resource was defined by drilling on regular sections across the seam strike and in the more prospective shallow areas drilling on a polygonal grid system. Geological mapping was successful in delineating the extent of the major seams in the Busang due to the good outcrop in gullies of the hilly terrain. At Paringin trenching and shallow augering predominated as surface exposure of the seam was less frequent. Early evaluation of the Busang resource showed 80m was the maximum depth which could be economically mined. Paringin mining economics allowed a resource depth of up to 150 metres however, geotechnical and hydroological factors reduced viable open cut mining to between 80 and 100m. Busang and Paringin resource definition was thus confined to resources less than 80m and 100m depth respectively. At the Busang, grid spacing was progressively reduced to 150m, though seam discontinuities, including faulting, gentle folding, seam warps and drifts necessitated localised drill spacing to 25m. Paringin drill sections were reduced from 500m to 125m along the deposit strike. Spacing along section lines was normally 100m except close to the anticline axis where intense faulting exists. Downhole geophysical logging was a very useful tool to distinguish the Busang coal seams and significantly enhanced correlation confidence. Correlation was not a problem for the single seam Paringin resource. Close spaced core drilling and detailed ply sampling was required in the Busang due to variable coal quality and occasional dirt banding. In contrast, the consistently clean homogenous Paringin seam, free of partings or distinguishable coal plys permitted wide spacing of core drilling and large, evenly divided sample intervals. Exploration expenditure was similar for each programme though for the more complex multi seam Busang resource only 13 million tonnes of measured reserves were delineated in comparison with 55 million tonnes at Paringin.

TRANSMISSION CHARACTERISTICS OF IN-SEAM SEISMIC WAVES THROUGH DYKES AT GERMAN CREEK CENTRAL COLLIERY, OLD LA. Drake* and R.D. Hewson Centre for Geophysical Research, Macquarle University A face to borehole in-seam seismic survey was conducted by the Australian Coal Industry Research Laboratories at the German Creek Central Colliery, Queensland, to detect and delineate dykes obstructing mining operations within the coal seam. Previous attention to the data concentrated on a reflection analysis and established the location of the three dykes within the range of the reflected raypaths. A transmission analysis of the Love, Rayleigh and compressional waves has since been carried out to

128 test for absorption of the seismic energy by the dykes and hence to determine the viability of locating the dykes' position using this technique. The seismograms and amplitude spectra for these three wave types indicated significant attenuation across the survey area which included the three dykes. Estimates of Q were subsequently calculated from the seismic data to indicate the degree of attenuation due solely to the coal. Finite difference and finite element modelling of the dykes was used to test the absorption properties of the dykes and to identify other possible transmission characteristics. Margins of cindered coal and altered sandstone are two additional characteristics associated with the dykes at German Creek Central Colliery which have been measured and incorporated into the numerical modelling.

129 Technical Session 7(d) Exploration Management II - Legal Aspects PERSONAL LEGAL LIABILITY OF CONSULTANTS Michael Sharwood Blake Dawson Waldron, Sydney In addition to the contracting role commonly filled by geotechnical consultants, they are frequently called upon to prepare reports for inclusion in public documents such as prospectuses, explanatory memoranda for corporate schemes of arrangement, takeover documents and company meetings called to comply with the requirements of Section 12(g) of the Companies (Acquisition of Shares) Act or with Section 3J(3) of the Stock Exchange Listing Rules. The common law, statute law and the rules of various professional organisations establish a minefield of regulation of which the consultant should have a good working knowledge. Any departure from the regulatory regime can result in considerable personal liability occurring including substantial monetary penalties, imprisonment, the obligation to make restitution to persons suffering loss as well as loss of professional accreditation. Common law liability usually arises under the tort (civil wrong) of negligence if harm (whether or not intentional) is caused to some other person. The law of negligence imposes a duty of care in a wide variety of circumstances. The failure by a consultant to satisfy that duty can expose him to liability. It is not always easy to identify the class of persons to whom the duty is owed. Common law liability can arise also for breach of contract. Whilst the law of negligence itself gives scope for the reporting geoscientist to disclaim liability, current regulatory policy denies that option in many cases. Furthermore, liability arising under statute cannot be denied. The third principal source of common law liability lies in the area of fiduciary obligations, i.e. obligations requiring the exercise of the utmost good faith. In the case of the consultant this obligation includes the obligation to avoid a conflict between his personal interests and of those by whom he is engaged or for whose benefit he is reporting. The statutory basis of the consultant's liability may be found in numerous statutes. For example, the Companies Code prescribes both civil and criminal liability for untrue statements or non-disclosure in prospectuses; the Securities Industry Act imposes liability on a person who makes a statement or disseminates information relating to securities that is false or misleading in a material particular; the Companies (Acquisition of Shares) Act imposes a liability to pay damages in respect of the omission of material matter or materially false or misleading statements made, for example in a report included in a takeover document; Section 52 of the Trade Practices Act furnishes remedies to those who suffer loss or damage by reason of conduct in trade or commerce which is misleading or deceptive; and the Crimes Acts of the Commonwealth and the States include the offence of knowingly making false statements.

130 Finally, the various professional organisations to which consultants usually belong have published ailes which give them power to suspend or expel any member whose conduct fails to conform to generally accepted professional standards.

RECENT DEVELOPMENTS IN ENVIRONMENTAL LAW AS THEY RELATE TO EXPLORATION D. Maloney Allen, Allen & Hemsley It has been said that no single issue will focus the minds of politicians and lawyers more in the current decade than the environment. The enormous ground-swell of public opinion in favour of environmental protection and rehabilitation has turned a matter of political expediency into a political necessity. The legislative trends are towards strict liability coupled with personal liability of directors and officers and severe penalties. Mandatory reporting in relation to environmental matters, freedom of information legislation, class actions and a more robust approach to litigation all auger badly for the environmental delinquent. Recent Australian legislative trends and their particular relevance to companies, directors, officers, employees and contractors engaged in exploration operations are examined.

THE CHANGING LEGISLATIVE ENVIRONMENT FOR EXPLORATION Peter J. Rose Freehlll Holllngdale & Page The legislation concerning mineral exploration in Australia is in a state of change. Since mining legislation is State based, the changes are far from uniform. Nonetheless some general trends can be perceived. The Commonwealth Government also exerts some control over the exploration industry in situations where Commonwealth approvals are required. This paper will provide a review of legislative changes affecting the exploration industry across Australia. It will focus on three areas which are the subject of most active change. 1. Modernisation of Mining Codes The legislative framework for mining is often criticised as antiquated, incomplete and unsatisfactory. An update and review of the old Mining Codes is but timely. Queensland has recently enacted a new Mineral Resources Act and in Victoria drafting of a new Act is well advanced. The reforms range from reclassification of available Tenements and a revamp of the registration system to the revision of the rent and royalty rates. In Victoria, the extensive reforms create an entirely new mining regime. There are now indicators that other States will also review their mining legislation.

131 2. Competing Land Use Issues It is not uncommon for legislation to provide that competing interests in land use like agriculture, forestry, planning and conservation must be considered before approval for exploration is given. Today, the swing towards environmental protection is evident from recent legislation which limits access to land for exploration. In NSW and Western Australia, National Parks legislation is being amended to further restrict or entirely ban mining in National Parks. On the other hand, there are a few legislative changes which improve access to land. In South Australia, "regional reserves" may now be proclaimed in which wildlife and the natural or historic features of the land will be conserved, while at the same time utilisation of its natural resources is permitted. In NSW, changes to the Mining Act may improve access to rural lands for exploration. Further, the Resource Assessment Commission (RAC) was established in 1989 by the Commonwealth Government to aid the government in improving its decisions on important resources issues. The paper will examine the role of the RAC and the challenges that the exploration industry faces in incorporating the concepts of environmental management in development projects. 3. Access to Aboriginal Lands The legislation on Aboriginal land rights in the Northern Territory and South Australia is perceived as a major obstacle to mineral resource development. The Australian Mining Industry Council recently observed that half the land in the Northern Territory was severely restricted or closed to mining under the Aboriginal Land Rights Act. However, a new concept of land access has been introduced in the Northern Territory which allows development which does not pose a "substantive risk of damage or interference with sacred sites". This may open up more Aboriginal lands to exploration. Conclusion Whilst at one level steps have and are being taken to revise and update antiquated Mining Codes to the general benefit of the industry, at the same time access to land for the purposes of exploration is being restricted. It is important that the impact of these developments be understood so that the industry may adapt or take advantage of them.

132

Technical Session 7(e) Petroleum Exploration IX - Cretaceous to Recent Tectonics

THE CRUSTAL STRESS PATTERN IN THE AUSTRALIAN CONTINENT David Denham^* and Christopher R. Windsor^ ^Bureau of Mineral Resources, Geology & Geophysics, Canberra, ACT ^CSIRO Division of Geomechanlcs, Nedlands, WA The state of stress in the crust is an important factor in the design and performance of underground excavations, the behaviour of oil reservoirs and in the design and construction of major civil works such as dams, bridges and road cuttings. A compilation of 'near surface' stresses, measured from tunnels, mines and rock outcrops has recently been conducted by Brown and Windsor (1990). This compilation has been extended to include the results from more than 40 earthquake focal mechanisms, and breakout data from 31 deep (>1 km) drill holes. The results of this compilation show that most of the crust is experiencing compressive stress and that in some regions, e.g. the south west part of the continent, the levels of stress are very high (greater than 20 MPa at depths less than 10 m). The orientations of the axes of maximum compression vary considerably across the continent but within regions the stress direction appears consistent. For example, in the south east part of the continent it is northwest-southeast, whereas in the south-west it is close to east-west. The results obtained within the upper 500 m exhibit more scatter than those obtained at greater depths. This is indicative of local perturbations in the stress field at shallow depth caused by tectonic decoupling, topography and weathering effects. A major factor in the continent-wide stress regime is probably the movement of the Australian Plate and its subsequent deformation as it collides along its northern margin. However, there are other factors influencing the situation because the observations do not fit a simple continent-wide pattern.

THE ROLE OF INTRAPLATE STRESS IN TERTIARY (AND MESOZOIC) DEFORMATION OF THE AUSTRALIAN CONTINENT AND ITS MARGINS: A KEY FACTOR IN PETROLEUM TRAP FORMATION Mike Etheridge*, Herb McQueen and Kurt Lambeck Research School of Earth Sciences, Australian National University, Canberra, ACT The horizontal stress field within plate interiors is largely the result of interactions at plate boundaries. There is considerable geological evidence and theoretical support for the hypothesis that large horizontal stresses can propagate for thousands of kilometres into plate interiors, and that changes in plate geometry or boundary configurations therefore lead to significant variations in stress in plate interiors. Because there is a global interdependence of all plate motions, a major change in the nature of one plate

133 boundary (e.g. the India-Asia collision) nfiay have global implications and observable geological consequences many thousands of kilometres from the source. There are two important consequences of large horizontal intraplate stresses and stress variations for petroleum exploration. First, flexural distortions of the plate will be localized by variations in strength and/or thickness of the plate, such as at sedimentary basin boundaries. These distortions may give rise to transgressions/regressions and unconformities that may be confused with eustatic sea-level effects. Second, an increase in stress or change in stress orientation may be relieved by reactivation of a pre-existing structure in the plate interior. Reactivation of basin-forming faults is a particularly widespread consequence of intraplate stresses. Analysis of the structural petroleum traps in Australia's main producing basins shows that a large proportion of the traps were generated by reactivation of underlying, usually basin-forming faults. We discuss examples from the Carnarvon, Bonaparte and Gippsland Basins, and relate them to the global and regional plate tectonic history in the Tertiary and Mesozoic.

TECTONIC EVOLUTION OF THE DURROON BASIN, TASMANIA Peter Baillie'' * and Robert P i c k e r i n g ^ ^Tasmania Department of Resources & Energy ^Bridge Oil Limited The Durroon Basin containing up to 7 km of predominantly Cretaceous sedimentary infill is recognised on the basis of a different structural history to that of the adjacent Bass Basin. Structural development and sedimentation patterns of the Durroon Basin are the result of two distinct Cretaceous rifting episodes related to major regional tectonic events. The first episode (Otway Rift; 125-100 Ma) was a pronounced Late Jurassic (?) - Early Cretaceous rift phase during which volcaniclastic sediments were deposited in an elongate series of troughs formed by the initial separation of the Australian and Antarctic Plates. This stage was succeeded by a further rift phase which was responsible for much of the structural character of the Durroon Basin. The second extensional episode (Tasman Rift; 90-80 Ma), was caused by the opening and subsequent rapid development of the Tasman Sea. This episode created a series of post-depositional, detached, roll-over structures along margins formed by listric faults and formed updip culminations to tilted blocks. Post-Tasman Rift sedimentation was influenced by both Otway and Tasman drift. The effect was to cause subsidence to move to central parts of the Bass Basin, and by Early Tertiary times the Durroon Basin was buried beneath Cainozoic sediments of the Bass Basin.

134 TERTIARY UPLIFT ESTIMATION FROM VELOCITY DATA IN THE EROMANGA BASIN Jane R o d g e r s " ' F r e d L. Wehr'''^ and John W. Hunt"" "JESSO Australia Resources Limited, Sydney

'Exxon Production Research Co., Houston ^ESSO Norge a.s, Stavanger The Tertiary uplift of the Eromanga Basin over P E L ' S 5 and 6 (SA) and ATP 259P (Queensland), has significantly complicated depth-porosity relationships in the important oil-bearing Hutton Sandstone, as well as altering migration pathways. Because seismic reflection data in the Eromanga Basin are focussed on the lower part of the succession, they are not suitable for imaging and mapping the Tertiary unconformities. In this study, an estimate of the magnitude of Tertiary uplift across the acreage has been made by cross-plotting interval velocity and depth for the lithologically homogenous Cretaceous marine shales near the top of the succession. Deviations from a depth-velocity baseline fitted to data from the basin depocentres have enabled quantification of uplift. The uplift estimates have been used to produce pre-uplift depth structure maps which can be used to map pre-uplift hydrocarbon migration pathways. Maximum burial depth can also be calculated, providing a better predictor of porosity in the Hutton Sandstone than present-day burial depth.

135 Technical Session 7(f) Theoretical Research SEISMIC MIGRATION AND MATHEMATICAL MAPPING Peter W. Buchen Department of Applied Mathematics, University of Sydney This paper is concerned with fundamental properties of seisnnic imaging (forward modelling) and migration (inverse modelling). The precise mathematical nature of the transformations connecting model space and data space are analyzed and found to belong to a family of mappings called contact or symplectic transformations. The transformations are found explicitly for the case of constant velocity media, so that their structure and properties can be analytically developed. Both geometrical and dynamical aspects of the transformations are discussed. The analysis provides a powerful insight into the nature of seismic imaging and migration.

HIERARCHICAL DECOMPOSITION AND INVERSION Jacob Tjeerd Fokkema Delft University of Technology, The Netherlands In inverse scattering one attempts to reconstruct the material composition of a domain whose interior is inaccessible to direct measurement by probing it from the outside. To this end the domain Is considered as a contrasting domain In a known background configuration. The probing is carried out by exciting the object with a number of sources, while the resulting wavefield is detected at a number of receiver positions. In the corresponding mathematical description of the experiment the wavefield quantities are subject to a spatial-temporal differential operator, and to the boundary conditions such as for example source conditions and the radiation conditions. In general terms inversion can be formulated as a non-linear expression where the measurements are related to the contrast-function in the medium. This representation is equivalent to a volume integral over the contrasting domain where the contrast function together with the actual field act as weights of the kernel function. This kernel function depends on the position of two points in the contrasting domain and is known as the Green's function. The Green's function represents the inverse of the differential operator. In the usual formulation of the inverse problem the wavetheoretical character of the inverse operator is predetermined, only the constitutive parameters are allowed to vary. In this sense inversion is equal to inverse forward modelling. l-1owever, this approach leads to a restriction on the inversion process. The data to be inverted are harnessed due to this assumption. The parameters do not have enough flexibility to compensate for the discrepancies between observed and calculated data when the observed data cannot be attributed to such a wave problem. In the hierarchical approach it is proven that any wave problem can be decomposed into a set of subproblems. By arranging this set of subproblems in increasing order of complexity the associated inverse process is divided into two steps. The first step consists of

136

determining the contribution of the sub-set members to the whole data set. In the second step a linear inversion is performed to each sub-set member. In this process the influence of less complex and previously determined members is taken into account. This procedure is not equal to inverse fonA^ard modelling.

SOURCE SCALING AND THE DYNAMITE SIGNATURE A.M. Ziolkowski Delft University of Technology, The Netherlands In seismic data acquisition with dynamite it is normally impossible to measure the source signature. In most geologies the measurement is contaminated by scattered energy, and it is impossible to separate the incident source field from the scattered field. However, this is not normally regarded as a problem, because the exploration industry has for years trusted statistical deconvolution methods, particularly least-squares predictive deconvolution, to handle the dynamite signature problem.

In any serious attempt to invert seismic data using sound wave propagation theory, it is essential to determine the signature at the source. This source signature cannot be determined from the seismic data using the normal methods of statistical deconvolution, because these rely on statistical assumptions about the earth response for which there is no supporting theory. The assumptions are made only for convenience, and cannot be justified by any argument based on the physics of the problem. I present an approach to this problem that uses two different shots at each shot point, and relies on a scaling law between the source signatures proposed by Ziolkowski and Lerwill. The two shots give different shot records. The basic assumption of the scaling law is that the fraction of energy radiated by the shot depends only on the properties of the medium and the type of explosive, but not on the mass of the explosive. The ratio of the energies of the two shots is proportional to the ratio of the masses of the two dynamite charges. The signature of the larger shot is an amplified and stretched version of the signature of the smaller shot. The amplification and stretch factors are equal, and proportional to the ratio of the charge masses. At a given receiver, the response to one shot is a convolution of the source signature with the impulse response of the earth, plus noise. The two shots and the scaling law give three independent equations relating the three unknowns, which are the two source signatures and the impulse response of the earth (plus noise). In the bandwidth where the signal-to-noise ratio is good, these three equations may be solved for the three unknowns. In a common shot gather the source signature is the same on every trace and the signal-to-noise ratio can be improved with a multi-channel approach. Unlike statistical deconvolution methods, this approach is based on physics, and may be put at risk in a physical experiment. The experiment requires a third shot at the same shot point, using a known mass of dynamite different from the other two. The resulting shot record should be different from the other two and, apart from the noise, should be predictable from the other two records. This experiment was performed in Tubbergen in the Netherlands in April 1990, and repeated 100 times at 50 m shot point intervals, using a 240-channel recording system. The results will be presented.

137 Technical Session 8(a) Petroieum Expioratlon X - Seismic Data Processing

MAXIMUM ENTROPY REFLECTION TOMOGRAPHY Peter Whiting Halliburton Geopiiyslcai Services and Dept. Applied Piiysics, University of Sydney Conventional reflection tomography attempts to reconstmct an image of the subsurface velocity field by minimising the differences between measured travel times and the travel times through the proposed image. Such schemes have been widely documented. Conventional algorithms also parameterise depths to major reflectors in the inversion and hence necessitate data times to be measured consistently from these reflectors. In areas of complex geology, strong coherent reflectors may be hard to find. In such cases conventional tomographic imaging would be at least difficult to work with and may be completely inapplicable. The angles of emission and reception can be obtained from the standard reflection seismic data to enable ray tracing for travel times without reflector parameterisation. This means any moderately strong event can be included in the inversion and allows for simpler automatic data picl^ing routines to be employed. Any inversion that is controlled by 'a priori' and/or smoothness constraints implicitly selects a solution that fits the users preconceptions to some degree. The maximum entropy image, on the other hand, ensures that the solution contains no structure other than that implied in the data. Inversions controlled by a maximum entropy criterion have already been used successfully in astronomy and medical imaging and have similar application in seismic traveltime inversion. To facilitate rapid convergence, this nonlinear maximum entropy inversion incorporates subspace searching methods and stages of decreasing parameterisation scale lengths.

MODEL BASED INTERVAL VELOCITY ANALYSIS Shannon Maher, George Mellman and David Hadley* Sierra Geophysics Inc. USA A velocity analysis process, SIVA, is described which combines the information in CMP gathered trace data with interpreted seismic data(e.g. time maps) to create a model of structure and P wave interval velocity. The technique works one depth interval at a time, in a top down fashion. Raytracing is used to estimate the shape of the reflecting surface and determine a family of non-hyperbolic moveout trajectories associated with a range of trial interval velocities. The trace data are stacl^ed along the computed moveout curves, and semblance techniques are used to determine the best-fit velocity for the interval being analyzed. The analysis is performed for a number of gathers to yield a spatially varying interval velocity field. This field is then used to re-determine the shape and depth of the reflector, the model is updated with the velocity field and stmctural information, and analysis continues to the next lower interpreted horizon. The resulting depth/velocity model is fully consistent with all the information in the seismic

138 trace data, as well as the interpreted time picks, and is fully compensated for overburden structure as well as structure and reflection-point smear on the reflector. SIVA analysis may be performed to produce a 2D model from a single line, or to create a 3D model for input data from multiple crossing lines or a 3D survey.

A NEW CMP STACK CONCEPT BASED ON THE BORN APPROXIMATION Friedemann Wenzel CSIRO Division of Exploration Geosclence, Sydney The standard CMP stack procedure becomes questionable as soon as varying reflector dips at about the same TWT are involved. There are several ways to handle this problem ranging from pre-stack migration to DMO. This paper presents a new alternative which employs the same physical model of the medium that is in common use for migration: scatterers embedded in a known reference velocity field. Provided that backscattering can be described by the (first) Born approximation it is possible to derive a zero-offset trace from a CMP gather by a procedure that relies entirely on known processing steps like NMD and stacking.

A HIGHER ORDER APPROXIMATION FORMULA FOR TRAVEL TIME OF REFLECTION WAVES AND ITS APPLICATION TO NMO CORRECTION AND VELOCITY ANALYSIS Yuzuru Ashida^*, Norio Tenma^ and Koichi Sassa"" ^ Kyoto University, Japan 'National Res. Inst, for Pollution and Resources, Japan In reflection seismic method, travel time and velocity of seismic waves are conventionally approximated by a hyperbolic X^/T^ model. This model, however, does not stand with the real multi-layered or heterogeneous earth because of refraction and raypath distortion. The error in approximation progressively increases as the offset becomes large compared with the depth of the reflector. A higher order approximation formula proposed here provides a means of more accurate approximation of travel time and velocity for NMO correction and velocity analysis. Model examination shows superiority of the third order approximation formula over the conventional method.

139 Technical Session 8(b) Mineral Exploration VI - Airborne Resistivity Mapping PROCESSING OF AIRBORNE TEM DATA TO ALLOW ACCURATE CONDUCTIVITY MAPPING Andrew 0. Duncan Aerodata, Perth W.A. Airborne transient electromagnetic systems can provide inexpensive regional scale information about sub-surface conductivity distributions - a valuable tool for mineral explorers and environmentalists. However, accurate measurement of conductivity from the air requires the use of real-time and post-acquisition processing techniques not needed in a ground-based survey. The fact that the platform is airborne and mobile gives rise to four major differences between airborne and ground TEM data: a) b) c) d)

the transmitter-receiver geometry is time-varying, as is the geometric relationship between the system and the ground; motion of the coil sensors in the Earth's magnetic field causes an undesirable low frequency contribution; a limited time is available to stack transients to increase the signal-to-noise ratio for individual readings; the aircraft, being in close proximity to the transmitter antenna, is a source of secondary magnetic fields synchronous in time with transmitter waveforms.

These factors conspire to reduce the ability of airborne TEIVI systems to produce accurate conductivity measurements. This paper summarises processing methodologies which take these problems into consideration. Potentially the most important factor is a) above. While surveying in conductive Australian environments, changes in system geometry along a flight line can create effects which mask subtle conductivity variations and limit the ability of the system to detect discrete targets at depth. These effects can be easily modelled over simple geological structures and strategies for the treatment of geometry-related artifacts in airborne electromagnetic data are being evaluated. The response of the aircraft to the nearby transmitter loop is significant in the case of fixed-wing towed-receiver EM systems. As the receiver moves with respect to the aircraft the vector describing the aircraft's EM response at the receiver changes in magnitude and direction. This interfering response must then be estimated and removed to allow the response of the earth to be observed. Existing airborne systems utilise information from the primary field measured at the receiver to assess the contribution to the measured transient from currents flowing within the aircraft's skin. However, this methodology becomes more difficult as the aircraft traverses increasingly conductive terrain - the primary field becomes modified by the large ground response and is not a good indication of the aircraft's contribution in isolation. A comparison will be made of several techniques for removal of the aircraft response in conductive areas.

140 Due to the limited time available to an airborne EM system to stack and average information, incoherent atmospheric noise can become a problem where it would be insignificant in a ground-based EM survey. The application of non-linear filtering techniques in real time in the aircraft can make enormous improvements in data quality without any deleterious effects. This type of processing completely removes contaminated signals before they can be integrated into stacked data. A comparison of data acquired with and without any filtering of this kind will demonstrate the utility of realtime incoherent noise processing. Airborne EM data and experimental results will be used to highlight the problems noted above. With a combination of new real-time and post-flight data processing techniques, significant improvements can be made in the quality of interpretations from airborne EM data sets.

SIGNAL PROCESSING CONCEPTS FOR AIRBORNE SIROTEM DATA J.P. Cull Dept. of Earth Sciences, Monash University, Melbourne Conventional stacking techniques are not generally suitable for airborne TEM surveys conducted at speeds exceeding 150 km/hr. For late channels (2-50 msec) linear stacking can be tolerated for no more than 8 cycles representing lateral translations of 30-40 m accompanied by variations in coupling. The Nth root stack developed to reduce the effect of spikes in geophysical data can result in considerable distortion complicating the effects of sferics activity. Consequently other procedures are required including bandpass filters to compensate for bird motion, decay curve analysis, and spike rejection based on base station observations or predictive filtering.

AN APPLICATION OF AIRBORNE GEOTEM* IN AUSTRALIAN CONDITIONS A.P. Annan* and R. Lockwood Geoterrex Pty Ltd, Sydney The transition to fully digital data acquisition systems has been the major advance in virtually all areas of geophysics. In 1985, GEOTEM*, the first fully digital airborne EM system, was introduced into commercial operation. Geoterrex commissioned an Australian based GEOTEM system in 1989. Over 250,000 line kilometres of survey have now been flown with the system allowing a greater appreciation of the advantages of a fully digital operation. Data acquired over the Freddie Well massive sulphide deposit, near Mt. Magnet in Western Australia, provides a good example of the advantages of new technology applied to the detection of difficult targets. The deposit was undetected by the early versions of the Mark V and Mark VI INPUT+ receivers. The enhanced Mark V receiver detected the deposit though the response never dominates the high amplitude response of the adjacent overburden. The GEOTEM survey which employed dual transmitter

141 frequencies of 75 Hz and 125 Hz, clearly detected the deposit with late channel response exceeding the amplitude of the surrounding conductive cover. * GEOTEM (Geoterrex Transient EM). Trademark of Geoterrex Ltd. + INPUT (Induced Pulse Transient). Trademark of Barringer Research Ltd.

GEOLOGIC-GEOPHYSICAL MODELS OF KIMBERLITE PIPES V.A. Erkhov USSR Ministry of Geology, Moscow, USSR Geologic-geophysical models of kimberlite pipes, host and overlying rocks have been developed based on long-term studies during exploration for kimberlite pipes in the Siberian and East European Platforms. The identified kimberlite pipes have generally the shape of a cone directed by apex downwards. Contacts of kimberlite bodies with host rocks are almost vertical. Host rocks near kimberlite bodies are poorly deformed. Post-mineralization alterations of host rocks are insignficant and are expressed in the form of serpentinization and femjginization. Kimberlite rocks in the Siberian Platform are divided into two groups according to textural and genetic features: kimberlite and eruptive breccias of kimberlites with serpentine-carbonate cement. In the East European Platform there have been recognized two fades, vent funnel and crateral. Vent funnel facies is usually represented by tuff breccias, xenotuff breccias, eruptive breccias and porphyritic kimberlites. Crateral facies is represented by tuffaceous sedimentary rocks. The Siberian Platform kimberlites are characterized by higher values of magnetic susceptibility with regards to practically non-magnetic host carbonate and claycarbonate rocks jFig. 1). Low-magnetic pipes with magnetic kimberlite susceptibility of less than 60.10"^ SI (5.10"5 CGS) are 10 to 15% of the total number of bodies. There are mainly pipes of small diameter and strongly weathered bodies. Most of the pipes in the southern part of province have low magnetization. Seventy percent of known pipes have a magnetic susceptibility of more than 250.10'® SI. The component induced by the Earth's magnetic field prevails among constituent components of kimberlite magnetization. Remanent magnetization does not exceed one tenth of the induced component, and total magnetization vector has a positive sign. Therefore local positive magnetic anomalies with intensity from 5-8 nT to some thousands of nT are marked over kimberlite pipes in the Siberian Platform. In northern regions of diamond-bearing provinces there occur pipes in which remanent magnetization is substantially higher than the induced one that results in total negative kimberlite magnetization and negative anomalies over pipes. Among practically non-magnetic terrigenous deposits overlying the pipes there occur local sand and sandy conglomerate lenses with accumulations of magnetite or magnetic rock destruction products with magnetic susceptibility from 100 to 1 000.10'® SI.

142 Trappean complex rocks with a high intensity of magnetization are characterized by dominance of remanent magnetization over induced one. Remanent magnetization vector has both positive and negative signs causing both direct and reverse trappean magnetization. Kimberlite density in natural frozen environment to depths of 300 to 500 m is less than that of host rocks in most kimberlite pipes. The difference is 0.05 to 0.10 g/cm^, sometimes it reaches 0.15 g cm^. About 20% of kimberlite pipes do not actually differ in average density from host sedimentary rocks. Longitudinal wave propagation velocity (Vp) in kimberlites in the upper portions of pipes is 2500 to 3000 m/sec and increases at the depth of 1.1 to 1.3 km to 4600 m/sec. At the same time local velocity changes inside the pipes are of complex character. Differences in velocities at the pipe contacts with limestones and dolomites are 1200 to 2000 m/sec. However at the contacts with halogenic and clay layers Vp values in kimberlites and host rocks are similar. In host rocks key reflecting horizons are recognized at depths of about 300, 600, 1400 and 2000 m. Some of the key horizons are well expressed dynamically and have areal distribution. Kimberlite resistivity in the upper portions of pipes in most cases is lower than that of the host carbonate rocks. Polarization coefficient value of kimberlites is somewhat higher than that of host rocks. Radioactivity level in kimberlites is close to background values. Some increase of thorium concentration is observed in the part of kimberlites. The East European Platform kimberlites differ significantly from the known kimberlites in the Siberian Platform as they are altered metasomatically, filled by sedimentary and clay rocks. The main mineral of kimberlites, olivine, is highly altered, and pyrope content is lower. The important physical rock property which has played a significant role during the initial stage of the first kimberlite pipe detection is their total magnetization which depends strongly on magnetic kimberlite susceptibility, and the observed anomalous effect - on magnetic susceptibility of host and overlying rocks (Fig. 2). Magnetic susceptibility of the Quaternary deposits represented by clay-pebble sediments, is (2-500).10"® SI, glacial deposits is (5-3000).10"^ SI. Host rocks are represented by sardstones, siltstones and mudstones - (1-250).10"^ SI, limestones and

dolomites (0-3).10"5 SI and tuffs (100-300).lO'^ si.

Physical properties of the Archean crystalline rocks are poorly studied. Granitegneisses are low-magnetic (10-50).10"^ SI. Magmatites are inhomogeneous, their magnetic susceptibility changes from 10 to 4600.10"^ SI. Magnetic properties of the East European Platform kimberlites are on average lower than those in the Yakutsk diamond-bearing Province. Magnetic susceptibility of eruptive breccias is on average 150.10"^ SI, and that of tuff breccias is 600.10"^. When observed at the surface, anomaly amplitude is mainly 5 to 15 nT, rarer to 30-40 nT.

143 The most favourable conditions of anomaly detection are in the regions of a relatively deep occurrence of low-magnetic basement overlapped by the Vendian low-magnetic deposits. It should be marked that in the upper portion of the section there are always inhomogeneities which may cause anomalies similar in shape and amplitude to anomalies of pipe-like type. The most difficult conditions for magnetic anomaly detection due to kimberlite pipes are observed in areas of near-surface occurrence of magnetic horizon. In this case the role of processing and interpretation techniques increases substantially and application of other geophysical exploration methods becomes necessary. Resistivity values of kimberlite bodies both inside the pipe and in near-pipe space differ essentially in their magnitude. Thus, for example, the Quaternary deposits have = (1-3000) Ohm.m. The Permian rocks underlying them are represented by carbonate rocks and have resistivity values = (150-1800) Ohm.m. The Carbonaceous sandy-clay rocks have more narrow variation limits of pi. = (100-500) Ohm.m. " ' The general character of resistivity variation of rocks with depth correlates with the variation of mineralization level and pore waters. In spite of humidity coefficient decrease, increase of fine-grained rock content in the section and of pore water mineralization provides a critical effect on resistivity decrease with depth. Resistivity

of crystalline rocks is within the range of 300 to 3000 Ohm.m.

Based on sonic log data, the Quaternary deposits have small longitudinal seismic wave velocities (Vp = 1.6 - 1.9 km/sec). In the Vendian section 5 seismic horizons with formation velocities of 2.4 km/sec to 6.0 km/sec can be distinguished. Kimberlite bodies have different velocities Vp depending on their composition. Thus, the upper undivided tuffaceous member of magmatic body has Vp of seismic waves varying within the range of 1.9 to 2.4 km/sec. Xenotuff breccias have Vp = (2.8-3.5) km/sec, eruptive breccias - (2.5 - 3.2) km/sec. ^ The Quaternary deposit density varies within the ranae of (1.9 - 2.1) g/cm^. Rocks which underlie them have a density of (2.4 - 2.9) g/cm^. The Middle Paleozoic sandyclay stratum is substantially lower in density than the Permian carbonates (2.2 - 2.3) g/cm^. The Vendian density section is quite simple as regular increase of density with depth is being determined. Density of magmatic bodies varies essentially in the section. Thus, at their average density (2.25 - 2.35) g/cm^ its decrease in the body top is observed to 2.0 g/cm^ due to weathering. Such variations are distributed mostly deeply in near-contact region of the body and over zones of disjunctive dislocations. Analysis of physical properties of kimberlite bodies and their relationships with host and overlying rocks has provided the opportunity to develop geologic-geophysical models of objects for the Siberian and East European Platforms and create high-efficient geologicgeophysical complexes of kimberlite pipe exploration in quite different geologic sections and environments.

144 V

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Venedict A. Erkhov deputy Chief Geophysical Department USSR Ministry of Geology, Doctor of Geology in mineralogical sciences. After graduating from the Perm State University (USSR) in 1959, he was engaged in prospecting for mineral deposits including diamonds, gold, tin, copper and rare-earth metals, carried out in different regions of the Soviet Union using a variety of geophysical exploration methods. He also concerned himself with the studies of the deep structure of the Earth's crust and upper mantle. Dr Erkhov has experience in training specialists in geophysics and has published over 50 scientific papers.

146 Technical Session 8(c) Coai, Groundwater and Engineering 11 - Coai

HIGH RESOLUTION SEISMIC FOR RESOLVING COAL SEAM STRUCTURE IN DIFFICULT TERRAIN J. Saunders''

P. Lamb^ and D. Sweeney^

''international Geopiiysicai Consultants Pty Ltd ^Kembia Coai and Coke Pty Ltd ^Pazground Pty Ltd The paper describes a high resolution seismic survey in the Southern Coalfields of New South Wales over rugged terrain in areas yet to be mined. The aim of the survey was to identify faults in the working seam, which are very disruptive to longwall mining operations. Rapidly changing topography with deep gorges, swamps and dense bush created access and environmental difficulties for seismic operations. For the first time attempts have been made to acquire seismic data across difficult gorge and swamp country. The techniques used were successfully adapted from previous surveys carried out in less difficult terrain. Current indications are that there will be minimal impact on the environment. The data collection and processing parameters developed enabled good coherent data to be obtained across deeply incised terrain. Faults with various throws have been interpreted.

A NUMERICAL STUDY OF ELECTROMAGNETIC WAVE PROPAGATION (RIM) IN DISRUPTED COAL SEAMS G. Liu^*, G. Smith2, 8. Thomson^, K. Vozoff^ and P. Hatherly^ ^Centre for Geophysical Exploration Research, Macquarie University ^School of Mathematical Sciences, University of Technology, Sydney ^Mine Exploration and Technical Services ^Australian Coai Industry Research Laboratories Finite difference and integral equation methods are used to model electromagnetic wave propagation in a disrupted coal seam. The results show that easily detectable changes of electromagnetic signals will occur if a modest geological anomaly (e.g. a 60 x 6 x 2 m^ dyke) disnjpts the seam.

147 3D SEISMIC REFLECTION: EXAMPLES OF ITS APPLICATION TO MINE PLANNING AND SAFETY IN AUSTRALIAN COALFIELDS A.N. Lambourne^*, P.J. Hatherly^ and B.J. Evans"' ^Dept. Exploration Geophysics, Curtln University ^ACIRL, Nortii Ryde, NSW Two low fold, high resolution, three-dimensional {3D) seismic reflection data sets have been used to delineate potential hazards in underground mining operations in the Sydney Basin, New South Wales. Data were acquired using orthogonal source and receiver lines, and were conventionally processed. Interpretations were performed on an interactive work station. Results from the first survey have resolved a previously ambiguous interpretation, and produced a preferred location for future longwall panels. Subsequent mining and in-seam drilling have confirmed the interpretation. Results from the second survey have defined a synclinal feature which has yet to be proved by drilling or mining.

SEISMIC MODELLING - AN AID TO SHALLOW REFLECTION SEISMIC ACQUISITION AND INTERPRETATION O. Dixon

and S. Hearn^

^ Dept. of Resource Industries, Brisbane ^University of Queensland INTRODUCTION Finite-difference modelling of the elastic wave equation is used to generate synthetic seismic reflection field records over given geological structures. The analysis of these records, including production of processed seismic sections, indicates potential acquisition and processing problems, and aids in planning and interpretation of surveys. High resolution seismic reflection surveys are currently employed in coal exploration and mine development. The best acquisition and processing parameters are usually determined by trial and error. Acceptance of the seismic reflection technique has been limited by a lack of clear foreknowledge of what can be detected, and poor understanding of the resolving power. Detection capability and resolving power depend on local conditions - depth and regularity of weathering, surface topography, seismic properties of the target and the surroundings. Unreasonably high expectations of the technique are sometimes generated by the presentation of ideal case examples. These expectations are seldom met, leading to a general dismissal of seismic methods, even in situations where the data can provide valuable information. Modelling of the geological structure can determine whether the target can be successfully resolved, before money is committed to the field survey. Preliminary planning of the survey may also be done prior to test shooting. Validity of the synthetic seismic record depends on the accuracy of the geological model. For coal resource

148 assessment, sufficient drilling and logging will have been completed to provide these data. METHOD Numerical solution of partial differential equations via finite- difference and related techniques has established itself as a valuable tool in the simulation of physical wave phenomena (Altermen and Karel, 1968). Such techniques yield accurate synthetic seismograms for arbitrarily inhomogeneous media. Other modelling methods such as ray-tracing are faster, but are restricted in the models used and do not provide complete solutions for converted and boundary waves. First-order finite difference formulations for two dimensional structures (Kelly and others, 1976), and three dimensional structures with cylindrical symmetry (Hatherly,1983), are used to generate the synthetic seismograms. Transparent boundary conditions derived from paraxial approximations to the wave equation are used to eliminate edge reflections (Stacey, 1988). The grid spacing and time step that are required for acceptable stability and accuracy depend on the elastic parameters of the model (Man and Loewenthal, 1976), and on the dynamic range of the arithmetic (eg. single or double precision). A tradeoff occurs between accuracy and computing time. On a mid-range computer (PRIME 9750) a typical model (512 X 512 grid with 1000 time steps) requires approximately 5 hours computing time. This is conveniently run overnight when there is little demand on the system. Developments in computer technology now allow useful models to be run on desktop microcomputers. The output of the modelling program is a synthetic field record. It may be processed through a standard reflection processing sequence. A range of acquisition parameters are tested on each modelling run to determine the best configuration for a particular target. Comparison of the synthetic records and field data aids in identification of events and allows for separation of noise and signal. APPLICATIONS Finite-difference modelling has been used to test the seismic response for a variety geological problems : •

testing detection and resolution limits of faulting and multiple seams in coal measures.

•

obtaining seismic data from beneath near-surface basalt.

•

analysis of ground roll, and effects of geophone arrays, burial of geophones and depth of shot.

•

evaluation of ground motion for placement of seismometers for microearthquake recording.

•

modelling of underground coal mine collapses, which were detected on a microearthquake network.

149 EXAMPLE Seismic reflection data from areas of near surface basalt are generally poor quality. The example in Figure 1 shows the sequence of processing a synthetic seismic record from a simple model of basalt overlying sedimentary rocks. The model (a) represents a single coal seam beneath a thick layer of basalt with a 20 metre deep weathering profile. The source is an impulse with a centre frequency of 80 hertz at a depth of 10 metres within the weathered layer. Geophones are situated at 10 metre intervals on the surface, recording both the vertical and horizontal motion. The record of vertical motion (b) is dominated by ground roll. Recording of both vertical and horizontal motion enables the study of wave propagation in the near surface layer. In this very simple case, the Rayleigh wave and various P and S arrivals can be distinguished. Models with varying weathering, and irregular interfaces produce a much more complex picture. F-K filtering (c) successfully removed the masking noise, but also attenuated the reflection signal on the outer traces of the geophone spread. The primary reflection from the coal seam, at 0.12 seconds two-way time, is now clearly defined, as well as multiples and converted waves. There is evidence of a reflection from the base of the basalt, at 0.05 seconds two-way time, but it is hidden amongst residual shot generated noise. The normal moveout corrected record (d) shows the P-wave reflection from the coal seam, followed by a converted S-wave arrival. On a 24-fold stacked section (e) the primary reflection from the coal seam is prominent, but later multiples are also present. The reflection from the base of the basalt layer cannot be identified. In this simple example the desired reflection signal could be retrieved from the noise. In situations of more complex weathering and varying basalt thickness, the surface noise is more difficult to remove in processing. The modelling can be used to determine field parameters to reduce this noise on recording. CONCLUSIONS The finite-difference technique provides an accurate means of assessing the seismic response from given geological models. Definition of a particular target can be tested prior to field operations, allowing informed decision on exploration priorities. ACKNOWLEDGEMENTS The numerical modelling was done within the Department of Resource Industries, Queensland. The processing was carried out at the University of Queensland, Department of Geology and Mineralogy. O.Dixon publishes with the permission of the Chief Government Geologist, Department of Resource Industries.

150 REFERENCES Alterman Z., & Karal F.C., 1968. Propagation of elastic waves in layered media by finite difference nfiethods. Bulletin of the Seismological Society of America, 58, 367-398. Hatherly P.J., 1983. The analysis of shallow refraction seismograms. Ph. D. thesis. School of Earth Sciences, Macquarie University, (unpublished) Man A., & Loewenthal D., 1976. Instabilities of finite difference schemes due to boundary conditions in elastic media. Geophysical Prospecting, 24, 431-453. Kelly K.R., Ward R.F., Treitel S., & Alford R.M., 1976. Synthetic seismograms: a finite difference approach. Geophysics, 41, 2-27. Stacey R., 1988. Improved transparent boundary formulations for the elastic-wave equation. Bulletin of the Seismological Society of America, 78, 2089-2097.

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152

Technical Session 8(d) Petroleum Exploration XI - Cretaceous to Recent Tectonics TERTIARY STRUCTURING IN SOUTHWEST QUEENSLAND: IMPLICATIONS FOR PETROLEUM EXPLORATION R.D. Shaw Petroconsultants Australasia Pty Ltd, North Sydney Southwest Queensland is covered by sediments of the Eromanga Basin. Although deposition occurred during a structurally quiet time the basin shows extensive folding, faulting, uplift, and sequence truncation. This structuring is attributed to postdepositional (post-Cenomanian) tectonism involving essentially mild, east-west directed, basement compression. The detailed chronology of this tectonism is vague but uplift began during the Late Cretaceous and at least two discrete episodes of Tertiary folding are recognised. Deformation also involved the reactivation of pre-existing basement trends. The style of deformation is always dominantly compressional, although along the east-southeast oriented Gidgealpa-Merrimelia-lnnamincka (GMI) trend wrenching is conspicuous. Across areas of shallow basement, deformation has been preferentially expressed as vertical displacements involving the formation of reverse fault bounded, tilted blocks, pop-up blocks, and trap door structures. As hydrocarbon traps, these structures have limited prospectivity. Formation of these structures post-dates the peak phase of hydrocarbon generation and critical closure is often fault dependent. Where sediments of the Adavaie Basin are preserved, Teritary deformation reactivated Kanimblan structural trends resulting in the development of folds and faulting. Folding and faulting has modified pre-existing structures and created new structures within the overlying Eromanga sequence. The common occurrence of stacked hydrocarbon pools not filled to spill-point, often located adjacent to reactivated fault escarpments, provides strong evidence that Tertiary, reactivated, reverse faults do not seal and provide conduits for vertical migration of hydrocarbons up into reservoirs lying in crestal locations. The most prospective structural targets appear to be those involving reactivated, large palaeohighs. By absorbing much of the Tertiary deformation along their flanks, the crestal integrity of the stmcture remains relatively intact. Tertiary deformation and espcially the uplift of the eastern margin established the current regional groundwater movements and hydrocarbon drainage patterns. "C-P" isopachs, corrected for post-depositional thinning, provide the best indication of drainage patterns during the critical period of peak generation. Contemporary hydrocarbon drainage patterns were probably established during the Middle Tertiary and after peak hydrocarbon generation. Thus predictions of hydrocarbon drainage areas based on structural maps, such as the "C" or "P" horizons, can lead to erroneous conclusions. "C-P" isopachs, corrected for post-depositional thinning, provide the best indication of drainage patterns during the critical Late Cretaceous and Early Tertiary period of peak generation.

153 STRUCTURAL STYLES, CEPU OIL FIELDS, JAVA, INDONESIA N. Soeparyono^* and P. Lennox^ "•PPT-MIGAS Jin Sarogo 1 ^Dept. Applied Geology, UNSW Reinterpretation of 18 local and 7 regional seismic lines in north east Java, numerous exploration wells and their integration with newly measured stratigraphic sections has enabled a new structural model to be developed for the Cepu oil fields. The generally shallow water limey-clastic sequence developed in a rifting back-arc basin with many northeast-southwest oriented basement faults. Deformation in the early Middle Miocene caused reactivation of the basement faults in the Nglobo-Semanggi area with wrenching and the initial development of flower structures. This deformation caused areally restricted erosion of the main reservoir rocks in this area. Later Pliocene deformation accelerated the development of the flower stnjctures in the Nglobo-Semanggi area which were reflected at the surface as a series of en echelon, hydrocarbon-bearing anticlines. The Tambakromo-Kawenga area underwent minor north over south thrusting along east-west oriented listric, reverse faults with detachment at shallow depths and the development of hydrocarbon-bearing anticlines in the cover sequence. It is possible that further hydrocarbon-bearing folds exist in the subsurface north of the Tambakromo-Kawengan structure. These folds would be related to blind imbricate thnjsts parallel to the Tambakromo-Kawengan thrust.

TECTONIC EVOLUTION OF BASS STRAIT ORIGINS OF TERTIARY INVERSION Ian M. Young, Mark A. Trupp* and Michael J. Gidding The Shell Company of Australia Ltd., Melbourne The sedimentary basins of Bass Strait display a marked asymmetry of structure. This is particularly evident in the Gippsland Basin and Torquay Sub-basin where Tertiary structures are better developed along their northern margins. The origins of this asymmetry are reviewed and a structural model for the evolution of Bass Strait basins set out. Mapping of the regional structures developed at three stages of the region's evolution demonstrates that dextral strike slip movement was important throughout. During the Cretaceous the regional stress regime was dextral transtensive, changing to transpressive by the mid-Eocene. Despite early similarities in these basins' formation, their Tertiary histories diverge contributing to the wide variations in hydrocarbon potential seen today. It is suggested that the present day structural asymmetry is a consequence of partial inversion of initial half-graben basin geometries.

154 Technical Session 8(e) Regional, Crustal and Geothermai IV Electrical Conductivity, Temperature and Petrology THE ELECTRICAL CONDUCTIVITY STRUCTURE OF THE OCEANIC LITHOSPHERE BENEATH THE TASMAN SEA G.S. Heinson* and F.E.M. Lilley Research School of Earth Sciences, ANU Seafloor magnetotelluric observations of natural fluctuations of the Earth's magnetic and electric fields provide information about the electrical structure of the suboceanic lithosphere and upper mantle. However, such measurements may be distorted by three-dimensional induction effects in the overlying ocean, associated with the geomagnetic coast-effect and changes in bathymetry. In the present paper electromagnetic three-dimensional modelling is applied to the Tasman Sea. A thin-sheet algorithm is used, and calculated magnetotelluric parameters are compared to observations made during the Tasman Project of Seafloor Magnetotelluric Exploration (TPSME). The model calculations suggest that, away from coastlines, three-dimensional induction in the ocean distorts the electromagnetic signature of the sub-oceanic lithosphere and upper mantle in a frequency-dependent but smooth manner. The model calculations thus permit the observed TPSME responses to be corrected for distortion, to give improved estimates of the electromagnetic response of the solid-Earth underlying the observation sites. Inversion of such (corrected) response estimates for one-dimensional electric structure reveals that the structures beneath 55 and 70 Ma seafloor sites are very similar. Furthermore, constraints imposed by the thin-sheet modelling indicate that to replicate the TPSME observations, a poorlyconductive (less than 10"^ S/m) upper lithosphere is required. This result implies that electric currents which are induced and 'trapped' in the ocean may contaminate magnetotelluric observations far inland.

HETEROGENEITY IN THE THERMAL STATE OF THE LOWER CRUST AND UPPER MANTLE BENEATH EASTERN AUSTRALIA N.J. Pearson""*, S.Y. O'Reilly"' and W.L Griffin^ ^School of Earth Sciences, Macquarie University ^CSIRO Division of Exploration Geoscience, North Ryde Xenolith-derived paleogeotherms for the lower crust and upper mantle beneath the eastern margin of the Australian craton (EMAC) and beneath the Phanerozoic Tasman Fold Belt (south-eastern Australia - SEA) indicate distinct thermal regimes. The SEA geotherm passes through 800°C at 7 kbar and 1200°C at 25 kbar. The strong curvature of the constructed geotherm from 10 to 30 kbar indicates significant advective heat transfer in the lower crust and upper mantle. The EMAC geotherm lies some 150 to 200°C below the SEA curve and stretches from 600°C at 7 kbar to 1000°C at 21 kbar. This is well above the steady state conductive geotherm calculated from (low) surface heat flow for cratonic areas.

155 The lower crustal suite xenoliths from EMAC and SEA are dominated by mafic lithologies. The EMAC mafic xenoliths represent igneous intrusions into the lower crust and uppermost mantle metamorphosed to granulites and eclogites. The large lateral variations in temperature at the base of the crust (depending on tectonic environment) are significant to the relative stability of eclogite and granulite mineral assemblages. The restriction of lower crustal eclogite suites to cratons or craton margins, and their apparent absence from younger terranes, is a consequence of this temperature difference. The definition of distinct thermal regimes in different tectonic settings provides a basis for examining the response of magnetic properties and Vp-depth profiles with changes in temperature. The seismic Moho and the crust mantle boundary do not coincide in areas that have high geothermal gradients. Differences in the seismic characteristics of cratonic areas and areas with high geothermal gradients can be modelled as the effect of temperature on similar lithological columns and do not necessarily imply large petrographic differences. A lower crust beneath cratonic areas dominated by eclogite facies assemblages may be misinterpreted seismically as mantle.

IMPLICATIONS FOR GEOTHERMAL PROFILING FROM MAGNETOTELLURIC DATA J.D. Gray* and J.P. Cull Dept. of Earth Sciences, Monash University Laboratory studies of the temperature dependence of the electrical conductivity of rock materials can be used to relate electrical conductivity to temperature in the Earth. Electrical conductivity models advanced for central and southeastern Australia are compared with profiles predicted from such laboratory measurements and are then used to generate representative magnetotelluric response curves. The response curves differ sufficiently to give confidence in their use to detect gross conductivity changes at depth. Observed data from Broken Hill and Ivanhoe, NSW, are interpreted to indicate a temperature contrast in the upper mantle of some 200°C between these two sites (hotter to the east beneath Ivanhoe). The temperature at these large depths is a vital factor in constraining models of crustal underplating and intrusion.

IMPORTANT PETROLOGICAL EVIDENCE FOR THE EROMANGA-BRISBANE TRANSECT Y.D. Chen""*, S.Y. O'Reilly"' and W.L Griffin^ ^School of Earth Sciences, Macquarle University ^CSIRO Division of Exploration Geoscience, North Ryde The seismic data from the Eromanga-Brisbane Transect are very important in revealing the nature of lower crust and upper mantle, and crustal/mantle boundary across the Eromanga Basin, Australia. However, a geological realistic interpretation of the seismic data can only be reached when petrologic data are available and integrated with the geophysical data. Therefore, a suite of upper mantle-derived xenoliths from Mt. Gowrie and a locality near Toowoomba were studied to provide direct petrological evidence on

156 the compositions, crust and mantle rocl< types and the depth of the crust/mantle boundary for that part of the Transect which is close to the xenolith localities. The xenolith suites studied consist mainly of upper mantle wall-rock spinel Iherzolites, with minor occurrences of pyroxenites and wehrlites. The spinel Iherzolite xenoliths are composed of the typical 4 phase assemblage (olivine, orthopyroxene, clinopyroxene and spinel); their fabrics include coarse, porphyroclastic and mosaic-porphyroclastic varieties (Harte, 1977). This indicates that the upper mantle Ilthologies in this part are similar to those in other regions beneath the eastern Australian basaltic provinces. Temperatures of the Iherzolite xenoliths calculated using the thermometer of Sachtleben & Seek (1981) range from 930 to 1040°C. When these temperature values were projected to the xenolith-derived, eastern Australian Geotherm (O'Reilly and Griffin, 1985), equilibrium pressures from 10.5 to 15.5 kilobars are indicated, these being equivalent to depths between 33 and 50 km. The occurrence of volumetrically significant Iherzolites has been considered to mark the crust-mantle boundary; this rationale Indicates that the depth of crust-mantle boundary beneath the area of Mt. Gowrie is about 33 km. This is consistent with the depth deduced from the seismic data near the area. The Eromange-Brisbane seismic traverse (Finlayson, 1990) shows a package of reflectors above and below this depth. The xenolith data suggest the base of the crust is located within this zone of reflectors. Even though the Ilthologies and thermal states of this part of the upper mantle are similar to those in other regions beneath the eastern Australian basaltic provinces, the xenoliths also record some important distinctions. For instance, when compared with mantle xenoliths from western Victoria localities, Iherzolite xenoliths near Toowoomba do not show modal metasomatism, have a narrower range and lower abundance in incompatible elements, and indicate relatively more primitive isotope (Sr, Nd) characteristics. This hints that there may exist distinct geochemical terranes in the upper mantle beneath eastern Australia.

157 Plenary Session V

A CASE HISTORY OF GEOSCIENTISTS K.R. Glasson Consulting Geologist, MInnmurra, NSW The address is perhaps an introductory case for the two speal<ers who will outline the case histories of both the Mineral and Petroleum Discoveries, bearing in mind the contribution of the various components that make up the Geoscience profession, i.e. geophysicists, geologists, geochemists etc. I want to review the case histories of the geoscientists who have contributed to the discovery of our mineral deposits. Anyone who has studied the case history of the discovery of diamonds in Australia or nickel in Western Australia, or the more recent copper, gold, uranium discovery at Olympic Dam in South Australia, will appreciate the vast amount of data that has accrued and has been applied by geoscientists involved in these programmes that have evolved from the respective company "in-house" expertise. In Monograph 17 "Geological aspects of the discovery of some important Mineral Deposits in Australia" recently published by the AusIMM, these discoveries have been reported in detail. In this address I want to discuss a number of parameters which I believe have shaped the thinking of geoscientists in exploration. 1.

Geoscientists - the evolving change from academic/government experience to industry trained and the development of the specialist groups within the profession, i.e. geologists, geophysicists, geochemists.

The compilation of basic data on which the geoscientist has worked and how early success has given the impetus for the funding of the continuation of data collection.

The contribution of the mining/exploration companies to the accumulation of background data, especially in detail mapping.

The evolution of concepts based on geophysical and geological models.

The development of the technologies necessary to prove up or disprove these models.

In the address I want to mention the cross fertilisation that has occurred between those engaged in mineral exploration and those engaged in oil exploration. Finally I want to discuss some of the strengths and weaknesses of our profession. Perhaps the two most important developments have been; a)

the growth of geophysics, the training of geophysicists in the universities, and the expansion in numbers and experience of those teaching geophysics, and

158 b)

the increase in numbers and tlie development of expertise in the consultant/ contract group.

THE TALE OF THE BIG OCKER AND THE FINK: The Evolution of Geophysics In BHP Phillip G. Harman BHP-Utah Minerals International, East Perth WA The growth of geophysical expertise in BHP has paralleled the development of geological science in the Company's businesses. This has occurred in three main areas: in the extraction of minerals where the aim has been to help improve efficiency and safety; in the upgrading of the reserve base of the Company's ongoing operations; in the drive for diversification away from existing businesses through the discovery of major new mineral deposits. Geophysics in BHP had its beginnings in 1950 with magnetic surveys to help locate additional iron ore reserves in the Middleback Ranges. Since then, the main responsibility for geophysical application and development in the Company has rested with the Minerals Exploration Group. This has taken the form of organising and supervising geophysical programmes as part of exploration activities and when required, advising various Company mining operations on the use of geophysics. This latter role has led to developments in the area of coalfields geophysics where exploration department geophysicists were involved in the introduction of high resolution reflection and in-seam seismic techniques. The role of geophysics in exploration has varied over the years, depending on the types of deposit targetted. Magnetics and gravity had particular application when the search was mainly for steel industry raw materials. In the early 1960's, aeromagnetic and seismic surveys were the first stages of the early exploration which led to the discovery of the Bass Strait oil and gas fields and the birth of a new business. In the late 1960's, exploration became more directed at base metal targets and electrical methods grew in importance. Aeromagnetic surveys have been the most consistently and widely applied geophysical method. Technological developments over the last ten years have seen increasing sophistication in the way geophysical data are acquired and processed. Parallel research has led to a greater understanding of geological and geophysical phenomena which effect data quality and interpretation. BHP has consistently supported the development of new technology by testing and applying new techniques and by research and development programmes both in-house and with external groups. The role of the geophysicist in the modern exploration group has evolved beyond that of the pure technocrat. Geological understanding is critical to effective interpretation. This requires geophysicists to have greater geological skills and be committed to using them in the interpretation of large data sets. BHP management is committed to ensuring the tools are available and the right people are employed in an environment which allows this to happen.

159 THE CASE FOR EXPLORATIONISTS J.P. Froning BHP Petroleum, Melbourne The invitation from the Conference Organising Committee emphasises "the growing inter-relationship of the professions" involved in the exploration for oil and gas and indeed "the necessity, for all, of a broader knowledge base." It is with this theme and goal in mind that we examine the role, not of geologists or geophysicists, but of explorationists in several case histories. The task of creating explorationists is difficult. The true explorationist is one who looks for oil and gas using all of the skills available. These skills include geology, geophysics, petrophysics, palaeontology, geochemistry, and reservoir engineering. Some of these skills the individual will possess; for others he will need the involvement of specialists. But he directs the effort, knows what is required and more importantly, combines the information into a prospect and, if successful, into a case history. Case histories are simply the stories of successful exploration, and successful exploration involves a hierarchy of knowledge. One must satisfy certain minimum criteria before moving to the next level of knowledge or understanding. The necessary hierarchy, starting with the most fundamental, is: structure, reservoir and seal, source and migration (including maturation and timing). With this concept in mind we will examine three areas: the Bass Strait, the Carnarvon Basin and the Browse Basin, to see how explorationists were able to resolve the difficulties at each level of this hierarchy, resulting in discoveries and the successful exploitation of same. In conclusion, companies are urged through their training, both formal and on-the-job, to encourage exposure to all of the disciplines involved in exploration. In evaluating the risk associated with a drilling prospect in a wildcat area, proper attention should be given to the hierarchy of knowledge (and riski) in determining the probability of success and subsequent economic evaluations. As an area matures, the first levels of the hierarchy become more predictable and the emphasis (and riskingi) shifts to the other levels. Finally, we begin to consider stratigraphic plays when our confidence has reached a satisfactory level on each tier.

160

Technical Session 9(a) Petroleum Exploration Xii - interpretation i\/lethocls SEiSMiC AVO ANALYSIS OF A PERiVIiAN GAS SAND AT KERNA FIELD, COOPER BASIN, SOUTH AUSTRALIA J. Pinchin^* and A.B. Mitchell^ ^Gaffney Cllne and Assoc. Ltd - formerly SANTOS Ltd 2NCPGG

The Kerna gas field is located in the south-central part of the Cooper Basin close to the large Dullingari and Toolachee Fields. Kerna is a domal anticline and contains gas structurally trapped within sandstones of the Early Permian Patchawarra Formation. The overlying Epsilon Formation sands also contain gas which may be stratigraphically trapped around the south and west flanks of the field. Seismic reflection amplitudes are used to map the extent of this Epsilon gas sand. Seismic modelling studies show that the gas sand displays an amplitude-versus-offset (AVO) response which distinguishes it from a wet sand or from a coal bed at the same stratigraphic level. Constructive and destructive interference from the top and base of the gas sand, and from overlying coal seams, have a marked effect on the overall seismic stack response of the target horizon. The modelled AVO response shows a good correlation with AVO changes on c.d.p. gathers from seismic lines across the area. The spatial distribution of the AVO anomalies (AVO increases), and of the overall seismic stack response, has been mapped across the field and can be used to locate future appraisal and exploration wells. This study has implications for other areas of the Cooper Basin where adequate separation between coal beds and gas sands allows the AVO effect of the latter to be observed. These AVO effects can then be used as a direct indicator of gas in stratigraphic or even structural traps.

HARRIET FIELD TWO DIMENSIONAL MODELLING STUDY Mark W. Ballesteros Hadson Energy Limited, WA A series of two dimensional interpolation models was constructed using wells from the Harriet Field. These models were designed to assess the effects of: (a) shale interbeds within the Flag Sand and (b) the fluid content (i.e. gas vs. oil vs. water) on the seismic response. The model responses closely resemble the seismic data. The results indicate that both of these factors have an impact on the seismic expression of the top Flag Sand interface and the associated amplitude anomaly which occurs immediately below it. In addition, apparent velocity variations which have been observed over the field are probably related, at least in part, to tuning effects resulting from shale and fluid content variations.

161 In the models constmcted, the presence of hydrocarbons correlates with low frequency zones in the seismic data which occur in association with high amplitude in the trough beneath the top Flag Sand reflector.

COASTAL EOLIAN DEPOSITS AND OIL PRODUCTION: MODERN AND ANCIENT EXAMPLES Steven G. Fryberger Ampol Exploration (USA) Inc Eolian dunes and related fades are a significant component of coastal sediments in many areas worldwide. Settings include narrow shoreline sand strips, barrier and back barrier settings, and coastal impingement by major ergs that extend landward great distances. Each of these settings offers significant potential for hydrocarbon accumulation in stratigraphic traps within generally porous and permeable eolian sands of both carbonate and quartzose composition. Eolian origin of many shoreline sandstones has been difficult to recognize due to sedimentologic complexity. This may in turn have slowed exploitation of hard-to-find yet prolific hydrocarbon reservoirs in eolian shoreline deposits. These deposits may be several meters thick but extremely widespread, or on the other hand, exist as many isolated pods in the subsurface depending upon conditions of deposition and preservation. The Minnelusa formation of NE Wyoming, USA, is an excellent example of a coastal impinging erg, in which much of the oil (approximately 750 MMBO) is trapped in fields ranging in size from 1 MMBO to 40 MMBO in the coastal zone of a Permian sand sea. The oil is trapped in eolian dune reservoirs in the larger fields, such as Raven Creek, by a combination of an irregular unconformity topseal and bottomseals consisting of shoreline marine carbonates intercalated with the dune sands. Numerous other traps exist solely by virtue of the enclosure of eolian sands by marine sabkha and shoreline carbonates. Both the large and small scale petroleum traps are detectable using high resolution seismic data. The basis for use of the high resolution seismic approach is the impedance contrast between low velocity eolian sands and high velocity carbonates in the Minnelusa, as discussed further by Frederick, (this volume), in the second part of our joint presentation. While the Minnelusa formation provides a good example of the potential of coastal eolian deposits as petroleum reservoirs, the developed play itself, as a mature play in the USA illustrates the potential that may exist in shoreline plays in other less drilled basins worldwide, including those in Australia. Further, modern Australian coastal deposits themselves comprise an extensive resource for the continuing development of realistic subsurface exploration models based on modern analogs for both carbonate and quartzose terrains.

162 THE SEARCH FOR SUBTLE STRATIGRAPHIC TRAPS WITH HIGH RESOLUTION SEISMIC DATA: EXAMPLES FROM THE POWDER RIVER BASIN, NE WYOMING, USA John B. Frederick Ampol Exploration (USA), Inc Optimizing the temporal resolution of seismic data in both the acquisition and processing stages increases the detection rate of subtle, multiple stratigraphic traps in complex lithologic sequences. Field sizes ranging from 1 MMBO to 40 MMBO are found in the coastal fades of eolian sandstone reservoirs of the Permian Minnelusa Formation in northeast Wyoming, USA. Generally, three main trap styles exist: (1) an erosional unconformity providing the top and lateral seals with a shoreline marine carbonate acting as the bottom seal; (2) marine carbonates providing both the top and bottom seals; and (3) topographic relief at the top of dune complexes that lack a bottom seal but are overlain by marine carbonates. Usable frequencies in excess of 100 Hz from depths greater than 3300 m allow resolution of 10 m sandstone reservoirs with 15-20% porosity. With this frequency it is possible to distinguish not only porous sandstone reservoir signatures, but also the trapping mechanisms involved. High resolution seismic data acquired prior to a recent oil discovery is shown here to demonstrate a successful methodology used to discover and develop Minnelusa oil in subtle stratigraphic traps. Successful exploration in coastal deposits such as the Minnelusa Formation requires an integrated approach to exploration. This includes broad band, high frequency seismic data acquisition and processing with a combined geological and geophysical interpretation. Using these techniques, discoveries are possible even in mature basins at exploratory drilling success rates well above the US onshore industry average of 812%.

163 Technical Session 9(b) Mineral Exploration Vii - Case Studies

PROTEROZOiC DYKES AS AN iNDiCATOR OF STRUCTURAL CONTROLS ON GOLD DEPOSITS IN THE YILGARN BLOCK, WA D.J. Isles and A.C. Cooke* World Geosclence Corporation Limited, Pertli Major Archaean gold districts tliroughout ttie world are commonly associated with late intrusive, mafic dykes suites. Most often these are of Proterozoic or late Archaean age and generally considered a product of processes associated with the formation of Archaean cratons. The relationship between these dykes and specific deposits or gold camps is intriguing since there is good evidence for a strong spatial association although the dykes are clearly much younger than the mineralisation. It is possible therefore that the dykes and gold have a causal relationship, whereby they are not directly related to each other but are both related to a common factor. A model for this common origin of both dykes and gold deposits may be found in recent studies into the structure and stress regimes of the Archaean goldfields of the WA Yilgarn Block. Study of the regional stmcture in the Eastern Goldfields of the Yilgarn, made possible in recent years through high-resolution regional aeromagnetics, clearly shows the dominant strain on the region has been considerable shortening along an axis between 060° and 090°. This is based on the NNW trend of the regional fabric and the trends of the main dyke suites, assuming the main fabric of the greenstone belts is due to flattening and not horizontal shearing, and that the 030°-090° dykes trends are related to tensile fracturing of the crust. Both these assumptions are supported by observations made from the regional aeromagnetics. For instance, the tensile origin of the dykes is supported by their 'Griffith fracture' style and the lack of any significant displacements along their strike. Figure 1 illustrates the form and distribution of the dykes in the Norseman to Laverton Region, interpreted from Aerodata non-exclusive aeromagnetic surveys. A general classification of the dykes has been made on the basis of trend and form. In the Eastern Goldfields model for approximately E-W shortening it follows that the principal stress must have been compressive along the axis of shortening. If this stress regime was responsible for both the deformation of the greenstones and the emplacement of the dykes then it was probably the dominant stress during gold mineralisation. In these types of stress regimes the favoured sites for structurally controlled gold mineralisation are those of high differential stress, controlled by the geometry of structures and geology in conjunction with the lithological properties. It is possible to model these complex mechanics using sophisticated computer modelling packages based on the Distinct Element Method of modelling deformation in discontinuous blocks under specified boundary conditions. This technique is currently being applied commercially and the results support the proposition that gold is associated with areas of high differential stress under E-W compression. The common link between gold mineralisation and the dykes is the centres of high differential stress. Our simple model for gold mineralisation predicts these centres to be favoured sites for mineralisation, due to fluid overpressuring and fracturing. And the structural style of the dykes is consistent with a tensile fracture system in which numerous centres of high differential stress have been the centres for propagation of

164

fractures along the axis of maximum compressive stress. Hence, it is possible that individual dyke segments originate from the same areas as gold deposits are formed in, due to these areas being subject to high differential stresses under a regime of E-W stress. In the case of the Eastern Goldfields there appears to be a more complex system of conjugate tensile fractures. It is also evident that many other factors play important roles in the localisation of gold deposits, but few of these factors can be characterised.

AIRBORNE, GROUND AND BOREHOLE ELECTRICAL SURVEYS - A CASE HISTORY OF THE FLYING DOCTOR DEPOSIT, BROKEN HILL E.D. Tyne""* and S.S. Webster^ •"Geological Survey of NSW, St Leonards, NSW ^Austlrex International Ltd, Gordon, NSW The Flying Doctor deposit is typical of Broken Hill Pb-Zn-Ag style mineralization and has become an important geophysical test site for the evaluation of many electrical and electromagnetic techniques. A synthesis of airborne, ground and borehole survey results from the deposit provides a valuable insight into the electrical characteristics of this style of base metal mineralization and allows the suitability of each survey technique to be investigated. Furthermore, general conclusions from the case history study are applicable to exploration for base metals in other geological environments. Survey results are presented from airborne transient electromagnetic (GEOTEM) surveys, ground self potential (SP), resistivity, time, frequency and spectral induced polarization (IP) and JEM surveys as well as borehole electrical logging and mise-a-lamasse surveys. The airborne ElVI results over the shallow, steeply dipping massive sulphide deposit indicate the deposit to be a moderate conductor. This is in accordance with bulk estimates of conductivity made from borehole logging. Time and spectral domain IP surveys clearly define the characteristic surface electrical response of the deposit as a coincident low resistivity and moderate IP anomaly, the source of which appears to be at a depth of about 15 m. It is not possible to uniquely resolve mineral discrimination parameters from the surface IP data due to EM coupling dominating to relatively low frequencies. Borehole spectral IP measurements indicate a variable polarization time constant for this mineralization, but a short time constant of only several seconds appears common. At low frequencies, there appears to be no distinct advantage in the use of either time or phase domain IP methods. Ground TEM methods produce anomalies over the deposit which are diagnostic of a steeply dipping tabular conductor. However, care is required in the choice of loop configuration; separated loop (Slingram) and large loop systems would appear to produce the optimum anomalous response. Extensive borehole electrical logging at this deposit illustrates the detailed geological resolution provided by continuous resistivity and IP logs and their relevance to the interpretation of surface electrical and electromagnetic data. Electrical properties established from these high resolution logs have clarified the conductive and polarizable

165 nature of the base metal sulphide body. Narrow massive sulphide lenses may exhibit resistivities of less than 0.1 ohm m, but in general the sulphide zones display very irregular resistivities. The in situ IP response of the sulphide zones is generally high with apparent phase shifts exceeding -1000 mR. The use of multiple spacing logs for empirical determination of the borehole effect is demonstrated. High resolution logging with a 0.25 m dipole dipole array produces geologically meaningful logs which are much simpler in character than magnetic susceptibility and radiometric logs. A computeraided interpretation method is presented for electrical logs of varying array spacings in a hole which is a 'near miss' to the main sulphide body. The results convincingly show that a large array spacing anomaly which intuitively appears to detect the body off-hole can be wholly explained by the additive effects of many small conductive intersections in the hole. These results emphasize the value of electrically logging with several array spacings. A surface and borehole mise-a-la-masse survey localizes the massive sulphide body into several discrete lenses. Borehole mise-a-la-masse together with the high resolution resistivity logging indicate a highly irregular geometry for the ore deposit. In general, the interpreted geological boundaries of the ore horizons are an oversimplification from the electrical geophysical point of view. The implications of this case study for future electrical prospecting in the region are that TEM offers the most appropriate tool for initial detection of conductive drilling targets. However, the occurrence of other types of conductors in the region along with the highly irregular electrical properties of the Flying Doctor sulphide deposit strongly supports the use of follow-up borehole TEM, electrical logging and mise-a-la-masse as a means of evaluating the subsurface geometry of the conductive source.

THE APPLICATION OF DRILLHOLE MAGNETOMETRY AND MISE-A-LA-MASSE IN THE EXPLORATION FOR NICKEL SULPHIDES, FINLAND DISCOVERY OF THE TELKKALA OREBODY. R. Pietila Outokumpu FInnmlnes Oy Exploration, Outokumpu Finland During the 1980's Outokumpu Exploration carried out several exploration programs for nickel sulphides in Eastern Finland. Geophysical methods have been significant both in locating nickel-bearing intrusives hosted by mica gneiss and in detailed downhole investigations of the dimensions of the ore zones. In-hole 3-component magnetic and mise-a-la-masse measurements contributed to the discovery of a small but high grade orebody beneath a worked out shallow deposit at Telkkala, southeastern Finland. The high contrast in magnetization and conductivity between the ore mineralization and host gneisses provided suitable circumstances for effective quantitative interpretation of the geophysical data.

166

FREQUENCY ELECTROMAGNETIC SOUNDINGS FOR DEEP MASSIVE SULPHIDE OREBODY DETECTION J. Bernard*, B. Bourgeois and P. Valla BRGM, France Time domain EM methods have widely shown their ability in detecting deep targets, in particular in the case of mining exploration. Traditionally, artificial source frequency domain EM methods have been more dedicated to shallow applications, through VLF and slingram procedures for instance. However, recent developments both in instrumentation and in interpretation now permit a reconsideration of the application of Frequency EM methods in the detection of deep massive sulphide orebodies. To illustrate these new possibilities of frequency methods, a field survey has been performed with a loop source audio frequency EM system called MELIS, over the Masa Valverde deposit. This massive sulphide orebody has been recently discovered in the Iberian Pyritic belt (Spain) by the ENADIMSA and SMMPE companies, through a gravity anomaly. The mineralization is four to five hundred meters deep, and its thickness reaches one hundred meters. Multifrequency measurements of the ratio between the horizontal and the vertical magnetic field components have been carried out with various loop positions, using a lightweight transmitter of one l^ilowatt power. The interpretation of the soundings located above the deposit points out a deep conductive layer corresponding to the mineralization. However, its depth is overestimated and the boundaries of the orebody are very poorly defined. Much better results have been obtained through the use of a 2-D modelling program based on the finite element method and using a specific algorithm for automatic mesh generation. Using this program, it has been possible to give a rather accurate location of the orebody, based on the lower frequency measurements. Moreover, an extension of the orebody to the northwest has been predicted, which has been confirmed by a later drill hole.

167 Technical Session 9(c) Coal, Groundwater and Engineering III - Groundwater

THE USE OF ELECTRO-GEOPHYSICAL METHODS FOR GROUNDWATER POLLUTION AND SOIL SALINITY PROBLEMS G. Buselli''*, C. Barber^, G.B. Davis^ and D.R. Williamson^ ^CSIRO Division of Exploration Geosclence, NSW ^CSIRO Division of Water Resources, WA Over the past five years, the use of the transient electromagnetic (TEM) method for both lateral and vertical profiling of polluted groundwater and saline soil has been Investigated, and the results have been compared with dc sounding and frequency domain methods. In the groundwater pollution studies, it has been found that with either two-layer or three-layer inversions of the TEM data a subtle low-resistivity feature which correlates with the presence of a pollution plume in the aquifer near a landfill site can be detected. Data obtained since 1985 at approximately six-month intervals have shown a continuing development of the resistivity low. In the soil salinity studies, investigations have concentrated on the use of TEM and dc sounding methods to determine the thickness and resistivity of the surface leached layer and of salt accumulations. Modelling of the response obtained with a ground-based TEM system shows that measurements at delay times earlier than 1 ms are required to resolve the relevant parameters of a layered-earth model used to approximate a saline soil environment.

RECHARGE, SALINITY AND LAND-USE CHANGE IN NORTH-EASTERN NSW S.J. Lawson*, R.M. Williams, G.W. Gates and J.A. Odins Department of Water Resources, NSW Land salinisation and river salinity are recognised as one of the highest priority issues for resolution in the Murray Darling Basin. Recent regional work covering some 18200 km^ in north eastern NSW (Williams and Saunders, 1990) has indicated that increased groundwater recharge is occurring, caused by the replacement of deep rooted native eucalypt forest with shallow rooted crops and pasture. The water table will continue to rise until a new equilibrium is reached. Groundwater discharge to the land surface will continue to occur causing waterlogging and dryland salinisation. The area studied is shown in Figure 1. Three rock types; basalt, metasediments and to a lesser degree granite were recognised as prone to salinisation from groundwater rises. Maximum water level rises of 20 m were recorded with annual rises of 0.3 m not uncommon. Average water level changes are shown in Figure 2. To examine the geologic framework in which salinisation occurs and the hydrogeologic processes under which it develops a trial catchment was instrumented. The catchment

168

selected covers some 640 ha in the headwaters of the Gwydir River and is shown in Figure 3. As discussed by Lawson (1990), it is underlain by Tertiary basalt which has a contact with deeply weathered Carboniferous granite near the catchment outlet. Seismic refraction and drilling have defined the basalt which forms the regional aquifer system as a complex composite flow which can be in excess of 160 m thick. The granite, both where it outcrops and underlies the basalt, has a low permeability weathered zone which is approximately 40 m thick. The geology is shown in cross section in Figure 4.

• Max increase •Average change 22

BOX HILL TRIAL CATCHMENT

irisbane

•Max decrease

RECONNAISSANCE SURVEY AREA

18 16

14 12

I E

8 6 4 2 0

Legend Murray Darling Basin Murray Geological Basin

C D CZ)

-2

Rgure 2: REGIONAL WATER LEVEL CHANGES

Rgure 1: LOCALITY PU\N

HORIZONTAL

Legend

Legend Contour- relative to assumed dotum ^ ^ Groundwater Row Direction

^Cr^^^

Shallow Water Table Salinized Area

0 200 m

C l U ^

Piezometer

Rgure 3: TRIAL CATCHMENT WATER TABLE

Groundwater Flow Direction

^ ^

DWR Investigation Bore Potentiometric Surface (Granite/Basalt Aquifers)

Rgure 4: TRIAL CATCHMENT HYDROGEOLOGICAL SECTION

169 The quantity and quality of rainfall, stream flow and groundwater are monitored in conjunction with land use changes and practices. The extent of the salt store and its distribution has been defined by electromagnetic induction techniques in conjunction with soil survey and piezometer information. The results of these regional and catchment scale studies are being used by the Soil Conservation Service and Department of Water Resources to develop and implement an effective, economic long term strategy to minimise the impact of salinisation on the land and water resources of north-eastern NSW. References Lawson, S.J. (1990) - Box Hill trial catchment: an investigation for the management of dryland salinity in northern NSW. DWR TS 90.003. Williams, R.M. and Saunders, B.J. (1990) - Groundwater Reconnaissance Survey Inverall Region DWR TS 90.031.

THE USE OF ELECTRICAL IMAGING TECHNIQUES FOR THE INVESTIGATION OF DRYLAND SALINITY R.I. Acworth* and D. Scott The Centre for Groundwater Management and Hydrogeology UNSW, Sydney The processes of dryland salinisation involve enhanced recharge to the groundwater system as a result of clear felling of natural bush for farm land. Infiltrating rainfall flushes stored salt through the soil both recharging and potentially contaminating the groundwater. The heightened groundwater level, which results from the increased recharge, gives rise to saline seeps and springs in the lower parts of catchments causing stunting or death of vegetation, destabilisation of the soil and the initiation of gully erosion. This simple model of dryland salinity is complicated by the observation that not all catchments develop salinity after clearing, although the hydraulic conductivity of parts of the weathered basement material which comprise the catchments are often extremely low and it may be that the process, once initiated, takes tens of years to result in the development of dryland salinity. Electrical conductivity profiling methods provide a rapid means of mapping areas containing high conductivity groundwater which are thought to be associated with outbreaks of dryland salinity. Contour plots of apparent electrical conductivity have been shown to correlate well with areas of saline or potentially saline soils, determined by bulk sampling methods. If the presence of high salinity groundwater can be detected at depth before the soils become affected then a means of mapping potential salinity outbreaks can be developed and thus used as a catchment management tool. Values of apparent electrical conductivity obtained from profiling can not be used to predict the electrical conductivity of the groundwater without resolving the lateral and vertical variations of electrical resistivity which exist in the weathered profile. The same problem exists with the interpretation of VES data where lateral variation often makes impossible an interpretation in terms of homogeneous plain layers.

170

In this paper we describe the use of new automated resistivity imaging equipment at two salinity research sites in the Yass area of New South Wales. This approach provides a two-dimensional cross-section of the dryland salinity occurrence and therefore reveals previously unobtainable information concerning the hydrogeological processes involved. Seven electrical resistivity image sections were acquired with a station separation of 5m and electrode separations of 5m, 10m, 15m, 20m and 25m with less compete coverage at 30m, 35m and 40m. A total of 2100m of image data was acquired in a ten day period by a two man team. The electrical image data has been interpreted using a 2.5 D finite difference algorithm. Interpretation control was achieved using the results of electromagnetic induction logs (GEONICS EM-39) and shallow offset resistivity soundings. Field measurements of fluid electrical conductivity and bulk analyses from drill cuttings have been used to develop a hydrogeological model of the electrical resistivity image data sets which can be used for further salinity reconnaissance work.

PRE-TERTIARY BASEMENT STRUCTURE OF THE CENTRAL MURRAY BASIN, AND ITS EFFECT ON GROUNDWATER FLOW PATTERNS

J.A. Odins*, R.M. Williams, D.J. O'Neill and S.J. Lawson Department of Water Resources, NSW

The Murray Basin has an area of 320,000 km^ and is one of the most important sedimentary basins in Australia in terms of agricultural and cultural development. It is essentially a closed groundwater basin which consists of a thin coverage (200-600 m) of sediments containing 4600 million megalitres of water varying in salinity from 500 mg/L to over 35,000 mg/L total dissolved salts. This study of the central Murray Basin covers an area of 200 x 300 km, and is based on 1700 km of seismic refraction, over 300 vertical electrical soundings and the analysis of several thousand bore logs. The pre-Tertiary basement surface was found to have highly variable relief of up to 300 m. A rectilinear system of crustal fractures has been responsible for the formation of a basement ridge complex, identified as the Ivanhoe Block. A three dimensional (3D) representation of the basement has been developed to highlight dominant trends. Occlusion of aquifers across the Ivanhoe Block is a controlling factor affecting the regional groundwater flow, and is a contributing cause of the outflow of saline groundwater to the land surface and the river system.

171 Technical Session 9(d) Petroieum Exploration XIII - Seismic Data Acquisition and Case Histories (Note: No abstract available for 1 st paper: "The Application of Refraction Methods and Replacement Dynamics to Seismic Data Over Irregular Sea-Floor Surfaces" NJ. Fisher Digital Exploration Ltd., Brisbane)

THREE-COMPONENT SEISMIC: FIELD IMPLEMENTATION AND OPERATIONS WITH OMNIPHONE D.R. l\/liles*, G.S. Gassaway and J.E. DeBoer Terra Linda, Canada The OMNIPHONE is a three-component geophone containing a processor which incorporates the Omniphone Polarization Filter. Shooting and recording of threecomponent data is greatly simplified since the OMNIPHONE requires only one recording channel per station and only one geophone per station. This reduces the time, manpower and equipment needed for a three-component seismic crew to about the same as a conventional crew, since the polarization filter attenuates the groundroll at the geophone, without affecting the body waves, 4.5 Hz elements are being used. This increases the bandwidth of the data. In addition, by attenuating groundroll in the geophone, one eliminates the need for a geophone array. The OMNIPHONE has shown its dependability and durability in the severe heat of the Australian desert, the severe cold of the Canadian North and the swamps of the Texas desert. The OMNIPHONE was designed to operate between -40°C and +60°G. Both the OMNIPHONE's computer processor and batteries have withstood the rigours of field work, with less than 5% failure in nine (9) months of operations.

THE 'OCEAN'S OVERTURE' ON THE NORTH WEST SHELF OF AUSTRALIA Charles Ramsden Digicon, Singapore The North West Shelf of Australia presents problems in data acquisition and processing. In particular the hard water bottom and near surface prograding carbonate wedge set up a standing wave multiple train analogous to that of a closed organ pipe. This strong multiple energy and the observed rapid attenuation of the high frequencies in the source spectrum degrade the quality of the recorded data. The data quality can be improved by careful selection of the acquisition parameters. The multiple energy appears to be reduced by reducing the output power of the source and restricting the high frequency end of the source spectrum to useable frequencies. The frequencies in the low range of the seismic spectrum can be used to improve the seismic data through broadening of the bandwidth and improved penetration.

172 (Note: No abstract available for 4th paper: "The Point Torment Area of Western Australia: A Case Study of a Structural/Stratigraphic Hydrocarbon Accumulation" Ron Prefontaine Oil Company of Australia, Sydney)

173 Technical Session 9(e) Regional, Crustal and Geothermal V Seismic Studies, Worldwide

DEEP CRUSTAL STRUCTURE IN THE GULF OF ST LAWRENCE FROiVI COINCIDENT SEISiVliC REFLECTION AND REFRACTION SURVEYS M.C. Dentith""*, J. Hall^, F. Marillier^, K. Michel^ I. Reid^ and B. Roberts^ ^ University of Western Australia, WA ^i\/lemorlal University of Newfoundland, Canada ^Atlantic Geoscience Centre, Canada "^Daliiousle University, Canada Coincident seismic refiection and refraction profiies were recorded in 1986 and 1988 across tiie Gulf of St Lawrence as part of tlie Canadian Litlioprobe program. Tlie profiles are about 250 l<m In length and trend nortliwest-southeast from tfie Quebec coast to tlie Bay of Islands, Newfoundland. The profiles cross the Appalachian structural front which separates the Proterozoic Grenville Block to the northwest, from the suspect terranes of the Appalachian deformation zone to the southeast. On the reflection data, the structure of the upper crust is obscured by multiples. However, in the lower crust the data allow the recognition of two zones with different reflection characteristics. At the southeastern end of the profile, a wedge shaped zone of high reflectivity, with horizontal layering, contrasts with the rest of the section in which the lower crust is less reflective. The Moho is well defined beneath the reflective wedge at a TWT of about 12 s. Elsewhere the Moho occurs at between 13 and 15 s and is less distinct. The refraction/wide-angle reflection survey was carried out to confirm the interpretation of the Moho as the base of the reflective lower crust, and to further investigate the two different lower crustal blocks. The survey involved the recording of over 300 airgun shots by an array of 9 land receivers and 3 ocean bottom seismometers. Processing included frequency filtering and deconvolution to remove reverberations due to the airgun source. Data are of excellent quality with refracted and/or reflected arrivals recognised from the top of basement, the top of the lower crust, the top of the reflective wedge and from the Moho. Initial ray-trace modelling of the data has concentrated on data from 3 of land sites and the CBS at the northwest end of the line. Two layers in the upper crust have velocities of 4.7 and 5.7 km/s and are probably of sedimentary origin. These layers are underlain by basement with a velocity of about 6.35 km/s which extends to a depth of between 10 and 25 km. The lower crust has a velocity of about 6.7 km/s, whilst the reflective wedge is shown to have the unusually high velocity of 7.25 km/s. The Moho occurs at about 45 km depth at the northwestern end of the profile, and at about 39 km depth at the southeastern end. Conversion of the ray-traced depth section to an equivalent normal incidence reflection section allows direct comparison of the reflection and refraction profiles. These data are shown in Figure 1. The reflection data are presented as a line drawing. The dots show the positions of the layers defined by the refraction experiment. There is excellent agreement between the two data sets in terms of crustal thickness and the position of

174 the lower crustal wedge. However, the top of the lower crust does not coincide with a reflectivity boundary though this is probably due to multiples obscuring structure at this depth. The origin of the high reflectivity, high velocity lower crustal wedge is uncertain. The block does not obviously correlate with any surface feature of the Appalachian Orogen. One possibility is that the zone contains mafic or ultra-mafic rocks that underplated the crust during Late Precambrian to Early Cambrian rifting of the lapetus Ocean. Another possibility is that underplating occurred during Late Palaeozoic strike-slip movements that led to the formation of pull-apart basins in the Canadian Appalachians. Alternatively, the Late Palaeozoic strike-slip movements may have juxtaposed deep crustal zones of different types.

7 ^

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. 8.15?

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EVOLUTION OF THE CAPE EGMONT FAULT ZONE, TARANAKI BASIN, NEW ZEALAND Glenn P. Thrasher DSIR-Geology and Geophysics, New Zealand Taranaki Basin is a major sedimentary basin located along the western side of New Zealand. The basin is moderately explored for petroleum, and all of New Zealand's commercial production is from this basin. The Cape Egmont Fault Zone is a north-south system of en-echelon faults which separates the stable Western Platform from the rapidly subsiding Taranaki Graben. The fault zone controls the distribution of mature source rocks in the basin, and the formation of many petroleum-bearing structures, including the giant Maui Gas Field. The Cape Egmont Fault Zone is a system of down-to-the-east normal faults extending about 200 km north of the Maui Field. Its expression is lost south of the Maui Field, where reverse faulting dominates the structural style over a broad region. The fault zone has generally been interpreted as a right-lateral wrench system. The results of a recent DSIR reinterpretation of seismic and well data can be used to study the history of motion of the fault zone, and test the wrench hypothesis.

175 During late-Cretaceous oblique rifting, which initially formed Taranaki Basin, the presentday Cape Egmont Fault Zone was part of a larger system of normal and left-lateral faults. Many of the faults associated with this rifting have been inactive since the early Tertiary. Those presently associated with the Cape Egmont system, however, have undergone Neogene reactivation, hence their prominence on structure maps of the region. Miocene shortening of the southern half of Taranaki Basin resulted in reversal of many of the late-Cretaceous normal faults, forming spectacular anticlinal structures. This affected the present Cape Egmont Fault Zone as far north as Cape Egmont (the tip of Taranaki Peninsula). Thus the Maui Field, which is on a high-standing basement block on the upthrown side of the fault zone was, during the late Miocene, on the downthrown side of a major reverse fault. Most of the normal motion on the Cape Egmont Fault Zone is Pliocene and Pleistocene. Sea floor rupture along portions of the fault zone indicates recent activity. The enechelon pattern of the Neogene fault trend does indicate some right-lateral shear. However, the lack of through-going faults argues against major wrench offset. Miocene volcanic edifices in the subsurface of northern Taranaki straddle the fault zone and are vertically offset by the normal motion of the faults; they do not have lateral offset. Similarly, late Cretaceous and early Tertiary sediments do not appear to have significant lateral offset across the fault zone. Because any late-Tertiary right-lateral shear has been minor, the fault zone should be considered a mainly-extensional feature.

GEOPHYSICAL DATA PROCESSING AND INTERPRETATION IN AN AREA OF COMPLEX STRUCTURE - THE SOUTHERN TARANAKI FAULT ZONE J.F. Montalbetti* and D.J. Norris TCPL Resources Ltd, NSW During 1989, a closely-spaced offshore seismic grid was acquired over an area of thnjst faulting along the Taranaki Boundary Fault Zone, New Zealand, and complemented by simultaneous gravity recording along a number of profiles. Production seismic data processing included DMO and steep dip migration. Subsequent reprocessing of selected lines with full prestack time migration improved the imaging in the zone of complex structuring. Integrated interpretation of the seismic and gravity data developed a model for the geometry of the Taranaki Boundary Fault in this region. From north to south, the structural style is shown to change from low to high angle overthrusting of Mesozoic basement with truncation of the (younger) sediments against the basement.

176 DEEP STRUCTURE OF BAIKAL RIFT ZONE - THE BIGGEST ASIAN CONTINENTAL STRUCTURE M. Mandelbaum PGO "Irkutskgeophysica", USSR In recent years geological science has concentrated on studying rift zones. The continental Baikal Rift Zone is of particular importance. Investigations accomplished by PGO "Irkutskgeophysica" and the Geophysics Institute of the USSR Academy of Sciences have led to a model of its main structural features. The complex geophysical investigation of the Baikal Rift Zone has determined important characteristics of the Earth Crust and Upper Mantle structure and the peculiarity of its junction with the Siberian Platform. According to geotectonic structure this rift zone runs across different Cambrian and Precambrian formations and its present structure is manifested by a system of Mezo-Cenozoic depressions. Suture structures, rimming the Siberian Platform, have been considerably changed by Mezo-Cenozoic Rift genesis. The Baikal Rift Zone is characterized by complex crustal structure, and geophysical parameters testify to the anomalous state of underlying mantle. Waveguides in the crust were defined by deep seismic soundings and reduced values of boundary velocities on the mantle surface are marked over the entire rift zone (7.7-7.9 km/s). The largest rift zone structures are: Baikal Rift Valley, Verhneangarskaya, Muiskaya and Charskaya depressions in the North-East and Tunkinskaya and Hubsugulskaya depressions in the South-West. They form a complex broken line more than 3000 km long. The position of the depression axis changes from meridional to latitudinal. As is shown by the geophysical data analysis, in particular parts of these large depressions there are relics of Cambrian sediments up to 2000 m in thickness. It is possible to trace retrospectively paleotectonic changes of the marginal part of the platform. Besides this peculiarity of velocity on the mantle surface, Baikal Rift Zone is characterized by a variable crust thickness (38-44 km), increased heat flow, and increased electrical conductivity. Magnetotelluric sounding data shows the uplifting crust and mantle conductive layers. The highest position of these layers is in the axial part of Baikal Rift Zone. Both gravimetric and magnetic data analysis leads to conclusions about the large scale of Riphean-Paleozoic granitoid masses related to the upper part of the Crust. Rift depressions have been formed on the heterogeneous basement with old fractures and contacts of rocks of different physico-mechanical properties. Baikal Rift Zone is a geological structure where deep changes extend up to the mantle surface. There is a decrease of velocity anomalies with depth and moreover the velocity changes in the upper part of the mantle constitute 0.2 km/s and in the lower part - 0.1 km/s. The Upper Mantle is very well studied by deep seismic soundings. It differs considerably from the marginal stable regions of the Baikal Rift Zone. The Crust overlies the layer with an anomalous velocity 7.7-7.9 km/s. This layer thickness is 20 km. It is underlain by a normal velocity mantle with 8.1-8.2 km/s. The anomalous velocity layer stretches over an area of 350000 sq km. As a rule this layer crosses the ancient geological structures, but in some places its boundary is defined by deep fractures. The upper part of the mantle in Baikal Rift Zone is characterized by considerable horizontal changes. The bottom depth of the

177 anomalous layer is about 40-90 km and this layer thickness is from 0 to 50 km. Within the limits of the large rift depressions one can trace a relation between near surface and upper mantle structures. The layer thickness under depressions is about 30-50 km and in the links between depressions it is pinched out. The block-layered structure of Crust within the Siberian platform and mountainous faulted regions of TransBaikalie is characterized by constant average velocity and thickness. Marked anomalies are only found within the rift zone. The rift zone is of different type over crustal basement relief: there is a deeper zone position on the marginal sites than in its central part. One more important thing is that there is a wider difference of crust elastic properties. It can be suggested that anomalous seismic features of the Crust such as irregularity of its stratigraphy, presence of a waveguide, and anomalous velocities in mantle rocks are determined by the processes of neotectonical activation; but the activation in deep structures is not larger than in the near surface part of the section. High seismic activity is characteristic of the Baikal Rift Zone. Some regularities can be established when comparing the position of Earthquake epicentres with deep structure. As a rule the strongest earthquakes take place in the junction between the depressions. According to their composition the links are marked as a gravity minimum if there are granitoids and as a maximum if they relate to basic blocks of magmatic rocks. Such determined regularities of geophysical field distribution and of the Baikal Rift Zone structure give new approaches to the solutions of problems of continental rift genesis and the search for mineral deposits. The ascertained coincidence of seismic activity and physico-mechanical rock mhomogeneities defined by this complex of geophysical methods permits the use of these regularities for seismic regionalization.

178 Technical Session 10(a) Petroleum Exploration XIV - Case Histories

THE ROLE OF SEISMIC ADVANCES IN REDUCING EXPLORATION RISK IN THE NORTHERN PERTH BASIN R.L Neale Barrack Energy Management Pty Ltd Seismic data from the northern onshore Perth Basin has generally been of poor quality and as a result, many exploration wells have been drilled off structure. Combined with other factors, this has contributed to a lack of consistent exploration effort in the basin over the past 20 years. However, by applying recent advances in seismic technology, data quality is being significantly improved. Reasons for these improvements are given along with supporting examples, providing a comparative summary of seismic methods employed in the basin. Better structural definition has resulted from the improved seismic data and initial drilling results indicate that this is having a positive impact on the success rate.

EROMANGA BASIN SEISMIC STRATIGRAPHY AND TECTONIC MODELLING - KEYS TO EXPLORATION SUCCESS IN ATP 299P B. Edwards Ampol Exploration Pty Ltd Within the Eromanga Basin, stratigraphic variations in the Jurassic Birkhead Formation are recognizable on seismic sections as lateral character changes. Understanding these character changes and developing representative depositional and structural models results in lower risk and hence more favourable economics when exploring for Birkhead Formation oil. Authority to Prospect (ATP) 299P is located in the Eromanga Basin, on the southeastern flank of the Cooper Basin. It is 120 km northwest of the Jackson Oil Field. Over 1.5 million barrels of oil have been produced from the permit, of which 500,000 barrels have been produced from the Birkhead Formation, highlighting it as an important exploration target. By late July 1989 Cranstoun-1, a Birkhead Formation oil well, had produced more than the mapped proved and probable reserves and was still producing 203 barrels of clean oil per day. To investigate this anomaly the existing seismic data was reprocessed with additional 80 m uphole control and a seismic stratigraphic interpretation was carried out. The mapped data identified a Devonian wrench system overlain by a large low relief structure known as the Greater Cranstoun Structure (GCS). Endeavour-1 was drilled on this structure 3 km north of Cranstoun-1 and was completed as a Birkhead oil producer. Post drill analysis revealed that the interpreted top intra-Birkhead seal seismic marker crossed a geologically correlated boundary - from the top Birkhead ('A' sand) seal at the Endeavour wells switching down to the top 'B' sand seal at the Cranstoun wells. A further three wells were drilled based on the mapping of this seismic marker resulting in limited success. Detailed 2D seismic modelling, using the sonic logs from the five wells

179 on the GCS as input, indicated that an increase in the frequency bandwidth of the seismic data was needed to resolve those geologically correlated boundaries within the Birkhead Formation which have an acoustic impedance contrast. Future seismic acquisition and processing should use good statics together with optimum recording parameters (defined from the 2D modelling results) to produce the required seismic resolution for accurate stratigraphic interpretation and mapping. Quantitative understanding of the limitations and possible resolution of seismic data is crucial to accurate seismic stratigraphy, which, combined with a valid tectonic model are keys to exploration success in the Birkhead Formation in ATP 299P and throughout the Eromanga Basin.

THE CHALLIS AND CASSINI OILFIELDS TIMOR SEA, AUSTRALIA T. Slate* and G. Gmbitz BHP Petroleum The Challis/Cassini Oilfield development has recently been the second field development undertaken by BHP Petroleum and co-venturers in the Timor Sea. From the discovery at Challis-1 in 1984 till 1986, five wells had been drilled on the Challis structure with mixed success, as a result of the geological complexity of the field. At that time it was estimated that 22 mmbis of reserves had been structurally trapped within two major Triassic reservoirs. Since that time with a re-evaluation of existing seismic data, and further work defining the structural model, the Challis Field limits were interpreted to extend significantly to the northeast of the existing wells. It was in this area that recent step-out wells Challis-6, 7, 8 and 9 were drilled. All of these were commercially successful, and combined with the success at nearby Cassini1 have doubled the reserves of the Field to approximately 42 mmbis. Seven wells are producing oil from a number of separate reservoirs at an average rate of 27,000 bbls/day to a Floating Production Facility - the "Challis Venture". Currently, a development drilling phase is underway to boost oil production up to the maximnum capacity of the "Challis Venture", of 70,000 bbls/day.

180 DIAGENETIC RESERVOIR EVALUATION, SOUTHERN COOPER BASIN J.P. Schultz-Rdahn''*, A. Alsop"', J. Eleftheriou^, A. Thomas^, B.B. Farrow^ N. Lemon^ S.E. Phillips^ and WJ. Stuart'' "" National Centre for Petroleum Geology & Geophysics ^Santos Ltd ^Amdel Core Services Pty Ltd ^South Australian Institute of Technology The Cooper Basin, containing Permo-Triassic sediments of fluvio-lacustrine origin, is characterised by dominantly low-porosity, low-permeability reservoir sandstones for oil and gas. Ambient core porosity averages 10.7% and permeability 30 md, with over 75% of sandstones having permeabilities less than 5 md. Despite its overall poor reservoir characteristics, the basin ranks as one of Australia's most important hydrocarbon provinces; sales gas reserves amount to about 6 TCP, and gas-liquids and oil reserves approach 310 MMSTB. The objective of NERDDC project 1775 was to define the interaction of factors influencing reservoir quality in Permian sandstones of the southern Cooper Basin. A total of 887 core and ditch samples from 82 wells were collected, including the Big Lake, Daralingie, Moomba, Munkarie, Strzelecki, Toolachee and Wancoocha Fields. The samples were studied using an array of different techniques such as thin section petrography. X-ray diffraction, scanning electron microscopy, cathodoluminescence, electron microprobe analyses and isotope geochemistry. Diagenetic factors, sedimentary fades and basin architecture all influence reservoir quality. Principal cementing agents include authigenic quartz and various carbonate minerals, mostly siderite but also ankerite, dolomite and calcite. Authigenic clay minerals include illite, kaolinite, dickite, chlorite and pyrophyllite. An early phase of silicification provided a rigid grain framework which suppressed mechanical compaction in numerous sandstones from the Toolachee, Epsilon and Patchawarra Formations. As a result, effective primary intergranular porosity was retained in sandstones mainly of point bar origin particularly in midflank and marginal areas of the basin, but also in more basinal areas to depths approaching 3 km of burial. Preservation of primary porosity is prominent in the Daralingie, Strzelecki, Toolachee, Munkarie and Wancoocha Fields. With increasing depth of burial, there is a broad transition towards reservoirs dominated by microporosity associated with kaolin clays. For example, microporosity in sandstones of the Moomba and Big Lake Fields accounts for much of the total porosity in reservoirs which have produced more than a trillion cubic feet of gas. Scanning electron microscopy studies support this conclusion by exhibiting the interconnection of pores between authigenic dickite crystals, individual micropores being up to 20 microns in diameter. Petrological evidence of hydrocarbon migration is apparent in samples from the Big Lake, Strzelecki, Toolachee, Moomba and Wancoocha Fields. The main phase of petroleum migration postdated quartz cementation, although there may have been minor oil migration synchronous with the silicification of some reservoir sandstones. At Wancoocha, no differences in the amount of silicification between water-wet and oilsaturated sandstones in the Patchawarra Formation were detected. Similarly, no diagenetic changes immediately above or below gas/water contacts are noticeable in the Moomba and Strzelecki Fields.

181 Technical Session 10(b) Mineral Exploration Vlii - Case Studies

GEOPHYSICAL METHODS FOR MINERAL EXPLORATION IN THE SOVIET FAR EAST V.N. Gagaev^* and N.K. Zhdan^ V G O Dalgeologia, Khabarovsk, 680649 USSR ^PGO Dalgeologia, Khabarovsk, 680041 USSR ABSTRACT. Geophysical methods play an important role in mineral exploration in the Soviet Far East. Concrete examples are given to show the resolution of geophysical methods at all stages of geological activity: from regional investigations to detailed exploration. Examples of gold, tin, and platinum deposits and their geophysical characteristics are given. Geophysical aspects of some objects are studied in detail, and they can be considered as natural testing grounds. The original methods and geologicalgeophysical exploration technologies can be useful for exploration in different regions. KEY WORDS. Alternating earthquake waves, telluric sounding, induced polarisation, unconsolidation zones, pipe-like structures, nuclear methods, X-ray radiometric enrichment. INTRODUCTION The Soviet Far East represents the eastern margin of the USSR. In its central part, the vast Priamurie territory, the author has extensive experience of introducing geophysical methods into mineral exploration practice. In a geological sense the Priamurie region covers the eastern margins of the Siberian platform, Khingano-Alinsky and Sikhote-Alinsky volcanogenic belts, Gorinsky Syncllnorlum, Bureinsky iVIedian Massif, and some of its crystalline benches in the Amur region where they are jointed to the Aldan shield through the complex tectonic zone of the Stanovik - Dzugdzur. The territory is rich in gold, tin, silver, titanium, platinum group elements and gem-stone deposits. There are numerous prospective ore occurrences of copper, molybdenum, tungsten, polymetals, zirconium, rare earths and other minerals which give the territory great potential for mining development. Geophysical methods are of great importance in mineral exploration in Priamurie and they are introduced at all stages of geological activity. STEPS AND GOALS OF GEOPHYSICAL INVESTIGATIONS Regional geophysical studies include aerogeophysical and gravimetric surveys at 1:200000 scale, depth profiles by seismic sounding (GSS), exchange earthquake waves (MEEW), and telluric soundings (MIS) methods. Depth profiles are accompanied by aerogeophysical flights at different altitudes.Cosmic survey data are used for complex interpretation. For gravity surveys in inaccessible areas a new technique was developed. It uses a helicopter which hovers over the observation point and lowers the instrument without landing. More effective systems of MEEW and MIS data processing were also developed. A detailed study of deep structure is executed by gravity surveys at 1:50000 scale, electrical sounding and seismic profile shooting. The main task of

182 regional geophysical investigations is studying the deep structure of the territories and redetermination of the relationship of endogenous mineralization distribution. Localization and delineation of the areas and redetermination of their deep structure investigations also have great importance in connection with seismic hazards. General prospecting geophysical investigations mainly use remote sensing methods where the leading role is played by multichannel aerogeophysical surveys of 1:50000 1:25000 scale in a helicopter at heights of 50-100 m draped around the relief. Gamma ray spectrometry uses a crystal with 42 I capacity. Digital magnetic tape recording is measured in steps of 0.25 sec at a velocity 120 kms/hr. For the sake of reliability the digital record is duplicated by an analogue one. Navigation is carried out by an autonomous radiogeodetic system or photographic picking. Geophysical prospecting at 1:25000 scale - 1:10000 scale is concentrated within ore areas and fields, selected at earlier stages of the activity. The basics of the prospecting complex are ground methods of electrical exploration, magnetic exploration and geochemistry. The most used electrical exploration methods for systematic areal studies are induced polarization (IP), self potential (SP), VLF radio waves (VLRW), and transient processes (TP) methods. The choice of electrical exploration methods for specific areas is determined by geoelectrical conditions. At the stage of detailed studying of ore fields and zones (1:5000 scale) in the search for hidden mineralization and sorting of the revealed anomalies we have accumulated extensive experience of IP sounding (VES/vertical electrical sounding - IP), IP irreversible process (IP-IP), IP temporary characteristics (TC-TP), dynamic geophysical methods and detailed gamma spectrometry. We have experience of partial and diffusive metal extraction (PME, DME), mercurymetry. Field nuclear methods are widely used for rapid assessment of element content in diluvium and indigenous rock and ore occurrence. Detailed prospecting and evaluation uses methods of volumetric and mining geophysics. They are based on IP methods, electrocorrelation, charged body (MALM), magnetic exploration, piezomethod, and gamma-ray, density and X-ray-radiometric logging. Nuclear testing is widely used for nonferrous and rare earth exploration. A combination of traditional geological and geophysical exploration methods makes it possible to reduce the volume of sampling and drilling , and in some cases to eliminate mine or adit driving as was done at the Sobolinoe deposit. The following requirements are considered necessary when choosing rational exploration programs of geophysical methods: 1. 2. 3. 4.

Usefulness of the method for the specific geoelectrical conditions of the area and in connection with the peculiarities of the geologic-geophysical model of the bodies. Satisfactory resolution capability of the method (or complex) for determination of ore zones location and their preliminary assessment. Increased depth of investigations. Economic efficiency of the method.

The final form of the geophysical program is determined using detailed case studies over known bodies. When studying geophysical properties of the models drill hole measurement data and petrophysical data are used. Electrical properties of the models of tin ore deposits are wholly determined by sulphide mineralization closely associated with tin ore. This determines higher induced and natural polarisation of tin bodies, anomalies of which form banded pillars in space, with great depth extent. The central

183 parts of tin ore zones are characterized by higher electrical conductivity, and their margins and upper noneroded levels are characterized by higher resistivities. The magnetic properties of tin ore objects are related to pyrrhotite, occurrences of which are not always present. The central parts of ore zones are characterized as a rule by depletion of radioactive elements and their accumulation in margins and upper levels. A detailed study of gold ore deposit models showed that the main part of gold ore zones is characterized by the presence of intensive pyritization cover. This is particularly clear in extrusive rocks, where the processes of near-ore propylitization occur. When pyrites physical properties were studied, differences in electrical conductivity character were established: electron conductivity of pyrites correspond to nonproductive zones (or concealed at depth). The sites of quartz-gold ore mineralization are accompanied by active silicification of supra-ore and marginal zone parts. An intensive depletion and redistribution of radioactive elements is characteristic of ore intervals. Quartz of gold ore zones is piezoactive. EXAMPLES OF THE RESULTS OF GEOPHYSICAL WORK The main thrust of area selection at the stage of regional geophysical works is confinement of endogenous mineralization to deep faults and blocks of rock with various crustal thicknesses as indicated by variations in the depth to Moho. It is noted that rare earth mineralization mainly located in unconsolidated blocks of high earth's crust thickness (36-42 km), but platinum and gold ore occurrences gravitate to consolidated blocks of decreased thickness (to 32 km). Ore areas of rare metal, tin in particular, are usually areas of local unconsolidation with corresponding intensive minimum gravity anomalies. Spatially they correspond with areas of higher granite saturation. In a geodynamic sense they are zones of stable extension (expansion). According to the results of microstructural analysis of relief these areas are distinguished as positive morphostructures (domes) sometimes with pronounced asymmetry. The main stage of dome formation by paleolevel reconstruction correspond to the Late Cretaceous. Potassium silicate metasomatism and adularization of rocks accompanied by anomalous redistribution of radiogenic elements (potassium, uranium, thorium) as a rule correspond to zones of unconsolidation. Clear metallogenic zonation is established with respect to the zones of unconsolidation. In their epicentral parts high-temperature tungsten-molybdenium mineralization is concentrated, changing at the flanks to copper-tin, then tin-polymetallic, and finally to mercury mineralization at the distant periphery. According to GSS and MTS methods granite-metamorphic domes occur at 2-10 km depth in the Badzalsky and Komsomolsky prospect ore regions, and at the depth of 2030 km (according to MTS data) there occurs an anomalous zone of electrical conductivity (Fig.1). The above anomalous geophysical characteristics of the tin ore regions are the basis of their physical boundaries and delineation of potential ore areas. According to the results of aerogeophysical surveys the most informative are thorium anomalies at minimum uranium concentrations and higher potassium values. Goldbearing regions are mostly characterized by local zones of low density. In this case, however, productive mineralization is localized in outlying areas. According to geophysical airborne surveys, gold-bearing areas are characterized by complex zones of radiogeochemical anomalies: in the central part of the field potassium prevails while thorium and uranium predominate on outlying areas. In Upper-Amur ore-bearing region only, 11 gold-bearing regions are distinguished by these characteristics, economically important gold fields are found in a significant number of them.

184

Pronounced geophysical anomalies are associated with pipe-like structures of alkaline ultrabasic content. In the East of the Siberian platform these structures are characterized by platinum, rare-earth and zirconium and hafnium deposits. These areas of occurrence are characterised by zones of gravity maxima within which specific pipelike structures are distinguished by isometric gravity anomalies of great intensity and coincident circular magnetic anomalies. Studying these anomalies in detail is done by complex airborne geophysical surveys at a scale of 1:50000 -1:25000. Platinum-bearing structures of Konder and Chad, now under study, are characterized, by circular aeromagnetic and spectrometric anomalies.The central dunite core of these structures is characterized by lower magnetic field data and a deep minimum of radiometric anomalies. As to the circular margin of the core, it is distinguished by positive magnetic anomalies, while outer areas are characterized by gammaspectrometrical anomalies of uranium, thorium and potassium connected with graniteporphyry and rocks of sedimentary cover which are subject to hornfels processes. According to mathematic modelling of gravitation and aeromagnetic anomalies, these structures have a conic form extending to more than 10 km depth (Fig. 2). The above stereotype of anomalies indicates means of detecting specific types by airborne geophysical methods. While checking spectrometric and magnetic anomalies fixed over the Inglliysk pipe-like structure, rare-earth and zirconium mineralization is connected with carbonatites and apatite ores. Zirconium mineralization is localized on the flanks of the structure in dolomite strata and represented by baddeleyite. Positive results of airborne geophysical surveys are obtained also while searching for deposits of iron, titanium-magnetite-apatite ores, phosphorites and kimberlite bodies where they are especially efficient. In Komsomolsk ore area, as a result of a geophysical survey at the scale of 1:25000 1:10000 on an area of over 1500 square km, 8 ore bearing structures were localized and followed along flanks with the length of 25 - 30 or 40 kilometers each. All tin-bearing ore zones are characterized by linear anomalies of self potential from -50 to -500 mV and induced polarization with intensity from 5 to 15%. These zones are also duplicated with linear anomalies of electric conductivity and with resistivity anomalies. By now a significant part of ore bearing structures are thoroughly investigated to a scale of 1:5000 by methods of induced polarization, vertical-electric sounding, charged body (MALM) and by a complex of sorting approaches. Nine large deposits are controlled by the above structures. One of them situated at depth is revealed by geophysical methods. According to geophysical data, prospects for the southern flanks of the area are enhanced. Earlier the flanks were considered unpromising. Here seven areas are delineated which are of a practical importance in the search for gold, copper, tungsten and molybdenum deposits of stockwork (disseminated) type. In Khingan region the ore field of Khingan, Dzalindinsk and Karadub deposits is clearly localized by induced polarization. As a result of a geophysical survey the Karadub ore field was completely revalued. Earlier the field was considered unpromising. Here, when checking recommendations by geophysiclsts, the Kamenistoye deposit was found which is at the stage of preliminary prospecting.

185

In Badzhal ore-bearing area within the limits of Urminsk ore concentration zone the prospects were extended by resistivity prospecting and nuclear methods. A new zone Alyonushka was found characterized by industrial concentration of tin, copper and tungsten. Possibilities of geophysical methods in searching for gold-bearing deposits may be seen in the results of surveys withing the limits of Pokrovsky, Belogorsky and Sbrosovy goldbearing deposits. The Pokrovsky gold-bearing deposit has sub-horizontal bedding of quartz metasomatites. According to geophysical data, the ore-bearing field of the deposit is characterized by a resistive zone clearly localized in profile by electric sounding. A similar anomalous area is located on the northern flank of the deposit. Its prospects were confirmed by the method of partial extraction of metals (CHIM) where some evidence of gold was found. The Belogorsk ore-bearing field is clearly fixed by an anomaly of polarization, by a zone of lower magnetic field and increased resistance of rocks. The productive interval of the anomalous zone corresponds to spreading of pyrites with mixed electrical conductivity. While studying the ore-bearing field of Sbrosovy deposit, apart from electric sounding methods (irreversible process of induced polarization, natural electric field) the mercury vapour method proved to be efficient. Positive results of geophysical surveys are also achieved on other gold-bearing deposits and when searching for and outlining of magnetite-titanium-apatite ores, tungsten, zirconium and other minerals. One good example of successful utilization of geophysical methods in search for and evaluation work as well as in prospecting of deposits is the evaluation of the deposits in Komsomolsk district. The above deposit was unfavourable for usual geological methods due to the conditions of ore-bearing horizons and the relief. Mine-sinking was necessary for the survey. It would require buying special expensive equipment, prolongation of prospecting time and additional allocations of money. Specialists from "Dalgeologia" developed another approach to prospecting the above deposit without mine-sinking and other hard underground work. The basic methodology comprises a complex utilization of column drilling, borehole geophysics, nuclear methods of logging, acquiring parameters of mineralization (thickness of ore-bearing bodies, content of useful components) directly in natural bedding of rocks and ores. On this basis, it was possible, without losses in quality, to fulfil the complete volume of mining and geological tasks in accordance with the required reliability and exactness of evaluation, correlation of ore-bearing bodies, determining the degree of mineralization, solving hydrogeological and engineering problems of preparation and transferring the deposit to industrial exploitation. Summarizing of bore hole geophysics and logging data is carried out on vertical longitudinal and cross sections, and horizontal plans. It makes geophysical and geological data comparable and contributes to the high quality and reliability of outlining and correlation of ore-bearing zones in space.

186

Utilization of technological mapping methods and selection of physical samples from the core of specially drilled holes of large diameter made it possible to solve the problem of quality and physical property evaluation of the ores in the deposit. For the first time in this deposit the method of X-ray radiometric enrichment (separation) of ores was tested. Later the experience was successfully used for evaluation of pre-enrichment of ores in other tin deposits. With X-ray radiometric enrichment, 40% of the ore is removed, with a tail content of only 0.07% Sn. The enriched remainder can then be processed economically. Complexing of geophysical methods and new drilling technologies made it possible to change to partially non-core drilling in a significant number of holes. At the same time the utilization of X-ray radiometric logging made it possible to significantly shorten sampling, transportation and processing of geological samples. As a result additional economic efficiency was achieved. Long-term experience accumulated by the specialists of "Dalgeologia" in the Komsomolsk region contributed greatly to the successful design and introduction of the above highly efficient prospecting technology In many areas. The economic benefit of utilizing this new prospecting technology exceeds 25 million roubles. REFERENCES 1. 2.

Yu.l. Bakulin, V.N. Gagaev. Criteria and methodology of complex evaluation of ore-bearing areas. Moscow, 1982. M.M. Konstantinov, I.Z. Isakovich et al. Methods of local forecast of latent gold and silver deposits. Moscow, 1989

Valery N. Gagavev is a chief geophysicist of "Dalgeologia" Association of the USSR Ministry of Geology. After graduation from the Sverdlovsk Mining Institute, he has acquired experience of long standing in applying geophysical methods of prospecting and exploration of ore deposits in Priamurie. He was closely concerned with the problem of local forecast and utilization of data on well geophysics and nuclear-physical methods when developing deposits and assessing reserves. He is a co-author of a monograph and of a number of scientific papers.

187

"tt

' I ' M

'Wl-mr

Fig. 1. Deep seismic (A) and geoelectric (B) sections of Konfisomoisl< (I) and Badziial (II) tin ore regions. 1 - observation stations; 2 - seismic boundaries; 3 - inversion seismic boundaries; 4 boundary M from gravitation prospecting data; 5 - isolines of relative electric conductivity; 6 - gravity anomaly; 7 - objects of increased electric conductivity; 8 tectonic zones (faults); 9 - ore-bearing structures.

188

Fig. 2. Model of Kondyor structure, and corresponding magnetic field AT, observed (A) and rated (B). 1 - metamorphic complexes of basement rocks; 2 - corneous rocks of plateau-form cover; 3 - olivinites, pyroxenites; 4 - dunites; 5 - ore pyroxenites with titanium-apatitemagnetite metallization.

189 DEPOSIT MODELS FOR DETRITAL HEAVY MINERALS ON EAST ASIAN SHELF AREAS AND THEIR GEOPHYSICAL EXPLORATION John Ringis UNDP/ESCAP, Bangkok, Thailand During the past ten years, many marine geophysical surveys for detrital heavy minerals have been conducted over the continental shelves of East Asia. The aim of the surveys has been to recognise and delineate the extent of sediment units or "packages" which constitute the most favourable depositional "models" for the detrital heavy minerals being sought. The main types of terrestrial sedimentary deposits or models in which economic detrital tin and other heavy minerals are found are alluvial/colluvlal deposits Immediately overlying bedrock, which grade into residual deposits and alluvial channel deposits. The main types of marine sedimentary deposits are shoreline beach/barrier placers formed along the present coastlines and at lower levels during previous lower sea level stands. The older shoreline deposits have undergone varying degrees of rewori<lng and modification during subsequent rises In sea level. In some cases this process may also have resulted In the formation of erosional lag placers. At the mouths of some rivers and estuaries, river mouth sand bar deposits may also be formed. The most important geophysical technique used In delineating the above depositional models is high resolution single channel seismic reflection profiling. Magnetics can be useful In helping to determine bedrock composition. Wide angle reflection/refraction profiling can also help in this and can be used to determine the sonic velocity in the unconsolidated sediments, a knowledge of which is necessary for accurate calculation of layer velocities and depths below datum. Seabed gamma-ray spectrometers are also being evaluated. Seismic stratigraphic concepts are the basis for interpreting the unconsolidated sediment sequences in terms of the composition (type) of sediments In different units and their depositional environments and thereby delineating units with the greatest potential for the occurrence of the minerals being sought.

THE ROLE OF GEOPHYSICS IN EXPLORATION AT JUNCTION REEFS AND THE SHEAHAN-GRANTS GOLD MINE, CENTRAL N.S.W. Steve Collins Arctan Services P/L, NSW Four economic gold deposits occur In the Junction Reefs area near Orange, N.S.W. Three of these are metasomatic replacement deposits within calcareous sediments. The fourth Is a structurally controlled stockwork zone adjacent to a late phase intrusion. The shallow dipping replacement deposits are associated with semi-massive pyrrhotite skarn and are both magnetic and electrically conductive. The stockwork body, which contains disseminated pyrite/arsenopyrite, is recognisable as a coincident magnetic low and radiometric high and is responsive to Induced Polarisation (IP) techniques.

190 Early geophysical exploration concentrated on ground magnetic and IP surveys. These surveys were generally unsuccessful in defining either the known mineralisation at the Sheahan-Grants deposit or new deposits due to the geometry of the mineralisation and strong magnetic and IP responses from surrounding country rock. An airborne magnetic and radiometric survey was flown over the Junction Reefs area. This survey helped to identify and map a large diorite intrusion which lies approximately three kilometres north of the mine. Within the magnetic response due to this intrusion is the magnetic low and radiometric high associated with the Glendale (stockwork) deposit. Recent geophysical work in the area has concentrated on detailed ground magnetic and electromagnetic surveys, searching for further gold reserves of the Sheahan-Grants style. The use of electromagnetic techniques has only been possible following the development of software for stripping the responses due to the many fences which cross the prospective area.

THE MOUNT LEYSHON ORE DEPOSIT: IMPLICATIONS

FOR REGIONAL EXPLORATION I. Hodkinson^ and B.D. Kay^* V a n Australian Mining, Mt Leyshon, Old ^Poseidon Exploration Limited, Adelaide, SA The Mount Leyshon gold mine, situated 23 km south of Charters Towers in Queensland, is operated by Pan Australian Mining Limited, a Company within the Normandy Poseidon Group. The mine produced 184,558 ounces of gold and 209,944 ounces of silver in 1989/90, with remaining ore reserves of 20.4 million tonnes grading 1.87 g/t Au. This is contained within an overall ore resource of 30.28 million tonnes grading 1.6 g/t Au (0.7 g/t Au cut-off). Additions to the ore resource during 1989/90 were achieved by drill testing of the extension of the Southern Orebody beneath Mt Hope. The Mount Leyshon gold mineralisation is hosted in breccias, porphyry plugs and basement rocks within a large diatreme or breccia complex. The diatreme complex of Permo-Carboniferous age occurs on the contact between Cambro-Ordovician metasediments (Puddler Creek Formation) and Ordovician-Devonian granitoids (Ravenswood Batholith). Three main stages of mineralisation have been identified with most gold being deposited during the final stage. Stage I contains quartz molybdenitechalcopyrite and pyrite gold veins with potassic alteration; Stage II involves chlorite pyrite matrix replacement and gold-bearing base metal sulphide veins and Stage III is quartz-base metal sulphide-bismuth sulphide electrum veins with sericite alteration. Mineralisation is thought to be high temperature (300-500^C) related to porphyry intrusive bodies, and possibly similar to other deposits in the United States (e.g. Cripple Creek, Ortiz). Key geophysical (magnetic, gravity and IP) and geological features (structure, intrusive activity, setting) have important implications for local and regional exploration programmes.

191 Technical Session 10(c) Coal, Groundwater and Engineering IV - Engineering

GROUND PENETRATING RADAR RESPONSE TO BOUNDING SURFACES AND LITHOFACIES VARIATIONS IN SAND BARRIER SEQUENCES P.L Baker Department of Earth Science, Monash University, Vic This paper investigates the ground penetrating radar amplitude response of typical lithofacies bounding surfaces in a sand barrier sequence. Ground penetrating radar reflection coefficients of typical bounding surfaces in a sand barrier sequence are computed using Time-average and Hanai-Bruggeman-Sen effective-medium mixing laws for the dielectric properties. The effects of lithological contrasts due to packing, porosity, grain shape and orientation, mineralogy and fluid content are calculated. Reflection coefficients are typically 0.05 to 0.1 but may range up to 0.45 for large dielectric permittivity contrasts. For a radar example recorded over a beach strandline, the relative reflection amplitude alone is generally insufficient to uniquely determine a specific type of bounding surface between two lithofacies. Other attributes of the section such as apparent dip magnitude and direction and the external form help to refine the interpretation. This interpretation approach is formalised by defining radar facies units as "groups of radar reflections whose parameters (configuration, amplitude, continuity, frequency, Interval velocity, attenuation, dispersion) differ from adjacent groups". Radar facies are distinguished by types of reflection boundaries, configuration of the reflection pattern within the unit, and the external form or shape of the unit.

INTEGRATING GEOPHYSICAL TECHNIQUES TO STUDY A SMALL CONFINED AQUIFER Paul J. Wolfe* and Benjamin H. Richard Depts of Physics and Geological Sciences, Wright State University, USA A small nature preserve in Ohio (USA) has an unusually cool environment due to artesian springs supplying cold ground water. This cool environment supports a collection of rare plants and animals. To understand the water supply so that it can be protected from encroaching development, a series of geophysical studies have been conducted over an extended period of time. The techniques include seismic refraction, seismic reflection, gravity, magnetics, and resistivity. These were supported by drilling and hydrochemical analyses. The results of these studies show that the nature preserve sits on the edge of a major buried valley which has been filled with outwash and till. The ground water appears to flow from a high area in the northeast through an outwash layer which is capped by till. Near the nature preserve later glacial advances caused erosion of channels through the till layer. These channels were back filled with permeable sand and gravel which allowed the cold confined ground water to upwell and cool the nearby areas.

192

EVALUATION OF P- AND S-WAVE SOURCES FOR SHALLOW SEISMIC REFLECTION S J . Hearn^*, M.H. Kay^ and O. Dixon^

Department of Geology, University of Queensland, Old ^Department of Resource Industries, Old The theoretical attractiveness of utilising both P and 8 reflection information is offset in the shallow environment by the practical difficulty of isolating high resolution reflections from other non-reflection energy. Source design is a critical component in a range of mandatory acquisition and processing optimisations. Four near-surface P-wave sources (high explosive, shotgun, weight drop, and hammer) have been evaluated in terms of their suitability for shallow reflection at a test site in the Ipswich Basin, southeast Queensland. Cross power spectral analyses of trace segments in the reflection window provide an estimate of the 'coherent bandwidth' of the different sources. Although the high explosive has superior signal levels, consideration of spectral symmetry, autocorrelation shape, and logistic aspects indicates that the shotgun source is a viable alternative. A pneumatic powered S-wave generator has been constructed and tested. Integrated spectral energies have been used to monitor piston velocity limitations and hence define optimum operating parameters. The pneumatic source is more controllable and of higher energy than a sledgehammer powered equivalent.

CHARACTERISATION OF AUSTRALIAN GROUNDWATERS AS AN EXPLORATION STRATEGY Angela Giblin CSIRO, Division of Exploration Geosclence Geochemical exploration techniques use the chemical composition of samples of soil, rock or water to identify sample sites that are close to potentially economic mineralization. The advantages of groundwaters as geochemical sample media derive from their chemical reactivity with crustal rocks and soils, coupled with their physical mobility. Advantages also attached to water as an exploration sample that integrates the geochemistry of a larger volume of the upper crust than do single samples of rock or soil. In addition, because groundwaters contact geological formations concealed beneath deep in situ or transported cover, groundwater geochemistry permits initial exploration in zones hitherto inaccessible to more conventional geological and geochemical techniques. Before any groundwater property can be interpreted as reflecting the presence of ore minerals in the aquifer, the non-mineralised, or baseline characteristics of the groundwater need to be assessed. For example, groundwater concentrations of trace elements that are not related to ore minerals, often correlate with groundwater salinity, which is influenced by both climate, and groundwater flow rates; with acidity or alkalinity, which is controlled by aquifer lithology; and with the groundwater's anionic

193 concentrations, as trace element solubilities can be either increased or diminished by complexing ions. Groundwaters can be characterised by aquifer type (hydrogeology) or more precisely by composition (hydrogeochemistry). Using the former, aquifers are classified by lithology as porous sedimentary, or fractured crystalline. These categories are further sorted by groundwater flow or productivity. Because aquifer lithology and groundwater flow directly control groundwater composition, hydrogeochemical characterisation of groundwaters refines hydrogeological classifications. In a continuing CSIRO, Division of Exploration Geoscience project geochemical exploration techniques have been developed that use groundwaters as sample media and apply the complete geochemistry of the water, not merely variations in concentrations of a target element. Principal groundwater geochemical properties that are applied to exploration for concealed mineral deposits are pH and redox potential, major ion composition and the trace element content. Procedures have been developed for data collection and interpretation using techniques that include statistical analysis of chemical data and comparison of measured trace element concentrations with their thermodynamically calculated concentrations in model Australian groundwaters equilibrated with common ore minerals. In addition, the important relationship between the major ion composition of a groundwater and aquifer minerals is investigated using major ion composition plots, normalised major ions, equilibrium with chemical precipitates such as carbonates, sulphates and carbonates! and products of groundwater alteration of silicate minerals. Data from this study have been compiled into a database that represents groundwaters from mineralised and barren regions within the major geological and climatic zones of Australia. The trace element content of groundwaters from each zone is depicted by overall concentration ranges, and by 95% confidence intervals of the median for each element. These provide predictive measures for baseline trace element concentrations for each different geological andclimatic zone of Australia. An example from this database illustrates the baseline concentrations of trace elements U, F, Cu, Pb, Zn, Cd, Al, Fe, Mn, B, P, Co, Mo, As and Li in a selection of study areas that includes examples of both fractured and porous aquifers, and waters which range in salinity from low to very high (median TDS ~ 72.5 g/l). In this example, for each trace element at least one study area has water samples in which the concentration exceeds the seawater, average fresh water and standard drinking water values. These values are also exceeded by the median 95% confidence interval, in at least one study area for all elements except Cu, As and Zn. Clearly, recorded average values for trace element concentrations in common natural waters are not adequate as indicators of baseline concentrations in Australian groundwaters. An example of the exploration value of groundwater geochemistry comes from a 197678 study of groundwaters beneath the Mageela flood plain in what is now the Kakady area. Many samples of pristine groundwater had sulphate concentrations exceeding 1000 mg/l, pH values as low as 3, and concentrations of Cd, Pb, Cu and Zn such that had mining ever taken place they would probably have exceeded the allowed limits for water release from the mine site. These groundwater characteristics set the area apart from non-mineralised regions of the Northern Territory and can be used as evidence for the proximity of the Jabiluka U-Au deposits, upflows from the sites where groundwater samples were collected.

194 Technical Session 10(d) Regional, Cmstal and Geothermal VI Sediments and Stmcture of Basins and Rifts

MODELLING THE FILL OF SEDIMENTARY BASINS J.C. Tipper Department of Geology, Australian National University Conventional sediment transport models are ideal, in theory, for modelling how sedimentary basins fill, but in practice there is rarely adequate data to constrain them. An alternative approach recognises that any basin is a spatially varying sedimentation system, evolving in time towards a steady state, and that its state at any time can be characterised by what can be termed the 'degradation potential' field. (The instantaneous degradation potential at any point is a reciprocal function of the expected survival time of any sediment then being deposited there.) The process of basin filling can be modelled as one of potential-driven flow: as the degradation potential field changes in time, so does the configuration of the depositional surface, and this can be calculated. This potential-driven flow model has been implemented using a finitedifference approximation over an irregular triangular mesh. It predicts realistic basin fill patterns, in three dimensions, and is computationally very economical.

STRUCTURE AND STRATIGRAPHY OF THE NEW CALEDONIA BASIN Chris Uruski and Ray Wood* DSIR Geology and Geophysics The New Caledonia Basin is a major bathymetric feature extending northwest from Taranaki, New Zealand, between the Challenger Plateau/Lord Howe Rise and the Norfolk Ridge. Interpretations of gravity data and seismic refraction velocities indicate that crustal thinning did not proceed to formation of ocean crust. Rifting was preCenozoic, and may be pre-Cretaceous. Major transverse or transform faults may have accommodated oblique rifting. Cenozoic volcanism was influenced by these earlier structures. Channels and turbidites within the Plio-Pleistocene section reveal the continuation of a submarine distributary system from the Taranaki continental shelf. Seismic stratigraphy, the volume and thicknesses of sediment observed, and the likely maturation levels suggest potential for hydrocarbon accumulations.

195 DEEP SEISMIC REFLECTION LINES ACROSS THE RHINE GRABEN Friedemann Wenzel* and the ECORS/DEKORP Working Group CSIRO, Division of Exploration Geoscience Two reflection seismic lines across the Tertiary Rhine Graben in Central Europe were recorded in 1988 as a joint venture of the French ECORS and the Germany DEKORP deep seismic programs. As a main result the asymmetry of the graben, as documented by the sedimentary fill, is accompanied by asymmetric features throughout the entire deep crystalline crust. Moho depth, lower crustal thicl^ness and reflectivity pattern vary significantly across the graben. Extension occurred along shear zones that are documented in the upper crust and at the crust/mantle boundary.

RIFTING AND PETROLEUM POTENTIAL OF SIBERIAN SEDIMENTARY BASINS V.S. Surkov* and V.I. Lotyshev USSR Ministry of Geoiogy, NPO SIBGEO Krasnii prospekt, 67, Novosibirsk, 630104, USSR ABSTRACT. The main features of modern Earth crust structure in Siberia were formed under the influence of major tectonic-magmatic megacycles. Within the limits of each megacycle the crust undenwent two principal stages: predominant extension (destructive stage) and predominant compression (constnjctive stage). By the beginning of Riphean the Earth continental crust was formed, affected by the tectonic-magmatic megacycles. Its further development was predetermined by subsequent megacycles, each appeared to begin, as we believe, with rifting. The most striking rifting manifestation is found in Riphean on the ancient Siberian Platform and in Triassic within the limits of the young West Siberian Plate. Modern sedimentary basins here resulted from rifting. They were formed in conditions of the Earth Crust Extension, increased tectonic activity and heat flow, which favoured high hydrocarbon concentrations in sedimentary units. Key words: tectonic-magmatic megacomplexes, rifting, graben-rift, sedimentary basins, petroleum potential. INTRODUCTiOl^ Tectonic-magmatic megacycles in Pre-Karelikum and Karelikum development stages led to the formation of continential crust over the vast Laurasian area at the end of the Middle Proterozoic. Being heterogeneous in thickness and composition the crust consisted of the oldest granite-greenstone cores, separated by Archean - Early Proterozoic permobile granulite-greenstone and paragneiss belts. Beginning with the Riphean, a principally new stage in the Earth crust development began. Within 1600 million years the Riphean, Late Riphean - Paleozoic and Late Paleozoic - Mesozoic megacycles manifested themselves, each of them commenced with crust destructive associations and completed with constructive ones. PaleozoicMesozoic megacycles, the destructive stage of which has begun in the Triassic and

196 continues nowadays, is an exclusion. Riphean rifting within the limits of the ancient Siberian Platform and Triassic rifting on the young West Siberian Plate exert most influence on the formation of the Earth crust structure and petroleum potential of sedimentary basins. INTERPRETATION Combination of gravitational, aeromagnetic, electrical, seismic, and well data available was interpreted in terms of the technique of geophysical and geological cointerpretation. This gave information on the structure of the Earth crust and upper mantle, thickness and structure peculiarities of major tectonic-magmatic megacomplexes of consolidated crust and sedimentary cover, development of the Earth crust, formation of sedimentary basins and their oil and gas potential. A part of the information is represented here as a map of Riphean sedimentary basin types (Figure 1), a section of the upper Earth cnjst (Figure 2), and a scheme of Triassic rift system of the West Siberian Plate (Figure 3). DISCUSSION 1. Riphean rIftIng At the beginning of the Riphean, mantle processes resulted in splitting of a single Laurasian protoplatform into plates, their divergence and isolation of East Russian, Siberian, North Chinese and Tarimian Plates. Intracontinental rifts were formed mainly where granulite-greenstone belts occurred that resulted in initiation of the Ural and Central-West Siberian branches of the Ural - Mongolian foldbelt as well as aulacogens and sedimentary basins of various types within the Siberian Platform. The Riphean sedimentary basins (Figure 1) are differentiated into two groups: marginal cratonic and intracratonic ones (Surkov et al., 1987). The first group consists of sedimentary basins of pericratonic troughs, foredeeps and transversal aulacogens. The marginal transversal aulacogens have been incorporated into a special type. A graben feature of structural forms, the nature of their position in regional structure of the Siberian Platform as well as their genetic relation to geosynclinal system were the reasons for their distinguishing. The section is characterized by a complex combination of volcanogenic and volcanogenic-terrigenous, carbonate-terrigenous and carbonate rocks with thickness variation from 1 to 3 km. A group of intracratonic sedimentary basins includes aulacogen basins and cataplatform depressions. Main features of aulacogen-type sedimentary basin structure are now due to their rift origin and style of subsequent development. Early stages are marked by alternation of volcanogenic-terrigenous and volcanogenic-carbonate rocks. There is rhythmical interbedding of terrigenous and terrigenous-carbonate rocks up the section. The thickness of sediments varies from 0.5 to 3.5 km. Distribution of particulate organic matter and its catagenetic transformation indicate high petroleum-generating potential for the Riphean sedimentary basins. Regional development of high-quality seals of Upper Vendian argillaceous evaporite-carbonate units and Lower Cambrian salts favours high preservation of hydrocarbon accumulations.

197

2. Triassic rifting At the destructive stage of the Late Paleozoic-Mesozoic the megacycle systems of linear tension faults, rifts, were formed in consolidated crust of the West Siberian Plate under the influence of mantle inhomogeneities. Figure 2 shows rift zones along basement surface which form graben depressions. Graben-rift zones are filled with magmatic units of basic and ultrabasic composition. They are characterized by higher seismic wave velocities, positive gravitational and magnetic anomalies (Surkov, Smirnov, and Zhero, 1987). Stable downwarping, started in the Triassic, resulted in the formation of the West Siberian sedimentary megabasin. Graben-rifts formed by rifting continued inherited movements in Mesozoic-Cenozoic time. Being the youngest tectonic elements of consolidated crust they were dominated in the formation of Mesozoic-Cenozoic sedimentary cover structures. Major trench zones with thick Mesozoic-Cenozoic deposits were formed over the graben-rifts as a result of their downwarping (Figure 3). In the West Siberian megabasin rifting predetermined the formation of two structural stages: lower plate (continental deposits T3-J2) and upper plate (marine deposits J3, coastal-marine deposits Cr and Q) ones. Tectonic movements within rift zones affected mostly structures and facies composition of the lower plate complex. Within the limits of graben-rifts the thickness of this complex is higher, up to 5 km. It has high concentration of organic matter both of sapropelic and humic types. The complex deposits had all prerequisites for enhanced generation, emigration and formation of large hydrocarbon accumulations.

3. Global rifting manifestation The Riphean and Triassic rifting manifested itself within the whole of the Northern hemisphere. Riphean rift systems and associated sedimentary basins occurred within the Russian (the Dnepr - Donetsk aulacogen, etc.) and North American Platform (the Midcontinental Rift, etc.). Triassic rifting resulted in the formation of Mesozoic-Cenozoic sedimentary basins of the North, Non/vegian, Barents, Kara Seas, as well as Saint Lawrence, Baffin Bay, and Paris basins. The Northern hemisphere paleorift and rift zones are characterized by several similar geophysical, geological and geomorphological features. They include linear extensive positive anomalies in gravity and magnetic fields, linear negative relief forms (rift valleys), decreased thickness of the Earth's crust, lower velocity on the upper mantle surface, increased heat flow and wide development of basaltoid magmatism.

CONCLUSIONS Rifting manifested in the Riphean has resulted in Riphean sedimentary basins on the Siberian Platform. For the first time in world geological practice, commercial hydrocarbon accumulations have been discovered there. Rifting in the Triassic has induced the vast West Siberian megabasin with its unique oil and gas fields within the upper plate structural complex.

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The lower plate complex with maximum thickness within graben-rlft zones also shows high petroleum potential. Geological and geophysical characteristics observed allow the distinguishing of rift zones in poorly studied regions or In regions hidden by the platform cover including the ancient Australian Platform. ACKNOWLEDGMENTS The authors are thankful to M.P. Grishin, O.G. Zhero, L.V. Smirnov from HPO SIBGEO for their contribution to the interpretation of geological and geophysical data. Our thanks go to Robert J. Smith, Chief Geophysicist of CRA Exploration Pty. Limited and Keeva Vozoff of the Technical Program Sub-committee, for their proposal to submit this paper to the 8th ASEG - GSA Conference. REFERENCES Surkov, V.S. et. al. (1987), "Megacomplexes and Earth deep structure of oil and gasbearing Provinces of Siberian Platform", Moscow, Nedra, 204 p. Surkov, V.S., Smirnov, L.V., Zhero, O.G. (1987), "The early Mesozoic Rift genesis and its effect on the structure of llthosphere of the Western Siberian Platform". Geology and Geophysics, 9, 3-11.

Victor S. Surkov Is an Academician of the USSR Academy of Sciences, Director General of NPO "SIBEGO", Director of Siberian Institute of Geology, Geophysics and Mineral Resources of the USSR Ministry of Geology. He graduated from the University of Kazan in 1950. For over 35 years he has worked on problems related to geology, tectonics, geophysics of Siberia and forecasting of its oil, gas and mineral reserves. He has participated in many sessions of the International Geological Congress. Vassilly Lotvshev graduated from the University of Gorkii with M.Sc. in 1957. For 15 years he worked for the Siberian Geophysical Trust of the USSR Ministry of Geology as a geophysicist then as a Party Executive dealing with field geophysical surveys and the interpretation of gravity and magnetic data. In 1961-1965 and 1968-1971 he served with Oil and Gas Development Corporation of Pakistan as Technical Leader of three field gravity parties. In 1972 he joined the Siberian Institute of Geology, Geophysics and Mineral Resources (SNIIGGIMS). in 1980 he received Ph.D. in Geology and Mineralogy. From 1983 he has been a Science Secretary of SNIIGGIMS. His main research interest is in the interpretation of geophysical and geological data to study the deep crustal structure of Siberia and the ancient platforms of the northern hemisphere. He was a participant In the 27th and 28th International Geological Congress. He is the member of ASEG.

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50 Hm

Figure 1. Types of Riphean sedimentary basins on the Siberian Platform (after IVI.P. Qrishin, V.I. Lotyshev, V.S. Surkov, et al.) -1,2 - marginal-cratonic basins: basins of pericratonic troughs and foredeeps (1), basins of marginal transversal aulacogens (2); 3,4 - intracratonic sedimentary basins: aulacogenic ones (3), basins of cataplatform troughs and depressions (4); 5 - areas of Riphean complex lacking; 6 - marginal sutures of Siberian Platform.

200

S, m/m\n years 60-

Berezovo -1

Igarka

Figure 2. Structure of upper Earth crust of the West Siberian Plate (after V.S. Surl^ov, L.V. Smirnov, O.G. Zhero) - 1 - upper plate complex (J3-Q); 2 - Lower plate complex (T3-J2); 3 - Paleozoic platform mantle of Siberian Platform; 4 - consolidated crust; 5 paleorifts; 6 - faults; 7 - residual gravity; 8 - boundary velocities along consolidated crust surface; 9 - S plot of sediment accumulation rate (lower plate complex).

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Figure 3. Triassic rift system of the West Siberian Plate (after V.S. Surl<ov, O.G. Zhero, et al.) - 1 - Triassic graben-rifts; 2 - trench zones over Triassic graben-rifts with increased thickness of iVIesozoic-Cenozoic deposits; 3 - boundary of iVlesozoicCenozoic cover.

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Poster Session Petroleum Exploration PALAEOGEOGRAPHY AND SEQUENCE STRATIGRAPHY John Bradshaw''*, Marita Bradshaw''Robert Langford^ and Gerry Wilford'' ^Bureau of Mineral Resources, Canberra, ACT ^BHP-Utah The BMR-APIRA Palaeogeographic Maps Project has produced a series of palaeoenvironmental maps for Australia for seventy time slices covering the period from the Cambrian to the Recent. The second phase of the study, the BMR-APIRA Phanerozoic History of Australia Project, has supplemented the original "map" view of the continent with a grid of regional cross-sections based on well, seismic and outcrop data. The poster shows the integration of the seven Cainozoic palaeogeographic time slice maps with seismic from the offshore Canning Basin regional cross-section. The seismic line (JN-07), shows a series of sedimentary packages that include thick prograding units in the Cainozoic. Similar prograding sequences are repeated along the margins of the continental shelf of northwestern Australia, and in many places around the world producing the characteristic "sedimentary signature of the Neogene" as recognised by Vail. In this Australian example there is a close correlation between the palaeogeographic maps for each of the respective time slices in the Cainozoic with the seismic packages. Periods suggesting low sea level from the palaeogeography correlate with thick prograding sedimentation on the continental margin (Cainozoic time slice 5). Conversely periods of high sea level on the palaeogeographic maps correspond to coastal onlap on the continental margin sequences (Cainozoic 1,2,4,6 and 7). Within single time slice intervals, two or more different sequences can be identified. A major time break in the Oligocene (Cainozoic 3), which was due to rapid sea level fall, is indicated by the sparseness of data on the palaeogeographic maps, and corresponds to an unconformity and the base of the thick prograding units on the seismic section.

NON-DESTRUCTIVE CORE ANALYSIS USING X-RAY COMPUTED TOMOGRAPHY L. Cosheir, J. Scott, A.M. Knights, B.J. Evans and M.W. Hill Curtin University of Technology, School of Physical Sciences and Key Centre for Resource Exploration, Perth X-ray computed tomography (CT) is a non-destructive means by which the internal structure of an object may be viewed. It produces a digital image that is a map of the Xray attenuation in a slice through the object. At Curtin University, this technique has been successfully applied in the analysis of various rock materials, including four inch diameter cores from the petroleum exploration industry. Two scanners, an EMI CT5005 (second generation machine) and a Seimens SOMOTOM DR/H (third generation), both in routine medical use at local Perth hospitals, have been used in this work. Interpretation of X-ray CT results is facilitated by high resolution colour graphic display on a Landmark seismic workstation. CT images have revealed sedimentological and stnjctural features in cores that are, in some cases, quite unexpected, and would not be

203 apparent utilizing conventional (i.e. destnjctive) core analysis techniques. X-ray CT has much potential for core characterisation and reservoir modelling; it can measure mineral distributions, depositional textures, porosity variability, fracture frequency and orientation, and fluid saturations. Core quality parameters such as the degree of drilling mud invasion can also be assessed. Importantly, X-ray CT can image the internal structure of sealed (i.e. preserved at the rig site) cores.

THE NUMERICAL MODELLING OF SANDSTONE PINCH-OUTS AND DRAPES IN THE BOWEN BASIN, QUEENSLAND Brian Evans^*, Paul Carter^ and David Khoo^ ^Curtln University of Teclinoiogy ^Minora Resources NL Although the Bowen Basin is considered to provide good quality seismic exploration records, the limits of seismic resolution are tested when attempting to interpret sandstone pInch-outs and drapes. Exploration is hindered by seismic resolution constraints in both the vertical and lateral directions. Exploration in the Bowen Basin frequently concentrates on the Rewan Formation and Showgrounds Sandstone, one objective being to determine if a sandstone pinch-out, drape or fault has disrupted hydrocarbon migration paths. This paper stresses that to assist the determination of whether a potential target is a drape over, or a pinch-out against a basement high, it is desirable to initially build a geophysical model to simulated seismic surveys over a number of models, results indicate that the top of the Showgrounds Sandstone could be interpreted where its thickness was greater than 10 metres. It was also apparent that a 10 metre drape over the top of the basement high could not be detected with reflection data of frequency content less than 70 hz.

SOURCE OF METALS IN THE MISSISSIPPI VALLEY-TYPE DEPOSITS IN THE CANNING BASIN, NORTHWESTERN AUSTRALIA B.L Gulson''", H. Etminan^ and K.J. Mizon'' ^CSIRO Division of Exploration Geoscience ^BMR, Canberra Debate on the source of metals within Mississippi Valley-type deposits has occupied the literature for over 20 years. Earlier Pb isotope source rock investigations in the USA were inconclusive because of the uncertainty of the role of the supposed source rocks versus their role as aquifers for the hydrothermai solutions. The Cannina Basin is an extensive Phanerozoic intracratonic basin covering over 400 000 km^. In its northern part, the basin hosts the fault-bounded Fitzroy Trough, containing over 10 km of Palaeozoic sediments. The northern margin of the basin is occupied by a 350 km long Devonian reef system (the Lennard Shelf) which is separated from the Fitzroy Trough by a series of major basin-margin faults trending northwest to southeast. The Lennard Shelf is underlain by Proterozoic granitic

204

basement. Minor petroleum and significant Zn-Pb mineralization is found in the Lennard Shelf (Blendevale, Cadjebut, Wagon Pass), whereas in the south of the Canning Basin Zn-Pb mineralization occurs at depths of > 1200 m and the area is therefore less explored. Some non-economic oil has also been found in association with Zn-Pb deposits in the southern Canning Basin. As part of the BMR Canning Basin Project on aspects of the hydrology of oil and metal bearing brines, Pb isotope analyses of sulfides, potential source rocks, basinal brines and oil have been undertaken to constrain the source of metals for Zn-Pb mineralization and to examine the relationship between the sulfides and oil. Sulfides from the Wagon Pass, Pillara (Blendevale) and Admiral Bay deposits show relatively uniform internal isotopic homogeneity but the individual populations, represented by 95% confidence ellipses, lie along linear trends {Fig. 1). Data from the Sorby Hills deposit in the Bonaparte Gulf also lie on these trends. In the Lennard Shelf, data for Proterozoic basement granites and their possible conglomerate and sandstone derivatives lie on linear arrays and have higher 208pb/204pb and 207pb/204p|3 ratios than argillaceous sediments and carbonates (Fig. 1). Most granite analyses lie within or close to the 95% confidence ellipse for the G. Ir wncoN pnss IG.O Q_ sr o _Q CL fv o

GRRNITES 8.

piLinRn 15.9

LENNRRD SHELF

RDMIRni BRY 15.8

YULLEROO FM / FITZROY TROUGH

15.7

LENNRRD SHELF SILTSTONE/SHflLE

o LENNARD SHELF CflRBONflTES •

STH CANNING BflSIN CflRBONflTES

15.G

STH CflNNING BflSIN SHRLE/SILTST

206p

.204 D

Figure 1. 207pb/204pb vs 206pb/204pb pj^^ f^^ samples from the Canning Basin. Lines of best fit are drawn for the granites and possible derivative sandstones from the basement, and sediments from the Lennard Shelf. The 95% confidence ellipses for the sulfides are also drawn. Dashed line is Pb evolution curve of Cumming and Richards (1975).

205 Wagon Pass sulfides whereas data for the argillaceous sediments lie within or close to the Pillara ellipse. Points for the Yulieroo siltstones from the Fitzroy Trough lie well below the Lennard Shelf data (Fig. 1) showing that the siltstones are not a direct nor major source for the Pillara mineralization. Pb isotope data for argillaceous and carbonaceous sediments from the South Canning Basin plot very close to the 95% confidence ellipse for the Admiral Bay sulfides (Fig. 1). On the basis of the relationships between the rocks and sulfides it is suggested that the main metal contribution to the Wagon Pass deposit was from the Proterozoic granite and its derivatives. This is supported in part by the shorter vertical distance from the deposit to the underlying basement compared with the Pillara and Admiral Bay deposits. At Pillara, and in the South Canning Basin, the main contributor was the argillaceous sediments, with a significant component of granitic basement for Pillara. Fluid inclusion homogenization temperatures for Zn-Pb deposits are all in the range 80 to 115°C (Etminan and Hoffmann, 1989) indicating that temperature was not a significant factor in the formation of the deposits. Thus the large isotopic variation at Wagon Pass is attributed to: (1) the isotopic variability in the granite and derivatives arising over the period from the time of formation of the granite to accumulation of metals in the sulfide deposit, (2) poor isotopic homogenization during the formation of sandstones and conglomerates, and (3) a smaller hydrothermal system. At Pillara, a larger hydrothermal system and extraction of the metals mainly from argillaceous sediments, already partially homogenized during sedimentation, would provide a more homogeneous isotopic signature. Any contribution from the Proterozoic basement (allowed by the intersection of the "granite" line with the 95% confidence ellipse for the Pillara sulfides) would be homogenized by the larger hydrothermal system. A relatively homogeneous argillaceous source and large hydrothermal system would also explain the Admiral Bay sulfide data. The low Pb content and absence of a hydrothermal overprint in most of the carbonates indicate that they have not been a major contributor to the Pb-Zn deposits. Oils and a basinal brine from the Harvey Fault show evidence of anthropogenic contamination, possibly from drilling mud. References Cumming, G.L. and Richards, J.R., 1975. Earth Planet. Sci. Lett. 28,155-171. Etminan, H. and Hoffmann, C.F., 1989. Geology 17,19-22.

TECTONOSTRATIGRAPHIC EVOLUTION OF THE VULCAN SUB-BASIN R.R. Hillis*, J. Lorenzo and C.C. von der Borch The Flinders University of South Australia The Jabiru and Challis/Cassini fields of the Vulcan Sub-basin (Timor Sea, North West Shelf, Australia) contribute over 10% of Australia's current oil production. Another field, Skua, is in the process of coming into production. Further significant, but currently noncommercial discoveries have been made at Puffin, Oliver, Montara/Bilyara, Talbot and recently Tahbilk. The combined exploration budget for the area over the period 19891991 inclusive is some $1 billion (Aust). Within the context of this exploration an ERDC

206

(Energy Research and Development Corporation, formerly NERDDC) sponsored study of the tectonostratigraphic evolution of the Vulcan Sub-basin is being undertaken at Flinders University through 1991-1992. This poster display presents some of the initial results of this project. Borehole Breakout Analysis: Borehole breakout data suggest the current maximum horizontal stress in the Vulcan is oriented NE-SW, parallel to the post-mid Pliocene Australia/Banda Arc collison zone at Timor Trough. This initially surprising result has important implications for the nature of the trap-forming and modifying Miocene-Recent tectonism in the Vulcan. See conference volume paper for further details. Neogene Wireline Log Stratigraphy: Only limited biostratigraphic analysis may be applied to the sparsely sampled Neogene sequence of the Vulcan. Nonetheless the timing and distribution of Neogene deposition hold important clues to the nature of Miocene-Recent tectonism. A Neogene wireline log stratigraphy has been developed with limited biostratigraphic calibration. The development of this log stratigraphy has already revealed uplift in excess of 1 km at Ashmore Reef-1 during the mid Pliocene, N20 zone unconformity associated with collision in the Timor area. Subsidence Analysis: Interpreted seismic reflection records have been depthconverted and decompacted in order to analyze the syn-(Callovian-Valanginian) and post-(Valanginian-Palaeocene) rift subsidence of the Vulcan. The 2-D subsidence data have been modelled by the sophisticated coupled simple shear/pure shear model of lithospheric extension. The results reveal the likely distribution of crustal and mantle lithospheric stretching during basin formation, and hence provide data on palaeoheatflow in the basin.

GEOLOGICAL DEVELOPMENT AND HYDROCARBON POTENTIAL OF THE OFFSHORE NORTH PERTH BASIN J.F. Marshall", C.-S. Lee, D.C. Ramsay, G.W. O'Brien and A.M.G. Moore Division of Marine Geosclences and Petroleum Geology Bureau of Mineral Resources, Canberra The major tectonic and stratigraphic elements of the offshore North Perth Basin have been delineated from regional BMR multichannel seismic reflection lines, together with industry seismic and well data. An interpretation of these data indicates that three subbasins, the Edel, Abrolhos, and Houtman Sub-basins, have each formed as a result of distinct rifting episodes during the Early Permian, Late Permian and Early Cretaceous respectively. During this period, rifting has propagated from east to west, and has culminated in the separation of this part of the Australian continent from Greater India. During the Early Permian, the Edel Sub-basin underwent a period of rifting and extension, resulting in a series of rotated fault blocks with relatively shallow decollement of their extensional faults. A post-rift aggradational phase is considered to have laid down Late Permian to Middle Triassic marine, fluvial and alluvial sediments. The Edel Sub-basin has accumulated about 6000 m of sediment and has undergone relatively little subsidence compared to the other sub-basins. This is attributed to the relative lack of sub-detachment thinning during the rifting phase. The sub-basin is relatively unexplored and its petroleum potential is difficult to assess. However, Permian and

207 Early Triassic sediments that have generated hydrocarbons onshore are believed to extend into this sub-basin. Rifting in the Abrolhos Sub-basin during the Late Permian created a series of rotated fault blocks that subsided progressively to the west. The relatively thin basal syn-rift sequence within the sub-basin was followed by a prolonged rift phase of Early Triassic to Early Cretaceous alluvial, fluvial and marine deposits. Reactivation of the fault blocks during the third phase of rifting in the Early Cretaceous produced numerous "flower-like" structures that are potential hydrocarbon traps. This, and the deposition of significant source rocks, makes this sub-basin highly prospective. T h e Houtman Sub-basin is considered to have undergone rifting in the Late Jurassic/Early Cretaceous, prior to breakup in the Neocomian. Whatever syn-rift sediments were deposited at this time have been removed by erosion, presumably as a consequence of thermal uplift produced by cmstal thinning immediately before the onset of drift. The sub-basin contains an earlier rift sequence of mainly Jurassic rocks, which have undergone wrench faulting to produce numerous positive and negative flower structures. Sediment thicknesses and geohistory analysis assume that the Early to Middle Jurassic sequence is mature to marginally mature; the only well drilled so far in this sub-basin encountered shows of gas. Water depth (generally greater than 750 m) is presently a major impediment to exploration in the Houtman Sub-basin. However, in the northeastern sector a considerable part of the sub-basin exists beneath the outer continental shelf. Differential subsidence of the margin, following decay of the thermal anomaly subsequent to breakup in the Early Cretaceous, has produced a seaward-thickening wedge of predominantly marine sediments on the upper slope, terminating in the deposition of pelagic oozes on what is presently a sediment-starved continental margin. The boundaries between the sub-basins and many structures within individual subbasins are considered to have been produced by oblique-slip motion. The North Perth Basin is believed to be a product of transtension, possibly since the earliest phase of rifting. This has culminated in separation and seafloor spreading along the Wallaby Fracture Zone to form a transform passive margin. This style of rifting and extension has tended to produce relatively thin syn-rift sequences, some of which have been either partly or completely removed by erosion. While the source rock potential of the syn-rift phase is limited, there are marine transgressional phases and coal measures within the sub-basins that do provide adequate and relatively widespread source rocks for hydrocarbon generation. Differences in the timing of rifting across the basin have resulted in a maturation pattern whereby mature sediments become younger to the west.

208 INTERPRETATION OF THREE-COMPONENT SEISMIC DATA D.R. Miles'"*, G.S. Gassaway^, LE. Bennett^ and R.A. Brown^ ^Terra Linda, Canada ^Terra Linda Group The three waves types, Pressure (P) waves, Shear (S) waves and Converted waves, which are generated from dynamite, vibroseis, or other conventional seismic sources, contain the information most used in seismic interpretation: time and velocity. The interpretation of three-component seismic data hinges upon the ability to correlate the P, 8 and converted waves to each other, so that their velocity and time information can be related to specific formations. Thus the first step in the interpretation is to process the data and then to tie the processed sections from each of the three types of data to each other. This is accomplished through either well log velocity ties for P, S and converted waves or through a three-component AVO inversion (Miles and Gassaway, 1989). The AVO analysis has the benefit of being self checking; the P wave velocity predicts the 8 wave velocity and the 8 wave velocity in turn predicts the P wave velocity. Once the P, 8 and converted wave correlations are known, the P and 8 wave isochron thicknesses, tp and ts respectively, can be found. The ts/tp ratio is the Vp/Vs ratio for that layer and from it Poisson's ratio can be calculated for the zones of interst. Poisson's ratio versus P wave velocity crossplots are then used to interpret lithologies and pore fluids in specific layers. Thus with three-component seismic data and three-component AVO analysis, correlation of the P, 8 and converted wave data is available to the explorationist. This added information assists in estimating lithology and pore fluids in the zone of interest and thereby improves the success ratios in exploration.

ADVANCES IN TECHNIQUES OF SURFACE GEOCHEMICAL EXPLORATION FOR HYDROCARBONS IN AUSTRALIA Don Rigby* and Rob Pallaser CSIRO Division of Expioration Geoscience, Sydney The chemical composition and abundance of hydrocarbons which migrate from underground accumulations to the soil surface is affected by many factors. A lack of understanding and/or poor data quality has resulted in a limited acceptance of surface geochemical prospecting methods for petroleum and robbed the industry of a potentially powerful exploration technique. In contrast to changes which occur in chemical composition, the isotopic composition of gases found in the surface of soils is not greatly affected by migration or by meteorological effects. However the isotopic composition can be changed by mixing and by isotope effects during secondary alteration. These changes in isotopic composition can provide a basis for the interpretation of data collected during geochemical surveys.

209 Methods have been developed to investigate the changes which occur in abundance and composition of soil hydrocarbons using stable isotope techniques. It was found that meteorological factors could be reduced by changing the sampling strategy to suit the environmental conditions. The reconstruction of hydrocarbon profiles in soils by "delayed gas sampling" or soil sorbed gas analysis resulted in a dramatic smoothing of the original profiles. The residual variance in these profiles was explained on the basis of stable isotope measurements as gas mixing with non petroleum related hydrocarbons or by aerobic bacterial oxidation of the soil hydrocarbons. Variations in soil type, moisture, Eh and pH control the microbial activity and can result in "pseudo" hydrocarbon anomalies. It is concluded that the major factor which controls the abundance and composition of hydrocarbons as they migrate from the reservoir, through the soils and into the atmosphere is the "soil gas residence time". When soil gas residence times are low meaningful data can be obtained by geochemical shallow (1 m) pore gas surveys as commonly used in Australia. As the residence time rises other sampling strategies are required. This can explain the varying degrees of success which have been achieved when only 1 sampling method is used for surveys in all environments. The investigation has resulted in a proposed petroleum exploration strategy based on geochemical soil gas analyses. This investigation was funded by a National Energy Research, Development and Demonstration Grant number 1250.

RECENT ADVANCES IN SEISMIC IMAGING Karl L. Schleicher* and Matthew A. Brzostowski Halliburton Geophysical Services, Inc. Recent advances in prestack and post-stack seismic techniques have resulted in improved final images. The greatest improvement has been made in the increased dip range that can be routinely processed using DM0 and steep-dip post-stack time migration. Moderate cost and insensitivity to velocity errors have contributed to the acceptance of these processes. We discuss recent advances that improve the accuracy of these processes and describe the limitations that still remain. DM0 has become standard in prestack processing sequences. Recently true amplitude 3-D DMO with an economic approach to 3-D asimuth and midpoint distribution was introduced.d The steep dips imaged by DMO has caused an increased sensitivity to velocity. This has led to new interest in migration velocity analysis. Other advances have been in post stack imaging. Frequency (grid) dispersion in finite difference migration is a well known problem. This is due to the replacement of partial derivatives in the wave equation by finite difference operators. Recent wori< has shown, careful selection of sampling parameters allows these errors to be minimized. Finally! errors in the depth conversion of time-migrated data using an image ray correction have been computed. These errors indicate the dip limitations of the image ray concept.

210 These advances involve improved event positioning in addition to amplitude and wavelet preservation. Incorporating these advances into a production sequence ensures more accurate seismic sections.

THE CHARACTERIZATION AND EVALUATION OF CRUDE OILS AND SOURCE ROCKS - THE ALKANE APPROACH John W. Smith''*, Don Rigby^ Luo Binne^, Song Zhiguang^ and Wang Yuxiao^ ^CSIRO Division of Expioration Geoscience ^Lanzhou Institute of Geoiogy, Academia Sinica, Cliina A factor often given insufficient attention in the estimation of the potential petroleum prospectivity of source rocks is the chemical composition of the liquid products generated in the source rock assessment procedures. All too commonly the yield of liquid or volatile products from laboratory tests is accepted as a guide to sediment prospectivity without regard to the chemical composition of the products in relation to that of crudes. Clearly it would be of advantage to the exploration industry if a simple direct method for such a comparative chemical assessment of these laboratory products relative to crudes were available. In this regard, a range of primary terrestrial Australian and Chinese crudes have been characterized in terms of their alkane distributions and contents. When these data are presented in a ternary diagram it is evident that primary crudes may be identified by a nalkane/total alkane (n/T) ratio of 0.20 to 0.56 and by a non-alkane content of < 60%. By the use of these compositional parameters, the maximum petroleum potential of liquid products resulting from any procedure for evaluating source rocks may be directly determined. In this preliminary study, the products from the hydrous pyrolysis of carbonaceous rocks from the Sydney and Gunnedah Basins and from Chinese lacustrine and shallow swamp, coal-forming environments have been evaluated by this procedure and the maximum petroleum potentials of these rocks determined.

A MULTI-DISCIPLINARY APPROACH TO AVO ANALYSIS J.A. Ward^*, M.A. Hall^, T.C. Southren^ '•simon-Geoiithlc, Houston, Texas, U.S.A. ^Simon-Geolithic, Swanley, Kent, England The RECON AVO method described by Nelson (1989) is based on the SHUEY approximation (Shuey 1985). A linear regression is fit to amplitude as a function of the incident angle. The intercept (Rd) of the regression is approximately the reflectivity at zero-offset, and is the best match to borehole derived synthetic seismograms. The slope of the regression (G) is the gradient, a complex term that is related to the change in Poisson's ratio, density and velocity at the interface.

211 In order to highlight AVO anomalies, a number of attributes were generated from combinations of the Rd and G Values (namely Rci, G, Rci * G sign (RoS) * G and Rc5 + G) for two gas sands from different geological environments, one from the Gulf of Mexico, one from an Eocene turbidite from the North Sea, and a carbonate from S.E. Asia. These are fully discussed in Simon-Geolithic's video "Reconnaisance AVO Plots for Stratigraphic Mapping". Both sands and the carbonate showed significant differences in their attribute responses and indicated that a model gather needs to be generated for every prospect area to evaluate the significance of the AVO anomaly. This creates a problem as the general lack of well control hinders the calculation of forward models. To solve this dilemma, Simon-Geolithic launched a world-wide AVO calibration programme; one of it's aims being to determine to what extent a relationship exists between the type of AVO anomaly found and the geological setting. The programme involves RECON AVO modelling of seismic lines where well control is available. As illustrated in figure 1, the initial investigation proceeds along two independent routes: 1)

Using the borehole sonic and lithology calculated from conventional logs, a series of empirical algorithms are used to calculate the shear wave sonic at the log sampling rate. A synthetic gather is then generated from the start of the log at the processing sample rate.

The real gathers are processed so as to maintain tnje relative amplitude.

The real and synthetic gathers are then compared to determine if log editing or correction is necessary. The next step in this investigation is a RECON AVO study of the real gathers on a sample by sample basis. This is based on the estimation of R6 and G from a linear regression of amplitude as a function of incidant angle. This may be obtained from a mapping of incident angle to offset as a function of two way travel time using the synthetic model. Seismic amplitudes are contaminated by noise and multiples that can erroneously influence the regression analysis. For this reason a statistical analysis of the data at each sample is undertaken and a robust regression analysis (Walden 1990) is performed in preference to simple linear regression (figure 2). Full details of the statistical analysis is given in Simon-Geolithic's video "AVO forward models and statistical calibration". It is hoped that the application of these techniques to a wide variety of AVO anomalies from different geological settings will help to answer the following important issues: 1) 2) 3) 4)

How accurate are the empirical VP-VS transformations? What rock type combinations favour significant AVO response? What are the statistical thresholds below which AVO measurements lose meaning? Are there combinations of geologic settings and AVO response that optimize extraction of lithologic and/or fluid information?

References Nelson, V., 1989, SEG Convention Abstracts, Pg. 447. Shuey, R.T., 1985, Geophysics, Vol. 50. Pg. 609-614. Walden, A.T., 1990, EAEG Copenhagen Pg. 1-27.

212

Fig.1 A flow chart showing the major steps involved in Simon-Geolithic's world-wide AVO Calibration programme.

Least Squares Vs. Robust Least Squares Data set with simulated amplitude loss on far traces

Q) "D :D

"Q.

LEAST SQUARES ROBUST LEAST SQUARES Sln^ Incident Angle Fig. 2 This shows the advantage of the Robust least squares method over a simple least squares method when spurious amplitudes are present.

213 APPLICATION OF THE LASER RAMAN MICROPROBE IN PETROLEUM EXPLORATION John R. Wilmshurst*, George HIadky, Michael V. Ellacott and Carol P. Buckingham CSIRO Division of Exploration Geosclence The laser Raman microprobe installed in the CSIRO Division of Exploration Geoscience is probably the only instrument of its type, world-wide, which is dedicated to petroleum exploration. The instrument enables the acquisition of Raman and fluorescence spectra from micronsized particles of organic matter. It Is therefore equally applicable to studies of coal or dispersed organic matter (DOM) in petroleum exploration well samples. The CSIRO instrument has been automated to acquire sequentially, Raman and fluorescence data from pre-selected maceral grains. Insofar as visible radiation is directed through a microscope onto organic matter, the technique is closely related to vitrinite reflectance, but because it is possible to examine the emitted radiation as a function of wavelength or time, a very large amount of data realting to the structural and chemical properties of maceral grains is obtained. In this way several parameters sensitive to thermal maturity of the organic matter are obtained (Wilkins et al., 1990). The new data enables solutions to two major problems of the vitrinite reflectance technique to be devised. The problems are 1. 2.

The identification of vitrinite in DOM. The suppression of vitrinite reflectance.

The problem of mis-identification of vitrinite can be responsible for large discrepancies in interpretation among organic petrologists studying the same wells. The laser Raman microprobe approach to this problem is to use multi-linear regression on spectral data from both inertinites and vitrinites to calculate equivalent vitrinite reflectance. Suppression of vitrinite reflectance may be identified and evaluated using fluorescence alteration data acquired automatically by the microprobe. References Wilkins, R.W.T., Wilmshurst, J.R., HIadky, G., Ellacott, M.V. and Buckingham, C.P. 1990 Laser Micro-Raman Spectroscopy - A New Tool for Petroleum Exploration. Final Report NERDDP Project 981 pp. 1-87.

214

USING SEISMIC WAVETESTS TO DETERMINE VELOCITY STRUCTURE Roger A. Young Department of Exploration Geophysics Curtin University of Technology Seismic wavetests (or walkaway noise analyses) are routinely conducted prior to land CMP surveys in order to set acquisition parameters. Little use is made of tlie velocity information contained in the wavetest data despite its potential impact on successful acquisition. The probable reason for such neglect is the low S/N ratio inherent in singlefold data. However, S/N enhancement is possible due to the large effective aperture of wavetests. Through tau-p transformation, wavefront segments are compressed and are cast in a coordinate frame which makes possible the direct determination of interval velocity and layer thickness. A modelling approach in the tau-p domain is derived which accommodates both vertical velocity gradients and jumps. This is inverted as a layer stripping procedure analogous to the tausum method. Then, a reversed wavetest dataset from the Perth Basin is transformed to the tau-p domain. Semblance threshholding and multi-panel stacking are used to enhance events. Finally, forward modelling and inversion are used together to extract velocity structure from the wavetest.

215 Poster Session Mineral Exploration NORTHEASTERN NEW SOUTH WALES CAN RADIOMETRIC DATA MAP DIFFERENT GRANITOIDS? A. Agostini''*, E.D. Tyne^ P.L. Kennedy^ and W. Worakanok^ Geological Survey of New South Wales Department of Minerals and Energy ^Economic Geology Division, Thailand Department of Mineral Resources, currently University of New South Wales Qualitative interpretations, supported by a semi-quantitative methodology using the relative strengths of the Total Count, Potassium, Uranium, and Thorium channels, of the airborne radiometric data in an area about 40 km west of Armidale lead to better defining the geological boundaries of the Gwydir River Adamellite, inferring a possible extension of The Basin Adamellite and suggesting a differentiation between the Baldersleigh Volcanics and the Parlour Mountain Granite. Analysis of ground radiometric measurements in the Tingha area, 25 km south of Inverell, have largely resolved the complex and gradational nature of the boundary between the Tingha Adamellite and the Gilgai Granite.

HUMINEX SYSTEM OF GEOCHEMICAL EXPLORATION W.E. Baker Tasmania Department of Resources and Energy, Hobart Where climatic processes result in extensive leaching during soil profile development the "B" horizon, which has been generally used in geochemical exploration, tends to be depleted in heavy metals. This problem has long been recognised by mineral explorers and the common solution has been to make use of the "C" horizon for soil geochemical exploration. This approach is expensive, environmentally intrusive and difficult to apply in heavily vegetated, strongly dissected terrain such as exists in western Tasmania. Studies undertaken by the Tasmania Department of Resources and Energy found the humic substances, produced during soil formation, to be extremely aggressive in the degradation of economic minerals (Baker, 1986). The humic substances - metal associations are reasonably stable and should provide a medium for exploration geochemistry. This idea was tested over an area southwest of Waratah, Tasmania for which "0" horizon data had been previously obtained. Analysis of "A" horizon samples collected at 20 m intervals on a traverse spacing of 100 m enabled recognition of anomaly patterns similar to those revealed by results from the "0" horizon (Fig. 1). Subsequent drilling of one anomalous site intersected sub-economic mineralisation at a depth of 90 m where a 25 m zone carried veins varying in width from 0.1 to 1.0 m with metal values of up to 23% Zn, 19% Pb, 460 g/t Ag and 5 g/t Au. Several other less extensive tests of the huminex system were successful in detecting geochemical anomalies. Provided that the soils of a region are not subjected to lengthy drying periods, the humic substances remain mobile and eventually enter the drainage system. Their monitoring

216 in association with metal analysis can provide useful information for hydrogeochemical exploration and this technique is currently being tested in Tasmania. The huminex system, which has been patented by the Tasmania Department of Resources and Energy, can be applied with minimal impact on the environment and is very cost effective with respect to sampling.

C O D w m «Q«0 ^^^^

Target

"C" Horizon Huminex system

Figure 1. Comparison of Huminex and "C" horizon anomaly definition. Reference Baker, W.E. (1986) in Mineral Exploration: Biological Systems and Organic matter. Donald Carlisle et al. (eds.) Rubey Volume V. 197-212. Prentice Hall.

QUANTITATIVE DESCRIPTION OF SHAPE IN PETROGRAPHIC IMAGE ANALYSIS M. Benhamou, A.R. Ramsden*, D.H. French CSIRO Division of Exploration Geosclence, Sydney Shape has special significance in petrographic descriptions because of its Importance for interpreting the processes that have occurred during formation and modification of rocks; processes, for example, that could indicate proximity to mineralization. Computer-based image analysis provides quantitative measurement of grain shape that can be used as an objective petrographic tool. Simple measures such as the ratio of feret diameters or the commonly used shape factor Area/Perimeter^ are inadequate for a petrographic description because they can have the same value for widely different shapes. What is needed is a repertoire of more complex measurements that will help the petrographer recognize and understand subtle differences not readily visible to the human eye. A combination of several measurements has been found to be necessary: 1. 2. 3. 4.

Fourier transform analysis to describe the degree of convexity of the grain. Intercept analysis to describe the degree of convexity of the grain. Use of the Hough transform to detect the straight edges of the grain. Similarity measurements to distinguish shapes on the basis of their properties on rotation.

217 Multivariate statistical analysis of these measurements not only yields sensible classification of grains having obvious shape differences but also reveals subtle differences between grains of generally similar morphological appearance that would not be recognized from subjective observations. The work presented in this paper is being carried out on false colour backscatter electron images obtained from a Cameca Camebax electron microprobe, with processing and analysis of these images carried out off-line on a Microvax 3100 computer. Integration with the electron microprobe provides a powerful tool for investigating relationships such as between shape and trace element content of a given mineral (for example, different generations of pyrite) in the search for guides to mineralization in exploratory drill-core. The algorithms used for image analysis, however, are independent of the source of the digitized image and could be applied equally well to images obtained from light optical systems.

INVESTIGATION OF TAILINGS DAMS RESERVES, EMPEROR GOLD MINE, FIJI Malcolm E. Cox^* and Andrew M. Foley^ ^Surtec Geosurveys Pty Ltd, Brisbane, Old ^Surtec Geosurveys Pty Ltd, Sydney, NSW An investigation of four tailings dams at Vatukoula was conducted in January, 1989. Surface areas of the dams are 3.75, 8.47, 12.21 and 7.37 Ha, respectively. Younger dams partly overlie older dams which are also comprised of numerous smaller dams containing tailings from both oxidised and sulphide ore. Drilling on abandoned Dams 1 and 2 used a truck mounted Mindrill NX(L) rig and an NQ coring rod connected to 3 metre BQ rods, and on semi-saturated Dams 3 and 4 was from a steel barge, using a Mindrill BB10. One-metre length cores were taken with recovery mostly over 80%, but low in sections of high water content. Most holes in Dams 3 and 4 required the use of a spring steel basket catcher (in a BQ core lifter case). A total of 691.28 m was drilled with 11 to 15 holes per dam. The deepest hole was 23.5 m in Dam 3. Variations in moisture content needed definition to enable calculation of insitu dry densities. Fifteen 500 g samples were tested by commercial laboratory and showed a strong inverse correlation between dry density and moisture content, which enabled the use of field estimated moisture to approximate dry density for each core section. For Dams 1 and 2 average moisture contents were 24 and 36% and for Dams 3 and 4, 46 and 44%. Splits of 150 g were taken for gold assay on 50 g by AAS (detection limit of 0.02 ppm). Fire assay duplicates were within 2-7% and usually lower. Gold ranged from 0.70 to 2.90 ppm but was mostly 1.10 to 1.80 ppm. Additional assays of 85 samples from 5 holes produced the following mean values (ppm): Ag = 1.2, Cu = 137, Pb = 40, Zn = 185, As = 552, Sb = 17, Te = 20 and Fe = 5.46%. Volumes and grades were calculated with a software package HOLPAK. Two-metre thick levels were selected as optimum and data over the interval composited. For each hole on a level, a polygon of influence was generated, the area of which was established by taking into account bottom contours and the edge of dam surfaces. The

218

radii of polygons depended upon hole spacing and dam size and ranged from 70 to 150 m. The "skirts" of dams were treated as a series of triangular prisms and volumes calculated manually using weighted averages for each dam. Dam 1 2 3 (model A) 3 (model B) 4 Total Reserves

Dry Density (t/m-^) 1.49 1.34 1.23 1.23 1.25

Summary of Results Tonnes Gold (g/t) 554003 134699 3083294 3807618 1120789

1.85 1.40 1.49 1.48 1.38

6892785

1.47

Silver (approx g/t) 1.94 1.58 0.86 0.86 0.70

A COMPARISON OF TEM (TRANSIENT ELECTROMAGNETIC) SYSTEMS CURRENTLY AND MOST WIDELY USED IN AUSTRALIA PJ.EIIiott Elliott Geophysics P/L, Adelaide, SA This paper provides an objective appraisal of five TEM (Transient Electro-Magnetic) systems which are readily available on a commercial basis. These are the Sirotem MK II and MK 3, EM37, UTEM III and the Zonge GDP-16 based systems. The specifications of the transmitters, receivers and receiver coils of the 5 systems are tabulated and compared. Both qualitative and quantitative assessments are made. The Sirotem MK II and MK 3 low powered impulse systems are light weight portable systems which combine the transmitter and receiver in one box. This makes it an ideal system for hand carried, moving loop surveys in semi-rugged terrain where fixed loop is inappropriate or not desired. The medium powered option on the other hand utilises another instrument (SATX-1) and a larger power source which restricts it to vehicle borne moving loop, or fixed loop surveys. The medium powered system has a maximum power output of 2 kW compared to 240 W for the low powered system. The MK 3 covers a frequency range of .5 Hz to 10 kHz (4.5 decades of frequency) compared to the MK II which covers a frequency range of 6 Hz to 10 kHz (3.5 decades of frequency). The systems are therefore broad band with good coverage at the low frequency end of the spectrum. The MK 3 has 53 windows which provide dense sampling of the transient decay. A shortcoming of the system is limited temperature range of operation (-20 deg to +45 deg). The upper limit is sometimes restrictive in the hot arid areas of Australia. The EM37 is also an impulse system. It has greater power output than the medium power Sirotem system (4.5 kW max.) and as a result is less portable. It can be used in its higher powered form as a vehicle borne moving loop system but is generally used in fixed loop mode. The sensitivity of the receiver coil is relatively low with an effective area 520 square metres compared with 10000 for the Sirotem RVR. This is counter balanced to some degree by increasing the gain in the receiver. The effective frequency range of EM37 is 14 Hz to 14 kHz (3.0 decades). This is similar to Sirotem MK 11 but shifted into a higher frequency range. The UTEM III system is a step response system achieved through a modified triangular output waveform. It has a highly sensitive receiver/receiver coil combination. The

219 receiver coil has an effective area of 62,700 square metres and the receiver has an optional gain up to 256 times unity. The receiver system covers a frequency range of 33 Hz to 40 kHz (4.0 decades) but is limited at the low frequency end (33 Hz). This is compensated to some degree by measuring the step response of the ground which assists the detection of good conductors at higher frequency (earlier in time). The signal to noise ratio of the receiver is improved by clever stacking and pre-whitening of the received signal. The transmitter has a maximum power output of 1.5 kW which is less than the Sirotem or EM37 systems. The UTEM system can be used to acquire induced polarisation and galvanic resistivity data by measuring the electric field in conjunction with the dB/dt field. The Zonge system is a recent system which is still finding its feet in the market place. The receiver has a large frequency range of .16 Hz to 30 kHz (5.5 decades) which is limited by the resonant frequency of the receiver coil to about 20 kHz (giving a 5.0 decade range). The receiver coil has the same effective area as the Sirotem RVR (10000 square metres) but is made more portable by its reduced size (effected by using a ferrite core). The sensitivity of the receiver system can be increased by using gains ranging from .125 to 4096. The voltage resolution of the receiver is quoted at .03 uV (c.f. Sirotem, 1 uV). The output power of the Zonge systems vary from 24 V for the small transmitter up to 30 kW for the large transmitter. This enables it to be used to drive very large transmitter loops or grounded loops as well as the smaller loops. The Zonge system therefore has the largest power capacity and greatest frequency bandwidth of the systems under study. It has greater sensitivity than the Sirotem and EM37 systems. It also has a better temperature range of operation (-20 deg to +60 deg). If it can prove its reliability as a TEM system then it will gain wide acceptance in the industry. Other facilities the Zonge system can provide are up to 8 independent receiver channels, and ability to provide MMR, IP/CR, and CSAMT data in the same area.

GEOCHEMISTRY AND MORPHOLOGY OF GOLD IN LATERITIC PROFILES IN SAVANNA AND SEMI-ARID CLIMATES P. Freyssinet^ L.M. Lawrance^ and C.R.M. Butt^* ^BRGM, France ^CSIRO Division of Expioration Geoscience, Wembiey, Western Australia Three supergene gold deposits in contrasting lateritic terrains have been compared to demonstrate how changes in climates and dominant weathering processes over time are reflected in the distribution, composition and morphology of particulate gold. Kangaba, Mali, West Africa, has a savanna climate with an annual rainfall of 1300 mm. Secondary dispersion is confined to the cuirasse and mottled zone and extends laterally for 100 m from the source. In the saprolite, gold grains associated with quartz tends to be xenomorphic, whereas those derived from sulphides are highly irregular in shape. Most grains are pristine, with only a few (15%) exhibiting any corrosion features. Grains in the mottled zone have similar morphologies but over 40% are corroded. In the cuirasse, 90% of the grains are corroded and over half have lost their primary morphology. Secondary gold is present in the dispersion halo in the mottled zone and cuirasse as micro-spherules (<1 Im), micro-dendrites and secondary rims around primary grains.

220

Bardoc and Hannan South, Western Australia, have a warm, semi-arid climate with an annual rainfall of approximately 200 mm. At Bardoc, gold is widely dispersed in the lateritic soil and also enriched in the lower saprolite. Primary and secondary gold grains are present in all weathering horizons. Primary gold grains occur as pristine xenomorphic forms or as etched and rounded forms, commonly with progressive Ag depletion on grain boundaries and along cracks. Secondary gold grains occur as xenomorphic forms, individual or intergrown subhedral to euhedral crystals, and complex irregular aggregates. The grains may be pristine or corroded, and commonly have a later generation of fine Au crystals or spherules adhering to them. In the lower saprolite, about 20-40% of the grains are primary but only 4-10% have survived the intense leaching of the upper saprolite and the mottled zone. In comparison, more than 40% of the grains in the ferruginous soil are primary. At Hannan South, the lateritic regolith has been truncated by the migration of a saline drainage system and the residual saprolite is overlain by 2-5 m of playa sediments. Gold is strongly leached from the top 20 m but concentrated in a dispersion halo extending over 80 m into weathered wall-rocks. Beneath this halo, gold is confined to the weathered sulphidic host unit as primary ovoid inclusions (<1-100 Im) in pyrite grains and as secondary grains (<20 Im) and clusters, dispersed around partly weathered pyrite. Gold in the dispersion halo occurs as secondary hexagonal and trigonal plates (0.015-3 mm), octahedral crystals (5-20 Im) and irregular semi-crystalline aggregates (<40 Im). Many crystals show some corrosion but may be associated with grains that are pristine. At each site, silver is the only major alloy with gold. All primary gold contains 4-10% Ag and secondary gold in the sulphidic unit at Hannan South has 2-4% Ag. All other secondary grains and rims contain no detectable silver. The differences in the nature and distribution of gold at the three sites can best be explained by gold having been mobilized by different processes at different times. Firstly, at each site, gold was mobilized as organic complexes and dispersed in the ferruginous upper horizons of the profile. Secondly, at Bardoc and Hannan South, further mobilization occurred as chloride complexes under arid conditions, principally in the mottled zone and saprolite; at Hannan South, gold has also been mobilized in the weathering sulphidic unit as a thiosulphate complex.

NEUTRON ACTIVATION ANALYSIS IN THE 1990s - UNIQUE SOLUTIONS TO MINERAL EXPLORATION PROBLEMS David L. Garnett* and Helen M. Waldron Becquerel Laboratories Neutron activation analysis (NAA) is unique in being able to report gold from 5ppb to ore grade and also report another 28, or more, elements on the same large sample (typically 40-50g for a pan concentrate). Results for neutron activation analysis of pan concentrates from Papua New Guinea; gold-bearing metasediments from Victoria and iron rich lateritic material from Western Australia are used to highlight features of the technique which can be applied to mineral exploration problems, particularly in the search for gold. These problems fall into two broad categories: how to extract maximum information from a sample and how to extract accurate information.

221 A. Extraction of maximum information. Costs of sample collection are often far greater than subsequent analytical costs. This is particularly true for pan concentrates yet these are often pulverised and analysed for gold alone. Many deposits have been found by this method, including Porgera (Handley, 1987), but much more information can now be obtained using NAA, with little increase in analytical costs. No pulverising is required, thus avoiding possible loss of gold onto pulveriser surfaces and leaving the sample available for subsequent mineralogical study. Figure 1 summarises inter-element relationships in pan concentrates from the Porgera region of Papua New Guinea, analysed by NAA. 1.0

Sb As Br

Au Ba K

Na Cs

LTLI

Rb Sc Zn

Fe Co

Th La Ce Sm Eu Yb Lu

4iJ

t 0.0

Figure 1. Cluster analyses of elements detected by NAA in pan concentrates from the Porgera region of Papua New Guinea, using Spearman rank correleation coefficients. Such multi-element geochemistry may detect new, and unexpected, patterns and may also dispel preconceived ideas about the sample area. In this data set Au is shown to be most closely correlated with Ba, rather than with As or Sb as might have been expected. Gold is also closely associated with distinctive Hf/Th and La/Lu patterns which may be significant for exploration. Similar studies, also using NAA, at the Umuna epithermal gold-silver deposit, Misima Island, Papua New Guinea lead to recognition of broad geochemical haloes around the mineralisation which could allow reduction of sample density or increased confidence in interpretation (Clarke et al, 1990). B. Extraction of accurate information. Since NAA does not rely on sample dissolution there is no problem with incomplete sample digestion. Equally, there is no danger of contamination from laboratory chemicals and a total analysis is achieved regardless of mineralogy, even with highly refractory samples. This places it in a unique position for gold analysis: it is virtually interference free (Potts, 1987) and is the simplest of all gold analytical techniques. Two inter-laboratory analytical surveys are described, one using a suite of iron rich lateritic samples from Western Australia (Birrell and McCrow, 1989), and one using auriferous greywacke from Victoria, prepared as a reference standard (Ore Research and Exploration, 1990). In the latter case there is little difference between results for gold obtained by NAA and those obtained by fire assay, while for the lateritic samples NAA tends to report slightly higher results than those obtained by most fire assay laboratories. Wet chemical analysis of the same samples gives significantly lower gold values. Figure 2 summarises some of these results, and further highlight the differences in values that can be obtained for As, Sb and W when determined by different analytical techniques.

222

NAA

ACID AAS

NAA

HYDAAS ICPMS XRF ICPOES DCP

NAA

HYDAAS ICPMS XRF ICPOES DCP

ppm 10

ppm

NAA

XRF

ICPMS

COL

Figure 2. Comparison of analyses of a single sample for Au, As, W and Sb, using neutron activation analysis (NAA) and a variety of otiier analytical methods. Individual points represent values obtained by different laboratories. FA - Fire assay; ACID AAS Acid digestion, atomic absorption finish; XRF - X ray fluorescence; HYDAAS - Hydride, atomic absorption finish; ICPOES - ICR optical emission; ICPMS - ICP mass spectrometry; DCP - DC plasma; COL - colorimetry. (Results from Birrell and McCrow, 1989). It is noteworthy that NAA and XRF, which do not require sample dissolution, tend to report higher values for As and Sb than are reported by the other procedures which all rely on wet chemistry. Problems with acid dissolution of lateritic samples were described by Gedeon et al (1977) and it may be that this is partially responsible for these lower values. Similarly it is possible that this same problem of incomplete extraction is responsible for the wide range of gold values reported for theoretically homogeneous samples when analysed by different techniques and different laboratories (Radford, 1987; Birrell and McCrow, 1989; Hall, 1989). Arguments will always rage as to which analytical method gives the most accurate results and it is not always easy to decide between conflicting claims. At the very least, NAA's inherent simplicity; its ability to activate a sample totally regardless of mineralogy and without the need for sample digestion; its relative freedom from interferences and its unique ability to determine a broad range of elements including gold in a single, large analytical sample all make it an attractive alternative for analysis of exploration samples. References Birrell, R.D. and McCrow, B.H. (1989). Unpublished report. Geochemex Australia, Perth, WA. Clarke, D.S., Lewis, R.W. and Waldron, H.M. (1990). J. Geochem. Explor., 36. Gedeon, A.Z., Butt, C.R.M, Gardner, K.A. and Hart, M.K. (1977). J. Geochem. Explor., 8.

Hall, G.E.M. (1989). Explore, No. 65, Assoc. of Explor. Geochemists. Handley, G.A. (1987). In 'Proceedings Pacific Rim Congress 87', Aus IMM.

223 Ore Research and Exploration (1990). Unpublished report. Certificate of analysis, Ore Research and Exploration, Heidelberg, Victoria. Potts, P.J. (1987). A handbook of silicate rock analysis. Blackie, Glasgow and London. Radford, N.W. (1987). In 'Meaningful sampling in gold exploration'. Bull No. 7, Aus. Inst, of Geoscientists.

THE GENESIS AND SEDIMENTATION OF SAPPHIRES FOUND AT WELLINGROVE Phillip G.L. Harlow Ipswich Grammar School, Ipswich, Old The association between basalts and sapphires had been reported by various authors, such as Stellar Mining NL (1971). The relationship between the distribution of detrital sapphire in streams in the Inverell - Glen Innes District and that of the Tertiary basaltic rocks led numerous authors (eg. MacNevin, 1972) to conclude that the detrital sapphires were derived from the basalt in which they were xenocrystic from depths between 100 and 50 km below the surface (Chalmers, 1979). In 1982 the discovery of sapphire in acidic voicaniclastic rocks near the base of the Tertiary basaltic pile (Brown and Pecover, 1986) at Braemar and Kings Plains in the Inverell-Glen Innes district enabled a change of thinking about the sapphires in the alluvial deposits in this area (Lishmund and Oakes, 1983). These authors interpreted the tuffs and breccias containing sapphires as having formed around the vent of a diatreme which was the eruptive expression of a subsequent intrusion along the path of an earlier deep seated diatreme. Later workers have suggested the origin of the acidic voicaniclastic material to be tuffaceous deposits resulting from maar volcanism (Pecover, 1987). The association of sapphire and pyroclastic rocks in basaltic terrains in Tasmania, Eastern Australia, South-East Asia, South-East China, and Nigeria (Chalmers, 1979, Barr and MacDonald, 1981, Wright, 1969, and Irving, 1986) is used to support this argument. Some work on the geomorphology of the area has been done (Oilier and Schmidt, 1988), while other work has been carried out on the relationships of structural controls, the timing of volcanism and the occurrence of sapphire bearing rocks in various areas (Coenraads, 1988 and Mumme, 1988). In addition, the petrology and chemistry of the rocks of the Inverell sapphire district has been investigated by some workers (Barron, 1987). It has been thought that the wear of sapphires is an indication of river transport, but it is now apparent that the surface features of sapphire may reflect a volcanic mode of transport and reaction with magma in which it is in disequilibrium (Coenraads, Sutherland and Kinney, 1990). Furthermore, the alluvial minerals associated with sapphires may have a less fortuitous association than previously accepted. The exploration for economic concentrations of sapphire bearing volcanic rocks would be considerably simplified if the genesis and sedimentation could be resolved. This paper examines the genesis of the sapphire, the eruptive mechanism and the sedimentation that formed the Wellingrove deposit. The three models for the genesis of sapphire presented in this paper are:

224 1.

The formation of the sapphire in an eclogite arising from subducted crustal material and the subsequent eaiption of the sapphire as xenocrysts in magma derived from the upper mantle. The formation of the sapphire in a silicic cap developed on top of a basaltic diapir developed by melting and assimilation of the country rocl< during ascent of the diapir. The formation of the sapphire as a result of differentiation at shallow levels in the crust of an originally basaltic magma.

Evidence for each of the models is presented and further work to clarify the issues raised is suggested. The paper concludes that the sapphire was deposited as an unwelded ignimbrite or coignimbrite breccia flow laid down during an initial explosive eruptive phase of a central vent basaltic volcano about 35.9 + or -1.9 million years ago (Coenraads, Sutherland and Kinney, 1990). The flow shows a distinct layered staicture corresponding to a mass flow deposit where the material has been separated into distinctive layers during the flowage. A consequence of this mechanism is that the sapphire is concentrated in particular layers which has applications to the commercial exploitation of similar deposits. The source volcano is not conclusively identified but some evidence is presented to suggest that it may be "Mayboie" near Glen Innes. References Barr, S.M. and MacDonald, A.S., 1981. Geol. Soc. Am. Bull. 92(1), 508-512 and 92(11), 1069-1142. Barron, L.M., 1987. NSW Geological Survey - Report GS 1987/058. Brown, R.E., and Recover, S.R., 1986, NSW Geological Survey - Report GS 1986/270. Chalmers, O., 1979. The observers book of Rocks and Minerals of Australia. Methuen of Australia, Sydney. Coenraads, R.R., 1988. New England Orogen Tectonics and Metallogenesis. ed J.D. Kleeman. University of New England, Australia. Coenraads, R.R., Sutherland, F.L, and Kinney, P.D., 1990. Min. Mag. 54,1,1990. Irving, A.J. 1986. International Kimberlite Conference, 4th Perth - Extended Abstracts, pp. 262-263 (Geological Society of Australia - Abstracts 16). Lishmund, S.R. and Oakes, G.M., 1983. NSW Geological Survey - Qtly. Notes 53, 2327. MacNevin, A.A., 1972. NSW Geological Survey - Records 14 (1), 19-35. Mumme, I.A., 1988. The World of Sapphires. Mumme, Sydney. Oilier, C.D., and Schmidt, P.W., 1988. New England Orogen Tectonics and Metallogenesis. ed. J.D. Kleeman. University of New England, Australia. Recover, S.R., 1987. NSW Geological Survey - Report GS 1987/058. Stellar Mining N.L, 1971. Quarterly Reports. EL372, Burraga area (unpubl.). Wright, J.B., 1969. Bulletin Vulcanologique 34, 833-847. APPLICATION OF PHYSICAL PROPERTY MEASUREMENTS IN BASE METAL EXPLORATION: SHEEP CREEK DEPOSIT, MONTANA, U.S.A. Gregory M. Hollyer BHP - Utah Minerals International, Toronto, Canada Physical property data (natural gamma, gamma - gamma density, normal resistivity, induced polarization (IP), spontaneous potential (SP), electromagnetic conductivity and magnetic susceptibility) were acquired from a Proterozoic sediment-hosted massive

225 sulphide deposit near Slieep Creel< in Central Montana, U.S.A. Both pyritic and ore grade mineral intersections were characterized by strong electrical responses and an increase in apparent density. Gamma and magnetic susceptibility responses were unique to each sulphide occurrence. Results are presented from two case studies which demonstrate the applicability of using physical property measurements (borehole geophysical logging) In this geologic environment.

THE APPLICATION OF A NEW FIELD-PORTABLE REFLECTANCE SPECTROMETER (PIMA) FOR IN-SITU MINERAL IDENTIFICATION IN EXPLORATION J.F.Huntington''* and T.D.Cocks^ ••CSIRO Division of Exploration Geosclence, North Ryde NSW ^Integrated Spectronlcs Pty Ltd., Baulkham Hills, NSW A new compact, two kilogram, field-portable, infrared spectrometer has been developed to allow in-situ measurement of shortwave infrared spectra of rocks, minerals, and soils as an aid to field identification of many hard-to-recognise minerals, including alteration products. The device has emerged as a by-product of the latest remote sensing research, but as its name implies (PIMA, for Portable Infrared Mineral Analizer) it is not intended merely as an adjunct to remote sensing surveys. The PIMA operates independently of sunlight and can be used in contact with any dry surface whether it be in a mine or on the surface. The advent of such new technology should bring increased efficiencies to field programmes where previously samples had to be sent off to laboratories for expensive XRD analysis. Applications for this type of instrument include the identification of sometimes hard-to-recognise phyllosilicate and other alteration minerals, such a kaolinite, dickite, alunite, jarosite, illites, smectites, calcite/dolomite/siderite, Fe/Mg ratios in chlorites, as well as Na, Ca, K, Fe, Mg, and NH elemental substitutions in various minerals possibly indicative of alteration intensity or position in mineralised systems. Recent studies have indicated significant spatial links between shortwave infrared absorption intensity and shape and mineral crystallinity and order states. Surveys can be conducted rapidly in the field along systematic traverses and charted to highlight areas worthy of more detailed exploration. Previous applications have been corroborated with X-ray diffraction measurements and have provided insight into chemical and temperature zonation around mineralized plumbing systems and may go some way, hopefully, to separating the effects of weathering and alteration. The poster-paper includes case histories of the application of this new instrument in Australia. The device can provide survey and mine geologists with a "new set of eyes" to map previously unseen spatial variations in mineralogy and fades and relate these to refined models of mineralisation. For example, maps or bore-hole profiles of sericite crystallinity indices and specific alteration minerals maybe envisaged along with the detection of swelling clays in engineering situations.

226 THE SPECTREM AIRBORNE ELECTROMAGNETIC SYSTEM P.S. Klinkert Anglo American Corporation SPECTREM is a new, wideband, digital towed bird AEM system capable of operation in either the time or frequency domains. The system is an extensive modification by Anglo American Corporation of the prototype PROSPECT 1 ™ System built by A-Cubed Inc of Toronto, Canada. It was designed with two main purposes in mind namely detection of massive sulphides at depth in conductive environments and accurate electromagnetic sounding to depths in excess of 300 metres below surface. To achieve these design aims, the system has the following. 1.

Wide bandwidth. Time domain operation covers delay times from 0.047 to 6.7 milliseconds. High power over the full bandwidth. The RMS dipole moment of the transmitter is 120 000 Am^ currently being upgraded to 300 000 Am^.

2. 3.

A high drag bird for fixed transmitter-receiver separation during flight. This results

4. 5. 6. 7. 8. 9. 10. 11.

in accurate EM sounding and reduced noise levels. A three component receiver coil for improved geometrical discrimination of conductors. A fully digital system allowing real time signal processing and storage of fullwave TX, X, Y and Z component data for subsequent ground processing. An accurate calibration system. Transmitter-receiver coil separation of 122 metres giving a large ground "footprint" and good depth of penetration. High sensitivity magnetometer with signal processing allowing simultaneous operation of EM system and magnetometer. Decca Doppler navigation system. DC3 airborne platform for large TX coil area, long flight duration and good weight carrying capability. Custom software and hardware package to process the large amount of data generated by the system.

The system design considerations are illustrated together with a case history of the SPECTREM anomaly recorded over a discrete bedrock conductor overlain by conductive cover rocks, and an example of AEM sounding with borehole control using the IMAGE algorithm

NORTHWESTERN NEW SOUTH WALES CAN REGIONAL GEOPHYSICS LEAD TO MORE EXPLORATION? J.I. Mclntyre Geological Survey of New South Wales, Department of Minerals and Energy Bouguer gravity maps and aeromagnetic maps of the Koonenberry 1:500,000 map area in northwestern New South Wales have been compiled from Bureau of Mineral Resources data bases. Low magnetic field strength within the area of Precambrian Willyama Supergroup and Adelaidean sediments extends about 90 kilometres north of the northernmost

227 Precambrian outcrop, suggesting some continuity of crustal structure through this region. Shallow basement on the western edge of the area around 30°30'S shows a magnetic pattern which could be more clearly delineated by a detailed aeromagnetic survey. The Bancannia Trough is underlain by strongly magnetised daclte/andesite. This dacite/andesite is terminated at its southern end by an ENE trending lineament which extends through the Wonominta Block Into the basement of the Darling Depression. Bouguer gravity values over the Kanmantoo Fold Belt are markedly higher than over the Willyama Supergroup, reflecting a probable convergent plate margin associated with the Kanmantoo Fold Belt. The full extent of the Koonenberry Fault (which Is the main component of the Kanmantoo/Lachlan boundary) is clearly delineated by the magnetic data. The few near-surface magnetized rock units east of the Koonenberry Fault generally give rise only to isolated anomalies, except In the restricted area of Ordovician metasediments surrounding the Tibooburra Granite. The Eromanga Basin is distinguished from the Darling Depression by higher Bouguer values (indicating shallower sedimentary basement depths), and basement structures with generally northwesterly trend (compared with no discernable basement trend directions in the Darling Depression).

USE OF ZIRCONS TO RESOLVE ORIGINS OF SAPPHIRES IN EAST AUSTRALIAN GEM FIELDS - THE MYSTERIOUS CASE OF THE SHUFFLING SAPPHIRE VOLCANOES F.L Sutherland^

P.D. Kinny^ and J.D. Mollis''

^ Division of Earth Sciences, The Australian Museum, Sydney ^Research School of Earth Sciences, Australian National University, Canberra Zircons are common associates of sapphires in East Australian basalt gem fields (Mollis and Sutherland, 1985). Their fission track and isotopic ages are powerful tools In resolving the volcanic evolution of the gem fields (Sutherland and KInny, 1990). The spatial distribution and timing of gem producing volcanoes can provide refined models for origin of the concepts for exploration for sapphire, zircon and diamond deposits. Fission track ages of zircons shed from basalts represent re-set ages corresponding to times of eruption. These supplement radiometric dating of the host volcanic rocks to give a greater understanding of the volcanic evolution. The zircon Pb/U isotopes, such as measured by the SMRIMP technique at A.N.U., give the age of formation of the zircons. This may be related to or older than the fission track ages. Zircon inclusions of syngenetic origin in the sapphires allow a direct means of dating sapphire formation relative to the host volcanic eruptives. The Pb/U Isotope results are useful In the search for potential source rocks. The geochemistry (U and Th contents) and crystal habits of the zircons also provide constraints on their origin as sapphire indicators. The conventional picture of the New England gem field, from K-Ar dating of basalts, suggests two main volcanic episodes. An earlier undersaturated alkali basaltic episode

228 between 31-35 Ma is usually tied in with the sapphire hosts (New South Wales Geological Survey, 1987). A later, partly tholeiitic episode, between 19-25 Ma, to the west is not linked to sapphire sources, but overlies diamondiferous leads (Coenraads, 1988). The zircon data give a nfiore extended and complicated picture, though Pb/U isotope ages of zircon inclusions in sapphires demonstrate sub volcanic sources related to 35 Ma activity (Coenraads, et al, 1990). The new picture shows that over five successive volcanoes formed across the gem field, with four producing gemstones in a period of over 20 Ma. The suggested evolution is:1. 'Kimberlitic' zircons erupted from near Bald Nob (50 Ma). 2. A gem-rich volcano near Elsmore (38-41 Ma). 3. A large basalt shield at Maybole (36-38 Ma), with late-stage gem-rich eruptives (31-36 Ma). 4. A felsic gem-rich volcano near Swan Peak (28-31 Ma). 5. A minor gem-rich centre at Bald Nob (21 -25 Ma). 6.

A major tholeiitic shield near Inverell (19-24 Ma).

This mysterious shuffling back and forth of the five centres of activity, first west, then east, across a hundred kilometre zone for over 30 Ma seems inexplicable under conventional concepts of East Australian volcanism (Johnson, 1989). However, in a multiple 'hot spot' model (Sutherland, 1990), these volcanoes represent the northward passage of the New England gem field over formal thermal triple point sites of the 65 Ma Coral Sea - Cato Trough - North Tasman Sea spreading rift system. Clearly, such a model has wide implications in exploring for these gem deposits in Eastern Australia. References Mollis, J.D. and Sutherland, F.L, 1985. Rec. Aust. Mus. 36, 299-311. New South Wales Geological Survey, 1987. NSW Geol. Surv. Rep. 87/058. Coenraads, R.R., 1988. In Kleeman, J.D. (ed.). New England Orogen Tectonics and Metalogenesis, Univ. of New England, Armidale, 302-307. Johnson, W.R., (ed) 1989. Intraplate Volcanism in Eastern Australian and New Zealand. Cambridge University Press. Sutherland, F.L. and Kinny, P.D., 1990. Geol. Soc. Aust. Abstr. Ser. 25, 241-242. Coenraads, R.R., Sutherland, F.L. and Kinny, P.D., 1990. Min. Mag. 54, 113-122. Sutherland, F.L, 1990. In Williams, M.A.J, and deDecker P. (eds). Cenozoic of the Australian Region: a reappraisal of the evidence. Spec. Publ. Geol. Soc. Aust., 16 in press. Table: Calculated age positions, for Coral Sea-Cato Trough - North Tasman basin 65 Ma spreading features, compared with ages of New England volcanic centres at 29°45'S. Spreading Feature

Lat. S

Long. E

Volcanic Centre

Long. E

Calculated Age (Ma)

Dated Ages (Ma)

E Coral Basin N Cato Basin Cato Basin S Cato Basin N Tasman Basin

16.0 17.0 20.5 23.5 24.7

153.0 156.0 155.2 155.0 154.3

Inverell Bald Nob Swan Peak Maybole Elsmore

150.8 152.0 151.3 151.6 151.2

20.5 22.5 30.5 35.5 38.0

19-23 21-25 28-31 33-38 38-41

Calculated age migrations are based on slow early Southern Ocean Opening (9mm/yr, 65-43 Ma), then fast Southern Ocean opening (53mm/yr, 43-20 Ma).

229 Poster Session Coal, Groundwater and Engineering

MICROGEOMETRICAL MODELS OF THE ELECTROMAGNETIC PROPERTIES OF GRANULAR GEOLOGICAL MATERIALS P.L Baker Department of Earth Science, Monash University Many physical properties of porous granular geological media are strongly influenced by the microgeometry and physical properties of the constituents. Mixing models that can quantitatively relate the bulk properties to the volumes of constituents find wide application in exploration geophysics, wire-line logging and non-destructive testing. In the past, only very simple porous media have been successfully modelled with sphere packs and network models. This paper presents a more geologically realistic approach for complex rocks by explicitly modelling the grains as meta-ellipsoids of different shape and orientation. The bulk physical properties are computed using extended Hanai-Bruggeman-Sen effective-medium mixing models for isotropic and anisotropic media. The models can be used for various geophysical measurements: electrical conductivity and dielectric permittivity, magnetic permeability and thermal conductivity. For the electrical conductivity of rocks with non conductive grains these models simplify to Archie's Law where the cementation exponent, m, is a function of the grain shape and orientation. The effects of different porosity reduction mechanisms on electrical conductivity are modelled and verified with experimental data. Mechanical compacting by grain rotation is modelled by an isotropic distribution of grains with many tangential point contacts and low coordination number changing to an anisotropic fabric with many long contacts and high coordination number. Further porosity reduction by grain deformation is modelled by changing the grain shape. Cementation by smooth grain coating is also modelled by changing the grain shape. Pore filling by clay particles is modelled by adding a suspension of platy grains of appropriate shape. The effects of conductive grains such as metallic minerals and double-layers around clay grains are examined. The conductivity enhancement in very fresh waters is shown to be a geometrical effect rather than an ion mobility effect as assumed in the commonly used Waxman-Smits equation. This geometrical model indicates that knowledge of the clay type is important since different clays have distinct morphologies.

230 EFFECT OF PORE PRESSURE ON COMPRESSIONAL WAVE VELOCITY IN COALS G. Yu*, K. Vozoff and D.W. Durney Centre for Geophysical Exploration Research Macquarle University A system has been developed for determining precisely the compressional wave velocities in coal specimens subjected to independent hydrostatic confining pressure and internal pore pressure. The velocity Vp of compressional waves has been measured, by the pulse transmission technique, on ten water saturated coal specimens in directions perpendicular and parallel to the bedding plane as functions of confining pressure (P^,) and pore pressure (Pp) to 25 MPa. Velocity changes due to changes in confining pressure were not exactly cancelled by equivalent changes in pore pressure. An effective pressure defined by Pg = P^ - nPp, n ^ 1, rather than an effective pressure defined simply by the differential pressure P^ = P^, - Pp, is found to be the determining factor in the behaviour of Vp. As pore pressure and confining pressure are increased at constant effective pressure, the value of n increases and approaches 1. But as effective pressure increases at constant pore pressure, the value of n decreases. Our experimental results are consistent with Blot's theory of the elastic wave propagation in a fluid-saturated porous solid.

231 Poster Session Regional, Crustal and Geothermal APPLICATION OF SECTION BALANCING TECHNIQUES TO DEEP SEISMIC REFLECTION DATA FROM OFFSHORE EASTERN CANADA M.C. Dentith^*and J. Hall^ ^ University of Western Australia ^ Memorial University of Newfoundland Deep seismic reflection profiles across the Grand Banks, offshore Newfoundland, were recorded as part of the Canadian Lithoprobe project. These data show the nnajor Mesozoic extensional basins in the region to be half-grabens which formed in the hangingwalls of faults that penetrate deep into the crust. Though these faults are well imaged in the shallow part of the section, their geometry at depth is poorly constrained, particularly as regards their relationship to dipping reflectors in the lower crust (interpreted as shear zones) and to the Moho. We have used section balancing techniques to constrain the interpretation of the deep seismic data. These techniques allow the determination of fault geometry from the structure of the hangingwall basins, for an assumed deformation mechanism. Due to the scale of structures involved, the section balancing techniques have to be adapted to account for isostasy and ductile deformation of the footwall. Figure 1 shows line drawings of the seismic data and our balanced section interpretations of basement, Moho and basin-bounding-fault structure (dots). The stippled areas are post-rift sediments. Our results show the Murre Fault, which bounds the Jeanne d'Arc Basin, to die out in the lower crust. In contrast, the Whale and Horseshoe Basin bounding faults detach at the Moho, the former having a ramp and flat geometry. The calculated fault geometries coincide with the dipping reflectors in the lower crust, suggesting the shear zone interpretation of these structures to be correct.

232

Borehole Breakout Analysis: Borehole breakout data suggest the current maximum horizontal stress in the Vulcan is oriented NE-SW, parallel to the post-mid Pliocene Australia/Banda Arc collision zone at Timor Trough. This initially surprising result has important implications for the nature of the trap-forming and modifying Miocene-Recent tectonism in the Vulcan. See conference volume paper for further details. Neogene Wireline Log Stratigraphy: Only limited biostratigraphic analysis may be applied to the sparsely sampled Neogene sequence of the Vulcan. Nonetheless the timing and distribution of Neogene deposition hold important clues to the nature of Miocene-Recent tectonism. A Neogene wireline log stratigraphy has been developed with limited biostratigraphic calibration. The development of this log stratigraphy has already revealed uplift in excess of 1 km at Ashmore Reef-1 during the mid Pliocene, N20 zone unconformity associated with collision in the Timor area. Subsidence Analysis: Interpreted seismic reflection records have been depthconverted and decompacted in order to analyze the syn-(Callovian-Valanginian) and post-(Valanginian-Palaeocene) rift subsidence of the Vulcan. The 2-D subsidence data have been modelled by the sophisticated coupled simple shear/pure shear model of lithospheric extension. The results reveal the likely distribution of crustal and mantle lithospheric stretching during basin formation, and hence provide data on palaeoheatflow in the basin.

IMPROVED ESTIMATION OF LATERAL VELOCITY INHOMOGENEITY FOR USE IN SEISMIC MIGRATION Beverley Moore University of Technology, Sydney The determination of an appropriate velocity model for use in the migration of seismic data is still considered to be one of the crucial steps in the procedure. This paper presents a more effective method for estimating the lateral velocity inhomogeneity in the uppermost few kilometres of the Earth from a seismic survey of the region concerned. Specifically, the input data consists of stacking velocities and horizon times from an unmigrated stacked section. These correspond to the 'horizons of interest' chosen by the seismic interpreter. As usual, the aim is to obtain a coarse-scale velocity model for the region underneath the survey line; such a coarse-scale model is required to 'migrate' the data to its correct location, to give the finer details of the model. As in earlier work (Sutton and Moore, 1987), the procedure uses a generalised linear inversion technique. Lateral variations in interval velocity are permitted. Assuming the deviation from constant velocity within each layer is small, the curved rays are replaced by straight rays with corrections (Moore, 1989). The formulae for the corrections to straight ray geometry are obtained by applying the method of small perturbations to the ray and energy transport equations (Moore, 1980). Input data has been weighted according to the accuracy with which it has been acquired. Weighting of data becomes desirable especially in the over-determined problem and also when mixed data sets are used such as a combination of stacking velocities and two-way travel times from an unmigrated stacked section of seismic data. Jackson (1972) has shown that for statistically independent data, the choice of a

233 diagonal weighting matrix whose elements are the reciprocals of the variance of the data causes the residual for each data point to be compared with its expected error; data which are not statistically independent require the use of the inverse of the covariance matrix for the data as the weighting factor. Unlike the earlier work which was limited to handling lateral distances of only 2.25 km (making it necessary for the entire line of data to be split into overlapping sections which were processed independently of one another), the procedure has now been modified to handle data from an entire seismic line simultaneously. Spline representations of boundaries and velocity profiles have been incorporated into the eariier procedure. The procedure has been applied to data from the Gippsland Basin. This has resulted in significant improvement in the velocity profile obtained because of the reduction in the distorting edge effects which were inherent in the earlier work with its small lateral dimensions. The paper examines the consistency between solutions obtained when different parts of the data are omitted. References Jackson, D.D. Geophys. J.R. astr. Soc., 28, 97-109,1972. Moore, B.J. Geophys. J.R. astr. Soc., 63, 671-689,1980. Moore, B.J. Ultrasonics International 89 Conference Proceedings, 1001-1006, 1989. Sutton, G.R. and Moore, B.J. Geophysical Prospecting, 35, 895-907,1987.

APPLICATION OF DYNAMIC PROGRAMMING TO THE PROCESSING OF STRONG MOTION ACCELEROGRAMS Ivan A. Mumme CSIRO, Division of Mineral & Process Engineering Lucas Heights, NSW Although the mathematical concept behind the computation of ground velocity and displacement time-histories (quantities which are important to earthquake engineers) becomes relatively simple when the strong motion accelerogram is in digitized form, considerable drifts in the integrated velocity and displacement characteristics generally occur. This results from the fact that before coming available as a digital signal the analog trace produced by a strong motion accelerograph undergoes several transformations. Associated with each of these transformations are several sources of error that affect the reliability of the resulting signal. As a result, various procedures have been developed to minimize the presence of errors in the ground motion signals. Largely dependent on purely filtering techniques, however, such approaches tend to destroy some of the information contained in the ground motion signals. In this thesis, a more direct procedure is adopted by formulating the problem as a general inverse one, which is then solved using the mathematical theory of multistage decision processes.

234 The reason for this is that dynamic programming formulation leads to a greatly simplified method of computational solution. The main concept of this technique lies in the principle of optimality (Bellman, 1967) which may be stated in a form suitable for this study. An optimal policy has the property that, whatever the initial state and the initial decision are, the remaining decisions must constitute an optimal policy with regard to the state resulting from the first decision. However, while the error criterion developed in this approach is not necessarily the best criterion in many cases, because of the nature of the random errors introduced by an operator in digitizing acceleration records, a frequency dependent criterion has been developed to remove extraneous noise. This noise is dominated by the lowest frequencies and largely results from inaccuracies in the tracking mechanism of the digitizer. High frequencies can also be adequately removed by this filtering process. The significant improvements in the reliability of ground motion estimates that arise from using dynamic programming techniques from solving the problem in hand are illustrated through the use of a number of examples.

TOWARDS ACTUALISTIC MODELS Suzanne Y. O'Reilly"'* and W.L Griffin^ ^School of Earth Sciences, Macquarie University ^CSIRO Division of Exploration Geosclence The integration of petrologic and geophysical data sets provides a powerful, synergistic methodology for geologically realistic modelling of the composition, structure and tectonic evolution of the crust and upper mantle. Petrologic data from inaccessible deep crust and mantle regions are provided by fragments (xenoliths) of deep-seated rock types entrained in ascending magmas. These xenoliths are transported to the surface in 10-30 hours, too fast for alteration or significant re-equilibration. They yield the locations of specific rock types in the underlying crust-mantle section, and large specimens can be used to determine the petrophysical characteristics (density, acoustic velocity, magnetic properties, electrical and thermal conductivity, heat production) of specific rock types existing at given depths. This paper presents a summary and overview of some of the applications of these data for eastern Australia. Geothermobarometry calculations using mineral equilibria in such xenoliths define an empirical geotherm for eastern Australia which has a high curvature at 24-30 km and is inconsistent with previous thermal conduction model geotherms. Thermal modelling based on the petrologic constraints show that the best fit to the empirical geotherm is obtained if basaltic magma is intruded in a layer 4 km thick at 28 km, at a rate of about 900 m/Ma. This model is consistent with tectonic uplift rates for the Eastern Highlands and with seismic reflection profiles showing a layered crust. It is also consistent with a heat flow of over 84 mW/m% higher than for oceanic regions. Xenolith P-T data also define the stratigraphy of the crust-mantle boundary (CMB) and upper mantle. In eastern Australia, the CMB boundary is defined by the incoming (with

235 depth) of dominant ultramafic (spinel Iherzolite) rocl< types. This crust-mantle boundary is deeper (about 35 km) in central and southern NSW and in eastern Queensland than it is in north Queensland and western Victoria (25-30 km). Preliminary data suggest the crust-mantle boundary shallows rapidly towards the continental margin. The horizontal layering with significant velocity contrasts seen at the CMB in some seismic profiles for eastern Australia is interpreted as representing sills of basaltic rock under- and over-plated around the CMB mainly during Cainozoic volcanic activity. These basaltic sills and layers decrease in number away from the CMB; this decrease accounts for the Vp velocity gradients observed in seismic profiles at these depths. Acoustic wave velocity measurements have been carried out (O'Reilly et al., 1990) on three mantle wall-rock samples (spinel Iherzolites) and one mantle-derived basaltic rock type (garnet pyroxenite) typical of some of the sills and lenses in the upper mantle. The measured acoustic velocities range from 7.7 to 7.9 km/sec for the mantle wall-rocks, assuming the pressure and temperature conditions beneath eastern Australia derived from xenolith geothermobarometry. Therefore the use of dunite as a generalised mantle rock type results in overestimation of model mantle Vp's, especially when also assuming a standard continental geotherm. The measured spinel Iherzolites which have foliations due to preferred orientation of olivines, show a high degree of anisotropy (up to 10%) in acoustic velocity. It is thus possible that some large-scale seismic phenomena (such as dipping upper mantle reflectors) may represent mantle shear zones or domains with a directional fabric and hence Vp contrasts. It is also possible to use a combination of measured acoustic velocities and singlecrystal elasticity data of constituent minerals, to interpolate Vp for a wide modal range of mantle rock types. Triangular grids which allow graphical estimation of Vp for spinel Iherzolites, garnet Iherzolites and garnet pyroxenites have been constructed (O'Reilly et al., 1990). Reference O'Reilly, S.Y., Jackson, I. and Bezant, C., 1990. Tectonophysics, in press.

AU-PGE IN LAYERED MAFIC INTRUSIONS OF THE PINE CREEK GEOSYNCLINE R.G. Warren Bureau of Mineral Resources Geochemical data now permit subdivision of the Zamu Dolerite, Pine Creek Geosyncline, into NEZ dolerite northeast of the Jim Jim Fault, Zamu Dolerite s.s. in the South Alligator Valley, and BZ dolerite in the Burnjndie district. Meta-dolerite NE of the Mary River, previously placed in the Oenpelli Dolerite, is renamed Goodparia dolerite (revision of Goodpalah Diorite). The Zamu Dolerite s.s., the most siliceous unit in the umbrella Zamu Dolerite, evolved petrographically from early cumulus Opx with Cpx, through augite-pigeonite (mostly inverted) to granophyres and is characterized by graphic quartz-feldspar, still recognizable in the altered rocks of the Coronation Hill orebody. Geochemically, the Zamu Dolerite has a well-defined fractionation trend which is quartz-normative throughout, and is a high-silica tholeiite with hints of calc-alkaline affinities. PGE

236 concentrated within the fractionation trend, probably with S, and not with early high Cr in the basal zone. The Zamu Dolerite is a possible source for the PGE in the Coronation Hill orebody, along with the Koolpin Fornfiation, and perhaps thicker sills may carry higher PGE values than present sampling indicates. There is also potential for lateritic concentrations. Shovel Billabong Andesite, with a distribution similar to the Zamu Dolerite, appears to be chemically related, but data show it is neither chilled margin nor parent magma. Samples of Shovel Billabong Andesite carry trace PGE. The NEZ dolerite (after altered rocks are removed from the data base) forms a set of samples whose analyses fall within the tholeiite field on an AFM plot and give consistent trends on geochemical plots distinct from the Zamu Dolerite s.s. The BZ dolerite crops out as thin sills intruding the Koolpin Formation, and as amphibolites within the Masson Formation east of Francis Creek. Quartz is less abundant than in the Zamu Dolerite s.s., but graphic intergrowths occur in some speciments. The BZ dolerite is olivine-normative at high Mg. Samples from the Mg end of the series show significant values for PGE and Au. The lack of a distinct peak within the series may reflect failure of the thin sills to crystallize so as the yield a pronounced concentration of PGE. No reports of PGE near the BZ dolerite exist, though the potential for secondary concentrations should be considered. Gold deposits occur close to the BZ dolerite in the Golden Dyke dome and near the Hayes Creek Shear. Goodparia dolerite forms massive, partly metamorphosed bodies within the Masson Formation. Analyses trend from olivine-normative at high Mg to quartz-normative at low Mg. XY and ternary plots with P2O5, Ti02 and Ba show it is distinct from the Oenpelli Dolerite. Analysed samples of Goodparia Dolerite contain no significant PGE or Au values.

THE HAMMER BASIN, NEW ZEALAND Ray Wood DSIR, New Zealand Three 24-fold seismic reflection lines have been collected in the Hanmer Basin, a pullapart basin on the Hope Fault, New Zealand. The data were collected at the east end of the basin and show a well-bedded sequence of Pleistocene alluvial silts and gravels overlying Mesozoic basement. The sedimentary sequence thickens to the south where about 1 km of sediments are present. No faulting is observed in the sediments. A strong unconformity is seen on sediments uplifted in association with strike-slip movement on the Hope Fault. This uplift may be due to bending of the Hope Fault as part of regional deformation.

237 Poster Session Computer Applications

FAST, VERY ACCURATE POSITIONING WITH GPS Erwin Frei^, Rod Eckels^* and Chris Rizos^ ""Lelca Heerbrugg Ltd, Switzerland ^Leica instruments, Australia ^School of Surveying, University of NSW The Global Positioning System (GPS) has been used for accurate positioning in Australia since 1985. Since that time geodetic and navigation GPS receivers have been used on a vast range of surveys. These include low accuracy work (10m-20m) like borehole location and positioning of seismic lines to the highest accuracy required for geodetic control densification (1 mm-1cm). To achieve the highest accuracy, classic GPS observing techniques require that each station be occupied for about one hour. Lower accuracies can be achieved, however, with significantly shorter observing windows. Over the last 5 years many theories have been promoted to improve the speed of the high accuracy observations. Kinematic techniques have been proposed that allow the centimetre level accuracies to be achieved with only 45 seconds of observations. All of these techniques, however, have major drawbacks, and require very strict observation and processing procedures before they will work. Recent developments in post-processing techniques have been developed to overcome many of these restrictions and limitations. Some results of the first test of these new software developments show that within two minutes of observations at any site it will be possible to determine the position of that site to centimetre accuracy. Once these developments are fully tested and implemented they will have a revolutionary impact on the entire survey and positioning industry.

DC RESISTIVITY INVERSION USING GENERAL-PURPOSE OPTIMISATION SOFTWARE N.P. Merrick Department of Applied Geology, The University of New South Wales PO Box 1, Kensington NSW 2033, Australia DC resistivity sounding data usually are interpreted in terms of a layered earth by an iterative inversion scheme. This paper presents an alternative mechanism for the inversion process by formulating the resistivity inverse problem as an optimisation problem. By invoking the commercial mathematical programming software package called GAr\/IS, an inversion routine has been developed without having to linearise the problem explicitly and without having to know details of the convergence algorithm. The GAMS high-level programming language provides a structure for coding the forward problem, for specifying an initial model and for declaring reasonable bounds on model parameters. GAMS inversion is extremely versatile in allowing ad hoc constraints of any

238 complexity, but converges more slowly than special-purpose resistivity inversion algorithms. After familiarity is gained with the GAMS language, new code for more complex resistivity models or different geophysical methods can be developed in much less time than is required for the development of dedicated geophysical inversion software.

AN IMPROVED NAUDY BASED TECHNIQUE FOR ESTIMATING DEPTH FROM MAGNETIC PROFILES Zhiqun Shi Department of Geology and Geophysics University of Adelaide Techniques for automatic determination of the depths of sources from magnetic profiles represent fast and inexpensive interpretation tools. The automatic technique proposed by Naudy Is widely used. This technique requires accurate locations of the centers of anomalies in order to obtain reliable final estimation of the depths. In the proposed improvement in the Naudy technique, the total magnetic fields on the profiles are split into horizontal and vertical components. It is demostrated that this procedure leads to accurate locations of the centers of anomalies. Final estimates of the depths are less ambiguous and agree well with data obtained from drilling. Application of the Naudy technique to vertical gradient, data is discussed.

ENGINEERING SEISMIC REFRACTION: AN IMPROVED FIELD PRACTICE AND A NEW INTERPRETATION PROGRAM, REFRACT Chris Walker""*, Tak Ming Leung"", Maung Aung Win"", Robert J. Whiteley2 ''Roads and Traffic Authority of NSW ^Selsets Pty Ltd, NSW Shallow seismic refraction is the principal geophysical method for engineering site investigations. The Roads and Traffic Authority of New South Wales applies the method for roadworks, chiefly in the investigation of road cuttings for design and excavation assessment. The need to obtain reliable and detailed interpreted seismic sections, particularly for intermediate layers with seismic velocities in the range 800 to 2500 m/s, has led to an improved field practice with a 3 to 5 m geophone interval and sourcepoint intervals of 10 to 15 m with offsets up to 50 m. As a result of the deficiencies of currently available interpretation software a new interactive and graphically oriented computer program called REFRACT, for IBM AT compatible computers, has been developed. A field example from a variably weathered, basaltic area demonstrates the effectiveness of the improved field and interpretation practice which is state-of-the-art for the shallow engineering refraction method in its application to roadworks.

239 Standby Papers

RARE EARTH ELEMENT EXPLORATION IN AUSTRALIA Bernd G. Lottermoser Institute of Geoscience, University of Mainz Federal Republic of Germany The steadily increasing applications of rare earth elements (REE: lanthanum to lutetium) in industry and the encouraging research results on high-temperature superconductors and permanent magnets using REE has led to the increasing interest of the mining industry towards the exploitation of new REE resources. REE minerals, once a nuisance to sand miners, have the potential to be an industry of their own. Traditional REE resources, beach sands, placers and carbonatites, may have to compete in the next century with new REE deposits. In 1989, world production of REE minerals has been estimated at 80250 t which would represent a rise of nearly 3% over the 1988 level. In Australia, current production of REE minerals is solely as a by-product from titanium-enriched placer deposits and beach sands (monazite and xenotime) and to a very minor amount from tin-mining (xenotime). In spite of the by-product status, in 1989 Australia accounted for approximately 45% of the world's monazite production (148501 of 327001) and supplied approximately 20% of the world's REE oxide production. However, Australian producers on average derive only 3% of their revenues from monazite. Thus the supply of REE from these resources largely depends on the titanium-market. Undeveloped REE resources in Australia are associated with carbonatites, alkaline igneous rocks, pegmatites, phosphorites, bauxites, cemented fluvial sandstones, and uranium mineralisations. The REE are incorporated into a range of common and also unusual REE ore minerals including silicates, phosphates, aluminophosphates, carbonates, and oxides. In some of the undeveloped resources, the unusual crystallographic siting of the REE, the exceptionally fine grain size of the REE minerals and their intense intergrowth with other phases may require new processing and extraction methods. This in turn may lead to new patents for the processing of REE minerals and for the extraction of REE. The currently worldwide mined REE ore minerals, monazite and bastnaesite, do not possess REE distributions requested by the market. Exploration for new REE resources should be focussed on ores with more favourable REE distributions including heavy REE, neodymium, samarium, europium and yttrium enrichments. Such ores are found in uranium mineralisations, in alkaline igneous rocks, in laterites overlying carbonatites and alkaline igneous rocks, and in placers derived from low-grade regional and contact metamorphic sediments. REE-bearing minerals are not readily identifiable in the field and they may be overlooked in regional geological and exploration work. In addition, REE are usually not reported in routine geochemical analyses. Thus exploration for REE has to be conducted diligently and it also requires the application of some specific analytical techniques. It is not sufficient to establish the mere presence of one REE or of the REE as a group, but the concentrations of each individual REE must be determined. In contrast to conventional methods, inductively coupled mass spectrometry (ICP-MS), neutron activation analysis (NAA) and high-performance liquid/ion chromatography (HPLC/HPIC) techniques allow

240 the precise and accurate quantification of all REE in rock samples. Identification of REE minerals requires X-ray diffraction (XRD) and energy dispersive electron microprobe analyses (EDS). Quantification of REE contents (wt% levels) within REE ore minerals is best achieved with wavelength dispersive electron microprobe analyses (WDS). The parameters that will influence whether or not a REE resource can compete with the traditional REE resources (beach sands, placers and carbonatites) will depend on the REE grade, the REE distribution, the process costs and the presence of possible byproducts. Weathering products derived from alkaline igneous rocks and carbonatites are exploration targets for high-grade, large tonnage REE deposits. The REE and yttrium may be incorporated into primary igneous minerals and also secondary minerals. REE and yttrium may also be adsorbed onto minerals, mineraloids, amorphous substances and clays which could be recovered using hydrometallurgical treatment methods. Lateritic REE deposits may be easily and economically mined by shovel in open pits and they are unlikely to require extensive crushing and milling. Placers derived from regional and contact metamorphic sediments may possess large amounts of europium enriched, thorium depleted monazites. Weathering product REE ores have the potential to contain REE distributions requested by the market and thus represent high-value, very demanded commodities.

DRYLAND SALINITY AND RECLAMATION N. Mattocks Tesla-10 Pty Ltd., Western Australia Previous geophysical work commencing in the mid-70's, principally in North America and Australia had indicated the utility of ground E-M in outlining rural salinity. The salinity itself is a direct outcome of rising water tables provoked by land clearing and lower water utilisation under present farming techniques. The controlling influence of dolerite dykes detected by magnetics was added to this in the mid-80's through work by the Department of Agriculture in Western Australia particulariy in the south-west where dyke swarms are abundant. Much of the processing of this latter work was undertaken by Tesla-10 to whom it became apparent that interpretations often suffered from insufficient data density as a result of which minor dykes would be either missed or mis-correlated. Typically surveys were collected on 100-200 metre lines with 20 metres readings. Such surveys, although adequate for catchment studies, can be misleading in detailing specific paddock remedies. More data was not collected because it is difficult, time consuming and expensive. Gridding needs to be relatively accurate because it is critical to have the two surveys, magnetics and E-M, exactly located in relation to each other. Their complementary nature forms part of the strength of the interpretation. Is the salinity backed up behind the dyke? Is it spilling over, particularly in the drainage? Is the conductivity response merely due to the clays of the weathered dyke itself? The Geolinear commenced development in Tesla-10 in 1988. The aim was to minimise gridding costs, retain the resolution of near-surface sensors, collect all parameters simultaneously whilst increasing the speed of collection and reading density. A suitable

241 vehicle was selected on the basis of its low magnetic effect. An articulated trailing system on which a patent is pending was found to be the best means of sufficiently distancing the magnetometer sensor, whilst retaining full manoeuvrability. Electromagnetics and other sensors were added forward of this. The examples to be shown together with the proposed reclamation strategies are form farms and catchments in the wheatbelts of the south west of Western Australia. One such strategy involves treatments based on the lineaments outlined and this is also the subject of a patent application. Even in areas where dykes are either non-magnetic or non-existent the magnetics are still found to be a useful contributor to the hydrogeological picture from which a successful reclamation strategy can be formulated.

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Corporate Sponsors AERODATA HOLDINGS LIMITED Aerodata Holdings Limited operates a worldwide network of contracting groups specialising in airborne geophysical applications for earth resource exploration, mapping and evaluation. Its subsidiary, World Geoscience Corporation provides the link between operating groups based in Perth (Aerodata), Sydney (Austirex) and Toronto (Questor). Aerodata is a world leader in the application of high resolution aeromagnetic surveys and has an established involvement in research and development in acquisition, data processing and interpretation. Aerodata also owns and markets extensive multiclient airborne data sets covering many active exploration areas for both minerals and petroleum. The Questem airborne EM system is now operating in Australia through Aerodata, with emphasis on groundwater and mineral exploration applications. Aerotrac provides an airborne video surveillance system suitable for cultural and environmental monitoring. TImmlns Geophysics offers a wide range of ground geophysical services particularly suited to following up airborne surveys. Recent developments in the Aerodata group have included the acquisition of PICODAS INC which manufactures new generation data acquisition systems yielding higher sensitivity and data quality. Data processing and interpretation developments have centred on the SUN workstation based processing and imaging system which provides new dimensions in geological resolution from airborne data.

AGL PETROLEUM AGL Petroleum, based in Brisbane, was formed in 1988 by the merger of TMOC Resources Ltd and CSR Petroleum. It currently operates exploration in the Surat Basin, Denison Trough and Galilee Basins in Queensland, the Sydney and Clarence-Moreton Basins in NSW, the Amadeus Basin in the Northern Territory, as well as Indonesia and PNG. It also has interests in the Surat, Gunnedah, Gippsland, Amadeus and Canning Basins in Australia and the Pearl River Basin in China. AGL Petroleum produces significant volumes of oil and gas from the Surat Basin, Denison Trough, Amadeus Basin and Seram (Indonesia). Encouraging, longterm production testing of the Lufeng Field (Pearl River, China) is currently underway. AGL Petroleum is also the largest Australian gas and oil pipeline operator. AGL Petroleum looks to the future in the Australian Oil and Gas Industry with confidence.

243 AMPOL EXPLORATION LIMITED Ampol Exploration Limited ("Ampolex") has been engaged in exploration for and production of petroleum (both oil and natural gas) for over thirty years. Originally most of its activities were located in the State of Western Australia, but, in more recent times, it has extended those activities into other States of Australia and overseas. Currently, it or its subsidiary companies are members of joint ventures (in some as operator) holding exploration and/or production concessions in most States of Australia, the Peoples Republic of China, Papua New Guinea, the United States of America, New Zealand and Argentina. These concessions cover both onshore and offshore areas. In the last three years Ampolex has grown through acquisition and exploration and has achieved the most rapid production growth in the oil sector. From 3.0 million barrels in the 1989 Year, production is expected to peak at 7.4 million barrels in 1993. The major source of income will come from the Kutubu Project in PPL100 to which Ampolex and its partners are expected to commit to develop in October/November of 1990. Ampolex's share of the project represents about 35% of its Nett present Value. Ampolex also has large exposures and receives substantial cash flow from operations in the following production fields: Barrow Island; Talisman; Saladin, Yammaderry and Cowie; Dongara (crude oil and natural gas); Naccowlah/Jackson area; Nockatunga and Tintaburra area; Blina area. Canning Basin; Jabiru, Challis, Cassini and Skua; North Herald/South Pepper; Chervil; USA crude oil and natural gas operations in 7 States and offshore Gulf of Mexico; and Lufeng crude oil production from the Pearl River Mouth Basin, Peoples Republic of China.

ASHTON MINING LIMITED Ashton was formed in 1978 and is now one of Australia's top resource companies. Ashton's main project is its 41% interest in the Argyle diamond mine in Western Australia. Argyle is the world's largest diamond producer at an annual rate of 35 million carats a year. Ashton is also involved in three medium sized gold mines in Western Australia, the wholly owned and managed Laverton and Harbour Lights projects, and the 43% owned Bardoc project. Ashton's equity gold production share from these three mines is around 100,000 ounces a year. Exploration for both diamonds and gold is occurring worldwide, with concentrated efforts in Western Australia and Indonesia.

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BHP PETROLEUM BHP Petroleum is a new force in the ranl^s of tlie major international oil producers. While the company has been successful in Australia since its beginnings less than 30 years ago, the strategy it has followed over the past few years has gained it a strong international profile. Today, on the basis of its proven reserves of oil and gas, BHP Petroleum ranks 12th among the world's listed oil companies, with interests in some 24 countries and an active exploration and development program. BHP Petroleum has more than 2,000 directly employed personnel, two-thirds of whom are based outside of Australia. Formed in 1960 by the Broken Hill Proprietary Company Ltd, BHP Petroleum quickly rewarded its founders' confidence with the discovery five years later of the Bass Strait oil and gas fields. These fields supply about 60% of Australia's oil and gas needs and all the natural gas in the State of Victoria. The success of Bass Strait gave the company the financial strength to take a direct share in the North West Shelf Project in 1976. BHP Petroleum operates production from the Jabiru and Challis/Cassini oil fields located in the Timor Sea. The company also has major interests in the USA, Canada and the U.K. BHP Petroleum was restructured in 1990 to make it better equipped to meet new challenges.

BLiGH OIL AND MINERALS N.L. Bligh Oil & Minerals N.L. commenced oil exploration in 1980 and was publicly listed in July 1981. The company and its four wholly owned subsidiaries are active in oil and gas exploration and production in Australia, New Zealand, North America and Argentina. Bligh's current nett production is 1200 BOPD and 1.8 MMCFGPD which is derived from properties in Australia, New Zealand and North America. In 1989/90, Bligh participated in 53 wells of which 33 were completed as oil and/or gas producers. In the current financial year it is anticipated that the company will have an interest in approximately 45 wells. At present the company's primary effort is focussed on the Navajo Nation Project in the Four Corners Area of the United States where it has an 11.875% Wl / 9.5% NRI in over 50,000 acres under lease. The acreage was selected from an exploration concession covering 254,000 acres after more than 2000 kilometres of seismic data were recorded. The main targets in the area are Pennsylvanian aged algal mound traps within carbonates of the Desert Creek and Ismay Zones of the Paradox Basin sequence. The mounds are identifiable using state of the art seismic and, to date, seven mound exploration wells have resulted in six new field oil and gas discoveries. Five of these wells are in production for an average of over 400 barrels of oil per day with associated gas. The acreage position encompasses over 100 seismically defined mound anomalies. Bligh Oil & Minerals N.L. is Brisbane based, with a branch office in Dallas, Texas and has a staff of 12.

245 BMR Geology and Geophysics BMR is a research Bureau of the Commonwealth Department of Primary Industries and Energy and is the principal Australian geoscientific agency. The purpose of BMR is to: generate publicly accessible information of the nation's petroleum, mineral and groundwater resources participate in monitoring and developing an understanding of the natural environment participate in global and regional geoscientific programs of importance to Australia provide independent scientific advice to government, industry and the public for • • • •

management of Australia's resources development of multiple land-use policies and environmental protection mitigation of natural hazards detection of underground nuclear explosions.

The Bureau has been restructured recently to bring together its scientific programs in two client and outcome orientated groups: Minerals and Environment and Petroleum and Marine Geosclence, each headed by an Associate Director. High priority projects for 1990/91 are: mineral province projects in Eastern Goldfields, Kimberley-Arunta, Mcarthur Basin, North Queensland, Lachlan-Kanmantoo Fold Belts and Musgrave sedimentary basin projects in Canning, East Australia and Officer Basins the Continental Margins Programme will focus on Australia's western and northwestern margins. A new Environmental Geoscience unit is developing projects concerned with providing information necessary to understand changes in the natural environment and to increase public awareness of the geological significance of Australia's wilderness areas.

BP IN AUSTRALIA - A BRIEF OVERVIEW The BP Group world wide can trace its links with Australia back to 1883, the year the D'Arcy family arrived at Rockhampton, Queensland, from England where young William Knox D'Arcy began work as a solicitor in his father's law firm. William eventually made a fortune from a gold mine at Mount Morgan and returned to England where he later invested his money in oil exploration in Persia. Oil was discovered at Masjid-i-Sulaiman in 1908 and this became the foundation for the Anglo-Persian Oil Company, later to become British Petroleum.

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The Commonwealth Oil Refineries (C.O.R.) was established in Australia in 1920 through an agreement between Anglo-Persian Oil Company and the Australian Government headed by Prime Minister Billy Hughes. By 1924 the Company had constructed Australia's first oil refinery at Laverton, Victoria. Like all other oil companies in Australia, C.O.R. became a part of Pool Petroleum during the Second World War and then, in the 1950s, undertook a major expansion program throughout Australia. A large refinery was constructed at Kwinana, Western Australia in 1955 and the Laverton refinery was closed. Two years later, British Petroleum acquired the Australian Government's interest in C.O.R. and the company became BP Australia Limited. In 1966 a second refinery was constructed at Westernport, Victoria which was subsequently closed in 1985 following the acquisition by BP of Amoco Australia, which included the small but efficient refinery at Bulwer Island, near Brisbane. BP'S association with Papua New Guinea goes back seventy years through its search for petroleum and minerals but the Company did not commence marketing there until 1969. Subsequently BP has established a strong presence throughout the nation with major installations and a strong service station network. In the southern highlands near Tari, BP is the operator in a joint venture that will see natural gas being produced commercially at the Hides Gasfield in early 1992. In addition, BP is involved in a number of other promising finds in Papua New Guinea and has licences to extensive acreage offshore Australia. Recognising the vital importance of diverse energy sources to Australia, BP became a partner in the huge natural gas project on the North West Shelf of Western Australia in 1967 and later became involved in the production and marketing of solar energy. As well as its business operations, BP provides extensive support to a range of community activities in a number of areas including the arts, health, sports, education, the environment and community welfare. In these and many other ways, BP continues to make valuable contributions to its stakeholders and the community.

BRIDGE OIL - "THE ENERGETIC AUSTRALIAN" Bridge Oil Limited is an Australian resource company which explores for and produces oil and gas in Australia and the U.S.A. In Australia, the company operates oil and gas fields in the Surat Basin (Queensland) and participates in production from the Cooper Basin (South Australia) and the Carnarvon Basin (Western Australia). In Queensland, Bridge Oil Limited's wholly owned subsidiary. Bridge Gas Queensland Pty. Ltd., manages and operates the Queensland Government's Wallumbilla to Gladstone Gas Pipeline. In the U.S.A., Bridge Oil's principal assets are in Texas and New Mexico and are managed through Bridge Oil (USA) Inc., headquartered in Dallas, Texas. Bridge Oil (USA) has a wholly-owned subsidiary. Bridge Gas USA Inc, to broker third party gas and Bridge Oil equity gas.

247 Bridge Oil currently produces approximately 33,000 barrels of oil equivalent per day from its combined USA and Australian operations. At year-end 1990, Bridge Oil's forecast total remaining reserves will be in excess of 100 million BOE. Bridge Oil now has over 250 employees worldwide and in 1989 achieved a record operating profit of A$16.0 million (before foreign exchange gains or losses).

CARPENTARIA EXPLORATION COMPANY PTY LTD (C.E.C.) CEO is the Exploration Division of MIM Holdings Ltd, exploring for base and precious metals, and oil and gas in Australia, New Zealand, Ireland and Papua New Guinea. CEC currently operates from bases in Brisbane, Mount Isa and Townsville in Queensland, Perth in Western Australia, Darwin and McArthur River in the Northern Territory and Navan in the Republic of Ireland. MIM is a large-scale, Australian-based producer of copper, silver, lead, zinc, gold and coal, with expanding international involvement in exploration, mining, refining and recycling of minerals and metals in the United States of America, Germany, Ireland, Australia, Canada, the United Kingdom and Papua New Guinea. MIM holds stakes in strategically important resource-related companies including ASARCO, Cominco, Teck, Granges and Metallgesellschaft. MIM traces its origins to the discovery in 1923 of silver-lead-zinc ore at Mount Isa in north-west Queensland. Today, Mount Isa is the world's largest single mine producer of both lead and silver and among the ten leading zinc and copper producers. MIM's three large coal mines in Queensland's Bowen Basin produce high quality coking and steaming coals for domestic use and for export to customers in Japan, Asia, Western Europe and elsewhere. MIM has also become a significant gold producer through subsidiary, Highlands Gold Limited, which has a 30 per cent interest in the world-class Porgera gold mine in Papua New Guinea, and through operating gold mines in Queensland and the Northern Territory. MIM is also a world leader in the development of mining and mineral processing technology and has successfully marketed that technology around the world.

THE CHAMBER OF MINES AND ENERGY OF WA INC The Chamber of Mines and Energy of Western Australia Inc represents the collective interests of companies involved in mineral exploration, production and processing in Western Australia. Its activities are entirely funded by its member companies which in 1989 produced some 90 percent, by value, of Western Australia's mineral output (worth more than $9,000 million).

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The Chamber exists to promote a social and political environment favourable to the commercial well-being of mining which is the State's biggest industry. The Chamber's Exploration Council meets in Perth six times a year to discuss relevant issues. The Council acts as a means of informing exploration representatives of mining industry issues and proposals. It is the mechanism for the exploration industry to provide a co-ordinated voice to other organizations, for example the Department of Mines or Bureau of iVIineral Resources, on their plans and policies. In 1989 the Western Australian exploration industry undertook 56% of Australia's mineral exploration expenditure. Access to land remains the major issue for the exploration industry. The Chamber is addressing this issue through the development of Codes of Practice, information seminars and liaison with other land user groups and the Government.

CLASSIC LABORATORIES LIMITED Classic Laboratories is an Australia wide laboratory group focussing on geoanaiysis and environmental analysis. Classic's commitment is to provide clients with a fast, reliable service at a competitive cost. The range of highly trained professional and technical staff is backed up by advanced instrumentation and computerised laboratory automation systems. The systems incorporate stringent quality controls and sophisticated reporting procedures. Classic's range of services include: exploration analysis mine control analysis metallurgical testing industrial minerals analysis general chemical analysis water analysis environmental analysis and radiochemistry Classic Laboratories is a wholly owned subsidiary of Amdei Limited, and has the benefit of 30 years' experience in analytical work. The Head Office is located in Perth, and branch offices are found in the major mining areas of Kalgoorlie, Meekatharra, Darwin Townsviile and Mt isa, with the Adelaide laboratory adjacent to Amdel's major facilities in Adelaide. Attention to clients' requirements has ensured that Classic Laboratories is a stable, successful company with strong links to the mining industry. Consistent high quality work with fast turnaround is the hallmark of the group.

249 CRA EXPLORATION PTY LTD CRA, through its wholly owned subsidiary CRA Exploration (CRAE), is committed to explore for and/or acquire world class mineral and petroleum deposits in order to improve its existing resource base and to underpin future growth. CRAE is a multi-commodity explorer and maintains a high level of exploration activity. Historically, its exploration activities have been directly instrumental in the discovery of several world-class ore deposits which support a large part of CRA's present operations. These include Mount Tom Price iron ore deposit in Western Australia; the Weipa bauxite deposits in Queensland; the Panguna porphyry copper/gold deposit in Papua New Guinea; coal at Tarong, Queensland; the Argyle diamond deposits in Western Australia and the Pinang steaming coal and Kelian gold deposits in Indonesia. CRAE's more promising current prospects include base metals in Queensland, uranium, base metals and thermal coal in Western Australia, gold in Papua New Guinea, Western Australia and Indonesia, and mineral sands in Victoria. Exploration operations are conducted by regionally organised teams with a total complement of approximately 100 geoscientists based in most of the capital cities and some of the larger country centres located close to the principal areas of exploration activity. CRAE also maintains a research and technical support group based in Canberra which is primarily responsible for undertaking applied research into relevant exploration topics and for maintaining a central geotechnical information data-base.

CRUSADER Crusader is a successful independent company based in Brisbane whose primary business is oil and gas exploration. Crusader has interests in many Australian Basins including the Cooper, Eromanga, Gippsland, Otway and Surat. Through its interest in the Nappacoongee-Murteree Block in PEL's 5 & 6 in South Australia, Crusader is a participant in the Cooper Basin Unit which sells gas to the Adelaide and Sydney markets. It is also a participant in the Cooper Basin liquids project. Crusader is involved in several overseas projects. It holds interests in New Zealand, Canada and the United States Navajo Reservation where it is exploring with other Australian oil companies. Through its holding in Triton Energy Corporation it has indirect interests in Europe, Africa, Asia, North America and South America. Crusader is a major shareholder in Australian Hydrocarbons N.L. whose petroleum interests complement Cmsader's both in Australia and the United States. Crusader has widespread coal interests through its subsidiary Company, Allied Queensland Coal. It also is involved in the search for gold and other minerals via another subsidiary Company, Saracen Minerals N.L. Crusader is pleased to be associated with the ASEG/GSA Conference.

250 DIGICOM GEOPHYSICAL CORPORATION Headquartered in Houston, Texas. Digicon is a major, international, advanced technology oil service company providing geophysical exploration services to the oil and gas industry. Digicon's advancement has been led by its commitment to innovation and delivery of superior quality. Digicon's capability and capacity to respond to seismic acquisition and data processing requirements throughout the Far East and Australasia has been significantly strengthened over the last 18 months. Illustrative of the hardware upgrading in Digicon's Singapore (Earth Search Processing Inc) and Jakarta (P T Digicon Mega Pratama) centres is Brisbane (Digital Exploration Limited) where a further 2 VAX 8650's and 2 Vector Numerix processors have been added. To complement expanded core processing equipment workstations for interactive capability such as velocity analysis, refraction statics, array design, etc have been added. The commissioning of the M/V Beata has brought a new dimension to Digicon's Far Eastern operations. Acquisition programs in Indian, IVIalaysian and Indonesian waters have proved extremely successful. The mobilization of the M/V Geo Tide into Australian waters provides clients with the ability to shoot from shallow to deep water without internjption. This unique water depth capability coupled with the boat's advanced technology inclusive of digital cable for 2D and 3D recording at very economical rates makes the Geo Tide an obvious choice.

ENCOM TECHNOLOGY PTY LTD Encom Technology provides specialist services to the Minerals and Petroleum Exploration industry In the areas of software, bureau processing, consulting and information services. Since incorporation in 1984, Encom has grown rapidly by developing and expanding its services and now employs 18 specialised technical staff in its Sydney and Melbourne offices. Encom software is exported throughout the world with sales of its mapping and modelling systems in the USA, Canada, Europe, South-East Asia and the Middle-East. Petroleum exploration software includes SEISDB, a seismic mapping system, LOGDB, a system for the interpretation and display of downhole log data and GRIDCON, a general purpose gridding and contouring system. Popular Mineral Exploration software includes TOOLKIT for 3D gravity and magnetic modelling, INFIELD for field magnetic data collection and XLMAP for airborne data processing and map analysis. To complement our own software, Encom markets ER Mapper image processing systems and Geopak mapping and modelling products. In 1990, CSIRO granted Encom the world wide marketing and development rights to the complete suite of EM, resistivity and IP modelling software which is now marketed under the name SIROEX. Encom publishes the Petroleum Permit Map of Australia each year along with a permit ownership book. This information is now available on PCs with monthly updates through our GPINFO graphical software and data package.

251 Other services include geophysical consulting, bureau processing and computer installation and support. We operate and support PC local area networks (LANs) and Sun workstations. New systems can be supplied and advice and support provided for existing installations.

ENCOR TCPL RESOURCES LTD Encor Inc. is a Canadian public energy company which explores for, develops and produces cnjde oil, natural gas and related products in Canada and internationally. In Australia, Encor operates through TCPL Resources Limited which is a fully owned subsidiary company. Encor's excellent portfolio of assets ranks It among the top 12 senior producers in the Canadian upstream oil and gas sector. The company produces about 40,000 barrels of crude oil and natural gas liquids, and over 200 million standard cubic feet of gas per day.

EARTH RESOURCE MAPPING ERM (Earth Resource Mapping) is an Australian company which develops Image Processing software for companies involved in the Earth Sciences. ERM is a oneproduct company, concentrating on the effective development and marketing of that product, ER Mapper, which is only available via distributors. These distributors also fully support the product. ER Mapper constantly undergoes cycles of development. As potential markets are identified, the product is enhanced to address these markets and then the product is marketed into these areas via the distributor base. ER Mapper assists exploration Geophysicists in identifying ore deposits, mineral zones delineation, surface features and weathering, discontinuities, lineaments, fault lines and other structures critical to effective exploration. Multiple data formats such as Landsat, SPOT, gridded magnetic and gravity, radiometric, airborne scanners, digital terrain and geochemical datasets can be processed, integrated and displayed. Full scene images can be processed. Vector information (such as annotations) and value data may be displayed over raster data. Rules for processing, display and integration of data sets can be stored in algorithm files, to be called up later to manipulate the same or different data sets. A sophisticated dynamic algorithm compiler reduces algorithms down to optimal machine code, providing true flexibility while giving very high performance. Image processing operations include: • • • •

Real Time Shading Histograms, convolutions, filters and transformations Statistics, Principal Components and user defined formulae Field strength operators (for magnetic and gravational data)

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• • •

Multiple map projections Runs on 8, 24 and 32 bitplane color frame buffers Color printer and film writer hardcopy output

ER Mapper allows images to be displayed on multiple X displays across networks, and supports X11R3, X11R4 and Open Windows.

GEOTERREX PTY LTD Geoterrex Pty Ltd is a contracting and consulting company that has been providing geophysical services to the exploration industry in Australia since 1972. Geoterrex currently has offices in Sydney and Ottawa, with world-wide support from it's parent company, Compagnie General de Geophysique, based in Paris. Geoterrex currently offers the following techniques: GEOTEM Airborne Transient EM High sensitivity Cesium Vapour Magnetics 256 channel radiometrics ULTRAMAG towed bird magnetics Helicopter aeromagnetics A choice of Syledis, Doppler, GPS or Visual navigation systems is available for all airborne surveys. Geoterrex is established as the industry leader in ground geophysics, offering a comprenehsive range of geophysical survey techniques such as: • • •

IP and Resistivity Time and Frequency domain Electromagnetics and Down-Hole Logging Gravity Magnetics

Geoterrex Pty Ltd in Australia currently has a staff of approximately 35 people, sixteen of whom are geophysicists involved in data acquisition, processing and interpretation. Geoterrex is also the Australian representative for DIGHEM (helicopter EM surveys), Geonics (ground EM survey equipment) and Terradex (Tracl< Etch Radon Detectors).

GEOVISION GeoVislon leads the world in providing Geographic Information System, Advanced Mapping Systems and Automated Mapping/Facilities Management Systems. These systems tal<e advantage of the latest developments in relational database stnjcture, geographical analysis, topology, distributed processing, distributed databases and integration with information networl<s. Adherance to standards such as Unix, C, XWindows, Ethernet, TCP/IP, and SQL, allows total flexibility in the choice of hardware configurations, system application and system expansion.

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A development unique to Geo Vision is the spatial/relational database management system. This system comprises an embedded copy of Oracle tightly coupled to the spatial indexing provided by quadtrees. Our continuous "seamless" geographical database, together with topological structures allow unlimited database layering which permits complex analyses. GeoVision's user interface is unequalled in its ease of use and versatility. All commands and processes are menu-driven. This interface is achieved through the use of pull-down menus and pop-up forms. Command macros are also provided and can also be easily defined by operators if preferred. The Sydney office provides full support of GeoVision's products, including writing application software, installation, training and maintenance. The Sydney Office is responsible for Australia, New Zealand, India and Asia and performs these duties with a highly skilled and motivated staff of 19. Geo Vision Australia is part of Geo Vision Corporation, a company internally recognised for its visionary approach to GIS, its technologically advanced product architecture and its commitment to the success of every project. Applications range from multi-user systems; nation-wide cadastral GIS to diverse local government geoprocessing; facilities management for utilities; hydrographic surveys and databases for project feasibility studies.

HALLIBURTON GEOPHYSICAL SERVICES INC Halliburton Geophysical Services (HGS) is a subsidiary of Halliburton Company - one of the world's largest diversified oil field services, engineering and construction companies. HGS - formed in 1988 from a combination of Geophysical Service Inc. and Geosource Inc. with headquarters in Houston, Texas - is one of the largest geophysical contractors. As well as providing seismic data collection and processing services in 42 countries (including the USSR), it is a major manufacturer of seismic data acquisition equipment such as the TITAN 1000 marine digital streamer and recording system, the VSX sleeve guns, the MDS 18X recording system and the VCS V vibrator control system. For over 30 years, HGS has been acquiring and processing seismic data in and around Australia. Currently, it has seismic data processing centres in both Sydney and Adelaide which utilise an IBM 3090 180E computer, with Vector Facility, located in the Sydney office. A full suite of 2D and 3D processing software, including various 2D and 3D (1-pass & 2-pass) migration algorithms, 2D and 3D Kirchhoff DMO, wave equation datuming and layer replacement, multiple removal using f-k, generalised Radon transform or wave equation approaches is available in both centres. HGS's marine data acquisition system, as carried by the MV Pacific Titan and MV Magnificent Creek in Australia, includes the TITAN 1000 digital fibre optic streamer and recording system which allows up to 960 channels to be recorded in a multiple VSX sleeve gun array/streamer configuration. The system has full 3D capability. The land crew capability consists of an MDS distributed system for either dynamite or Vibroseis* recording - the latter utilising HGS'sophisticated VCS 5 vibrator control system. * Trademark of Continental Oil Inc.

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KEVRON GEOPHYSICS Since its inception in 1986, Kevron Geophysics lias provided the mineral and oil industries with the highest resolution airborne magnetic and radiometric data. The aircraft have been equipped with a Caesium Vapour Magnetometer coupled with RMS Automatic Aeromagnetic Digital Compensator (AADC). The AADC corrects the total magnetic field for errors introduced by aircraft heading and altitude, resulting in high resolution of 0.001 nT with a sample interval of 0.125 seconds (less than 9 metres on the ground) and the lowest noise envelop in the industry. The aircraft are fitted with the latest Geometries Model GR-800D Spectrometers. High crystal volumes are routinely carried to collect high spectral resolution data and an upward looking crystal is used to monitor airborne radon. A Lightweight Doppler Navigation System with a Sperry CI 2 Gyro Compass System is fitted to both aircraft. This data is available to the navigator for real time navigation and then incorporated into the processing to interpolate between visually recovered points. High resolution radio positioning using the Maxiran II Radio Positioning System is utilized whenever precise positioning is required. In house data processing based on Sun Microsystems work stations and interactive graphical based software allows data sets to be produced faster. The software suite has been designed to run on high performance work stations and makes maximum use of the windowing environment. ER Mapper Image processing software is used extensively to ensure data integrity is of the highest order. Kevron Geophysics is committed to providing the highest quality and resolution airborne data to the geophysical exploration industry.

LANDMARK GRAPHICS CORPORATION Founded by geoscientists and computer specialists in 1982, Landmark Graphics Corporation pioneered computer-aided exploration and production (CAEX) technology with the first commercial microcomputer-based 3D workstation. Since that time. Landmark has continued to set the standard for seismic interpretation systems, with innovations such as optical disk storage systems, integrated horizon and fault mapping, and user-controlled windows. Landmark Voyager Workstations with 3Dplus(TM), 2DPIus(TM), TurboZAPI(TM), and Syntheseis(TM) software enhance the quality and speed of seismic interpretation. Visualisation and analysis of subsurface structure and stratigraphy is much more complete and is accomplished in a fraction of the time required by traditional methods. With StratWorks(TM), Landmark brings similar benefits to the geologist through log correlation, cross section construction and mapping. For the first time, the geologist and geophysicist can easily integrate the results of their work through the interactive sharing of common data and interpretations. Landmark has also broadened the scope of its geoscience solutions to include presentation quality mapping and interactive seismic processing through the recent acquisition of Zycor, Inc. and ITA.

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Landmark's commitment to standards is reflected in tlieir adoption of the liigiiperformance of UNIX/RISC-based systems from both IBI\/I and Sun Microsystems. Landmarl< marl<ets Its products through a direct sales force and has sales offices located in Sydney, Singapore, Houston, Dallas, New Orleans, Calgary, London and Panama. Support offices are also located in these cities as well as Jakarta, Bakersfield, Rio de Janeiro, Caracas and Lagos. To date, the company has shipped more than 550 systems worldwide. Landmark's customers include independents of all sizes, government-owned oil companies, and 18 of the 20 largest multi-national oil companies in the world.

NORCEN IN AUSTRALIA Norcen International Ltd is a wholly owned subsidiary of the Canadian company Norcen Energy Resources based in Calgary. The company has been exploring for petroleum in Australia since 1977. After an initial acquisition of two permits in the Timor Sea, Norcen now has eight permits in Northern Territory and Western Australian waters. Through the years the main exploration effort has been directed towards the Timor Sea where the company participates in permits AC/P2, AC/P4, AC/PI0, AC/PI 2 and WA-199-P. The other permits lie in the Carnarvon Basin (WA-209-P, WA-216-P) and Perth Basin (WA220-P). Norcen is currently operator in three of these permits. By the end of 1990, Norcen will have participated in 14 exploration wells and 3 development wells. This represents an expenditure of some A$20 million. In addition to the drilling activities, Norcen as operator has acquired a substantial amount of marine seismic data. It is anticipated that 1991 will see this level of exploration activity maintained. Norcen participates in production from the Jabiru and Challis oil fields, located in the Timor Sea. These fields will deliver some 15% of Norcen's worldwide production. Norcen's share of production from these fields is expected to average more than 10,000 BOPD for 1990. The company expects to maintain the tempo of exploration and development through 1991. Capital expenditure will be approximately A$60 million, 44% of which should be on exploration.

OIL ON FILM PTY LTD. Oil on Film Pty. Limited was established three years ago in St Leonards, N.S.W. with the objective of providing exploration companies with complete drafting and plan printing services, with a realistic pricing structure. During this time we have built up a client base of over twenty-five companies in the exploration and associated industries. We act as the sole drawing office for some companies and as an overflow facility for other companies with their own drafting and plan printing facilities. The principals, with a combination of over thirty years experience exclusively in Oil and Mineral exploration, offer through Oil On Film not only an accurate drafting and

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professional plan printing service but advise in the most efficient and cost effective way to proceed witii mapping, drafting and printing projects. We are confident in continuing tiiese services to meet the three demands of Promptness, Quality, and Economy for the exploration Industry In the nineties.

PEKO OIL LIMITED Since incorporation of the company in 1981, Peko Oil Ltd's exploration activity has been focused In the Timor Sea. The company currently has interest In five Timor Sea permits, the most notable being AC/P2, AC/P4 and AC/P6 where significant oii discoveries have been made. In AC/P2 a development plan was approved for the Skua Field with first oil expected In late 1991. Combined oil production from the Jabiru and Challls/CassinI fields In AC/P4 is currently 90,000 BOPD with an additional 10,000 BOPD from Challls likely in the near future. Further delineation of the Oliver oil and gas field in AC/P6 and the Puffin oil field In AC/P2 could lead to the development of these petroleum accumulations In the mid 1990's. Over the next two years Peko Oii will be involved with the drilling of 15-20 wells in the Timor Sea alone. Peko Oil's international interests are managed from an office In the UK and two offices in the USA. Collective USA oil and gas production totals 1750 BOPD and 25 MMCFGD respectively. Peko Oil Ltd is a 100% owned subsidiary of SANTOS since December 1988 but remains an autonomous body with offices in Sydney and a staff of 21.

PLACER PACIFIC LIMITED Placer Pacific Limited is one of Australia's top 20 companies. It is a growth oriented, metalliferous mining company with major operations in Western Australia, Queensland and Papua New Guinea and interests in Fiji and the South West Pacific. The company also directs an aggressive exploration effort for precious and base metals throughout Australia and the South West Pacific region. In just two years annual gold production from Placer managed mines has surged from around 200,000 ounces to over 1 million ounces. Through its 70% owned subsidiary KIDSTON GOLD MINES LIMITED, Placer Pacific shares in production from one of Australia's biggest gold mines. Production from the KIdston mine in North Queensland has exceeded 200,000 ounces a year for the first five years of operation. Placer Pacific is 50% owner and manager of Big Bell Mine in Western Australia. Construction at Big Bell was completed in april 1989 and the mine is expected to produce about 120,000 ounces of gold a year from open pit mining until 1994. Placer is 60% owner and manager of Granny Smith Mine in Western Australia. Gold production is expected to average 145,000 ounces a year from open pit mining over the first five years from early 1990. Placer Pacific also has significant gold properties in Papua New Guinea.

257 Gold production at Mislma Mine began early in 1989 and is expected to average 240,000 ounces a year from large scale open pit mining operations. Placer is 80% owner and manager. Also in Papua New Guinea Placer, as manager of the Porgera Joint Venture, has completed construction of the first stage of the Porgera Mine. Porgera is one of the world's largest gold deposits. Gold production began in September 1990 and is expected to average 900,000 ounces a year over the first six years of operation. Placer has a 30% interest in the mine. With a 60 year group involvement in the Pacific region. Placer Pacific can point to a proven record of success. Planned production over the next few years will make Placer Pacific a gold miner of world significance.

SAGASCO RESOURCES LTD In June 1988 the South Australian Oil & Gas Corporation (SAOGC) became a wholly owned subsidiary of the listed SAGASCO Holdings Ltd, and changed its name to SAGASCO Resources Ltd. SAOGC, formed in 1977, had been one of the most active explorers in Australia. In its core permits (PELs 5&6 of the SA Cooper-Eromanga basins) it explored above and beyond the Santos-Delhi joint venture program (about 50 wells per year) through its own sole risk program of some 6000 km and 22 wells. In frontier programs it was involved in onshore and offshore exploration in the Duntroon, Bass, and Murray basins and in the USA. In the Bass Basin the exploration program resulted in the Yolla discovery (oil, gas and condensate). Following the merger with the SA Gas Company (effectively a reverse takeover) and the creation of the SAGASCO Holdings Group, the Company positioned itself to become a major player in tho oil and gas Industry. ThG busin6ss has grown stGadily and now sits at 75 on the Australian listed public company rankings with a marl^et capitalisation over $350 million. The Company enjoys the highest credit ranking accorded to non-bank listed companies by Australian Ratings. SAGASCO ranks number 4 amongst listed oil and gas sector companies, based on reserves and production. Annual sales turnover is about $300 million. Since the merger, SAGASCO Resources was awarded Otway Basin permit PEL40 in SA where it recently operated the Hatherleigh 1 well on behalf of Shell and itself. It has also been involved in joint ventures in the Perth Basin (EP320, EP321 and EP351), the Papuan Basin (PNG PPL76), and the Carnarvon Basin (EP325) where a noncommercial gas discovery was made with offshore Rivoli 1. SAGASCO Resources acquired the Hartogen interests in Southwest Queensland {ATP259P) and SA PELs 5&6, and recently farmed into the area containing the Beharra Springs gas discovery in the Perth Basin. The Company currently has interests in about 30 joint ventures. In order to manage its wide Australian region interests, SAGASCO Resources employs a staff of 57 based in Adelaide. The exploration staff of 14 has an experience base which covers major producing provinces around the world.

259 SHELL DEVELOPMENT (AUSTRALIA) LTD Shell Development (Australia) Limited, a wholly owned subsidiary of Shell Australia Ltd., started exploration work in the late 1930s in Queensland. Little was achieved before the early 1960s when interests were taken up in WAPET and Burmah-Woodside in Western Australia. First production came from WAPET's discoveries in Barrow Island and at Dongara. Shell currently has interests in 25 permits around Australia. Since 1985 the Exploration and Production sector has been housed in Melbourne within the Shell Australia Head Quarters.

SIMON-HORIZON AUSTRALIA Simon-Horizon Australia Pty Ltd is part of the Simon-Horizon Group, an international operation which specialises in marine, land and transition zone seismic data acquisition, processing and interpretation. Data processing facilities are located in Brazil, Canada, USA, Indonesia, Australia and at the Head Office in Swanley, just outside London. Significant hardware upgrades have taken place at all centres, for example, an FPS 522 EA vector computer, manufactured by FPS Computing, Oregon has recently been installed in Swanley. Simon-Horizon Australia has increased the data processing centre in Perth to that of 5 times the 1987 capacity. This has enabled Simon-Horizon Australia to continue to meet stringent turnaround requirements without compromising the quality of the final product. The centre currently has the capacity to process 3,000 km of 300 channel data per month through an intensive marine sequence whilst still offering an excellent service on smaller contracts with a dedicated team for onshore work. The increase in disk storage capacity to 9 Gigabytes also allows efficient processing of 3D surveys up to 5000 km. Additional upgrades are currently under consideration to enable the company to continue to meet the demands for increasingly sophisticated data processing, including the larger 3D surveys.

SOUTH AUSTRALIAN DEPARTMENT OF MINES AND ENERGY The mineral and energy resources of South Australia are owned by the Crown. Exploration and development of those resources are undertaken by the private sector within an organisational framework administered, controlled and directed by the Government of South Australia through the Department of Mines and Energy. The Department takes an active role in promoting and encouraging private sector mineral exploration through a variety of programs, including geological mapping, geophysical surveys and stratigraphic drilling. It has helped to establish principles for multiple land use through initiatives such as the Regional Reserve concept which permits land to be set aside for conservation purposes, while still allowing access for exploration and development purposes. This was assisted by the Department's positive approach to environmental matters, which has led to demonstrably improved operational techniques to minimise environmental impact and encourage rehabilitation.

260 The Department provides a "one-stop" shop for all matters concerning mineral and energy resources, through publications of reports and maps which augment an excellent information service, backed up by advice from sl<illed and experienced geoscientists specialised in many disciplines.

SURTEC GEOSURVEYS PTY LIMITED SURTEC GEOSURVEYS PTY LIIVIITED is a major independent Australian consulting and contracting group serving the IVIineral Resources Industry and Environmental Sciences. It was formed in 1977 to provide a broad range of services throughout Australia and the Pacific operating from its head office in Sydney and regional office in Brisbane. SURTEC principals and staff include widely experienced geologists, geophysicists, geochemists, surveyors, computer programmers and operators, technicians and draftsmen. Dependent on the requirements of our clients, SURTEC delivers its services in a variety of ways that include: • • •

provision of technical services on a contract basis provision of "turn-key" field program implementation under client supervision management and operation of major exploration projects from the "grass roots" stage up to and including pre-feasibility studies

Each area of the company's technical activities is supervised by one of the company's four technical directors who each have around 20 years' experience in their particular disciplines. SURTEC is frequently involved in research activities for the development and testing of new exploration concepts and techniques. A major developmental thrust within the company over the past 8 years has been the integration of computer technology into most aspects of field exploration. This technology has been developed to facilitate "on-site" data processing and evaluation through the use of graphical presentations to enhance pattern recognition.

TENSOR PACIFIC PTY. LTD. Tensor Pacific Pty. Ltd. is a joint venture company, founded in 1988 by Tensor Geophysical Service Corporation and Leading Edge Technologies Limited. Tensor Pacific was formed to provide the Australasian oil exploration industry with the latest seismic data processing technology. Tensor offers a full range of seismic data processing services including some of the most advanced 2-D and 3-D processing procedures available today. Dr. Bill French (President, Tensor Geophysical Service Corporation) is the Technical Director of the company and provides the very latest developments in 3-D seismic

261 processing. Specific applications relevant to Australasian problems are developed in house at our Melbourne processing centre. Processing techniques such as simultaneous DMO:NMO velocity analysis and stacking procedures for 2-D and 3-D surveys are recommended and offered as standard processing procedure. Tensor Geophysical's experience is considerable, spanning over 150 3-D surveys of all shapes and sizes. This experience and our True 3-D processing software, combined with the supercomputing power of the CRAY Y-MP (666 megaflops potential) at Leading Edge, provides the Australasian industry with a premier seismic data processing facility.

VELSEIS PTY LTD VELSEIS is a wholly owned Australian company operating out of its own premises in Brisbane, specialising in the acquisition and processing of high resolution refraction and reflection data and is Australia's leading contractor in this field. VELSEIS was formed from a split in field operations of VELOCITY DATA PTY LTD in 1988 so a considerable amount of it's reputation and client base originates from this history. The shareholders consist of a mix of geophysicists, electronics engineers and field seismic personnel who have a wealth of industry experience and are all actively involved in Velseis's operation. This contributes to the ability of VELSEIS to consistently provide superior data collection. VELSEIS has conducted seismic surveys throughout Australia, New Zealand, Indonesia and Thailand and can provide assistance in all aspects of a client's projects, management, planning, mobilisation, surveying, drilling, data acquisition and interpretation. VELSEIS has an ongoing and consistent commitment to research and development both in hardware and software to meet the needs of the industry and to provide state of the art technology.

WAPET In 1953 West Australian Petroleum Pty Ltd ("WAPET") drilled the first well to flow oil in Australia, Rough Range No. 1, south east of Cape Range. It was not until 1964 however that WAPET made its first two commercial discoveries: oil at Barrow Island and gas at Yardarino. Next came the discovery of offshore gas on the "North West Shelf" with WAPET's West Tryal Rocks No. 1 well, followed by a discovery in its Spar No. 1 in 1976. They were overshadowed by the giant Gorgon field discovered by WAPET in 1981. Development of these vast gas reserves depends on markets and will probably be on a scale similar to the existing North West Shelf Gas Project.

262

The Saladin oilfield, offshore from Onslow, was discovered by WAPET in 1985 with reserves of over 25,000,000 barrels. Production facilities were commissioned in 1989. Oilfields were then discovered at Yammaderry (1988) and Cowie (1989) and have proved economic. They are in the course of development with first production expected in the first quarter of 1991. Nearby the Roller oilfield is undergoing appraisal and showing great promise. Exploration is continuing with wells now being drilled on Barrow Island and offshore in WA-25-P. On Barrow Island, an "A" Class Reserve for the conservation of flora and fauna, WAPET's careful management of the environment has been widely acclaimed. WAPET's function is to act as Operator for joint venture groups composed of Chevron Asiatic Limited, Texaco Oil Development Company, Shell Development (Australia) Pty Ltd, Ampol Exploration Limited and Western Mining Corporation Ltd.

WESTERN GEOPHYSICAL WESTERN GEOPHYSICAL, since 1933, a world leader in geophysical exploration, conducts marine, land and shallow-water transition zone surveys worldwide. These surveys range from speculative 2-D and 3-D surveys for prospect evaluation, through complex multi-cable multi-source 3-D surveys for delineating hydrocarbon reservoirs, and on to advanced processing to better describe the petrophysical properties of the reservoirs. WESTERN'S world headquarters in Houston serves as a centre for over 5,000 employees engaged in field operations, data processing, research and support services. Major regional offices and data processing centers are located in London and Singapore. Field offices and processing facilities are located throughout the Americas, Europe, the Middle East, Africa, Australia and the Asia Pacific region. With WESTERN'S worldwide participation in exploration including frontier regions, our crews have gained a reputation for acquiring high quality data despite harsh environmental conditions and logistical difficulties. Generous funding of R & D programs to improve the quality and efficiency of seismic surveying has lead to many WESTERN developed field recording methods and data processing techniques being adopted as industry standards. Developments in reservoir geophysics using stratigraphic and lithological information from seismic data are now being correlated with borehole data, wireline logs and core analysis to enhance formation evaluation, and thereby, reduce drilling and development costs.

263 WESTERN MINING CORPORATION LIMITED PETROLEUM DIVISION (AUSTRALASIA) The Western Mining Group of Companies is one of Australia's largest corporate groups, with assets and investments of $3.5 billion (equity based), and employing over 7000 persons including 450 people involved in petroleum and minerals exploration. Exploration for petroleum in Australia was initiated in 1973 by WMC as a participating company which led to discoveries of substantial gas reserves in the Cooper-Eromanga Basin. The Petroleum Division (Australasia) currently has interests in 33 Leases (28 Exploration Leases, 5 Production Leases) of which 17 are managed by WMC. Exploration is currently focused on the Carnarvon Basin, Timor Sea and in Malaysia. Under the management of WMC, the development of the South Pepper and North Herald offshore oil fields, discovered in 1983, was completed with first oil production in 1987/88, seven months after the joint venture participants decided to proceed with the Airlie Project. The Project viability has been enhanced by WMC's use of development wells drilled horizontally into the thin oil columns in the fields. They were the first horizontal wells drilled in Australia. Production from the nearby Chervil oil field in the Airlie Block commenced in August 1989. Again horizontally drilled wells were successfully utilised to develop this field. The energy innovation award was made to WMC in recognition of the novel use of a jack-up drilling rig as a production platform and the drilling of horizontal wells at the Airlie Project. WMC also participates in production from the nearby Saladin Field (10%) and from fields in the Bodalla Block (12%) in the Eromanga Basin. The Company's oil production operations are presently conducted in shallow waters off the North-west coast of Western Australia. WMC acknowledge the environmental risks of oil production operations and maintains strict monitoring of all operational procedures to protect the environment of this area.

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Authors Index Session 9(c) Post 4(a) 10(a) 5(d) 7(c) 8(b) 4(a) 8(a) 7(b) 3(b) 7(a) 10(c) Post Post 7(e) 9(a) 3(a) 9(c) 6(e) 5(a) 2(a) 3(a) 2(a) Post Post 4(a) 6(a) 6(c) 9(b) 3(b) 5(b) 9(b) 6(d) Post Post 6(e) 3(e) Post 4(b) Post 7(f) Post 5(b) 7(b) 9(c) 1(a) 3(d) 6(b) Post

Name

Page

Session

Acworth, R.I.* Agostini, A.* Allen, T.J. Alsop, A. Amano, H.* Amier, R.* Annan, A.P.* Ashdown, J. Ashida, Y.* Asten, M.W.* Bacchin, M. Bai, G.* Baker, P.L* Baker, P.L* Baker, W.E.* Baillie, P.* Ballesteros, M.W.* Bancroft, J.C.* Barber, C. Barton, T.J. Bauer, J.* Beams, S.D.* Beasley, C.J.* Belford, S.M. Benhamou, M. Bennett, LE. Beresford, G.* Beresford, G.* Beresford, G.* Bernard, J.* Bishop, J.R. Bishop, J.R.* Bourgeois, B. Bradbury, R. Bradshaw, J.* Bradshaw, M.* Braun, J.* Brown, M.C. Brown, R.A. Browne, P.R.L. Brzostowski, M.A. Buchen, P.W.* Buckingham, C.P. Buckingham, M.J. Buselli, G. Buselli, G.* Bush, D.* Bush, D. Butt, C.R.M.* Butt, C.R.M.*

169 215 49 180 85 125 140 49 138 124 33 122 191 229 215 133 160 29 167 112 74 20 28 22 216 208 51 98 106 166 35 77 166 109 202 202 112 47 208 52 209 135 213 78 123 167 11 44 102 219

2(b) 5(b) Post 3(d) 8(e) 6(a) 2(a) Post 2(b) 4(c) 10(b) 2(b) 1(b) 7(c) 3(d) 9(b) Post 3(c) 4(a) 4(c) 4(c) 4(b) Post 5(a) 2(a) 5(c) 1(b) 3(d) 8(b) 8(e) 6(a) 3(b) 9(c) 9(d) 7(e) 9(e) Post 8(c) 10(c) 5(b) 7(c) 5(b) 6(e) 6(d) 8(b) 5(a) 5(c) Post 7(a) 7(a)

Name

Page

Campbell, I.H. Carswell, J.T. Carter, P. Chant, I.J.* Chen, Y.D.* Chiupka, J. Churchill, J.N. Cocks, T.D. Collins, C.D.N. Collins, S.* Collins, S.* Colwell, J.B. Condon, J.L.* Cook, A.C. Cooke, A.C. Cooke, A.C.* Coshell, L* Court, R.J. Cousins, M.G.* Cowan, D.R.* Cowan, S. Cox, M.E.* Cox, M.E.* Crabb, T.N.* Craig, M.D. Cram, A.A. Creer, G.* Cull, J.P.* Cull, J.P.* Cull, J.P. Cvetanovic, M.R. Dalgarno, R.* Davis, G.B. DeBoer, J.E. Denham, D.* Dentith, M.C.* Dentith, M.C.* Dixon, O.* Dixon, O. Doe, A.R.D.* Drake, LA.* Dransfield, M.H.* Dmmmond, B.J.* Dujmovich, T.J.* Duncan, A.C.* Dunne, P.R. Duke, J.H.* Durney, D.W. Eadington, P.J.* Eadington, P.J.

23 77 203 42 155 98 18 225 23 56 189 23 15 125 44 163 202 36 49 57 57 52 217 75 18 79 17 41 140 155 97 33 167 171 132 173 231 147 192 77 127 78 112 109 139 75 79 230 119 122

265 Post 10(a) 5(b) 10(a) Post 7(b) Post 5(b) 8(b) 3(d) 6(e) 7(e) 6(c) Post 3(a) 4(f) 8(c) Post Post 10(a) 4(d) 6(a) Plen IV 7(f) 3(c) Post 5(c) 5(a) 9(a) Post Post Post Plen V 9(a) 10(b) 3(a) Post 9(d) Post 4(d) 9(c) 5(f) 10(c) 8(d) 7(a) 4(c) 6(d) Plen V 4(d) 6(e) Plen IV 5(e) 4(d) 8(e)

Eckels, R.* Edwards, B.* Edwards, C. Eleftherlou, J. Ellacott, M.V. Elliott, P.J.* Elliott, PJ.* Erickson, IVI.E. Erkhov, V.A.* Etheridge, IVI.* Etheridge, IVI. Etheridge, M.* Etheridge, M.A. Etminan, H. Evans, B.J.* Evans, B.J. Evans, B.J. Evans, B.J. Evans, B.J.* Farrow, B.B. Fielding, C.R. Fittall, A.M.* Flynn, J.* Fokkema, J.T.* Foley, A.M.* Foley, A.M. Fountain, R.J.* Fraser, 1. Frederick, J.B.* Frei, E. French, D.H. Freyssinet, P. Froning, J. P.* Fryberger, S.G.* Gagaev, V.N.* Gardner, G.H.F. Garnett, D.L.* Gassaway, G.S. Gassaway, G.S. Gatehouse, C.G. Gates, G.W. Gerrard, C.* Giblin, A.* Gidding, IVI.J. Giles, M. Given, J.W. Glasson, K.R.* Glasson, K.R.* Glikson, M.* Goleby, B.R. Gould, I.G.* Graham, T.G. Gravestock, D.I. Gray, J.D.*

237 178 78 180 213 123 218 77 141 44 112 132 106 203 29 72 147 202 203 180 59 97 96 135 36 217 80 74 162 237 216 219 159 161 181 30 220 171 208 63 167 89 192 153 118 57 110 157 64 113 95 86 63 155

2(a) 4(a) 5(d) 6(b) 8(e) 8(e) Post 2(b) 5(f) 10(a) Post 7(c) 8(a) 9(e) Post Post 7(a) 7(a) 7(a) 7(a) 4(f) Post Plen V 4(a) 3(d) 8(c) 8(c) 8(c) 10(c) 8(e) 6(c) 7(c) 6(c) Post 2(b) 5(e) Post Post Post 4(e) 10(b) 3(d) Post Post 2(b) 7(e) 2(a) Post 6(c) 4(e) 5(e) 9(b) 4(b) 6(d)

Green, A.A. Greenhaigh, S.A.* Greenhaigh, S.A.* Griffin, W.L Griffin, W.L. Griffin, W.L. Griffin, W.L. Griffiths, R.W. Groves, D.I.* Grubitz, G. Gulson, B.L* Hadiyanto* Hadley, D.* Hall, J. Hall, J. Hall, M.A. Hamilton, P.J.* Hamilton, P.J. Hamilton, P.J. Hamilton, P.J. Harlow, P.G.L.* Harlow, P.G.L.* Harman, P.G.* Haskey, P.* Hastie, LM. Hatherly, P.J. Hatherly, P.J. Hearn, S.J. Hearn, S.J.* Heinson, G.S.* Henley, R.W. Hewson, R.D. Higgins, N.C.* Hill, M.W. Hill, R.I.* Hillis, R.R.* Hillis, R.R.* Hillis, R.R.* HIadky, G. Hochstein, M.P.* Hodkinson, 1. Hoerdt, A. Hollis, J.D. Hollyer, G.M.* Houseman, G.A.* Hunt, J.W. Huntington, J.F.* Huntington, J.F.* Hurst, C. Hutton, LJ. lasky, R.P.* Isles, D.J. Johari, S.* Johnson, B.D.*

18 50 84 104 154 155 234 23 90 179 203 125 137 173 231 210 118 119 120 122 70 223 158 49 42 146 147 147 192 154 106 127 106 202 23 88 205 231 213 67 190 41 227 224 23 134 18 225 106 68 86 163 53 109

266

4(b) Johnson, C.C. 6(e) Johnstone, D.W. 5(f) Katz, M. 10(b) Kay, B.D.* 10(c) Kay, M.H. 7(a) Keene, J. 5(a) Kelsall, B. Post Kennedy, P.L Post Khoo, D. Post Kinny, P.D. 6(a) Kirk, R.B.* Kissitch, R.V. 3(b) Post Klinkert, P.S.* Post Knights, A.IVI. 6(e) Korsch, R.J. 6(e) Korsch, R.J.* 8(c) Lamb, P. 7(e) Lambeck, K. 8(c) Lambourne, A.N.* Post Langford, R. 5(f) Large, R.R.* 5(e) ^ Lavering, 1. 6(b) Lawrance, L.M. Post Lawrance, L.M. 9(c) Lawson, S.J.* 9(c) Lawson, S.J. 5(b) Leaman, D.E.* Lean, J.* 3(c) Post Lee, C.-S. 1(b) Legchenko, A. 10(a) Lemon, N. 8(d) Lennox, P. Post Leung, T.M. 4(e) Lilley, F.E.IVI.* 8(e) Lilley, F.E.M. 5(c) Lilly, 1.* 6(b) Lintern, M.J.* 8(c) Liu, G.* 8(b) Lockwood, R. Post Lorenzo, J, Post Lorenzo, J. Standby Lottermoser, B.G.* 10(d) Lotyshev, V.I. Post Luo, B.J. 5(b) Lutherborrow, C.H. 3(a) Lynn, W. 7(a) i\/lacdougall, 1. 7(b) Macnae, J.* 8(a) Maher, S. 4(a) Mair, D. 7(d) IVIaloney, D.* 9(e) Mandelbaum, M.* 5(b) Mann, A.G. 9(e) Marillier, F.

53 114 89 190 192 122 74 215 203 227 97 35 226 202 113 114 146 132 147 202 91 86 102 219 167 170 78 37 206 17 180 153 238 67 154 82 101 146 140 205 231 239 195 210 77 28 122 124 137 51 130 176 78 173

5(e) Marshall, J.F.* Post Marshall, J.F.* 7(c) Mason, D.J.* 5(d) Mason, I.M. 5(b) Matthews, R. Standby Mattocks, N.* Mayer, W. 3(e) McCoss, A.* 1(a) 3(a) McDonald, J.A. 7(b) McGowan, P. Post Mclntyre, J.I.* 4(d) McKirdy, D.M.* 6(e) McQueen, H. 7(e) McQueen, H. 3(e) McQueen, K.G.* 8(a) Mellman, G. Post Merrick, N.P.* 9(e) Michel, K. 5(e) Middleton, M.F. 9(d) Miles, D.R.* Post Miles, D.R.* 9(a) Mitchell, A.B. Post Mizon, K.J. 9(e) Montalbetti, J.F.* 5(e) Moore, A.M.G. Post Moore, A.M.G. Post Moore, B.* 5(c) Moore, R.F.* 4(d) Morris, D. 4(f) Morton, D.H.* 3(b) Mudge, S.T.* Post Mumme, I.A.* 4(b) Nand, A.S. 10(a) Neale, R.L* 3(b) Nelson, R.G. 4(e) Nelson, R.G. 6(f) Nicholls, B.* Nixon, S.* 3(c) 9(e) Norris, D.J. 5(e) O'Brien, G.W. Post O'Brien, G.W. 9(c) Odins, J.A. 9(c) Odins, J.A.* 5(d) Ohta, Y. 9(c) O'Neill, D.J. 8(e) O'Reilly, S.Y. 8(e) O'Reilly, S.Y. Post O'Reilly, S.Y.* Post Pallaser, R. 5(d) Pant, D.R. 4(c) Paterson, R.G. 8(e) Pearson, N.J.* 3(e) Perrin, A.* 3(b) Pettifer, G.R.

86 206 126 84 78 240 47 13 30 124 226 63 112 132 47 137 237 173 86 171 208 160 203 175 86 206 232 81 64 71 34 233 55 178 31 68 116 38 175 87 206 167 170 85 170 154 155 234 208 84 56 154 47 33

267 4(c) 10(a) 7(e) 9(b) 9(a) 4(e) Plen III 1(a) Plen IV 3(c) 3(d) 4(b) 5(e) Post Post 9(d) 9(e) 10(c) Post Post 10(b) Post 9(e) 6(f) 3(e) 6(c) 2(a) 5(f) 7(e) 7(d) 4(d) 4(b) 5(a) 6(b) 6(b) 8(a) 8(c) Post 1(b) 10(a) 9(c) Post 6(e) 7(d) 6(e) 6(e) 8(d) 3(b) Post 1(b) 6(b) 3(c) 10(a) 5(b)

Pettifer, G.R.* Phillips, S.E. Pickering, R. Pietila R.* Pinchin, J.* Pitt, J.C. Plimer, 1.* Powell, T.G. Power, P.E.* Pratt, D.A. Pridmore, D. Pwa, A. Ramsay, D.C. Ramsay, D.C. Ramsden, A.R.* Ramsden, C. Reid, 1. Richard, B.H. Rigby, D.* Rigby, D. Ringis, J.* Rizos, C. Roberts, B. Roberts, J.* Roberts, W.* Robey, A. Robinson, S.H.* Rock, N.M.S. Rodgers, J.* Rose, P.J.* Russell, N.J. Rutherford, N.F.* Ryall, A.* Ryan, C.G.* Ryan, R.* Sassa, K. Saunders, J.* Schleicher, K.L.* Schneider, G. Schultz-Rojahn, J.P.* Scott, D. Scott, J. Sexton, M.J. Shanwood, IVI.* Shaw, R.D. Shaw, R.D.* Shaw, R.D.* Sheard, S.N.* Shi, Z.* Shirov, M. Sie, S.H. Singh, R.* Slate, T.* Smith, C.K.

56 180 133 165 160 68 26 12 94 37 44 55 86 206 216 171 173 191 208 210 189 237 173 115 46 106 22 90 134 130 61 54 74 104 100 138 146 209 15 180 169 202 112 129 112 113 152 35 238 17 104 40 179 77

8(c) Post Plen III 7(b) 4(d) 8(d) Post Post Plen II 3(c) 4(e) 3(d) 5(f) 10(a) 3(e) 5(f) 6(f) 1(a) 10(d) 6(c) 6(b) Post 8(c) 6(a) 4(d) 3(e) 8(a) 10(a) 6(f) 8(c) 9(e) 1(a) 10(d) 8(d) 3(b) 4(e) 5(b) 9(b) Post 3(a) 4(f) 10(d) 9(b) 5(b) 4(b) 1(b) Post Post 3(d) 4(f) 6(c) 8(c) Post 6(e)

Smith, G. Smith, J.W.* Smith, M.J.* Smith, R.* Smyth, M.* Soeparyono, N.* Song, Z. Southren, T.C. Sprigg, R.C.* Stanley, M. Stockill, B.D.* Strack, K.-M.* Stuart, W.J.* Stuart, W.J. Stutchbury, R.* Stutchbury, R. Stutchbury, R.* Summons, R.E.* Surkov, V.S.* Sutarno, D. Suter, G.F. Sutherland, F.L.* Sweeney, D. Tadiar, E. Taylor, D. Taylor, G. Tenma, N. Thomas, A. Thomson, J.* Thomson, S. Thrasher, G.P.* Tilbuty, L.A.* Tipper, J.C.* Trupp, M.A.* Tucker, D.H.* Tucker, D.H.* Turner, P.J. Tyne, E.D.* Tyne, E.D. Uren, N.F.* Uren, N.F.* Uruski, C. Valla, P. van Kann, F.J. van Moort, J.C.* Verhoeven, T.J.* von der Borch, C.C. von der Borch, C.C. Vozoff, K. Vozoff, K.* Vozoff, K.* Vozoff, K. Vozoff, K. Wake-Dyster, K.D.

146 210 25 123 59 153 210 210 1 40 68 41 93 180 45 89 117 12 195 108 104 227 146 98 64 47 138 180 116 146 174 11 194 153 31 68 78 164 215 30 72 194 166 78 55 14 205 231 41 73 108 146 230 114

268 5(a) Post Post Post Post Plen II Post 5(d) 9(b) 7(e) 5(e) 8(a) 10(d) 3(c) Post 7(a) 4(a) 8(a) Post 4(d) 2(b) 9(c) 9(c) 9(c)

Walcott, M.K/ Waldron, H.M. Walker, C.* Wang, Y. Ward, J.A.* Ward, S.H.* Warren, R.G.* Watkins, A.D/ Webster, S.S. Wehr, F.L. Wellman, P.* Wenzel, F.* Wenzel, F.* White, R.M.S. Whiteley, RJ. Whitford, D.J.* Whiting, P.M. Whiting, P.M.* Wilford, G. Wllkins, R.W.T.* Wlllcox, J.B. Williams, R.M. Williams, R.M. Williamson, D.R.

75 220 238 210 210 10 235 84 164 134 87 138 195 36 238 120 49 137 202 61 23 167 170 167

2(b) Post Post 6(b) 5(d) 7(e) 10(c) 3(d) 10(d) Post 6(a) Post 6(e) 8(d) 5(d) 5(e) Post 4(c) Post 10(b) 4(d) 4(a) 7(f)

Williamson, P.E.* Wilmshurst, J.R.* Win, M.A. Win, T.T. Windhofer, M.* Windsor, C.R. Wolfe, P.J.* Wolfgram, PA. Wood, R.* Wood, R.* Woods, E.P.* Worakanok, W. Wright, C. Young, I.M. Young, R.A. Young, R.A. Young, R.A.* Youngmann, C.E.* Yu, G.* Zhdan, N.K. Zhong, N.N. Zhou, B. ZIolkowski, A.M.*

23 213 238 104 85 132 191 41 194 236 98 215 113 153 85 86 214 57 230 181 61 50 136

N C Brown & Associates Petroleum

Geo-Consultants

Nigel Brown 68 Evans Street Rozeile NSW 2039 AUSTRAUA Tef. (02)810-4823 Fax, {02)224-8910

QUADRANT GEOPHYSICS Geophysical and Computing Contractors to the Mining Industry

Electrical Zonge equipment, 25 and 2.5 kW, for — Induced Polarisation — Resistivity — Transient EM Magnetics and Gravity Radiometrics Equipment Rental

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WONGEIA GEOPHYSICAL GEOPHYSICAL CONTRACTORS AND CONSULTANTS LINDSAY N. INGALL Managing Director

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Contact Richard Bennett or Adrian Brett Quadrant Geophysics Pty Ltd 3 Julian Street, Mosman, NSW 2088 Sydney: Telephone: (02) 969 1058 Fax: (02) 969 5837 Towns ville: Telephone: (077) 754 410

GEOVISION Advanced

While other GIS vendors promise the moon G E O V I S I O N gives you the earth

Geographic

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GEOVISION Australia Pty Ltd

Suite 403,165 Walker Street North Sydney NSW 2060 Ph: (02)959 3310 Fax: (02) 959 4885

Systems

See why Australia's major mining operators choose to use at the 1991 ASEG/GSA Conference, Stand 90; Sydney Convention and Exhibition Centre, Darling Harbour, 17-21 February 1991. Fully integrated modules on display include: • Enhanced Open-Pit Planning including Haul Road Design • Full Production Scheduling • 3-D Visualisation • CAD Integration • Exploration system Discuss Datamine's full capabilities with Tim McAuley or Phil Edmiston at the Exhibition

or Phone 018 916 897.

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EE?

EXPLORATION FIELD SERVICES PTY LTD PROVIDING THE INDUSTRY WITH ENVIRONMENTALLY SENSITIVE SERVICES

Including:

• n • • •

Permitting and public relations for seismic & drilling programmes Full logistical & technical supervision for seismic surveys Environmentally friendly access for geophysical & geological exploration Environmental impact studies • Restoration & rehabilitation of land degradation Rig Site construction • Loss assessment and compensation adjudication.

Additional Services Available Through Association

• Global positioning system surveys • Rotary & reverse circulation drilling • Geological & geophysical interpretation For further information Ray Willox RMB 8280 TIMBOON Vic 3268 Phone: 055 665173 Fax: 055 665193

Mike Walcott "Willowie" BOMBALA NSW 2632 Phone: 064 587263 Fax: 064 587263

Classic Assays • Classic Service Classic Laboratories offers a comprehensive geoanalytical service for exploration and mine control, and a full range of inorganic and environmental analysis. Classic Laboratories have up to date instrumentation for fast, reliable, cost competitive analyses. Techniques include:

• A A S • XRF • ICP With an ongoing commitment to quality control and service to clients, Classic Laboratories has the experience and expertise required.

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SGS Australia Pty Ltd SGS Australia is part of the international SGS (Societe Generate de Surveillance) Group, which is the world's largest inspection and testing company, and has been operating worldwide for over 100 years. In Australia our activities centre on traditional inspection and superintending of commodities (mineral, agricultural, coal, oil and petrochemical) and the testing to confirm required specifications are met. SGS accordingly has five laboratories involved in the testing and analysis of coal, four involved in testing and analysis of minerals, one primarily in agricultural products, and a laboratory specialising in testing and certification of petroleum or oil based products. Each of the mineral laboratories is equipped with the latest analytical instrumentation and staffed by experienced chemists and technicians. We specialise in services to the mineral exploration industry, especially in the areas of gold, base metal, mineral sands, iron ore, bauxite, tin and tantalum, and industrial minerals. Our prices are very competitive, and the quality of all work is guaranteed by our own internal assurance programs. All laboratories are constantly monitored to maintain the highest quality of work, through internal Round Robins, external testing authorities (viz. National Association of Testing Authorities), and the use of many certified international standards. SGS is at the forefront of technology, and with some 150 laboratories worldwide involved in testing and analysis, there is a wealth of knowledge and experience which is disseminated amongst all of the group. Our Perth laboratory has been established as a centre of technical expertise to provide knowledge and information to the rest of the group in the field of geochemical exploration. For further information about SGS and its activities, please contact the following: Adelaide (08) 384 6888; Brisbane (07) 393 0877; Burnie (004) 42 2435; Gladstone (079) 72 4288; Kalgoorlie (090) 931733; Mackay (079) 51 3455; Melbourne (03) 689 2233; Newcastle (049) 69 2222; Perth (09) 410 2727; Port Kembia (042) 28 3766; Sydney (02) 319 7625.

Petroleum Information PUTS AN INTEGRATED QUALITY SERVICE FIRST BECAUSE EXPLORATIONISTS DO CONSIDER THE BENEFITS Complete data sets held inhouse for client examination Complete archive of Western Australian seismic, well and shotpoint data NW Shelf/Timor Sea database, including latest biostratigraphic interpretations Complete set of data brochures for Western Australian Basins Integrated service - Government contractor, archivist, information service, printer Digital well logs from 2000 Australian/PNG wells Digital well logs from 560 Australian/PNG wells on CD-ROM Application of latest digital technology to databases and now we offer substantial discounts on all paper prints contact us for a quotation P.I. Energy Services Ptv Ltd

l^O Stirling Hwy, P.O. Box Telephone: (09) 389 8499

433, Claremom 6010, Western Australia Fax: (09) 389 8243

AD178

Western Rises in tiie East

Western Geophysical has opened its new Australasian headquarters in Singapore to meet the increasing needs of oil and gas exploration in the region. The Singapore center is part of Western's "super" seismic center network and also serves as the headquarters for our marine and land operations. The Singapore computer facility offers the technology, capacity, and fast turnaround required to process today's large-volume 3-D surveys. A research and development group has also been formed to assist clients in addressing their specific exploration problems.

Western Atlas

international

A Litton/Dresser Company

WESTERN GEOPHYSICAL Ang Mo Kio Street 64 Singapore 2056 Tel (65) 482-2221 Fax (65) 482-2220 Telex RS21416 447-449 Belmont Avenue Kewdale 6105 Western Australia Tel (09) 353-1999 Fax (09) 353-3963 Telex AA94706

I 1990 Western Atlas International, Inc.

IBilBiiii

NORTHERN TERRITORY GEOLOGICAL SURVEY Promoting Growth Through Resources

Join the rush - follow the GEOLOGICAL SURVEY. We have done the ground-work - now its up to you

If you are in the exploration business - We can help you.

Over the last 10 years our on-going geophysical mapping programme has produced 771:100 000 mapsheets of magnetic and radiometric data of the Territory to help you. We have also produced numerous geological and metallogenic maps, technical reports, commodity studies, and for the petroleum explorer, Hydrocarbon Basin Studies. Our data bases are second to none. Call our friendly staff at the Geoscience Resource Section now. We can supply you with the info!

RECENT PUBLICATIONS MITCHELL RANGES AIRBORNE GEOPHYSICAL SURVEY-Maps and tapes HYDROCARBON BASIN STUDIES MINERAL COMMODITY STUDIES MINERAL DEPOSITS MAP of the NT, 1:2 500 000

GPO Box 2901 Darwin NT 0801 S'^* Floor Centrepoint Building, The Mall Darwin NT 0801 r>hone 089-895281 - Fax 089-814806

The clearest view possible without getting your feet wet.

si-'S?

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• SASl- a new digital standard in multi- sensor shallow marine geophysics. State^f-the-art high capacity digital acquisition at up to 20kHz sample rate replaces conventional analogue recording of boomer, sparker and airgun data. • Record digital high resolution magnetics (.OlnT), electronic positioning, precision depth sounding and other data. • Low cost seismic processing- swell filtering, stacking, TVG, deconvolution for maximum resolution and clarity. • Computer generated track, bathymetry and magnetic maps. • Data enhancement, analysis and interpretation services.

• Applications to offshore minerals, site investigations, aggregate exploration, pipelines, tunnels, environmental, dredging, and siltation studies.

Seismic Acquisition System HydroSets Pty. Limited

Encom Technology Pty. Limited

Suite 18, 71-77 Penshurst Street Willoughby NSW 2068 Australia Phone (02) 958 3699 Fax (02) 958 0691

Level 1, 110 Alfred Street Milsons Point, NSW 2061 Australia Phone: (02) 957 4117 Fax: (02) 922 6141

AIRBORNE GEOPHYSICAL DATA BASE

NON EXCLUSIVE AIRBORNE MAGNETIC AND / RADIOMETRIC TA BASE 1990 UPDATED TO IMAGE QUALITY GYMPIE AREA QUEENSLAND

FOR SPECIFICATIONS AND INFORMATION CONTACT

AUSTIREX INTERNATIONAL LTD

austirex

27 Merriwa Street, GORDON, N.S.W. 2072 TEL: (02) 498 2299 FAX: (02) 418 1292

AIRBORNE GEOPHYSICAL DATA BASE

NON EXCLUSIVE AIRBORNE MAGNETIC AND RADIOMETRIC DA TA BASE A TENNANT CREEK AREA NORTHERN TERRITORY / \

FOR SPECIFICA TIONS AND INFORM A TION CONTACT

/ V

AUSTIREX INTERNATIONAL LTD

austirox

27 Merriwa Street, GORDON, N.S.W. 2072 TEL: (02) 498 2299 FAX: (02) 418 1292

/ WHETHER YOU ARE INTO HARD ROCK OR HEAVY METAL, WE HAVE THE INSTRUMENTS FOR YOU./

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'GEO\

INSTRUMENTS

Pty Limited (Inc. in N.S.W )

348 Rocky Point Road, Ramsgate NSW 2219 Australia. Phone: (02) 529 2355 Fax: (02) 529 9726 Telex: AA22624

It takes skill and experiencB tobepjo/|

For almost a quarter of a century, Exploration Computer Services has been an acknowledged world leader in the development and application of computer software and technology for the minerals exploration and mining industries. , I We're proud of our reputation. We eamed It the hard way: , j j ,_ ' • By being the first to recognise the true potential of the computer for geophysical maw)ing, ore-body devaluation, mine-site development andproductlon J profiling and...

III

By setting the pace in research, innovationT product development and customer service.

The result? A progressive, Australian-owned organisation, with off ces here and In the United States and over 200 satisfied customers worid-wide. 1

We're also proud of our people.

You'll teve to search far and wide (as we did) to find ' isulting group with the collective skills, experiand credentialsjof an ECS team of geologists, icists, mining engineers, surveyors and simiqualified professfonais. On the other phone.

y<Hi,

mi pick up the

For more information on ECS software, processing facilities and consulting services, call: EXPLORATION COMPUTER SERVICES BOWRAL: ECS House 500 Moss Vale Rd., BOWRAL, N.S.W. 2576 Ph: (048) 61 2122. Fax: (048) 61 3902. Telex: AA22769 ECSAUS PERTH: 68 Churchill Ave., SUBIACO. W.A. 6008 Ph: (09) 382 1788. Fax: (09) 381 3699.

KALGOORLIE: 72 Brookman St., KALGOORLIE. W.A. 6430 Ph: (090) 21 5139. Fax: (090) 91 2304. U.S.A 66 South Van Gordon, LAKEWOOD, COLORADO 80228, U.S.A. Ph:(lnt.): +1 303 9881183. Fax: (Int.): +1 303 988 4493.

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Win a 6 week FREE trial of a Personal IRIS workstation* - and experience the exhilarating power of visual computing. You'll get a chance when you visit Silicon Graphics in the Skyline Room No. 1 Darling Harbour Convention Centre during the ASEG-GSA Conference and Exhibition. You'll also see v^hy Silicon Graphics is the widest hardware platform being used in the mining industry And why all major mining software houses choose Silicon Graphics 3D visualisation workstations. *The Personal IRIS is part of the broadest, most powerful binary compatible family of graphics workstations and servers ranging fem 10 mips through to 240 mips.

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Schlumberger^s New Three-Component Seismic Imagers—Unmatched Quality and Efficiency in a Combinable Package. The CSP Combinable Seismic Imager and the ASI* Array Seismic Imager quantitatively measure compressional and shear waves on three axes in open and cased holes. Both of these seismic imagers provide high-quality, distortion-free measurements, and their combinability in arrays can significantly improve productivity and cut your costs. The CSI and ASI seismic imagers give you the industry's best signal-tonoise ratios, thanks to the light weight of their sensing components and their acoustical coupling to the borehole or casing wall. Both imagers can be calibrated and coupling quality verified while in the hole. Their signals are digitized downhole to avoid distortion by cable noise. This unique combination of features ensures measurements of the highest quality that are repeatable and virtually unaffected by modal resonances across the seismic spectrum. Talk to your Schlumberger representative about bringing unmatched clarity to geophysical features with the cost-effective, combinable, CSI and ASI seismic imagers. They set new standards of productivity and measurement quality in borehole geophysical d^ta acquisition. *Mark of Schlumberger^ a MAXIS 500 tool

From the Leader in Integrated Geoscience PC Software

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Geopak Systems The Software Resource Australian Agents

Encom Technology Pty Limited Level 1, 110 Alfred Street P.O. Box 422 Milsons Point, N.S.W. 2061 Phone No: 02-957-4117 Fax: 02-922-6141

GMS Kalgoorlie 270 Egan Street P.O. Box 646 Kalgoorlie, W.A. 6430 Phone No: (090) 21-7600 Fax: (090) 21-7799

Geopak Systems, Toronto, Canada, Fax (416) 588-9789

The proven technologytohelp you reduce risk and increase your success rate - worldwide.

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Halliburton Geophysical Services 6909 Southwest Freeway

Houston, TX77074

Ph: (713) 774-7561 FAX:(713)778-3487/Telex: 76-2781