Geological Society of Australia
ABSTRACTS Number 78
Sprigg Symposium Uranium: Exploration, Deposits, Mines and Minewaste Disposal Geology Graham F. Taylor, Editor
Geological Society of Australia - South Australian Division AMF Centre, Adelaide December 2005
Geological Society of Australia
ABSTRACTS Number 78
4th Sprigg Symposium Uranium: Exploration, Deposits, Mines and Minewaste Disposal Geology Graham F. Taylor, Editor
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Geological Society of South Australia - South Australian Division AMF Centre, Adelaide r* December 2005
Sponsored by Heathgate Resources and BHPBilliton ISSN Number 0729 OllX
SPRIGG SYMPOSIUM Uranium: Exploration, Deposits, Mines and Minewaste Disposal Geology Programme 8.15 8.30 8.45 9.30 9.50
Registration Introduction (Graham Taylor) and Opening (Colin Brooks) Keynote - Uranium in South Australia - Politics and Reality - R.K.Johns Uranium Prospectivity in South Australia - Martin Fairclough (PIRSA) Crocker Well Uranium Field and Mount Victoria Uranium Deposit- Norm Kennedy (Pepinnini) 10.10 Exploration for Paleochannel-Hosted Uranium by Cumamona Energy- Mark Randell (Cumamona Energy) 10.30 Discussion 10.45 Morning Tea 11.15 Geology of the Honeymoon Uranium Deposit - Colin Skidmore (Southern Cross ) 11.35 Exploring for Radiogenic Heat - Peter Reid (Petratherm) 11.55 U-Th-REE Mobility in and around the Mt Painter and Mt Babbage Inliers, Northern Flinders Ranges (South Australia) - P-A Wulser (U of A) 12.15 Discussion 12.30 Lunch
1.30 Olympic Dam - Andy Bennett (BHPBilliton) 2.00 Geological Setting and Mineralogy of Uranium Mineralisation at the Beverley Deposit, Frome Basin, SA.- Andrea Marsland-Smith (Heathgate) 2.30 Discussion 2.40 Rum Jungle Waste Rock Rehabilitation - Graham Taylor 3.00 Impacts from the Waste Rock Stockpiles at ERA Ranger Mine and their Rehabilitation - Ian Hollingsworth (EWL Sciences) 3.20 Afternoon Tea
3.40 The Effects of Weathering and Diagenetic Processes on the Geochemical Stability of Uranium Mill Tailings- Greg Sinclair (Rio Tinto) 4.00 Environmental Review of the Mary Kathleen and Radium Hill Uranium Mine Sites - Rehabilitation Success in a Modem World? - Paul Ashley (UNB)) 4.20 Impacts of the Acid In-situ Leach Uranium Mining Process- Graham Taylor 4.40 Discussion 5.00 Close
Uranium in South Australia - Politics and Reality R.K.Johns Geology and geography have conspired to assure South AustraHa a special place in the international uranium industry. Thus, during the past century Radium Hill, Mount Painter, Maralinga, Beverley, Honeymoon and Olympic Dam have, in tum, acquired special significance in evolution of the nuclear fuel cycle. Governments at both the Federal and State levels were quick to accept the challenges offered and sought to maximize the benefits that might accrue from the mining, processing and utilization of uranium - at first for strategic military purposes and, since World War II, to power nuclear reactors for the generation of electricity. Since 1975, uranium and the associated nuclear industry have become divisive issues for the politics of the Left. The ensuing debate which has given rise to negative perceptions of weapon proliferation, safety of nuclear reactors and disposal of radioactive wastes, culminated in protests, demonstrations and blockades in the 1980's. Opportunities that were presented for enrichment of uranium have been passed over through political expediency, and the potential to add greatly enhanced processed value to product from the World's largest resource has been foregone. Likewise, the rejection recently of a national radioactive waste repository near Woomera could be interpreted as being counter-productive and another opportunity lost to the State. This paper briefly traces significant events which relate to exploration, mining, processing and usage of uranium in South Australia for medical research, in atomic weaponry and as a fiiel to satisfy increasing nuclear power demand from overseas.
URANIUM PROSPECTIVITY OF ^Omn
AUSTRALIA
Martin Fairclough, Adrian Fabris, Baohong Hou Geological Survey Branch, PIRSA , Sue Daly, Mineral Promotions, PIRSA The current surge in the uranium commodity price has led to a renewed interest for uranium exploration. South Australia is well placed as it contains many known deposits and significant uranium enriched geological units. The state hosts the world's largest uranium deposit, Olympic Dam, which contains 65% of Australia's reserves plus resources. Similarly, Mount Painter is renown as being one of the most radiogenic locations in the world. Mount Painter is host to over 40 historic mines and prospects and is the source of uranium to the Tertiary Beverley Uranium Mine. South Australia is prospective for four main uranium deposit styles. These comprise; breccia complexes, sandstone (roll-front) style, vein related and unconformity-redox related uranium deposits. Breccia complex deposits are hosted by breccias formed at high crustal levels in active hydrothermal systems (+/- phreatomagmatic) and are associated with regionally uranium enriched country rocks. Examples of this type of deposit include the Proterozoic iron-oxide copper-gold (lOCG) Olympic Dam deposit of the Gawler Craton, South Australia. Olympic Dam lies in a belt defined as an lOCG province (Ferris and Schwarz, 2003) which also hosts the smaller Acropolis, Wirrda Well, Canegrass and Oak Dam breccia-uranium prospects. The Mount Painter uranium occurrences are hosted by the Palaeozoic Radium Ridge Breccias and show some similar characteristics to breccias at Olympic Dam. Of most significance are the Armchair, Streitberg, Radium Ridge and Mt Gee prospects. The Olympic Dam Deposit with 3810Mt @ 0.04% U308 (1.524Mt contained U308) contains 38% of the world's resource. Sandstone (roll-front) deposits are hosted by medium to coarse-grained fluvial, marginal marine or alluvial sands. Uranium mineralisation results from the interaction of uranium-rich oxidising fluids and reduced lithologies (i.e. redox fronts). The controlling factor on sandstone uranium ore is sedimentary facies and its association with reducing agents (e.g. carbonaceous material, sulphides and ferro-magnesian rich basic volcanics). South Australia contains significant examples of this style of deposit. They include Beverley, Honeymoon, East Kalkaroo and Gould's Dam within the Tertiary Callabonna Sub-basin, and Warrior and Yarranna prospects of the Tertiary Eucla Basin. The Beverley Deposit is the only deposit of its type currently being mined in Australia. Mining operations commenced in 1999 with a resource of 21Mt ore at 0.18% U308 (21 600t contained U308). Vein style deposits are hosted by cavity fill (e.g. fractures, veins, apophyses) and can be related to fault planes and shear zones. The most significant area for this style of deposit in South Australia has historically been at Radium Hill and Crocker Well within the Willyama Supergroup of the Cumamona Province. Radium Hill was mined for uranium between 1954-1961. The remaining resource is 890 OOOt @ 0.009% U308. The Crocker Well area encompasses 3 prospects with a combined resource of >10Mt at 0.05% U308. Mount Painter also contains significant uranium mineralisation of this style which include the higher grade Hodgkinson Prospect with 226800t @ 0.25% U308 (567t contained U308).
Unconformity-redox related models have not traditionally been explored for in South Australia. Examples of this style of deposit are found in the Pine Creek Inlier, NT and include the Alligator Rivers Field (Ranger, Jabiluka), Rum Jungle and South Alligator Valley Fields. Mineralisation occurs immediately below and/or above major unconformities separating basement from overlying clastic sediments. A similar architecture occurs on the Gawler Craton. Mesoproterozoic sandstones of the Pandurra Formation unconformably overly the uranium enriched PalaeoMesoproterozoic Hutchinson Group, Hiltaba Suite granitoids and Gawler Range Volcanics. Potential mineralised hosts include reduced facies of the Pandurra Formation or fractured zones of the Hutchinson Group. The most prospective areas are the Cariewerloo Basin margin (host to Pandurra Formation) and in areas of elevated basement (e.g. Devil's Playground). Also prospective is the Corunna Conglomerate within the Gawler Range Volcanics. Olympic Dam, Prominent Hill and Moonta all sit in a belt that is prospective for breccia complex-hosted uranium deposits. Recent recognition that active deformation was occuring during (or shortly after) intrusion of the Hiltaba Suite, and related hydrothermal activity, has led to a re-evaluation of the importance of structural controls of Mesoproterozoic lOCG mineralising systems in South Australia, with remobilisation into vein and fault systems. The Mt. Painter region and adjoining Benagerie Ridge complex of the Cumamona Craton is similarly highly prospective for this style of deposit. Vein style uranium mineralisation is known to occur in a number of small areas of the state. Most significant is within sodic granitiods of the Willyama Supergroup. With the abundant uranium rich source rocks in South Australia, a large portion of the state is prospective for sandstone hosted roll-front style deposits, predominantly within Tertiary palaeochannels. Current work by PIRSA includes detailed palaeochannel definition over the highly prospective Gawler Craton and Cumamona Province. South Australia currently contains over 68% of Australia's U resources and with the high degree of uranium prospectivity is set to increase. References Coats, R.P. and Blissett, A.H., 1971. Regional and economic geology of the Mount Painter Province. South Australia. Geological Survey. Bulletin, 43. Drexel. J.F. and Major, R.B., 1990. Mount Painter Uranium - rare earth deposits, in Geology of the Mineral Deposits of Australia and Papua New Guines (Ed. F.E. Hughes). Pp. 993-998 (The Australian Institute of Mining and Metallurgy: Melbourne). Ferris, G. and Schwarz, M., 2003. Proterozoic gold province of the central Gawler Craton. MESA Journal 30. Pg 4-12. Heithersay, P.S., Drexel, J.F., Hibburt, J.E. and Thomas, C.A. (Eds), 2002. South Australian mineral explorers guide. Office of Minerals and Energy Resources. South Australian Department of Primary Industries and Resources, Adelaide, CD. McKay, A., and Miezitis, Y, 2001. Australia's uranium; resources, geology and development of deposits. AGSO, Canberra.
Abstract - 4TH SPRIGG SYMPOSIUM - Adelaide, 1 December, 2005
Crocker Well Uranium Field and Mt Victoria Uranium Deposit Norman Kennedy - Managing Director, PepinNini Minerals Limited
With the granting of exploration licence EL 3278 in November, 2004 PepinNini Minerals inherited an extensive amount of data relating to uranium exploration conducted by the South Australian Mines Department and private companies within the Olary Domain between 1951 and 1978. Approximately 1,000 boreholes were drilled to assess the Crocker Well Uranium Field and Mt Victoria Deposit located in the west of the tenement. Seven shafts were sunk to obtain bulk samples for metallurgical tests. The Crocker Well area remains the most prospective 'hard-rock' uranium prospect in the Olary district of the Curnamona Province with areas of extensive shallow cover over prospective zones yet to be investigated. Numerous outcropping prospects identified from radiometric data require investigation by drilling to determine the extent of mineralisation already recognised. High grades ranging up to 2.1% UsOe have been reported for surface samples collected from outcropping prospects. Crocker Well and Mt. Victoria lie in the northwest part of the Olary Domain within the Paleoproterozoic metasediments and Mesoproterozoic granitoids of the Willyama Complex. The region comprises leucocratic, commonly foliated biotite S-type grantoids, migmatites, gneisses and schists. The Willyama Inlier has widespread occurrences of highly radioactive granitoid, pegmatoid and metasedimentary rocks. The radioactive minerals are dominantly complex uranium - titanium oxides found as primary hypogene deposits in association with granitic rock types of the crystalline basement. The most abundant form of mineralisation is pegmatitic or aplitic, but there are also a wide variety of stock-work type deposits and replacements which are attributed to related pneumatolytic and hydrothermal activity. The Mt. Victoria deposit is the only lode-type orebody located in the Crocker Well area. At Mt Victoria davidite mineralisation occurs at the surface in several elongated outcrops of schistose biotite rock lying within an area of sub-outcropping granite and granitised meta-sediments. There are four main outcropping bodies of the mineralised rock, each of which strike east-west and dip southerly. The northern one known as the Main lode is the largest, extending laterally east-west for a distance of approximately 80 metres at an average width of 3 metres. Of the others, the South Limb is 30 metres long and converges to meet the Main Lode at its eastern extremity. The Central Lode and South Lode are elliptical in surface plan, the largest dimensions being 15 metres and 12 metres respectively. In addition to the Main area of mineralisation described above, several small exposures of davidite-biotite lode rock have been mapped to the south-west of the Main Lode outcrop, at the margin of a narrow alleviated belt along the line of strike of the Central and Main Lodes. Similar mineralisation is also known to occur over a short
strike length beneath alluvium at two localities in the south eastern part of the prospect area, in a gully 150 metres south of the Main Lode. The mineral composition and paragenesis of the Mt. Victoria ore-bodies is remarkably similar to that of the Radium Hill lodes. The lode rock consists of disseminated daviditic iron-titanium minerals in a matrix of mediumgrained biotite, albitic feldspar and apatite. The biotite, which constitutes 50-80 percent of the whole, is mostly orientated parallel to the lode dip, but there are also a number of flakes lying across the schistosity which effectively bind the rock into a felted and compact form. Unstressed segregations of albite up to a few centimetres in diameter replace biotite in a random manner, and apatite and subordinate orthite and monazite are widely disseminated in the biotite as small grains. Impure davidite, rutile and hematite occur as composite granules and irregular segregations replacing, or partly replacing, the biotitic matrix. In most of the grains, davidite is the host to minute inclusions of rutile and hematite, but others are equigranular intergrowths of davidite and rutile. These complex ores have a steel grey, metallic appearance, but davidite with a high lustre and conchoidal fracture resembling that of the pure mineral is found locally in albite segregations. Granular magnetite - pyrite rock occurs at the margins of the lodes, and as narrow veins parallel to foliation -in the hanging wall migmatites. In all observed cases, no davidite or biotite is associated with these veins. Small amounts of chalcopyrite, bornite, covellite and pyrrhotite are associated with davidite, and with the magnetite-pyrite veins, and molybdenite is a rare lode mineral. Some pyrite is partly replaced by enargite. Sulphide aggregates intersect the davidific ore and are thus later in the paragenetic sequence. In the Crocker Well area uranium occurs primarily as thorian brannerite mineralisation as a disseminated accessory mineral or in fractures, breccias or quartz veins in sodic plagioclase rich anatectic granitoids and gneisses . Outcropping mineralisation is evident over a 4 square kilometre area and has two common modes of occurrence. At the Eastern Prospect coarse brannerite crystals occur intimately related to soda alaskite which intrudes trondhjemite and these crystals seem to have formed synchronously with the alaskite. The thorian brannerite is occasionally intergrown with davidite and has an association with rutile. Elsewhere, brannerite occurs in features such as fractures, breccias, or quartz veins in the soda plagioclase rich rocks. In this mode of occurrence it is nearly always accompanied by rutile, apatite, biotite (phlogopite) and bluish sagenitic quartz. Brannerite also occurs at various locations in the area of mixed sediments hosted by sodic gneisses, but not in the K-feldspar rich granitoids. Pegmatites found in the mineralised zone are generally high in uranium, thorium and rare earth minerals. Secondary uranium minerals have been recognized in the region. Torbernite occurs in the Ninnerie area on fracture surfaces with altered brannerite in trondhjemite and alaskite. Bright green, yellow and orange radioactive minerals are often seen on fracture surfaces associated with other primary radioactive phases. The commonest occurrence of these is in biotite or muscovite cleavage planes in granitoids and pegmatites. These occurrences are of unknown significance at this time. Additionally, gummite after uraninite and brannerite has been interpreted. Carnotite and possible pitchblende have also been noted from radiometric anomaly sources. Anomalous grades of titanium, vanadium, chromium and rare earths have been noted with lanthanum grades of up to 20,000ppm and cerium grades often in excess of 3,000ppm being reported. A resource of 12.65 million tonnes at an average grade of 0.053% containing 6,740 tonnes (14,850,000lbs) of U3O8 has been estimated in compliance with the 2004 JORC Code for the Crocker Well Uranium Field and Mt Victoria Deposit. The table below details the resource estimates for each of three deposits comprising the Crocker Well Field and the Mt Victoria Deposit. ESTIMATED INFERRED MINERAL RESOURCES Category Cut-off Deposit ppm
Resource tonnes
U3O8
%
U3O8 kgs/t
Contained IbsUgOe
Mt Victoria
Inferred
300
250,000
0.160
1.60
880,000
Crocker Original
Inferred
300
8,400,000
0.046
0.46
8,520,000
Crocker Central
Inferred
300
1,100,000
0.043
0.43
1,040,000
Crocker Eastern
Inferred
300
2,900,000
0.069
0.69
4,410,000
Total
Inferred
300
12,650,000
0.053
0.53
14,850,000
Sprigg Symposium, V December, 2005 EXPLORATION FOR PALAEOCHANNEL-HOSTED URANIUM BY CURNAMONA ENERGY LIMITED M. H. Randell ABSTRACT: Cumamona Energy Limited (henceforth referred to by its ASX code, CUY) has access to most of Havilah Resources N.L.'s Cumamona Craton tenements to explore for Tertiary palaeochannel-hosted uranium deposits. The tenements cover some 5000 square kilometres and include approximately 100 kilometres of known palaeovalley systems as well as extensive areas of "blanket sands" which have potential to host uranium mineralisation. Palaeochannels in the district were discovered in the late 1960's and '70's by reconnaissance drilling along any convenient boundary fence or station track, often with holes spaced miles apart. The channels were interpreted as braided streams meandering across a peneplaned surface before coalescing into sheeted sand deposits in the northern downstream regions. The best defined example is the Yarramba Palaeo valley which is 2-10 kilometres wide but has a shallow profile of about 50 metres. The valley is filled with Tertiary Eyre Formation sands and clays. Later lake sedimentation capped the valley and adjacent basement rocks with up to 70 metres of clay (Namba Formation). Evidence from drilling and geophysical imaging now indicates that the course of the Yarramba Palaeovalley was strongly influenced by underlying basement lithologies. Aeromagnetic surveys readily identify the stratigraphic top of the magnetic Ethiudna Subgroup which is the position occupied by the Bimba Formation. This unit has a deeper weathering profile due to the presence of sulphides which promote the formation of easily eroded clays from feldspar and calcsilicate minerals. River action in the Yarramba Palaeovalley has exploited this softer horizon as shown by several marked changes in direction of the valley. Gravity imaging also shows the presence of a palaeotopographic ridge coinciding with the Mooleulooloo Psammopelite unit, which lies stratigraphically above the Bimba Horizon. This unit can be traced in the sub-surface throughout the district and has its only outcrop in the Mooleulooloo Hills from which it derives its name. The final course of the Yarramba Palaeovalley is now believed to be largely governed by this bedrock ridge. Further evidence for palaeochannel margins is found in Airborne Electromagnetic surveys. These detect the presence of saline water in aquifers of the palaeochannel system. A HoistEM™ survey flown by CUY in September 2005 shows strong correlation with gravity results supporting the importance of palaeotopography. As well as controlling the course of the valley, the palaeotopography is now considered to provide other important controls on uranium deposition. Eyre Formation sediments in the palaeovalleys are generally neutral to oxidised although organic debris (often as lignite in clay horizons) provide local sites of reduction. Oxidised groundwater moving through aquifers can transport dissolved uranium to these sites where precipitation as uraninite can occur. Economically significant
deposits require more reductant than that provided by thin clay bands and these are thought to occur at specific traps sites, for example, at the Honeymoon deposit. Other sites modelled on Honeymoon are believed to occur on CUY's tenements and are the focus of the company's current exploration efforts. In November 2005 CUY commenced a drilling campaign to systematically test palaeochannel systems using a company owned rotary mud drill rig and downhole logging equipment.
Geology of the Honeymoon Uranium Deposit Colin Skidmore Project History Exploration for Tertiary sediment-hosted uranium occurrences commenced in the southern Lake Frome region in 1968. Philosophy followed closely on United States sediment-hosted uranium exploration experience, particularly that from the Tertiary basins of Wyoming. In the Cumamona region, assessment identified potentially favourable buried fluviatile sands adjacent to uranium-enriched source rocks. The genetic model assumed leaching from permeable sands, transport down the hydrological gradient and deposition at a reduction-oxidation interface. Exploration methods employed open-hole rotary drilling (initially along station tracks) and wire-line geophysical logging as a reconnaissance exploration tool, although surface geophysical methods, primarily resistivity and gravity surveys, were also used with limited success to locate and map Tertiary Palaeo-valleys. Oilmin-Transoil-Petromin JV discovered Beverley in 1969 and Sedimentary Uranium NL discovered the East Kalkaroo Uranium Deposit and the Yarramba Prospect on the Yarramba Exploration Licence in 1970. A MIM-Minad-Teton JV discovered the Honeymoon Uranium Deposit on the neighbouring South Eagle Licence in November 1972. By 1983, the Honeymoon Uranium Project had advanced through a full feasibility study including construction of a pilot plant, field leach trials, EIS preparation and was ready to commence a full scale mining operation. The change in government in 1983 resulted in a refusal to grant full licensing permits necessary to commence full-scale commercial mining and the project was subsequently placed on care and maintenance. During a more favourable political environment in 1997, SXR became interested in the Honeymoon Uranium Project. SXR refurbished the pilot plant, ran extensive field leach trials and completed the final EIS submissions. In February 2002 SXR was granted an Export Licence and Mining Lease 6109. Initially SXR planned production at 750-1000tpa however re-evaluation of the deposit favours a more conservative production rate. SXR is currently drilling out the deposit to improve the 3D geological model and to determine an optimal well field design and ISL final plant design. Production is likely to commence in 2007. Geology The uranium at Honeymoon occurs as pitchblende coatings on reduced pyritic quartz sand and gravels in the buried Tertiary Yarramba Palaeovalley in the Southern Frome Embayment. The Yarramba Palaeovalley was incised into MesoProterozoic Willyama Supergroup basement during a period of uplift and subsidence during the early Tertiary. It is a confined aggrading fluvial system comprising -50m thick upwardly fining successions of interbedded sand, silt and clay which is up to 6km in width. Palynological analysis of core has determined the fill to be Eocene Eyre Formation. The braided Basal Member which contains the majority of the mineralisation at Honeymoon appears to be layercake with laterally extensive tabular clast supported sand and gravel units. Towards the top of the Basal Member highly carbonaceous lithofacies are locally present at
Honeymoon which includes coarse Hgnitic wood fragments. The middle and upper members are more clay dominant with a labyrinth of compartmentalised meandering channel sands, well preserved overbank facies and clay wedges. Unconformably overlying the Eocene Yarramba Palaeovalley sediments is a thick ('-^75m thick) succession of lacustrine lake sediments of Miocene Namba Formation. At Honeymoon the static groundwater level is ~50m below ground level within the Namba Formation and naturally flows at 10-15 metres per year. The highly permeable Basal Aquifer is very saline (~20,000TDS) whereas salinities in the Upper Aquifers is less saline (~11,000TDS). The source of Honeymoon's uranium is considered to have been derived from both chemical and mechanical weathering of a high-level granite located to the immediate south of Honeymoon (~2km). Geophysically, this buried granite features as one of a number of discrete circular magnetic and gravity lows (-5km diameter) which appear to form a district scale ring centred on the Benagerie Ridge and extending across to the NSW border. It is proposed that underlying these high-level protuberances is an evolved batholith complex of around 40 kilometres diameter which is responsible for the lOCG mineralisation of North Portia and Kalkaroo. Only one drill hole is known into one of these features which was drilled in 2002 by SXR. Petrology of a shallow cored sample describes a weathered muscovite-rich syenogranite with altered biotite. Most interestingly however, assays of this sample returned 76ppm uranium (typical crustal granite averages 2ppm U). Further investigation of this granite is planned in the near future. The shape and sinuosity of the palaeodrainage system is strongly controlled by the stratigraphy and structure of the underlying basement geology. Block warping during the Tertiary defined a northward flowing drainage system however the morphology of the Tertiary palaeosurface diverted the main Yarramba Palaeovalley to the southwest for some 12 kilometres along a gutter defined by the deeply weathered meta-evaporitic Bimba Horizon adjacent to the more competent graphitic pelite (Stratheam Group) ridge. The main palaeodrainage eventually breached the ridge in a faulted zone which can be discerned from geophysical datasets. It is at this breach where Honeymoon is located. Tempest™ AEM has proved highly useful in mapping palaeodrainage as the salinity of the groundwater contrasts the less conductive geology. The AEM datasets show a number of tributaries entering the main Palaeovalley and in particular a complex tributary system is evident shedding off the "hot" granite which joins the main channel at Honeymoon. The entire Yarramba Palaeodrainage system is known to be oxidised through to the blanket sands under Lake Frome to the north. This is unlike the traditional roll-front models of North America and Kazakhstan where uranium carried in oxidised groundwater precipitates along broad easily recognised redox interfaces. Honeymoon is an island of reduction in the oxidised system where organic matter has been trapped and preserved as it passed trough the constriction in the breached highly graphitic pelite ridge. Drilling has shown that the Palaeovalley floor across the breach is a shallow basin and preservation of reduced channel fill has likely been further enhanced by the strongly
reduced graphitic basement lithology. As the groundwater system in the Yarramba Palaeochannel is still active, Honeymoon is dynamic and slowly redissolves and migrates gradually downstream at the same time as fresh uranium dissolved out of the chemically weathering granite is precipitated back in the reduced organic trap.
Exploring for Radiogenic Heat Peter W. Reid (Petratherm Ltd) & Dr Martin Hand (School of Earth and Environmental Sciences, University of Adelaide) The Earth is a heat engine. Its centre, 6371 km below our feet, has an ambient temperature of 4150'^C while the average internal temperature is 1700®C. The Earth's heat is constantly generated through the radioactive decay of long-lived isotopes of potassium, thorium and uranium, elements which are present throughout the Earth. Extreme surficial cooling of the "hot earth" by the cold vacuum of space has formed a thin relative cool skin (crust) on which life precariously occupies. Apart from active volcanic regions, temperatures in the crust increase on average 1730°C/km. In certain areas where heat producing elements are concentrated and insulating cover strata act as a heat trap, highly elevated near surface crustal temperatures will occur. These areas have temperature gradients ranging between 40-90''C/km, and so temperatures in excess of 200°C may occur at 3-5 kilometres depth, well within reach of modem drilling methods. The Hot Rock Energy (HRE) process involves extracting heat energy through the engineered circulation of hot water through a hot rock mass. The superheated water can then be used for direct heating purposes or passed through a binary power generator to convert the heat energy to electrical energy. HRE can provide large scale, base load power that is CO2 emission free. Australia has phenomenal HRE resource potential. Recent estimates indicate that there is enough stored heat energy to provide all of Australia's electricity requirements for several thousand years (Somerville, et. al 1994). Proterozoic crust in the eastern part of South Australia (Figure 1) is characterised by significantly elevated heat flows compared to typical Proterozoic crust (Cull, 1982; Houseman et al, 1989). Although the dataset is sparse, the South Australian Heat Flow Anomaly (SAHFA, Figure 1) (Neumann et al, 2000) is defined by an average heat flow of around 90 mWm"^. To put this into perspective, the global average continental heat flow from Proterozoic continental crust is around 48 mWm ^ The SAHFA appears to extend in a northerly direction, merging with the thermally anomalous Cooper Basin system. 135°E The absence of recent magmatism in northern South Australia, and the lack of evidence of for significant crustal extension suggest that high mantle heat flows associated with either recent volcanism or lithospheric extension is unlikely to be the cause of the SAHFA. Furthermore, seismic shear wave velocities beneath eastern South Australia point to a comparatively cool mantle to depths of around 250km (Fishwick et al, 2005), again suggesting that the high heat flow does not arise from the manfle.
Figure 1 South Australian Heat Flow Anomaly. (Neumann et al 2000)
In this context, it is significant that outcropping felsic rocks in the Cumamona Province (including the Mt Painter Inlier) and eastern Gawler
Craton contain anomalously elevated U and Th contents and are therefore likely to be the source of the high crustal heat production (Neumann et al, 2000). For example the average heat production rate in the Mt Painter Inlier is lO^Wmwhich is around 3 times the rate of average granite (Neumann et aL, 2000).
Petratherm Ltd is the first public company in the world whose sole business is to explore for heat. It has designed a work program focused on locating economic geothermal reserves in a cost effective and timely manner. Petratherm's focus areas are based on two specific geological models known as the thermally anomalous granite (TAG) model and the radiogenic iron oxide (RIO) model. Each has clearly defined geological parameters. The TAG model is the focus for Petratherm's licences adjacent to the Mt Painter and Mt Babbage Inliers, within the SAHFA, where heat flow measurements from the nearby Parabarana area are amongst the highest recorded in Australia. Measurements from outcropping granites in the Mt Painter Inlier indicate their average heat production is eight times (and locally up to twenty five times) that of average granite, and at least twice that of other radiogenic granites used to successfully generate geothermal power elsewhere in the world. Thermal modelling indicates that rocks meeting the TAG criteria at Mt Painter could generate temperatures of around 225°C at depths of around 3.5 kilometres. The RIO model exploits highly elevated hydrothermal U and Th enrichment associated with hydrothermal lOCG development during the Mid-Proterozoic ('-1590Ma) Gawler magmatic event. Measured heat production rates in RIO bodies may be as much as 50 times greater than those from average granite (Houseman et al, 1997) and thermal modelling shows that under favorable conditions temperatures in excess of 200°C could be generated at depths of around 3.5 kilometres.
References
Cull J.P., 1982. An appraisal of Australian heat flow data, BMR J. Aust. Geol. Geophys. 7 11-21.
Fishwick, S., Kennett, B.L.N. &. Reading, A.M., 2005. Contrasts in lithospheric structure within the Australian craton—insights from surface wave tomography. Earth and Planetary Science Letters 231, 163- 176. Houseman G.A., Cull, J.P., Muir P.M., and Paterson H.L, 1989 Geothermal signatures and uranium ore deposits on the Stuart Shelf of South Australia, Geophysics 54 (1989) 158-170. Neumann, N. Sandiford, M. & Foden, J. 2000. Regional geochemistry and continental heat flow: implications for the origin of the South Australian Heat Flow anomaly. Earth and Planetary Science Letters, 183, 107-120. Somerville, M., Wybom, D., Chopra, P., Rahman, S., Estrella, D. and Van der Meulen,T. 1994. Hot Dry Rock Feasibility Study. The Energy Research and Development Corporation. Report 94/243.
U - T H - R E E MOBILITY IN AND AROUND THE M T PAINTER & M T BABBAGE INLIERS, NORTHERN FLINDERS RANGES (SOUTH AUSTRALIA)
Pierre-Alain Wiilser^ Joel Brugger^'^ and John Foden^ ^ CRC-LEME and Discipline of Geology & Geophysics, School of Earth & Environmental Science, University of Adelaide, Adelaide, SA-5005, Australia ^ Department of Mineralogy, South Australian Museum, North Terrace, Adelaide, SA-5000, Australia
INTRODUCTION
The Mesoproterozoic basement of the north-western edge of the Cumamona craton outcrops in the form of two inliers: the Mt Painter Inlier (MPI) & the Mt Babbage Inlier (MBI), which are structurally separated by a transcurrent crustal fault system. These inliers have been uplifted above the level of the Lake Frome Mesozoic to Quaternary sediments, and provide a window into an unusually U-Th-REE-rich anorogenic alkaline magmatic province. Late magmatic processes, contact metamorphism, hydrothermal circulation, and finally mechanical and chemical erosion have affected the distribution of uranium in the Inliers, and resulted in a variety styles of uranium mineralisation in the Inlier and in the surrounding sediments. The granitic magmas were generated from a mantle source and intruded into Mesoproterozoic continental detrital sequences. The granites can be divided into two suites, intruded at 1560 Ma (e.g., Terrapinna granite) and 1575 Ma (e.g., Mt Neill granite). They have been compared to the Gawler Range Volcanics and the Hitalba granitoid suite (especially the Roxby Dows subsuite -1590 Ma; Johnson & Cross 1991). These granites are anorogenic alkaline granites characterised by high K20/Na20, and high enrichments in REE, Th, U, Y, and Nb relative to the average Proterozoic Australian granites. During the Devonian (-440 Ma), the Inliers have been intruded by peraluminous-metaluminous granitoids (British Empire Granite) and pegmatites (Mudnawatana tonalite).
with
minor
volumes
of
MESOPROTEROZOIC MAGMATISM AND METASOMATISM
tonalites
Figure 1: Radiometric map of the Mt Painter Inlier and surrounding units. YG = Yerila Granite, HSG = Hot Spring Gneisses. The location of the Beverley Limine in the Lake From embayment is also indicated.
The U- and Th-enriched plutons stand out on calibrated radiometric maps (Fig.l). Two groups of granitic intrusions can be distinguished: the first group (Yerila Gneiss (YG) and related units; Hot Spring Gneisses (HSG)) is characterised by extremely high U and Th contents (70-200 ppm U; 300-600 ppm Th). The second group contains 10-60 ppm U and 50-200 ppm Th and comprises the Mt Neill granite, the Pepegoona rhyolite, the Box Bore granite and many other bodies thought to be related to the Mt Neill granite. Heavy minerals have been extracted from several samples fi-om the YG and fi-om stream sediments from creeks draining the HSG and the YG, with the aim of obtaining a quantitative picture of U speciation in the granites, forming the basis of the understanding of U-mobility through hydrothermal and weathering processes. The YG is a medium- to coarse-grained recrystallised monzogranite with porphyritic tabular microcline phenocrysts. Calcsilicate-bearing, allanite-rich lenses interpreted as skam, are crosscutting the main foliation of the gneiss or float in the allanite-rich granite. The whole-rock composition is extremely enriched in REE, Zr, Nb, F, U, Th, Y and W. The Yerila gneiss can be divided into two main types based upon the mineralogy: (1) a biofite, potassic-ferrihastingsite, allanite-(Ce)-epidote, uranothorite, Y-rich titanite, Y-rich fluorapatite, uraninite, Th-rich synchysite-(Ce) type, which corresponds to main type; and (2) a biotite-muscovite-monazite-xenotimerutile-ilmenite type. The first mineralogical type reflects an original magmatic paragenesis overprinted by a metasomatic late-magmatic event. Magmatic minerals include Mn-rich ilmenite, fluorite, microcline, oligoclase, biotite, dark alkaline zircons (3000 ppm U), potassic-hastingsite, molybdenite, euhedral allanite, arsenopyrite, euxenite-(Y) and apatite. The second type is related to a Paleozoic metasomatism (see below). Fluorite is a common late mineral in YG, occurring as fissure fillings in microcline, or at mineral boundaries, or crystallizing with the late-potassic-hastingsite-biotite pods. F is also structurally present in titanite, biotite (nearannite), synchysite-(Ce), euhedral fluorapatite, and allanite-(Ce). Mineral reactions attributed to a F-rich, oxidizing, peralkaline fluid are observed in allanite-rich samples: molybdenite is rimmed with powellite; Mnrich ilmenite transformed into an Al-F-Y-rich titanite; and allanite-(Ce) shows an enrichment in U and Th near the rim. Anhedral coarse Al-F-Y-rich titanite, Y-rich fluorapatite and allanite-(Ce), as well as potassicferrihastingsite appear in the late-magmatic paragenesis. The metasomatic zircons are mostly located in biotite pods and along grain boundaries. Zircon is also the host of uraninite, apatite, and uranothorite inclusions.
documenting the simultaneous deposition of Zr, Th and U. Hence, it appears that the high levels of Zr, REE, Th and U are essentially due to the late-magmatic episode. Fe^"^ is only present in this late-magmatic paragenesis. PALEOZOIC METASOMATIC EVENT
The progressive replacement of allanite and thorite by monazite and xenotime in the Mesoproterozoic granites is correlated to the distance from Paleozoic granites and tonalites. For example, the heavy minerals populations in the creeks draining the YG next to the Paleozoic Mudnawatana tonalite contain abundant xenotime-(Y) and monazite-(Ce), and minor cerite-(Ce) "Ce9Fe(Si04)6(Si03)(0H)4", euxenite-(Y), samarskite, hollandite "BaMngOie", tomebohmite-(Ce) "Ce2AlSi208(0H)", ilmenite, fluorite and allanite-(Ce). Cerite-(Ce), tomebohmite-(Ce) and hollandite are indicative of contact metamorphism. The radiometric map also clearly shows a Th-U decrease next to the 440 Ma intrusions or their pegmatitic network extension, indicating that some U and Th has been released from the rock during this contact metamorphism episode. The mineralogical changes observed in the three major U-Th-rich units in the Babbage and Mt Painter inliers underline reworking by a F-rich fluid during the Late-Ordovician magmatic-thermal event recognised by Elburg et al. (2003). Fluorine was remobilized from the magmatic and late magmatic biotite, titanite, apatite, and fluorite during the Paleozoic contact and regional metamorphism. These F-rich fluids have leached out Ca, REE, U, Th, Y and Nb from the already metamict allanite-(Ce), uranothorite, Y-bearing titanite, euxenite-(Y) and Yrich fluorapatite. REE, Y and Th were partly immobilized into newly-formed xenotime-(Y) and monazite-(Ce). U, Nb, Y, hREE were carried together with Ca and Fe on longer distances. The titanite veins located to the south and the west of the B.E. intrusion, and dated at 440 My by Elburg et al. (2003), are related to this event. The UY-Nb-rich hematitic breccia around Radium Ridge (Brugger et al. 2004) probably also precipitated from such fluids. These hematitic breccia are associated with the Mt Gee-Mt Painter epithermal system, which contains abundant fluorite (mainly as pseudomorphs; fluorite veins are preserved in the root of the system) and is locally enriched in U and Mo. This epithermal system may hence represent a distal, near-surface expression of the Paleozoic metasomatism. TERTIARY-QUATERNARY U - T H - R E E DISPERSION & BEVERLEY URANIUM DEPOSIT
The radiometric map (Fig. 1) shows a clear dispersion plume for Th and U in the modem alluvial fans issued from the Mt Painter & Babbage Inliers. The channels give the highest radiometric values. Th concentrations decrease from 60-70 ppm next to the edge of the ranges down to 20 ppm at the Lakes Callabonna and Frome. Uranium is following the same trend. Dispersion is principally controlled by placer concentration in the channels, and disintegration and leaching of mechanically or chemically unstable minerals (metamict allanite, thorite, zircon and U-Nb complex minerals). Most of the Th and U is hosted by monazite and xenotime. The Lake Frome Embayment hosts sedimentary U deposits, which are currently mined by in-situ leaching technology at the Beverley deposit. This deposit is located in the Namba Formation, consisting of intertonguing sands, silts & clays, carbonaceous mudstone (Callen 1975; Ellis 1980, Heathgate 1998). Heavy mineral assemblages show an authigenic mineralogy consisting of native copper and native lead, barytine, apatite, pyrite, marcasite, sphalerite and clausthalite. U is hosted in camotite, coffinite and uraninite. U"^"^ minerals appear as botryoidal aggregates or small spheres with framboidal pyrite cores, located in mudstone and silts. The proportion of detrital heavy minerals in Namba varies between 0.1 and 1.0 % in sands, with white euhedral to well-rounded zircons being the dominant mineral. Some zircons show a UV-fluorescent rim related to presence of uranyl ions. Pupin (1980) introduced the use of zircon morphology as a tool to distinguish the nature of granites. The relative abundance of prisms and pyramids provides precious information about the environment of crystallisation of zircons (melt composition, pressure, and temperature). Zircon crystals are divided into 64 subtypes based on unique combinations of crystal faces; these subtypes can be related to specific types of granites. The zircon typology method has been successfully applied to determine the sources of the sediments in two specific cases: (1) the Beverley uranium deposit and (2) a tributary of the Four Mile Creek, the main sediment supplier for the upper Willawortina Formation, which caps the Miocene Namba Formation in which the Beverley uranium mine is located. Four distinct zircon populations occur in the Willawortina Formation: a rounded population attributed to metasedimentary rocks; a dark coloured D-P5-P2 alkaline population attributed to the HSG; a minor population of D-P5 alkaline pink euhedral zircons of unknown origin; and finally a minor population of white euhedral transparent to slightly milky S-types zircons corresponding to a calc-alkaline granodioritic-monzogranitic source: the Paralana Granodiorite. Zircon typology confirms that the Paralana Granodiorite contains both cmstal and mantle components. The Four Mile Creek also contains a large amount of monazite and xenotime, which host nearly all the Th and U. These minerals originate from the HSG. The WC2 core through the Beverley uranium deposit was used to study zircon morphology from a more evolved sediment from the Willawortina Formation (coarse sands at a depth of 75 m) and from the Namba Formation. The Willawortina sands contain abundant (50%), large alkaline D to P3 zircons. The dark, brown, red, yellow crystals are metamict and fissured. They are mainly coming from the Mesoproterozoic alkaline granites (HSG especially). Another population of detrital rounded white and pink zircons is coming from the metasedimentary Mesoproterozoic basement (30%). Zircons sourced from the Paralana Granodiorite-British Empire granite are
also present (<10%). The heavy minerals in these sands consist of detrital magnetite, hematite, apatite, monazite, xenotime, tourmaline, epidote, rutile, fluorite and corundum. All these minerals are coarse and slightly worn. Namba sands were selected at a depth of 123-127 m, right in the mineralized levels. The zircons show a majority (70%) of the clear colourless euhedral Q1-S1-S6-L1-L2 morphological subtypes, which can only correspond to zircons from S-type peraluminous monzogranites. The closest source for these zircons is undoubtedly in the Lachlan Fold Belt in NSW. Darker D-P5 to P3 zircons from the alkaline Mesoproterozoic granites are less represented (5%), whereas rounded pink or white zircons account for 20% (Fig. 2). The detrital heavy minerals abundant in Willawortina are nearly absent in the Namba sands. The most resistant minerals (tourmaline, zircon, rutile, corundum) account for more than 80% of the whole heavy mineral fraction. The source of uranium in the Beverley deposit is to be found either in the original detrital U-bearing minerals issued from the Lachlan Fold Belt granitoids, or in the Willawortina U-Th rich sediments. In this later case, a connection between the aquifers of the Willawortina and Namba aquifers is or has been in activity. CONCLUSIONS
The Mt Painter and Babbage Inliers show a polyphase history of U-Th-REE mobility, resulting in a complex distribution pattern, and in contrasting mobility of U in the weathering environment. The primary mineralogy of the Mesoproterozoic granites is in accordance with the alkaline K-rich anorogenic origin. The late-magmatic metasomatic event lead to an exceptional accumulation of U, Th, REE and Zr in the upper level of some of these plutons. The second metasomatic event (Paleozoic) remobilized part of the U, Th and REE present in the Mesoproterozoic basement. These two major metallogenic events have provided many opportunities for forming U-Th-REE+/- base metals deposits. The yet poorly described Paleozoic event is probably responsible for the historic deposits at Mt Painter, Mt Gee and East Painter. W E Uranium in the channel-hosted deposits may not be derived from Lake Eyre basin the MPI, but from the granitoids from the North-Eastem side of the Lake Eyre Basin (Lachlan Fold Belt), where most of the zircons come from. Also, the uranium contained in the detrital minerals of the Miocene sediments (Namba) is in large enough concentration to be the Aluminous leucogranites IMixed local basement Alkaline Mesoproterozoic Calc-alkaline Ordovician zircons (Lachlan Fold Belt) granites & rhyolites granodiorite & pegmatites granitic zircons, 30% of main source of U concentrated in & Minor Mesoproterozoic rounded undetermined crystals alkaline zircons the economic deposits. The Pliocene-Quaternary Willawortina formation, which Figure 2: Zircon typology in the MtPainter Inlier and the Tertiary-Quaternary presently accumulates the U-Thsediments REE-rich detrital minerals of the Mt Painter Inlier, is a major uranium reservoir. However, unless some unknown exchange between Willawortina and Namba aquifers have happened, the Mt Painter Inlier rocks have no genetic connection with the U Beverley deposit. REFERENCES
Brugger J. 2004. Amer. Mineral.: 89, 339-347. Callen R.A. 1975. Mon. Set., AuIMM 5, Econ. geol. of Australia and Papua New Guinea: 1, 803-807. Ellis G.K. 1980. AAPG Bulletin 64 (10): 1643-1657. Elburg M.A. et al. 2003. Aus J. Earth Sc. 50: 611-631. Heathgate Resources 1998. Beverley Uranium Mine. Heathgate Resources Pty Ltd, South Australia Johnson J.P. & Cross K.C. 1991. In Pagel, M & Leroy, J.L., in Source transport & deposition of ore metals, Balkema, Rotterdam, 395-400. Neumann N. 1996, BSc (Hons) thesis, Univ. of Adelaide. Unpublished Pupin J.-P.1980, Contrib. Min. Petrol. 73:207-220. Teale G.T. 1993, in Geology of South Australia, Mine & Energy Geol. Surv. South Australia. 54, 1, 93-98.
Geological Setting & Mineralogy of Uranium Mineralisation at the Beverley Deposit, Frome Basin, SA Andrea Marsland - Smith The Beverley Uranium mine located in the northwestern Frome Basin, South Australia is the largest and the most recently constructed In Situ Leach (ISL) Mine in the westem world. In 2004 it produced 2.4 m lbs U3O8 using a sulfuric acid lixiviant, ion exchange capture and a plant and wellfield flow capacity of approximately 300 litres/second. The mineral resources at Beverley have been estimated at 32Mlbs at an average grade of O.lSyoUaOg based on current and historical drill data. Regional Setting Beverley is situated east of and parallel to, the Poontana and Wooltana Faults which displace both the cover sequences and basement rocks of the westem Frome Basin. This area between Lake Frome and the Northern Flinders Ranges forms part of the northwestem Cumamona Province. The ore host is the Late Oligocene to Middle Miocene sands of the Namba Formation; part of the Cretaceous-Quaternary cover sequence which unconformably overlies deformed Proterozoic and Cambro-Ordovician crystalline basement. Regionally, the Namba Formation comprises a series of up to 5 disconformity bounded sedimentary sequences. Each sequence fmes-upwards from fluvio-deltaic sands into lacustrine sihs and laminated and carbonaceous clays. The uppermost of these cycles is the mineralised 'Beverley Sequence' where quartzose sands infill palaeo-depressions incised into a laterally extensive smectite-dominated clay sequence, locally termed the Alpha Mudstone. The distribution of the host sands are stongly influenced by local structure. Depth of mineralisation is occurs between 120m and 150m. Exposures of uranium-rich granites and metasediments of the Mt Painter Inlier are exposed less than 5km west of the deposit. Recent exploration results imply a strong genetic association with the major Poontana and Wooltana fault systems, and a source of Uranium from possibly the same Uraniferous crystalline rocks at depth beneath the Tertiary and Mesozoic cover. Mineralogy, Ore Distribution & Geochemistry The ore mineralogy comprises very fine-grained (<10um) coffinite. Coffinite is intimately associated with kaolinite which forms coatings on the surfaces of quartz grains and partially fills the interstices between them. Other accessory gangue minerals comprise minor montmorillonite, fine detrital sericite, rutile and ilmenite. Beverley comprises three princpal orebodies (North, Central and South Beverley) and, more recently, near-mine exploration has identified additional ore trends (Beverley East, Russell and Poontana Trends) to the south and east of these deposits. There is an intimate spatial relationship between the occurrence of Uranium Ore with the edges of undulations and/or scours and the presence of highly reduced zones in the top surface of the Alpha Mudstone. This latter would also have acted as an impediment to the flow of mineralising fluid, thus providing and effective trap mechanism for ore deposition. Uranium, sulphur, carbon and cobalt show some of the highest variations within the Beverley sands, with Uranium being the most variable. Distal to the primary mineralised areas. Uranium exhibits a background of only a few ppm, whereas within ore zones. Uranium varies from 25ppm to over 3% U3O8. Sulphur averages 0.05%S and is in general, concentrated in the base of mineralised sand. The modal abundance of sulphur also increases with proximity to the Alpha Mudstone contact (up to 2-
3%S). Carbon (TOC) grades from 0.02-0.05% and has a range in the upper sand zones of 0.3-0.8% approaching the Alpha Mudstone contact. Cobalt levels are consistently elevated by one to several orders of magnitiude and there is a weak light rare earth element (LREE, Y, Ce, La etc.) association with the the ore zone. The modal abundance of iron averages 1-5%, which is low by comparison with other sediment-hosted Uranium deposits. There is a robust association of U-Bi-Pb-Co±Ni,Cu,Cd coupled with weak Zn anomalism, which is compatible with the geochemistry of the granitic rocks of the Mt. Painter Inlier to the west. Beverley ore is characterised by porosities averaging 33%, very high permeabilities, highly leachable coffmite ore minerals and a relative absence of additional and interfering elements in the ore. The Beverley sands are confined by impermeable clays both laterally and vertically which makes this environment ideally suited to mining by ISL and to natural containment of the mining solutions. The Beverley Model Beverley fits most of the descriptors for a roll-front deposit model in terms of the age of host rock, source for Uranium, transport and depositional mechanisms. One significant departure from the model however, is that the ore morphologies do not resemble crescent shape "rolls" and lack a diffrise boundary with reduced sand on the down-gradient side, and sharp contacts with the oxidized sands on the up-gradient. One of the reasons for this is that the host rock is erratically distributed unconsolidated sand and is not a thick, uniformly dipping, regionally-extensive sandstone where large geochemical/groundwater cells can permeate. Rather, Uranium has been precipitated in a reducing environment within sand-filled scours or depressions in the underlying Alpha Mudstone. The mineralisation is tabular in nature and occurs along the edges of the depressions; the frindamental control on the depression architecture being either primarily structure (ie. faulting) and/or a combination of structure and palaeoenvironment. Historically, drilling has been the principal method used in exploration for roll-front deposits and is appropriate when exploring areas where oxidation and reduction interfaces in sand are clearly identifiable (i.e. when the roll-front model applies in totality). Downhole surveys such as Resistivity, Neutron and Self Potential are used to identify the depth, thickness and relative porosity of the aquifer sands. Gamma-ray and Prompt Fission Neutron (PFN) downhole surveys are used to calculate depth, grade and thickness of the Uranium mineralisation. Improved instrumentation and processing techniques have dramatically increased precision and resolution of reconnaisssance geophysical exploration techniques. Airborne magnetic and ground gravity surveys have assisted in mapping regional and local structures. High-resolution airborne EM has assisted in mapping the variations in the palaeotopography of the top of the Alpha Mudstone unit and the location of sand bodies with the potential to host Beverley-style mineralisation. Other potential host sands include sands at deeper levels within the Namba Formation, the Eyre Formation and deeper Mesozoic sediments, and have also more recently been identified as valid exploration targets.
The Medium - Term Performance of Waste Rock Covers - Rum Jungle as a Case History Graham F Taylor, Alister Spain, Gregg Timms, V Kuznetsov and John Bennett Earthen covers are now widely used in the mining industry to control the generation rate an/or release rate of low quality drainage from piles of radioactive and sulfidic minewastes. Covers are usually designed to reduce water infiltration rate and in some case may also reduce the oxygen flux to the underlying sulfides. Engineered covers have only been used since the 1980's, however there is very little field data on their performance in the longer term. This lack of information has implications for the degree of confidence that can be placed on the predictions of the environmental impacts of sulfidic minewastes, for the acceptance of close-out criteria by regulatory authorities and for the financial liability of the mining industry. Covers were placed on the sulfidic wasre rock dumps at the abandoned Rum Jungle uranium mine during 1984 - 1985. These covers were designed to reduce water infiltration to less than five per cent of incident rainfall by both water shedding and storage-release mechanisms. Regular monitoring by the Australian Nuclear Science and Technology Organisation (ANSTO) demonstrated that the covers performed better than the design criterion for about 10 years, but infiltration rates subsequently increased. There is a 66percent probability that the infiltration rate now exceeds five per cent of incident rainfall. The cover on the largest pile. White's Heap, was sampled in pits dug at eight locations. Sampling was carried out at the end of the monsoonal wet season and again at the end of the "dry" season. This together with laboratory testing, enabled cover performance to be assessed against five criteria: design, construction, cover material characteristics, physico - chemical characteristics and biological; characteristics. This revealed that the design of the cover was suitable to achieve the objectives of stability, water shedding, storage - release, and provision of a sustrate for vegetative growth. Over most of the surface of the heap, the construction of the covers, drains and erosion prevention structures was in accordance with design specifications. However , several small and localized bare patcheson the upper surface of White's Heap coincide with a reduced cover thickness, which is likely to have been due to poor construction in those patches. The construction of covers on minewastes is dependent on an adequate source of material meeting design specifications. Fro the limited examination, it appears that there was shortage of material for each of the three zones - a lower impervious clay layer, the moisture storage - release layer and the upper erosion - resistant layer for vegetative
growth. An indication of this was the upper layers in some areas were observed to be thinner than specified. This shortage of suitable material has been responsible for some of the changes observed ten years after emplacement. Physical and geotechnical testing indicated that the cover materials no longer meet the original specifications. In particular, the permeability at the 8 locations was found to be greater than specified by up to several orders of magnitude. The higher permeability may explain the higher observed rainfall infiltration and moisture content of the waste rock. This increased permeability appears to be due to a combination of biological and physical processes - galleries formed by termites and ants and an extensive system of shrinkage/desiccation cracks formed by the development of polygonal blocky structure involving the entire lower clay layer. The desiccation cracks may fill with coarser illuviated materials and form a conduit through which roots access the underlying waste rock. Measurements were made of oxygen flux into the heap as cover layers were excavated in the pits. They indicated that the full cover currently reduces the oxygen flux to 20-23 per cent of that into bare waste rock and that this reduction seems to be proportional to the cover thickness. It was also found that the oxygen flux into the cover is about four times higher at the end of the dry season than at the end of the wet season and that the difference is due primarily to the difference in moisture content of the cover.
IMPACTS FROM THE WASTE ROCK STOCKPILES AT ERA RANGER MINE AND THEIR REHABILITATION Ian Hollingsworth EWL Sciences, PO BOX 39443 Winnellie, NT 0821. ABSTRACT
Background The Ranger Uranium Mine (RUIVI) is located within the 78 km^ Ranger Project Area (RPA), 250 km east of Darwin, in the Alligator Rivers Region of the Northern Territory. The mine is operated by Energy Resources of Australia (ERA). The project area is surrounded by World-Heritage-listed Kakadu National Park (KNP). Ranger is an unconformity related deposit with mineralization occurring mainly as uraninite. The Ranger project came into full production on of October 1981, with the commissioning phase successfully completed. Mining is due to cease in 2008 and decommissioning to begin in 2014. The environmental requirements for mine closure at the Ranger Uranium Mine specify that the mine landscape must be rehabilitated such that the final landform and environmental impacts from it are compatible with the environmental values in the surrounding Kakadu National Park. Waste Rock Stockpiles The current mine plan estimates at the end of mining in 2008 there will be 60,372,000 loose cubic metres of waste rock (<0.02% UaOs) in stockpiles adjacent to two mined out pits (Pit #1 and Pit #3). The waste rock is comprised of chloritised schists in the mine sequence overlying dolomite in the lower mine sequence. A weathered zone of kaolinised mine sequence rocks extends to a depth of approximately 40 m. Our understanding of the chemistry of the seepage from waste rock is derived from operational water quality monitoring and limited core leaching studies of a range of Pit #1 and Pit #3 waste rock types. The dominant ions in leachate are magnesium and sulfate with trace levels of manganese, uranium, and lead produced from weathering of chlorite, secondary uranium minerals and sulfides. Testing has confirmed the generally non-acid producing nature of the waste rock. However, water quality monitoring has identified initial low pH and high U concentration in seepage emanating from stockpiles of freshly placed Pit#3 waste rock.
Modelling of sulfate evolution from seepage expression in Pit #1 materials indicates a peak in solute concentration occurs within six to ten years of placement. Further modelling needs to describe the seepage expression from Pit #3 waste rock. Stockpile Rehabilitation A low relief landscape in context with the surrounding area will be constructed from the waste material. The main rehabilitation operation will involve placement of approximately 59,000,000 loose cubic metres of waste rock over deep tailings deposits in the pits. The placement of waste materials in the final landform will be based on geochemical characterisation of the waste rock types and a strategy of containing mineralised or potentially acid forming material low in the pits. ERA is applying a landform design approach based on natural analogues in the local landscape. The aim is to ensure that the final mine landform supports similar surface and near-surface environmental processes as the natural landscape. A substantial part of the environmental evaluation of landform design is based on erosion and landform evolution modelling. However, ERA is developing methods to assess design options in terms of ecosystem support and seepage impacts. A draft landform design has been created based on the 2004 life of mine plan, and evaluated using a digital elevation model to highlight areas where the design did not meet the specification. Rehabilitation will be a challenge. The scale of the planned backfill operation at Ranger is unprecedented. Groundwater impacts from backfill and waste rock landforms are yet to be clearly elucidated. Successful rehabilitation of the waste rock stockpiles will require an integration of landscape sciences with geochemistry and engineered solutions to meet high expectations in a world heritage listed landscape.
The Effects of Weathering and Diagenetic Processes on the Geochemical Stability of Uranium Mill Tailings Greg Sinclair^ Graham Taylor^ and Paul Brown^ 1 2 3
Rio Tinto Technical Services, 1 Research Avenue, Bundoora, VIC 3083, Australia PO Box 43, Stirling, SA 5152, Australia Australian Sustainable Industry Research Centre, Building 4W, Gippsland Campus, Monash University, Churchill, VIC 3842, Australia
Uranium mill tailings from the Ranger mine, located in the Alligator Rivers Region of the Northern Territory, Australia, were examined to assess the effects of weathering and diagenesis on their long-term geochemical stability. Run of mill uranium tailings are a complex heterogeneous mixture of lithogenic (primary gangue minerals and weathering products) and secondary (components that form during milling) minerals, residual process chemicals and biogenic (products of biological activity) phases. Following transfer to the tailings storage facility, post depositional reactions alter the mineralogical and hydrochemical characteristics of the tailings solids and pore waters in accordance with weathering and diagenetic processes. In the present study, a detailed examination of tailings cores and pore waters, kinetic column test work and geochemical modelling was combined with results from earlier studies to examine the key processes governing the geochemical stability of the Ranger tailings. Conclusions drawn from the work clearly demonstrates that the solid state speciation and mobility of metals and radionuclides in the tailings pile are governed by the processes of oxidative dissolution of sulfide minerals, weathering of phyllosilicates and organic matter diagenesis. The processes are spatially dependent, evolve over time and are influenced by the following key factors: • • • •
Tailings water content or degree of saturation; The nature and content of organic matter in the tailings; Redox potential of the tailings solid-pore water interface; and The specific reactivity of precursor minerals (primary/secondary) from the milling process and pore water solutes.
Combined, these processes lead to the formation of authigenic minerals, which control the solubility of pore water constituents. These mechanisms will also have a profound impact on the long-term geochemical stability of the tailings pile and, as such, will need to be taken into account in the design, management and closure of the final tailings repositories at the Ranger site.
ENVIRONMENTAL REVIEW OF THE MARY KATHLEEN AND RADIUM HILL URANIUM MINE SITES - REHABILITATION SUCCESS IN A MODERN WORLD? B.G. Lottermoser School of Earth Sciences, James Cook University, PO Box 6811, Cairns, Qld 4870 P.M. Ashley Earth Sciences, University of New England, Armidale, NSW 2351
Recent research on rehabilitated uranium mine sites located in wet climates has revealed the varied success of the applied rehabilitation efforts. In comparison, there is little knowledge of the status and environmental impacts of rehabilitated uranium mines in dry climates. Mary Kathleen and Radium Hill represent first generation Australian uranium mines, which are located in semi-arid regions. The aim of this communication is to report on the current environmental status and potential hazards of these former uranium mine sites. Mary Kathleen Mary Kathleen, in northwest Queensland, operated from 1956-1963 and again from 19761982. It is situated in a region with a semi-arid climate, high evaporation rate and a summer rainfall maximum causing ephemeral flooding and sediment transport. The open scrub and woodland has been used for low density cattle grazing. Rehabilitation of the Mary Kathleen open pit mine, mill and tailings repository sites occurred between 1982-1985. This involved the dry capping of the tailings repository with rolled soil/loam/clay and overlying unmineralised waste rock, disposal of contaminated waste into the bottom of the pit and allowing its subsequent flooding, and the partial to complete capping of many of the waste rock dumps. The area was returned to cattle grazing and public access. In the 1980s, it was predicted (a) that the tailings porewaters would not infiltrate into the local aquifer, (b) that there would be little chance of acid mine drainage and of metal and radionuclide mobility from the waste rock dumps and tailings repository, and (c) that seepage water quality would not pose a problem for human or stock health, despite sulphate contamination of the groundwater being the main long term environmental impact. Mineralised rock at Mary Kathleen (ore and waste rock) is dominated by a metasomatic calcsilicate assemblage, with minor amounts of sulphide minerals, rare earth minerals and uraninite. Although calcite is commonly present, there is oxidation of sufficient sulphides to generate acid conditions in the pit lake, the upper part of the tailings dam and seepage from the latter. Pit walls are locally encrusted with transient soluble sulphates and there is evident mobility of Fe, Ca, Cu, U and REE. Pit water is slightly acid, Ca-S04-rich and exceeds recreational water quality guideline values for TDS, Fe, Mn, SO4, Cu and Ni, and livestock water guidelines for Cu and U. Seepage water from the tailings dam is slightly acid (pH 5.5), metal- and S04-rich, and radioactive. There is rapid precipitation of Fe oxyhydroxides, with absorbed U, REE, Y, As and radionuclides. Further downstream, surface and groundwaters become near-neutral, but increase in salinity such that there is widespread precipitation of sulphates. Although release of U and other metal/metalloid contaminants from the tailings dam is insignificant, concentrations of TDS, U and SO4 in surface waters exceed livestock water guidelines. Waste rock dumps at Mary Kathleen have steep sides and are not stable long-term landforms. They are subject to physical and chemical processes that can contribute to stream and soil loadings of U and other metal/metalloid contaminants. Where covered by benign soil/rock, plant growth has occurred, but sulphide oxidation processes has restricted plant colonisation in uncovered or disturbed zones. Many plant species at Mary Kathleen growing in the mine void, on waste dumps and contaminated soil display uptake of U and other metal/metalloids at levels of 10-100 x those on background sites.
At Mary Kathleen 20 years after rehabilitation, it is evident that some measures have been quite successful in reducing dispersion of U and related elements into the surrounding environment (e.g. the tailings dam cover). However, there is still significant physical and chemical mobility, including transfer into plants. Radiation levels in the open pit average 5.65 mSv year"^ and are less on the waste dumps. Consequently, casual visitation to the site is not considered a hazard. Radium Hill The Radium Hill mine, in northeastern South Australia, operated from 1954-1961. It is in semiarid grazing land, drier and of lower relief than at Mary Kathleen. At Radium Hill, underground mining occurred with processing of ore on site, resulting in the generation of mill tailings dams and numerous dumps of waste rock material. Some of the latter was crushed and used for local construction purposes, including buildings, roads and railway ballast, despite it exhibiting low-level radioactivity. After mining ceased, most infrastructure was demolished and removed, but there was no remediation of the waste dumps and tailings repositories. About 1980, capping of the main tailings dam was performed and this action lessened the effects of wind and water erosion. The region is currently used for low density grazing and has low human visitation. Mineralised rock at Radium Hill comprises quartzofeldspathic gneiss, schist, amphibolite and pegmatite, with the ore minerals (davidite-brannerite-uraninite) being part of a refractory FeTi-U-REE oxide assemblage. Sulphide minerals are very sparse and together with the dry climate, there is little evidence for chemical processes mobilising U and related elements from tailings and waste rock dumps. Physical dispersion processes have been significant at Radium Hill, with wind dispersion of tailings fines occurring in the district prior to capping of the main tailings repository, and water erosion of both the tailings material and waste rock dumps. Local soils have been impacted through physical dispersion by increased geochemical (U, Th, REE, V, Cr) and radiochemical loadings. Plants growing on impacted soils and waste rock dumps display biological uptake of U and other lithophile elements. Capped tailings repositories are unstable landforms and since 1980 have been subject to rill erosion, exposing significantly radioactive tailings. At Radium Hill, rehabilitation efforts have been restricted to capping of tailings, but following a 20 year period of prior extensive wind dispersal of exposed tailings that has impacted local soils. Physical dispersion continues and it is evident that the capped tailings repositories will degrade in time, causing increased erosional dispersal unless further remediation measures are implemented. However, radiation doses at Radium Hill are low, except in the immediate vicinity of exposed tailings. Visitors to the site will not be exposed to excessive radiation levels. Conclusions The standards of rehabilitation of the Radium Hill and Mary Kathleen mine sites were basic compared by today's criteria. At Mary Kathleen, the physical erosion and chemical leaching of waste rock repositories and the leaching of the tailings repository are the dominant pathways of contaminants into surrounding environments. At Radium Hill, physical erosion of waste repositories is of on-going concern. Both uranium mine sites require monitoring and additional rehabilitation measures. Acknowledgements Support was given by the Australian Research Council, the Australian Institute of Nuclear Science and Engineering, the Australasian Institute of Mining and Metallurgy Gold 88 Endowment Fund, James Cook University, and the Queensland Department of Mines and Energy. M Costelloe, N Beresford-Smith and Alistair Crooks (PIRSA) are thanked for contributing to various aspects of this research.
Impacts of the Acid In-situ Leach Uranium Mining Process Graham F Taylor, Vic Farrington, Peter Woods, Robert Ring and Robert Molloy In response to claims that acid in-situ leaching (ISL) mining of uranium in South Australia and disposal of wastes will contaminate groundwaters, the State Government requested the EPA to conduct an indeo pendent review of the environmental impacts of the mining process. CSIRO Land and Water together with Parsons Binckerhoff and ANSTO conducted the review. The review consisted of visits to both the Beverley and Honeymoon operations, a study of company and govemment documents, literature review, consultation with the community including a public meeting and receipt of written submissions, preparation of a background document and liaison with the Steering Committee. The Review document was submitted to the EPA in June 2004. During the period of the review, only the Beverley mine was operational with Honeymoon on a care and maintenance basis. Many of the observations and conclusions, although generally applicable, are derived from Beverley. Overall, the process of ISL mining has considerably less impact than other conventional mining techniques. There is no requirement for tailings storage facilities or waste rock dumps and by comparison with other mines, the surface imprint is relatively small. Solid wastes are disposed of in HDPE-lined pits with less bulky low-level radioactive waste being disposed of in 205L drums, stacked two high around the perimeter of the pits. Hydrology and hydrogeochemistry are the most contentious issues. The mineralization occurs in paleoaquifers constrained by aquicludes.Grounwater within the mineralized paleoaquifers is saline (EC = 10-30 mS/cm), near-neutral pH (7-8), radioactive and reducing. The nature of the microbial populations is presently unknown, but are presumed to be site-specific. The groundwater has no apparent beneficial use other than by the mining industry. Uranium is extracted from the aquifers by injecting groundwater modified with sulfuric acid to a pH of approx 2 and an oxidant (hydrogen peroxide or sodium chlorate). The uranium in the pregnant solutions is precipitated using site-specific techniques, and the lixiviant recharged and reinjected. At Beverley the lixiviant is recycledSO - 80 times. Bleed solutions, waste solutions from uranium recovery, plant washdown, and bleed streams from reverse osmosis plants are collected in HDPE lined evaporation/holding ponds prior to disposal into the aquifers via disposal wells. These liquid wastes are saline (EC =10-100 mS/cm), acid (pH = 2 -4), oxidizing and have higher levels of uranium and radium than the original groundwaters. International experience and limited data collected by Heathgate Resources indicate that natural attenuation will result in the contaminated water chemistry retuming to pre-mining conditions over several years to decades.
The more conventional methods of waste water disposal would involve construction of much larger evaporation ponds thus increasing the surface imprint, increasing the risk of surface contamination and necessitating disposal of radioactive evaporites. This was not considered to be environmentally friendly. There is a pattern of monitoring bores installed to provide information on the hydrogeochemistry of the various aquifers, leaks and spillages from all surface installations and chemistry of the re-injection water. These show that there has been no vertical leakages into other aquifers or migration away from the well field. In conclusion, acid in-situ leaching of uranium and associated disposal of wastes in South Australia is more cost-effective and environmentally responsible than any other suggested alternative technique.