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GoldOreProcessing ProjectDevelopmentandOperations SecondEdition
Editedby MikeD.Adams FuguePteLtd,Singapore
Elsevier
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Notices
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ListofContributors S.Acar,AcarConsultingLLC,HighlandsRanch,CO,USA
M.D.Adams,FuguePteLtd,Singapore
N.Ahern,AuTecInnovativeExtractiveSolutionsLtd., Vancouver,BC,Canada
A.U.Akcil,SuleymanDemirelUniversity,Isparta,Turkey
C.Aldrich,WesternAustralianSchoolofMines,Perth, Australia
J.E.Angove,AFTMetallurgy,NorthBeach,WA, Australia
E.Asselin,TheUniversityofBritishColumbia, Vancouver,BC,Canada
M.G.Aylmore,JohndeLaeterCentre,FacultyofScience andEngineering,CurtinUniversity,Perth,WA, Australia
J.Y.Baron,BarrickGoldstrikeMinesInc.,Carlin,NV, USA
P.Bateman ,InternationalCyanideManagementInstitute, Washington,DC,USA
G.Beale,Schlumberger,Denver,CO,USA
M.M.Botz,ElbowCreekEngineering,Sheridan,WY, USA
P.Breuer,CSIRO,Perth,WA,Australia
N.Briggs,SedgmanLimited,Perth,WA,Australia
A.R.G.Brown,AllanRGBrown&AssociatesPtyLtd, Booragoon,WA,Australia
A.Charitos,OutotecGmbH&Co.KG,Oberursel, Germany
Y.Choi,BarrickGoldCorporation,Toronto,ON,Canada
S.L.Chryssoulis,Amtel,London,ON,Canada
A.P.Cole,BarrickGoldstrikeMinesInc.,Elko,NV,USA
M.Costello,PreviouslyLycopodiumLtd.,Perth,WA, Australia
F.K.Crundwell,CMSolutions(Pty)Ltd,Johannesburg, SouthAfrica
G.Deschênes,BBAInc.,Toronto,ON,Canada
X.Díaz,UniversityofUtah,SaltLakeCity,UT,USA, EscuelaPolitécnicaNacional,Quito,Ecuador
D.Donato,DonatoEnvironmentalServices,Adelaide, Australia
D.B.Dreisinger,UniversityofBritishColumbia, Vancouver,BC,Canada
R.Dunne,WesternAustralianSchoolofMines,Curtin University(GoldTechnologyGroup),Perth,WA, Australia
S.Ellis,Perth,WA,Australia
C.J.Ferron,HydroProcConsultants,Peterborough,ON, Canada
S.Flatman,PreviouslyAngloGoldAshanti,Ergo Operation,Brakpan,SouthAfrica
C.A.Fleming,SGSMinerals,Lakefield,ON,Canada
M.Fullam,FLSmidthLtd,KnelsonTechnologies, Langley,BC,Canada
A.Götz,FraserAlexander,Boksburg,SouthAfrica
S.Gray,GekkoSystemsPtyLtd,Ballarat,VIC,Australia
B.Green,Retired(previouslyMintek,Randburg,South Africa)
N.Greenwald,InternationalCyanideManagement Institute,Washington,DC,USA
Y.Gu,YingshengTechnology,Darra,Queensland, Australia
J.Güntner,OutotecGmbH&Co.KG,Oberursel, Germany
F.Habashi,DepartmentofMining,Metallurgical,and MaterialsEngineering,LavalUniversity,QuébecCity, QC,Canada
J.Hammerschmidt,OutotecGmbH&Co.KG,Oberursel, Germany
R.J.Holmes,CSIROMineralResources,Melbourne,VIC, Australia
D.G.Hulbert,Retired(previouslyMintek,Randburg, SouthAfrica)
x ListofContributors
M.Jeffrey,Newmont,Denver,CO,USA
E.Johanson,LycopodiumEngineeringPtyLtd.,Perth, WA,Australia
J.Johnson,WesTechEngineering,Inc.,SaltLakeCity, UT,USA
D.W.Kappes,Kappes,Cassiday&Associates,Reno,NV, USA
B.Kerstiens ,OutotecGmbH&Co.KG,Oberursel, Germany
M.Kotze,Lanxess,SouthAfrica(previouslyMintek, Randburg,SouthAfrica)
G.Kyriakakis,ExtractiveResourcesLLC,Townville,SC, USA
H.Lacy,MWHGlobal,Perth,WA,Australia
G.Lane,AusencoLimited,Brisbane,QLD,Australia
G.T.Lapidus,UniversidadAutónomaMetropolitana, Iztapalapa,Mexico
A.Laplante,Metallurgist(1953 2006)
D.Lunt,StirlingProcessEngineeringLimited,Lincoln, UK
J.Mackenzie,MurdochMackenzieMetallurgy,Perth, Australia
T.J.Manning,Kappes,Cassiday&Associates,Reno,NV, USA
M.L.McCaslin,WesTechEngineering,Inc.,SaltLake City,UT,USA
J.McMullen,J.McMullen&Associates(previously BarrickGoldCorporation),Toronto,ON,Canada
P.Messenger,AusencoLimited,Brisbane,QLD,Australia
M.Millard,Metallurgist(1951 2007)
J.D.Miller,UniversityofUtah,SaltLakeCity,UT,USA
P.Miller,SulphideResourceProcessingPtyLtd,Hillarys, WA,Australia
J.Mitchell,PreviouslyAngloGoldAshanti,ErgoOperation,Brakpan,SouthAfrica
M.B.Mooiman,FranklinPierceUniversity,Manchester, NH,USA
J.B.Mosher,FreeportMcMoRanInc.,Phoenix,AZ,USA
T.I.Mudder,TimesLtd.,Sheridan,WY,USA
A.Muir,PreviouslyAngloGoldAshanti,ErgoOperation, Brakpan,SouthAfrica
J.Muller,OnkaparingaMining&MetallurgyPtyLtd, Perth,WA,Australia
N.D.Overdevest,DonatoEnvironmentalServices, Adelaide,Australia
M.S.Pearson,AutoclaveTechnologyGroup,HatchLtd, Mississauga,ON,Canada
M.Reuter,HelmholtzInstituteFreibergforResource Technology,Freiberg,Germany
D.Rogers,LycopodiumEngineeringPtyLtd.,Perth,WA, Australia
P.Rohner,CoreResources,Brisbane,Australia
A.Ryan,LycopodiumEngineeringPtyLtd.,Perth,WA, Australia
C.Sabbagha,PreviouslyAngloGoldAshanti,Ergo Operation,Brakpan,SouthAfrica
B.Sceresini,AustralianMining,Perth,WA,Australia
R.Shaw,GoldcorpInc.,Vancouver,BC,Canada
L.Simpson,ElemetalRe fining,Jackson,OH,USA
H.Smith,KWAKenwaltAustralia,Perth,WA,Australia
W.P.Staunton,WesternAustralianSchoolofMines, CurtinUniversity,Perth,WA,Australia
D.Stephenson,AusencoLimited,Brisbane,QLD,Australia
K.G.Thomas,KenThomas&AssociatesInc.,Oakville, ON,Canada
A.vanSchaik,MARAS,MaterialRecyclingand Sustainability,DenHaag,TheNetherlands
M.Virnig,BASF(previouslyCognisCorporation), Tucson,AZ,USA
R.Walton,RayWaltonConsultingInc.,Aurora,ON, Canada
R.-Y.Wan,Metallurgist(1932 2009)
J.Wates,FraserAlexander,Boksburg,SouthAfrica
B.Watson,ConsepPty,Perth,WA,Australia
T.Weeks,AquilaVenturesPtyLtd,Perth,WA,Australia
D.Williams,GolderAssociates,Perth,WA,Australia
J.Zhou,JoeZhouMineralogyLtd,Peterborough,Ontario, Canada
Foreword The fi rsteditionof AdvancesinGoldOreProcessing arrivedatatimewhenthegoldpricehadincreasedfromlowvalues ofaroundUS$270/troyozin2001toanaverageof$444/troyozin2005.Sincethattime,thepricehassoared,reachingan averageof$1669/troyozin2012beforesofteningtothe2015levelsof$1100/troyoz.Thisremarkableperformancehas ledtoaresurgenceinprimarygoldproductionworldwide,aswellasrenewedinterestinexploration,research,development,andtechnologicalinnovationthroughouttheindustry.However,thishasbeentemperedtoasignificantextentbya near-threefoldincreaseincashoperatingcostsfrom$269/troyozin2005to$750/troyozin2014andsimilarincreased ratiosincapitalcostsfornew(Green field)andexpansionproductioncapacity.Capitalcostintensityfornewgoldproductioncapacitynowrangesfrom$1500to$4500/annualtroyozproduced,dependingontheorefeedgrade,processing method,byproducts,andorecomplexity.Thisleavesmuchoftheindustryfacingsignificantchallengestoprofitabilityfor existingoperationsandforaddingnewcapacity.Akeypartofthisstoryisthataverageoregradeshavedecreased significantlyfromabout1.8g/tin2005toapproximately1.3g/tin2014.Oredepositsarebeingdevelopedwith increasinglycomplexmineralogyandmetallurgicalpropertiesasthemoreeasilytreatableresourcesaredepleted.Thisnot onlyaddstothecostofextraction,bothcapitalandoperatingbutalsoincreasesthedevelopmenttimeforprojectsandadds technicalrisk.
Theglobalgoldproductionprofilewasverydifferentin2005.SouthAfricawasthetopproducerwith300metrictons, followedbyAustralia,UnitedStates,China,andPeru.Totalglobalgoldproductionincreasedfromalmost2520metrictons in2005toover3100metrictonsin2014;however,Chinaincreaseditsproductiontotakethetopposition,followedby Australia,Russia,UnitedStates,andPeru.MuchofChina’sproductioncomesfromsmall,distributeddeposits,using conventionaltechnologythatcanbeappliedeffectivelyatasmallscale forexample,gravityconcentration, flotation, amalgamation,cyanidation,anddirectsmelting/processingofconcentrates.Inparallelwiththis,productionfrommanyofthe majorproducingminesdroppedoffsignificantly,suchasYanacocha,Peru(NewmontGold),andDriefontein,SouthAfrica (GoldFields).Thisservestounderscorethedramaticchangesthathaveoccurredwithintheindustryoverthepast10years.
Turningtotheprocessingaspectsoftheindustry,goldoreprocessingisdominatedbythecyanidationprocess.Since theinceptionoftheprocessinthelate1800s,cyanidehasbeenusedwidelytoextractgoldbecauseofitsrelativelylow cost,greateffectivenessforgoldandsilverdissolution,selectivityforgoldandsilveroverothermetals,aswellasrelative easeandefficiencyofmetalrecoveryfromsolution.Also,despitesomeconcernsoverthetoxicityofcyanide,itcanbe appliedwithlittlerisktohumanhealthandtheenvironment.Theoxidantmostcommonlyusedincyanideleachingis oxygen,usuallysuppliedfromair,whichcontributestotheattractivenessoftheprocess.
Sincethemid-1970s,alternativeleachingreagentschemestocyanidehavebeeninvestigatedforanyorcombinationsof thefollowingreasons:
l Environmentalpressures,andinsomecasesrestrictionsorlimitations,maymaketheapplicationofcyanidedif ficultin certainlocations;
l Somealternativereagentschemesprovidefastergold(and/orsilver)leachingkinetics;
l Severalcanbeappliedinacidicmedia,whichmaybemoresuitableforrefractoryoretreatment,and
l Somearemoreselectivethancyanideforgoldandsilveroverothermetals,suchascopperandzinc.
Someofthemoreimportantreagentsystemsthathavebeeninvestigated(orreinvestigated)arechlorine chloride, thiosulfate,thiocyanate,thiourea,ammonia,ammonia cyanide,alkalinesulfide,andotherhalidecombinations.Aside fromtheadvantageslistedhere,allofthealternativereagentschemeshavedisadvantagescomparedwithcyanideand,at thistime,noneappeartobewidelyapplicable,atleastnotwithoutfurthersignificantadvancesinthetechnology.However, thiosulfatehasemergedasthefrontrunnerofthealternativeschemesfornicheapplications,andBarrickGoldhas
advancedandimplementedthecommercialdevelopmentofthiosulfatetechnologytotreatcarbonaceous ‘preg-robbing’ materialatGoldstrikeinNevada.Carbonaceous,preg-robbingoresaretheprimarypotentialapplicationforthisemerging technology.
Theapplicationofultrafinegrindingtotreatoresandconcentratesbyliberatinggoldandsilvervaluesfromsul fideshas gainedmomentumfollowingthedevelopmentofefficient fine-millingequipment,includingtheXstrataIsaMill,theMetso SMDDetritor,andtheMetprotechmillasoptions.Thesedevelopmentspavedthewayformoreefficientgrindingdownto finersizes,around80%passing10 15 mmandbelow hence,theterm “ultrafine” grinding.Also,furtherdevelopment oftheMetsoVertimillfollowingmanysuccessfultertiarygrindingandregrindinginstallationshasledtoitsconsideration forultrafinegrindingapplications(downtoabout80%lessthan15 mm).Other finegrindingmillsareindevelopment.The abilitytoeconomicallygrindtosuch finesizespresentedtheopportunitytoliberatepreciousmetalsfromrefractorysulfi de oresandconcentrateswithouttheneedformorecostlyoxidativetreatment,suchasroasting,pressureoxidation,and biologicaloxidation.Whilenotthe firsttouseultrafinegrindingtotreatconcentrates,theapplicationatKalgoorlie ConsolidatedGoldMines(KCGM,WesternAustralia)in2001totreatrefractorysulfidegoldoretosupplementtheroaster capacityopenedupthetechnologytotheindustry.Theultra fi nemilledproductwascyanideleached,achievingagold recoveryofover90%.Thiswasasignifi cantdevelopmentasitwasthe firstmajorcommercialapplicationtoavoidthe needforoxidativepretreatment.UltrafinegrindinghassubsequentlybeeninstalledatKumtor(Kyrgyzstan)in2005,Pogo (Alaska)in2006,andLakeCowal(Australia)in2006.Theproductgrindsizeswere80%lessthan12 mm,80%lessthan 10 mm,and80%lessthan15 mm,respectively,fortheseoperations.In2015,manyotheroperationsareconsideringor usingasimilarprocessingapproach,emphasizingtheneedforcontinuedresearchanddevelopmentinthisarea.
Duringthepast10yearsorso,signi ficantinnovationshaveoccurredinprocessmineralogy.Attheforefrontofthis workhasbeenthedevelopmentofautomatedscanningelectronmicroscopytechniques(e.g.,QEMSCAN,providedby FEI,andtheMineralLiberationAnalyzer,developedbytheJKInstituteofTechnology,Australia).Thesetechniquesare nowwellknowntomostintheindustry,andthesignificanceofbeingabletoperformaccurate,quantitative,mineralogical analysisonrepresentativesamplesofore,intermediateprocessingproducts,andresiduesfromprojectsandoperations cannotbeoverstated.Theindividualmineralgrainidenti ficationandquanti fication,size-by-sizeanalysis,andmineral liberation/lockinganalysesthatcanbegeneratedhaverevolutionizedtheapproachtodesignandoptimizationofmineral andmetalextractionworldwide.Otheradvancedmineralogicaltechniquesarealsonowavailablethatprovideimportant diagnosticsforgoldandsilverrecoveryoptimization,troubleshooting,andprocessdesign.
Otherkeyareasofprocessdevelopmentsthatarecoveredwithinthisvolumeincludethefollowing:
l Centrifugalgravityconcentrationequipment,withincreasingvolumetreatmentrates
l Intensiveleachingequipmentandsystemstomosteffectivelytreathigh-gradegravityand flotationconcentrates
l Enhancedheap-leachingtechnology,especiallycoldclimateanddryclimateoperationsandthepotentialuseof high-pressuregrindingrollstoprepareheapleachfeedmaterial
l Refractoryoreprocessing,includingimprovedpressureoxidationandroastingtechnology
l Continuedandimprovedapplicationofbiologicaloxidationtotreat flotationconcentrates
l Gold copperandcopper goldoretreatment,includingtheuseofsulfi dization,acidi fication,recycle,andthickening (SART)technologyandeffectivecontrolofcyanidespeciation
Inparallelwiththeseprocessingdevelopments,amajoreffortwithrespecttothegoldextractionindustrywasthe publicationoftheInternationalCyanideManagementCode(2002),towhichmostofthemajorgoldandsilverproducers thatusecyanidehavecommittedtofollow.ThiscodewasdevelopedbytheInternationalCyanideManagementInstitute (ICMI),anonpro fitorganizationsetupundertheUnitedNationsEnvironmentProgram(UNEP)andtheInternational CouncilonMetalsandtheEnvironment(ICME).Allofthisactivityrepresentedsignifi cantlyincreasedemphasisonthe controlandtreatmentofgoldextractionbyproductsandeffluents,whichshouldbeconsideredasanintegralpartofgold extractionprocesses.Detoxificationofcyanidesolutionsandslurriesisanimportantaspectofgoldoreprocessingglobally andtherearemanyalternativesfordetoxi ficationofcyanide-containingsolutions.Whereapplicable,thepreferredmethod istoallowthecyanideconcentrationtodecaynaturallythroughthecarbon-in-pulp/carbon-in-leach(CIP/CIL)circuittothe pointatwhichitreacheslevelsacceptablefordischargetothetailingscontainmentfacility.Therearemanyoperationsthat areabletomeetstrictdischargelimitstotailingsfacilitieswithouttheneedforanyformofcyanidedestructionotherthan naturaldegradationovertime.However,theseoperationscarefullymanagecyanideconcentrationsdowntheleachingand CIP/CILcircuit,aswellaswashratiosinthickeners,usingre-circulated,reclaimedorfreshwaterinthecircuit.The cyanidedegradesfurtherovertimeinthetailingsfacility,ultimatelytonon-toxicproducts,andtheunderstandingofsuch degradationprocesseshasimprovedsignifi cantlyoverthepast25 30years,includingnaturaldegradationoffree,weak acid-dissociable(WAD)andtotalcyanidespecies,thiocyanate,andcyanate.Theuseoftailingsthickenersand,where
necessary,tailings filtrationcanassistwithrecoveringandrecyclingcyanide-bearingsolution.Allofthesepracticeshelpto reducecyanidenaturallywithintheoverallextractioncircuit.
Wheretheabovemethodsarenotsuffi cienttomeettheCyanideCodeguidelines(e.g., 50mg/LWADcyanide dischargetotailingsstoragefacilities)and/orregulatoryenvironmentalrequirements,othermethodsofdetoxifi cationmust beused,withtheexceptionofsomeoperationsusingthehypersalineprocesswaterintheEasternGoldfieldsofWestern Australia,wherenaturalprocessesprovideaCode-certi fiableprotectivemechanism.Afteralmost30yearsofapplicationat operationsthroughouttheworld,theuseofsulfurdioxide airhasbecomethepreferredandmostcost-effectivemethodof cyanidedestructionwherenaturaldegradationisnotadequate.Manyothermethodshavebeentestedandused commercially;forexample,hydrogenperoxideandCaro’sacid(hydrogenperoxideandsulfuricacid)havebothbeenused successfullyatavarietyofoperationsinvariousconfigurations.
Waterconservationis,andwillcontinuetobe,anareaforinnovationandthisishighlightedinthissecondedition. Dry-stackedtailing,suchasusedatLaCoipa(Chile),hasadditionalbenefitsofcyaniderecyclingandreducedenvironmentalconcernsforgroundwatercontamination.UseofbrackishandsalinewateriscommonplaceinWesternAustralia andiscurrentlyextendingtoapplicationsinChileandPeru.
Animportantlessonfromallofthemajorinnovationsingoldandsilverextractionisthatinnovationsarerarely “eureka” moments,butrathertheyresultfromasustainedperiodoftesting,investigating,modifying,andimprovinga particulartechnologicalapproachtoaproblem.Inthecaseofcyanidation,carbonadsorption,heapleaching,andrefractory oretreatmentprocesses,thetechnologyhadbeenknown,andversionsofeachprocesshadbeenpatented,testedandtried forseveraldecades.Thosewhosuccessfullycommercializedtheseinnovationslearnedfromthepriorversionsofthe technology,borrowedfromotherbranchesoftheindustry(andinsomecasesfromotherindustries),andimprovedthe applicationofthetechnologywithoftensimplemodi fications.The fi rst-userrecognizedthebenefitoftheemerging technologyovertheincumbentprocess;theywerepersistentandrelentlessintheirpursuitofsuccessfulcommercialization; andinallcasestheyreliedoninnovativeandtenaciousprocessoperators(notnecessarilytheinventororresearcher)to implementthetechnologyeffectively.Successwasnotintuitivelyobviousintheseefforts,andinmostcasestherewere severalfailuresor,atbest,marginaland/orsmallapplicationsofthetechnologythatprecededwidespread commercialization.
Assuch,thissecondeditionisparticularlytimelyandvalued.Theformatusedinthe firsteditionhasbeenretained,but thenumberofchaptershasbeenexpandedtocoverimportantissuessuchasgeometallurgicaldevelopments,CyanideCode compliance,alternativelixiviants,watermanagement,arsenicandmercurymanagement,goldrecoveryfrome-waste,and emergingandtransformationalgoldprocessingtechnologies asignificantenhancementandupdatetotheprevious edition.Thecontributingauthorsrepresentanexcellentglobalcrosssectionofgoldmetallurgists,researchers,developers, andexpertsinrelated fields.MikeD.Adamsistobecongratulatedonbringingtogetherthisvaluablecontributiontothe literatureongoldextractionandprocessing.
JohnO.Marsden,PE Phoenix,Arizona,USA August21,2015
PrefacetoSecondEdition Thissecondeditionof GoldOreProcessing arrivesadecadeafterthe firsteditionwaspublishedin2005andhas establisheditselfasawidespreadreferenceworkinthegoldprocessingandminingindustry.Arevisedandextended editionwasthereforetimely.The55chaptersinthissecondeditionvolumebringtogethermanytechnicalaspectsof relevancetogoldoreprocessing,fromprojectfeasibilitystudystage,throughoperationsstagetotheclosureandrehabilitationstage.Thevariousprocess flowsheetunitoperationsthatmaybeapplicabletoanyparticularoretypearecovered, alongwithnewemergingtrendsandpotentiallytransformationaltechnologies.Inadditiontoupdatesoftheexisting chapters,advancesinseveral fieldshavenecessitatedextensiverewrites,sometimeswithnewauthors.Ontheotherhand, scantdevelopmentsinseveralmatureareasmeantthatrevisionwasnotwarranted,witheditorialcommentsprovidingsome measureofupdate.
Thiseditionincorporates13newchapters,includingsome90contributingauthors,spanningenvironmentalconsiderations,moderninstrumentaltechniques,andemergingtechnologies.Additionaltopicscoveredareasdiverseasthe evaluationandfundingofcapitalprojects,solid liquidseparation,alternativelixiviants,goldrefining,tailingstreatment, andrecyclingofelectronicwasteinthecirculareconomy.Anewchapterongeometallurgyandautomatedmineralogyhas beenincluded.Increasingemphasisonenvironmentalaspectsingoldmininghasresultedinadditionalchapterscovering managementofarsenicandmercury,aswellaswatermanagement.Atthetimeofthe fi rstedition,theInternational CyanideManagementCodewasinitsinfancy afteradecadeofprogress,twonewchaptershavenowbeencontributed, coveringperspectivesfrombothregulatorandauditor.
Existingchaptershavebeenupdatedtoincluderelevantnewprocesses, fl owsheets,technologies,andphilosophies. Examplesandindicativedata,aswellasindustryprofilesforparticulartechnologies,havebeenreviewedandrevisedfor currencyandrelevancy.Somechaptershaveadditionalco-authorsorleadauthors.Sadly, firsteditioncontributorsAndré Laplante,DavidMuir,Rong-YuWan,andMartinMillardhavepassedonintheintervening10yearssincethe firstedition waspublished.
Thisbookshouldbeofuseacrossthegoldindustry,anditishopedthatmetallurgists,geologists,chemists,mining engineers,managers, fi nanciers,operations,projects,andresearchstaffalikewill findthecontentbothusefuland stimulating. MikeD.Adams
PrefacetoFirstEdition Thegold-processingindustryisexperiencingchange.Asfree-millingandoxideoresbecomedepleted,morecomplex polymetallicandrefractoryoresarebeingprocessed,coupledwithincreasingpressureforstricterenvironmental compliance.Recentyearshavealsoseenasteadyreductioninmineralprocessingandmetallurgygraduatesandagradual lossofolderoperatingexperience.Acontributiontodocumentingcurrentandfuturebestpracticeingoldoreprocessing seemstimely.
Thefocusofthisvolumeisonadvancesincurrentgoldplantoperation,fromconceptiontoclosure;eachchapteralso coversrecentinnovationsatthebenchandpilot-scalelevelthatwouldbeexpectedto findcommercialapplicationatsome stage.Coverageofessentialchemistryandengineeringaspectsisincluded.
PartIofthebookfocusesonprojectdevelopment,withanemphasisonthevariousaspectsoffeasibilitystudy managementandtakingthepaththroughcommissioning,safetyandenvironmentalmanagementinoperation,and finally closureofbothplantandtailingsstoragefacility.Withincreasingpressuresontheresourcecompanytoensureminimal socioenvironmentalimpactthroughtheentirelifecycleofthemine,itisimportanttoaimatgettingit “rightthe fi rsttime.”
PartIIcentresontheprocessplant,sequentiallyprobingthegenericgoldprocessing flowsheetforadvances,best practice,andpotentialfuturepracticalinnovations.Thisistheheartofthebook;thereiscoverageofthevariousunit operationsinvolvedwithcomminution,concentration,oxidation,leaching,goldrecovery,anddisposalofresiduesand effl uents.InnovationsdescribedinthecomminutionchapterincludethoseundertakenatFreeport,whichisoneofthe largestgoldmillsintheworld(despitebeingacoppermine).Concentrationofgoldbygravityhasseeninnovationdriven partlybythedevelopmentofnewitemsofequipmentandnovelapplicationwithinthemillingcircuit,suchasisnow commonplaceinareassuchaswesternAustralia.Flotationhassimilarlybeeninfluencedbytheadventof flashandcolumn flotation,aswellastheapplicationofdifferential floatsforcomplexores.
Treatmentofrefractoryoreshasnecessarilybecomeincreasinglyimportant,andthesectioncoveringpressureand bacterialoxidationaswellasroasting(bothoxygenatedand fl uidizedbed)hasparticularrelevancetothemoderngold metallurgist.Whilethesetechnologiescannowbedeemedasestablished,therecentadvancesoutlinedinthebookare clearlybothnovelandpractical.Developmentofmethodsthatincreaserecoverieswhiledecreasingreagentconsumption byminimizingcyanicideformationareclearlyattheforefrontoftheseareasandfurtherdevelopmentiscertain.
Again,intheleachingsection,theemphasisisontreatmentofproblematicoressuchasthosearisingfromoxidation processes.Therehasbeenadriveinrecentyearstowardthedevelopmentofalternativelixiviantsforgold,mainlyasa resultofenvironmentalpressures.Themostlikelycandidatefornicheapplicationisthiosulfateleaching;theamountof recentworkinthisareahaswarrantedinclusionofthistopicasaseparatechapter.Cyanidehasseenpracticalapplication formorethan100yearsnow,andthiswillcontinue,withtheongoingpositiveinitiativesincyanidemanagementsuchas theCyanideCode(whichhasalsowarrantedachapterinitsownright)andtheinherentbenefitsofareagentthat,ina well-designed flowsheet,islowlevelandbiodegradable.
Advancesintherecoveryofgoldfromleachsolutionareagaininfluencedbydevelopmentsinequipmentandreagents. Ongoingimprovementsintherefiningofgoldarealsobeingmade.InnovationssuchastheAngloAmericanCorporation (AAC)pumpcellcontactorandgold-selectiveresin-in-pulp(RIP)havefoundnicheapplicationatafewoperatingplants. Theextentoftheirusewilldependonanumberoffactors,butthetrendtowardpolymetallicandrefractoryoresislikelyto openupnewapplicationsthatmayrequiresomeinnovative flowsheetingifthebase-metalandprecious-metalvaluesare bothtobeeconomicallyrecovered.
Thereisanotherareathathasapositivebearingonthefutureofcyanideingoldprocessing.Theapplicationofcyanide detoxificationorrecoveryprocessesinto flowsheetsisbecomingmuchmoreprevalent.Thismaywellagainreflectan increasingsenseofenvironmentalstewardshipbyresourcecompanies,undoubtedlydrivenbytheneedforthetwoprongs ofpublicandoperatorperceptiontomeetinacommonreality.Anumberofnewtechnologiesfortheeconomicrecovery andrecycleofcyanidefromplanttailingshavenowbeendeveloped,andthismaywellbeakeyelementtotheongoing
responsibleuseofcyanide.Perhapsthemainareawherepublicperceptionhasbeennegativelyinfluencedhasbeenwith tailingsstoragefacilities.Placementofpasteordrytailingsusingtechniquessuchascentrallythickeneddischarge,for example,isaninnovationthataddressesissuesofdamstabilityandwaterrecovery,whileresultinginamore natural-lookinglandformonclosure.
PartIIIassessestheprinciplesanddevelopmentsoutlinedinthe firsttwoparts,bymeansoffocusedcasestudiesof typical flowsheetsforthetwomajortypesofproblematicgoldoresthatarebeingencountered polymetallicand refractoryores.Adistinctionismadeoneconomicgroundsbetweengold copperoresandcopper goldores;process flowsheetsandissuesdifferbetweenthetwo.Orescontaininghighsilver,base-metalandplatinum-groupmetal(PGM) gradeswillcontinuetobemoreofteninresourcecompanies’ fieldsofviewasthequestforpaydirtcontinues.Asorebodiesbecomemorecomplex,so,too,dotheprocess flowsheets,withanincreasingrelianceonhydrometallurgical treatmentsthatresultinavarietyofproducts,notonlygoldbutalsocopper,nickel,cobalt,silver,PGMs,andsometimes leadandzinc.
Whilerefractorysulfideshavebeenaroundforsometime,anunderstandingisbeinggainedofthesubtlechemistrythat canariseinhigh-pressureautoclavestreatingasometimesextensivemixofdifferentsul fideminerals.Asboththe knowledgebaseandthenumberofapplicationsincrease,sotheriskofapplyingtheseprocessesbecomessmaller.The samecanbesaidofotherproblematicores,suchascarbonaceouspreg-robbing,tellurides,andantimonialores.
Thegeneralprinciplebehindthestructureofthevolumeisthatof flowsheetingbasedonunitoperationsandappliedto amineralogicalclassifi cationofgoldoretypes.Knowledgeofthemineralogyofanorebodyisthekeytounlockingthe wealthcontainedwithin.Theextensivechaptercoveringthisaspectnecessarilydoessothroughprocesseyes; flowsheet definitioncanthenfollowusingthebuildingblockscomposingtheunitoperationsdescribedinthesecondpartofthe volume.
Practicalexperienceisvitaltothesuccessfuldevelopment,operation,andclosureofanyoperation.The42chapters havebeencontributedbyatotalof66authorsandcoauthorswhoareexpertsfromcountriesspanningtheglobeand representexhaustivepracticalknowledgecoveringmanydisciplinesrelevanttogoldprocessing.Withinthechaptersare numeroustidbitsofpracticalpersonalexperience,muchofwhichisasyetunpublished.Thecontentwillbeusefulto operators,engineersandresearchersworldwide.
TheoriginalintentionwastoprovideaselectionofappendicescoveringSIunits,conversionfactors,pulpdensity tables,andthelike.Thereadyavailabilityofthisinformationontheinternethasmadetheirinclusionredundant;however, aperiodictablekindlymadeavailablebyProf.FathiHabashihasbeenincluded.
Thisbookisintendedformineral-processingengineers,metallurgists,processmineralogists,miningengineers, environmentalengineersandconsultants,andresourcecompanymanagers.Itwillbeofinteresttoprofessionalsand studentsalike.
MikeD.Adams
Acknowledgments Thisvolumereflectstheeffortsofabodyofsome90expertindividuals,includingthecorrespondingauthorsandcocontributorsofthe55chapters,whoarethankedfortheirwillingnesstoassistwiththisendeavorandforthehours spenttowardgeneratingthisexhaustiveupdate.Gratitudeisexpressedtothevariouscompaniesthatarerepresentedinthe authorship,fortheirpermissiontoallowtheauthorstotackletheircontributionsand,insomecases,forthesupplyof materialandpermissiontopublishillustrationsandphotographs.Thehardwork,patience,andcooperationinparticularof MarisaLaFleur(EditorialProjectManager),andofAmyShapiro(AcquisitionsEditor,EarthandPlanetarySciences)and MohanapriyanRajendran(ProductionProjectManager),withthismajorundertakingaregratefullyacknowledged.Many thanksarealsoduetoCarolAdamsforherpatiencewiththiscommitmentandforpreparingsomeoftheillustrations.
ListofAcronyms AAC AngloAmericanCorporation
AARL AngloAmericanResearchLaboratories
AAS atomicabsorptionspectroscopy
ABA Acid-baseaccounting
AC activatedcarbon
ACF AuditorCredentialsForm
ADIS AutomatedDigitalImageSystem
AG autogenousgrinding
AGC AshantiGoldfieldsCompany
AI arti ficialintelligence
AI abrasionindex
AIA automatedimage-analysis
AIChE AmericanInstituteofChemicalEngineers
AIME AmericanInstituteofMining,Metallurgical,andPetroleumEngineers
AMD acidmine-drainage
AMICS AdvancedMineralIdentificationandCharacterisationSystem
ANC acidneutralizingcapacity
ANFO ammoniumnitrateandfueloil
APELL AwarenessandPreparednessforEmergenciesatLocalLevel
ARD acidrockdrainage
ASGM artisanalandsmall-scalegoldmining
ASTM AmericanSocietyforTestingandMaterials(nowASTMInternational)
AusIMM AustralasianInstituteofMiningandMetallurgy
AVR Acidi fication-volatilization-regeneration
AWWA AmericanWaterWorksAssociation
BAT bestavailabletechnology
BBMWI Bondball-millworkindex
BDAT best-demonstratedavailabletechnology
BEP bestenvironmentalpractice
BFB bubbling fluidizedbed
BGMI BarrickGoldstrikeMines
BMP bestmanagementpractice
BRMWI Bondrod-millworkindex
BRPS Bright/RarePhaseSearch
BSE back-scatteredelectron
BTAC-CIL bench-topautoclavingfollowedbycarbon-in-leach
BTU BritishThermalUnit
CAP CorrectiveActionPlan
CAPEX capitalexpenditure
CCD counter-currentdecantation
CCTV closed-circuittelevision
CCW counter-currentwash
CE circulareconomy
CEC cationexchangecapacity
CELP CANMETEnhancedLeachProcess
CEN CommitteeforStandardization
CEPA CanadianEnvironmentalProtectionAct
CESL ComincoEngineeringServicesLimited
CFB circulating fluidizedbed
CFD computational fluiddynamics
CIL carbon-in-leach
CIM CanadianInstituteofMining,MetallurgyandPetroleum
CIP carbon-in-pulp
CIS carbon-in-solution
CIS CommonwealthofIndependentStates
CM carbonaceousmatter
CMC carboxy-methylcellulose
COMEX CommodityExchange
CPS controlled-potentialsulfidization
CSTR continuousstirred-tankreactor
CTC carbon-tetrachlorideactivity
CTD centrallythickeneddischarge
CVAAS cold-vapouratomic-absorptionspectroscopy
CVAFS cold-vapouratomic- fluorescencespectrometry
CWI crushingworkindex
DAFR DetailedAuditFindingsReport
DCF discountedcash flow
DCS distributedcontrolsystem
DETA diethylenetriamine
DfD DesignforDisassembly
DfR DesignforRecycling
DfRE DesignforResourceEfficiency
DFS definitivefeasibilitystudy
DNA dionylamine
DO dissolvedoxygen
DOE DepartmentofEnergy
DPO dynamicprocessoptimization
DR directreduction
D-SIMS dynamicsecondary-ionmassspectrometry
DWI dropweightindex
EBRD EuropeanBankforReconstructionandDevelopment
EDS energy-dispersivespectrometry
EDTA ethylenediaminetetraaceticacid
EDX energy-dispersiveX-rayanalysis
EEE electricandelectronicequipment
EFA ecosystemfunctionanalysis
EHS environmental,healthandsafety
EMS engineeredmembraneseparation
ENR enhancednaturalremoval
EoL End-of-Life
EPA EnvironmentalProtectionAgency
EPC engineering,procurementandconstruction
EPCM engineering,procurementandconstructionmanagement
EPMA electron-probemicroanalysis
ESP electrostaticprecipitator
EU EuropeanUnion
EW electrowinning
FAG fullyautogenousgrinding
FAMS fluegasadsorbentmercuryspeciation
FAT factoryacceptancetesting
FB fluidizedbed
FRP fiber-reinforcedplastic
FSTM fluegassorbenttotalmercury
FSU formerSovietUnion
FTIR Fourier-transforminfraredspectroscopy
G&A generalandadministrative
GGFL Gekkogravity-float-leach
GPS globalpositioningsystem
GRG gravity-recoverablegold
GSA globalsensitivityanalysis
HAZOP hazardandoperabilitystudy
HBF horizontal-belt filter
HCR hydrographcontrolledrelease
HDPE high-densitypolyethylene
HMSO HerMajesty’sStationeryOffice
HOPG highlyorganizedpyrolyticgraphite
HPGR high-pressuregrindingrolls
HR-TEM high-resolutiontransmissionelectronmicroscopy
HSGE high-speedgold-electrolysis
HSSE high-speedsilver-electrolysis
ICME InternationalCouncilonMetalsandtheEnvironment
ICMI InternationalCyanideManagementInstitute
ICOLD InternationalCommissiononLargeDams
IEP isoelectricpoint
IFC InternationalFinanceCorporation
ILR InlineLeachReactor
IMM InstituteofMiningandMetallurgy
IoT Internet-of-Things
Io(M)T Internet-of-(Metallurgical)-Things
IPMI InternationalPreciousMetalsInstitute
IPS integratedpressurestrip
IR industrialrelations
IRMA InitiativeforResponsibleMiningAssurance
IRR internalrateofreturn
ISO InternationalStandardsOrganization
KPI keyperformanceindicator
LBMA LondonBullionMarketAssociation
LCA life-cycleassessment
LCD liquidcrystaldiode
LED light-emittingdiode
L-ICP-MS laserinductivelycoupled-plasmamass-spectrometry
LME LondonMetalExchange
LPG liquidpetroleumgas
LSTK lump-sumturnkey
MAC magneticactivatedcarbon
MAC MiningAssociationofCanada
MBT mercaptobenzothiozole
MCC MotorControlCentre
MCL maximumcontaminantlevel
MEBA MercuryExportBanAct
MGS MozleyGravitySeparator
MIBC methylisobutylcarbinol
MIBK methylisobutylketone
MLA MineralLiberationAnalyzer
MLS MozleyLaboratorySeparator
MNR MetallgesellschaftNaturalResources
MPA maximumpotentialacidity
MPC modelpredictivecontrol
MWMP MeteoricWaterMobilityProcedure
NAG netacidgeneration
NAPP netacid-producingpotential
NCV netcarbonatevalue
NGO non-governmentalorganization
NHE normalhydrogenelectrode
NIR nearinfrared
NPI NationalPollutantInventory
NPRI NationalPollutantReleaseInventory
NPV netpresentvalue
NRS netsmelterreturn
NSG non-sulfidegangue
OCS optimizingcontrolsystems
OM opticalmicroscopy
OPEX operatingexpense
ORP oxidation-reductionpotential
OSA opticalspectrumanalyzer
OT OutokumpuTechnology
PAX potassiumamylxanthate
PC personalcomputer
PCA principalcomponentanalysis
PCB printedcircuitboard
PCS processcontrolsystem
PECTU N-propyl-N-ethoxycarbonylthiourea
PFS preliminaryfeasibilitystudy
PGMs platinum-groupmetals
PI proportional-integral(feedbackcontrol-loops)
PIXE particle-inducedX-rayemission
PLC programmablelogiccontroller
PLS partialleastsquares
PLS pregnantleachsolution
PMs preciousmetals
POX pressureoxidation
PP polypropylene
PPE personalprotectiveequipment
PSA pressure-swingadsorption
PSD particle-sizedistribution
PTFE polytetrafluoroethylene
PTFI PTFreeportIndonesia
PVC polyvinylchloride
PVDF polyvinylidenedifluoride
QA qualityassurance
QEMSCAN QuantitativeEvaluationofMaterialsbyScanningElectronMicroscopy
RBC rotatingbiologicalcontactor
REQCM rotatingelectrochemicalquartz-crystalmicrobalance
RIL resin-in-leach
RIP resin-in-pulp
RIS resin-in-solution
RLE roast-leach-electrowinning
ROI returnoninvestment
ROL rapidoxidativeleach
ROM run-ofmine
RPS rarephasesearch
SABC SAGmill/ballmill/crusher
SAG semi-autogenousgrinding
SAIMM SouthAfricanInstituteofMiningandMetallurgy
SALI surfaceanalysisbylaserionization
SAR SummaryAuditReport
SART sulfidization-acidi fication-recycling-thickening
SCE saturatedcalomelelectrode
SCR selectivecatalyticreduction
SDGM SunriseDamGoldMine
SEM scanningelectronmicroscopy
SEM/EDX scanningelectronmicroscopy/energy-dispersiveX-rayanalysis
SERS surface-enhancedRamanspectroscopy
SET silver-enhancementtreatment
SG speci ficgravity
SHE standardhydrogenelectrode
SIBX sodiumisobutylxanthate
SIMP systemintegratedmetalproduction
SIMS secondary-ionmassspectrometry
SLS sodiumlaurylsulfate
SMC SAGMillComminution
SME SocietyforMining,MetallurgyandExploration
SPI SAGPowerIndex
SPL sparsephaseliberation
SPLP syntheticprecipitationleachingprocedure
SWEP specialwasteextractionprocedure
SX solventextraction
TBRC top-blownrotaryconverter
TCLP toxicitycharacteristicsleachingprocedure
TCM totalcarbonaceousmatter
TDM tertiarydodecylmercaptan
TDS totaldissolvedsolids
TIMA TESCANIntegratedMineralAnalyser
TLV thresholdlimitingvalue
TMS TheMinerals,MetalsandMaterialsSociety
TOA trioctylamine
TOC totalorganiccarbon
TOF-LIMS time-of- flightlaser-ionizationmassspectrometry
TOF-RIMS time-of- flightresonant-ionizationmassspectrometry
TOF-SIMS time-of- flightsecondary-ionmassspectrometry
TOMAC trioctylmethylammoniumchloride
TRI ToxicsReleaseInventory
TSF tailingsstoragefacility
UBC UniversityofBritishColumbia
UCS unconfinedcompressivestrength
UFG ultra- finegrinding
UFM ultra- finemilling
UNEP UnitedNationsEnvironmentProgramme
USEPA UnitedStatesEnvironmentalProtectionAgency
USMR USMetalsRefining
UV ultraviolet
VAW VereinigteAluminiumWerke
VMS volcanogenicmassivesulfide
VUV vacuumultraviolet
VUV-TOF-LIMS vacuumultravioletTOF-LIMS
WACC weightedaveragecostofcapital
WAD weak-aciddissociable(cyanide)
WDX wavelength-dispersiveX-rayanalysis
WEEE wasteelectricalandelectronicequipment
WGC WorldGoldCouncil
WHO WorldHealthOrganization
WoM WebofMetals
WoP WebofProducts
WWF WorldwideFundforNature
XANES X-rayabsorptionnear-edgestructurespectroscopy
XPS X-rayphotoelectronspectroscopy
XRD X-raydiffractometry
XRF x-ray fluorescence
m-PIXE micro-particle-inducedX-rayemission
ListofMineralFormulae acanthite Ag2S
altaite PbTe
alumina Al2O3
andorite Sb3PbAgS6
argentojarosite Ag2Fe3(SO4)4(OH)12
arsenianpyrite AsFeS2
arsenopyrite FeAsS auricupride Cu3Au
auroantimonate AuSbO3
aurostibite AuSb2
azurite 2Cu(CO)3,Cu(OH)2
bassanite CaSO4,1 2H2O
berthierite FeSb2S4
bezsmertnovite Au4Cu(Te,Pb)
bogdanovite Au5(Cu,Fe)3(Te,Pb)2
bornite FeS,2Cu2S,CuS
braggite PtS
calaverite AuTe2
chalcocite Cu2S
chalcopyrite CuFeS2
chlorargyrite(cerargyrite) AgCl
chlorite (Mg,Al,Fe)12[(Si,Al)8O20](OH)16
chrysocolla CuSiO3,nH2O
cinnabar HgS
coloradoite HgTe cooperite (Pt,Pd,Ni)S cordierite Mg2Al4Si5O18 corundum Al6Si2O13
covellite CuS cuprite Cu2O
dolomite CaMg(CO3)2 electrum (Au,Ag);20-80%molarAg enargite Cu3AsS4
fayalite Fe2SiO4 ferrihydrite 5Fe2O3,9H2O ferrisymplesite Fe(III)3(As(V)O4)2(OH)3,5H2O ferrouspyroarsenite Fe2AsO5 fischesserite Ag3AuSe2
galena PbS goethite FeO(OH) goldamalgam (Au,Ag)Hg gudmundite FeSbS guerinite Ca5(AsO4)2(AsO3OH)2,9H2O
gypsum CaSO4,2H2O haidingerite Ca(AsO3OH),H2O
hematite Fe2O3 hessite Ag2Te
hunchinite Au2Pb
hydroxyapatite
Ca10(AsxPyO4)6(OH)2;whereAs/P <0.2
iodargyrite AgI
iridicgold (Au,Ir)
jarosite H3OFe3(SO4)2(OH)6
kostovite CuAuTe4
kotulskite (Pt,Pd,Ni)(Te,Bi,Sb)2
krennerite (Au,Ag)Te2
laurite (Ru,Fe,Os,Ir,Pt)S2
litharge PbO
loellingite FeAs2
maghemite Fe2O3 with <5%FeO
magnetite Fe3O4
malachite 2CuCO3(OH)2
maldonite Au2Bi
marcasite FeS2
moncheite (Pt,Pd,Ni)(Te,Bi,Sb)2
montbrayite (Au,Sb)2Te3
mullite Al6Si2O13
muthmannite (Au,Ag)Te
nagyagite [Pb(Pb,Sb)S2][Au,Te]
nativecopper Cu
nativegold Au(<20%molarAg)
orpiment As2S3
palladiangold(porpezite) (Au,Pd)
parasymplesite Fe(II)3(As(V)O4)2,8H2O
pentlandite (Fe,Ni)9S8
petrovskaite AuAg(S,Se)
petzite Ag3AuTe2
pharmacolite CaHAsO4,2H2O
platinumgold (Au,Pt)
Pt-Fealloys Pt3Fe
pyrite FeS2
pyrophyllite AlSi2O5OH
pyrrhotite Fe1-xS
realgar AsS
rhodiangold(pyrite) (Au,Rh)
schwertmannite Fe(III)8O8(OH)x(SO4)y ,nH2O
scorodite FeAsO4,3.5H2O
sphalerite (Zn,Fe)S stibnite Sb2S3
sylvanite (Au,Ag)Te2
tennantite (Cu,Fe)12As4S13
tetra-auricupride AuCu
tetrahedrite (Cu,Fe,Ag,Zn)12Sb4S13 thucholite variablemixtureofhydrocarbons,uraniniteandsulfides tooeleite Fe(III)6(AsO3)4SO4(OH)4,4H2O uraninite UO2
uytenbogaardite Ag3AuS2
weilite CaHAsO4
weishanite (Au,Ag)3Hg2
zincblende ZnS zinkenite Pb9Sb22S42
Chapter1 Gold e AnHistoricalIntroduction F.Habashi
DepartmentofMining,Metallurgical,andMaterialsEngineering,LavalUniversity,QuébecCity,QC,Canada e-mail:Fathi.Habashi@arul.ulaval.ca
1.GOLDINANCIENTEGYPT Fromancienttimestothepresentday,goldhasbeenvaluedbyhumans.Egyptwastheprincipalgold-producingcountryin ancienttimes.Coptos,thepresentQuftontheeasternsideoftheRiverNile,wasthechieftownoftheNomosofHarawi andwasoncepoliticallyimportant.Intheeleventhdynasty(2133 1991BC)itwasovershadowedbyThebes,50kmto thesouth,whichbecamethecapitaloftheMiddleKingdom(2133BC)ofancientEgypt,thepresent-dayLuxor (Figure1.1).
Coptoswastheworld’s fi rstgoldboomtown.ItwasthereintheWadiHammamatthatalluvialgoldhadbeenwashed downfromthegold-bearingveinsfoundlaterinthegranitehillsabove.Theworld’soldestminemap(Figure1.2),whichis madeonpapyrusandheldattheTurinMuseum(MuseoEgiziodiTorino)inItaly,showsthehutsoftheEgyptianminers, theroadtothegoldmines,andthehillswithinwhichthegoldveinsoccurred.Themapis0.4 2.8m;itisbelievedthatit
FIGURE1.1 LocationofCoptosinUpperEgypt,themostancientgold-miningcenter.
wasmadeduringthereignofRamsesIV(1162 1156BC).ThescrollwasfoundinatombnearThebesshortlybefore 1824whenitappearedinTurin.RuinsofthesehutscanbeseentodayatFawakhirintheEasternDesert.
IntheoldEgyptianlanguage,theword nubia signi fies “gold.” By1300BC,undergroundminingofveingoldwaswell establishedinNubiaunderEgyptiancontrol.Thereweremorethan100minesinthearea.Aseriesoffortswerebuiltto protectthe flowofNubiangoldalongtherichtraderoutes.EgyptbecamethedominantpowerintheMiddleEast,having thegreatestgold- filledtreasuryintheancientworld.
TheancientEgyptiansdidnothaveanimportantportontheMediterraneanandalltheirtradewasthroughtheRedSea. CoptoswasatthestartingpointofthetwogreatroutesleadingtothecoastoftheRedSea,onetowardtheportofTââou (MyosHormos)andtheothermoresoutherly,towardtheportofShashirit(Berenice).Underthepharaohs,thewholetrade ofsouthernEgyptwiththeRedSeapassedoverthesetworoads.UnderthePtolemys,andinRomanandByzantinetimes, merchantsfollowedthesameroadsforpurposesofbarterwiththecoastsofZanzibar,SouthernArabia,India,andtheFar East.Thisplaceandthesurroundingareawereknownfortherichnessofitsgoldminesandsemipreciousstones.Atemple wasbuilttherebyTahutmesIII,whoruledfrom1503to1450BCandwasco-regentwithQueenHatshepsutfor21years. TheareathatitoccupiedwasabouttwiceaslargeashistempleatMadinetHabuinLuxor.
TheEgyptianswerethe firsttotreatgold-bearingrocks.Thisiswelldocumentedonwallpaintings,anexampleof whichisgivenin Figure1.3
FIGURE1.3 AncientEgyptianwallpaintingdatingfromabout1450BCinthetombofRekhmire,viziertoThothmesIIIatThebes,showingmetal workerscastingmoltengoldinthemolds.
FIGURE1.2 Theworld’soldestminemap.
2.EARLYGOLD-MININGCENTERS Herodotus(484 425BC)referstoseveralgreatgold-miningcentersinAsiaMinor,andStrabo(63BC)mentionsgold mininginmanydifferentplaces.Pliny(23 79AD)givesmanydetailsofancientplacermining,whichwasextensive.The Romanshadlittleofthemetalintheirownregions,buttheirmilitaryexpeditionsbroughtthemmajoramountsintheform ofbooty.Theyalsoexploitedthemineralwealthofthecountriestheyhadconquered,especiallySpain,whereupto40,000 slaveswereemployedinmining.Thestate’saccumulationofgoldbarsandcoinswasimmense,butduringthebarbarian invasionsandthecollapseoftheempirethisgoldwasscattered,andgoldmininglanguishedintheMiddleAges.
FollowingthediscoveryofAmericaattheendofthe fifteenthcentury,theSpaniardstransferredconsiderableamounts ofgoldfromtheNewWorldtoEurope.AlthoughtheconquistadorsfoundahighlydevelopedminingindustryinCentral America,theireffortstoincreasegoldproductionwerelargelyunsuccessfulbecausemostofthe findsconsistedofsilver. Colombia’sMuiscaIndians,whodweltinthehighlandsnearpresent-dayBogota,installedtheirkingsbydustingtheir nakedbodieswithgoldandthenwashingtheminnearbyLake.Totheconquistadores,thiswealthychieftainbecame knownasElDorado aSpanishwordmeaning “theGildedMan” (Figure1.4).
ItwasnotuntilthediscoveryofdepositsinBrazil,in1691,thattherewasanoticeableincreaseinworldgoldproduction.Sinceabout1750,goldhasbeenminedonamajorscaleontheeasternslopesoftheUralMountains.In1840, alluvialgoldwasdiscoveredinSiberiaandthenatColoma,California,inJanuary1848,afewdaysbeforethesigningofa treatybetweenMexicoandtheUnitedStatestoendtheirhostilities.CaliforniawasthuscededbyMexicoafteradiscovery thatwasapparentlynotknowntoeithergovernment.Colomaisabout50kmsoutheastofSacramentoontheslopesofthe SierraNevada.
ThediscoveryofgoldinBritishColumbiawasanepoch-makingevent.Inthelate1850s,alluvialgoldwasfoundalong theThompsonRiver,andin1858thefamousFraserRiverrushtookplace.Extraordinarilyrichdepositswerediscoveredin 1860onWilliamsandLightningcreeks.Formanyyears,BritishColumbiawastheleadinggoldproduceramongthe Canadianprovincesandterritories,butwiththediscoveryoftheKirklandlakedepositsin1911,andtheopeningupofthe Porcupinedistrictin1912,Ontarioheld fi rstplaceeversince.
GolddepositswerealsofoundinEasternAustralia(1851),Nevada(1859),Colorado(1875),Alaska(1886),New ZealandandWesternAustralia(1892),andWesternCanada(1896).However,thesedepositssoonlostmuchoftheir importance.Thestrongestimpetuswasgiventogoldproductionthroughthediscoveryofthegold fieldsofthe WitwatersrandinSouthAfricain1885.SouthAfricangoldsoonoccupiedacommandingpositionintheworldmarket. ProductiongrewcontinuouslyexceptforashortinterruptionbytheBoerWar(1899 1902).GoldmininginGhana(Gold Coast)begantoplayamodestroleinthetwentiethcentury,althoughthedepositswereknownintheMiddleAge.
FIGURE1.4 Eldorado.
3.GOLDANDALCHEMY Tothemedievalalchemists,goldhasbeenregardedasametalofperfection.Theyidentifieditwiththesunbyvirtueofits brightyellowcolor,anditwasgiventhesymbolofacirclewithadotinthecenter.Goldwassopreciousthatfromearliest timesmanhasleftnostoneunturnedinsearchingforitinnature.Itisnotsurprising,therefore,thathumansshouldhave soughttoconvertothermetalsintogold.Theagentfortransmutingbasemetalsintogoldwasknownasthe philosopher’ s stone.Inadditiontoitstransmutatorypower,thestonewasbelievedtohavethepropertiesofauniversalmedicinefor longevityandimmortality.Theattemptstotransmutebasemetalsintogoldandtoprolonglifeindefi nitelycontributed muchtomodernchemistryintheformofnewchemicalsubstancesandlaboratorytechniques.Alchemicalprincipleshave alsofoundtheirwayintomodernpsychologicalideas,notablybytheSwisspsychiatristCarlJung(1875 1961).
AncientEgyptisconsideredthebirthplaceofalchemy.Zosimos(ca.350 420),whotaughtinAlexandria,isthe earliestwriterknowntohavepracticedalchemy.Becauseoftheirlackofknowledgeofthecompositionofcommon substancessomealchemistsviewedmanyordinarychemicalreactionsastransmutations.Forexample,thedepositionof copperonironmetalplacedinasolutionofbluevitriol(coppersulfate),areactionknownsinceRomantimes,was assumedbysometobeatransmutationofironintocopperuntilthelateRenaissance.Similarly,themineralgalena[PbS], onheating,liberatessulfurdioxideandappearstobetransformedintosilver,whichisoftenpresentasanimpurityin galena.
Throughthecenturies,gold-makinghasbeenalternatelyencouragedandbannedbymonarchsandtheChurch.For example,Diocletian(AD245 316),EmperorofRomefrom284to313,fearingthattheEgyptians(Egyptwasthenunder thedominationoftheRomanEmpire)mightbecomepowerfulthroughtheirknowledgeofalchemy,orderedinAD296 thatallbooksandmanuscripts “whichtreatedtheartofmakinggoldandsilver” tobeburned.Consequently,onlyveryfew Egyptianalchemicalworkshavebeenpreserved.Duringmedievaltimes,Europeankingsandprincessupportedalchemists attheircourts,hopingtoacquirewealththroughtheirwork.
4.USESOFGOLD Humanshavevaluedgoldforitslustrouscoloranditsresistancetotarnishing,soitwasusedforspecialdecorative ornamentsandjewelry.Thevenerationreservedforgoldbytheancientshasledtoitsuseformanycenturiesforreligious artifacts.Goldwasoftencastintheformofidolsorhammeredintofoiltomakemasksforthedead.Goldwasusedfor barterandsubsequentlyforcoinage.BytheeighthcenturyBC,small,irregularbarsofimpuregoldwerebeingexchanged ascurrencyinAsiaMinor,andbythe fi fthcenturyBC,goldcoinswerebeingusedfreely.Eventoday,themajorityofthe goldproducedisturnedintogoldbars(i.e.,bullionthatactsasthestandardfortheworld’smonetarysystems),andtheyare usedininternationaltradeandexchange.
Golddiffersfrommostothermetalsinthatthemajorityofthemetalthathaseverbeenminedisstillinexistence.The totalamountofgoldnowinexistenceisestimatedtoamounttoaround125,000tons.Ifallofthisgoldcouldbecollected together,itwouldproduceacubewithanedgeofabout18.6m.Goldhasalwaysbeenasymbolofimmortality,andthis wasalsoacommonsubjectinmythology.Forexample,KingMidasrequestedthateverythingthathetouchedbeturned intogold.Whenthisblessinghadturnedouttobeacurseindisguise,MidasprayedtoBacchustotakebackhisgift.The mythoftheGoldenFleecehasbeensubjecttovariousinterpretations.ThelegendofElDorado,theIndianrulerwho plasteredhisbodywithgolddustinfestivals,ledtotherapidconquestofSouthAmerica.InanancientSanskrittext,there isareferenceto Pipilika gold(theSanskritwordfor “ants”),whichreferstogoldparticlesthatarecollectedbyantsand thenpresentedtothekinginaspecialceremony.In ThousandandOneNights,therearenumerousreferencestopalaces beingbuiltusingbricksmadeofgold.
GoldornamentshavebeenfoundinEgyptiantombsoftheprehistoricStoneAge,andtheEgyptiangoldsmithsofthe earliestdynastieswereskillfulartisans.Today,goldusedinjewelrysumstoabout2000tonsannuallyworldwide,which represents75%ofthetotalconsumption.Goldinjewelryservesdifferentpurposesindifferentpartsoftheworld.Inthe West,ithasaprimarilydecorativerole;itisnotnormallyregardedasaninvestmentandconsequentlythegoldusedforthis purposeislesspure.IntheEast,exactlythereverseistrue;goldhasastronglymonetaryrolethere,istypicallyhigh caratage(22carat 91.7%puregold,or24carat 100%gold),andisboughtandstoredasaninvestment.Itistypically wornbywomenandsohasanornamentalroleaswell;thepresenceoflargeamountsofgoldornamentsinOrientalbazaars atteststothisfact.TheAmericanIndiansbeforetheSpanishconquestusedgoldforornamentsbutalsoasofferingsin religiousceremonies,ortobeburiedwiththedeceased.
Theextremeductilityofthemetalisshownbythefactthat1gcanbepulledintoawire3kmlong.Thegoldthreads thatwereusedinembroideryandweavingweremadeinavarietyofways.Generallyspeaking,theyconsistedofmetal
stripsthatwereusedeitherdirectlyor,moreoften,intheproductionofcompositethreads,inwhichthemetalstrip waswoundarounda fibrouscoreofsilk,linen,cotton,orotheryarns.Wirewasalsouseddirectlyorforwindingaround suchcores.
4.1Gilding Becauseofitsoccurrenceinnatureinminuteamounts,goldwasanexpensivemetal.Itwasnotnecessarytohavearticles madeofsolidgoldsinceitwaspossibletopreparegoldinthinfoilsandcovertheobjectcompletelywiththemsothatthey appearasiftheyweremadeofgold.Gildingistheartofapplyingandpermanentlyattachinggoldleaforgolddustto surfacesofwood,stone,andmetals.Goldisthemostmalleableofmetalsandcanbereducedtoextremelythinleavesby hammering.Suchleavessometimesdonotexceed0.1mm(1000Å)inthickness,andtheytransmitgreenlight.Onegram ofgoldcanbemadetocovernearly1m2 ofsurface.ManyobjectsgildedbytheEgyptianshavesurvivedtothisday;the treasureofTutankhamen’stombisoneexampleoftheirskill(Figure1.5).TheEgyptiansappeartohavebeentheearliest practitionersoftheartofmakingthingoldfoil,andtheillustrationsontombsatSaqqaraandThebesshowtheirgoldbeaters workingtogetherwithgoldfoundersandgoldsmiths(Figure1.6).
FIGURE1.5 ThingoldfoilcoveringawoodenstatuefromanancientEgyptiantomb.
FIGURE1.6 AnancientEgyptianwallpaintingshowingaworkerpoundingongoldtoprepareafoil.
Goldfoilwas firstusedforgilding;whenthetechnologywasdeveloped,thefoilbecamethinnerandthinnerandwas referredtoasgoldleaf.Theinventionofgoldleafwasimpossiblebeforetheperfectionofmethodsforthepurificationof gold,asonlypuregoldorgold-richalloysfreefromcertainimpuritiescanbebeatenouttoproducethethinnestleaf. Indeed,themethodsofbeatinggoldhavenotchangedsignificantlysincethedaysoftheearlyEgyptians.Therounded stonehasbeenreplacedbyacastironhammerwithawoodenshaftandsomemachineryhasbeenintroducedtoreducethe effortofbeatingbyhandbut,inessence,theprocessremainsthesame.Theabilitytomakegoldinverythinleavesmadeit moreeconomicaltouseforgildinglargeobjectssuchasstatues,ceilings,columns,domesofchurches,etc.,withthe minimumconsumptionofgold.Goldleafisinsuf ficientlystrongtosupportitsownmassandsonewmethodsofattaching ittothesubstratehadtobedeveloped.Oneobviouswaywastouseanadhesive,andthismethodisstillusedtodayforthe gildingofwoodandstoneandforthedecorationofleatherbook-binding.
4.1.1GildingofMetals Whenthegoldleafisappliedonmetal,theadhesionofthegoldisenhancedbytheapplicationofheattopromote interdiffusionwiththeunderlyingmetal.Tocoveralargemetallicobjectsuchasthedomeofachurchorastatuestanding inthestreetwithaverythinlayerofgoldthatwouldresistexposuretorainandwind,mercuryusewasmadeofasa stickingmedium.Copper,notbronzeorbrass,wasusuallythemetalofchoice,althoughitismoredifficulttocastthanthe alloys.Thereasonisthatthealloyingelementstin,zinc,andleadinterferewiththegildingprocessbecausethesemetals haveahighsolubilityinmercuryandthusresultinadefectivelayer.Althoughgildingwithmercurywasarareandcostly processinthe fi rstcenturyAD,ithadbecomethestandardmethodofgildingbythethirdorfourthcenturiesandit remainedunchallengedthroughouthistory.
Twoprocessesweredevelopedtogildacoppersubstrate.Inthecoldprocess,mercuryisrubbedonthecleancopper surfaceuntilithasamirror-like finish.Somecopperdissolvesinthemercuryandformsathinlayerofcopperamalgam. Anyexcessmercuryismechanicallyremoved.Goldleafisthenpresseduponthesurface.Itbondswiththe copper-amalgamvery firmly.Morethanonelayerofgoldleafisusuallynecessarytoobtainthedesiredcolor.Thehot processwasdevelopedatalaterdatetogildcopperalloysandovercomethediffi cultyofcastingunalloyedcopper.Inthis method,goldleafisdissolvedinmercury;thistakesplaceveryrapidly.Theamalgamisappliedonthecoppersubstrateto thedesiredthickness.Theobjectisthenheatedtoexpelthemercury,leavingatenaciousgoldlayer.Thepoisonousfumes emittedduringtheprocesswereahealthhazardnotonlytotheworkersbutalsotothoselivingintheneighborhoodofa gildingworkshop.St.Isaac’scathedralinSt.Petersburgwasconstructedinthe40-yearperiod1818 1858withagilded dome21.83mindiameter(Figure1.7).
4.1.2GildingofGlassandPorcelain Thegildingofglass,porcelain,andpottery,rangingfromthesimpleedgingonaplatetotheelaboratelydecoratedvase withrichlygiltpanels,hasalwaysbeenaprominentfeatureinindustry.TheChineseappliedgoldleafoveralayerof
linseedoilandlitharge[PbO],orwitheggwhiteorshellac;however,thesegildedlayerswerenotdurable.Otherworkers usedgoldleafgroundupinhoney,washed,dried,andappliedwitha flux;inthesecases;however,theproductwas expensivebecausethegoldlayerwasthick.TheGermanchemistJohannKunckel(1630 1703)discoveredtheprecipitationofgoldpowderbytheadditionofasolutionofferroussulfatetoasolutionofgoldin aquaregia.Thiswas publishedinhisbook LaboratoriaChymica,whichappearedin1716,13yearsafterhisdeath.Theprecipitate,separated bydecantationandthendried,wasthoroughlymixedwitha finelygroundlead-silicate fluxandappliedtotheware,then fixedbyheatinginakiln.In1827,anewgildingprocesswasdiscoveredintheMeissenfactorynearLeipzigbyHeinrich Kühn.Theprocessconsistedofasolutionofgoldchloridein balsamofsulfur,anoilysubstanceobtainedbyreacting sulfurwithturpentine.Thismedium,whichisofsomewhatunknownchemicalcomposition,hadbeenknownformany years.Kühnwasthusabletoproducealiquidpreparationofanorgano-goldcompoundthat,on firingatarelativelylow temperature,yieldedabrightandshininggoldthatneedednopolishing.
4.2GoldintheGlassIndustry Inthe1650s,theGermanchemistAndreasCassius(1605 1673)discoveredapurplepigmentthatcanbeusedincoloring glassandporcelain,yieldinganexceptionallybeautifulpurplecolor(Figure1.8).Thecolorwasknownas Purpleof Cassius.Itwaspreparedbyaddingasolutionofstannouschloridetoadilutegoldchloridesolutionandwasappliedinthe mostfamousglassandporcelainfactoriesofEuropeinMeissenandSèvre.Thenatureandconstitutionof Purpleof Cassius presentedscientistswithaproblemthatwastackledthroughoutthewholeofthenineteenthcenturybysomeofthe mostdistinguishedchemistsofthetime.Notuntiltheturnofthecenturywasthetruenatureofthispigmentelucidated. RichardZsigmondy(1865 1929),aViennesechemistwhohadspentsomeyearsstudyinggoldcolorsandhadjoinedthe SchottGlassworksinJenain1897,developedtheultramicroscopefortheexaminationofcolloids.Heshowedconclusively thatthe PurpleofCassius consistedofvery fi nelydividedgoldwithstannicoxide.Forthisinvestigation,hewasawarded theNobelPrizeinChemistryin1925.
Inmoderntimes,gold fi lmsdepositedonglassviathermalevaporationaresuperiortoothermetalsforrefl ectivityinthe infraredwavelengthrange.Such fi lmsappliedtoglasswindowsforofficespermitgoodvisionbysubstantiallyreducing thetransmissionofinfraredenergybyreflectionratherthanbyabsorption.Thecostofproductionisverylow,andthe economyinenergysavingduetocuttingdownonheatinginwinterorairconditioninginsummerisappreciable.Many modernofficebuildingsarenowconstructedusingglasswindowswithagoldcoatingabout0.01mmthick.Inthe depositionprocess,goldisheatedtoabout1390 Candatalowpressure.Thevaporizedgoldatomsmoveinnearly straightlinesfromthesourcetothesurfacetobecoated.
4.3GoldMasks Fromancienttimes,funeralgoldmaskswereusedtocoverfacesofthedead(Figures1.9 1.11).
5.OCCURRENCEOFGOLD Mostgoldoccursasnativemetal,nearlyallalloyedwithvariousamountsofsilverasthemineralelectrum,butnotwith copper.Certainmineralsarecharacteristicallyassociatedwithgold,andthemostimportantarepyrite[FeS2],galena[PbS],
FIGURE1.8 MuseumpiecesofglasscoloredwithPurpleofCassius.
zincblende[ZnS],arsenopyrite[FeAsS],stibnite[Sb2S3],pyrrhotite[Fe(1 x)S],andchalcopyrite[CuFeS2].Various seleniummineralsandmagnetite[Fe3O4]mayalsobepresent.InWitwatersrand,SouthAfrica,uraninite[UO2]and,toa lesserextent,thucholite[avaryingmixtureofhydrocarbons,uraninite,andsul fides]areassociatedwiththegoldore; uraniumwasrecoveredasabyproductofgoldmilling.Carbonaceousmatterisassociatedwithsomegoldores.Goldhas affinityfortellurium,anditformstwomaintellurideminerals:calaverite[AuTe2]andsylvanite[(Ag,Au)Te2].Itwasin thesemineralsthattelluriumwas firstdiscovered.Ontheotherhand,itoccurswithpalladiumasporpezite(Aucontaining 5 10%Pd)andwithrhodiumasresinrhodite[Au,Rh].Inplacerdeposits,itmaybepresentasminuteparticlesorlarge nuggets.Incertainoresknownas refractory ores,goldisassociatedwithsulfi demineralsinanextremely finelydivided state.
FIGURE1.9 AncientEgyptiangoldmask.
FIGURE1.10 AncientGreekgoldmask.
