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1、高级矿床学-斑岩型矿床斑岩铜矿2021/9/211斑岩铜矿(Porphyrycopperdeposits)为世界提供了50%以上的铜金属(over100producingmines)。Theircloserelativestheporphyrymolydepositsproduce70%oftheworldsmoly.Bothdeposittypeswillbediscussedseparately,buttheysharemanycharacteristicsandareformedinsomewhatsimilarmanners.2021/9/212全球斑岩铜矿分布图绝大多数斑岩铜矿形成于
2、中新生代，与离散板块边缘上及附近的火山链有关（环太平洋、古地中海和古亚洲洋）。极少数为古生代，分布在古生代板块边缘上，如U.S.S.R、UnitedStates。2021/9/213全球已知最大的88个斑岩铜矿产于美国西南部，成矿时代为58-72Ma。岩体形态岩体形态典型斑岩铜矿床呈圆筒状，产于岩株状岩体中，出露面积为1.5x2km（椭圆状），核部为斑岩质，向外到边部为中粗粒等粒的成分相似的岩石。主岩岩石学主岩岩石学一般地，容矿主岩为长英质侵入体，成分为石英正长岩、石英二长岩、花岗闪长岩系列；闪长岩正长岩系列2021/9/214热液蚀变热液蚀变LowellandGuilbert总结的斑岩铜矿蚀
3、变模式，围绕斑岩株依次出现4个蚀变晕钾化带-都存在。特征：次生的钾长石、黑云母和/或绿泥石交代原生的钾长石、斜长石和镁铁质，及微量的绢云母。绢英岩化带可存在。特征：脉石英、绢云母、黄铁矿和微量绿泥石、伊利石和金红石，交代钾长石和黑云母。泥化带（Argillic ）-可存在。特征：高岭石、蒙脱石等粘土矿物及微量浸染黄铁矿。斜长石强烈蚀变、钾长石不受影响，黑云母绿泥石化。青盘岩化带（Propylitic ） -都存在。特征：绿泥石、方解石、微量绿帘石。镁铁质矿物强烈蚀变，斜长石消失。在深部，上述各带融为一体，构成石英-钾长石-绢云母-绿泥石组合。2021/9/2152021/9/216Hypoge
4、ne Mineralization矿体产出环境:1）整个岩株内；2）部分岩株部分围岩；3）仅在围岩内矿体通常为陡壁圆筒状，也有板状、扁圆锥状（tabulartoflatconical）矿化为浸染状或细网脉状，铜品位0.4-1%Cu，含微量Mo和gold。矿化呈带状：Inner Zone与钾化带吻合，一般直径数百米，相对地硫低，但钼最高。黄铁矿2-5%，py/cp比约3:1。矿化为浸染状而非细网脉状。Ore Zone大致分布在potassic-phyllic带边界上，黄铁矿5-10%，py/cp比约2.5:1。主要矿物为黄铜矿，呈细网脉状。其他矿物有斑铜矿、硫砷铜矿和辉铜矿。Pyrite Zon
5、e包括phyllicandargillic(若存在)的大部。黄铁矿相当高，可达10-15，py/cp比约15:1。矿化即有浸染状又有脉状。许多附加的外来硫化物相开始出现在上部。Outer Zone与propyliticzone吻合。黄铁矿微量，铜矿物稀有。闪锌矿和方铅矿常见，但常为边界品位级。矿化为脉状。2021/9/2172021/9/218BrecciaZones-Oftenmajororecarriersintheporphyrysystem.Haveveryhighgrades(2-5%Cu)andcanoccurbothintheporphyryorthecountryrock.Ma
6、ybeformedbyhydrothermalactivity,gravitationalcollapseorlaterexplosivevolcanism.2021/9/219在成矿区带上，斑岩铜矿、钼矿和锡矿明显呈带状分布，与距板块俯冲带的距离有关，铜矿离海沟最近，而钼锡依次分布在海沟内侧。2021/9/2110Vertical Extent of Porphyry Bodies斑岩铜矿与小高位小岩株和陆相钙碱性火山作用有关。因而侵入体为层火山所覆盖，青盘岩化延展到火山岩中，其它蚀变于其界面处。一般地，此模式说明斑岩铜矿是更大的成矿体系的一部分，包括高位浅成低温贵金属矿床。2021/9/2
7、111闪长岩模式闪长岩模式斑岩矿床有两个不同的体系：其一为“LowellandGuilberttype”，以美国西南部以石英二长岩-花岗闪长岩为特征。其二为AndesandPacificIslands.主岩为闪长岩，偶为正长岩。两者的特征对比见表。闪长岩体系的特征为：低硫逸度，存在磁铁矿，蚀变仅有钾化带和青盘岩化带，金为重要组分，而钼稀有或缺失。2021/9/2112Comparison of the Lowell-Guilbert and Diorite Types of Porphyry Copper Deposits FEATURE LOWELL-GUILBERT DIORITE Hos
8、t Pluton QuartzMonzonitetoGranodiorite(S)Qtz.DioritetoDiorite(I)AlterationPotassicPhyllicArgillicPropyliticPotassicPropyliticMineralizationQuartzinfracturesCommonCommonErraticOrthoclaseinfracturesCommonErraticMagnetiteMinorCommonPyriteinfracturesCommonLessCommonMolybdeniteCommonRareChalcopyrite/born
9、ite3:13:1GoldRareImportantStructureBrecciaMayOccurRareStockworkImportantImportant这些差异可以理解为：日本岛弧侵入体没有斑岩铜矿，在岩相学上他们属于两类花岗岩（“S”and“I”type）。前者为陆壳深熔作用形成的，后者为板块俯冲期间部分熔融的最后阶段的分异产物。2021/9/2113Characteristics of S & I Type GranitesFEATURE S TYPE I TYPEGabbro:diorite: granite2:18:8015:50:35Na2O (felsic)3.2%Al2
10、O3/Alkalis+CaO1:1.706.704-.706NormativecorundumdiopsideAssoc. metalsSn,WAuGenesisCrustalanatexisofsedimentsPartialmeltofmantleSandItypegranites的特征对比，与LowellandGuilbertandDiorite斑岩矿床所揭示的特征相似。闪长岩模式的矿床形成于大洋岩石圈俯冲所致的部分熔融作用，而LowellandGuilbert模式矿床代表远离板块边界陆壳的熔融作用。2021/9/2114成因成因典型斑岩体系的最明显特征是其大小。热液不仅渗透到母侵入体中
11、，而且渗透至围岩中。认为容矿岩体侵入至浅部（0.5-2km深)。侵入体结晶开始时，岩浆房的蒸汽压随不相容元素进入蒸汽相而增大，当蒸汽压超过上覆岩石的围压时发生退化沸腾。快速沸腾的液体最终克服岩石的拉伸强度从硅酸盐熔体中分离出来，导致强烈的网脉状角砾化(如:waterat2Kb压力和5000C的水由于沸腾体积增加至少10%)。此外，沸腾是吸热反应，正在逸出的蒸汽膨胀时需要岩浆中的热，因而，快速降低了岩浆房中的温度,，形成侵入体中心的斑状结构。2021/9/21152021/9/2116流体包裹体证据流体包裹体证据氧同位素研究表明钾化带黑云母的值与岩浆水相当，而绢英岩化带的绢云母亏损18O，表明为
12、天水。泥化带也是如此。1）侵入体上升至地壳开始结晶；2）岩浆热液对流在侵入体内和附近形成钾化带；3）围岩中的天水对流形成青盘岩化，对流由侵入体热所驱动；4）随着侵入体的冷却，天水体系叠加至岩浆体系之上，形成phyllic-argillicalterationzones。2021/9/2117问题：1）为什么闪长岩模式矿床仅有potassic-propyliticalteration?2）为什么闪长岩模式岩浆水-天水系统从不互相侵入？2021/9/2118Bingham Canyon, UtahLocationLiesabout30kmsouthwestofSaltLakeCity,Utahat
13、analtitudeof2000meters.FromahistoricperspectiveoneofthemostfamousminesintheUnitedStates.2021/9/2119Regional GeologyBinghamissituatedintheBasinandRangetectonicprovince.TheOquirrahMountainsformahorstblockoffoldedPaleozoicrocksboundedbynorthtrendingfaults.TheprincipalcountryrocksarePennsylvanianquartzi
14、tesandlimestonesfoldedandintrudedduringtheMesozoic.TheorebodyitselfoccursinoneofaseriesofsmallerhorstsboundedbythenorthwesttrendingBearandOccidentalFaultswhichupliftthenortheasttrendingCoppertonAnticline.MineralizationisinoradjacenttotheBinghamstock,aporphyriticgranodiorite.Theslightlyyounger(?)Last
15、Chancestocktothesouthisbarren.BothhavebeenagedatedatEocene.TherearethreetypesofmineralizationintheOquirrahMountainsalluvialgoldAg-richgalenaandsphaleriteveinsinlimestonesporphyrycoppermineralization2021/9/2120Geology of the Bingham Canyon Porphyry Copper DepositThedepositoccursinatriangularzoneofdis
16、seminatedandveinletcoppersulfidemineralization1.5x2.5kminplanandatleast500metersinthickness.Themajorityoftheoreisinthegranodiorite,butsubstantialreservesarepresentinthemetamorphosedPaleozoics.Theoriginalhostintrusivewasagranodiorite,butsubsequenthydrothermalalterationhasresultedinarockmorecloselyapp
17、roximatingagranite.Thestockhasawelldefinedpotassicalterationzonecharacterizedbysecondarybiotite,poorlydefinedphyllicalterationandaspottyandirregularpropyliticalterationzone.Argillicalterationisabsent.Extensivebrecciationofboththeintrusiveandcountryrockiscommon.Theprimarymineralizationaverages1-4%oft
18、herock.Thecoreoftheintrusiveismolyrichwithpyriteabundantonlyinthephylliczone.Chalcopyriteandminorbornitearetheonlyprimarycoppersulfidesrecovered.Peripheralskarndepositsconsistingofenargite,galena,sphaleriteandtetrahedriteareimportantinthesurroundingmetasediments.TypicalofmostAmericandeposits,earlymi
19、ningwasfromasupergeneenrichmentzoneofchalcocite,malachiteandnativecopperlyingbeneathabarrenlimonitecap10-100metersthick.Muchofthissupergeneorehasbeenminedout.2021/9/2121GenesisNospecificgeneticmodelhasbeenproposedfortheBinghamCanyondeposit.Ratheritsgenesisisthoughttobesimilartothatofallthesouthweste
20、rnporphyrycopperdeposits.2021/9/2122Porphyry Moly and Tin DepositsInadditiontocopperthereareotherporphylyrelatedtypesofmineralization,mostnotablymolybdenumandtin.Whileeachofthethreetypesofporphyrydepositscontainappreciablequantitiesoftheotherelements,theyarenonethelessgeologicallydistinctenoughtocon
21、stituteendmembersoftheporphyryspectrum.Originallyitwasthoughtthatallmolydepositsbelongtoasinglegroup.Itisnowacceptedthattherearetwosubtypes.ThenomenclatureisconfusingsinceonetypeistermedsimplyporphyrymolywhilethesecondtypeistheClimaxtype.2021/9/2123Porphyry Moly Subtype1）与花岗闪长岩石英二长岩类I型花岗岩有关。与I型斑岩铜矿（
22、闪长质）相比，略显酸性。矿物只有辉钼矿，脉状和浸染状，品位低(0.1-0.2%MoS2)。2）蚀变不易识别，但钾蚀变普遍。由于岩石富钾，难以识别钾化。有些硅化仅出现在钼矿脉周围。Orebodiesaresheet-liketotabular.Depositsrangeinagefrom30-80MYandoccurinassociationwithMesozoictorecentsubductionzones,particularlythosewithsteepangles.Nosimplegeneticmodelseemstofitallofthedepositsinthissubgroup
23、.Clearlytheyarerelatedtosubductionandevidencefromfluidinclusionsandisotopesfavorsagenesissimilarifnotidenticaltothedioritetypeporphyrycopperdeposits.Anunansweredquestionistherelationshipofthemolydepositstothecopperdeposits.QuartzHillinAlaskalieslessthan50kmfromanactivetrenchleadingsomegeologiststosu
24、ggestthatporphyrymolydepositsformatshallowerdepthsnearerthetrenchthandoporphyrycopperdeposits.However,intheAndeswherebothmolyandcopperdepositshavebeenextensivelymappedthemolydepositslieinabelttotheeastofthecopperdepositsandfartherfromthetrench.Unfortunately,agedifferencesbetweenthecopperandmolybelts
25、aswellaschangesintheangleofsubductioncomplicatethepictureintheAndes.2021/9/21242021/9/2125Climax Type Moly DepositsClimaxtype钼矿与A型(S型亚类)花岗岩有关。其与S型不同点是富K2O和F。矿体均在岩体中，辉钼矿为主矿物，但可回收锡钨。品位高于斑岩钼矿，平均约0.35% MoS2,某些矿床高达0.7%。蚀变为弥散型，强烈的硅化及钾化、青盘岩化、磁铁矿-黄玉化，偶见弱的绢英岩化/泥化。矿体为伞形。成矿年龄约30Ma。已知的Climaxtypemolydeposits位于西C
26、ordillera,大致从中Montana至北NewMexico。若与中生代俯冲带有关（尚有争议），矿床则分布于板缘1000km内。A-type或非造山花岗岩认为是大陆裂谷的产物（尚有争议）。另一可能性是与俯冲有关,矿床形成在俯冲浅角度的地区。锶同位素比大于0.706，常超过0.740。高氟说明陆壳混染。俯冲带深部的热使加厚的陆壳基底发生熔融。这些岩浆慢慢混染陆壳物质而富集K和Mo。2021/9/2126Climax, Colorado位置位置位于Denver西部约100km，海拔4000m的陆地分界线。概述概述位于ColoradoFrontRange，由元古代片岩和片麻岩(IdahoSpri
27、ngsGroup)所组成，被元古代SliverPlumeGranite所侵入。FrontRange构造复杂，但褶皱却以北东向为主。古生代沉积岩不整合于元古代基底之上。MosquitoFault切割Climax岩株，为区内主要断裂，它从古生代活动至今。早第三世浅侵入体和流纹质火山作用是本区最后的地质事件。Geology of the Climax Deposit主要矿化带直径约1.5km，成为了侵入于IdahoSpringsGroup中的岩株和岩脉的顶帽。MosquitoFault切过矿带的西部。4个岩体控制了矿化，时代为Oligocene世。岩株西南部最老，次为中央岩株，共同构成了Climax
28、花岗闪长岩体。最后它们被AplitePhaseandthePorphyriticGranite所侵入。2021/9/21272021/9/21282021/9/2129Alterationconsistsofearlypotassicalteration,weaksericiticalterationandlate,intensesilicification.Fourphasesofmineralizationarerecognized,eachcorrelatedwithanintrusion.Thefirstthreeformthethickumbrella-likeorebodies(F
29、igure).Theearliest,anduppermost,Cerescoorebodyhasbeenalmostcompletelyremovedbyerosion.BeneaththeCerescolietheUpperandLower(younger)orebodies,correlatingwiththesecondandthirdintrusions.Thefourthintrusionproducedsilicification,butnomineralization.Mineralizationconsistsofazoneofirregularveinletscontain
30、ingquartz,K-sparandfine-grainedmolybdenite.Someoreoccursinlargerveinlets(pseudo-pegmatites)andalongjointsurfaces.Fluoriteandtopazarecommonaccessoryminerals,asarewolframite,pyriteandcassiterite.GenesisThoughttobesimilarinmanyrespectstoporphyrycopperdeposits,howevertherocksaremoresilicicsuggestingeith
31、ersignificantcrustalcontaminationoranentirelycrustaloriginfortheintrusives.Whilesomecopperdepositsoccurinsettingssuggestiveofmultipleintrusivephasesthereappearstobeonlyasingleorebody,inmarkedcontrasttomolydepositswhereeachintrusivehasanassociatedorezone.2021/9/2130Tin DepositsPorphyrytindepositsarer
32、estrictedtoalinearbeltintheAndesMountainseastofthecopper-molybelts.Hostintrusivesaregenerallylatiteporphyrystockstotruegranites.Thereisacloseassociationwithstratovolcanoesindicatingveryshallowlevelsofemplacement.Ratherthanthetypicalflaringstock,intrusionsassociatedwithtindepositsappeartobenarrowfing
33、er-likeprojections.Themainoremineraliscassiterite,oregradesaveraging0.1-0.2%SnO2.Theoreoccursasanearlydisseminatedphasethatissub-oregradefollowedlaterveins.Alterationconsistsofsilicification,sericitization,propylitizationanddeeplevelquartz-tourmaline.Thereisanabsenceofpotassicalteration.Insomeinstan
34、ces,thereareassociatedperipheralbasemetalvein-typedeposits.2021/9/2131GenesisThoughttobeatwostagemodel(Figure).Emplacementofshallowplug-likestockintheventofafelsicstratovolcano.Magmatic-meteoricwatersystemdevelopsasigneousactivitywanescausingpervasivealterationandthedisseminatedtinmineralization.Ast
35、emperaturedeclinescoolingcausesfracturingoftherocks.Thesefractureswidenanddeepeneventuallytappingthedeepermagmachamberfeedingthevolcano.Thisallowsvolatilestoescapethechamberandstreamupward.Coolingcausesdepositiononfracturewallsgeneratingthevein-typetinmineralization.2021/9/21322021/9/2133Characteris
36、tics of Porphyry Cu-Mo-Sn Deposits1RestrictedtothePhanerozoic(mostlyMesozoic-Tertiary).Closelyassociatedwithfelsicintrusivesofqtzdioritetoqtzmonzonitecomposition.2Accompaniedbycharacteristicalterationenvelope.potassic-phyllic-argillic-propylitic.3Strongzoninginrelationshiptoplateboundaries.CuMoSnmov
37、inginlandfromtheplatemargin.4Closelyassociatedwithislandarcdevelopmentandsubductionzonesatconvergentocean-continentplateboundaries.5Oreoccursinalarge,low-gradeshelladjacenttothepotassiczone.Chalcopyriteandbornitemostcommonmineralswithlessermolybdeniteandcassiterite.6Isotopicevidencesuggestsshallowde
38、pthsofmagmagenerationandsignificantgroundwaterinteraction.2021/9/2134Vein-type DepositsThesewereonceoneofthemostsoughtafterandheavilyminedtypesoforedeposits.ThefamousminingdistrictsoftheWestaremainlyvein-typedeposits.Vein-typedepositsrepresentaprogressionintotruehydrothermaldepositsthatlieatsomedist
39、ancefromtheigneoussource.Todaythisgrouphasdeclinedmarkedlyinimportance,butstillproducesmuchoftheworldssilverandtungstenandsomegoldandbasemetals.Thesearchforthistypeofdeposithasbeenabandonedlargelybecausetheytendtobesmallanddifficulttofind.LindgrenClassification-Stillmuchinvogueforthedescriptionofvei
40、n-typedeposits(SeeHandoutsforHypothermal,MesothermalandEpithermaldeposits).Thesehandoutsdatefromthe1930s,butwiththeexceptionoftemperaturedata,theinformationhaschangedverylittle.2021/9/2135General CharacteristicsAlthoughasagroupthedepositsvaryconsiderablyinsize,mineralogyandgeologicenvironments,allha
41、vecertainunifyingfeatures:associationinspaceandtimewithcalc-alkalineigneousactivity;clearlyepigeneticwithoreshavingvein-likeformandclosespatialrelationshiptofaulting;oremineralsaredepositedasopenspacefillingalongdilatantzonesorasreplacementsofcarbonatehostrocks;zonationischaracteristicandalwaysprese
42、nt(Figure);depositionisfromhydrothermalfluidsatdepthsoflessthan3km;sulfurisusuallyofmagmaticorigin(34S=0);districtsarestructurallycomplex;someformofalterationisalwayspresent,oftensericiticataminimum;oftenseeaprogressionfrommagmaticwatertometeoricwaterlaterintheparageneticsequence.2021/9/2136Variousm
43、orerecentclassificationsofvein-typedepositshavebeenproposed,butnonehavebeenadopteduniformly.Mostgeologistshaveswitchedtotypegroupsofdeposits(e.g.Carlin-type,Creede-type).Thisoftenleadstoacertaindegreeofconfusion.2021/9/2137Hypothermal Deposits300 - 500 C (high pressure; great depth)Character of Vein
44、s-Markeddevelopmentofreplacementtextures.Gradationaltopegmatiticoredeposits.Diagnostic Ore Minerals cassiteriteSnO2hematiteFe2O3graphiteCilmeniteFeTiO3magnetiteFe3O4molybdeniteMoS2marmatite(Zn,Fe)SpyrrhotiteFe1-xSrutileTiO2scheeliteCaWO4topazAl2SiO4(OH,F)woiframite(FeMn)WO4Other Common Metallic Mine
45、ralsarsenopyriteFeAsSbismuthBibismuthiniteBi2S3chalcopyriteCuFeS2galenaPbSgoldAupyriteFeS2Characteristic Gangue MineralsfeldsparpyroxeneamphibolegarnetmicasspineltourmalineWall Rock Alteration Iron-magnesium Metasomatism 以富铁黑云母、电气石、钙铁榴石（石榴石）、角闪石和辉石为特征。Sericitic 存在但不广泛。Propylitization -Hasbeendescrib
46、ed,butisveryrare2021/9/2138Mesothermal Deposits200 -300 C (moderate pressure; moderate depth)脉体特征脉体特征均匀板状脉，脉壁较平直。交代常见，以碳酸盐为盛。少见张性充填，分带良好，脉系长而大。skutterrudite(Co,Ni)As3smaltite(Co,Ni)As3chloanthite(Ni,Co)As3arsenopyriteFeAsSbismuthiniteBi2S3bournonitePbAuSbS3borniteCu5FeS4chalcociteCu2SchalcopyriteCuF
47、eS2covelliteCuScobaltiteCoAsSenargiteCu3AsS4galenaPbSgoldAumolybdeniteMoS2pyriteFeS2niccoliteNiAstetrahedriteCu12Sb4S4tennantiteCu12As4S4sphaleriteZnSQuartzSiO2ankeriteCa(MgFe)(CO3)2CalciteCaCO3dolomiteCaMg(CO3)2FluoriteCaF2sideriteFeCO3Wall Rock Alteration - DependentonthetypeofhostrockSericitic -D
48、evelopsinfeldspathicrocksFeldsparsaltertosericiteandmaficmineralstopyrite.Dolomitization -Developsincarbonaterocks.Characterizedbyankeriteandsecondarycalciteanddolomite.Silicification -Alsomostcommonlydevelopedincarbonates,butnone-the-lessalsocommoninfeldspathicrocks.Jasperization -Characterizedbyth
49、eappearanceofjasper,aniron-richvarietyofamorphoussilica.2021/9/2139Epithermal Deposits50 - 200 C ( low pressure; shallow depth)Character of Veins 受主岩构造控制受主岩构造控制张性充填，脉常呈皮壳状、条带状、梳状。Diagnostic Ore Minerals cinnabarHgSacanthiteAg2SstibniteSb2S3argentiteAg2SchalcociteCu2SproustiteAg3AsS3pyargyriteAg3SbS3
50、arsenopyriteFeAsSborniteCu4FeS5bismuthiniteBi2S3chalcopyriteCuFeS2copperCuelectrumAuAggalenaPbSgoldAumarcasiteFeS2polybasite9Ag2S-Sb2S3orpimentAs2S3silverAgpyriteFeS2realgarAsStetrahedriteCu12Sb4S13tennantiteCu12As4S13adulariaKAlSi3O8aragoniteCaCO3aluniteKAl(OH)12(S04)bariteBaSO4calciteCaCO3chalcedo
51、nySi02dolomiteCaMg(CO3)2fluoriteCaF2rhodochrositeMnCO3quartzSi02Silicification 不一定直接与成矿流体有关，早阶段蚀可紧随矿化之后。Propylitization 发育绿泥石、绿帘石、方解石，似与矿化有关，岩石呈特征的绿色。Sericitic -Formationoftheassemblagesericitepluspyrite.Notalwayspresentandusuallyoflimitedaerialextent.Alunitization -Nearsurfacealterationassociatedwi
52、thdescendingmeteoricwaters.Characterizedbytheformationofalunite.2021/9/2140Mesothermal Base-Metal VeinsOccurinrocksofallages,butmostimportantdistrictsareofPaleozoic/Mesozoicage.Seemtoberestrictedtoorogenicbelts,inparticulartheRockyMountains.Assuch,thewesternCordilleraisfamousfortheconcentrationofthi
53、stypeofdeposit.FormMostofthelargedepositsarereplacement-typeassociatedwithmajorfaultsystems.Overalltheshapeofmostdistrictsislinearreflectingthestrongcontrolfaultinghasonoredeposition.Setting矿床与钙碱性火山作用及其侵入体密切相关，尽管大部分地区地质情况复杂，但成矿时代却集中在侵入事件的峰期后不久。典型岩株为浅成相石英闪长岩至花岗岩。断裂作用是区内主要特征，可填出至少一条区域断裂。一般地矿体与主断裂无关，但与
54、其平行的次级断层或年轻的交切断层有关。2021/9/2141Alteration变化大，决定于主岩性质。砂岩中蚀变限于矿脉两侧数厘米，而碳酸盐内可达数千米。碎屑岩内为简单的硅化，而碳酸盐和变质岩内有绢英岩化+泥化+青盘岩化。蚀变通常是复杂的，难以区分，特别是脉体之间的蚀变相互叠加。MineralogyCu,Fe,Pb,Zn硫化物为主，次为硫盐矿物。常见矿物为黄铁矿、黄铜矿、斑铜矿、方铅矿、闪锌矿、砷黝铜矿tennantite、黝铜矿tetrahedrite、硫砷铜矿enargite、辉铜矿chalcocite和蓝辉铜矿digenite。磁黄铁矿缺失，由此限定了其上限。所列矿物大多是银的重要载体
55、，为世界银资源的主体。共生序列极其复杂，显示其形成历史长。在中温区沿走向矿物分带，从而呈现出亚带来。Gangue脉石矿物种类少，主要为方解石、石英、菱铁矿、白云石、铁白云石2021/9/2142Geochemistry流体包裹体表明成矿温度为250-4000C，盐度较低(1-4wt%)。稳定同位素数据支持岩浆硫的观点，说明至少早期矿物与岩浆水有关。GenesisEarlygeneticmodelssuggestedthatthemajorfaultswithinthedistrictsservedasconduitsformagmaticwaterswhichflowedalongthefau
56、ltsinsearchofeasilyreplaceablerocks(carbonates)wheredepositionoccurred.Thismodelisnotwithoutitsproblems.Firststableisotopesindicatethatinmanydistrictsmeteoricwaterhasplayedasubstantialrole.Secondthereistheproblemofcarryingsulfurandoremineralsinthesamefluid.Despitetheseproblemsthemodelhasbeenlittlech
57、angedormodified.Thelackofemphasisonthesedepositsinrecentyearsisprobablyamajorreasonfortheratherincompletemodel.Forinstance,comparethemtoepithermaldepositsthatwillbediscussedinaseparatelecture.Modelsforepithermaldepositsarecomplexandleavefewunansweredquestions.2021/9/2143Coeur dAlene District, IdahoT
58、heCoeurdAlenedistrictisoneofthemostfamousintheUnitedStates.Ithasproducedalmostcontinuouslysinceitwasdiscoveredin1857.Thedistrictproducesmainlysilverwithbyproductlead,zincandcopper.LocationTheCoeur dAlenedistrictextendseast-westabout50 kmandnorth-southabout25kmalongthewestflankofthenorthernRockyMount
59、ains.2021/9/2144Regional GeologyThebasalrocksintheregionareapartoftheweaklymetamorphosedsandstonesandshalesoftheProterozoicBeltSupergroup.TheseareunconformablyoverlainbyCambrianrocks.Allrocksarehighlyfoldedandfaulted.Thefoldstrendgenerallynorth-south,althoughimmediatelysouthoftheOsborneFaultthefolds
60、strikemorenearlyeast-west.Thelargestfaultintheregionistheeast-westtrendingOsborneFault(Figure)whichhasbeentracedfor800kmalongstrikeandisknowntohaveadisplacementof15,000meters.Manyothersmallersubparallelfaultshavebeenmappedmanyofwhichseemtocontrolthemajorveinsystems.2021/9/2145Intrusivesarenotconspic
61、uousintheCoeurdAlenedistrict,butseveralsmallCretaceousagestocksofgranodioriteandmoazonitearepresenttothenorthoftheOsborneFault.ThesearethoughttobeoffshootsofthemuchlargerIdahobatholithtothesouth.2021/9/2146Ore DepositsHundredsofveinandlodedepositsoccurwithinthedistrict,mostalongdilatantfaultzonesand
62、asreplacements alongbeddingplanesofthehostrocks.VeinstrendsubparalleltotheOsborneFault.Quartzitestendtobebetterorehoststhanargillitessincetheformerhasagreaterdensityofbrittlefractures.Thesefracturesarethoughttohaveformedasaconsequenceofoblique-slipalongtheOsborneFault.Somedepositsappeartobeclearlyas
63、sociatedwiththeCretaceousageintrusives,butforothersthatassociationismoretenuous.Silveristhemostsignificantmineralization,butthereisalsorecoverablelead,zinc,copperandgold.Associatedganguemineralsarepyrite,arsenopyrite,quartz,siderite,andcalcite.Thereisastrongmineralzoningwithinthedistricts:silver-zin
64、cwithpyritenearthestockssilver-copperwithsideritealongthesouthandsoutheastedgeofthedistrictsilver-leadeastandwestsidesofthedistrictAlterationislargelyrestrictedtosericitization.Otheralterationincludeslocalsilicificationandweakbleaching.2021/9/2147GenesisTheCoeurdAleneveinswerelongthoughttoberelatedt
65、ointrusionoftheMesozoicIdahobatholith,howeverU/PbisotopesindicatedagesthatwereProterozoic.Thispresentedamajorproblem.DiscoveryofundeformedstratiformoresintheBeltSupergrouptotheeastinMontanathatareclearlyunrelatedtoigneousactivityhavecausedsomegeologiststoproposeamodifiedgeneticmodel.TheybelievethattheCoeurd扐leneoreswereoriginallydepositedasstratiformsediment-hostedsulfidesduringthePrecambrianandremobiizedtotheircurrentlocationsduringtheMesozoicbyheatfromtheintrusives.2021/9/21482021/9/2149
