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1、姓名学号Report1BROKENHILLTYPEDEPOSITSGeneralfeature,Genesis:BHTtypedepositsoccurinhighgrademetamorphicrocks,dominantlyofMiddleProterozoicage.Anassociationwithvolcanismisapparentinsomedeposits,wheremaficandfelsicmetavolcanicrocksarerecognisedinthestratigraphicfootwall;hangingwal
2、lrocksaremetasedimentary.Mineralisationisassociatedwithaverycomplexexhalitefaciesstratigraphicunit,nowconsistingofBIF,marble,calc-silicates,gahnite-bearingquartzites,sulfidicquartzites,amphibolites,andpeliticandpsammiticschistsandgneisses.ThegenesisofBHisofgreathistoricalim
3、portancetogeologists,andoneofthemoststudiedintheworld,withover1,500paperspublishedtodate.Itisalsoofgreatcurrentimportance,asconceptionsofthegenesisofthisenigmaticoredepositanditsstructuralandstratigraphicsettingdrivesexplorationforrepetitionsoftheoredepositalongstrike,andin
4、findinganalogueselsewhereintheworld.Characterofmineralization:massivetodisseminatedsphaleriteandgalenainstructurallythickenedpodsandlenseswithinaveryvariablemetamorphosedexhalativehostunit.Ironsulfidesarecommonlyminororabsent,butmaybepresent,andinsomecasespyrrhotitemaybeloc
5、allyabundant.Manganesemineralsandfluoritearecommon.Fluidsourceanddeposition:Fluidsofuncertainorigin,probablymagmatic,possiblymarineorconnatebrines;depositionbydilution,cooling,andpHincrease.Age:MiddleProterozoicmostfavorable(about1600Ma).Controlsondistribution:Stronglydefor
6、medintracratonicriftorpassivecontinentalmargin,withhighheatflow(usuallywithabundantvolcanicrocks).Lookfor:IntenselydeformedandstronglymetamorphosedMiddleProterozoicterrainswithmetasedimentaryandmetavolcanicschistsandgneisses;thinbutextensiveandveryvariableexhalativestratigr
7、aphicunitswithbasemetaloccurrences;localthickeningandincreaseddiversityofexhalites;manganeseenrichment;gahnite-bearingrocks.Examples:BrokenHill,NSW(235Mtat11.3%Pb,9.8%Zn,178g/tAg)5Mainexplorationmethods:Identifyfavorableterrainsfromgeologicalmaps,aeromagneticdataandgeochron
8、ology.Regionalaeromagneticsurveystoidentifyfavorablestratigraphyanddirecttargets;r
