SourceofMetalsforGiantVMSOreDeposits超大型VMS礦床的金屬物質(zhì)來源SteveScottDepartmentofGeologyUniversityofTorontoCUGBOctober2009OUTLINE

綱要Volcanogenichydrothermalmassivesulfidedepositsandthequestionoftheirmetalsource(Cu,Zn,Pb,Ag,Au)

火山成因熱液塊狀硫化物礦床及其金屬（Cu、Zn、Pb、Ag、Au）來源問題Evidencefrommeltinclusionsforamagmaticsourceofmetals

巖漿源金屬熔體包裹體證據(jù)VolcanogenicmassiveFe-Cu-Zn-Pb-Ag-Ausulfideoresareproductsofhightemperaturehydrothermalactivityinsubmarinevolcanicand

sedimentary

terrainsPhotocourtesyofRayBinns,CSIRO,Australia火山成因塊狀Fe-Cu-Zn-Pb-Ag-Au硫化物礦石是水下火山和沉積地體中高溫熱液活動的產(chǎn)物PACMANUSsite(1600m)EasternManusBasin,PNGVMSdepositscanbeverylargesuchasKiddCreek,Canadaat170x106mtorBrunswick#12,Bathurst,Canadaat236x106mtor

85depositsintheIberianPyrite

Belt(SpainandPortugal)

at1,765x106mt

VMS礦床可能規(guī)模巨大，如加拿

大的KiddCreek（1.7億噸）等。Whatisthesourceofallthatmetal?

其金屬來源如何？Thesourceofthemetalsinavolcanogenicmassivesulfidedeposithasbeendebatedfor150years….

這種金屬來源之爭已持續(xù)了150年之久….Leachedfrom

theunderlying

volcanicrocks?

淋濾下伏火山巖

ORMagmatic

fluid?

巖漿流體PhotocourtesyofRogerHekinianLeachingproducesdilutesolutions

淋濾產(chǎn)生稀熔體Metalscanbecontributed

directlyfromamagma

巖漿直接提供金屬GasesinsubmarineventsaresimilartomagmaticgasesfromsubaerialvolcanoesDeRonde(1995)水下噴氣孔中的氣體與海底火山中的巖漿氣體相近。Kurokoore-formingfluidslieonamixinglinebetweenseawater(SMOW)andmagmaticfluidat~30%magmaticfluid

黑礦成礦流體位于海水和30％巖漿流體的混合線上Calculationoffluidvolumesrequiredtoproduce100million

metrictonsofmassivesulfides

流體體積計算需要

產(chǎn)生1億噸塊狀硫化物

Convectiveseawateronly

Totalmetals=88ppm

Volumeofventfluid

=790km3

只是海水對流時，總金屬量＝88ppmX790km3的噴氣孔流體溶液44thousandm3/dayfor100,000years

如果每天4.4萬m3，只需10萬年Additionofa“magmaticfluid”…

StableisotopedataforKurokodepositssuggest30%magmaticfluid.

For30%ofmagmaticfluidcontaining100xmoremetalsthantheconvectivesystem,totalmetals=5586ppm

另外，巖漿流體中：黑礦的穩(wěn)定同位素顯示有30％巖漿流體；30％的巖漿流體含有較循環(huán)系統(tǒng)多100倍以上的金屬，總量=5586ppmVolumeofmixedventfluidrequired=26km3

所需噴氣孔流體混合量＝26km3LeachingModelfor100mmtVMSDepositwith2%Cuand7%Zn(e.g.,KiddCreek,Canada)

KiddCreek礦床（VMS型，1億噸礦石，2%Cu,7%Zn）的淋濾模型

Rockleachedis75%basalt(99ppmCu,65ppmZn)and25%dacite(17ppmCu,90ppmZn).

巖石淋濾75%玄武巖(99ppmCu,65ppmZn)

和25%英安巖(17ppmCu,90ppmZn).

Assume100%ofthemetalintheventfluidisprecipitated(actual5-10%).

假設100%的噴氣流體中的金屬均沉積下來（通常5－10%）Heatsourceat2kmmaximumdepth..

熱源位于最大2km的深度Leachingmodelcont’d….淋濾模型

For10%metalsprecipitated,multiplyx10

沉積10%的金屬，乘以10LeachingEfficiency淋濾程度Km3LeachedforCuKm3LeachedforZnDimensionsinKmCu/Zn100%40264.5x4.5x23.6x3.6x210%40026014x14x211x11x21%4000260045x45x236x36x2AtHorneMine,Noranda(MacLeanandHoy,1991,EconomicGeology)

以加拿大Horne

礦為例59milliontonsmined@2.2%Cu

采出的銅礦石5+km3ofalteration

蝕變范圍

Fromprevioustable,expectalterationzone8times(@100%efficiency,100%precipitated)to8000times(@1%efficiency,10%precipitated)thissizeifleachingistheonlymetalsource

根據(jù)前表，預計蝕變帶為8倍（100％淋濾，100％沉積）到8000倍（1％淋濾，10％沉積），如果發(fā)生淋濾，這樣大小的范圍完全可以提供礦床全部金屬。Meltinclusionsandsmallvesiclesprovidedirectevidenceformetal-richmagmaticfluids

熔體包裹體及氣泡提供了富金屬巖漿流體的直接證據(jù)Growingphenocryststrapmagmawithdissolvedvolatiles(CO2,H2O)

生長的斑晶包裹了巖漿及氣泡

…or…

magmaANDexsolvedvolatiles.

巖漿及出融氣泡Vesiclesareformedbydegassingofmagmaorlavaandcanpreserve

volatiles.

氣泡由巖漿或者熔巖

脫氣而成，能夠呈揮

發(fā)份保留。

VesicularbasalticandesitefromEasternManusBasin,PNG

巴布亞新幾內(nèi)亞的氣孔玄武安山巖Thetrappedmagmaticfluidcontainsveryhighconcentrationsoforemetalsandrelated

elements

所圈閉的巖漿流體富含成礦金屬及相關元素

Examples:

實例EasternManusBasin,PapuaNewGuineaBathurst,CanadaGlassVapourbubblesPyroxenephenocrystEasternManusBasin:modernimmatureriftedarc

現(xiàn)代正在活動的擴張弧

Bathurst:Ordovicianarconcontinentalmargin

奧陶紀大陸邊緣弧GeologyofEasternManusBasin

盆地地質(zhì)圖MeltinclusionsinManusVolcanics

Manus盆地火山巖中熔體包裹體zoneofmeltinclusions200mmfluidbubble100mmglassdaughtermineral0.05mmOlivinePyroxenePyroxenePlagioclaseCl,SandH2OinManusBasalticAndesite:Evidencefordegassinginthemagmachamberbeforeeruption

Manus玄武安山巖中Cl、S、H2O證據(jù)：巖漿房在噴出前脫氣

H2O+wr=0.7%,S=0.01%H2O+=1.6%,S=0.09%MetalPrecipitatesinVaporCavityofMeltInclusioninManusAndesite

Manus安山巖所含熔體包裹體的氣孔中金屬沉積EDSSpectraofPrecipitatesinManusMeltInclusions

EDS光譜顯示熔體包裹體沉積AgandAuinVapourCavityofMeltInclusioninPyroxenebyTOF-SIMS(Yang,unpublished)EasternManusBasin

(PGEsalsoweredetected)

輝石熔體包裹體氣孔中Ag,Au,還測到了PGE元素MetalPrecipitatesinVesicleofManusBasalticAndesite

Manus

玄武安山巖氣孔中金屬沉積

MetalPrecipitatesinVaporCavityofMeltInclusioninBathurstQuartz

石英所含熔體包裹體的氣孔中的金屬沉積Bathurstaqueousinclusions1.Primarysaline(KCl,NaCl)fluidinclusionsinquartzphenocrysts

石英斑晶中原生鹽流體包裹體2.FluidinclusionwithPbandZnsulfidesinmagmaticzircon

巖漿鋯石中流體包裹體及Pb、Zn硫化物3.Fluidinclusionsinhigh-F(5.3%)magmaticapatite

高F（5.3％）巖漿磷灰石中的流體包裹體ApatitefluidinclusionsfluidinclusionZircon123OreMetalsinPrecipitatesandVapourCompositioninVesiclesandinMeltInclusionsvsLavaComposition,Manus

沉積中的成礦金屬及氣孔和熔體包裹體中氣體成分與熔巖成分關系圖CO2-richvapourH2O+CO2-richvapourNotdegassedpriortoeruption

Degassedinmagma常規(guī)模型對比MagmaticModel

巖漿模型Take-homemessagesConclusionsLeachingcannotprovideenoughmetalstoformmostgiantandsomesmallVMSdeposits.

淋濾不能提供足夠的金屬以形成多數(shù)的巨型礦床和許多小型VMS礦床Magmaticfluidsareme