藏北商旭造山型金矿床成矿物质来源探讨:C、S、Pb同位素证据  

Sources of Ore-forming Materials in the Shangxu Orogenic Gold Deposit,Northern Xizang(Tibet) : Constraints form C,S,and Pb Isotopes

作　　者：刘洪[1] 李光明[1] 黄瀚霄[1] 肖万峰[2] 闫国强[3] 马东方[1] 张海[1] 张红[1] LIU Hong;LI Guangming;HUANG Hanxiao;XIAO Wanfeng;YAN Guoqiang;MA Dongfang;ZHANG Hai;ZHANG Hong(Chengdu Center,China Geological Survey,Chengdu,610081;Henan Institute of Geological Survey,Zhengzhou,450001;Tianjin Center,China Geological Survey,Tianjin,300170)

机构地区：[1]中国地质调查局成都地质调查中心,成都610081 [2]河南省地质调查院,郑州450007 [3]中国地质调查局天津地质调查中心,天津300170

出　　处：《地质论评》2018年第5期1285-1301,共17页Geological Review

基　　金：国家重点研发计划(编号:2016YFC0600308;SQ2018YFC060162);中国地质调查项目(编号:DD20160015;DD20160026);中国地质调查局成都地质调查中心青藏高原国际大科学计划;国家自然科学基金资助项目(编号:41702080;41702086)的成果~~

摘　　要：西藏双湖县商旭金矿床位于班公湖—怒江缝合带中段。矿床受近东西向断裂控制,赋存于中—下侏罗统木嘎岗日群浅变质增生混杂岩中。本文研究主成矿阶段石英流体包裹体中CO_2的C同位素及共生硫化物的S—Pb同位素组成特征,并与木嘎岗日群、虾别错—木嘎岗日山花岗岩等主要地质体对比。含金石英脉流体包裹体中CO_2的δ^(13)C_(V-PDB)值范围为-17.8‰～-23.1‰,均值为-21.3%,接近沉积岩或者变质岩源有机碳,表明商旭金矿床的成矿流体可能来自于木嘎岗日群的变质流体,而含金石英脉中发育着与虾别错—木嘎岗日山花岗岩同时代的少量岩浆锆石,暗示成矿流体还有岩浆热液的加入。共生硫化物δ^(34)S_(V-CDT)值变化于-4.5‰～4.6‰,均值为-1.6‰,具有深源硫(地幔或下地壳,δ^(34)S_(V-CDT)=-3‰～+3‰)的特征;共生硫化物Pb同位素位素[n(^(206)Pb)/n(^(204)Pb)=18.350～18.690、n(^(207)Pb)/n(^(204)Pb)=15.632～15.700、n(^(208)Pb)/n(^(204)Pb)=38.570～38.980]与早白垩世虾别错—木嘎岗日山花岗岩[n(^(206)Pb)/n(^(204)Pb)=18.558～19.169、n(^(207)Pb)/n(^(204)Pb)=15.616～15.651、n(^(208)Pb)/n(^(204)Pb)=38.838～39.154]基本一致,同时向侏罗统木嘎岗日群[n(^(206)Pb)/n(^(204)Pb)=18.630～18.970、n(^(207)Pb)/n(^(204)Pb)=15.619～15.673、n(^(208)Pb)/n(^(204)Pb)=38.887～39.260]略有漂移,暗示商旭金矿床的Pb可能来源于早白垩世岩浆活动,同时还有部分来自木嘎岗日群中铅的加入。本次研究认为,商旭金矿的成矿物质部分来自深部壳幔岩浆作用,并被成矿热液携带至浅部。木嘎岗日群围岩也贡献了部分成矿物质,被地层中的变质热液携带到成矿流体中。Objectives： The Shangxu gold deposit in the Shuanghu County,Xizang（ Tibet）,is located in the central segment of the Bangong Lake — Nujiang River suture.The deposit is controlled by EW-trending faults,and is hosted in melange of the Middle—Lower Jurassic Mugagangri Group.In this study we focus on the sources of oreforming materials in the Shangxu orogenic gold deposit,was beneficial for the study of genesis for the ore deposit,and provide new constraints for understanding the dynamic background of orogenic gold metallization in the Bangong Lake — Nujiang River suture.Methods： In this study,the Carbon isotopes of the CO2 inclusions in ore-stage quartz,and the sulfur and lead isotopes of sulfides are analyzed for discuss the sources of ore-forming materials in the Shangxu orogenic gold deposit.Results： The δ^13C（CO2（V-PDB）） values of fluid inclusions range from -17.8‰ to -23.1‰,with a mean of -21.3%,which is similar to that of the sedimentary or metamorphic rocks.This indicate that the ore-forming fluids of the Shangxu gold deposit may originated from the Mugagangri Group.Meanwhile,a few magmatic zircons,which yield the same U-Pb age with the Xiabie Co–Mogagangri San granite,are detected in auriferous quartz veins,suggesting that the magmatic hydrothermal fluids may have been involved during the ore-forming process.The δ^34S（V-CDT） values of sulfides vary from-4.5‰ to 4.6‰,with a mean of-1.6‰,which is characteristic of a deep sulfur source,The Pb isotopic compositions of the sulfides（ n（^206Pb）/n（^204Pb） = 18.350～18.690,n（^207Pb）/n（^204Pb） = 15.632～15.700,n（^208Pb）/n（^204Pb） = 38.570～38.980） are similar to those of the Xiabie Co–Mogagangri San granite（ n（^206Pb）/n（^204Pb） = 18.558～19.169,n（^207Pb）/n（^204Pb） = 15.616～15.651,n（^208Pb）/n（^204Pb） = 38.838～39.154） and slightly drifting to the Jurassic Mugagangri Group（ n（^206Pb）/n（^204Pb） = 18.630～18.970,n（^207Pb）/n（^204Pb） = 15.619～15.673

关 键 词：西藏 班公湖—怒江 商旭金矿 造山型金矿床 物质来源 稳定同位素 

分 类 号：P618.51[天文地球—矿床学]