贵州贞丰水银洞金矿矿床成因与成矿模式:来自载金黄铁矿NanoSIMS多元素Mapping及原位微区硫同位素的证据
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摘要
贵州贞丰水银洞金矿是中国"滇黔桂"金三角地区最具代表性的超大型卡林型金矿床之一。黄铁矿和毒砂是水银洞金矿的主要载金矿物。背散射电子图像和NanoSIMS高分辨率元素面扫描分析显示载金黄铁矿普遍发育环带结构,不同环带的微量元素种类和含量有显著差别。如增生环带富集Au、Cu、As元素,而核部则相对贫这些元素,富Se。同时,即使在富Au环带中,Au和微量元素也并非均匀分布,环带之中又发育次一级环带。这表明热液来源呈现阶段性和"脉冲式"特征。在元素面扫描分析(Mapping)基础上,本次研究对载金黄铁矿中不同成分特征的核部和环带分别进行了原位硫同位素分析。结果表明:黄铁矿核部的δ34S值变化范围为1.3‰~6.5‰,而富金环带的δ34S值为-3.5‰~7.4‰。与国内外同类矿床的硫同位素特征比较之后发现,这些硫同位素显示岩浆硫特征,暗示载金黄铁矿的硫主要来源于深源岩浆。计算表明,有部分沉积硫混入了成矿流体。最终,我们为水银洞金矿建立了岩浆-热液模式:从深源岩浆分异出的超临界气-液流体携带Au、As等元素沿区域深断裂上升,在区域不整合面和灰家堡背斜轴部破碎带等构造薄弱部位,通过充填、交代围岩的方式沉淀成矿。大气降水的淋滤和渗透在一定程度上有利于金矿化。
The Shuiyindong gold deposit is a typical large Carlin-type gold deposit.It is located in the"Golden Triangle"area crossing Yunnan,Guizhou and Guangxi provinces where arsenian pyrite and arsenopyrite are the significant Au-carrying minerals with invisible gold.In this study,Back Scattered Electron(BSE)imaging and high-resolution Multi-Element Mapping by NanoSIMS show that the pyrites usually have the zonal texture containing lower Au,As in the core and higher Au,As and Cu in the overgrowth rim.The trace element pattern implies that the ore fluid is Au,As,Cu-rich during the pyrite overgrowth stage.In addition,highresolution NanoSIMS mapping reveals that the Au-rich rim is composed of several unevenly distributed fine subzones,marked by the banded pattern of Au,As and Cu due to episodic hydrothermal fluid variation.Meanwhile,in situ sulfur isotopic analysis of pyrite shows that theδ34 S values of cores and rims range from1.3‰to 6.5‰ and-3.5‰ to 7.4‰,respectively,focusing generally around 0‰.This result,combined with similar gold deposits around the world,indicates that sulfur is likely originated from the deep magmatic source contaminated by sedimentary sulfur.Finally,a magmatic-hydrothermal model is proposed for the Shuiyindong gold deposit.It suggests that the As and Au-bearing acid magmatic fluid upwelled along the deep fault to fill or react with Fe-rich wall rocks,which led to the deposition of gold;in addition,the meteoric water might have been involved in the ore formation.
The Shuiyindong gold deposit is a typical large Carlin-type gold deposit.It is located in the"Golden Triangle"area crossing Yunnan,Guizhou and Guangxi provinces where arsenian pyrite and arsenopyrite are the significant Au-carrying minerals with invisible gold.In this study,Back Scattered Electron(BSE)imaging and high-resolution Multi-Element Mapping by NanoSIMS show that the pyrites usually have the zonal texture containing lower Au,As in the core and higher Au,As and Cu in the overgrowth rim.The trace element pattern implies that the ore fluid is Au,As,Cu-rich during the pyrite overgrowth stage.In addition,highresolution NanoSIMS mapping reveals that the Au-rich rim is composed of several unevenly distributed fine subzones,marked by the banded pattern of Au,As and Cu due to episodic hydrothermal fluid variation.Meanwhile,in situ sulfur isotopic analysis of pyrite shows that theδ34 S values of cores and rims range from1.3‰to 6.5‰ and-3.5‰ to 7.4‰,respectively,focusing generally around 0‰.This result,combined with similar gold deposits around the world,indicates that sulfur is likely originated from the deep magmatic source contaminated by sedimentary sulfur.Finally,a magmatic-hydrothermal model is proposed for the Shuiyindong gold deposit.It suggests that the As and Au-bearing acid magmatic fluid upwelled along the deep fault to fill or react with Fe-rich wall rocks,which led to the deposition of gold;in addition,the meteoric water might have been involved in the ore formation.
引文
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[6]刘家军,刘建明,顾雪祥,等.黔西南微细浸染型金矿床的喷流沉积成因[J].科学通报,1997(19):2126-2127.
[7]刘建中,邓一明,刘川勤,等.水银洞金矿床包裹体和同位素地球化学研究[J].贵州地质,2006,23(1):51-56.
[8]刘建中,邓一明,刘川勤,等.贵州省贞丰县水银洞层控特大型金矿成矿条件与成矿模式[J].中国地质,2006,33(1):169-177.
[9]刘建中,夏勇,张兴春,等.层控卡林型金矿床矿床模型:贵州水银洞超大型金矿[J].黄金科学技术,2008,16(3):1-5.
[10]刘建中,刘川勤.贵州水银洞金矿床成因探讨及成矿模式[J].贵州地质,2005,22(1):9-13.
[11]唐波,张敏,黄建国,等.黔西南“水银洞式”金矿成因研究[J].矿物学报,2008,27(3):450-455.
[12]CHEN M H,ZHANG Z Q,SANTOSH M,et al.The Carlin-type gold deposits of the“Golden Triangle”of SW China:Pb and S isotopic constraints for the ore genesis[J].Journal of Asian Earth Sciences,2015,103:115-128.
[13]CHEN M M,CAMPBELL I H,XUE Y X,et al.Multiple sulfur isotope analyses support a magmatic model for the volcanogenic massive sulfide deposits of the Teutonic Bore volcanic complex,Yilgarn Craton,western Australia[J].Economic Geology,2015,110:1411-1423.
[14]SU W C,ZHANG H T,HU R Z,et al.Mineralogy and geochemistry of gold-bearing arsenian pyrite from the Shuiyindong Carlin-type gold deposit,Guizhou,China:implications for gold depositional processes[J].Mineralium Deposita,2012,47(6):653-662.
[15]宋发治.贵州水银洞金矿床地质特征及成因研究[D].成都:成都理工大学,2009:1-50.
[16]赵静,梁金龙,韩波.水银洞金矿与阳山金矿载金矿物成分分析及金的赋存状态[J].科技通报,2017,33(1):24-31.
[17]ZHANG J C,LIN Y T,YANG W,et al.Improved precision and spatial resolution of sulfur isotope analysis using NanoSIMS[J].Journal of Analytical Atomic Spectrometry,2014,29:1934-1943.
[18]张锦让,侯林,邹志超,等.泥堡金矿床载金含砷黄铁矿的微量元素LA-ICP-MS原位测定及其对矿床成因的指示意义[J].岩石矿物学杂志,2016,35(3):493-505.
[19]LARGE R R,DANYUSHEVSKY L,HOLLIT C,et al.Gold and trace element zonation in pyrite using a laser imaging technique:implications for the timing of gold in orogenic and Carlin-style sediment-hosted deposits[J].Economic Geology,2009,104:635-668.
[20]OHMOTO H,RYE R.Isotopes of sulfur and carbon[M]∥BAMES H L.Geochemistry of hydrothermal ore deposits.2nd ed.New York:John Wiley and Sons,1979:509-567.
[21]尹观,倪师军.同位素地球化学[M].北京:地质出版社,2009:1-409.
[22]陕亮,郑有业,许荣科,等.硫同位素示踪与热液成矿作用研究[J].地质与资源,2009(3):197-203.
[23]张宏飞,高山.地球化学[M].北京:地质出版社,2012:1-410.
[24]陈道公,支霞臣,杨海涛.地球化学[M].2版.安徽:中国科学技术大学出版社,2009:1-449.
[25]王泽鹏,夏勇,宋谢炎,等.黔西南灰家堡卡林型金矿田硫铅同位素组成及成矿物质来源研究[J].矿物岩石地球化学通报,2013,32(6):746-752+758.
[26]赵静,梁金龙,向启荣,等.甘肃阳山金矿载金黄铁矿硫同位素Nano-SIMS原位分析[J].矿床地质,2016,35(4):653-662.
[27]陈骏,王鹤年.地球化学[M].北京:科学出版社,2014:1-418.
[28]肖德长,李葆华,顾雪祥,等.贵州水银洞金矿床成矿物理化学条件及金的迁移和沉淀[J].物探化探计算技术,2012,34(1):73-79.
[29]曾键年,范永香,林卫兵.江西金山金矿床成矿物质来源的铅和硫同位素示踪[J].现代地质,2002,16(2):170-176.
[30]TAN Q P,XIA Y,XIE Z J,et al.S,C,O,H,and Pb isotopic studies for the Shuiyindong Carlin-type gold deposit,Southwest Guizhou,China:constraints for ore genesis[J].Chinese Journal of Geochemistry,2015,34(4):525-539.
[31]HOU L,PENG H J,DING J,et al.Textures and in situ chemical and isotopic analyses of pyrite,Huijiabao trend,Youjiang Basin,China:implications for paragenesis and source of sulfur[J].Economic Geology,2016,111:331-353.
[32]彭义伟,顾雪祥,章永梅,等.黔西南灰家堡金矿田成矿流体来源及演化:流体包裹体和稳定同位素证据[J].矿物岩石地球化学通报,2014,33(5):666-680.
[33]张瑜,夏勇,王泽鹏,等.贵州簸箕田金矿单矿物稀土元素和同位素地球化学特征[J].地学前缘,2010,17(2):385-395.
[34]YANG L Q,DENG J,LI N,et al.Isotopic characteristics of gold deposits in the Yangshan Gold Belt,West Qinling,central China:implications for fluid and metal sources and ore genesis[J].Journal of Geochemical Exploration,2016,168:103-118.
[35]韩春明,袁万明,于福生,等.甘肃省玛曲大水金矿床地球化学特征[J].地球学报,2004,25(2):127-132.
[36]张静,苏蔷薇,刘学飞,等.滇东南老寨湾金矿床地质及同位素特征[J].岩石学报,2014,30(9):2657-2668.
[37]章永梅,顾雪祥,摆祥,等.云南富宁者桑金矿床硫铅同位素地球化学特征与成矿物质来源[J].地学前缘,2013,20(1):32-39.
[38]KESLER S E,RICIPUTI L C,YE Z.Evidence for a magmatic origin for Carlin-type gold deposits:isotopic compositiion of sulfur in the Betze-Post-Screamer Deposit,Nevada,USA[J].MIneralium Deposita,2005,40:127-136.
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