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  

LA-ICP-MS in situ trace element analysis of auriferous arsenic pyrites from the Nibao gold deposit and its constraints on the ore genesis

作　　者：张锦让 侯林 邹志超[2] 朱斯豹 吴松洋 

机构地区：[1]成都地质调查中心,四川成都610081 [2]成都理工大学地球科学学院,四川成都610059

出　　处：《岩石矿物学杂志》2016年第3期493-505,共13页Acta Petrologica et Mineralogica

基　　金：国家自然科学基金青年基金项目(41403038);国家重点基础研究发展计划项目(2009CB421005);中国地质调查局综合研究项目(12120113094400)~~

摘　　要：泥堡金矿床为黔西南地区新近发现的又一个重要的卡林型金矿床,显微镜下观察和电子探针分析显示,含砷黄铁矿是其主要的载金矿物。在详细的野外调研和室内观察的基础上,将该矿床中的载金含砷黄铁矿分为3种类型,即环带状含砷黄铁矿(PyⅠ)、胶状含砷黄铁矿(PyⅡ)和生物结构状含砷黄铁矿(PyⅢ)。电子探针和LA-ICP-MS原位主微量元素测定结果显示,PyⅠ明显存在继承核和增生环带,内核富S、Fe,贫Au、As、Ag、Cu等中低温成矿元素,为沉积成因或成矿前热液成因黄铁矿;增生环带则相对贫S、Fe,富Au、As、Ag、Cu等中低温成矿元素,为主成矿期热液成因黄铁矿。PyⅡ和PyⅢ均为均质结构,具有富Au、As、Ag、Cu等中低温成矿元素及贫S、Fe的特点,类似PyⅠ的增生环带,应与PyⅠ的增生环带为同一成因类型,可能是同期形成的。毒砂中普遍富As,而贫Au、Ag、Hg、Cu等元素,应为成矿热液晚期的结晶产物。综合分析认为,泥堡金矿床载金矿物的结晶顺序为:贫砷的沉积成因或早阶段热液成因黄铁矿(PyⅠ内核)→含砷黄铁矿颗粒+含砷黄铁矿环带(PyⅠ增生环带)→毒砂。矿床中Au、Ag、As、Cu等成矿物质主要来自于燕山晚期的岩浆热液系统。Located in southwestern Guizhou Province, the Nibao gold deposit discovered recently is an important Carlin-type gold deposit. Pyrite is the major gold-bearing mineral in the deposit. Petrographic observations and electron microprobe analysis （EPMA） of sulfides from the Nibao gold deposit show that arsenic pyrites is the major gold-bearing mineral. A combined detailed field work, ore petrographic investigation and EPMA studies revealed three kinds of arsenic pyrites, i.e., zoned arsenic pyrite （PyⅠ）, colloidal arsenic pyrite （PyⅡ）, and bioclastic arsenic pyrite （PyⅢ）. The EPMA and LA-ICP-MS analyses indicate that PyⅠ is mainly composed of pyrite core and arsenic pyrite zones, formed in different metallogenic stages. Pyrite core is characterized by high S, Fe concentrations and low Au, As, Ag and Cu, indicating a sedimentary-diagenetic origin or precipitation in the early metallogenic stage. Zoned arsenic pyrite, growing along pyrite core, is characterized by high Au, As, Ag, and Cu concentrations, indicating a main mineralization hydrothermal origin. The colloidal and bioclastic arsenic pyrites with homogeneous texture are similar to the rims of zoned pyrite with characteristics of high Au, As, Ag, Cu and low S, Fe, indicating that PyⅡ and PyⅢ were probably formed synchronously with the arsenic pyrite zones of PyⅠ. Arsenopyrite mainly occurs as overgrowths on arsenic pyrite and has rich As and poor Au, Ag, and Cu concentrations, suggesting that arsenopyrite was probably formed in the post-mineralization stage. The precipitation order of gold-bearing sulfides is as follows：As-poor sedimentary pyrites or early metallogenic stage pyrites→arsenic pyrites→arsenopyrite. Textures, paragenesis and trace element geochemistry of pyrite indicate that As-poor pyrite core mainly deposited during sedimentation, while most of economic metals （Au, Ag, As, and Cu） were introduced through the Late Yanshanian subsequent hydrothermal superimposition. The compositions of the gold-bearing pyrite

关 键 词：LA-ICP-MS 含砷黄铁矿 微量元素 泥堡金矿床 黔西南 

分 类 号：P578.292[天文地球—矿物学] P618[天文地球—地质学]