新疆包古图金矿中发现的自然铋及其找矿勘探意义  

Native bismuth found in Baogutu gold deposit and its geological significance

作　　者：郑波[1] 安芳[1] 朱永峰[1] 

机构地区：[1]北京大学地球与空间科学学院,造山带与地壳演化教育部重点实验室,北京100871

出　　处：《岩石学报》2009年第6期1426-1436,共11页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(40572033);国家科技支撑计划重点项目(2006BAB07BO8)资助.

摘　　要：包古图金矿Ⅺ区位于新疆西准噶尔包古图地区,为富金属硫化物脉型金矿床,其赋矿围岩为下石炭统希贝库拉斯组凝灰岩和安山岩。成矿过程可划分为热液演化期和表生氧化期,其中热液演化期是主要的金矿化期,由三个热液演化阶段组成:(Ⅰ)石英-硫化物阶段,形成不含金的石英-硫化物脉,主要矿物组合为石英-毒砂-黄铁矿-黄铜矿,成矿流体的温度为460～510℃,logf_(s_2)=-4.8～-6.4;(Ⅱ)硫化物-金-铋阶段,该阶段早期形成毒砂-黄铁矿组合,流体温度为420～470℃,logf_(s_2)=-5.2～-7.0,晚期沉淀了黄铜矿-辉铋矿-自然铋-自然金组合,是主要的金矿化阶段;(Ⅲ)钠长石-方解石阶段,在围岩中形成以钠长石为主,含少量方解石和石英的细脉。自然铋通常以熔滴状、不规则粒状被毒砂、黄铜矿和黄铁矿包裹,呈脉状充填于毒砂和闪锌矿裂隙中。自然金是该矿中主要的含金矿物,与自然铋共生或在自然铋中呈出溶结构,自然铋常被辉铋矿部分或全部交代。在热液演化早期(阶段Ⅰ)铋主要以Bi_2S_2(OH)_2~0、HBi_2S_4^-的形式运移,随着热液温度和硫逸度的变化Bi_2S_2(OH)_2~0、HBi_2S_4^-分解形成自然铋,但此时热液的温度(420～470℃)高于自然铋的熔点271℃,因此,自然铋主要呈熔融状态存在于热液中,熔融态的自然铋吸附热液中的金形成Bi-Au熔体体系,随着温度下降,Bi-Au熔体固结形成自然铋-自然金组合。成矿体系温度下降,液态Bi-Au合金结晶并分解是包古图金矿的重要成矿机制。The Baogutu gold deposit composed of gold-bearing sulfide veins is located in Baogutu region of western Junggar, Xinjiang. The gold-bearing sulfide veins are hosted in tuff and andesite in Lower Carboniferous Xibeikulasi Formation. Ore-forming process of the Baogutu gold deposit is divided into hydrothermal period and supergene period. The hydrothermal period is further subdivided into three stages: Quartz-sulfide stage ( I), sulfide-gold-bismuth stage) and albite-calcite stage (III). Quartz-arsenopyrite-pyrite-chalcopyrite is the major mineral assemblages formed at stage I Arsenopyrite-pyrite and chalcopyrite-native bismuth-native gold-bismuthinite assemblages formed at stage H. The temperature ( 510 similar to 420 degrees C) and sulfur fugacity ( -4.8 similar to -7 log units) decrease from stage I to stage II-a. The stage II -b is the main period for gold precipitation. Native bismuth co-precipitated with native gold. It is always enclosed by arsenopyrite, chalcopyrite and pyrite as droplets, or fills the fractures of arsenopyrite and sphalerite as veinlets. The native bismuth, replaced by bismuthinite, generally coexists with or exsolves native gold. Bismuth is transported as Bi(2)S(2)(OH)(2)(0) or HBi(2)S(4)(-) specie in stage I ore-forming fluid of the Baogutu gold deposit. Bi(2)S(2) (OH)(2)(0) or HBi(2)S(4) begin to decompose into native bismuth at stage II-a, which is induced by The decrease of temperature and sulfur fugacity. The bismuth is in molten state, as the temperature of the ore-forming fluid at stage II-a (420 similar to 470 degrees C) is higher than its melting temperature. The bismuth melt scavenges An in ore-forming fluid. The temperature decrease in such fluid leads to the crystallization of native gold and native antimony assemblage in the Baogutu gold deposit.

关 键 词：自然铋 金矿化 包古图 西准噶尔 新疆 

分 类 号：P618.51[天文地球—矿床学] P618.69[天文地球—地质学]