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DOI:
:2009,Vol.>>Issue(5):539-557

滇黔桂“金三角”卡林型金矿含砷黄铁矿和毒砂的矿物学研究
中国地质科学院矿产资源研究所
Mineralogy of arsenian pyrites and arsenopyrites of Carlin_type gold deposits in Yunnan-Guizhou-Guangxi “golden triangle" area, southwestern China
陈懋弘,毛景文,陈振宇,章 伟
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中文摘要:滇黔桂“金三角”卡林型金矿不同矿床亚类的典型矿床硫化物显微镜下观察和电子探针显微分析(EPMA)表明,含砷黄铁矿和毒砂是主要的载金矿物。载金黄铁矿主要以环带状含砷黄铁矿、细粒自形含砷黄铁矿为主。环带状黄铁矿核部贫As、Au,富S、Fe,而环带则相反,且Au与As具有正相关关系。核部贫As的黄铁矿成因复杂,既有成矿早阶段的热液成因,又有受热液蚀变交代的沉积成因。核部和环带是不同成矿阶段的产物。元素的相关关系表明环带中As主要取代S的位置。多环带的特点还表明,热液活动是脉动式的,含矿流体化学成分也是在不断变化的。不论是核部还是环带,均有Au含量高出检出限的测点,但环带是主要的载金部位。细粒含砷黄铁矿为均质结构,具有高As、Au,低S、Fe的特点,类似环带状黄铁矿的环带特征,推测与富砷环带是同期热液活动形成的。毒砂_黄铁矿集合体中的黄铁矿分为环带结构和均质结构2种,并分别具有上述2种黄铁矿的特点。载金毒砂可以细分为3个世代,具均质结构,热液成因。各世代毒砂Au含量均有高出检出限的测点,同时Au、As、S、Fe的含量变化不大,均为主成矿阶段的产物。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→富砷的细粒黄铁矿颗粒和富砷黄铁矿环带→毒砂。黄铁矿和毒砂中的Au在EPMA微束的分辨率下均显示分布是不均匀的,环带状黄铁矿中Au元素图出现的均匀结构可能为一种假象,说明金主要以“不可见”的纳米级超显微包裹金形式存在,少量为“不可见”晶格金和微米级显微“可见金”。整个滇黔桂“金三角”卡林型金矿不同亚类矿床之间的载金矿物特征和金的赋存状态没有本质区别,说明它们具有相同的成矿作用过程和成矿背景。
Abstract:Petrographic observations and electron-probe micro_analysis (EPMA) of sulfides from different subclasses of typical Carlin-type gold deposits in Yunnan-Guizhou-Guangxi “golden triangle" area show that both arsenian pyrites and arsenopyrites are major gold-bearing minerals. Gold_bearing pyrites are dominated by zoned arsenic pyrites and fine-grained euhedral arsenian pyrites. Zoned arsenian pyrites are characteristics by As-poor and S, Fe-rich cores mantled by later-formed As-rich and S, Fe-poor rims, and there is a positive correlation between Au and As. Pyrites with As-poor cores have complex origin, with some being hydrothermal pyrites precipitated in the early metallogenic stage and the others being syngenetic pyrites altered by hydrothermal fluid. Core pyrite and rim pyrite were formed in different metallogenic stages. The correlation between element contents indicates S was replaced by As in rims. The characteristics of multirims suggest that the hydrothermal fluid acted pulsatorily and the components of hydrothermal fluid varied constantly. Even if Au of some analytical spots from the cores exceeds the detection limit, rims can serve as the primary gold_bearing location. The fine_grained euhedral arsenian pyrites with homogeneous texture are similar to the rims of zoned pyrite with characteristics of high As, Au and low S, Fe, indicating that the As_rich mantles of zoned pyrite were probably formed synchronously with the As-rich tiny euhedral arsenian pyrite. The pyrites from the aggregation of pyrite-arsenopyrite are classified into two groups, which are of zoned texture and homogeneous texture and have the characteristics of the above two types of pyrites respectively. Arsenopyrites are subdivided into three generations, all having homogeneous texture and belonging to hydrothermal precipitation. There are some analytical spots from every generation whose Au exceeds the detection limit and whose contents of Au, As, S, Fe are different insignificantly in different generations, indicating they were deposited in the main metallogenic stage. The arsenopyrites have higher Au abundances than pyrites in the aggregation of pyrite-arsenopyrite. The precipitation order of gold_bearing sulfides is as follows: As-poor sedimentary pyrites or early metallogenic stage pyrites → As-rich zoned arsenian pyrites and fine-grained euhedral arsenian pyrites → arsenopyrites. The distribution of Au in all types of pyrites and all generations of arsenopyrites is heterogeneous under the resolution of EPMA microbeam, and the homogeneous texture of Au map from zoned arsenic pyrites is likely to be a pseudomorph. The major modes of occurrence for gold are “invisible" nanometer-size submicroscopic inclusion gold grains, with minor ones being “invisible" lattice gold and “visible" micrometer-size microscopic native gold. The gold-bearing minerals and the gold modes of occurrence have no essential difference in different subclasses of Carlin_type gold deposits in Yunnan_Guizhou_Guangxi “golden triangle" area,suggesting that they had the same ore_forming process and setting.
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基金项目:中央级公益性科研院所基本科研业务费专项资金(K2007-1-2)、中国博士后科学基金 (20080430456)和国家重点基础研究发展计划 (973 计划)(2007CB411407)
引用文本:
陈懋弘,毛景文,陈振宇,章 伟.2009.滇黔桂“金三角”卡林型金矿含砷黄铁矿和毒砂的矿物学研究[J].矿床地质,28(5):539~557
陈懋弘,毛景文,陈振宇,章 伟.2009.Mineralogy of arsenian pyrites and arsenopyrites of Carlin_type gold deposits in Yunnan-Guizhou-Guangxi “golden triangle" area, southwestern China[J].Mineral Deposits28(5):539~557
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