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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.
keywords:geology, arsenian pyrites, arsenopyrites, gold occurrence,Carlin-type gold deposit, Yunnan-Guizhou-Guangxi “golden triangle" area
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）
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