安徽铜陵狮子山矿田夕卡岩型金矿床的矿物组合、化学成分及成因意义

摘要

包村和朝山金矿床位于安徽铜陵狮子山矿田，属于夕卡岩型金矿床，侵入岩体分别为包村石英闪长岩体和白芒山辉石闪长岩体。通过矿相鉴定和电子探针分析，对矿床中的自然金进行了详细的观察和研究。结果表明在两个矿床中，金矿物均以独立的自然金颗粒形式产出，且常具有“银边结构”，但在自然金的嵌布方式、载体矿物、形态、大小、金银含量变化范围和成色等方面表现出显著差别。根据自然金的不同特征，对金矿床的成因进行分类，包村金矿床属于Cu-Au共生，而朝山矿床为Cu-Pb-Zn-Au共生型金矿床。不同矿床不同的金产状主要是由于金的运移、络合物种类、温度、pH和金银络合物活度比值等因素造成的。此外，包村矿床和朝山矿床在地表均遭受氧化作用形成表生矿床，其表生金成色均明显高于原生金，且成分均一。%The Baocun and Chaoshan gold deposits in Shizishan orefield are of skarn type,and their intrusive rocks are Baocun quartz diorite and Baimangshan augite quartz diorite respectively.Gold grains from the deposits were thoroughly examined and analysed by means of reflected light microscope and electron probe microscope ,and the results show that gold minerals in the primary zone of the Baocun and Chaoshan deposits all occur as individual native gold and often display silver-rim structure but exhibit obvious differences in modes of occurrence,carrier minerals,shape,sizes,content of Au and Ag,and fineness of gold grains in the two deposits.Gold minerals in the Baocun deposit occur as electrum and native gold,and electrum finenesses range from 605 to 911 with a mean of 831.Gold grains in the Chaoshan deposit consist of kustelite,electrum and native gold.Their finenesses range from 256 to 948 (averagely 729),being quite different in different sulfide minerals.According to the mode of occurrence of primary gold in deposits,the Baochun deposit is a Cu-Au association deposit,whereas the Chaoshan deposit is of Cu-Pb-Zn-Au association type.rn　　A comparison of the two deposits reveals that the significantly different modes of occurrence of gold between them are attributed to such factors of the fluids as gold complexes,temperature,pH and activity ratios of Au and Ag complexes.As gold was probably transported in the form of AuCl-2,and its fineness was only controlled by temperature and aAgCl-2/aAuCl-2,gold from the Baocun Cu-Au association has higher fineness and much narrower fineness variation range.Nevertheless,in the Chaoshan deposit,gold migrated in the form of Au(HS)-2,its fineness was related to temperature,aAgCl-2/aAu(HS)-2,aH2S and pH,so the gold grains there have lower fineness and wider range of variation.rn　　In the oxidized zones of Baocun and Chaoshan deposits,supergene gold occurs as native gold uniform in composition,and has higher fineness than primary gold,suggesting that in the case of moderate pH and high Eh,gold migrated mainly in the form of gold thiosulfate complex fluids.