中甸普朗还原性斑岩型铜矿床:矿物组合与流体组成约束  

Pulang reduced porphyry copper deposit in the Zhongdian area,Southwest China: Constrains by the mineral assemblages and the ore-forming fluid compositions

作　　者：刘江涛[1] 杨立强[1] 吕亮[1] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,北京100083

出　　处：《岩石学报》2013年第11期3914-3924,共11页Acta Petrologica Sinica

基　　金：国家重点基础研究发展计划项目(2009CB421008);教育部新世纪优秀人才支持计划(NCET-09-0710);北京市优秀博士学位论文指导老师科研项目(20111141501);高等学校学科创新引智计划(B07011)联合资助

摘　　要：成矿流体高氧逸度是斑岩铜矿床模式的一个基本原则。虽然亚洲单个矿体储量最大的普朗铜矿床的成矿母岩——普朗复式岩体具氧化性岩浆特点,但其矿物组合及流体成分却与还原性斑岩型铜金矿床一致:矿石中以发育大量磁黄铁矿为特征,构成黄铜矿-磁黄铁矿-黄铁矿为主的矿物组合,不发育表征高氧逸度的原生磁铁矿和硫酸盐(硬石膏等)矿物;成矿流体中含较多CO2、CO和CH4等还原性组分,氧逸度低于铁橄榄石-磁铁矿-石英缓冲剂。成矿流体中还原性组分可能来源于普朗复式岩体周围的含碳质千枚岩或深部铁镁质岩浆。还原性流体中铜元素的溶解度比氧化性流体中的低,但金元素的溶解度不受氧化还原条件的影响;而CH4可使SO2还原形成S2-,为辉钼矿的形成提供物质基础;可能是导致普朗铜矿床Cu品位偏低而伴生大量Au、Mo矿化的主要原因之一。普朗铜矿床还原性特征的厘定有益于深入研究其矿床成因、乃至区域斑岩型铜矿床成矿机制。Porphyry Cu deposits are usually closely related to ore-forming fluid with high oxygen fugacity. The Pulang complex, parent rock of the Pulang copper deposit which has the largest single ore reserves in Asia, has oxidized magma characteristics, but the mineral assemblages and fluid compositions are consistent with those of reduced porphyry copper-gold deposits. The minerals in ores are characterized by large amount of pyrrhotite, the assemblages of chalcopyrite-pyrrhotite-pyrite, and there are lots of reducing compositions, such as CO2, CO and CH4 in the ore-forming fluid, and with fo2 values below the fayalite-magnetite-quartz oxygen buffer. These reduced compositions probably originates from the carbonaceous phyllite that surrounds the Pulang complex or the deep mafic magma. The copper solubility in reduced fluid is lower than that in the oxidized fluid, but the gold solubility is not affected by the redox conditions. The CH4 reduced the SO2 into S2- which is the basic material of molybdenite. The reduced ore fluids are probably the main reason of low Cu grade mineralization hut with massive Au, Mo mineralization. The discussion of reduced characteristic of the Pulang copper deposit benefits the further studies of the deposit genesis, and the metallogenic mechanism of regional porphyry deposits.

关 键 词：普朗斑岩铜矿 磁黄铁矿 氧逸度 还原性 

分 类 号：P618.41[天文地球—矿床学]