Madouzi-type (nodular) sedimentary copper deposit associated with the Emeishan basalt

作     者：WANG FuDong ZHU XiaoQing WANG ZhongGang 

作者机构：State Key Laboratory of Ore Deposit Geochemistry Institute of Geochemistry Chinese Academy of Sciences Guiyang 550002 China Graduate University of Chinese Academy of Sciences Beijing 100049 China 

出 版 物：《Science China Earth Sciences》 (中国科学（地球科学英文版）)

年 卷 期：2011年第54卷第12期

页      面：1880-1891页

核心收录：

学科分类：081803[工学-地质工程] 08[工学] 0708[理学-地球物理学] 0818[工学-地质资源与地质工程] 0704[理学-天文学] 

基　　金：supported jointly by National Basic Research Program of China (Grant No. 2007CB411401) Special Fund of State Key Laboratory of Ore Deposit Geochemistry and National Natural Science Foundation of China (Grant No. 40773035) 

主　　题：峨眉山玄武岩 铜矿床 沉积型 结节 硫同位素组成 同位素分析 沼泽环境 热液叠加 

摘      要：Ore minerals in the sedimentary-type Cu deposits in the Xuanwei Formation overlying the Emeishan basalt are dominated by copper sulfides and native copper. As the ores mostly exhibit concretionary structure, previous researchers named them the Madouzi-type Copper Deposit. Here the authors carried out mineralogical and isotopic studies on copper nodules in this ore deposit. The mineralogical study shows that copper nodules are composed of copper sulfides that have been cemented by ferruginous amorphous minerals, clay, and carbonaceous fragments in the modes of metasomatism and sedimentation. The nodules are preliminarily present as aggregates of gelatinous material. The isotopic analysis shows that the δ 13CPDB values of an- thraxolite are within the range of-24.8‰--23.9‰, indicating that the anthraxolite is the product of sedimentary metamorphism of in-situ plants. The δ 34SV-CDT values of chalcocite are within the range of 7.6‰-13.1‰, close to those (about 11‰) of Permian seawater. The δ 34SV-CDT values of bornite and chalcopyrite are 21.6‰-22.2‰, similar to the sulfur isotopic composition (20‰) of marine sulfate, indicative of different sources of sulfur. The above characteristics indicate that the copper nodules were formed in such a process that Cu-bearing basalt underwent weathering-leaching and copper-bearing material was transported into waters (e.g., rivers, lakes, and swamps) and then adsorbed on clay and ferruginous amorphous mineral fragments. Then, the copper-bearing material was suspended and transported in the form of gelinite. In lake or swamp environment, it was co-deposited with sediments to form copper nodules. At later stages there occurred metasomatism and hydrothermal su- perimposition, followed by the replacement of chalcocite by bornite and the superimposition of chalcopyrite over bornite, finally resulting in the formation of the Madouzi-type nodular copper deposit.