Primitive mantle normalized Platinum group elements (PGE) concentration patterns for the Zhengziyanwo intrusion and Dashibao Formation basalts are of positive slope, similar to most of the world class magmatic Ni Cu P...Primitive mantle normalized Platinum group elements (PGE) concentration patterns for the Zhengziyanwo intrusion and Dashibao Formation basalts are of positive slope, similar to most of the world class magmatic Ni Cu PGE sulfide deposits. Characters of this intrusion and its related ores and Dashibao Formation basalts are their negative Pt anomaly and high concentration of Rh relative to Pt and Pd, facts being interpreted to be the results of crystallization and fractionation of Pt alloys and spinel phase free crystallization history for the magma, respectively. PGE parameters of the Dashibao Formation basalts are consistent with the general trend of those found for the Zhengziyanwo intrusion, and this might infer a genetic link between them.展开更多
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 ...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 anhraxolite 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 superimposition, 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.展开更多
基金supported by NSFC(Grant Nos.40072037,40273025)NKBRSF Project(Grant No.G1999043200)
文摘Primitive mantle normalized Platinum group elements (PGE) concentration patterns for the Zhengziyanwo intrusion and Dashibao Formation basalts are of positive slope, similar to most of the world class magmatic Ni Cu PGE sulfide deposits. Characters of this intrusion and its related ores and Dashibao Formation basalts are their negative Pt anomaly and high concentration of Rh relative to Pt and Pd, facts being interpreted to be the results of crystallization and fractionation of Pt alloys and spinel phase free crystallization history for the magma, respectively. PGE parameters of the Dashibao Formation basalts are consistent with the general trend of those found for the Zhengziyanwo intrusion, and this might infer a genetic link between them.
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)
文摘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 anhraxolite 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 superimposition, 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.
