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
The hafnium isotopic analysis using laser ablation has been widely conducted on Hf-rich minerals （zircon/baddeleyite/ calzirtite/eudialyte）, however, little work has been reported on Hf-poor （〈100 ppm） minerals. ...The hafnium isotopic analysis using laser ablation has been widely conducted on Hf-rich minerals （zircon/baddeleyite/ calzirtite/eudialyte）, however, little work has been reported on Hf-poor （〈100 ppm） minerals. This work presents a detailed procedure of in situ hafnium isotopic analysis from ruffle using laser ablation multiple collector inductively coupled plasma mass spectrometry （LA-MC-ICP-MS）. The rutile U-Pb dating reference material JDX shows homogeneous hafnium isotopic ratios, with 176Hf/177Hf=0.281795±0.000015 （2SD, n=33） and176Lu/177Hf=0.000018±0.000004 （2SD, n=17） that suggest the possibility of using JDX as a new reference material hafnium isotopic measurement. We also measure hafnium isotopic compositions of other rutile U-Pb dating reference material （R10, Sugluk-4 and PCA-S207） and the 176Hf/177Hf values are similar to previously reported results, which confirms that we can acquire accurate and precise hafnium isotopic compositions using our developed analytical protocol. We analyzed hafnium isotopic compositions and U-Pb ages of rutile in high-temperature and ultrahigh-temperature granulites from various terrains of the Khondalite Belt from the North China Craton, combined with zircon results in the same area, suggesting that the metamorphic evolution history of the granulite is much more complicated than previously thought.展开更多
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.
基金supported by the National Natural Science Foundation of China(Grants Nos.41130313&41525012)
文摘The hafnium isotopic analysis using laser ablation has been widely conducted on Hf-rich minerals （zircon/baddeleyite/ calzirtite/eudialyte）, however, little work has been reported on Hf-poor （〈100 ppm） minerals. This work presents a detailed procedure of in situ hafnium isotopic analysis from ruffle using laser ablation multiple collector inductively coupled plasma mass spectrometry （LA-MC-ICP-MS）. The rutile U-Pb dating reference material JDX shows homogeneous hafnium isotopic ratios, with 176Hf/177Hf=0.281795±0.000015 （2SD, n=33） and176Lu/177Hf=0.000018±0.000004 （2SD, n=17） that suggest the possibility of using JDX as a new reference material hafnium isotopic measurement. We also measure hafnium isotopic compositions of other rutile U-Pb dating reference material （R10, Sugluk-4 and PCA-S207） and the 176Hf/177Hf values are similar to previously reported results, which confirms that we can acquire accurate and precise hafnium isotopic compositions using our developed analytical protocol. We analyzed hafnium isotopic compositions and U-Pb ages of rutile in high-temperature and ultrahigh-temperature granulites from various terrains of the Khondalite Belt from the North China Craton, combined with zircon results in the same area, suggesting that the metamorphic evolution history of the granulite is much more complicated than previously thought.
