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H‐O‐S‐Cu‐Pb Isotopic Constraints on the Origin of the Nage Cu‐Pb Deposit, Southeast Guizhou Province, SW China

2013; Wiley; Volume: 87; Issue: 5 Linguagem: Inglês

10.1111/1755-6724.12132

1755-6724

Jia‐Xi Zhou, Wang Jing-song, Dezhi Yang, Jinhai Liu,

earthquake and tectonic studies

Abstract: The Nage Cu‐Pb deposit, a new found ore deposit in the southeast Guizhou province, southwest China, is located on the southwestern margin of the Jiangnan Orogenic Belt. Ore bodies are hosted in slate and phyllite of Neoproterozoic Jialu and Wuye Formations, and are structurally controlled by EW‐trending fault. It contains Cu and Pb metals about 0.12 million tonnes with grades of 0.2 wt% to 3.4 wt% Cu and 1.1 wt% to 9.27 wt% Pb. Massive and disseminated Cu‐Pb ores from the Nage deposit occur as either veinlets or disseminations in silicified rocks. The ore minerals include chalcopyrite, galena and pyrite, and gangue minerals are quartz, sericite and chlorite. The H‐O isotopic compositions of quartz, S‐Cu‐Pb isotopic compositions of sulfide minerals, Pb isotopic compositions of whole rocks and ores have been analyzed to trace the sources of ore‐forming fluids and metals for the Nage Cu‐Pb deposit. The δCu NBS values of chalcopyrite range from −0.09% to +0.33‰, similar to basic igneous rocks and chalcopyrite from magmatic deposits. δ 65 Cu NBS values of chalcopyrite from the early, middle and final mineralization stages show an increasing trend due to 63 Cu prior migrated in gas phase when fluids exsolution from magma. δ34S CDT values of sulfide minerals range from −2.7‰ to +2.8‰, similar to mantle‐derived sulfur (0±3‰). The positive correlation between δCu NBS and δ 34 S CDT values of chalcopyrite indicates that a common source of copper metal and sulfur from magma. δD H2O‐SMOW and δ 18 O H2O‐SMOV values of water in fluid inclusions of quartz range from −60.7‰ to −44.4‰ and +7.9‰ to +9.0‰ ( T =260°C), respectively and fall in the field for magmatic and metamorphic waters, implicating that mixed sources for H 2 O in hydrothermal fluids. Ores and sulfide minerals have a small range of Pb isotopic compositions ( 208 Pb/ 204 Pb=38.152 to 38.384, 207 Pb/ 204 Pb=15.656 to 17.708 and 206 Pb/ 204 Pb=17.991 to 18.049) that are close to orogenic belt and upper crust Pb evolution curve, and similar to Neoproterozoic host rocks ( 208 Pb/ 204 Pb=38.201 to 38.6373, 207 Pb/ 204 Pb=15.648 to 15.673 and 206 Pb/ 204 Pb=17.820 to 18.258), but higher than diabase ( 208 Pb/ 204 Pb=37.830 to 38.012, 207 Pb/ 204 Pb=15.620 to 15.635 and 206 Pb/ 204 Pb=17.808 to 17.902). These results imply that the Pb metal originated mainly from host rocks. The H‐O‐S‐Cu‐Pb isotopes tegather with geology, indicating that the ore genesis of the Nage Cu‐Pb deposit is post‐magmatic hydrothermal type.