摘要
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 oSCUNBs values of chalcopyrite range from -0.09% to ＋0.33%0, similar to basic igneous rocks and chalcopyrite from magmatic deposits. J6SCUNBS values of chalcopyrite from the early, middle and final mineralization stages show an increasing trend due to 63Cu prior migrated in gas phase when fluids exsolution from magma, ja4ScDT values of sulfide minerals range from -2.7‰ to ＋2.8‰, similar to mantle-derived sulfur （0±3‰）. The positive correlation between J65CUNBs and ja4SCDT values of chalcopyrite indicates that a common source of copper metal and sulfur from magma. JDu2o- SMOW and JlSOH2O-SMOW values of water in fluid inclusions of quartz range from -60.7‰ to -44.4‰ and ＋7.9‰ to ＋9.0%0 （T=260℃）, respectively and fall in the field for magmatic and metamorphic waters, implicating that mixed sources for H20 in hydrothermal fluids. Ores and sulfide minerals have a small range of Pb isotopic compositions （208Pb/204pb=38.152 to 38.384, 207Pb/204Pb=15.656 to 17.708 and 206Pb/204Pb=17.991 to 18.049） that are close to orogenic belt and upper crust Pb evolution curve, and similar to Neoproterozoic host rocks （208Pb/204Pb=38.201 to 38.6373, 207pb/204pb=15.648 to 15.673 and 206pb/204pb=17.820 to 18.258）, but higher than diabase （208Pb/204pb=37.830 to 38.012, 207pb/204pb=15.620 to 15.635 and 206pb/204pb=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.
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 oSCUNBs values of chalcopyrite range from -0.09% to ＋0.33%0, similar to basic igneous rocks and chalcopyrite from magmatic deposits. J6SCUNBS values of chalcopyrite from the early, middle and final mineralization stages show an increasing trend due to 63Cu prior migrated in gas phase when fluids exsolution from magma, ja4ScDT values of sulfide minerals range from -2.7‰ to ＋2.8‰, similar to mantle-derived sulfur （0±3‰）. The positive correlation between J65CUNBs and ja4SCDT values of chalcopyrite indicates that a common source of copper metal and sulfur from magma. JDu2o- SMOW and JlSOH2O-SMOW values of water in fluid inclusions of quartz range from -60.7‰ to -44.4‰ and ＋7.9‰ to ＋9.0%0 （T=260℃）, respectively and fall in the field for magmatic and metamorphic waters, implicating that mixed sources for H20 in hydrothermal fluids. Ores and sulfide minerals have a small range of Pb isotopic compositions （208Pb/204pb=38.152 to 38.384, 207Pb/204Pb=15.656 to 17.708 and 206Pb/204Pb=17.991 to 18.049） that are close to orogenic belt and upper crust Pb evolution curve, and similar to Neoproterozoic host rocks （208Pb/204Pb=38.201 to 38.6373, 207pb/204pb=15.648 to 15.673 and 206pb/204pb=17.820 to 18.258）, but higher than diabase （208Pb/204pb=37.830 to 38.012, 207pb/204pb=15.620 to 15.635 and 206pb/204pb=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.
基金
supported by Science Foundation of Guizhou province (No. 2012-2334)
Open Foundation of State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences (Nos. 2011001 and 2009014)
National Natural Science Foundation of China (Nos. 41102055 and 41102053)
