Isotope and fluid inclusion geochemistry and genesis of the Qiangma gold deposit,Xiaoqinling gold field,Qinling Orogen,China |
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| Institution: | 1. Key Laboratory of Orogen and Crustal Evolution, Peking University, Beijing, 100871, China;2. Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, China;3. State Key Laboratory for Mineral Deposits Research, Department of Earth Sciences, Nanjing University, Nanjing 210093, China;1. Bureau of Geology and Mineral Resources of Shandong Province, Jinan 250013, China;2. Key Laboratory of Gold Mineralization Processes and Resources Utilization of Ministry of Land and Resources of the People''s Republic of China, Jinan 250013, China;3. College of Marine Geosciences, Ocean University of China, Qingdao 266003, China;4. School of Earth Science & Resources, China University of Geosciences, Beijing 100083, China;5. The Sixth Exploration Institute of Geology and Mineral Resources of Shandong Province, Weihai 264209, China;6. Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100088, China;7. Institute of Geological Sciences and Laboratories of Shandong Province, Jinan 250013, China;1. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China;2. Department of Earth, Ocean and Atmospheric Sciences Florida State University Tallahassee, FL 32310, USA;1. Beijing Institute of Geology for Mineral Resources, Beijing 100012, China;2. Key Laboratory of Orogen and Crust Evolution, Peking University, Beijing 100871, China;3. School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China;4. Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;1. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, PR China;2. U. S. Geological Survey, Box 25046, Denver Federal Center, Denver, CO 80225, USA;3. Jiaojia Gold Company, Shandong Gold Mining Co., Ltd., Laizhou 261441, Shandong, PR China;4. Shandong Provincial Bureau of Geology and Mineral Resources, Jinan 250013, PR China;5. Shandong Gold Mining Stock Co., Ltd., Laizhou 261400, Shandong, PR China |
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| Abstract: | The Qiangma gold deposit is hosted in the > 1.9 Ga Taihua Supergroup metamorphic rocks in the Xiaoqinling terrane, Qinling Orogen, on the southern margin of the North China Craton. The mineralization can be divided as follows: quartz-pyrite veins early, quartz-polymetallic sulfide veinlets middle, and carbonate-quartz veinlets late stages, with gold being mainly introduced in the middle stage. Three types of fluid inclusions were identified based on petrography and laser Raman spectroscopy, i.e., pure carbonic, carbonic-aqueous (CO2–H2O) and aqueous inclusions.The early-stage quartz contains pure carbonic and CO2–H2O inclusions with salinities up to 12.7 wt.% NaCl equiv., bulk densities of 0.67 to 0.86 g/cm3, and homogenization temperatures of 280?365 °C. The early-stage is related to H2O–CO2 ± N2 ± CH4 fluids with isotopic signatures consistent with a metamorphic origin (δ18Owater = 3.1 to 5.2‰, δD = ? 37 to ? 73‰). The middle-stage quartz contains all three types of fluid inclusions, of which the CO2–H2O and aqueous inclusions yield homogenization temperatures of 249?346 °C and 230?345 °C, respectively. The CO2–H2O inclusions have salinities up to 10.9 wt.% NaCl equiv. and bulk densities of 0.70 to 0.98 g/cm3, with vapor bubbles composed of CO2 and N2. The isotopic ratios (δ18Owater = 2.2 to 3.6‰, δD = ? 47 to ? 79‰) suggest that the middle-stage fluids were mixed by metamorphic and meteoric fluids. In the late-stage quartz only the aqueous inclusions are observed, which have low salinities (0.9?9.9 wt.% NaCl equiv.) and low homogenization temperatures (145?223 °C). The isotopic composition (δ18Owater = ? 1.9 to 0.5‰, δD = ? 55 to ? 66‰) indicates the late-stage fluids were mainly meteoric water.Trapping pressures estimated from CO2–H2O inclusions are 100?285 MPa for the middle stage, suggesting that gold mineralization mainly occurred at depths of 10 km. Fluid boiling and mixing caused rapid precipitation of sulfides and native Au. Through boiling and inflow of meteoric water, the ore-forming fluid system evolved from CO2-rich to CO2-poor in composition, and from metamorphic to meteoric, as indicated by decreasing δ18Owater values from early to late. The carbon, sulfur and lead isotope compositions suggest the hostrocks within the Taihua Supergroup to be a significant source of ore metals. Integrating the data obtained from the studies including regional geology, ore geology, and fluid inclusion and C–H–O–S–Pb isotope geochemistry, we conclude that the Qiangma gold deposit was an orogenic-type system formed in the tectonic transition from compression to extension during the Jurassic?Early Cretaceous continental collision between the North China and Yangtze cratons. |
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