A hydrothermal origin for the large Xinqiao Cu-S-Fe deposit,Eastern China: Evidence from sulfide geochemistry and sulfur isotopes |
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| Institution: | 1. Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;2. Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitor (Central South University), Ministry of Education, Changsha 410083, China;3. School of Geosciences and Info-Physics, Central South University, Changsha 410083, China;4. Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou 510640, China;1. MLR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China;2. Sino-mine Resource Exploration Co., Limited, Beijing 100089, China;3. Faculty of Geosciences, China University of Geosciences, Beijing 100083, China;1. Key Laboratory of Crust–Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, China;2. State Key Laboratory of Continental Dynamics, Northwest University, Xi''an, China;3. Department of Geosciences, University of Tübingen, 72074 Tübingen, Germany;4. Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China;1. Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, China;2. Department of Earth Sciences, Durham University, Durham DH1 3LE, UK;3. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;4. 321 Geological Team, Bureau of Geology and Mineral Exploration of Anhui province, Tongling 244033, China;5. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China |
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| Abstract: | The Xinqiao Cu-S-Fe deposit in the Tongling ore district, Middle-Lower Yangtze River Valley Metallogenic Belt (MLYB; Eastern China), is located along the northern margin of the Yangtze Craton. The stratiform- and skarn-type Xinqiao mineralization comprises five stages, namely the early skarn (Stage I, garnet and diopside), late skarn (Stage II, epidote-dominated), iron oxides (Stage III, hematite and magnetite), colloform pyrite (Stage IV) and quartz-sulfides (Stage V). There are three pyrite types at Xinqiao, i.e., colloform (Py1; Stage IV), fine-grained (Py2, from Py1 recrystallization; Stage V) and coarse-grained (Py3; Stage V) pyrites.Scanning Electron Microscope (SEM) imagery for Py1 reveals that they are cubic microcrystalline pyrite aggregates, and the EDS and XRD data indicate that some Py1 contain minor siderite impurities. Electron Microprobe Analysis (EMPA) and LA-ICP-MS geochemical data demonstrate that the three pyrite types have relatively high Fe/S ratios and distinctly high Mn, Cu and As concentrations. Compared to Py2 and Py3, Py1 has higher Pb, Bi and Ag, but lower Co, Ni, Se, Cd, Te and Au. Ratios of Fe/S (0.837 to 0.906), Se/Te (2.39 to 14.50) and Co/Ni (0.67 to 4.67) of the Xinqiao pyrites resemble typical hydrothermal pyrites. δ34SCDT of Py1 (? 0.6‰ to 2.7‰, average 0.58‰), Py2 (1.8‰ to 2.5‰, average 2.1‰) and Py3 (1.9‰ to 4.4‰, average 3.5‰) are close to those of the Xinqiao skarn-type orebodies (1.3‰ to 4.1‰), but distinct from those of the Upper Carboniferous Huanglong Formation limestone (? 9.5‰ to ? 15.4‰), suggesting that the three pyrite types (especially Py1) were genetically linked to the Yanshanian (Jurassic-Cretaceous) magmatic-hydrothermal events, with Py1 probably reflecting rapid crystallization during fluid mixing. We interpret that the Xinqiao stratiform mineralization may have been associated with the Jitou quartz diorite stock, as may be the case also for the skarn-type mineralization hosted in the contact between the Yanshanian Jitou stock and the Lower Permian Qixia Formation limestone. Overall, the Xinqiao Cu-S-Fe mineralization may have been generated by the Jurassic-Cretaceous tectono-thermal event in Eastern China. |
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