Trace element geochemistry of magnetite from the giant Beiya gold-polymetallic deposit in Yunnan Province,Southwest China and its implications for the ore forming processes |
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| Affiliation: | 1. Faculty of Land and Resource Engineering, Kunming University of Science and Technology, Kunming 650093, China;2. Yunnan Geological Survey, Kunming 650051, China;3. Yunnan Gold and Minerals Group Co. Ltd, Kunming 650224, China;4. Yunnan Nonferrous Metals Geological Bureau, Kunming 650051, China;1. State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China;2. Yunnan Non-ferrous Metals Geological Bureau, Kunming 650051, China;3. Department of Land Resources Engineering, Kunming University of Science and Technology, Kunming 650093, China;4. University of Chinese Academy of Sciences, Beijing 100049, China;1. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China;2. School of Earth, Atmosphere and Environment, Monash University, VIC3800, Australia;1. School of Marine Sciences, Sun Yat-sen University, Guangzhou 510006, China;2. Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering, Guangzhou 510275, China;3. School of Earth Science and Geological Engineering, Sun Yat-sen University, Guangzhou 510275, China;4. South China Sea Bio-Resource Exploitation and Utilization Collaborative Innovation Center, Guangzhou 510006, China;1. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China;2. School of Earth, Atmosphere and Environment, Monash University, Clayton, VIC3800, Australia;3. Centre for Exploration Targeting, Australian Research Council Centre of Excellence for Core to Crust Fluid Systems (CCFS), School of Earth and Environment, University of Western Australia, Crawley, WA 6009, Australia;4. Geological Survey of Western Australia, East Perth, WA 6004, Australia;5. Mineral Exploration Research Centre, Department of Earth Sciences, Laurentian University, Sudbury, Ontario P3E 2C6, Canada |
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| Abstract: | The Beiya gold–polymetallic deposit is one of the largest gold deposits in China and is considered to be a typical porphyry-skarn system located in the middle of the Jinshajiang–Ailaoshan alkaline porphyry metallogenic belt. Massive magnetite is widespread in the Beiya ore district but its genesis is still the subject of debate. Five representative magnetite types are present in the Beiya deposit, namely magmatic magnetite (M1) from the ore-related porphyry, disseminated magnetite (M2) from the early retrograde alteration, massive magnetite (M3) from the early quartz-magnetite stage, massive magnetite (M4) from the middle quartz-magnetite stage and magnetite (M5) from the late quartz-magnetite stage. Compared with the M1 magnetite, the magnetites from stages M2 to M5 are depleted in Ti, Al and high field strength elements, implying a hydrothermal origin, distinct from the magmatic accessory magnetite in the ore-related porphyry (M1). The concentrations of cobalt in the hydrothermal magnetites decrease gradually from M2 to M5, and can be used to discriminate the magnetite types. The Al + Mn and Ti + V contents of the successively precipitated magnetite grains (M2–M5) suggests that the ore forming temperature decreased from M2 to M4, but increased from M4 to M5, possibly as the result of a new pulse of magma entering the chamber, which may have triggered the gold mineralization. The V content in the hydrothermal magnetite suggests that the oxygen fugacity increased from M2 to M4 but decreased as soon as the sulfides entered the system (M5). |
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| Keywords: | Magnetite Trace element geochemistry Beiya giant deposit Skarn Ore forming process |
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