Mineralogy and mineral chemistry of Bi-minerals: Constraints on ore genesis of the Beiya giant porphyry-skarn gold deposit,southwestern China |
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| Affiliation: | 1. School of Earth Science and Geological Engineering, Sun Yat-sen University, Guangzhou 510275, China;2. School of Marine Sciences, Sun Yat-sen University, Guangzhou 510006, China;3. Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering, Guangzhou 510275, China;4. South China Sea Bio-Resource Exploitation and Utilization Collaborative Innovation Center, Guangzhou 510006, China;1. State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;3. Chengdu Institute of Geology and Mineral Resources, China Geological Survey, Chengdu 610081, 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. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China;2. China Minmetals Corporation, Beijing 100010, China;3. Department of Earth Sciences, University of Adelaide, SA 5005, Australia;4. Yunnan Geological Survey, Kunming, Yunnan 650051, China;5. School of the Environment, Washington State University, Pullman, WA 99164, USA;1. Geological Survey of Western Australia, Mineral House, 100 Plain St, EAST PERTH 6004, Australia;2. Centre for Microscopy Characterisation and Analysis, The University of Western Australia, 35 Stirling Hwy, CRAWLEY, WA 6009, 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 |
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| Abstract: | The Beiya deposit, located in the Sanjiang Tethyan tectonic domain (SW China), is the third largest Au deposit in China (323 t Au @ 2.47 g/t). As a porphyry-skarn deposit, Beiya is related to Cenozoic (Himalayan) alkaline porphyries. Abundant Bi-minerals have been recognized from both the porphyry- and skarn- ores, comprising bismuthinite, Bi–Cu sulfosalts (emplectite, wittichenite), Bi–Pb sulfosalts (galenobismutite, cosalite), Bi–Ag sulfosalt (matildite), Bi–Cu–Pb sulfosalts (bismuthinite derivatives), Bi–Pb–Ag sulfosalts (lillianite homologs, galena-matildite series), and Bi chalcogenides (tsumoite, the unnamed Bi2Te, the unnamed Ag4Bi3Te3, tetradymite, and the unnamed (Bi, Pb)3(Te, S)4). Native bismuth and maldonite are also found in the skarn ores. The arsenopyrite geothermometer reveals that the porphyry Au mineralization took place at temperatures in the range of 350–450 °C and at log fS2 in the range of − 8.0 to − 5.5, respectively. In contrast, the Beiya Bi-mineral assemblages indicate that the skarn ore-forming fluids had minimum temperatures of 230–175 °C (prevailing temperatures exceeding 271 °C) and fluctuating fS2–fTe2 conditions. We also model a prolonged skarn Au mineralization history at Beiya, including at least two episodes of Bi melts scavenging Au. We thus suggest that this process was among the most effective Au-enrichment mechanisms at Beiya. |
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