Anomalously silver-rich vein-hosted mineralisation in disseminated-style gold deposits,Jiaodong gold district,China |
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| Institution: | 1. School of Geosciences, Monash University, Melbourne, Australia;2. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China;1. Czech Geological Survey, Geologická 6, 152 00 Praha 5, Czech Republic;2. ARC Centre of Excellence for Core to Crust Fluid Systems (CCFS),Department of Earth and Planetary Sciences, Macquarie University, Sydney, NSW 2109, Australia;3. GEMOC National Key Centre, Department of Earth and Planetary Sciences, Macquarie University, Sydney, NSW 2109, Australia;4. Andean Geothermal Center of Excellence, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Santiago, Chile;1. AGH University of Science and Technology, Faculty of Geology, Geophysics and Environmental Protection, Department of Economic Geology, al. A. Mickiewicza 30, 30-059 Krakow, Poland;2. Economic Geology Research Institute, School of Geosciences, University of the Witwatersrand, Private Bag 3, 2050 Wits, Johannesburg, South Africa;3. Resource Mineralogy, Department of Applied Geosciences and Geophysics, Montanuniversitaet Leoben, Peter-Tunner-Str. 5, 8700 Leoben, Austria;4. Department of Geological Sciences, Stockholm University, 10691 Stockholm, Sweden;5. Kryvorizkiy National University, Kryvyj Rig, XXII Partzyizdu Str., 11, 50027 Krivoy Rog, Ukraine;6. Burlinson Geochemical Services Pty. Ltd., Darwin, NT, Australia;1. Far East Geological Institute, Far Eastern Branch, Russian Academy of Sciences, 159, Pr 100-let Vladivostoku, Vladivostok 690022, Russia;2. Engineering School, Far Eastern Federal University, 8, Sukhanova Str., Vladivostok 690950, Russia;3. Institute of Geology and Geochemistry, Ural Branch, Russian Academy of Sciences, 7, Per. Pochtovy, Ekaterinburg 620151, Russia;4. Geoscience, Australian Museum, 6 College St, Sydney, NSW 2010, Australia;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. Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;2. School of Earth Sciences and Resources, China University of Geosciences Beijing, 29 Xueyuan Road, Beijing 100083, China;3. Centre for Exploration Targeting, University of Western Australia, Crawley, WA 6009, Australia |
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| Abstract: | Structural measurements and geochemical analyses, including bulk and in situ pyrite geochemistry, sulfur isotopes, and whole-rock geochemistry, are presented for the No. 3 orebody of the Jiaojia gold deposit (JJ3), located in the Jiaodong district of northeast China. The JJ3 orebody is distinct from the main orebody of the Jiaojia deposit (JJ1) because it is characterised by steeply dipping sub-metric quartz-pyrite veins with up to 300 ppm of gold, whereas the JJ1 orebody represents an archetypal example of the disseminated and veinlet style mineralisation characteristic of regional faults in the Jiaodong district. Measurements on JJ3 veins and the host Jiaojia-Xincheng regional fault are consistent with development of mineralised, steeply dipping extension fractures during normal faulting, which produced the fault-hosted disseminated-style JJ1 orebody. Trace element geochemistry of pyrite in these veins shows that JJ3 pyrite is geochemically distinct from those of the main Jiaojia and Xincheng orebodies, being relatively enriched in Ag and Pb, as well as Ba, Bi, Te and Au, and relatively depleted in Cu and As. Enrichment in Ag and Pb is possibly related to infiltration of a saline hydrothermal fluid, as both are effectively transported as chloride complexes; however, depletion of Cu, which is also mobile as chloride complexes, requires a low temperature saline fluid where Cu is no longer soluble. The textural setting of the ore minerals suggests that these cooler fluids likely infiltrated during the waning stages of the hydrothermal system. The relative abundance of barite in the JJ3 orebody, which formed from late-stage oxidised magmatic–hydrothermal fluids, also supports the interpretation that the JJ3 orebody represents a late mineralisation event. The pervasive alteration surrounding the JJ3 orebody is K-feldspathic with a minor sericitic overprint, indicating an earlier higher temperature pervasive fluid flow event that was followed by low-temperature mineralising fluids. This interpretation implies that fracture dilation post-dated the earliest alteration, and that mineralisation and pervasive alteration in the JJ3 orebody are geochemically disconnected. Thus structural analysis is expected to be the most effective targeting method in future exploration for similar ore bodies. |
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