External sulphur in IOCG mineralization: Implications on definition and classification of the IOCG clan |
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| Institution: | 1. State Key Laboratory of Geological Processes and Mineral Resources, and Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, China;2. Department of Earth Sciences, The University of Hong Kong, Hong Kong, SAR, China;1. Northwest Territories Geological Survey, Box 1320, Yellowknife, Northwest Territories X1A 2L9, Canada;2. Geological Survey of Canada, 601 Booth Street, Ottawa, ON K1A 0E8, Canada;3. Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada;4. Geological Survey of Canada, 490 rue de la Couronne, Québec, QC G1K9A9, Canada;5. Department of Geology, Brandon University, Brandon, Manitoba, R7A 6A9, Canada;6. Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Section 3.1: Inorganic and Isotope Geochemistry, Telegrafenberg B121, 14473 Potsdam, Germany;7. Department of Earth and Environmental Sciences, University of Windsor, Windsor, Ontario N9B 3P4, Canada;8. Red Pine Exploration, 141 Adelaide Street West, Suite 520, Toronto, ON M5H 3L5, Canada;1. School of Chemical Engineering and Advanced Materials, The University of Adelaide, Adelaide, SA 5005, Australia;2. BHP Olympic Dam, Adelaide, SA 5001, Australia;3. School of Mathematical Sciences, The University of Adelaide, Adelaide, SA 5005, Australia;4. ARC Centre of Excellence in Ore Deposits, School of Natural Sciences, University of Tasmania, Hobart, TAS 7005, Australia |
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| Abstract: | Although the sources of the ore metals remain problematic in most Iron-oxide Cu and Au (IOCG) deposits, external sulphur, either from surficial basinal brines and seawater (e.g., Central Andean and Carajás deposits) or from formation water and metamorphic fluids (e.g., the Cloncurry deposits), or introduced by magmatic assimilation of metasedimentary units (e.g., Phalaborwa), has been documented in many major Cu-rich IOCG centres. However, only the evaporite-sourced fluids yield diagnostically high δ34S values (i.e., > 10‰), while sedimentary formation water or metamorphic fluids commonly have lower values and are less clearly distinguishable from magmatic fluids, as in the Cloncurry deposits in which the involvement of external fluids is revealed by other evidence, such as noble gas isotopes. On the basis of these arguments, IOCG deposits could be redefined as a clan of Cu ( AuAgU) deposits containing abundant hypogene iron oxide (magnetite and/or hematite), in which externally-derived sulphur probably plays an important role for the Cu (AuAgU) mineralization. In this definition, all “Kiruna-type” magnetite deposits, hydrothermal iron deposits (e.g., skarn Fe deposits) and magnetite-rich porphyry CuAu and skarn CuAu deposits are excluded. Two subtypes of IOCG deposits are recognized on the basis of the predominant iron oxide directly associated with the Cu (Au) mineralization, whether magnetite or hematite. Neither magnetite- nor hematite-rich IOCG deposits show any preference for specific host rocks, and both range in age from Neoarchean to Pleistocene, within a broad tectonic environment. |
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