Geochronological,geochemical and Pb isotopic compositions of Tasmanian granites (southeast Australia): Controls on petrogenesis,geodynamic evolution and tin mineralisation |
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| Institution: | 1. ARC Centre of Excellence in Ore Deposits (CODES), University of Tasmania, Private Bag 79, Hobart, TAS 7001, Australia;2. Transforming the Mining Value Chain, an ARC Industrial Transformation Research Hub, University of Tasmania, Private Bag 79, Hobart 7001, Australia;3. Geoscience Australia, GPO Box 378, Canberra, ACT 2601, Australia;4. School of Earth Sciences, University of Melbourne, VIC 3010, Australia;1. State Key Laboratory for Mineral Deposits Research, Department of Earth Sciences, Nanjing University, Nanjing 210093, Jiangsu, China;2. State Key Laboratory of Geological Processes and Mineral Resources, Collaborative Innovation Center for Exploration of Strategic Mineral Resources, Faculty of Earth Resources, China University of Geosciences, Wuhan 430074,China;3. Max-Planck-Institut für Chemie, Hahn-Meitnerweg 1, D-55128 Mainz, Germany;4. Lamont-Doherty Earth Observatory of Columbia University, P.O. Box 1000, Palisades, NY 10964, USA;5. Faculty of Land Resources and Engineering, Kunming University of Science and Technology, Kunming 650093, Yunnan, China;1. Key Laboratory of Metallogenic Prediction of Nonferrous Metals, Ministry of Education, School of Geosciences and Info-physics, Central South University, Changsha 410083, PR China;2. State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, PR China;3. Solid Earth Studies Laboratory, Department of Geology, University of Regina, Regina, Saskatchewan S4S 0A2, Canada;4. Lunar and Planetary Science Research Center, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, PR China |
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| Abstract: | Large volumes of Devonian-Carboniferous granites were emplaced across Tasmania in southeast Australia, which was along the easternmost boundary of mid-Palaeozoic Gondwana. Some of these granites are associated with world class Sn–W deposits. Previous studies have focused mainly on relationships between granite petrogenesis and source rocks, and rarely on geochemical controls on Sn mineralisation. New zircon U-Pb ages of 405 to 396 Ma reveal that the George River Granodiorite, Grant Point Granite and Mt. Pearson Granite from eastern Tasmania intruded prior to the Tabberabberan Orogeny. The Coles Bay Granite has a U-Pb age of 388 ± 7 Ma, implying that it was emplaced simultaneously with the Tabberabberan Orogeny in Tasmania. The western Tasmanian granites mostly intruded from 374 to 360 Ma, after the Tabberabberan Orogeny. Granites associated with Sn–W deposits are moderately to strongly fractionated, including the Housetop, Meredith, Pine Hill and Heemskirk granites. Lead isotopic compositions of K-feldspars from the analysed granites, combined with isotopic evidence from other studies, suggest that differentiated granites in Tasmania had been highly contaminated by a crustal (sedimentary) component, and that western Tasmanian granites had a crustal source with substantially different isotopic characteristics to that of eastern Tasmania, which has a character similar to the Lachlan Orogen in southeast Australia. Tin-mineralised granites in Tasmania formed in a post-collisional extensional margin, a favourable environment for the production of Sn-rich melts from the lower crust. Prolonged fractional crystallisation, low oxygen fugacity and enrichments of volatiles are crucial factors to promote Sn enrichment in magmatic-hydrothermal fluids exsolved from crystallised felsic magmas. |
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