Isotope geochronology,geochemistry, and mineral chemistry of the U-bearing and barren granites from the Zhuguangshan complex,South China: Implications for petrogenesis and uranium mineralization |
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| Institution: | 1. ARC Centre of Excellence for Core to Crust Fluid Systems (CCFS) and the Institute for Geoscience Research (TIGeR), Department of Applied Geology, Curtin University, GPO Box U1987, Perth, WA 6845, Australia;2. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;3. NSW Institute of Frontiers Geoscience, School of Environment and Life Sciences, University of Newcastle, University Drive, Callaghan, NSW 2308, Australia;4. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;1. Faculty of Earth Sciences, China University of Geosciences, 430074 Wuhan, China;2. Guangdong Geological Bureau of Nuclear Industry, 510800 Guangzhou, China;3. Faculty of Mathematics-Natural Science, Department of Geosciences, University of Tübingen, 72074 Tübingen, Germany;4. Institute of Mineralogy, Leibniz University Hannover, 30167 Hannover, Germany;1. UMR CNRS 6118, Géosciences Rennes, OSUR, Université Rennes 1, 35042 Rennes Cedex, France;2. Université de Lorraine, CNRS, CREGU, GeoRessources, Boulevard des Aiguillettes, BP 70239, 54506 Vandoeuvre-lès-Nancy, France;3. Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Muséum National d''Histoire Naturelle, Sorbonne Universités, CNRS, UPMC & IRD, 75005 Paris, France;4. Department of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, United Kingdom;5. Institute of Earth Surface Dynamics, Géopolis, University of Lausanne, CH-1015 Lausanne, Switzerland;6. CRPG, UMR 7358 CNRS-Université de Lorraine, BP20, 54501 Vand?uvre Cedex, France |
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| Abstract: | The Zhuguangshan complex carries some of the most important granite-hosted uranium deposits in South China. Here we investigate the Changjiang and Jiufeng granites which represent typical U-bearing and barren granites in the complex, using zircon U-Pb ages, whole-rock geochemistry, Sr-Nd isotopic and zircon Hf isotopic data, and mineral chemistry, to constrain the petrogenesis and uranium mineralization. LA-ICP-MS zircon U-Pb dating shows that both the Changjiang and Jiufeng granites were emplaced ca. 160 Ma. These rocks show high silica, weakly to strongly peraluminous compositions, enrichment in Rb, Th, and U, and depletion in Ba, Nb, Sr, P, and Ti. These features coupled with the high initial 87Sr/86Sr ratios, negative εNd(t) values and εHf(t) values, and the Paleoproterozoic two stage model ages of these two granites suggest that the two granites belong to S-type granites, and the parental magmas of the two granites were derived from the Paleoproterozoic metasedimentary rocks. However, the granitoids show different mineralogical characteristics. The biotite in the Changjiang granite belongs to siderophyllite, marking higher degree of chloritization, whereas the biotite in the Jiufeng granite is ferribiotite, characterized by only slight chloritization. Compared with the Jiufeng granite, the biotite in the Changjiang granite has lower crystallization temperature and oxygen fugacity, but higher F content, and the uraninite has higher UO2 content but lower ThO2 content, and stronger corrosion. The chemical ages of uraninites from both granites are (within error) consistent with the zircon U-Pb ages and are considered to represent the emplacement ages of granites. Chemical ages of pitchblende in the Changjiang granite yield 118 ± 8 Ma, 87 ± 4 Ma, and 68 ± 6 Ma, representing multiple episodes of hydrothermal events that are responsible for the precipitation of U ores in the Changjiang uranium ore field. Our study suggests that the degree of magma differentiation and physicochemical conditions of the magmatic-hydrothermal system are the key factors that control the different U contents of these two granites. The mineralogical characteristics of uraninite and biotite can be used to distinguish between U-bearing and barren granites, and serve as a potential tool for prospecting granite-hosted uranium deposits. |
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| Keywords: | Geochemistry Mineral chemistry U-bearing and barren granites Uranium mineralization The Zhuguangshan complex South China |
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