Columbitization of fluorcalciopyrochlore by hydrothermalism at the Saint-Honoré alkaline complex,Québec (Canada): New insights on halite in carbonatites |
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| Institution: | 1. Instituto de Geociências, Universidade de Brasília, Campus Universitário Darcy Ribeiro, Brasília, DF 70.910-900, Brazil;2. Faculdade de Ciências e Tecnologia, Universidade Federal de Goiás, Campus Aparecida de Goiânia, Aparecida de Goiânia, GO 74.968-755, Brazil;1. State Key Laboratory of Geological Processes and Mineral Resources, Collaborative Innovation Center for Exploration of Strategic Mineral Resources, China University of Geosciences, Wuhan 430074, China;2. State Key Laboratory for Mineral Deposits Research, Department of Earth Sciences, Nanjing University, Nanjing 210093, China;3. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;1. School of Civil and Environmental Engineering, University of Science and Technology Beijing, Beijing 100083, PR China;2. Chengdu Centre of China Geological Survey, Chengdu 610000, PR China;3. Institute of Geology, China Academy of Geological Science, 100037, PR China;4. CODES ARC Centre of Excellence in Ore Deposits, University of Tasmania, Private Bag 126, Hobart, TAS 7001, Australia;5. Snowden Group, 1 Kingdom Street, Paddington Central, London W2 6BD, UK;6. Camborne School of Mines, University of Exeter, Cornwall Campus, Penryn, Cornwall TR10 9FE, UK;1. Dipartimento di Scienze Psicologiche, della Salute e del Territorio - Università G. d''Annunzio, Via dei Vestini 30, 66100, Chieti, Italy;2. University of Western Australia, Centre for Exploration Targeting, 35 Stirling Highway, Crawley, WA 6009, Australia;3. Vinograd Institute of Geochemistry, SB RAS, P.B. 4019, Irkutsk 664033, Russia |
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| Abstract: | Niobium (Nb) in carbonatite is mainly hosted in fluorcalciopyrochlore and columbite-(Fe). Information related to Nb petrogenesis is useful for understanding the processes related to Nb mineralization and carbonatite evolution. The Saint-Honoré, Quebec, alkaline complex offers a rare opportunity for studying these processes as the complex is not affected by post-emplacement deformation, metamorphism nor weathering. Columbite-(Fe) is shown to be an alteration product of fluorcalciopyrochlore (columbitization). Columbitization is characterized by the leaching of Na and F from the A- and Y-sites of the pyrochlore crystal structure. As alteration increases, Fe and Mn are slowly introduced while Ca is simultaneously leached. Leached Ca and F then crystallize as inclusions of calcite and fluorite within the columbite-(Fe). A-site cations and vacancies in the crystal structure of fresh and altered pyrochlores demonstrate that pyrochlore alteration is hydrothermal in origin. Moreover, halite is a ubiquitous mineral in the Saint-Honoré alkaline complex. Petrographic evidence shows that halite forms in weakly altered pyrochlores, suggesting halite has a secondary origin. As alteration increases, halite is expelled by the hydrothermal fluid and is carried farther into the complex, filling factures throughout the carbonatite. The hydrothermal hypothesis is strengthened by significant enrichments in Cl and HREEs in columbite-(Fe). Chlorine is most likely introduced by a hydrothermal fluid that increases the solubility of REEs. |
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| Keywords: | Pyrochlore Columbite-(Fe) Halite Niobium Carbonatite Saint-Honoré |
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