Kaolinization — a tool to unravel the formation and unroofing of the Pleystein pegmatite–aplite system (SE Germany) |
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| Institution: | 1. Bundesanstalt für Geowissenschaften und Rohstoffe, D-30631 Hannover, P.O. Box 510163, Germany;2. Landesamt für Bergbau, Energie und Geologie, Stilleweg 2, D-30655 Hannover, Germany;3. Department of Earth and Planetary Sciences Birkbeck, University of London, Malet St., London WC1E 7HX, United Kingdom;1. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China;2. Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, China;3. Third Geological Survey Team, Henan Bureau of Geo-exploration and Mineral Development, Xinyang 464000, China;1. Division of Geosciences and Environmental Engineering, Luleå University of Technology, SE-971 87 Luleå, Sweden;2. Boliden Mineral, Exploration Department, SE-776 98 Garpenberg, Sweden;1. Centre for Exploration Targeting, School of Earth and Environment, University of Western Australia, Crawley, Western Australia 6009, Australia;2. Instituto de Geociências, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais 31270-901, Brazil;3. CODES-ARC Centre for Excellence in Ore Deposits, University of Tasmania, Sandy Bay Campus, Hobart 7001, Tasmania, Australia;4. Instituto de Geociências, Universidade de Brasilia, Distrito Federal 70910-900, Brazil;1. Université de Lorraine, GeoRessources-CNRS-CREGU, BP239, F54506 Vandoeuvre-lès-Nancy, France;2. East China Institute of technology, 56 Xuefu Road, Linchan, 344000 Fuzhou, Jiangxi, China;3. Geological Team No.208, BOG, CNNC, Baotou, Inner Mongolia, China |
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| Abstract: | The Hagendorf–Pleystein Pegmatite Province, SE Germany, is known for the largest feldspar–quartz pegmatite in Central Europe and renowned for its rare elements, e.g., Li, Nb, and Ta, giving rise to a spate of exotic minerals, mainly phosphates. Argillaceous rocks are scarce and eclipsed by the numerous mineralogical investigations on rare phosphates. These phosphate pegmatites are for the first time subjected to a clay mineralogical study, rendered possible by the newly discovered strongly kaolinized aplite near the Kreuzberg Quartz Pegmatite at Pleystein. The supergene kaolin akin to the residual kaolin deposit at Tirschenreuth, SE Germany, was analyzed for its major and minor elements by XRF and micro-chemically by EMPA. Mineralogical investigations involved XRD, IR spectroscopy, thermoanalytical studies, CEC analyses and SEM-EDX. Supergene kaolinization forms a repository for heavy minerals critical for the interpretation of the emplacement of the Late Paleozoic pegmatites as well as a matrix for pegmatite-related trace elements and thereby may be used as an ore guide during exploration of these rare metal pegmatites. The resultant kaolin is also the protagonist in the story of exhumation and destruction of a pegmatite by weathering and erosion. Irrespective of the strength of kaolinization, Nb–Ta–Ti heavy minerals can be identified in the regolith atop the host pegmatite or aplite and used for genetic interpretation of the primary mineralization and the origin of the felsic intrusive. Nb–Ta solid solution series (s.s.s.) have to be treated cautiously because of the disposition of Ta-enriched Nb–Ta oxide s.s.s. to undergo corrosion in their tantalite lamellae more easily than in their niobium-enriched zones. Kaolinization may alter the primary Nb/Ta ratio but not to the extent that Ta is released completely. The most strongly kaolinized new aplite is the youngest member of a series of felsic intrusive rocks in the Pleystein pegmatite–aplite system. The supergene kaolinization extending from the Miocene through the Pliocene can easily be correlated by “minero-stratigraphy” with the larger Tirschenreuth kaolin deposit. The four stages established in the area furnish evidence of gradual alkalinization of the meteoric pore fluids throughout the Neogene and the Quaternary. Youngest stages are found at Tirschenreuth, the oldest regolith stage is present at Pleystein. |
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