REE mineralogy and geochemistry of the Western Keivy peralkaline granite massif,Kola Peninsula,Russia |
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| Institution: | 1. Departamento de Geologia, Centro de Ciências Exatas e da Terra, Universidade Federal do Rio Grande do Norte, Campus Universitário Lagoa Nova, Natal, RN 59078-970, Caixa Postal 1639, Brazil;2. Departamento de Mineralogia e Geotectônica, Instituto de Geociências, Universidade de São Paulo, Rua do Lago, 562, Cidade Universitária, São Paulo, SP 05508-080, Brazil;3. Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, Notre Dame, IN 46556, USA;1. Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China;2. School of Earth Science and Resources, China University of Geosciences, Beijing 100083, China;3. Department of Earth Sciences, Durham University, Durham DH1 3LE, UK;4. GeoZentrumNordbayern, Universität Erlangen-Nürnberg, D-91054 Erlangen, Germany;1. Department of Geology, University of Johannesburg, P.O. Box 524, Auckland Park 2006, South Africa;2. School of Geosciences, University of the Witwatersrand, P.O. Wits, Johannesburg 2050, South Africa;1. Department of Geosciences, University of Oslo, PO Box 1047, Blindern, N-0316 Oslo, Norway;2. Department of Geology, University of Johannesburg, PO Box 524, Auckland Park, 2006, Johannesburg, South Africa |
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| Abstract: | The authors have studied the geology, geochemistry, petrology and mineralogy of the rare earth elements (REE) occurring in the Western Keivy peralkaline granite massif (Kola Peninsula, NW Russia) aged 2674 ± 6 Ma. The massif hosts Zr- and REE-rich areas with economic potential (e.g. the Yumperuaiv and Large Pedestal Zr-REE deposits), where 25% of ΣREE are represented by heavy REE (HREE). The main REE minerals are: chevkinite-(Ce), britholite-(Y) and products of their metamict decay, bastnäsite-(Ce), allanite-(Ce), fergusonite-(Y), monazite-(Ce), and others. The areas contain also significant quantities of zircon reaching potentially economic levels. We have discovered that behavior of REE and Zr is controlled by alkalinity of melt/solution, which, in turn, is controlled by crystallization of alkaline pyroxenes (predominantly aegirine) and amphiboles (predominantly arfvedsonite) at a late magmatic stage. Crystallization of mafic minerals leads to a sharp increase of K2O content and decrease of SiO2 content that cause a decrease of melt viscosity and REE and Zr solubility in the liquid. Therefore, REE and zirconium immediately precipitate as zircon and REE-minerals. There are numerous pod- and lens-like granitic pegmatites within the massif. Pegmatites in the REE-rich areas are also enriched in REE, but HREE prevails over light REE (LREE), about 88% of REE sum. |
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| Keywords: | REE geochemistry REE mineralogy Peralkaline granite Kola Alkaline Province |
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