Columbite-tantalite, rutile and other accessory minerals from the St. Austell topaz granite, Cornwall

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Authors:Scott, P. W.; Pascoe, R. D.; Hart, F. W.
Author Affiliations:Primary:
University of Exeter, Camborne School of Mines, Cornwall, United Kingdom
Goonvean, St. Austell, United Kingdom
Volume Title:Geoscience in South-west England
Volume Authors:Williams, Brian J., editor
Source:Proceedings of the Ussher Society, Vol.9(Part 3), p.165-170; Annual conference of the Ussher Society, Bideford, United Kingdom, Jan. 1998, edited by Brian J. Williams. Publisher: Ussher Society, Bristol, United Kingdom. ISSN: 0566-3954
Publication Date:1998
Note:In English. 14 refs.; illus., incl. 5 tables, geol. sketch map
Summary:The topaz granite in the area west of Nanpean is geochemically different from and younger than the biotite granite, lithium mica granite and tourmaline granite, which make up the major part of the St Austell granitoid pluton. Kaolinization has released the accessory minerals from the host granite, and these fine grained minerals (up to 100 µm) separate into the hydrocyclone underflow waste during the production of china clay. The accessory minerals can be concentrated further by gravity separation. Topaz, columbite-tantalite, Nb-Ta rutile, cassiterite and apatite are the major phases. Zircon, monazite, Fe oxide, Mn-ilmenite, pyrite, arsenopyrite and sphalerite also occur, but wolframite is absent and uranium-bearing phases are only found very rarely as inclusions in other minerals. The columbite-tantalite shows considerable variation in Nb/Ta and Fe/Mn ratios, and the rutile varies in its Nb, Ta and Fe contents. The data may be interpretated as arising from simultaneous crystallisation of the two minerals on a pseudo-binary solid solvus. Two types of Ce-rich monazite are found. Th-poor monazite and the absence of uranium minerals may be accounted for by mobilization of Th and U during kaolinization. Cassiterite is considered to have a magmatic origin in the topaz granite. The Fe oxides and sulphides most probably come from from cross-course mineralization in the china clay pits. As with other similar evolved granites elsewhere in the world, the topaz granite and the waste tailings dams in the St Austell area, in which the accessory minerals from past extraction of kaolinized granite now reside, should be considered potential sources for Nb, Ta and Sn metals.
Subsections:Igneous petrology
Subjects:Accessory minerals; Assemblages; Clay minerals; Columbite; Geochemistry; Kaolinization; Metal ores; Metasomatism; Mineral composition; Mineral resources; Niobates; Niobium ores; Oxides; Rutile; SEM data; Sheet silicates; Silicates; Tantalates; Tantalum ores; Tin ores; Cornwall England; England; Europe; Great Britain; South-West England; United Kingdom; Western Europe; China clay; Clays; Niobotantalates; Saint Austell Granite
Coordinates:N501000 N503000 W0040000 W0050000
Abstract Numbers:99M/3144
Record ID:1999047749
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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