Kaolinisation, mineralisation and structures in biotite granite at Bodelva, St. Austell, Cornwall

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Authors:Mueller, S.; Scott, P. W.; Evans, M. J.
Author Affiliations:Primary:
University of Exeter, Camborne School of Mines, Exeter, United Kingdom
Other:
Goonvean, Saint 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 4), p.310-317; Annual conference of the Ussher Society, Cornwall, United Kingdom, Jan. 1999, edited by Brian J. Williams. Publisher: Ussher Society, Bristol, United Kingdom. ISSN: 0566-3954
Publication Date:1999
Note:In English. 21 refs.; illus., incl. 2 tables, geol. sketch map
Summary:Bodelva China Clay Pit until recently was providing kaolin for the paper and other industries and at closure was yielding around 40,000 tonnes per annum of product. It is entirely located within the medium to coarse grained biotite rich facies of the eastern part of the St. Austell granite. Four distinct stages of alteration have been delineated: slightly, medium, highly and completely altered biotite granite. These occur together with minor exposures of fine grained biotite granite and a few areas of primary greisening. Various types of mineralised veins and dykes are widespread throughout the china clay pit and follow mainly west-south-west--east-north-east and north-north-west--south-south-east trends respectively. Two major sets of iron oxide stained fracture zones, following the same trends are spatially related to completely altered biotite granite. There is strong evidence for the extreme form of kaolinisation within these areas being predominantly structurally controlled. The intense iron oxide staining along the southern rim of the pit is considered a result of de-ferruginisation of biotite. Analyses of micas show an almost continuous trend of compositions, represented by changes in the cation distributions in octahedral sites from tri-octahedral (Fe+Mn+Mg rich) biotite to di-octahedral (Al rich and Fe+Mn+Mg poor) types approaching stoichiometric muscovite.
Sections:Petrology
Subsections:Igneous petrology
Subjects:Alteration; Biotite granite; Dikes; Granites; Greisen; Igneous rocks; Intrusions; Kaolin deposits; Kaolinization; Metamorphic rocks; Metasomatic rocks; Metasomatism; Mineral deposits, genesis; Mineralization; Plutonic rocks; Structural analysis; Supergene processes; Veins; Cornwall England; England; Europe; Great Britain; United Kingdom; Western Europe; Bodelva England; Saint Austell England
Coordinates:N500000 N505000 W0041500 W0063000
Abstract Numbers:00M/3214
Record ID:2002013606
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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