The origins of late-stage rocks in the St Austell Granite; a re-interpretation

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doi: 10.1144/gsjgs.141.3.0581
Authors:Manning, D. A. C.; Exley, C. S.
Author Affiliations:Primary:
Univ. Keele, Dep. Geol., Keele, United Kingdom
Univ. Newcastle-upon-Tyne, United Kingdom
Volume Title:Journal of the Geological Society of London
Source:Journal of the Geological Society of London, Vol.141(Part 3), p.581-591. Publisher: Geological Society of London, London, United Kingdom. ISSN: 0016-7649
Publication Date:1984
Note:In English. 39 refs.; illus. incl. 4 tables, geol. sketch maps
Summary:In this Cornish granite there were essentially two stages of magmatic activity: the first represented by several phases of biotite granite, the second by a later non-megacrystic Li-mica granite which crystallized from a volatile-rich residual differentiate of the biotite granite magma. Both intrusions suffered hydrothermal alteration involving a two-stage exchange of components via a single aqueous fluid phase. In the non-megacrystic Li-mica granite, topaz and Li-mica were among the first phases to break down, releasing F and Li to the aqueous phase; F was locally fixed as fluorite, removing Ca from the fluid. Apart from losing Ca from plagioclase, the biotite granite gained Li, expressed as Li-rich mica, resulting in an aureole of megacrystic Li-mica granite surrounding the second intrusion. Water-rock interaction during fluid circulation modified the composition of predominantly meteoric water to give the hydrothermal fluid responsible for greisenization and mineralization; this alteration phenomena may have culminated in the products of the major kaolinite deposits of the area. [R.A.H.]
Subjects:Biotite granite; Clay minerals; Feldspar group; Fractures; Framework silicates; Genesis; Geochemistry; Granites; Hydrothermal alteration; Igneous rocks; Intrusions; Joints; Kaolinite; Magmas; Metamorphic rocks; Metasomatism; Meteoric water; Mica group; Petrography; Petrology; Plagioclase; Plutonic rocks; Sheet silicates; Silicates; Cornwall England; England; Europe; Great Britain; United Kingdom; Western Europe; Bugle; Carclaze; Clays; Fluorite granite; Goonbarrow; Hydrothermal processes; Lithium-mica granite; Luxulyan; Melbur; Nanpean; Roche; Saint Austell Granite; Wheal Remfrey
Coordinates:N500000 N510000 W0040000 W0054000
Abstract Numbers:84M/3344
Record ID:1985081107
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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