Geochemical constraints on kaolinization in the St Austell Granite, Cornwall, England

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doi: 10.1144/gsjgs.155.5.0829
Authors:Psyrillos, Agamemnon; Manning, David A. C.; Burley, Stuart D.
Author Affiliations:Primary:
University of Manchester, Department of Earth Sciences, Manchester, United Kingdom
Volume Title:Journal of the Geological Society of London
Source:Journal of the Geological Society of London, Vol.155(Part 5), p.829-840. Publisher: Geological Society of London, London, United Kingdom. ISSN: 0016-7649
Publication Date:1998
Note:In English. 54 refs.; illus., incl. 4 tables, geol. sketch map
Summary:Kaolinization of the St Austell granite is the youngest mineralization event that can be identified in the pluton on the basis of field relations and petrography. The kaolinization is spatially associated with hydrothermal quartz veins, and progressed through the migration of alteration fronts away from reactivated pre-existing hydrothermal vein structures; kaolin veins, sometimes with a quartz core, also occur. Kaolinization gave the formation of kaolin + smectite assemblage, with no precipitation of quartz. Geochemical models of kaolinization at 25-100°C show that appropriate assemblages are produced from parent granite by reaction with meteoric water at these T, and with high-salinity brine at 75 and 100°C. The kaolin + smectite assemblage reflects the elevation of fluid silica activities in excess of quartz saturation as a consequence of feldspar dissolution. Quartz failed to nucleate because of slow precipitation kinetics at the kaolinization T (< 100°C). Kaolinization of the granites was a dynamic process, controlled by feldspar dissolution kinetics, the precipitation kinetics of silica minerals and the initial log a (K+/H+) of the fluids that interacted with the granites. [R.A.H.]
Sections:Clay minerals
Subsections:Petrology; weathering; soils
Subjects:Brines; Chemical composition; Geochemical controls; Geochemistry; Granites; Hydrothermal alteration; Igneous rocks; Intrusions; Kaolin deposits; Kaolinization; Metasomatism; Meteoric water; Mineral assemblages; Mineral composition; Mineral deposits, genesis; Mineralization; Models; Petrography; Plutonic rocks; Plutons; Precipitation; Quartz veins; Salinity; SEM data; Solution; Temperature; Veins; Cornwall England; England; Europe; Great Britain; United Kingdom; Western Europe; Saint Austell Granite
Coordinates:N500000 N520000 W0020000 W0040000
Abstract Numbers:99M/187
Record ID:1998055225
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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