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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100 1 |a Psyrillos, Agamemnon  |e analytic author  |u University of Manchester, Department of Earth Sciences, Manchester 
245 1 0 |a Geochemical constraints on kaolinization in the St Austell Granite, Cornwall, England 
300 |a p. 829-840 
500 |a In English. 54 refs. 
500 |a Abstract number: 99M/187 
500 |a Abstractor: R.A.H. 
500 |a Category Section: Clay minerals 
500 |a Category Subsection: Petrology; weathering; soils 
500 |a Affiliation: University of Manchester, Department of Earth Sciences; Manchester; GBR; United Kingdom 
500 |a Key title: Journal of the Geological Society of London 
500 |a Source note: 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 
500 |a Publication type: journal article 
504 |b 54 refs. 
510 3 |a GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom 
520 |a 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 (#LT 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. 
650 7 |a Brines  |2 georeft 
650 7 |a Chemical composition  |2 georeft 
650 7 |a Geochemical controls  |2 georeft 
650 7 |a Geochemistry  |2 georeft 
650 7 |a Granites  |2 georeft 
650 7 |a Hydrothermal alteration  |2 georeft 
650 7 |a Igneous rocks  |2 georeft 
650 7 |a Intrusions  |2 georeft 
650 7 |a Kaolin deposits  |2 georeft 
650 7 |a Kaolinization  |2 georeft 
650 7 |a Metasomatism  |2 georeft 
650 7 |a Meteoric water  |2 georeft 
650 7 |a Mineral assemblages  |2 georeft 
650 7 |a Mineral composition  |2 georeft 
650 7 |a Mineral deposits, genesis  |2 georeft 
650 7 |a Mineralization  |2 georeft 
650 7 |a Models  |2 georeft 
650 7 |a Petrography  |2 georeft 
650 7 |a Plutonic rocks  |2 georeft 
650 7 |a Plutons  |2 georeft 
650 7 |a Precipitation  |2 georeft 
650 7 |a Quartz veins  |2 georeft 
650 7 |a Salinity  |2 georeft 
650 7 |a SEM data  |2 georeft 
650 7 |a Solution  |2 georeft 
650 7 |a Temperature  |2 georeft 
650 7 |a Veins  |2 georeft 
651 7 |a Cornwall England  |2 georeft 
651 7 |a England  |2 georeft 
651 7 |a Europe  |2 georeft 
651 7 |a Great Britain  |2 georeft 
651 7 |a United Kingdom  |2 georeft 
651 7 |a Western Europe  |2 georeft 
653 |a Saint Austell Granite 
700 1 |a Manning, David A. C.,  |e analytic author 
700 1 |a Burley, Stuart D.,  |e analytic author 
773 0 |t Journal of the Geological Society of London  |d London : Geological Society of London, Sep. 1998  |x 0016-7649  |y JGSLAS  |n 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 type: journal article  |g Vol. 155, Part 5  |h illus., incl. 4 tables, geol. sketch map 
856 |u urn:doi: 10.1144/gsjgs.155.5.0829