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The nature and significance of illite associated with quartz- hematite hydrothermal veins in the St. Austell pluton, Cornwall, England

Published online by Cambridge University Press:  09 July 2018

A. Psyrillos ,
D. A. C. Manning  and
S. D. Burley
A. Psyrillos*
Affiliation:
Department of Earth Sciences, University of Manchester, Oxford RoadManchester M139PL, UK
D. A. C. Manning
Affiliation:
Department of Earth Sciences, University of Manchester, Oxford RoadManchester M139PL, UK
S. D. Burley
Affiliation:
Department of Earth Sciences, University of Manchester, Oxford RoadManchester M139PL, UK
*
*E-mail: [email protected]
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Abstract

Quartz-hematite veins in the St. Austell pluton feature an assemblage of authigenic kaolin, illite, chlorite and hematite. Similar assemblages occur in altered granites adjacent to the veins. Complex textures in the veins and altered granites show that kaolin was an initial precipitate from hydrothermal fluids that was subsequently replaced by illite, hematite and chlorite. The sequence of mineral precipitation reflects a kinetic control on crystal growth, with early nonequilibrium precipitation of kaolin from fluids with compositions appropriate for the equilibrium formation of illite. Hematite formed under relatively oxidizing conditions that subsequently became more reducing to permit the late precipitation of chlorite. Illite associated with the quartz-hematite veins differs texturally, mineralogically and chemically from the coarsely crystalline hydrothermal muscovite (sericite or gilbertite) associated with quartz-tourmaline veins and greisen. Quartzhematite veins are thus considered to record a distinct mineralization event that is not related to the early greisenization or the economic kaolinization.

Keywords

illitehematitekaolinchloriteauthigenesisCornwallEngland
Type
Research Article
Information
Clay Minerals , Volume 36 , Issue 4 , December 2001 , pp. 585 - 597
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2001

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Footnotes

Present Address: B' Parodos Andrea Miaouli 9, Katerini 60100, Greece

Present Address: Department of Agricultural & Environmental Science, University of Newcastle, Newcastle upon Tyne NE1 7RU, UK

Present Address: BG Group plc., Subsurface Technology, 100 Thames Valley Park, Reading RG6 1PT, UK, and Basin Dynamics Research Group, University of Keele, Keele ST5 5BG, UK

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