The Crummock Water Aureole: a Zone of Metasomatism and Source of Ore Metals in the English Lake District
Journal of the Geological Society, London, Vol. 145, 1988, pp. 523-540, 17 figs, 5 tables. Printed in Northern Ireland The Crummock Water aureole: a zone of metasomatism and source of ore metals in the English Lake District D. C. COOPER,' M. K. LEE,'N. J. FORTEY ,l A. H. COOPER,'C. C. RUNDLE,3 B. C. WEBB2 & P. M. ALLEN' British Geological Survey, Keyworth, Nottingham NG12 5GG, UK 'British Geological Survey, Winhior Court, Windsor Terrace, Newcastle upon Tyne NE4 2HE, UK 3NERC Isotope Geology Centre, 64 Grays Inn Road, London WClX 8NG, UK Abstract: The Crummock Water aureole, an ENE-trending elongate zone of bleached and recrystall- ized Skiddaw Group rocks, 24 kmin length and up to 3 kmwide, is azone in which pervasive metasomatism has modified the composition of the dominantly siltstone and mudstone lithologies. The bleached rocks show a substantial net gain of As, B, K and Rb and loss of Cl, Ni, S, Zn, H,O and C. Carbon loss is responsible for the bleaching. There are smaller and morelocalized net losses of Cu,Fe, Li andMn, and gains of Ca, F and Si, whilst CO, Pband REE areat leastlocally redistributed.Many chalcophile elements show evidence of initialwidespread depletion and sub- sequent local enrichment. The mineralogy of the rocks is little affected by the geochemical changes. Like their counterparts outside of the bleached zone, the metasomatized rocksconsist essentiallyof quartz, chlorite,muscovite, paragonite and rutile. Small aggregates and porphyroblasts of white mica and chlorite are developed. The metasomatism,which was accompanied by tourmalineveining, is superimposed on acontact metamorphic event.
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