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Pre-Acadian copper mineralization in the English Lake District

Published online by Cambridge University Press:  01 March 1999

D. MILLWARD
Affiliation:
British Geological Survey, Murchison House, West Mains Road, Edinburgh, EH9 3LA, Scotland
B. BEDDOE-STEPHENS
Affiliation:
British Geological Survey, Murchison House, West Mains Road, Edinburgh, EH9 3LA, Scotland
B. YOUNG
Affiliation:
British Geological Survey, Murchison House, West Mains Road, Edinburgh, EH9 3LA, Scotland

Abstract

The Ordovician sedimentary and igneous rocks of the English Lake District host a widespread suite of epigenetic metalliferous veins dominated by copper sulphides with abundant arsenopyrite, pyrite and accessory galena and sphalerite. New field and microstructural evidence from examples of this suite at Coniston, Wasdale, Honister, Newlands and Borrowdale shows that the veins were strongly cleaved during the Early Devonian (Emsian) Acadian orogenic event. The principal evidence includes the continuity of wall-rock cleavage fabrics with pressure solution seams in the veins and consistently orientated cleavage through enclosed, rotated wall-rock fragments and chloritic mats. There is also widespread complex intracrystalline deformation in quartz, cataclasis of arsenopyrite and pyrite, fracturing and/or buckling of bladed hematite, and growth of quartz or mica-fibre strain fringes. Chalcopyrite was partially or totally remobilized, enabling it to migrate along quartz crystal boundaries, and invade brecciated pyrite. Previous K–Ar Early Devonian age determinations for the mineralization are considered to have been reset. The pre-Acadian age of this mineralization, its style and relationship to the volcanic rocks permits a genetic link with the final phases of Caradoc magmatism.

Type
Research Article
Copyright
© 1999 Cambridge University Press

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