Pre-Acadian copper mineralization in the English Lake District

The Ordovician sedimentary and igneous rocks of the English Lake District h ost a widespread suite of epigenetic metalliferous veins dominated by coppe r sulphides with abundant arsenopyrite, pyrite and accessory galena and sph alerite. New field and microstructural evidence from examples of this suite at Coniston, Wasdale, Honister, Newlands and Borrowdale shows that the vei ns were strongly cleaved during the Early Devonian (Emsian) Acadian orogeni c event. The principal evidence includes the continuity of wall-rock cleava ge fabrics with pressure solution seams in the veins and consistently orien tated cleavage through enclosed, rotated wall-rock fragments and chloritic mats. There is also widespread complex intracrystalline deformation in quar tz, cataclasis of arsenopyrite and pyrite, fracturing and/or buckling of bl aded hematite, and growth of quartz or mica-fibre strain fringes. Chalcopyr ite was partially or totally remobilized, enabling it to migrate along quar tz crystal boundaries, and invade brecciated pyrite. Previous K-Ar Early De vonian age determinations for the mineralization are considered to have bee n reset. The pre-Acadian age of this mineralization, its style and relation ship to the volcanic rocks permits a genetic link with the final phases of Caradoc magmatism.