Supergene mineralisation at Arm O'Grain, Caldbeck Fells, Cumbria

Green, David I.; Tindle, Andrew G.; Bridges, Trevor F. and Neall, Tim (2006). Supergene mineralisation at Arm O'Grain, Caldbeck Fells, Cumbria. Journal of the Russell Society, 9 pp. 68–72.

URL: http://www.russellsoc.org/pubs.htm#V9

Abstract

A north-south trending quartz vein is exposed over a strike length of a few metres in scree on the east side of the Arm O'Grain valley in the Caldbeck Fells, Cumbria. The vein is extensively weathered, little remains of the primary mineralisation except quartz. A variety of supergene minerals including mimetite, pyromorphite, vanadinite, mottramite, duftite, plumbogummite and beudantite occur as microscopic crystals. The supergene lead-vanadium mineralisation is relatively rich; it includes the only definite occurrence ofvanadinite in the Caldbeck Fells. There is extensive anionic substitution in the lead-bearing members of the apatite group and between mottramite and duftite. There is also considerable substitution of calcium for lead in the lead-bearing members of the apatite group. About 25 m south of the vein exposure, in the west bank of the beck, a rib of quartz-rich rock contains disseminated arsenopyrite and pyrite, which has oxidised on hairline fractures to brown crustose scorodite.

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