Evidence for the historical exploitation of possible bedrock gold in the upper Mennock Water, Wanlockhead, Dumfries and Galloway

摘要

Microchemical characterization of gold grains collected from a probable site of old gold processing at the confluence of the Mennock Water and Whitestone Cleuch in the Leadhills–Wanlockhead auriferous area has led to the identification of a type of gold previously unrecorded in the area. Within the Leadhills–Wanlockhead gold region the alluvial gold is dominated by a type which contains typically 10–12% Ag, little or no Cu and Hg, and an opaque inclusion suite containing sulphides (about 60%) and sulpharsenides (about 40%). Alluvial gold grains recovered from the Mennock Water and Whitestone Cleuch during this study are of this type. In contrast, gold grains recovered from the base of pits at the study site contain between 5.6 and 7.4% Ag, negligible Cu and Hg, and an opaque mineral inclusion suite characterized by pyrite, chalcopyrite, galena, sphalerite and tetrahedrite. Sulpharsenides are absent. This microchemical signature is more similar to that previously recorded in alluvial gold from two other sites in the Southern Uplands: the Tweed headwaters and the Glengaber Burn. The distinctive microchemical signature of gold from the study site has not been observed in any other gold grains recovered from the Mennock Water catchment (c. 20 km2) or elsewhere in the Leadhills–Wanlockhead region. These grains frequently exhibit textures incompatible with any fluvial transport, but characteristic of gold grains liberated through crushing ore. Thus, the evidence from gold composition and grain textures suggests that a distinctive bedrock source of gold was crushed and presumably beneficiated at this site. This discovery represents evidence for an unrecorded site of possible in-situ gold exploitation.