Gold in Devono-Carboniferous red beds of northern Britain

Authigenic gold occurs in Devono-Carboniferous red beds in northern Britain. Red beds exhibit concentrations of gold and pathfinder elements for gold mineralization including tellurium and mercury, at redox boundaries. Detailed studies of samples from Millport, Isle of Cumbrae, Firth of Clyde, show particles of native gold up to 10 µm size, typically with less than 15 wt% silver. Their context indicates that the gold was concentrated during diagenesis, in rocks that had not experienced regional temperatures above 100°C. These occurrences add to other evidence of a role for red beds in the genesis of gold mineralization.

There is a growing awareness that sedimentary red beds (continental successions dominated by coarse siliciclastic sediments) play a role in the cycling of gold in the upper crust. In Europe, Permo-Triassic red beds in particular have been proposed as a source of gold-mineralizing fluids (Stanley et al. 1990; Leake et al. 1997; Shepherd et al. 2005). Continental Devono-Carboniferous rocks, the Old Red Sandstone sensu lato, have received less attention in this respect. However, gold-bearing grains in modern streams cutting through Devonian red beds in Scotland (Chapman et al. 2009) and the proven availability of gold to the Devonian surface environment in the Rhynie hot spring system, Scotland (Rice et al. 1995) suggest that these red beds merit investigation for evidence of gold concentration. This study reports the low-temperature occurrence of native gold in Devono-Carboniferous red beds in Scotland.