Investigation of polymetallic mineralisation in Lower Devonian volcanics near Alva, central Scotland

The subsurface characteristics of three known occurrences of fracture-controlled mineralisation in the Lower Devonian Ochil Volcanic Formation near Alva, central Scotland, were tested by shallow boreholes. Target structures were intersected by each borehole, but they contain only minor amounts of baryte and geochemical enrichments of copper, arsenic and uranium. Differential fracturing within the variegated volcanic sequence and enhanced brecciation at fault intersections are principal controls. Earlier silver-cobalt mineralisation appears to have been followed by copperbarium mineralisation. The andesitic rocks of the volcanic pile represent a suitable source for the metals.