Lead, zinc and copper mineralisation in basal Carboniferous sediments at Westwater, south Scotland

A zone of lead, zinc and copper mineralisation is developed over a minimum of 4 km of strike of basal Carboniferous cementstone group sediments and immediately underlying Birrenswark Lavas at Westwater, near Langholm in south · Scotland. Grades so far obtained from sparse rock exposures and from shallow boreholes are usually 0.1-0.3% of combined metals over 1-2 m of thickness, but a fissure vein of higher grade and a relatively thick zone of disseminated sulphides were also located. Galena, sphalerite, chalcopyrite and baryte occur mainly in thin dolomite veins but disseminations of galena are also present in sandstone unite. The mineralisation is or low temperature type and was emplaced along northeasterly trending normal faults and cross faults regarded as late Carboniferous in age. Mineralisation has been controlled by faulting, regional facies variation and local lithological variation as well as by stratigraphic position. These controls are applicable in further exploration of Lower Carboniferous rocks in both south and central Scotland. The heavy mineral fraction of stream sediment is the optimum sampling type in reconnaissance exploration of areas of calcareous rocks such as the Lower Carboniferous of south Scotland and· basal till sampling is the most effective method of follow-up exploration in those areas where glacial deposits are widespread and often thick.