Mineral exploration for gold and base metals in the Lewisian and associated rocks of the Glenelg area north-west Scotland

An exploration programme for gold and base metals in the Glenelg area of the north-west Highlands of Scotland is described. Regional drainage sampling of the area between Loch Carron and the Strathconon fault was conducted and 212 samples of both stream sediments and panned concentrates were analysed for base metals, gold and a variety of indicator elements. The area covered by the reconnaissance drainage survey is underlain by Lewisian rocks of both the Eastern and Western facies and, also, Moinian rocks in the Caledonian erogenic belt of the Northern Highlands. The Ratagain igneous complex of late Caledonian age is also covered by the drainage survey. Detailed investigations, involving geophysics, shallow overburden sampling and geological mapping, were carried out over one area underlain by iron-rich rocks, called eulysites in the literature, at Carr Brae near Loch Duich. Iron-rich rocks of a similar character are associated with the copper-gold deposit at Gairloch hosted by the supracrustal Loch Maree Series, which may be of the same age as the Eastern Lewisian. Eulysites within the Eastern Lewisian were traced along strike from Carr Brae for 14 km to the south-west but, despite chemical evidence that the rocks are metamorphosed chemical exhalites, no significant gold or base metal mineralisation was found associated with them. Calc-silicate gneisses within the Eastern Lewisian assemblage of metamorphosed sediments and volcanics do show some copper enrichment but the high gold values found in them in the earlier records of mining trials at Loch Duich could not be repeated Graphitic gneisses in the same assemblage do show some potential as a source of crystalline graphite with the carbon content of the rocks reaching 16 %. Further work is needed to assess the economic potential of this occurrence. The Ratagain igneous complex, despite the recorded occurrence of veins carrying electrum, is not considered to be a good target for further mineral exploration as the complex is well exposed and the mineralisation is widely scattered and of relatively low grade. Veins within the Strathconon fault system are a more favourable target given its long, 100 km, strike length and the occurrence of gold at two localities within this area and at Scardroy 40 km to the north-east.