Polymetallic mineralisation in Carboniferous rocks at Hilderston, near Bathgate, central Scotland

摘要

Five boreholes in the vicinity of the ancient Ag-Ni-Pbudmine at Hilderston, near Bathgate have yielded newudstratigraphic, mineralogical and geochemical information.udThese results, together with a critical reexaminationudof old records, are interpreted in relation to audpalaeo-environment profde across a volcanic island withudcoastal lagoon and fringing reef deposits, as proposed byudJameson (1980).udStratabound Zn-Pb mineralisation occurs in the lower,udargillaceous part of the Petershill Limestone, which wasuddeposited in an anaerobic lagoon on the edge of a volcanicudlandmass during the Lower Carboniferous Epoch (LowerudLimestone Group, Vi&an Stage). The best intersectionudshows 8 m of mineralised limestone, with underlying carbonaceousudmudstone (1 m) and tuffaceous seat rockud(2 m), having an average concentration of 0.14 % Pb andud0.66% Zn and maximum values of 0.6% Pb and 3.1%udZn in the carbonaceous mudstone. Further drilling wasudsubsequently carried out in order to investigate possibleudlateral extensions of the stratabound mineralisation and toudtest for mineralisation in similar lithologies and geologicaludenvironments at other stratigraphic levels, and a reportudon the results will be available at Edinburgh.udLate-Carboniferous hydrothermal veins occur withinudthe Petershill Limestone and in immediately overlyingudelastic sediments, where they are cut by E-W faults andudquartz-dolerite dykes. At Hilderston Mine twoudassemblages are recognised in the vein: Ba-Fe-udNi-Co-Ag-As on a dyke margin adjacent to the elasticudsediments and Fe-Pb-Zn-S at lower levels adjacent toudthe limestone. Zones of alteration in the dolerite dykesudcarry hydrocarbons and weak Ba-Fe-Cu-F mineralisation.udNo potentially-valuable vein deposits wereuddiscovered in the present investigation.