Regional variation in gold mineralization in the vicinity of the Glengaber Burn, Scottish Borders

The alluvial gold at Glengaber Burn in the valley of the Megget Water is of interest because of its coarse size and historical working. A total of 350 alluvial gold grains from 17 sites in Glengaber Burn and the vicinity have been studied using the technique of microchemical characterization, and two major types of gold have been identified, each with well defined geographical distribution. Tppe 1a gold contains only pyrite inclusions, and has an Ag content of between 8% and 11%. Type 1b has a similar Ag content, but the inclusion assemblage contains galena together with pyrite. Type 2a gold typically contains between 3% and 7% Ag, and a suite of inclusions comprising chalcopyrite, sphalerite, tetrahedrite, arsenopyrite and gersdorffite. Type 2a gold occurs in a SW-NW trending zone which contains the catchments of the Glengaber and Craigierigg Burns. Type 2b gold is confined to the catchment of the Cramalt Burn and contains an inclusion suite similar to Type 2a, but is more silver-rich. The abundance of alluvial gold of all types falls dramatically to the south of Megget Water, although the occurrence to the north of the Glengaber Burn and Craigierigg Burns has not been established. The distribution of Type la gold is mutually exclusive with Type 2a and flanks the zone of Type 2a and 2b to both east and west suggesting zonation in a single mineralizing event. Type Ib gold occurs to the west of Type la and is probably unrelated to the other gold types. The mineralization acting as the source for the alluvial gold could be controlled by deep structures roughly perpendicular to the regional strike, revealed by prominent gravity lineaments, and their intersections with other structural features.