Gold in the serpentinite weathering cover of the Szklary massif, Fore-Sudetic Block, SW Poland

Abstract

The average gold content in the serpentinite and weathered serpentinite rocks of the Szklary massif (20 samples from the surface and 38 samples from boreholes) is about 4.97 ppb; for the individual rock types: 0.72 ppb for the fresh serpentinite, 3.83 ppb for the weathered serpentinite, and 2.59 ppb for the serpentinite residual soil. The highest gold content was recorded for the talc-rich rocks - 27.84 ppb, while the chalcedony veins accompanying the weathered serpentinite rocks contain 12.03 ppb. The gold distribution in the serpentinite weathering cover has characteristics typical of gold migration in laterite debris. The increased gold content often associated with the lithological boundaries and with the water-table level has a clear connection with a higher content of other elements, such as Cu, As, Sb, Ni and Zn. However, elevated gold content in the chalcedony veins was not observed to be related to an increase in the amount of chalcophile metals. The native gold in the serpentinite weathering cover usually forms separate irregular blades up to 0.2 mm long, which are isolated or, rarely associated with oxides (chromite, magnetite) and silicates (enstatite, tremolite, anthophyllite). The narrow rims of gold around the rock-forming minerals indicate its secondary nature. The gold bearing phase (Au+Sb+Cu) was also identified, occurring as rare fine grains up to 10 micrometres in length.