Morphology and chemistry of placer gold grains – indicators of the origin of the placers: an example from the East Sudetic Foreland, Poland

Abstract

The gold in the vicinity of Głuchołazy – Prudnik (the East Sudetic Foreland) is associated with Pliocene piedmont fans and Pre-Pleistocene river systems, primarily with the paleobeds of the Prudnik river and its tributaries. The morphology (roundness, flatness index and particles folding), surface textures and chemical composition of the gold particles suggest that the placer gold occurrences in the East Sudetic Foreland are multicycled (recycled paleoplacers) and multisourced. The most significant primary gold source was the sedimentary and epimetamorphic cover of the Żulova granitoids, eroded and removed during the Neogene. The majority of the gold was transported (redeposited) in a suspended form as flakes, scales, small grains and gold dust. This entered the river directly as a result of erosion of auriferous sediments. The homogeneous, porous, gold particles were formed in the weathering zones of polymetallic veins and other types of mineralization. Coatings of both crystalline and amorphous gold on particle surfaces suggest chemical accretion of authigenic gold on to pre-existing grains. Some porous gold particles may have been formed post-depositionally as the result of precipitation from colloidal solutions.