Placer gold and other economic minerals from the remnants of palaeofan deposits in the foreland of the East Sudetes, Poland

Abstract

Gold-bearing palaeofan deposits in the East Sudetic Foreland region are associated with the White Gravel series, which is the richest gold-bearing horizon. The remnants of the White Gravels in the vicinity of Gierałcice and Sławniowice contain between 0.33 g/m3 Au near the base and <0.05 g/m3 Au in the upper part. The gold is associated with other heavy minerals, such as Fe-Ti oxides (magnetite, ilmenite, and hematite), zircon and rutile. Concentration of these minerals increases significantly with depth and three-quarters of the total gold is found in the lower half of the palaeofan deposits. The alluvial palaeofan placers were formed by repeated scouring and reconcentration of resistant heavy minerals from a number of sources, including pre-existing placers and bedrock. The gold grains are composed of variable proportions of Au and Ag with trace amounts of Cu, Te and Se. Rims have high gold (>93 wt % Au) and low silver (<6 wt % Ag) contents, whereas cores contain average 85 wt % Au and 14 wt % Ag. Porous gold grains are homogeneous and of high purity (>95 wt % Au). The bedrock source of gold is probably related to quartz veins in Palaeozoic schist and quartzite. There are several local point sources of gold, mainly quartz veins of the Zlaty Chlum Massif. Data presented for the Gierałcice–Sławniowice
palaeofan placers may be useful for prospecting and exploration for similar deposits.