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

Wierchowiec J.

Acta Geologica Polonica

2007

Vol. 57, no. 4

523-537

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/m[^3] Au near the base and <0.05 g/m[^3] 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.

Preglacial to Holocene auriferous sediments from the East Sudetic Foreland: gold grades and exploration

Wierchowiec J.

Geological Quarterly

2006

Vol. 50, No. 2

289-302

Auriferous sediments in the East Sudetic Foreland region include up to five gold-bearing horizons associated with preglacial and Quaternary fluvial sediments. The largest placer potential lies in the preglacial (Eopleistocene?) drainage system, primarily in palaeochannels of the Biała Głuchołaska River. The White Gravel series is the richest gold-bearing horizon. It contains between 0.37 g/m3 Au near the base and <0.10 g/m3 Au in its upper part.Maximumgold grade occurs in the first 1–2mabove the contact with the bedrock. Gold concentration in this area was controlled by the ability of streams to aggradation and the development of sedimentologic traps, where gold was accumulated during the preglacial valley erosion. Oblique orientation of the palaeo-Biała Głuchołaska valley and its tributaries to the regional ice-flow direction probably prevented the glaciers fromeroding deeply into the palaeochannels. From the exploration prospective, study of palaeochannel systems in the vicinity of Otmuchów–Prudnik could identify other buried placer gold occurrences. Gold-bearing sediments, correlated stratigraphically with the Biała Głuchołaska palaeochannel White Gravels occur in several other areas, including the Nysa Kłodzka, Kwisa and Kaczawa valleys.