SILNIE KRZEMIONKOWY ZAŻELAZIONY METASOMATYT (BIRBIRYT) ZE STREFY ZWIETRZENIA MASYWU SERPENTYNITOWEGO W ZŁOŻU NIKLU W SZKLARACH NA DOLNYM ŚLĄSKU

Abstract

STRONGLY SILICEOUS AND FERRUGINEOUS METASOMATITE (BIRBIRITE) FROM THE WEATHERED ZONE OF THE SERPENTYNITE MASSIF IN THE SZKLARY SAPROLITIC NICKEL DEPOSIT IN LOWER SILESIAAbstract. The paper describes strongly siliceous ferruginous metasomatite – birbirite found in two boreholes (Bobolice B2 and B5) located in the southern part of the Szklary–Wzgórze Siodłowe nickel saprolitic deposit in Lower Silesia. Birbirite forms a 5–6 m thick horizon (?lense), ca. 0.03km2 in area (its horizontal extent is at least 300×100 m). The birbirite is a hard rock with a very characteristic light-rusty colour, strongly porous and of very low specific gravity. Amorphous silica, fine-grained recrystallized quartz (ca. 90 wt % SiO2), hydrated oxides and iron hydroxides (mainly goethite – ca. 4–9 wt%Fe2O3) definitely dominate in the birbirite composition. The birbirite is also characterised by a low MgO content (<1 wt %) and traces of nickel, cobalt and chromium. Birbirite formed as a result of strong leaching out and enrichments of saprolitic wastes (loss of MgO, Ni, Cr and Co and enrichment in amorphous silica and goethite). Saprolitic waste formed previously in the Palaeogene during exogenic changes of serpentinitized and fractured Upper Devonian peridotites in a humid and wet climate, and subsequently changed by local water table fluctuations resulting from a morphological uplift caused by the youngest tectonic activities.