Sulfate minerals and their origin in the weathering zone of the pyrite-bearing shists at Wieściszowice (Rudawy Janowickie Mts, Western Sudetes)

Abstract

A model of weathering alterations for the pyrite-bearing schists outcropping at the abandoned pyrite mine at Wieściszowice (Rudawy Janowickie Mts, Western Sudetes, Poland) is proposed as based on the studies of supergene sulfate minerals, as well as shallow groundwaters and surface waters of the region, experimental decomposition of the schists in sulfuric acid solutions, and calculation of the crystal-solution equilibrai of rock-forming minerals. Formation of magnesiocopiapite, aluminocopiapite, pickeringite (and its new variety ferropickeringite), fibroferrite, slavikite, gypsum, epsomite, and alunogen is recognised in the studied weathering zone. Analyses of the sulfur and oxygen isotope rations in sulfate ions, and oxygen and hydrogen isotope rations in crystallization water, were used to characterise the origin and stability ranges of the studied minerals. Sulfur isotope ratios in sulfates indicate water as the main source of oxygen. The best soluble mineral display seasonal changes of isotope composition of crystallization water, which can be likely correlated to composition of atmospheric precipitation.