Supergene sulphate minerals from the burning coal mining dumps in the Upper Silesian Coal Basin, South Poland

Sulphate minerals of various chemical compositions form subtle mixtures of small aggregated crystals on some burning coal-mining dumps in the Upper Silesian Coal Basin, Poland. They include Na and Mg sulphates — blödite and konyaite. Magnesium sulphates belong to the second group and hexahydrite is its most common representative. Aluminium sulphates include tamarugite, pickeringite, and alunogen. Iron sulphates are copiapite-group minerals, metavoltine, butlerite, and voltaite-group minerals. Calcium sulphates are almost exclusively represented by gypsum. EDS proved to be, in general, a better tool than WDS for the chemical analysis of the sulphates. Both the Rietveld and Pawley methods were found to be useful in the calculation of unit cell parameters. The analysed sulphates contain some rare and interesting elements, the most important being Tl, Ga, In, Cd, Se, and As. The sulphates formed as a result of the mutual action of various supergene processes, including the oxidation of S-rich coal-fire gases, metal leaching from waste-rocks by H2SO4 solutions and evaporation. The complexity of the sulphate efflorescence composition is explained by the chaotic nature of settings involving a variety of waste rocks, hydration–dehydration reactions, and access of both ground and rain water- and atmospheric oxygen.

► Researched minerals include mixtures of sulphates of Na-Mg, Mg, Al, Fe and Ca.
► They arise due to the oxidation of S-rich coal-fire gases followed by evaporation.
► Their complexity has to do with waste set and humidity and temperature change.
► They may capture some rare elements: Tl, Ga, In, Cd, Se, and As.
► Standardised EDS is a good method for analysing such mixtures.