Micromorphological indicators of pedogenesis in Technosols developed from mine wastes and tailings containing iron sulphides

The study aimed to use soil micromorphology to reveal the microscopic effects of soil-forming processes in young (up to about 200 years) Spolic Technosols developed from mine wastes and tailings containing iron (Fe) sulphides. Thin sections were analysed under petrographic microscopes. Three soil profiles developed from sulphide-rich mine wastes and tailings were studied in two abandoned pyrite mines in Rudki and Wieściszowice, southern Poland. Morphological observations showed that the studied profiles were poorly developed. However, microscopic investigations allowed for the identification of a set of pedogenic features as follows: (1) pedogenic structure (in particular in the topsoil) being an effect of soil organic matter accumulation and physical and biological alteration of technogenic parent materials; (2) Fe oxide hypocoatings and quasicoatings, which are the result of Fe mobilisation in the strongly acidic soil environment, followed by translocation in pore waters and precipitation of Fe oxides inside a soil groundmass; (3) clay coatings and infillings along pores which are the result of clay translocation in strongly acidic soils; (4) pedogenic gypsum in a form of rosettes or single crystals dispersed in the groundmass as an effect of crystallisation from pore waters rich in Ca and sulphate ions; and (5) bioturbations (e.g., root channels) being an effect of biota activity. The study showed that despite their young age and initial stage of soil profile development, the Technosols investigated are subject to natural soil-forming processes on the microscale that transform technogenic parent materials into functioning soils.