Tl-retention by jarosite-group minerals in technosoils from the central part of the Allchar deposit, North Macedonia

Areas naturally enriched in thallium (Tl) represent a severe threat to surrounding ecosystems as the bioavailability of this highly toxic heavy metal strongly depends on its retention by the weathering-induced formation of secondary Tl-minerals. Estimations on the remediation potential of such areas therefore require a detailed mineralogical characterization of included Tl-bearing secondary minerals. This study focusses on the Allchar Sb-As-Tl-Au deposit in the southern part of North Macedonia, as its mineralogical composition is a rarity in the world. It contains remarkable concentrations of Tl, estimated to be around 1,000 tons of metal. In this study, stockpile material from abandoned, surface-exposed mining wastes and surrounding soils of the Sb-rich central part of the Allchar deposit was examined for the presence of secondary Tl-minerals. A combination of optical microscopy, powder X-ray diffraction (PXRD) and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) was performed to determine the speciation of Tl in heavily weathered technosoils.