Crven Dol Tl deposit in Allchar: Mineralogical investigation, chemical composition of Tl minerals and genetic implications

Ore samples enriched in sulfides and sulfosalts from the Tl-rich zone (entrance no. 21) of the Allchar deposit were investigated with reflected light microscopy and scanning electron microscopy, and the phase compositions were determined quantitatively with the electron microprobe. Major phases encountered are orpiment (As2S3), realgar (AsS) and pyrite. Lorandite is the major Tl-bearing mineral and it was indicated as pure stoichiometric (Tl: 60.1%, As: 20.6%, S: 18.4%). No, Sb and Pb were encountered. An entirely new Tl mineral was discovered with much higher Tl-concentrations and lower As-concentrations than in lorandite (Tl: 74.09%, As: 9.67%, Sb: 0.42%, S: 16.66%). The presence of this mineral as the last mineralization episode presents for the first time unequivocal evidence for a drastic enrichment of the ore-bearing fluids in Tl in the youngest stage. (orig.)