Study on andorite-series minerals from Meleg Hill, Velence Mts., Hungary

Abstract

During the last decades, different sulphosalts were observed in several samples that were investigated from the Meleg hill, Velence Mts. The investigated sample of this study was collected from the less studied north-eastern, stibnite-rich part of the hydrothermal breccia at the Meleg Hill. Based on the results of electron microprobe analysis, we found that the sample contained two sulphosalt minerals of the andorite series that have not been described from Hungary before. The andorite series is a subgroup of the lillianite homologous series. The individual minerals, andorite VI and roshchinite, within the andorite series were identified on the basis of their chemical composition and the andorite substitution percentage (L%). Andorite VI has Ag1.06Cu0.04Pb0.80Sb2.49Bi0.22As0.3S6 average chemical formula (normalized to 6 sulphur atoms) and L%=102.65–109.84, whereas roshchinite has Ag17.23Cu0.53Pb10.4Hg0.04Zn0.04Fe0.02Sb39.73Bi5.52As5.98S96 average chemical formula (normalized to 96 sulphur atoms) and L% = 119.52–123.48. Our results suggest that the formerly used comparative ternary diagrams of the system (Ag2S + Cu2S)–(Sb2S3 + Bi2S3 + As2S3)–(PbS + HgS + FeS + ZnS + CdS) is not adequate to differentiate the andorite-series minerals from each other, due to the highly variable element substitution of Me+, Me2+ and Me3+ cations. The andorite substitution percentage (L%) and the andorite homologue order value (N) are always necessary to calculate to distinguish the mineral species.