New data on gersdorffite and associated minerals from the Peloritani Mountains (Sicily, Italy)

Abstract

Gersdorffite, ideally NiAsS, and associated minerals from Contrada Zillì (Peloritani Mountains, Sicily, Italy) have been characterized through electron microprobe analysis and X-ray diffraction. Primary minerals, hosted in quartz veins, are represented by gersdorffite, tetrahedrite-(Fe), and chalcopyrite with minor pyrite and galena. Rare aikinite inclusions were observed in tetrahedrite-(Fe) and chalcopyrite. Gersdorffite occurs as euhedral to subhedral crystals, up to 1 mm in size, with (Sb,Bi)-enriched cores and (Fe,As)-enriched rims. Its chemical composition is (Ni_0.79−0.95Fe_0.18−0.04Co_0.04−0.01)(As_0.90−1.03Sb_0.10−0.00Bi_0.02−0.00)S_0.98−0.92. It crystallizes in the space group P2₁3, with unit-cell parameters a=5.6968(7) Å, V=184.88(7) ų, and Z=4, and its crystal structure was refined down to R₁= 0.035. Associated tetrahedrite-(Fe) has chemical formula (Cu_5.79Ag_0.07)_Σ5.86(Cu_3.96Fe_1.59Zn_0.45)_Σ6.00(Sb_3.95As_0.17Bi_0.03)_Σ4.15S_13.06, with unit-cell parameters a= 10.3815(10) Å, V=1118.9(3) ų, and space group I-43m. Its crystal structure was refined to R₁=0.027. Textural and crystallographic data suggest a polyphasic crystallization of gersdorffite under low-temperature conditions.