Hg-bearing sphalerite from the Rujevac polymetallic ore deposit, Podrinje Metallogenic District, Serbia: Compositional variations and zoning

Rujevac is a low-temperature hydrothermal polymetallic Sb(As)–Pb–Zn vein-type ore deposit, hosted in volcanogenic-sedimentary zone situated in Rujevac-Crvene Stene-Brezovica Diabase-Chert Formation (DCF) of the Podrinje Metallogenic District (PMD), Serbia. The mineralogical composition of the deposit consists of sulfides (stibnite, sphalerite, pyrite, arsenopyrite, galena, realgar and orpiment), sulfosalts (zinkenite, plagionite, robinsonite, twinnite and gratonite), native arsenic, Sb-oxides (valentinite, senarmontite and kermesite), and gangue minerals (quartz, calcite and dolomite). Minerals containing mercury as a major element have not been detected. According to optical features, sphalerite belongs to the cleophane, low Fe content variety (yellowish to colorless). Electron Probe Micro-Analyses (EPMA) of sphalerite revealed wide compositional variations. The Hg content in sphalerite varies between 0.30 and 6.47 wt%. The range of other minor elements (Fe and Cd) is highly variable; Mn, Sn, Ge, In, Tl, and As were analyzed, but not detected. Hg-rich zones occur as narrow lamellae and are related to the crystallographic directions of sphalerite. The average values of the EPMA results gave the crystallochemical formula of this sphalerite (Zn0.981, Fe0.007, Cd0.007, Hg0.008)∑1.003S0.997. Strong negative correlations have been determined between ∑Fe + Cd + Hg vs. Zn, and Hg vs. Zn, while these are absent between all other analyzed elements.