Original paper

Origin of ferroan alabandite and manganoan sphalerite from the Tisovec skarn, Slovakia

Hurai, Vratislav; Huraiová, Monika

Abstract

Sulphidic skarn in an exo-contact zone between diorite and Triassic carbonates contains the Mn-rich minerals ferroan alabandite (Mn0.84-0.89Fe0.11-0.16S), manganoferroan sphalerite (Zn0.37-0.76Mn0.01-0.36Fe0.22-0.28S), hübnerite, manganoan magnesiohornblende, and Mn-carbonates. The Mn-content in sphalerite (up to 21.4 wt. %) is the highest ever recorded in hydrothermal settings. Magnetite and sulphides like galena, pyrite, pyrrhotite, arsenopyrite are also present. Anhydrite is ubiquitous as inclusions in sulphide minerals and crystals in drusy cavities, postdating hydrothermal Ca-Mn-Fe carbonates. Primary aqueous inclusions with variable salinity (2.9-44.8 wt. % NaCl eq.) occur in sphalerite and Mn-calcite. The fluid inclusions locally exhibit textural evidence for heterogeneous entrapment of boiling fluids. Crystallization temperatures of 300-350 °C were obtained from various mineral geothermometers, δ34S values in coexisting galena and sphalerite, and infrared fluid inclusion microthermometry. The observed anhydrite-chalcopyrite-magnetite-pyrrhotite-arsenopyrite-alabandite assemblage constrains fO2 and fS2 values to −34.5 ± 1.5 and −12.5 ± 0.5 log units, respectively, at 300 °C and atmospheric pressure. Together with an assemblage of silicate minerals (chlorite, sericite, K-feldspar, hyalophane) and high-salinity fluids, the calculated oxygen and sulphur fugacities are consistent with an intermediate sulphidation hydrothermal system. The increased δ34S values of the ore-forming fluids, 2-2.5 ‰, result from the disequilibrium isotopic exchange between mantle-derived H2S and marine sulphate.

Keywords

alabanditemanganoan sphaleriteskarnsulphur isotopesinfrared microthermometrywestern carpathians