Chemical variations in tetrahedrite - tennantite minerals from the Furtei epithermal Au deposit, Sardinia, Italy: Mineral zoning and ore fluids evolution

Tetrahedrite-tennantite series minerals occur extensively in hydrothermal deposits although in minor quantities compared with other sulfides. Quantitative electron microprobe analysis show that, in the Furtei epithermal gold deposit, these minerals exhibit compositional variations in which base metals substitute for copper, Sb for As, and there is substitution of Te 4+ for (Sb, As) 3+ ; goldfieldite, tellurian tetrahedrite, tennantite and Te-free tetrahedrite coexist in a polymetallic assemblage highly enriched in telluride minerals. The association of hessite, stutzite, sylvanite, petzite, coloradoite, altaite, with native tellurium indicates direct magmatic inputs to the mineralizing solutions: a transition of this zoned magmatic hydrothermal system from porphyry to high sulfidation epithermal mineralization environments is envisaged. Sulfidation states of telluride-bearing ore fluids fluctuated between IS and HS conditions within the same mineralization, with telluride minerals and sulfosalts related to both HS and IS assemblages. On the basis of available chemical data for tennantite-tetrahedrite series minerals and the telluride-rich parts of drillcore samples, the relationship between mineral assemblages and sulfidation states is assessed, and the evolution of ore solutions outlined.