GEOLOGY, MINERALOGY, AND GEOCHEMISTRY OF GRANITE-HOSTED GOLD TELLURIDE MINERALIZATION AT PANORMOS BAY, TINOS ISLAND, GREECE

The largest low-sulfidation epithermal gold-telluride deposits in the world (e.g., Emperor, Fiji; Cripple Creek, U.S.A.) occur in intrusive volcanic rocks of alkaline or calc-alkaline affinity. By contrast, unexploited Au-Ag-Te mineralization at Panormos Bay, Greece, is relatively unusual in that it is genetically related to a F- and B-bearing granite (Tinos leucogranite). The Panormos Bay vein system, which is hosted in Miocene marbles, is composed primarily of thirty nearly parallel, high-angle quartz veins that extend for at least 500 m. In places, gold mineralization occurs in breccias. Zones of chlorite, talc, and muscovite-albite-tourmaline alteration, up to 50 cm wide, are associated with precious metal-bearing milky and clear quartz veins. The Au-Ag-Te mineralization is developed in stage V of eight hydrothermal stages. Stage V consists of three sub-stages (early, middle, and late) that are characterized by Ag-, Cu-, and Au-bearing tellurides, respectively. Hessite, sylvanite, altaite, native tellurium, stützite, and Cu-bearing cervelleite characterize the early stage whereas melonite, rickardite, vulcanite, weissite, and native tellurium are present in the middle stage. Late stage V contains rickardite, kostovite, krennerite, petzite, and calaverite. Fluid inclusion studies suggest that hydrothermal mineralization was deposited under hydrostatic pressures at a minimum depth of 1km from moderate-temperature (155^o-321^oC), low to moderately saline (0.2 to 6.3 equiv. wt % NaCl), effervescing, CO₂-bearing fluids that contained appreciable amounts of CaCl₂ and MgCl₂. Calculated isotope compositions of δ¹⁸O = -3.3 to 5.1 per mil and δD of -73 to -62 per mil for waters in equilibrium with muscovite, quartz, and talc are consistent with ore fluids being derived from the Tinos granite that subsequently mixed with a more dilute, low temperature meteoric fluid. Calculated δ¹³C_CO2 (-2.0 to -0.3 per mil) and δ³⁴S_H2S (-10.5 to 0.8 per mil) compositions of the ore fluids indicate an igneous source of carbon and sulfur, which were highly exchanged with a meta-sedimentary source. Epithermal gold mineralization at Panormos Bay is one of several granite-related gold occurrences (including nearby Apigania Bay) in Greece.