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The Genesis of Epithermal Au-Ag-Te Mineralization, Panormos Bay, Tinos Island, Cyclades, Greece

Stylianos Tombros and Karen St. Seymour

Department of Geology, University of Patras, Rion, 26500, Patras, Greece

Anthony E. Williams-Jones

Department of Earth and Planetary Sciences, 3450 University Street, Montreal, Quebec H3A 2A7, Canada

Paul G. Spry

Department of Geological and Atmospheric Sciences, 253 Science I, Iowa State University, Ames, Iowa 50011–3212

Corresponding author: e-mail, tombros{at}mailbox.gr

The Panormos Bay Au-Ag-Te vein system, Tinos Island, Greece, which is hosted in Mesozoic marbles, comprises 30 subparallel, steeply dipping quartz veins that extend for at least 500 m. In places, gold telluride mineralization occurs in hydraulic breccias and alteration halos, which are the products of CO₂ effervescence of the ore fluid and wall-rock interaction, respectively. Seventy ore and gangue minerals have been identified. 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 substages (early, middle, and late) that are characterized by Ag-, Cu-, and Au-bearing tellurides, respectively. Hessite, sylvanite, altaite, native tellurium, stützite, cuprian cervelleite, and an unnamed Cu-bearing precious metal sulfotelluride [(Ag,Au,Cu)₉Te₂S₃] characterize the early substage, whereas melonite, rickardite, vulcanite, weissite, and native tellurium are present in the middle substage. The late substage contains rickardite, kostovite, krennerite, petzite, and calaverite. Unexploited Au-Ag-Te mineralization at Panormos Bay is though to be genetically related to a fluorine- and boron-bearing per-aluminous leucogranite (Tinos leucogranite).

A combination of fluid inclusion microthermometry and sylvanite geothermometry suggests that the hydrothermal mineralization was deposited under hydrostatic pressures at a minimum depth of 1 km from moderate-temperature (155°–320°C), low- to moderate-salinity (0.2–13.2 wt % NaCl equiv), effervescing, CO₂-bearing fluids that contained appreciable amounts of CaCl₂ and MgCl₂. Calculated isotope compositions of ¹⁸O = –3.3 to +5.1 per mil and D of –73 to –62 per mil for waters in equilibrium with muscovite, quartz, and talc are consistent with the ore fluids being derived from the Tinos leucogranite (¹⁸O = +4.2 and D = –71) and their subsequent mixing with a more dilute, low-temperature Miocenic meteoric hydrothermal fluid. Calculated ¹³C_fluid (–2.0 to –0.3) and ³⁴S_H2S (–10.5 to +0.8) compositions of the ore fluids indicate an igneous source of carbon and sulfur, which were highly exchanged with a metasedimentary source. Physicochemical conditions of the ore fluids were T = 300° to 200°C, pH = 4.6 to 6.5, f_S2 = 10^–10.9 to 10^–15, f_O2 = 10^–31.5to 10^–41, f_Te2 = 10^–7.7 to 10^–10.7, f_CO2 = 10^–0.2 to 10^–0.8, and f_H2S = 10^–1.7 to 10^–1.8.