Description and conditions of formation of new unnamed Ag-Cu and Ag-Cu-Au sulfotellurides in epithermal polymetallic Ag-Au-Te mineralization, Tinos Island, Hellas

摘要

Two new unnamed Ag-Cu [(Ag,Cu)_(12)Te_3S_2] and Ag-Au-Cu [(Ag,Au, Cu)_9Te_2S_3] or [(Ag,Cu)_(25)Au_2Te_6S_9] sulfotellurides were identified in low sulfidation epithermal Au-Ag-Te mineralization at Panormos Bay, Tinos Island, Greece. The sulfotellurides occur in stage V of nine paragenetic stages as minute, up to 13 mum in length, moderately reflective, white-gray isometric grains, with yellowish to brownish tint, depending on the gold and copper contents. The Ag-Cu sulfotelluride coexists with hessite and sylvanite in early stage V, whereas the Ag-Au-Cu sulfotelluride is intergrown with petzite and kostovite in late stage V. Both sulfotellurides also occur along the cleavages of hessite and petzite and replace stage II tetrahedrite. Based on silicate, sulfide, and telluride stabilities and fluid inclusion data, the conditions of formation in stage V and the sulfotellurides formed between 230 deg to 260 deg C at fS_2 = 10~(-9) to 10~(-9.5), Fo_2 = 10~(-35.86), fTe_2 = 10~(-11.92) to 10~(-9.38), pH = 5.74, aHTe_((aq))~- = 10~(-10.88) and aH_2Te_((aq)) = 10~(-12.08), approximately. The gold and silver ion content in stage V solutions was 0.24 and 0.079 ppb, respectively.