, Volume 101, Issue 3-4, pp 169-183
Date: 24 Feb 2011

A cervelleite-like mineral and other Ag-Cu-Te-S minerals [Ag2 CuTeS and (Ag,Cu)2 TeS] in gold-bearing veins in metamorphic rocks of the Cycladic Blueschist Unit, Kallianou, Evia Island, Greece

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A cervelleite-like mineral, two unnamed silver sulfotellurides in the system Ag-Cu-Te-S [Ag2CuTeS, (Ag,Cu)2TeS], Te-rich polybasite and cadmian tetrahedrite occur in gold-bearing quartz veins in metapelites and faults within brecciated marbles of the Cycladic Blueschist Unit in the Kallianou area (southern Evia Island, Greece). The quartz veins and faults are discordant to syn-metamorphic structures and formed during ductile to brittle deformation in the final stages of exhumation of the Styra Nappe extrusion wedge (~21 Ma). Te-rich polybasite (up to 7.4 wt. % Te), cadmian tetrahedrite (up to 12.4 wt. % Cd), together with electrum (23–54 wt. % Ag) and the sulfotellurides, are the main silver carriers in the mineralization. The two unnamed sulfotellurides, Ag2CuTeS and (Ag,Cu)2TeS are believed to be new quaternary minerals in the system Ag-Cu-Te-S. These minerals and the cervelleite-like phase could have exsolved from galena during cooling (below 200°C). Initial temperatures for the formation of the sulfotellurides, in the form of hessite-intermediate solid solution, at Kallianou may be up to 300°C under logfS2 values between ~ −11.5 to −8.3, and logfTe2 from ~ −14.8 to −7.8. The values of logfTe2 and logfS2 during re-equilibration (at ~200°C) were constrained to −19.5 to −15.2 and to −15.8 to −11.5 respectively.