THE MINERALOGY OF SKARNS OF THE SPURRITE–MERWINITE SUBFACIES, SANIDINITE FACIES, GÜNEYCE–IKIZDERE AREA, EASTERN BLACK SEA, TURKEY

Abstract

Rare high-temperature and low-pressure contact-metamorphic assemblages are known to occur in the Guneyce–Ikizdere area, eastern Black Sea, Turkey. The emplacement of plutonic rocks of the calc-alkaline Rize batholith has caused the development of assemblages belonging to the spurrite–merwinite subfacies of the sanidinite facies. We provide compositional data for spurrite, rustumite, hillebrandite, tilleyite, cuspidine, vesuvianite, monticellite and gehlenite, and the secondary calc-silicates foshagite, dellaite, killalaite, bicchulite, hydroxylellestadite and two mineral species first discovered in these skarns, defernite and trabzonite. Our data point to the possible existence of a fluorine-rich variant of rustumite and a hydroxyl-dominant variant of cuspidine. These minerals are associated with familiar skarn minerals. The temperatures achieved are considered to be in the range 800–850°C on the basis of published phase-equilibrium results. The unusually high temperatures of contact metamorphism next to compositionally intermediate magmas may well reflect the presence of an underplating of basic magma in the vicinity and the efficient transfer of heat by the rising fluid phase. The relatively high concentrations of Cl and F encountered in these skarn assemblages are consistent with hydrothermal activity leading to Kuroko-type mineralization in this orogenic setting.