Genesis of the stibnite-cinnabar-scheelite deposits of the Gumusler area, Nigde, central Turkey and implications on their gold potential.

The project aims to describe the geology and hydrothermal fluid evolution of mineral deposits of the Gumusler area in the Nigde massif. Two types of deposits can be differentiated in this area: Sb Hg W Ba Au veins and associated replacement type Ba- Sb mineralization at the Rasih-Ihsan deposit, and a breccia hosted Hg Sb Au prospect at the Mehmetler Yurdu Sivrisi Tepe (MYST). The vein deposits are localized along E-W trending and N-dipping faults in marbles, and along marble-gneiss contacts. There is a spatial relationship between the mineral deposits and the felsic dykes of Cenomanian age which are cut by tlie Sb-Hg- W Ba vein. Similar dykes, together with intensive fracturing of marbles along the gneiss- marble contacts, also contributed to the formation of approximately E-W trending breccias containing the Hg Sb Au prospect at the MYST area. The Gumusler deposits have a diverse mineralogy including scheelite, barite, stibnite, cinnabar, sulphosalts and gold. Gold is associated with the cinnabar deposition stage, and is locally enriched in near surface zones with concentrations as high as 37 ppm at the MYST prospect. Silicification is the dominant wall rock alteration at the mineralized locations but sericitization, kaolinization, dolomitization and tourmalinization also occur at the periphery of the mineralization. Mineral deposition took place from aqueous fluids over a wide temperature range ( 350 °C to 150 °C). The pre-sulphide alteration (tourmalinization) occurred from fairly saline (8 2.5 eq. wt % NaCl) and moderately high temperature (216-254 °C) fluids. The main barite deposition also took place from fairly saline (8 2.5 eq. wt % NaCl) fluids at temperatures of 149-213 °C which are diluted towards the stibnite stage with a salinity of 4 eq. wt % NaCl and a temperature range of 137-168 °C. This probably indicates increasing involvement of non-magmatic waters. delta34S values of pyrite and stibnite range from -4.3 to +2.2 ‰ whereas those of barite are ~18 %, which suggests a magmatic origin for the sulphur of both sulphide and sulphate. Tourmaline mineral chemistry of hydrothermal alteration zones indicates a mixture of granitic and metapelitic sources, but comparison with tourmalines of other magmatic deposits favours a magmatic origin for boron.