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Age and source of the Kure/Odemis arsenopyrite-gold mineralization (Menderes Massif, Turkey) determined by Re-Os-He isotopes

2020    Sonmez, Fatma Nuran; Yilmaz, Huseyin; Cicek, Mustafa; Koralay, Osman Ersin; Niedermann, Samuel; Kirk, Jason

The Menderes Massif (MM) is considered to be one of the principal regions hosting vein-type quartz-arsenopyrite orogenic gold deposits and occurrences in Turkey. Gold mineralizations in the MM can be grouped into: (i) schistosity-conformable E-trending veins and (ii) shear-controlled NW-trending veins. Arsenopyrite is one of the major gold-bearing minerals in these deposits or occurrences. Rhenium-Osmium isotopic dating of two types of arsenopyrite from the schistosity-conformable and vein-type Kure (Odemis) gold deposit has yielded two groups of model ages (maximum ages) at 557-574 Ma and 246-250 Ma, respectively. The data suggested that the quartz-arsenopyrite gold deposit formed in the Neoproterozoic and Early Triassic, with the former and the latter corresponding to Pan-African compressional orogenesis and Palotethys rifting, respectively. Fluid inclusions in Kure arsenopyrite have He-3/He-4 ratios of similar to 0.08-0.09 Ra (Ra = 1.39x10(-6), the He-3/He-4 ratio of air) being within the range of middle to upper crustal values. A minor helium contribution of mantle fluids to the Kure gold deposit is possible because the He-4 concentrations in arsenopyrite are enriched 170 to 9520 times relative to argon and typical atmospheric values, indicating that contribution of atmospheric He to the mineralizing fluids is negligible, and 0.08-0.09 Ra is slightly above typical crustal He-3/He-4 ratios. Arsenopyrite yields relatively non-radiogenic initial Os isotopic compositions, also indicating possiblecontribution from mantle fluids. Carbonic fluid inclusion type-2 (H2O-CO2-NaCl +/- CH4) in quartz of NW-trending veins at Kure are gas-liquid-hydrate-crystal-rich and their homogenization temperatures (T-h) range from 244 to 387 degrees C. Salinity values range from 0.2 to 5.7 wt% NaCl equiv. The homogenization temperatures (T-h) of aqueous fluid inclusions type 1 (H2O-NaCl) in quartz from NW-trending veins at Kure vary between 237 and 358 degrees C whereas salinity values range from 1.7 to 7.7 wt% NaCl equiv. Quantitative EPMA spot analyses on arsenopyrite minerals have shown that As concentrations in EW-trending and NW-trending veins range from 32.5 to 33.8% and 32.3-33.8%, respectively. Based on a phase diagram for the Fe-As-S system along with the arsenopyrite geothermometer, the ranges of temperature and corresponding logf S2, at which arsenopyrite is in equilibrium with pyrite are between 380 and 480 degrees C, and -7.4 and -4.3 for Apy-1, respectively. These values are between 390 and 475 degrees C, and -7.0 and - 4.5 for Apy-2, respectively.