Low-sulfidation type Au-Ag mineralization at Bergama, Izmir, Turkey


Yilmaz H., Oyman T., Arehart G. B. , Colakoglu A. R. , Billor Z.

ORE GEOLOGY REVIEWS, cilt.32, ss.81-124, 2007 (SCI İndekslerine Giren Dergi) identifier identifier

Özet

Bergama, the center of Bergarna County, is located in western Turkey and includes the villages of Ovacik, Narlica and Saganci. The Ovacik epitherinal gold-silver deposit is located in the Western Anatolian Volcanic and Extensional Province, adjacent to the ENE-trending Bergama graben, some 100 kin north of the city of Izmir. Gold of economic grades at the Ovacik deposit (reserves 4.19 Mt at 7.6 g/t) occurs in epithermal quartz veins which display low-temperature epithermal textures, including crustiform banding, quartz pseudomorphs after bladed calcite, and multiphase hydrothermal breccias. Alteration minerals at both Ovacik and Narlica are dominated by smectite, mixed-layer illite/smectite, chalcedonic quartz and adularia, whereas major kaolinite and minor inixed-layer smectite/illite (> 13.4 angstrom) occur at Saganci. The total sulfide content at Ovacik is low (< 2%) and is dominated by pyrite with traces of electrum, chalcopyrite, arsenopyrite, acanthite, tetrahedrite, pyrargyrite, stibmte, galena, chalcocite, bomite, covellite and sphalerite, occurring mainly within breccia clasts. Pyrite and mareasite appear to be the most common opaque minerals at Narlica and form dark sulfide-rich bands along with traces of electrum, native silver and chalcopyrite; pyrite is the only sulfide identified at Saganci. Ar-40/Ar-39 dating of adularia from gold-bearing quartz veins indicates an age of mineralization of about 18.2 +/- 0.2 Ma. Fluid inclusion studies at Ovacik reveal that main-stage quartz contains predominantly liquid-rich inclusions with homogenization temperatures (T-h) ranging from 150 to 305 degrees C, with the majority of T-h, varying between 165 to 205 degrees C: ice-melting temperatures (T-h) ranging from - 0.4 to - 1.2 degrees C (salinity < 2 wt.% NaCl equiv.) are dominant. Higher T-h, (220 to 248 degrees C) at the Narlica deposit may be attributed to the deeper level of exposure.