Original paper

Stable isotope (O, H and S) studies on the vein-type Cu–Mo–Au mineralization in Qarachilar area, Qaradagh pluton (NW Iran)

Simmonds, Vartan; Moazzen, Mohssen; Harris, Chris

Abstract

The Qarachilar area is located in the central part of the Qaradagh pluton (NW Iran) in the north western part of the Urum- ieh–Dokhtar volcano–plutonic belt, which formed during the subduction of Neo-Tethyan oceanic crust beneath the Central Iranian plate. The Qaradagh pluton consists of several discrete intrusions that formed from middle Eocene to Oligocene. The dominant rock type in the study area is granodiorite, which hosts hydrothermal alterations and vein-type and disseminated Cu–Mo–Au mineralization. Quartz–sulfide and mono-phase sulfide veins and veinlets in the area contain pyrite, chalcopyrite and molybdenite with lesser amounts of bornite and digenite. Quartz crystals within these veins contain mono-phase vapor, 2-phase (liquid–vapor) and multiphase (halite, sylvite and opaque-bearing) primary, as well as secondary and pseudo-secondary fluid inclusions. The homogenization temperatures obtained for 2-phase and multiphase inclusions range from 220 to 540 °C, mainly clustering between 260 and 420°C. Salinities calculated for these inclusions lie in the range of 15 to 65 wt% NaClequiv, with a peak between 25 and 45 wt% NaClequiv. Stable isotope studies of O, H and S on the quartz and sulfide samples taken from quartz–sulfide veins–veinlets reveal a magmatic origin for the ore-bearing fluid and its sulfur content. The δ 18 O values for quartz and fluid are about 11.13ndash;12.47 ‰ and 5.78–6.89 ‰ (SMOW), respectively, and the δD values of the entrapped fluid inclusions within the quartz crystals range between –93 and –50 ‰ (SMOW). The δ 34S values of sulfide minerals are about –1.37–0.49 ‰ (VCDT), with pyrite and chalcopyrite showing the highest and lowest values, respectively. The calculated δ34 SH2S is between –1.90 and –0.58 ‰, while the calculated δ34 Sfluidis about –3.53 to –2.20 ‰ (VCDT). All these data lie within the range of sulfurisotopic composition of fluids derived from granitic magmas.

Keywords

vein-type mineralizationqarachilarqaradagh plutonstable isotope