The Ay Qalasi deposit: An epithermal Pb–Zn (Ag) mineralization in the Urumieh–Dokhtar Volcanic Belt of northwestern Iran

The Ay Qalasi Pb–Zn (Ag) deposit, located at the intersection of the Urumieh–Dokhtar Volcanic Belt (UDVB) and the Sandaj-Sirjan Metamorphic belt of northwestern Iran, is hosted by Miocene sandstone and siltstone of the Upper Red Formation (URF), and by a post Miocene feldspar porphyry dyke that intrudes the URF. The Ay Qalasi deposit (reserves ~30000 tonnes at 8 % Zn, 5 % Pb and 60 ppm Ag) occurs in quartz-base metal sulfide veins, vug infill, and breccias with comb, crustiform, and cockade textures. The total sulfide mineral content of up to 60 vol.% is dominated by sphalerite, galena, pyrite, and chalcopyrite with minor amounts of tennantite–tetrahedrite. Hydrothermal alteration minerals include sericite, illite and quartz. The calculated d34SH2S values in the sulfide ore samples average +3.7 ‰ for pyrite and galena, and +4.3 ‰ for sphalerite, suggesting a magmatic input for the sulfur. Low Fe contents of the sphalerite, the hydrothermal style of alteration together with estimated temperatures of formation correlate with an intermediate-sulfidation style of epithermal mineralization. Our data suggest that the mineralization at Ay Qalasi took place as a result of hydrothermal activity related to the late Cenozoic high-level magmatism in the UDVB similar to other hydrothermal deposits of the Takab–Angouran region.