![]() Keywords: Ay Qalasi, reactivation of fault, EPMA, fugacity of sulfur and arsenic, tennantite-tetrahedrite series. In the new condition, the clasts of sphalerite, chalcopyrite, and pyrite ores react with these fluids to form sulfosalt minerals of tennantite-tetrahedrite series. The penetration and circulation of these fluids in the brecciated parts of the deposit, due to the high fugacity of sulfur and arsenic, impose new thermodynamic conditions on the system, which in turn leads to the instability of sulfide minerals. ![]() ![]() Due to the fault's reactivation, the initial sulfide minerals to be brecciated and provides the conditions for the penetration of these fluids. Tertiary dacitic domes replacement adjacent to the deposit has led to the formation of hydrothermal solutions with high fugacity of sulfur and arsenic, and to a lesser extent antimony. The EPMA analysis data show that their chemical composition is a function of the mineralogical composition of the sulfide ores in which they have been replaced. These minerals are mainly replaced in host minerals. Based on microscopic and EPMA analysis, the composition of this series is tennantite-tetrahedrite. ![]() The Ay Qalasi Pb-Zn (Ag) epithermal deposit is located in the south east of Takab, northwest of Iran and is formd at the Urmia-Dokhtar magmatic belt and the Sanandaj-Sirjan zone intersection. 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. 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. The calculated δ34SH2S 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. Hydrothermal alteration minerals include sericite, illite and quartz. The total sulfide mineral content of up to 60 vol.% is dominated by sphalerite, galena, pyrite, and chalcopyrite with minor amounts of tennantite?tetrahedrite. 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 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. ![]()
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