Abstract The Zaglic and Safikhanloo epithermal gold prospects are located in the Arasbaran zone, to the west of the Cenozoic Alborz-Azarbaijan magmatic belt in NW Iran. Mineralization is mainly restricted to quartz and quartz -carbonate veins and veinlets. Pyrite is the main sulphide, associated with subordinate chalcopyrite and bornite. Gold occurs as microscopic and submicroscopic grains in quartz and pyrite. The country rocks are Tertiary intermediate–mafic volcanic and volcaniclastic rocks of andesite to trachy-andesite composition intruded by a composite granitic to syenitic pluton. They are medium- to high-K, calc-alkaline and alkaline rocks and display fractionated REE (rare earth element) patterns, with light rare earth elements (LREE) significantly enriched relative to the heavy rare elements (HREE). On primitive mantle normalized plots, they display depletions in Nb, Ti and P, and enrichments in Pb, which are common characteristics of arc-related magmas worldwide. Hydrothermal alteration minerals developed in the wall rocks include quartz, calcite, pyrite, kaolinite, montmorillonite, illite, chlorite, and epidote. Minor alunite occurs in Safikhanloo. Gold is locally enriched in the altered rocks immediate to the veins. The ore-stage quartz from both prospects is dominated by liquid-rich fluid inclusions; vapour-rich inclusions are rare. The homogenization temperature varies between 170–230 and 170–330 °C and salinity varies between 1.4 to 9.5 and <1 to 6.7 wt% NaCl equivalent, for Safikhanloo and Zaglic, respectively. The occurrence of hydrothermal breccias, bladed calcite, adularia, and rare coexisting vapour- and liquid-dominant inclusions suggest that boiling occurred in the course of the evolution of the ore fluids. The large variations in Th and the salinity values can be explained by boiling and/or mixing. Lack of sulphate minerals in the veins suggests that sulphides and gold precipitated from a reduced, H 2 S-dominant fluid. Calculated δ 34 S values for the ore fluid vary between −4.6 and −9.3‰. Sulphur could have been derived directly from magmatic sources, or leached from the volcanic and plutonic country rocks. Ore formation in Zaglic and Safikhanloo occurred in response to mixing, boiling, and interactions with wall rocks. Considering the intermediate-argillic alteration, the low contents of base metal sulphides, and the overall low salinities, the Zaglic and Safikhanloo can be classified as low-sulphidation epithermal systems.
Abstract The Dochileh stratiform copper deposit in the Sabzevar Zone of northeastern Iran is hosted in the basaltic sequence of the Upper Eocene age. The host rock displays two hydrothermal events: zeolite–carbonate alteration that is a stratigraphic–lithologic feature and chlorite and chlorite/ferruginous alterations in the local mineralized structures. Ore formation is related to both hydrothermal events and occurs in both stratiform and vein mineralization types. Mineralization consists of main chalcocite with variable amounts of bornite, chalcopyrite, native copper, malachite, and cuprite minerals, which occur as hydrothermal breccias, and disseminated, vein, and veinlet forms. Geophysical field studies using resistivity and induction polarization (IP) methods were conducted along nine survey lines in the area. As a result of modeling and interpretation of the acquired geophysical data, high values of IP and resistivity corresponding to mineralization were observed at two depth levels: 0–20 m and more than 40 m. Based on these geological and geophysical investigations, six locations for drilling exploration boreholes were proposed. Drilling data confirmed the mineralization containing high copper values in the two depth levels: the vein‐type mineralization in the surface and shallow depth level, and the stratiform mineralization at the deeper level. Fluid inclusion studies in calcite and quartz from stratiform‐ and vein‐type mineralization show the evidence of mixing, and a linear dilution trend during the ore formation occurred at a wide range of temperatures: 121–308°C and 80–284°C, respectively, and varying salinities of between 3.2–16.8 and 0.8–22 wt% NaCl equivalents. The stable isotope composition of δ 34 S that falls in a range of −2.4 to +25.0‰ could be considered biogenetic sulfur from bacterial sulfate reduction and leaching of sulfur from hosting basalt. The δ 13 C values of calcite vary between −0.6 and −7.6‰, suggesting a major contribution of marine carbonates associated with igneous carbonates, and the δ 18 O SMOW values of calcite are between +15.2 and +19.9‰, suggesting a contribution of δ 18 O‐rich sedimentary rocks and δ 18 O‐poor meteoric water. Copper and sulfide‐rich hydrothermal fluid have flowed upward through the local faults and permeable interbeds within the Eocene volcanic sequence and have formed the mineralized veins and horizons. The geophysical results have detected the local faults as the channel ways for mineralization.
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