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Professor, Department of Earth Sciences, Faculty of Natural Sciences, University of Tabriz, Tabriz, Iran
10.22128/ijcm.2025.2980.0
Abstract
The Sari-Nou porphyry body is part of the mineralized Arasbaran zone within the Western Alborz–Azerbaijan structural belt. The intrusion of quartz monzonite to quartz monzodiorite (Oligocene–Miocene age) into Late Cretaceous volcanic (trachyandesite to andesite) and sedimentary (shale and sandstone) rocks has led to potassic, phyllic, argillic, and propylitic alterations, along with gold, copper, and molybdenum mineralization. The ore minerals include pyrite, chalcopyrite, sphalerite, and molybdenite, while the main gangue minerals are quartz and calcite. Disseminated and vein-veinlet textures are predominant.
Microthermometric studies show that homogenization temperatures of fluid inclusions in chalcopyrite–quartz (potassic zone) and pyrite–quartz (phyllic zone) veins are mostly >550⯰C and ~400⯰C, respectively. Fluid salinity ranges from 50 to over 60 wt% NaCl equiv. in the potassic zone and 3 to 14.5 wt% in the phyllic zone. These data indicate that gold-copper mineralization occurred concurrently with potassic and phyllic alterations, driven by hydrothermal fluid deposition during initial and secondary boiling phases.
In the first stage, boiling produced supersaturated and vapor-rich inclusions in quartz, synchronous with chalcopyrite precipitation in the potassic zone. In the second stage, renewed boiling formed liquid–vapor inclusions in quartz associated with pyrite in the phyllic zone, where gold mainly occurs as fine inclusions within pyrite. Pressure estimates based on halite-saturated inclusions suggest potassic alteration occurred at ~800 bar (≈3 km depth, lithostatic), while less-altered inclusions in the phyllic zone indicate ~300 bar (≈3 km depth, hydrostatic) conditions.
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