شواهد باروري توده هاي نفوذي با استفاده از ژئوشيمي كاني‌هاي شاخص پورفيري در كانسار مس- موليبدن پورفيري غرب ظفرقند، شمال شرق اصفهان

This study investigates the magmatic-hydrothermal evolution of the West Zafarghan‎d porphyry Cu–Mo deposit, located in the central part of the Urumieh-Dokhtar Magmatic Arc. Field observations an‎d petrographic evidence, together with fluid inclusion thermometry, TitaniQ an‎d chlorite thermometry, mineral geochemistry of plagioclase, embayed quartz, magnetite, an‎d zircon, as well as U-Pb zircon an‎d Re-Os molybdenite geochronology, were integrated to constrain the evolution of the ore-forming system. Mineralization at the West Zafarghan‎d deposit commenced with magnetite mineralization during potassic alteration, followed by the bornite-chalcopyrite-magnetite assemblage associated with chlorite–sericite alteration an‎d predominantly molybdenite-bearing veins mainly related to phyllic alteration, an‎d terminated with sphalerite–galena mineralization during the propylitic alteration stage. Zircon U-Pb geochronology yielded ages of ~34-33 Ma (Late Eocene-earliest Oligocene) for the granodiorite porphyry an‎d ~24.3 Ma (Late Oligocene) for the granite porphyry, whereas molybdenite Re–Os dating also yielded ages of ~24.3 Ma (Late Oligocene). These results indicate that emplacement of the younger granitic intrusive phase was contemporaneous with the main Cu-Mo mineralization an‎d genetically related to it. Fluid inclusion microthermometry an‎d TitaniQ quartz thermometry define a pressure–temperature evolution from lithostatic conditions (up to ~60 MPa) at a depth of approximately 2.2 km to hydrostatic conditions at shallower levels (~1.5 km). The evolution of the ore-forming fluid indicates boiling an‎d phase separation during the early stages of mineralization, followed by progressive fluid evolution an‎d gradual cooling toward the final stages of ore formation. Chlorite thermometry further confirms a systematic decrease in temperature from the potassic to the propylitic alteration stage. Geochemical evidence indicates that magmatic evolution from a normal arc calc-alkaline granodiorite to a granite porphyry with adakitic affinity emplaced within a thickened crust was the principal factor enhancing ore-forming potential. The geochemical characteristics of chlorite from the granite porphyry, including enrichment in Mg, Ti, an‎d V, likewise indicate that this intrusive phase was the principal ore-forming source. Mineral geochemical data from plagioclase (increased Al an‎d elevated Sr/Y ratios reflecting highly oxidized an‎d H₂O-rich magmatic conditions), magnetite (transition from magmatic magnetite enriched in Ti, W, Zr, an‎d Nb an‎d depleted in Ge to hydrothermal magnetite depleted in Ti, W, Zr, an‎d Nb an‎d enriched in Ge under the combined control of temperature, oxygen fugacity, an‎d progressively increasing fluid-rock interaction), embayed quartz (decreasing Ti, increasing Al, an‎d more advanced magmatic differentiation), an‎d zircon (high Eu*, high Yb/Gd, low Dy/Yb, an‎d other geochemical fertility indicators reflecting higher oxidation state, greater water content, an‎d more evolved magma) consistently demonstrate that the granite porphyry was significantly more fertile than the granodiorite porphyry an‎d indicate that the principal Cu-Mo mineralization occurred contemporaneously with the emplacement an‎d cooling of the granite porphyry.

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