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چکیده
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Hydrothermal alteration is caused by fluid–rock interactions which accompany the flow of hot aqueous fluids along fractures and grain boundaries under various physicochemical conditions. Geochemical changes caused by hydrothermal alteration can be used to quantify mass transfer during alteration and mineralization, and to determine the behavior and possible sources of the fluids involved. The Oshvand ore district, which is located in the westernmost part of the Sanandaj-Sirjan Zone (SaSZ), hosts one of the largest concentrations of Cu, Fe, and Au skarn deposits in Iran. The SaSZ is located along the southwestern edge of the Iranian plateau and is a portion of the Tethyan orogeny that records the transition from a passive continental margin to a continental arc during the Late Triassic-Early Jurassic. Igneous activity in the SaSZ has been a major focus of earlier studies, with the voluminous calc-alkaline intrusive and volcanic rocks used as evidence for Jurassic arc magmatism. To understanding of metallogenesis of the Oshvand Fe (Cu-Au) skarn deposit, a cross-section through the complete rock sequence, from the carbonate wall rock to the pluton, was systematically sampled, and analyzed for bulk-rock major and trace elements. Underpinned by the skarn zonation model, ln(SiO2/Al2O3), ln(SiO2/TiO2), and REE + Y values in the skarns were used to distinguish the various skarn protoliths. The effectiveness of the ln(SiO2/Al2O3) and ln(SiO2/TiO2) is supported by the variable mobility of Si, Al, and Ti during magma-derived fluid infiltration into the carbonate wall rocks at Oshvand. The effectiveness of REE + Y is based on their significant concentration differences in the carbonate wall rocks and igneous rocks at Oshvand. These geochemical indexes may be applicable to the characterization of protoliths and mass transfer in skarn deposits where igneous rocks intruded carbonate wall rocks. Its significance for exploration models is that relatively poorly mineralized skarn protoliths in this setting may be associated with more substantive exoskarn deposits on their margins. In the isocon diagram for diopside exoskarn formation, the isocon line defined by CaO, V, Li, Cs, Sr, Y, and rare earth elements has a slope of 0.87, suggesting a mass gain of 14%.
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