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Hossein Kouhestani

Majid Ghaderi, Hossein Kouhestani, Sebastien Meffre, Khin Zaw
Constraints on the Chah Zard Au–Ag mineralization, west-central Iran using whole-rock and Sr–Nd isotope geochemistry of volcanic host rocks
Abstract


The Chah Zard gold–silver deposit, a typical breccia-hosted low- to intermediate-sulfidation epithermal system, with a total measured resource of ~2.5 Mt @ 1.7 g/t Au and 12.7 g/t Ag, is located within late Miocene andesitic to rhyolitic volcanic complex in the central part of the Urumieh-Dokhtar Magmatic Arc (UDMA). The orebodies are emplaced in breccia bodies dominantly hosted by rhyolite porphyries. Systematic whole–rock geochemical investigations of the volcanic rocks show that both intermediate and felsic rocks are characterized by significant Large Ion Lithophile Element (LILE) and Light Rare Earth Element (LREE) enrichment coupled with High Field Strength Element (HFSE) depletion. These geochemical data indicate subduction–related magmatic arc affinity for the volcanic rocks, and suggest that hornblende fractionation appears to be an important controlling factor on the evolution of mineralized subvolcanic rocks. Although the rhyolite porphyry has relatively high 87Sr/86Sr ratios, the volcanic rocks show narrow variation in the Sr and Nd isotopic compositions, displaying initial 87Sr/86Sr range of 0.704910 to 0.705967 and εNd(i) values of +2.33 to +2.70. These data suggest that the rhyolitic magmas probably represent the final differentiates of parental andesitic magmas with minor crustal contamination. This indicates that the parent melts generated from partial melting of a mixture of a depleted asthenospheric mantle and an enriched sub-continental lithospheric mantle source in an extensional tectonic setting, in response to slab break-off and resultant upwelling of asthenospheric mantle. The rhyolite porphyry is inferred to have supplied heat that drove the convective hydrothermal system at the Chah Zard deposit, but also provided some of the fluid sources responsible for the development of the Chah Zard epithermal system

 

 

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