The Chah-Mesi epithermal Cu-Pb-Zn-(Ag-Au) deposit and its link to the Meiduk porphyry copper deposit, SE Iran: Evidence from sulfosalt chemistry and fluid inclusions

The polymetallic Chah-Mesi epithermal vein deposit is located about 2.5 km south of the Meiduk porphyry Cu(Mo-Au) deposit in the Kerman Cenozoic Magmatic Arc (Kerman Belt), representing the southeastern sector of the Urumieh-Dokhtar Magmatic Belt in Iran. The veins are N-S to NNE-SSW oriented and hosted in volcanic rocks of basaltic, andesitic to dacitic composition and pyroclastics, which were affected by intense local silicification and sericitization in proximity to mineralized veins. Propylitic, argillic, as well as potassic alteration show a more regional distribution; the latter only observed closer to the Meiduk deposit. Mineralization occurs in various types of veins (massive, banded, crustiform) and to minor extent in replacement and breccia bodies. It encompasses several stages: An early higher-sulfidation stage, characterized by pyrite, chalcopyrite, enargite/luzonite and bornite, is followed by the main intermediate-sulfidation state assemblage with pyrite, chalcopyrite, tetrahedrite group minerals and sphalerite. The late Pb-Zn rich stage with sphalerite, galena, chalcopyrite and pyrite overprints the earlier associations. Gold and silver of up to 7 g/t and 150 g/t, respectively, are associated with the main and late stages of mineralization. The main carriers of these precious metals are Ag-rich gold (electrum) and tetrahedrite; other Ag-bearing sulfosalts like pearceite are rare. The chemical composition of tetrahedrite group minerals ranges from tennantite-(Fe) to tetrahedrite-(Fe) and tetrahedrite-(Zn) exhibiting a positive correlation between Sb and Ag contents. The tetrahedrite group minerals show complex zoning and display an increase of Sb away from the Meiduk deposit. Primary fluid inclusions in sphalerite and quartz from the banded and crustiform veins are low saline aqueous H2O-salt inclusions with only traces of CO2. Homogenization temperatures of twophase LV inclusions (T-h (LV -> L)) have an average of 210 degrees C in sphalerite and 260 degrees C in quartz. Salinity values range from 1.2 to 9.9 and 2.1 to 9.2 mass% NaCl equivalent in sphalerite and quartz, respectively with an average of c. 6 mass% NaCl equiv. Low CO2 concentrations in the vapor phase detected by Raman spectroscopy together with previously published stable isotope data indicate fluids of magmatic origin as the main fluid source that were mixed with meteoric water. Mineralization is linked to ascending hydrothermal fluids which evolved from high-to intermediate-sulfidation state due to cooling, dilution with meteoric water and progressing fluid-wallrock interaction. Similar low salinity, but higher CO2-bearing fluids were previously reported from the nearby Meiduk porphyry deposit. Conclusively, Chah-Mesi is classified as an intermediate-sulfidation epithermal deposit that developed in the peripheral parts of the Meiduk porphyry system.

Automated summary

The Chah-Mesi polymetallic epithermal vein deposit is located in the Southeastern sector of the Urumieh-Dokhtar Magmatic Belt in Iran. The deposit is characterized by a variety of vein types hosting gold, silver and other precious metals, closely related to the nearby Meiduk porphyry Cu(Mo-Au) deposit.