Pb-Zn deposits in Cretaceous carbonate host rocks, northeast Shahmirzad, central Alborz, Iran

A multidisciplinary study including geology, petrography and reconnaissance isotope analyses has been carried out on the Reza-Abad, Reza-Barak and Heydar-Abad Pb-Zn deposits, hosted by different types of Cretaceous dolostone and limestone in northeast of the city of Shahmirzad in the central Alborz region of Iran. Dolostones are dominated by replacement dolomite with minor dolomite cements. The studied deposits are strata-bound vein and breccia type and are associated with tensional faults and fractures. Mineralisation occurs in veins and in karstic and tectonic breccias. Hypogene minerals include galena with minor sphalerite and pyrite. Supergene minerals comprise Fe-oxide, cerussite, anglesite, plattnerite, minimum and mimetite. Calcite, quartz and dolomite form gangue minerals. The 18O and 13C values of dolomites vary between -5.8 and +2.1 parts per thousand VPDB and between 0.0 and +2.9 parts per thousand VPDB, respectively. Isotopic and previous fluid inclusion studies suggest that deposits formed from brines (15-25 wt.% NaCl equiv.) at temperatures of 70 to 110 degrees C. Lead isotope data are homogeneous and represent upper crust source. This study provides an insight into the ore-forming processes of MVT deposits in the northeast Shahmirzad region.