Chahmir Zn-Pb Deposit, a Typical Selwyn-Type (Vent Proximal) Sedex Deposit, Bafq Basin, Central Iran

Chahmir Zn-Pb deposit is one of several sediment-hosted Zn-Pb deposits (e.g., Koushk, Zarigan, Dareh Dehu & Cheshmeh Firuzeh) located in southeast of Bafq basin hosted within a Early Cambrian volcano-sedimentary sequence, simultaneous with global Cambrian ocean anoxic event, forming in a rift environment. The host rock units of the Chahmir Zn-Pb deposit includes organic-rich black siltstones with intercalations of tuff and silty tuff overlain by green carbonaceous tuffs. Based on nature of sulfide mineralization, mineralogy and textures of sulfide minerals, the Chahmir deposit can be divided into four different facies. Based on their situation towards the vent of mineralization fluid, these facies include: 1) A massive ore facies (Vent Complex) forms the thicker part of generally massive higher grade ores in east of the deposit. This facies includes two subfacies: the sulfide-silica-carbonate subfacies in center of massive ore and sulfide-carbonate subfacies around it. Sulfide minerals are observed as massive, replacement, vein-veinlets and brecciated colloform textures. 2) Vein-veinlets facies (Feeder Zone) includes sulfide veins and silica that form as a scissors of host rocks under the massive ore facies. Vein-veinlets and replacement textures form main features of this facies. 3) Bedded ore facies which is thinner than the massive ore facies and is characterized by layered and banded feature and low grade ore. This facies occurs as stratiform laminated and banded sulfides contemporaneous with the formation of the host rocks. 4) Distal facies is formed at west of the deposit which is actually a sedimentary equivalent of bedded ore facies. Main characteristics of this facies are presence of disseminated pyrite, banded chert and barite. The most important characteristics of mineralization at the Chahmir deposit such as tectonic setting, host rocks, mineralogy, diffrent facies, show similarities to siltstone and shale hosted Zn-Pb Sedex type deposits. Accordingly, Chahmir is regarded as a Selwyn-Type (Vent Proximal) SEDEX deposit.