Geology, Mineralogy and geochemistry of the Chomalu polymetallic epithermal deposit, NW Zanjan

The Chomalu ore deposit is located in the western part of the Alborz magmatic belt (Alborz-Azerbaijan) and geology includes Lower Eocene volcanic to volcanoclastic, including olivine basalt, andesite basalt, andesite to trachyandesite, dacite to rhyolite, and Upper Eocene granitoids including quartz monzonite to quartz monzodiorite. Ore formation in the Chomalu deposit is hosted by olivine basalt and andesite to trachyandesite rocks. The main ore minerals at Chomalu deposit consist of galena, sphalerite, tetrahedrite, pyrite, chalcopyrite, and magnetite. Quartz and fluorite are the main gangue minerals in the Chomalu deposit. Ore mineralization occur as veins and open space filling textures. Field observation shows that mineralization occurred in E-W and NW-SE trending quartz veins. Three mineralization stages were recognized at Chomalu deposit. The geochemical studies show high correlation coefficient indexes between Pb -Zn, Pb-Ag and Cu-Pb and Zn. Vein-veinlets, open space filling and colloform textures; galena, Fe-poor sphalerite, tetrahedrite, pyrite and chalcopyrite mineralization; relatively high base metal sulfides (e.g., Cu, Pb, and Zn); gangue minerals including quartz, fluorite and minor calcite, mineralization with olivine basalt and andesite to trachyandesite as host rocks show that Chomalu mineralization can be classified as IS epithermal deposit.