Structural and Chemical Controllers of the North and Northwest of Torud Based on Involved Fluid Studies, Structural and Geochemical Analyses

Abstract

Chah Mura mining area in Semnan province is located 30 km southwest of Shahroud and 20 km north of Torud village with an area of 35 km2 and includes a part of 1:250,000 Torud plate. Structurally, this area is located in the northeastern part of Central Iran and in the center of the volcanic-intrusive arc of Torud-Chah Shirin. Rock units of the area are volcanic and pyroclastic, depending on the Eocene age. Exposed assemblages in the Chah Mura area, based on field and laboratory studies, can be divided into basalt, andesite, andesite-basalt, trachyandesite, trachyandesibasalt and small outcrops of pyroclastic units in the form of agglomerates and sediments of sandstone and conglomerate. Volcanic rocks are influenced by sub-volcanic masses younger than Eocene with an intermediate to basic composition, and their predominant textures are granular, porphyroid with microcrystalline to microintragranular background. Finally, the units are cut by dikes. In this area, mineralization is mainly in the control of sub-faults and subvolcanic massifs. Mineralization is in the form of vein-veinlet, filling empty and scattered space in the oxidation-supergen stage. Mineral sequences include pyrite, chalcopyrite, chalcocite, digenite and covellite, cuprite, tenorite, natural copper, malachite, azurite, and iron oxides and hydroxides. Geochemical studies indicate that copper does not correlate well with any of the base metals and depositing elements. Copper shows only a relative correlation with silver. Micrometric studies of fluid inclusions in samples from this area indicate dilution as a result of mixing hydrothermal solutions with atmospheric fluids in formation of this reserve.