Northern Chah-Farsakh copper deposit; an example of Besshi- type VMS deposit in the Torud-Chahshirin metallogenic belt

The NE-trending Torud-Chahshirin metallogenic belt, lying in the central to the eastern portion of the Alborz Mountain system is approximately 300 km in length, with a complex tectonic, magmatic, and stratigraphic history (Alavi, 1996). The major ore deposits of the Torud-Chahshirin metallogenic belt (Fig. 6) include many mineral occurrences and abandoned mines, particularly epithermal precious and base metal veins, hosted by volcanic and subvolcanic alkaline rocks, such as Gandy, Abolhassani, Cheshmeh Hafez, Ghole Kaftaran, Pousideh, Darestan and Chahmessi (Shamanian et al, 2004; Fard et al, 2006; Mehrabi and Ghasemi, 2012). In addition, other types of deposit in the district include turquoise and placer gold at Baghu (Au ± Cu), Fe–skarn deposits at Chalu, and Pb–Zn (Ag) carbonate-hosted deposits (MVT) at Reshm, Khanjar and Anarou (Shamanian et al, 2004; Niroomand et al, 2018). The Northern Chah-Farsakh deposit is located 75 km south of Damghan city, and lies within the western part of the Torud-Chahshirin metallogenic belt. This paper describes the local stratigraphic and geological features together with, the relationships between the copper mineralization and the host rocks. Descriptions are supplemented by fluid inclusion studies to constrain the conditions for the genesis of the Northern Chah-Farsakh deposit.

This study focused on the geological and mineralogical of the Northern Chah-Farsakh deposit. Determination of the mineralogy and paragenesis of the deposit is based on logging of drill cores and petrographic studies of over 48 polished thin and thick sections, supplemented by XL30 scanning electron microscopy conducted at Tarbiat Modares University. Doubly polished wafers using standard techniques were prepared from seven samples collected in the presumed feeder zone of the Northern Chah-Farsakh deposit. Micro-thermometric measurements of fluid inclusions were performed on a Linkam THMS 600 combined heating/ freezing stage with a German Zeiss microscope at the Tarbiat Modares University, Iran.

The Northern Chah-Farsakh copper deposit is located in the Torud-Chahshirin metallogenic belt and formed in the Neoproterozoic-early Cambrian volcanic-sedimentary sequence. Mineralization occurred in the form of a sulfide horizon in the meta-volcanic rocks. It formed less frequently in the hanging wall units of meta-volcanic, including the muscovite- quartz schist, the meta-sandstone, the tuffaceous sandstone, and the marble units. The main ore minerals in the deposit include chalcopyrite, pyrite, sphalerite magnetite, pyrrhotite, tetrahedrite, tennantite and bornite, respectively, and the secondary minerals include covellite and chalcocite, and the most abundant gangue minerals are quartz and calcite. Based on the orebody structure, mineralogy, and ore textures, we recognize tree different ore facies types in the Northern Chah-Farsakh deposit: 1) stockwork/feeder zone; 2) massive ore facies; and 3) bedded ore facie.  Siliceous and carbonate alterations are the main alterations associated with mineralization. Banded, disseminated, replacement, massive, veins-veinlets are main ore-bearing textures in this deposit According to fluids inclusion studies on the quartz minerals of the stringer zone, the average homogenization temperature of the fluids inclusions is 355 °C and the salinity is 6 to 16 wt% NaCl eq.

According to geological studies, mineralogy, structure and texture and fluids inclusions the Northern Chah-Farsakh deposit is formed in the submarine volcanic activity environment and this deposit shows most similarities with the Besshi-type VMS mineralization.