Study of geology, alteration and geochemicall of Qesari copper deposit, west Torud, Semnan province

Introduction
The Qeysari copper deposit is located on the 1:100,000 scale of Kalateh-e-Resham, 105 km south of Damghan, with geographical coordinates of 54 ˚18´ 00 ˝to 54 ˚19´ 00 ˝east longitude and 35 ˚19´ 00˝ to 35 ˚ 21´ 00 ˝ north latitude. Along the Troud-Chah-Shirin volcanic belt, copper mineralization has occurred in various forms under the influence of younger semi-deep masses (with Oligo-Miocene age). In some places, such as the Chah-Musa and Koh-Zar deposits, mineralization has taken place adjacent to relatively large intrusive masses. In some parts, major intrusive masses are not present, but traces of younger magmatic activity are exposed in the form of dykes composed of diabase and microdiorite, but they are directly related to mineralization. In the Qeysari region, diabase dykes have played a direct role in mineralization. As it occurs, it is limited only to the edge of the dike and sometimes inside the dike itself.
 
Materials and Methods
In this study, after preparing a 1:2000 geological map of the region and conducting field surveys and sampling of the rocks of the region, 25 microscopic thin sections and 15 polished sections were prepared and examined to identify the mineralogical composition, petrology and textural relationships. For geochemical studies, 8 samples were selected for XRD analysis, 8 samples for XRF analysis and 8 samples for ICP-MS analysis.
 
Results and Discussion
The Qeysari copper deposit is located in the northern part of the Central Iran structural-sedimentary zone. The volcanic and volcanic-sedimentary rocks host the semi-deep intrusive masses of the region, equivalent to the Karaj Formation of the Eocene period. In this area, andesitic, andesite-basalt, basalt and pyroclastic rocks of Middle Eocene to Oligomiocene age are exposed. The uplift of the Troud-Chah-Shirin mountain range has been formed under the influence of the action of the two main Troud faults in the south and Angelo in the north with left-lateral action. The mechanism of these two faults has caused the creation of smaller faults with two trends of northeast-southwest and northwest-southeast within this mountain range. Faults with these trends are also observed in the Qeysari copper area. The controlling factor of mineralization in this area is the diabase dyke with a northeast-southwest trend, which was probably a function of faults with this trend. Mineralization in the study area is seen as veins of different thicknesses along fractures and fault zones, and most mineralization has occurred in basalts and andesites of the area.Amphibole and plagioclase have generally been transformed into chlorite and sericite, which indicates the effect of atmospheric waters on the rocks of the area. Pyroxenes are also seen in the background composition. In order to investigate the petrogenesis, determine the tectonic setting and chemical nomenclature of the rocks containing the deposit, the results of chemical analysis of 8 samples by ICP-MS method were used. Based on the Na2O+K2O vs. SiO2 variation diagram, the volcanic rocks containing the deposit are in the range of andesite, trachyandesite, and basalt. In order to determine the composition and nature of the rocks in question, diagrams related to trace elements, including Zr, Ti, Nb, and Y, which are HSF and immobile elements, were used. In order to determine the tectonic environment, the ratios of trace elements were used. The ratio of trace elements Th/Ta>2 indicates the location of continental arc formation for the constituent rocks. There are various geochemical diagrams to determine the tectonic location of igneous rocks, and in this study, more diagrams based on immobile elements were used.
Conclusion
 Based on geochemical studies, the lavas belong to the high-potassium alkaline and calc-alkaline magmatic series, which formed in a tectonic regime of volcanic arcs associated with active continental margins. This feature is related to the tectonic environment associated with subduction zones and shows the phenomenon of crustal contamination in the rocks. Among the factors controlling magmatism in subducting oceanic crust magmatic arcs are subducting sediments, which represent the effects of crustal contamination and digestion in the magma forming the rocks of the studied area.