نوع مقاله : علمی -پژوهشی
گروه زمینشناسی، دانشکده علوم، دانشگاه اصفهان، اصفهان، ایران
عنوان مقاله [English]
IntroductionEpithermal deposits have been studied by several researchers and their properties have been considered in various respects (Silito & Hednoquist, 2003; Hednoquist et al., 2004).One of the metamorphic magmatic zones in Iran that has always been considered by researchers, is the Urumih-Dokhtar magmatic belt (Bazin & Hubner, 1969; Amin al-Raiei et al., 2017). This belt, as part of the Tethys belt, is one of the most important metallogenic belts in Iran.Recent studies in the Shojaabad region, include Zamani studies (2013). In this research, the geochemistry and genesis of Cu-Au Index of western Shojaabad has been studied and classified as one of the porphyry deposits in relation to one of the Oligomiocene-Miocene intermediate-acidic intrusive rocks.Based on the location of the Cu-Au Index located in the middle part of the Urumieh-Dokhtar belt near to the Natanz Fault, alteration studies, geochemistry, mineralization and fluid inclusions were carried out in the area and finally genesis of the Cu-Au Shojaabad index was determined.Material and methodsDuring field investigations, 20 sample of rocks were randomly sampled from mineralization outcrops and hydrothermal alteration zones. Then, thin and polished thin sections were prepared. In order to highlight hydrothermal alteration, Aster data of study area was prepared and final map of alteration zones was drawn in ArcGIS environment.In the next step, more than 10 samples were selected for geochemical studies. The samples were analyzed by X-ray fluorescence (XRF) method at the University of Isfahan to determine the amount of major elements. Also, to obtain trace and rare earth elements, samples were examined by ICP-MS method at ACME Laboratory of Canada. Moreover, in order to evaluate the formation temperature and the nature of mineralization fluids in the region, 6 samples were selected to study the fluid inclusions. Thermometric measurements of fluid inclusions were carried out in the Department of Geology of Isfahan University.Results and discussionAccording to field surveys and microscopic studies, dominant rocks of the area include volcanic and pyroclastic rocks. The volcanic rocks are often porphyritic and exhibit a more rhyodacitic composition based on microscopic studies.According to the field surveys, processing of ASTER images, and microscopic studies, the presence of argillic alteration in the center of the region and the extension of propylitic alteration around the area is evident.The main texture observed in the ore of the area is disseminate texture. Other textures include replacement, zonal and veinlet textures.Thus, mineralization in the Shojaabad area is disseminated and often associated with quartz veins.Based on the petrographic studies of fluid inclusions, they are predominantly primary fluids and low secondary fluids.The studied fluids’ inclusions are mainly from liquid-rich type, indicating that the mineralization in this region was by hydrothermal solutions and that the mineralization temperature was not high (up to 268 ° C).The homogenization temperature for the two-phase fluid inclusions was 187 to 268 ° C and the salinity was 1.6 to 10.5 wt% NaCl. For the determination of genesis of Shojaabad index, Kesler diagram was used (2005). It is clear that the most concentrated fluid inclusions are in the seawater domain. The magmatic fluid is probably in this range due to cooling and dilution by fluids with less salinity (atmospheric waters). The most important application of fluid inclusions is to determine the characteristics, and evolution of hydrothermal fluids and ultimately the origin or genesis of the deposit. Based on the temperature results obtained from the fluids’ inclusions (homogenization temperature below 300 ° C) as well as low salinity in the region, the study area appears to be part of the epithermal reservoirs.ConclusionMineralogical studies indicate hypogene mineralization with pyrite, chalcopyrite and magnetite minerals and supergene stage with presence of chalcocite, covellite, malachite, hematite and goethite minerals.Based on the fluid inclusion studies, important factors such as the low existence of sulfide minerals in the form of fine and scattered crystals and large amounts of carbonate minerals around the ore mineralization, the Shojaabad index can be considered as low sulfidation epithermal deposits.