پترولوژي سنگ‌هاي دگرگوني مجاورتي و هيدروترمال با نگرشي ويژه بر كانسارسازي در گستره كانسار مس مهرآباد(جنوب شرق اردستان)

Petrology of contact an‎d hydrothermal metamorphic rocks with special focus on copper deposit formation in Mehrabad area (SE of Ardestan)

زمين شناسي

Abstract: The copper deposit is located in the Mehrabad intrusive massif, northwest of the Nain ophiolite zone an‎d approximately 68 km southeast of Shahrab, in the east of Ardestan County. Structurally, this area is located in the central part of the Urumieh-Dokhtar magmatic arc an‎d on the Iran copper belt. According to geochemical studies, the rock units of this area are type I granitoid an‎d are probably Oligocene-Miocene in age, are calc-alkaline to shoshonitic an‎d meta luminous to slightly peraluminous, an‎d were formed in a volcanic arc located on an active continental margin. According to field observations an‎d petrographic studies conducted in this zone, the most important petrological composition includes a set of acidic an‎d basic rocks, including granodiorite, an‎desite, basaltic an‎desite, rhyolite, carbonate diorite, gabbro, an‎d tonalite, which have been altered under the influence of hydrothermal processes an‎d have undergone changes in both their physical nature an‎d chemical composition. The main an‎d important mineral phases of these rocks are plagioclase, quartz, alkaline feldspar, amphibole, an‎d clinopyroxene, an‎d the minor an‎d secondary minerals include: sphene (titanite), zircon, apatite, opaque, epidote, chlorite, sericite, kaolinite, limonite, muscovite, tremolite-actinolite, an‎d calcite. The most important alteration zones of the region include: alunite, clay (argillic), carbonate, quartz-sericite (phylic), an‎d propylitic, an‎d the propylitic zones include: iron oxide, chlorite, epidote, an‎d silici. In the field study, copper mineralization is observed in the form of oxides including malachite in the copper-bearing silica-iron oxide zone in the vicinity of basic dykes an‎d also in the form of veins-veinlets in an‎desite an‎d basaltic an‎desite rocks. In the vicinity of the above mineral complex, a skarn mass with characteristic mineralogical phases of this mass including vesuvianite (idocrase), wollastonite, garnet, clinopyroxene, an‎d calcite (in petrographic study) was observed, which are located next to subsidiary minerals such as plagioclase, amphibole, an‎d quartz. The rocks of this area exhibit dominant granular, poikiloblastic, poikilitic, perthite, antiparasite, sieve, comb, cover, porphyry, flow, an‎d poreures. Possible metallic minerals in the microscopic study of polished thin sections include pyrite, chalcopyrite, malachite, hematite (spicularite), goethite an‎d covellite along with other minerals such as quartz, calcite an‎d alkali feldspar, which are characterized by characteristic blade, cluster, cauliflower, chlorophyll, replacement, fissure-filling, vein-vein an‎d residual textures. In the study of samples taken from this area, according to XRD analysis based on the abundance, the mineral complex of pectolite, perhenite, sodalite, clinochlore an‎d xenolith has been detected. Considering the conditions of formation of pectolite mineral due to the rodengitization process in ultramafic rocks an‎d its presence in the samples of this region, it is likely that a kind of rodengitization process has occurred in these rocks, which has formed pectolite mineral at the expense of plagioclases due to the abundance of feldspars. Also, evidence obtained from semi-quantitative SEM analysis indicates a kind of enrichment in the altered rocks of this region with respect to elements such as: Al, Si, Fe, Mg, S, Na, Ca, K. According to the peak of elements an‎d their abundance in weight percent, according to EDS tables, alunite mineral with high weight percent of elements such as Al, K, S an‎d vesovianite-chlorite minerals with high weight percent of elements such as Al, Mg, Fe, Ca an‎d pectolite mineral with high weight percent of elements such as Na, Ca, Si have formed in the altered samples of the region. Keywords: Copper deposit, hydrothermal alteration, contact metamorphism, Urumieh-Dokhtar magmatic belt, Mehrabad, Ardestan.

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