Geology, alteration, mineralization and geochemical study in copper mine, Golcheshmeh Area, South of Neyshbour
Subject Areas :فاطمه نجمی 1 , سید احمد مظاهری 2 , سعید سعادت 3 , اعظم انتظاری هرسینی 4
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Abstract :
The Golcheshmeh copper deposit is located in the NE of Iran (south of Neyshabour) at the margin of Sabzevar Structural Zone. Based on geological and labratory studies, the outcroped rocks consist of Eocene volcanic rocks such as andesite, basaltic- andesite and basalt that associated with the sedimentary and volcanosedimentry rocks including limestone, tuff and breccia. The alteration hosted andesitic layers include carbonatization, propylitization and less argilic and sericitic alterations. The carbonatization zone is the most important alteration in this area. Mineralization mainly occurs in Eocene or younger volcanic rocks as vein- veinlets, amygdaloidal fillings and some replacement and disseminated styles. According to the minerallographical studies, the main ores which contain copper are divided into oxide and sulfide types. Mineralization mainly consists of oxide phases and can be seen as contamination of fracture surfaces and filling pores or voids in the host rocks. The main oxide minerals are malachite, azurite and chrysocolla, and sulfide minerals are chalcocite, covellite, with some minor pyrite, chalcopyrite, bornite, digenit and also native copper. Chalcocite is the most abundant ore sulfide in this area. There are probably two generations of sulfides, the first generation is a primary ore that was formed directly in joints, cracks, and fractures from the ore-containing solution and currently is replaced by covellites; and, the second generation is chalcocite that was probably formed from the conversion of bornite and chalcopyrite through substitution under supergene conditions. In most cases, the observed intergrowth between copper ores suggests the multi-stage mineralization in this region. Geochemical studies of minor and trace elements indicate that the igneous rocks in this region are characterized by the calc-alkaline basalt characteristics and, in terms of tectonic setting, could be attributed to subduction zone-related continental arc magmatism. Moreover, based on the performed geochemical analyses, the copper grade in the region varies from 13668 to 164000 g/ton. On the basis of the results of this study and with respect to some evidences such as tectonic setting, host rock type, structure and texture of ore body, mineral paragenesis, shape of the ore body and associated elements, this area is compared to Manto type deposit located in Chile. Though there are some differences, it is suggested that golcheshmeh copper mine is classified in Cu- Manto type deposit.
