چكيده لاتين
The volcanic rocks studied are constitute a segment of the Cenozoic volcanic belt within the central Urumieh-Dokhtar Magmatic Arc. In the exploratory Chakad regions, Safafoulad, and Mehrando, volcanic lavas include basalt, basaltic andesite, andesite, rhyolite, and mafic dikes with a combination of diabase and dolerite. Geologically, basic-intermediate volcanic rocks of the Eocene are found in large quantities in these areas and play an essential role in the host rock of copper mineralization.
The interpretation and processing of remote sensing data revealed argillic, phyllic, and propylitic alteration, fragile structures, and identified faults. Petrographic studies indicate that volcanic rocks and mafic dikes in the Northwest of Nain exhibit a porphyritic texture with a fine-grained microlithic groundmass contan and intergranular. They primarily comprise phenocrysts of plagioclase, clinopyroxene, quartz, K-feldspar, biotite, and minerals resulting from calcite, chlorite, and epidote alteration. Based on mineral chemistry investigations, the plagioclase mineral ranges from andesine to labradorite, and the pyroxene mineral belongs to the Fe-Mg-Ca pyroxene group, precisely the augite type. The clinopyroxenes in the volcanic rocks of Northwest Nain and its host rock are in equilibrium, and all the samples are formed from the same parental magma with different degrees of fractional crystallinity.
Based on geochemical investigations, the volcanic rocks display enrichment in light rare earth elements (LREE) and large ion lithophile elements (LILE) and depletion in high stability field elements (HFSE). These findings indicate volcanic arc magmatism related to the subduction zone. The results of the geochemical surveys suggest that the melted material originated from the subcontinental lithospheric mantle. This mantle experienced partial melting in the lherzolitic spinel-garnet facies. The rhyolitic rocksʹ pattern differs from the regionʹs basic-intermediate lavas and is more consistent with the upper crust. The basic parental magma resulted from the partial melting of the asthenosphere, leading to the delamination of the sub-continental lithospheric mantle. The parental magma accumulated in the upper crust and caused partial melting of the crust, resulting in acidic magma. The contamination of parental magma with crustal components and the mixing with acidic magma play critical roles in the diversity of compositions found in the studied volcanic rocks.
The mafic dikes in the northwest of Nain have cut the volcano-sedimentary units of the area with the NE-SW trend. Regarding geochemical features, mafic dikes are subalkaline basalt with a calc-alkaline nature. The distribution of minor elements in terms of enrichment of LILEs compared to HFSEs, as well as the positive anomaly of Cs and Ba and the negative anomaly of Nb, Zr, Ta, and Ti, indicate that they are related to subduction magmatism and metasomatization by subduction fluids in their origin. The dikes were formed in an intra-arc extension setting associated with the subduction of the continental margin. This transition occurred from a continental arc to a back-arc basin during the Paleocene to Miocene.
Mineralization in Chekad, Safafolad, and Mehrando exploratory areas is the result of hydrothermal activity and the movement of associated fluids through fractures in Eocene-hosted rocks such as basaltic-andesite, basalt, and volcanic breccia. The pyroclastic host units are particularly favorable for mineralization due to their high porosity and permeability along fractures. Investigation of the faulting patterns about the alteration zones and mineralization areas showed that the copper mineralization events are directly associated with the areaʹs main faults and fractures (Kacho Mesqal and Zafarghand faults) and related secondary faults with mineralization events.
