Geology, mineralization, and geochemistryof ore and intrusive rocks in the North of Bahariyeh area,East of Kashmar, NE Iran

Bahariyeh deposit is located in the central segment of the Khaf-Kashmar-Bardaskan magmatic belt (KKBMB), NE Iran. This belt is dominated by plutons of Kashmar batholith and associated volcanic rocks along the northern side of the Dorouneh Fault and is one of the most important metallogenic provinces in Iran. Based on geochemical data carried out for the purpose of the present study, the expansion of Cu and other metals mineralization is determined, and on the basis of investigation of trace and rare earth elements behavior, the genetic-lithological relationship of the intrusive rocks is determined in the North of Bahariyeh region.

Method of study:

 About 80 thin sections of intrusive rocks were prepared and 10 least altered 10 samples were selected and analyzed by X-ray fluorescence (XRF; PHILIPS PW 1480) at the Analytical Laboratory of the Kansaran Binaloud Institute of Mashhad, Iran. Also, 10 samples were selected for geochemical analysis by (ICP-OES) at the Zarazma Mineral Studies Co., Mashhad, Iran. Regional Geology Based on field observations a 1:10,000 geological map prepared from the study area, the existing rock outcrops mainly include an alternative of pyroclastic units, Eocene-Oligocene lavas, as well as subvolcanic and intrusive rocks. Field observations show the North of Bahariyeh area is composed of dacite-rhyodacite and andesite volcanic units, and has been intruded by granodiorite, quartz monzonite, monzodiorite-diorite porphyry. These acidic-intermediate intrusive masses have a granular texture and are mainly porphyroid, which have been affected by propylitic, siliceous, argillic, and sericitic alterations. Copper mineralization is observed in the form of veins in different parts of the region, the thickness of these veins varies from about 5 mm to more than 10 cm. Two types of vein-veinlets can be distinguished in the mineralization zone of North of Bahariyeh: 1) vein-veinlets containing quartz + chalcopyrite + specularite + pyrite; 2) specularite-rich veins. Petrography Granodiorite: Granodiorite shows a coarse-grained granular texture with graphic and myrmekitic intergrowths. The main minerals consist of plagioclase, K-feldspar (orthoclase), quartz, hornblende, and opaque minerals. The euhedral-subhedral plagioclase and K-feldspar phenocrysts have been altered to sericite, clay minerals, epidote, and chlorite.Monzodiorite porphyry: This unit has porphyritic and glomeroporphyritic textures with medium-grained groundmass. The monzodiorite porphyry contains up to 45-50 vol.% phenocrysts, consisting of plagioclase (15–20 vol.%), K-feldspar (10–15 vol.%), hornblende (5–7 vol.%), clinopyroxene (5–8 vol.%), and biotite (2–5 vol.%). The same minerals are also present in groundmass. Hornblende and biotite are replaced by chlorite in some places. Also, some plagioclase and feldspar phenocrysts have been altered to sericite, chlorite, and epidote.Quartz monzonite porphyry: The quartz monzonite porphyry has a porphyritic texture (0.1–0.2 mm) with a fine-grained groundmass and normally contains 40–45 vol.% phenocrysts that are 0.1–4 mm in diameter. It is mainly composed of plagioclase (30-35 vol.%), K-feldspar (25-30 vol.%), quartz (15–20 vol.%), and hornblende (5-10 vol.%). The same minerals are also present in groundmass.Diorite porphyry: This unit has porphyritic and glomeroporphyritic textures, with medium-grained groundmass with phenocrysts 0.1–5 mm across, and 40-50 vol.% phenocrysts including 25-30 vol.% plagioclase and 15-20 vol.% clinopyroxene and hornblende with minor biotite and alkali feldspar. The same minerals are also present in groundmass. Its accessory minerals are quartz, zircon, and magnetite (2–3 vol.% and 0.5 mm).

North of Bahariyeh provides important insights for reconstructing the Middle Eocene tectono-magmatic evolution of the NE of Iran. Significant outcomes of this work are:The intrusive sequence in the North of Bahariyeh is inferred as monzodiorite porphyry, diorite porphyry, quartz monzonite, and granodiorite of middle Eocene. and all intrusive rocks belong to I-type metaluminous-peraluminous granites. Major and trace element geochemistry indicate the acidic-intermediate intrusive rocks in the North of Bahariyeh were likely generated by partial melting from the subcontinental lithospheric mantle affected by both slab-derived fluids and lower continental crustal components.The enrichment of LILE (Ba, K, and Cs), depletion of HFSE (Nb, Ti), and the enrichment of LREE relative to HREE indicate crustal contamination and formation of the source magmas in a subduction environment zone by low degrees of partial melting. Trace element geochemistry confirms the evolution of dioritic rocks by a partial melting process (1-5%). Geochemical results, combined with regional geological data, demonstrate a shallow mantle with a clear subduction imprint (metasomatized mantle wedge melts). The post-collisional transtensional tectonic regime favored magma genesis with decompression melting and magma rise through the well-developed fault system and the subvolcanic and intrusive units in the North of Bahariyeh area form the active continental margin-related subduction zone.Overall, the data of the rare earth elements of acidic-intermediate units in the area of study shows that the rocks under investigation were originated by partial melting of enriched mantle under the influence of the fluids released from the subduction blade and then under the contamination of the crust.