PETROLOGY
Year:2019 | Volume:10 | Issue:39|Papers Count:6

In this research, the altered and non-altered zones in Marbin exploration area has been determined by VNIR and SWIR wavelengths processing of ASTER satellite images and by False Color composite and band ratio methods. The Marbin exploration area lies in the Urumieh-Dokhtar magmatic belt. The Marbin index is located in the east of the Zefreh fault within the central part of the Zefreh pull apart basin. Rhyolite to dacite are the predominant rock types of the Eocene subvolcanic and volcanic units of the area under study. The spectral of sericite, epidote, calcite and chlorite minerals in this area have been recognized using the Spectral angle mapper (SAM). Finally, with combination of spectral of index minerals in phyllic and propyllitic alteration zones with field observations, petrograghy and geochemical analysis, the alteration zones map in Marbin area have been prepared. As a result, the phyllic and the propyllitic alterations as well as the silicification are index alterations in this area. Based on litho-geochemical analyses, the high Mo/Cu contents, the occurrence of hydrothermal alterations in combination with several other evidences, we concluded that the Marbin index can be introduced as a porphyry deposit with Mo anomaly. This could be indicative of the potential of this area for the molybdenum mineralization in detailed exploration phase.

In the northeast of Iran, there are some outcrops of high-Mg ultramafic volcanic rocks. These rocks have been interpreted as an ideal ophiolite sequence related to the closure of Paleo-Tethys. According to detailed field observations, the komatiitic lava flows in Shandiz-Virani-Mashhad Complex (SVMC) and Fariman Complex (FC) are interlayered with the Upper Paleozoic submarine turbiditic sediments (Carboniferous-Permian). These rocks have a wide range of volcanic facies and according to the lithofacies characteristics, are divided into three groups of differentiated, undifferentiated lava flows and pillow lavas with a variety of volcanic textures and glass groundmass and with the main minerals of olivine, chromian spinel, clinopyroxene and amphibole. In this paper, the komatiitic nature of these rocks has been proven by explicit evidence from the field features petrography, internal stratigraphy and mineral chemistry. Also, the interaction of a mantle plume with the late Paleozoic (Permian) northeast subduction zone of Paleo-Tethys in NE Iran is considered as the suitable petrogenetic model involved in the genesis of the Komatiitic magma. This model can well justify and interpret the various geochemical characteristics of the studied rocks.

The Baharieh copper deposit with an approximately of 1 million tons of copper ore, located in Khorasan Razavi Province, 30 km northeast of Kashmar. On the base of structural view point of Iran, the deposit is situated in Sabzevar zone and Taknar metallogenic area. The mineralization as stratabound nature in an ore-horizon with a length of approximately 200 m and 5 to 10 meters thickness, trending E-W occurs in the middle Eocene andesitic to rhyolitic-tuff. Chalcopyrite and pyrite are the main sulfide minerals, which are accompanied by accessory minerals including bornite, galena, sphalerite, covelline, chalcocite, malachite and hematite. According to the data obtained by electron probe micro analysis (EPMA) the maximum gold amount (0. 21 wt%) and the silver content (0. 1 wt%) are in the chalcopyrite and the highest silver concentration (0. 14 wt%) is in the galena. The average ratio of Co/Ni (2. 71) in the pyrite study can be indication of its hydrothermal source. On the base of geo-thermometry data as well as Sb/Bi ratio in the galena and the geochemistry of the sphalerite (high content of Cd with an average value of 0. 92 wt% and low Zn/Cd=67. 54) the physico-chemical and the thermodynamic conditions of ore-bearing fluid in the Baharieh deposit consistent with an average-temperature hydrothermal-magmatic deposits. The variation ranges of δ 34S isotopic in the chalcopyrite and the pyrite samples vary from-7. 3 to 0. 5 ‰ . According to the results obtained from sulfur isotopic data, the origin of primary magma for δ 34S values close to zero and its relative depletion was confirmed as a result of performance of reduce processes for negative δ 34S values. The overall, the primary fine-grained pyrites in the mineralized host rock are most likely the source of sulfur in the sulfide mineralization of the area under study, which caused the negative δ 34S values.

Zajkan area as a part of Tarom-Hashtjin magmatic belt is dominated by some granitic intrusions intruding the Eocene volcano-sedimentary rocks. The Eocene volcano-sedimentary rocks are as alternation of acidic to intermediate tuffs and lavas. These intrusions composed of gabbro, pyroxene quartz monzodiorite, pyroxene quartz monzonite and granodiorite with high-K calc-alkaline composition and I-type metaluminous nature. On the spider diagrams, the studied rocks have similar trace elements patterns indication of their genetic relation. The rocks also display LILEs enriched along with negative HFSEs anomalies. Based on chondrite-normalized REE patterns, these intrusions are characterized by LREE enrichment, high LREE/HREE and LaN/YbN (6. 1-9. 1). The overall field investigation, petrological and geochemical studies, as well as tectonic setting discrimination diagrams show that the Zajkan intrusions were possibly formed from a subduction related metasomatized lithospheric mantle in a post-collisional setting.

The Shahini ophiolitic complex in the west of Iran and northwest of Kamyaran, as a ring connection between the Kermanshah and the Kurdistan ophiolites exposed along the Zagros and the Neotethys suture zone. The complex contains the mantle peridotites and the crustal sequence. The peridotites with cpx-bearing harzburgite and lherzolite are serpentinized and cross cut by isolated diabasic dikes. The crustal sequence consists of pegmatitic and isotropic gabbros, microgabbroic dykes, basalt and pyroclastic andesite. The sedimentary-volcanic sequence is dominated by radiolarite, shale, pelagic limestones, sandstone and tuff horizons covering the extrusive sequence. Based on chemical analyses, the crustal sequence ranges in composition, from tholeiitic to calcalkaline. On the tectonomagmatic diagrams these rocks are mainly plotted on the MORB field and occasionlly, are clustered in the volcanic arc region. The LILE enrichment, slight depletion in HFSE as well as the enrichment of some LREEs along with linear trends of HREE suggest that the parent magma originated in the arc environment from the heterogeneous mantle with varying degrees of partial melting. However, the low ratios of Th/Yb, La/Nb, Ce/Nb and Ce/Th indicate the tendency between the IAB and MORB environments. The depth of partial melting estimated at the depth of 50 to 60 km representing the partial melting of spinel lherzolite mantle. Field relationships and geochemical evidences indicate that the Kamyaran ophiolites formed in oceanic basin in the ocean-continent borders zone in the north portion of the Neotethys Ocean.

The Alborz Range, as a part of the Alpine-Himalayan orogeny, formed during the Cimmerian orogeny due to northward movements of the Central Iran micro-plate towards Eurasia. Subsequently, it underwent different compressional and extensional geological events from the Late Triassic collision to the recent ongoing contraction and volcanism. The gabbros in the Gasht-Masuleh area are small kilometer-sized cumulate and isotropic gabbro bodies that intruded the Paleozoic metasediments and Mesozoic sediments in the three localities including Chapul, Gilvandehrud, and Zudel. Clinopyroxene chemistry suggests that the calc-alkaline parent magma formed in a transitional environment between arc and extension related tectonic settings. Diopside clinopyroxene composition is Wo47-51 En43-49 Fs4-9 and enstatite orthopyroxene has Wo0-3 En71-79 Fs20-28 composition. The low TiO2 content of clinopyroxene indicates a depletion of parental magma source during old subduction in the north of Iran. Using different thermometers, based on clinopyroxene and orthopyroxene composition suggest that the crystallization temperature of pyroxene was low (~800 ℃ ). Al2O3, Na2O and Cr2O3 contents of orthopyroxene and clinopyroxene are low indicating the crystallization of the parent magma at low pressure at upper crustal levels.