Determination of physicochemical indicators of magma, tectonic setting and mineralization potential of the Cheshmeh Ghasaban gabbro massif, Hamedan

Document Type : Research Article

Authors

Adel Saki ¹

Milad Jahani ²

Maryam Dorani ³

¹ Associate Professor, Department of Geology, Faculty of Earth Sciences, Shahid Chamran University of Ahvaz, Ahvaz, Iran

² Ph.D. Student, Department of Geology, Faculty of Basic Sciences, Lorestan University, Khorramabad, Iran

³ Ph.D., Department of Geology, Faculty of Basic Sciences, Shahid Bahonar University of Kerman, Kerman, Iran

10.22067/econg.2025.1152

Abstract

The formation and mineralization conditions of the Cheshmeh Gasaban gabbroic massif in Hamedan have been studied using the chemistry of biotite and clinopyroxene minerals. In terms of petrography, biotite, plagioclase, and clinopyroxene minerals are the most important rock-forming minerals, and amphibole, chlorite, muscovite, zircon, and sericite are visible as minor minerals in microscopic sections. The chemical composition of most of the biotites studied is in the range of coexistence with muscovite in calc-alkaline igneous rocks and is within the range of magnesian and primary biotites. The tectonic origin of the rocks in the studied area is related to the magmatic arc. The clinopyroxenes studied are also of the diopside type and are located in the Quad range. Based on geothermobarometric surveys, it can be said that the gabbro in question was formed at a temperature of over (691°C) and a pressure of about 0.7 MPa. Due to the low SiO₂/Al₂O₃ ratio, these rocks are subalkaline, and due to the low TiO₂ content, the magma forming the rock is in the calc-alkaline range. The mass in question is located in the orogenic zone and the nature of the magma is calc-alkaline. Considering the importance of halogens and their fundamental role in the transport of minerals and metals, the study of their chemistry in biotite shows that mineralization has not occurred in these masses due to the lack of chlorine and fluorine and the high Al^T content. These factors are among the most important reasons for the lack of fertility in the gabbros of Cheshmeh Gasaban in Hamedan.
 
Introduction
Iran is a paradise for geology, with numerous metallic and non-metallic mineral resources. The country has multiple structural-sedimentary zones, one of which is the Sanandaj-Sirjan zone. In terms of dimensions, this zone has a length of approximately 1,500 kilometers and a width ranging from 150 to 200 kilometers. The orientation of this zone follows a northwest-southeast trend. In the Sanandaj-Sirjan zone, metamorphic phenomena, magmatism, and tectonic activities occur continuously and in harmony with globally recognized tectonic phases at their highest intensity. For this reason, this zone is considered the most unstable a the petrology of gabbroic rocks in Cheshmeh Qasaban, Hamadan, has been studied, but the ore mineralization of zinc has not been investigated.nd, in other words, the most dynamic tectonic region in Iran. The Sanandaj-Sirjan zone can generally be divided into three sections: northern, central, and southern. The study area is located in the central part of this zone. In an earlier study gabboeic rocks of the Cheshmeh Ghasaban in north SSZ yield late-Jurassic U -Pb zircon SHRIMP ages of 166.5 ± 1.8 Ma. The aim of this paper is determinated of mineralization using the minerals chemistry for the cheshmeh ghasaban rocks from hamedan, Iran. By analyzing the chemistry of these rocks, the physicochemical properties of the magma and its ore-forming potential have been examined.
 
Materials and Method
Major Elament composions of biotite, clinopyroxen and plagioclase in selected gabbroeic were determined by EMPA (Jeol – JXA 8200) at potsdom university, Germany, the operational conditions 20 Kv, accelerating voltage and 20 nA specimen current. The analytical spot diameter was set 1 mm. keeping the same current conditions. Natural and synthetic standard were used for calibration. Ferric iron contents in ferromagnesian minerals are calculated using stoihciometeric criteria.
 
Results
The mineral chemistry of biotite and clinopyroxene from the Cheshmeh Ghasaban gabbro (Hamadan) was investigated to constrain geochemical evolution, tectonomagmatic setting, geothermobarometry, and ore-forming potential. Biotites are predominantly magnesium-rich, low in Ti, and commonly coexist with muscovite within calc-alkaline igneous assemblages, consistent with a primary magmatic origin. Clinopyroxene compositions support an arc-related, calc-alkaline magmatic affinity. Halogen chemistry shows a clear deficiency of Cl; combined with high tetrahedral Al (Al^T) in biotite and low inferred fluid activity from biotite–hornblende chemistry, this precluded effective metal transport and hydrothermal mineralization. Overall, despite a tectonic setting favorable for arc magmatism, the Cheshmeh Ghasaban gabbro is geochemically infertile due to low halogen contents and limited fluid flux.
 
Discussion
The mafic rocks of Cheshmeh Ghasaban, Hamadan, are classified into two groups: olivine and gabbro. The absence of olivine crystals in the gabbros and the ratio of clinopyroxene and plagioclase minerals, from the perspective of their modal composition, represent the major differences between these two groups. The crystallization sequence of minerals in the gabbros of this region follows this order: olivine, clinopyroxene, plagioclase, phlogopite, brown amphibole, and biotite, which reflects their textural characteristics. Various methods have been proposed for examining the geomorphology of an intrusive body. One approach for assessing pressure-temperature (P-T) conditions in biotites is the method introduced by Henry et al. (2005), which has been employed to study the formation and crystallization conditions of the gabbroic intrusion.Factors such as the composition of the parent magma, the available foci, and the total amount of biotite present affect mineralization. To determine the type of mineralization, the relationships between Al^T and the molar ratio of Mg/(Mg+Fe) in biotite of various granitoids in Japan have been used, along with determining the phase type and comparing it with gabbroic rocks from Cheshmeh Ghasaban, Hamedan. Since the total aluminum content in biotite is more than 2.3, it is in the sterile range. Magmatic mixing and the amount of water in magma are also factors affecting mineralization. In general, the halogen content (F,Cl) of biotite can be used to investigate magmatic indicators and associated hydrothermal fluids. Halogens, especially volatile elements F and Cl, play an important role in magmatic and hydrothermal mineralization systems. Therefore, it is of great importance to study and evaluate the fugacity of halogens in igneous and hydrothermal mineralization systems. In general, the halogen content (F,Cl) of biotite can be used to investigate magmatic indicators and associated hydrothermal fluids. Halogens, especially volatile elements F and Cl, play an important role in magmatic and hydrothermal mineralization systems. Therefore, it is of great importance to study and evaluate the fugacity of halogens in igneous and hydrothermal mineralization systems.

Keywords

Mineral Chemistry

Geothermobarometery

Tectonic settings

Mineralization

Cheshmeh Ghasaban

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