Petrogenesis and Economic Potential of the Almogholagh Intrusive Body, Using the Zircon Chemistry; Central Sanandaj-Sirjan Zone

Document Type : Research Article

Authors

• Fatemeh Sarjoughian ¹
• Kosar Allahvaisi ²
• Hossein Azizi ³

¹ Associate Professor, Department of Earth Sciences, Faculty of Sciences, University of Kurdistan, Sanandaj, Iran

² M.Sc., Department of Earth Sciences, Faculty of Sciences, University of Kurdistan, Sanandaj, Iran

³ Professor, Department of Mining, Faculty of Engineering, University of Kurdistan, Sanandaj, Iran

10.22067/econg.2025.1142

Abstract

In this study, the mineralization potential of the Almogholagh intrusive rocks (Northwest Hamedan), Central Sanandaj-Sirjan Zone, was investigated using the chemical composition of zircon grains. The Almogholagh intrusive rocks comprises three main types of rocks: (1) diorite and gabbro, (2) syenite and quartz monzonite, and (3) granite. The primary minerals in these rocks include plagioclase, amphibole, orthoclase, and quartz, with minor occurrences of biotite and pyroxene. Diorite is associated with iron mineralization, forming Fe-rich veins and skarn deposits. Zircon, though a minor mineral, serves as a valuable tool for understanding the petrogenesis and ore-forming potential of the magma. The chemical composition of zircon was analyzed using LA-ICP-MS. The results indicate that the zircons are of magmatic origin and belong to the alkaline to sub-alkaline magmatic series. The geochemical signatures of the zircons suggest that the magma originated from the mantle and underwent contamination with continental crustal rocks during its ascent. This process, accompanied by magmatic fractionation and assimilation (AFC), led to the observed chemical characteristics. Additionally, the magma was formed under relatively low oxidation conditions, as indicated by slightly Eu/Eu*, Ce/Ce*, and Ce⁴⁺/Ce³⁺ ratios. Based on these findings, the formation of Cu skarn and porphyry copper deposits is unlikely. However, the rocks fall within the Fe-skarn field, suggesting potential for iron mineralization. This study highlights the utility of zircon chemistry in evaluating the mineralization potential of intrusive rocks.
 
Introduction
Zircon is a highly durable and chemically resistant mineral that is commonly found in a variety of rock types. Its ability to retain detailed records of geological events makes it an invaluable tool for geologists (e.g., Hoskin and Schaltegger, 2003). In this study, we focus on the petrogenesis of the Almogholagh intrusive rocks and assess their mineralization potential by examining the chemistry of zircon.
The crystallization of zircon is influenced by several factors, including temperature, the chemical composition of the magma, water content, the rate of crystallization, and the degree of zircon saturation within the magma. Due to these dependencies, zircon serves as an excellent mineral for extracting critical information about the origin of rocks, magmatic processes, and the age of crystallization. Additionally, zircon can provide insights into the composition of the initial melt and reflect the oxidation state of the parent magma (Hoskin and Schaltegger, 2003; Trail et al., 2011, Trail et al., 2012; Watson et al., 2006; Hofmann et al., 2014; Geisler et al., 2007; Li et al., 2014). By analyzing zircon chemistry, we aim to unravel the geological history of the Almogholagh intrusive rocks, understand the magmatic processes that led to their formation, and evaluate their potential for mineralization. This approach will help us to better understand the conditions under which these rocks formed and the potential resources they may contain.
 
Materials and methods
After field works and collecting samples from the Almogholagh intrusive rocks, suitable samples were selected for thin section preparation and microscopic studies. The samples were selected from diorite, quartz monzonite granite, and zircon crystals were separated from the host rocks. The LA-ICP-MS method has been used to study the chemical composition of zircon in the diorite, quartz monzonite, and granite of Almogholagh. LA-ICP-MS analysis is one of the most important analytical method for geochemistry studies.
 
Field and petrography studies
Based on field observations, this intrusion is divided into three main groups: (1) diorite-gabbro; (2) syenite-quartz monzonite; and (3) granite.
The first group is mainly located in the northeastern part of the Almogholagh intrusion, which is characterized by a rough morphology. The second and third groups have a mild morphology, cover a wide range, in the southeast, west and center of the area. The results of the U-Pb analysis of zircon grains of the samples show that the studied rocks crystallized in the Late Jurassic-Early Cretaceous (Sarjoughian et al., 2023).
Gabbro-diorite is mostly coarse-grained to medium-grained granular and it is the main host of the Baba Ali iron deposit. These rocks contain the main minerals plagioclase, amphibole, and minor pyroxene. Syenite and quartz-monzonite has a granular and microgranular texture and contain orthoclase, amphibole, plagioclase and minor quartz biotite, and pyroxene. Granite has a microgranular and porphyritic texture. Its mineralogical composition is quartz, orthoclase, plagioclase, biotite, and hornblende in medium to fine grain size.
 
Result and Discussion
In the diagram of the REE variation of in zircon, normalized to chondrite (Sun and McDonough 1989), from diorite, quartz monzonite, and granite show a similar pattern. In this diagram HREE are higher than LREE and Ce has a positive anomaly and Eu has a negative anomaly, and it seems that these rocks are in an oxidation state. Granite have higher REE than diorite and quartz monzonite, which maybe due to magmatic fractionation. Using zircons chemistry we distinguished that most zircons in the studied rocks have high Sm/La and Th/U ratios and are magmatic (Hoskin, 2005) and they are mostly subalkaline and alkaline nature (Mathieu, et al 2022).
Using the element content in zircon chemistry, the petrogenesis of the study area can be identified, using the U/Yb to Hf ratio (Kamaunji et al., 2023). As revealed, magma originating from mantle (NMORB or enriched OIB), which are contaminated by continental crustal component, as indicated by high U/Yb ratio in zircon chemistry (Grimes et al., 2007).  In this samples, Gd/Yb ratio in zircon decreasing but Hf value in zircon increase, indicating magmatic fractionation along with contamination.
Intrusions associated with Fe skarn, in contrast to intrusions associated with Fe-Cu skarn and Cu porphyry deposits, have lower oxidation states, are generally less oxidized. Studies have shown that 
zircon Eu/Eu* is useful in ore exploration for assessing the mineral potential of intrusions (Lu et al., 2016; Ghasemi Siani et al., 2022). Fe skarn-associated intrusions have zircon Eu/Eu* values ​​less than 0.45, while these values ​​are greater than 0.65 for Cu-Mo skarn-associated intrusions. Cu-Au-Fe skarn-associated intrusions have most zircon Eu/Eu* values ​​in the range of 0.45 and 0.65.
Using the Yb/Dy and Eu/Eu* ratios of zircon, the amount of magmatic water can be evaluated. As with increases of Eu/Eu* and Yb/Dy, the water content increases, and mineralization type tends from Fe skarn to Cu-Fe-Au skarn. The studied samples have Eu/Eu* between 0.1 and 0.3 and Yb/Dy less than 5 and fall in Fe skarn field with lower water (Wen et al., 2020).
The studied zircons have intermediate Ce/Ce* and Ce⁴⁺/Ce³⁺ ratios (between 10 and 100) and are in the range of Fe-bearing deposits. Also, the low Hf content at temperature 700 to 800°C in the studied zircons indicates that the magma forming the Almogholagh intrusive rocks may be susceptible to Fe mineralization (Wen et al., 2020). It should be noted that the intermediate Eu/Eu*, Ce/Ce*, Ce⁴⁺/Ce³⁺, and Yb/Dy ratios in the Almogholagh intrusive rocks indicate the Fe mineralization potential.
 
Acknowledgements
The authors acknowledge support of this project by the University of Kurdistan and also Farhangian University.

Keywords

• Zircon chemistry
• mineralization
• Almogholagh
• Sanandaj-Sairjan zone
• Iran

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