Evolution and genesis of the Bardeh-Rash iron deposit in northwest Baneh (Northwestern Sanandaj–Sirjan Zone): Based on geological, mineralogical, and geochemical studies

Introduction
The Bardeh-Rash iron mineralisation is located approximately 30 km northwest of Baneh and 7 km north of Bardeh Rash village, within the Sanandaj–Sirjan tectonic zone. This NW–SE trending belt is one of the most significant metallogenic provinces in Iran, hosting a wide spectrum of iron deposits, including volcanic-sedimentary, skarn-type, and IOCG (iron oxide–copper–gold) deposits (Nabatian et al, 2015). Tectonic evolution associated with the opening and closure of the Neotethys Ocean and the interplay of extensional and compressional regimes during the Triassic to Jurassic led to intense regional metamorphism and deformation (Saki, 2010). Recent investigations in the northwestern segment of the Sanandaj–Sirjan zone have led to the identification of several iron occurrences and deposits. Notable examples include the Gurgur, Halab, Kosaj and Mianaj iron deposits (Pourmohammadi et al, 2019), as well as the Ghaluzendan and Qaderabad iron deposits (Karimi et al, 2021), all hosted within metamorphosed equivalents of the Kahar Formation. The Bardeh-Rash deposit, discovered by locals in 2016, represents one of the previously unstudied iron occurrences in this region. The mineralisation is stratiform in nature, hosted within upper Precambrian metarhyolitic tuff units and exhibits concordant layering and foliation with its metamorphosed volcanic host rocks. The primary objective of this study is to provide a comprehensive geological, mineralogical, geochemical, and genetic framework for the Bardeh Rash iron deposit, aiming to propose a viable exploration model for similar geological settings.
 
Materials and Methods
This research comprises both field-based and laboratory investigations. During fieldwork, a 5 km² area was systematically mapped at a scale of 1:5000, wherein lithological units, structural features, and mineralised horizons were carefully delineated. Over 100 rock samples, including both barren and ore-bearing lithologies, were collected. Structural measurements of bedding, foliation, and geometry of ore horizons were recorded to reconstruct the geometry of the mineralised system. In the laboratory, 12 thin sections were prepared for petrographic analysis and 33 polished thin sections for ore microscopy. For geochemical analysis, 31 representative samples were selected; 21 were analysed via XRF at Tarbiat Modares University and 10 by ICP-MS at ZarAzma Analytical Laboratories.
 
Results and Discussion
Field and laboratory investigations reveal that iron mineralisation occurs in three distinct stratiform horizons within metarhyolitic tuff units.
Horizon I is hosted in dark grey metarhyolite and comprises banded hematite with an outcrop length of \~20 m and thickness ranging from 10 to 40 cm. Horizon II, the main ore body, occurs in light grey metarhyolite, is \~200 m long and 0.5 to 2.5 m thick, and hosts massive, banded, and disseminated hematite textures. Horizon III is composed of magnetite and hematite lenses hosted in dark green metarhyolite, with dimensions of \~30 m in length and 0.2 to 1.5 m in thickness. The metallic assemblage, primarily hematite and magnetite with minor pyrite, occurs in banded, massive, and disseminated textures, accompanied by gangue minerals such as quartz and barite within the altered metavolcanic host rocks. Evidence of metamorphism and deformation—including foliation, folding, boudinage, and S–C fabrics—is well developed in both ore bodies and host rocks. Geochemical analyses indicate that the host rocks are metarhyolitic tuffs of calc-alkaline affinity, formed in a volcanic arc setting on an active continental margin. Tectonomagmatic discrimination diagrams (e.g., Nb/Yb vs. Th/Yb) confirm a subduction-related magmatic source. Enrichment in large ion lithophile elements (LILEs) such as K, Rb, and Ba, together with positive Ba anomalie, implies a significant role for crustal contamination. REE patterns show light REE enrichment and positive Eu anomalies, indicative of oxidising conditions during ore formation. Mineralogical and paragenetic data suggest four main stages of deposit evolution: Syn-volcanic mineralisation with deposition of banded and disseminated hematite and magnetite during tuff emplacement. Regional metamorphism under greenschist facies, resulting in the formation of sericite, chlorite, and recrystallisation of pre-existing phases. Tectonic deformation, leading to the development of boudinage structures, folding, faulting, and pressure shadow features. Supergene alteration, during which surface weathering led to oxidation of primary sulfide and oxide phases and the formation of iron hydroxides. These features are consistent with other volcanogenic–sedimentary iron deposits in Iran, such as those in the Bukan and Takab districts, supporting a sedimentary–hydrothermal origin.
Conclusion
The Bardeh-Rash iron deposit is interpreted as a deformed and metamorphosed volcanic-sedimentary system that formed contemporaneously with late Precambrian rhyolitic volcanic activity. Subsequent metamorphic overprint and deformation significantly modified the primary textures and structures. Stratiform and lensoidal geometry of the ore horizons, coupled with enrichment in LILEs and anomalies in Ta and Ba, support a sedimentary–hydrothermal genesis within a subduction-related volcanic arc setting. REE patterns further confirm oxidising conditions and a genetic link between the host rocks and mineralisation. The recognition of four distinct mineralisation stages provides a robust framework for understanding the ore-forming processes. The results of this study contribute to the metallogenic models of iron in the Sanandaj–Sirjan zone and offer valuable insights for exploration strategies in analogous tectonic and geological settings.