Pb-Zn Deposits in Ruchun-Mazar Region, Kerman Province: Geology, Alteration and Mineralization

زمین شناسی اقتصادی

Volume 15, Issue 2 - Serial Number 37, September 2023, Pages 109-134   

Document Type: Research Article

DOI: 10.22067/econg.2023.81763.1072

Authors

Mahdi Ghorbani Dehnavi¹; Azadeh Malekzadeh Shafaroudi^{* 2}; Mohammad Hassan Karimpour²

¹Ph.D. student, Department of Geology, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran

²Professor, Department of Geology and Research Center for Ore Deposits of Eastern Iran, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran

Abstract

Ruchun-Mazar region is located in southern Sanandaj-Sirjan Zone, southwest of Baft city in Kerman province, Iran. Seh Chah, Chah Sorbi, Chah Nar, Zardbazi Dar, and Chah Sorbi Arjmand Pb-Zn deposits located in this region were investigated. The most outcrops of the geological units in the area include the Paleozoic metamorphic complexes of Gol Ghohar (amphibolite, gneiss and micaschist), Ruchun (schist, marble, calcschist, black chert, slate and phyllite), and Khabar (marble, calcschist). Microdioritic, monzodioritic and diabasic dykes have intruded into the metamorphic units. Dolomitic and calcitic marble of Ruchun complex is the host rock for Pb-Zn mineralization. Primary mineralization in Seh Chah, Chah Sorbi, and Chah Nar deposits includes galena, sphalerite, and pyrite ± chalcopyrite along with quartz, calcite, and dolomite ± barite. Vein-veinlet, open space filling, brecciated ± disseminated ± laminate structures and textures can be seen in these deposits. The most important alterations in these deposits are silicification and carbonitization (calcitic and dolomitic alterations). Primary sulfide ore in Zardbazi Dar and Chah Sorbi Arjmand deposits has been weathered and mining has been carried out on nonsulfide ore (supergene ore). The nonsulfide ore formed at the expense of sulfides, and mainly consists of smithsonite, hydrozincite, hemimorphite, and cerussite. It seems that these deposits belong to the direct replacement and, to a lesser extent, wall rock replacement nonsulfide zinc deposits. Based on the geological, mineralogical and alteration evidence, the primary mineralization in the region can be divided into two groups of SEDEX type (Chah Sorbi deposit) and vein type (Chah Nar and Seh Chah deposits). It was concluded that under supergene conditions in some deposits, nonsulfide ore was also formed. Moreover, the deposits of this region can be categorized into primary sulfide (hydrothermal) and nonsulfide (supergene).
 
Introduction
Iran embraces extensive areas having high potential for carbonate-hosted (CH) Zn-Pb deposits due to the suitable geodynamic conditions and the occurrence of large carbonate platforms (Rajabi et al., 2012). A wide variety of Zn-Pb deposits have been reported along Sanandaj-Sirjan Zone (SSZ) in Iran. The development of SSZ is related to the generation of the Neo-Tethys Ocean during the Permian and its subsequent destruction due to the convergent and continental collision between the Arabian and Iran plates during Cretaceous to Tertiary periods (Mohajjel et al., 2003; Ghasemi and Talbot, 2006). Ruchun-Mazar (Rechan) region is located in the southern Sanandaj-Sirjan zone (Fig. 1). This area is located at 75 km southwest of Baft city in Kerman province, Iran. In this region, the lower paleozoic marble rocks of Ruchun complex host numerous Zn-Pb deposits (Fig. 2). Although sulfide mineralization is dominant in this region (e.g., Seh Chah, Chah Sorbi, and Chah Nar deposits), secondary non-sulfide ores are common (e.g., Zardbazi Dar and Chah Sorbi Arjmand deposits). Based on geology, mineralogy, mineralization and alteration, the similarities and differences among the Pb-Zn deposits of this region were investigated.
 
Material and methods
At the first step, a 1:50,000 integrated geological map of Ruchun-Mazar region was prepared. Then, a more detailed investigation of the deposits, including field sampling of rock units, ore veins, tunnels and other mining works was done. Field observations were supplemented by petrographic studies and X-ray powder diffraction (XRD) analysis. From the collected samples (224 samples), 95 thin sections, 48 polished thin sections, and 41 polished sections were prepared for petrographic and mineralogical studies. Twenty-eight samples (sulfide and nonsulfide ores and gossan) were analyzed by XRD at the GSI. Nonsulfide ores, which contain Zn, were identified (stained bright red) by Zinc Zap, a solution of 3% potassium ferricyanide K₃Fe(CN)₆ and 0.5% diethylaniline dissolved in 3% oxalic acid.
 
Results
Ruchun-Mazar mining area is located in the southern part of Sanandaj-Sirjan zone (Fig. 1). Based on stratigraphy of the region, chronological sequences from the oldest to youngest include Paleozoic Gol Gohar, Ruchun and Khabar metamorphic complexes, Permian-Triassic metamorphosed carbonates, Jurassic-Cretaceous meta flysch, Cretaceous marbles (Koh-e-Khabar), Eocene-Oligocene flysch, and Quaternary sediments (Fig. 2). Gol Gohar complex (unit Pz₂) contains gneiss, micaschist and amphibolite with a probable Cambrian age which has been intruded by mafic intrusive bodies. The Ruchun complex (unit Pz₃) is the host complex for lead, zinc and iron mineralizations in the region. Sequence of stratigraphic layers from bottom to the top contains Gol Gohar complex (Camberian), Ruchun complex (Camberian-Ordovician), and Khabar complex (Middle-Upper Devonian), respectively. Metamorphosed carbonate rocks (dolomitic and calcitic marbles) of Ruchun complex (Pz₃^d and Pz₃^m) are seen in brown and light to dark gray colors and often alternate associated with metamorphosed sedimentary and volcanic rocks (Pz₃^sch unit) (Fig. 3A). The Ruchun complex was intruded by microdiorite, monzodiorite, microgabbro, and diabase dikes (Fig. 3B). Quartz and calcite veins have cut most of the Ruchun complex units (Fig. 3C and 3D). Calcitic and dolomitic marbles with probable Permian-Triassic age (Fig. 3E and F) can be seen on Ruchun complex (units PTm and PT^d). Mafic (gabbro) to felsic (granite) intrusive bodies (gabbro to granite) were exposed in the west of DehSard village, next to Permian-Triassic dolomite (Fig. 3F).
Pb-Zn mineralization in the Mazar-Ruchun region is formed in the calcitic and dolomitic marble (Pz3d and Pz3m) of the Ruchun complex (Fig. 4A, B, C and D). These metamorphosed carbonates are composed of calcite and dolomite, and minor minerals such as muscovite, quartz, and opaque minerals (Fig. 4E and F). Based on the morphology of calcite blade (Burkhard, 1993), and the presence of calcite (type I and II), the temperature of metamorphism of this marble is between 250 and 350 degrees, which corresponds with the green schist facies. Marbles alternate associate with schist (green schist, mica schist and graphite schist) and phyllite (Fig. 3A, E and G).
Primary mineralization in Seh Chah, Chah Sorbi and Chah Nar deposits includes galena, sphalerite, pyrite ± chalcopyrite associated with quartz, calcite, and dolomite ± barite. Vein-veinlet, open space filling, brecciated ± disseminated ± laminated structures and textures can be seen in these deposits. The most important alterations in these deposits are silicification and carbonitization (calcitic and dolomitic alterations). Carbonate host rock and structural control can be considered as the most important factors for controlling primary ore mineralization in the Seh Chah and Chah Nar Pb-Zn deposits. Dolomitic and calcitic marble in the Seh Chah deposit are highly altered (Fig. 4B). A number of basic to intermediate intrusive bodies (often as dykes) can be seen in this area. Chah Nar and Seh Chah deposits were formed epigenetically with vein-veinlet, open space filling and brecciated structures and textures (Fig. 5B and C). Graphite schist in Chah Sorbi deposit is sometimes seen alternating with marble in the Ruchun complex sequence. In this deposit, in addition to vein-veinlet, open space filling and brecciated textures (which were also observed in the Seh Chah and Chah Nar deposits), part of the ore has a laminated and disseminated textures. It seems that the type of sulfide mineralization in Chah Sorbi deposit is different from the other two deposits (Fig. 6A to C). In Chah Sorbi deposit, galena, sphalerite, pyrite and chalcopyrite associated with quartz, calcite, organic matter, dolomite and barite were deposited in the hydrothermal mineralization stage (Fig. 6D and Table 1). The effects of metamorphism and deformation in this deposit can be traced by such evidence as microscopic and mesoscopic folds and faults in the ore and host rock (Fig. 6E and F). In contrast, Chah Nar and Seh Chah deposits were formed after the last metamorphic event (probably post Late Cretaceous) and no evidence of metamorphism can be seen in them.
Primary sulfide ores in Zardbazi Dar and Chah Sorbi Arjmand deposits have been weathered and mining has been carried out on nonsulfide ore (supergene ore). The nonsulfide ore formed at the expense of sulfides, and mainly consists of smithsonite, hydrozincite, hemimorphite, and cerussite (Fig. 8A and G, and Table 1).
 
Discussion and conclusion
Sediment-hosted Pb-Zn deposits represent the world’s largest accumulations of base metals (Goodfellow and Lydon, 2007; Wilkinson, 2014). Table 2 shows a comparison of the general characteristics of these deposits with Pb-Zn deposits in Ruchun-Mazar area. The host rock of the studied deposits (calcitic and dolomitic marble) is different from the SEDEX type deposits (shale as the dominant host rock). Chah Nar and Seh Chah, deposits were formed epigenetically (within fracture and fault and as replacements) and deposited after the last metamorphic event (probably post Late Cretaceous). These deposits are classified as a group of epigenetic deposits and show a significant similarity to MVT deposits, although they also display fundamental differences with this category of ore deposit (especially host rock alteration).
The presence of laminated and disseminated textures (before the metamorphism event) in Chah Sorbi deposit classified it as a syngenetic to early diagenetic Pb-Zn deposit (e.g., Irish type or SEDEX). Chah Sorbi deposit shows notable similarity to Howard’s Pass district, Selwyn Basin, of sedimentary exhalative (SEDEX) Zn-Pb deposits (Gadd et al., 2017). Mineralization in Howard’s Pass district (Late Ordovician to Early Silurian) was hosted by carbonaceous, calcareous and, to a lesser extent, siliceous mudstones.
Mining works in Zardbazi Dar and Chah Sorbi Arjmand deposits was carried out on nonsulfide ore (supergene ore). The supergene nonsulfide deposits are unmetamorphosed and undeformed. They consist of low-temperature and low-pressure assemblages that precipitated from meteoric fluids, replacing sulfides and carbonate groundmass to form encrustations and fill pore spaces, veins, and fractures.
Some of the key controls on the formation of carbonate-hosted nonsulfide Zn-Pb deposits are the nature and availability of near-surface sulfide protore, lithology, sub-aerial exposure, tectonic uplift, climate and favorable hydrology (Hitzman et al., 2003). Hitzman et al. (2003) described two specific forms of nonsulfide ore from various nonsulfide deposits around the world: red ore and white ore. Red ore is gossanous, usually found immediately above the sulfide protore, and typically contains >20% Zn, 7% Fe and Pb, and minor silver (Simandl and Paradis, 2008). Typical red ore nonsulfide minerals include iron-oxyhydroxides, goethite, hematite, hemimorphite, smithsonite, and/or hydrozincite and cerussite (Reichert and Borg, 2008). White ore contains up to 40% Zn but less than 7% Fe and Pb. Smithsonite and hydrozincite are common minerals in white ore with only small amounts of Fe-oxyhydroxides and cerussite (Reichert and Borg, 2008). Zinc and Pb nonsulfides can be used as indirect indicator minerals in exploration for MVT, SEDEX, Irish-type, carbonate replacement, and vein-type Zn-Pb deposits.
It seems that Zardbazi Dar and Chah Sorbi Arjmand deposits belong to the direct replacement and lesser extent wall rock replacement nonsulfide zinc deposits.
 
 
Acknowledgments
This study was done supported by a grant of Ferdowsi University of Mashhad. The study is part of the Project number 41179 and also part of the first author’s doctoral thesis. We gratefully thank Dr. Mohammad Salehi Tinoni, Mohsen Jorjandipour, Ali Rashidi, Dr. Ali Amiri and Dr. Ahmad Rashidi Bosharabadi who helped us in different field works. We are grateful to the respected reviewers who played a significant role in the scientific improvement of the article.

Keywords

Mineralogy; Alteration; Pb-Zn deposits; Mazar-Rutchun region; Sanandaj-Sirjan Zone

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