Alteration, mineralization, geochemistry and fluid inclusion investigations in Joftrud prospect area, southwest of Birjand

Document Type : Research Article

Authors

• Omid Shareipour ¹
• Azadeh Malekzadeh Shafaroudi ²
• Maryam Javidi Moghaddam ³

¹ M.Sc., Department of Geology, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran

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

³ Ph.D., Department of Geology, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran

10.22067/econg.2024.1130

Abstract

The Joftrud prospect area is located in the central Lut Block and 60 Km of Birjand city. The area comprises outcrops of pyroclastic (andesitic tuff), volcanic (hornblende andesite, pyroxene andesite, basaltic andesite), intrusive (diorite porphyry, monzodiorite, gabbro) rocks. Mineralization as vein-type with mostly northeast-southwest trend has formed in andesitic units. Main alterations are consist of silicified, argillic, carbonate and propylitic. Primary minerals include chalcopyrite, pyrite, and secondary minerals are consist of chrysocolla, chalcocite, covellite, azurite, malachite, goethite, and hematite. Maximum of geochemical anomalies in veins are for copper 6000 ppm, lead 2934 ppm, zinc 6904 ppm, and Au 144 ppb. Quartz-sulfide veins are formed of fluids with temperature of 265 to 408ºC and salinity of 11.1 to 19 NaCl wt.‌% equivalent. Decreasing temperature and fluid mixing by high-salinity fluid can cause metal deposition. According to the available evidence of structural control of mineralization, alterations and their narrow expansions, mineralogy, texture, fluid inclusion data and depth of formation, prospect area is similar to intermediate sulfidation deposit.
 
Introduction
The Joftrud prospect area is located at 60 Km Birjand city, and belongs to the central Lut Block, Eastern Iran. Extensive magmatic activity in the Lut Block, is accompanied with numerous mineralization events such as porphyry copper, IOCG, vein and skarn (Karimpour et al., 2012).
The central Lut Block is significant part of this Block due to widespread Tertiary volcano–plutonic rocks (Lotfi, 1982; Salim, 2012; Javidi Moghaddam et al., 2019; Javidi Moghaddam et al., 2021) and many cases of Cu (e.g., Mire-e-Khash, Shikasteh Sabz, Rashidi, Ghar-eKaftar, Shurk, and Howz-e-Dagh), Pb-Zn (e.g., Chah Noghreh, Hows-e-Raise and Sechangi veins), Pb-Zn-Cu-Sb veins (e.g., Ghale-Chah, Shurab, Chupan and Kuh Shuru) in the neighboring areas (Malekzadeh Shafaroudi and Karimpour, 2013; Malekzadeh Shafaroudi and Karimpour, 2015; Javidi Moghaddam et al., 2013; Javidi Moghaddam et al., 2014; Javidi Moghaddam et al., 2018; Mehrabi et al., 2019).
Recently, Karjo (2021) has studied geochemistry of ore-veins in the area. For the first time, detailed studies of base metal mineralization and genesis of veins have been conducted. The purpose of this research is the geology, examine the geochemical and fluid inclusion data, and finally discus mineralization model of occurrence of ore veins in the Joftrud prospect area.
 
Materials and methods
In the field work, a total of 80 samples were taken mainly from igneous units and ores. 40 thin sections and polished slabs were examined by an optical microscope. The geological map of the prospect area (scale of 1:5000) was produced in Arc GIS software. Geochemical analysis were done at Zarazma laboratory of Iran (ICP-OES technique) on 15 samples selected from veins by the Kavoshgaran of Eastern Birjand Company (Karjo, 2021). Also, 9 samples were selected for Au analysis with Fire assay in the same laboratory.
Microthermometric tests and salinity determination of fluid inclusions were performed on 3 wafers of quartz minerals using a heating-freezing system, model THM 600 at Ferdowsi University of Mashhad, Iran. The precision of this device during the heating and refrigeration stages is C ± 1◦C and the thermal range is − 190 to 600 ◦C.
 
Result
The rock units of the prospect area are divided into three categories: pyroclastic (andesitic tuff), volcanic (hornblende andesite, pyroxene andesite, basaltic andesite), intrusive (diorite porphyry, monzodiorite, and gabbro) rocks. The ore-veins are mostly formed in andesite rocks, in fault zones with trending NE–SW and subordinate NW-SE. The veins are associated with wall rock alterations of silicified, argillic, carbonate and propylitic. Petrography studies represent that the ore-veins include pyrite, chalcopyrite as hypogene minerals and malachite, azurite, chrysocolla, chalcocite, covellite, goethite, and hematite as secondary minerals. Quartz is significant gangue mineral accompanied with the ore-veins. Based on geochemical data of the ore-veins, maximum anomalies are for copper (6000 ppm), lead (2934 ppm), and zinc (6904 ppm). Based on the criteria of Roedder (1984), three types of primary fluid inclusions (two-phase liquid-rich (L+V), single-phase aqueous (L) and single-phase vapor (V) inclusions) were distinguished in the ore-veins, without evidence of daughter minerals.
In the ore-veins, quartz-hosted LV inclusions have homogenization temperatures (T_h) between 270˚–408˚C for stage-1 and 265 °–385˚C for stage-2. These LV inclusions show salinities between 11.1–13.4 wt.% NaCl equivalent in quartz of stage1 and 15.9–19 wt.% NaCl equivalent in quartz of satage-2.
 
Discussion 
The fluid inclusion data illustrate that the ore-forming fluids had a magmatic signature and were diluted by meteoric water. Quartz of ore-veins dominated by non-boiling textures such as massive and comb textures of quartz (without coexisting liquid-rich and vapor-rich inclusions). So, boiling is not the depositional mechanism in the ore-veins. Decreasing temperature and fluid mixing by high-salinity fluid can cause metal deposition.
In the pressure–temperature diagram (Fournier, 1999), the trapping pressures for the ore-forming fluids of the veins were determined to be within the range of 10–30 MPa which can be equivalent to a depth of approximately 1.2 km assuming lithostatic pressure. So, the ore-veins formed in shallow environment (e.g., Hedenquist and Henley, 1985).
Based on the evidence of geology, alteration, mineralization, texture, and fluid evolution processes probably the Joftrud district is interpreted as an intermediate sulfidation deposit. Numerous ore-veins are present in the central Lut Block (e.g., Mir-e-Khash, Rashidi, Shikasteh Sabz, Howz-e-Dagh, Chah Khareh, Chah Noghreh, Hows-e-Raise, Sechangi, Shurab, Chupan and Kuh Shuru) (e.g., Malekzadeh Shafaroudi and Karimpour, 2013; Malekzadeh Shafaroudi and Karimpour, 2015; Javidi Moghaddam et al., 2018; Mehrabi et al., 2019). These veins mostly have NW-SE and subordinate NE–SW trends and are hosted by andesitic to dacitic composition (andesitic tuff breccia, andesite and dacite). These ore-veins entail copper, lead, zinc and antimony without significant gold anomaly. The similarities in structural control of mineralization, ore mineralogy, geochemistry and fluid inclusion data suggest that ore-veins can be related to part of a large-scale magmatic-hydrothermal system with economic potential. 
 
Acknowledgements
The Research Foundation of Ferdowsi University of Mashhad, Iran, supported this study (Project No. 59744.3).

Keywords

• Mineralization
• base metals
• fluid inclusion
• Joftrud
• Lut Block

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