Mineralogy, alteration, fluid inclusions microthermometry and genesis of the Cu-Au Kalateh Dasht deposit, south of Shahrood, NE Iran

Document Type : Research Article

Authors

• Mohadeseh Eskandari ¹
• Fardin Mousivand ²
• Maryam Sheibi ²
• Bernd Lehmann ³

¹ Ph.D. student, Department of Geology, Faculty of Earth Sciences, Shahrood University of Technology, Shahrood, Iran

² Associate professor, Department of Geology, Faculty of Earth Sciences, Shahrood University of Technology, Shahrood, Iran

³ Professor, Department of Geology, Institute of Mineralogy and Mineral Resources, Technical University of Clausthal, Clausthal-Zellerfeld, Germany

10.22067/econg.2024.1121

Abstract

The Kalateh Dasht deposit is situated in the northern part of the Central Iran structural zone, northeast of the Toroud-Chah Shirin magmatic arc. The Cu-Au mineralization is hosted by diorite porphyry subvolcanic rocks with a post-Eocene age. The mineralization occurs in the form of hydrothermal breccia and vein-veinlet along a fault zone with an approximately N30E extension and vertical dip. Several mineralized veins consisting of pyrite, chalcopyrite, sphalerite, bornite, galena, barite, hematite, chalcocite, covellite, malachite, and chrysocolla are observed parallel to each other in this fault zone. The gangue minerals include comb quartz, crustiform, and a small amount of amethyst as veins and blades. SEM data indicate the presence of gold within sphalerite. The porphyritic diorite host rocks have been significantly altered due to the action of hydrothermal fluids, resulting in sericitic, siliceous, and propylitic alteration (chlorite, epidote, and calcite), particularly at the margins of mineralized veins. The fluid inclusions in calcite and barite host minerals reveal that homogenization temperatures range between 143.2 and 213.1ºC and salinity varies between 3.06 and 7.73 wt.% NaCl eq. In close proximity to this ore deposit, an argillic alteration zone and other mineralization systems in this region increase the likelihood of a porphyry system at greater depth.
 
Introduction
Despite the abundance of mineralization in the Toroud-Chah Shirin magmatic arc (TCSMA), certain deposits, such as the polymetallic Kalateh Dasht deposit with its post Eocene diorite porphyry host rock, have not yet been thoroughly investigated in terms of their geology, mineralogy, and genesis. The studied area is located in the northern part of the Central Iran (CI) zone and is a small part of the 1:100,000 geological map of Moaleman (Eshraghi and Jalali, 2006). This mining area is situated northeast of the TCSMA and east of the Chah-Musa copper deposit - 13 km north of the Toroud village (Fig. 1). This article comprehensively analyzes the field characteristics, mineralogy, mineralography, and fluid inclusion data of the Kalateh Dasht deposit. Given the likely hydrothermal origin of the deposit, which can be linked to the Eocene magmatic activity and controlled by fault structures, the investigation of these deposits assumes great significance in exploring epithermal mineralization within the Toroud-Chah Shirin magmatic arc.
 
Material and methods
Following a thorough field investigation, a total of 50 samples were collected from the exploratory trenches of Kalateh Dasht to conduct precise mineralogy, mineralography, and hydrothermal alteration studies. These samples consist of ore minerals and quartz-calcite-(barite) veins containing sulfides of both base and precious metals. The locations of these collected samples are indicated in Figure 2. Subsequently, thin (10 samples), polished (13 samples), and thin-polished (25 samples) sections were prepared at both Shahrood and Clausthal University of Technology in Germany. These sections were then examined using an Olympus polarizing microscope. To investigate the physicochemical properties of the mineralized fluid, two double-polished cross-section samples of barite-calcite veins were prepared and analyzed. Temperature and salinity measurements of fluid inclusions were carried out at the Economic Geology Laboratory of Shahrood University of Technology, using the Linkam MDSG600 model heating-freezing stage. Additionally, the Field Emission Scanning Electron Microscope (FE-SEM) model Sigma 300-HV, at Shahrood University of Technology, was utilized to identify specific minerals.
 
Results
According to the data presented in the research, mineralization primarily occurs along a fault zone with an approximately N30E trend and vertical dip. In the field, various structures including hydrothermal breccia, banded, and vein structures can be observed. Within the fault zone in the trench, multiple parallel mineralized veins are present. These veins host minerals such as pyrite, chalcopyrite, sphalerite, bornite, galena, and hematite, accompanied by gangue minerals like comb-style, crustiform, amethyst, and barite, with variable thicknesses ranging from 3 to 5 cm. SEM studies have revealed the presence of gold within the ores. The porphyritic diorite host rocks have undergone significant alteration due to the infiltration of hydrothermal fluids. Sericite, silicic, and propylitic (chlorite + epidote + calcite) alteration zones have been identified along the margins of the mineralized veins, exhibiting high intensity. Fluid inclusion studies conducted on quartz and barite minerals indicate homogenization temperatures ranging between 143.2 and 213.1°C. The degree of salinity falls within the range of 3.06 to 7.73 wt.% NaCl eq. The mineralogical characteristics of the Kalateh Dasht deposit are comparable to base and precious metal intermediate sulfidation (IS) epithermal deposits.
 
Discussions
The field studies, mineralogy, structure and texture, alteration patterns, and fluid inclusion analysis in the Kalateh Dasht deposit show mineralization occuring in subvolcanic rocks composed of porphyry diorite, taking the form of vein-veinlet, hydrothermal breccia, open space-filling, and disseminated. The deposition of ore minerals occurred during two stages: the deposition of primary sulfide minerals (such as pyrite, chalcopyrite, galena, sphalerite, bornite, and hematite) in quartz veins and the formation of secondary minerals (such as covellite, digenite, cuprite, malachite, azurite, and chrysocolla). The formation of mineral veins is associated with a fault zone, as well as other joints and fractures in the area. The study of fluid inclusions trapped in calcite and barite minerals reveals that the homogenization temperature ranges from 143.2 to 213.1 ºC, and the salinity ranges from 3.06 to 7.73 wt.% NaCl eq. Such a thorough analysis of this type of mineralization can be of great value in identifying similar occurrences in the TCSMA. Light-colored sphalerite has been observed at the eastern end of the Kalateh Dasht deposit and close to a zone exhibiting argillic alteration. The presence of light-colored sphalerite, which indicates a low iron content, serves as an additional indicator of epithermal systems with moderate sulfidation. This observation is consistent with the occurrence of relatively oxidized fluids and the formation of sphalerite at the interface of two IS and HS systems (Wang et al., 2019). Strong spatio-temporal-genetic associations with porphyry molybdenum mineralization have been documented in the metallogenic belts of numerous IS systems. Consequently, the proximity of the Kalateh Dasht IS system to an argillic zone may indicate the presence of a profound porphyry system and offer the potential the discovery of similar deposits.

Keywords

• Geology
• fluid inclusion microthermometry
• intermediate sulfidation
• Kalateh Dasht
• Toroud Chah Shirin
• Central Iran

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