Document Type : Research Article
Authors
1
Ph.D. student, Department of Geology, Faculty of Sciences, 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; Department of Geological Sciences, University of Colorado, CB-399, Boulder, CO 80309, USA
3
Professor, Department of Geology, Faculty of Sciences, Ferdowsi University of Mashhad, Mashhad, Iran
4
Assistant Professor, Department of Geology, Faculty of Sciences, Ferdowsi University of Mashhad, Mashhad, Iran
Abstract
The Lut Block in the eastern Iran hosts numerous magmatic-hydrothermal mineral systems and represents one of the most prospective metallogenic provinces of the Iranian Plateau. The Kaviran prospect area, located in the northwest of Dehsalm, and is characterized by widespread hydrothermal alteration, and structurally controlled gold mineralization. Despite several exploration campaigns in the region, the genetic characteristics and mineralizing processes of the Kaviran system have not been comprehensively investigated. Therefore, this study integrates geological mapping, petrography, alteration mineralogy, XRD Analysis, geochemical investigations, and fluid inclusion microthermometry to constrain the ore- forming processes and metallogenic setting of the deposit.
Introduction
The Lut Block in the eastern Iran represents one of the most important metallogenic provinces of the Iranian Plateau and hosts numerous porphyry and epithermal mineral systems formed during extensive Eocene- Oligocene magmatic activity (Sillitoe, 2010; Richards, 2015). Hydrothermal gold mineralization in this region is commonly associated with volcanic–subvolcanic complexes and structurally controlled fluid pathways. The Kaviran prospect, located the northwest of Dehsalm in the central Lut Block, exhibits widespread hydrothermal alteration, silicification, pyritization, and gold-bearing quartz veins. Despite its exploration significance, the ore-forming processes and physicochemical evolution of the hydrothermal system have not been fully constrained.
The present study integrates field geology, petrography, alteration mineralogy, XRD Analysis, geochemical investigations, and fluid inclusion microthermometry to characterize the mineralization system and determine the genetic relationship among hydrothermal alteration, ore deposit, and magmatic activity.
Materials and Methods
Geological mapping and detailed field investigations were conducted throughout the prospect area. Representative samples were collected from mineralized veins, alteration zones, and host rocks for petrographic and mineralogical studies. X-ray diffraction (XRD) Analysis were carried out to identify alteration minerals, particularly within advanced argillic assemblages. Geochemical data were evaluated to investigate metal associations and element distribution patterns. In addition, microthermometric measurements were performed on primary fluid inclusions hosted by quartz and calcite to estimate the temperature, salinity, and evolution of ore-forming fluids following the procedures described by Bodnar et al., 2014.
Results
Hydrothermal alteration in the Kaviran prospect comprises silicic, advanced argillic, argillic, sericitic–carbonate, and propylitic assemblages. The alteration pattern is characterized by intensely silicified cores surrounded by progressively weaker alteration zones. Field observations revealed the occurrence of vuggy silica, one of the most diagnostic features of high-sulfidation systems (Sillitoe and Hedenquist, 2003; Arribas, 1995). Furthermore, XRD Analysis confirmed the presence of pyrophyllite within the advanced argillic zone, indicating alteration under acidic hydrothermal conditions.
Mineralization occurs as veins, veinlets, stockworks, and disseminations. Pyrite is the dominant sulfide mineral and is accompanied by chalcopyrite and bornite. Secondary minerals include hematite, goethite, and covellite. Extensive pyritization and silicification are closely associated with gold-bearing structures and hydrothermal alteration zones.
Geochemical investigations indicate significant Au enrichment associated with Cu, Ag, Mo, Pb, Zn, and As anomalies. Positive correlations among Au, Cu, and Mo suggest a contribution from magmatic-hydrothermal fluids and imply a possible genetic link to a deeper porphyry system.
Microthermometric studies of 168 primary fluid inclusions revealed homogenization temperatures ranging from 112 to 320°C and salinities between 1.74 and 23.1 wt.% NaCl equivalent. Coexistence of liquid-rich inclusions (LV), vapor-rich inclusions (VL), and vapor-only inclusions (V) provides strong evidence for fluid boiling during ore formation. The distribution of temperature and salinity data suggests mixing between magmatic and meteoric fluids during hydrothermal evolution.
Discussion
Several geological and mineralogical features support the interpretation of the Kaviran hydrothermal system as a high-sulfidation deposit. These features include advanced argillic alteration, widespread silicification, the occurrence of vuggy silica, the presence of pyrophyllite, and extensive pyritization. Such features are widely recognized as characteristic indicators of high-sulfidation environments generated by acidic magmatic fluids above shallow intrusive centers (Hedenquist et al., 2000; Sillitoe and Hedenquist, 2003; Simmons et al., 2005).
Fluid inclusion data indicate that ore mineralization occurred in a shallow hydrothermal environment at relatively low pressures. The coexistence of vapor-rich and liquid-rich inclusions demonstrates that boiling played a significant role in destabilizing metal complexes and triggering gold precipitation. Boiling is considered an effective mechanism for precious-metal deposition in epithermal systems (Bodnar et al., 2014., Moncada et al., 2012).
Mixing between ascending magmatic fluids and cooler meteoric waters appears to have been another important factor controlling mineralization. Dilution of hydrothermal fluids likely caused changes in fluid chemistry, temperature, and sulfur activity, thereby enhancing metal deposition. Similar processes have been documented in numerous epithermal systems worldwide (Rottier et al., 2021; Yasami et al., 2025).
The geochemical association of Au with Cu and Mo, together with the presence of dioritic to quartz monzodioritic porphyry intrusions, suggests that the Kaviran hydrothermal system may represent the upper expression of a larger magmatic-hydrothermal complex. High-sulfidation epithermal deposits commonly occur above porphyry systems and may constitute their shallow-level equivalents (Sillitoe, 2010; Richards, 2015). Therefore, the possibility of a concealed porphyry center beneath the prospect should be considered in future exploration programs.
Conclusions
Integrated geological, mineralogical, geochemical, XRD, and fluid inclusion evidences indicates that the Kaviran prospect represents a high-sulfidation gold system developed in association with the Eocene magmatism in the central Lut Block. Advanced argillic alteration, vuggy silica, pyrophyllite-bearing assemblages, intense silicification, and widespread pyritization collectively support this interpretation. Fluid inclusion studies reveal that ore-forming fluid have temperatures of 112–320°C and salinities of 1.74–23.1 wt.% NaCl equivalent, indicating the involvement of low- to moderate-salinity hydrothermal fluids. Boiling has caused a drop in pressure and reduced solubility or instability of metal-bearing complexes such as gold, and fluid mixing can cause changes in fluid chemistry or changes in sulfur fugacity. The association of Au with Cu and Mo anomalies further suggests a probable genetic linkage between the high-sulfidation mineralization and a concealed porphyry system at depth. Consequently, the Kaviran prospect represents a promising exploration target for both high-sulfidation gold and porphyry-style mineralization within the central Lut Block.
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