Geography and Regional Planning

Geography and Regional Planning

Hydrogeochemistry and geothermometry of hot and cold springs in the Sahand Volcanic Region (Northwest of Iran)

Document Type : Original Article

Authors
Fariba Aghazadeh 1
Mousa Bagheri 2
Morteza Derakhshi 3
Nosrat Aghazadeh 4
1 PhD Student, Department of Geology, Ur.C., Islamic Azad University, Urmia, Iran
2 Assistant Professor, Department of Geology, Urmia Branch, Islamic Azad University, Urmia, Iran
3 Department of Geology, Ur.C., Islamic Azad University, Urmia, Iran
4 Assistan Professor, Department of Civil Engineering, Ur.C., Islamic Azad University, Urmia, Iran
10.22034/jgeoq.2026.594886.4516
Abstract
The Sahand Volcanic Region in northwest Iran, within the Urumieh-Dokhtar Magmatic Arc, hosts numerous hot and cold springs that are useful for understanding hydrogeochemical processes and geothermal-system behaviour in volcanic environments. This study characterizes the hydrogeochemistry of the springs and estimates subsurface reservoir temperatures to evaluate the area's geothermal potential. In summer 2023, water samples were collected from four hot springs (31-54 C) and thirty-four cold springs (20-24 C); temperature, pH and electrical conductivity were measured in situ, and major ions (Ca, Mg, Na, K, HCO3, SO4, Cl) and SiO2 were analyzed. Hydrochemical facies were classified using Piper, Durov and Cl-SO4-HCO3 diagrams, and reservoir temperatures were derived from silica and cation geothermometers with the aid of PHREEQC and AquaChem modelling. The waters show low mineralization (average TDS about 220 mg/L) and are dominated by a Ca-HCO3-SO4 facies, reflecting intensive water-rock interaction. Hot and cold springs share broadly similar hydrochemistry, pointing to a common source with differing circulation depth and mixing. Quartz geothermometry yields reservoir temperatures of 88.7-123.2 C, indicating a moderate- to high-temperature system, whereas cation geothermometers give unreliable results owing to chemical disequilibrium, consistent with the immature classification of the waters on the Na-K-Mg diagram. Saturation-index calculations show oversaturation with respect to silica and undersaturation with respect to carbonate and sulfate minerals. Overall
Keywords
Geothermometry
Hot springs
Volcanic geothermal systems
Sahand Volcanic Region
Northwest Iran
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