What question did this study set out to answer?

To investigate the hydrochemical signatures and thermal reservoir characteristics of a geothermal field influenced by fault systems in the northern Qinghai Lake region.

March 1, 2026Open Access

Hydrochemical Characteristics and Thermal Reservoir Temperature Estimation of a Fault-Controlled Geothermal Field in the Northern Qinghai Lake Coalfield Area

Key Points

To investigate the hydrochemical signatures and thermal reservoir characteristics of a geothermal field influenced by fault systems in the northern Qinghai Lake region.
Conducted hydrochemical analyses of geothermal waters, cold springs, and surface waters.
Utilized isotopic tracers including δ2H, δ18O, 14C, and 3H for analysis.
Estimated reservoir temperatures using quartz and chalcedony geothermometry.
Applied silica-enthalpy mixing models to assess cold water integration during geothermal upwelling.
Geothermal water identified as low-temperature HCO3-Ca•Mg type with temperatures between 35.6 to 46.2 °C.
Isotopic data indicates distinct signatures in geothermal waters suggesting deeper circulation compared to local water sources.
Mixing ratios of cold water during geothermal upwelling ranged from 74.5% to 85.6%.
Estimated reservoir temperatures between 150–202 °C and circulation depths from 3211–4291 amsl.

Abstract

This study explores the hydrochemical and thermal characteristics of a fault-controlled geothermal field within the Northern Qinghai Lake Coalfield Area on the northeastern Qinghai–Tibetan Plateau (QTP). This research integrates hydrochemical analyses, isotopic tracers, and the regional geological framework to define hydrochemical signatures, identify recharge sources and flow paths, assess cold–hot water mixing, estimate reservoir temperatures, determine circulation depths and residence times, and explain the geothermal system’s formation. Systematic sampling included geothermal waters, cold springs, and surface waters, followed by laboratory analysis of major ions, stable isotopes (δ2H, δ18O), radiocarbon (14C), and tritium (3H). The geothermal water is categorized as a low-temperature, weakly acidic to near-neutral HCO3-Ca•Mg type, exhibiting temperatures from 35.6 to 46.2 °C. Isotopic analyses indicate that cold spring and river waters align with the local meteoric water line, while geothermal waters display distinct isotopic signatures, suggesting deeper circulation. A silica–enthalpy mixing model reveals substantial cold-water mixing during upwelling, with mixing ratios between 74.5% and 85.6%. The corrected recharge elevation is estimated to be 4378–4456 amsl, implying a primary recharge zone in the branch of the Qilian mountains—the middle section of Datong Mountain to the northeast. Geothermometry, employing quartz and chalcedony temperature scales and accounting for mixing, estimates reservoir temperatures of 150–202 °C. The calculated circulation depth spans 3211–4291 amsl. Low tritium levels and carbon dating suggest a deep-cycling system predating 1952, characterized by deeply circulating “ancient water”. The geothermal system’s development is associated with regional tectonics, fault systems, and the Kesuer Formation (Jxk) acting as the reservoir. This study provides a scientific foundation for the development and sustainable use of geothermal resources in the northern Qinghai Lake region and offers insights applicable to comparable fault-controlled geothermal systems across the QTP.

Hydrochemical Characteristics and Thermal Reservoir Temperature Estimation of a Fault-Controlled Geothermal Field in the Northern Qinghai Lake Coalfield Area

Key Points

Abstract

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