Hydrogeochemistry and geothermometry of thermal groundwater from the gulf of Suez Region, Egypt

Abstract EN

The combined chemical composition, O and H isotopes, and the basic geologic setting of the geothermal system of the Gulf of Suez, Egypt have been investigated to evaluate the origin of the dissolved constituents and subsurface reservoir temperatures.

Hydrochemical characterization of thermal waters discharged from springs and flowing artesian wells in the Gulf of Suez region show that there are two groups.

One is Hammam Faroun thermal waters with salinity values exceeding 10,000 mg / l, discharge temperatures reach to 70ºC, and Na-Cl hydrochemical facies.

The other group is thermal waters discharged at Hammam Mousa, Ain Sukhna, and shallow flowing artesian wells at Ayoun Mousa and Ras Sudr.

They are characterized by salinity values less than 10,000 mg / l, discharge temperatures ranging from 32.5 to 72ºC and Na-Mg-Ca-Cl (Hammam Mousa), Na-Cl-SO4 (Ain Sukhna), and Na-Ca-Cl (Ayoun Mousa-2 well and Ras Sudr-2 well) water types.

Different graphical presentations using major and minor ions indicated that little mixing with sea water is probably a source of dissolved constituents.

Water / rock interaction is also a major source for the dissolved constituents as revealed from Ca and HCO3 enrichment of the thermal waters that is attributed to dissolution of carbonate minerals.

Thermal waters from Hammam Faroun and Ras Sudr-2 well have the highest discharge temperatures and SiO2 concentrations that indicate that ascending hot water at the Hammam Faroun area is slightly mixed with cold water.

The thermal waters from the study area are depleted in 18O and 2H and fall on the Global Meteoric Water Line (GMWL) and below the local eastern Mediterranean Meteoric Water Line (MMWL) with d-excess values ranging between 3.42 and 10.6 %, which is similar to the groundwater of the Nubian aquifer in central Sinai and the Western Desert of Egypt and suggesting a common origin.

This indicates that these waters are paleo-meteoric water which recharged and flushed residual saline water in the Nubian aquifer under different climatic conditions than the modern ones.

All thermal waters of the study area are undersaturated with respect to sulfate minerals (gypsum and anhydrite) and oversaturated or nearly in equilibrium with respect to aragonite, calcite and dolomite indicating that these minerals occur in the reservoir.

All the thermal waters are oversaturated and nearly in equilibrium with quartz and chalcedony indicating equilibration with a sandstone aquifer free of gypsum and anhydrite with minor carbonate minerals.

The subsurface reservoir temperatures were calculated using different solute geothermometers and gave temperatures ranging between 13.0 and 190.5ºC.

Na / K and Na-K-Ca geothermometers gave the maximum reservoir temperatures (135-190.5 º C), whereas Na-K-Ca-Mg and Mg / Li geothermometers gave the lowest temperatures (13.0-45.9 º C).

Quartz geothermometer gave the most reasonable subsurface temperatures (61.5-104.5ºC).

The Hammam Faroun and Ras Sudr areas have the highest subsurface reservoir temperatures, which is consistent with the estimated high geothermal gradient of about 48 º C / km.