Geothermal Potential of an Emergent Na-Cl Thermal Spring, Clarendon Plains Basin , Jamaica

English Abstract:

Analyzed chemical compositions of emergent low-temperature, Na-Cl type mineral waters from Milk River (MKR) spring situated in the Miocene Age limestone of central Jamaica were combined with a multicomponent geothermometric approach to estimate the geothermal reservoir temperature and depth of fluid circulation. Geochemical data provide interesting information on the origin, circulation, and temperature of this thermal fluid. Boron (B), lithium (Li), and strontium (Sr) concentrations reveal important information about mixing between seawater and geothermal fluids. Cationic ratios of Li/B vs. SO₄^2-/Cl^- indicate deep circulating fluid signatures derived mainly from water/rock interactions involving clastic rocks with water essentially resulting from seawater-derived brine. The drastic shift of δ¹⁸O and δ²H isotopes from the global meteoritic water line (GWML) indicates significant depletion of δ¹⁸O in the region of influence from seawater. Log(Q/K) curves show a cluster of equilibrium temperatures over a range of 150-170°C for MKR. Quartz silica solubility geothermometers underestimated reservoir temperatures. A comparison of temperatures estimated from cation-exchange (Na/K, Na-K-Ca and Na-K-Mg) geothermometers computed from SOLGEO and geothermometric equations range between 153 to 197°C. The higher temperatures estimated for the fluids at depth compared to the emergence temperatures may be due to the circulation of seawater in permeable fractures serving as conduits supporting the upward flow of the geothermal fluids along a major tectonic structure-the east-west trending South Coast Fault (SCF). Chemical and isotopic data suggest the up-flow of deep, thermal, saline brines along fractures of the SCF. Based on hydrochemical, isotopic, geological, and structural data, a hydrogeological conceptual model for the circulation of geothermal fluids at Milk River spring is proposed.