INTEGRATED HYDROGEOCHEMISTRY AND PRELIMINARY GEOTHERMAL ASSESSMENT OF THERMAL SPRINGS OF JAMAICA

Integrated hydrogeochemical and geothermometry studies were performed to evaluate fluid evolution and estimate the geotemperatures of subsurface hydrothermal reservoirs in eastern and central Jamaica. Hot spring, low-temperature thermal and cold mineral water samples were analyzed for major ions and trace elements. Four water types: Na-Cl-SO₄, Na-Cl, Ca-Na-Cl and Ca-Na-Mg-HCO₃ were validated from hydrogeochemical modeling and graphical interpretation. All thermal water samples plot as “partially-equilibrated” and cold waters plot as “immature” on the Na-K-Mg Giggenbach (1988) geoindicator diagram. Chemical compositions, δ²H–δ¹⁸O analysis and saturation indices imply the processes involved in the fluid evolution as minimal mixing between shallow cold waters and deep thermal waters, direct mixing with seawater, dissolution of the wall rock, and hydrothermal alteration. The data suggest deep circulating thermal waters undergo mixing during ascent and fluid brines are attributed to fracture and fault-controlled hydrothermal circulation. Silica minerals attained chemical equilibria in the circulating waters but are undersaturated with respect to evaporites (Cl and SO₄ salts) and carbonates. Na/Cl and Cl/Br ratios signify seawater or saline impact. The saline source of chloride (Cl) may have resulted from connate waters trapped in geologic formations or hydrothermal fluids. Several geothermometers were applied in order to assess the temperature of the hydrothermal reservoir. Some agreement exists between Na-K geothermometers and quartz geothermometers, whereas Na-Li and chalcedony geothermometers provided unreliable estimated temperatures. The geotemperatures estimated from Na-K geothermometers vary between 80°C - 160°C and the depth to circulation is estimated to be between 1 km and 3 km. Multivariate analysis–principal component analysis (PCA) and discriminant analysis (DA) show the emergence of three independent hydrothermal systems.