Geochemistry of trace elements in spring waters of the lourdes area (France)

Abstract

Geochemical studies on the waters of four springs, including the Massabielle (MS) Spring, were carried out at Lourdes (France) following a long, rainless and warm period, with the aim of at least documenting the groundwater chemistry that was affected by the current meteoric input. The existence of anecdotal reports about anomalously elevated concentrations of trace constituents in the water of the MS Spring in the absence of any detailed studies inspired these first geochemical investigations of trace elements in the spring waters at Lourdes. The main common features of waters from the four springs studied in Lourdes are low total dissolved solids (255-318 mg/L), a slightly alkaline pH (7.50-7.68), oxidizing conditions (EH = 458-472 mV), similar temperatures (11.3-13.1 °C), and their Ca-HCO3 hydrochemical type, all of which are typical characteristics for an active zone within a hydrogeological system that is developed in carbonate-dominated bedrock. The spring waters, which represent an active turnover zone in the hydrogeological system, are only in partial chemical equilibrium with the minerals of the aquifer rocks. The enrichment of the MS Spring water with numerous elements (Li, Na, Cs, Ba, S, F, Br, REE, B, Sb and Bi), when compared with other springs studied and with the bedrock geochemistry, probably is caused by contributions from fluids (originating from the Pyrenees basement and/or from Triassic saliferous deposits) in the formation of the hydrogeochemical content of the zone under investigation. The germanium concentration in all of the waters studied was significantly lower than the concentrations typically found in fresh groundwater in the active zone; accordingly, the hypothesis concerning an anomalously high concentration of this element in the MS Spring water was invalidated. The preliminary geochemical research presented is part of an interdisciplinary geochemical-biological-tensiometric study of the spring waters at Lourdes.