Application of Principal Components Analysis to the study of CO2-rich thermomineral waters in the aquifer system of Alto Guadalentin (Spain)

The southeast of the Betic Cordilleras has long been recognized as an area with numerous geothermal anomalies of regional character. Many thermal spri ngs appear related to currently tectonically active fault systems. Carbon d ioxide and other gases in these waters have been mobilized through those fa ult systems. The great depth of these "slip-strike zones" affects the entir e thickness of the lithosphere and leads to contrasting crustal domains of different natures and structures. In this area, the detrital aquifer of the Alto Guadalentin has thermal waters with high salinity and unusually high contents of CO2 gas. The utilization of Principal Components Analysis (PCA) in the hydrogeochemical study of this aquifer has revealed that the origin of the salinity of its waters is due essentially to processes of dissoluti on of the Miocene evaporite rocks, principally sulphate, and to the contrib ution of deep hydrothermal waters that show signs of endogenous CO2 contami nation. To a lesser extent, infiltration waters also form an input, with el evated sulphate, chloride and nitrate content. Likewise, PCA has enabled th e differentiation of distinct groups of water to which these processes have had a variable contribution.