GEOCHEMISTRY OF TRAVERTINE DEPOSITS AS A GEOTHERMAL EXPLORATION TOOL: A CASE STUDY AT CAJÓN DEL MAIPO, CENTRAL ANDES, CHILE

Abstract

Travertine deposits have been widely studied due their relevance in palaeoenvironmental studies. By means of morphological, mineralogical and geochemical studies, it is possible to constrain the physicochemical conditions of the parental fluids from which they formed. In this research, we studied active and fossil travertine deposits near the Baños Colina (2500 m a.s.l., 30-52°C) and Baños Morales (1850 m a.s.l, 14-23 °C) hot springs located in the Andean Cordillera near the city of Santiago (33°S -34°S). Field observations were combined with X-ray diffraction, scanning electron microscopy and isotope ratio mass spectrometry determinations in travertine and water samples from the hot springs. Different field morphologies were recognized including cascades, dams, terraces, and fissure ridges. The mineralogy of the deposits consists of calcite and aragonite on shrubs and fan disposition, respectively. The ?13C(PDB) values of travertine range from -3.06 to 15.48 ‰, while the ?18O(PDB) vary from -19.47 to -6.73 ‰, showing a high correlation between them (R:0.75-0.95 and P>0.05). The ?D and ?18O data of the hot spring water plot along the local meteoric water line, and their ?13C(PDB) values range from -4.19 to 8.05 ‰. These data indicate that the studied travertine deposits have a thermometeogenic character. The close spatial relationship of the studied travertines with regional structures suggest that they may have formed due the fault-related infiltration of meteoric fluids. We propose a model where surficial waters mix with deeper fluids followed by CO2 exsolution driven by depressurization, triggering the surface carbonate precipitation. According to this model, the travertine deposits at Cajón del Maipo can be considered as surface expressions of a deeply seated convecting geothermal system.