The salar de Olaroz is the main Li project in Argentina but the sources and dynamics of the element in this basin are still unknown. In order to identify sources and to understand the dynamics of Li in the salt pan, chemical and isotopic analysis (δ<SUP>7</SUP>Li, and <SUP>87</SUP>Sr/<SUP>86</SUP>Sr) of brines, thermal waters, ignimbrites and sediments outcroping in the basin were performed. The results indicate that the origin of the Li present in the brines is the result of bedrock weathering (likely volcaniclastic sediments and ignimbrites), enhanced by warm thermal waters circulating at depth. An important fraction of Li is likely adsorbed onto clay minerals and Fe (hydr)oxides present in deep fine-grained sediments. Therefore, it is expected that high concentrations of Li are also found in sediments.Centro de Investigaciones Geológicas