CAFFE pablo Jorge
congresos y reuniones científicas
Hydrothermal systems and Lithium deposits. Northern Puna, Jujuy Argentina.
San Salvador de Jujuy
Workshop; 3rd IWLiME; 2016
The Puna region in the western portion of the Jujuy province (from 3,500 to 5000 m a.s.l.) ischaracterized by an arid climate and internally drained basins producing extended salt deposits (saltpans) and ephemeral salt lakes. In this area, the geologic setting is dominated by Miocene-Pliocenevolcanic complexes and extensive ignimbrite plateaus (Alonso et al., 1984; Ramos, 2000; Coira etal., 1993; Kay et al., 2010). Ore deposits rich in Ag, Pb, Zn, Sn, B, Li, salt and alluvial gold alsooccur and are currently under exploitation. In this region, several hydrothermal discharges withoutlet temperatures up to 62°C are typical, and geographically related to late Miocene to Pliocenecalderas and central volcanic edifices (Peralta Arnold et al., 2016).However, little is known about the hydrothermal systems in this area and a complete geochemistrycharacterization is fundamental for understanding the origin and the hydrogeological patterns ofthermal fluids circulation, as well as the processes controlling water and gas chemistry and theproduction of exploitable mineral resources.In particular, the present study aims to investigate the genetic processes controlling the compositionof waters associated to lithium-rich deposits. According to this goal, the water, as well as theassociated gas phase, were sampled from 26 cold and hot spring and analysed.Water temperature, pH and TDS values are in wide ranges, from 11.7 to 62.4 °C, from 4.84 to 8.65and from 254 mg/L to 315 g/L, respectively. Five different chemical facies were recognized:Na+(Cl−, HCO3−), Na+(HCO3−), Ca2+(HCO3−), Ca2+(SO42−) and Na+(Cl−) (Fig. 1-a). Interaction ofmeteoric water with different type of lithotype explains such a large variations of the waterchemistry. The Na+(Cl−) waters had the highest TDS values and were characterized by a wide rangeof outlet temperatures (from 11.7 to 62.4 °C), whilst their pH values range between 5.92 and 7.73.Hence, they represent the most mature term of the geochemical dataset (Fig. 1-b). They also showedthe highest concentrations of Li+(up to 602 mg/L) and B (up to 178 mg/L). Water geothermometrysuggests equilibrium temperature ranging from 140°C and 220°C (Fig. 1-c). The R/Ra valuesindicate up to 17% of mantle He, whereas the CO2/3He ratios are 2.9×1012, up to three orders ofmagnitude higher than the MORB value, suggesting a dominant crustal CO2 contribution.These hydrothermal systems are an important contribution of lithium concentrations, either by abrine geothermal input or by water-rocks interaction process. They provide a constant lithiumsource that must be taken into account and thoroughly evaluated in mass balance models within theevaporite cycle, as well as in future studies assessing lithium sources, metal liberation, transport anddeposition.