Northern Puna, Jujuy Argentina. Peralta Arnold, Y.J. ... and from 254 mg/L to 315 g/L, respectively. Five different chemical facies were recognized: Na. +. (Cl. â.
Hydrothermal systems and Lithium deposits. Northern Puna, Jujuy Argentina. Peralta Arnold, Y.J.12, Tassi, F.34 and Caffe, P. J.12 1
INECOA (UNJu-CONICET), Av. Bolivia 1661, 4600 San Salvador de Jujuy (Argentina) Instituto de Geologìa y Minerìa de Jujuy, UNJu, Av. Bolivia 1661, 4600 San Salvador de Jujuy (Argentina) 3 Department of Earth Sciences, University of Florence, Via G. La Pira 4, 50121 Florence (Italy) 4 CNR – Istituto di Geoscienze e Georisorse, Via G. La Pira 4, 50121 Florence (Italy)
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The Puna region in the western portion of the Jujuy province (from 3,500 to 5000 m a.s.l.) is characterized by an arid climate and internally drained basins producing extended salt deposits (salt pans) and ephemeral salt lakes. In this area, the geologic setting is dominated by Miocene-Pliocene volcanic complexes and extensive ignimbrite plateaus (Alonso et al., 1984; Ramos, 2000; Coira et al., 1993; Kay et al., 2010). Ore deposits rich in Ag, Pb, Zn, Sn, B, Li, salt and alluvial gold also occur and are currently under exploitation. In this region, several hydrothermal discharges with outlet temperatures up to 62°C are typical, and geographically related to late Miocene to Pliocene calderas and central volcanic edifices (Peralta Arnold et al., 2016). However, little is known about the hydrothermal systems in this area and a complete geochemistry characterization is fundamental for understanding the origin and the hydrogeological patterns of thermal fluids circulation, as well as the processes controlling water and gas chemistry and the production of exploitable mineral resources. In particular, the present study aims to investigate the genetic processes controlling the composition of waters associated to lithium-rich deposits. According to this goal, the water, as well as the associated 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 8.65 and 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 of meteoric water with different type of lithotype explains such a large variations of the water chemistry. The Na+(Cl−) waters had the highest TDS values and were characterized by a wide range of 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 showed the highest concentrations of Li+ (up to 602 mg/L) and B (up to 178 mg/L). Water geothermometry suggests equilibrium temperature ranging from 140°C and 220°C (Fig. 1-c). The R/Ra values indicate up to 17% of mantle He, whereas the CO2/3He ratios are 2.9×1012, up to three orders of magnitude higher than the MORB value, suggesting a dominant crustal CO2 contribution. These hydrothermal systems are an important contribution of lithium concentrations, either by a brine geothermal input or by water-rocks interaction process. They provide a constant lithium source that must be taken into account and thoroughly evaluated in mass balance models within the evaporite cycle, as well as in future studies assessing lithium sources, metal liberation, transport and deposition.
Figure 1. (a) δD-H2O vs. δ18O-H2O (‰vs. V-SMOW) binary diagram for cold and thermal spring. The Local Meteoric Water Line build with rain samples is olso reported. (b) Square diagram (Langelier and Ludwig, 1942). (c) Na–K–Mg ternary diagram proposed by Giggenbach (1988) for thermal and cold springs.
Keywords: Hydrothermal systems, Fluids geochemistry, Lithium. Acknowledgments: This research was partly funded by the PIO project UNJu-CONICET 14020140100010CO “Dinámica y evolución de los ambientes evaporíticos de la Puna de Jujuy: factores y procesos que controlan la distribución de Li y B. With indispensable support from the laboratories of Fluid Geochemistry and Stable Isotopes of the Department of Earth Sciences of the University of Florence. References: [1] Alonso, R., Viramonte. J. y Gutiérrez. R. (1984). Puna Austral. Bases para el suhprovincialismo geológico de la Puna Argentina. IX Cognr. Geo/. Argcntino, T. 1:43-63 [2] Coira, B.L., Kay, S.M., Viramonte, J., 1993. Upper Cenozoic magmatic evolution of the Argentine Puna — a model for changing subduction geometry. International Geology Review 35, 677–720. [3] Giggenbach, W.F., 1988. Geothermal solute equilibria. Derivation of Na–K–Mg–Ca geoindicators. Geochim. Cosmochim. Acta 52 (12), 2749–2765. http://dx.doi.org/10. 1016/0016-7037(88)90143-3. [4] Kay, S.M., Coira, B., Caffe, P.J., Chen, C-H, 2010. Regional chemical diversity, crustal and mantle sources and evolution of central Andean Puna Plateau Ignimbrites. Journal of Volcanology and Geothermal Research 198: 81-111. [5] Langelier,W.F., Ludwig, H.F., 1942. Graphical methods for indicating the mineral character of natural waters. JAWWA 34, 335. [6] Peralta Arnold, Y.J., Cabassi J., Tassi, F., Caffe, P.J. and Vasell, O., 2016. Geochemistry of the hydrothermal systems in the Jujuy Province, Argentina, and relationship with the regional geology. EGU General Assembly Conference Abstracts (Vol. 18, p. 16348). [7] Ramos, V.A. 2000. Las provincias geológicas del territorio argentino. En: Caminos, R. (Ed.): Geología Argentina, Instituto de Geología y Recursos Minerales, Anales 29(3): 41-96. Buenos Aires.
