Salar de Maricunga Lithium Brine, Chile: An Integrated Review of Geology, Hydrogeology, Hydrogeochemistry, Resources and Environmental Challenges

The Maricunga Salar (Atacama Region, Chile; 3750–3800 m.a.s.l.) hosts Chile’s second-highest average lithium concentration in continental brines. This review integrates the scientific literature, technical resource-estimation reports and environmental information to provide a unified geological, hydrogeological and geochemical assessment of the basin and its resource evolution from 1982 to 2021. The brine averages 1122 mg/L Li (460–3375 mg/L), 12,847 mg/L Ca, 711 mg/L SO4 and 311 g/L total dissolved solids. Although its Mg/Li ratio (6.53) is comparable to that of the Atacama Salar, its Ca/Li (11.45) and SO4/Li (0.63) ratios distinguish Maricunga as the most Ca-rich and SO4-depleted major Chilean salar brine. Comparison with other Andean brines reveals a systematic inverse Ca–SO4 relationship, consistent with geochemical control by gypsum saturation. Maricunga occupies the Ca-rich endmember of this trend, which requires a Ca–Cl component; a deep hydrothermal origin is proposed as a testable hypothesis rather than an established result, because Na–Ca exchange within the basin fill cannot yet be excluded. Drainable porosity, determined from 561 undisturbed samples, ranges from 0.02 in the lacustrine core to 0.14 in marginal alluvial deposits. Importantly, the apparent increase in lithium resources between 1982 and 2021 primarily reflects progressive expansion of the investigated depth rather than increasing lithium grade, and the 2021 estimate refers to a block of only 11.25 km2, less than 8% of the official salar surface. This synthesis therefore identifies hydrogeological architecture, rather than brine quality, as the principal development uncertainty, particularly regarding lateral continuity of the lacustrine unit and potential hydraulic connectivity with Laguna Santa Rosa and the Paipote drainage system. A recurring limitation is that most project-scale parameters derive from a single non-peer-reviewed technical report, so their reproducibility cannot be assessed independently from public data; resolving this, rather than acquiring further grade data, is the priority for advancing the basin towards development.