Soluble lithium deposits (lithium brines) include continental brines hosted in salars (salt flats), oilfield brines and geothermal brines. Currently, continental brines account for around 66% of the global lithium resource, excluding inferred resource, and have been the first source for lithium carbonate production since 2021. Continental brine is currently the most important source of soluble lithium as research on oilfield and geothermal brine production is relatively new and resources account for less than 7% of the global soluble lithium resource. Thus, since the discovery of economic soluble lithium in the Atacama salar (Chile) by the late 1960s, the start of systematic exploratory studies in the Argentinean salars in the 1970s and 1980s and production of lithium from brine in the Hombre Muerto salar (Argentina) in the 1990s, exploration programs and resource estimation techniques have been continually improving, with accelerated progress since 2010. The main challenge that has been triggering improvements in exploration techniques and resource and reserve estimation is the fact that lithium is a soluble dynamic resource in a liquid and thus grades change with time during production due to pumping extraction. The acceptable range for brine quality has recently widened together with the rapid progress of direct lithium extraction technologies: lower lithium grade brine with higher impurity contents (such as magnesium and boron) is now acceptable for classification as an exploration target.
The design of exploration programs should be aimed at collecting data to fully define brine chemistry and its variability, the potential volume of brine that can be drained (drainable porosity), hydraulic properties to assess brine extractability, sustainability of brine quality and brine levels and sustainable fresh-water availability during long-term pumping of both brine and water. Fresh-water is not only important as a source for industrial water but is also related to lithium reserve during production as lithium is soluble in water, and water ingress to the lithium deposit by fresh-water recharge is therefore the main source of dilution of the ore. Hence, exploration of both lithium in brine and fresh-water sources should start together and be part of the deposit exploration plan. Additionally, preliminary mapping of wetlands and collection of water samples from wetlands as well as other natural springs and streams related to the salar environment should be performed early in the exploration program to establish a basis for environmental monitoring. Simultaneously, a data quality assurance plan with strict QA/QC procedures should be applied for brine chemistry, drainable porosity, and hydraulic parameters.
Currently, lithium brine exploration is not just a matter of building a geology and resource model. Soluble lithium must also be extractable by pumping and brine quality must meet process plant requirements throughout production, despite changes over time. Exploration of brine is a matter of collecting data for multi-disciplinary purposes.
