Brine or Hard Rock: Understanding the Two Main Sources of Lithium
According to the IEA, global lithium demand could be multiplied by more than 40 by 2040, depending on the energy transition scenarios currently being considered. [3] A figure that illustrates how this metal has shifted, in just a few decades, from the status of a scientific curiosity to that of a critical input for global electrification. [6]
That said, lithium is not a homogeneous resource. It is found mainly in brine or hard rock deposits, two geological contexts with distinct technical characteristics. Global resources, estimated at around 115 million tonnes [2], are distributed among these different types of deposits. It is therefore worth examining more precisely where this lithium comes from and the methods used for its extraction.
Definition and geological origin of brine
In geology, a brine is groundwater highly concentrated in dissolved salts, notably sodium chloride and potassium chloride. In certain contexts, its salinity far exceeds that of seawater, owing to natural concentration processes that take place over long periods.
These saline solutions generally form in closed basins or porous geological formations where water circulates slowly, interacts with the surrounding rocks, and gradually becomes enriched in dissolved elements. When evaporation exceeds water inputs, as in arid high-altitude regions, the salt concentration increases even further.
Lithium is present in these brines in dissolved form, at concentrations that vary depending on the basin. In operated systems, the pumped brine typically contains between 200 and 1,400 mg/L of lithium [11]. These grades may seem modest compared with those of hard rock deposits, but the volumes that can be mobilized are very large, which makes their exploitation economically viable.
There are several types of brine according to their geological context:
Evaporitic brines (salars): these are closed basins located at high altitude, characteristic of the Andean region in South America. The famous "lithium triangle", which brings together Argentina, Bolivia, and Chile, is the best-known example.
Brines from deep sedimentary formations: arising from buried porous geological layers, they are often found in association with oil or gas fields.
Geothermal brines: these are linked to the Earth's natural deep-heat systems, and are of particular interest for combined valorization with geothermal energy.
The two main families of lithium deposits
Having defined the notion of brine, it is useful to present how geological institutions classify lithium deposits. This classification rests on the geological context in which lithium is concentrated. These different categories coexist and together contribute to global supply.
A classification in three types
Natural Resources Canada distinguishes three main categories of lithium deposits [1]:
Hard rock deposits, mainly associated with spodumene-bearing pegmatites
Brine deposits, present in salars, deep sedimentary formations, or geothermal systems
Clay deposits
In practice, current global production comes mainly from the first two categories, namely hard rock and brine [4]. Clay deposits represent recognized potential, but they remain little exploited on a large scale.
Geological context and formation
Brines and hard rock result from fundamentally distinct geological processes, which directly influence their lithium grade, their geographic location, and their mode of exploitation.
Formation of hard rock deposits: spodumene pegmatites
In hard rock deposits, lithium is mainly concentrated in a mineral called spodumene, a silicate belonging to the pyroxene family, recognized for having some of the highest lithium grades of all commercially exploitable minerals. This spodumene forms within rocks known as pegmatites: igneous rocks with very large crystals, resulting from the slow cooling of deep magmas rich in so-called lithophile elements, that is, elements with a natural chemical affinity for lithium.
To assess the economic value of a hard rock deposit, geologists refer to grade, namely the concentration of lithium in the rock, expressed as a percentage of Li₂O (lithium oxide). The higher this value, the more profitable the deposit is to exploit.
Exploitable pegmatites generally show grades of 1% to 2% Li₂O. [12] For spodumene in particular, economic viability lies between 1% and 2% Li₂O. The Greenbushes mine in Australia, the largest spodumene mine in production in the world, shows a grade of 1.47% Li₂O. [4] On a global scale, hard rock deposits contain an estimated 5.4 million tonnes of lithium oxide, or about 2.5 million tonnes of lithium metal. [1]
Formation of brine deposits: natural accumulation and concentration
Lithium-bearing brines, for their part, form through an entirely different process. Waters laden with salts and lithium gradually infiltrate closed basins, the salars, deep porous sedimentary formations, or geothermal systems. In Andean salars, natural evaporation at high altitude concentrates the lithium over millennia, producing basins of remarkable mineral richness.
Unlike hard rock, the grade of brines is markedly lower, ranging between 0 and 0.3%. [9] What compensates for this low concentration is the immensity of the brine volumes available. This contrast between low grade and large volumes constitutes one of the fundamental differences between the two types of deposits, and partly explains why their extraction methods diverge so much.
Extraction methods
The geology of a deposit directly determines how lithium is extracted from it. The methods differ radically between brine and hard rock, with concrete implications for development timelines, costs, resource consumption, and the final products obtained.
Lithium in brine
Brine exploitation consists of pumping a saline solution to the surface in order to extract the lithium from it. The traditional method relies on solar evaporation in large ponds, a process that is low in energy use but slow, and that can require more than a decade of development and several months of concentration before production [6][7]
More recent technologies, grouped under the term direct lithium extraction (DLE), make it possible to extract lithium by adsorption or ion exchange. These processes reduce the land footprint and shorten production timelines.
Lithium in hard rock
In hard rock deposits, lithium is extracted by open-pit mining. The ore is then crushed, concentrated by flotation, and chemically transformed into lithium carbonate or hydroxide [4][10].
This pathway is more energy-intensive, but it allows continuous production once the infrastructure is in place and frequently supplies lithium hydroxide, sought after for certain battery cathodes [8].
Table I — Comparison of lithium extraction methods by deposit type
| Criterion | Brine | Hard rock |
|---|---|---|
| Form of lithium | Dissolved in a saline solution | Contained in a solid ore |
| Main method | Solar evaporation or DLE | Open-pit mining + chemical processing |
| Development timelines | Long (often > 10 years) | Intermediate (5 to 10 years) |
| Energy intensity | Low to moderate | High |
| Common product | Lithium carbonate | Hydroxide or carbonate |
Conclusion
Lithium is not a homogeneous resource. It comes from distinct geological contexts that determine extraction methods, development timelines, and the products obtained. The demand projections for the 2040 horizon [3], and the current estimate of global resources, valued at around 115 million tonnes [2], underline the importance of a detailed understanding of this diversity.
Brines and hard rock respond to different but complementary technical logics. The evolution of processes, notably in the field of direct extraction, could gradually modify the balance between these pathways. In any case, the ability to identify, characterize, and develop new deposits remains a central factor for securing long-term supply.
To stay informed about developments in the critical minerals and energy sector, follow Squatex on LinkedIn.
References
[1] Natural Resources Canada. "Lithium Facts." Natural Resources Canada, Government of Canada, https://natural-resources.canada.ca/minerals-mining/mining-data-statistics-analysis/minerals-metals-facts/lithium-facts.
[2] U.S. Geological Survey. "Lithium." Mineral Commodity Summaries 2025. USGS, 2025, https://pubs.usgs.gov/periodicals/mcs2025/mcs2025-lithium.pdf.
[3] International Energy Agency. "The Role of Critical Minerals in Clean Energy Transitions." IEA, 2021, https://iea.blob.core.windows.net/assets/ffd2a83b-8c30-4e9d-980a-52b6d9a86fdc/TheRoleofCriticalMineralsinCleanEnergyTransitions.pdf.
[4] Center on Global Energy Policy. "Fact Sheet: Lithium Supply in the Energy Transition." Columbia University SIPA, https://www.energypolicy.columbia.edu/publications/fact-sheet-lithium-supply-in-the-energy-transition/.
[6] Lithium Harvest. "The Lithium Mining Market." Lithium Harvest Knowledge, https://lithiumharvest.com/knowledge/lithium/the-lithium-mining-market/.
[7] Lithium Harvest. "Lithium Extraction Methods." Lithium Harvest Knowledge, https://lithiumharvest.com/knowledge/lithium-extraction/lithium-extraction-methods/.
[8] Kemeny Capital. "Lithium Mining: Key Considerations for Brine and Hard-Rock." Kemeny Capital, 17 Nov. 2022, https://www.kemenycapital.com/2022/11/17/lithium-mining-key-considerations-for-brine-and-hard-rock/.
[9] ACF Equity Research. "Lithium Extraction – Mineral Deposits vs. Salt Brines." ACF Equity Research, https://acfequityresearch.com/lithium-extraction-mineral-deposits-vs-salt-brines/.
[10] EnergyX. "What Is the Difference Between Hard Rock vs. Brine Lithium Sources?" EnergyX Blog, https://energyx.com/blog/what-is-the-difference-between-hard-rock-vs-brine-lithium-sources/.
[11] https://pubs.usgs.gov/of/2013/1006/OF13-1006.pdf
[12] https://www.energypolicy.columbia.edu/wp-content/uploads/2023/12/Lithium-CGEP_FactSheet_121223-2.pdf
