Special Issues on the Geology and Origin of Lithium Deposits—Introduction: Lithium Deposit Types, Sizes, and Global Distribution

Lithium (Li) is a soft, silvery-white alkali metal with the lowest density of all known solid metals in the periodic table under standard conditions on Earth (Rumble, 2025). In its pure form it is soft enough to be cut with a knife but is highly reactive and flammable in the presence of water or moisture. It therefore must be stored in vacuum, in an inert argon atmosphere (not nitrogen, which forms lithium nitride), or in inert liquid such as purified kerosene or mineral oil to prevent vigorous exothermic reaction with water (vapor) that forms highly flammable hydrogen (Rumble, 2025). When alloyed with other metals and used as a building block for pharmaceuticals, its unique properties make it essential for a wide range of applications (Kesler and Simon, 2015). Today, Li is chiefly used for manufacture of rechargeable batteries, yet these are only the latest in a long line of applications for Li (Emsley, 2011). It is used in some nonrechargeable batteries for applications including heart pacemakers, toys, and clocks (Thakur et al., 2025). Lithium oxide is used for manufacturing special ceramics and glass where it is used to control thermal expansion (Kesler and Simon, 2015). Lithium is also used to expand the usable temperature range of lubricating greases and improve water resistance (Delgado et al., 2006). Its natural hygroscopic properties also mean that Li is frequently used in industrial air conditioning and dehumidification systems (Kelley, 1938). Lithium is added to aluminum-base alloys for manufacture of aerospace materials, aircraft, bicycle frames, and high-speed trains to reduce their density and improve their response to stretching (tensile stress) and deformation (tensile strain) and increase fatigue-crack-growth resistance, and lithium-magnesium alloys are used for armor plating (Starke, Jr., 2014). Lithium and Li hydride are used as solid fuel and as high-energy additives to rocket propellants, and lithium hydride and deuteride serve as a fusion fuel in staged thermonuclear weapons (Simone and Bruno, 2012). Several psychiatric medicines also contain lithium compounds in the form of lithium salts, primarily for treating bipolar disorder and for major depressive disorder (Rybakowski, 2020). These uses combined with the increasing demand for use in lithium-ion batteries mean that lithium is considered one of the most critical of the critical metals and minerals in national and organizational criticality assessments (e.g., McNulty and Jowitt, 2021; Jowitt, 2024).

Lithium production to date has been dominated by two very different types of deposits (Kesler et al., 2012; Mohr et al., 2012; Gardiner et al., 2024). The first is pegmatites, which are igneous rocks of generally granitic composition with crystals that can be greater than 1 m in length (London, 2008) that form through fractionation of peraluminous granitic melts or anatexis of metasedimentary rock (Wise et al., 2022). Lithium-bearing pegmatites, commonly called lithium-cesium-tantalum (LCT) pegmatites (Černý and Ercit, 2005), were first mined at a large scale in Kings Mountain, North Carolina. Now, most production of Li from pegmatites comes from deposits in Australia, Canada, Portugal, Brazil, and Zimbabwe (U.S. Geological Survey, 2024). Lithium is also produced from saline solutions, referred to as closed-basin brines (Munk et al., in press), which form by evaporation of high-altitude inland lakes to form playas or salars. Brines formed by evaporation of lake waters differ from those formed from seawater, because surrounding rocks contribute unusual elements to the water, including Li. Brine deposits with Li were first recognized and exploited in Silver Peak, Nevada, but much larger and higher-grade deposits have since been discovered in the Lithium Triangle of Chile, Argentina, and Bolivia (Munk et al., in press), and even more recently in China (Zhang et al., in press).

In response to the battery market, world production of lithium has increased by nearly 3,000% compared with 1960 (Fig. 1). However, despite this positive response to increased demand for Li, demand for this critical commodity from the Li-ion battery sector, primarily for vehicle electrification, is forecast to grow by at least 30% annually through 2030 (McKinsey and Company, 2023), indicating a need for the identification and development of new lithium resources. The global lithium market size is projected to grow from $26.88 billion in 2024 to $134.02 billion in 2032 (Fortune Business Insights, 2025). This has stimulated significant exploration for lithium deposits to replace existing deposits that are being depleted and research and development to develop new technologies such as direct lithium extraction (DLE) to produce lithium from sedimentary-basin (oil-field) brines (Butler et al., in press), geothermal brines (Humphreys et al., in press), and volcano-sedimentary deposits (Putzolu et al., in press a).

These Special Issues group Li deposits into three major types based on historical and active production and a mineral systems approach to classification (e.g., McCuaig and Hronsky, 2014, and references therein). These include pegmatites (e.g., Černý and Ercit, 2005; Wise et al., 2022), closed-basin brines (e.g., Munk et al., 2016, in press), and volcano-sedimentary deposits (e.g., Benson et al., 2023; Putzolu et al., in press a). Pegmatite deposits are by far the most widespread type globally (Fig. 2), occurring in all seven continents with reported ages ranging from the Mesoarchean to Cenozoic (Bradley et al., 2017). Closed-basin Li brine deposits are primarily constrained to high-altitude, hyper-arid basins of the modern Andean and Himalayan mountain ranges (Fig. 2) though lower-grade saline brine deposits are known to occur at lower elevations globally (Munk et al., in press, and references therein). Volcano-sedimentary Li deposits are also prevalent throughout the globe (Fig. 2), with the largest and highest-grade occurrences of these deposits predominantly constrained to Cenozoic closed basins in extensional continental settings near centers of contemporaneous rhyolitic volcanism such as the Basin and Range province of the United States and Mexico (Hampton and Benson, in press; Putzolu et al., in press a). Additional types of Li deposits include continental brines (Butler et al., in press), geothermal brines (Humphreys et al., in press), and rare metal granites (Burisch et al., in press), though the technology to extract lithium from these deposits has not yet been demonstrated at commercial scale.

The classification of coarse- to fine-grained granitic pegmatites containing Li-bearing minerals such as spodumene, lepidolite, and petalite (Table 1) has varied within the geologic literature over the past century. Currently, the most used classification scheme is that of Černý (1991) and Černý and Ercit (2005), who divide pegmatites into families and classes based on variations in the temperatures and depths of pegmatite emplacements. In this scheme, pegmatites containing Li-bearing minerals belong to the LCT family and occur within abyssal, miarolitic, and rare element classes (Černý and Ercit, 2005). Müller et al. (2022) point out that this methodology, though widely used, is not ideal, because it relies on prior knowledge of pressure-temperature conditions of pegmatite emplacement for classification, which may not be known for a given pegmatite. Because of this and other ambiguities associated with the Černý and Ercit (2005) classification scheme (see Müller et al., 2022), Wise et al. (2022) presented a new framework to divide pegmatites into three groups based on the composition of accessory minerals present in pegmatites. Under this new scheme, pegmatites containing Li-bearing minerals are all classified as “group 1” pegmatites that are not dependent on genetic conditions for classification, as it is noted that Li-bearing minerals in pegmatites can form at a variety of temperatures and pressures as either residual melts of granitic magmatism or direct products of anatexis (Wise et al., 2022).

Of the 10 papers in these Special Issues on Li-bearing pegmatites (hereafter referred to as Li pegmatites for the sake of simplicity), the majority are comprehensive reviews of continental- or district-scale pegmatite fields. Goodenough et al. (in press) present an overview of Li pegmatites across Africa, reviewing the key orogenic processes and paragenetic sequences responsible for the vast untapped pegmatites on the continent. The genesis of Li pegmatites in western Australia (Fig. 2), the current largest global producer of Li, is reviewed in two papers in these Special Issues. Wells et al. (in press) examine mineralogical, geochemical, and geochronological perspectives of Li pegmatites in the Archean Pilbara craton, whereas Grigson et al. (in press) document the timing of pegmatite emplacement in this craton relative to key deformation events to improve exploration efforts.

Pegmatite belts of the Americas are examined in these Special Issues through the lens of deposit genesis. Lithium pegmatites in the Appalachian Mountains of North America are shown to have formed as direct products of anatexis and not residual melts of granitic magmatism, as demonstrated by detailed geochronological analysis in the Rumford pegmatite district of Maine (Fig. 2; Felch et al., in press) and geochemical comparison of pegmatites in the Kings Mountain (North Carolina) area (Fig. 2) to previously presumed nearby granite sources (Curry et al., in press). On the other hand, Pedrosa-Soares et al. (in press) demonstrate that spodumene-rich pegmatites of the Eastern Brazilian pegmatite province (Fig. 2) postdate regional metamorphism and are spatially associated with post-tectonic peraluminous granites.

In addition to regional studies on pegmatite genesis, papers in these Special Issues also highlight the complexities of individual pegmatites and guide best practices in Li pegmatite exploration from deposit to provincial scales. Acke et al. (in press) discuss how magmatic, hydrothermal, and deformation processes lead to a complex distribution of Li within Musha-Ntunga pegmatites (Fig. 2) of Rwanda and the surrounding host rocks. Similar metasomatic processes leading to the alteration of wall rocks and formation of geochemical halos are also discussed for the Big Whopper/Separation Rapids (Fig. 2) pegmatite of the Canadian Shield (Bodeving et al., in press). The primary and secondary processes involved in the formation of Li pegmatites and their halos can be detected using a diverse set of geochemical and geophysical tools (Müller et al., in press), as well as machine learning algorithms (Pierangeli et al., in press), leading to improved success during exploration campaigns.

Closed-basin brine deposits, commonly referred to as salar or evaporative brine deposits, differ from the other major types of Li deposits by virtue of being a fluid and not a solid mineral resource. In these deposits, Li typically exists as a hydrated free ion (Li⁺) or to a lesser extent, weakly complexed to an anion such as chloride (Cl^–) or sulfate (⁠$SO4−$⁠) within an Na-Cl or Na-SO₄-Cl brine (Munk et al., in press). These brines predominantly occur within salt flats in the high-altitude Andean and Himalayan mountain ranges (Fig. 2), though notable exceptions occur at lower elevations such as the actively producing operation at Silver Peak, Nevada, United States (Fig. 2). Houston et al. (2011) characterized two types of closed-basin brine deposits: “mature halite” salars, characterized by basins in arid to hyper-arid environments that reach halite saturation, and “immature clastic” salars, which host brine in pore spaces of alternating clastic and evaporative sedimentary sequences.

In these Special Issues, we adopt the terminology of closed-basin brine to clearly distinguish the traditional, proven salar-type deposit from emerging unconventional brines that have yet to reach economic or commercial viability, such as sedimentary-basin (oil-field) brines and geothermal brines (Fig. 2). Munk et al. (in press) present an updated detailed overview of closed-basin brine deposits that builds on the seminal review by Munk et al. (2016) and discuss seven major characteristics common to economically viable Li-bearing brines. This review paper is based primarily on research performed at Silver Peak and in the Lithium Triangle of South America (Fig. 2), the largest concentration of closed-basin brine deposits in the world. The second-largest concentration of salars and salt lakes globally is the Qinghai-Tibet Plateau of the Himalayan Mountains, and Zhang et al. (in press) review the geology and origin of closed-basin brines of the Qaidam basin (Fig. 2), the largest endorheic basin within this province.

One of the seven critical processes in generating a closed-basin brine that is economically viable for Li extraction is the presence of a volcanic and/or hydrothermal Li source during brine formation (Munk et al., in press). Though classic models for closed-basin brine deposits posit volcanic rock weathering as the primary source for Li (e.g., Price et al., 2000; Risacher and Fritz, 2009), recent work by Ellis et al. (2021) demonstrates that posteruptive loss of Li from volcanic glass only occurs over a limited time frame while the rock cools. To account for additional sources of Li, Cortes-Calderon et al. (in press) demonstrate that magmatic volatile phases exsolving from magmas and rising to the surface via hydrothermal systems likely provide a long-lived source of Li within watersheds of major Andean salars. Myers et al. (in press) measure Li concentrations in magmatic melt inclusions and embayments to demonstrate that the partitioning of Li between magma and coexisting vapor is a complex process that varies between volcanic centers based on the composition of the magma.

Volcano-sedimentary deposits are poised to be the next major type of producing lithium deposits with the Thacker Pass project (Nevada, United States) actively under construction and several other projects in the western United States and eastern Europe under rapid development (Fig. 2). Previous classifications (e.g., Bowell et al., 2020) refer to these deposits as clay type or hectorite type. All papers in these Special Issues adopt the volcano-sedimentary classification of Benson et al. (2023; e.g., Putzolu et al., in press a), as not all phases that contain Li in this mineral system are clay minerals sensu stricto (Table 1). The primary example of this is the Li-bearing borosilicate, jadarite, found at the eponymous Jadar deposit in Serbia (Putzolu et al., in press b).

Putzolu et al. (in press a) present a foundational comprehensive global overview of this emerging type of Li and boron (B) deposit through a detailed review of the tectonic, environmental, structural, and volcanic source characteristics of the deposits. Through this, two key volcano-sedimentary districts are defined by Putzolu et al. (in press a): the Tethyan district of eastern Europe and western Turkey and the Basin and Range district of North America (Fig. 2). The Basin and Range district is examined in detail by Hampton and Benson (in press) who utilize machine learning analysis on a new district-wide sedimentary rock data set to define key characteristics of volcano-sedimentary resources and predict Li concentrations in unknown systems to aid in exploration efforts.

These Special Issues also include five papers on typical volcano-sedimentary deposits, defined by the presence of smectite, illite, and/or jadarite as the main Li-bearing minerals (Table 1). Emproto et al. (in press) review the mineralogy and genesis of the largest known Li reserve in the world, the smectite- and illite-bearing Thacker Pass project (Nevada, United States) located in the mid-Miocene McDermitt caldera (e.g., Benson et al., 2017, 2023; Fig. 2). The only other volcano-sedimentary deposit known to occur within a volcanic edifice is the maar-hosted Basin Li-smectite deposit of the Kaiser Spring volcanic field in northwestern Arizona (Fig. 2), United States (Thompson et al., in press). The more common hosts of volcano-sedimentary Li deposits are structurally bound extensional basins, including the recently discovered smectite-illite deposit at Barstow, California, United States (Gagnon et al., in press) and the Rhyolite Ridge (Fig. 2; Nevada, United States) joint Li-B deposit (Darin et al., in press). The most globally significant joint Li-B deposit is the Jadar deposit, which hosts Li in jadarite (Table 1) as well as hectorite (Li-Mg-F smectite) clays (Putzolu et al., in press b).

A number of other Li deposits that occur within volcano-sedimentary systems but do not contain typical mineral assemblages are not specifically discussed in papers of these Special Issues outside of brief mentions in the overview paper (Putzolu et al., in press a). This includes coal seams and some of their aluminous underclays (e.g., Tourtelot and Brenner-Tourtelot, 1977; Feineman et al., 2020), cookeite-bearing karst-bauxite deposits (e.g., Ling et al., 2023; Yan et al., 2025), and fresh and altered volcanic rock (MacDonald et al., 1992; Ramirez Briones, 2024) of the Macusani volcanic field of Peru (Fig. 2).

Several other potential sources of Li are known but have not been exploited in any significant way to date. The sources are discussed in three papers of these Special Issues and include geothermal brines (Humphreys et al., in press), rare element granites (Burisch et al., in press), and sedimentary-basin brines (Butler et al., in press). Although nascent in their development and perhaps requiring the successful rollout of technologies such as DLE, all these systems are indicative of the wider Li potential of a variety of systems known to contain Li.

The largest known Li measured and indicated mineral resource in the world is the volcano-sedimentary Thacker Pass project with 8.37 million metric tonnes (Mt) Li (Fig. 3; App. 1). This deposit is located within caldera lake sediments on the Nevada side of the mid-Miocene McDermitt caldera of Nevada and Oregon (Emproto et al., in press). An additional measured and indicated resource of 2.09 Mt Li occurs in caldera lacustrine rocks on the Oregon side of the border in the McDermitt project (Jindalee, 2023), resulting in a total measured and measured and indicated resource contained within the McDermitt caldera of 10.46 Mt Li, still considerably lower than the academic estimate of ~20 to 40 Mt Li presumed to occur within the whole caldera (Castor and Henry, 2000; Benson et al., 2023), highlighting the scalability of the resource.

The largest brine deposits in the world are on par with the combined 10.46 Mt Li mineral resource calculated for the McDermitt caldera. The Salar de Uyuni of Bolivia contains roughly 10.2 Mt Li based on an academic estimate (Gruber et al., 2011). The Salar de Atacama contains 10.21 Mt Li, representing a combination of the measured and indicated resources published by SQM (8.21 Mt Li) and Ablemarle (2.0 Mt Li). Similarly, the Caucharí-Olaroz system contains a total of 7.91 Mt Li when combining the measured and indicated resources of the companies operating within the basin: Lithium Argentina/Ganfeng (3.74 Mt Li), Rio Tinto (3.73 Mt Li—Caucharí and Olaroz projects), and Lithium Energy Limited (0.44 Mt Li). Farther south in Argentina, the Salar del Hombre Muerto contains a total of 4.89 Mt Li when including all the projects in the basin (App. 1).

On average, closed-basin brine and volcano-sedimentary deposits are the largest Li deposits globally, with most deposits containing greater than 0.5 Mt Li (Fig. 3). Closed-basin brine deposits of China do not have any publicly available measured and indicated resources, but academic estimates for these districts suggest that projects are on par with Andean salars, including the 1.53 Mt Li Zhabuye deposit and a combined 2.02 Mt Li for the Qaidam basin (Gruber et al., 2011; Zhang et al., in press). The large tonnages reported for some volcano-sedimentary deposits in the Basin and Range (Fig. 3) are artificially high because of low cutoff values (e.g., 300 ppm cutoff in the 3.16 Mt Li Tonopah Flats project, 400 ppm cutoff in the 1.66 Mt Li TLC project) relative to the cutoffs used in the Thacker Pass (858 ppm) and McDermitt (1,000 ppm) projects.

Though the average pegmatite deposit is smaller than a typical closed-basin brine or volcano-sedimentary deposit (Fig. 3), some notably large exceptions occur. The Manono-Kitolo pegmatite (Democratic Republic of the Congo) contains the largest pegmatite measured and indicated resource in the world, with 3.79 Mt Li. Close behind is the Greenbushes (Australia) pegmatite with a measured and indicated resource of 3.01 Mt Li (Fig. 3). Most of the other large measured and indicated pegmatite resources occur in Western Australia (Grigson et al., in press; Wells et al., in press), including Pilgangoora (1.78 Mt Li), Mt. Holland (1.27 Mt Li), Wodgina (1.07 Mt Li), Buldania (0.83 Mt Li), Kathleen Valley (0.81 Mt Li), and Mt. Cattlin (0.70 Mt Li). Elsewhere, large measured and indicated resources are reported at projects in Mali (Goulamina: 0.69 Mt Li), Brazil (Grota do Cirilo: 0.61 Mt Li), and Canada (Shaakichiuwaanaan: 0.54 Mt). Other globally significant pegmatite deposits without measured and indicated resources include the Jiajika (China) and Nuristan (Afghanistan) pegmatites with academic estimates of 1.33 Mt Li (Gruber et al., 2011) and 0.99 Mt Li (Peters et al., 2011), respectively (App. 1). Ongoing drilling at these and other pegmatites will add to known deposit resources over the coming years; this compilation merely serves as a time stamp for Li exploration for this Special Issue (App. 1).

Because pegmatites can contain high proportions of Li-rich minerals spodumene and lepidolite (Table 1), they typically have higher grades (>5,000 ppm Li) than closed-basin brine, volcano-sedimentary, and rare metal granite deposits (Fig. 3). The one notable known exception to this is the Jadar deposit (Serbia; Fig. 2) with a grade of 8,166 ppm Li across the whole measured and indicated resource (Fig. 3) due to the presence of the Li-rich borosilicalte, jadarite (Putzolu et al., in press b). Most other volcano-sedimentary measured and indicated resources contain grades between approximately 1,000 and 3,000 ppm Li (Fig. 3), reflecting the presence of the primary clay mineral smectite (Table 1). At Thacker Pass, portions of the smectite-bearing claystones were altered under hydrothermal conditions to a Li-rich illite (Table 1) with in situ concentrations greater than 10,000 ppm Li, leading to higher grades locally within the deposit (Benson et al., 2023; Emproto et al., in press).

On average, the lowest-grade Li resources globally are sedimentary-basin, geothermal, and low-concentration closed-basin brines (Fig. 3). These deposits are not yet economically viable at scale using current extraction techniques. Recent advances in DLE technologies that utilize ion exchange, adsorption, or organic solvents to selectively remove Li from host fluids are being tested at scale and will likely soon lead to more diverse sources of Li globally.

The rapid global adoption of technologies requiring Li necessitates a significant surge in new Li deposit discoveries to obtain sufficient supply to meet the projected global market demand. To this end, the geologic reviews and deposit-specific investigations presented in these Special Issues serve as foundational blueprints for the research and discovery of new pegmatite, closed-basin brine, and volcano-sedimentary deposits globally. In addition, the utilization of traditional exploration methodologies (e.g., Bodeving et al., in press; Müller et al., in press), and cutting-edge techniques such as machine learning (e.g., Hampton and Benson, in press; Pierangeli et al., in press) offer exciting opportunities for improving and optimizing exploration efforts. As new mineral processing technologies are introduced and inchoate Li resources become economic, such as rare-metal granites and sedimentary-basin and geothermal brines, a diverse and global array of Li deposits will be able to meet the demands of future sustainable energy storage.

The guest editors would like to thank the editor in chief of Economic Geology, David Cooke, for his peer review of this paper and for his efforts in the compilation of the Special Issues of Economic Geology. We thank all reviewers for timely review of the manuscripts. We also thank Larry Meinert, John Dilles, Shaun Barker, Myra Holmes, Jennifer Craig, and Jens Gutzmer for their advice and support during volume conceptualization and compilation. Lithium Argentina AG and Lithium Americas Corp. are thanked for their in-kind support of these Special Issues. A.C.S. acknowledges funding from the U.S. National Science Foundation EAR grants 2214119 and 2233425.

Tom Benson is vice president of global exploration at Lithium Argentina (formerly Lithium Americas), adjunct research scientist at Lamont-Doherty Earth Observatory, and technical advisor to lithium companies worldwide. Through his positions at the intersection of academia and industry, he has pioneered modern lithium deposit research while advancing lithium project development from exploration to construction/production stages at Thacker Pass and Caucharí-Olaroz. Tom holds a Ph.D. degree from Stanford University, where he specialized in lithium deposits and caldera volcanology. Previously, he researched geothermal systems as an undergraduate at Harvard University, a researcher at MIT, and a Fulbright Scholar at the Iceland GeoSurvey.