Why the Puna Concentrates Lithium: The Geology Behind the Andean Salars

The Lithium Triangle: A Global Geological Anomaly

The region where the territories of Argentina, Bolivia and Chile converge concentrates a very significant share of the world's identified lithium resources, with estimates often placing more than half of the known brine reserves there. This strip of the Andean Puna, located above 3,500 meters above sea level, does not owe its wealth to chance: it is the result of an uncommon coincidence of geological, climatic and hydrological factors that operated over millions of years.

Understanding why lithium accumulates precisely in these salars, and not in other arid regions of the planet, requires reviewing each of these factors and, above all, understanding how they reinforced one another. The answer lies in the combination of active volcanism, closed drainage and intense evaporation.

Volcanism as the Primary Source of Lithium

The lithium present in the brines of the Puna has an essentially volcanic origin. The subduction of the Nazca plate beneath the South American plate generated, throughout the geological history of the central Andes, intense magmatic activity. Volcanic rocks, particularly silica-rich ignimbrites and rhyolitic tuffs, contain lithium in low but significant concentrations within their minerals and volcanic glasses.

Over time, weathering and interaction with waters—many of them thermal, heated by the residual heat of the magmatic system—gradually released and mobilized that lithium. The element, highly soluble, passed into groundwater and surface water, beginning its journey toward the lower areas of the landscape.

Endorheic Basins: Natural Traps With No Outlet to the Sea

A distinctive feature of the Puna is the abundance of endorheic basins, that is, closed basins whose waters do not flow into any ocean. The uplift of the Andes and the formation of the Puna plateau left numerous internal depressions surrounded by mountain ranges. The water that enters these basins, whether through scarce rainfall, snowmelt or underground inflows, has only one possible way out: evaporation.

This confinement is key. In any open hydrological system, dissolved lithium would end up diluted and carried toward the sea. In the closed basins of the Puna, by contrast, the element is trapped and progressively concentrated, accumulating over tens or hundreds of thousands of years at the bottom of each depression.

The Arid Climate and the Decisive Role of Evaporation

The Puna is one of the driest regions with the highest solar radiation on the planet. With annual precipitation that in many areas does not exceed 100 to 200 millimeters and evaporation rates several times higher than those values, the water balance is markedly negative. This extreme aridity, sustained over long geological periods, acts as an engine of concentration.

As water evaporates, the dissolved salts are left behind and the residual brine becomes increasingly dense and concentrated. Lithium, along with potassium, magnesium and boron, increases its proportion until reaching levels that in the best salars range from several hundred to more than a thousand milligrams of lithium per liter of brine, exceptional values on a global scale.

The Formation of the Salar: Salt Layers and Interstitial Brine

The visible result of these processes is the salar itself: a crust of salts, predominantly halite and other evaporites, that can reach considerable thicknesses. Beneath that crust and among the porous sediments that accompany it, brine circulates, housed in the interstitial spaces like water in a sponge.

This underground brine is the true resource of economic interest. Its exploitation through pumping and evaporation in ponds allows obtaining lithium carbonate or hydroxide at comparatively low operating costs relative to other sources, such as spodumene rock. The quality of each salar depends on its lithium concentration, its ratio to impurities such as magnesium and the properties of the aquifer that contains it.

The Argentine Puna in the Global Production Context

Argentina hosts in its portion of the Puna—mainly in the provinces of Jujuy, Salta and Catamarca—some of the most promising salars in the Lithium Triangle, such as those of Hombre Muerto, Olaroz and Cauchari. These favorable geological conditions, combined with competitive production costs, placed the country among the world's leading producers, with prospects for sustained growth in installed capacity.

The framework of incentives for large investments in force since 2024 and the growing international interest in securing lithium supply for the energy transition reinforce the region's appeal. Understanding the geology that gave rise to these salars is not a merely academic exercise: it is the basis for assessing resources, planning projects and rigorously sizing the potential of one of the most relevant mineral frontiers in the world.