Lithium Inventory of the Cerro Galán Volcanic System (Argentina): The Role of Magmatism as a Source for Li-Bearing Brine Deposits

Abstract

Lithium-rich brines in South America’s Li triangle host Earth’s largest Li reserves, crucial for the global energy transition. Although Cenozoic magmatism near salars in the Li triangle often is considered as a major potential Li source, there is limited characterization of Li behavior in these magmatic systems. To address this, we present the first detailed Li study of the voluminous ignimbrites within the Cerro Galán volcanic system, a potential Li source for the Salar del Hombre Muerto, which is actively producing Li for batteries. Although most Cerro Galán volcanic system units exhibit normal Li concentrations in groundmass glass (30–50 ppm) relative to rhyolitic centers globally, the ~630-km3 Cerro Galán ignimbrite contains glass with significantly higher Li contents (>90 ppm), reflecting increased melt differentiation. Throughout the volcanic system, plagioclase and quartz display varied Li contents influenced by syneruptive degassing, and additionally for plagioclase, posteruptive modifications. Biotites in the Cerro Galán volcanic system are magmatic and range from 1 to 689 ppm Li, with biotites returning low analytical totals (low total biotites) enriched in Li, Pb, and Cs, consistent with the entrapment of an Li-rich magmatic volatile phase during biotite crystallization. Such a magmatic volatile phase is isotopically light (δ7Li as low as –23‰) and may reach 10,000 ppm Li according to binary mixing modeling. We propose that large magmatic centers, like the Cerro Galán volcanic system, may sustain exsolution of such a magmatic volatile phase and its transport through caldera-hosted hydrothermal systems. When such volcanic centers overlap with closed-basin watershed, magmatic Li-rich fluids could be selectively transported into basins, representing a source for Li-bearing salars, such as in the Salar del Hombre Muerto situated near the Cerro Galán volcanic system.