Mineralogical and chemical transformations of volcanic ash and rocks through interaction with water: insights into the genesis of lithium deposits in Puna Brines

Abstract

The release of lithium (Li) from volcanogenic material is a key process in the formation of Li-rich brines in the Central Andes. Mineralogical, geochemical, and isotopic analyses, together with leaching experiments at room temperature and 80 °C on ignimbrite and volcanic ash from the Olaroz basin (Puna Plateau, Argentina), were conducted to identify the Libearing phases involved in Li mobilization to water. The weathering indexes indicate limited chemical weathering under arid conditions. Accordingly, negative and slightly positive δ⁷Li values (− 7 to + 0.7‰) of the studied volcanic material suggest isotopic fractionation during magmatic or syn-eruptive stages rather than later low-temperature weathering. Leaching experiments with ultrapure water at room temperature reveal a multistage Li-release process: an initial rapid dissolution of soluble surface phases, followed by slower incongruent dissolution of Li-bearing aluminosilicates, such as biotite and R0-type illite–smectite (I/S) clays coating glass shards, particularly within the clay-size fraction, and a subsequent stage associated with the hydrolysis of previously unexposed volcanic glass. At 80 °C, Li release is enhanced, except in samples where newly formed illite-rich R1-type interstratified phases weakly retain Li through adsorption or partial structural incorporation, moderating its release. Although volcanic ash releases less Li in absolute terms, both ignimbrite and volcanic ash, exhibit similar release patterns controlled by the same mineral phases. The results highlight a transient stage in the Li cycle, where part of the Li released from primary sources is temporarily retained in secondary clay minerals before entering the hydrological system.