Volcano-Sedimentary Deposits: Overview of an Emerging Type of Lithium Resource

Abstract Volcano-sedimentary (VS) deposits represent a relatively poorly studied and still underdeveloped type of Li resource. These deposits consist of mixed volcanic-sedimentary successions deposited in closed basins developed in felsic magmatic provinces. The Li ore in VS systems includes complex mineralogical assemblages dominated by phyllosilicates, borosilicates, and phosphates. In this paper we review the geologic features of VS Li deposits with the goal of providing a generalized deposit model, as well as an updated classification scheme, which can be used to aid a better understanding of this unconventional ore type and inform mineral exploration of VS-fertile geologic terranes. We focus on several key characteristics of VS deposits, including the following: (1) tectonic and climatic settings of VS-endowed districts, (2) geochemical footprint of Li-fertile magmatic rocks found in VS deposits, (3) mechanisms of transport and enrichment of Li from the primary igneous rocks to the critical zone, (4) physical and structural features of the geologic trap, (5) triggers for the Li deposition in the secondary ore assemblages, and (6) preservation and aging behavior of VS deposits, with implications for mineral exploration. These aspects are discussed based on published available data and also by presenting new observations on representative VS deposits from the western United States, eastern Europe, and elsewhere.