Origin of the Jadar Volcano-Sedimentary Li-B Deposit, Serbia

Abstract

Abstract: The Jadar deposit (Serbia) is a unique end member of the volcano-sedimentary Li deposit class, where the main ore mineral is jadarite (LiNaSiB3O7(OH)), to date only recorded at the Jadar locality. We provide the first account of the features of the Jadar deposit based on the study of drill hole material, complemented by petrographic analysis, whole-rock, and isotopic geochemistry. The Li-B mineralization is hosted by sediments interlayered with tuffs that were deposited in a fault-bounded lacustrine basin. Mineralization processes initially involved alteration of volcanic glass through near-neutral and heated meteoric fluids, which resulted in the formation of hectorite. Lithium clays were later overprinted by higher-pH brines, which underwent significant evaporation, combined with conditions of Na+ and SiO2(aq) saturation, resulting in formation of siliceous gels that were the precursors to jadarite formation and extensive zeolitization of the intrabasinal sediments. Formation of jadarite occurred in two stages: (1) early diagenesis accompanied by zeolitization and precipitation of primary dolomite, which resulted in the sediment-hosted Li mineralization, (2) late remobilization of Li(B-Na)–saturated fluids, leading to formation of epigenetic jadarite-albite infills of fractured rocks. Isotopic geochemistry combined with mineral chemistry proxies indicate that early mineralizing processes were largely dominated by diagenetic fluids that experienced a thermal influence from the coeval cooling of the Miocene S-type granite member of the nearby Cer Mountain Complex. Late thermal maturation of organic matter then resulted in acidic fluids that dissolved the early ore assemblage and led to formation of late diagenetic lithiophosphate and low-Na borates.