DEPOSITS OF CRITICAL METALS (LI, NI AND CO) ASSOCIATED WITH CLAY HORIZONS

Abstract

Lithium, Ni and Co have been classified as critical metals for the EU, due to their economic importance and risk for their supply. Notwithstanding their different geochemical affinities, with Ni and Co being compatible elements and Li an incompatible element, their occurrences converge to one common denominator: they are all hosted also in clay horizons often forming deposits of economic importance. Yet, these clay horizons have different origins, although all these critical elements are hosted mainly, but not exclusively, in trioctahedral smectite. Lithium-B deposits associated with clayey rocks belong to the volcano-sedimentary type and form in alkaline lake environments characterized by intense evaporation. They are quite common in the Balkan Peninsula forming the Miocene Li-B Western Balkan lithium‑boron metallogenic zone. With a few exceptions, the Ni-Co deposits of SE Europe are not laterites sensu stricto (s.s.), but transported lateritic mantles that were deposited mainly within carstic cavities at a marine environment. Nickel and Co are hosted mainly in Mg-phyllosilicates and to a lesser degree in goethite. Based on their mineralogical characteristics the Fe-Ni (± Co) sedimentary ores of SE Europe represent a mixture of the three types of Ni-lateritic deposits, thus reflecting a complex mode of origin and their mineralogy indicates formation in non-equilibrium conditions.