Trace and rare earth elements contents of a Sardinian sedimentary Mn-rich deposit: preliminary results.

Mn oxides are important scavengers of trace elements from waters. They often form deposits with high metals concentrations that sometimes have economic significance. Within a thick sedimentary deposits of northern Sardinia, Mn oxide mineralization was found as both matrix and coatings on clasts of a conglomeratic deposit, and subrounded nodules in residual clays. Lithiophorite and birnessite are the sole Mn phases that are also accompanied by variable amounts of Fe oxides and hydroxides, clay minerals, and phyllosilicates. Chemical analysis of the studied samples revealed high concentrations of most of trace metals (Co, Ni, Zn, Cu, Ba, Y, U and Pb) and all rare earth elements (REE). The latter were used to provide the first hypothesis regarding environmental conditions and chemical processes determining the precipitation of Mn oxides.