Indicator role of rare and rare-earth elements of the Northwest manganese ore occurrence (South Africa) in the genetic model of supergene manganese deposits

Abstract

The authors analyzed the content of a number of rare and rare-earth elements in the rocks of the Northwest manganese ore occurrence, confined to the Neoarchean dolomites of the Malmani series of the Transvaal Basin. 30 samples of manganese ores and host rocks were analyzed by ICP-MS and XRF methods. Average values of Post-Archean Australian Shale (PAAS) were used as the geochemical standard for data calculation and normalizati on. The concentrations of elements normalized on PAAS reveal the LREE anomal y in manganese ores. Positive Ce and negative Y–anomalies indicate the hydro-genetical t ype of sedimentation of ore minerals from manganese-bearing aqueous solutions. This is consistent with the ratios of the elements: Ce and Y SN/Ho SN, Ce and Nd, Fe – Mn – (Co + Ni + Cu) × 10. A clear correlation between the contents of rare-earth elements in manganese nodules and the underlying Malmani dolomites indicates their close geneti c relationship. Negative Ce and positive Y–anomalies in manganese wad minerals indicate differences in the conditions of their formati on. The manganese wad formed earlier than the rest of the ore with the active participation of mi croorganisms.