Specific Features of the Rare Earth Element Distribution in Rocks and Ores of the Porozhinsk Manganese Deposit (Yenisei Ridge, Krasnoyarsk Region)

The rare earth element (REE) composition of host rocks (dolomites, Neoproterozoic Pod’’emsk Formation) and manganese ores (manganese oxides and carbonates of supergene zone) are studied. The Pod’’emsk Formation is subdivided into the lower and upper subformations. The upper Pod”emsk subformation is characterized by the elevated manganese content and considered to be a Mn source for supergene ores of the deposit. Dolomites of the lower Pod’’emsk subformation show no pronounced cerium anomalies ( ). They were formed in the absence or low concentrations of free oxygen in seawater. It is also probable that these dolomites experienced postsedimentary transformations, which could have resulted in the REE redistribution. Dolomites of the upper Pod’’emsk subformation from a karst depression (positive Ce/*Ce NASC anomaly) were formed under anoxic conditions, in a hydrodynamically weakly active shallow-marine environment. The elevated cerium concentrations in the dolomites could be also associated with the introduction of oxidized Ce into the sedimentation basin with river colloids. The positive europium anomaly in the dolomites of the Pod’’emsk Formation ( = 1.22–2.16) could be related to the europium influx with subaquatic hydrothermal solutions (probably enriched in iron and manganese) or to the supply of europium with river runoff. Manganese was likely supplied in the Late Proterozoic sedimentation basin during the dolomite accumulation together with hydrothermal solutions and continental ablation. Manganese oxide ores show a sharp enrichment in HREE (by an order of magnitude), which likely occurred at the late (acidic) stage of supergene weathering as a result of LREE removal and HREE and yttrium retention in the weathering crust.