Catagenetic type of manganese ores: REE and isotope (δ¹³C, δ¹⁸O) geochemical features (on the example of the Usa deposit, Russia)

Chemical (REE and major elements) and isotope (δ¹³C, δ¹⁸O) composition of carbonate manganese ores and manganese-bearing carbonates of the Usa deposit (Siberia, Russia) were studied. Received data on the composition of REE exhibit both the distinct negative (Ce/Ce*_PAAS < 1) and positive (Ce/Ce*_PAAS˃1) cerium anomalies and the positive Eu-anomaly (Eu/Eu*_PAAS˃1). Negative Eu-anomalies are not observed. The contents of Mn, Fe, REE, and Ce-anomalies show a positive correlation with each other. Ce-anomalies and the amount of manganese and REE in relation to the carbon isotope composition (δ¹³C) show a negative relationship and indicate that oxidized carbon of organic matter played an important role in the concentration of manganese and REE in manganese ores. The chemical and isotope composition of examined rocks indicates on secondary formation of Mn-ores. Two major phases and sources are distinguished in the ore-forming process characterized by different chemical (REE and ore elements) and isotope composition: (i) high-grade manganese ores (with high contents of REE and light carbon isotope composition) and (ii) low-grade manganese ores (with low contents of REE and heavy carbon isotope composition).