Geochemical classification of oxidized Mn-ores from Úrkút (W Hungary) and its consequences for ore genesis

Abstract Analytical data of primary oxidized manganese ores were processed by statistical methods. Six hundred and twenty-one samples were measured (Mn, Fe, Si, and P); thus 2,426 assay data were available. The statistical pointer numbers, the distribution of the elements and the results of the correlational analysis showed the heterogeneity of the ore samples where the measured elements correlated weakly. The samples were grouped by the 4 elements to decrease the heterogeneity and the concentration of elements, and these relationships in the groups were examined. Very few and weak relationships were proved in the groups by the results of the correlational and regressional analysis. It is possible that not the heterogeneity of the samples but one or more syngenetic or postgenetic processes caused the absence of relationships. The multivariate statistical processes (principal component analysis, discriminance analysis) allow the determination of the background factors, namely which are the effects that produced the ore. Consequently — with high probability — the ore was formed by two processes. The most likely are hydrothermal and microbial ones (on the basis of geochemical results), but supergene enrichment processes can also be taken into consideration. Both hydrothermal and microbial processes played a significant role in the majority of the samples (81%), which are the ferruginous manganese ores. In the smaller group of samples (19%) the hydrothermal process predominates but the microbial one is also influential, namely for the low iron-bearing manganese ores of excellent quality

Mössbauer characterization of microbially mediated iron and manganese ores of variable geological ages

A combination of various techniques was applied to investigate the mineralogy of the Neoproterozoic Urucum iron and manganese deposit (Brazil) and Carboniferous and Permian manganese carbonate deposits (China). The examined deposits exhibited signs of microbial mediation from Fe and Mn bacteria and cyanobacteria. The studied samples showed diversity in their composition and particle size. Probes from Urucum deposit revealed that the rocks consist mainly of hematite, showing Mn substitution which reflects the oxidation of Mn on the active surface of Fe-rich biomat. Nanominerals occurring in significant concentration also supported the microbial contribution to the formation of these ores. Representative samples of Neoproterozoic and Permian deposits showed considerable amount of mixed carbonates with variable composition. 57Fe Mössbauer spectroscopy analysis supported by X-ray diffraction and transmission electron microscopy data provided a detailed characterization of Fe-rich mineral phases of the samples, including metal ratio outlooks, particle size dimension and presence and type of impurities. Integrity and high resolution of the methods allowed to determine new features of the samples reflecting important signatures of microbial activity revealing the biogeochemistry of the biomat formation