RESUMEN

Samples of rock from the Tomtor Nb - REE (rare-earth elements) deposit (Russia) have been investigated by Raman micro-spectroscopy using visible 532 nm wavelength excitation. Raman spectra of different samples of this rock confirm their composition as calcites and other carbonates such as rhodochrosite, and mixed solid solution phases (Ca, Mn, Fe, Mg, Ba, Sr, REE)(CO3). An association between cyanobacteria and the apatite crystals has been noted Cyanobacteria exhibited Raman modes at 1520-1517 cm-1 located in the double bonds of the central part of the polyene chain of carotenoids. A slight shift of this mode in the apatite-containing samples are dependent upon the compositions of carotenoids, the ratio of the rare earth elements adsorbed by cyanobacteria as well as their interaction with the environment. Laser-induced photoluminescence of REE and Mn+2, obtained as an analytical artifact in the Raman spectra, has been observed in most cases with significant spectral intensity. The luminescence emission of Mn 2+, Sm3+, Eu 3+, Pr3+, Ho3+, Er 3+ in the spectra of the apatite-containing samples obtained with 532 nm excitation can be attributed both to apatite and to other mineral phases with a low concentration which contain these elemental ions. The results obtained in this study allowed us to confirm that the biogenic presence of the cyanobacterial mat had a significant impact on the formation of the unique Nb-REE Tomtor deposit.

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RESUMEN

Natural organic matter (NOM) within the dispersion train of Novo-Ursk tailings (Salair Ridge, Kemerovo region, Russia) is composed of remnant sedge peat mounds and is located either on the surface or is buried under cyanide wastes. The organic material interacts with AMD and with the wastes, which leaves imprint on its composition. This interaction produces geochemical anomalies (g/t: 1582 Cu, 41,300 Zn, 6060 Se, 11,700 Hg, 114-155 Au, 534 Ag, 416 I). The contents of elements depend on Fe in three groups of NOM samples that contain <10 wt% Fe (group I), 10-22 wt% Fe (group II), and >22 wt% Fe (group III). NOM with higher Fe enrichment contains less Cu, Zn, Se, Hg, Ag and I, as well as Cd, Ba, Sr and Rb, Y, Zr, Nb, Mo, Sn, Sb, and Te but more As. Yet, gold may reach high concentrations in NOM with any Fe contents. Accumulation of elements by NOM during its prolonged interaction with wastes and AMD is maintained by physical, chemical, biochemical, and mineralogical processes. They are, respectively, migration of waters controlled by permeability of material in the dispersion train depending on its grain sizes and by AMD flow direction; oxidative dissolution of sulfides, complexing, and adsorption on organic matter and Fe(III) hydroxides; microbial mediation; and secondary mineralization. The chemistry of waters interacting with NOM at the time of its deposition can be reconstructed with regard to several factors, including microbial mediation. Namely, local geochemical anomalies with ultrahigh element concentrations may arise because microorganisms can immobilize Hg to make it less toxic; sulfate-reducing bacteria can maintain precipitation of Zn, Cu, and Cd sulfides; microbial activity can mediate redistribution of elements between clastic and organic materials, etc. The inferred inheritance of AMD geochemical signatures by NOM has implications for the conditions and mechanisms of element accumulation.

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RESUMEN

Migration and redistribution of elements during prolonged interaction of cyanide wastes with the underlying natural organic-bearing material have been studied in two ~40cm deep cores that sample primary ores and their weathering profile (wastes I and II, respectively) in the dispersion train of gold-bearing sulfide tailings in Siberia. Analytical results of SR-XRF, whole-rock XRF, AAS, CHNS, and SEM measurements of core samples show high K, Sr, Ti, and Fe enrichments and correlation of P2O5 and Mn with LOI and Corg. Organic material interlayered or mixed with the wastes accumulates Cu, Zn, Se, Cd, Ag, Au, and Hg. The peat that contacts wastes II bears up to 3wt.% Zn, 1000g/t Se, 100g/t Cd, and 8000g/t Hg. New phases of Zn and Hg sulfides and Hg selenides occur as abundant sheaths over bacterial cells suggesting microbial mediation in sorption of elements. Organic-bearing material in the cores contains 10-30g/t Au in 2-5cm thick intervals, both within and outside the intervals rich in sulfides and selenides. Most of gold is invisible but reaches 345g/t and forms 50nm to 1.5µm Au0 particles in a thin 2-3cm interval of organic remnants mixed with wastes I. Vertical and lateral infiltration of AMD waters in peat and oxidative dissolution of wastes within the dispersion train of the Ursk tailings lead to redistribution of elements and their accumulation by combined physical (material's permeability, direction AMD), chemical (complexing, sorption by organic matter and Fe(III) hydroxides) and biochemical (metabolism of sulfate-reducing bacteria) processes. The accumulated elements form secondary sulfates, and Hg and Zn selenides. The results provide insights into accumulation of elements in the early history of coal and black shale deposits and have implications for remediation of polluted areas and for secondary enrichment technologies.