Microbially Mediated Ore-Forming Processes and Cell Mineralization

Abstract

Sedimentary black shale-hosted manganese carbonate and oxide ores were studied by high-resolution in situ detailed optical and cathodoluminescence microscopy, Raman spectroscopy, and FTIR spectroscopy to determine microbial contribution in metallogenesis. This study of the Urucum Mn deposit in Brazil is included as a case study for microbially mediated ore-forming processes. The results were compared and interpreted in a comparative way, and the data were elaborated by a complex, structural hierarchical method. The first syngenetic products of microbial enzymatic oxidation were ferrihydrite and lepidocrocite on the Fe side, and vernadite, todorokite, birnessite, and manganite on the Mn side, formed under obligatory oxic (Mn) and suboxic (Fe) conditions and close to neutral pH. Fe- and Mn-oxidizing bacteria played a basic role in metallogenesis based on microtextural features, bioindicator minerals, and embedded variable organic matter. Trace element content is determined by source of elements and microbial activity. The present Urucum (Brazil), Datangpo (China), and Úrkút (Hungary) deposits are the result of complex diagenetic processes, which include the decomposition and mineralization of cell and extracellular polymeric substance (EPS) of Fe and Mn bacteria and cyanobacteria. Heterotrophic cell colonies activated randomly in the microbialite sediment after burial in suboxic neutral/alkaline conditions, forming Mn carbonates and variable cation-bearing oxides side by side with lithification and stabilization of minerals. Deposits of variable geological ages and geographical occurrences show strong similarities and indicate two-step microbial metallogenesis: a primary chemolithoautotrophic, and a diagenetic heterotrophic microbial cycle, influenced strongly by mineralization of cells and EPSs. These processes perform a basic role in controlling major and trace element distribution in sedimentary environments on a global level and place biogeochemical constraints on the element content of natural waters, precipitation of minerals, and water contaminants.

Precipitation of Mn Oxides in Quaternary Microbially Induced Sedimentary Structures (MISS), Cape Vani Paleo-Hydrothermal Vent Field, Milos, Greece

“…The emphasis of this paper is to decipher the link between Mn oxide formation, low-T hydrothermal fluid flow, and microbially induced sedimentary structures (MISS) from Early Quaternary shallow-marine/tidal-flat siliciclastic sandstones/sandy tuffs of the CVSB. To the best of our knowledge, Mn oxide mineralization preserved in the siliciclastic sedimentary rock record has never been spatiotemporally and genetically linked to the growth and preservation of MISS, especially not under sunlit low-temperature hydrothermal metal exhalation conditions [2,3,[5][6][7]29].…”

“…Despite the inference that Mn oxide formation is largely a biomineralization process, identifying geobiological evidence in the marine sedimentary record that are conducive and favorable for the formation of Mn oxide ores under conditions relevant to low-temperature hydrothermalism remains an unsettled area of Mn biometallogenesis research [2,3,29]. Here we report potentially biogenic hydrothermal Mn oxide mineralization hosted by microbially induced sedimentary structures (MISS) in a paleohydrothermal vent field associated with Mn-ore on Milos Island, Greece.…”

“…The link between geobiology and economic geology, i.e., the role of microbial activity on the formation of mineral ore deposits, is a relatively new topic [1][2][3]. One of the best examples is the microbial precipitation of Mn minerals and the formation of economic sediment-hosted Mn ore deposits [2,[4][5][6].…”

“…Most recent publications on Mn biometallogenesis deal with Mn-carbonate (±Mn-silicate, Mn oxide) deposits ranging in age from Precambrian to Mesozoic, and the role microbes play in their genesis [2,3,6,[30][31][32][33][34][35][36][37][38]. Manganese enrichment in black shale-hosted Mn-carbonate deposits is thought to start with microbially mediated oxidation of hydrothermally sourced Mn 2+ (aq) to solid Mn 3+/4+ oxide proto-ore, subsequently reduced by microbial heterotrophic oxidation of organic carbon during early diagenesis resulting in Mn carbonate ore [2,3,[5][6][7]29,35]. A biogeochemical origin has been assigned to the Cretaceous sediment-hosted Groote Eylandt deposit, which has both carbonate-and oxide-dominated orebodies [39,40].…”