Microbial metallogenesis of Cryogenian manganese ore deposits in South China

Abstract

The Datangpo Formation manganese deposits (DFMnD) in South China formed during the interglacial stage between the Sturtian and Marinoan glaciations of the Cryogenian period. These black shale-hosted deposits are composed of massive Mncarbonates with microscopic laminae/laminations and cherty veins. To date, it has been thought that the DFMnD formed through inorganic processes, which were controlled by redox changes in the post-Sturtian Nanhua Rift Basin, South China. However, in this study, systematic petrographic, mineralogical, and geochemical analyses indicate a microbially mediated origin of the Mn ore deposits. Mineralized microbial woven micro-textures (observed at the μm scale) and microbial fossils are common in the laminated Mn-carbonate ores. We infer that microbial enzyme activity formed poorly crystallized Mn oxide/hydroxides and carbonaceous material, which 2 transformed to rhodochrosite, kutnohorite, ankerite/dolomite, framboidal pyrite, and apatite via diagenesis. Some micro-scale quartz and K-feldspar may be detrital but most appears to have formed during diagenesis or through hydrothermal activity. A micro-mineralogical profile determined by 2500 spectra via high-resolution in situ micro-Raman spectroscopy also revealed cyclic laminations of Ca-rhodochrosite as microbialite (ankerite/dolomite) and quartz, indicating a mineralized biomat system. Ca-rhodochrosite transformed to kutnohorite under elevated temperatures, as indicated by the maturation level of organic matter (determined via Raman spectroscopy). Alternating micro-laminae denote cyclic changes in microbial groups (Mn-and Fe-oxidizing microbes versus cyanobacteria) during the formation of the Mn ore deposits. Our proposed model for the microbially mediated metallogenesis of Mn-carbonate deposits begins with enzymatic multi-copper oxidase processes associated with autotrophic microbial activity under obligatory oxic conditions, which results in the precipitation of Mn bio-oxides. Following their burial in organic-rich sediments, the Mn(IV) oxides and hydroxides are reduced, producing soluble Mn(II) via processes mediated by heterotrophic microbes under suboxic conditions, which in turn form the Mn-carbonates. This microbial metallogenesis model for the Cryogenian DFMnD in South China is similar to that proposed for the Jurassic Úrkút Mn deposit in Hungary, indicating that a two-step microbially mediated process of Mn ore formation might be common throughout geological history.

Nucleation and stabilization of Eocene dolomite in evaporative lacustrine deposits from central Tibetan plateau

“…The silicates (mainly quartz and feldspar) are characterized by the intense absorbance bands of Si-O stretch at ca 1000 cm À1 . The prominent CH2 and CH3 infrared stretching bands (2850 to 3000 cm À1 ) in the strong luminescence film can be identified as the typical peak of aliphatic organic moieties (Washburn & Birdwell, 2013;Yu et al, 2019).…”

Microbially Mediated Ore-Forming Processes and Cell Mineralization

“…This microbial microtexture is a basic feature of all of the samples, in transmitted as well as reflective light. In all thin sections, adequately high-resolution OM supports a series of mineralized biomat microstructures and mineralized microbially produced textures as the main constituents, which are similar to the Hungarian Úrkút and Chinese Datangpo deposits (Polgári et al, 2012b; Yu et al, 2019). Thus, morphological features suggest that this is a mineralized biomat, which shows the structure of the former microorganism cells.…”

“…The method was also used to estimate the time necessary for melting after the last glacial period in the Neoproterozoic Otavi Formation in Namibia, where climatic changes responsible for the melting were studied in the iron-biomat layers (Gyollai et al, 2015). The model was also used successfully in a Neoproterozoic Chinese black shale-hosted Mn carbonate deposit of the Datangpo area (Yu et al, 2019), and research is continuing on the Neoproterozoic Brazilian Urucum Mn and Fe oxide deposit (Banded Iron Formation). The Úrkút Model represents an important complex biomineralization methodology in international research.…”

“…In this paper, we provide a comparison of results published in several case studies in three deposits including black shale-hosted Mn carbonate deposits of Neoproterozoic Datangpo, China (Yu et al, 2019), the Jurassic Úrkút manganese occurrences, Hungary (Polgári et al, 2012a, b, 2013, 2016a, 2016b, 2017), and the Neoproterozoic jaspilite and ironstone-hosted basically Mn oxide deposit, Urucum, Brazil (Biondi and Lopez, 2017; Biondi et al, 2019; Figure 1). The case studies are supplemented by a detailed high resolution study on the Brazilian Urucum Mn-1 bed, to characterize fine scale diagenetic element-mineral transformations supporting the important role of decomposition and complex mineralization of cell and EPS material.…”

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

“…[6,29]. 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].…”