The Role of Organic Matter on Uranium Precipitation in Zoovch Ovoo, Mongolia

Rallakis, Dimitrios; Michels, Raymond; Brouand, Marc; Parize, Olivier; Cathelineau, ‪Michel

doi:10.3390/min9050310

Cited by 30 publications

(21 citation statements)

References 42 publications

(58 reference statements)

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“…In addition, the maceral composition is an important factor in evaluating the coal seam quality. Precise identification of the maceral components has a multitude of uses across various industry sectors, including hydrogenation, combustion, carbonization and gasification [2][3][4].…”

Section: Background and Motivationmentioning

confidence: 99%

Intelligent Identification of Maceral Components of Coal Based on Image Segmentation and Classification

et al. 2019

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Featured Application: Maceral Analysis; Coal Processing.Abstract: An intelligent analytical technique which is able to accurately identify maceral components is highly desired in the fields of mining and geology. However, currently available methods based on fixed-size window neglect the shape information, and thus do not work in identifying maceral composition from one entire photomicrograph. To address these concerns, we propose a novel Maceral Identification strategy based on image Segmentation and Classification (MISC). Considering the complex and heterogeneous nature of coal, a two-level coarse-to-fine clustering method based on K-means is employed to divide microscopic images into a sequence of regions with similar attributes (i.e., binder, vitrinite, liptinite and inertinite). Furthermore, comprehensive features along with random forest are utilized to automatically classify binder and seven types of maceral components, including vitrinite, fusinite, semifusinite, cutinite, sporinite, inertodetrinite and micrinite. Evaluations on 39 microscopic images show that the proposed method achieves the state-of-the-art accuracy of 90.44% and serves as the baseline for future research on maceral analysis. In addition, to support the decisions of petrologists during maceral analysis, we developed a standalone software, which is freely available at https:/github.com/GuyooGu/MISC-Master.

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Section: Background and Motivationmentioning

confidence: 99%

Intelligent Identification of Maceral Components of Coal Based on Image Segmentation and Classification

et al. 2019

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“…Vitrinite reflectance measurements in the Zoovch Ovoo sands led to %Rr=0.302±0.02 (Rallakis et al, 2019). Thus, it may be concluded that the highest temperature experienced by the dolomite cements can be estimated at about 40°C.…”

Section: Dolomite Burial Diagenesismentioning

confidence: 88%

Dolomite cements in Cenomanian continental sand deposits: Time evolution and significance (Zoovch Ovoo U-deposit, East Gobi Basin, Mongolia)

Rallakis

Michels

Brouand

et al. 2020

Sedimentary Geology

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Shallow buried unconsolidated sands generally provide very little information about diagenesis as most detrital minerals remain unchanged. However, in rare cases carbonate cemented nodules or sandstone layers may occur inside unconsolidated series. These cements could help to reconstruct the chronology of events from early to late phase stages of diagenesis. The Late Cretaceous sequence of the Zoovch Ovoo depocenter in East Gobi Basin is represented by 600m of clastic deposits. The 60-80m of Cenomanian unconsolidated sands and clays, deposited in alluvial-deltaic to lacustrine settings, compose the upper part of the post-rift medium-grained siliciclastic reservoir, the Sainshand Formation which hosts uranium roll-front systems. Dolomite cemented sandstone layers with 10-20cm thickness occur among the unconsolidated rock facies. Calcite is absent from this formation, but is present only in the overlying, also outcropping, Bayanshiree Formation. Samples from the dolomite cemented sandstone layers were investigated in detail to uncover their origin and diagenetic history. Four dolomite cement types were recognized that indicate recrystallization episodes and were classified based on the size and shape of the crystals, namely: (i) microcrystalline dolomite frequently associated with siderite, (ii) euhedral dolomite also associated with siderite, (iii) subhedral dolomite and (iv) finally anhedral dolomite. Their REE content varies significantly from dolomite I to IV, in particular by a strong depletion in LREE about 30 times. The contrasted precipitation of calcite in Bayanshiree and dolomite cements in Sainshand formations could be attributed to different Mg/Ca ratio of the circulation fluids in the two aquifers. Both carbonates display however rather homogenous oxygen and carbon isotopic compositions for δ 18 O (-10±1‰ V-PDB) and δ 13 C (-7±1‰ V-PDB). The δ 18 O values are interpreted as inherited from typical meteoric waters quite close to present day waters. The δ 13 C values indicate a mixed source of both organic and mineral carbon. All data taken into account, a full paragenetic succession was constructed. It includes the evolution of dolomite during burial diagenesis and the effects of the oxidizing roll-front uranium rich waters in the system. The latter induces partial dissolution followed by precipitation of a dolomite phase typical of roll-front zones. Carbonate cements can be thus considered as the best and rather unique geochemical indicators for the recognition of a burial history framework to paleofluid circulations and fluid-rock interactions in these intracontinental series of unconsolidated sands.

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“…In this tectonic framework, the burial history of the regional area of Zoovch Ovoo as well as the geothermal gradient (4.5°C/100m) were based on Graham et al (2001), Prost (2004), Rallakis et al (2019;.…”

Section: Stratigraphy Of the East Gobi Basinmentioning

confidence: 99%

“…The Central Asia Uraniferous Province, one of the most strategic areas in the world for uranium reserves, extends from Kazakhstan to the West towards the Transbaikal region to the East (Dahlkamp, 2009;Le Goux et al, 2015;IAEA 2018). Significant roll-front deposits exist all over this region, examples include the Chu-sarysu and Syrdarya basins in Kazakhstan (Aubakirov, 1998;Petrov 1998;Jaireth et al, 2008;Munara, 2012;Lach et al, 2015), the Songliao, Ordos and Erlian basins in China (Huang Xian-Fang et al, 2005;Min et al, 2005;Cai et al, 2007;Bonnetti et al, 2015a,b;Cao et al, 2016;Akhtar et al, 2017;Bonnetti et al, 2017;Jiao et al, 2018;Zhang et al, 2018;Yue et al, 2019) and the Unegt and Zuunbayan basins in Mongolia (Le Goux et al, 2015;Grizard et al, 2018;Boissezon et al, 2020;Rallakis et al, 2019;.…”

Section: Introductionmentioning

confidence: 99%

Conditions for uranium biomineralization during the formation of the Zoovch Ovoo roll-front-type uranium deposit in East Gobi Basin, Mongolia

Rallakis

Michels

Cathelineau

et al. 2021

Ore Geology Reviews

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The Zoovch Ovoo uranium roll-front-type deposit is hosted in the Sainshand Formation, a Late Cretaceous siliciclastic reservoir, which constitutes the upper part of the post-rift infilling of the Mesozoic East Gobi Basin in SE Mongolia. The Sainshand Formation consists of unconsolidated medium-grained sand, silt and clay intervals deposited in fluvial-lacustrine settings. The uranium deposit is confined within a 60-80 m thick siliciclastic sequence inside aquifer-driven systems. The overall system experienced shallow burial and was never subjected to temperatures higher than 40°C. This study proposes a comprehensive metallogenic model for this uranium deposit. Sedimentological and mineralogical observations from drill core samples to the microscopic scale (optical and Scanning Electron Microscopy) together with in situ geochemistry of late-formed phases (Laser Ablation-Inductively Coupled Plasma Mass Spectrometry, Electron Probe Microanalysis, Fourier Transform-Infrared Spectroscopy) were considered for the reconstruction of the main stages of U trapping.In the mineralized zone, the uranium ore is expressed as Ca-enriched uraninite (UO 2 ) and less commonly as Ca-enriched phospho-coffinite (U, P)SiO 4 . Trapping mechanisms include i) complexation (i.e. uranyl-carboxyl complexes), ii) adsorption on organic or clay particles) and iii) reduction by pyrite and by bacterial activity to amorphous uraninite. In all cases, the organic matter plays either the role of trap for uranium or nutrient for bacteria that can trap uranium through their metabolism. The shallow burial diagenesis conditions do not allow direct reduction of U(VI) by organic carbon. The δ 34 S values of the iron disulfide are very diverse, fluctuating in extreme cases between -50 to +50‰, with an average δ 34 S value for framboidal pyrite at 2‰, and -20‰ for euhedral pyrite. The positive and negative values reflect close versus open fractionation systems, while bacterial sulphate reduction (BSR) is active during the whole diagenetic history of the deposit as an essential source of reduced sulfur. Therefore, using detrital organic matter as a carbon source, microorganisms play a significant role in uranium trapping, either as a direct reducing agent for uranium or pyrite formation, which will trap uranium redox driven epigenetic processes.

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The Role of Organic Matter on Uranium Precipitation in Zoovch Ovoo, Mongolia

Cited by 30 publications

References 42 publications

Intelligent Identification of Maceral Components of Coal Based on Image Segmentation and Classification

Intelligent Identification of Maceral Components of Coal Based on Image Segmentation and Classification

Dolomite cements in Cenomanian continental sand deposits: Time evolution and significance (Zoovch Ovoo U-deposit, East Gobi Basin, Mongolia)

Conditions for uranium biomineralization during the formation of the Zoovch Ovoo roll-front-type uranium deposit in East Gobi Basin, Mongolia

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