Uranium deposits of Franceville basin (Gabon): Role of organic matter and oil cracking on uranium mineralization

Kaolinite is a common mineral found in most Chinese sandstone-hosted uranium deposits. It occurs particularly in coal-bearing clastic rocks in northwest China, such as the uranium deposits in the Yili Basin, which is well known for hosting several large-scale roll-front uranium deposits. Previous studies have provided limited information on the origin of kaolinization and its role in the uranium mineralization. This study uses gas hydrocarbon, fluid inclusions, O and H isotope analysis, and scanning electron microscopy observations to investigate the formation of kaolinite in ore-hosting rocks from the Mengqiguer uranium deposit in the southern margin of the Yili Basin and to determine its role in the uranium mineralization. Results suggest that kaolinization is intense in the coal- and ore-bearing clastic rocks and that it is related to leaching of feldspar by acidic fluids. Vermicular kaolinite was formed by hydrocarbon-bearing fluid generated from coal and carbonaceous mudstone during a shallow-burial diagenetic stage at low homogenization temperatures ranging from 69 to 78°C and at relatively high salinities of 7.6−11.0 wt% NaCleq. Consequently, silicate minerals (such as feldspar) were leached and created secondary pores that hosted the subsequently formed uranium minerals. In contrast, micritic kaolinite was formed by infiltration of meteoric fluid enriched in U and O2 at low homogenization temperatures of 51−63°C and low salinities of 1.2−3.7 wt% NaCleq. U6+ was sorbed by the micritic kaolinite through cation exchange, forming a U-bearing kaolinite complex; it was also reduced by pyrite and carbon detrital, thereby precipitating at the acidic oxidation front. The results of this study confirm that intense kaolinization is closely related to uranium mineralization in coal-bearing clastic rocks.

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Structural Controls of Uranium Mineralization in the Basement of the Athabasca Basin, Saskatchewan, Canada

Geofluids ◽

10.1155/2021/3853468 ◽

2021 ◽

Vol 2021 ◽

pp. 1-30

Author(s):

Antonio Benedicto ◽

Maher Abdelrazek ◽

Patrick Ledru ◽

Cameron MacKay ◽

Dwayne Kinar

Keyword(s):

Regional Scale ◽

Structural Data ◽

Shear Zones ◽

Uranium Mineralization ◽

Uranium Deposits ◽

Athabasca Basin ◽

Structural Controls ◽

The Right ◽

Drill Holes

The occurrence of unconformity-related uranium mineralization requires the combination of three components: fluids with the right composition, geochemical traps with the right agents that produce precipitation, and structural traps with the right geometry. In the Athabasca Basin unconformity-related uranium deposits, while basinal brines are commonly accepted as the principal mineralized fluids and graphite and gases (CH4, CO2, and H2S) are well known as the reductants, only few case studies describing structural traps are published. A number of recent works, including numerical modelling, have improved the understanding of the role of inherited shear zones on fluid flow and the development of uranium deposits at a micro- and regional-scale. Nevertheless, there is still a lack of knowledge about the meso- or deposit-scale structural controls that lead to the present (and potentially predictive) localization of uranium deposits along a given shear zone. The present work examines new structural data from drill holes and deals with (i) the identification of mesoscale structural traps that lead to the formation of the Athabasca unconformity-related uranium deposits hosted within the basement and (ii) with the understanding of the role and mode of reactivation of the inherited shear zones. The Sue deposits (McClean Project), the Tri-Island showing (Martin Lake Project) in the Eastern Athabasca, and the Spitfire prospect (Hook Lake Project) in the Western Athabasca have been selected for a detailed analysis of structures and related uranium mineralization. The structural analysis performed brings new insights about the mesoscale structural controls, the role the inherited ductile fabric had on the mode of brittle reactivation and to trap mineralization, and the tectonic regime to which basement-hosted uranium deposits may be associated in the Athabasca Basin.

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Uranium Deposits of Erlian Basin (China): Role of Carbonaceous Debris Organic Matter and Hydrocarbon Fluids on Uranium Mineralization

Minerals ◽

10.3390/min11050532 ◽

2021 ◽

Vol 11 (5) ◽

pp. 532

Author(s):

Lin-Fei Qiu ◽

Xi-De Li ◽

Wu-Sheng Liu ◽

Bao-Qun Hu ◽

Long Gao ◽

...

Keyword(s):

Organic Matter ◽

Uranium Mineralization ◽

Sedimentary Organic Matter ◽

Raman Spectroscopic ◽

Laser Raman ◽

Two Stages ◽

Relationship Of ◽

Oil Gas ◽

Erlian Basin

The relationship of sedimentary organic matter, oil-gas and sandstone-type uranium (U) deposits is the key problem of U-mineralization. Whether migrate hydrocarbons participate in U-mineralization is still a controversy. Typical U deposits of the Erlian Basin in northeast China have been investigated through detailed petrography, mineralogical, micro spectroscopic, organic geochemical and C-isotope studies. Petrographic observations, Microscopic Laser Raman Spectroscopic, Infrared Spectroscopic and Scanning Electron Microscope analyses indicated there are three types of organic matter (including carbonaceous debris and migrated hydrocarbons). A significant amount of uranium was associated with pyrites, clay minerals and carbonaceous debris organic matter, either coexisted with hydrocarbon fluids. There are at least two stages mineralization events, stage Ⅰ is related to sedimentary organic matter (syngenetic pre-enrichment stage), and stage Ⅱ is related to mobile hydrocarbon fluids (main mineralization stage). Therefore, our results support that migrated hydrocarbons were involved as a reducing agent for the main uranium mineralization after synsedimentary mineralization.

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