Abstract
Broadly similar U(-V) deposits are hosted by Permian to Jurassic sandstones in the Paradox Basin of the Colorado Plateau. Common features of all the Paradox Basin deposits include occurrence in bleached red bed sandstones; accessory barite and/or celestine; authigenic Ti minerals; lack of correlation between mineralization and plant coal distribution; and evidence for or actual traces of hydrocarbons in the rock before and/or during mineralization. All but the structure-hosted Cutler deposits also show a mix of hematite, pyrite, and hypogene U and/or V minerals enclosed under authigenic overgrowths surrounding detrital quartz cores, which are extensively replaced by fringes of vanadian phyllosilicates. In the Entrada-hosted deposits, all but traces of hypogene U and V oxides have been removed to leave mainly the V-phyllosilicate minerals, but otherwise they resemble the mineralogy and paragenesis in the rest of the Paradox Basin U-V deposits. This paper presents and compares the deposit types to each other and to global sandstone-hosted U resources. Deposits hosted in the Jurassic Salt Wash Member of the Morrison Formation mostly form tabular, V-dominated bodies in permeable, trough cross-bedded horizons of bleached former red beds. Common quartz overgrowths entrap pyrite, pitchblende, and montroseite. Pitchblende and montroseite also form interstitial masses in cementing V-phyllosilicates, which corrode and partially replace the quartz overgrowths. Common accessory phases include pyrite (some framboidal), chalcopyrite, ferroselite, clausthalite, galena, sphalerite, and barite, with minor asphalt globules that corrode quartz overgrowths and cores and contain pitchblende and pyrite. Down the stratigraphic section, the Jurassic Entrada hosts minor lenticular deposits in aeolian sandstones just below a capping limestone. Ore minerals consist mainly of roscoelite replacing quartz overgrowths and cementing the sandstone. Except for small vanadiferous pitchblende inclusions trapped under quartz overgrowths, minor U-vanadates are the only U minerals observed. Continuing down-section, U-V deposits in the Triassic Chinle occur in conglomerates and sandstones just above the Chinle-Cutler unconformity in the Big Indian district, and in the basal Chinle in White Canyon. Quartz overgrowths are rarer but also enclose inclusions of hematite and pitchblende, more rarely V minerals. Pitchblende, montroseite, and V-phyllosilicates are the main ore minerals, forming interstitial masses and replacing some of the plant coal in the rocks. Accessory minerals include pyrite, sphalerite, galena, and barite. Secondary fluid inclusions fluoresce bright blue in ultraviolet light, indicating hydrocarbons. Chinle-hosted deposits in the San Rafael Swell occur as uraniferous asphalt that also contains V-Cr-Fe oxide. Roscoelite hosts most of the V and the deposits contain a large suite of accessory minerals, including pyrite, chalcopyrite, Ni-arsenide, sphalerite, galena, realgar, and barite. Where bleached, the coarse sandstone of the underlying Cutler Formation hosts small deposits below or near Chinle orebodies, either along permeable sandstones or along steep faults. Cutler-hosted deposits showing stratigraphic control share most features with the nearby Chinle orebodies, including quartz and rarer feldspar overgrowths enclosing U-V minerals and an assemblage dominated by pitchblende and montroseite with minor V-phyllosilicates. Deposits hosted along faults in the Cutler are highly distinct, mineralized with pitchblende and uraniferous asphalt in the fault cores and V-phyllosilicate in surrounding areas. Alone among the U and V deposits of the Paradox Basin, no quartz overgrowths have been observed in this type. Deposits’ interpreted parageneses are also similar, with bleaching of original red beds during or shortly before the beginning of mineralization, followed by further U-V deposition in the main ore stage. Late in the ore stage, fresh V or V (hydr)oxide minerals back-reacted with silica in quartz overgrowths to form V-phyllosilicates, while accessory base metal sulfides and selenides precipitated along with barite. These similarities of mineralogy and texture imply a similar mechanism of formation for most of the Paradox Basin U-V deposits, corresponding either to a single basinwide ore-forming event or to the same geologic processes independently repeated in different strata at different times. Hydrocarbons were likely a major reductant, with ore precipitating where an oxidized metal-bearing fluid either mixed with hydrocarbons or entered a rock previously reduced by their passage. Lastly, the Paradox Basin deposits’ most remarkable feature is their high V content, which is unique worldwide and makes the area a world-class resource for this critical green energy metal.
Original language | English (US) |
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Pages (from-to) | 3703-3740 |
Number of pages | 38 |
Journal | Mining, Metallurgy and Exploration |
Volume | 41 |
Issue number | 6 |
DOIs | |
State | Published - Dec 2024 |
Externally published | Yes |
Keywords
- Paradox Basin
- Sandstone-hosted uranium
- Tabular uranium
- U-V deposits
- Uranium
- Vanadium
ASJC Scopus subject areas
- Control and Systems Engineering
- General Chemistry
- Geotechnical Engineering and Engineering Geology
- Mechanical Engineering
- Metals and Alloys
- Materials Chemistry