Uranium-vanadium Deposits Research Articles

Paradox Basin Uranium-Vanadium Deposits: History and Significance of Geological Research

Paradox Basin Uranium-Vanadium Deposits: History and Significance of Geological Research

The Recovery of Vanadium Pentoxide (V2O5) from Spent Catalyst Utilized in a Sulfuric Acid Production Plant in Jordan.

Vanadium is a significant metal, and its derivatives are widely employed in industry. One of the essential vanadium compounds is vanadium pentoxide (V2O5), which is mostly recovered from titanomagnetite, uranium-vanadium deposits, phosphate rocks, and spent catalysts. A smart method for the characterization and recovery of vanadium pentoxide (V2O5) was investigated and implemented as a small-scale benchtop model. Several nondestructive analytical techniques, such as particle size analysis, X-ray fluorescence (XRF), inductively coupled plasma (ICP), and X-ray diffraction (XRD) were used to determine the physical and chemical properties, such as the particle size and composition, of the samples before and after the recovery process of vanadium pentoxide (V2O5). After sample preparation, several acid and alkali leaching techniques were investigated. A noncorrosive, environmentally friendly extraction method based on the use of less harmful acids was applied in batch and column experiments for the extraction of V2O5 as vanadium ions from a spent vanadium catalyst. In batching experiments, different acids and bases were examined as leaching solution agents; oxalic acid showed the best percent recovery for vanadium ions compared with the other acids used. The effects of the contact time, acid concentration, solid-to-liquid ratio, stirring rate, and temperature were studied to optimize the leaching conditions. Oxalic acid with a 6% (w/w) to a 1/10 solid-to-liquid ratio at 300 rpm and 50 °C was the optimal condition for extraction (67.43% recovery). On the other hand, the column experiment with a 150 cm long and 5 cm i.d. and 144 h contact time using the same leaching reagent, 6% oxalic acid, showed a 94.42% recovery. The results of the present work indicate the possibility of the recovery of vanadium pentoxide from the spent vanadium catalyst used in the sulfuric acid industry in Jordan.

Mineral–Geochemical Features of Paleoproterozoic Gold–Copper–Sulfide, Noble Metal-Copper–Uranium, and Noble-Metal–Copper–Uranium–Vanadium Deposits and Ore Occurrences of Karelia

Mineral–Geochemical Features of Paleoproterozoic Gold–Copper–Sulfide, Noble Metal-Copper–Uranium, and Noble-Metal–Copper–Uranium–Vanadium Deposits and Ore Occurrences of Karelia

湘中石牛矿区黑色岩系中钒铀矿床地质特征及综合利用

湘中石牛矿区黑色岩系中钒铀矿床地质特征及综合利用

Calciodelrioite, Ca(VO3)2(H2O)4, the Ca analogue of delrioite, Sr(VO3)2(H2O)4

AbstractCalciodelrioite, ideally Ca(VO3)2(H2O)4, is a new mineral (IMA 2012-031) from the uraniumvanadium deposits of the eastern Colorado Plateau in the USA. The type locality is the West Sunday mine, Slick Rock district, San Miguel County, Colorado. The new mineral occurs on fracture surfaces in corvusite- and montroseite-impregnated sandstone and forms as a result of the oxidative alteration of these phases. At the West Sunday mine, calciodelrioite is associated with celestine, gypsum, huemulite, metarossite, pascoite and rossite. The mineral occurs as transparent colourless needles, bundles of tan to brown needles and star bursts of nearly black broad blades composed of tightly intergrown needles. Crystals are elongate and striated parallel to [100], exhibiting the prismatic forms {001} and {011} and having terminations possibly composed of the forms {100} and {61}. The mineral is transparent and has a white streak, subadamantine lustre, Mohs hardness of about 2½, brittle tenacity, irregular to splintery fracture, one perfect cleavage on {001} and possibly one or more additional cleavages parallel to [100]. Calciodelrioite is soluble in water. The calculated density is 2.451 g cm– 3. It is optically biaxial (+) with α = 1.733(3), β = 1.775(3), γ = 1.825(3) (white light), 2Vmeas = 87.3(9)° and 2Vcalc = 87°. The optical orientation is X = b; Z ≈ a. No pleochroism was observed. Electronmicroprobe analyses of two calciodelrioite samples and type delrioite provided the empirical formulae (Ca0.88Sr0.07Na0.04K0.01)Σ1.00(V1.00O3)2(H2.01O)4, (Ca0.76Sr0.21Na0.01)Σ0.98(V1.00O3)2(H2.01O)4 and (Sr0.67Ca0.32)Σ0.99(V1.00O3)2(H2.00O)4, respectively. Calciodelrioite is monoclinic, I2/a, with unit-cell parameters a = 14.6389(10), b = 6.9591(4), c = 17.052(2) Å, β = 102.568(9)°, V = 1695.5(3) Å3 and Z = 8. The seven strongest lines in the X-ray powder diffraction pattern [listed as dobs Å (I)(hkl)] are as follows: 6.450(100)(011); 4.350(16)(013); 3.489(18)(020); 3.215(17)(022); 3.027(50)(multiple); 2.560(28)(15,413); 1.786(18)(028). In the structure of calciodelrioite (refined to R1 = 3.14% for 1216 Fo > 4σF), V5+O5 polyhedra link by sharing edges to form a zigzag divanadate [VO3] chain along a, similar to that in the structure of rossite. The chains are linked via bonds to Ca atoms, which also bond to H2O groups, yielding CaO3(H2O)6 polyhedra. The Ca polyhedra form a chain along b. Each of the two symmetrically independent VO5 polyhedra has two short vanadyl bonds and three long equatorial bonds. Calciodelrioite and delrioite are isostructural and are the endmembers of the series Ca(VO3)2(H2O)4–Sr(VO3)2(H2O)4. Calciodelrioite is dimorphous with rossite, which has a similar structure; however, the smaller 8-coordinate Ca site in rossite does not accommodate Sr.

Mineralogy of the U - Se-polymetallic deposit Niederschlema-Alberoda, Erzgebirge, Germany. IV. The continuous clausthalite-galena solid-solution series

In a sample from the Niederschlema-Alberoda U - Se-polymetallic deposit, western Erzgebirge, Germany, the entire PbSe - PbS solid-solution series was observed associated with uraninite, coffinite, hematite, acanthite, sphalerite, chalcopyrite, pyrite, and lollingite. Early deposited, Se-rich members of the Pb(Se, S) series occur as fracture fillings inside spherical uraninite or on its surface or form anhedral to subhedral grains precipitated in the immediate neighbourhood of the U minerals. Later crys- tallized, S-rich members of the series are affiliated with the sulfide minerals. The solid-solution series covers the range PbS1.00 - Pb(S0.04Se0.96)Σ1.00 virtually free of gaps, consistent with a temperature of formation of ≥ 100 uC. The PbSe - PbS solid solutions were likely deposited from hydrothermal fluids that became successively depleted in Se and enriched in S. The fugacities of sele- nium and sulfur covered the range -17 < logƒSe2 < - 26 and -17 < logƒS2 < - 22, respectively, implying ƒSe2/ƒS2 ≤ 1. The spher- ical texture of the uraninite, as well as its U-Th - total Pb age (192 ± 21 Ma), imply deposition of the Pb(Se, S) series during the Jurassic, contemporaneous with the formation of the bulk of the other selenium minerals. The electron-microprobe data from this study confirm earlier inferences on complete miscibility between clausthalite and ga- lena deduced from X-ray patterns of PbSe - PbS solid solutions from different uranium-vanadium deposits of the Colorado Pla- teau (Coleman 1959). In Niederschlema-Alberoda, the entire clausthalite - galena series occurs in a single section.

Organic matter diagenesis as the key to a unifying theory for the genesis of tabular uranium-vanadium deposits in the Morrison Formation, Colorado Plateau

Interstitial, epigenetic amorphous organic matter is intimately associated with uranium in the Grants uranium region on the southern part of the Colorado Plateau in northwestern New Mexico and is considered essential to genetic models for these deposits. In contrast, uranium minerals are intimately associated with authigenic vanadium chlorite and vanadium oxides in amorphous organic matter-poor ores of the Slick Rock and Henry Mountains mining districts on the northern part of the plateau, and therefore, in some genetic models amorphous organic matter is not considered crucial to the formation of these deposits. Differences in organic matter content can be explained by recognizing that amorphous organic matter-poor deposits have been subjected to more advanced stages of diagenesis than amorphous organic matter-rich deposits, during which organic compounds were broken down, solubilized, and removed during various diagenetic stages (e.g., sulfate reduction, methanogenesis, and organic acid production). Most diagenetic alterations (e.g., dissolution of framework grains and cements and precipitation of coarse-grained coffinite, vanadium clays, and vanadium oxides) characteristic of amorphous organic matter-poor deposits occurred when temperatures exceeded 80 degrees C--a temperature typical of the organic acid stage of diagenesis.Two factors combined to assure that a high percentage of the amorphous organic matter was removed from the Morrison Formation during diagenesis: the fact that the organic matter was humic (and therefore highly oxygenated), and that the juxtaposition of authigenic smectite and amorphous organic matter on grain rims facilitated clay mineral-organic catalysis reactions leading to the breakdown of large organic molecules into smaller, soluble molecules.Evidence that amorphous organic matter was involved in the genesis of organic matter-poor, as well as organic matter-rich, deposits includes the presence of leached iron-titanium oxides and strongly etched garnets (both attributed to leaching by organic acids), the gradation from organic matter-rich to organic matter-poor deposits in the Grants uranium region, the inverse correlation between the amount of amorphous organic matter and the intensity of diagenetic alteration, the ubiquitous occurrence of amorphous organic matter inclusions in coffinite, and the similarity in geometry of tabular uranium-vanadium ores and Holocene humate deposits. By recognizing that amorphous organic matter was crucial to the initial concentration of uranium (even in those deposits that presently contain little amorphous organic matter) and by recognizing the effects of the various stages of diagenesis on the ore, one genetic model may be applied to all of the sandstone-hosted, tabular-type uranium-vanadium deposits in the Morrison Formation on the Colorado Plateau.

Genesis of the tabular-type vanadium-uranium deposits of the Henry Basin, Utah; discussion

Genesis of the tabular-type vanadium-uranium deposits of the Henry Basin, Utah; discussion

Genesis of the tabular-type vanadium-uranium deposits of the Henry Basin, Utah; reply

Genesis of the tabular-type vanadium-uranium deposits of the Henry Basin, Utah; reply

Mineralogy and geochemistry of reduction spheroids in red beds

The mineralogy and geochemistry of reduction spheroids from continental and marine red beds of Europe, North America and Oman were investigated. Reduction spheroids are spheroidal, isolated reduction sites in hematitic rocks. They consist of a mineralized core (0.1 to 5 cm diameter) and a hematite-dissolution halo (1 to 20 cm diameter). Irrespective of origin and age of host rocks, all reduction spheroid cores show a very similar mineralogy dominated by the vanadian mica roscoelite and a similar pattern of element enrichment relative to their host rocks dominated by V and U. Element enrichments in most reduction spheroids are very similar to those of sandstone-hosted vanadium-uranium deposits except for a lack of a molybdenum enrichment. Isotopically light sulfide of in-situ, low-temperature origin is an indication for the involvement of bacterial sulfate reduction during reduction spheroid formation.

Geochemistry of vanadium in an epigenetic, sandstone-hosted vanadium-uranium deposit, Henry Basin, Utah

The epigenetic Tony M vanadium-uranium orebody in south-central Utah is hosted in fluvial sandstones of the Morrison Formation (Upper Jurassic). Although the deposit is mined for uranium, vanadium has a higher average abundance in the ore. Thus, the geochemistry of vanadium in the orebody was studied to characterize ore-forming processes within the inferred ground-water flow regime. Measurements of the relative amounts of V (super +3) and V (super +4) in ore minerals show that V (super +3) is more abundant. Thermodynamic calculations show that vanadium was more likely transported to the site of mineralization as V (super +4) . The ore formed as V (super +4) was reduced by hydrogen sulfide, followed by hydrolysis and precipitation of V (super +3) in oxide minerals (e.g., montroseitc or paramontroseite) or chlorite. Uranium was transported as uranyl ion (U (super +6) ), or some complex thereof, and reduced by hydrogen sulfide, forming coffinite. Detrital organic matter in the rocks served as the carbon source for sulfate-reducing bacteria. It was this bacteriogenic H 2 S that reduced the metals in the mineralization process.Possible sources for the V and U in this deposit have been identified previously. Vanadium most likely was derived from the dissolution of iron-titanium oxides, which liberated Fe as well as V. A zone of titanium-rich remnants is observed updip and up the hydrologic gradient from the deposit (M. Goldhaber and R. L. Reynolds, unpub. data). Uranium probably was derived from the overlying Brushy Basin Member of the Morrison Formation (Northrop, 1982). A preliminary age date for the deposit of 115 Ma (K. Ludwig, 1986, pers. commun.) indicates that the ore formed after deposition of the Brushy Basin Member.Previous studies have shown that the ore formed at the density-stratified interface between a basinal brine and dilute meteoric water. The mineralization processes described above occurred within the mixing zone between these two fluids. Stable isotope analyses of ore-stage dolomite show a progressively heavier carbon and oxygen isotope signature with increasing depth through an ore horizon, consistent with the two-solution interface model.

Genesis of the tabular-type vanadium-uranium deposits of the Henry Basin, Utah

Genesis of the tabular-type vanadium-uranium deposits of the Henry Basin, Utah

Diagenesis of Amorphous Organic Matter as an Essential Aspect of Genesis and Alteration of Tabular-Type Uranium-Vanadium Deposits, Colorado Plateau: ABSTRACT

Organic matter was the key to the initial concentration of uranium and vanadium (during the sulfate reduction stage of early diagenesis) in all sandstone-hosted, tabular deposits in the Morrison Formation, Colorado Plateau. In deposits rich in amorphous organic matter, as are many in the Grants uranium region (GUR), diagenesis did not proceed beyond sulfate reduction. In contrast, in organic-poor, chlorite deposits of the Henry Mountains district, /sup 13/C- and /sup 18/O-enriched dolomites preserve evidence of a subsequent methanogenic stage. In these and similar organic-poor deposits in the Slick Rock district and in parts of the GUR, aluminosilicate dissolution (including a distinctive, organic-acid-induced etching of garnets) and growth of coarse-grained coffinite, albite, ankerite, and chlorite suggest diagenesis reached the organic acid stage. Temperature and thermal maturation indicators (vitrinite reflectance, type IIb chlorite, ordered illite/smectite, and fluid inclusion data) are consistent with temperatures of organic-acid stage diagenesis (approx. 100/sup 0/C). The localization of these alterations in and around organic-poor, clay-rich ore; the similarities in type and sequence of these alterations to the normal alteration of organic-bearing sediments; the alteration of iron-titanium oxides (attributed to the action of soluble organic complexes) around both organic-rich and organic-poor deposits; and the gradation from organic-rich tomore » organic-poor, chlorite-rich deposits (in GUR) suggest that (1) amorphous organic matter was involved in the genesis of all of these deposits and (2) differences among deposits may reflect varying degrees of diagenesis of the organic matter.« less

Vanadium Chlorite from a Sandstone-Hosted Vanadium-Uranium Deposit, Henry Basin, Utah

AbstractAn unusual vanadium chlorite precipitated during the formation of a vanadium-uranium ore deposit in the Henry Basin, southeastern Utah. The ore deposit formed by reduction and precipitation of U and V in the presence of organic matter at the interface between a stagnant brine and overlying, circulating meteoric water. Some samples of the vanadium chlorite (heated before analysis) contain ≥ 10% V2O5. In fresh samples, most of the vanadium is in the trivalent oxidation state. X-ray powder diffraction data suggest that Fe and V are concentrated preferentially in the interlayer hydroxide sheets of the chlorite. A d(060) value of 1.52 Å indicates that the chlorite probably has a dioctahedral structure which is distended by the presence of octahedral Fe and V. The vanadium ore zone is flanked by peripheral zones containing perfectly ordered chlorite/smectite. This chlorite/smectite contains much less V than the pure chlorite. This chlorite may have formed by the progressive precipitation of vanadium-rich interlayer hydroxide sheets in the mixed-layer chlorite/smectite in the most reducing portion of the ore zone. The pure chlorite is a IIb polytype, which, for nonvanadiferous analogs, is ordinarily found in high-temperature environments; however, no evidence exists to show that these rocks have ever been exposed to elevated temperatures. In fact, the presence of unreacted smectite in a potassium-rich setting and the low vitrinite reflectance of coalified plant debris indicate a low-temperature history for these sediments.

MINERAL ASSEMBLAGES AND PHYSICOCHEMICAL CONDITIONS FOR CARNOTITE-AUTUNITE-TORBERNITE MINERALIZATION IN CARBONACEOUS PHYLLITES

Subsurface occurrences of uranium minerals of the carnotite-autunite-torbernite (Uranglimmer) group are fairly common in carbonaceous phyllites, particularly in regions with arid climate, where deposits can sometimes be followed to depths of several hundred meters. The paper integrates field observations and laboratory experiments to explain the complex mineralogy of some supergene uranium-vanadium deposits in terms of the changing composition of descending solutions. Geophysical and geochemical data are discussed. Laboratory studies included: solubilities of chemically pure synthetic carnotite, autunite, and torbernite in acid and alkaline conditions; oxidation of these phyllites under hydrogeochemical conditions; and slow infiltration of uranyl sulfate and vanadium pentoxide through a strong neutralizer (calcite) to illustrate the possible formation of uranyl vanadate ores during neutralization. Results are described and discussed. 11 references, 7 figures, 2 tables.

Geochemical Evaluation of Proposed Ore Genesis Models for Colorado Plateau Tabular-Type Uranium-Vanadium Deposits: ABSTRACT

The elemental, isotopic, and mineralogic examination of core samples from the Tony M orebody, a typical Colorado Plateau tabular-type, uranium-vanadium deposit, located in the Henry structural basin of south-central Utah, allows a critical evaluation of proposed ore genesis models. Uranium mineralization is concentrated into two horizontally oriented tabular horizons hosted within the Salt Wash member of the Jurassic Morrison Formation. The ore zones are not strata bound and rise stratigraphically toward the center of the ancestral Henry basin. Preservation of fossil plant debris and the lack of oxidative destruction of iron disulfide minerals in the interval between the uranium-enriched units argue this zone is not the oxidized tongue formed by a roll-type mineralizing p ocess. The selenium-molybdenum trace element pattern is also inconsistent with the roll-front model. The necessary interbedding of gray lacustrine mudstones and nearshore lacustrine sandstones, as required by the lacustrine-humate model, is present within the Tony M deposit. However, absence of quantitatively significant amounts of transported humic substances either associated or remote from mineralization suggests that mudstone-derived organic acids were not involved in uranium localization. Vanadium oxide is the major vanadium-bearing phase within the lower uranium lense whereas vanadium is partitioned within chlorite in the supra-adjacent barren zone. Such a sharp vertical break in vanadium mineralogy implies vanadium deposition within two chemically different environments. The lower ore zone is characterized by isotopically light (^dgr34S ^cong -26^pmil - 46^pmil) FeS2. Bacterial sulfate reduction is shown to be the most likely fractionating agent. The uniformity of the sulfur isotopic composition of the iron disulfide minerals requires a non-depletable sulfate reservoir. Dissolution of gypsum (^dgr34S ^cong + 14^pmil) occurring below the Tony M orebody is demonstrated to be a plausible sulfur source thereby establishing the presence of a sulfate brine. From this data we conclude that the solution-interface model, which postulates uraniferous meteoric fresh water flowing over a denser brine, best explains the genesis of this deposit. End_of_Article - Last_Page 436------------

Localization of Tabular, Sediment-Hosted Uranium-Vanadium Deposits of Henry Structural Basin, Utah: ABSTRACT

Tabular uranium-vanadium mineralization characteristic of the Colorado Plateau occurs in fluvial sandstones of the Salt Wash Member of the Morrison Formation (Jurassic) within the Henry structural basin, south-central Utah. The ore consists of a mineralized interval (MI) of two closely spaced uranium and vanadium-rich zones separated by one barren of uranium but enriched in vanadium. No known stratigraphic feature controls the position of this MI which occurs at successively higher stratigraphic levels toward the interior of the basin. The dominant clay mineral throughout the MI is an unusual vanadium-rich di,trioctahedral chlorite. Laterally continuous with and below the MI, mixed-layer chlorite/smectite and illite/smectite (greater than 75% expandable layers) predominat . Above the MI, kaolinite in sandstone beds and illite/smectite plus kaolinite in bentonitic beds are the dominant authigenic clay minerals. The MI and its unmineralized lateral extensions are bounded, both above and below, by zones rich in authigenic dolomite cement. Petrographic evidence places the dolomite as pre-ore to contemporaneous with ore, and the chlorite contemporaneous with ore. Geochemical and mineralogical data, ^dgr18O to ^dgrD values of clay minerals and ^dgr18O to ^dgr13C values of dolomite indicate the presence of an interface between two isotopically and chemically distinct fluids. The lower fluid was typical of closed-basin evaporated brines with a high Mg/Ca ratio and high SO42- content. The upper fluid was meteo ic water. Elemental zoning patterns and isotopic data suggest that the upper (meteoric) fluid carried the uranium and vanadium to the solution interface, but that ore grade mineralization occurred only where the brine-meteoric water interface intersected horizons with anomalous concentrations of organic matter (dominantly detrital plant debris). End_of_Article - Last_Page 613------------

Some Chemical Characteristics of Uranium-Vanadium Deposits in Ambrosia Lake Area, Northwest New Mexico: ABSTRACT

Comparison of the elemental abundances of six suites of ore-bearing sandstones from the Upper Jurassic Morrison Formation suggests that certain elements form haloes around these deposits. Field relations and uranium contents were used to classify approximately 700 samples of sandstone from the Morrison Formation in the Ambrosia Lake area, New Mexico, into the following groups: (1) primary U-V ore (prefault or trend), (2) secondary U-V ore (postfault or stack), (3) reduced rock adjacent to ore, and (4) oxidized rock adjacent to ore. The chemical characteristics of each of the groups were compared with each other and with the characteristics of two control groups of samples taken farther from ore deposits. One of these was a suite of 70 samples of Morrison sandstones from t e Thoreau area; the other consisted of approximately 200 samples of Morrison sandstones from various locations in the southern San Juan basin. Differences in the geometric means of the elemental abundances indicate that relative to the control groups, the primary ores are enriched in Fe, Mg(?), Ca, Mn, Ba, Be, Cu, Mo, Pb, U, V, Y(?), Na, Se, Sr, organic C, and carbonate C; the secondary ores are enriched in Fe, Ca, Mn, Ba, Cu, Na, Sr, U, V, and carbonate C. The data indicate that Ca, Ba, Sr, V, and carbonate C are more concentrated in End_Page 569------------------------------ the secondary ore than in the primary ore. Barren rocks adjacent to the ore are enriched in Ca, Ba, Cu(?), Sr, V, U, Na, Se, and carbonate C, compared with barren rock farther from the deposits. Both the enrichment of these elements in the vicinity of the deposits, and the better correlation of them (except for U) with eU than with U, suggest that these elements are mobile and form haloes that may be useful exploration guides. The data also suggest that Ga is depleted in and around the ore. Thus, a decrease in Ga might be an indication of proximity to a deposit. End_of_Article - Last_Page 570------------

The role of semipermeable membranes in the formation of certain vanadium-uranium deposits

The Rifle-Garfield vanadium-uranium deposit, Garfield County, Colorado, is believed to have formed at an interface between a carbonate solution and a sulfate solution. Vanadium-silicate minerals in the ore appear to have acted as a semipermeable membrane which maintained the solution interface for a long enough time for the ore to develop. Selective diffusion through the membrane resulted in concentration gradients and pH changes on both sides of the growing ore deposit. Mineralogical zones of the deposit and alteration associated with the ore formed in response to the changes in the chemical conditions generated by the membrane.

Diffusion features of uranium-vanadium deposits in Montezuma Canyon, Utah

U-V deposits in the Salt Wash Member of the Morrison Formation in Montezuma Canyon, San Juan County, exhibit zoning that is interpreted as a result of metal transport by diffusion. The concentric zones consist of a brown nonmineralized core, an olive- gray mineralized shell, and a gray nonmineralized outer zone. The brown zone is Fe stained, porous sandstone commonly containing abundant carbonaceous material. The curved mineralized layer completely encloses the brown zone and is composed of oxidized U-V minerals that impregnate sandstone. The gray zone is light-gray sandstone tightly cemented with calcite and commonly freckled with limonitic specks. Formation of the deposits most likely took place during Late Cretaceous or early Tertiary time when the ore-bearing sandstones were deeply buried and saturated with connate waters. The concentration of organic material in the brown zone suggests that this zone was once saturated with a reducing solution containing soluble organic compounds like alcohols and aldehydes derived from the organic material. The gray zone, on the other hand, was probably saturated with an oxidizing solution containing U and V. Where these 2 solutions were in contact, oxidation-reduction reactions took place that caused the precipitation of low-valent U and V minerals. The ellipsoidal shape of the ore layer and the lack of any exit or entrance for flowing solutions indicates that the dissolved metals moved through the gray zone by diffusion and were precipitated at the periphery of the reducing zone. Recent weathering and oxidation have altered the primary low-valent minerals to high-valent forms without noticeable leaching of the ore metals.