This review of the geology, geophysics, and origin of the unconformity-associated uranium deposit type is focused on the Athabasca Basin. Pods, veins, and semimassive replacements of uraninite (var. pitchblende) are located close to unconformities between late Paleoto Mesoproterozoic conglomeratic sandstone basins and metamorphosed basement rocks. The thin, overall flat-lying, and apparently unmetamorphosed but pervasively altered, mainly fluvial strata include red to pale tan quartzose conglomerate, sandstone, and mudstone. Beneath the basal unconformity, red hematitic and bleached clay-altered regolith grades down through chloritic altered to fresh basement gneiss. The highly metamorphosed interleaved Archean to Paleoproterozoic granitoid and supracrustal basement gneiss includes graphitic metapelitic that preferentially hosts reactivated shear zones and many deposits. A broad variety of deposit shapes, sizes and compositions ranges from monometallic and generally basement-hosted veins to polymetallic lenses located just above or straddling the unconformity, with variable Ni, Co, As, Pb and traces of Au, Pt, Cu, REEs, and Fe.

Unconformity-associated uranium deposits of the Athabasca Basin, Saskatchewan and Alberta

Alteration of uraninite from the Nopal I deposit, Pen˜a Blanca District, Chihuahua, Mexico, compared to degradation of spent nuclear fuel in the proposed U.S. high-level nuclear waste repository at Yucca Mountain, Nevada

The interaction of thermal neutrons with 235U results in fission with a probability of ∼85% and in the formation of 236U (t1/2 = 2.3 × 107 yr) with a probability of ∼15%. While anthropogenic 236U is, therefore, present in spent nuclear fuel at levels of 236U/U up to 10−2, the expected natural ratios in the pre-anthropogenic environment range from 10−14 to 10−10. At VERA, systematic investigations suggest a detection limit below 236U/U = 5 × 10−12 for samples of 0.5 mg U, while chemistry blanks of ∼2 × 107 atoms 236U per sample limit the sensitivity for smaller samples. We have found natural isotopic ratios in uranium reagents separated before the onset of human nuclear activities, in uranium ores from various origins and in water from a subsurface well in Bad Gastein, Austria. Anthropogenic contamination was clearly visible in soil and rivulet samples from Salzburg, Austria, whereas river sediments from Garigliano river (Southern Italy) were close to the detection limit. Finally, our natural in-house standard Vienna-KkU was calibrated against a certified reference material (IRMM REIMEP-18 A).

https://publik.tuwien.ac.at/files/PubDat_175334.pdf

Natural and anthropogenic 236U in environmental samples

Dissolution and alteration of uraninite under reducing conditions

Determination of plutonium and other transuranic elements by inductively coupled plasma mass spectrometry: A historical perspective and new frontiers in the environmental sciences

Nature`s uncommon elements: Plutonium and technetium

Sandstone-hosted uranium deposits in northern Saskatchewan as natural analogs to nuclear fuel waste disposal vaults

The authors have taken advantage of the extremely sensitive method of thermal ionization mass spectrometry to measure technetium and plutonium concentrations in sample masses that are smaller by as much as three orders of magnitude than those used in the early research efforts. The work reported in this paper extends the understanding of the geochemistry of plutonium and technetium by developing detailed descriptions of their associations in well characterized geologic samples, and by using modern neutron-transport modeling tools to better interpret the meaning of the results. Analyses were conducted on samples from three uranium ore deposits selected for their contrasting geochemical environments. The Cigar Lake deposit is an unweathered, unaltered primary ore in a reducing environment which is expected to closely approximate a system that is closed with respect to uranium and its products. The Koongarra deposit is a shallow system, both altered and weathered, subject to active ground water flow. Finally, a sample from the Beaverlodge deposit is included because it is a commercially-available uranium ore standard that allows demonstration of the precision of the analytical results.

/pdf/nature-s-uncommon-elements-plutonium-and-technetium-5auq3tdsg5.pdf

Jan J. Cramer

Papers

Nature`s uncommon elements: Plutonium and technetium

Sandstone-hosted uranium deposits in northern Saskatchewan as natural analogs to nuclear fuel waste disposal vaults

Nature`s uncommon elements: Plutonium and technetium