Unconformity-Type Uranium Systems: A Comparative Review and Predictive Modelling of Critical Genetic Factors

Abstract

A review of descriptive and genetic models is presented for unconformity-type uranium deposits with particular attention given to spatial representations of key process components of the mineralising system and their mappable expressions. This information formed the basis for the construction of mineral potential models for the world’s premier unconformity-style uranium provinces, the Athabasca Basin in Saskatchewan, Canada (>650,000 t U3O8), and the NW McArthur Basin in the Northern Territory, Australia (>450,000 t U3O8). A novel set of ‘edge’ detection routines was used to identify high-contrast zones in gridded geophysical data in support of the mineral potential modelling. This approach to geophysical data processing and interpretation offers a virtually unbiased means of detecting potential basement structures under cover and at a range of scales. Fuzzy logic mineral potential mapping was demonstrated to be a useful tool for delineating areas that have high potential for hosting economic uranium concentrations, utilising all knowledge and incorporating all relevant spatial data available for the project area. The resulting models not only effectively ‘rediscover’ the known uranium mineralisation but also highlight several other areas containing all of the mappable components deemed critical for the accumulation of economic uranium deposits. The intelligence amplification approach to mineral potential modelling presented herein is an example of augmenting expert-driven conceptual targeting with the powerful logic and rationality of modern computing. The result is a targeting tool that captures the current status quo of geospatial and exploration information and conceptual knowledge pertaining to unconformity-type uranium systems. Importantly, the tool can be readily updated once new information or knowledge comes to hand. As with every targeting tool, these models should not be utilised in isolation, but as one of several inputs informing exploration decision-making. Nor should they be regarded as ‘treasure maps’, but rather as pointers towards areas of high potential that are worthy of further investigation.

Location of Uranium‐Rich Brines Determines the Distribution and Grade of Unconformity‐Related Uranium Deposits

“…Despite this general understanding, the exact origin of the large amount of uranium remains uncertain and continues to be a debated topic. Two possible uranium sources have recently been proposed (Bruce et al., 2020), though the surface and near‐surface evaporitic conditions might also enhance the uranium concentration in the brines (Richard et al., 2011). One version considers the overlying basinal sediments as the source of both uranium and oxidized brines (e.g., Fayek & Kyser, 1997; Kotzer & Kyser, 1995), and the other uses the basement as the uranium source while oxidized fluids still originate from sedimentary basins (e.g., Hecht & Cuney, 2000; Mercadier et al., 2010).…”

“…They are located in or around the unconformities between Proterozoic basin fill and underlying Archean to lower Proterozoic metamorphic basement rocks, where faults exist (Jefferson et al., 2007). The largest and highest grade deposits of this type occur in Paleoproterozoic sedimentary basins, particularly in the Athabasca Basin, Canada, and the Northern Territory, Australia (Bruce et al., 2020).…”

“…They are located in or around the unconformities between Proterozoic basin fill and underlying Archean to lower Proterozoic metamorphic basement rocks, where faults exist (Jefferson et al, 2007). The largest and highest grade deposits of this type occur in Paleoproterozoic sedimentary basins, particularly in the Athabasca Basin, Canada, and the Northern Territory, Australia (Bruce et al, 2020).Geological, structural, geochemical, and mineral paragenetic studies have resulted in a widely accepted model in which unconformity-related uranium deposits formed when oxidizing brines mixed with basement-derived reducing fluids or reacted with reducing minerals in the basement, at or near the regional unconformity between Proterozoic conglomeratic sandstones and Archean to Paleoproterozoic metamorphosed basement rocks that were intersected by reactivated fault systems (e.g., Fayek & Kyser, 1997). Despite this general understanding, the exact origin of the large amount of uranium remains uncertain and continues to be a debated topic.…”

Editorial for Special Issue “Geology of Uranium Deposits”

“…The papers by Wilde [1] and Bruce et al [2] present reviews of the shear-zone-hosted and unconformity types of deposits, respectively. Wilde [1] proposes that deposits formerly known as "albitite-type" or "metasomatite-type" (IAEA classification) are better regarded as shear-zone-hosted.…”

“…The Bruce et al paper [2] provides a substantial review of the unconformity-type of uranium deposit, which currently accounts for approximately 20% of global uranium production, mainly from Canada's Athabasca Basin. The paper also discusses how to predict the location of unknown deposits using an innovative approach to geophysical data processing and interpretation that offers a virtually unbiased means of detecting cryptic basement structures.…”