The IAEA released it's report in 2018 and indicated that unconformity-related uranium deposits made up 25% of the total production of uranium in 2016, and hence can be considered a significant resource of uranium. In marked contrast to most other deposit types of uranium, unconformity-related ores are both high grade and have among the largest uranium inventories (570,000 tU at a cost especially, given their low mining cost compared to other deposit types, exploring for these deposits is challenging as they are associated with basal units of Proterozoic basins normally in the subsurface.
Proterozoic unconformity deposits occur below, along or above the unconformable contact between an Archean to Paleoproterozoic crystalline basement with highly reducing lithologic units and oxidized siliciclastic sediments (red beds) of Proterozoic age. The basement rocks immediately below the unconformity are hematized, chlortized and argillized in a transition zone with the fresh basement. This alteration has been attributed to paleo-weathering and diagenetic/hydrothermal alteration.
Deposits consist of lenses, pods or veins of massive uranium dioxide commonly with associated strong quartz dissolution and intensive clay alteration. They are mainly found in two major areas the Athabasca Basin in Canada and the East Alligator River district in Australia. Three sub-types are distinguished by the IAEA uranium deposit classification scheme:
1) unconformity-contact deposits such as Cigar Lake that essentially occur in the Athabasca Basin in Canada;
2) basement-hosted deposits such as Ranger and Jabiluka in Australia, Eagle Point, Millennium, the lower pod of Kianna and Arrow in the Athabasca Basin, and Kiggavik and Andrew Lake in the Thelon Basin in Canada; and,
3) stratiform structure-controlled deposits only known in India at Chitrial and Lambapur in the Cuddapah Basin. The resources range from medium to large, with very high grades for the Canadian deposits to low grades for the Indian deposits. A recently proposed classification with four end members, based on lithostructural characteristics, is described in Chapter 2.
An International Atomic Energy Agency (IAEA) publication with reference to unconformity related deposits was published as TECDOC stratabound uranium. Given the extensive research and exploration that has occurred subsequently for these types of deposits, an update is well overdue on what is now known about their characteristics, formation, evolution and exploration.
The scope of this TECDOC includes a description of existing and emerging technologies to effectively integrate geological, geophysical and geochemical data to recognize the footprint (i.e. the total extent that the mineralizing system has affected its environment) of the deposit and the key vectors to the uranium mineralization. In addition, insights into exploration strategies and risks associated with country and basin selection are discussed, including the role of the IAEA and academia in supporting the exploration process.
The TECDOC has received inputs from diverse sources, including the IAEA, uranium-based and related industries and researchers from governments and universities. The focus is meant to be both basic and applied, with an emphasis on integrating technologies to enhance exploration success. There is a large body of published research on the deposits, as summarized in this TECDOC.
Topics addressed include: how the deposits are classified; descriptions of the deposits and empirical models; current theories on how they form (with an emphasis on critical factors when formulating exploration strategies); exploration processes; and, exploration techniques.
[This is an outstanding source on unconformity-related uranium deposits.]
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