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.
Highlights
Unconformity-type uranium deposits (Figure 1a) are structurally controlled and typically located at, or within a few hundred metres above or below, a prominent regional unconformity, separating locally reduced Archaean and Paleoproterozoic crystalline basement from relatively undeformed, oxidised Paleo- to Mesoproterozoic clastic cover rocks of intracratonic basin affinity [1,2].The group of unconformity-type uranium deposits is economically significant, having accounted for >15–25% of the world’s uranium production in the period from 2016 to 2018 [2]
In this paper we review descriptive and genetic models for unconformity-type uranium deposits with particular emphasis on their common spatial footprints enabling the prediction of undiscovered resources at the basin-scale
An ore deposit can be thought of as the product of five critical genetic processes: (i) source: all geological processes required for extracting the necessary ore components from their crustal and/or mantle sources; (ii) transport: all geological processes required for driving the melt- or fluid-assisted transfer of the ore components from source to trap; (iii) trap: all geological processes required for focusing melt or fluid flow into physically and/or chemically responsive sites that can accommodate significant volumes of ore and gangue; (iv) deposition: all geological processes required for efficient extraction of metals from melts or fluids passing through the traps and (v) preservation: all geological processes required to preserve the accumulated metals through time
Summary
Unconformity-type ( called unconformity-related and unconformity-associated) uranium deposits (Figure 1a) are structurally controlled and typically located at, or within a few hundred metres above or below, a prominent regional unconformity, separating locally reduced Archaean and Paleoproterozoic crystalline (metamorphic/magmatic) basement from relatively undeformed, oxidised Paleo- to Mesoproterozoic clastic cover rocks of intracratonic basin affinity [1,2]. In this paper we review descriptive and genetic models for unconformity-type uranium deposits with particular emphasis on their common spatial footprints enabling the prediction of undiscovered resources at the basin-scale. (e) The Paleoto Mesoproterozoic McArthur Basin and adjacent exposed Paleoproterozoic Pine Creek Inlier in the Northern Territory, Australia is host to several large unconformity-type uranium deposits, including the Ranger mine. A compilation of all available U-Pb and Ar-Ar ages for the Athabasca Basin deposits by Chi et al [59], suggests that most of the unconformity-type uranium systems formed at approximately 1540 Ma. The broad time span of the compiled U-Pb and Ar-Ar ages, from approximately 1650 Ma to
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