The availability of uranium resources will not impede the nuclear power industry for the foreseeable future [22]. Economic uranium resources will be continuously replenished through new discoveries or by moving existing deposits into economic categories. Replenishment
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occurs in response to supply and demand, price, new exploration and mining technologies, the development of new deposit models [21, 23], and substitution among other factors [24]. Some of the mechanisms that inform the process of replenishing the pool of economic deposits from an exploration perspective are described below.
A core activity of exploration program management involves reducing exploration discovery risk and slowing the rise in average discovery costs that are typically realized as an exploration area matures. This can be achieved through the application of knowledge that equates to the development of innovative approaches to exploration management.
FIG. 19. Relationship of exploration risk of failure, average discovery costs, and time linked with exploration.
Economic uranium mineral resource depletion relates to the fact that there are only so many economic deposits available in the natural environment to be discovered. After each economic discovery, the number of available economic deposits is reduced (depleted).
The history of exploration also suggests that in a virgin geological setting that is prospective for economic uranium deposits, large economic deposits will typically be discovered earlier in the exploration process than later. The risk of failure of an exploration program at this stage in a fertile environment is relatively lower, compared to a mature exploration play that has received intense exploration effort over time (Fig. 19).
Average discovery costs will also increase with time as the probability of economic discovery decreases. At some time in the history of the exploration region, the discovery rate will become so low that explorers will abandon exploration and invest in other project areas. Innovations in exploration geophysics and geochemistry have contributed to extending the life of exploration regions in some instances.
The relationship between exploration effort, the quantum of economic discovery, and the role of technology in reaching discovery can be understood through a model know as the ‘learning curve.’ A learning curve can be developed for an exploration region where economic deposits have been discovered and where the history of exploration expenditure, or other measures of effort, has been documented. The curve is constructed by plotting the cumulative exploration
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expenditure versus cumulative discovery of economic uranium. It is also possible to predict the magnitude of future discovery given future exploration expenditure using this model.
A learning curve for Canada’s Athabasca Basin is illustrated in Fig. 20, based upon prior work [25]. An analysis of the learning curve suggests that the basin has experienced two periods of exploration correlated with a prospector-driven, and a deposit model-driven technology phase.
Large high-grade deposits were discovered earlier in the history of each cycle. The absence of discoveries on the second learning curve, given more recent expenditure, suggests that a technological breakthrough will be required to drive future economic discovery. That is, future discoveries will likely occur on a third learning curve. Reliance on existing modes of exploration will not likely be efficient or effective. A discussion of the Athabasca learning curve can be found in [21].
A learning curve for ‘economic’ uranium deposits discovered in Australia is depicted in Fig.
21. Seven deposits discovered during 1969–1985 define the curve. The Olympic Dam deposit is excluded from this analysis. Over 3.5 billion dollars was spent on uranium exploration across Australia during 1967–2015, yielding ~400,000 t U. One-half of that resource is reasonably assumed to be mineable at this time due to the marginal nature of economics or political constraints. The Kintyre deposit is included in the analysis even though it was discovered during a diamond exploration program. Less than one-half of the deposits have reached production.
The Australian learning curve is analogous to the first learning curve for the Athabasca Basin that was similarly dominated by prospector discoveries using radiometric exploration methods.
The absence of discoveries in response to more recent expenditure (and the long-time frame since the last discovery) suggests that the current technology is not effective and that additional discoveries using this technology will be limited. Additional exploration using the current technology will be a value-destroying activity. The learning curve analysis is a call for innovation for new discoveries on a second learning curve.
FIG. 20. Athabasca Basin learning curve for the discovery of economic uranium deposits (constant dollars). Adapted from [21].
65 FIG. 21. Australia learning curve for the discovery of economic uranium deposits (excluding Olympic Dam). Based on data from [18] and [26].
An assessment of the impact of exploration expenditures on the frequency of Australian economic uranium resource discoveries supports the learning curve analysis (Fig. 22). More recent exploration expenditures have not resulted in new economic discoveries, and economic and geopolitical factors have likely removed significant resources from the pool of deposits that will reach production.
FIG. 22. Impact of exploration expenditures on the frequency of Australian economic uranium resource discovery. Expenditure data from [26]. Resources from the Olympic Dam deposit are excluded.
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The history of the discovery of significant uranium deposits in the Athabasca Basin is represented in Fig. 23. Discoveries made during the period from the late 1960’s through to the mid-2000s are characterized by increasing depth of initial discovery. The discoveries can be divided into two phases that also correspond to the Athabasca Basin learning curve analysis.
Generally speaking, earlier discoveries in the Athabasca Basin were made near surface, through the follow-up of radioactive boulder trains identified by radiometric prospecting methods. Later discoveries can generally be attributed to innovations in ground and airborne geophysical technology given the recognition of a close spatial relationship between the occurrence of uranium deposits and electromagnetic features. Exploration at greater depths in the basin is currently restricted by some limits related to capacity of geophysical technology to resolve targets, and by the high cost and longer time frames to drill to these depths. New geochemical technologies have been offered as an innovative approach to identifying deep, blind, deposits [11]. A breakthrough in the development of a more efficient drilling or other geoscientific technology could be a catalyst for discoveries on the third learning curve.
Deposit grade-and-tonnage models can be used to characterize the statistical distribution of uranium deposits per type [27]. These models provide a guide for predicting the occurrence of economic deposits. A plot of grade versus ore tonnage for selected Canadian and Australian economic and sub-economic uranium deposits is presented in Fig. 24. The isolines define several thresholds of contained metal. In this example, the largest Canadian deposits are characterized by their high grade and their relatively low ore tonnage. In contrast, the largest Australian deposits are characterized by their relative low grade and high ore tonnage. In this example, many uneconomic deposits fall below the lower isoline for contained metal. Only a few deposits are large enough to be deemed economic within the grade-tonnage spectrum (Fig.
25).