Are World Uranium Resources log-normally distributed?

in: Quantitative and Spatial Evaluations of Undiscovered Uranium Resources, pages 173-202, IAEA

Abstract

Investigating uranium resources is a significant opportunity for the future energy policy. Uranium deposits are usually classified according to their host rocks, for instance, in the uranium database of the International Atomic Energy Agency (IAEA) in which the uranium deposits are re-grouped into 15 major types18. This work investigates uranium resources using a mineralogical and process-based approach. Emphasis is put on re-grouping the deposits into three main classes according to their geological types. The statistical study of more than 1,500 uranium ore deposits recorded in the IAEA database shows that their grades and tonnages are remarkably distributed according to a log-normal distribution, their median tonnages being linearly inversely correlated to their median grades into a log-log cross plot. The log-normal characteristic is attributed to overprints of successive concentration first-order processes. The log-normal grade-and-tonnage model seems to be applicable globally as well as per main type, making these models comprise useful for estimation of potential resources of under-explored areas. The 15 major types of uranium deposits can be re-grouped according to their median grades and into three main genetic families, namely superficial, syn-sedimentary and hydrothermal. Uranium, as sub-product of phosphate deposits, constitutes the largest world uranium potential resources with an estimated median tonnage19 estimated as ~30,000 t U [3,450 – 246,150] but at the lowest median grade of 0.18‰ U [0.06 – 0.6]. The following world uranium resources, in decreasing order, are: superficial 4,575 t U [970 – 21,650] @ 0.3‰ U [0.1 – 0.8], sedimentary 3,025 t U [750 – 12,250] @ 0.8‰ U [0.3 – 1.9], and hydrothermal deposits 2,350 t U [680 – 8,130] @ 1‰ U [0.4 – 2.4]. The largest median grades, but also associated with the lowest tonnages, are observed in collapse breccia pipe (Colorado type) 780 t U [385 – 1,575] @ 4‰U [2.1 – 8.1], and Proterozoic unconformity (Saskatchewan) type deposits 4,550 t U [900 – 22,750] @ 7‰U [1.5 – 29], with average grade reaching maximum grades as high as 19.5% U with resources greater than 200,000 t U for unconformity deposits (McArthur River, Canada).

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BibTeX Reference

@INPROCEEDINGS{,
    author = { Royer, Jean-Jacques },
     title = { Are World Uranium Resources log-normally distributed? },
 booktitle = { Quantitative and Spatial Evaluations of Undiscovered Uranium Resources },
    series = { TECDOC },
    volume = { 1861 },
      year = { 2018 },
     pages = { 173-202 },
 publisher = { IAEA },
  abstract = { Investigating uranium resources is a significant opportunity for the future energy policy. Uranium deposits are usually
classified according to their host rocks, for instance, in the uranium database of the International Atomic Energy Agency
(IAEA) in which the uranium deposits are re-grouped into 15 major types18. This work investigates uranium resources using a
mineralogical and process-based approach. Emphasis is put on re-grouping the deposits into three main classes according to
their geological types. The statistical study of more than 1,500 uranium ore deposits recorded in the IAEA database shows that
their grades and tonnages are remarkably distributed according to a log-normal distribution, their median tonnages being
linearly inversely correlated to their median grades into a log-log cross plot. The log-normal characteristic is attributed to
overprints of successive concentration first-order processes. The log-normal grade-and-tonnage model seems to be applicable
globally as well as per main type, making these models comprise useful for estimation of potential resources of under-explored
areas. The 15 major types of uranium deposits can be re-grouped according to their median grades and into three main genetic
families, namely superficial, syn-sedimentary and hydrothermal. Uranium, as sub-product of phosphate deposits, constitutes
the largest world uranium potential resources with an estimated median tonnage19 estimated as ~30,000 t U [3,450 – 246,150] but at
the lowest median grade of 0.18‰ U [0.06 – 0.6]. The following world uranium resources, in decreasing order, are: superficial
4,575 t U [970 – 21,650] @ 0.3‰ U [0.1 – 0.8], sedimentary 3,025 t U [750 – 12,250] @ 0.8‰ U [0.3 – 1.9], and hydrothermal deposits 2,350
t U [680 – 8,130] @ 1‰ U [0.4 – 2.4]. The largest median grades, but also associated with the lowest tonnages, are observed in collapse
breccia pipe (Colorado type) 780 t U [385 – 1,575] @ 4‰U [2.1 – 8.1], and Proterozoic unconformity (Saskatchewan) type deposits
4,550 t U [900 – 22,750] @ 7‰U [1.5 – 29], with average grade reaching maximum grades as high as 19.5% U with resources greater
than 200,000 t U for unconformity deposits (McArthur River, Canada). }
}