This chapter contains a brief description of the wide variety of geological settings that host uranium deposits worldwide, and then a more specific description of known uranium occurrences in the Commonwealth of Virginia. This latter section also notes the exploration status and a first-order indication of the exploitation potential of existing uranium resources in Virginia. The final section in this chapter describes uranium resource and reserve concepts, and reviews global and national uranium market trends.
Uranium deposits are known to occur as a result of a wide range of processes, from magmatic and fluid fractionation deep in continental crust to evaporation at the Earth’s surface (Box 3.1; Figure 3.2). The resulting concentrations of uranium within different rock types have an equally broad range, from a fraction of a part per million in ultramafic rocks up to 76 ppm in phosphorites (Lassetter, 2010; see Table 3.1). Uranium deposits have been mined with the most extreme range of grade (from about 1 × 102 grams/tonne of uranium for the phosphates of Florida, to nearly 2 × 105 grams/tonne of uranium in the unconformity-related McArthur River deposit in Canada) and tonnage (from a few tonnes for some intragranitic veins in the French Massif Central to nearly 2 million tonnes of uranium (tU) in Australia’s Olympic Dam deposit).
IAEA Classification of Uranium Deposits
The International Atomic Energy Agency (IAEA) has classified uranium resources—on the basis of their geological setting and morphology—into a number of ore deposit types (IAEA, 2009). These are presented here in order of their approximate global economic significance:
These deposits are spatially related to an unconformable contact separating crystalline basement from an overlying thick siliciclastic sediment sequence, with the deposits occurring at the contact level, and/or below or above the contact. Two subtypes of unconformity-related deposits are recognized (IAEA, 2009):
• Fracture controlled, dominantly basement-hosted deposits (e.g., McArthur River, Rabbit Lake, and Eagle Point in Canada; Jabiluka, Ranger, Nabarlek, and Koongarra in Australia)
• Clay bounded, massive ore developed along and just above, or immediately below, the unconformity in the overlying cover sandstones (e.g., Cigar Lake and Key Lake in Canada)