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Development and Redevelopment
Published in F.G.H. Blyth, M. H. de Freitas, A Geology for Engineers, 2017
F.G.H. Blyth, M. H. de Freitas
Alpha particles emitted from actinide elements are the principle cause of damage to the lattice of host minerals. The crystal lattice becomes disordered and up to 10% volumetric expansion may occur: crystals in this condition are described as being in a metamict state. Zircon is most susceptible to radiation damage (see examples in Fig. 4.34) and its volumetric expansion may exceed 10% (this contributes to the halo seen in micas and mentioned earlier). Zircon crystals that were 500 my old and in a metamict state, have been subjected to prolonged periods of heating and leaching in the laboratory but tenaciously retained their uranium. Such treatment did remove, from the crystals, lead that had been produced by the decay of uranium, the lead not being incorporated into the lattice of the zircon by reason of its incompatible ionic radius and charge. Ringwood quotes other examples: crystals of uraninite retrieved intact from conglomerates of the Wit-watersrand in S. Africa (2000 my old); thorianite derived from weathered pegmatites, occurs in 500 my old deposits of alluvial gravel, in Sri Lanka.
Nuclear reactors and their fuel cycles
Published in R.J. Pentreath, Nuclear Power, Man and the Environment, 2019
Uranium ores occur widely in many countries and in a variety of complex forms such as uraninite, uranothorite, thorianite and carnotite. Major reserves are those in the USA – notably in the area of the Colorado plateau spanning the states of Utah, Colorado, Arizona and New Mexico, and also in the state of Wyoming; other major reserves occur in Canada, Australia, South Africa, Namibia, Niger, France and Zaire. Uranium-bearing minerals often occur in mines in conjunction with other ores, as in the silver mines of Czechoslovakia, the gold mines of South Africa and the cobalt and silver mines in Canada’s Northwest Territory. A few mines, such as those in Zaire, are opencast, but the majority are hardrock underground mines. The principal hazard to the miners is the 222Rn and its daughters already discussed in chaper 2. The concentration of radon daughters is expressed in a unit called the working level (WL), not a very apt term. The WL is defined as any combination of radon daughters which, in 1 litre air, will result in the ultimate emission of 1.3 x 105 MeV potential alpha energy; it corresponds to an activity concentration of 3.7 Bq 1-1(100 pCi 1-1) 222Rn in equilibrium with its short-lived daughters. There is no doubt that miners of uranium have, in the past, died from cancers of the respiratory system as a result of inhaling radionuclides in poorly ventilated mines. Inevitably, strict correlations between exposure and the incidence of such cancers have been difficult, particularly when habits such as smoking have also to be considered.
Mineralogy of various types of Th-U-REE mineralisation in the iron oxide – apatite deposits of the Bafq district, Central Iran
Published in Applied Earth Science, 2023
Khalegh Khoshnoodi, Samaneh Ziapour, Mohammad Yazdi, Michel Cuney
The Saghand Anomaly No.2 is an iron-uranium ore with significant concentration of REEs. The ore consists of a magnetite-serpentine-talc paragenesis or of predominantly talcitised rock with aggregates of pyrite and molybdenite crystals. There are veinlets of pink calcite (up to 2 cm thick) or light-grey ferrodolomite as well as notches of chlorite. The main U-REE minerals in Anomaly No.2 of the Saghand deposit are uraninite, cleveite and minor brannerite and thorianite. Sometimes, uraninite (Figure 11(a)), brannerite and molybdenite are included within the magnetite crystals. Haematite grains within talc form accumulations around the uraninite crystals or replace magnetite. Uraninite is presented as cubic, hexagonal and trigonal crystals from a few microns up to 75 µm in size (10–20 µm in average) with varying compositions from pure uraninite to cleveite (Figure 11(b)). Most uraninite crystals have a zonal structure. I Inclusions of magnetite may occur in the uraninite crystals or as intergrowths (Figure 11(b)). Small parts of uraninite crystals are found within molybdenite aggregates (Figure 11(c)) and also intergrown with brannerite. The individual brannerite crystals form aggregates up to 0.5 mm large. Uraninite and cleveite from Anomaly No.2 of the Saghand deposit contain significant amounts of Y, Ce, Gd, Dy, Yb, Er, Nd and Sm (Table 7), and brannerite contains small quantities of REEs (twice lower than in uraninite). The Y2O3 content of Y-uraninite ranges between 11.35 and 20.77 wt-%. The uranium content of brannerite decreases while it is gradually altered into titanium oxides.