Uranium ore-forming systems of the - Geoscience Australia

Uranium ore-forming systems of the Lake Frome regionAluminous hydroxy phosphates Aluminous hydroxy phosphates of the crandallite group arepresent in four of the analysed samples. The general formula of the minerals of this group isAB3(XO4)2(OH)6.H (Schwab et al., 1990). The XRD and EDAX data indicate that it is aphosphate of the florencite-crandallite series containing LREE, Ba and Ca. The A position is filledby Ce, La, Ba and Ca, the B position by Al or Fe and X by P or S. Figure 6.8 shows thephosphates forming along cleavages in kaolinite (also evident in XRD spectra, see Fig. 6.7). Thenearby uraninite also forming along kaolinite cleavages does not contain LREE or Ba.6.3.2.3 Other secondary mineralsSphalerite was observed in minor quantities in one sample. Titanium-oxides (most likely lowtemperatureforms, possibly anatase or lucoxene) may be considered a secondary phase, as theyare commonly seen to replace detrital ilmenite.Figure 6.8: FESEM micrograph (backscattered electron image) showing kaolinite with uraniniteand a La-Ce-Ba-Ca aluminous hydroxy phosphate forming along cleavages.6.3.3 Uranium-hosting mineralogy6.3.3.1 UraniniteUraninite is the dominant U-hosting mineral in all Four Mile East samples. Electron microprobeanalysis of uraninite grains contain up to 68 wt. % U. The rare earth elements including La, Ce,Nd, Sm, Gd, and Dy, which substitute for U 4+ in the uraninite crystal structure (Janeczek andEwing, 1992), are present at concentrations of up to 3.6 wt. %. Of the REE, Dy is particularlyabundant, constituting up to 2.1 wt. % of the uraninite. By comparison, Ca, which also substitutesfor U 4+ , is relatively low (average of 1.3 wt. %). Arsenic and S reach concentrations of 1.3 wt. %and 1.5 wt. %, respectively.Page 73 of 151