Uranium ore-forming systems of the - Geoscience Australia

Uranium ore-forming systems of the Lake Frome regionFigure 6.12: FESEM micrograph (secondary electron image) showing the relationship between earlyconcentrically zoned framboidal pyrite (replaced by uraninite), euhedral pyrite, uraninite andkaolinite. Note that uraninite pseudomorphs of framboidal pyrite appear to be overgrown by theeuhedral pyrite, which also includes some uraninite. U = uraninite, Kaol = kaolinite, Py = pyrite.6.3.3.2 Other uranium mineralsDespite the high grade of mineralisation, other U minerals are rare in the Four Mile East deposit.A rare U-V mineral was detected. It is probable that this mineral is carnotite(K(UO 2 ) 2 Si 2 O 7 .6H 2 O). Another minor U-bearing phase containing S was also observed. A preciseidentification is not possible at this stage, although uranopilite ((UO 2 )6[(OH)10SO 4 ].12H 2 O) is apotential candidate. Alternatively this mineral may represent the replacement of pyrite byuraninite, with remnant S remaining in the crystal structure, although no Fe is present. Coffinitemay also be present in minor quantities, although this is inconclusive.6.3.3.3 Uranium-bearing phosphatesThe hydrated LREE-rich phosphates (rhabdophane and ningyoite) contain significant U, withningyoite containing more U than rhabdophane. Ningyoite has been observed only in the U-mineralised samples. Thus there appears to be a positive correlation between the presence of U-rich phosphates and uraninite. Further work is required to confirm this observation.6.4 COMPARISON WITH THE BEVERLEY URANIUM DEPOSITThe Beverley uranium mine is situated approximately 8 km from the Four Mile deposit. Despitetheir proximity, there are important mineralogical differences, the most significant of which is theU-hosting mineralogy. In contrast to the uraninite-dominant assemblage at Four Mile, uranium atthe Beverley deposit is hosted almost entirely by coffinite (U(SiO 4 ) 1-x (OH) 4x ) with only veryminor uraninite reported. The coffinite is present as fine disseminations amongst the clay-richmatrix. In some cases, coffinite mineralisation is preferentially concentrated around grains ofdetrital ilmenite (Fig. 6.13).Page 76 of 151