Weathered Bastnaesite Zone Mineralogy

The large size of the Ngualla rare earth deposit has enabled Peak to select the geologically and mineralogically most favourable portion for initial development. Metallurgical test work has identified this to be the high grade weathered Bastnaesite Zone due to the combination of host rock and rare earth mineralogy.

The weathered Bastnaesite Zone occurs as a thick blanket of high grade rare earth mineralisation from surface on Ngualla Hill. The mineralisation contains very low levels of uranium (15ppm) and thorium (53ppm) compared to other large rare earth deposits.

Optical mineralogy, SEM, XRD and QEMSCAN studies completed by Peak confirm that the majority of rare earth minerals occur as the flourocarbonate mineral bastnaesite, with trace amounts of monazite and cerianite in some local areas. The rare earth minerals are predominantly liberated, with grain sizes in the range of 10-120μm, with the majority under 50μm. The dominant gangue minerals are barite, haematite, goethite and quartz. Primary carbonate minerals (dolomite and calcite) have been completely removed through natural weathering processes.

The rare earth minerals occur as discrete fibrous or porous crystals or as inclusions in iron oxides. Some relict, predominately liberated grains of bastnaesite have also been identified. Barite is a dominant gangue species but is less associated with the REO carbonates compared to iron oxides.

The beneficiation and acid leach extraction stages of the mineral process developed for Ngualla take advantage of this favourable association of gangue and rare earth mineralogy to enables an efficient, low cost metallurgical process. 

Mineral summary for weathered Bastnaesite Zone mineralisation:

 Barite 40%
 Iron Oxides (Haematite and Goethite) 35%
 Quartz 15%
 Bastnaesite 6.5%

SEM image of weathered Bastnaesite Zone rare earth and gangue minerals:


Peak Resources Ground Floor,
5 Ord Street, West Perth,
Western Australia.

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