Vancouver — With a scoping study in hand,
The bench-scale metallurgical study, slated to start next month, is intended to precede development of the potential open-pit tungsten resource. Drill results indicate that the mineralized zone is a flat-lying body up to 160 metres thick, which stretches for 2 km east-west and 300-400 metres across. Four drill rigs are operating.
Mineralization is hosted in skarns and their greisenized or retrograde equivalents. Greisenization refers to a replacement process whereby quartz, fluorine and micas — as well as accessory minerals such as tourmaline, rutile, cassiterite and wolframite — replace skarns or granites.
At Nui Phao, the greisenization consists of high-fluorine, beryllium, tungsten, tin and limited rare earth metals, which have replaced granitic dykes and earlier-formed skarn units.
The scoping study was completed by New Brunswick-based Thibault & Associates. It determined that tungsten, the primary commodity, is easily recoverable by both gravity and flotation methods.
The processing concept envisions the use of gravity preconcentration to raise the grade of tungsten trioxide from to 1% from 0.5%. A gravity concentration test increased the tungsten grade by 3.8 times and recovered 94% of the tungsten (concentrate and middling) using a minus-150-micron grind.
Preconcentration would be followed by the recovery of tungsten, copper and fluorite through a combination of gravity and flotation. Bismuth may be recovered by hydrometallurgy. As a final step, the tungsten concentrate would be processed into a high-purity ammonium paratungstate.
The potential recovery of the gold content was not included in the study. It will be addressed as part of an upcoming bench-scale study.
This new study will evaluate the relationship of grade recovery to grind size. It will also assess how the operations will comply with grade and market specifications and environmental guidelines. It will include a design of the process flow-sheets, equipment sizing and layouts.
The Nui Phao project is in the Dai Tu district of Thai Nguyen province, about 80 km northwest of Hanoi.
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