Vancouver — Tiberon Minerals (TBR-T) has kicked off a metallurgical test program to enhance the bismuth recovery at the Nui Phao tungsten polymetallic deposit in Vietnam.
The measured resource at the Nui Phao deposit hosts 27.1 million tonnes of ore that contains an average of 0.1% bismuth. Only 10% of this will be recovered as a cleaning by-product from the tungsten gravity circuit. Previous test work indicates that the sulphide waste stream contains about 60% of the bismuth at an estimated grade of 0.17%. Tiberon estimates that the waste stream would loose about 2,100 tonnes of bismuth annually under the current processing scheme.
In addition, metallurgical studies indicate that gold is associated with the bismuth, therefore any increase in bismuth recovery will likely have the potential to enhance gold recovery.
If the studies are successful, increased bismuth recoveries will have a significant positive impact on the economics of the project. Results are expected in May.
Bismuth is a relatively rare metal that has a very low melting point and very low thermal conductivity. It is used mainly in the pharmaceutical sector but is also used in zinc galvanization, cosmetics, electronics and various chemical applications.
China is the single largest producer of bismuth, with more than half of that production resulting as a by-product of tungsten production. The current price of bismuth is approximately US $3.00 per pound or $6,600 per tonne.
The measured resource at Nui Phao stands at 27.1 million tonnes averaging 0.68% tungsten trioxide equivalent, or 0.25% tungsten trioxide, 0.25 gram gold per tonne, 0.23% copper, 0.11% bismuth and 8.2% fluorite. The calculation was based on a 0.2% Tungsten trioxide equivalent cut-off grade. The indicated portion of the resource is pegged at 22.3 million tonnes averaging 0.60% tungsten trioxide equivalent, or 0.19% tungsten trioxide, 0.22 gram gold, 0.21% copper, 0.104% bismuth and 7.9% fluorite. Inferred resources are 24 million tonnes averaging 0.55% tungsten equivalent, or 0.18% tungsten trioxide, 0.16 gram gold, 0.16% copper, 0.081% bismuth and 8.1% fluorite.
The prefeasibility study envisages that the Nui Phao project will be operated as a conventional truck and loader open-pit mine. The mine is would operate at 10,000 tonnes per day for a mine life of 16 years. The single open pit is expected to have an overall strip ratio of 1.6 tonnes waste to 1.0 tonnes ore.
The process plant design envisages a conventional “gravity plus flotation” tungsten concentrator. Preliminary metallurgical test work indicated that recoveries of 80% tungsten, 70% fluorite, 75% copper, 20% gold, and 10% bismuth were possible. The plant would consist of conventional three stage crushing circuit, ore storage and reclaim, grinding, sulphide and copper flotation, gravity concentration of tungsten, tungsten and fluorite flotation, and storage of concentrates.
Results of a financial analysis indicate that the project has a potential after-tax internal rate of return of 20.9% and an after-tax net present value US$125.6 million at a discount rate of 7.5%.
Tiberon holds a 70% interest in the Nui Phao deposit with the minority interest divided equally between two Vietnamese partners.
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