The earliest geological investigations on the Brockman rare metals deposit were undertaken during the period 1982-85 by Union Oil Development Corporation ((UODC). In 1983-84, UODC completed detailed geological mapping, and reconnaissance stream sediment, soil and rock chip geochemistry. Nineteen (19) trenches (3,500 metres) were established across the outcrop of the Niobium Tuff, returning grades up to 0.45% Niobium and 0.23% Tantalum.
UODC drilled nineteen reverse circulation (RC) and diamond drill (DD) holes and commissioned mineralogical studies which identified the fine-grained nature of the mineralisation, with an average grain size of less than 10 microns.
In 1985, UODC passed management of the project to its joint venture partner, West Coast Holdings (WCH) which undertook further drilling in 1988, with an additional 23 RC/DD holes.
WCH commissioned extensive metallurgical test work programmes that led to the establishment of a flow sheet devised to extract all minerals of potential economic interest. At that stage, the project was considered as a rare metals project, and as a consequence the flow sheet was developed to maximise the value of the rare metal elements including zirconium and niobium. The rare earths were only considered as a by-product. In 1990 a pilot plant was established at the Warren Spring laboratory in the UK and 100 tonnes of material was processed to confirm the rare metals flow sheet.
Following the acquisition of the project in December 2010, Hastings completed a 51-hole drilling programme (8,200m) which provided 7 DD and 41 RC intersections of the mineralised zone. These intersections confirmed previous results and provided deeper intersections of the mineralisation. This enabled a new interpretation of the deposit to be completed and allowed resource estimates to be undertaken.
Having established a large resource of heavy rare earths, the Company appointed metallurgical consultants to confirm the results of the previous test work. ANSTO completed the first stage of testwork on REO recoveries. Low temperature sulphation baking and water leaching tests were conducted to optimise recovery of the valuable components. Recoveries of rare earths (75%), niobium (75%) and zirconium (70%) were obtained. This confirmed the results of the 1990 pilot plant.
The next phase of processing work was to devise a method of separating the valuable components from the waste (non-valuable) components. A solvent extraction circuit similar to the Warren Spring pilot plant was trialled but required additional design work to overcome operational issues. ANSTO developed a two-stage primary solvent extraction circuit, where the rare metals, zirconium and niobium, can be extracted from the water leached sulphation product. The remaining liquor is then processed through another solvent extraction circuit to extract the rare earths values. The waste components are left behind. This separation of the rare metals, zirconium and niobium, from the rare earths and waste is the vital second stage of the process flow sheet development. The valuable components are now separated and work can begin on adding value. It is Hastings’ intention to produce high quality dysprosium oxide and yttrium oxide, with remaining rare earths as a mixed oxide, whilst producing rare metal by-products meeting customer specifications.
Although a successful process route has been identified and bench tested, the Company is still considering a number of alternative beneficiation and processing options.
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