Blackham Resources Ltd (ASX:BLK) has added a further 620,000 ounces to its gold bounty at the Wiluna Gold Operations in Western Australia.
The new ounces come from an initial resource estimate for the historical tailings which have accumulated at a site within 2 kilometres of Wiluna’s processing plant since the 1930s.
Recent metallurgical test work has shown that potential gold recoveries between 42-50% can be achieved through standard mining and gold leaching processes.
Blackham is also continuing its exploration programs into priority targets at the Lake Way prospect, the first new drilling in the area in 12 years.
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Resources were estimated by Blackham for the various tailings impoundments using historical data and the data from two recent drill campaigns.
The first campaign of rotary auger drilling undertaken in 2017 tested tailings across six prospects and 26 holes, for a total of 475.5 metres.
Only 16 holes drilled in Dam H from this program were used in the resource estimation.
The second campaign of aircore drilling was completed last month, totalling 63 holes for 1,576 metres.
Tailings deposits at the Wiluna operations
Tailings mostly from sulphides treatment
The tailings material has been deposited around the plant from over 4.4 million ounces of gold production over 80 years.
A significant proportion of the tailings result from processing of the Wiluna underground sulphide ores through the Biox plant over the last 13 years.
Historical processing records indicate the average tailings grade of these sulphides is 0.72 g/t.
The notable exception to the sulphides is material in the bottom part of Dam C, the largest single resource, with upper layers of sulphides and the lower part from oxide ore treatment.
These oxide and transitional ore residues are from the mining of the Wiluna open pits between 1985 and 1997.
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A scoping study was completed for the Wiluna tailings retreatment in 2016 by Independent Metallurgical Operations Pty Ltd.
It comprised preliminary metallurgical test work using Dam H tailings data and a review of potential recovery and treatment options for all storage facilities and pits.
The options considered produced acceptable financial returns and indicated a potential gold recovery of 42-50% via a whole of ore leach.
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Initial test work confirmed the tailings material is sized between 38-75 microns, removing the need for further grinding and significantly reducing reprocessing costs.
The tailings can be treated through the current operating carbon-in-leach circuit without the need for further milling or concentration.
Blackham is continuing to undertake technical work on the tailings to confirm potential mining and processing options for possible integration into the company’s future operations.
Feasibility studies will be aimed at confirming the best metallurgical properties and optimal flowsheet; assessing best method of materials handling; and integration with the existing free milling and planned sulphide operations.