A new cobalt and gold inferred resource estimate totals 6.683 million tonnes at 0.17% cobalt and 0.17 g/t gold, confirming Mutooroo as one of Australia’s highest-grade sulphide cobalt deposits associated with copper.
When added to previously estimated measured and indicated resources the total combined Mutooroo sulphide resource is 12.53 million tonnes at 1.53% copper, 0.16% cobalt and 0.20 g/t gold for 20,000 tonnes of cobalt and 80,600 ounces of gold.
Large cobalt inventory
The new cobalt estimate combined with the Kalkaroo project resource expands the company’s total cobalt metal inventory by 37% to 43,400 tonnes with appreciable upside potential.
Havilah’s technical director Dr Chris Giles said: “Mutooroo’s 0.16% cobalt resource grade makes it one of the highest-grade sulphide cobalt deposits with associated copper in Australia.
“Such sulphide cobalt deposits are generally rarer and smaller than nickel-cobalt laterite deposits but they usually have significant mineral processing advantages.”
Mutooroo JORC mineral resource summary.
Havilah shares have been almost 10% higher at 10 cents intra-day, up from 5.3 cents at close on March 13.
The new JORC-compliant cobalt and gold inferred resource was estimated by Havilah using the previously reported Mutooroo copper sulphide inferred mineral resource shell.
In that previous resource estimation, there was insufficient assay data to define either a JORC inferred cobalt or gold resource, as noted at the time.
Subsequently, diamond drill core from five deep Mines Exploration Pty Ltd (MEPL) Mutooroo drill holes dating from the 1960s was located and re-sampled in the South Australian Drill Core Reference Library and then re-assayed.
The mineralised sulphide intervals in each hole were analysed for a number of elements, including cobalt and gold that were not previously assayed.
Diamond core re-assayed
These re-assays provided the critical additional cobalt and gold data required to allow the estimation for these metals in the deeper part of the sulphide lode.
There is good potential to convert the deeper inferred resources to the indicated and measured categories by infill drilling between the existing, widely-spaced, MEPL 1960’s diamond drill intersections. Thus far, only approximately 700 metres of the more than 2,000 metres strike of the sulphide mineralisation has been drilled to JORC measured and indicated resource status by Havilah, predominantly to a depth of less than 200 metres.
The cobalt-bearing iron sulphides are potentially an attractive grade cobalt feedstock for subsequent processing to recover cobalt and also if feasible, significant amounts of associated gold and sulphur.
Establishing recovery process
Establishing the most efficient metallurgical process for recovery of cobalt from the iron sulphides is an important focus of Havilah’s pre-feasibility study (PFS) metallurgical test work.
Havilah’s overall cobalt resource is substantial, especially considering it will be potentially produced as a by-product of mining operations sustained by copper at Mutooroo and copper-gold at Kalkaroo.
Cobalt recovery from sulphide deposits typically relies on well-established concentration processes with a considerably lower capex and opex compared to nickel-cobalt laterites that normally require large volumes of sulphuric acid for the high-pressure acid leach processing.
Giles said: “The economics of Mutooroo as an open pit, and later as an underground, mining operation are underpinned by comparatively high grades of copper (1.53%) in the sulphide ore.
“Any revenues from by-product cobalt, gold and sulphur can substantially improve returns from the Mutooroo project.
“Our immediate PFS tasks at Mutooroo are to increase the shallow open pit sulphide resource through further drilling and to determine the best possible option(s) for the recovery of cobalt from iron sulphide concentrates.”