MNN Awards: De Grey flying high with potential 'world class' Hemi gold discovery

A WORLD-class gold discovery looks well in the making at De Grey Mining’s Hemi prospect in the Pilbara region of Western Australia.
MNN Awards: De Grey flying high with potential 'world class' Hemi gold discovery MNN Awards: De Grey flying high with potential 'world class' Hemi gold discovery MNN Awards: De Grey flying high with potential 'world class' Hemi gold discovery MNN Awards: De Grey flying high with potential 'world class' Hemi gold discovery MNN Awards: De Grey flying high with potential 'world class' Hemi gold discovery

Hemi, near Port Hedland, WA

First aircore results in December last year pointed to an exciting find, and ongoing, outstanding RC and diamond core results since have confirmed the discovery.

Based on De Grey's market capitalisation of late, how big the discovery-is, is the ‘one billion dollar question'.

While there have previously been suggestions a maiden estimate would be forthcoming in the second half of 2020, more recent indications are 2021 is the more likely timeframe.

"The scale of Hemi is such that we have needed to keep testing the mineralised extents of Hemi," De Grey MD Glenn Jardine told MNN this week.

"We are allowing ourselves time to do that before getting into resource definition."

Earlier this month the company said Hemi's dimensions had grown to "approximately 2.5km north to south and 2km west to east with three main zones (Aquila, Brolga and Crow) defined within this large gold system".

A current estimate by Argonaut analyst Matthew Keane is 3.8 million ounces at 1.5-1.7 grams per tonne gold.

"This estimate does not extrapolate beyond current drilling or below 200m down-dip," Keane said this week in a note to clients, with drilling underway to 350m depth.

Keane speculates the internal target for Hemi is more than 5Moz.

He also sees the potential for the overall Malina project containing Hemi to grow beyond 10Moz within 2-4 years.

Malina currently has 2.2Moz.

Those ounces are in multiple deposits including the 524,000oz Toweranna deposit grading 2.2gpt.

Toweranna was a key factor in the discovery of Hemi.

"I have been saying the Hemi discovery is a ‘four-year overnight success'," De Grey's technical director (and geologist) Andy Beckwith told MNN.

"The discovery came about by securing a large tenement package over a highly prospective structural corridor.

"Then a lot of forensic geological work was done on a good geological data set based on the past work done by De Grey and other explorers including Resolute and Range River, and our Chinese major shareholders.

"The work we did on Toweranna highlighted the potential of the intrusion hosted (mineralisation).

"This was supported by work done by the WA Mines Department which supported the (concept) intrusions (Sanukitoids) occur in our project and … are related to gold in the Yilgarn.

"From there we applied that knowledge (and) strong belief and targeted the Hemi corridor as a consequence."

Other intrusions in the region remain to be tested.

Meanwhile, aside from the size of Hemi remaining the big unknown, the other key question to play out is the metallurgy of the discovery.

Initial results released last month showed the sulphide mineralisation had a refractory element and would require additional processing - involving, for example, pressure oxidation.

However, the good news was 92-93% of gold was recovered in less than 10% of the initial mass from flotation of fresh rock.

"This would substantially reduce the scale of POX plant under a development scenario (assuming POX is the preferred method for sulphide oxidation)," Argonaut's Keane said.

"As a comparative, Alacer Gold's Çöpler sulphide ore is less amenable to flotation and applies whole ore POX."

Aside from Alacer, Keane pointed out POX is a commonly utilised oxidation process used in profitable mines such as Porgera and Lihir, as well as Carlin deposits in Nevada, USA.

And given the geometry and scale of mineralisation continuing to be revealed at Hemi, there's every indication a large, profitable gold mine in the Pilbara region of WA could ultimately join that group.

De Grey Mining is a nominee for Explorer of the Year in the 2020 MNN Awards for the Hemi gold discovery.

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