A conceptual study of De Grey’s Hemi gold mine in Western Australia has demonstrated the potential for underground mining to increase the project’s production profile.
The study builds upon the recently released regional scoping study and the Hemi mineral resource estimate from November 2023.
The study found that there is potential for underground mining to run in parallel with open-pit mining at Hemi, which “presents a strong case for further studies, while not distracting from the primary focus of the Hemi project development”.
Other findings include:
- Hemi’s mineral resources beneath the definitive feasibility study (DFS) open-pit designs at the Diucon and Eagle deposits are mostly in the inferred category;
- access to mineral resources beneath Hemi’s DFS open-pit designs could be achieved with two separate declines; and
- a combination of each decline’s maximum haulage rate of 2–2.5 million tonnes per annum (Mtpa) and potential mine plan stope widths and stoping methods point to a maximum haulage rate of 4–5Mtpa.
De Grey managing director Glenn Jardine said Hemi provides the company with a provincial scale exploration and production opportunity.
“The [underground mining conceptual] study presents an opportunity to potentially introduce underground mining concurrently with open-pit mining at Hemi,” he said.
“Pleasingly, the study has been successful in demonstrating there is a potential to support this objective. This has potential to introduce additional flexibility during the operations phase.”
In November, Hemi’s MRE increased by 1.3 million ounces (Moz) and now stands at 264 million tonnes (Mt).
A total of 2Moz sits beneath the maximum depth for open-pit mining of 390m. However, the extent of mineral resources at depth is limited by drilling.
To address this, De Grey will use the next 12 months to continue drilling at Hemi to confirm extensions to mineralisation and complete infill drilling at Eagle, while progressing metallurgical testwork, geotechnical and hydrological studies for the project.
“This will allow the assessment to progress at a modest rate while maintaining our organisational focus on the development of the main Hemi project,” Jardine said.
The successful underground mining conceptual study follows the De Grey board unanimously recommending Northern Star’s $5 billion takeover offer.
Hemi is located in the Pilbara region of WA, with exploration tenements stretching approximately 150km east to west.
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