Prieska's maiden mineral resource is 24.2 million tonnes at 3.47% zinc and 1.23% copper for 873,655 tonnes of zinc and 297,129t copper.
This is in the ballpark of the historical resource at the South African project, which said it had about 1Mt of zinc and 370,000t copper to offer.
The vast majority of the estimate (23.8Mt) is in the inferred category, and 22.6Mt in the deep sulphide section of the orebody.
The resource estimate comes as Orion prepares its mining rights and environmental permit applications, expected to be filed by the end of the quarter.
Orion CEO Errol Smart said the resource was better than originally thought.
"This maiden mineral resource for Prieska far exceeds our original expectations for the target tested and demonstrates...