Prieska crown pillar +105 level resource increases ahead of trial mining

25th July 2023 By: Cameron Mackay - Creamer Media Senior Online Writer

Diversified metals explorer and developer Orion Minerals on July 25 announced that the company has taken another key step in its early mining strategy at the Prieska copper/zinc project in South Africa’s Northern Cape.

This includes the completion of an updated mineral resource estimate (MRE) for the near-surface +105 level crown pillar comprising indicated and inferred resources of 2.3-million tonnes, grading 1.7% copper and 1.6% zinc.

“Our strategy to bring the Prieska copper/zinc mine back into production is now rapidly gaining momentum, with the completion of this updated mineral resource for the near-surface, +105 resource block, outlining a very attractive early mining opportunity at this fully permitted mine,” enthuses Orion MD and CEO Errol Smart.

“The supergene sulphide, indicated resource, with a grade of 2.6% copper, is a compelling focus for our early mining strategy. This resource block is accessed from existing underground development through a short ramp, allowing trial mining to begin in the coming weeks.

“Ore sourced from the trial mining will be used for metallurgical optimisation tests and for the detailed design of an initial processing plant at Prieska.”

He adds that discussions with metallurgical processing and engineering groups interested in offering processing facilities under build-own-operate-transfer arrangements are also under way.

“The trial mining phase, metallurgical process optimisation and a resultant updated bankable feasibility study (BFS) are fully funded with a total of R370-million, available from our Industrial Development Corporation and Triple Flag funding facilities.

“A first drawdown call for R167-million was made from this facility in the past week. Orion is now getting ready to embark on its transformation to an operating mining company,” he adds.  

The updated MRE for this shallow portion of the Prieska deposit represents a robust focus for the trial mining programme scheduled to begin in the next few weeks. The updated MRE is based on a successful drilling programme completed in 2022. 

The +105 level crown pillar is located in close proximity to existing underground infrastructure and can be readily accessed, allowing trial mining activities to commence immediately with all required permits and funding now in place.

This programme will generate key metallurgical and other data that will assist with process plant design and also feed into an updated BFS for the early production strategy at Prieska.

The updated MRE for the +105 level crown pillar brings the total indicated and inferred mineral resource, including the deep sulphide mineral resource of the Prieska project, to 31-million tonnes, grading 1.2% copper and 3.6% zinc.

The geological wireframe and resource estimate for the +105 level mineral resource have been updated to include additional drill data from the 2022 drill campaign. There has also been a review of the modelling of metallurgical zonation in all areas of the +105m level mineral resource with refinements applied, where appropriate.

Additional drilling and changes to the resource model successfully increased the total +105m Level mineral resource from 1.8-million tonnes, grading at 1.5% copper and 2% zinc to 2.3-million tonnes, grading 1.7% copper and 1.6% zinc, including indicated resources of 1.9-million tonnes, grading 1.82% copper and 1.7% zinc and inferred resources of 0.4-million tonnes at 1% copper and 0.8% zinc. 

Since the previous +105 m level mineral resource, 14 holes comprising 918 m were successfully drilled to intersect supergene sulphide mineralisation.  A further five holes were drilled and abandoned owing to poor ground conditions and unacceptable core loss.


The Prieska copper/zinc deposit is a volcanogenic massive sulphide deposit that is situated in the southernmost exposures of the north-northwest trending Kakamas Terrain, which forms part of the MidProterozoic Namaqualand Metamorphic Complex. The deposit is hosted by the Copperton Formation of the Areachap Group. 

The structural sequence at the mine consists of a footwall Smouspan Gneiss Member; Prieska Copper Mines Assemblage, which hosts the sulphide mineralisation; and the hangingwall Vogelstruisbult Gneiss Member.

The +105 m level resource occurs above the upper limit of the historically mined Prieska copper/zinc deposit at about 105 m depth below surface, up to surface. It has a strike length of about 1 km and thicknesses vary between 1.5 m and 23 m.

The +105 m level resource block comprises six defined zones.

This includes a haematite-goethite-quartz oxide zone (gossan) from surface to about 33 m, clay (kaolinite)/leach zone developed in places below 33 m, and a chalcocite dominant supergene sulphide zone between about 42 m and 70 m.

Mixed supergene-hypogene sulphide zone between about 70 m and 90 m below surface. This has a relatively sharp contact with the underlying hypogene massive sulphides.

This comes in addition to a hypogene sulphide zone consisting of the unaltered, fresh massive sulphides.

Lastly, a separate zone of elevated copper and zinc values in the oxides (where there is adequate drilling information) in the hangingwall to the main +105 m level crown pillar is present in the northwest of the deposit for about 300 m strike. The zone converges with the main zone towards the southeast.

Four zones have been defined for inclusion as part of the +105m level mineral resource and these are referred to as the HW oxide zone, the oxide zone, the supergene sulphide zone and the hypogene zone.

The total tonnes increased to 2.3-million tonnes, from 1.8-million tonnes in 2019.

The copper tonnes have increased from 27 000 t in 2019 to 38 000 t, and the zinc tonnes have slightly increased by 300 t.

The increase in overall tonnes can be largely attributed to the extension of the interpreted crown pillar mineralised zone towards the southeast to where it intersects the sidewall of a sinkhole.

The more comprehensive interpretation of the mineralised zone in the hangingwall to the main crown pillar mineralisation also contributes significantly to this increase in tonnage, and to that of the oxide tonnage.

The changes in the interpretation of the bottom of the oxide zone, particularly in the northwest, had a significant positive impact on the oxide tonnage.

The increase in copper tonnes can be largely attributed to higher grades in the southeast of the supergene sulphide zone from the 2022 drilling, the extended interpretation of the crown pillar mineralisation to the southeast, and the changes in the interpretation of the bottom of the oxides.

The +105 m level mineral resource is reported above a 0.3% copper cut-off. This corresponds with the wireframe modelling and is similar to that used in many opencast mining deposits worldwide.

While openpit mining was previously evaluated for the deposit, underground mining for the +105 level resource is now being considered as an optimisation alternative, with underground trial mining to begin in coming weeks


An infill drilling programme of about 1 700 m on the oxide resource to provide a further upgrade in confidence and additional metallurgical information is planned for the third quarter of this year.

This is, however, not critical to the current early mining BFS studies. Apart from this infill drilling of the oxide resource, no additional drilling is planned for mining of sulphide ore before the completion of the updated BFS later this year

Grade control drilling on a closely spaced grid will be executed during the operational phase of mining.