Orion remoulds an old footprint

With most of the infrastructure intact, Orion Minerals’ Prieska copper and zinc project is one of the most exciting developments in South Africa, writes Leon Louw, who visited the mine in February.

Venturing down ASX-listed Orion Minerals’ Prieska copper and zinc mine in the Northern Cape Province of South Africa, is like travelling back in time. Its feels as if everybody suddenly left, but not before they made sure no rock was out of place. The only indication that there were once people in these tunnels, which were mined by Anglovaal between 1971 to 1991, are white-painted markings on the rocks, exit and no entry signs, and a myriad of stopes and crosscuts – all perfectly intact, just as it used to be, frozen in time. 

The Anglovaal Group was formed in 1933 as the Anglo-Transvaal Consolidated Investment Company and in 1981 became Anglovaal. It was majority owned throughout its existence by the Hersov and Menell families. In 2003, Anglovaal became part of African Rainbow Minerals, a listed black empowerment company headed up by South African billionaire, Patrice Motsepe.

Anglovaal initially drilled 27 holes from 1968 to 71 and proved up a resource that they guessed would deliver in the region of 47 million tonnes of ore. Interestingly, according to Louw van Schalkwyk, executive: exploration at Orion Minerals, to prove up a resource of this size today, a company would have to drill more than 80 holes to be JORC-complaint. Nonetheless, when Anglovaal capped all the mine’s shafts in 1991, they had moved almost 45.68 million tonnes of ore to surface, using a vertical shaft 1 024m deep, and a single, reasonably steep portal decline access to level 120 (100m underground). From 120 level (which runs the entire length of the ore body), there are a series of four declines (one every 400m) that provides access to the bottom level of the mine.

Perfect mining conditions

As our vehicle descends the decline one cannot but notice the perfect ground conditions. According to Walter Shamu, chief operating officer at Orion, and a qualified rock mechanic, the old timers didn’t use a lot of ground support. “The gneiss rock in the hanging wall and footwall is extremely competent at 300MPA, and even the ore measures at about 200MPA. Nonetheless, despite these above-average mining conditions, we will still respect the integrity of the mine and will use a patterned support system and paste-filling as we develop the ore body underlying the existing infrastructure further,” says Shamu.         

He adds that there are more than 37km of primary access development in place and even more lateral ore development. All the underground infrastructure is perfectly intact, and this is Orion’s great advantage – they are developing a new footprint underneath an old one, and more than 70% of the work has already been done.

When Orion broke through the concrete caps plugging the shafts and removed backfill material placed to seal the network of underground tunnels thirty years ago, they found a gem. Despite fears that the mine had caved in on itself, pre-empted by the appearance of several sinkholes on the surface, all the infrastructure was still neatly in place, albeit flooded to within 300m of the surface. “The fact that the underground network of tunnels and steelwork in the vertical shaft were still in such good condition, will save Orion more than R5-billion of development costs in the long run. To sink a similar vertical shaft today will cost at least R1.2-million per metre of development, in addition to the time wasted and the technical and safety risks involved,” says Shamu.

The vertical shaft is an absolute key part of the Prieska project, and it is critical that the integrity of the headgear and shaft is maintained and that it can be used again. Once up and running, the vertical shaft will be used to transport men and material as well as for ventilation. Therefore, the most important project underway when I visited Prieska, was to do a detailed inspection of the steel used in the original construction of the shaft. A critical part of the mine re-entry will be dewatering the historic workings, which have rising water levels, and have risen about 40m in three years. During our visit, the water level was 300m below surface, which means almost 700m of the shaft was now submerged.

Shaft remains intact

Normally this would be of major concern for a project of this nature, but there are a number of reasons why Prieska is unique: the water is PH neutral and not acidic – which would have weakened the steel structure and damaged the concrete walls; runoff and precipitation is the main cause of flooding and not groundwater, and when Anglovaal built the shaft, they did it properly and way above required specifications.

“The water is not our main challenge. At the moment, we are running pilot water treatment trials, pumping 5 cubic metres of water per hour. At full scale we intend to be pumping out about 1 000 cubic metres of water per hour. In total, we need to get rid of about 8.5 million cubic metres that has accumulated in the shaft over the past 30 years or so,” says Shamu, standing on the solid platform erected in the shaft by the reconnaissance team contracted by PCDS, the engineering company appointed to test the integrity of the vertical shaft. The platform is at 299m below surface just above the water level. Next to the platform there is a big screen on which close-up images of the steel structure and shaft are relayed via two underground cameras. The camera’s stop every four and a half metres to get detailed images. These images are scanned, inch by inch, by a team of structural engineers and steel construction and shaft sinking specialist.

Any anomalies in terms of pattern, colour, water movement, or cracks are closely monitored and scrutinised again and again, to look for signs of potential failure. “We had to use divers to get the cameras and other equipment into the water so that we could test the main steel members of the shaft, which is really our primary concern. The lighter steel components will be removed and replaced,” explains Shamu. At first glance the steel frame looks fraught, but the team explains that the top part of the structure which has remained above the water level, has deteriorated more rapidly as a result of being exposed to oxygen.

According to Shamu, closer inspection of the steel members (above the water), has revealed that the main structural steel members are still 9mm thick, despite the wear and tear, which is still above the specs for a framework of this size and strength. The original steel installed by Anglovaal was 10mm in diameter. “A shaft of this size needs beams of only 7mm for the duties we plan for. Besides, we are not intending to overwork the shaft. In the Anglovaal days the mine was hauling out 250 000 tonnes of ore per month (tpm); we will only be carrying 200 000tpm with two skips, each weighing 22 tonnes, so we will be well below the maximum capacity,” says Shamu. He adds that Orion has made provision for 30% of the shaft’s steel to be removed and replaced.

Access to a world-class VMS deposit

Errol Smart, managing director and CEO of Orion says that initially they felt the water would be too murky to get a clear view all the way to the bottom of the shaft. “But at the moment (at the time of writing in early February 2020) we are at 758m below the water surface with the camera and we have visual confirmation that there are no skips or cages in the shaft, which was our other initial concern, says Smart.

So, is there a plan B in case the steel structure and headgear are found to be unsafe and cannot be used? Shamu explains that it will obviously result in a drop in margins, but that it would have to be almost a complete collapse to render the shaft unusable. “In the worst-case scenario, we still have the decline, which means we won’t be working optimally, but the project will still be viable,” says Shamu.            

Below 1025 level, underneath the bottom level of the historic mine workings, Orion intends accessing what Van Schalkwyk regards as “world class VMS copper and zinc deposit of 30.49 million tonnes (Mt) at 1.2% copper and 3.7% zinc.”

The ore body dips steeply and remains open to strike but flattens out considerably at depth, which is why Anglovaal packed up and left. They needed to recapitalise to go deeper and just couldn’t do it, exactly why Orion needs to raise an additional USD400-million in funding before work can continue.

The bulk of Orion’s new footprint will start below the 957m level. That is where they will construct new declines. Anglovaal made a start in the eighties and blasted an initial trail starting at 1025m below surface. They used small trucks and Load Haul Dumpers (LHDs), which wasn’t very efficient, and they just couldn’t keep up with development. “We will use more efficient methods of lateral development which will allow us to extract more ore and build an excellent business case of mining the rich, deeper deposit, “says Shamu.

Mining the ore

To get the ore out, Anglovaal utilised extremely intensive mining methods. They used 3.4m by 3.4m drives, 2.4km long. At that time, they obviously didn’t use remotely operated equipment and used crosscuts instead of open stopes, in the process leaving fantastically sound hanging and footwalls. Thereafter they put in long holes and had three levels to work from and dropped the ore down ore passes to a rail system at the bottom level. At the peak of mining, Anglovaal deployed up to 42 LHD’s at any one time in the mine.

Thus, the mining method then was extremely development intensive. Orion, on the other hand, will automate as much of the operation as possible and aim to reduce the amount of development that needs to take place. Where the ore body dips, the mine will use footwall drives, and when it flattens out, the method will be to drift and fill, so in a way those voids can be regarded as development as well. For Orion to mine 21 million tonnes of ore, they will have to do about 110km of additional lateral development, which will include decline shafts, drives and crosscuts.

According to Shamu, the ore will be mined using a bulk mining method, creating large voids backfilled with a cemented paste. “We’ll use Jumbo drill rigs for lateral development of the tunnels, longhole drill rigs for establishing the large production voids and LHDs to clean up all the blasted ore and transport it to the main haulage shaft. The loaders in production areas will all be remotely-controlled so that we don’t have operators at the face. A fleet of trucks will take the ore to the shaft bottom, from where it will be hauled up the vertical shaft,” says Shamu.

“Our intension from the beginning is to make sure that our design future-proofs the mine. In these early stages, we’re looking at remote loading to remove workers from the open stopes. At the same time, we are investigating battery technology and how much of it we can incorporate and adopt. The mine is not fully-automated, but we are looking at systems to put in place to lay the foundation to a switchover to complete automation,” says Shamu.

Good location and infrastructure

The Prieska mine is about four kilometres from Copperton, where the Anglovaal workers were housed. It is 65km from the town of Prieska, located on the banks of the fertile Orange River. The mine will send on average between 20 to 24 truckloads of concentrate a day to a rail siding 50km away, where it will be put on the Transnet line to Coega in Port Elizabeth, 800km to the southeast.

Orion has entered into a Memorandum of Understanding with Australian Byrnecut Offshore. Byrnecut will be doing the mine development while, similarly, Minopex have been co-opted to look at operating the ore processing plant. juwi Renewable Energies, the Cape Town based subsidiary of international project developer juwi AG, and Repli Trading No 27, a subsidiary of Orion Minerals, recently entered into a collaboration agreement to investigate generating renewable energy at the Prieska mine, and juwi will generate and supply 35MW of electricity from a hybrid power system using integrated wind and solar technologies. The renewable energy generation site will fall within 20km of the project site, making the establishment of a dedicated feed via overhead power transmission line possible.

Following the successful conclusion of value engineering studies on the ore processing plant design and layouts Orion recently placed orders and secured specific mills required to realise the identified improvements.

According to Smart, the company can now begin to lock in the anticipated project optimisations with associated positive capex and opex savings. “The plant optimisation studies progressed alongside studies on improved water treatment and optimisation of our mine-to-market schedule, all of which are nearing completion. The successful metallurgical optimisation of the process flowsheet has culminated in the opportunistic purchase of two unused, pre-owned mills which are available at a significant discount to mills which would otherwise have to be placed on order as a long-lead item,” says Smart.

The two 3600kW mills consist of a 16.5-foot diameter x 27-foot long ball mill and a 22-foot diameter x 26-foot semi-autogenous grinding (SAG) mill, complete with all motors, gearboxes, ancillary fittings with associated commissioning spares.

Securing these pre-owned but unused mills facilitates the incorporation of SAG milling into the ore processing flowsheet, in place of the ball milling arrangement selected in the Prieska Project Bankable Feasibility Study (BFS).

The revised ball and SAG mill configuration will allow significant operational flexibility and facilitate processing of Prieska ore at a rate of up to 20% above design throughput, allowing capacity for future expansion.

The use of SAG milling simplifies plant layout and operation, with significantly reduced upfront capital expenditure and a reduction in estimated operating cost, removing the requirement for multi-stage crushing and screening of rock ahead of milling.

Overall capital expenditure for the processing plant has been reduced by about AUD15-million from the total plant capital, originally estimated at AUD109-million and the plant unit operating costs reduced by 5% from a base estimate of AUD16.10 per tonne. This represents a significant improvement to be incorporated into the optimised and updated BFS report, due for completion in the second quarter of 2020.

The infrastructural advantages will make mining easier at Prieska. Moreover, the copper zinc project could be the start of a whole new mining complex in the Northern Cape. These deposits usually occur in clusters and Orion holds several licenses on land where there is a lot of potential for further discoveries. Moreover, the company is undertaking a number of additional exploration projects at sites with good prospects for nickel and cobalt, minerals that will be in high demand in the future.

Orion’s Prieska project is one of the few new mining developments in South Africa, and certainly a trailblazer in the Northern Cape. It is certainly a project to keep an eye on this year.

Leon Louw is a specialist in African affairs and mining. For more about doing business in Africa, mining and mining operations in Africa, and the political risk of operating in Africa, contact Leon by sending a message on Linkedin