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Treated water boosts Prieska’s business case

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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. Image credit: Leon Louw for WhyAfrica

Treated water boosts Prieska’s business case  

Trails are underway to treat underground water pumped from the historic shaft at Orion Mineral’s Prieska Copper-Zinc Mine (PCZM).

By Leon Louw founder and editor of WhyAfrica (Treated water boosts Prieska’s business case)

When WhyAfrica visited the Prieska mine in late July this year, plans were already afoot to start pumping water from the old historic shaft.

The shaft infrastructure is still in top condition, despite being submerged since the mid-1990’s. Being able to pump and use the underground water will add additional value to a project already regarded as high value.

According to Orion’s Managing Director and CEO, Errol Smart, the company has started a series of field trials for the treatment of mine water using a proprietary electrolytic technology to produce saleable products. “The process has the potential to extract valuable products such as calcium and magnesium, for agri-nutrient use,” says Smart.

Smart adds that other products with potential for byproduct sales in the chemicals industry will also be extracted by the process.

“The water treatment trials are being undertaken in collaboration with Free Radical Process Design (FRPD), a South Africa-based technology company which has developed an innovative and proprietary process and equipment for the continuous extraction of metals and other valuable minerals from water using electrowinning via a rotating cathode (Electrosoftner),” Smart explains.

The Electrosoftner has the potential to extract iron hydroxide, hydrogen, calcium, magnesium and base metals such as nickel, zinc and copper from contaminated mine waters. The ability to harvest the agri-nutrients at the Prieska Copper-Zinc Project has the potential to offer important host-community development opportunities.

Prieska is located in a region where renewable energy is abundant and where irrigation agriculture is a core industry.

This will advance Orion’s vision of establishing a ‘green’ footprint for the Prieska Project with broad stakeholder benefits as part of its objective to have a world-class ESG framework to support its operations.

Treated water boosts Prieska’s business case

The extensive underground workings at Prieska hold approximately 9 million cubic metres of water, which has accumulated since the mine was closed by Anglovaal in 1991. While the quality of the mine water is relatively benign, with pHs ranging between 6.6 to 7.1 (neutral pH is 7.4), and total dissolved solids measured in the shaft water range between 6,000 and 11,000 mg/l, some water treatment is required if the water is to be considered for off-site discharge and subsequent agricultural or potable applications.

The dewatering set-up consists of pump sets and reticulation that will extract mine water from underground workings at a pumping rate that will build up from 120m3/hr to 500m3/hr.

Once on the surface, some of the water will be treated by reverse osmosis (RO) while the balance will be treated by electrolysis. Some brine water will be retained in evaporation dams.

The treated waters will be used for irrigation projects, which will benefit local host communities. Dewatering is planned to occur over a three-and-a-half-year period, during which time mining is planned to commence in those parts of the Prieska deposit above the water level so that copper and zinc concentrate production can commence within less than three years, as scheduled in the original project development plan (BFS-20 Plan).

Rotowinner Metal Extraction Process FRPD has patented technology for the continuous electrowinning of selected minerals from mineralised leachate using a rotating cathode.

The Rotowinner consists of a rotating cathode, submerged in pregnant leachate with a scraper arrangement to remove the precipitation of minerals on the cathode.

The scraped material is discharged into a collection launder and the spent leacheate is collected to be recycled in the leach circuit. A mobile demonstration scale plant has been constructed that has been successfully used to produce base metals on a continuous basis.

A sold mining foundation

With most of the infrastructure intact, Orion Minerals’ Prieska copper and zinc project is one of the most exciting developments in South Africa. Hopes are high that the project will come into fruition soon and kickstart the Northern Cape region, and South Africa’s faltering economy.

Venturing down Prieska’s decline is like travelling back in time. The ore body was mined by Anglovaal between 1971 to 1991, and the infrastructure was left intact.  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. 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. The old timers didn’t use a lot of ground support. According to Clive Benhura, Geologist at Orion, 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, Orion will still use a patterned support system and paste-filling as they develop the ore body underlying the existing infrastructure further.

There are more than 37km of primary access development in place and even more lateral ore development at Prieska. 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. The challenge is that this infrastructure is flooded, and the water needs to be pumped out.

The fact that the underground network of tunnels and steelwork in the vertical shaft were still in such good condition, will save Orion significant development costs in the long run.

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.

A detailed inspection of the steel used in the original construction of the shaft was undertaken and has proven to be successful.

The main structural steel members of the vertical shaft are 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. In the Anglovaal days the mine was hauling out 250 000 tonnes of ore per month (tpm); Orion plans to only carry 200 000tpm with two skips, each weighing 22 tonnes, so  well below the maximum capacity.

Below 1025 level, underneath the bottom level of the historic mine workings, Orion intends accessing a world class VMS copper and zinc deposit.

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.

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. Orion will use more efficient methods of lateral development which will allow them to extract more ore and build an excellent business case of mining the rich, deeper deposit.

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 Smart, 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.”

Good location and infrastructure

The Prieska mine is about four kilometres from Copperton, where the Anglovaal workers were housed. It is close to 70km from the town of Prieska, located on the banks of the Orange River. The mine will send 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.

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 over the next few years.

Treated water boosts Prieska’s business case

During our recent WhyAfrica Road Trip we ventured down Prieska’s magnificent decline. Watch it here on our YouTube channel

Leon Louw is the founder and editor of WhyAfrica. He specialises in the extraction and responsible utilisation of natural resources, the primary sector of African economies and Africa’s political economy. 

Treated water boosts Prieska’s business case

WhyAfrica reports about, and publishes newsletters, magazines and research reports about natural resources and the primary sectors of African economies, and the infrastructure, equipment and engineering methods needed to extract and utilise these resources in an efficient, responsible, sustainable, ethic and environmentally friendly way, so that it will benefit the people of Africa.

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Treated water boosts Prieska’s business case        

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