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Rockwell’s big comeback: Alluvial mining in the Middle Orange

Having visited Middle Orange River operations, it’s clear Rockwell Diamonds has made a dramatic turnaround, pumping new life into assets with great potential.

It is a little over two years since alluvial diamond junior Rockwell Diamonds put CEO James Campbell at the helm. Having visited the company’s Middle Orange River operations, one thing is clear. The company has since made a dramatic turnaround, pumping new life into assets with great potential writes Laura Cornish.

Campbell, his operational team and the board members who stand alongside him, are breathing life into the company and its assets, which under previous management was struggling to keep its head above water.

To say the company has made a dramatic turnaround is an understatement. Non-core assets have been sold (Klipdam), new mines and process plants built (to the value of US$3.6 million), and fit-for-purpose technologies implemented to deliver best production targets. And the future for Rockwell Diamonds looks bright as its goal to achieve 500 000 m³/month is well within reach considering it is more than halfway there (360 000 m³/month) from current production volumes.

“We have also celebrated our fifth consecutive quarter of improved earnings, thanks to the increased recovery of large, high value diamonds,” says Campbell.

Flagship status reinstated

Situated on the south bank of the Orange River, about 50 km south west of Douglas, Rockwell DiamondsSaxendrift mine is proving it deserves the flagship title once again, having produced substantially more carats in the 2013 financial year (10 276 carats) than in 2012 (6 944 carats).

This can be attributed to a number of reasons, including the newly established Saxendrift Hill Complex, Saxendrift extension (formerly known as the Jasper project, acquired early this year) and the incorporation of state-of-the-art diamond technology.

“We built the Saxendrift Hill Complex (SHC) plant for a number of reasons, the primary reason being to incorporate a technology which we believed would improve our recovery capability for larger Type IIA carats, while reducing operational costs when compared to DMS or rotary pans. This concept was also intended as a proof of concept for our large resource Wouterspan asset,” explains Campbell.

Situated on the Saxendrift property, production ramp up at the new SHC plant is nearing operational nameplate capacity (100 000m3 /month) and celebrates what could become a revolutionary change in the local diamond sector. Having successfully pilot tested a Russian Bourevestnik X-Ray bulk sorter for six months to October 2012, which yielded positive results and 1 596 carats from old tailings re-processing, the company purchased an additional sorter, as well as two single particle sorters, which from an integral component of the SHC plant.

Although Rockwell Diamonds was not the first company in South Africa to use the bulk X-Ray sorter, it has undoubtedly pioneered it in South Africa, being the first local company to incorporate the technology in both a concentration and recovery mode, making it one of the first South African diamond mining companies to do so. Walter Bold, Rockwell Diamonds’ projects manager says the first machine imported into the country was used to test tailings material at Letseng.

“The bulk X-Ray plant has a lower environmental footprint with lower water consumption and power requirements than traditional DMS or pan processing plants. It also picks up flat stones which no other technology has successfully achieved,” says Wickus de Winnaar, Saxendrift mine manager. It also only requires one operator to run the four modules. The capital investment in the project was paid back with gross revenue generated from the sales of diamonds recovered during the first two months of production.  “It is purely based on diamond detection through luminescence, is mechanically robust, and is an extremely simple process,” adds Bold.

In order to fully evaluate the effectiveness of the bulk X-Ray technology, gravels from the Saxendrift extension project were processed in parallel through both the bulk X-Ray system as well as Saxendrift’s traditional pan plant (with Flowsort X-Ray machines) in July.

Results to date indicate that the X-Ray plant is achieving grades at least 40% higher than the conventional plant, and its large stone recovery capability very high (two rough diamonds exceeding 30 carats were recovered in July). The SHC plant is further projected to have 30% lower unit processing costs than the conventional Saxendrift pan plant, providing further commercial benefits.

While the combination lifespan of Saxendrift and SHC is three and one and a half years respectively, the key to operational life beyond that is Saxendrift extension, which has at least five years of life. “This is excluding what we may discover from further exploration down the line,” De Winnaar adds.

Saxendrift extension is located 5 km, uphill, from the SHC plant and this is becoming a challenge for our Komatsu and Volvo equipment fleet, which is considered old in mining terms. We have brought in a consulting engineer to look at the fleet who will help us evaluate various options. This includes doing an extensive mid-life overhaul of the kit, to keep it running another five years,” Campbell explains.

“The other option is to convert our Dabmar in-field screen (which removes all sand, banded iron formation stone and oversize material before going to the main Saxendrift pan plant) to a mobile unit which can be transported into the pit. This would enable us to leave two thirds of the material in the pit which would alleviate the pressure on the fleet, enabling it to last the life of mine. Standardising the fleet would also help.”

Campbell says the company opted for a Dabmar screen because it can take moisture content of up to 15%. “The Dabmar is the only machine which can dry screen with damp gravels, with an efficiency well over 90%.”

“Ultimately, the success at Saxendrift, or any alluvial diamond project for that matter, requires high volumes to be moved continuously. This makes our fleet is an integral part of our business and our production targets. The greater the volumes, the more certainty there is around the number of carats recovered,” De Winnaar adds.

A new star is born

Located only 8 km (as the crow flies) from Saxendrift, also situated on the south bank of the Middle Orange River, Niewejaarskraal has been rejuvenated, taken out of care and maintenance, repaired, upgraded and expanded. And it is already producing diamonds.

The existing DMS plant, originally built by former owner Trans Hex, was recommissioned and certain plant components incorporated from the sold Klipdam mine. A new DMS plant, ‘a first of its kind in South Africa as well’, was installed in September and is currently being tested. Could Rockwell pioneer a new revolutionary DMS technology for diamonds? It’s possible.

“It took about 150 trucks loads to transport all the necessary components from Klipdam, including the FlowSort X-Ray machines, and the 220 strong work force came with. “Our investments to grow Middle Orange production will have socio-economic benefits for this region which is impacted by high unemployment. All but eight of the workforce from Klipdam accepted to transfer to Niewejaarskraal, enabling us not only to preserve jobs, including the opencast contracting staff complement, but also retaining key skills to quickly bring the new mine on stream.”

Production commissioning of the first phase of the new plant started during July 2013 within ten weeks of the project being approved. The first diamonds recovered included two stones exceeding 20 carats. High diamond values have compensated for slightly lower than anticipated grades for the initial gravels that have been processed during commissioning, due to a greater variability in the Rooikoppie particle size distribution. The plant efficiency was confirmed however after plant tailings were re-processed through the Bulk X-Ray system, with no diamonds being recovered.

The plant has been constructed using elements of the existing DMS plant that had been on care and maintenance at Niewejaarskraal since 2007. The next phase of commissioning entails processing a mix of Palaeo and Rooikoppie gravels which commenced during the third week of August when the first blast was carried out to access the main Palaeo deposit that is expected to be the mainstay of operations at Niewejaarskraal. The company has standardised bottom cut-off Size) of 5 mm for the Middle Orange resources.

Campbell is confident of this project’s performance going forward. “We have contracted CML Operations to do all our mining for us, having previously worked with them to turn Klipdam around before we sold it.”

The combined grade between Rockwell’s mines is approximately 0.5 carats/100 m³. This combines Saxendrift’s average 0.4 with Niewejaarskraal’s 0.6 carats/100 m³. The newest production addition also has a healthy estimated lifespan of 10 years.

“Future growth plans include options to further increase the production capacity at Niewejaarskraal, where we would consider the BV technology. We are also evaluating the next steps at Wouterspan, both of which would have flow through benefits for employment in the region.”

An even brighter future

Dr Kurt Petersen, a doctor of diamond metallurgy, has completed a preliminary economic assessment on Rockwell’s Wouterspan property, situated between Saxendrift and Niewejaarskraal.

The study indicated positive economics, sufficient to take the project to the detailed design stage.

Key assumptions of the study include a 1 200 tph or 354 000 m³/month plant comprising three processing streams, two Bourevestnik bulk X-Ray systems to handle the course and mid-sized gravels and the third stream being a DMS to process fine material. This would make it by far the largest operation in the Rockwell stable.

“We have a preference for contract mining and will use this model for Wouterspan. Because it is large, we will look at developing it in a phased approach using equipment we already have on site, hopefully starting early next year,” Campbell indicates.

Rockwell Diamonds has made a big ‘comeback’ in the Middle Orange River region and is set to grow even bigger over the next few years. With the right management in place, it appears this company is capable of anything when it comes to successfully mining alluvial diamonds, especially with great technology driving the process.

The situation at Tirisano

The Tirisano mine situated just outside of Ventersdorp has been Rockwell’s problem child since it acquired it in March 2010. After numerous attempts to resolve operational difficulties the mine was placed on care and maintenance in December 2012.

During fiscal 2013, Rockwell launched its royalty mining contractor strategy to leverage the value at Tirisano. Smaller areas within the mining right, which are unsuited to a high volume operating model are operated by smaller operators who can mine these sections economically. The royalty miners incur all operational costs for these activities while Rockwell maintains responsibility for diamond security and generates a 12.5% royalty on diamond sales.

At the end of this year, there will be five different contractors on site, after which monthly volumes are expected to exceed 150 000 m³/month.

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