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An alluvial mining dredge designed and developed in South Africa will soon be working on the Tshikapa River in the DRC’s Kasai Province recovering diamonds from the river bed. The iDredge™, as it is known, was recently demonstrated at a dam near Balmoral in Mpumalanga. The function was attended by the development team, representatives of the owner of the dredge, Africa Resources AB (a non-listed Swedish company), suppliers of the heavy-duty dredging pump and other interested partners. Modern Mining’s Arthur Tassell was present at the event.

The iDredge is put through its paces at a dam in the Balmoral area.

The company responsible for developing the dredge is Imilingo Mineral Processing, based in Centurion near Pretoria. Founded three years ago, Imilingo describes itself as an “engineering company with a vision to be the leading integrator of sensor-based sorting technologies.” In essence, it offers the mining industry fit-for-purpose complete sorting systems, based on pace-setting technologies such as XRT (X-Ray Transmission). Its modular products include iPlant™, iFeed™, iConvey™ and iScreen™, with the iDredge being the latest addition to its line-up.

“We have a good relationship with Tomra and are great believers in their XRT technology, which has been so spectacularly successful at the Karowe diamond mine in Botswana and indeed other projects,” says Imilingo’s Managing Director, Jaco Prinsloo.

Explaining the background to the iDredge, Prinsloo says that the project site in the DRC was visited in October 2016 with the purpose of assisting Africa Resources with the overall project strategy and planning. “Arising from discussions we had on site and further discussions by Africa Resources back in Sweden, it was decided to develop a mining dredge to undertake the mining of the diamond-bearing gravels in the Tshikapa River,” he states. “Once this is up and running and producing results, the intention is that a suitable sorting solution will be installed at the site as a second phase of development.”

The new dredge, which should be on site in the DRC and commissioned by early 2018, will augment the much less effective dredging methods currently being used to mine the alluvial diamonds of the Tshikapa River.

Africa Resources, established in 2014, is the 75 %-holder of a licence (Permit 674), which is 36 km2 in size and includes a stretch of the Tshikapa River around 20 km north of the border with Angola. The remaining 25 % is held by a DRC national, Clement ‘Papa’ Leta, and related parties. Leta has operated in the area since the early 1990s and has huge local expertise. Leta is also the holder of an adjacent licence (Permit 665). Africa Resources and Leta are partnering on the development of both concessions, which between them have an inferred resource of approximately 3,4 million carats.

According to Thomas Häggkvist, CEO of Africa Resources, the Tshikapa River project offers excellent potential. “The river originates in the diamond-rich areas of Lunda Norte Province in northern Angola and has been a source of diamonds for many decades,” he says. “What has generally been lacking is modern mining techniques and sorting technology and this is what we intend providing, starting with the iDredge, which will be the most advanced dredge yet to have been deployed in Kasai.”

He adds that existing dredges in use on the river are relatively unsophisticated. “Basically, what you have is barges from which divers equipped with suction hoses operate,” he explains. “It’s a simple, relatively low-cost approach but production is slow and the divers can’t get down to the river bed in some of the deeper potholes that occur. One pothole in Clement’s concession could be more than 40 m deep and this is where we will probably deploy the iDredge first.”

Development of the iDredge has taken just several months. Put simply, it consists of a Dragflow 60 kW submersible pump complete with high depth compensators accommodated on a pontoon structure. The pump boasts a nominal flow rate of 200 m3/h, with up to 60 mm-sized particles pumped through a 150 NB pipe. The pump is suspended from a rotatable crane structure, which also serves as the lifting equipment for maintenance tasks.

The Dragflow submersible dredge pump has been supplied by Tsurumi Pumps Africa who are the sole agents for Dragflow pumps and Dragflow dredging equipment.

The position of the iDredge on the river is controlled via an onboard control panel through four winches mounted inside the pontoons. The winch cables are fed through the four corners of the dredge and anchored to the river bank. The depth of the Dragflow pump is also controlled from the central panel and depth readings provided for logging of pumping operations.

The pump is driven electrically and fed via a cable from the river bank and space has been created in the pontoons to house two diesel gensets as a more mobile option.

The material from the dredging operation will be fed through a sizing screen on the river bank, which will remove the undersize and oversize fractions. At this stage, sorting will be by hand although, as mentioned, the intention is to install a customised solution incorporating a suitable sorter.

Prinsloo notes that the iDredge is collapsible for transport. This is an important feature as getting it to site in the DRC is likely to be a demanding task, given the fact that it will have to be taken by road all the way from the port of Matadi (via Kinshasa) to the Tshikapa area. This is a distance of around 1 200 km over a road network that in many parts is in a state of disrepair. The dredge and associated equipment needed will be transported in two 40 ft containers and two 20 ft containers.

Although not ordered by Africa Resources, an optional extra for the iDredge is a 3D Sonar scanner and monitor, which would enable viewing of the suction area. Another option available is the protection of the pontoon hulls against rock damage via the addition of Ultra High Molecular Weight Polyethylene.

The effectiveness of the iDredge as a diamond mining tool is obviously still to be evaluated but Häggkvist is confident that it will deliver production rates well in excess of those currently been achieved. “The pumps being used by existing dredging operations have only a fraction of the capacity of our Dragflow pump,” he observes. “We are expecting
to increase production significantly.”

While in South Africa recently (and with the addition of a sorting system at Tshikapa in mind), Häggkvist, together with Sven-Erik Zachrisson, the Chairman of Africa Resources, and Clement Leta, visited an XRT installation in Lesotho being handled by Imilingo.

Thus far, Imilingo has built three plants for diamond-mining clients and has also installed an XRT sorting solution at a tungsten project in Zimbabwe. Prinsloo himself has extensive experience in the diamond field and prior to joining Imilingo in 2015 worked for DRA. While with DRA, he was the lead project engineer on Karowe phase 2, which saw the installation of several XRT sorters at the mine, and was also closely involved with the design of the recovery section – housing a 2,4 m XRT sorting machine – at Stornoway’s Renard diamond mine in Quebec, Canada.

Summing up Imilingo’s approach, Prinsloo says the company looks at projects holistically. “We address the complete project lifecycle, from business concept through the study phase and into execution. We treat each project as unique and our solutions are tailored to the characteristics of the orebody, with equipment being sized and specified accordingly,” he concludes.

Photos of the iDredge by Charles Corbett (on behalf of Imilingo)

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