The Venetia underground diamond mine project is at an exciting juncture, with the erection of the production shaft headgear completed, and sinking headgear in the process of being commissioned for main sinking to commence, reports Jaco de Kock, project manager at project delivery company WorleyParsons RSA.

The De Beers Venetia Underground Project will when complete begin mining ore to replace the existing Venetia open pit mine in the Limpopo Province. The mine is  South Africa’s largest producer of diamonds. In 2021 as the kimberlite ore reserve is depleted   in the open cast mine  , the method of mining will change from open cast to underground mining to access the diamond bearing kimberlite ore body at greater depths. In order to extend the life of the mine, De Beers and Anglo American took the decision in 2007 to construct an underground mine beneath the operating open pit above. The project scope provides for a techno-economic underground mining and infrastructure solution to continue the mining of the K01 and K02 ore bodies into the 2040s.

The K01 ore body will be mined by means of a Sub Level Caving mining method, with K01 producing 4 Mt per annum (average of 3.5 million carats per annum). The K02 ore body will be mined by means of a Modified Sub Level Caving  mining method producing 1.9 Mt per annum (average of 0.9 million carats per annum). This equates to 5.9 Mt, which matches the throughput capability of the existing main treatment plant.

The K01 and K02 ore bodies will be accessed through two vertical shafts, blind sunk to a depth of 1040 m; the Service Shaft has a finished diameter of 7 m and provides all the services to the underground workings, while the Production Shaft, also with a finished internal diameter of 7 m, will be fitted with two rock winders, each having two 24 tonne payload skips. Both the Service and Production Shafts will serve as downcast air intakes to the underground workings.

The decline will assist with early access to underground for the construction of the K01 and K02 production infrastructure, concurrent to the vertical shafts still being sunk and will also serve as an additional air intake and logistics management facility, reducing the requirement of the loading stations on the Service Shaft. The decline portal is sited off the surface terrace and due south of the vertical shafts. The decline will serve as a third means of egress from the underground workings whereas the Service and Production Shafts are the other two means of egress.

The surface infrastructure will comprise of a surface terrace hosting a main consumer substation, winder houses and head gears, an office complex, change house, lamp room, proto room, concrete batch plant, surface ventilation fans, compressor house, shaft workshop, rope store/skip workshop, cage workshop, fire- and process water pump station, process water settlers, domestic water tank, process water dam, firewater tanks, ore and waste conveyors and a stockpile.

The underground infrastructure will comprise of vertical shaft systems for personnel, ore transport and the routing of services, lateral access levels on 600 m, 900 m, 960 m, 990 m and shaft bottom at 1040 m. The trackless fleet will be maintained through underground maintenance facilities, which are located on 600 and 900 levels. Underground dewatering will be achieved through dedicated water passes, a water launder tunnel, de-gritting trommel screens, settlers, and dams and pumping to surface. The ground handling will comprise of rock breakers, vertical ore passes, an automated truck-loop, underground crushers, ore waste conveyors and ore and waste silos.

WorleyParsons RSA has been involved in the Venetia Underground Project since feasibility stage and was appointed as the engineering consultant for the project. The company was commissioned to execute the detailed engineering design for both the surface and underground infrastructure as well as support the Owners Project Management Team and Site Project Management Team related to procurement, fabrication, logistics and construction.

Besides the production shaft structural headgear, construction has been completed on a number of other structures, including the terrace areas with all the access roads and storm water drainage systems and three electrical sub-stations. Once the main sink is underway, attention will then be drawn to the remaining surface and underground structures. De Beers expects the start of the ramp up to full production on the mine to commence in 2021.