Overview
The Venetia Diamond Mine, wholly-owned by DeBeers, produces over 50% of South Africa's diamonds making it the country's largest producer. It is situated close to the South African town of Alldays in the Limpopo province.
With construction of this open-pit mine started in 1990, Venetia opened in 1992 with full production achieved in 1993. In 2005, 8.52Mct was recovered from 5.93Mt leaving the mine with an expected life of 20 years. Venetia has 956 permanent employees and 500 long-term contractors used mainly for outsourced 'non-core' work, such as machine repairs and maintenance.
Venetia is the youngest of all the large mines owned by DeBeers and as such has excellent technology and the latest diamond-processing equipment. It is also the only major diamond mine to be developed in the country during the past 25 years so is one of De Beers' single biggest investments in South Africa.
Location
Location - Located in South Africa's northern province called Limpopo, Venetia is found 25 km south of the intersection of the international borders of Botswana, Zimbabwe and South Africa, and is 450 km northeast of Johannesburg in the town of Alldays.
Alldays, with a population of 1,800, is located within the 36,000ha Venetia Limpopo Nature Reserve and serves a large area of private game and hunting farms.
Limpopo province has excellent road, rail, and air systems. The main route from Johannesburg, which extends the length of the province, is the busiest overland route in Africa in terms of cross-border trade in raw materials and beneficiated goods.
Geology & Mineralization
The Venetia kimberlite cluster comprises twelve, Group I kimberlite bodies. The two largest pipes are currently being mined in a single open pit operation at an average grade of 110.7 cpht.
The main pipe is an irregular elongate body that strikes east west and has maximum dimensions of 640 x 260 metres, covering 12.7 hectares at surface.
The pipe dips at an angle of 82 degrees to the north and is intruded along the axis of a plunging anticline and follows the structure of the country rock.
The country rock comprises gneiss, amphibolite and minor pegmatite of the cratonised Limpopo Mobile Belt. The pipe, dated at 500 Ma, consists largely of diatreme facies tuffisitic kimberlite breccia. Three relatively small hypabyssal facies intrusions occur close to the pipe margins. One of these pre-dates and two post-date the main TKB intrusion. Numerous late-stage hypabyssal facies kimberlite dykes also occur.
Operation
The mining method employed is hard-rock drilling and blasting combined with a shovel and truck load-and-haul operation. The mine operates on a continuous basis, seven days a week.
Prestripping is carried out using 2 P&H 250XP blasthole drills. Blasted waste material is loaded into 9 Caterpillar 785 haul trucks by 3 RH340 hydraulic excavators. The amount of waste removed from the mine increased recently from 42 Mtonnes per year to 70 Mtonnes per year. The increase was initiated partly to expose larger areas of kimberlite but also partly from a desire to increase employment at the mine.
Kimberlite is drilled for blasting by smaller drills such as the Terex Reedrill SK and Sandvik models. Liberated ore is loaded into a fleet of 39 Caterpillar 789 and 793 haul trucks by O&K RH200E electric-powered hydraulic excavators. The O&K RH200E is also used for other mine activities such as highwall pin-up.
A high clay content in roughly 10% of the kimberlite in the stockpile requires that it be blended before entering the process stream. Blending is accomplished by equipment ranging from 2 Caterpillar 994 wheel loaders as well as D10 tractors and 16H and 24H graders.
Ore is delivered to the gyratory primary crusher is below 1m x 1m in size, and a product smaller than 150mm is produced. The primary scrubbing and screening section consists of two identical modules, each designed to treat a maximum of 800tph. This section produces three products: 1) a -1mm fraction that is discarded, 2) a 1 to 25mm that reports to the DMS and 3) a +25mm fraction that is sent to secondary crushing.
Process
After primary crushing, ore is transferred to cone crushers which are used for secondary crushing. The crushed material is then conveyed to the secondary scrubbers. The product from these scrubbers is split into two fractions: a minus 8mm and a + 8mm for feed to the DMS.
The DMS section is separated into coarse (8 to 25mm) and fines (1 to 8mm) sections. Both sections have two modules designed to treat a maximum of 200tph. The modules also contain sub-processes that are used to recover ferrosilicon from the process and to regulate the operational parameters. Coarse DMS tails are sent to the re-crush section to liberate any smaller diamonds that are locked up in the coarse float fraction. High-pressure roll crushers, designed to treat 270tph, are used in the re-crush section, to crush the kimberlite without damaging the locked diamonds. The re-crush product joins the secondary crusher product and is fed to the secondary scrubbers.
All concentrate produced in the coarse and fines DMS reports to the re-concentration plant, that has a rated capacity of 40tph. The recon plant is designed to reduce the quantity of material fed to the recovery section by producing a higher-grade concentrate. The recon plant utilizes DMS cyclones in its process. The product from the recon is sent to the recovery section, and the recon tails are sent to the re-crush stockpile.
The concentrate from the recon plant is passed through the recovery plant, where the product is recovered using x-ray technology and grease belt technology. The recovery plant concentrate then passes through the sort-house, where the product is recovered using magnetic perm-rolls, x-ray technology, caustic soda and hand-sorting. The product is secured in a safe until it is transported under security to HOH in Kimberley. About 85% of the diamonds produced at Venetia are gem quality and the rest sold for industrial uses.
Environment & Community
There are two main environmental initiatives underway at Venetia: ecological conservation and water treatment.
In terms of ecological conservation, DeBeers established the 36,000ha Venetia Limpopo Nature Reserve adjacent to the mine and recently moved a large number of animals from a new mining area to the reserve as a result of the destruction of grazing due to the expanding waste rock dumps and the new fines residue deposit.
Water treatment initiatives involve the reduction of raw water and reagent consumption including improvements to the thickening circuit, reclaimed water from coarse residue deposits, optimization of slime deposition system and pilot plant test work on paste thickening.
The mine is also involved in community initiatives relating to HIV/AIDS awareness and education and home-based health care volunteer training.
The region's main economic activities are agriculture, tourism and mining. There is significant unemployment in the area and the company makes every effort to source its 800 permanent and 130 temporary employees from the surrounding local communities.
