Namdeb’s ships coming in

Watched critically by the sabre-horned gemsbok antelopes that wander casually through this town, Namdeb Diamond and its predecessors have turned a desolate shoreline into Namibia’s biggest moneymaker.

Namdeb, owned 50% by the Namibian government and 50% by De Beers Consolidated Mines (DBRS-Q), provides 34% of Namibia’s gross domestic product, and is Namibia’s largest company in terms of both sales and payroll. Nevertheless, it’s an upstart, having been formed only four years ago.

Diamond mining in the southwestern corner of Namibia is anything but a novel idea. In 1908, Zacharias Lewala, a maintenance-of-way worker, was shovelling sand from the rail line south of Luderitz, in what was then German South-West Africa. He noticed some small stones in the sand and, realizing they were diamonds, pointed them out to railway official August Stauch. Thus was formed the German Diamond Company, which operated until South African troops occupied the colony in 1915. Systematic mining of South-West Africa’s Atlantic beaches began in the late 1920s, managed by Consolidated Diamond Mines of South-West Africa, but poor market conditions forced the company to suspend mining in 1931. Production resumed in 1936, and despite political upheaval during the creation of independent Namibia in the early 1980s, has been continuous since.

Namibia’s diamond resources extend past the low-tide line as well. The first attempt to assess the ocean gravels for diamonds was made in 1961, when U.S.

businessman Sam Collins organized Marine Diamond Corp. (MDC). The early days were difficult, as available technology restricted MDC to operating with divers in shallow water. Weather and sea conditions kept the ships in port more than half the time.

In 1965, De Beers bought a majority share in MDC and operated it until 1971, when it decided in-shore mining was uneconomic and threw in the towel.

Taking the long view, De Beers evaluated resources in deeper water and developed mining techniques that could be used at sea. By 1991, Namdeb’s predecessor, Consolidated Diamond Mining, was ready to bring the offshore resources into production.

De Beers Marine, which acts as contractor for Namdeb’s offshore mining, was formed in 1983 to develop and apply deep offshore mining methods. Its services, which are also marketed to other companies in the De Beers fold, extend the full length of the marine-mining chain, from geophysical surveys through sampling and assessment to production mining.

De Beers’ survey ship Zealous can perform ocean-bottom surveys using side-scan sonar, coupling these with shallow-penetrating sonar and reflection-seismic surveys that profile the top half-metre or so of the ocean floor. The Zealous can take grab and core samples of unconsolidated seabed sediments and has a video-equipped submersible for visual investigations.

Two sampling vessels, the Douglas Bay and the Coral Sea, do the systematic sampling needed to determine diamond resource figures offshore. The Coral Sea, which does the detailed evaluation, has a diamond recovery plant on board, allowing the crew to ship heavy-mineral concentrates to a land-based lab in Cape Town for diamond counts.

Debsmarine maintains a fleet of four production ships. Three, the Debmar Atlantic, Debmar Pacific and Grand Banks, are former oil-drilling ships that use a large-diameter bit mounted on a 0.5-metre-diameter string of drill rods. The fourth, the Louis G. Murray, has a tracked seabed crawler that can be lowered to the sea floor.

All the vessels have conventional dense-medium separation (DMS) plants and final x-ray sorting.

Aboard the Debmar Pacific, mining is controlled by two drillers from a cabin on board the ship. Video feeds from the sea floor are supplemented by computer-generated displays that show the control room crew their exact location and the circular area of the seafloor the 6.8-metre drill bit is currently covering. Global positioning shore beacons enable the ship’s location to be tracked within 1 metre.

A 10- to 15-minute mining cycle consists of breaking up the sea-floor sediments and then drawing the gravel up the hollow drill string using compressed air. The cycle ends with the ship moving about 5 metres by paying out, or winching in, each of four anchor chains. With the drill bit positioned over the next area to be mined — about 40% of which overlaps with the old area — the crew begins mining again. Mining a square 300 metres on each side will generally take the ship four to six weeks.

On-board processing starts with screening the mined material and retaining the size fraction between 2 and 19 mm. Oversize and undersize material is poured over the side as a slurry, and returns to the seabed.

The feed goes through a primary DMS unit retaining grains denser than 2.1 grams per cubic centimetre (diamond has a density of 3.5). The sinks from the first DMS unit go through a gyratory crusher and ball mill, and then through a second DMS unit retaining grains denser than 2.6. Following a magnetic-separation process to remove the ferrosilicon, the concentrate is separated in an x-ray sorting unit and the diamond concentrate is canned for later sorting at Namdeb’s on-shore facilities in Oranjemund.

Security becomes progressively tighter down the process stream; DMS units are caged and locked, but the x-ray separator is in a locked room and canning is fully automated. “The only way to actually get to diamonds would be to hijack the ship,” says Sebastian De Beer of Debsmarine.

The Debmar Pacific’s crew is principally South African, though more Namibians are being hired on. Crews work 12-hour shifts on a 28-day rotation, changing from night to day shift halfway through.

Namdeb now gets about 450,000 carats per year from the Debsmarine ships, and purchases another 135,000 carats from smaller in-shore operators. The land-based mining operations are more than twice as large: Namdeb produced 1.36 million carats from beach mining in 1997.

Beach mining is concentrated in Mining Area 1, a strip of coastline about 40 km wide and 150 km long running north from the mouth of the Orange River.

Alluvial sands, generally grading between 3 and 6 carats per 100 tonnes, provide most of the production. Smaller satellite operations farther north along the coast at Elizabeth Bay, Bogenfels and Douglas Bay, exploit dune sands.

The mining sequence on the beaches is simple, but done on a mammoth scale.

The diamond deposits occur in a horizon of terrace gravels beneath thick sand and gravel beds. The overburden, 5 to 15 metres thick, is stripped using large mechanized equipment, including bucket wheels capable of moving up to 3,500 cubic metres per hour. The terrace gravels — which can be as much as 15 metres below sea level, and are protected with sand dykes — are excavated and trucked to one of three processing plants, then the basal zones are vacuumed and the spoils are sent to the plants.

A floating dredge and DMS plant is also in operation, processing large volumes of overburden gravels with low diamond grades.

Namdeb maintains a network of screening, treatment and recovery plants in the mining area, including major satellite plants at Elizabeth Bay on the coast and at Auchas, about 40 km inland. The plants use established DMS and x-ray-separation technology.

Hand sorters at Namdeb’s sorthouse in Oranjemund take concentrate from the x-ray unit and manually separate diamonds. The concentrate stays inside a glove box, and the diamonds — which the sorters remove with tweezers — go into a large hopper and are fed to a central collector. Reject concentrate is returned to the x-ray unit for a second pass to ensure as many diamonds as possible go to the sorthouse.

Because larger and better-crystallized diamonds tend to be the most resistant during erosion and transportation, about 98% of Namdeb’s beach and offshore production is gem quality.

Security has long been a concern at Namdeb; Namibian law permits random searches and x-rays of employees, but theft remains a concern. At least 47 employees have been charged with theft since 1993.

Namdeb has been g
radually decreasing the size of its workforce to accommodate a shrinking production level. Much of the reduction has been accomplished through retirements, since the average age of the employees is 51. By 2000, the company expects to be employing about 3,200 people, down from 4,100 in 1997. The marine operation, which has fewer employees, is not being reduced and the balance of production will continue to shift in its favor.

At the same time, Namdeb is changing from a hostel-based workforce to one with permanent homes in Oranjemund, and is steadily replacing expatriate staff with Namibian citizens. Oranjemund is palpably a “company town,” with uniform architecture and civic life very much centred on the company, but it is in the process of becoming a true municipality, with the government slowly replacing Namdeb as the provider of services. Its easiest access to the outside world is through South Africa, but there are plans to upgrade desert tracks to enable employees to drive on paved roads to the Namibian national highway system.