Rich coastal deposits in southern Africa — Namibian Minerals

About half the world’s diamonds have come from river and coastal deposits along the west coast of South Africa and Namibia. And while virtually all of that has been produced by De Beers, the industry giant now faces a challenge to its reign. Newcomer Namibian Minerals (Namco) hopes to be the next company to strike it rich mining diamonds from marine gravels off this desolate, windswept coast.

The company, which began trading on the Vancouver Stock Exchange last fall, owns prospecting licences totaling 1,035 sq. km over three marine diamond concessions off the west coast of southern Africa. Two concessions, Luderitz and Hottentot Bay, are in Namibian waters and the third, known as 12b, is in South African waters, north of the Olifants River.

“Marine diamonds represent the last great frontier in southern Africa,” Namco President Alastair Holberton told The Northern Miner on a recent visit to the Luderitz concession.

Until now, the marine diamond business has been viewed largely as a cottage industry, but recent advances in geophysical data-processing and technology have made marine diamond mining more viable.

More than 100 million carats of gem-quality material have been mined from the west coast since diamonds were first discovered near the Atlantic port of Luderitz in 1908. An estimated 500,000 carats were recovered from the sea off Namibia and South Africa in 1992, plus two million carats from conventional mining of onshore beach deposits.

For Holberton, the idea of diamond mining “started as a dream.” The dream became reality after a social meeting in 1988 with Sam Nujoma, Namibia’s future president. Subsequent to the meeting, Holberton proposed forming a company to mine diamonds in the country and began negotiations for the Luderitz and Hottentot Bay concessions. Last year, Namco was granted the Namibian licences and proceeded to buy the 12b concession from Rio Tinto. In December, 1993, Namco began a $3-million program of hydrographic and geophysical surveys over each of the concession areas. Data have now been collected for Hottentot Bay and 12b and a survey is under way on a 220-sq.-km portion of Luderitz.

The survey entails the use of four main instruments: an echo sounder, side scan sonar, a sub-tow boomer and a CHIRP system. The echo sounder measures the depth of the water and the side scan sonar produces a 3-dimensional picture of the sea floor, equivalent in many ways to an aerial photograph of dry land. The sub-tow boomer and CHIRP system provide seismic reflection data which profiles marine sediments.

Once the data are collected, several sea floor sites are tested using a Vibrocorer. This machine can collect up to a 6-metre-long-by-8.4-cm-wide sample of marine sediments. The sampling information is then correlated with the seismic and sonar data to produce detailed maps of the sea floor. Target areas such as old shorelines, beach terraces and paleo-stream channels are then selected for prospecting and bulk sampling.

Andrew Clark, Namco’s general manager, says “the proof of the interpretation will be in the bulk sampling.”

Sampling is scheduled to begin on either Hottentot Bay or 12b by mid-June. The program is expected to last up to three months and cost $2 million. An independent consultant’s report estimates that the three concessions contain a total of 37 million carats, which would be worth US$6.1 billion at today’s prices.

Diamonds recovered in Namibia are generally expected to be small (4-5 stones per carat) but of extremely high quality as a result of their transport distance. On the other hand, diamonds from 12b (off the South African coast) are expected to be much larger (about 1 carat) and command a higher price. Sampling work will be contracted out to Alluvial Mining, a wholly owned subsidiary of Dutch marine mining and dredging company Royal Boskalis Westminster.

Samples will be collected with a remotely operated “Amrod” dredging system. The 10-tonne unit, controlled with video cameras and sonar, is lowered onto the sea bed and a 5-sq.-metre sample is excavated to bedrock using a powerful, jet-pump assembly capable of removing solids up to 25 cm in diameter. Material is then conveyed to surface for processing in a dense media separation (DMS) plant.

A modular DMS plant, capable of processing 10 tonnes per hour, has been ordered from Bateman Engineering of South Africa. The firm has designed processing plants for various companies around the world.

Once bulk sampling is under way, Namco will consider the economics and feasibility of trial mining. Alluvial has also been retained to carry out the mining phase.

Holberton expects bulk sampling to be completed by December, with initial production beginning as early as the first quarter of 1995.

De Beers holds the largest land position off southern Africa’s west coast, controlling 80% of all existing concessions. Namco and Australian mining giant BHP are the two largest independents operating in the region. BHP can earn a 75% interest in several properties held by South African-based Benguela Concessions. However, Namco has brought a $72-million lawsuit against Benguela, claiming repudiation of a previously existing agreement.