the accord signed in windhoek gives de beers : the assurance that it will be able to continue to exploit its existing on and off-shore assets in the country and that its renewable prospecting licences will protected ; a guarantee that all of namdeb 's output will be marketed through de beers ' london -based central selling organisation , which controls 80 per cent of world trade in rough -lrb- uncut -rrb- diamonds ; retained control of de beers marine , the company that provides the technology and equipment for off-shore diamond mining .