AFTER waiting for 25 years, Burundi has decided to develop the rich Musongati nickel deposit in the southern part of country by entrusting its exploitation to a Canadian-Australian company. With reserves of about 18-million tons of nickel laterite, the Burundian deposit is said to be among the three largest in the world, behind those of Voiseyboie in Canada and of Murrn and Bulong in Australia. Andover Resources NL, an association of Canadian and Australian interests, has been licensed to mine the nickel.