Lurching under loads of blasted rock, a fleet of 15-ton trucks at Oka, Quebec, play follow-the-leader from open-pit-mine face to crusher shed. They haul Canada's newest mineral export on the first part of a journey that is expected to culminate in super-sonic sub-space flights around the outer limits of the earth and form a key part of interplanetary rocketships of the future. Columbium, already used as a toughening additive for steel, has so far been too scarce to play its most exciting role -- a heat-resistant metal for spacecraft and vital nuclear-engine parts. Discovered, proven and now in regular production by a Montreal mining group, the deposits at Oka (already world famous for its cheese) are North America's first dependable supply of a much sought after metal. Added advantage of the rich Oka ore(10 pounds to the ton) is its closeness to transportation. Only 30 miles from Canada's largest city, Montreal, the powdered concentrate is easily shipped to Canadian steel makers, the United States, Europe and Japan. In the clattering mill at Oka, growing production of Canada's newest mineral wealth is engraving the village name on the space-age map of tomorrow.