A geologic detective story at Olympic Dam

Olympic Dam: It's the biggest uranium deposit in the world, but it will cost the joint venturers exploring there almost $150 million just to see whether, given current and foreseeable yellowcake prices, it's worth developing.

It takes its name from a cattle dam built, at the time of the 1956 Melbourne Olympics, on a ranch called Roxby Downs. Western Mining, with a 51 percent interest, and British Petroleum, with a 49 percent share, have built more than a mile and a half of underground tunnels to explore this site, some 350 miles north of Adelaide. After nearly 10 years of mapping, digging, testing, they are still about a year away from a completed feasibility study.

''It's been a fairly exciting detective story - quite romantic,'' project manager John Copping says, with quiet enthusiasm, of the geological research involved. ''There were no surface expressions of the minerals,'' he adds. But satellite photography and the study of magnetic anomalies in geological formations yielded some hints.

''Finding this deposit, some 350 (yards) underground, took some good theoretical geology and some acute observations.''

Indeed, an official at a competing mining company generously describes the find as ''an absolutely world-shattering piece of geological research.''

The deposit - thought to consist of some 2 billion tons - is unusual in that it consists of uranium and copper together; a new technique (''quite an elegant solution,'' Mr. Copping says) had to be devised to extract both from the same ore. The pilot plant built just to make sure the processing technique would really work cost $15 million - a figure that pales in comparison with the $1.5 billion it will cost to develop the mine. But once opened, the mine could last 50 to 100 years.

Yet for all this scientific drama, the Olympic Dam project seems like the quiet eye of a storm. Uranium mining is an issue that has sharply divided the Australian Labor Party. The right wing (Hawke faction) has favored mining and exporting of uranium; the center-left faction has recently signaled an inclination in that direction. But the left wing, opposed to both nuclear power and nuclear weapons, wants to phase out the entire uranium industry - as the official party platform calls for. Around a quarter-million people turned out across Australia for antinuclear demonstrations on Palm Sunday.

In fact, that work goes on at Olympic Dam owes in part to a party compromise whereby the uranium to be mined there is construed as ''incidental'' to the more plentiful, but much less valuable, copper. The issue is to be taken up at the party conference in July, when the right wing and center-left are expected to get the party policy liberalized.