International team locates large ocean deposit

A team of Canadian, Australian and Papua New Guinean scientists has discovered a large metallic mineral deposit forming on the ocean floor off the Papua New Guinean island of New Britain.

Although Pacmanus is not the first such deposit to be found, the discovery is considered the best modern-day example of how ancient massive sulphide deposits — the basis for mines around the world — were formed more than 2.7 billion years ago.

“This is the Holy Grail of what I do,” Steve Scott, co-chief scientist of the Pacmanus expedition told students at the University of Toronto. “Geologically, the particular type of volcanic rock at this deep sea floor environment is very similar to the rocks of many ore deposits in Australia and Canada that are rich in copper, zinc and lead.”

Because Pacmanus is hosted by felsic volcanics, uncommon on the ocean floor but characteristic of ancient ore deposits, the information gleaned from Scott’s expedition and subsequent studies should prove invaluable to exploration geologists.

But although preliminary analyses suggest that the Pacmanus deposit contains reserves of at least 10 million tonnes rich in copper, zinc, lead, silver and gold, any consideration of mining under 1,700 metres of water is purely academic at this stage.

“I think (seafloor mining) will come, eventually,” Scott, an ore deposit geologist, told his audience at the Canadian Institute of Mining, Metallurgy and Petroleum’s (CIM) student night. “The kind of problems associated with ocean mining are, perhaps, far less severe than land mining.” Scott said that acid mine generation, a common dilemma associated with mining, would not pose a problem on the ocean floor because the metal sulphides are already in contact with sea waters. Shipping would be a bargain, since the ore could be hauled directly on to a freighter. As for processing, studies completed to date suggest magnetic separation would produce “fantastic results,” including recoveries of up to 90% for zinc. A related investigation is taking place on the Juan de Fuca Ridge, about 200 km off the coast of southern British Columbia, where the Geological Survey of Canada recently intersected 94 metres of massive sulphides grading an average 6% zinc and 1.5% copper (T.N.M., Oct. 7/91). The intersection was pulled from a thick sediment layer overlying the basaltic ocean crust.

Scott and his team of U of T graduate students are funded by government grants and a $50,000 annual donation from the Bank of Nova Scotia. But since expenses often run into the six digits (e.g. $30,000 per day for a ship and submersi-ble), expeditions often require international co-operation and support.

Scott recently returned from Moscow, where the Russian researchers expressed an interest in contributing to a return trip to Pacmanus and the associated “Pual” (fork) Ridge.