Earth's rifts pour forth riches

Forty thousand miles of mineral riches may be strung around the globe like a great crown, and concern about diminishing world supplies of some nonrenewable resources may be premature.

This is the implication of recent discoveries of metal-rich ore deposits on the floor of the Pacific Ocean.

Girdling the earth, mainly at great depths beneath the sea, are rift systems. These are long chains of so-called geothermal vents and attendant volcanic activity. These rifts are fountains literally pouring forth materials that spread out laterally to make up the crust of the earth. Over a span of 200 million years, the planet creates an almost totally new face, spewing out new (and pushing along older) material at the stately pace of about three inches per year.

At the ridges, hydrothermal fluids at temperatures around 400 degrees C. billow up to meet deep ocean waters with temperatures averaging only 2 degrees C. Minerals contained in the hot fluids (formed when solutions rise from a cooling magma) crystallize, precipitate out, and fall to the ocean floor. The precipitated materials build to form chimneys rich in copper, zinc, lead, and other metals.

Only about 100 miles of the 40,000-mile-long rift system have so far been explored. But the explorations have been remarkably successful, and the potential seems tremendous.

French explorers had previously found ''smokers'' -- vents spouting hydrothermal effluents -- along the East Pacific Rise at 12 degrees north latitude (south of Mexico) and at 21 degrees north latitude (near Baja California) in 1978. Last August, at the conclusion of a four-year search, Dr. Alexander Malahoff, chief scientist of the National Oceanic and Atmospheric Administration's National Ocean Survey, and others found the first weighty deposits of precipitated polymetallic sulfides at the Galapagos Rise off Ecuador. They estimate their discovery at a hefty 25 million tons -- bearing metals worth $2 billion. Samples plucked from the deposits contain on the order of 20 percent iron, 10 percent copper, 1 percent zinc, 0.1 percent vanadium, .01 percent silver, and .01 percent lead.

Then last fall, Randolph Koski of the United States Geological Survey at Menlo Park, Calif., working with John Delany and Paul Johnson of the University of Washington, found zinc-iron sulfide deposits at a depth of 2,200 meters along the Juan De Fuca Rift 200 miles west of Oregon.

What might this mean in terms of mineral riches? To take but one example, the Galapagos sulfides contain 10 percent copper. Conrad Welling, vice president of Ocean Minerals Company, a consortium of companies working to mine the first great ocean-bottom find, manganese nodules, commercially, says this is 20 times the norm. On land, the copper mining industry typically earns its living by drawing the metal from rock containing only one-half of 1 percent copper.

Further, these findings mean that many ''nonrenewable resources'' are in fact constantly, at a snail's pace but over a vast area, being renewed by the earth's creative forces.

The riches envisioned for the world when manganese nodules were first discovered almost 100 years ago have yet to affect the global minerals market. The ability to mine at great depths has been quicker to achieve than has a clear legal right to the ores once they are in hand. (Lockheed Corporation, for example, has developed a seabed mining prototype process.) The nine-year-old Law of the Sea negotiations are complicated by such issues as whether these newfound treasures of the deep may one day be considered nationally owned resources for the countries nearby or whether they should be deemed global resources to be shared among all nations. For example, the sulfides found west of Oregon would fall within the 200-mile exclusive economic zone proposed by US Rep. John B. Breaux (D) of Louisiana.

With the manganese nodules, at least, we know the extent of the riches. Today they are estimated at 1.5 trillion tons, a quarter of which is manganese, 1.2 percent copper, 1.5 percent nickel, and 0.2 percent cobalt. The extent of hydrothermal deposits has yet to be determined.

Also, the lead time between discovery and exploitation carries any vision of reaping seabed polymetallic sulfides well past the year 2000. In this case, is it fair, as Dr. Malahoff insists, to extrapolate from a sample of 100 miles to project an undersea bonanza of minerals encircling the globe?

There is supporting evidence. Particularly significant may be the fact that the sulfides found at the Galapagos Rise are similar to sulfides that are today mined for copper in distant Cyprus. There, ocean crustal material was thrust up during the island's formation. Furthermore, the Red Sea, which is itself the product of a rift running down its center, has been found to contain sulfide brines. These are mineral-rich muds that may soon begin to be mined commercially. If the rift system is a global one, experts ask, why shouldn't the phenomenon of thermal effluents yielding metal-rich sulfide deposits exist worldwide?

That is the good news. The bad news is that winning the riches from the ocean floor may cost more than selling them could bring in. We do not yet know whether extracting these resources will be industrially feasible. It is expected to cost as much as $1 billion to find out. But if cost-effective methods are developed over the next 20 or 30 years, what may be welcome news for metal-consuming industries could spell disaster for existing land-based mining industries. Whether or not they can adapt to competition from seabed mining will be a major question for the industry.

Commercial mining of metal-rich sulfides, which is decades away, should be considered complementary, rather than threatening, to land mining, according to some experts. Others point out that the fact that seabed sulfides exist by no means ensures that they will undergo eventual exploitation. The greatest contribution of these discoveries may be the clues they give for locating similarly formed deposits on land.