Mining companies -- which couldn't dig minerals out of the earth fast enough just a few months ago -- today are struggling to climb out of a very deep hole.

Last week, the world's biggest miner, BHP Billiton, said major Chinese customers are trying to delay purchases of iron ore and other minerals as China's building boom and demand for electricity slows sharply. The scale of the December delays could cut BHP's iron-ore deliveries by at least 5 percent for the full year.

The mining giants that feed the world's appetite for iron, copper and other industry staples earned piles of money as commodities prices soared the past few years. But those days are over for now.

Metals prices fell 35 percent in just four weeks last month -- the steepest decline ever recorded, according to Barclays Capital. Prices for palladium, a key ingredient in automobile catalytic converters, are down 70 percent since midyear as car buyers make themselves scarce. Half or more of the world's aluminum production is now unprofitable.

Mining companies, a significant barometer of global economic health, are shuttering operations and firing thousands of workers across South Africa, Australia, Canada and Russia.

Rio Tinto, which owns Kennecott Utah Copper, cut 10 percent of its iron-ore production last week, matching a similar move by the world's largest iron-ore producer, Brazil-based Companhia Vale do Rio Doce. Xstrata PLC announced plans to close two nickel mines in Northern Ontario. Alcoa Inc. has so far cut about 15 percent of its annual capacity.

Big steelmakers worldwide have been cutting production as much as 35 percent. U.S. Steel Corp., the largest steelmaker in the United States last week said it was laying off 2 percent of its work force because of the slowing economy.

Nearly every mineral is affected. Molybendum, which gives steel its strength, fell 60 percent, to $12 a pound, in the past year. Copper -- recently so expensive that burglars would break into houses not to steal jewelry, but to steal the plumbing -- is off more than 50 percent since April. Tin smelters across Indonesia, where nearly 25 percent of the world's tin is made, are halting production.

Mining ranked among the fastest-growing sectors of the world economy in recent years. That money flowed to the four corners of the globe. China's voracious appetite for commodities helped spur waves of investment in poor but resource-rich Africa, a rare economic bright spot there.

That's changing now, as Chinese demand slows at the same time that consumers worldwide start penny-pinching. In the past few days, the world's largest producer of steel ingredient ferrochrome, Merafe Resources Lindiwe Montshiwagae, said it would shut down six of its South African furnaces. In Kenya, a $25 million titanium project was put on hold.

The question is whether these cutbacks, while sizable, will be enough to stabilize prices and the industry. Markets got a brief boost two weeks ago when China announced a nearly $600 billion spending spree to perk up its economy by building new roads and railways, among other things. By last week, however, prices for many commodities resumed their decline as the reality set in that even China's plan might not be enough to prop up demand in the short term.

The mining business has been through cycles before, and is exceedingly volatile. But analysts say they can't recall a more sudden, sharp decline in prices.

Of course, this slump is still in its early days. Prices could bounce back if China's housing market regains its vigor. After all, China, India and other developing nations still need massive helpings of copper, zinc and other metals as they strive to catch up to rich countries' living standards. China consumes only about one-fourth as much copper per capita as Germany.

Still, at current market prices, it's hard to make money running many mines, which have high labor, equipment and energy costs. About 30 percent of nickel mines and more than 15 percent of zinc mines have turned unprofitable because of falling prices.