This is how it all started…

In July 2003, copper prices finally broke above the $0.75 per pound level, which had shown some strong resistance during the previous year and a half.

By the same time the following year, that price had climbed to $1.25 a pound, and by the end of 2004, copper prices stood at roughly $1.50. But copper wasn't done. Quite the opposite. Once gaining the $1.50 mark, copper shot up to more than $3.75 per pound by May 2006.

In short, copper prices rose 400% in less than three years. Gold didn't do that, and neither did silver. In fact, most base metals outperformed these two precious metals, with copper, nickel, and zinc leading the way.

Zinc rose 329% and nickel rose 125%.

Since May 2006, nickel has climbed another 77%, making its total run from July 2003 a rise of 300%. Zinc rose a further 39% for a total run of 494%.

But copper's moved way off its high from May 2006. In the last seven months, copper's dropped below $2.60 a pound. Still 247% higher than July 2003 prices, but 31% lower than last year's high.

That's a big difference compared to the continued success zinc and nickel had.

All three metals are widely used with zinc and copper among the top five most-produced base metals. And of course, all three have strong applications in industrial use. Think Chinese growth, and how huge cities have been built up in a matter of years, not decades.

So could a significant drop in one or more signal a slowdown in industrial growth and therefore economic growth?

It's possible.

Nick Godt of MarketWatch.com makes the case:

“Most commodities are used in the production of industrial goods. When producers start demanding fewer raw materials, it becomes noticeable in commodities prices much earlier than in official economic statistics, explained Barry Ritholtz, chief market strategist at Ritholtz Research & Analytics.

“Copper, in particular, is often used as a reliable economic indicator because of its widespread use in production.”

Furthermore, “One would have to admit that the recent slide in copper's price seems worrisome, yet there has been little discussion in the media about why this might be happening or its implications, said Richard Bernstein, chief investment strategist at Merrill Lynch, in a recent note.

“Merrill metals analyst Vicky Binns has predicted that copper could fall an additional 30% in 2007, while sector strategist Brian Belski lowered his rating on the materials sector to an underweight on Wednesday.”

So it would seem that the metal is going to have a tough year ahead of it. And if these factors turn out to be true, I'd keep a sharp eye on zinc and nickel. They'll be the next to drop. You can throw aluminum into that mix as well, despite the nice little comeback it's had recently.

Based on the sharp inclines nickel and zinc have had, we may see similarly sharp declines, should world economies really put the brakes on.

This could be bad for miners, but not necessarily all miners. I'd look to the smaller, more specialized miners for gains this year. Perhaps a gold and silver mining company is the spoonful of sugar to help the metallic medicine go down easier.

For you speculators, check out Hecla Mining (HL:NYSE) or Coeur d'Alene (CDE:NYSE).

For a more conservative approach, stick with the streetTRACKS Gold Shares ETF (GLD:NYSE) and perhaps take a look at the newish silver ETF, iShares Silver Trust (SLV:AMEX).