What happened 

Shares in copper miner Freeport-McMoRan (FCX -0.49%) declined 10.4% in the week as of the close of trading on Thursday. The move reflects the ongoing sell-off in commodity-related stocks as the market prices in slower economic growth, due to the Federal Reserve hiking interest rates. As such, economically sensitive commodities like copper have sold off, along with the the miners that produce them, like Freeport-McMoRan.

A fair amount of speculative money has also flown out of the "buy inflation plays" trade (such as buying into copper), which has exacerbated the volatility of price movements. 

Whereas earlier in the year, traders flocked to buying copper on fears of near-term supply shortages in the face of ongoing demand, investors are now worried about slower demand due to slower economic growth. That's a pretty reasonable assumption to make, given that the price of copper spiked to about $4.90 per pound in the spring from about $4.30 at the start of the year, only to fall to about $3.20 at the time of writing.

The implied volatility in these price movements suggests they're more about investor sentiment than reflections of changes in the long-term demand/supply balance. 

So what

That said, lower prices mean lower profits for Freeport-McMoRan, and investors will be hoping the rout in commodity prices ends sometime soon. That's likely to happen when the market gets comfortable with the overall growth outlook. History suggests that will happen in time, but predicting when is fraught with uncertainty. 

Now what

All investors can do now is be patient and reflect that while copper is currently in a sharp correction, the long-term trend is still positive, with demand underpinned by increased use of copper in electric vehicles, renewable energy, and electrification in the economy. As such, copper remains an excellent way to play growth in the global economy, and Freeport-McMoRan is well-positioned to take advantage.