An analysis in Mineweb.com finds that Phoenix-based Freeport-McMoRan is one of 8 mining companies that have a combined debt of $100 billion. Freeport, the world's biggest publicly-listed copper producer, has a debt-to-market-value (DMV) around 56%, which is large enough to push down the stock price substantially.
The parent companies of Arizona's Resolution Copper, Rio Tinto and BHP Billiton, are also among the eight.