Cecilia Jamasmie | October 28, 2014

Freeport-McMoRan (NYSE:FCX), the U.S. largest miner by market value and revenue, reported Tuesday a 32% drop in quarterly profit, as weaker average prices for copper, gold and oil weighed on revenue.

The Phoenix-based company, which also has oil and gas assets, logged a profit of $562 million, or 53 cents a share, down from $830 million, or 79 cents a share, a year earlier. The latest period included net charges of 11 cents a share for items such as accounting adjustments and asset sales gains. The year-earlier period included nine cents a share of derivatives-related charges. Revenue fell 7.6% to $5.7 billion.

Gold sales rose to 525 thousand ounces from 305 thousand ounces, and production of the precious metal surged to 449,000 ounces from 327,000 ounces a year ago. However prices fell to $1,220 per ounce from $1,329 per ounce in the period.

Copper production dipped slightly to 1.03 billion pounds from 1.06 billion pounds a year earlier, despite the long-dragged dispute between the miner and Indonesia, where Freeport operates Grasberg, the world's third largest copper mine.

Only yesterday unionized workers reported that some 10,000 employees at the mine would begin a month-long strike next week to protest recent fatal accidents at Grasberg, sending shares lower.

The company's shares have fallen about 20% since the beginning of the year.