Freeport-McMoRan Copper & Gold Inc's second-quarter profit dropped by half as metal prices slipped, but the results beat Wall Street estimates and its stock rose.

The company also said it planned to increase its copper production by 25 percent over the next three years through development of brownfields - projects nearby existing mines.

They were hurt by the copper price which they can't control, said analyst Charles Bradford, of Bradford Research in New York. But it was a good quarter and they gave terrific outlook for projects ahead.

Net earnings were $710 million, or 74 cents per share, compared with $1.4 billion, or $1.43 per share in the same quarter of 2011, the company said on Thursday.

Excluding charges for environmental obligations and related litigation reserves totaling $53 million or 6 cents per share, the company earned 80 cents per share, on which basis it beat analyst estimates of 75 cents per share, according to Thomson Reuters I/B/E/S.

Revenue fell to $4.48 billion from $5.81 billion, the company said, as the average copper price it received fell to $3.53 per pound from $4.22 a year earlier.

Freeport's stock rose 1.7 percent to $33.60 in pre-market trading on the New York Stock Exchange.

Freeport said consolidated sales from mines in Indonesia, Peru, Democratic Congo and Nevada totaled 927 million pounds of copper, 266,000 ounces of gold and 20 million pounds of molybdenum. That was down from 1.0 billion pounds of copper, 356,000 ounces of gold and 21 million pounds of molybdenum in the second quarter of 2011.

During the second quarter, the price of copper fell over 10 percent, from $3.93 per pound to $3.49, according to Thomson Reuters data. Gold prices fell 4.7 percent to $1,598 an ounce from $1,677 at the start of the quarter.