Demand for copper has slipped in the past year on concerns about economic growth during the ongoing trade spat between the United States and China, weighing on results of Freeport and other miners.

Copper is a key material used in construction and manufacturing. Longer-term, demand for the metal is expected to rise due to the electrification trend.

Freeport posted fourth-quarter net income of $140 million (107 million pounds), or 9 cents per share, compared to $1.04 billion, or 70 cents per share.

Excluding one-time items such as asset sales and tax credits, Freeport earned 11 cents per share. By that measure, analysts expected earnings of 18 cents per share, according to IBES data from Refinitiv.

Copper production fell 17 percent to 841 million pounds during the quarter. The average price Freeport received for its copper fell 14 percent during the quarter to $2.75 per pound.

"Despite recent market uncertainty, we remain confident in the fundamentals and long-term outlook for copper," Chief Executive Richard Adkerson said in a statement. Still, Freeport forecast a 13 percent drop in copper production for 2019, calling it a "transition year."

Phoenix-based Freeport last month relinquished majority control of Grasberg, the world's second-largest copper mine, under pressure from the Indonesian government even though it will remain the project's operator.

Freeport sees the United States, where more than 40 percent of its reserves sit, as a key growth area. The company is spending $850 million to open a new U.S. copper mine by next year.

The company plans to hold a conference call with investors and analysts to discuss the results on Thursday morning.

Freeport's shares fell 4.2 percent to $11.79 in premarket trading.

(Reporting by Ernest Scheyder; Editing by Chizu Nomiyama)