Barrick, the world's biggest gold producer by output, said it now expects its all-in sustaining costs to come in between $880 and $920 per ounce of gold this year, down from a previously expected range of $900 to $940 an ounce.

Barrick and its peers have been slashing costs as the industry tries to restore profits eroded by a 35 percent fall in the gold price in the past three years, soaring mine site costs and over-priced acquisitions.

Toronto-based Barrick, which also mines copper, increased its forecast for copper production this year to between 440 million pounds and 460 million pounds from a previous forecast of 410 million to 440 million pounds.

The company said its net earnings fell to $125 million, or 11 cents a share, in the quarter to end-September from $172 million, or 17 cents a share, in the same period a year ago on the back of weaker gold and copper prices and lower sales volumes.

Adjusted net earnings fell to $222 million, or 19 cents a share, from $577 million, or 58 cents a share, before. Analysts expected the company to earn 18 cents a share, according to Thomson Reuters I/B/E/S.

Barrick, with mines in the Americas, Australia and Africa, said it produced 1.649 million ounces of gold in the third quarter, down from 1.845 ounces in the comparable quarter in 2013. Production has been falling partly as Barrick has sold off high-cost mines.

The company narrowed its forecast range for production this year to between 6.1 million and 6.4 million ounces from a previous estimate of 6 million to 6.5 million.

Barrick's all-in sustaining costs, the industry cost benchmark, were $834 per ounce in the quarter compared with $914 an ounce in the same quarter a year ago.

The average price Barrick was able to get for its gold in the quarter fell to $1,285 an ounce from $1,323 a year ago.

(Reporting by Nicole Mordant in Vancouver; Editing by Chris Reese and Gunna Dickson)