(Recasts with analyst forecast, other financial details)

Oct 28 (Reuters) - Barrick Gold Corp, the world's biggest gold producer, reported lower quarterly adjusted earnings on Wednesday due to weaker gold and copper prices but results were better than the market expected.

The Toronto-based miner, which has the highest debt of any gold miner, said it had reduced its debt to $11.2 billion as of Wednesday. That is down from $12.8 billion at the end of June and $13.1 billion at the start of the year.

Barrick, like rival Newmont Mining Corp, gave an improved cost outlook for the year.

It also expects to announce the outcome of the sale of a package of six U.S. gold assets in the fourth quarter.

Earlier, Barrick reported adjusted net earnings of $131 million, or 11 cents a share in the three months to end-September, compared to $222 million, or 19 cents a share in the same period a year ago. Analysts expected the miner to earn 7 cents a share, according to Thomson Reuters I/B/E/S.

On a net basis, Barrick swung to a third-quarter loss of $264 million, or 23 cents a share, as it booked a $455 million impairment charge related primarily to an accounting reclassification of its Zaldivar copper mine in Chile as "held-for-sale."

Barrick agreed in July to sell 50 percent of its Zaldivar mine to copper miner Antofagasta Plc for $1 billion in cash.

Barrick said it now expected lower all-in sustaining costs of between $830 and $870 per ounce this year. That compared with a previous forecast of between $840 and $880 per ounce.

Full-year gold production is expected to be between 6.1 million and 6.3 million ounces, as Barrick lowered the top end of the band from 6.4 million ounces to reflect expectations of lower gold production from Acacia Mining Plc.

Barrick said it plans to use about $1 billion of the proceeds from the Zaldívar sale, which is expected to close in the fourth quarter, to reduce debt. This would bring total debt repayments this year to about $2.9 billion. It will use free cash flow to reach its target of $3 billion for the year.

Barrick, which has mines in the Americas, Australia and Africa, said it produced 1.663 million ounces of gold in the third quarter, slightly up from 1.649 million ounces in the comparable quarter in 2013.

The miner said its all-in sustaining costs, the industry cost benchmark, were $771 per ounce in the quarter, compared with $834 an ounce in the same quarter a year ago.

(Reporting by Nicole Mordant in Vancouver; Editing by Diane Craft and Tom Brown)