The company on May 26 had said it had halted production at the mine, one of its smallest and newest mines that is still in ramp-up mode, after a rockfall.

An initial assessment was inconclusive in assessing the impact on production, but further investigation showed the event would "have a more significant impact on 2015 production than originally indicated", Iamgold said a statement on Monday.

The Toronto-based company said it expects the mine to produce 60,000 to 75,000 ounces in the year ending December, nearly half its previous forecast of 110,000 to 130,000 ounces.

The company lowered its forecast for the year ending December to 780,000 to 815,000 ounces from 820,000 to 860,000 ounces.

Production in the second quarter ending June is expected to be slightly below the 208,000 ounces produced in the first quarter, the company said.

Iamgold said it expects the lower output to 'adversely' impact costs at the mine.

The company's shares were down 2.8 percent at C$2.605 in early trading on the Toronto Stock Exchange. Through Friday, the stock had fallen nearly 38 percent in the last 12 months.

(Reporting by Anannya Pramanick in Bengaluru; Editing by Savio D'Souza)