On May 26, the company halted production at its Westwood mine, one of its newest mines, after a rockfall that trapped nine miners for about 18 hours.
The Westwood mine, which is located near the Cadillac fault, experience two seismic events, with magnitudes of 1.2 and 1.7.
The Westwood event will "have a more significant impact on 2015 production than originally indicated," Iamgold said a statement on Monday.
CEO Steve Letwin said mining companies working in the region 'know that this district is prone to seismic activity and we are taking the necessary measures to keep our excellent safety record intact."
Iamgold now projects the mine will produce 60,000 to 75,000 ounces in the year ending December, reducing by nearly half its previous forecast of 110,000 to 130,000 ounces.
The company's second-quarter production is expected to be slightly below the 208,000 ounces produced in the first quarter and it has revised downward its 2015 annual production to a range of 780,000 to 815,000 ounces from the previous estimate of 820,000 to 860,000 ounces.
Iamgold said it expects the mine, in the Abitibi region of Quebec, to eventually become one of its lowest-cost mines as it ramps up production, but it will have to adapt its practices. The mine is projected to last about 20 years.