All monetary amounts are expressed in U.S. dollars, unless otherwise indicated.

Toronto, Ontario--(Newsfile Corp. - January 12, 2023) - IAMGOLD Corporation (TSX: IMG) (NYSE: IAG) ("IAMGOLD" or the "Company") is pleased to announce an updated Mineral Resource Estimate ("MRE") for the Nelligan Joint Venture Project ("Nelligan") (IAMGOLD: 75%, Vanstar Mining Resources Inc. ("Vanstar"): 25%), located 60 kilometres southwest of Chibougamau, Quebec, Canada.

Highlights:

Nelligan Joint Venture Project updated MRE comprises (on a 100% basis using a US$1,500 per ounce gold price):

72.2 million tonnes of Indicated Mineral Resources averaging 0.85 grams of gold per tonne for 1.97 million ounces of gold

114.1 million tonnes of Inferred Mineral Resources averaging 0.88 grams of gold per tonne for 3.24 million ounces of gold

Mineral Resources have increased by 92% in tonnage, with a 15% decline in gold grades, for an overall gain of 63% in metal content - relative to the 2019 Mineral Resource estimate

Additional infill drilling completed from 2020 to 2022 and refinement of the deposit and structural models contributed to the conversion of 62% of Inferred Mineral Resources to an Indicated Mineral Resource category relative to the 2019 Mineral Resource estimate

Potential highlighted for further resource expansion

The estimate was completed in accordance with the Canadian Institute of Mining, Metallurgy and Petroleum ("CIM") Definition Standards incorporated by reference in National Instrument 43-101 - Standards of Disclosure for Mineral Projects ("NI 43-101").

Craig MacDougall, Executive Vice President, Growth for IAMGOLD, stated: "We are very pleased to see that our drilling programs have confirmed the anticipated expansion potential at Nelligan resulting in a significant increase of Mineral Resources within a wide and persistent mineralized system. This Mineral Resource estimation has not only resulted in a significant increase in resources, but also resulted in upgrading nearly 2 million ounces from Inferred to an Indicated resource classification. Potential for further resource expansion appears favourable, noting that the deposit has areas within the resource pit shell, along strike and at depth that remain open for further drilling. Our exploration efforts continue to highlight the significance of this pure grass-root discovery."

"I also want to commend the exploration team which has conducted the recent drilling programs safely and through challenging times with the wide ranging impacts of the COVID-19 pandemic, including costs increases and service availability across our industry. We also thank all of our service providers who have worked with us to contribute to the success of this project," added Mr. MacDougall.

Since 2020, IAMGOLD has drilled 53 additional holes (for 22,045 metres) to expand the resource base particularly to the west and at depth. As at December 31, 2021, IAMGOLD had previously reported Mineral Resources at Nelligan (on a 100% basis) comprised of Inferred Mineral Resources of 97.0 million tonnes grading 1.02 g/t Au for 3.2 million contained ounces (see news releases dated October 22, 2019 and February 23, 2022). Relative to the 2019 MRE, the current estimated Mineral Resources have increased by 92% in tonnage, with a 15% decline in gold grades due to a reduction in the calculated cut-off grade from 0.50 g/t Au to 0.35 g/t Au, for an overall gain of 63% in contained gold.

MINERAL RESOURCE STATEMENT - NELLIGAN PROJECT, CANADA

As at December 31st, 2022 (100% Basis)

Category Cut-off Grade
(g/t Au) Tonnage
(Mt) Grade
(g/t Au) Contained Au
(koz Au)
Indicated 0.35 72.2 0.85 1 970
Inferred 0.35 114.1 0.88 3 238


Notes:

2014 CIM definitions were followed for classification of Mineral Resources.
Mineral resources are estimated at a cut-off grade of 0.35 g/t Au.
Mineral Resources are reported using a gold price of US$1,500 per ounce and a US$ : C$ exchange rate of 1:1.2.
Mineral Resources are constrained by a Datamine Studio NPVS Scheduler optimized pit shell using a 0.35 g/t Au cut-off grade and are considered to have reasonable prospects for eventual economic extraction.
High grade assay values have been capped from 7 g/t Au to 40 g/t Au in the main mineralized domains of Renard and Footwall, and from 3 g/t Au to 12 g/t Au in the other domains. The spatial influence of high grade samples within Footwall, Renard and Liam domains were further controlled using high grade restriction distance parameters within the respective search ellipsoids.
Bulk density values were determined by measurements on core and range from 2.70 to 2.75 g/cm3 for the different domains and host lithologies, to 2.00 g/cm3 for overburden.
Mineral Resources are not Mineral Reserves and do not have demonstrated economic viability.
All figures have been rounded to reflect the relative accuracy of the estimates.
The updated MRE for the Nelligan Project used all available validated data, and includes results incorporated into the resource model from the 2020 to 2022 drilling programs (53 holes for a total of 22,045 metres drilled), as well as an additional 24 historic drill holes previously located outside mineralized domains, for a total of 84,490 metres in 267 diamond drill holes. Drill holes are variably spaced from 35 to 100 metres apart in the core resource area. The deposit was modelled using Leapfrog to create domains using lithology, structure and alteration type (or assemblage) and intensity, with gold grade continuity analysis of each domain. The mineralized domain model comprises five (5) main gold-bearing domains (Renard Footwall, Renard, Z36, Liam and Dan) cut by a northeast-striking post-mineralization fault which locally cuts and offsets several domains.

The estimate was prepared using a block model approach (10.0 x 5.0 x 5.0 metres block dimensions) employing Ordinary Kriging (OK) interpolation constrained by 3D wireframes using hard domain boundaries during estimation. A Datamine Studio NPVS Scheduler Mine Planning Software was run on the block model to constrain the resource and to support the CIM requirement that Mineral Resources have "reasonable prospects for eventual economic extraction". Pit slopes in rock were assumed at 45° and at 18.4° in overburden and the resource estimate assumes a long-term gold price of US$1,500 per ounce. Gold recoveries are assumed at 83% as indicated by metallurgical test work completed to date. Only mineralization contained within the optimized pit shell has been included in the resource estimate. The resource estimate was completed by SRK Consulting (Canada) Ltd. ("SRK") with an effective date of December 31st, 2022 and is reported at a 0.35 g/t Au cut-off grade.

IAMGOLD will file an updated NI 43-101 technical report for the updated Mineral Resources estimation for Nelligan on SEDAR at www.sedar.com within 45 days of the date of this news release.

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