IAMGOLD Provides Westwood Updated Mine Plan and Mineral Resource & Mineral Reserve Estimates

Press Release

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

Toronto, Ontario–( – December 5, 2024) – IAMGOLD Corporation (NYSE: IAG) (TSX: IMG) (“IAMGOLD” or the “Company”) is pleased to provide updated Mineral Resource and Mineral Reserve (“MRMR”) estimates and an accompanying updated life of mine (“LOM”) plan for the Company’s Westwood Complex (the “Project” or “Westwood”), located in Quebec, Canada. IAMGOLD will file an updated NI 43-101 technical report for the updated MRMR and LOM plan on SEDAR at www.sedarplus.ca within 45 days of the date of this news release. The MRMR estimates were prepared 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”).

Highlights of updated Technical Report

• Update life of mine from 2025 to 2032, driven by underground Mineral Reserves at Westwood of 2.6 million tonnes (“Mt”) averaging 11.45 grams per tonne gold (“g/t Au”) containing 955,400 ounces.
• Overall LOM production of 925,000 ounces of gold (“oz Au”), with an annual average gold production of approximately 146,000 oz Au in the first three years (2025 to 2027).
• Average recoveries of 95% from the processing plant with capacity of 1.0 Mt per year. Mine plan envisions adjusting to a batch processing schedule to manage excess capacity as Grand Duc open pit supplementary ore feed ends.
• Average estimated operating costs over the LOM (2025-2032) on a unit basis for Westwood Complex estimated at $239.91/t processed.
• Total sustaining capital expenditures over life of mine estimated at $260.7 million.
• Measured and Indicated Mineral Resources (inclusive of those Mineral Resources converted to Mineral Reserves):
  • – Westwood: 3.97 Mt grading 12.80 g/t Au containing 1.6 million ounces;
  • – Grand Duc: 3.01 Mt grading 1.25 g/t Au containing 121,000 ounces.
• Inferred Mineral Resources:
  • – Westwood: 4.29 Mt grading 13.03 g/t Au containing 1.8 million ounces;
  • – Grand Duc: 0.08 Mt grading 1.28 g/t Au containing 3,300 ounces.
• Grand Duc mine life assumed to conclude in 2025 with processing completed in 2027. The Grand Duc deposit remains open westward and locally to the east.
• Westwood deposit remains open at depth, westward and locally to the east along the untested mineralized Westwood, North and Zone-2 corridors.

“The transformation of Westwood is among the top mining success stories in our industry,” commented Renaud Adams, President and Chief Executive Officer of IAMGOLD. “The ability of our teams to re-engineer, rebuild, and resume full underground mining activities was the result of tireless commitment, teamwork, and a steadfast commitment to safety. The updated mine plan demonstrates the ability of Westwood to continue to expand underground operating areas, with a mine plan based on reserves of nearly a million ounces and mining assumptions at a $1,500 per ounce reserve gold price. This plan provides a good frame of reference for our stakeholders, and it is worth highlighting that underground mining activities at Westwood have historically extracted a significant portion of resources alongside reserves during day-to-day operations – particularly during periods of higher gold spot prices. Financially, in the last two quarters, we have seen Westwood begin to generate significant value, reporting total mine-site free cash flow of $42.6 million in this period. As mining continues to upgrade ounces and open up new mining areas through improved ground control methods and seismicity mitigation measures, we see high potential for further mine life extension and expansion of the current mineralized envelope.”

IAMGOLD holds a 100% interest in the Westwood Complex. The Project consists of two property areas, Doyon-Westwood and Fayolle. The Doyon-Westwood property includes the Westwood underground mine, and Grand Duc open pit, collectively the Westwood Complex. The Westwood mine has been in operation since 2014, when commercial production was declared, and Grand Duc since October 2019. Open pit operations at the Fayolle deposit commenced in February 2023 and the deposit was mined out in June 2024. The Fayolle open pit and associated infrastructure were being reclaimed at the Report effective date.

Mineral Resources

Table 1 – Mineral Resource Statement, Westwood Mine

Class	Tonnes	Gold Grade (g/t Au)	Contained Ounces
Measured	777,000	13.09	327,000
Measured (Stockpiles)	4,000	8.64	1,200
Indicated	3,190,000	12.74	1,306,700
Measured + Indicated	3,971,000	12.80	1,634,900
Inferred	4,289,000	13.03	1,797,400

Notes:

1. The effective date of the Mineral Resource estimate is 30 September, 2024.
2. The Qualified Person for the estimate excepting stockpiles is Martin Perron, P.Eng., from Norda Stelo Inc. The Qualified Person for the stockpile estimate is Mr. Louis Nkoy Manda Mbomba, P.Eng., an IAMGOLD employee.
3. Mineral Resources are reported inclusive of Mineral Reserves. Mineral Resources that are not converted to Mineral Reserves have not demonstrated economic viability.
4. The estimate encompasses 128 mineralized lenses in three zones (Corridor North, Westwood, and Zone 2 Extension) using the grade of the adjacent material when assayed or a value of zero when not assayed. Three dilution buffer zones encompassing all mineralized zones (one for each zone) were created to better reflect the internal dilution within the constraining shapes.
5. High-grade capping supported by statistical analysis was done on raw assay data before compositing. It was established on a zone-by-zone basis, varying from 75-500 g/t Au for mineralized zones and 10-20 g/t Au for the dilution buffer zones. Composites (1.0 m) were calculated within the zones using the grade of the adjacent material when assayed or a value of zero when not assayed.
6. The estimate was completed using a sub-block model in Isatis.neo 2024.04. The parent block size was 4 x 1 x 4 m (subblocks of 1 x 0.5 x 1 m).
7. Grade interpolation was obtained by multiple-indicator kriging for 13 lenses and ordinary kriging for all remaining lenses and buffers using hard boundaries.
8. Density values were assigned by lens group. Densities of 2.9, 3.7, 3.1, 3.0, 3.0 and 3.1 g/cm3 were assigned to groups A, B, C, E, F and G, respectively. A value of 2.8 g/cm3 was assigned to the Corridor North buffer, 2.9 g/cm3 to the Westwood buffer and 2.9 g/cm3 to the Zone 2 Extension buffer.
9. The mineral resource estimate is classified as Measured, Indicated, and Inferred. The Inferred Mineral Resource category is defined with a minimum of two drill holes in areas where the drill spacing is <75 m, and reasonable geological and grade continuity have been demonstrated. The Indicated Mineral Resource category is defined with a minimum of two drill holes in areas where the drill spacing is <15 m, and reasonable geological and grade continuity have been demonstrated. Measured Mineral Resources were classified when Indicated Mineral Resources are present within 10 m of an underground opening within a mineralized zone. The initial resource classification was edited with a mix of automated and manual methods to eliminate isolated blocks of one confidence category, considering the spatial continuity of drill holes, and was run in each mineralized solid to upgrade inferred blocks, or downgrade indicated blocks locally, as needed. The measured resources from the original classification were checked and confirmed with the mining development data. The Measured Mineral Resources from the original classification were not smoothed to prevent downgrading the classification.
10. The Mineral Resource estimate is locally constrained within Deswik Stope Optimizer shapes using a minimal mining width of 2.4 m for long hole stoping. It is reported at a cut-off grade of 5.7 g/t Au. The following parameters were used: mining cost = $200.16/t; processing cost = $24.65/t; G&A = $41.11/t; sustaining capital cost = $80.22/t; refining costs = $4.56/oz; gold price = US$1,800.00/oz; US$/C$ exchange rate = 1.25; and process recovery = 95.0%. The cut-off grades should be re-evaluated in light of future prevailing market conditions (metal prices, exchange rates, mining costs etc.).
11. The number of metric tonnes was rounded to the nearest thousand, as required by Form 43-101F1, and any discrepancies in the totals are due to rounding effects. The metal contents are presented in troy ounces (tonnes x grade / 31.10348) rounded to the nearest hundred. Numbers may not add up due to rounding.
12. The Qualified Person is not aware of any known environmental, permitting, legal, political, title-related, taxation, socio-political, or marketing issues that could materially affect the Mineral Resource estimate.

Table 2 – Mineral Resource Statement, Grand Duc

Notes:

1. Mineral Resources are reported at an effective date of 30 September, 2024. The Qualified Person for the estimate is Mr. Abderrazak Ladidi, P.Geo. an IAMGOLD employee.
2. Measured Mineral Resources are reported in place as stockpiles. Indicated and Inferred Mineral Resources are in situ.
3. Mineral Resources are reported inclusive of Mineral Reserves. Mineral Resources that are not converted to Mineral Reserves have not demonstrated economic viability
4. Mineral Resources are reported using the 2014 CIM Definition Standards.
5. Mineral Resources are reported assuming a gold price of US$1,800 and a US$:C$ exchange rate of 1.25. Mineral Resources are constrained within an optimized open pit shell, which use input assumptions including: mining costs of $12.71/t mineralization and variable waste costs ranging from $4.07-$5.71, process costs of $19.29/t and metallurgical recoveries that average 92%. Mineral Resources that are not in stockpiles are reported at a cut-off of 0.54 g/t Au. Mineral Resources in stockpiles have variable cut-offs, depending on the stockpile, which range from 0.54-0.9 g/t Au.
6. The number of metric tonnes was rounded to the nearest thousand and any discrepancies in the totals are due to rounding effects. The metal contents are presented in troy ounces (tonnes x grade / 31.10348) rounded to the nearest hundred. Numbers may not add up due to rounding.

Mineral Reserves

Table 3 – Mineral Reserves Statement, Westwood

Notes:

1. Mineral Reserves are reported at the point of delivery to the process plant with an effective date of 30 September, 2024. The Qualified Person for the estimate is Mr. Louis Nkoy Manda Mbomba, P.Eng., an IAMGOLD employee.
2. Mineral Reserves are reported using the 2014 CIM Definition Standards.
3. Mineral Reserves are reported using a gold price of US$1,500/oz Au and assume a C$:US$ exchange rate of 1.25. Mineral Reserves are constrained within mineable shapes, that use input assumptions including long-hole open stope mining methods, mining costs of $200.16/t, process costs of $24.65/t, general and administrative costs of $41.11/t, Sustaining capital cost of $80.22/t, gold treatment and refining costs of $4.56/t, minimum mining width of 2.4 m, dilution assumption of 63% at 0.5 g/t Au, mining recovery of 85%, and metallurgical recoveries averaging 95%. Mineral Reserves are reported at a 6.82 g/t Au cut-off, which is inclusive of a 10% mine call factor.
4. Table numbers have been rounded. Totals may not sum due to rounding

Table 4 – Mineral Reserves Statement, Grand Duc

Notes:

1. Mineral Reserves are reported at the point of delivery to the process plant with an effective date of 30 September, 2024. The Qualified Person for the estimate is Mr. Louis Nkoy Manda Mbomba, P.Eng., an IAMGOLD employee.
2. Mineral Reserves are reported using the 2014 CIM Definition Standards.
3. Mineral Reserves are reported using a gold price of US$1,800/oz Au and assume a US$:C$ exchange rate of 1.25. Mineral Reserves are constrained within an optimized open pit shell, which use input assumptions including: mining costs of $12.71/t of ore and variable waste costs ranging from $4.07-5.71/t, process costs of $19.29/t, 10% dilution, bench face angles that range from 70º (north)-75º(south), and metallurgical recoveries that average 92%. Mineral Reserves are reported at a cut-off of 0.54 g/t Au.
4. Table numbers have been rounded. Totals may not sum due to rounding.

Table 5 – Westwood MRMR Comparison Summary¹

1. Mineral Reserves and Mineral Resources on a 100% basis
2. M&I Mineral Resources are inclusive of Mineral Reserves
3. Mineral Resources as of September 30, 2024 are reported using a gold price of US$1,800/oz Au. Mineral Reserves for Westwood are reported using a gold price of $1,500/oz Au, and Mineral Reserves for Grand Duc are reported using a gold price of $1,800/oz. Mineral Resources and Reserves assume a US$:C$ exchange rate of 1.25.
4. December 31, 2023 Mineral Resources were reported assuming a gold price of $1,600/oz for Westwood and $1,700/oz for Grand Duc. Mineral Reserves were reported assuming a gold price of US$1,300/oz for Westwood and $1,600/oz for Grand Duc.

The decrease in Measured and Indicated Mineral Resources estimated for Westwood from the prior estimate is primarily due to tighter confidence criteria applied to the mine planning process. To reduce variations in mine planning, Indicated Mineral Resources were classified based on the completed definition drill pattern requirements. The changes to the Indicated Mineral Resources classification requirements were primarily responsible for the increase in Inferred Mineral Resources; the other key factor contributing to increases in Inferred Mineral Resources was identification of additional mineralization through exploration drilling.

Life of Mine Plan

Westwood – Mining

The mine life based on Mineral Reserves for the Westwood Complex is forecast from 2025-2032. The Westwood mine plan assumes long-hole open stoping methods and conventional underground equipment accessed via the Westwood shaft or the Warrenmac ramp. The mine is owner-operated. An extensive seismic risk analysis was performed in 2021 following significant seismic events in October 2020. In-depth geotechnical analyses were performed by mine staff and external consultants to identify risks associated with mining sequence, infrastructure location, and support requirements. These included evaluations of stress state and rock mass classifications as well as a review of the seismic history.

Following the application of the different mitigation plans, the mine has experienced a decline in seismic events as shown in Figure ‎1 below. Key items to note from that figure include:

• The seismic activity rate appears to have been reduced by half, which represents a significant decrease;
• This reduction is mainly attributed to changes in mining practices including:
  • – Mining sequencing
  • – The extraction rate
  • – Mine planning based on the seismic potential of different areas (implementation of the geo-seismic strategy)

Figure ‎1: Westwood Seismic Events History

Note: Figure prepared by IAMGOLD, 2024

To view an enhanced version of this graphic, please visit:
https://images.newsfilecorp.com/files/6077/232557_c50585a3a41ad9a6_001full.jpg

The majority of the stopes will be mined in a bottom-up pillarless manner for better stress management. The transition from the primary-secondary method to a pillarless method is the result of a geotechnical study conducted after the major seismic event on October 30th, 2020, which recommended using a pillarless approach with a sequence designed, generally, to move stresses away from the mining front unidirectionally. The mining strategy is to mine the East, Central and Western sections of the mine simultaneously with as many as six mining areas mined concurrently to minimize production risk should one section be impacted by seismicity for a prolonged period of time. Consideration has been applied in the LOM to mitigate colliding mining fronts, as they create diminishing pillars that are detrimental to mine stability.

All underground material mined (ore + waste) must be hoisted to the surface, and the overall hoisting capacity depends on the loading pockets used. The LOM plan assumes a hoisting rate of 3,000 t/d. Once on surface, the ore is transported 2.5 km with 30 t haul trucks to the Doyon process plant.

The Westwood deposit remains open at depth, westward and locally to the east along the untested mineralized Westwood, North and Zone-2 corridors.

Grand Duc – Mining

Mining is carried out using a conventional drill, blast, load, and haul surface mining method with a contractor-operated fleet. Equipment is conventional for open pit operations.

The open pit is designed to reach a total depth of 110 m and will be about 309 m long. Benches are designed on 10 m heights in overburden and 20 m heights in fresh rock. Berm widths are 20 m in overburden and 10 m in fresh rock. Ramps and roadways are typically 20 m wide, reducing to single-lane, 12 m, widths at the base of the pit.

The Grand Duc operations share a portion of the infrastructure required for the mining operations with Westwood, including the Doyon process plant, waste rock storage facility, and tailings storage.

The remaining mine life for Grand Duc is to 2025, with processing continuing into 2027. The LOM production is included in Table 6.

The Grand Duc deposit remains open westward and locally to the east. The Company is evaluating the potential for a second phase extension of Grand Duc.

Processing

The Doyon plant treats ore via a conventional cyanidation process. Run-of-mine (ROM) ore is processed using a conventional single stage primary crusher followed by a two-stage semi-autogenous grinding (SAG) mill and ball mill grinding circuit, gravity circuit, pre-leach, carbon in leach (CIL) and carbon in pulp (CIP) circuits, in addition to associated gold recovery and carbon handling circuits to produce gold/silver doré.

The process plant was originally constructed in the 1970s and last refurbished in 2013 to increase throughput to 1.0 Mt/a. Upgrades were made to the grinding, cyanidation, strip, and tailings cyanide destruction circuits. A new paste backfill plant was also built to meet the Westwood Complex operational needs.

The plant has been operated both continuously, and in batch mode, since 2013, depending on ore availability. Currently, operations are 24 hours a day, seven days a week, 52 weeks a year. However, there will be portions of the current mine plan which will see reduced ore availability, and the plan is to have the plant operate in batch mode. Depending on the period, this may result in operating a certain number of weeks in a month of operations or select days within a week of operations.

There have also been instances over the plant history where the process plant toll-treated custom material from other mining operations. This remains an option since the process flowsheet is flexible and can accommodate third-party custom materials outside the LOM plan.

Closure and Reclamation Planning

Closure plans must be submitted to the relevant regulator before commencement of activities. Closure plans must be revised every five years, however, in certain cases, the regulator can require more frequent revisions. A financial guarantee is required to cover reclamation and closure costs.

The most recent closure plan update was submitted for Westwood and Doyon in 2021, with separate closure plans for each of Doyon and Westwood. The combined closure costs for Westwood, Doyon/Grand Duc and Fayolle, including contingency and ongoing Doyon care and maintenance costs, are estimated to be approximately $223.7 million. The 2021 Westwood closure plan was approved by the ministry in June 2024 and IAMGOLD has provided financial guarantees of $54.2 million to date in accordance with the government’s payment schedule, increasing to $57.2 million by 2026. The Doyon/Grand Duc closure plan was approved by the ministry in July 2024 and IAMGOLD provided financial guarantees of $97.0 million to date in accordance with the government’s payment schedule, increasing to $122.1 million by 2026. The Fayolle closure plan was approved by the ministry in 2022 and IAMGOLD provided financial guarantees of $2.3 in accordance with the government’s payment schedule, increasing to $3.0 million by Dec. 19th, 2024. The final Fayolle closure plan is required no later then December 19, 2027.

The next planned updates for Doyon and Westwood are July and June 2029, respectively. The Company is conducting studies to determine the ability to decrease the closure costs of the Westwood Complex through ongoing rehabilitation and analysis of remediation methods.

Table 6 – Westwood Complex: Mine Plan Summary

Note: Numbers may not add up due to rounding

QUALIFIED PERSON AND TECHNICAL INFORMATION

Mineral Resources and Mineral Reserves are reported in accordance with the Canadian Institute of Mining, Metallurgy and Petroleum (CIM) Definition Standards for Mineral Resources and Mineral Reserves (May 2014; the 2014 CIM Definition Standards) and were prepared with reference to the CIM Estimation of Mineral Resources & Mineral Reserves Best Practice Guidelines (November, 2019; the 2019 CIM Estimation Guidelines).

The following serve as the qualified persons (QPs) for this news release as defined in National Instrument 43-101, Standards of Disclosure for Mineral Projects, and in compliance with Form 43-101F1:

• Mr. Bernard Haley, P.Eng., Mining Manager, IAMGOLD;
• Mr. Abderrazak Ladidi, P.Geo., Principal Resource Geologist, IAMGOLD;
• Mr. Martin Perron, P.Eng., Director Centre of Excellence Geology, Norda Stelo Inc.;
• Mr. Louis Nkoy Manda Mbomba, P.Eng., Superintendent Mine Engineering, IAMGOLD;
• Dr. Ali Jalbout; P.Eng., Principal – Geotechnical Specialist, ASA Geotech Inc.;
• Mr. Steve Pelletier, P.Eng., Principal Director, Environment, IAMGOLD.

Lisa Ragsdale, Director, Mining Geology, IAMGOLD Corporation is the QP for the purposes of NI 43-101 with respect to the mineralization being reported on and is responsible for the review and approval of all mineral resources estimates for IAMGOLD. Guy Bourque, Director, Mining, IAMGOLD Corporation is the QP for the purposes of NI 43-101 with respect to the mineralization being reported on and is responsible for the review and approval of all mineral reserves estimates for IAMGOLD. The technical information in this news release has been included with the consent and prior review of Ms. Ragsdale and Mr. Bourque, as applicable. The QPs have verified the data disclosed and data underlying the information or opinions contained in this news release.

About IAMGOLD

IAMGOLD is an intermediate gold producer and developer based in Canada with operating mines in North America and West Africa. The Company has commenced production at the large-scale, long life Côté Gold Mine in partnership with Sumitomo Metal Mining Co. Ltd., which is expected to be among the largest gold mines in Canada. In addition, the Company has an established portfolio of early stage and advanced exploration projects within high potential mining districts. IAMGOLD employs approximately 3,600 people and is committed to maintaining its culture of accountable mining through high standards of Environmental, Social and Governance practices, including its commitment to strive for the goal of Zero Harm®, in every aspect of its business. IAMGOLD is listed on the New York Stock Exchange (NYSE: IAG) and the Toronto Stock Exchange (TSX: IMG).

IAMGOLD Contact Information

Graeme Jennings, Vice President, Investor Relations
Tel: 416 360 4743 | Mobile: 416 388 6883
Toll-free: 1 888 464 9999
info@iamgold.com

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