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Iamgold Announces Initial Resource Estimate at Gosselin Zone – Growing Côte GOLD District BY 3.4 Million GOLD Ounces IN Indicated Resources and 1.7 Million GOLD Ounces IN Inferred Resources

Resource Estimates

NEWS RELEASE

TSX: IMG NYSE: IAG

IAMGOLD ANNOUNCES INITIAL RESOURCE ESTIMATE AT GOSSELIN

ZONE – GROWING CÔTE GOLD DISTRICT BY 3.4 MILLION GOLD OUNCES IN

INDICATED RESOURCES AND 1.7 MILLION GOLD OUNCES IN INFERRED

RESOURCES

HIGHLIGHTS:

• Gosselin deposit initial mineral resource estimate comprises:

o 124.5 million tonnes of indicated resources averaging 0.84 grams of gold per tonne for

3.35 million ounces of gold

o 72.9 million tonnes of inferred resources averaging 0.73 grams of gold per tonne for 1.71

million ounces of gold

• Addition of Gosselin deposit mineral resources represents a 33% increase in total contained

gold in measured and indicated resource categories and 45% increase in total contained gold

in inferred resource category for the Côté Gold project

• Deposit only drilled to approximately half the depth of Côté Gold deposit itself; remains open

at depth and along strike

• Potential for significant future resource expansion

Toronto, Ontario, October 18, 2021 – IAMGOLD Corporation (TSX: IMG) (NYSE: IAG) (“IAMGOLD” or

the “Company”) is pleased to announce an initial mineral resource estimate for the Gosselin zone discovery,

centered approximately 1.5 kilometres northeast of the Côté Gold construction project (“Côté Gold”). 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”). The Gosselin delineation drilling program was undertaken as

part of the Côté Gold 70:30 joint venture between IAMGOLD , as the operator, and Sumitomo Metal Mining

Co., Ltd. (“SMM”). Côté Gold, located 175 km north of Sudbury, Ontario, Canada and 125 km southwest of

Timmins, Ontario, Canada, is currently under construction with commercial production anticipated in the

second half of 2023 (see news releases dated July 21, 2020 and August 4, 2021).

The mineral resource estimate for the Gosselin deposit (on a 100% basis using a US$1,500 per ounce gold

price) comprises:

• 124.5 million tonnes of indicated resources averaging 0.84 grams of gold per tonne for 3.35 million

ounces of gold; and

• 72.9 million tonnes of inferred resources averaging 0.73 grams of gold per tonne for 1.71 million

ounces of gold.

Current reported mineral resources for the adjacent Côté Gold deposit, on the same basis, are comprised

of measured and indicated resources totalling 365.5 million tonnes averaging 0.8 7 grams of gold per tonne

for 10.2 million ounces of gold and inferred resources totalling 189.6 million tonnes averaging 0.63 grams of

gold for 3.8 million ounces (see news release dated February 17, 2021).

Craig MacDougall, Executive Vice President, Growth for IAMGOLD, stated: "We are very pleased to have

reached this significant milestone disclosing an initial mineral resource estimate for the Gosselin discovery.

The exploration team is to be especially congratulated for safely completing a series of successive,

logistically challenging, delineation-drilling programs while navigating the evolving challenges presented by

the COVID-19 pandemic.”

“We believe that the Gosselin deposit will continue to enhance the long term value and district-scale potential

of the Côté Gold project. The Gosselin deposit remains open along strike to the northeast and has only been

drilled to approximately half the depth of the Côté Gold deposit itself, so there remains significant potential

to further expand total resources,” added Mr. MacDougall.

page 2 of 5

The mineral resource estimate for the Gosselin zone incorporates assay results from 163 diamond drill

(“DD”) holes totalling 54,775 metres, including 95 DD holes totalling 38,398 metres completed by IAMGOLD

as part of its delineation drilling program. Drill holes are spaced at approximately 70 metres apart . The

estimate was prepared using a block model constrained with 3D wireframes of the principal mineralized

domains. Values for gold were interpolated into blocks using inverse distance cubed . A Whittle open pit

optimization algorithm 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 ”. The

optimization algorithm considered only the Goss elin block model and the original unmined surface,

independent of the Côté estimated block model. Pit slopes in rock were assumed at 45° and t he resource

estimate assumes a long -term gold price of US$ 1,500 per ounce. Only mineralization contained within the

preliminary pit shell has been included in the resource estimate . Gold recoveries are assumed at 91.8% as

indicated by preliminary metallurgical test work. The resource estimate was completed by SLR Consulting

(Canada) Ltd. (“SLR”) with an effective date of October 4, 2021.

IAMGOLD will file an updated NI 43 -101 technical report for Côté Gold , including a description of the

Gosselin deposit mineral resource estimate, on SEDAR at www.sedar.com within 45 days of the date of this

news release.

MINERAL RESOURCE STATEMENT – GOSSELIN ZONE, CANADA

At October 4, 2021 (100% Basis)

Category Cut-off Grade

(g/t Au)

Tonnage

(Mt)

Grade

(g/t Au)

Contained Au

(Moz)

Attributable

Contained Au

(Moz)

Indicated

0.6 74.1 1.10 2.62

0.5 90.6 1.00 2.91

0.4 108.5 0.91 3.17

0.3 124.5 0.84 3.35

0.2 133.1 0.80 3.42

Total Indicated 0.3 124.5 0.84 3.35 2.17

Inferred

0.6 36.9 1.02 1.21

0.5 46.6 0.92 1.38

0.4 58.9 0.82 1.56

0.3 72.9 0.73 1.71

0.2 100.2 0.60 1.93

Total Inferred 0.3 72.9 0.73 1.71 1.11

Notes:

1. 2014 CIM Definition Standards were followed for the definition of Mineral Resources.

2. Mineral Resources are estimated at a cut-off grade of 0.3 g/t Au.

3. Mineral Resources are reported using a gold price of US$1,500 per ounce and a USDCAD exchange rate of 1:1.2.

4. Mineral Resources are constrained by a Whittle optimized pit shell using economic parameters consistent with those used for the

mineral resources estimate in the “Côté Gold Project, Ontario, NI 43 -101 Technical Report on Feasibility Study” effective

November 1, 2018 prepared in accordance with NI 43-101.

5. High grade assay values from the main mineralized domains have been capped from 6 g/t Au to 20 g/t Au, and at 3 g/t Au in the

low grade domain.

6. Bulk density values were determined by measurements on core and range from 2. 69 g/cm3 to 2.85 g/cm3 for the different host

lithologies.

7. Mineral Resources that are not Mineral Reserves do not have demonstrated economic viability.

8. All figures have been rounded to reflect the relative accuracy of the estimates.

About the Gosselin Deposit

The Gosselin zone discovery is located immediately northeast of the Côté Gold deposit (see figure 1 below),

and is accessible by construction roads on the developing mine property. Diamond drilling to date has

delineated wide intervals of low -grade gold mineralization hosted in altered and brecciated intrusive

lithologies similar to that observed at the adjacent Côté Gold deposit, extending from the Young -Shannon

historical shaft in the west to the Gosselin zone in the east. Drilling to date has outlined mineralization over

a strike length of 1,400 metres, width of 400 metres and a depth extent of 425 metres. The deposit outcrops

below the shallow Three Ducks Lake, and remains open at depth, to the northwest, and along strike to the

northeast and southwest.

page 3 of 5

Next Steps

The resource estimation process has identified a number of areas with potential for resource expansions at

depth, along strike and in areas where drill hole spacing remains too wide to classify resources at this time.

In addition, the saddle area between the Gosselin resource pit shell and the adjacent Côté Gold deposit

design pit is a priority area to review for a potential connection of mineralization . These areas will be

evaluated in order to plan future drilling campaigns designed to expand resources as well as upgrade

resource classification.

With this initial resource estimation now complete, planning and sample selection will commence to advance

future metallurgical test work to evaluate recoveries across a range of ore types and grades and evaluate

the comminution characteristics of the mineralization.

The Côté technical team will also begin mining and infrastructure studies to review alternatives to optimize

the inclusion of the Gosselin resource into future Côté life-of-mine plans. As part of these studies, the

Company will commence work on defining th e baseline data and permitting requirements for different

development scenarios and initiate discussions on these different optio ns with our First Nations and Mé tis

stakeholders.

Figure 1: Longitudinal section of the Côté Gold and Gosselin deposits resource block models within the

constraining Whittle resource pit shells.

Qualified Persons, Technical Information and Quality Control Notes

The mineral resource estimate, including verification of the data disclosed, has been completed by SLR and

has been prepared in accordance with NI 43-101 and CIM Estimation Best Practice Guidelines. The resource

estimate was pre pared by Tudorel Ciuculescu, P. Geo., who is a Consultant Geologist with SLR. Mr.

Ciuculescu is an independent “qualified person”, as defined by NI 43 -101 (a “QP”), and has reviewed and

approved the contents of this news release.

The QPs responsible for the supervision of the supporting drilling programs, data validation and verification,

deposit modelling and review of the technical information in this news release are Al Smith, P.Geo., District

Manager – Exploration for IAMGOLD in the Ontario Côte Distric t and Brad McKinley , P.Geo., Senior

Geologist for IAMGOLD in the Ontario Côte District . Each of Mr. Smith and Mr. McKinley is a QP for the

purposes of NI 43-101 with respect to the technical information being reported on in this news release. The

technical information has been included herein with the consent and prior review of the above noted QPs.

Longitudinal Section

0.3 – 0.5 g/t Au

0.5 – 0.7 g/t Au

0.7 – 1.0 g/t Au

1.0 – 2.0 g/t Au

2.0 – 5.0 g/t Au

> 5.0 g/t Au

0 500 m

0 500 m

Looking North

Inclined View

Looking North

Côté Deposit Gosselin Zone

Côté

Resource

Shell

Gosselin

Resource

Shell

Open

Open

Block Model Gold Grades

page 4 of 5

The information in this news release was also reviewed and approved by Craig MacDougall, P.Geo .,

Executive Vice President, Growth for IAMGOLD, who is also a QP.

The sampling of, and assay data from, the drill core is monitored through the implementation of a quality

assurance-quality control (“QA-QC”) program designed to follow industry best practice. Drill core (NQ and

BTW size) samples are selected by the IAMGOLD geologists and sawn in half with a diamond saw at the

project site. Half of the core is retained at the site for reference purposes. Sample intervals may vary from

0.5 to 1.5 metres in length depending on the geological observations. Samples were stored in sealed plastic

bags and packed into fiber bags onto a pallet where they were shrink wrapped for transport. A formal chain-

of-custody procedure was adopted for security of samples until their delivery at the laboratory.

Activation Laboratories Limited ( “ACTLABS”) of Timmins, Ontario, was utilized for assay analyses,

performing crushing, pulverizing, and fire assay. ACTLABS completed the following laboratory procedure:

samples are coarse crushed to 80% passing 2.0 mm screen (10 mesh screen), riffle split (250 gram) and

pulverized to 95% passing 105 µm. Cleaner sand is included. Samples were analyzed using a standard 30

gram fire assay (30 g aliquot) with an Atomic Absorption finish.

For samples that returned assay values over 3.0 grams per tonne (g/t), another cut is taken from the original

pulp and fire assayed with a gravimetric finish. For samples showing visible gold or samples which have

returned values greater than 5.0 g/t, these were re-analyzed by pulp metallic analysis.

IAMGOLD inserts blanks and certified reference standards in the sample sequence for quality control.

In accordance with recommendations from our on -going QA-QC program, additional check analyses are

underway at a secondary (umpire) laboratory.

The mineral resource data set out in this news re lease are estimates, and no assurance can be given that

the anticipated tonnages and grades will be achieved or that the indicated level of recovery will be realized.

CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING INFORMATION

This news release contains forward -looking statements. All statements, other than of historical fact, that address

activities, events or developments that the Company believes, expects or anticipates will or may occur in the future are

forward-looking statements. Forward-looking statements are generally identifiable by, but not limited to, the use of the

words “may”, “will”, “should”, “would”, “continue”, “expect”, “expected”, “budget”, “forecast”, “anticipate”, “estimate”,

“believe”, “intend”, “appear” “plan”, “schedule”, “ guidance”, “outlook”, “potential”, “plans”, “targeted”, “focused”, or

“project” or the negative of these words or other variations on these words or comparable terminology. Forward-looking

statements are subject to a number of risks and uncertainties, many of which are beyond the Company's ability to control

or predict, that may cause the actual results to differ materially from those discussed in the forward-looking statements.

Factors that could cause actual results or events to differ materially from cur rent expectations include, among other

things, without limitation, differences in the mineral content within the material identified as mineral resources or mineral

reserves from that predicted, the failure to accurately estimate mineral resources or miner al reserves, unexpected

increases in capital expenditures, operating expenditures and exploration expenditures, changes in development or

mining plans due to changes in logistical, technical or other factors, the possibility that future exploration results will not

be consistent with the Company's expectations, changes in world gold markets and other risks disclosed in IAMGOLD's

most recent Form 40 -F/ Annual Information Form on file with the United States Securities and Exchange Commission

at https://www.se c.gov/edgar.shtml and Canadian securities regulatory authorities at www.sedar.com, which are

incorporated herein. Any forward-looking statement speaks only as of the date on which it is made and, except as may

be required by applicable securities laws, the Company disclaims any intent or obligation to update any forward-looking

statement. The Company disclaims any intention or obligation to update or revise any forward -looking statements

whether as a result of new information, future events or otherwise except as required by applicable law.

CAUTIONARY NOTE TO U.S. INVESTORS REGARDING DISCLOSURE OF MINERAL RESOURCE

ESTIMATES

The mineral resource estimates contained in this news release have been prepared in accordance with NI 43-101. These

standards are similar to those used by the United States Securities and Exchange Commission (the “SEC”) Industry

Guide No. 7, as interpreted by the SEC staff. However, the definitions in NI 43-101 differ in certain respects from those

under Industry Guide 7. Accordingly, mineral resource information contained in this news release may not be comparable

to similar information disclosed by United States companies.

As a result of the adoption of amendments to the SEC’s disclosure rules, which more closely align its disclosur e

requirements and policies for mining properties with current industry and global regulatory practices and standards,

including NI 43-101, and which became effective on February 25, 2019, the SEC now recognizes estimates of "measured

mineral resources", "indicated mineral resources" and "inferred mineral resources." In addition, the SEC has amended

page 5 of 5

definitions of "proven mineral reserves" and "probable mineral reserves" in its amended rules, with definitions that are

substantially similar to those used in NI 43-101. Issuers must begin to comply with the se SEC Modernization Rules in

their first fiscal year beginning on or after January 1, 2021, though Canadian issuers that report in the United States

using the Multijurisdictional Disclosure System ("MJDS") m ay still use NI 43 -101 rather than the SEC Modernization

Rules when using the SEC's MJDS registration statement and annual report forms.

United States investors are cautioned that while the SEC now recognizes "measured mineral resources", "indicated

mineral resources" and "inferred mineral resources", investors should not assume that any part or all of the mineral

deposits in these categories will ever be converted into a higher category of mineral resources or into mineral reserves.

These terms have a great amount of uncertainty as to their economic and legal feasibility. Under Canadian regulations,

estimates of inferred mineral resources may not form the basis of feasibility or pre -feasibility studies, except in limited

circumstances. Investors are caution ed not to assume that any "measured mineral resources", "indicated mineral

resources", or "inferred mineral resources" that the Company reports in this news release are or will be economically or

legally mineable.

Further, "inferred mineral resources" have a great amount of uncertainty as to their existence and as to their economic

and legal feasibility. It cannot be assumed that any part or all of an inferred mineral resource will ever be upgraded to a

higher category.

The mineral resource data set out in this news release are estimates, and no assurance can be given that the anticipated

tonnages and grades will be achieved or that the indicated level of recovery will be realized.

About IAMGOLD

IAMGOLD is a mid -tier gold mining company operating in three regions globally: North America, South

America and West Africa. Within these regions the Company is developing high potential mining districts

that encompass operating mines and construction, development and exploration projects. The Company’s

operating mines include Essakane in Burkina Faso , Rosebel (including Saramacca) in Suriname and

Westwood in Canada . A solid base of strategic assets is complemented by the Côté Gold construction

project in Canada, the Boto Gold development project in Senegal, as well as greenfield and brownfield

exploration projects in various countries located in the Americas and West Africa.

IAMGOLD employs approximately 5,000 people. IAMGOLD is committed to maintaining its culture of

accountable mining through high standards of Environmental, Social and Governance practices, including

its commitment to Zero Harm®, in every aspect of its business. IAMGOLD (www.iamgold.com) is listed on

the New York Stock Exchange (NYSE: IAG) and the Toronto Stock Exchange (TSX: IMG) and is one of the

companies on the JSI index1.

1 Jantzi Social Index (“JSI”). The JSI is a socially screened market capitalization-weighted common stock index modeled on the S&P/TSX 60. It consists

of companies which pass a set of broadly based environmental, social and governance rating criteria.

For further information please contact:

Philip Rabenok, Manager, Investor Relations, IAMGOLD Corporation

Tel: (416) 933-5783 Mobile: (647) 967-9942

Toll-free: 1-888-464-9999 [email protected]

Please note:

This entire news release may be accessed via fax, e-mail, IAMGOLD's website at www.iamgold.com and through Newsfile’s website

at www.newsfilecorp.com. All material information on IAMGOLD can be found at www.sedar.com or at www.sec.gov.

Si vous désirez obtenir la version française de ce communiqué, veuillez consulter le www.iamgold.com/French/accueil/default.aspx.