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Iamgold Reports Positive Assay Results from the 2021 Resource Deline Ation Drilling ON the Gosselin Zone and Continues to Extend the Mineralized System – Côté GOLD Project, Ontario

Drill Results

NEWS RELEASE

TSX: IMG NYSE: IAG

IAMGOLD REPORTS POSITIVE ASSAY RESULTS FROM THE 2021

RESOURCE DELINE ATION DRILLING ON THE GOSSELIN ZONE AND CONTINUES

TO EXTEND THE MINERALIZED SYSTEM – CÔTÉ GOLD PROJECT, ONTARIO

Toronto, Ontario, September 21 , 2021 – IAMGOLD Corporation (“IAMGOLD” or the “Company”) is

pleased to announce additional positive assay results from its delineation diamond drilling program at the

Gosselin zone discovery, centered approximately 1.5 kilometres northeast of the Côté Gold construction

project (“Côté Gold”). The Gosselin delineation drilling program is being 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 A ugust 4, 2021).

In March 2021, IAMGOLD reported the results of the remaining nine (9) diamond drill holes totaling 3,686

metres as part of the resource delineation drilling program completed in the fourth quarter of 2020 (see news

release dated March 8, 20 21).

IAMGOLD is now reporting assay results from an additional thirty one (31) diamond drill holes totaling 11,735

metres completed in 2021. Drill holes were completed from land -based drill platforms on the north and south

shores of Three Ducks Lake, and also on lake ice and barge-based platforms directly on Three Ducks Lake.

The assay results reported herein are provided in Table 1, below, and include the following highlights (see

plan map attached to this news release for drill hole locations – Figure 1):

 Drill hole GOS21-66: 242.0 metres grading 1.57 g/t Au

includes: 154.0 metres grading 2.31 g/t Au

includes: 32.9 metres grading 6.00 g/t Au

 Drill hole GOS21-76: 151.5 metres grading 1.25 g/t Au

 Drill hole GOS21-80: 48.5 metres grading 7.83 g/t Au

includes: 3.5 metres grading 96.1 g/t Au

 Drill hole GOS21-81: 430.5 metres grading 0.95 g/t Au

includes: 274.2 metres grading 1.31 g/t Au

 Drill hole GOS21-86: 393.0 metres grading 1.41 g/t Au

 Drill hole GOS21-88: 220.0 metres grading 1.25 g/t Au

includes: 96.0 metres grading 2.10 g/t Au

 Drill hole GOS21-92: 304.3 metres grading 1.14 g/t Au

 Drill hole GOS21-93: 350.0 metres grading 1.25 g/t Au

includes: 177.0 metres grading 1.91 g/t Au

Craig MacDougall, Executive Vice President, Growth for IAMGOLD, stated: “These additional drilling results

continue to demonstrate the continuity and strength of this wide mineralized system. The Gosselin zone

remains open to the northeast and southeast as well as at depth. I want to acknowledge the tremendous

effort of our exploration team to safely complete this logistically challenging drilling campaign, as well as our

core shack technicians who processed and prepared large numbers of core samples to fac ilitate a timely

submission for analysis. Additionally I want to acknowledge the support of our assay laboratory partner to

expedite the assaying of the drill core samples allowing for their inclusion in the drilling database to support

the completion of a maiden resource estimate , which we expect to release in the fourth quarter of 2021 .”

page 2 of 8

The Gosselin zone discovery is located immediately northeast of the Côté Gold deposit, and is accessible

by construction roads on the developing mine property. Diamond d rilling to date has delineated wide intervals

of low-grade Au mineralization extending from the Young -Shannon historical shaft in the west to the Gosselin

zone in the east. This continuous zone of mineralization is herein referred to as the Gosselin zone.

The 2021 diamond drilling program continued to in -fill and delineate the Gosselin zone at a nominal drill hole

spacing of approximately 70 metres, including the shallowest parts of the deposit under Three Ducks Lake

and on the Young-Shannon peninsula. Two of the completed drill holes were oriented in the opposite

direction from the regular drill pattern to cross -cut the central part of the Gosselin zone, providing additional

information on the central breccia core of the deposit .

Diamond drilling data c ollected from this program, including oriented drill core, have been used in the

creation of a robust geology model incorporating vein orientation and the observed associated structural

controls. Results continue to demonstrate gold concentrations associat ed with two principal vein

compositions, which have been modelled and used to underpin the deposit model to support the mineral

resource estimate.

Drilling results to date confirm widespread Au mineralization which has now been defined over a strike length

of 1,400 metres, width of 400 metres and a depth extent of 425 metres. The zone lies immediately northeast

of the Côté Gold deposit outcropping below Three Ducks Lake, and remains open at depth, and along strike

to the northeast and southeast.

Next Steps

The finalization of the deposit model and supporting drill hole database, including QA / QC validations have

been completed and is now being used to support an initial resource estimate for the Gosselin zone, which

is expected to be completed in the fourth quarter of 2021.

Drilling continues with additional in-fill drill holes in progress utilizing one barge-based drill rig on Three Ducks

Lake and two land-based drill rigs on Young -Shannon peninsula, with the program expected to continue into

late October of 2021.

page 3 of 8

Figure 1 – Gosselin Drill Hole surface plan and highlighted 2021 assays

Figure 2 – Longitudinal Section - Gosselin Zone. Drill hole traces with Au grades represent holes reported in this release

page 4 of 8

Hole No. AZ DIP EOH From To Core

Interval (1) Au (2) (3)

Easting Northing Elevation (°) (°) (m) (m) (m) (m) (g/t)  

GOS21-63 430892 5267830 381 330 -64 258.00

GOS21-64 430952 5267845 382 328 -67 199.50 5.00 23.00 18.00 0.63

109.00 141.00 32.00 0.79

GOS21-65 430931 5267695 381 329 -66 426.00 105.00 121.00 16.00 0.62

185.30 376.00 190.70 0.43

GOS21-66 431352 5267683 381 330 -65 439.50 188.00 430.00 242.00 1.57

Including (3) 276.00 430.00 154.00 2.31

Including (3) 384.08 417.00 32.92 6.00

Including (3) 399.00 400.33 1.33 23.00

Including (3) 407.00 409.00 2.00 26.55

GOS21-67 431308 5267757 381 330 -65 162.00 113.00 162.00 49.00 1.21

GOS21-68 431023 5267546 381 330 -65 453.00 92.70 453.00 360.30 0.67

Including (3) 220.50 453.00 232.50 0.81

Including (3) 282.00 390.00 108.00 1.02

GOS21-69 431192 5267725 381 330 -60 343.50 93.15 343.50 250.35 0.79

Including (3) 168.00 342.00 174.00 0.97

Including (3) 231.00 232.05 1.05 23.60

Including (3) 325.93 326.78 0.85 14.10

GOS21-70 430840 5267488 383 330 -60 430.50 68.00 412.00 344.00 0.62

Including (3) 153.00 411.00 258.00 0.72

Including (3) 283.50 284.50 1.00 13.10

Including (3) 310.50 311.50 1.00 12.30

GOS21-71 430832 5267547 382 330 -60 424.50 97.00 424.50 327.50 1.35

Including (3) 97.00 213.70 116.70 0.72

Including (3) 234.50 235.50 1.00 239.00

GOS21-72 430724 5267462 389 315 -60 423.00 206.00 231.00 25.00 0.35

259.00 285.45 26.45 0.58

397.00 407.00 10.00 0.48

GOS21-73 430773 5267478 388 330 -60 349.50 67.00 91.00 24.00 0.43

GOS21-74 430780 5267581 385 335 -60 448.50 176.84 435.00 258.16 0.77

Including (3) 176.84 347.20 170.36 0.97

Including (3) 322.00 323.00 1.00 14.00

GOS21-75 430731 5267399 396 330 -60 424.50 73.00 151.00 78.00 0.42

293.30 399.00 105.70 0.79

GOS21-76 430839 5267424 386 330 -60 455.00 60.00 72.80 12.80 0.51

144.00 157.00 13.00 0.42

217.05 293.32 76.27 0.48

302.47 454.00 151.53 1.25

Including (3) 308.47 309.97 1.50 13.30

Including (3) 379.00 380.00 1.00 25.20

GOS21-77 430659 5267378 398 330 -60 109.50

Table 1 Gosselin Project Drilling Results - 2021 Drilling program

UTM NAD83 Zone17

No significant results

No significant results

page 5 of 8

Hole No. AZ DIP EOH From To Core

Interval (1) Au (2) (3)

Easting Northing Elevation (°) (°) (m) (m) (m) (m) (g/t)  

GOS21-78 430610 5267440 390 330 -60 466.50 16.00 32.00 16.00 1.41

Including (3) 28.00 29.00 1.00 13.50

260.00 291.50 31.50 0.36

309.00 333.50 24.50 0.42

387.00 455.50 68.50 0.53

GOS21-79 430659 5267378 398 317 -60 424.50 21.00 112.85 91.85 1.57

Including (3) 59.26 60.00 0.74 69.40

Including (3) 75.21 76.35 1.14 31.10

138.00 182.00 44.00 1.52

Including (3) 144.00 144.94 0.94 21.70

Including (3) 162.50 163.00 0.50 26.00

189.00 211.08 22.08 1.08

Including (3) 206.00 207.00 1.00 11.00

343.00 379.00 36.00 0.46

GOS21-80 430578 5267387 396 330 -60 462.00 10.00 47.00 37.00 0.54

85.00 133.50 48.50 7.83

Including (3) 130.00 133.50 3.50 96.11

158.60 198.00 39.40 0.36

270.00 281.00 11.00 1.36

333.00 402.00 69.00 0.84

Including (3) 339.00 340.30 1.30 11.60

GOS21-81* 431308 5267757 381 330 -65 474.00 21.55 452.00 430.45 0.95

Including (3) 146.80 421.00 274.20 1.31

Including (3) 164.00 166.00 2.00 14.00

Including (3) 356.00 358.00 2.00 24.70

Including (3) 367.00 368.00 1.00 16.00

GOS21-82 430626 5267491 384 323 -59 441.00 267.00 275.75 8.75 1.58

308.00 324.00 16.00 0.53

GOS21-83* 431406 5267758 381 330 -60 471.00 25.30 471.00 445.70 0.66

Including (3) 119.35 141.00 21.65 0.93

Including (3) 190.00 191.00 1.00 11.70

Including (3) 304.00 471.00 167.00 1.06

Including (3) 319.50 320.85 1.35 23.20

GOS21-84 430520 5267356 391 330 -60 424.87 22.00 60.00 38.00 0.43

Including (3) 254.00 317.00 63.00 0.77

Including (3) 302.00 303.00 1.00 19.50

GOS21-85 430887 5267828 382 330 -65 438.00 210.00 438.00 228.00 0.66

Including (3) 349.00 433.00 84.00 1.10

Including (3) 349.00 350.00 1.00 12.70

GOS21-86* 431077 5267810 381 78 -60 482.00 88.00 481.00 393.00 1.41

Including (3) 215.85 217.00 1.15 13.40

Including (3) 386.00 388.00 2.00 19.35

Including (3) 464.00 465.00 1.00 74.60

GOS21-87 430714 5267631 382 355 -50 436.50

Table 1 Gosselin Project Drilling Results - 2021 Drilling program

UTM NAD83 Zone17

No significant results

page 6 of 8

Notes:

1. Insufficient drilling has been completed to accurately determine the Gosselin Zone orientation. Actual core w idths are

estimated at approximately 60 to 95% of the core interval.

2. Drill hole intercepts are calculated w ith a low er 0.30 g/t Au cut-off.

3. Assays are reported uncut but high grade sub-intervals are highlighted.

* BTW drill core. Core diameter is 42.0 mm

Technical Information and Quality Control Notes

The drilling results contained in this news release have been prepared in accordance with National

Instrument 43-101 Standards of Disclosure for Mineral Projects (“NI 43-101”).

The Qualified Person (“QP”) responsible for the supervision of the preparation, verification and review of the

technical information in this release is Al Smith, P. Geo, District Manager – Exploration for IAMGOLD in the

Ontario Côte Gold District. He is considered a QP for the purposes of NI 43-101 with respect to the technical

information being reported on.

The QP responsible for the planning, supervision and execution of the diamond drilling program is Brad

McKinley, P. Geo, Senior Geologist for IAMGOLD in the Ontario Côte Gold District. The technical information

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

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

Vice President, Growth for IAMGOLD. Mr. MacDougall is a QP as defined by NI 43-101.

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 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

Hole No. AZ DIP EOH From To Core

Interval (1) Au (2) (3)

Easting Northing Elevation (°) (°) (m) (m) (m) (m) (g/t)  

GOS21-88 431197 5268009 385 164 -49 432.00 207.00 427.00 220.00 1.25

Including (3) 272.00 368.00 96.00 2.10

Including (3) 291.00 292.00 1.00 30.60

Including (3) 301.11 302.05 0.94 10.30

GOS21-89* 431121 5267814 381 330 -65 36.00 19.70 36.00 16.30 2.26

Including (3) 22.00 23.00 1.00 16.80

GOS21-90* 431121 5267814 381 330 -65 441.00 20.40 51.00 30.60 1.06

139.00 400.00 261.00 0.66

Including (3) 360.00 361.00 1.00 23.40

GOS21-91* 431065 5267618 382 327 -65 40.50

GOS21-92 431202 5268006 385 142 -55 528.13 223.70 528.13 304.43 1.14

Including (3) 255.50 256.00 0.50 25.10

Including (3) 264.00 264.90 0.90 10.40

Including (3) 266.00 267.00 1.00 27.00

Including (3) 440.00 441.00 1.00 18.80

Including (3) 483.79 485.00 1.21 13.90

GOS21-93* 431066 5267616 382 327 -65 390.00 40.00 390.00 350.00 1.25

Including (3) 192.00 369.00 177.00 1.91

Including (3) 197.00 198.00 1.00 10.20

Including (3) 212.00 213.00 1.00 24.80

Including (3) 242.60 244.00 1.40 11.10

Table 1 Gosselin Project Drilling Results - 2021 Drilling program

UTM NAD83 Zone17

No significant results

page 7 of 8

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 un til 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 90% passing 2.0 mm screen (10 mesh screen), riffle split (250 gram) and

(mild steel) to 95% passing 105µm. Cleaner sand is included. Samples were analyzed using a standard 30

gram fire assay (30 g aliquot) with an Atomic Absorption (AA) 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 (VG) 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 ACTLABS.

CAUTIONARY STATEMENT REGARDING FORWARD -LOOKING INFORMATION

This new s release contains forw ard -looking statements. All statements, other than of historical fact, that address activities,

events or developments that the Company believes, expects or anticipates w ill or may occur in the future are forw ard -looking

statements. Forw ard -looking statements are generally identifiable by, but not limited to, the use of the w ords "may", " w ill",

"should", "w ould", "continue", "expect", "expected", "budget", "forecast", "anticipate", "estimate", "believe", "intend", "appear"

"plan", "schedule", "guidance", "outlook", "potential", "plans", "targeted", "focused", or "project" or the negative o f these w ords

or other variations on these w ords or comparable terminology. Forw ard -looking statements are subject to a number of risks and

uncertainties, many of w hich are beyond the Company's ability to control or predict, that may cause the actual resul ts to differ

materially from those discussed in the forw ard -looking statements. Factors that could cause actual results or events to differ

materially from current expectations include, among other things, w ithout limitation, differences in the mineral con tent w ithin the

material identified as mineral resources or mineral reserves from that predicted, the failure to accurately estimate mineral

resources or mineral 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 possibilit y

that future exploration results w ill not be consistent w ith the Company's expectations, changes in w orld gold markets and oth er

risks disclosed in IAMGOLD's most recent Form 40 -F/ Annual Information Form on file w ith the United States Securities and

Exchange Commission at https://w w w.sec.gov/edgar.shtml and Canadian securities regulatory authorities at w ww.sedar.com ,

w hich are incorporated herein. Any forw ard-looking statement speaks only as of the date on w hich it is made and, except as

may be required by applicable securities law s, the Company disclaims any intent or obligation to update any forw ard -looking

statement. The Company disclaims any intention or obligation to update or revise any forw ard -looking statements w hether as

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

About IAMGOLD

IAMGOLD is a mid -tier gold mining company opera ting 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, construction, development, and exploration projects. The Company’s

operating mines include Westwood in Canada, Rosebel (including Saramacca) in Suriname and Essakane

in Burkina Faso. A solid base of strategic assets is complemented by the Côté Gold construction project in

Canada, the Boto Gold development project in Seneg al, 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 stan dards 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 index 1.

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 env ironmental, s ocial and gov ernance rating criteria.

page 8 of 8

For further information please contact :

Indi Gopinathan , VP, Investor Relations & Corporate Communications, IAMGOLD Corporation

Tel: (416) 360-4743 Mobile: (416) 388-6883

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 new s release may be accessed via fax, e-mail, IAMGOLD's w ebsite at www.iamgold.com and through New sfile’s website

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

Si vous désirez obtenir la version française de ce communiqué, veuillez consulter le

https://www.iamgold.com/French/accueil/default.aspx.