Iamgold Expands GOLD Potential ON the Monster Lake Project, Quebec

NEWS RELEASE

TSX: IMG NYSE: IAG

IAMGOLD EXPANDS GOLD POTENTIAL ON THE MONSTER LAKE PROJECT, QUEBEC 

Toronto, Ontario, May 11, 2017 – IAMGOLD Corporation (“IAMGOLD” or the “Company”) today

provided an update on the ongoing exploration program at its Monster Lake joint venture project located

50 kilometres southwest of Chibougamau, Quebec, Canada. The company is reporting assay results from

the first eleven drill holes, totaling just over 5,100 metres, from a total of 24 diamond drill holes, totaling

10,657 metres, completed this past winter.

The assay results are provided in Table 1 below and include the following highlights:

(A drill hole plan map and longitudinal sections are attached to this news release.)

Monster Lake Shear Zone, Megane Zone and Annie Shear Zone:

 Drill hole ML17-190: 4.4 metres grading 5.21 g/t gold

o Includes: 1.3 metres grading 15.99 g/t gold

and 1.9 metres grading 9.82 g/t gold

o Includes: 0.6 metres grading 25.10 g/t gold

and 0.6 metres grading 36.90 g/t gold

 Drill hole ML17-194: 3.1 metres grading 121.67 g/t gold,

o Includes: 1.1 metres grading 316.89 g/t gold

Lower Shear Zone:

 Drill hole ML-17-191: 1.8 me tres grading 85.27 g/t gold.

The 2017 winter drilling program was designed to target high potential areas along the 3-kilometre trend of

the Monster Lake Structural Cor ridor (“MLSC”) and associated sh ear zones to improve confidence and

expand known zones of mineralizat ion, including the recently di scovered second zone located 200 to 400

metres to the north of the Megane Zone, as well as mineralization in a parallel lower shear zone. Structural

patterns suggest the potential for additional mineralized shoots along this major corridor.

The results from hole ML17-190 drilled in the new zone to the n orth of the Megane Zone confirm previous

results in hole ML15-147 that intersected multiple mineralized shears and may indicate an extension of the

zone. Two areas of mineralization were also intersected in the Lower Monster Lake Shear Zone in drill holes

ML17-184 and 191 which will require further testing. Infill drilling in the Megane Zone positively demonstrated

continuity of the very high grade nature of this lens where tes ted. Further results from this drilling program

are pending and will be assessed when they are received, validated and compiled.

Craig MacDougall, Senior Vice President, Exploration for IAMGOLD, stated: “Assays from this winter drilling

program continue to return encou raging results, including those from a new zone along the main hosting

structure, as well as from a lower parallel shear zone. The potential for the discovery of additional mineralized

shoots is considered favourable.”

page 2 of 5

Next Steps

Once the remaining assay results are in hand, they will be assessed and may lead to an estimation of an

initial mineral resource by yearend. Further drilling will be required to evaluate the potential of the new

mineralized areas, the timing of which will be dependent on ground conditions to allow the access of drilling

equipment.

About the Monster Lake Project

The Monster Lake project is underlain by Archean volcanic rocks of the Obatogamau Formation and is

traversed by an important deformation corridor and associated gold-bearing mineralized structures.

Historical drilling and exploration by TomaGold Corporation (“TomaGold’) have identified a four-kilometre

long structural corridor, along which most of the known gold occurrences discovered to date on the

property are associated, including the Megane Zone.

IAMGOLD holds a 50% interest in the Monster Lake project. Pursuant to an earn-in option agreement with

TomaGold amended on October 30, 2015, IAMGOLD holds an option to earn a further 25% undivided

interest, for a total 75% undivided interest in the project, should it spend a further C$10.0 million on the

project within a seven-year period, beginning January 1, 2015. Should a development decision be made

by the joint venture, or should the joint venture declare commercial production, TomaGold would be

entitled to a further C$1.0 million payment. IAMGOLD has completed its first year commitment under the

terms of the amended option earn in agreement.

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" responsible for the supervision of the preparation and review of this information is

Marie-France Bugnon, P. Geo., General Manager Exploration. Marie-France is considered a "Qualified

Person" for the purposes of National Instrument 43-101 with respect to the technical information being

reported on. The technical information has been included herein with the consent and prior review of the

above noted Qualified Person. The Qualified person has verified the data disclosed, and data underlying

the information or opinions contained herein.

The sampling of, and assay data from, 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 half a metre

to one and a half metres in length depending on the geological observations.

Samples are transported in sealed bags to ALS Minerals Laboratory located in Val-d’Or,

Québec. Samples are coarse crushed to a -10 mesh and then a 1000 gram split is pulverized to 95%

passing -150 mesh. ALS Minerals processes analytical pulps directly at their facilities located in Val-d’Or

which is ISO / IEC 17025 certified by the Standards Council of Canada. Samples are analyzed using a

standard fire assay with a 50 gram charge with an Atomic Absorption (AA) finish. For samples that return

assay values over 5.0 grams per tonne (g/t), another pulp is taken and fire assayed with a gravimetric

finish. Core samples showing visible gold or samples which have returned values greater than 10.0 g/t are

re-analyzed by pulp metallic analysis. IAMGOLD inserts blanks and certified reference standard in the

sample sequence for quality control.

Forward Looking Statement

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 (including, without limitation, statements regarding expected, estimated or planned gold

production, cash costs, margin expansion, capital expenditures and exploration expenditures and

statements regarding the estimation of mineral resources, exploration results, potential mineralization,

potential mineral resources and mineral reserves) are forward-looking statements. Forward-looking

statements are generally identifiable by use of the words “will”, “should”, “continue”, “expect”, “anticipate”,

“estimate”, “believe”, “intend”, “to earn”, “to have’, “plan” 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

page 3 of 5

of risks and uncertainties, many of which are beyond the Company’s ability to control or predict, that may

cause the actual results of the Company to differ materially from those discussed in the forward-looking

statements. Factors that could cause actual results or events to differ materially from current expectations

include, among other things, without limitation, failure to meet expected, estimated or planned gold

production, cash costs, margin expansion, capital expenditures and exploration expenditures and failure to

establish estimated mineral resources, 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 and Canadian provincial securities regulatory authorities. 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.

About IAMGOLD

IAMGOLD ( www.iamgold.com) is a mid-tier mining company with four operating gold mines o n three

continents. A solid base of strategic assets in North and South America and West Africa is complemented

by development and exploration projects and continued assessmen t of accretive acquisition opportunities.

IAMGOLD is in a strong financial position with extensive management and operational expertise.

For further information please contact:

Ken Chernin, VP Investor Relations, IAMGOLD Corporation

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

Laura Young, Director, Investor Relations, IAMGOLD Corporation

Tel: (416) 933-4952 Mobile: (416) 670-3815

Shae Frosst, Investor Relations Associate

Tel: (416) 933-4738 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 CNW Group’s website

at www.newswire.ca. 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

http://www.iamgold.com/French/Home/default.aspx.

page 4 of 5

Table 1

Notes: 

1. Drill hole intercepts are calculated using a 0.50 g/t Au assay cut-off.

2. True widths of intersections are approximately 75-90% of the core interval.

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

Hole No. AZ DIP EOH from To Interval True Width

(2) Au (1) NOTE

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

ML-17-184 5488649 520146 371 288 -60 408 319,40 322,25 2,85 2,18 3,20 Lower Shear Zone

ML-17-186 5488702 520396 372 295 -53 684 409,05 409,54 0,49 0,42 3,71 Main Shear Zone

423,80 425,30 1,50 1,30 4,66

579,00 581,50 2,50 2,17 0,93 Lower Shear Zone

ML-17-187 5488011 520001 372 289 -50 429 No significant results

ML-17-188 5488058 520002 369 289 -50 399 253,50 254,00 0,50 0,43 1,76 Main Shear Zone

256,10 256,70 0,60 0,32 1,56

ML-17-189 5488928 520307 373 315 -55 336 264,20 265,10 0,90 0,87 3,08 Annie Shear Zone

ML-17-190 5489005 520343 373 315 -55 348 253,60 258,30 4,70 3,32 2,92 Main Shear Zone

Including (3) 253,60 254,50 0,90 0,64 7,25

283,30 291,00 7,70 4,42 5,21

Including (3) 283,80 286,00 2,20 1,26 15,99

308,60 311,60 3,00 1,93 9,82

Including (3) 309,60 310,60 1,00 0,64 25,10

344,10 345,00 0,90 0,64 36,90

ML-17-191 5488111 520137 370 290 -55 552 383,80 386,20 2,40 2,32 0,72 Main Shear Zone

509,90 512,45 2,55 1,80 85,27 Lower Shear Zone

ML-17-192 5488777 520278 373 300 -60 493,5 271,00 273,00 2,00 1,29 1,83 Mai n Shear Zone

274,60 277,60 3,00 1,93 0,98

ML-17-193 5488784 520331 372 305 -60 603,8 379,90 380,50 0,60 0,46 1,29 Mai n Shear Zone

575,90 577,00 1,10 0,84 1,47 Lower Shear Zone

ML-17-194 5488306 520134 371 293 -58 381 333,50 334,60 1,10 0,71 3,45 Main Shear Zone

339,00 343,85 4,85 3,12 121,67

Including (3) 340,40 342,10 1,70 1,09 316,89

ML-17-196 5488813 520417 372 300 -55 468 387,50 388,50 1,00 0,71 2,37 Main Shear Zone

417,80 418,70 0,90 0,64 1,14

UTM NAD83 Zone18

Monster Lake Project Drilling Final Results - 201 7 Winter Drilling Program

page 5 of 5