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First Mining Announces Updated Mineral Resource Estimate at Duparquet Gold Project in Quebec

Resource Estimates

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NEWS RELEASE

First Mining Announces Updated Mineral Resource Estimate at

Duparquet Gold Project in Quebec

September 12, 2022 – Vancouver, Canada – First Mining Gold Corp. (“First Mining” or the “Company”)

(TSX: FF) (OTCQX: FFMGF) (FRANKFURT: FMG) is pleased to provide an updated Mineral Resource

Estimate (the “MRE”) on the Duparquet gold project (“Duparquet” or the “Project”) located in Quebec,

prepared by InnovExplo Inc. in accordance with the National Instrument 43-101 Standards of Disclosure

for Mineral Projects (“NI 43-101”).

The updated MRE is derived from the master database of drill data, which contains 904 holes totalling

270,119m and 173,831 sampled intervals. This MRE includes 57 drill holes totaling 9,548m not included

in the previous MRE with drilling occurring after the effective date of February 28, 2013. The drilling

was carried out by Clifton Star Resources Inc., Beattie Gold Mines Ltd., and 2588111 Manitoba Ltd. By

incorporating these previous drill holes, Duparquet’s resource increases to 3.4 Moz in the measured and

indicated category, an increase of 327 koz, and to 1.6 Moz in the inferred category, an increase of 193

koz.

“First Mining is very excited to announce an updated mineral resource estimate at the Duparquet Gold

Project,” stated Dan Wilton, CEO of First Mining Gold. “Duparquet is an advanced stage project that has

benefited from 270,000m of historical drilling and was advanced to a PFS level in 2014. This resource

growth from incorporating the 2013-2018 drilling is just the beginning of what we see as immense value

potential here at Duparquet. Based on the size of its current resource, Duparquet represents one of the

top four undeveloped gold projects in the province of Quebec. Its above average M&I open pit grade of

1.52 g/t Au provides excellent mining flexibility and along with its size and location, make it a very

versatile deposit amenable to different potential mining scenarios with good future growth potential.

The project site is well located and has access to excellent infrastructure and skilled labour. First Mining

intends to complete an updated economic study in the near future and to develop an exploration path

to support potential resource expansion, resource classification upgrading, and discovery of new

deposits in this underexplored district.”

Table 1: Duparquet Gold Project Mineral Resource Estimate

Area Cut-off Measured resource Indicated resource Inferred resource

(mining

method) (g/t) Tonnage

(t)

Au

Ounces Tonnage (t)

Au

Ounces Tonnage (t)

Au

Ounces

(g/t) (g/t) (g/t)

Open Pit 0.40 163,700 1.37 7,200 59,410,600 1.52 2,909,600 28,333,000 1.07 970,400

UG Mining 1.50 - - - 5,506,900 2.26 399,300 9,038,900 2.29 665,600

Tailings 0.40 19,900 2.03 1,300 4,105,200 0.93 123,200 - - -

Total 183,600 1.43 8,500 69,022,700 1.55 3,432,100 37,371,900 1.36 1,636,000

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Notes to accompany the Mineral Resource Estimate:

1. The independent and qualified persons for the mineral resource estimate, as defined by NI 43 101, are Marina Iund, P.Geo. and Carl Pelletier,

P.Geo., both from Innovexplo. The effective date of the estimate is September 12, 2022.

2. These mineral resources are not mineral reserves, as they do not have demonstrated economic viability. There is currently insufficient data

to define these Inferred mineral resources as Indicated or Measured mineral resources and it is uncertain if further explorat ion will result

in upgrading them to an Indicated or Measured mineral resource category. The mineral resource estimate follows current CIM Definition

Standards.

3. The results are presented in situ and undiluted and have reasonable prospects of economic viability.

4. In-pit and Underground estimates encompass sixty (60) mineralized domains and one dilution envelop using the grade of the adjacent

material when assayed or a value of zero when not assayed; The tailings estimate encompass four (4) zones.

5. In-pit and Underground: High-grade capping of 25 g/t Au; Tailings: High-grade capping of 13.0 g/t Au for Zone 1, 3.5 g/t Au for Zone 2, 1.7

g/t Au for Zone 3 and 2.2 g/t Au for Zone 4. High -grade capping supported by statistical analysis was done on raw assay data before

compositing.

6. In-pit and Underground: The estimate used a sub-block model in GEOVIA SURPAC 2021 with a unit block size of 5m x 5m x 5m and a minimum

block size of 1.25m x 1.25m x1.25m. Grade interpolation was obtained by ID2 using hard boundaries. Tailings: The estimat e used a block

model in GEOVIA GEMS with a block size of 5m x 5m x 1m. Grade interpolation was obtained by ID2 using hard boundaries.

7. In-pit and Underground: A density value of 2.73 g/cm3 was used for the mineralized domains and the envelope. A density val ue of 2.00

g/cm3 was used for the overburden. A density value of 1.00 g/cm3 was used for the excavation solids (drifts and stopes) assum ed to be

filled with water. Tailings: A fixed density of 1.45 g/cm3 was used in zones and waste.

8. In-pit and Underground: The mineral resource estimate is classified as Measured, Indicated and Inferred. The measured category is defined

by blocks having a volume of at least 25% within an envelope built at a distance of 10 m around existing channel samples. The Indicated

category is defined by blocks meeting at least one (1) of the following conditions: Blocks falling within a 15 -m buffer surrounding existing

stopes and/or blocks for which the average distance to composites is less than 45 m. A clipping polygon was generated to constrain Indicated

resources for each of the sixty (60) mineralized domains. Only the blocks for which reasonable geological and grade continuit y have been

demonstrated were selected. All remaining interpolated blocks were classified as Inferred resource s. Blocks interpolated in the envelope

were all classified as Inferred resources. Tailings: The Measured and Indicated categories were defined based on the drill hole spacing

(Measured: Zones 1 and 2 = 30m x 30m grid; Indicated: Zone 3 = 100m x 100m grid and Zone 4 = 200m x 200m grid).

9. In-pit and Underground: The mineral resource estimate is locally pit-constrained with a bedrock slope angle of 50° and an overburden slope

angle of 30°. The out-pit mineral resource met the reasonable prospect for eventual economic extraction by having constraining volumes

applied to any blocks (potential underground extraction scenario) using DSO. It is reported at a rounded cut -off grade of 0.4 g/t Au (in -pit

and tailings) and 1.5 g/t Au (UG). The cut-off grades were calculated using the following parameters: mining cost = CA$70.00 (UG); processing

cost = CA$11.9 to 17.0; G&A = CA$8.75; refining and selling costs = CA$ 5.00; gold price = US$ 1,650/oz; USD:CAD exchange rate = 1.31; and

mill recovery = 93.9%. The cut -off grades should be re -evaluated in light of future prevailing market conditions (metal prices, exchange

rates, mining costs etc.).

10. The number of metric tons and ounces was rounded to the nearest hundred, following the recommendations in NI 43 101. Any discrepancies

in the totals are due to rounding effects.

11. The authors are not aware of any known environmental, permitting, legal, title-related, taxation, socio-political, or marketing issues, or any

other relevant issue not reported in the Technical Report, that could materially affect the Mineral Resource Estimate.

Project Description

Duparquet consists of four (4) contiguous mineral exploration properties: Beattie, Donchester, Central

Duparquet, Dumico and the tailings from the former Beattie mine. The Project is located in the Abitibi

region of the province of Quebec, approximately 50 km north of the city of Rouyn-Noranda.

The Project site has infrastructure which includes paved, provincial highways from Rouyn-Noranda to

the south and LaSarre to the north, both mining communities that can provide mining infrastructure and

skilled labour to develop a mine. The Project site is also proximal to Quebec’s hydroelectric power grid.

Duparquet, previously comprised of 2 separate Mining Concessions (Beattie and Donchester mines), now

comprises of fifty (50) map -designated claims (“CDC”) covering an area of 1,079.2 ha covering a strike

length of 8 km in an E-W direction.

Duparquet is geologically located in the southern portion of the Abitibi, straddling the SE trending

prolific Destor-Porcupine Fault Zone (DPMFZ). Structurally the project includes numerous E-W

mineralized splays off of the Destor-Porcupine Fault Zone, as well as several syenite intrusions.

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Surrounding host rocks include mafic to ultramafic volcanic rocks and younger Temiskaming age

conglomerates.

The predominant structures on Duparquet are the E-W splays of the DPMFZ. The Beattie Fault Zone

(“BFZ”) is located along the north contact of the main syenite body, whereas the Donchester Fault Zone

(“DFZ”) is located along the south contact. The Central Duparquet Fault Zone (“CDFZ”) is located along

the south contact of the second smaller syenite intrusive to the east.

Figure 1: Geology of the Duparquet Project. Structural and geometric details are represented by

surface projections of the relevant structural elements from the deposit-scale 3D litho-structural

model

The main style of gold mineralization in the Duparquet deposit generally occurs within shears or

brecciated zones along or within the adjacent intrusive syenitic masses and is associated with finely

disseminated pyrite and minor arsenopyrite replacement. Sulphide content is generally low (0.5 to 4%),

although it can be up to 10% in some cases. Gold is associated and hosted with the pyrite and lesser

arsenopyrite and arsenian pyrite.

Gold was initially discovered in the Duparquet Township in 1910 by John Beattie. The Beattie and

adjoining Donchester mines were in production from 1933 to 1956, producing upwards of 1.3 million

ounces of gold. In the mid-1930’s Beattie Gold Mines was the largest gold producer in Quebec. From

the 1980’s to 2007, very limited exploration was carried out. Clifton Star had an option on the property

between 2009 and 2014. During this time a substantial amount of surface diamond drilling, channel

sampling was carried out. The company also completed an environmental baseline study, environmental

assessment study and numerous metallurgical studies. Mineral resource estimates were also carried out

that were included in the preliminary economic assessment and a prefeasibility study. The Clifton Star

option was terminated in 2014 and the property was returned to the previous owners, with Clifton Star

retaining a 10% interest in the companies that held the properties.

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Drilling Summary

Since the effective date of the previous mineral resource estimate (InnovExplo, Poirier et al., 2014), the

Company (Clifton Star) and the previous owners (Beattie Gold Mines and 2588111 Manitoba Ltd.) had

completed an additional 57 surface drill holes totalling 9,548 m, that were not included in the MRE.

Significant assay results added to this new MRE include 5.65 g/t Au over 34.0 m (BD13-22) on Beattie

and 5.58 g/t Au over 5.0 m (D13-18) on Donchester.

The 2022 MRE contains 904 drillholes and 892 channel samples in outcrops. It contains 173,831 sampled

intervals taken from 270,119 m of drilled core and 2,371 analyses from 1,827 m of channels. The 904

DDH cover the 4.5-km strike length of the Project at a reasonably regular drill spacing of 25-50 m.

Metallurgical Testing Summary

Bench-scale and pilot plant metallurgical testwork programs have been carried out for the Project. SGS

carried out preliminary metallurgical testwork in 2012 to support a PEA at that time. In 2013, SGS

carried out further flotation, pressure oxidation, cyanidation, rheology and environmental testwork,

including a pilot plant for a PFS. Outotec was also mandated in 2013 to carry out filtration testwork.

The overall gold results from flotation concentrate, pressure oxidation (POX) and CIL circuit as well as

flotation tail cyanidation for the ore resulted in an overall recovery of gold ranging from 91.9% to 95.4%.

A preliminary pilot test program investigated pressure oxidation and hot curing processing of a

Duparquet flotation concentrate to render precious metals extractable by cyanidation. The recovery of

gold from the pilot plant hot cure discharge ranged from 94.7% to 96.5%

Bench-scale test work was also performed on two samples of existing tailings on the Project. The test work

for the flotation-POX/CIL flowsheet resulted in overall gold recoveries ranging from 83.5% to 93.3%.

Mineral Resource Summary

The MRE update for the Project (the “2022 MRE”) was prepared by Marina Iund, P.Geo. and Carl

Pelletier, P.Geo., using all available information. The main objective was to update the results of

InnovExplo’s previous mineral resource estimate for the Project, dated June 26, 2013 (Poirier et al.,

2014). The updated MRE includes new drill holes on the Beattie, Donchester and Central Duparquet

properties.

The resource area has an E-W strike length of 4.5 km, a width of approximately 1 km, and a vertical

extent of 1,050 m below surface.

The 2022 MRE was prepared using GEOVIA GEMS 6.8.2.2 (“GEMS”) and GEOVIA Surpac 2021 (“Surpac”)

software. GEMS was used for updating the mineralized domains and the compositing. Surpac was used

for the estimation, which consisted of 3D block modelling and the inverse distance square (“ID2”)

interpolation method. Statistical, capping and variography studies were completed using Snowden

Supervisor v8.13 and Microsoft Excel software.

The 60 mineralized domain wireframes were created and updated by digitizing an interpretation onto

sections spaced 25 m apart or 12.5 m in areas with higher drill hole density. However, if barren intervals

were encountered, the mineralized zones were extended only to the mid-distance between the last

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known occurrence of mineralization and the barren hole. A 50-m extension around the zones was used

for the secondary mineralized domains.

A dilution envelope was defined as the parts of the block model that are not included in any of the

mineralized domain solids. The solid for the envelope contains “floating” gold intersects for which

continuity has not yet been demonstrated or interpreted.

High-grade capping was set at 25 g/t Au for all zones, including the envelope zone. Twenty-two (22) DDH

samples and one (1) channel sample were capped.

Analysis of 3,633 bulk density values and a 12 t composite drill core bulk sample from the mineralized

zones, yielded 2.73 g/cm3 (mean density of the syenite) for all 60 mineralized domains and the envelope.

A density of 2.00 g/cm3 was assigned to the overburden, and 1.00 g/cm3 was assigned to excavation

solids (drifts and stopes) assumed to be filled with water.

The intervals defining each mineralized domain were composited to 1-m equal lengths. A grade of 0.00

g/t was assigned to missing sample intervals as it was assumed that unsampled intervals were

considered to be unmineralized by the geologist in charge of the core logging.

A block model was built to enclose a sufficiently large enough volume to host an open pit. The model

corresponds to a sub-blocked model in Surpac with no rotation. The user block size was defined as 5m x

5m x 5m with a minimal sub-block size of 1.25m x 1.25m x 1.25m. Block dimensions reflect the sizes of

mineralized domains and plausible mining methods. All blocks with more than 50% of their volume

falling within a selected solid were assigned the corresponding solid block code.

Individual zones and the envelope were estimated separately using their own search ellipsoid. The

available geological and geostatistical information was used to establish the size of each search ellipsoid.

Seventy-two (72) distinct mineralized domains were studied. The mean azimuth and dip of each domain

were used to define 23 search ellipsoids, grouping zones of similar geometry.

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Figure 2: Plan view and isometric view of the categorized mineral resources and the Whittle optimized

pit-shells (blocks selection: in pit-shells or in DSO and above the respective COG)

Table 2: Cut-off grade sensitivity for the in-pit and underground portions of the Duparquet Project

Area

(Mining

Method)

Cut-off

(g/t)

Measured Resource Indicated Resource Inferred Resource

Tonnage (t) Au

(g/t) Ounces Tonnage (t) Au

(g/t) Ounces Tonnage (t) Au

(g/t) Ounces

Open Pit

0.7 137,321 1.53 6,755 23,142,210 2.05 1,525,279 2,592,695 1.62 135,038

0.65 141,757 1.5 6,836 25,666,698 1.98 1,633,902 3,334,098 1.48 158,647

0.6 149,158 1.46 7,001 32,690,577 1.86 1,954,908 5,716,620 1.34 246,283

0.55 154,634 1.42 7,060 36,556,977 1.77 2,080,340 7,727,020 1.23 305,568

0.5 156,938 1.41 7,122 41,152,335 1.70 2,253,068 11,007,061 1.13 400,881

0.45 161,081 1.39 7,187 53,548,726 1.58 2,722,586 22,032,449 1.16 824,601

0.4 163,709 1.37 7,222 59,410,612 1.52 2,909,551 28,332,980 1.07 970,424

0.35 165,800 1.36 7,248 66,307,600 1.46 3,117,172 37,354,222 0.96 1,147,282

UG

Mining

1.9 - - - 5,891,904 2.67 505,871 7,168,869 2.91 669,750

1.7 - - - 5,224,787 2.47 414,153 7,378,504 2.51 595,956

1.5 - - - 5,506,861 2.26 399,356 9,038,871 2.29 665,629

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1.3 - - - 5,302,381 2.10 357,603 11,459,118 2.05 756,440

Tailings

0.6 19,000 2.10 1,284 4,104,400 0.93 123,189 - - -

0.5 19,400 2.07 1,290 4,104,800 0.93 123,196 - - -

0.45 19,600 2.06 1,295 4,105,000 0.93 123,200 - - -

0.4 19,900 2.03 1,297 4,105,200 0.93 123,203 - - -

0.35 20,000 2.02 1,299 4,105,400 0.93 123,206 - - -

InnovExplo, the authors of the MRE report concluded that:

• The database supporting the 2022 MRE is complete, valid and up to date.

• Geological and gold-grade continuity has been demonstrated for all 72 mineralized zones.

• The key parameters of the 2022 MRE (density, capping, compositing, interpolation, search ellipsoid,

etc.) are supported by data and statistical and/or geostatistical analysis.

• The 2022 MRE includes measured, indicated and inferred resources for a combination of two mining

scenarios: open pit and selective underground. The 2022 MRE complies with C IM Definition

Standards and CIM Guidelines.

• Two cut -off grades of 0.40 and 1.50 g/t Au were used, corresponding to potential open pit and

selective underground mining scenarios.

• Cut-off grades were calculated at a gold price of US$1,650 per troy ounce and an exchange rate of

1.31 USD/CAD, using reasonable mining, processing and G&A costs.

• In a combined pit and selective underground mining scenario, the Project contains an estimated M+I

Resource of 65,081,200 t at 1.58 g/t Au for 3,316,100 oz of gold and an Inferred Resource of

37,371,900 t at 1.36 g/t Au for 1,636,000 oz of gold. The Project also contains the Beattie mine tailings

with an estimated M+I Resource of 4,125,100 t at 0.94 g/t Au for 124,500 oz of gold.

• The results of the 2022 MRE represent a 10.5% increase in the M+I Resource and a 13.4% increase in

the Inferred Resource compared to the previous 2014 MRE of Poirier et al., 2014. The increase in the

M+I Resource is due to a deeper optimized shell and the updated economic parameters. The same

reasons combined with the addition of 55 drill holes explain the increase in Inferred resources.

• Based on metallurgical tests, the Duparquet project appears amenable to standard gold recovery

processes. A combination of flotation, pressure oxidation and cyanide leach processes has shown a

gold recovery ranging from 94.7% to 96.5%.

• Additional diamond drilling on multiple zones would likely upgrade some of the Inferred Resource to

the Indicated category and/or add to the Inferred Resource since most of the mineralized zones have

not been fully explored at depth or close to surface infrastructures.

Updated Technical Report

The effective date of the updated MRE is September 12, 2022. A NI 43-101 Technical Report prepared by

InnovExplo Inc. will be filed on SEDAR within 45 days of this news release and will be available at that time

on the Company website.

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Qualified Persons

The independent and qualified persons for the MRE, as defined by National Instrument 43-101 Standards

of Disclosure for Mineral Projects , are Marina Iund, P.Geo. and Carl Pelletier, P.Geo., both from

Innovexplo. The effective date of the estimate is September 12, 2022.

Mr. Louis Martin P.Geo., (OGQ 0364), a consultant of First Mining, is a “Qualified Person” for the purposes

of National Instrument 43-101 Standards of Disclosure for Mineral Projects , and he has reviewed and

approved the scientific and technical disclosure contained in this news release.

About First Mining Gold Corp.

First Mining is a gold developer advancing a portfolio of gold projects in Canada, with our most advanced

project being the Springpole Gold Project in northwes tern Ontario, which is one of the largest

undeveloped gold projects in Canada, and where we have commenced a Feasibility Study and permitting

activities are on-going with a draft Environmental Impact Statement (“EIS”) for the project published in

June 2022. First Mining also own s the Cameron, Duparquet, Duquesne and Pitt gold projects, all

advanced-stage gold projects in Ontario (in the case of Cameron) and Québec. Our portfolio of gold

project interests also includes the Pickle Crow gold project (being advanced in partnership with Auteco

Minerals Ltd.), the Hope Brook gold project (being advanced in partnership with Big Ridge Gold Corp.), an

equity interest in Treasury Metals Inc., and a portfolio of 21 gold royalties.

First Mining was established in 2015 by Mr. Keith Neumeyer, founding President and CEO of First Majestic

Silver Corp.

ON BEHALF OF FIRST MINING GOLD CORP.

Daniel W. Wilton

Chief Executive Officer and Director

For further information, please contact:

Toll Free: 1 844 306 8827 | Email: [email protected]

Paul Morris | Director, Investor Relations | Email: [email protected]

Richard Huang | Vice President, Corporate Development | Email: [email protected]

Cautionary Note Regarding Forward-Looking Statements

This news release includes certain “ forward-looking information” and “ forward-looking statements” (collectively

“forward-looking statements”) within the meaning of applicable Canadian and United States securities legislation

including the United States Private Securities Litigation Reform Act of 1995. These forward- looking statements are

made as of the date of this news release. Forward -looking statements are frequently, but not always, identified by

words such as “ expects”, “anticipates”, “believes”, “plans”, “projects”, “ intends”, “estimates”, “envisages”,

“potential”, “possible”, “strategy”, “goals”, “opportunities”, “objectives”, or variations thereof or stating that certain

actions, events or results “may”, “could”, “would”, “might” or “will” be taken, occur or be achieved, or the negative

of any of these terms and similar expressions.