Val-d'Or, Quebec--(Newsfile Corp. - September 15, 2026) - Bonterra Resources Inc. (TSXV: BTR) (OTCQB: BONXF) (FSE: 9BR2) ("Bonterra" or the "Company") is pleased to present preliminary results of its 2026 exploration campaign at its 100% owned Desmaraisville South Project (the "Project"). To date, Bonterra has received assay results from 3,785 samples and 264 QA-QC samples from the 23 diamond drill holes completed. Bonterra drilled a total of 23 holes comprising 10,136 meters ("m"), with five holes abandoned totalling 125 m. Assay results have been received for 14 drill holes. There are five drill holes undergoing core cutting, while nine drill holes have either partial assay results or pending results. The drilling program started in January 2026 and, after a three-month pause, resumed in April and was completed in late August (see Figure 1). The objective of the program is to test deep targets on the eastern side of the O'Brien intrusive, which hosts the Bachelor and Moroy deposits and evaluate additional targets near the Bachelor Mill.

Cesar Gonzalez, Executive Chairman and Interim CEO commented: "Our 2026 drilling campaign at the 100%-owned Desmaraisville South Project has identified two exciting areas with strong potential for gold mineralization. These include a new target east of the O'Brien intrusive body, and an east-west corridor where drilling encountered strong alteration, abundant pyrite and visible gold. Importantly, we still have a significant amount of assay results pending, and data from our geophysical survey and structural mapping work. Bringing all of this information will provide an improved understanding of the mineralization controls, better refine our drill targets and guide the next phase of exploration at Desmaraisville South."

2026 Exploration Campaign Highlights to Date (see Table 1 and 2, Figures 1 to 4)

• O'Brien East Deep Target - 4.75 g/t Au over 1.4 m. including 16.03 g/t Au over 0.4 m (visible gold or VG), in hole BRDS-26-114, and 0.71 g/t Au over 2.2 m, in hole BRDS-26-124A
• Céré-Murgor Target - 0.79 g/t Au over 8.2 m, including 1.33 g/t Au over 2.7 m and 4.05 g/t Au over 0.6 m (VG), in hole BRDS-26-128A , and 1.99 g/t Au over 0.7 m, in hole BRDS-26-128A
• Mistik 13 Target - 1.03 g/t Au over 1.5 m, in hole BRDS-26-116A

Figure 1: Desmaraisville South Project - 2026 Diamond Drill Hole Locations

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Figure 2: Desmaraisville South Project - O'Brien East Deep Target Area Plan View - Assay Results

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O'Brien East Deep Target Highlights

• 4.75 g/t Au over 1.4 m. including 16.03 g/t Au over 0.4 m (VG), in hole BRDS-26-114
• 0.71 g/t Au over 2.2 m, in hole BRDS-26-124A

In drill hole BRDS-26-114, located east of the O'Brien intrusion, the zone containing visible gold corresponds to a quartz veinlet with fluorite, grading 16.03 g/t Au. The host rock consists of the O'Brien intrusive. Very weak hematization, thin quartz-fluorite veinlets are ubiquitous throughout the drill hole (see core photograph below).

This type of mineralization could be similar to the stockwork located on the western side of the O'Brien intrusive and may be pervasive and contain high-grade values.

BRDS-26-114 à 261.5 m: 16.03 ppm Au

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Drill hole BRDS-26-124A, with a total length of 1,566 m, was designed to intersect a mineralized system along the eastern side of the O'Brien intrusive. The emplacement of the intrusive may have generated a fracture network, providing pathways for hydrothermal fluids to percolate through the host rocks, or may have intersected pre-existing mineralized structures. Three zones containing anomalous gold grades were intersected. These zones are characterized by quartz-hematite-sericite alteration with approximately 1 to 2% pyrite.

Figure 3: Desmaraisville South Project - Céré-Murgor Target Area - Assay Results

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Céré-Murgor Target Highlights

• 0.79 g/t Au over 8.2 m, including 1.33 g/t Au over 2.7 m and 4.05 g/t Au over 0.6 m (VG), in hole BRDS-26-128A
• 1.99 g/t Au over 0.7 m, in hole BRDS-26-128A

The mineralized system is characterized by discordant quartz veinlets containing visible gold, as well as quartz veinlets parallel to the schistosity, hosted within strongly deformed and sericitized fine-grained sediments with disseminated pyrite. The drilling results indicate a favorable geological setting for extensive gold mineralization. This target area may be part of the Opiwaca-Guercheville deformation corridor.

BRDS-26-128 à 529.7 m

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Figure 4: Desmaraisville South Project - Mistik 13 Target Area Plan View - Assay Results

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Mistik 13 Target Highlights

• 1.03 g/t Au over 1.5 m, in hole BRDS-26-116A

The mineralized interval intersected in drill hole BRDS-26-116A occurs within a basalt cut by quartz-carbonate veinlets forming an anastomosing network and accounting for approximately 10% of the sample. Trace amounts of pyrite are present.

Other 2026 Exploration Activities

Bonterra completed a relogging and sampling program on 70 historic diamond drill holes in which altered and mineralized intervals had not previously been sampled. The Company has received 1,308 assay results, and several significant intercepts have yet to be incorporated into its database.

Laurentia Exploration ("Laurentia") based in Jonquière, Québec, has completed a metallogenic and structural study on the Desmaraisville South Property. Dr. Damien Gaboury, consultant for Laurentia, visited the site in late July to improve the understanding of the gold exploration potential.

Sander Geophysics ("Sander") based in Ottawa, Ontario, was commissioned to generate a 3D inversion model of the 2023 gravimetric data to model three-dimensional volumes that could correspond to late intrusions such as the O'Brien intrusion which hosts the Bachelor and Moroy deposits.

LithologIQ based in Montréal, Québec, has scanned 19 834 m of drill core using their hyperspectral core scanning technology. Historic and recent drill core from all gold mineralized environments at the Project have been scanned directly at the mine site. Identifying minerals associated with gold-bearing environments will allow for the rapid identification of new high-potential area during future drilling campaigns. Interpretation of the data collected and recommendations made by Laurentia, Sander and LithologIQ are being incorporated for future exploration work and better define drill targets.

Table 1: Drill Hole Locations - Desmaraisville South Project

UTM Coordinates, System: NAD83-UTM Z 18N

Table 2: Significant Mineralized Intersections from Drilling on the Desmaraisville South Project

1) Reported intervals represent drilled core lengths; true widths are not yet known.
2) Gold results obtained above 0.5 g/t Au with a Metal Factor above 1.
3) * Visible Gold (VG).

Quality Control and Reporting Protocols

The Desmaraisville South Project's drill core gold analyses were performed at the MSALABS and the AGAT Laboratories located in Val-d'Or, Québec. These external laboratories employ a rigorous QA-QC analysis program that meets industry standards. At the AGAT laboratory, the analyses are carried out by fire assay (A.A.) with atomic absorption finish and with gravimetric finish for assay above 10 g/t Au. Blanks, duplicates, and certified reference standards are inserted into the sample stream to monitor the Laboratory's performance. Other core samples gold analysis was performed at MSALABS of Val d'Or, Québec. The samples were crushed to a particle size of 70% passing through a two-millimeter sieve, and then a 500-gram portion was taken for gold analysis by gamma ray (PhotonAssayTM). As per MSALABS' internal procedure, blank samples, and certified reference materials are systematically inserted into the analysis sequence. MSALABS operates several laboratories worldwide and holds ISO-17025 accreditation for numerous metal determination methods, including the photon assay method.

The Company's QA-QC program requires that at least 5 to 10% of the samples be analyzed by an independent laboratory. These verification samples are sent to ALS Minerals laboratory facility located in Val-d'Or, Québec.
The verification shows a high degree of correlation with the laboratory's results.

Qualified Person

M. Donald Trudel, P.Geo. (OGQ # 813), Director Geology for the Company, oversees all exploration activities on the Desmaraisville Property and has compiled and approved the information contained in this press release. Mr. Trudel is a qualified person as defined by National Instrument 43-101 on standards of disclosure for mineral projects.

About Bonterra Resources Inc.

Bonterra is a Canadian gold exploration company with a portfolio of advanced exploration assets anchored by a central milling facility in Québec, Canada. The Company's assets include the Gladiator, Barry⁽¹⁾, Moroy, and Bachelor⁽²⁾ gold deposits, which collectively hold 16.8 million tonnes ("Mt") at an average grade of 3.02 g/t Au for 1.63 million ounces ("Moz") of Measured & Indicated Mineral Resources, plus 15.6 Mt at 4.32 g/t Au for 2.17 Moz of Inferred Mineral Resources.

In November 2023, the Company entered into an earn-in and joint venture agreement with Osisko Mining Inc. ("Osisko Mining") for the Urban-Barry properties (the "JV Agreement"), which include the Gladiator and Barry deposits. In October 2024, Gold Fields Ltd, through a wholly owned Canadian subsidiary, completed the acquisition of Osisko Mining for C$2.16 billion. Gold Fields is now the counterparty to the JV Agreement and can continue to earn a 70% interest in the joint venture by incurring C$30 million in work expenditures on or before November 2026 (including expenditures incurred by Osisko Mining prior to October 2024). This strategic transaction highlights Bonterra's dedication to advancing its exploration assets, marking a significant step towards development.

1) See news release of the Company dated February 23, 2026, and titled "Bonterra Reports Significant Mineral Resources Growth at Barry and Gladiator Deposits" for further details.
2) See news release of the Company dated April 1st, 2026, and titled "Bonterra Reports Significant Mineral Resource Growth at Bachelor and Moroy, 100% owned Deposits and Provides Corporate Updates" for further details.

Neither TSX Venture Exchange nor its Regulation Services Provider (as that term is defined in the policies of the TSX Venture Exchange) accepts responsibility for the adequacy or accuracy of this release.

Caution regarding forward-looking statements

This news release contains forward-looking statements within the meaning of applicable securities laws. All statements other than statements of historical fact may be forward-looking and are often identified by words such as "may", "will", "plan", "expect", "anticipate", "estimate", and "intend". Forward-looking statements in this release include, without limitation, statements regarding, the 2026 exploration program at the Desmaraisville South project and at the Phoenix JV, including planned drilling activities, deep-drilling objectives at the Barry deposit, proposed camp upgrades, and Gold Fields' ability to complete the remaining earn-in expenditures under the JV Agreement.

These statements are based on assumptions considered reasonable by management, including assumptions regarding exploration plans, budgets, schedules, regulatory approvals, and the continued advancement of work by Gold Fields. However, forward-looking statements involve known and unknown risks, uncertainties, and other factors that may cause actual results to differ materially. Such risks include, but are not limited to, changes to exploration plans, results that differ from expectations, operational or permitting challenges, the ability of the parties to complete the Joint Venture, the timing and completion of earn-in expenditures, the speculative nature of mineral exploration, commodity price fluctuations, and the availability of financing. Additional information regarding risks can be found in the Company's filings at www.sedarplus.ca.

Readers are cautioned not to place undue reliance on forward-looking statements. The Company does not undertake to update any forward-looking statement except as required by applicable securities laws. All forward-looking statements in this release are expressly qualified by this cautionary statement.

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Source: Bonterra Resources Inc.