Mosaic Begins a Drilling Campaign of at Least 2,000 Metres at Golden Island and Returns up to 72.8 g/t Au, 42.5 g/t Ag and 0.42% Cu at Surface

Montreal, Quebec--(Newsfile Corp. - October 29, 2026) - Mosaic Minerals Corporation (CSE: MOC) ("Mosaic" or the "Company") announces assay results for 343 samples collected during its summer 2026 exploration campaign on its Golden Island gold project in Abitibi, Quebec. The Company also announces the start of its diamond drilling campaign of at least 2,000 metres on the project. The drill rig and drilling crew are now on the island.

Highlights

• Gold grades: 72.79 g/t Au (C0381259) and 66.92 g/t Au (C0380541).
• Polymetallic mineralization: Sample C0381259 also returned 42.5 g/t Ag and 0.42% Cu.
• Coarse gold confirmed (nugget effect): Following receipt of the initial results, which showed high variability, Mosaic ordered metallic screen re-assays on the high-grade samples. This method confirmed the presence of coarse gold, with fractions grading up to 2,842 g/t Au.
• Sampling results: Of the 343 samples, 9 assayed above 10 g/t Au, 17 above 5 g/t Au, and 45 samples (13% of the total) exceeded 1 g/t Au.

"These results confirm the presence of high-grade gold across a large part of the areas sampled at Golden Island," said Jonathan Hamel, President and CEO of Mosaic. "With nine samples above 10 g/t Au and the recurring presence of coarse gold, we are now moving to drilling. The rig is in place on the island, and our campaign of at least 2,000 metres will test the high-grade zones identified at surface at depth."

Start of the 2,000-Metre Drilling Program

The surface results detailed above, combined with geophysical surveys (Mag-VLF), allowed the technical team to refine the drill targets. The drill rig and heavy equipment were transported to Golden Island by barge. The diamond drilling program, comprising a minimum of 2,000 metres in about a dozen holes, is officially under way. The primary objective is to test the down-dip geometric extension of the high-grade vein systems identified in the trenches, to depths ranging from 150 to 300 metres.

Best Gold Results (≥ 5 g/t Au)

The grade reported is the metallic screen result where one was performed; otherwise, it is the original gravimetric assay. Laboratory duplicates are shown for information only and are not averaged.

Best Silver Results (≥ 2 g/t Ag)

Best Copper Results (≥ 150 ppm Cu)

Stripping and Channel Sampling Campaign

The 343 samples analyzed come from a mechanical stripping and historical trench cleaning campaign aimed at exposing bedrock. The samples, cut with a diamond rock saw, consist mainly of continuous channels averaging 0.5 metre in length.

Detailed mapping of the stripped areas confirms that the mineralization is hosted in a (blue quartz-eye) granodiorite. The gold system consists of a complex structural network of shear veins, sub-vertical tension veins and stockwork zones, often accompanied by pyrite, hematization and, locally, visible gold (VG).

Analytical Methods and Quality Control (QA/QC)

Samples were shipped to Laboratoire Expert Inc. in Rouyn-Noranda. Gold was first determined by fire assay with an atomic absorption finish (FA-GEO), and samples exceeding the upper detection limit were re-assayed by fire assay with a gravimetric finish (FA-GRAV). Silver and copper were determined by atomic absorption following aqua regia digestion (AAT-7).

Due to the presence of coarse gold (nugget effect) observed in the field and the high variability noted in the initial laboratory duplicates (e.g., sample C0380541 went from 154.70 g/t to 619.17 g/t in the gravimetric duplicate), Mosaic requested additional metallic screen assays (FA-MET) on the complete pulverized samples. This method, the most representative in the presence of coarse gold, confirmed high grades in the coarse fraction (+100 mesh), up to 2,842 g/t Au (C0380541).

Mosaic applied a quality control protocol by inserting certified reference materials (standards) and blanks at a rate of approximately one control per 20 samples.

No contamination was detected.

Qualified Person

The scientific and technical content of this news release has been reviewed and approved by Suzie Tremblay, Géo/P.Geo, a qualified person as defined by National Instrument 43-101 Standards of Disclosure for Mineral Projects. OGQ #10664

About Mosaic Minerals Corporation

Mosaic Minerals Corp. is a Canadian mining exploration company listed on the Canadian Securities Exchange (CSE: MOC). The Company is developing the Golden Island (Au), Amanda (Au) and Gaboury (Ni) projects located in Abitibi and James Bay (Quebec).

This release contains certain "forward-looking information" under applicable Canadian securities laws concerning the Arrangement. Forward-looking information reflects the Company's current internal expectations or beliefs and is based on information currently available to the Company. In some cases, forward-looking information can be identified by terminology such as "may", "will", "should", "expect", "intend", "plan", "anticipate", "believe", "estimate", "projects", "potential", "scheduled", "forecast", "budget" or the negative of those terms or other comparable terminology. Assumptions upon which such forward-looking information is based includes, among others, that the conditions to closing of the Arrangement will be satisfied and that the Arrangement will be completed on the terms set out in the definitive agreement. Many of these assumptions are based on factors and events that are not within the control of the Company, and there is no assurance they will prove to be correct or accurate. Risk factors that could cause actual results to differ materially from those predicted herein include, without limitation: that the remaining conditions to the Arrangement will not be satisfied; that the business prospects and opportunities of the Company will not proceed as anticipated; changes in the global prices for gold or certain other commodities (such as diesel, aluminum and electricity); changes in U.S. dollar and other currency exchange rates, interest rates or gold lease rates; risks arising from holding derivative instruments; the level of liquidity and capital resources; access to capital markets, financing and interest rates; mining tax regimes; ability to successfully integrate acquired assets; legislative, political or economic developments in the jurisdictions in which the Company carries on business; operating or technical difficulties in connection with mining or development activities; laws and regulations governing the protection of the environment; employee relations; availability and increasing costs associated with mining inputs and labour; the speculative nature of exploration and development; contests over title to properties, particularly title to undeveloped properties; and the risks involved in the exploration, development and mining business. Risks and unknowns inherent in all projects include the inaccuracy of estimated reserves and resources, metallurgical recoveries, capital and operating costs of such projects, and the future prices for the relevant minerals. The Canadian Securities Exchange does not accept responsibility for the adequacy or accuracy of this release.

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