Mr. Jonathan Hamel reports

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

Mosaic Minerals Corp. has released 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 grams per tonne gold (C0381259) and 66.92 g/t Au (C0380541);
• Polymetallic mineralization: sample C0381259 also returned 42.5 grams per tonne gold and 0.42 per cent copper;
• Coarse gold confirmed (nugget effect): following receipt of the initial results, which showed high variability, Mosaic ordered metallic screen reassays 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, nine assayed above 10 g/t Au, 17 assayed above five g/t Au and 45 samples (13 per cent of the total) exceeded one 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 chief executive officer 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 downdip geometric extension of the high-grade vein systems identified in the trenches, to depths ranging from 150 to 300 metres.

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.

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, subvertical tension veins and stockwork zones, often accompanied by pyrite, hematization and, locally, visible gold (VG).

Analytical methods and quality assurance/quality control

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 reassayed 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 (for example, 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 (plus-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, Geo/PGeo (OGQ No. 10664), a qualified person as defined by National Instrument 43-101, Standards of Disclosure for Mineral Projects.

About Mosaic Minerals Corp.

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

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