Mr. Keith Bodnarchuk of Cosa reports

COSA INTERSECTS ANOMALOUS RADIOACTIVITY AND ADDITIONAL PROSPECTIVE GEOLOGY AT DARBY JOINT VENTURE WITH DENISON MINES

Cosa Resources Corp. has released results of the summer drilling program at the company's Darby project. Darby is a joint venture between Cosa and Denison Mines Corp., and is located 10 kilometres west of Cameco's Cigar Lake mine. Cosa is the project operator and holds a 70-per-cent interest with Denison holding a 30-per-cent interest.

Highlights:

• Anomalous radioactivity of 950 counts per second over 0.5 metre intersected by Gamma drill hole DB26-43 is associated with hydrothermal alteration.
• Drilling at Gamma further defined a zone of structure, alteration and over 55 metres of unconformity relief, and potentially identified a parallel and untested structural corridor.
• Drilling at the Bravo trend intersected structure and alteration, and defined over 40 metres of unconformity relief.
• Results from Gamma and Bravo strengthen Cosa's exploration strategy at Darby and support a focused and fully financed follow-up campaign in early 2027.

Keith Bodnarchuk, president and chief executive officer, commented: "Cosa's second drill program at Darby has highlighted the Gamma and Bravo trends for follow-up winter work and continues to demonstrate the prospectivity of Darby as a discovery-ready project alongside our Murphy Lake North joint venture with Denison Mines. Intersecting anomalous radioactivity at the Gamma trend, paired with a broad zone of structure and alteration that remains open in multiple directions, reinforces our belief in the increasing discovery potential at Darby, and we are excited to return for fully funded follow-up drilling in 2027. We aim to update the market regarding 2027 plans in the coming weeks, which are scheduled to include simultaneous drilling at both the Darby and Murphy Lake North joint ventures."

Andy Carmichael, vice-president, exploration, commented: "Anomalous uranium geochemistry at multiple trends and impressive amounts of structure with over 50 metres of unconformity relief makes for very exciting targets in Athabasca uranium exploration. At Gamma, elevated radioactivity and a broad zone of structure and alteration lie along trend of historical intersections of mineralization, and the sparse existing drilling has left several kilometres of this prospective geology untested."

Darby summer drilling

Since acquiring a 70-per-cent interest in the Darby joint venture from Denison, Cosa's objective has been to build on historical results to further evaluate and prioritize each of the prospective trends at Darby, four of which host uranium mineralization. Significant results from Cosa's inaugural drill program at Darby in winter 2026 include prospective geology intersected at the Gamma trend and weak uranium mineralization at the Charlie trend. The objectives of the four-hole (2,741-metre) summer program were to follow up winter results at Gamma, further evaluate prospective geology on trend with mineralization and follow up historical mineralization at the Bravo trend, which is best accessed by helicopter. Summer drilling expanded the zones of structure and alteration at both Gamma and Bravo. The company awaits geochemical assays to further vector drilling, notably at the Gamma trend, where elevated radioactivity was intersected adjacent to structure and alteration.

Gamma trend

Two holes were completed at Gamma, where previous drilling intersected a broad zone of structure with 35 metres of unconformity offset and alteration elevated to strongly anomalous uranium geochemistry on trend with multiple historical intersections of uranium mineralization north of Darby (see Cosa's news release dated May 6, 2026).

Completed on section with previous drilling, DB26-43 intersected multiple zones of moderate to strong faulting and alteration in the lower sandstone, as well as localized faulting in the basement. The unconformity was intersected 22 metres lower than Cosa's winter drill hole DB26-41, increasing total unconformity relief on section to 57 metres. A zone of anomalous radioactivity (1) (950 counts per second, 689.0 to 689.5 metres) intersected 33 metres below the unconformity is associated with hematite, limonite and argillization.

DB26-45 was completed 1,600 metres south along strike to follow up historical hole DB-23R, which intersected zones of anomalous uranium content in the sandstone. DB26-45 intersected a 37-metre-long interval of faulting in the upper sandstone, which may reflect an additional and untested structure.

Together, Cosa interprets that both DB-23R and DB26-45 may be overshots of an untested package of prospective rocks related to sandstone structure, alteration and anomalous uranium geochemistry. The Gamma trend warrants focused drilling, and follow-up is planned to further evaluate the source of anomalous uranium geochemistry and sandstone structure.

Bravo trend

Two holes were completed at Bravo to explore prospective geology intersected by historical drilling highlighted by intersections of weak uranium mineralization, broad zones of anomalous uranium, graphitic faulting and over 25 metres of unconformity offset. Summer drilling targeted 2.2 kilometres of untested strike length on the eastern Bravo trend, and intersected zones of faulting and alteration in the sandstone and basement.

DB26-44 followed up DB-12, which Cosa interprets to have undershot the Bravo trend's faulted graphitic rocks by approximately 175 metres. DB26-44 is considered a near-miss overshot of the ideal target by approximately 30 metres. The lower sandstone contains faulting and accompanying alteration, and the unconformity was intersected 41 metres lower than in DB-12.

DB26-46 targeted graphitic faulting 800 metres east along strike of DB26-44 and intersected weakly bleached lower sandstone above the unconformity at 516.1 metres. Variably graphitic gneiss from 542 to 568 metres is faulted and hosts weak to moderate hydrothermal alteration. DB26-46 is interpreted to have undershot the optimal target by 30 metres.

The presence of sandstone structure, alteration and unconformity offset defined by DB26-44 combined with basement structure and alteration in DB26-46 suggests that drilling 800 metres apart along strike narrowly bracketed the target graphitic horizon and indicates that Bravo hosts a significant, kilometre-scale hydrothermal system.

Next steps

Drilling at Gamma and Bravo has further demonstrated the prospectivity of both trends. Focused work at Gamma is a priority for 2027 and is expected to include significant drilling supported by geophysical surveys to refine drill targets within the 1,600-metre corridor of structure, alteration and anomalous uranium that remains open on multiple sections and along strike on this four-kilometre-long trend. At Bravo, pending geochemical assays are expected to guide follow-up drilling given the proximity of both summer drill holes to the target horizon.

Cosa remains committed to prioritizing areas for further work at Darby. In addition to Gamma and Bravo, multiple mineralized trends at Darby feature kilometres of untested or ineffectively tested strike length. Given the degree of structure and alteration intersected by both drill programs in 2026, Cosa awaits geochemical assays from summer drilling to further prioritize existing targets and follow-up work. The company is eager to return to Darby, and follow-up drilling for both Darby and Murphy Lake North is tentatively scheduled to commence simultaneously in January.

(1) All reported radioactivity was measured with an RS-125 hand-held spectrometer. Cosa considers radioactivity of 350 cps or greater to be anomalous when attributed to uranium by the spectrometer.

About Darby

Located 10 kilometres west of the Cigar Lake mine, Darby contains multiple prospective conductive trends and several intersections of weak uranium mineralization. Historical drilling indicates that many of these trends are highly prospective for uranium deposits characteristic of the eastern Athabasca basin, yet most of the strike length has not been effectively evaluated. Work by Cosa in 2025 prioritized these trends and identified several historical drill holes with results that suggest proximity to uranium mineralization (see Cosa's news releases dated Oct. 14, 2025, and Jan. 21, 2026).

About Cosa Resources Corp.

Cosa Resources is a Canadian uranium exploration company operating in Northern Saskatchewan. The portfolio comprises roughly 237,000 hectares across multiple underexplored 100-per-cent-owned and Cosa-operated joint venture projects in the Athabasca basin region, the majority of which resides within or adjacent to established uranium corridors.

In 2025, the company entered a transformative strategic collaboration with Denison that has secured access to several additional highly prospective eastern Athabasca uranium exploration projects. As Cosa's largest shareholder, Denison gains exposure to Cosa's potential for exploration success and its pipeline of uranium projects.

Cosa's award-winning management team has a record of success in Saskatchewan. In 2022, members of the Cosa team were awarded the AME Colin Spence award for the discovery of the Hurricane uranium deposit. Cosa personnel led teams or had integral roles in the discovery of Denison's Gryphon deposit, and held key roles in the founding of both NexGen and IsoEnergy.

Technical disclosure

Historical drilling and geophysical results for Darby were sourced from the Saskatchewan mineral assessment database. SMAD sources for Darby include file No. 74H14-0021, 74H14-0023, 74H15-0041, 74H15-0053, 74H15-0055, 74H15-0056, 74H15-0066, 74H15-0067, 74I02-0031, 74I02-0042, 74I02-0053, 74I02-0080, 74I02-0095 and MAW00516. Some confidential data and reports not currently available on SMAD were supplied to Cosa by Denison.

Verification of historical drilling results included confirming historical drill hole collar locations from air photos and ground checking selected collars with a hand-held GPS unit. Basement and lower sandstone sections from most historical drill holes were relogged in 2024 and 2025 by Cosa. Verification of geochemical results for drill holes completed between 2008 and 2010 was facilitated by the reissuance of analytical certificates to Cosa by the Saskatchewan Research Council. Cosa thanks the SRC for its valued assistance in increasing confidence in the historical data set.

Verification of historical geophysical results included confirming the locations of geophysical survey grids from air photos, compiling survey data and interpretations, and evaluating whether interpreted geophysical results could be reasonably explained by historical and current drilling results.

Samples from Cosa's drilling were transported to SRC Geoanalytical Laboratories in Saskatoon, Sask. (ISO/IEC 17025:2005 accredited), for triuranium octoxide assay and multielement analysis. Cosa inserts certified reference material blanks and standards into the split core sample series as a quality assurance/quality control measure. SRC conducts a QA/QC program, which includes repeat analyses and insertion of CRM standards CAR218, BL4A and BL2A, as appropriate. SRC's CRM results are verified by Cosa staff.

Qualified person

The company's disclosure of technical or scientific information in this press release has been reviewed and approved by Mr. Carmichael, PGeo, vice-president, exploration, for Cosa. Mr. Carmichael is a qualified person as defined under the terms of National Instrument 43-101. This news release refers to neighbouring properties in which the company has no interest. Mineralization on those neighbouring properties does not necessarily indicate mineralization on the company's properties.

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