CAMECO CORP files 6-K: foreign-issuer report (6-K)

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McArthur River mine production began in the fourth quarter of 1999 and entered commercial production November 1, 2000. In January 2018, production activities were suspended at McArthur River mine and Key Lake mill for approximately four years due to continued weakness in the global uranium market. In February 2022, as market conditions improved and long-term contracting activity increased significantly, Cameco and its joint venture partner, Orano Canada Inc. (Orano) announced the planned restart of both operations. Following the completion of automation upgrades and restart preparations, the operations were officially restarted in

November 2022.

This technical report supersedes the McArthur River Operation technical report filed in March of 2019 (2018 Technical Report). It incorporates updated technical and scientific information, and reflects operational knowledge and experience gained since the restart of operations.

Key highlights of this report include:

• Cameco has updated the mineral reserve and mineral resource estimates for the McArthur River mine. Cameco’s attributable share of the mineral reserves changed from 241.9 million pounds U 3 O 8 as of December 31, 2025 to 241.4 million pounds U 3 O 8 as of September 30, 2026. The changes to the mineral reserve estimates are primarily due to 2026 packaged production of 6.8 million pounds U 3 O 8 partially offset by the addition of 5.8 million pounds U 3 O 8 of proven reserves (Cameco’s share) from Zone B following the incorporation of new drilling results. The McArthur River production schedule has been updated to incorporate the additional mineral reserves.

• Production schedules in this report assume a ramp-up of annual production to 22 million pounds by 2030, after which an average production level of 22 million pounds is maintained. Assessments indicate that after the ramp-up period, the sites’ facilities will have the capacity to produce at a sustained average annual production rate of 22 million pounds with the flexibility to produce up to a peak of 25 million pounds. Actual annual production is expected to vary in the range of 18 million to 25 million pounds, depending on contract commitments, mining cycles, non-routine maintenance timing and unplanned events.

• As part of Cameco’s annual planning and budget cycle, production plans for the subsequent one-year period are approved, with disclosure of the one-year outlook being provided in Cameco’s annual management’s discussion and analysis. As such, formal production plans have not been approved or disclosed beyond 2026.

• Based on the current assumed production schedule, Cameco estimates that McArthur River will have a remaining mine life of approximately 17 years. See Section 16.4 for more details.

• Cameco’s share of the total estimated life of mine capital costs for the McArthur River and Key Lake Operations is $1.47 billion compared to $658 million in the 2018 Technical Report. The increase is related to increases in contract labour rates and material costs and the joint venture’s decision to pursue upward production flexibility at the mine and mill. See Section 21.1 and Table 21-1 for more details.

• Operating costs for the MRJV are estimated to average $24.03 per pound U 3 O 8 over the mine life. This is a significant increase from the estimate of $14.97 per pound U 3 O 8 in the 2018 Technical Report. The increase in operating costs is related to increased maintenance costs, general inflation on labour and input costs as well as an increase in expected workforce. See Section 21.2 for more details.

McArthur River is an underground uranium mine located in northern Saskatchewan’s Athabasca Basin. It contains the world’s largest known high-grade uranium deposit and has extracted approximately 386 million

2026 MCARTHUR RIVER OPERATION

TECHNICAL REPORT 1 pounds U 3 O 8 since the start of production in 1999. Cameco is the operator. McArthur

River is owned by the MRJV participants.

• Cameco Corporation (Cameco) (69.805%)

• Orano Canada Inc. (30.195%)

The mineral property consists of one mineral lease, totaling 1,338.474 ha (Mineral Lease or ML 5516), and 28 mineral claims (Mineral Claims), totaling

85,908.392 ha. The mineral lease and mineral claims are contiguous.

ML 5516, which hosts the McArthur River deposit, sits on the northwestern edge of the Mineral Claims ( Figure 4-2 ). The right to mine this uranium deposit was acquired under this Mineral Lease. A small portion of the reported mineral reserves crosses onto the adjacent Read Lake

Claim (CBS 8927) which is owned by the Read Lake Joint Venture.

The Mineral Lease expires in March 2034 with a right to renew for successive 10-year terms absent a default by the MRJV. Based on previous work submitted and approved by the Province of Saskatchewan, title to the Mineral Claims is secured until 2028 or later.

The surface facilities and mine shafts for the McArthur River Operation are located on lands owned by the Province of Saskatchewan. Cameco acquired the right to use and occupy the lands under a surface lease agreement with the Province of Saskatchewan. The lease presently covers approximately 1,425 ha and expires in May 2043.

See Section 4.2 and 4.3 for further detail.

1.4 Location and site description

The McArthur River mine is a fully developed property located near Toby Lake in northern Saskatchewan, approximately 620 kilometres north of

Saskatoon. The McArthur River mine site is compact, with the principal mine surface facilities occupying an area of approximately one km, excluding the nearby airstrip and camp facilities.

The McArthur River mine site contains all the services and infrastructure to support a remote underground mining operation. Site infrastructure includes a 1.6 kilometre long gravel airstrip and air terminal, permanent camp facilities, administration and maintenance buildings, warehouse facilities, water containment ponds and a water treatment plant, freeze plant, concrete batch plant, one full-service shaft and two ventilation shafts, site roads, electrical substations and backup generators, an ore slurry load out facility, freshwater pump house and water distribution systems plus other ancillary infrastructure and support buildings.

Access to the McArthur River property is by an all-weather road and by air. Supplies are transported to the site by truck on a year-round basis and can be shipped from locations throughout North America through Cameco’s transit warehouse in Saskatoon. An 80-kilometre gravel road connects the mine site and the

Key Lake Operation. Calcined uranium ore concentrate is shipped year-round by truck from the Key Lake Operation to Saskatoon and other destinations. The unpaved airstrip and terminal are located approximately one kilometre east of the mine site within the surface lease and provide air access to and from the McArthur River property.

The regional topography and the environmental setting are typical of the taiga forested terrain of the Athabasca Basin area of northern Saskatchewan. Surface facilities are at an elevation of approximately 550 metres above sea level.

McArthur River has sufficient surface rights to meet all its current mining operation needs. No tailings management facilities are required as McArthur

River mineralization is sent to the Key Lake mill for processing.

2026 MCARTHUR RIVER OPERATION

TECHNICAL REPORT 2 See Sections 4 . 1 , 5 and 18 for further detail.

1.5 Geology and mineralization

The McArthur River uranium deposit is located approximately 40 km west of the eastern margin of the Athabasca Basin of northern Saskatchewan ( Figure 7-1 ). Like other major uranium deposits of the basin, it is located at or near the unconformity contact separating late Paleoproterozoic sandstone of the basal portion of the Athabasca Group from

Paleoproterozoic metasedimentary gneisses and migmatites of the Wollaston Group which are interfolded with Archean granitoid gneisses.

High-grade uranium mineralization has been delineated from surface drilling over a strike length of 2,700 metres, occurring at depths ranging between 500 to 640 metres below surface. Underground drilling programs have covered approximately 2,300 metres of this overall strike length.

Mineralized widths are variable along strike, but the most consistent, high-grade mineralization occurs proximal to the main graphitic reverse fault by the upthrust basement rock. Less consistent and generally lower grade mineralization occurs downdip along this fault contact between basement rock and sandstone. The main part of the mineralization, generally at the upper part of the basement wedge, averages 12.7 metres in width and has a vertical extent ranging between 50 and 120 metres.

Nine mineralized areas at the

McArthur River deposit have been well defined with underground drilling, namely Zones 1, 2, 3, 4, 4 South, Zone A, Zone B, McA North 1 and McA North 2.