CAMECO CORP

Sampling, analysis and data verification

Surface samples

Surface holes were generally drilled on sections spaced between 50 and 200 metres with 12 to 25 metres between holes on a section when necessary. Drilled depths average 670 metres.

The orientation of mineralization is variable but, in general, vertical holes intersect mineralization at angles of 25 to 45 degrees, resulting in true widths being 40 to 70% of the intersected width. Angled holes usually intercept mineralization closer to perpendicular, giving intercepts that are closer to true width.

Any stratigraphy exhibiting noteworthy alteration, structures or radiometric anomalies is split and sampled.

Given that the vast majority of the deposit has been delineated from underground, few surface holes are used for mineral resource and reserve estimation purposes.

Underground samples

Underground drilling is generally planned to provide close to true thicknesses results. All underground exploration holes are core drilled and gamma probed whenever possible. McArthur River uses a high-flux gamma probe designed and constructed by alphaNUCLEAR, a member of the Cameco group of companies. This high-flux gamma probe utilizes two Geiger MÜller tubes to detect the amount of gamma radiation emanating from the surroundings. The count rate obtained from the high-flux probe is compared against chemical assay results to establish a correlation to convert corrected probe count rates into equivalent % U 3 O 8 grades for use when assay results are unavailable.

The consistency between probe data and chemical assays demonstrates that secular equilibrium exists within the deposit. A small portion of the data used to estimate mineral resources is obtained from assays, and in these cases, the core depth is validated by comparing the downhole gamma survey results with a hand-held scintillometer on core before it is logged, photographed, and then sampled for uranium analysis. Attempts are made to avoid having samples cross geological boundaries.

When sampled, the entire core from each sample interval is taken for assay or other measurements to characterize the physical and geochemical properties of the deposit. This reduces the potential sample bias inherent when splitting core. Core recovery throughout the deposit has generally been very good. However, in areas of poor core recovery, uranium grade determination is generally based on radiometric probe results.

The typical sample collection process at our operations is performed by or under the supervision of a qualified geoscientist and includes the following procedures:

Sample security

Current sampling protocols dictate that all samples are collected and prepared in a restricted core processing facility. The core samples are collected and transferred from the core boxes to high-strength plastic sample bags, then sealed. The sealed bags are then placed in steel drums and shipped in compliance with theTransport of Dangerous Goods Regulations with tamper-resistant security seals. Chain of custody documentation is present from inserting samples into steel drums to the final delivery of results by the Saskatchewan Research Council Geoanalytical Laboratories (SRCGL).

All samples collected are prepared and analysed under the close supervision of qualified personnel at SRCGL, which is a restricted access laboratory licensed by the CNSC.

Analysis

Drill core assay sample preparation is performed at SRCGL’s main laboratory, which is independent of the participants of the MRJV. It involves jaw crushing to 80% passing at less than two millimetres and splitting out a 100- to 200-gram sub-sample using a riffle splitter. Thesub-sample is pulverized to 90% at less than 106 microns using a puck and ring grinding mill. The pulp is then transferred to a bar coded plastic snap top vial. Assaying by SRCGL involves digesting an aliquot of pulp in concentrated 3:1 HCl:HNO 3, on a hot plate for approximately one hour. The volume is then made up in a 100-millilitre volumetric flask using deionized water prior to analysis by ICP-OES. Instruments used in the analysis are calibrated using certified commercial solutions. This method is ISO/IEC 17025:2017 accredited by the Standards Council of Canada.

Quality control and data verification

The quality assurance and quality control procedures used during early drilling programs were typical for the time. Many of the original signed assay certificates from surface drilling are available and have been reviewed by Cameco geoscientists.

More recent sample preparation and assaying was completed under the supervision of qualified personnel at SRCGL and includes preparing and analysing standards, duplicates and blanks. At least two standards are analysed for each 40-sample batch. We also include a pulp repeat and one split sample repeat with every group. Samples that fail quality controls arere-analysed.

In 2013, McArthur River implemented a SQL server based centralized geological data management system to manage all drillhole and sample related data. All core logging, sample collection, downhole probing and sample dispatching activities are carried out and managed within this system. All assay, geochemical and physical analytical results obtained from the external laboratory are uploaded directly into the centralized database, thereby mitigating the potential for manual data transfer errors. The database used for the current mineral resource and mineral reserve estimates was validated by Cameco qualified geoscientists. A review and minor update of the Zone 1 mineral resource estimate was completed in 2025.

Additional data quality control measures include:

Quality control and data verification activities described above will be finalized prior to the next resource estimate updates.

Since the start of commercial production, we have regularly compared information collected from production activities, such as freeze holes, raisebore pilot holes, radiometric scanning of scoop tram buckets and mill feed sampling, to the drillhole data informed models. We also compare the uranium block model with mine production results on a quarterly basis to ensure an acceptable level of accuracy is maintained. Results in 2025 were within acceptable tolerances.

Our geoscientists, including a qualified person as such term is defined in NI 43-101, have witnessed or reviewed drilling, core handling, radiometric probing, logging, sampling facilities, sampling and data verification procedures employed at the McArthur River operation and consider the methodologies to be satisfactory and the results representative and reliable. There has been no indication of significant inconsistencies in the data used or verified nor any failures to adequately verify the data.