Athabasca Exploration: Sampling, Analysis and Data Verification
The following section details procedures and protocols for all Athabasca exploration programs operated by Denison in reference to downhole radiometric surveying, core sampling, sample preparation methods, analytical procedures and the Quality Assurance and Quality Control ("QA/QC") procedures.
Drill Hole Surveying
Drill collars are typically sited and surveyed in the field using a Differential Global Positioning System (“DGPS”) to determine accurate coordinates and elevation. The drill rig azimuth and dip are aligned using a field compass (set to the appropriate magnetic declination) or a rig alignment tool. The trajectory of all drill holes is determined with a Reflex survey instrument in single shot mode, which measures the azimuth and inclination of the drill hole. Measurements are collected at approximately 50 metre intervals down the hole.
Downhole Radiometric Probe Surveying
When possible, all drill holes are surveyed immediately after drilling with a downhole radiometric probe to measure natural gamma radiation. Each survey consists of either a HPL2375 single sodium iodide (NaI) scintillation crystal tool or a 2GHF-1000 triple gamma (one sodium iodide crystal and two ZP1320 high flux Geiger-Mueller (GM) tubes) tool attached to a MX-Series winch with a MGX data recorder connected to a portable computer.
Downhole logging measurements are completed within the drill rods for both down and up survey runs using MSLog software provided by Mt Sopris. Logging speeds are maintained at approximately 10 metres/minute. Individual data recordings are stored separately for each run on a portable laptop computer.
Total count measurements from each survey are converted to radiometric equivalent grade U3O8 % (“eU3O8”) values using conversion coefficients derived from calibration facilities at the SRC test pits located in Saskatoon, Saskatchewan. The calibration facilities allow for regular checks on both probes and probing equipment and to monitor or identify maintenance issues before field operations begin. The site consists of four mineralized holes, with isolated uranium concentrations of 1.4, 1.6, 1.6 and 0.21 metres wide with U grades varying from 0.063, 0.29, 1.25 and 4.07%, respectively. Individual probes are calibrated using the NaI crystal measurements a minimum of two times per year, normally before and after the winter and summer field seasons. Survey results are also corrected for attenuation of signal in water and for the thickness of steel pipe in the hole. GM tubes are checked for drift at the site; however, calibration factors for these probes were derived separately using direct comparisons of total count values with assay core results as high as 80% U3O8. The “in-situ” nature of this calibration procedure allows for a wider spectrum of predicted results than using the SRC calibration facilities.
A deposit-specific radiometric-grade correlation has been developed for the Company’s Phoenix deposit, where the gamma signature obtained from the high flux Geiger-Muller tubes of the triple gamma probe can be used to estimate in-situ uranium grade. The radiometric-grade correlation was developed by an independent 3rd party by comparing geochemical sample assays collected from the Phoenix deposit to their corresponding probe data. Only intervals with high core recovery were selected for the correlation process to ensure a representative comparison between the data sets. Raw gamma probe data is first converted to adjusted counts per second (cps) by correcting raw gamma counts per second for fluid absorption, casing absorption, and dead-time. Adjusted cps are then calibrated into an equivalent grade based on the correlation between the grade-thickness (GT) product of the adjusted cps and assay data from representative mineralized intercepts. A total of 50 mineralized intercepts were used to develop the radiometric-grade correlation for Phoenix.
The Company typically reports eU3O8, derived from a calibrated downhole total gamma probe, as preliminary during its exploration programs and subsequently reports definitive assay grades following sampling and chemical analysis of the mineralized drill core.
Denison employs suitably qualified persons to log all drill core in detail at dedicated, custom-built core logging facilities proximal to drilling operations. Routine logs completed for each drill hole include lithology, sandstone texture, paleoweathering, mineralization, alteration, structure (interval and point), geotechnical and gamma (handheld scintillometer). Where deemed necessary, additional logs may be collected to assist in constraining geophysical survey results. These logs may include magnetic susceptibility or other physical property measurements. For advanced projects where mining studies may be applicable geotechnical logs are expanded and may also include point load testing. All logging data, together with collar and survey information and a drill hole summary, are uploaded to a DHLogger database with central storage on Denison’s server at the Saskatoon office. In addition, the drill core is photographed, both wet and dry, before it is stored at project sites either in racks or as cross-stacks. Drill core handling and sampling protocols are in accordance with industry best practices.
Core Sampling, Sample Preparation and Assaying
Denison submits drill core samples for chemical U3O8 assay for all mineralized intervals, where core recovery permits. Mineralized intervals are identified by handheld scintillometer and confirmed by downhole gamma probe logs. All mineralized core is broken into approximately 10-centimetre pieces and measured with a handheld scintillometer (RS-120 or RS-125) by removing each piece of drill core from the ambient background, noting the most pertinent reproducible result in counts per second (“cps”), and carefully returning it to its correct place in the core box. Any core registering over 500 cps is marked for sampling, typically over 50-centimetre intervals. A threshold of 300 cps has been used at Wheeler River’s Gryphon deposit since the beginning of 2017. Additional non-mineralized ‘shoulder’ samples are marked over 50-centimetre intervals to flank both ends of the mineralized intervals. In areas of strong mineralization, more than one sample on either end is sometimes required. All core samples are split in half with a hand splitter according to the sample intervals marked on the core. One-half of the core is returned to the core box for future reference, and the other half is tagged and sealed in a plastic bag. Bags containing mineralized samples are sealed for shipping in metal or plastic pails, depending on the radioactivity level.
Because the mineralized drill cores are classified as hazardous materials and are regulated under requirements governing the transport of dangerous goods, Denison staff have been trained in the proper handling and transport of the cores and deliver them from the core facility directly to the laboratory without outside contact.
All drill core U3O8 assays are conducted by SRC. The assay sample preparation and analytical procedures are as follows:
- Drill core samples are received by the analytical laboratory from Denison in sealed five-gallon plastic or metal pails. Each sample is contained in a sealed plastic bag with a sample tag. A packing slip is enclosed that contains instructions and a sample number list. Samples are verified against the packing slip. Any extra samples or missing samples are noted and Denison is informed.
- Samples are sorted and processed according to lithology (sandstone or basement) and level of radioactivity.
- Sample preparation includes drying, jaw crushing to 60% passing -2 millimetres and pulverizing to 90% passing -106 microns.
- The resultant pulp is split and digested using a two-acid partial digest (HNO3:HCl) and a three-acid ‘total’ digest (HF: HNO3:HClO4) and the respective solutions analyzed for multi-elements, including uranium, using ICP-OES (SRC analytical method ICP1). Boron values are obtained through NaO2/NaCO3 fusion followed by ICP-OES.
- When uranium partial values, as obtained above, are ≥1,000 ppm, sample pulps are re-assayed for U3O8 using SRC’s ISO/IEC 17025:2005 accredited method for the determination of U3O8 wt%. A split of the sample pulp is digested using aqua-regia (HCl:HNO3 in the ratio 3:1), and the solution analyzed for U3O8 wt% using ICP-OES.F
Bulk Dry Density Sampling
Samples are routinely collected from mineralized intersections for bulk dry density determination as required for mineral resource estimation. Density samples are typically collected at a frequency of one density sample per 10 assay samples, also ensuring the density samples are representative of the uranium grade range and the different domains of the deposit. The density samples comprise half-split core over 10-centimeter intervals, and for each sample, the depth, rock type and scinitllometer reading is recorded. Density samples are sent to SRC for analysis, along with the mineralized core samples for assay. At SRC, the density samples are first weighed as received and then submerged in de-ionized water and re-weighed. The samples are then dried until a constant weight is obtained. The sample is then coated with an impermeable layer of wax and weighed again while submersed in de-ionized water. Weights are entered into a database and the bulk density of each sample is calculated. Water temperature at the time of weighing was also recorded and used in the bulk density calculation. Following bulk density determination, the samples are sent for uranium assay using SRC’s ISO/IEC 17025:2005 accredited method for the determination of U3O8 wt% in order to ensure a direct correlation can be made between density and assay values.
Three other types of drill core samples are collected during routine exploration, the results of which are used to prioritize drill holes for follow-up exploration or determine geochemical and/or alteration vectors toward mineralization, as follows:
- Composite geochemical samples are collected over approximately 10-metre intervals in the upper Athabasca sandstone and in fresh lithologies beneath the unconformity (basement) and over 5-metre intervals in the basal sandstone and altered basement units. The samples consist of 1 to 2 centimetre thick disks of core collected from the top or bottom of each row of core in the box over the specified interval. Care is taken not to cross lithological contacts or stratigraphic boundaries. These samples are submitted to SRC for sample preparation and multi-element analysis. The same sample preparation procedures are used as described above for U3O8 assay samples. The pulps are analyzed using the ICPMS Exploration Package, which includes a total digest (HF:HNO3:HCIO4) and partial digest (HNO3:HCl) followed by ICP-MS analysis. Boron values are obtained through NaO2/NaCO3 fusion followed by ICP-OES.
- Representative/systematic core disks (one to five centimetres in width) are collected at regular 5 to 10-metre intervals throughout the entire length of core until basement lithologies become unaltered. These samples are analyzed for clay minerals using reflectance spectroscopy. Samples for reflectance clay analyses are analyzed by Denison using an ArcSpectro FT-NIR ROCKET spectrometer and sent to AusSpec International Ltd. (AusSpec) for interpretation.
- Select spot samples are collected from significant geological features (i.e. radiometric anomalies, structure, alteration etc.). Core disks ranging from 1 to 2 centimetres thick are collected for reflectance spectroscopy, while split core samples are collected for geochemical analysis. The same reflectance spectrometry or geochemical procedures as described above are used.
These sampling types and approaches are typical of uranium exploration and definition drilling programs in the Athabasca Basin.
After the analyses are completed, analytical data are securely sent using electronic transmission of the results by SRC to Denison. The electronic results are secured using WINZIP encryption and password protection. These results are provided as a series of Adobe PDF files containing the official analytical results (“assay certificates”) and a Microsoft Excel spreadsheet file containing only the analytical results. Analytical data received from the lab is imported directly into Denison’s DH Logger database. The data is subject to validation using triggers built into the database to identify blank or standard assays that fall outside the accepted limits that require re-analysis. Field duplicates are validated using control charts. The laboratory is immediately notified of any problematic samples or batches, which are re-analyzed. The lab reports assay values that fall below the method detection limit (MDL) as ‘less than’ values (<MDL). These values are automatically replaced with a value of half the MDL by the database during import. The database is backed up on- and off-site every day.
SRC has an internal QAQC program dedicated to the active evaluation and continual improvement in the internal quality management system. The laboratory is accredited by the Standards Council of Canada as an ISO/IEC 17025 Laboratory for Mineral Analysis Testing and is also accredited ISO/IEC 17025:2005 for the analysis of U3O8. The laboratory is licensed by the Canadian Nuclear Safety Commission (CNSC) for possession, transfer, import, export, use, and storage of designated nuclear substances. As such, the laboratory is closely monitored and inspected by the CNSC for compliance. All analyses are conducted by SRC, which has specialized in the field of uranium research and analysis for over 30 years. SRC is an independent laboratory, and no associate, employee, officer, or director of Denison is, or ever has been, involved in any aspect of sample preparation or analysis on samples. SRC uses a Laboratory Management System (LMS) for Quality Assurance. The LMS operates in accordance with ISO/IEC 17025:2005 (CAN-P-4E) “General Requirements for the Competence of Mineral Testing and Calibration Laboratories” and is also compliant with CAN-P-1579 “Guidelines for Mineral Analysis Testing Laboratories”. The laboratory continues to participate in proficiency testing programs organized by CANMET (CCRMP/PTP-MAL).
SRC routinely inserts standard reference materials and blanks into batches of the Company’s samples as an internal check on accuracy and contamination. Quality control samples (reference materials, blanks, and duplicates) are included with each analytical run, based on the rack sizes associated with the method. Before the results leave the laboratory, the standards, blanks, and split replicates are checked for accuracy and issued, provided the senior scientist is fully satisfied. If, for any reason, there is a failure in an analysis, the sub-group affected will be re-analyzed and checked again. A Corrective Action Report will be issued, and the problem is investigated fully to ensure that any measures to prevent the re-occurrence can and will be taken. All human and analytical errors are, where possible, eliminated. If the laboratory suspects any bias, the samples are re-analyzed, and corrective measures are taken.
Denison has developed several QAQC procedures and protocols for all exploration projects to independently monitor laboratory performance, which includes the analysis of uranium standards, blanks, field duplicates and exploration standards, as follows:
Uranium Standards - Due to the radioactive nature of the standard material, insertion of the standard materials is preferable at SRC instead of in the field. During sample processing, the appropriate standard grade is determined, and an aliquot of the appropriate standard is inserted into the analytical stream for each batch of materials assayed. Uranium standards are typically inserted at a minimum rate of 1 in every 40 samples. For the Wheeler River project up until the end of 2018, Denison used standards provided by Joint Venture partner Cameco for uranium assays. Six Cameco uranium assay standards were prepared for use in monitoring the accuracy of uranium assays received from the laboratory. For Wheeler River from 2019 and onward, and for other Denison projects, a suitable matrix-matched Certified Reference Material (“CRM”) is used as a standard.
Blanks - Denison employs a lithological blank composed of quartzite to monitor the potential for contamination during sampling, processing, and analysis. The selected blank consists of a material that contains lower contents of U3O8 than the sample material but is still above the detection limit of the analytical process. Due to the sorting of the samples submitted for assay by SRC based on radioactivity, the blanks employed must be inserted by SRC after this sorting takes place in order to ensure that these materials are ubiquitous throughout the range of analytical grades. In effect, if the individual geologists were to submit these samples anonymously, they would invariably be relegated to the minimum radioactive grade level, preventing their inclusion in the higher radioactive grade analyses performed by SRC. Blanks are typically inserted at a minimum rate of 1 in every 40 samples. For the Wheeler River project up until the end of 2018, Denison used blanks provided by Joint Venture partner Cameco. For Wheeler River from 2019 and onward, and for other Denison projects, another suitable blank material is used, as provided by SRC.
Field Duplicates - The Company inserts duplicate samples in the sample stream as a check on the precision of SRC. Core duplicates are prepared by collecting a second sample of the same interval, through splitting the original sample, or other similar techniques, and are submitted as an independent sample. Duplicates are typically submitted at a minimum rate of one per 25 samples. The collection may be further tailored to reflect field variation in specific rock types or horizons.
Exploration Standards – Denison has prepared three in-house ‘exploration standards’ to independently monitor laboratory performance during the processing of routine drill core exploration samples. These standards aim to test laboratory accuracy and precision for a variety of trace metals at low levels, as required for Athabasca uranium exploration.
Assay Checks – In addition to the QAQC described above, up until the end of 2018, Denison sent one in every 25 U3O8 assay samples to SRC’s Delayed Neutron Counting (DNC) laboratory, a separate umpire facility located at SRC in Saskatoon, to compare the uranium values using two different methods, by two separate laboratories. Subsequently, assay samples are sent to SRC’s X-ray fluorescence (“XRF”) lab for umpire analyses. Furthermore, the Company uses downhole radiometric probe results, with its equivalent uranium data (eU3O8), for comparisons with SRC U3O8 results.
Denison engages with independent consultants for estimation of mineral resources on its mineral properties, in accordance with CIM Standards and NI 43-101, as well as other studies, including the PFS and ISR field testing and engineering studies. In this regard, the independent consultants undertake rigorous data verification, including, but not limited to, Denison’s field procedures, databases and assay results.
Prior to public disclosure of drilling results, including preliminary radiometric equivalent grades (“eU3O8”) and chemical assay grades (“U3O8”), the results are subject to data verification by Qualified Persons employed by Denison. This includes checks of 10 to 20% of the results (typically as composited intervals) against non-composited eU3O8 determinations and laboratory assay certificates.