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.
Downhole Radiometric Probe Surveying
All drill holes are logged with a downhole radiometric probe to measure the natural gamma radiation, from which an initial indirect estimate of ‘equivalent uranium’ (eU3O8) can be made. The downhole probes are calibrated originally by the manufacturer at test pits with known mineralization in the United States. These probes are also regularly tested in the test pits at a government-owned facility in Saskatoon. In addition, Denison further calibrates the probes with a correlation curve of probe grades versus corresponding high-grade assays on split core as received from the laboratory. At the Wheeler River project, different probes are used depending on the observed grade of mineralization at the unconformity as the standard probes generally become saturated at grades above 20% U3O8. Data are typically logged at a speed of 10 m/min down hole and 15 m/min up hole through the drill rods.
Core Sampling, Sample Preparation and Assaying
Drill core samples are collected in the field at dedicated core logging and sampling facilities. The samples are logged, split, bagged and stored in pails for shipment to the laboratory. 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.
Denison submits drill core samples for chemical U3O8 assay for all mineralized intervals, where core recovery permits. All mineralized core is measured with a scintillometer by removing each piece of drill core from the ambient background, noting the most pertinent reproducible result in counts per second, and carefully returning it to its correct place in the core box. Any core registering over 500 cps is flagged for splitting and sent to the laboratory for assay. Early drill holes were sampled using variable intervals (0.2 m to 1.0 m) however all recent holes have been sampled using 0.5 metre lengths. Barren samples are taken to flank both ends of mineralized intersections, with flank sample lengths at least 0.5 metres on either end - this may be significantly more in areas with strong mineralization. All core samples are split 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 bagged, tagged, and sealed in a plastic bag. Bags of mineralized samples are sealed for shipping in metal or plastic pails depending on the radioactivity level. In addition, samples are routinely collected from mineralized intersections for bulk dry density determination as required for mineral resource estimation.
All drill core U3O8 assays are conducted by the Saskatchewan Research Council (“SRC”) using ISO/IEC 17025:2005 accredited method for the determination of U3O8. wt%. The assay sample preparation and analytical procedures are as follows:
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:
These sampling types and approaches are typical of uranium exploration and definition drilling programs in the Athabasca Basin. Drill core handling and sampling protocols are in accordance with industry best practices. Once the diamond drill core is geologically logged but before sampling, the core is photographed and the core boxes are labeled with aluminum tags. After sampling, all core is stored in specially constructed core racks out of doors in the event the core needs to be re-logged or re-sampled in the future.
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 and a Microsoft Excel spreadsheet file containing only the analytical results. Analytical data received from the lab is imported directly into Denison’s local database. The data is subject to validation using triggers built into the local 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 notified immediately of any problematic samples or batches and these are re-analyzed. Assay values that fall below the method detection limit (MDL) are reported by the lab as ‘less than’ values (<MDL). These values are automatically replaced by half MDL by the local database during import. The database is backed up on- and off-site every day.
The SRC laboratory has an internal QAQC program dedicated to 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 by CNSC Licence Number 01784-1-09.3. 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. The 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 to CAN-P-1579 “Guidelines for Mineral Analysis Testing Laboratories”. The laboratory continues to participate in proficiency testing programs organized by CANMET (CCRMP/PTP-MAL).
The 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 QA/QC procedures and protocols for all exploration projects to independently monitor laboratory performance which include 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, Denison uses standards provided by Joint Venture partner Cameco for uranium assays. Six uranium assay standards have been prepared for use in monitoring the accuracy of uranium assays received from the laboratory. In addition, for each assay group, an aliquot of Cameco’s blank material is also included in the sample run. In a run of 40 samples, at least one will consist of a Cameco standard and one will consist of a Cameco blank. Accuracy of the analyses and values obtained relative to the standard values, based on the analytical results of the six reference standards used, is acceptable for Mineral Resource estimates.
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 the 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.
Field Duplicates - The Company regularly submits a variety of duplicate samples in the sample stream as a check on the precision of the analytical lab. Core duplicates are prepared by collecting a second sample of the same interval, through splitting the original sample, or other similar technique, and are submitted as an independent sample. Duplicates are typically submitted at a minimum rate of one per 20 samples in order to obtain a collection rate of 5%. 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.
In addition to the QAQC described above, Denison sends one in every 25 U3O8 assay samples to the SRC’s Delayed Neutron Counting (DNC) laboratory, a separate facility located at SRC Analytical Laboratories in Saskatoon, to compare the uranium values using two different methods, by two separate laboratories. All radioactive samples are monitored and recorded as per CNSC licence 01784-1-09.0. Furthermore, down hole radiometric probe results provide equivalent uranium data (eU3O8) that is used internally by the Company for assessing the accuracy of the laboratory U3O8 results.