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- Nature and quality of sampling (e.g. cut channels, random chips, or specific specialised industry standard measurement tools appropriate to the minerals under investigation, such as down hole gamma sondes, or handheld XRF instruments, etc). These examples should not be taken as limiting the broad meaning of sampling.
The Mineral Resource estimation (MRE) databases include samples collected by various operators from 1986 to 30 September 2024. Any sample types considered not to have acceptable sample quality and representativity are excluded from the MRE. This includes Björkdal sludge samples from development drilling, direct circulation samples from historical open pit grade control drilling and samples with lengths less than 0.1 m.
The below commentary captures the main sampling techniques used since acquisition of the project by Mandalay Resources (now Alkane Resources) in 2014. As of 30 September 2024, the company had completed a total of ~420 km of DD core and ~120 km of RC drilling.
- Include reference to measures taken to ensure sample representivity and the appropriate calibration of any measurement tools or systems used.
RC – drill cuttings are dropped out of the cyclone into a riffle or rotary splitter at the completion of a 1 m drilling interval, to generate a homogenous 3 to 4 kg sample.
CH – after geologists mark up the area to be sampled, the sampler uses a hammer and bucket to collect chips from shoulder to knee height and across the entire face for a combined ~5 kg sample.
- Aspects of the determination of mineralisation that are Material to the Public Report. In cases where ‘industry standard’ work has been done this would be relatively simple (e.g. ‘reverse circulation drilling was used to obtain 1 m samples from which 3 kg was pulverised to produce a 30 g charge for fire assay’). In other cases, more explanation may be required, such as where there is coarse gold that has inherent sampling problems. Unusual commodities or mineralisation types (e.g. submarine nodules) may warrant disclosure of detailed information.
Samples are dried, crushed to >70% passing 2 mm and split to a 500 g sub-sample. As part of the PAL1000 analytical method, the sub-sample is then pulverized (typically to more than 90% < 75 µm) and simultaneously leached with cyanide, with the solution analysed for gold by atomic absorption spectroscopy (AAS). The PAL1000 method is considered suitable for deposits with coarse or particulate gold and, in the case of Björkdal, should provide a reduction in sampling errors over fire assay techniques.
- Drill type (e.g. core, reverse circulation, open-hole hammer, rotary air blast, auger, Bangka, sonic, etc) and details (e.g. core diameter, triple or standard tube, depth of diamond tails, face-sampling bit or other type, whether core is oriented and if so, by what method, etc).
RC drilling has been used for near-surface exploration and open pit grade control drilling, with 5 to 5.5 inch diameter face sampling hammer and 3 to 6 m drill rods.
- Method of recording and assessing core and chip sample recoveries and results assessed.
RC – sample weights are checked for selected sample intervals and monitored against the expected sample weight.
- Measures taken to maximise sample recovery and ensure representative nature of the samples.
RC – a booster compressor is used to maintain dry samples and sample return for deeper drillholes.
- Whether a relationship exists between sample recovery and grade and whether sample bias may have occurred due to preferential loss/gain of fine/coarse material.
- Whether core and chip samples have been geologically and geotechnically logged to a level of detail to support appropriate Mineral Resource estimation, mining studies and metallurgical studies.
- Whether logging is qualitative or quantitative in nature. Core (or costean, channel, etc) photography.
- The total length and percentage of the relevant intersections logged.
- If core, whether cut or sawn and whether quarter, half or all core taken.
- If non-core, whether riffled, tube sampled, rotary split, etc and whether sampled wet or dry.
- For all sample types, the nature, quality and appropriateness of the sample preparation technique.
- Quality control procedures adopted for all sub-sampling stages to maximise representivity of samples.
- Measures taken to ensure that the sampling is representative of the in-situ material collected, including for instance results for field duplicate/second-half sampling.
- Whether sample sizes are appropriate to the grain size of the material being sampled.
- The nature, quality and appropriateness of the assaying and laboratory procedures used and whether the technique is considered partial or total.
The PAS1000 technique is partial and determines the cyanide-soluble gold in samples. Checks have been conducted on residue material remaining after PAL assaying to confirm the completeness of the digestion stage and the transfer of gold to solution. The checks typically demonstrate that Björkdal mineralisation behaves well with this method and returns residue values of 0.6 to 1 % of the reported gold assay value.
- For geophysical tools, spectrometers, handheld XRF instruments, etc, the parameters used in determining the analysis including instrument make and model, reading times, calibrations factors applied and their derivation, etc.
- Nature of quality control procedures adopted (e.g. standards, blanks, duplicates, external laboratory checks) and whether acceptable levels of accuracy (i.e. lack of bias) and precision have been established.
Select batches of coarse reject duplicates were completed for DD core and underground chip/channel samples in 2023 and 2024, showing no systematic bias and acceptable levels of precision in sample preparation and analysis.
Laboratory QAQC includes blank tests throughout the PAL1000 procedure, with the AAS finish checked against standard solutions of known gold grades.
- The verification of significant intersections by either independent or alternative company personnel.
SLR have completed data verification during site visits including visual review of mineralised intersections, spot checks between database assay tables and original laboratory certificates. No check samples were taken by the SLR CP to independently confirm the presence of gold mineralisation, as the site has a long history of gold production, and the presence of gold was directly observed during the visit to the processing plant.
- The use of twinned holes.
- Documentation of primary data, data entry procedures, data verification, data storage (physical and electronic) protocols.
SLR validated the database using standard software tools to check for errors within the database. A check was also undertaken to ensure that the drill hole elevation was comparable with the digital terrain model (DTM) surface.
Electronic copies of all primary locations, logging and sample results data are filed for each hole.
- Discuss any adjustment to assay data.
- Accuracy and quality of surveys used to locate drill holes (collar and down-hole surveys), trenches, mine workings and other locations used in Mineral Resource estimation.
RC collars – Open pit grade control drillholes surveyed using a Trimble TSC3 GPS controller unit.
DD downhole surveys – Since 2015, carried out using a Reflex Gyro Smart tool at 3 m intervals upon completion of the hole.
RC downhole surveys – No downhole surveys were taken for grade control holes less than 70 m in length. All exploration drill holes are surveyed along their full length on completion, using gyroscopic tools.
Underground chip/channel samples – surveyed using Total Station surveying equipment.
Open pit and stockpiles – surveyed using drone-mounted LiDAR methods.
Underground mine – The excavated volume of development headings is determined using a hand-held Hovermap scanner. Cavity monitoring system (CMS) scans are typically used to survey stope voids.
- Specification of the grid system used.
The coordinate system used at Norrberget is SWEREF99, the official Swedish reference system.
- Quality and adequacy of topographic control.
- Data spacing for reporting of Exploration Results.
Björkdal underground – Underground diamond drill spacing is variable, due to fan-like drilling configurations that intersect multiple stacked sub-parallel veins at different depths down-hole. 10 m by 10 m to 20 m by 20m spaced pierce points are typically achieved on the main mineralised veins. Since 2015, face sampling has been completed for each 4m cut during on-vein development.
Storheden deposit – surface DD and RC collars typically ranges from 30 m by 30 m to 60 m by 60 m spacing.
Norrberget deposit – surface DD collars typically range from 25 m by 25 m to 50 m by 50 m spacing.
- Whether the data spacing and distribution is sufficient to establish the degree of geological and grade continuity appropriate for the Mineral Resource and Ore Reserve estimation procedure(s) and classifications applied.
- Whether sample compositing has been applied.
- Whether the orientation of sampling achieves unbiased sampling of possible structures and the extent to which this is known, considering the deposit type.
- If the relationship between the drilling orientation and the orientation of key mineralised structures is considered to have introduced a sampling bias, this should be assessed and reported if material.
- The measures taken to ensure sample security.
The Datashed database is located on the Björkdal server, with daily backups and access restrictions based on user level.
- The results of any audits or reviews of sampling techniques and data.
