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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.
- Include reference to measures taken to ensure sample representivity and the appropriate calibration of any measurement tools or systems used.
- 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.
Due to the discrete mineralisation of the deposit, not all diamond drill core was required to be sampled. Sample intervals were determined and marked on the core by Alkane geologists using the following general rules:
- All stibnite-bearing veins are sampled.
- Intersections of polyphase breccias, stockwork veins, laminated quartz veins or massive quartz veins were routinely sampled.
- A waste sample is taken either side of the mineralized vein (30–100 cm).
- Siltstone is sampled where disseminated arsenopyrite is prevalent.
- Fault gouge zones were sampled at the discretion of the geologist.
Diamond core sampling intervals were standardised wherever possible and ranged from 5 cm to 1 m in length. Diamond drill core samples have been cut in half using the orientation line or cut line, with a consistent side of the cut core selected for assay to ensure unbiased sampling. Whole core was sampled for LTK48 and Shepherd gold-rich zones. The methodology was validated by the Costerfield QA/QC protocols. No sampling instruments required calibration.
Channel samples were collected perpendicular to the dip of the mineralisation, extending from the footwall to the hangingwall. Where multiple mineralised structures were present in the face, intervening waste was also sampled. Sample lengths were measured on the face and ranged from 5 cm to 1 m across mineralisation, with typical sample weights between 1 kg and 3 kg. Each sample was collected using a geological hammer, placed into a pre-numbered sample bag with a unique identifier, and the face was labelled, dated, and photographed.
Assays were completed by On Site in Bendigo, which is independent of Alkane and holds current ISO/IEC 17025 accreditation. The general methods were as follows:
- Gold grades were determined by either fire assay (25 g charge) with an AAS finish, screen fire assay or Chrysos photon assay technology.
- Antimony concentrations were determined using an aqua regia based acid digest with an AAS finish.
- 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.).
- Method of recording and assessing core and chip sample recoveries and results assessed.
- Measures taken to maximise sample recovery and ensure representative nature of the samples.
- 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.
No relationship between grade and sample recovery has been established. Ore zones with poor recovery are redrilled until a representative sample is achieved.
- 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.
Data capture was digital into the AcQuire software using validated codes.
All drill core was photographed wet with high resolution photographs stored on the site’s server, which is routinely backed-up.
- 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 following sample preparation activities were undertaken by Alkane staff for both diamond drill core and underground channel samples:
- Sample information and characteristics were measured, logged, recorded in the acQuire database and assigned a unique sample ID.
- Sample material was placed into a calico bag previously marked with the unique sample ID.
- Calico bags were loaded into plastic bags such that the plastic bags weighed less than 10 kg.
- An assay submission sheet was generated and placed into the plastic bag.
- Plastic bags containing samples were sealed with a metal or plastic tie and transported to On Site in Bendigo via private courier or Alkane staff.
The following sample preparation activities were undertaken by On Site staff:
- Samples were received and checked for labelling, missing samples, etc. against the submission sheet.
- If the sample batch matched the submission sheet, sample metadata were entered into On Site’s LIMS. In the event that discrepancies were noted, Mandalay Resources was contacted by On Site to resolve the discrepancy prior to further work commencing. Records of all discrepancies and corrective actions taken are recorded by the Mandalay Resources database administrator.
- A job number was assigned, and worksheets and sample bags were prepared.
- Samples were placed in an oven and dried overnight at 106°C.
- Samples were weighed and recorded.
- The entire dried sample was crushed using a Rocklabs Smart BOYD Crusher RSD Combo with a jaw closed side setting of 2 mm.
- If the dried sample weight was less than 3 kg, the entire sample was retained for pulverisation. If the dried sample weight was greater than 3 kg, the sample was spilt to 3 kg using the rotary splitter that is incorporated in the BOYD crusher.
- Rejects from splits greater than 3 kg were retained as coarse rejects in labelled calico bags and returned to Mandalay Resources.
- The 3 kg sample was then pulverised in an Essa LM5 Pulverising Mill to 90% passing 75 µm.
For fire assay and base metal samples:
- The 3 kg pulverised samples were then subsampled to take a master ~200 g pulp split for assay by a manual scooping procedure across the full width and depth of the mill bowl and loaded sequentially into labelled pulp packets.
For photon assay:
- The ~3 kg pulverised samples were then subsampled to fill a ~280 g photon assay jar by a manual scooping procedure across the full width and depth of the mill bowl.
For all methods:
- For every 21 primary samples, a sample was randomly selected by LIMS and a duplicate 200 g split for fire assay or second jar for photon assay was submitted for analysis using the same analytical procedure as the primary sample.
- The remaining pulp was returned to its sample bag and then returned to Mandalay Resources for retention following the completion of assay.
A quarterly check-assay program is in place to monitor the representative nature of sampling and assay methodology.
- The nature, quality and appropriateness of the assaying and laboratory procedures used and whether the technique is considered partial or total.
- 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.
Samples were assayed for gold, antimony, arsenic, and iron using representative partial digest methodologies:
- Gold grades were determined either by a 25g charge with lead flux fire assay and an AAS finish, or by Chrysos photon assay technology.
- Antimony, iron and arsenic concentrations were determined using an aqua regia based acid digest with an AAS finish.
The quality control procedures utilised at Costerfield used CRMs prepared by commercial laboratories Geostats and OREAS.
CRMs were either prepared using Costerfield material or were otherwise matrix matched to ensure a representative nature.
At least one CRM was submitted with every batch of diamond core samples and typically at a rate of 1 standard per 25 samples. Up to six CRMs covering the expected ranges of gold and antimony mineralisation were in rotation during routine sampling.
An assay result for a CRM was considered acceptable when the returned assay fell within three standard deviations of the CRM certification grade. Outside this range, the CRM assay was considered to have failed and all significant mineralised samples within the batch were re-assayed, where significant grades were defined as mineralised samples that may have a material-impact in future resource estimates. All actions or outcomes were recorded as comments in the QA/QC register.
Alkane submitted uncrushed samples of basalt as blank material sourced from Geostats into assay sample lots, at a rate of 1 in every 30 samples, to test for contamination during sample preparation.
The failure threshold for gold is 0.10 g/t, which was chosen since it represents ten times the detection limit of 0.01 g/t for AAS. The failure threshold for antimony is 0.05%, which was chosen for being five times the detection limit of 0.01% for AAS.
Pulp duplicates were collected routinely at a rate of 1:22 by On Site and submitted with the primary sample for analysis. Precision was in line for the expected a variance in both gold and antimony.
Umpire laboratory checks to three additional commercial assay laboratories are completed each year covering all new assays generated at the property.
- The verification of significant intersections by either independent or alternative company personnel.
- The use of twinned holes.
- Documentation of primary data, data entry procedures, data verification, data storage (physical and electronic) protocols.
- Discuss any adjustment to assay data.
Internal validation of significant intercepts was completed by the exploration and senior geologists. Photographs, logging, sample weights and assay results were checked to ensure manual errors were eliminated.
Key intercepts at Costerfield were also validated by the Resource Geologist and Competent Person during the interpretation and modelling or the Costerfield resource estimation.
Assay and sampling data was automatically uploaded into the Acquire database system and QA/QC validated at the point of upload. Any issues were entered into a QA/QC register and resolved before data acceptance.
Alkane staff conduct periodic visits to the On Site Laboratory in Bendigo and meet regularly with the Lab managers. In early 2023 a review was conducted by a third party (RSC Consulting Pty Ltd) to ensure the practices are appropriate. Nothing of major concern was found.
Twinned holes are typically only drilled intentionally to get full recovery of an ore zone when the initial hole has core loss. There are inadvertent twinned intercepts within the database, particularly when the collar position is close to the mineralisation. Twinned intercepts provide consistent correlation of structure and mineralisation character however due to the short range grade variability common structurally controlled gold systems, may not have the same mineralisation tenor. No adjustment has been made to the assay data.
- Accuracy and quality of surveys used to locate drill holes (collar and downhole surveys), trenches, mine workings and other locations used in Mineral Resource estimation.
- Specification of the grid system used.
- Quality and adequacy of topographic control.
Downhole surveys are conducted using a digital Reflex EZ-TRAC tool, in both single-shot (30 m while drilling) and multi-shot mode (3 m spacing at end of hole) where required.
All downhole survey data is digitally uploaded to the Reflex EZ-TRAC and automatically imported into the acQuire database.
- Data spacing for reporting of Exploration Results.
- 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.
Where veins or mineralisation zones were sub-sampled, a full-length composite of variable thickness was used in the MRE.
- 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 drilling orientation compared to that of key mineralised structures is not considered to have introduced any sampling bias as the structures are currently interpreted.
- The measures taken to ensure sample security.
Drill core logging and sampling was completed in this secure facility.
Sample bags containing sample material are placed in heavy duty plastic bags in which the sample submission sheet is also included. The plastic bags are sealed with a metal twisting wire or heavy-duty plastic cable ties.
The bags are taken to a storage area that is under constant surveillance.
A private courier collects samples daily and transports them directly to On Site in Bendigo, where they are accepted by laboratory personnel.
Sample pulps from On Site are returned to Alkane for storage. The pulps are stored undercover, wrapped in plastic.
- The results of any audits or reviews of sampling techniques and data.
Routine monthly lab visits and reviews are conducted by site personnel and make up part of the QA/QC protocols.
RSC Consulting Pty Ltd reviewed the sampling and QA/QC procedures and practices in early 2023. There were no major outcomes related to sampling techniques and data.
