APPENDIX 1: Summary of Mining-Method Considerations and Developed Assay-Reporting Criteria
Mining Plus, a global mining services provider, reviewed the assay-reporting criteria developed by Nagambie Resources for the antimony-gold veins drilling program at the Nagambie Mine and agreed that the criteria were appropriate and meaningful in terms of reporting to the ASX. The developed criteria draw heavily on the publicly-available information for the Costerfield Mine, 45 km to the west of the Nagambie Mine and currently Australia’s only operating antimony-gold mine.
1) The C-veins (Costerfield-Mine-style veins) at Nagambie’s 100%-owned Nagambie Mine are generally striking N and dipping vertically or sub-vertically to the W or E. The Nagambie C-vein systems are geologically very similar to the Sb-Au vein systems at the Costerfield Mine, 100%-owned by Mandalay Resources Corporation, a Canadian company. The latest publicly-available comprehensive technical report for Costerfield (“Costerfield Report” is dated 25 March 2022:
2) The Nagambie C-veins could be mineable from ~60m vertical depth from surface, the depth of the oxidised zone. An appropriate vertical geotechnical pillar under the West Pit would be determined in due course but could be of the order of 10m.
3) Like the Costerfield veins, the Nagambie veins to date are sub-vertical (45 degrees to 90 degrees (vertical)) and have good continuity both vertically and horizontally. As such, they are amenable to mechanised mining methods. Long-hole CRF stoping (where CRF stands for cemented rock fill) is the preferred mining method employed at the Costerfield Mine (p254, Costerfield Report). Another description of this method at Costerfield is Up-Hole-Retreat (UHR) stoping with the stope drill drives being 10m vertically apart and these drives being typically 3m high, so that the up-hole blast holes would be typically 7.0m in vertical height. Using cemented rock fill (utilising the underground development waste) would allow for future stopes above, below and besides each filled stope (also as for the Costerfield mine). For an example of a typical Costerfield stope drill drive, from which the up-hole blast holes are drilled, refer p75 of the Costerfield Report.
4) Conceptual mine planning for a Nagambie underground mine already indicates that, mining only the C1 & C2 vein systems, sufficient stopes could be developed to effectively schedule stoping operations and optimise the antimony and gold grades delivered to the treatment plant. Nagambie remains very confident of discovering additional C-vein systems to the south west of The West Pit.
5) Minimum stoping width could be 1.2m estimated horizontal thickness (EHT) (similar to the Costerfield Mine).
6) For stopes side by side, the waste between them should be at least 1.5m EHT to cover the additional costs for multiple stopes of strike driving, stoping, backfilling and potential ore mining losses.
7) All individual sample assays to be weighted by both EHT and sample bulk density (BD) – using the Costerfield Mine BD formula based on Sb% (see below).
8) Gold equivalent grade (g/t AuEq) to be calculated for each sample by multiplying the Sb% by the AuEq factor and adding that figure to the g/t Au. For the relevant formula, see below.
9) All intersection grades (Au, Sb, AuEq) to be reported for the EHT of the vein and, where the vein EHT is less than 1.2m, for the minimum mineable EHT of 1.2m by adding appropriate waste dilution (similar to the Costerfield Mine).
10) Mineable cut-off grade (MCOG) of 3.0 g/t AuEq over 1.2m EHT or greater (similar to the Costerfield Mine).
NAG Price at posting:
4.2¢ Sentiment: Buy Disclosure: Held
is dated 25 March 2022:
(20min delay)