Costerfield Mine

• Cash cost and all-in sustaining costs are non-IFRS measures.
• See “Non-IFRS Measures” in our MD&A.
• Assumes average metal prices of: Au $1,797/oz, Sb $10,805/t 
• Consolidated all-in sustaining costs per Au Eq. oz includes corporate overhead spending.

Veins at Costerfield typically comprise quartz (laminated to brecciated) and sulphides. The dominant sulphide mineral is stibnite (Sb2S3). In addition to stibnite, arsenopyrite and pyrite occur in minor amounts.

The veins occur within discrete shear systems. The following paragenesis has been interpreted:

• sericitization of host rock sediments with minor pyrite deposition;
• faulting with associated open-space deposition of quartz, locally with coarse gold, and partial replacement of pyrite by auriferous arsenopyrite – only minor replacement of sericite-altered host rock by quartz occurs, with some remobilization of sericite into convoluted cross-cutting veinlets;
• open-space deposition of carbonate in quartz vugs;
• influx of Sb-rich solutions, resulting in massive stibnite infill and replacement of brecciated quartz-carbonate veins. The massive stibnite contains finely-disseminated Au; and
• re-crystallization / annealing of stibnite.

Ore shoots in the veins are typically 0.25 – 1.0 m thick and extend for 200 m or more along strike. They are typically displaced by flat faults so that they appear flat-bottomed. However, as with the Cuffley Lode, the Company is having success finding the offset parts of ore shoots below the flat faults; the deepest intercept in the district, approximately 500 m below surface in the Cuffley Lode, is also one of the highest-grade intercepts.

The Brunswick vein lies approximately 600 m northwest of the northernmost point of the Cuffley Lode.  The lode is sub-vertical and occurs over a strike length of approximately 450 m, with a down-dip extent of approximately 200 m and an average true thickness of approximately 1.28 m. Exploration drilling has identified mineralization to the south and at depth below the known Brunswick Lode. Mineralization is broken into two zones of mineralization below the Brunswick Lode, called the P-K domain and Brunswick Deeps. The P-K domain is capped by the shallow west-dipping Penguin Fault, and extends to the Kiwi Fault. The Brunswick Deeps zone is defined by the west-dipping Kiwi Fault and Adder Fault. Similar in nature to Cuffley and N-Lodes, the mineralization in the two domains is generally confined to sub-vertical quartz–stibnite veins.

The Youle deposit extends below the historical Costerfield, Minerva and Bombay group of mines located approximately 1.2 km northeast of Brunswick. Mineralization was identified in 2011, in drill hole MB012, which struck the down-dip continuation of the vertical Kendall Lode, offset westward over the west-dipping No. 3 thrust fault. In 2016, drill hole BC006W1 revealed the existence of a high-grade north–northwest striking, west-dipping lode structure, Youle. The Youle Lode dips at a shallower angle to the mineralized lodes in Augusta and Cuffley and has been identified as the down-dip continuation of the vertical Kendall Lode offset westward over the west-dipping No.5 thrust fault.

Youle has thus far demonstrated consistent structural and grade continuity over much of its extent. The Youle Lode has a strike length of 600 m (width of 150 m) and ranges in true thickness between 0.16 m and 1.37 m.  Similar to the Augusta and Brunswick Lodes, mineralization is confined to quartz‑stibnite veins.

1. The Mineral Reserve is estimated as of December 31, 2023, and depleted for production through to December 31, 2023.
2. Tonnes are rounded to the nearest thousand; contained gold (oz) is rounded to the nearest thousand; contained antimony (t) is rounded to nearest hundred.
3. Totals may appear different from the sum of their components due to rounding.
4. Lodes have been diluted to a minimum mining width of 1.5 m for stoping and 1.8 m for ore development.
5. A sustaining cut-off grade of 6.0 g/t AuEq is applied. An Incremental cut-off grade of 3.1 g/t AuEq is applied where mining rates do not meet mill capacity and the life of the mine is not extended.
6. Commodity prices applied are Au price of USD1,800/oz, Sb price of USD11,500/t and exchange rate USD:AUD of 0.70.
7. AuEq is calculated using the formula: AuEq = Au g/t + 1.22 * Sb %.
8. The Mineral Reserve is a subset, a Measured and Indicated only schedule, of a Life of Mine plan that includes mining of Measured, Indicated and Inferred Resources.
9. The Mineral Reserve Estimate was prepared by Brett Nevill MAusIMM who is a full-time employee of SRK Consulting, under the direction of Dylan Goldhahn, MAusIMM, who is a full-time employee of Mandalay Resources. The Mineral Reserve Estimate was independently verified by Robert Urie FAusIMM who is a full-time employee of SRK Consulting. Robert Urie fulfils the requirements to be a “Qualified Person” for the purposes of NI 43-101, and is the Qualified Person under NI 43-101 for the Mineral Reserve.

1. The Mineral Resource is estimated as of December 31, 2023 with depletion through to this date.
2. The Mineral Resource is stated according to CIM guidelines and include Mineral Reserves.
3. Tonnes are rounded to the nearest thousand; contained gold (oz) is rounded to the nearest thousand; contained antimony (t) is rounded to nearest hundred.
4. Totals may appear different from the sum of their components due to rounding.
5. 5.0 g/t AuEq cut-off grade over a minimum mining width of 1.2 m is applied where AuEq is calculated using the formula: AuEq = Au g/t + 1.88 * Sb %
6. The AuEq factor of 1.88 is calculated at a gold price of $1,900/oz, an antimony price of $12,000/t, and recoveries of 94% for Au and 89% for Sb.
7. Veins were diluted to a minimum mining width of 1.2m before applying the cut-off grade and peripheral mineralisation far from current development was excluded to comply with the Reasonable Prospects for Eventual Economic Extraction (RPEEE) criteria.
8. The Stockpile Mineral Resource is estimated based upon surveyed volumes supplemented by production data.
9. Geological modelling, sample compositing and Mineral Resource Estimation for updated models was performed by Joshua Greene, MAusIMM, a full-time employee of Mandalay Resources.
10. The Mineral Resource Estimate was independently reviewed and verified by Cael Gniel MAIG RPGeo (Mineral Resource Estimation), a full time employee of SRK Consulting. Mr Gniel fulfils the requirements to be a "Qualified Person" for the purposes of NI 43-101, and is the Qualified Person under NI 43-101 for the Mineral Resource Estimate.