Mandalay Resources Discovers New High-Grade Gold Trend at Brunswick South, Adjacent to Existing Costerfield Infrastructure

TORONTO, July 29, 2025 (GLOBE NEWSWIRE) -- Mandalay Resources Corporation ("Mandalay" or the "Company") (TSX: MND, OTCQB: MNDJF) reports exploration results from the Brunswick South extension, part of the operating Costerfield gold-antimony mine in Australia.

Highlights:

• Discovery sits just 300 m from active access drive along the Brunswick line.
• All three drillholes hit high-grade veining:
  • 76.6 g/t Au over 0.49 m (ETW 0.44 m) in BD387;
  • 265.0 g/t Au and 0.7% Sb over 0.29 m (ETW 0.17 m) in BD388; and
  • 52.3 g/t Au over 1.69 m (ETW 1.58 m) in BD391
• Intercepted veining over 175 m strike length and 50 m down dip.
• Extension drilling has commenced.

Note: Further intercept details including significant intercepts within composite intervals can be found in the Appendix to this document. Where antimony grades are not stated they are below detection. ETW refers to the Estimated True Width of the intercept.

Frazer Bourchier, President and CEO of Mandalay, commented: “We are extremely excited about the new discovery at Brunswick South following on the heels of our success at True Blue. Brunswick South is within 300 metres of existing underground infrastructure, providing potential near term mine life extension of Costerfield. The Company will ramp up drilling from both surface and underground to advance this discovery rapidly. When added to the ongoing drilling at the True Blue discovery, Costerfield is delivering value to shareholders through the drill bit. Costerfield is expected to be a strong cash-flow generator for the combined Alkane–Mandalay following the anticipated closing of the merger of the two companies on August 5, 2025.”

Chris Davis, VP of Exploration and Operational Geology, commented: “The Brunswick deposit, mined in the 1990s and again in 2018, is hosted within a vertical fault that has been traced along a 2km strike length. Two domains of gold and antimony endowment have been identified so far along the fault. Our 2025 program targeted the depth extension of the southern domain, and extraordinarily, all three drillholes intersected high-grade gold across a 175-metre strike and 30-metre vertical extent.

“Given the impressive results and ease of access from existing infrastructure, this discovery is now being prioritized for further drilling in parallel with True Blue. As part of this work, we will also investigate constructing an underground drill platform that could accelerate our drilling program and definition of the deposit. With only high-grade results at this level, the veining remains largely open along strike and at depth with historic drilling above, we have launched an extension program to further evaluate the full potential of this emerging discovery.”

Brunswick South Depth Discovery

The Brunswick deposit is situated between the Cuffley and Youle deposits and has direct access and portal to the Brunswick Processing facility that concentrates all ore produced at Costerfield. The deposit was mined by means of an open pit in the mid-1990s and underground mining commenced from 2018 under Mandalay. Current mining activity at Brunswick is primarily focused on a high-grade zone with limited vertical extent known as the K-R Panel, just below the historically mined block, separated by a flat-lying fault that has offset the lode laterally by several meters.

Figure 1. Oblique view (looking north-east) of the Costerfield gold-antimony field, showing Mandalay underground development, current resource outlines of the Brunswick deposits, and the central position of the three drill intercepts reported in this announcement.

The Brunswick vein is remarkably linear in the context of the field. Mineralization has been drill tested over a length of 2000m near surface with negligible offsets. The vein (where mined) occupies the hinge of an open north-south striking anticline, and typically contains a greater proportion of stibnite to quartz than most other Costerfield veins. The vein is intersected, and sometimes offset laterally by flat-lying faults that follow, or are at a low angle to, the flat or gently west-dipping bedding of the host Costerfield siltstone. As these faults pass over the axis of the Brunswick anticline, they tend to bifurcate and flatten to horizontal, creating sliced stacks with progressive downward western offest – occasionally creating bonanza-grade ore shoots and localized blowouts. Additionally, steep north-east trending shears create grade pods where found intersecting the vein, without causing significant lode offset.

At Brunswick South, near-surface historical drilling highlights a second panel of enrichment, separated from the Brunswick Main pannel by a grade-controlling north-east shear set. Reinterpretation of the previously drilled deepest low-grade intercepts suggested that interference from flat-lying faulting was highly likely given the ambiguous nature of the broken material recovered. Due to the assessment a two-hole drill testing program was designed to investigate the untested continuation below.

Figure 2. Longitudinal section of the Brunswick South vein showing the position of the new intercepts in relation to existing drilling data. The position of the Cuffley to Brunswick access is shown, with annotation showing its distance east of the target vein, decreasing to the north. The southern end of the mined Brunswick lode can be seen at the far right of the section. Annotations describe the intercepts grade over an estimated true width.

BD387 intersected the Brunswick vein approximately 270m south of the limit of existing development on the Brunswick Main lode. The vein intersected graded 76.6 g/t gold over 0.49m downhole, consisting of healed quartz breccia containing visible gold. BD388 passed through the vein 175m south of BD387, and found higher grade mineralization at 265 g/t gold and 0.7% antimony over 0.29m downhole. Clusters of fine visible gold are evenly spread throughout the quartz in this intercept, and stibnite is present as a late-stage vein infill phase. A third hole (BD391) was directed between and approximately 30m down-dip of the two prior intercepts and also intercepted high-grade gold mineralization, 52.3g/t gold over 1.69m downhole.

Figure 3. Tray photographs of the three new high-grade intercepts with individual grades annotated. An inset for BD388 shows a close-up of the style of mineralization encountered, predominantly free gold in quartz. BD391 is considerably more faulted than the others, interpreted to be due to proximity of a bedding-parallel fault as is commonplace in Costerfield ore veins.

The new intercepts are situated within the hinge of an open syncline; a slightly different structural setting to both the Brunswick Main lode (which occupies an anticlinal hinge) and the already defined mineralized panel above the newly targeted zone which does not appear to be associated with a well defined fold hinge (figure 4).

These encouraging intercepts are of immediate operational importance to the Costerfield mine, situated just 320m west of the Brunswick access drive. A high-grade resource in this location will be quick and cost-effective to access. Significant prospectivity surrounds these exciting new intercepts, not only along the so-far untested strike and down dip extents but also upwards into the existing Brunswick South resource, where drilling is relatively sparse and targeted infill may build considerable upside in steeply plunging high-grade pods as seen in the Brunswick Main deposit.

Figure 4. Cross section at 5350N (at BD391) through the Brunswick South system, with the two other intercepts of the program shown diagrammatically. The stratigraphy presented up-dip is repeated over several early thrust faults, which are crosscut by later subvertical faults and the Brunswick vein itself. Annotations describe the intercepts grade over an estimated true width.

Next Steps

Followup drilling has commenced and will investigate both strike and down-dip extension to the new high-grade area, and also further define the up-dip link with the near-surface veining. This program will be undertaken from underground by one of the three drill rigs currently focused on near mine expansion, and by an additional surface rig due to arrive in August 2025.

Drilling and Assaying

All diamond drill core was logged and sampled by Costerfield geologists or contracted geologists with significant industry experience who worked under Costerfield geologist’s oversight. All samples were sent to On Site Laboratory Services (OSLS) in Bendigo, Victoria, Australia, for sample preparation and analysis by fire assay for gold, and Atomic Absorption Spectroscopy (AAS) for antimony. Site geological and metallurgical personnel have implemented a QA/QC procedure that includes systematic submission of standard reference materials and blanks within batches of drill and face samples submitted for assay. Costerfield specific reference materials produced from Costerfield ore have been prepared and certified by OREAS, a specialist laboratory quality control consultancy. See Technical Report entitled “Costerfield Operation, Victoria, Australia NI 43-101 Report” dated March 30, 2025, available on SEDAR (www.sedar.com) for a complete description of drilling, sampling, and assaying procedures.

Qualified Person:

Chris Davis, Vice President of Operational Geology and Exploration at Mandalay Resources, is a Chartered Professional of the Australasian Institute of Mining and Metallurgy (MAusIMM CP(Geo)), as well as a Member of the Australian Institute of Geoscientists (MAIG) and a Qualified Person as defined by NI 43-101. He has reviewed and approved the technical and scientific information provided in this release.

For Further Information

Frazer Bourchier
Director, President and Chief Executive Officer

Edison Nguyen
Director, Business Valuations and Investor Relations

Contact:
647.258.9722

About Mandalay Resources Corporation

Mandalay Resources is a Canadian-based natural resource company with producing assets in Australia (Costerfield gold-antimony mine) and Sweden (Björkdal gold mine). The Company is focused on growing its production and reducing costs to generate cashflow. Mandalay is committed to operating safely and in an environmentally responsible manner, while developing a high level of community and employee engagement.

Forward-Looking Statements

This news release contains "forward-looking statements" within the meaning of applicable securities laws, including statements regarding the exploration and development potential of the Brunswick South discovery. Readers are cautioned not to place undue reliance on forward-looking statements. Actual results and developments may differ materially from those contemplated by these statements depending on, among other things, changes in commodity prices and general market and economic conditions. The factors identified above are not intended to represent a complete list of the factors that could affect Mandalay. A description of additional risks that could result in actual results and developments differing from those contemplated by forward-looking statements in this news release can be found under the heading “Risk Factors” in Mandalay’s annual information form dated March 30, 2025, a copy of which is available under Mandalay’s profile at www.sedarplus.com. In addition, there can be no assurance that any inferred resources that are discovered as a result of additional drilling will ever be upgraded to proven or probable reserves. Although Mandalay has attempted to identify important factors that could cause actual actions, events or results to differ materially from those described in forward-looking statements, there may be other factors that cause actions, events or results not to be as anticipated, estimated or intended. There can be no assurance that forward-looking statements will prove to be accurate, as actual results and future events could differ materially from those anticipated in such statements. Accordingly, readers should not place undue reliance on forward-looking statements.

Appendix

Table 1. Significant Intercepts from drilling program.

Notes

1. The AuEq (gold equivalent) grade is calculated using the following formula:

Prices and recoveries used: Au $/oz = 2,500; Sb $/t = 19,000; Au Recovery = 91% and; Sb Recovery = 92%

2. LLD signifies an undetectable amount of antimony. Detection limit for the analysis used is 0.01%

Table 4. Drill Hole Collar Details

Notes:

1. Coordinate System: MGA2020