New drilling highlights: Shepherd Southern extension drilling defines new high-grade domain including intercept highlights of 26.0 g/t gold and 39.9% antimony over 1.39 metres (estimated true width (ETW) 0.63m) in SQ020; 4.9 g/t gold and 10.4% antimony over 2.77 metres (ETW 1.74 m) in SQ026.
Additional veins within Shepherd identified though optimization drilling, including 797.0 g/t gold over 0.52 metres (ETW 0.29 m) in PD036; 122.0 g/t gold over 0.55 metres (ETW 0.52 m) in KD957.
Preliminary drilling underneath the Brunswick Deposit intercepts 2 parallel veins with highlight grades of 17.8 g/t gold over 1.87 metres (ETW 1.62 m) in BD357; 16.4 g/t gold and 1.5% antimony over 1.39 metres (ETW 1.12 m) in BD354.
Frazer Bourchier, president and CEO, commented: “The continuity and longevity of Costerfield is pivotal to Mandalay, and we’ve strategically focused on near-mine drilling in recent exploration activities. The operation stands as one of the highest-grade gold mines globally1 and, notably, the second-highest in Australia, surpassed only by the neighbouring Fosterville mine, situated approximately 30 km to the northwest.
“These recent encouraging results primarily cover infill and extension drilling related to the Shepherd orebody beneath Youle and the discovery of high-grade gold veining beneath the historic Brunswick deposit, 800 meters south of Shepherd. Replacing reserves and growing this mineral resource, with equivalent high margin ounces from both near mine and regional exploration success, remain a top priority for Mandalay. These results reinforce our intention to maintain our current healthy self-funding spending rate at Costerfield.”
Chris Davis, vice-president of exploration and operational geology, said: “Shepherd has revealed itself as a network of sheeted subvertical veins, extending from the base of the west-dipping Youle orebody. Initially, further exploration of Shepherd’s depth and southern extension faced temporary challenges due to access constraints. These constraints were resolved when a dedicated drill drive was developed earlier this year. Subsequently, much of the 2023 Shepherd drilling has been conducted from this drive, resulting in the modelling of 12 veins. Notably, a significant additional high-grade gold and antimony domain has been identified along the trend to the south.
“Drilling below Brunswick has delivered positive results, with two intercepts uncovering a new domain displaying substantial gold endowment.
“While the results from the initial campaign are encouraging, we have temporarily paused the step-out drilling program. This decision allows us time to define the faulted architecture and update our targeting model for the upcoming phase.”
During 2023 near mine exploration has focused on two major drilling campaigns: extension of the Shepherd orebody and testing the Brunswick orebody at depth.
The Shepherd drilling occurred simultaneously with the Brunswick Deeps program, including 23 holes drilled from the Brunswick – Youle access drive and the base of the Brunswick decline with the aim of building a new economic panel for extension of Costerfield mine by testing below the Brunswick orebody and workings.
Drilling over the past year has successfully extended both the 600 and 620 veins (previously called Shepherd and Suffolk veins respectively) to the south, adding approximately 100 metres of strike length to the 620 vein due to an upgrade to the orebody seen in SQ020 and SQ026. Updated modelling during the 2023 campaign has resolved the Shepherd system into 12 discrete veins.
Additionally, depth continuations of both the 600 and the 620 veins has been targeted and delineated from the 2023 drilling campaign.
In addition to southern and depth extension potential of Shepherd, the drilling indicates a westward step of gold endowment across of the southern veins, corresponding with an apparent enrichment of stibnite relative to the bulk of Shepherd.
Brunswick Deeps discovery: Mineralization below the currently defined Brunswick resource remains open at depth.
The program conducted in 2023 was designed to test this hypothesis with holes that would sweep under the Brunswick mine and cover the potential offset position.
The program successfully identified two veins – offset veins identified approximately 100 metres relative to the upper Brunswick Vein and 60 metres relative to the currently mined lower portion of Brunswick. Follow up drilling was also conducted following the hits on BD354 and BD357; these found the Breccia Vein to be somewhat continuous, striking in a northeast direction towards Youle and Shepherd.
The second vein intercepted appears to be the depth continuation of the Brunswick orebody as it shares many ‘Brunswick-like’ characteristics such as a strongly sheared footwall and well developed stibnite mineralization with lesser quartz relative to other Costerfield orebodies.
Some larger step-outs were conducted towards the end of the program, showing vein continuity in all directions for the Main Vein.
Near mine exploration will continue to focus on the Shepherd area and surrounds, particularly on the potential connection between Shepherd South and Brunswick at depth.
Drilling of regional prospects has taken place, and is continuing, at Costerfield throughout the year, particularly at the True Blue and West Costerfield prospects.
Mandalay Resources is a Canadian-based resource company with producing assets in Australia (Costerfield gold-antimony mine) and Sweden (Bjorkdal gold mine).