This article is a sponsored feature from Mining.com.au partner North Stawell Minerals. It is not financial advice. Talk to a registered financial expert before making investment decisions.
North Stawell Minerals (ASX:NSM) has the right connections, location and geology to accelerate its path to production.
The company has what it describes as “matched” mineralisation proximal to the Stawell Gold Mine in Victoria, which has produced over 5 million ounces since the 1980s and still has over 1.1 million ounces in underground resources.
North Stawell is exploring for shallow repeats of the multi-million-ounce gold deposits at Stawell on the margins of other basalts under cover.
The company dubs what it is looking for as the “Stawell-type model”, with the Stawell mine cored by a buttress of basaltic rock and the gold mineralisation wrapping around the basalt margin.
It is a simple concept: find more basalts, potentially find another Stawell.
CEO Campbell Olsen says North Stawell Minerals’ tenements are in the “economic footprint” of the Stawell mine, close enough for identified and defined satellite resources to be of possible strategic interest.
“A significant discovery on the NSM tenements may be of interest to the mine and offer a foreshortened and cost-effective pathway to production for NSM satellite deposits,” he tells Mining.com.au.
There is a 10km wide fault-bounded corridor that runs northwest to southeast that includes geology very similar to Stawell.
North Stawell holds 60km of this corridor where it continues to the north, but 85% of the ground is masked by a thin blanket of unmineralised sediment – or cover as it is also referred to – that starts just 6km north of the mine.
“The cover, which was an impossible barrier to historic prospecting, is readily explored through with geophysics and drilling,” Olsen explains.
“One of the key characteristics of ‘Stawell-type’ mineralisation is that the gold mineralisation is focused around the margins of large slabs of basalt – these are unique to the Stawell Corridor in Victoria – that pre-exist the gold.”
The Stawell Corridor forms one of the vertices of Victoria’s Golden Triangle. Resources Victoria says the state has 13 goldfields that have each produced more than 1 million ounces of gold. The 22-million-ounce Bendigo goldfield is the largest, followed by Ballarat, Castlemaine, Stawell and Woods Point-Walhalla.
The Geological Survey of Victoria estimates that there may still be up to 75 million ounces of gold to be found in the northern parts of the Stawell, Bendigo and Melbourne zones, including multiple million-ounce occurrences.
Decades of Stawell data guide exploration
With the basalts within the Stawell Corridor now able to be seen at depth through cover with the use of geophysics, North Stawell has quickly identified multiple additional basalts to the north of the Stawell mine.
Olsen says the company can use the structural, geological and research lessons learnt at the Stawell mine to prioritise basalt, and potential mineralisation, on its own ground.
“The long-established mine is the ‘type deposit’ where a huge amount of geological information and research has been completed over decades,” he notes.
“NSM’s exploration can utilise that info to make much better decisions about where and how to explore for repeats of the multi-million-ounce deposit at Stawell.”
North Stawell has drilled the first ever holes into three of the identified basalt domes – solidified lava from millions of years ago, which is essentially coated by the gold like icing on a cake.
The company has identified around 10 gold targets along strike from the Magdala deposit at the Stawell operation and is exploring the most attractive prospects.
One of these is Wildwood, which has the same geology and a similar scale to Magdala. While it currently has a modest resource of 87,300 ounces @ 2.4 grams per tonne gold, Wildwood is open and shallow-tested.
North Stawell is prioritising the targets where drilling has intercepted gold mineralisation in close proximity to the basalt.
“These get prioritised as the geology is ‘responding’ or ‘conforming’ to the Stawell-gold model and we know that gold-bearing fluids have interacted with the basalt,” Olsen says.
“Where we see mineralisation, the characteristics in the rocks and the mineralisation frequently look very similar to what’s been observed at Stawell – bellwethers that we might be close.”
North Stawell is also exploring for another style of mineralisation – Mariners-type – where the basalt is deeper.
The company is seeing this style of mineralisation at Darlington, which is located 6km north of the Stawell Gold Mine.
“Mariners is a mineralised structural splay that comes off the ‘roof’ of the basalt at Stawell and propagates 300m above the basalt,” Olsen explains.
“The mineralisation has significantly different geological characteristics, including notable visible gold and increased grades. The historic Mariners lodes included 0.95 million ounces @ 28g/t gold and is a very attractive target.”
Assessing economic viability of prospective targets
Olsen says the modest but important resource at Wildwood, particularly with the rising gold price and near-surface position, has increasing potential to be economically viable as a possible satellite deposit.
North Stawell is reviewing some of the potential economic factors that might make Wildwood viable over the next six months.
Meanwhile, Darlington is centred on an historical mine with roughly 2,800 ounces of shallow production. North Stawell drilled down-plunge of the mine in 2023, intersecting a continuation of the mineralisation and, 100m deeper, a possible controlling basalt.
This development allowed the exploration team to refine the targeting and step 200m south.
One drill hole hit 2.3m at 28.2g/t gold higher up in the hole than expected, which indicated shallow (90m) mineralisation, open in all directions, with strong similarities to the Mariners lodes at Stawell.
“Both the depth and the high grades make this a compelling target, and is a notable departure from the more typical lower grade gold results seen in the Stawell Corridor,” Olsen explains.
“Darlington is an exploration target, with all the speculative upside of a new, high-grade target. Planned work to follow up on this target lever off the shallow depth and high grades and similarity to Mariners to effectively and cost effectively assess its potential.”
North Stawell has done a lot of work to understand the regional geology, from reinterpretation of data, acquisition of high resolution geophysics, regional drill programs to establish a robust project pipeline, to collaborative research.
Two projects have been completed with Australia’s national science agency, the Commonwealth Scientific and Industrial Research Organisation (CSIRO).
Olsen says the most recent project with the CSIRO involved modelling the plumbing system beneath Stawell to identify the faults that are most likely to act as conduits to channel gold-bearing fluids to the basalt domes during the gold event.
Besides having the right location and geology, the North Stawell team has close ties to the team at Stawell.
North Stawell was spun out of Stawell Gold Mines to create an exploration arm with the resources and time to methodically explore the potential of the ground to the northwest of the existing Stawell mine.
“The NSM team has a strong relationship with the team at Stawell, and NSM benefits in multiple areas from this,” Olsen explains.
“From some of the administrative functionality, to constructive discussion about the geology. We cannot overstate the importance of ‘standing in the glow’ of the mine’s long, authentic engagement with the local community and exemplary environmental record to build trust in the community around exploration activities.
“Economically, the NSM ground is close enough to the mine that any discovery may be of interest to the mine’s long-term plans.”
Write to Angela East at Mining.com.au
Images: Mining.com.au & North Stawell Minerals
