To have a significant landholding as an exploration company increases the odds of making a discovery and ultimately developing a producing mine.
When that ground held by the company lies within a historically mined region well-endowed with gold, the prospects of success are boosted even further.
Gold explorer Alto Metals (ASX:AME) has a significant portion of tenure within the vast majority of the historic Archaean Sandstone Goldfield, located in the East Murchison mineral field of Western Australia.
Prospectors found gold about 20km southwest of the Sandstone in the heart of the East Murchison District some 740km northeast of Perth in 1894. The ground has been host to several large historic mines, which have produced more than 1 million ounces, making it a well-endowed gold region of Australia.
What Alto has discovered (other than plenty of gold), is that the majority of greenstone belt to date has only had shallow drilling and has barely been explored below 100m. By drilling further down at its “open-pitable” deposits, and by focusing on overlooked mineralised areas, the company is finding significant amounts of the yellow metal spanning a vast area.
Coupled with that, under the direction of Managing Director and CEO Matthew Bowles, who came on board in early 2019 as a non-executive director before being appointed to the helm in 2020, the company has ramped up its exploration focus to be more expansive.
As such, Alto is continuing to review the multiple advanced brownfields and early greenfields targets within its Sandstone Gold Project, as part of the company’s longer-term strategy to advance the overall project pipeline to support a stand-alone operation.
As Bowles explains, the historic Archaean Sandstone Goldfield still has a lot to offer long after gold was first discovered in the region in the late 19th Century.
“We continue to deliver multiple, shallow high-grade gold results and shareholders can look forward to further results in the near-term as we are looking forward to incorporating all of our results into the updated Mineral Resource Estimate planned for early next year.”
Digging deeper with open pits
The vast number of former open pits, underground workings, and prospects, in this historically mined gold precinct now owned by Alto, include Lord Nelson & Lord Henry, Havilah & Maninga Marley, Ladybird, Indomitable, Tiger Moth, Vanguard & Vanguard North, Oroya & Hacks, Bull Oak, Sandstone North, and Bulchina.
Alto has been drilling for several years but in late 2019 launched a major drilling campaign that has since grown the resource to 12.4Mt @ 1.6 g/t Au for 635,000 ounces (JORC 2012 Indicated and Inferred resources). These resources are shallow, defined to a depth of less than 200m and remain open. The company is continuing to step out and expand the footprint of the deposits with ongoing exploration drilling.
The company’s aggressive 60,000m drilling program for 2022 is targeting both resource growth and exploration, focusing on existing resources and several advanced regional prospects. Alto expects to launch a similar size drilling campaign in 2023 and is on track for another resource upgrade along the way.
“We are extremely pleased to be able to announce a substantial increase in the gold resource to 635,000 ounces at the Sandstone Gold Project”
“We are extremely pleased to be able to announce a substantial increase in the gold resource to 635,000 ounces at the Sandstone Gold Project. We still view this very much as an interim resource upgrade, with significant scope to delineate additional shallow, high-grade gold ounces with the current and planned drilling at the Lords Corridor, Vanguard and Indomitable.
The company remains focused on adding further ounces with extensional drilling and plans to mobilise additional rigs to fast-track this resource growth and also test a number of our high-priority regional targets.
Alto completed over 60,000 metres of drilling in 2021 and the scale of growth, particularly at Lord Nelson which has more than doubled and Vanguard which has tripled in size, gives us the confidence that we can continue to materially grow the resources beyond what is currently defined at Sandstone.”
Alto has some 20 brownfield and greenfield targets, including historic open cut and underground mines and a plethora of underexplored/untested targets. While it has a solid pipeline of resource projects – many of which could be a standalone company in their own right – it is prioritising advanced prospects.
Alto being Alpha
This prioritisation of assets has initially led Alto to focus on what it calls the ‘Alpha Domain’, a 20km trend which hosts all of its current mineral resources. Of particular interest for Alto is the 3km-long Lords Corridor target within the Alpha Domain, which continues to demonstrate the continuity of ‘significant, high-grade’ mineralisation with indications that the company is potentially onto a large gold system.
“Our strategy is to initially focus on the Alpha Domain to aggressively grow the current resources…”
Bowles explains: “Our strategy is to initially focus on the Alpha Domain to aggressively grow the current resources, which remain open, and we can see will continue to grow. While in the background continuing to work up the plethora of advanced, quality prospects in our pipeline, including looking to revisit other old mines where the is significant mineralisation which has not been recently followed up.
It is a very solid project pipeline, which the market still does not fully appreciate.”
Heavenly grades along Lords Corridor
That pipeline includes Alto’s major ongoing drilling program which focuses on both resource growth and exploration at existing resources, and a number of advanced regional prospects, including Lord Nelson and Juno, where the first phase of 7,000m RC drilling targeting high-grade extensions has been completed. Plans for follow up extensional drilling are underway at Lord Nelson and Juno.
At the Lords, Alto has uncovered strong continuity of thick, ‘high-grade’ gold including 67m @ 2.3 g/t gold from 172m, 45m @ 3.2 g/t gold from 161m and 48m @ 3.4 g/t gold from 214m. Other results further to the south along the corridor include 91m @ 2.8g/t gold from 56m(SRC257) from the Orion Lode and 13m @ 5.1g/t gold from 162m, including 3m @ 17g/t gold from 168m (SRC443) from the new Juno Lode.
Addressing the high grades at shallow depths at Lords Granodiorite, Bowles notes that the ground at this deposit is ‘fertile’ and could be a company-making asset on its own.
“Our first phase of drilling from 2022 at the Lords Corridor has successfully extended the high-grade mineralisation at Lord Nelson and extensional drilling at Juno has confirmed mineralisation remains open to the south. RC drilling, currently underway at Indomitable is consistently returning multiple near-surface high-grade oxide gold results and, sitting in within a +20-kilometre-long gold corridor, we can clearly see this becoming a much larger system.”
The company is also planning deeper drilling targeting the mineralised plunge of Lord Nelson at depth, targeting the margin of the footwall of the Lords Granodiorite,
Indomitable by name, indomitable by nature
At Indomitable, mineralisation is currently defined over a 2km strike. More than 20,000m wide-spaced extensional and resource definition drilling is ongoing, focused on growing the shallow resource, which is currently 74,000oz at 1.3 g/t gold.
The ongoing drilling is continuing to deliver multiple shallow, high-grade gold results including 13m @ 4.3 g/t gold from 24m and 15m @ 4.2 g/t gold from 30m and points to a very large system.
“Our systematic approach is continuing to deliver and the ongoing near surface results from Indomitable highlight a very large shallow oxide footprint, which is often the key to finding much larger high-grade gold deposits at depth.”
Solid base in Sandstone
Alto’s Sandstone Project is centred on the small township of Sandstone, a region that has had historic drilling since the discovery of the yellow metal at the end of the 19th Century. The Sandstone greenstone belt has produced more than 1.3Moz of gold from numerous underground and open pit mining operations. Of this, some 612,000 ounces were produced between 1994 and 2008 from the open-pit mining of shallow oxide ore by ASX-listed companies Herald Resources and Troy Resources.
Between 1994 and 2009, the exploration focus at Sandstone was largely on shallow oxide ore to feed the 1987 vintage Herald/Troy Nunngarra Mill, at a time when the Australian dollar gold price was substantially lower than it is currently. With a higher gold price, an excellent database and a better understanding of regolith and the structural control on large gold deposits, Alto is confident of achieving its goal of 1-5Moz of gold.
In essence, Alto is taking advantage of current conditions to bring new life to a historic mining region.
“The gold price is much higher today and much of the shallow exploration at Sandstone was driven by the historic oxide mill, hence the limited drilling below 100m depth. We are revisiting these historic mines and prospects, following up on known mineralisation and hunting for the prize at depth. While Sandstone has already produced a lot of gold compared to, for example, Agnew Belt (+10Moz), exploration has still only just scratched the surface.”
Write to Adam Orlando at Mining.com.au
Images: Alto Metals Ltd