It's already discovered two new lodes in 2021 at the previously-mined project, with its biggest drilling programme in years underway and starting to test the untapped potential.
What makes Alto unique for a junior is its control of virtually an entire underexplored greenstone belt in a gold-class address.
Alto recently acquired another tenement to take its holdings in the Murchison to more than 900sq.km, covering the majority of the Sandstone Greenstone Belt and in a region surrounded by multimillion-ounce gold mines such as Gold Fields' circa 10Moz Agnew to the east and Ramelius Resources' 6Moz Mt Magnet to the west.
Sandstone itself has previously produced more than 1Moz from shallow oxide pits and historical underground workings and the project has seen little exploration below 100m.
Alto last year increased its Lord Nelson resource by 60% to 109,000oz, taking the project's total to 331,000oz across several deposits, all of which remain open, but managing director Matthew Bowles has his sights set on a much larger update within the next 12 months or so.
With about A$7.8M in cash, the company now has two rigs at work on a 30,000m campaign and a strong news flow is anticipated.
The explorer has emerged from what Bowles described as a challenging year, with the company seeing off not one but three unsolicited takeover offers, raising $5.5 million and receiving strong shareholder support for its major exploration programme designed to prove up a bigger resource base.
"What we did last year was build foundations for what I think 2021 is going to be, an exceptional year," he told RESOURCEStocks.
Exploration is focused on resource growth and making more discoveries, like the Orion lode which Alto found towards the end of last year, 200m south of Lord Nelson.
"That's delivered some fantastic results," Bowles said.
"The highlight for me was 29m at 3.5g/t gold from 49m."
Other results at Orion included 23m at 3.8g/t gold from 106m.
"Orion was a key catalyst for us and highlighted that there's a lot more potential to be found at the Lords Corridor," Bowles said.
The corridor spans over 3km between the previously-mined Lord Nelson and Lord Henry deposits.
Wide-spaced "step out" exploration drilling in December, 1km south of the Lord Nelson pit, confirmed the discovery of a New Zone of gold mineralisation, where assays included 4m at 5.3g/t gold from 124m.
This news followed the discovery in February of another new lode 400m to the south on the edge of an undrilled IP anomaly, where assays included 8m at 1.6g/t gold from 65m and 1m at 6.1g/t gold from 222m within a broad "halo" of mineralisation.
Bowles said the mineralisation was the same as at Lord Nelson and reminded Alto of the first few holes which led to the Orion discovery, which further indicated the significant potential of the corridor and the entire Sandstone Gold Project.
"We're introducing the bigger picture of how big the corridor will be and then we're starting to look at other targets, because we've got multiple targets over the property," he said.
Back at Lord Nelson, which had produced 207,000oz of gold at 4.6g/t gold from a pit mined to about 90m, Alto has previously reported high grades at depth, including 5m at 13g/t from 99m and 16m at 5.2g/t gold from 240m in primary mineralisation.
Results below Lord Henry have included 2m at 51.3g/t from 70m.
"The mineralisation doesn't just stop at the bottom of the old pits, we're now looking into the continuation of mineralisation down plunge and along strike," Bowles said.
The cashed-up company is expanding the team as exploration heats up.
"My geological team are the happiest I've seen them in a long time because they can actually go out and systematically test a number of targets they have wanted to drill for such a long time," Bowles said.
He joined Alto as a director in 2019 and has been at the helm since mid-2020, saying he had long thought of Sandstone as an amazing asset.
"I just see so much potential," he said.
"There's still so much to be found at Sandstone and we are still only just scratching the surface, but our results are indicating the presence of a much bigger system.
"As one of the geos said: the more we drill, the more we find."
Not only is Western Australia a mining-friendly jurisdiction, with the government recently providing Alto with exploration incentive funding, but the isolated state has also been fairly insulated from COVID-19.
The only impact Alto is noticing, along with other industry members, is the skills and people shortage due to border closures.
In Alto's case this meant a slight delay in securing a drill crew last year, and the current backlog of assay results.
The current drilling programme began in February and Bowles expects results to start flowing in April.
From there, momentum is expected to build.
"We're looking forward to seeing the results when they come through from a number of different targets," Bowles said.
"We're quietly very excited to see what that's going to reveal."
Meanwhile Alto has already conducted preliminary metallurgical testwork on samples from Lord Nelson, which provided an average gold recovery of 96%.
Along with plus-92% recoveries from earlier testwork on other deposits including the Vanguard and Indomitable Camps, Alto said the results demonstrated the mineralisation was amenable to conventional cyanide extraction methods.
Bowles said the results gave investors comfort around the metallurgy so Alto could continue its current focus on exploration.
The company has strong backing from its key shareholders, and is tightly held with the top five holding about 48%.
The current exploration programme is about one-third complete and Bowles said there was already planning underway for an expansion.
The first rig is testing depth extensions at Lord Henry, Lord Nelson and the Orion lode, and will then remain in the Lords Corridor to further test the New Zone and IP target not yet drilled.
The second rig has started step-out drilling at Vanguard and will then move on to a maiden drill programme at the Chance target, before moving back to follow-up on first phase results in the Lords Corridor.
"2021 is an exciting year ahead for us and shareholders have a lot to look forward to," Bowles said.
"We are in the strongest position we've ever been in, we are well funded and have a major drilling programme underway to follow up recent high-grade drilling results, drive further resource growth and make further discoveries."