As far as watershed years go, 2023 was a big, capital-W one for the team at Hamelin Gold (ASX:HMG).
Speaking to Mining.com.au, Managing Director Peter Bewick explains how the Perth-based explorer faced — and subsequently overcame — trials and tribulations of “biblical” proportions to deliver a range of successes it now considers utterly transformative.
And with 2024 just a stone’s throw away, Hamelin seems primed to take full advantage of what could be an even bigger year to come.
Fires, floods, and explorational vigour
Chief among Hamelin’s successes was the completion of a whopping 17,500m drilling program at its 2,500km-square West Tanami Project in north-east Western Australia.
A sizeable chunk of work in its own right, that Bewick and his team were able to manage it between major flooding events at the start of the year, which knocked out bridges and access roads, and disastrous fires, which swept through the project in October, is all the more impressive.
“We didn’t have too much in the way of famine or disease, we had one COVID incident, but the fires and floods — it was biblical,” Bewick says.
“So to get all that work done by such a small team, with that condensed time frame and the issues we had with logistics, it was an absolutely outstanding effort by the guys. And in order to do that and actually keep the knowledge going, to keep learning as we were doing that, that was pretty special.”
“we had one COVID incident, but the fires and floods — it was biblical”
All told, Hamelin racked up 2,500m worth of reverse circulation (RC) and 15,000m worth of air core (AC) drilling at the West Tanami Project. Even more significant, however, were the three key lessons learned along the way; lessons that could potentially revolutionise the company’s exploration strategy going forward.
Go deep or go home
The first is that shallow drilling in the Tanami Desert just doesn’t work. The West Tanami Project, Bewick explains, has been held by a variety of junior explorers over the last 30 or 40 years, each of which seems to have undertaken simple, piecemeal drilling programs before moving on with little to show for them.
“We need to understand the geology, we need to work out what it is that makes a deposit in this sort of area. What are the key criteria you want to find to zero in on a gold deposit?” Bewick says.
“We’ve got to work out how to explore for them, given most of this area is under sand cover, so not a lot of the geology sticks up out of the ground. And if we just do what previous explorers did, which is very shallow drilling — what I’d call ’empirically based’, so just looking for a bit of gold and then drilling a lot of holes underneath it — if we do exactly what they did, it’s just the definition of insanity. We’re going to get exactly the same result, which is a lot of ineffective exploration.”
“if we do exactly what they did, it’s just the definition of insanity. We’re going to get exactly the same result, which is a lot of ineffective exploration”
An assessment of drilling efforts by previous explorers shows that 70% of all holes drilled at the West Tanami Project are less than 10m deep. In a geological setting where gold is stripped from the top of the profile — in some instances the top 20m — the lack of historical success starts to make sense.
The proof of such a geological theory is in Hamelin’s efforts at the Fremlins prospect.
“Previous explorers outlined a coherent, 3km-long surface geochemical anomaly and drilled it with 7m-deep holes. They got no gold and walked away,” Bewick explains.
“Then we went in with not a big rig, but an air core rig, and drilled down to hard rock, which is where you need to up here. And we’ve identified a nice, broad, consistent gold anomaly over 300m wide at around 20m or 25m below surface, and it’s completely open to the south.”
Hamelin completed a follow-up drilling program at the Fremlins prospect later in the season. Although the results are yet to come back from the lab, the story they might tell is already a source of excited anticipation.
Bismuth vs arsenic
Lesson number two relates to bismuth and arsenic as pathfinder elements for gold. With the intense weathering profile in the Tanami region, explorers have found these elements can be used to track the possible locations of gold mineralisation at depth.
“Previous explorers had said: ’Let’s go find the arsenic anomalies, and if we find the arsenic anomalies, that’ll lead us to where the gold will be’. And what we’ve proven is that there’s no relationship between gold and arsenic. In fact, the bismuth association is much better. Bismuth is a great pathfinder for gold up here because it appears to hang around in the regolith when the gold gets stripped out.”
“Bismuth is a great pathfinder for gold up here because it appears to hang around in the regolith when the gold gets stripped out”
In the early exploration work of most gold hunters, the focus is not necessarily on the high-grade veins themselves, but rather the dispersions — or plumes — that extend from them.
“In the Eastern Goldfields, for instance, where you’ve got lots of salt water and you’ve got lots of iron in the profile, you can actually generate a gold anomaly in the regolith that looks almost like a mushroom,” Bewick explains.
“The stalk of the mushroom is the primary gold deposit and the big head of the mushroom becomes the plume that surrounds that, which is dispersion from that primary position. And so you drill it on maybe 100m spaced holes or 200m spaced holes, just looking for any dispersion from that system.”
But in the Tanami, with the presence of fresh water combined with a very shallow weathering profile, that ‘mushroom’ can be narrow, thin, and deep.
“So what we’re seeing is literally none of that gold dispersion in the top of the profile. Whether the gold concentrates down lower or not, I’m not quite sure, but the actual position where we do see some gold dispersion is much, much lower in the profile than what you might find in the Eastern Goldfields.”
The bismuth, however, remains.
A report published in April 2022 by researchers from the British Geological Survey and Camborne School of Mines highlighted, among other things, the importance of bismuth in understanding geological structures.
“A changing attitude towards minor metals within the mining industry would result in an overall increased understanding of mineralisation and genetic models of geological systems, with more research and development of models for Bi mineralisation,” the report — ‘Bismuth: Economic geology and value chains’ — said.
“Its use as a pathfinder element, and the recent elucidation of the Bi collector model for gold, highlights its importance in understanding big scale geological processes.”
But given the extent of sand cover at the West Tanami Project and the dilutive effects of those sand particles in geochemical analysis, how, exactly, do you go about identifying this gold-bismuth interplay?
Unlocking the Tanami
The answer apparent to Hamelin — and the crux of lesson three — is ‘ultra-fine’ soil sampling.
Developed by the CSIRO under a program co-funded by Encounter Resources (ASX:ENR), the mother entity from which Hamelin was spun-out in November 2021, the UltraFine technology represents a potentially major revolution for mineral exploration.
“What happens in the desert is you tend to get clay particles that attach themselves to the sand. These clay particles are nano-sized, they’re sub-two microns. But because of their nature — they often carry a bit of an electrical charge — they preferentially absorb metals onto those fine clay particles,” Bewick explains.
“But if you assay that, because this sand grain has got no metal in it, it just gives you a super low reading, the sand just swamps out whatever metal signature is there and dilutes the signature to the point where it doesn’t register. So, how do we get that clay particle off the sand particle, concentrate it, and then assay that clay particle only, leaving the sand behind?”
Over the course of a three-year program, the brainiacs at the CSIRO were successful in developing a process by which those clay particles were centrifugally ripped from the sand, put in suspension, collected, and assayed.
Following a number of orientation programs in 2022, the technology was put to work at West Tanami in May, along a 4km-long section of the Sultan Corridor to the west of a reconnaissance drill hole completed in late 2022. Lo and behold, a “beautiful gold anomaly” sprung forth.
“It’s coherent along a number of lines, it follows the structure beautifully. It’s almost textbook. I guess I’ll be bold and say there’s more than likely going to be gold underneath this thing. Is it going 0.1 of a gram or is it 10 grams? That’s what we don’t know. That’s obviously why we drilled it.”
“It’s almost textbook”
It’s perhaps true that such a discovery would have been significantly more of a challenge using more traditional methods. It’s true, also, that UltraFine soil sampling has effectively ‘unlocked’ a prolific but challenging region of the world, and holds the potential to do so elsewhere.
In Bewick’s estimation, those would be areas similar in history to the Tanami, where sand-covered terrain has been ineffectively explored using traditional exploration techniques.
“We’ve actually pegged — not too long ago — a large tenement to the east of Kalgoorlie, and we’re going to apply some of the learnings that we’ve got in the Tanami to this area. There is gold out there but no one has found a big one — yet,” he says.
“If we can get some runs on the board and prove the methodology we’re applying — it would probably have to be tweaked a little because of the differences between each area — we may have a real competitive advantage in this greenfields gold exploration. And what tends to happen is, when you make a breakthrough, it tends to lead to a series of discoveries, not just one.”
The year ahead
Indeed, these are some big intellectual wins for a company staring down the barrel of what promises to be an interesting 2024.
“If [the soil geochemistry] comes up positive, obviously we’re probably in a drill-out phase at Sultan, hopefully putting ounces on the books throughout next year,” Bewick says.
“But also we’re going to be rapidly expanding the application of the fine fraction soil geochemistry to other parts of [the West Tanami Project]. I mean, it’s 100km long and it’s 25km wide. It’s a huge project which, when you take into account the lack of effective previous exploration, we’ve got a lot of work to do just to explore our own project.”
It’s necessary work on the path to Bewick’s ultimate goal: building a company capable of going the distance. Exploration, he says, is just the first step to building a mine.
“I want Hamelin to be around for 100 years and be a great explorer. I want to be finding big dots on the map and finding mines that last for decades, not little bits and pieces. I have no qualms at all about digging a hole in the ground. It actually can be quite good fun, especially if it’s a great deposit. And I think if we want to find great deposits, we need to go to places where people haven’t explored before.
“If someone wants to pay a lot of money for it and get it before it gets to its ultimate value, that’s just the business. Maybe we won’t get to dig it up, but we’ve got to go in with the view that we’re going to dig it up. So that’s what we’re doing.”
“I want Hamelin to be around for 100 years and be a great explorer”
Write to Oliver Gray at Mining.com.au
Images: Hamelin Gold