Western Mines Group has just kicked the door down and unveiled what appears to be the biggest nickel sulphide resource in Australian history, tabling a colossal 7.2 million tonnes of contained nickel metal at its Mulga Tank project in the Minigwal Greenstone Belt, 190km northeast of Kalgoorlie in WA’s Eastern Goldfields.

The company’s updated JORC-compliant resource estimate for this behemoth encompasses a staggering 2.647 billion tonnes grading 0.27 per cent nickel, 131 parts per million (ppm) cobalt, 77ppm copper and 19ppb combined platinum and palladium, at a 0.20 per cent nickel cut-off grade.

To put that monster nickel inventory into perspective, if all 7.2 million tonnes of contained metal were gathered into one solid lump, it would occupy more than 800,000 cubic metres – enough to fill roughly 320 Olympic-sized swimming pools.

The resource also contains a suite of potentially valuable by-products, including 347,000 tonnes of cobalt, 205,000 tonnes of copper and 1.6 million ounces of combined platinum group elements (PGE). The scale of the deposit firmly places it in globally significant territory and according to the company, makes it easily the largest of its kind in Australia by a country mile.

The new estimate incorporates results from an additional 32 reverse circulation (RC) and diamond drill holes put into the deposit over the past 18 months. The latest drilling delivered a more than 35 per cent increase in total tonnes and a whopping 98 per cent increase in the higher-confidence indicated resource category, now standing at 1.121 billion tonnes at 0.28 per cent nickel for 3.1 million tonnes of contained nickel.

The rest of the resource remains - for now - in the inferred category, comprising 1.526 billion tonnes at 0.27 per cent nickel for 4.1 million tonnes of contained metal.

The new numbers contrast with the company’s previous total resource in April 2025, already a hefty 1.968 billion tonnes at an average grade of 0.27 per cent nickel, 131ppm cobalt, 82ppm copper and 17ppb combined platinum and palladium, for 5.3 million tonnes of contained nickel.

The Mulga Tank deposit comprises a giant, disseminated nickel sulphide system hosted within the Mulga Tank ultramafic complex, a geological setting considered analogous to other major nickel deposits in the Yilgarn Craton such as BHP’s Mt Keith and Yakabindie operations.

Western Mines says that its initial resource estimate for Mulga Tank was a significant milestone for both the project and the company; however, the latest upgrade has taken things up another notch. Importantly, the enormous resource captures only the shallow, disseminated nickel mineralisation defined by drilling to date, potentially laying the foundations for a large-scale open-pit mining operation.

The sheer scale of Western Mines’ discovery puts it in a league of its own. The 7.2 million tonnes of contained nickel at Mulga Tank blows its Australian peers’ publicised total contained nickel out of the water by a factor of up to at least 3.4. For context, BHP’s massive Yakabindie deposit contains around 2.1 million tonnes of nickel and its Mt Keith deposit contains about 1.2 million tonnes.

One of the aims of the Phase 4 and 5 programs was to increase drilling density and upgrade the Indicated resource tonnes, which was successful with a 98% increase. A further aim was to try and target higher grade tonnes, which again appears successful with an 80% increase in Indicated resource tonnes.

The mineralisation at Mulga Tank is relatively shallow, starting at an average depth of just 65 metres below surface and extending to about 460m. The company says the deposit’s geometry makes it amenable to a large-scale, open-pit mining style of operation, a crucial factor for the economics of a bulk-tonnage, low-grade operation.

Better still, the current resource remains open in multiple directions, suggesting room for this monster to grow even bigger.

Another prize could be lurking deeper down. Previous drilling also highlighted the potential for richer, massive nickel sulphide mineralisation near the base of the giant ultramafic intrusion. One particularly intriguing reverse circulation hole targeted the deeper basal contact, well below the shallow disseminated resource, offering a tantalising glimpse of what could be hiding beneath the already enormous deposit.

That hole gave up 116m assaying 0.5 per cent nickel from 1303m depth in a deep, high-grade basal sulphide zone. The hole also turned in a higher-grade diamond tail core intercept of 38m going 0.71 per cent nickel from 1324m, pointing to a potentially significant accumulation of richer nickel sulphides deep beneath the giant shallow resource. Further support came from a one-metre chunk of individual sulphide segregation grading 2.34 per cent nickel within the basal zone, while the total system intercept for that hole delivered a huge run of 694m grading 0.31 per cent nickel from 120m.

With the upgraded resource now in hand, Western Mines is pressing ahead with its first scoping study for the project. The company has been benchmarking its project against other large-scale, low-grade nickel sulphide deposits, particularly in Canada, to gauge potential operating costs and development parameters.

Preliminary metallurgical test work on the disseminated material has already shown that nickel sulphides can be successfully recovered via conventional flotation methods at between 40 and 45 per cent, which is in line with feasibility studies for similar large-scale Canadian projects.

The recovery assumptions are also relatively conservative, based on early-stage rougher flotation tests and benchmarked against giant, low-grade “Type Two” Canadian nickel sulphide deposits such as Canada Nickel’s Crawford project, which uses a similar processing approach. As Western Mines progresses its metallurgical testing, the company says it will likely evaluate other standard industry optimisation paths.

In a world increasingly hungry for the key metals that power the green energy transition, the discovery of a deposit of this magnitude is a rare and significant event. While it is still early days, Western Mines has defined a resource that rivals and even surpasses those held by some of the world’s mining majors.

All eyes will now be on the upcoming scoping study, which will provide the first glimpse into the potential economics of developing this truly world-class nickel giant.

Is your ASX-listed company doing something interesting? Contact: matt.birney@wanews.com.au