Australia’s Most Important Mineral Deposit: Mount Weld

Mount Weld: The Story of a Rare Earth Treasure in Western Australia

Imagine journeying to a far-flung patch of the Western Australian outback, about 30 kilometres from the nearest town. In this quiet, red-dirt landscape lies Mount Weld, an unassuming hill concealing one of the richest caches of rare earth elements on the planet. Rare earths might not sound familiar, but they’re the hidden heroes inside your smartphone, electric car, and wind turbine. Mount Weld’s story spans two billion years of geologic drama and a modern mining operation that has turned this ancient deposit into a strategic powerhouse. Let’s explore how a prehistoric volcanic eruption, some fortuitous chemistry, and a lot of Aussie ingenuity combined to make Mount Weld a marvel of the rare earth world.

Geology of Mount Weld – A Two-Billion-Year Journey

Mount Weld’s origins read like a deep-time adventure. Over 2 billion years ago, in the Proterozoic Eon, a volcano punched through what is now Western Australia’s Yilgarn Craton and formed a carbonatite – essentially a magma pipe rich in carbonates and exotic minerals. You can think of carbonatite magma as a sort of mineral-rich soup. As it cooled and solidified into a 3–4 km wide cylindrical plug beneath the surface, it was loaded with rare metals like neodymium, praseodymium, cerium, and others that we prize today. For millions of years, this treasure brew lay hidden deep underground.

Fast forward through the ages, and nature’s forces took over. The region went through intense weathering – basically, eons of rain and groundwater percolating down, dissolving some minerals and concentrating others. Geologists call Mount Weld’s deposit a “carbonatite-derived laterite”, which is a fancy way of saying the top of that ancient volcanic plug got rusted and leached into a super-rich soil. Picture making a reduction sauce in cooking: as less stable ingredients (like calcium and magnesium carbonates) got washed out by water, the rare earth elements were left behind like a thick, flavourful syrup. The rare earths recombined into new secondary minerals. These minerals are finely dispersed in the iron-rich soil or regolith capping the deposit. The result was a supergene-enriched rare earth zone right near the surface, meaning incredibly high concentrations of rare earth oxides in the top 50–60 meters of ground.

One remarkable quirk is how intact Mount Weld’s rich cap remained. While other ancient carbonatite deposits in the region got scoured away by time (one nearby at Ponton was stripped by ancient glaciers), Mount Weld’s rare earth-laden blanket stayed put, protected by a gentle geologic history. This left an almost pure bowl of “rare earth soup” just below ground level. Geologists estimate that about 1.8 kilometres of the old volcano eroded away, leaving a residual high-grade ore lens at the top. The richest part, known as the Central Lanthanide Deposit (CLD), sits right in the centre of the carbonatite pipe and boasts some of the highest rare earth grades ever found. In fact, Mount Weld is often cited as one of the world’s highest-grade rare earth mines – with ore that can average around 6–8% TREO (total rare earth oxide) content or higher, which is several times richer than many other deposits around the globe. For context, an ore body with even 3% TREO is considered good; Mount Weld’s core zones are truly exceptional.

The Mount Weld Mining Operation – From Discovery to Production

Despite all that hidden wealth, Mount Weld didn’t draw attention until the 20th century. It doesn’t have flashy outcrops of minerals at surface, so discovery came by airplane – a geophysical survey in 1966 spotted a strange magnetic and gravity anomaly under otherwise ordinary alluvial flats. Drillers soon confirmed a carbonatite buried below, and by the 1980s explorers realized that the weathered cap contained extraordinarily high rare earth grades. The main rare earth zone (the CLD) was formally identified around 1988. Various companies poked at it over the years, but it wasn’t until Lynas Corporation (today Lynas Rare Earths) acquired full control in 2002 that things kicked into high gear.

Mining at Mount Weld began in earnest in 2007 with a small-scale start and ramped up around 2011 once financing and processing facilities were lined up. The operation is an open-pit mine, more akin to a shallow quarry than a giant pit. In fact, because the ore is so high-grade and near the surface, the pit doesn’t have to be enormous or deep. Lynas proudly notes that Mount Weld’s footprint is relatively small, and shallow compared to many mines, which also makes it easier to manage and rehabilitate. Imagine a scooper taking the top layer off a cake – that’s essentially what the mine does, peeling off soil and rock to get to the “frosting” rich in rare earths. And after two decades of mining, there’s still plenty left: as of 2024 the proven and probable ore reserves have grown to 32 million tonnes at about 6.4% TREO – roughly 2.0 million tonnes of rare earth oxides contained in the ground. That reserve supports decades of production ahead.

So how do they actually extract and process these special metals? The mining process at Mount Weld starts with traditional open-pit methods: drill, blast (in the harder zones), and scoop up the ore. The on-site concentration plant then takes over. Big haul trucks deliver the ore to the plant where it goes through crushing and grinding circuits to reduce the rock to a fine powder. Next comes a bit of mineral magic: flotation. In flotation tanks, chemicals and bubbles are used to make the rare earth-bearing minerals (like monazite) float and separate from the non-valuable minerals. This upgrades the material into a richer form. The concentrated slurry is then filtered to remove water, producing a mixed rare earth concentrate – a brownish powder that contains all the rare earths mixed together.

At this stage, Mount Weld’s output is still not the shiny metal or oxide that end-users need, so further refining is required. In the early years, Lynas would pack this concentrate into half-height shipping containers called “rotainers” and send it 2,500 miles by sea to Malaysia. There, at the Lynas Advanced Materials Plant (LAMP) in Kuantan, the concentrate undergoes complex chemical processing: cracking, leaching, solvent extraction, and purification steps that isolate individual rare earth oxides like neodymium and praseodymium. By 2013, LAMP was fully operational and could handle about 22,000 tonnes of REO output per year, nearly doubling Lynas’s capacity once it came online. This international supply chain turned Mount Weld’s raw dirt into high-purity rare earth products for global markets – but it also meant dealing with radioactive residues (from trace thorium in the ore) in Malaysia, which spurred some controversy and calls to bring more processing back onshore.

In recent years, Lynas has done exactly that by investing in a new processing facility in Kalgoorlie, Western Australia, much closer to the mine. As of late 2024, the Kalgoorlie Rare Earths Processing Facility has begun cracking and leaching Mount Weld’s concentrate to produce an intermediate mixed rare earth carbonate (MREC). This step neutralizes most of the radioactive elements and produces a cleaner product that is then shipped to Malaysia (or potentially other future separation plants) for final refining. The move not only addresses environmental concerns but also adds value within Australia. It’s a complex dance, but it’s one that has made Lynas the only significant producer of separated rare earth materials outside China.

Rare Earth Production – How Much Does Mount Weld Yield?

Mount Weld’s mine produces a remarkable quantity of rare earth material each year. In 2019, for example, the site hit a record output: about 19,737 tonnes of rare earth oxides in one year, of which roughly 5,900 tonnes were the in-demand NdPr oxides used for high-power magnets. That’s nearly 20 million kilograms of rare earth compounds – an impressive haul for a single mine in the desert! If you filled shipping containers with that much material, you’d have a long convoy heading to port.

Financial Performance – The Value of Rare Earths in Dollars

All those tonnes of rare earths translate into serious money. Rare earth elements are valuable – neodymium-praseodymium oxide (NdPr), for example, was selling for around US$50–55 per kilogram in mid-2025. So how does Mount Weld’s output stack up financially? In recent years, Lynas Rare Earths (the owner-operator of Mount Weld) has been pulling in on the order of 5 hundred million in revenue per year from its rare earth products. In the fiscal year 2025 results, Lynas reported about A$556.5 million in revenue (around US$360 million). The year before was a bit lower at A$463 million, reflecting some market price swings and a deliberate shift to produce fewer low-value elements. But the big picture is that Mount Weld has evolved into a hundreds-of-millions per year operation, a far cry from when it was a fledgling project in the 2000s.

Looking ahead, the projected lifetime earnings from Mount Weld are truly massive. With an expanded mine life of 20+ years at higher production rates (and possibly 35+ years at current rates), Mount Weld is expected to keep producing well into the 2040s or 2050s. If rare earth prices hold up, this one mine could generate tens of billions of Australian dollars in revenue over its lifespan.

What Makes Mount Weld Unique on the Global Stage?

Another unique aspect is Australia’s position versus China. Rare earths have been historically dominated by China (which produces over 80% of global supply). Mount Weld, however, turned Australia into a non-Chinese source of these critical elements. In fact, Lynas (fed by Mount Weld) remains the only significant rare earths producer outside China as of the mid-2020s. This gives Mount Weld outsized strategic importance. Governments around the world, from the U.S. to Japan and across Europe, have a keen interest in Lynas’s success because it provides a more secure and diversified supply of rare earths for high-tech industries. It’s not an exaggeration to say that Mount Weld is a linchpin of Western rare earth supply chains, making it a bit of a geopolitical asset as well as an economic one.

Few places on Earth combine such rich geology with favourable mining conditions in a safe jurisdiction as Mount Weld does. As a result, this once little-known Australian hill has become famous among engineers and policy makers alike. It stands shoulder to shoulder with the world’s top rare earth sites and, in certain respects, outshines them. Mount Weld is the kind of mine you might compare to a fine diamond – not the biggest rock in the room, but pound-for-pound one of the most valuable. And like a diamond, it was formed by unusual forces, discovered with a bit of luck, and ultimately brought to light to shine on the global stage, powering technologies that define our modern life. Mount Weld’s story, from ancient volcano to high-tech enabler, shows how something buried for billions of years in the Australian outback can suddenly become critical to the future of technology around the world.

Here's the video we made on this on the OzGeology YouTube channel: