2 New Massive Volcanic Calderas Full of Gold and Silver Were Just Discovered in Australia

A Permian Cataclysm Forgotten by Time

Nearly 290 million years ago, in the dawn of the Permian period, a series of cataclysmic volcanic eruptions tore through what is now central New South Wales, Australia. In this prehistoric landscape – long before the age of dinosaurs – enormous volcanoes roared to life. Vast magma chambers emptied in titanic blasts, each eruption likely rating a Volcanic Explosivity Index (VEI) \ of 7 or more, hurling tens to hundreds of cubic kilometers of ash and molten rock skyward. The collapsing volcanoes left behind gigantic cauldron-like craters known as calderas, spanning several kilometres across. These calderas, possibly akin to super volcanoes in scale, were ringed by towering rims of shattered rock. As the fury subsided, the land bore gaping scars: steaming caldera basins that would slowly cool and solidify. Ash blanketed the region, and rivers of tuff and lava flowed, crystallizing into the rock now called the Rylstone Volcanics. It was a scene of both utter devastation and crude beauty – the birth of a volcanic complex destined to be hidden by time.

In the ensuing millennia, nature gently reclaimed the surface. Rain and wind softened the volcanic badlands, and life cautiously returned. Thick layers of sediment from an ancient inland sea and swampy forests (the proto-Sydney Basin) gradually entombed the calderas under sand and shale, preserving their forms as if in a time capsule. Coal-bearing sediments eventually blanketed the area, turning the once fiery calderas into subterranean fossils of a forgotten world. For nearly 290 million years, the Bara Creek and Three Hills calderas lay silent and buried, their majestic cliffs and vents sealed beneath up to 60 metres of rock and soil. No mountain betrays their presence today – only rolling pastures and subtle hills hint at the awesome events that forged the land so long ago.

This is the story of two massive calderas in New South Wales whose existence were only just discovered.

Buried Giants Beneath the Sydney Basin

Fast forward to the present day: the Permian giants remain hidden beneath the gentle surface of the Sydney Basin. Generations came and went unaware of the sleeping calderas below. Farmers tilled fields above ancient volcanoes, and towns sprouted over what were once magma chambers. To the naked eye, nothing unusual interrupts the tranquil rural landscape near Rylstone and Lue in NSW. Yet, beneath foot and hoof lies a geological secret of staggering proportions. The Bara Creek Caldera, about 4 km by 4 km in size, and the Three Hills Caldera, 3.5 km by 3.5 km, have remained almost perfectly preserved under the sedimentary cover. Their circular outlines and internal structures, unmarred by erosion, are effectively time capsules from the early Permian. Such preservation is exceedingly rare – it required just the right conditions, where volcanic devastation was swiftly blanketed by sediment, protecting it from the relentless wear of wind and water through the ages.

For geologists, the notion that VEI 7-scale calderas could hide intact beneath a basin in New South Wales was the stuff of legend. But clues to their existence began to surface as early as the 1980s. In 1989, explorers from CRA (Conzinc Riotinto of Australia) panning through local streams found traces of gold, copper, and silver in the sediment draining the area. These geochemical breadcrumbs hinted at a mineral-rich source upstream – perhaps an ancient hydrothermal system. At the time, attention was drawn to a promising silver-lead-zinc find now known as the Bowdens Silver Deposit, just south of Rylstone. Bowdens would turn out to be a gigantic silver lode (currently 396 million ounces of silver equivalent in resources, the largest undeveloped silver deposit in Australia). Yet, even as Bowdens was discovered, the Bara Creek anomaly – named for the creek where those metal-rich grains were found – remained unresolved. Early prospectors noted “highly altered and veined” volcanic rocks in the Bara Creek area, suggesting a buried heat source, but they couldn’t pinpoint any visible ore body. The Three Hills area, by contrast, gave no surface hint at all; it lay completely concealed under layers of sandstone and clay. For decades, the buried giants kept their secrets close.

Seismic Sleuths and Hidden Calderas

It was not until modern times that science developed the tools to peer deep underground and unveil these ancient volcanoes. Silver Mines Limited, the company now spearheading exploration in the district, launched an ambitious geophysical campaign to map what lies beneath. In 2023, geologists and geophysicists crisscrossed the region with sensitive instruments, transforming the earth into a giant echo chamber. The team completed a major 2D seismic survey spanning nearly 96 kilometers, sending vibrations into the ground and recording the returning echoes. These seismic waves are like sonar through rock: as they passed through different layers – hard volcanic tuff, soft sediment, solid granite – they created a picture of the subsurface akin to a medical CT scan. What emerged on their monitors astonished the researchers: distinct bowl-shaped depressions and circular faults far below, matching the size of calderas suspected from the earlier geologic model. The seismic lines revealed structural lows and shattered zones exactly where a collapsed magma chamber would be expected, confirming that multiple caldera structures lay hidden within the ancient Rylstone Volcanics.

Other tools added to the revelation. Magnetic surveys detected subtle anomalies – the Three Hills area, for instance, is rimmed by younger intrusions that gave off strong magnetic signals, tracing the outline of a caldera’s edge beneath the cover. Gravity data helped differentiate dense volcanic rocks from lighter sedimentary layers, outlining the caldera shapes by their mass differences. VTEM (electromagnetic) surveys scanned for conductive minerals, and high-resolution Digital Elevation Models (DEM) picked out faint topographic patterns. All these disparate clues, when layered together with computer modeling, unveiled a coherent picture: at least five enormous volcanic craters from the Permian era, preserved underground. Two stood out in focus – Bara Creek and Three Hills – both part of the broader Bowdens volcanic complex, and never drilled or studied before.

Modern clues emerged from multiple datasets, converging on the same astounding conclusion. Key evidence included:

Seismic reflections: which traced the sunken caldera floors and ring faults under ~60 m of sediments, painted a 3D image of the hidden craters.

Magnetics and Gravity: which highlighted the circular pattern of Mesozoic-aged intrusions forming a magnetic rim around Three Hills, and large gravity lows likely corresponding to ancient magma chambers.

Geochemical Anomalies: such as historic stream sediment samples at Bara Creek carrying gold greater than 10 ppb and silver, suggested that mineral-laden fluids once flowed through these volcanic structures.

Geologic Mapping: limited outcrop mapping on what little of the Rylstone Volcanics is exposed showed hydrothermal breccias and quartz veins with pyrite (iron sulfide) and gossan – the oxidized remnants of sulfide minerals. These finds are telltale signs of an ancient hydrothermal system, possibly on the margins of the calderas.

Each dataset alone offered just a fragment of the story, but together they resolved into a clear narrative. Deep beneath the rolling hills lies a cluster of volcanoes that blew themselves apart, then collapsed and vanished under sediment – only to be found again by the keen eyes and ears of modern geology.

The Discovery of Bara Creek and Three Hills Calderas

Amid this newfound understanding, the Bara Creek Caldera and Three Hills Caldera have taken centre stage as targets of intense scientific interest. The Bara Creek Caldera measures about 4 km by 4 km and shows evidence of being “preserved by silicification” – its rocks hardened by silica-rich fluids, which likely helped shield it from erosion. The seismic data indicates that important fault structures controlling the Bowdens Silver mineralization continue right through the Bara Creek caldera. Along these structures, Silver Mines’ geologists have already found quartz veins laced with pyrite and gossanous coatings, clear indicators that hot, metal-bearing fluids once moved here. Though only a few rock and soil samples have been collected so far, assays are pending to reveal if traces of silver, gold, or copper linger in those veins. It is a tantalizing hint that Bara Creek could host an undiscovered precious metal deposit – perhaps even a “Bowdens look-alike,” a twin to the nearby silver lode. The area saw only minimal exploration historically, so it remains virtually untouched since its fiery creation eons ago. Now, for the first time, scientists are mapping it in detail and preparing to probe its depths with drilling. The air is thick with anticipation of what secrets the core samples might reveal.

Just a few kilometers away, the Three Hills Caldera presents a different but equally captivating story. This caldera, ~3.5 km by 3.5 km, is entirely hidden beneath Sydney Basin sediments – not a single outcrop of its volcanic rock touches the surface. No drill has ever pierced its layers, and even Silver Mines’ seismic lines happened to skirt past it. Yet the collective data screamed its presence: a near-perfect circular structure outlined by gravity lows and magnetic highs. Intriguingly, Three Hills appears to be “the most preserved structure” of all, with a well-defined shape and a relatively uniform shallow depth. It is covered by roughly 60–100 meters of sandstones and shales – a thin veil by geological standards. Such minimal burial suggests that, beneath that cover, the ancient caldera’s topography (the collapsed crater floor and its steep walls) might be largely intact. One can imagine an entire fossilized volcanic landscape down there: perhaps the remains of a central lava dome or a caldera lake bed, frozen in stone. Three Hills is thought to be ringed by major ring faults, now marked by slightly younger intrusions that poked up into the caldera’s margins. These faults would have been highways for hydrothermal fluids after the eruption, and thus prime sites for mineral deposits. However, because the caldera has been sealed off for ages, any riches it holds have never been tapped or even seen. Silver Mines geologists consider Three Hills a high-priority target precisely because of its untouched, preserved nature – a geologic canvas awaiting its first brush with a drill bit.

Together, Bara Creek and Three Hills form part of a greater puzzle. They are two of five calderas now identified in the district (the others being Coomber, Armentum, and the main Bowdens caldera itself). But Bara Creek and Three Hills are special in that they lie mostly hidden and have no modern exploration history. This means any discovery here would be truly new to science. As Dr. Joanne Battershill, Silver Mines’ Managing Director, remarked, each of these caldera structures “could potentially host Bowdens look-alikes or, if closer to the original heat source, copper-gold mineralisation.” In other words, these ancient volcanoes might not only illuminate the geologic past – they could also be the key to the future of mineral exploration in the region.

Science and Collaboration Unveil the Past

The discovery of these calderas was not a lone eureka moment, but rather a triumph of scientific collaboration and persistence. Silver Mines Limited worked closely with the Geological Survey of NSW and researchers from the University of New South Wales (UNSW) to piece together the caldera story. The project became a real-life “Journey to the Center of the Earth”. Specialists in geophysics, geochemistry, and petrology pooled their knowledge. The NSW government, recognizing the potential, supported the seismic program with funding under its New Frontiers Exploration Program, encouraging the hunt for critical minerals. University scientists helped with cutting-edge analysis: for instance, thousands of meters of drill core from the existing Bowdens deposit have been donated for research. Using advanced tools like hyperspectral scanners and geochemical assays, researchers are decoding the mineral signatures and alteration halos that might point to hidden ore bodies. This “mineral systems” approach – understanding how an entire volcanic system dispersed its metals – is guiding explorers back to the calderas. By studying the known Bowdens ore body, geologists can recognize similar patterns on the outskirts, effectively fingerprinting the giant’s offspring in the region.

Crucially, the seismic survey interpretation was cross-checked with all other data in iterative modeling sessions. A regional geology model was built, tested, and refined multiple times. The Mineral Systems team at NSW Mining, Exploration & Geoscience (MEG) provided regional expertise and data integration. Meanwhile, UNSW researchers contributed age dating of zircon crystals from volcanic rocks, confirming the Permian age (~292 million years) of the volcanic units. By late 2023, confidence was high enough that Silver Mines publicly announced the identification of multiple new calderas in the Bowdens district – a stunning validation of months of detective work. What had once been subtle hints in gravity models and odd blips in magnetic maps were now recognized as ancient megavolcanoes. The pieces clicked into place: yes, a Permian super-eruption complex lay below, and yes, it potentially held untold riches. This synergy of modern technology and collaborative science had effectively given geologists X-ray vision into the Earth’s crust, allowing them to map a hidden world for the first time.

Untapped Mineral Wealth and Geological Significance

From an economic and geological perspective, the uncovering of Bara Creek and Three Hills calderas is profoundly significant. The Bowdens Silver Deposit – the original prize of the district – was already a remarkable find, being the only major deposit in the Permian volcanic rocks of NSW. Now, the possibility that several more caldera-hosted systems exist opens an entirely new frontier. Calderas are not just volcanic craters; they are often the breeding ground of mineral deposits. When a caldera forms, the shattered ring faults and the still-hot magma below become the plumbing for hydrothermal fluids. Superheated water rich in dissolved metals circulates for thousands of years after the eruption, depositing veins of silver, gold, copper, lead, and zinc as it cools around the fractures. In world geology, many great ore deposits – from the gold-rich craters of Nevada to the silver veins of Mexico – were born this way, in the aftermath of colossal eruptions. The edges of calderas, known as ring margins, are especially fertile ground: here the cooled magma’s collapse leaves deep cracks that act as conduits for mineralizing fluids. At Bowdens, for example, it is believed that a large granitic intrusion at depth sent up metal-bearing fluids to create the rich silver deposit near the caldera’s edge.

Now consider Bara Creek and Three Hills – untouched calderas of similar size and age, with strong indications of hydrothermal alteration. The potential for precious metal mineralization here has geologists brimming with excitement. At Bara Creek, those stream sediments with gold and silver traces are like a treasure map’s faint X marking the spot. The presence of antimony in samples (noted by CRA back in 1989) is another intriguing clue, since antimony is often associated with epithermal gold-silver systems. The silicification preserving Bara Creek might also indicate extensive silica-rich hot spring activity, which often accompanies bonanza-grade silver or gold veins in other caldera environments. Meanwhile, Three Hills’ complete burial could mean it was capped and sealed quickly, potentially locking in any mineral deposits below without surface leaching. It’s as if nature hid away a vault, potentially filled with veins of galena (lead ore rich in silver) and sphalerite (zinc ore with silver), or perhaps even native gold in quartz, and then buried it for eons waiting for discovery.

For the scientific community, beyond the lure of wealth, these calderas represent a pristine laboratory. Because they are so well preserved, geologists can study an ancient volcanic system in 3D, almost as it was at the time of eruption. Every layer of ash, every intrusive dike cutting through, and every mineral vein is a clue to the dynamics of Permian volcanism in eastern Australia. The fact that these structures sat at the edge of the Lachlan Orogen (an older geological belt) means they might also inform us about how continents were evolving back then, as volcanic arcs and basins interacted. This discovery is rewriting geological maps of NSW – what was once thought to be just “boring old sediment” on the surface is now known to hide explosive secrets beneath. University researchers and the Geological Survey are keenly interested in mapping the full extent of the Rylstone Volcanics now, understanding why the eruptions occurred where they did, and what they might tell us about magma sources deep under the crust. It’s a reminder that even in well-trodden regions like rural NSW, the Earth can still spring astonishing surprises.

Awe in the Face of Geological Time

Imagine standing on a quiet hillside near Rylstone today: the breeze rustles through eucalyptus trees, and cattle graze calmly. Beneath your feet, spanning several kilometres, are the remains of gargantuan calderas – volcanic craters born in fire when Earth’s continents were still coming together. It fills one with humility to realize that the ground we consider solid, and enduring has undergone such radical transformations. “Beneath these green hills lies a hidden world… a world forged by unimaginable fury, then lost to time.” The discovery of the Bara Creek and Three Hills calderas invites us to ponder the immensity of geological time and the dynamic forces that shape our planet. The rocks remember an inferno under a Permian sky, and now, through human ingenuity and curiosity, we too can witness a trace of that long-ago cataclysm.

As the story of these hidden calderas unfolds, it carries a blend of wonder and promise. There is the wonder of peering into Earth’s deep past – seeing, in our mind’s eye, the eruption columns towering perhaps 30 kilometers high, the pyroclastic flows turning day into night, and then the centuries of quiet burial that followed. And there is the promise that these ancient structures may yet contribute to our future, perhaps through discoveries of new mineral resources that could power technologies or economies. Silver Mines Limited and its partners are now planning the next steps: detailed mapping, more geophysics, and the ultimate test – drilling into the calderas to retrieve core samples from the very heart of the ancient volcanoes. With each meter of drill core, more will be revealed about the mineral wealth and history entombed below. The anticipation is palpable; it’s as if we are on the brink of opening a treasure chest sealed since the Permian.

In the grand timeline of Earth, 290 million years is but a chapter, yet one that we are only now learning to read. The tale of Bara Creek and Three Hills calderas is a testament to the persistence of geological features and the power of human discovery. It reminds us that the Earth still holds secrets in the most unexpected places. With patient study and a little bit of daring, we have brought to light a hidden volcanic paradise – a Permian lost world – beneath the familiar soils of New South Wales. In doing so, we deepen our connection to the planet’s past and spark a sense of awe that, even now, new frontiers of discovery await just below the surface.