The Second Gold Rush That Changed Gold Mining Forever

The Cyanide Revolution: How a Deadly Discovery Transformed Australian Gold Mining

Gold Mining in the 1850s–1880s: The Mercury Era

In the mid-19th century, Australia was gripped by gold fever. Prospectors swarmed creek beds and dug deep into quartz reefs, desperate to extract every fleck of the precious metal. By the 1850s and 1860s, easy alluvial gold was dwindling, and miners turned to hard rock mining – crushing gold-bearing quartz and using mercury to recover gold. In a typical hard-rock mine, a stamp battery pounded ore into powder, which was then washed over mercury-coated copper plates. The mercury would amalgamate with (or bond to) the gold, forming a paste-like amalgam that could later be heated to retrieve gold. This mercury amalgamation process was state-of-the-art in the 1850s and allowed recovery of most coarse, visible gold. It worked well for larger gold particles and was simple but effective – early miners marvelled as globs of mercury “ate” the gold and made it appear as if the precious metal simply vanished into the liquid metal.

However, not all that glittered could be gathered. Mercury had its limits, especially as mining dug deeper or processed more complex ores. When gold was fine-grained or mixed with other minerals, problems arose. Sulfide minerals (like pyrite, arsenopyrite, copper sulfides, etc.) often accompanied gold in underground veins. These impurities could coat gold particles or “sicken” the mercury – turning it into a dull, scummy powder that refused to bond with gold. Miners noticed that if crushed ore contained certain impurities, the mercury on the plates would develop a black film and break into tiny droplets (a phenomenon called flouring). These tiny droplets of mercury – each potentially carrying some gold – washed away with the wastewater, lost to the tailings dumps. Even with careful operation, fine gold particles sometimes simply failed to contact the mercury or were carried off in slurry. The result: a significant portion of gold remained unrecovered, mixed in with the waste sand.

The gold was there – miners could see it in their tailings, assay it in their waste, even sometimes pan it from discarded heaps – but they just couldn't catch it. What they needed wasn’t more brute force. They needed a breakthrough. And in the closing years of the 19th century, that breakthrough came – not from a new machine, but from a deadly chemical.

By the 1870s and 1880s, as easily processed ore grew scarce, Australian miners increasingly encountered this “lost gold” problem. In Victoria, for example, companies like the Port Phillip and Colonial Gold Mining Co. at Clunes pioneered techniques to treat the residue (called “pyrites” or sulfide concentrates) that the stamp mills and mercury left behind. They found that standard crushing and amalgamation often failed to extract half of the gold in richer sulfide ores. In other words, more than 50% of the gold could be still sitting in the crushed rock “tailings” after the mercury plates had done their work. This was a frustrating realization: enormous mullock heaps and sand dumps around mine sites actually contained a fortune in fine gold that the old methods couldn’t capture. Miners tried to improve recovery by grinding ore more finely or using devices like Wheeler pans and Chilean mills to re-grind tailings, but many ounces still slipped through the process. Some forward-thinking engineers experimented with chemical methods in the late 1800s – notably chlorination (using chlorine gas to dissolve gold) – which achieved higher recoveries. For instance, a chlorination plant at Charters Towers (Queensland) could recover gold from complex ore that amalgamation couldn’t, but it was slow and costly, requiring skilled operators and expensive infrastructure. Chlorination had its successes (Mount Morgan in Queensland built the world’s largest chlorination works by the late 1890s), yet even that process was limited and considered too expensive for treating the mountains of old tailings. As the 1880s drew to a close, Australia’s gold industry was at a crossroads: high-grade surface gold was mostly gone, mines were struggling with lower-grade or refractory ores, and tons of gold lay trapped in tailings dumps across the country.

The Hidden Gold in Tailings and Mullock Heaps

By the late 19th century, the Australian landscape of the goldfields was dotted with mullock heaps and tailings dumps – the piled-up waste from decades of mining. These heaps weren’t just sterile mounds of dirt; they often contained significant gold that had been too fine or too chemically bound for recovery by mercury. Contemporary accounts and studies later revealed astonishing quantities of gold left in this “waste.” In Victoria alone, an estimated 131 tonnes of elemental mercury were lost in the mining process during the 19th century, often bound with unrecovered gold. Some of the tailings sands assayed at several grams of gold per ton – grades that had been uneconomical to process with old methods, but tantalizing in aggregate. At Clunes, as noted, the Port Phillip Company’s experiments in the 1860s showed tailings with over 4 ounces of gold per ton, virtually all of which had been unrecoverable until new techniques were applied. Other mines in Bendigo and Ballarat had similarly rich “waste” – golden treasure literally tossed aside in the rush for easy pickings.

Miners knew there was value in these heaps, but how to get it out? Some tried re-processing tailings via improved gravity or mercury methods, with limited success. By the 1880s, attention turned to chemistry. The chlorination process (invented overseas in the 1850s) was one attempt to unlock this gold. It involved roasting the tailings to oxidize sulfides, then bathing them in chlorine solution to dissolve gold, which could be precipitated out. A few chlorination plants sprang up in Victoria and Queensland and indeed recovered thousands of ounces from old concentrates. But the average prospector or smaller mine owner still had no practical way to re-treat a decade’s worth of mercury-laden sand. It was clear that a more efficient, accessible method was needed to spark a revival in these workings. Little did they know, the solution would come from a most unlikely source: a deadly poison.

Breakthrough in the 1890s: Enter the Cyanide Process

In 1887, in faraway Glasgow, Scotland, chemist John Stewart MacArthur and the Forrest brothers patented a new method that would revolutionize gold extraction. They discovered that a dilute solution of potassium cyanide could dissolve gold out of crushed ore – a process that came to be known as the MacArthur-Forrest cyanide process. The science behind it wasn’t entirely new (as early as 1783, chemist Carl Wilhelm Scheele had noted that “aquae regia” of cyanide could dissolve gold), but MacArthur and his colleagues turned it into a practical industrial technique. By suspending pulverized ore in a cyanide solution, and exposing it to air, they found gold would go into solution as a soluble complex. By 1890, this innovation was put to the test in the gold fields of the Witwatersrand in South Africa – with spectacular results. Up to 96% of the gold in the ore could be extracted via cyanidation, far surpassing what mercury or even chlorination could do. This high recovery was astounding: previously, an ore yielding maybe 50-70% recovery by amalgamation could now yield >90% recovery with cyanide. For mining companies, it was like alchemy – turning previously worthless ore into profit. A boom of investment followed on the Rand as mines rushed to build cyanide leaching plants. News of this “cyanide miracle” quickly spread around the mining world.

Australia, with its long history of gold mining, was among the first to take note. In 1891, two brothers from Scotland (Duncan and Peter McIntyre), who had been associates of MacArthur, arrived in Queensland to introduce the new technology. They initially experimented on old tailings at Ravenswood, QLD, but faced difficulty obtaining enough material for trials. Moving on to the famous Mount Morgan mine, they attempted cyanide on the refractory ore there in 1891 – but Mount Morgan’s ore had high copper content, which “devoured” cyanide and made the process uneconomical at first. Finally, they found a perfect testing ground at Charters Towers, a prolific goldfield with extensive tailings and compatible ore. In 1892, at the Charters Towers’ Excelsior Mill, the first commercial cyanide plant in Australia began operation. The results were immediate and dramatic. One eyewitness reported that the cyanide process “worked a treat” at Charters Towers – gold that had been left in the tailings for years was now being recovered in quantity. The success was such that within a few years, Charters Towers had multiple cyanide works re-treating old sands and slimes, effectively launching a new gold boom in that town. By 1897, the cyanide method had largely replaced the earlier chlorination process on that field, because it was cheaper and well-suited to the local ore.

Western Australia, too, would soon benefit enormously from this innovation. In June 1893, rich gold was discovered at Kalgoorlie – the start of the famous Golden Mile. This ore was rich but challenging, containing gold locked in sulfides and telluride minerals. Fortunately, the cyanide process was by then well established and ready to meet the challenge. The early Kalgoorlie mills combined traditional gravity and amalgamation with cyanide treatment of their concentrates and tailings, pioneering improvements (like fine grinding and roasting techniques) to handle the difficult telluride ores. By the late 1890s, massive cyanide plants with open vats sprang up around Kalgoorlie’s Golden Mile. One contemporary photograph from 1896 shows rows of giant timber and iron vats at the Lake View Consols mine, each vat filled with ore soaking in cyanide solution, with technicians overseeing the leaching process. These operations proved that even complex ore could be tackled by cyanide with enough innovation.

By 1900, the cyanide process was spreading across every gold camp in Australia. Dozens of plants were built in places like Gympie and Ravenswood in Queensland, at Boulder and Coolgardie in WA, and throughout Victoria. It is telling that by the early 1900s some form of cyanide treatment had become the preferred option for most gold mines in Australia. Even many small mines, which previously would have discarded low-grade ore or concentrates, adopted cyanide because it turned unprofitable material into payable gold. The 1890s depression and a general scarcity of capital in Victoria initially slowed adoption (as setting up a cyanide plant required investment and navigating patent licenses), but as soon as conditions improved, a cyanide boom followed. From 1900 onward, “cyaniding” became a buzzword in mining towns.

Why Cyanide Leaching Was a Game Changer

What made cyanide so revolutionary compared to mercury? The answer lies in chemistry and practicality. Mercury amalgamation relies on direct contact between mercury and clean gold surfaces – it struggles with microscopic gold or gold attached to minerals. Cyanide, by contrast, is a chemical solvent for gold. In an aerated alkaline solution, cyanide ions bond with gold to form a soluble complex ion (dicyanoaurate). This means cyanide can literally pull gold into a liquid solution, even if the gold is finely distributed or not visible to the naked eye. The gold-rich solution can then be processed to recover solid gold (historically by adding zinc dust or shavings, which causes gold to precipitate out of solution). Because of this mechanism, even very low-grade ores or tailings could yield gold with cyanidation.

Mercury amalgamation might recover (at best) 60-70% of gold from an ore, and much less if the gold was fine or refractory. Cyanide, as demonstrated on the South African Rand and in Australian trials, could recover over 90%. In practical terms, this boosted the efficiency and profitability of gold mining tremendously. A mine could now profitably mine lower-grade ore that would have been considered waste in the 1880s. For example, ore with only a quarter-ounce of gold per ton (which mercury might miss much of) could be treated with cyanide on a large scale and still turn a profit. Moreover, all those accumulations of tailings – the “rubbish” of earlier operations – suddenly became potential gold mines themselves. It was as if a magic key had been found to a treasure vault that had always been there. Miners often remarked that cyanide “picked up what mercury left behind,” scrounging gold from the nooks and crannies of processed ore that no pan or plate could reach.

Chemically, cyanide had another advantage: it could be tailored and tweaked. If early results were poor, metallurgists learned to adjust the cyanide concentration, ensure sufficient oxygen (by agitating or pumping air into vats), and keep the solution alkaline (adding lime) to prevent toxic hydrogen cyanide gas. Over the 1890s and 1900s, improvements like the Merrill-Crowe process (developed in 1890s) made gold recovery from cyanide solution even more efficient by using vacuum de-aeration and zinc dust. Each iteration made cyanide extraction faster, safer, and able to handle different ore types. In short, cyanide was chemically superior in extracting gold from the kinds of ore that Australia had in abundance by the late 19th century: low-grade, fine-grained, or mineral-bound gold. Mercury was simply no match for this dissolving power. As one historical analysis put it, without cyanide the vast pyritic ore deposits of places like Kalgoorlie would have been impossible to exploit fully – cyanide “was the cheaper and more effective system” that won out.

However, it’s worth noting that early cyanide use required careful handling – after all, cyanide is a deadly poison. The process was initially viewed as “highly technical…beyond the skill and means of the small men”. Large companies with capital led the way in adopting cyanide, hiring trained chemists and engineers to run the plants. But over time, the knowledge spread. Guides and manuals (like   famous 1939 book “Cyaniding for Gold”, which simplified the process for laymen) helped democratize the cyanide method, so that even small syndicates and lone prospectors could try their hand at treating old tailings. The result was an even broader uptake of cyanide across the Australian goldfields in the early 20th century.

Reprocessing Old Tailings: Australia’s Second Gold Rush

Perhaps the most dramatic impact of the cyanide revolution was the rush to reprocess old tailings dumps – a true second gold rush that swept across Australian mining districts around the turn of the century. Virtually overnight, those dusty heaps of “worthless” sand and slime acquired new value. Companies and opportunistic entrepreneurs began leasing or buying abandoned treatment sites just to run the tailings through cyanide. In Victoria, where mining had been in decline since the 1870s, this trend was especially pronounced. After about 1900, cyaniding became wildly popular in Victoria for re-treating tailings from earlier quartz mining. Small cyanide plants popped up near historic mine sites in Ballarat, Bendigo, Maldon, and elsewhere – often nothing more complex than a few large wooden or concrete vats, some pumps, and a precipitation system. These operations would collect the old tailings (sometimes by the thousands of tons), mix them with water and cyanide in the vats, and let the chemical do its work. After a number of days, the solution draining from the vats would carry dissolved gold, ready to be turned into bullion. The leftover sand, now largely stripped of gold, could be discarded (often forming new “cyanide tailings” heaps, which are an environmental legacy we still see today.

The yield from reprocessing was astonishing. A 1900 report in Victoria stated that nearly 450,000 ounces of gold had already been obtained from treating pyritic tailings and concentrates by chemical means (chlorination and cyaniding) up to that date. Much of that was gold which had been left behind by earlier methods and was now recovered from mullock and tailings heaps. In some localities, miners joked that the “ground had been mined twice” – once by the original diggers and now again by the chemists. Historical newspapers describe how old dumps and refuse sands were reworked profitably. One 1939 Australian newspaper noted that “thousands of old dumps, mullock heaps, tailings, slurries, etc. are now being again put through” and that a considerable portion of the country’s gold output was coming from these old refuse heaps. This was decades after cyanide’s introduction, showing how enduring and extensive the tailings retreatment phenomenon became. In effect, cyanide leaching stretched out the gold boom, giving many old goldfields a new lease on life.

Examples of cyanide-fueled second rushes abound. In the Bendigo district of Victoria, many cyanide plants were built after 1901 to retreat the “sand dumps” from 19th-century battery sites. At Maldon (VIC), the Grand Junction company re-treated 500,000 tons of tailings between 1900 and 1914, recovering significant gold. In Western Australia, rich tailings from the 1890s were later cyanided in large central plants. Charters Towers (QLD) saw an early surge: after the Excelsior Mill’s success, at least four other cyanide works around Charters Towers were soon processing not only new ore but also old tailings from defunct mines, squeezing out gold that had been long ignored.

A particularly vivid case comes from the Croydon Goldfield in Queensland. In 1900, an enterprising mining agent named Frederick William Cuthbert purchased the accumulated tailings of the Golden Gate mine (No. 3 and 4 South blocks) for a tidy sum. A new cyanide treatment works was set up at Station Creek to process this material. The venture paid off: Cuthbert “profited handsomely” by 1902 from cyaniding those tailings. Essentially, he made money from someone else’s leftovers. Similarly, at many other mines, old tailings that had been stockpiled for years were now seen as brown gold – already mined and milled, just waiting for chemical extraction. This secondary gold rush extended into the 1910s and 1920s in some regions, especially as economic downturns or war reduced the appetite for high-risk new mining, making the reworking of proven residues attractive. By 1914, one could travel across the Victorian goldfields and see cyanide plants operating at sites that had been silent for decades prior – the hum of engines and the clank of pumps announcing that the miners had returned with new tricks.

The amount of gold recovered through this tailings reprocessing was not trivial. Besides the hundreds of thousands of ounces in Victoria noted above, consider that at Mount Morgan (QLD), the adoption of chlorination and later cyaniding helped that mine achieve peak annual outputs around 300,000 ounces in the 1890s, much of it from ore that would have been unworkable with amalgamation alone. Across Australia, many tonnes of gold that would have simply remained in the ground or in waste dumps were added to national production thanks to cyanide. This significantly prolonged the profitability of gold mining regions. Towns that might have become ghost towns after the initial rush found new life as cyanide plants kept employment going. Investors who missed the first gold rush now had a second chance by financing tailings treatment companies. In essence, cyanidation didn’t just improve recoveries – it expanded the very definition of what was considered “ore” and what constituted a gold strike.

Lasting Transformation of Australian Goldfields

The introduction of cyanide changed Australian gold mining forever. Technologically, it marked the shift from a mechanical era (dominated by hammers, pans, and mercury) to a chemical era of mining. Gold extraction became a scientific endeavor as much as a manual one. The legacy is seen in the efficiency statistics: Before cyanide, even the best mines left a lot of gold behind; after cyanide, recovery rates routinely climbed into the 90+% range. Economically, cyanide extended the life of mines and allowed lower-grade deposits to be mined profitably for the first time. Districts like Kalgoorlie, which contained vast low-grade resources, could never have yielded as much gold as they did without cyanide leaching technology. For regions like Victoria that were past their peak by 1890, cyanide sparked essentially a renaissance – a wave of renewed mining activity that added significantly to Australia’s gold output in the early 20th century.

From a mining operations perspective, the cyanide process permanently altered how gold mining was done in Australia (and globally). By the 1910s, virtually every major gold mine had a cyanide plant as part of its operation. It became standard practice to finely grind the ore, extract what gold you could by gravity and mercury, then cyanide the remainder – a total process that left little gold behind. Many mines even reconfigured their workflow to optimize cyanidation, for example by installing tube mills and ball mills to achieve the fine slurry needed for best cyanide action. The Merrill–Crowe zinc precipitation method and later the activated carbon absorption (CIP/CIL) methods in the 20th century were refinements of the basic cyanide process, but the core idea remains the same. In fact, cyanide leaching is still the dominant gold extraction method worldwide over 130 years later. Modern mines in Western Australia, for instance, essentially use an updated version of the MacArthur-Forrest process, testifying to how impactful that 1887 discovery was.

Cyanide’s introduction also had broader implications. It encouraged the professionalization of metallurgy in mining – the chemist and the engineer became as important as the miner and the blacksmith on site. The success of cyanide in gold prompted its use for other metals and in other countries, but gold in Australia was one of the early showcases of its transformative power. There were, of course, environmental and safety downsides: both mercury and cyanide left a legacy of contamination (mercury in tailings, cyanide in residual wastes), and handling cyanide required caution to avoid deadly accidents. Over time, safety practices were developed, and miners learned to manage the risks, knowing that the rewards were too great to ignore. Cyanide turned out to be a double-edged sword – dangerous, yet invaluable.

In summary, the advent of cyanide processing in the 1890s was a turning point that redefined gold mining in Australia. It unlocked enormous value from previously unworkable ore, fueling a resurgence of gold production across the country. It made mining operations far more efficient and profitable, setting new standards for what yields were possible. Towns got a second chance, miners found new employment reworking old ground, and Australia’s overall gold output surged in the years around 1900 thanks to this innovation. The cyanide process didn’t just improve gold recovery – it fundamentally changed the narrative of Australian gold mining from one of dwindling returns to renewed prosperity. Whenever we look at an old Australian gold town that prospered into the 20th century, or modern mines still pulling gold from low-grade ore, we see the permanent mark of the cyanide revolution. A toxic compound, ironically, became the elixir of life for the gold mining industry – truly changing it forever and ensuring that the story of Australia’s gold rushes did not end in the nineteenth century, but continued into a new chemical age.