Hydraulic mining

• 1. Introduction

  ›

  Hydraulic mining shoots high-pressure jets of water at rock and sediment to tear minerals loose. Near Nevada City, California, in 1853, a man named Edward Matteson aimed such a jet at gold-bearing upland gravels and changed how people chased a fortune. The water washed entire hillsides through enormous sluices. It worked. By the mid-1880s, an estimated 11 million ounces of gold had been pulled from the ground this way.

  But the same force that exposed the gold buried farms, choked rivers, and poisoned a bay that will not recover for another century. How did a technique born in ancient Rome end up on trial in a San Francisco courtroom? Who fought to stop it, and who kept it alive? And why is a version of it still pumping today, from the South African Rand to the coal seams underground? The answers run from a Roman procurator's notebook to a 1973 act of war on the Suez Canal.

• 2. Roman Origins

  ›

  Pliny the Elder served as a procurator in Hispania Terraconensis in the 70s AD, and he watched Roman miners tear gold from the earth with water. He described the operations in vivid terms in his Natural History, published in the first century AD. The technique he saw was a precursor called ground sluicing, in which diverted surface streams eroded gold-bearing gravels.

  Las Médulas in Spain shows what that force could do. Roman engineers stored a large volume of water in a reservoir directly above the area to be mined, then released it in a sudden wave. The water stripped away overburden and exposed the bedrock, where gold veins were worked by hand. This release method became known as hushing. At least seven large aqueducts, some up to 30 miles long, fed water into Las Médulas, and the badland scenery left behind survives on a gigantic scale.

  Ground sluicing reached beyond Spain. Roman miners used it at Dolaucothi in South Wales, the only known Roman gold mine in Great Britain, where field survey and archaeology have confirmed the use of hushing. Centuries later the same approach turned up in Elizabethan England and Wales, and rarely in Scotland, to develop lead, tin, and copper mines. Las Médulas is now a UNESCO World Heritage Site, its scars preserved as the record of an industry that ran nearly two thousand years before anyone reached California.

• 3. The California Surge

  ›

  Edward Matteson used canvas hose to carry his pressurized water, and by the 1860s that canvas had been replaced with crinoline hose. The setup grew more ambitious from there. Water was brought from higher locations across long distances into holding ponds, sometimes several hundred feet above the ground being mined. From those ponds it dropped into an ever-narrowing channel, through a large canvas hose, and out of a giant iron nozzle called a monitor.

  Early placer miners in California had learned a simple lesson: the more gravel they could process, the more gold they were likely to find. Pans, sluice boxes, long toms, and rockers handled gravel one slow batch at a time. Miners collaborated to process far larger quantities far faster, and hydraulic mining became the answer, the largest-scale and most devastating form of placer mining.

  By the early 1860s the rich surface placers were largely exhausted, and the work changed character. The industry turned to hard rock, called quartz mining in California, or to hydraulic mining, both of which demanded larger organizations and much more capital. The 11 million ounces recovered by the mid-1880s were worth roughly 7.5 billion US dollars at mid-2006 prices, a haul that bankrolled the chaos coming downstream.

• 4. Rivers And Ruin

  ›

  Millions of tons of earth and water poured into mountain streams that fed the rivers running down into the Sacramento Valley. Where the valley flattened, the water slowed and the rivers widened. Sediment settled into floodplains and riverbeds, lifting them, pushing the rivers into new channels, and sending them over their banks during the spring melt.

  Marysville felt this more sharply than almost anywhere. Sitting at the confluence of the Yuba and Feather rivers, the town had been the final jumping-off point for miners headed into the northern foothills. Steamboats came up from San Francisco along the Sacramento River and then the Feather to unload passengers and cargo at its docks. Hydraulic mining shoaled the Feather so severely that few steamboats could still reach those docks from Sacramento, and the city built a complex levee system to hold back the floods and sediment.

  The debris carried poison as well as silt. Hydraulic mining left a trail of toxic waste called slickens, laced with harmful metals including mercury, that ran from the Sierras through the Sacramento River and into San Francisco Bay. The industry released 1.5 billion yards of slickens into the river during this period. The bay remains dangerously contaminated with mercury today, and estimates suggest it will take another century to clear naturally. The eroded ground left behind can still be seen at Malakoff Diggins State Historic Park in Nevada County.

• 5. Farmers Versus Miners

  ›

  Vast stretches of Sacramento Valley farmland lay deeply buried under mining sediment, and the farmers who worked that land had had enough. Flooded again and again, they demanded an end to hydraulic mining and took the operators to court. Their fight became the most renowned legal battle of farmers against miners.

  The landmark case of Woodruff v. North Bloomfield Mining and Gravel Company reached the United States District Court in San Francisco. On the 7th of January 1884, Judge Lorenzo Sawyer ruled for the farmers. He declared hydraulic mining a public and private nuisance and enjoined its operation in areas tributary to navigable streams and rivers.

  The industry was not finished. In 1893 the United States Congress passed the Camminetti Act, which permitted licensed mining where sediment retention structures were built, leading to operations above brush dams and log crib dams. By then an 1891 flood had destroyed most of the water-delivery infrastructure, so this revived stage ran at a much smaller scale. The sediment already deposited near Marysville was later reprocessed by mining dredges at the Yuba Goldfields.

• 6. Spreading Outward

  ›

  Jacksonville, Oregon, took up the technology in 1856, the first of many sites far from California. The method reached Clear Creek, Central City, and Breckenridge in Colorado in 1860, Idaho City in 1863, Bannack in Montana in 1865, Lynx Creek in Arizona in 1868, Deadwood in South Dakota in 1876, and Fairbanks in Alaska in 1920. It also moved into British Columbia, was used extensively in Dahlonega, Georgia, and continues in developing nations, often with devastating environmental consequences.

  The destruction changed at least one life directly. Edwin Carter, known as the Log Cabin Naturalist, gave up mining to collect wildlife specimens from 1875 to 1900 in Breckenridge, Colorado, after seeing what the method did to the land.

  The technique crossed oceans under different names. In the Australian gold rushes it was called hydraulic sluicing, and at the Oriental Claims near Omeo in Victoria it ran from the 1850s into the early 1900s, with the damage still visible. New Zealand miners called it sluicing during the Central Otago gold rush of the 1860s on the South Island. From the 1870s it became a mainstay of alluvial tin mining on the Malay Peninsula, and it was once used in Polk County, Florida, to mine phosphate rock.

• 7. Modern Monitors

  ›

  The Denny Regrade in Seattle was largely accomplished by hydraulic mining, used not to find minerals but to demolish hills as an excavation technique. The same force that washed away gold-bearing gravels could reshape a cityscape.

  Kaolinite clay is the principal target in Cornwall and Devon, in South-West England, where hydraulic mining remains the main way it is extracted. The technique also turned up in an act of war. In Operation Badr in 1973, which opened the Yom Kippur War, Egypt used hydraulic mining methods to breach the Bar Lev Line sand wall at the Suez Canal.

  On the South African Rand gold fields, the East Rand Gold and Uranium Company, known as ERGO, has run a surface tailings re-treatment facility since 1977. Hydraulic monitors turn older and richer tailings into slurry, which is pumped long distances to a concentration plant. The facility handles nearly two million tons of tailings each month at a processing cost below 3.00 US dollars per ton as of 2013. Gold is recovered at only 0.20 grams per ton, but the extremely low cost makes the thin yield worthwhile, with no risky or expensive milling required. Uranium and pyrite for sulfuric acid come off the same stream as co-products, and the old yellow mine dumps around Johannesburg have nearly vanished, freeing valuable land. Underground, the same idea persists: a hydro monitor blasts coal seams apart and washes the slurry toward collection, carrying a Roman idea into the working faces of modern mines.