Hydraulic mining
Pliny the Elder watched Roman miners work in Hispania Terraconensis during the 70s AD. He described the operations in his Natural History, published in the first century AD. These workers used a technique called hushing to erode gold-bearing gravels. They stored massive volumes of water in reservoirs above the mining sites. When released, the water wave removed overburden and exposed bedrock veins. The remains at Las Médulas show badland scenery on a gigantic scale today. At least seven large aqueducts fed supplies into the site. Some aqueducts reached lengths of up to ten miles. Archaeologists confirmed the use of hushing at Dolaucothi in South Wales. This was the only known Roman gold mine in Great Britain.
Edward Matteson used canvas hose near Nevada City, California in 1853. He directed high-pressure jets at gold-bearing upland paleogravels. By the 1860s, crinoline hose replaced the earlier canvas material. Miners built holding ponds several hundred feet above the areas they mined. A giant iron nozzle called a monitor washed entire hillsides through enormous sluices. Small-scale placer mining had largely exhausted rich surface placers by the early 1860s. The industry turned to hydraulic mining which required larger organizations and much more capital. By the mid-1880s, an estimated 11 million ounces of gold were recovered. These ounces were worth approximately US$7.5 billion at mid-2006 prices. The process became the largest-scale form of placer mining ever attempted.
Millions of tons of earth flowed into mountain streams feeding rivers toward the Sacramento Valley. Water slowed as it reached the flat valley floor. Rivers widened and sediment deposited itself in floodplains and river beds. Riverbeds rose and shifted to new channels, causing major flooding during spring melt. Marysville sat at the confluence of the Yuba and Feather rivers. Steamboats from San Francisco navigated up the Sacramento River then the Feather River to Marysville docks. Hydraulic mining shoaled the waters of the Feather River so severely that few steamboats could navigate. The industrial mining industry released 1.5 billion yards of toxic slickens into the Sacramento River. Slickens contained harmful metals such as mercury. The San Francisco Bay remains dangerously contaminated with mercury today. Estimates suggest it will be another century before the Bay naturally removes the mercury from its system.
Vast areas of farmland in the Sacramento Valley were deeply buried by mining sediment. Farmers demanded an end to hydraulic mining operations. The landmark case Woodruff v. North Bloomfield Mining and Gravel Company went to the United States District Court in San Francisco. Judge Lorenzo Sawyer decided in favor of the farmers on the 7th of January 1884. He declared that hydraulic mining was a public and private nuisance. The ruling enjoined operation in areas tributary to navigable streams and rivers. Hydraulic mining on a much smaller scale recommenced after 1893 when Congress passed the Camminetti Act. This act allowed licensed mining operations if sediment retention structures were constructed. Most water-delivery infrastructure had been destroyed by an 1891 flood. Later stage mining was carried on at a much smaller scale in California.
The technology spread widely to Oregon, Colorado, Montana, Arizona, Idaho, South Dakota, Alaska, British Columbia, and overseas. One notable location was the Oriental Claims near Omeo in Victoria, Australia. Miners used hydraulic sluicing there between the 1850s and early 1900s. Man-made cliffs up to 600 feet high remain visible throughout the area today. Extensive use occurred during the Central Otago gold rush in the 1860s in New Zealand. Starting in the 1870s, hydraulic mining became a mainstay of alluvial tin mining on the Malay Peninsula. Hydraulicking was formerly used in Polk County, Florida to mine phosphate rock. Edwin Carter switched from mining to collecting wildlife specimens from 1875, 1900 in Breckenridge, Colorado due to the devastation caused by this method.
East Rand Gold and Uranium Company has operated since 1977 on the South African Rand. The facility uses hydraulic monitors to create slurry from older tailings sites. It processes nearly two million tons of tailings each month at a cost below US$3.00 per ton. Gold is recovered at a rate of only 0.20 grams per ton. Low yield is compensated for by extremely low processing costs. No risky or expensive mining or milling is required for recovery. The resulting slimes are pumped further away from built-up areas. This permits economic development of land close to commercially valuable areas. Historic yellow-colored mine dumps around Johannesburg are now almost a rarity seen only in older photographs. Uranium and pyrite are also available for recovery as co-products under suitable economic conditions.
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Common questions
When did Pliny the Elder observe Roman miners using hydraulic techniques in Hispania Terraconensis?
Pliny the Elder watched Roman miners work in Hispania Terraconensis during the 70s AD. He described these operations in his Natural History, which was published in the first century AD.
What specific year did Judge Lorenzo Sawyer rule against hydraulic mining in Woodruff v. North Bloomfield Mining and Gravel Company?
Judge Lorenzo Sawyer decided in favor of the farmers on the 7th of January 1884. He declared that hydraulic mining was a public and private nuisance and enjoined operation in areas tributary to navigable streams and rivers.
How much gold was recovered by the mid-1880s from hydraulic mining operations in California?
By the mid-1880s, an estimated 11 million ounces of gold were recovered from hydraulic mining. These ounces were worth approximately US$7.5 billion at mid-2006 prices.
Where are the remains of Roman hushing operations visible today in Spain?
The remains at Las Médulas show badland scenery on a gigantic scale today. At least seven large aqueducts fed supplies into this site with some reaching lengths of up to ten miles.
Which modern facility uses hydraulic monitors to process tailings for gold recovery since 1977?
East Rand Gold and Uranium Company has operated since 1977 on the South African Rand. The facility processes nearly two million tons of tailings each month at a cost below US$3.00 per ton.