Hydraulic mining is a form ofmining that uses high-pressure jets ofwater to dislodge rock material or move sediment.[1] In theplacer mining ofgold ortin, the resulting water-sediment slurry is directed throughsluice boxes to remove the gold or tin. It is also used in miningkaolin andcoal.
Hydraulic mining developed from ancient Roman techniques that used water to excavate soft underground deposits. Its modern form, using pressurized waterjets produced by anozzle called a "monitor", came about in the 1850s during theCalifornia Gold Rush in the United States. Though successful in extracting gold-rich minerals, the widespread use of the process resulted in extensiveenvironmental damage, such as increased flooding anderosion, andsediment blocking waterways and covering farm fields. These problems led to its legal regulation. Hydraulic mining has been used in various forms around the world.
Hydraulic mining had its precursor in the practice of ground sluicing, a development of which is also known as "hushing", in which surface streams of water were diverted so as to erode gold-bearing gravels. This technique was developed in the first centuries BC and AD byRoman miners to erode awayalluvium.[2] The Romans used ground sluicing to remove overburden and the gold-bearing debris inLas Médulas of Spain, andDolaucothi inGreat Britain. The method was also used in ElizabethanEngland andWales (and rarely,Scotland) for developinglead,tin andcopper mines.[citation needed]
Water was used on a large scale by Roman engineers in the first centuries BC and AD when theRoman Empire was expanding rapidly in Europe. Using a process later known as hushing, the Romans stored a large volume of water in a reservoir immediately above the area to be mined; the water was then quickly released. The resulting wave of water removed overburden and exposed bedrock. Gold veins in the bedrock were then worked using a number of techniques, and water power was used again to remove debris. The remains at Las Médulas and in surrounding areas showbadland scenery on a gigantic scale owing to hydraulicking of the rich alluvial gold deposits.
Las Médulas is now aUNESCOWorld Heritage Site. The site shows the remains of at least seven largeaqueducts of up to 30 miles (48 km) in length feeding large supplies of water into the site. Thegold-mining operations were described in vivid terms byPliny the Elder in hisNatural History published in the first century AD. Pliny was aprocurator inHispania Terraconensis in the 70s AD and witnessed the operations himself. The use of hushing has been confirmed by field survey andarchaeology atDolaucothi inSouth Wales, the only known Roman gold mine inGreat Britain.[citation needed]
The modern form of hydraulic mining, using jets of water directed under very high pressure through hoses and nozzles at gold-bearing upland paleogravels, was first used by Edward Matteson nearNevada City,California in 1853 during theCalifornia Gold Rush.[3] Matteson used canvas hose which was later replaced withcrinoline hose by the 1860s.[4] In California, hydraulic mining often brought water from higher locations for long distances to holding ponds several hundred feet above the area to be mined. California hydraulic mining exploited gravel deposits, making it a form ofplacer mining.
Early placer miners in California discovered that the more gravel they could process, the more gold they were likely to find. Instead of working with pans, sluice boxes, long toms, and rockers, miners collaborated to find ways to process larger quantities of gravel more rapidly. Hydraulic mining became the largest-scale, and most devastating, form of placer mining. Water was redirected into an ever-narrowing channel, through a large canvas hose, and out through a giant ironnozzle, called a "monitor". The extremely high pressure stream was used to wash entire hillsides through enormous sluices.
By the early 1860s, while hydraulic mining was at its height, small-scale placer mining had largely exhausted the rich surface placers, and themining industry turned to hard rock (calledquartz mining in California) or hydraulic mining, which required larger organizations and much more capital. By the mid-1880s, it is estimated that 11 million ounces of gold (worth approximately US$7.5 billion at mid-2006 prices) had been recovered by hydraulic mining.
While generating millions of dollars in tax revenues for the state and supporting a large population of miners in the mountains, hydraulic mining had a devastating effect onripariannatural environment andagricultural systems in California. Millions of tons of earth and water were delivered to mountain streams that fed rivers flowing into theSacramento Valley. Once the rivers reached the relatively flat valley, the water slowed, the rivers widened, and the sediment was deposited in thefloodplains and river beds causing them to rise, shift to new channels, and overflow their banks, causing majorflooding, especially during the spring melt.
Cities and towns in theSacramento Valley experienced an increasing number of devastatingfloods, while the risingriverbeds made navigation on the rivers increasingly difficult. Perhaps no other city experienced the boon and the bane ofgold mining as much asMarysville. Situated at the confluence of theYuba andFeather rivers, Marysville was the final "jumping off" point for miners heading to the northern foothills to seek their fortune.Steamboats fromSan Francisco, carrying miners and supplies, navigated up theSacramento River, then the Feather River toMarysville where they would unload their passengers and cargo.
Marysville eventually constructed a complexlevee system to protect the city from floods and sediment. Hydraulic mining greatly exacerbated the problem of flooding in Marysville and shoaled the waters of the Feather River so severely that few steamboats could navigate from Sacramento to the Marysville docks. The sediment left by such efforts were reprocessed bymining dredges at theYuba Goldfields, located near Marysville.
.JPG)
The spectacular eroded landscape left at the site of hydraulic mining can be viewed atMalakoff Diggins State Historic Park inNevada County, California.[5]
TheSan Francisco Bay became an outlet for polluting byproducts during the Gold Rush. Hydraulic mining left a trail of toxic waste, called "slickens," that flowed from mine sites in theSierras through theSacramento River and into the San Francisco Bay.[6] The slickens would contain harmful metals such asmercury. During this period, the industrial mining industry released 1.5 billion yards of toxic slickens into the Sacramento River. As the slickens traveled throughCalifornia's water arteries, it deposited its toxins into local ecosystems and waterways.[7]
Nearby farmland became contaminated, which led to political pushback against the use of hydraulic mining. The slickens flowed through the Sacramento River before depositing itself into the San Francisco Bay. Currently, the San Francisco Bay remains dangerously contaminated with mercury. Estimates suggest that it will be another century before the Bay naturally removes the mercury from its system.[7]
Vast areas of farmland in the Sacramento Valley were deeply buried by the mining sediment. Frequently devastated by flood waters, farmers demanded an end to hydraulic mining. In the most renowned legal fight of farmers against miners, the farmers sued the hydraulic mining operations and the landmark case ofWoodruff v. North Bloomfield Mining and Gravel Company made its way to theUnited States District Court in San Francisco where JudgeLorenzo Sawyer decided in favor of the farmers and limited hydraulic mining on January 7, 1884, declaring that hydraulic mining was "a public and private nuisance" and enjoining its operation in areas tributary to navigable streams and rivers.[8]
Hydraulic mining on a much smaller scale was recommenced after 1893 when theUnited States Congress passed theCamminetti Act which allowed licensed mining operations if sedimentretention structures were constructed. This led to a number of operations above sediment catching brush dams and logcrib dams. Most of the water-delivery hydraulic mining infrastructure had been destroyed by an 1891 flood, so this later stage of mining was carried on at a much smaller scale in California.
Although often associated with California due to its adoption and widespread use there, the technology was exported widely, toOregon (Jacksonville in 1856),Colorado (Clear Creek,Central City andBreckenridge in 1860),Montana (Bannack in 1865),Arizona (Lynx Creek in 1868),Idaho (Idaho City in 1863), South Dakota (Deadwood in 1876),Alaska (Fairbanks in 1920),British Columbia (Canada), and overseas. It was used extensively inDahlonega, Georgia and continues to be used in developing nations, often with devastating environmental consequences. The devastation caused by this method of mining causedEdwin Carter, the "Log Cabin Naturalist", to switch from mining to collecting wildlife specimens from 1875–1900 inBreckenridge, Colorado, US.
Hydraulic mining was used during theAustralian gold rushes where it was called hydraulicsluicing. One notable location was at theOriental Claims nearOmeo inVictoria where it was used between the 1850s and early 1900s, with abundant evidence of the damage still being visible today.[9]
Hydraulic mining was used extensively in theCentral Otago gold rush that took place in the 1860s in theSouth Island ofNew Zealand, where it was also known assluicing.
Starting in the 1870s, hydraulic mining became a mainstay of alluvialtin mining on theMalay Peninsula.[10]Hydraulicking was formerly used inPolk County, Florida to minephosphate rock.[11]
In addition to its use in true mining, hydraulic mining can be used as anexcavation technique, principally to demolish hills. For example, theDenny Regrade inSeattle was largely accomplished by hydraulic mining.[12]
Hydraulic mining is the principal way thatkaolinite clay is mined inCornwall andDevon, in South-West England.
Egypt used hydraulic mining methods tobreach theBar Lev Line sand wall at the Suez Canal, inOperation Badr (1973) which opened theYom Kippur War.
On the South African Rand gold fields, a gold surface tailings re-treatment facility calledEast Rand Gold and Uranium Company (ERGO) has been in operation since 1977.[13] The facility uses hydraulic monitors to create slurry from older (and consequently richer) tailings sites and pumps it long distances to a concentration plant.
The facility processes nearly two million tons of tailings each month at a processing cost of below US$3.00/t (2013). Gold is recovered at a rate of only 0.20 g/t, but the low yield is compensated for by the extremely low cost of processing, with no risky or expensive mining or milling required for recovery.[14]
The resulting slimes are pumped further away from the built-up areas permitting the economic development of land close to commercially valuable areas and previously covered by the tailings. The historic yellow-coloured mine dumps around Johannesburg are now almost a rarity, seen only in older photographs.
Uranium andpyrite (forsulfuric acid production) are also available for recovery from the process stream as co-products under suitable economic conditions.
High-pressure water jets have also been used in the underground mining ofcoal, to break up the coal seam and wash the resulting coal slurry toward a collection point.[1] The high-pressure water nozzle is referred to as the 'hydro monitor'.[15]
{{cite web}}: CS1 maint: multiple names: authors list (link)| National | |
|---|---|
| Other | |
