Gold became highly concentrated in California, United States as the result of global forces operating over hundreds of millions of years. Volcanoes, tectonic plates and erosion all combined to concentrate billions of dollars' worth of gold in the mountains of California. During the California Gold Rush, gold-seekers known as "Forty-Niners" retrieved this gold, at first using simple techniques, and then developing more sophisticated techniques, which spread around the world.
Geologic evidence indicates that over a span of at least 400 million years, gold that had been widely dispersed in the Earth's crust became more concentrated by geologic actions into the gold-bearing regions of California. Only gold that is concentrated can be economically recovered. Some 400 million years ago, rocks that would be accreted onto western North America to build California lay at the bottom of a large sea. Subsea volcanoes deposited lava and minerals (including gold) onto the sea floor; sometimes enough that islands were created. [1] Between 400 million and 200 million years ago, geologic movement forced the sea floor and these volcanic islands and deposits eastwards, colliding with the North American plate, which was moving westwards. [2]
Beginning about 200 million years ago, tectonic pressure forced the sea floor beneath the American continental mass. [3] As it sank, or subducted, beneath the western margin of the North American plate portions of the sea floor and overlying continental crust heated and melted, producing large molten masses (magma). Being lighter and hotter than the ancient continental crust above it, this magma forced its way upward, cooling as it rose [4] to become the granite rock found throughout the Sierra Nevada and other mountains in California today. [5] As the hot magma cooled, solidified, and came in contact with water, minerals with similar melting temperatures tended to concentrate together. [5] As the magma solidified, gold became concentrated within hydrous silica solutions and was deposited within veins of quartz. [4] [6]
As the Sierra Nevada and other mountains in California were forced upwards by the actions of tectonic plates, the solidified minerals and rocks were raised to the surface and subjected to erosion. [7] The surrounding rock then weathered and crumbled, and the exposed gold and other materials were carried downstream by water. Because gold is denser than almost all other minerals, this process further concentrated the gold as it sank, and pockets of gold gathered in quiet gravel beds along the sides of old rivers and streams. [8]
The California mountains rose and shifted several times within the last fifty million years, and each time, old streambeds moved and were dried out, leaving the deposits of gold resting within the ancient gravel beds where the gold had been collecting. [9] Newer rivers and streams then developed, and some of these cut through the old channels, carrying the gold into still larger concentrations. [9]
The Forty-Niners of the California Gold Rush first focused their efforts on these deposits of gold, which had been gathered in the gravel beds by hundreds of millions of years of geologic action.
Because the gold in the California gravel beds was so richly concentrated, the early forty-niners simply panned for gold in California's rivers and streams, a form of placer mining. [10] [11] However, panning cannot take place on a large scale, and industrious miners and groups of miners graduated to placer mining "cradles" and "rockers" or "long-toms" [12] to process larger volumes of gravel. [13] Miners would also engage in "coyoteing". [14] This method involved digging a shaft 6 to 13 meters (20 to 43 ft) deep into placer deposits along a stream. Tunnels were then dug in all directions to reach the richest veins of pay dirt.
In the most complex placer mining, groups of prospectors would divert the water from an entire river into a sluice alongside the river, and then dig for gold in the newly exposed river bottom. [15] Modern estimates by the U.S. Geological Survey are that some 12 million ounces [16] (370 t) of gold were removed in the first five years of the Gold Rush (worth over US$16 billion at December 2010 prices). [17]
In the next stage, by 1853, hydraulic mining was used on ancient gold-bearing gravel beds on hillsides and bluffs in the goldfields. [18] In a modern style of hydraulic mining first developed in California, a high-pressure hose directed a powerful stream or jet of water at gold-bearing gravel beds. [19] The loosened gravel and gold would then pass over sluices, with the gold settling to the bottom where it was collected. By the mid-1880s, it is estimated that 11 million ounces (340 t) of gold (worth approximately US$15 billion at December 2010 prices) had been recovered by "hydraulicking". [17] This style of hydraulic mining later spread around the world.
A byproduct of these extraction methods was that large amounts of gravel, silt, heavy metals, and other pollutants went into streams and rivers. [20] As of 1999 [update] many areas still bear the scars of hydraulic mining, since the resulting exposed earth and downstream gravel deposits do not support plant life. [21]
After the Gold Rush had concluded, gold recovery operations continued. The final stage to recover loose gold was to prospect for gold that had slowly washed down into the flat river bottoms and sandbars of California's Central Valley and other gold-bearing areas of California (such as Scott Valley in Siskiyou County). By the late 1890s, dredging technology (also invented in California) had become economical, [22] and it is estimated that more than 20 million ounces (620 t) were recovered by dredging (worth approximately US$28 billion at December 2010 prices). [17]
Both during the Gold Rush and in the decades that followed, gold-seekers also engaged in "hard-rock" mining, that is, extracting the gold directly from the rock that contained it (typically quartz), usually by digging and blasting to follow and remove veins of the gold-bearing quartz. [23] By 1851, quartz mining had become the major industry of Coloma. [24] Once the gold-bearing rocks were brought to surface, the rocks were crushed and the gold separated, either using separation in water, using its density difference from quartz sand, or by washing the sand over copper plates coated with mercury (with which gold forms an amalgam). Loss of mercury in the amalgamation process was a source of environmental contamination. [25] Eventually, hard-rock mining wound up becoming the single largest source of gold produced in the Gold Country. [17] [26] The total production of gold in California from then until now is estimated at 118 million ounces (3700 t). [27]
There were decades of minor earthquakes, more than at any other time in the historical record for Northern California, before the 1906 San Francisco earthquake. Previously interpreted as precursory activity to the 1906 earthquake, they have been found to have a strong seasonal pattern and due to large seasonal sediment loads in coastal bays that overlie faults as a result of mining of gold inland. [28]
The California Gold Rush (1848–1855) was a gold rush that began on January 24, 1848, when gold was found by James W. Marshall at Sutter's Mill in Coloma, California. The news of gold brought approximately 300,000 people to California from the rest of the United States and abroad. The sudden influx of gold into the money supply reinvigorated the American economy; the sudden population increase allowed California to go rapidly to statehood in the Compromise of 1850. The Gold Rush had severe effects on Native Californians and accelerated the Native American population's decline from disease, starvation and the California genocide.
In geology, a placer deposit or placer is an accumulation of valuable minerals formed by gravity separation from a specific source rock during sedimentary processes. The name is from the Spanish word placer, meaning "alluvial sand". Placer mining is an important source of gold, and was the main technique used in the early years of many gold rushes, including the California Gold Rush. Types of placer deposits include alluvium, eluvium, beach placers, aeolian placers and paleo-placers.
Placer mining is the mining of stream bed (alluvial) deposits for minerals. This may be done by open-pit or by various surface excavating equipment or tunneling equipment.
Hydraulic mining is a form of mining that uses high-pressure jets of water to dislodge rock material or move sediment. In the placer mining of gold or tin, the resulting water-sediment slurry is directed through sluice boxes to remove the gold. It is also used in mining kaolin and coal.
The Gold Country is a historic region in the northern portion of the U.S. state of California, that is primarily on the western slope of the Sierra Nevada. It is famed for the mineral deposits and gold mines that attracted waves of immigrants, known as the 49ers, during the 1849 California Gold Rush.
The Otago Gold Rush was a gold rush that occurred during the 1860s in Central Otago, New Zealand. This was the country's biggest gold strike, and led to a rapid influx of foreign miners to the area – many of them veterans of other hunts for the precious metal in California and Victoria, Australia.
Gold mining is the extraction of gold by mining.
The Kiwalik River is a stream on the Seward Peninsula in the U.S. state of Alaska. The headwaters of the river originate in the eastern portion of the peninsula, around Granite Mountain. The river flows north to its mouth at Kiwalik Lagoon, Chukchi Sea. The start of the 20th century mining town of Candle is found on its western bank at the confluence of Candle Creek. The ore minerals and materials found in the river basin are galena, gold, pyrite, scheelite, silver and sphalerite, and the primary commodities are tungsten, lead and zinc.
In the United States, gold mining has taken place continually since the discovery of gold at the Reed farm in North Carolina in 1799. The first documented occurrence of gold was in Virginia in 1782. Some minor gold production took place in North Carolina as early as 1793, but created no excitement. The discovery on the Reed farm in 1799 which was identified as gold in 1802 and subsequently mined marked the first commercial production.
Silver mining in the United States began on a major scale with the discovery of the Comstock Lode in Nevada in 1858. The industry suffered greatly from the demonetization of silver in 1873 by the Coinage Act of 1873, known pejoratively as the "Crime of 73", but silver mining continues today.
Gold mining in Colorado, a state of the United States, has been an industry since 1858. It also played a key role in the establishment of the state of Colorado.
Silver mining in Nevada, a state of the United States, began in 1858 with the discovery of the Comstock Lode, the first major silver-mining district in the United States. Nevada calls itself the "Silver State." Nevada is the nation's second-largest producer of silver, after Alaska. In 2014 Nevada produced 10.93 million troy ounces of silver, of which 6.74 million ounces were as a byproduct of the mining of gold. The largest byproducers were the Hycroft Mine, the Phoenix Mine, the Midas Mine and Round Mountain.
Gold mining in Alaska, a state of the United States, has been a major industry and impetus for exploration and settlement since a few years after the United States acquired the territory in 1867 from the Russian Empire. Russian explorers discovered placer gold in the Kenai River in 1848, but no gold was produced. Gold mining started in 1870 from placers southeast of Juneau, Alaska.
The Leadville mining district, located in the Colorado Mineral Belt, was the most productive silver-mining district in the state of Colorado and hosts one of the largest lead-zinc-silver deposits in the world. Oro City, an early Colorado gold placer mining town located about a mile east of Leadville in California Gulch, was the location to one of the richest placer gold strikes in Colorado, with estimated gold production of 120,000–150,000 ozt, worth $2.5 to $3 million at the then-price of $20.67 per troy ounce.
Gold was discovered in the Yentna-Cache Creek Mining District in the U.S. state of Alaska of the upper Susitna River Valley in 1898, soon followed by claim staking. Placer mining was reported in the Cache Creek drainage of the Dutch Hills by 1906. Quaternary glaciofluvial deposits, alluvial deposits, and Cenozoic conglomeratic white quartz-breccia units have been mined in the Dutch Hills. About 200,000 oz of gold has been produced from these placer deposits. By 1927, a road from Talkeetna was constructed into the mining area, known today as The Petersville Road. The mining camp of Petersville, Alaska served as the area Post Office for several years in the late 1920s and early 1930s. Two areas have been set aside for recreational gold mining, the North and South units of the Petersville State Recreation Mining Areas. Many smaller one-man and family placer mining operations continue today.
Snow Point was a historic mining town in Nevada County, California on the San Juan Ridge about 2 miles east of Moore's Flat and about 6 miles west of Graniteville. It was located at an elevation of 4321 ft just off present day German Bar Road about midway between that road's intersections with present day Moore's Flat Road and Hagerty Road.
Cherokee is a former gold mining community in Nevada County, California. As explained below, it has also been known as Patterson, Melrose and Tyler. It is located on the San Juan Ridge about 4 miles east of North San Juan. Its elevation is 2,516 ft (767 m) above sea level.
Confederate Gulch is a steeply incised gulch or valley on the west-facing slopes of the Big Belt Mountains in the U.S. state of Montana. Its small stream drains westward into Canyon Ferry Lake, on the upper Missouri River near present-day Townsend, Montana. In 1864, Confederate soldiers on parole during the American Civil War made a minor gold discovery in the gulch, but the discovery of the sensationally rich Montana Bar the following year—one of the richest placer strikes per acre ever made—led to other rich gold strikes up and down the gulch, and touched off a frantic boom period of placer gold mining in the area that extended through 1869. From 1866 to 1869, the gulch equaled or outstripped all other mining camps in the Montana Territory in gold production, producing an estimated $19–30 million worth of gold. For a time, Confederate Gulch was the largest community in Montana. In 1866, Montana had a total population of 28,000, and of these, about 10,000 (35%) were working in Confederate Gulch.
The Silver Bow Basin, often written as Silverbow Basin, is a valley located 2.4 miles (3.9 km) northeast of Juneau, Alaska, USA. It is situated on Gold Creek in an area north of Icy Gulch, and approximately 1.5 miles (2.4 km) north of Gastineau Peak. A trail from Juneau leads directly to the mountainside. The basin was the site of the earliest gold discovery in the Juneau area, leading to the establishment of the town called Juneau.
The Juneau gold belt is located in the southeastern portion of the U.S. state of Alaska. This belt is approximately 100 miles (160 km) in length, north/northwest-trending, and extends from Berners Bay southeastward to Windham Bay, 60 miles (97 km) southeast of Juneau, and includes Douglas Island. The belt contains over 200 gold-quartz-vein deposits with production nearing 7,000,000 ounces (200,000,000 g) of gold. More than three-quarters of Alaska's lode gold was mined from the Juneau gold belt.
{{cite book}}: |author= has generic name (help)CS1 maint: multiple names: authors list (link)