Summary of Gold Mining Techniques in
Western United States
1842 - 1996
The first tools used to mine gold were extremely simple, knives, small wooden hand tools, such as picks and shovels. Extraction of gold from ore bearing gravel without water was termed “dry washing.” It was a crude and inefficient, but also inexpensive. After pay dirt was dug, it was sun dried on a large canvas and then pulverized into dust. It was then thrown by the pan full into the air in order to allow the wind to blow away lighter elements and to let the heavier gold dust fall back into the pan. This was originally an old agricultural procedure of “winnowing” and was first used by miners near the Pueblo of Los Angeles in the San Feliciano Canyon in 1842.
When water was available it was used to work away the lighter dirt and fine gravel concentrating the heavier gold in the bottom of the metal pan or a wooden basket call a “batea.” Panning was slow and hard. A good miner could barely handle 100 pans in a ten hour day. Introduction of the rocker or cradle, the “long tom,” and sluice boxes made of wood and some flat iron were the next improvements.
The rocker is a crude gold concentrating machine that combines shaking motion of the pan with some features of the sluice. Riffles or obstructions are placed across the bottom to catch the heavy flakes of gold. Dirt and gravel are washed over the tops of the riffles. Using the rocker both gravel and water were introduced by hand. Using a sluice, the water flows by gravity, but gravel is shoveled by hand.
The sluice box consisted of three boards nailed together to form a flume. It had slats or riffles to catch the gold. A number of these units could be fitted together, end to end, to make a long series of sluice boxes and men stationed at intervals along the line could shovel gravel into the swiftly flowing water inside the box.
The long tom (brought here by miners from Georgia) was simply a trough of boards usually about twelve feet long by eight inches deep. The opening at the head was 12 to 15 inches wide and the entire trough increased in width until it was about two feet wide at the lower end. A piece of sheet iron with holes punched in it was placed so that the fine sand would fall into a sluice box below, while the larger rocks would pass on by. It increased production so a man could work more gravel (even poorer gravel) in a day as he could with a pan or even with a rocker.
Placer gold mining peaked about 1852.
By 1860, gravel that would pay to work by these methods was now hard to find and gold production declined. Seeking increased mining efficiency the use of water in motion was further exploited. Ground sluicing used a stream of water which was brought to the top of a bank of gravel and allowed to flow down over the face. It softened the gravel and with a little help from the miner, carried it along to a natural sluice prepared on the bedrock below. This increased the volume of gravel one man could work.
Additional volume was achieved by taking advantage of water to also do the work of clearing away the sediment which was call “booming” or “hushing.” A dam was built and water diverted through the area being mined; the water carried the lighter elements downstream leaving the gold bearing ore easily accessible to be worked with some of the original placer methods. This water diversion depended on stream volume and time of the year. The dam structure was usually built by a team of men.
These later methods required a steady stream of water and resulted in the construction of the miners’ ditch. Many ditch companies were organized prior to 1853 for the sole purpose of delivering water to the placer miners at a price set by what the traffic would bear. Miners themselves organized their own companies and cooperatives to supply their own needs. This competition resulted in litigation and violence.
With the advent of hydraulic mining, water companies became big business and started a large effort to pursue dams, lakes, reservoirs, canals, and pipelines to supply water to miles of ditches, tunnels, and flumes. In 1860, an estimated 5,000 miles of artificial water courses were developed. This figure increased to about 8,000 miles at the height of the hydraulic mining.
Hydraulic Mining 1853-1884
Great jets of water under high pressure using nozzles called “giants” were directed against the banks of gravel hundreds of feet in height. After proper ditches and gravity fed pipe lines had been installed, thousands of cubic yards of gravel could be washed without hand labor. The gold was recovered in riffle-sluices and quicksilver (mercury) was usually added to aid in its recovery. However, the debris deposited in streams by hydraulic miners became so environmentally objectionable to agricultural interests this method was stopped by legal injunction in 1884. The Malakoff Mine at North Bloomfield was one of the largest hydraulic mine areas and is now a State Park.
Drift Mining/Tunnel Mining/Pocket Mining
Mining of buried ancient river channels by means of shafts and adits, was started very soon after the outcrops of gravel were noticed on the hillside. Drift mining developed at about the same time as hydraulic mining; it did not suffer from the same restrictions. However, they were more expensive and used on richer gold bearing gravels. These methods resembled coal mining. Much of the gravel was found to be cemented and had to be milled or washed several times after laying in the open air to aid disintegration. Stamp mills with coarse screens worked well for milling cemented gravel. The use of tunnels to mine Table Mountain in Jamestown was intense over the placer mining years. The Humbug Mine was one of the most successful reaching the ancient river bed capped by lava flow. In Sonora, the Bonanza Mine was one of the largest pocket mines in the Southern Mines.
The dredging idea was originally simple, an endless chain of buckets bringing up mud and gravel from the river bottom and depositing it in sluice boxes aboard a boat. The fine material was separated from the coarse material by screens and the free gold caught by the use of quicksilver. Both the propelling and dredging machinery would be operated by steam. This simple idea began early in 1850s but did not reach a practical implementation till as late as 1897, when the single lift bucket elevation type system was floated in California on the Yuba River. Throughout the history of dredging in California the Oroville district has floated more dredges and seen more dredging companies than any other areas in California. By 1909, gold dredging had become big business and although there were a number of small one-dredge operators, the bulk of the land was now controlled mainly by three large companies.
Modern dredging techniques included dredges held in position by shore line and a huge spud, vertical column at the boats stern, with the ladder and bucket line operator well below the water level. Rocks and gravel drop from the end of the tailings stacker and the muddy runoff from the riffles is discharged from chutes on both sides of the boat. Gold dredges not only work on river bottoms, but also operate well inland, taking their own ponds with them, by the simple expedient of cutting from the front and filling in at the back.
In 1927, as an example after various acquisition/mergers the Capital Dredging Company was working four dredges on 2200 acres of land on the American River near Folsom. This company ended dredging operations in 1968. Another large company whose name was synonymous with California gold dredging was the Natomas Company, which operated along the American River in the Folsom area, almost to the city limits of Sacramento which closed down dredging in 1962. Aerial views of dredge tailings near Folsom look like the tracks of a giant earthworm i.e. mounds of lumpy tailings that follow the boats path.
Dredging was the chief method of gold mining in California from 1900 to the 1960s. It continued into the 1970s in the Yuba goldfields north of Sacramento. Dredged property once considered virtually destroyed is now being leveled and made suitable for industrial sites and housing.
Quartz Hard Rock Mining 1850s-2000 - Early Days
It began in 1849, rose quickly between 1850 and 1852, collapsed, rising again later in the next decade and eventually dominating the industry. The path to commercial viability was tortuous, filled with geological, technological, economic pitfalls taking many years to overcome. Successful early quartz mining was relatively simple because only the shallow deposits were worked. Before 1860s, California mines rarely reached levels below three hundred feet, the basic maximum depth of ground water. Above three hundred feet gold deposits containing sulfides or “suplhurets” was subject to the natural process of oxidation, leaching and erosion leaving a zone of higher grade ore easier to mine and mill than deeper un-oxidized sulfide deposits.
Quartz Ore Crushing Methods
The arrastra was one of the first ore crushing devices. Mexican miners brought the method here in the very early hard rock mining activities. The arrastra was made up of a circle of stones arranged to hold the ore. In the center, a post driven into the ground was used to pivot a pole which was drawn by a mule pulling a heavy stone over the ore, crushing it into a powder. The mule would pull the stone for about three to four hours, quicksilver and water was added, creating a slurry. The water was drained off leaving quicksilver-gold amalgam, which was then panned out to remove the gold.
Modern crushing or milling processes was a technology that evolved from early importing of other European designs. By 1860s, newer approaches were based on Eli Whitney Blake’s design who had invented a crushing machine for road construction in Connecticut. Design modification resulted in the “California improved stamp mill” which became the standard design in the mining west. It was a single, five stamp battery manufactured in San Francisco foundries. Hand drills and black power were used entirely until 1868, when the first air drills and dynamite were introduced, but widespread use of these improvements did not come for another 30 years.
The 1860s through the 1880s became a period when many of the California miners went to the Comstock, Nevada to follow the gold and silver mine boom there. California miners brought their experiences and skills to the Comstock and learned and created many new techniques necessary to be successful in deep shaft mining there.
The early 1850s, quartz mining boom fell short of investor’s expectations. In 1855, there were only thirty-two quartz mines in California, but by 1857 there were as many as 150 and a larger number of stamp mills and arrastras for extracting the gold from the quartz. By 1870, quartz mining accounted for 31 percent of the dollars value of all gold mined in California.
In 1880-1905, a “Second Gold Rush” in California was based on industrialization and returning miners, new investors and improved deep shaft mining technology which was applied to older mines, pursuing new veins associated with the revised mines earlier abandoned. Electricity, steel stranded cables, square set timbering, water and ventilation pumps, use of steam and air powered drilling with diamond bits were some of the technology. New gold concentration and chemical extraction techniques all contributed to the recovery of gold quartz mining in California.
In 1880, the State Bureau of Mines was established by the California legislature, headed by a mineralogist appointed by the Governor. The Bureau was empowered to collect and preserve mineral specimens and detailed information on mining and milling, etc. and prepare detailed reports on mining operations in each mining district throughout the state.
Other chemical techniques, such as the chlorination process for recovery of gold from concentrate was brought to California from Europe, and improved to the point of being widely used. Chlorination was a process of dissolving gold ores, after crushing and roasting, by the use of chlorine gas.
In 1896, the cyanide process was introduced for the extraction of gold from finely crushed ores, concentrates and tailings by means of cyanide of potassium. The gold is dissolved by solutions and subsequently deposited upon metallic zinc or by other means. By 1900s, this process was most efficient since almost all California mines were deeper, working in lower-grade ore often higher in sulfides, which were ineffectually treated by using only gravity-separation technology. By 1936, there were an estimated 3,200 gold mines.
Open Air Mining
Large open air or “open pit” mining has become the leading method for new mining of precious metals in the last half of the 1900s. Major corporations with sophisticated mining methods require large capital investments, complex environmental licensing and scientific staffing. Much study and analysis is used to prepare detailed mapping, core drilling, and three dimensional computer modeling to define the mining operations.
Low grade ore can be processed with various modern cyanide processes which create special environmental restrictions. Open pit mining consists of developing a pit with concentric, circular cut rings or ledges. This allows excavation equipment to move along the cut, dislodging the ore, with pre-blasting, and using large loading shovels to load oversized hauling trucks. Removed from the pit, the gravel is hauled to concentration and extracting facilities. These may be nearby or transported in more conventional trucks to other states depending on environmental laws. The mines operate twenty-four hours a day removing thousands of tons of ore. Gold can be mined as a byproduct of a copper mine, such as the Kennocott Mine in Utah, where many additional metals and minerals are extracted.
Modern gold extraction techniques such as “heap leaching” is a new method of treating low grade gold ore by piling it into an outdoor heap, then sprinkling cyanide solution over it. Within a few weeks, the cyanide will have dissolved the gold and it runs down a sloping, impermeable pad into large sluices. The pad on which the ore is leached must be impermeable to prevent solution from leaking into the ground water, carrying not only the gold but poisons as well. An example is the McLaughlin Mine in northern California. Some ore can have a little as one ounce of gold per ton of ore and still is economically feasible to make it profitable. At the McLaughlin Mine the cost of installing the heap leaching equipment was $250 million.
Effects of U. S. Government on the Price Control of Gold and the Mining Industry
A number of economic constraints were put on gold mining by the U.S. government. The price of gold was controlled as a gold standard of $20 per ounce from 1792 until the 1930s during the Depression. President Franklin D. Roosevelt stopped the run on the banks and hording of gold in 1934, also raising for the first time the price of gold to $35 per ounce. In 1942, at the beginning of WW2, the gold mining industry was closed down with the intent to move the mining labor force into war related metals. At the end of the war, gold mining was re-instated, but many mines had caved in, were flooded, and in general disrepair. After the depression, some mines reopened when the price of labor and material were still low. It was not until 1971, that President Nixon tried to stop the flow of gold out of the U.S. and raised the price to $42 per ounce, but that was not the solution. Several other approaches were tried with the same negative result. Finally in 1972, the government gave up on controlling the price of gold in the U.S. and it became a commodity item on the N.Y. Stock Exchange.
This resulted in the price of gold rising rapidly in the next ten years, reaching $850 per ounce in 1980. The gold mining industry was now seen to be a good investment and large corporations started revitalizing old mines and using modern open air (open pit) mining technology and cyanide concentration and extraction techniques to recover gold. There was resistance later in the 1990s when the environmental laws were created to protect against poisoning ground water, air pollution, and loss of animal and plant life. These restrictions resulted in lower numbers of new mines but they became large and more environmentally controlled at major capital expense. As the price of gold rose (1980 gold peaked at $850 per ounce, averaging $594 per ounce), so did the mining investment. In the Mother Lode, the Carson Hill and the old Harvard mines, right on the quartz vein of the Lode had resurgence. More than two million ounces of gold in the ground were still available with ore containing only 0.073 ounce per ton. The Sixteen-To-One Mine and others in the Alleghany district mines in historic Grass Valley district (notable Idaho-Maryland Mine) and even some drift mines were cleared for working. Gold dredging shut down in 1967 and started up again in the Yuba Goldfield north of Sacramento.
Underground mines, dredging and small-scale placer mining accounted for much of the gold production in the 1970s.
In California, nearly all the gold output for the year 1986 (400,000 ounces) came from five large open pit mines using the new refining technique of heap leaching. By 1988, when California’s annual gold production exceeded 732,000 ounces ($320 million) most of the gold came from fifteen large open pit mines. The most productive of California’s revitalized mines were not in the Sierran gold country, but in the Coast Ranges in Napa and Yolo counties, north of San Francisco. This is an area long mined, not for gold, but for mercury. One of these, the McLaughlin Mine, had to get 327 different environmentally related permits before one gold bar was poured. By 1995, California was second in the nation in gold production, exceeded only by Nevada. In 1996, California mined 835,000 ounces ($326 million.)
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