When was placer mining

TABLE 1. This is a preview of subscription content, log in to check access. Boericke, W. New York: Wiley, p. Google Scholar. Lang, A. Ottawa, Ont. Geology Rept. Sydney, p. Prommel, H. Hopkins, n. Denver, Colo. Stone, D. Stone, , Gold Prospecting. Melbourne: Lansdowne Press Pty. Tolansky, S. London: Methuen and Co. These shafts and tunnels were typically dug in winter so that frozen ground would not melt and collapse on the miners.

Even so, the practice was arduous and dangerous. Using hydraulic "giants" to thaw frozen ground, ca. To speed up the process they use the flow of water through wooden troughs called sluice boxes. In the bottom of the box a series of riffles, like shallow fences, agitate the slurry of water and gravel, encouraging small particles of gold to fall out of solution again because they are heavier than sand and rock.

In this way gold can be captured while the waste material spills out of the end of the box. As an alternative to building lengthy sluice boxes on site, some early placer miners carried with them mobile sluicing units called rockers compact, boxy sluices operated by rocking the unit side to side and long-toms a portable sluice box that did not need to be built on site. Another technique that accelerated the placer mining process was hydraulicking, which harnessed the incredible power of water under pressure.

By constructing a penstock a wood and earthen reservoir of creek water and installing a system of sectional steel pipes, miners could create enough water pressure to blast away large amounts of earth. In order to allow a single person to direct the torrent of water, miners used a large counterweighted nozzle called a giant or monitor. Even after placer mining became more industrialized, hydraulicking continued to be used for removing topsoil and beginning the process of thawing permafrost in advance of enormous gold dredges.

In order to thaw many acres of frozen ground, early dredging operations also injected the ground with steam or water. Turning molten Coal Creek gold into bars, Moving gravel by hand is arduous work and often placer gold exists in very small quantities, so it is no surprise that gold miners turned to steam-powered and then diesel-powered machines to make poor ground profitable. The earliest gold dredges in Alaska arrived in the s, and by the s several dredges were imported to mines along the Yukon River.

They did the same work as earlier placer techniques but on an industrial scale, scooping thousands of cubic feet of gravel each day, washing it in revolving tumblers with water from all angles, and running it through multiple sluice boxes. The orderly piles of waste rock the dredges left behind as they moved across the landscape are called tailings. In order to capture as much gold as possible, dredge operators and small-scale placer miners alike added mercury to their sluice boxes because gold and mercury bond chemically to form what is called an amalgam.

After removing the riffles and scraping the amalgam out of the box, the process of retorting can begin. Retorting involves heating the amalgam in a crucible until the mercury vaporizes; then the gold can be melted to remove impurities and poured into a mold to create a gold brick. Placer miners using a small steam boiler and drift mining techniques on the Charley River, s. Yukon-Charley Rivers National Preserve was created in part to protect and interpret the history of the Klondike- Alaska Gold Rush and the legacy of gold placer mining in the region.

From the air over Coal Creek and Woodchopper Creek they will also see gold dredges and the neatly piled tailings that are the telltale sign of a dredge mining operation.