Clark C. Spence - A History of Gold Dredging in Idaho

Gold is where you find it, is an old mining saying. Whenever it is found, it appears in its natural form in two different ways, depending on the geologic environment. One form is in hard-rock lode deposits, deposits that may have had different origins but which remain locked within the original solid rock formations. Even if a lucky prospector located a so-called quartz mine, it was clear that development was for corporate, not individual, effort and might take years before it returned a profit. The work called for more and more capital for tunneling, timbering blasting ore, transporting it underground, and hoisting it to the surface. Moreover, gold in hard-rock ores was often difficult to removerefractory in the language of the engineers. In the worst cases, it might be in combination with other elements, which meant more intricate and costly processes would be needed. These kinds of deposits have produced the bulk of the worlds gold to date.

The second type is the secondary deposit, which occurs in several forms. Residual deposits are usually found where rocks have weathered and deteriorated, but without water. They have not yet been washed away, nor have

From ancient times, such placer deposits were easier to find and work than lode mines, and more than one technique would carry over into early gold mining in the American West. The panning of gold was the simplest way for the prospector to test for placer gold. The early Romans had used a pan of some sort for that purpose, and widespread usage continued through the ages. By the time Californians brought it to Idaho, the pan had become standardized in sheet iron, eighteen inches in diameter and four inches deep, with sides slanting outward at an angle of thirty-seven degrees. Fortunately for the early comers, gold was plentiful and easily panned in the early days of all of Idahos high-country placersPierce, Florence, Elk City, Warren, Salmon City, Stanley Basin, Boise Basin, and on the South and Middle Forks of the Boise River.

The rocker or cradle was a considerable improvement over the pan. This was a rectangular box, set at a downward angle and mounted on a rocking mechanism like that of a rocking chair. At the top was a removable hopper with a mesh screen or perforated iron plate; at the bottom was a series of cleats or riffles. The gravel was dumped into the top, followed by a bucket of water, after which the cradle was rocked by hand to agitate the mixture. Any rocks were caught by the screen or perforated plate; the smaller wasted

The machine was an advancement over the sluice, which in its most primitive form was simply a long ditch with its bottom cleated with rocks, gravel, and holes to act as riffle bars; more often it took the shape of a long tom. Built of wood, the latter was ten feet to twenty feet long, a foot-and-a-half deep, and tapered at one end so that a number of them might be fitted together to form a sluice sometimes several hundred feet long. The lower end of the long tom, called the riddle, replaced the hopper of the cradle, and a heavily perforated iron strained out the large debris while allowing water and small gravel to fall into a riffle box where the gold was captured. Widely used throughout the West, such equipment needed an available running stream of water, which was usually supplied by running a flume from a nearby river or creek.