Drywasher

The drywasher is a common desert mining tool for gold mining.

The drywasher is like a highbanker since it uses a motor and a form of sluice however it lacks the need for water. A drywasher operates by the use of air.^[1] By forcing air to flow up through the material as it moves down the sluice the heavier materials, like gold, will stay at the bottom and get trapped by the riffles while the lighter materials will flow up and over the riffles or be blown away. The lighterweight material that is not blown away will slowly flow down the sluice and fall out the end of the sluice.

Drywasher - A mechanical apparatus used for separating free particles of placer gold from dry sediments. Dry placers represent a major portion of all alluvial gold deposits around the globe. Extreme aridity in southern hemispheric regions of the planet causes a slower rate of erosion on placer deposits than if rainfall were plentiful and regional watersheds were hydrologically active. This absence of water directly correlates to the low moisture content of alluvial sediments and the short distance gold moves from its hardrock source. A drywasher works on the principle of gravity separation. Since gold, at 19.1 specific gravity, is much heavier than most other minerals found in local sediments, a facsimile of certain natural conditions (which would involve the use of water, if it were available) can be mechanically reproduced with a simple machine using dry air instead of water as the medium of separation. The process of excavating dry, compacted sediments will often loosen or unconsolidate them. Then, as long as the material is sufficiently dry, these gravels can be processed with a drywasher in a relatively efficient manner. A drywasher was also known, at one time, as a Mexican air jig. To use a Drywasher, first, you determine if the material you want to run is dry enough to be efficiently processed. Then, set the machine up and stabilize it. Once it's securely positioned, you transfer (shovel or load) the dirt, clay, sand, gravel, et al. onto the uppermost part of the device.....the 'grizzly'. Sediments classified by this screen (or grizzly), drop into another part of the apparatus known as 'the hopper'. Once the machine is activated, the reduced size, gold-bearing material is then agitated downward, at an angle, pulsing over a series of "riffles" in a recovery tray. This process varies ever so slightly from machine to machine. Heavier minerals, principally gold and fine-grained black sands (various iron minerals) are separated from the paydirt and reconcentrated by this means. Panning, or some other final separation process, comes afterwards.

Drywashers are a fairly modern invention. It is doubtful anyone knows for sure when early prototypes were first employed in the goldfields, but these primitive machines were, in all likelihood, operated manually (by hand). A simple one can be constructed using a wooden framework, a hopper, a recovery tray, bellows, lever, and cord. Before the advent of modern metal screening material, sorting of gravels into smaller particles might have been done by hand. Such elimination of larger rocks aids in separating gold from dry, auriferous sediments to be processed, consequently, any modern 'puffer-belly' could be outfitted with a screen, or 'grizzly' for sorting the dry gravels into two sizes.

References

• Smith, Alfred Merritt; Vanderburg, Wm. O. (15 December 1932), "Placer Mining in Nevada", University of Nevada Bulletin (University of Nevada, Reno, [Nevada State Bureau of Mines]) 36 (8): 31–35 .
• West, J. M. (republished in electronic format with forward by the ICMJ's Prospecting and Mining Journal. Date unknown) [1971], How to Mine and Prospect for Placer Gold, Information Circular 8517, Bureau of Mines  Check date values in: |date= (help).