A drywasher is a common

desert A desert is a landscape where little precipitation occurs and, consequently, living conditions create unique biomes and ecosystems. The lack of vegetation exposes the unprotected surface of the ground to denudation. About one-third of the la ...

mining Mining is the Resource extraction, extraction of valuable geological materials and minerals from the surface of the Earth. Mining is required to obtain most materials that cannot be grown through agriculture, agricultural processes, or feasib ...

tool for

gold mining Gold mining is the extraction of gold by mining. Historically, mining gold from Alluvium, alluvial deposits used manual separation processes, such as gold panning. The expansion of gold mining to ores that are not on the surface has led to mor ...

. A drywasher is like a highbanker, since it uses a motor and a form of

sluice A sluice ( ) is a water channel containing a sluice gate, a type of lock to manage the water flow and water level. There are various types of sluice gates, including flap sluice gates and fan gates. Different depths are calculated when design s ...

, but it has no need for water. It drywasher operates by the use of air. By forcing air to flow up through the material as it moves down the sluice, the heavier materials, like

gold Gold is a chemical element; it has chemical symbol Au (from Latin ) and atomic number 79. In its pure form, it is a brightness, bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal ...

, 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 lighter 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

sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

s. Dry placers represent a major portion of all

alluvial Alluvium (, ) is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. Alluvium is also sometimes called alluvial deposit. Alluvium is ...

gold deposits around the globe. Extreme

arid Aridity is the condition of geographical regions which make up approximately 43% of total global available land area, characterized by low annual precipitation, increased temperatures, and limited water availability.Perez-Aguilar, L. Y., Plata ...

ity in southern hemispheric regions of the planet causes a slower rate of

erosion Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...

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 Relative density, also called specific gravity, is a dimensionless quantity defined as the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for solids and liquids is nea ...

, is much heavier than most other minerals found in local sediments, a

facsimile A facsimile (from Latin ''fac simile'', "to make alike") is a copy or reproduction of an old book, manuscript, map, art print, or other item of historical value that is as true to the original source as possible. It differs from other forms of r ...

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 unpack them. Then, as long as the material is sufficiently dry, these

gravel Gravel () is a loose aggregation of rock fragments. Gravel occurs naturally on Earth as a result of sedimentation, sedimentary and erosion, erosive geological processes; it is also produced in large quantities commercially as crushed stone. Gr ...

s 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, one must determine if the raw material is dry enough to be efficiently processed. Once the machine is set up and stabilized, using a shovel, the

dirt Dirt is any matter considered unclean, especially when in contact with a person's clothes, skin, or possessions. In such cases, they are said to become dirty. Common types of dirt include: * Debris: scattered pieces of waste or remains * Du ...

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is usually defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural ...

, gravel, etc. is loaded onto the uppermost part of the device — the screen, or "grizzly". Sediments classified by the grizzly, drop into another part of the apparatus known as "the hopper". Once the machine is activated, the finer, gold-bearing material travels down an inclined, vibrating chute, passing over a series of "riffles" in a recovery tray. This process varies slightly from machine to machine. Heavier minerals, principally gold and fine-grained black sands (various

iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...

minerals), are separated from the paydirt and reconcentrated by this means.

Panning Pan or PAN may refer to: Food * Pan (cooking), a piece of cooking equipment * Harina P.A.N., a pre-cooked corn meal * Pan or Paan, a North Indian term for betel Prefix * ''Pan-'', a prefix meaning "all", "of everything", or "involving all ...

, or some other final separation process, comes afterwards. The first machines were, in all likelihood, operated manually. A simple one can be constructed using a wooden framework, a hopper, a recovery tray,

bellows A bellows or pair of bellows is a device constructed to furnish a strong blast of air. The simplest type consists of a flexible bag comprising a pair of rigid boards with handles joined by flexible leather sides enclosing an approximately airtig ...

lever A lever is a simple machine consisting of a beam (structure), beam or rigid rod pivoted at a fixed hinge, or '':wikt:fulcrum, fulcrum''. A lever is a rigid body capable of rotating on a point on itself. On the basis of the locations of fulcrum, l ...

, 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

*. *. Date unknown. Republished in electronic format with foreword by th
''ICMJ's Prospecting and Mining Journal''
{{Extractive metallurgy Gold mining