Gold Mining Techniques has evolved from grizzled prospectors panning for the yellow glint of gold to large scale operations. Scientists apply exploration drilling results to design a mine plan.
Placer miners use sluices to separate gold from sediments. As water washes the material down a sluice, gold particles captured by carpets or other capturing devices on the bottom of the sluice.
Sluicing
Gold-bearing sediment and alluvium washed by water as it flows down a channel or sluice. This method focuses on gold primarily because of its density relative to other materials in the ore or alluvium mixture. Gold particles sink and are captured by carpets or other catching devices on the bottom of the sluice.
Sluices may simple angled platforms a few feet in length or elaborately constructed. The sluice best operated when it has an available and constant water supply.
To mine large deposits of ore, a mining company applies exploration drilling results to a mineral resource estimate. The mine site then developed by blasting and excavating the rock that contains the desired amount of gold.
The gold containing material moved to stockpiles while waste rocks are removed and transported to waste rock stacks.
Some companies also use chemical leaching to extract the gold from the ores. This process is referred to as placer mining.
Panning
Gold is comparatively rare in the earth but concentrated in stream beds or beaches by the natural action of gravity.
The most common tool of the prospector a wide, shallow pan (typically metal but also plastic) which submerged in a river or creek to sort out the gold from the heavier sediments. The agitation of water causes the heavier materials to sink and wash away while the gold collects at the bottom of the pan.
To start a panning process the pan given a quick side to side shake which breaks up any larger gravel or dirt and helps stratify the material.
As the shaking continues the material agitated in a circular motion which moves the heavier materials to the center of the pan and washes them away while the lighter mineralized sand rises to the edge of the pan. Repeating this process, often called a “stage panning” process, results in a high grade concentrate which contains the desired quantities of black sand minerals and gold.
Shaking Tables
The shaking table used to separate heavy precious metals from other mineral concentrates. This separation takes advantage of the difference in density between gold and other minerals. It is also one of the oldest and most reliable concentration methods.
Shaking tables are rectangular-shaped platforms with riffled decks across which a film of water flows. A mechanical drive imparts reciprocating motion along the long axis of the table. The fluid film carries low-density particles across the riffles, leaving high-density materials to fall into beds behind the riffles.
The riffles allow very fine gold to washed out with the water, but coarser materials held back by the rapid backward movement of the table and their momentum.
The simplest shaker table made from strips of yellow pine 3 inches wide and 6 feet long, but professional miners use sophisticated equipment, including drive mechanisms from motorcycle frames and engines.
In some cases, these motors used to power large suction dredges that explore the area around boulders and along potential pay streaks until “color” (gold) observed.
Centrifuge
Gold mining involves extracting the metal from earth, and there several techniques that employed to achieve this.
This precious metal extracted by excavating underground deposits from a mine or by exploiting surface deposit sites, such as riverbed gravels (“placer diggings”), dry beds of streams that only flow after heavy rains (“gulch diggings”), and terrace gravels on the sides and tops of mountains (“bench diggings“).
In addition to these techniques gold separated by chemical leaching. A centrifuge is a powerful electronic device that can separate samples by their density and size using centrifugal force. This device operates in cycles that preprogrammed or determined manually depending on the equipment and the sample material. The centrifuge must adjusted for the correct operation by adjusting feed grain size, rate of feeding, rotation velocity and cycle duration. Centrifuges are very noisy devices and require expert maintenance. They must used in a well ventilated area to avoid noise disturbances.