Gold Mining Equipment

The list of gold mining equipment required to recovver alluvial material consists of two parts: sand and bedrock (6 -12 inches) which contains metallic gold. Heavy sands with gold (black sands) are found with some minerals such as magnetite, ilmenite, rutile, hematite, olivine, chromite, zirconium, pyrite, wolframite, cassiterite, and galena. Some placers are no associated with all the minerals mentioned above and it is very important that each place carries out microscopical studies and chemical analysis in order to determine the minerals and metals from the platinum group present in the specific alluvial material.

Gold particles are found in many sizes such as nuggets and fractions very fines which trends to float on the water. Generally a gold particle over 10 mesh is called “coarse”. In general, the gold from placer is coarser when its physical movement has been almost nothing. A gold particle less than 400 mesh is very difficult to observe macroscopically. Most the time this fine gold will be deposited with the coarse gold and can be transported with other sediments out of the placer.

Fine gold from placers looks like flakes and it is difficult to recover and commonly is lost due to most of placer operations employ cheap and simple gravimetric equipments.

Gravity concentration is the workhorse of mineral processing. It is not fancy and for many years it was overlooked by many manufacturers and researches. However, in the last years, the attitude has been different due to environmental and economical aspects. Thus, the development of new equipments such as centrifugal concentrators has been an aspect very important because it is necessary a high level of efficiency.

It is generally accepted that gravity concentration is the most simple and economical of all methods of concentration, permitting the recovery of values at as coarse a size range as possible. Mineral particles are separated by virtue of the differences in density, so if the difference in density is greater, the separation will be easy. Nevertheless, the smaller particles, the more important, relative to gravity are fluid and viscous forces, so the efficiency of gravity separation decreases sharply in the finer size ranges.

Gravity recovery had never ceased to be used in developing countries to recover gold alluvial, in Australia and South Africa to process beach sands. The advent of new equipment capable of treating finer particles will provide the impetus that it requires to conserve an important place in mineral processing.

It is important to understand the problem or what limits the use of gravity recovery. The basic problem has to do with settling velocities in water. For small spheres (100 µm) terminal settling velocity is given by the following relation:

V = 2*(ρ_s – ρ_f)*r²*g/ (9µ)
V: terminal settling velocity
ρ_s: density of solid
ρ_f: density of liquid
r: radius of solid sphere
g: acceleration of gravity
µ: viscosity of fluid

The equation points out the importance of particle size.