What is Mining? It is the process of removing minerals from the earth in their raw form to be processed into a usable form.
– Once this ore is extracted, a separation process takes place in which the mineral or metal is separated from the rock or sands, and then to be further processed into a usable form.
– Rocks containing minerals in smaller quantities (powder form) may need to be crushed and even ground into powder form, for the minerals to be extracted.
The two primary mining techniques:
Hard Rock Mining and Alluvial Mining
Alluvial Mining
Simply put, alluvial mining is the sorting of soil, sand, river/stream bed deposits or sediments for minerals, using water to separate the minerals from the sand.
Alluvial gold refers to the type of gold dust found in these deposits.
The gold has travelled from the host rock by water and other natural weathering occurrences.
– Panning for gold is done by holding a special pan and swirling the sand and water together from a river.
– The gold is heavy and will sink to the bottom of the pan.
– Gold wash plants, trommels with sluices and/ or gravity concentrators are used to recover gold flakes, nuggets, dust and other metals and minerals.
Hard Rock Mining
Rocks containing metals and minerals are called ores. The solid rock ore must be crushed to get to a powder form for the metals and minerals to be extracted.
– Crushers reduce the ore to smaller pieces and the mill ground the ore to fine slurry or powder.
– This slurry is thickened with water to form pulp in the leaching tanks. The most common chemical solvent to dissolve the gold out of the ore is cyanide, this process is known as carbon-in-pulp or carbon-in-leach.
– The gold is recovered from the cyanide solution by adding activated carbon to the slurry. The carbon is screened out and Electrowinning recovers the gold from the carbon.
– Smelting in a furnace is the next step.
– A chemical mixture known as flux is added to the molten material. The flux is then poured off. The gold is poured into molds and liquid gold transforms to solid bars called doré bars.
– These are normally high purity (85% and higher) and then sent to a refinery to produce pure gold.