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Gold exploration used to be hit or miss prospecting and following the ‘Rush’. When a prospector got lucky it created a stampede to work the surrounding areas. A century and a half ago finding gold meant sifting and panning from riverbeds and then trying to locate the source upstream. This was known as ‘alluvial’ or surface gold and it is probably safe to say that most of that has been found.
EXPLORING
Finding gold today is largely a matter of technology. Geologists use geology maps to look for areas to explore. Ore deposits are not easy to find and many of the ones exposed on surface have already been found. Gold today has to be found and taken from beneath the surface sometimes many thousands of meters down. Gold is usually found in various host rocks or formations which vary depending on the areas geology. Geologists use the physical and chemical characteristics of the rocks they are looking for to zero in on prospective areas. Once the right geology is established, remote sensing, airborne surveys and ground geophysics and geochemistry are used to outline targets for drill testing.
DRILLING
Drilling for gold brings up rock samples from beneath the surface in the drill’s core. Core samples from the drill hole are sent to accredited assayers to be analyzed to determine if there is any gold, the amount of gold and the quality.
Engineers use this information to plot additional drilling targets to try and determine the length, width and breadth of the orebody. After enough holes are drilled the mining engineers will have sufficient information to determine if there is a large enough quantity of gold to make miming worthwhile, the type of mine needed, the obstacles in place that must be overcome and the environmental impact a mine would have. If the gold is close to the surface it can be extracted using an open-pit mine, if deeper then an underground mine will be planned.
PRODUCTION
The time between finding gold and getting it out of the ground, by any method, can and does take many years. Since mines are often in remote locations, an entire infrastructure – roads, administrative offices, equipment storage areas, even towns, schools and medical facilities – must be built. The plans for the mines must be approved by a number of levels of government. Plans must be in place to re-claim the area once all the economically feasible amount of gold has been mined. In all, the preparation process can end up costing hundreds of millions of dollars – before a single ounce of gold is mined.
PROCESSING
The mine site infrastructure could include a processing area where the ore is crushed and undergoes various processes. Smaller mining operations could ship their ore to larger facilities to be processed under some kind of fee arrangement.
Depending on the nature of the host minerals the loose rock is sent through an appropriate processing method. Low-grade ore gets processed using a cyanide solution applied to the heap, dissolving the gold, which is then collected. High-grade ore goes to the grinding mill. Different ore types require different processes for gold recovery.
• Oxide ore goes directly to the cyanide leaching circuit, which dissolves the gold.
• Refractory ore, which contains carbon, is heated at 1000 degrees F, burning off the sulphide and carbon, then heads to the leaching circuit.
• Sulphide refractory ore, which does not contain carbon, is oxidized in an autoclave to separate the sulphide safely from the ore which then enters the leaching circuit.
PURIFICATION
The gold is extracted from the solution and deposited onto activated carbon, from which the gold is then chemically stripped and made into bars which are about 90 percent pure gold. These bars are usually shipped to a refinery where they undergo further processing. Another complicated refining process strips out the remaining impurities from the gold; the end product is 99.99 percent pure gold. |
