Gold is a valuable precious metal known mainly for its use in jewelry and coins. At one time, some countries used the gold standard as the basis their monetary systems, but by the 1930s, many nations had converted to a fiat system. Today, no countries use a gold standard. The price of gold hit an all time high in 2011 and has been dropping ever since.
Mining gold is a costly endeavor, requiring a substantial capital investment to uncover what is usually an elusive target. Nevertheless, gold remains a highly sought-after commodity and mining companies continue to pursue it.
In the face of declining gold prices, cost control becomes even more critical to maintaining sustainability, so companies mining for precious metals are under more pressure than in other areas of mining to quickly identify the most economically viable resources. Some of the issues they face are:
- Gold deposits are difficult to find and delineate because gold typically occurs in very low concentrations.
- When deposits are located, few of them have large enough concentrations to be financially worthwhile to pursue; many discoveries will be abandoned without further development.
- The major Brownfield sites are getting depleted and it’s becoming harder to find Greenfield sites with potential, so mining companies are spending more to get less.
- Typical prospecting involves examining samples from just a few areas throughout the mine site to determine if the region is worth exploring. Because gold occurs in such small concentrations, it’s easy to miss using this technique.
To enhance their chances of finding gold, geologists may use geophysical methods to measure variations in the physical properties of rocks (e.g. density, magnetism, electrical conductivity, natural radioactivity, etc) that may indicate the presence of suitable environment for gold deposition. Some common geophysical methods include airborne gravity, 3D modeling of electrical data, and infrared spectroscopy (satellite, airborne, and field-based).
Although these geophysical methods can be crucial for gold exploration, geochemical methods – including portable x-ray florescence (XRF) – are the only methods that can measure concentrations of gold and other associated elements. Today, portable XRF is used in various stages of gold exploration and mining including grass-root exploration (particularly using pathfinder elements), finding source of gold in stream sediments, core logging, identification of lithologies, and even grade control.
The sampling techniques are aimed at mapping the distribution of gold and in particular, the various elements associated with gold known as the pathfinder elements (silver, copper, zinc, nickel, mercury, arsenic and barium). Pathfinder elements are very important in finding gold because they help focus the search area. It’s much easier to find the pathfinder elements than it is to find gold, and once found they can help determine if gold is nearby.
See how geologists used portable XRF analysis as a direct check on the identification of lithology and base metal anomalies used in gold exploration.