A GPS (Global Positioning System) is a device that uses satellites to determine its position on the earth. This position can be shown on a map within the GPS itself, as well as listed as coordinates that can be exported to GIS software or simply for reference against a paper map. The GPS units used by explorers are the same as those used by fisherman, hikers, and other outdoor users. They are practically the same as auto GPS navigation units but with with more data import/export ability.
It is difficult to overstate how much of a benefit the introduction of GPS was to exploration several decades ago. At every stage of exploration all data, whether sampling points or mapping features, are useless unless recorded with location data. Before GPS, exploration geologists relied on topographic maps to orient themselves in the landscape and then mark down the coordinates from the map’s grid. With more detailed exploration work, surveyors used tachometers to create base points as a reference for tape and chain measurements. With the introduction of hand held GPS, geologists were able to record sampling or mapping points to within meters accuracy anywhere in the world in real time.
The GPS used in exploration are small hand held units with an accuracy to within around 5m, though the accuracy can decrease under heavy storm cloud or narrow gorges. These stand-alone units are being challenged by apps on smartphones by their ease of use and price.
Sampling used in resource estimation should be surveyed more accurately with a DGPS, which can much higher accuracy.
GIS (Geographical Information System) is software that allows data to be shown and manipulated in either two or three dimensions. Google Earth, Google Maps and your car navigation unit are types of GIS.
The GIS software used by gold exploration companies allow the user to import and manipulate data from a range or sources and formats. Typical applications of GIS in gold exploration are geological maps, satellite imagery, geophysics, and sample analysis. These applications are used both in planning and in interpreting completed work. The most common exploration GIS software include Mapinfo Professional, Encom Discover, ArcGIS and Global Mapper.
Once exploration work reaches resource stage other much more expensive software packages are usually used. These are most commonly Gemcom, Surpac, Micromine and Datamine.
PORTABLE XRF, XRD AND ASTER
Portable XRF (X-Ray Fluorescence) allows a measure of the percentages of elements making up a rock (or other material) in the field in real time and without destroying the sample.
Portable hand-held XRF devices are most useful for commodities that have economic concentrations in percentage levels eg. copper, lead, nickel and zinc. Gold concentration is typically so low that it is measured in parts per million (1ppm = 0.0001%). Because of this, portable XRF are unable to detect gold mineralisation directly. However, XRF is still useful to gold exploration by detecting elements such as Arsenic that do occur at percentage levels and are sometimes associated with gold deposits.
In very basic terms, XRF works by firing X-Rays at a sample, exciting the electrons within it. These emit radiation that is measured. As each element that has been hit by the X-Rays emits a unique spectrum of radiation, the make-up of a sample can be determined by measuring the relative levels of each spectrum. For example copper emits a known spectrum of radiation, so when this is detected, the XRF knows copper is present.
XRF technology has been around for almost as long as X-Rays have been used, however the equipment was large and expensive meaning commercialisation only occurred in the middle of last century. Development of portable XRF devices began in the 1980’s, but has only become practical and affordable enough to be widespread in exploration companies in the last 10 years. The most common hand held XRF are Niton and Olympus.
XRD (X-Ray Deffraction) is used to identify minerals in the field in real time. This is useful to gold exploration where minerals of a certain type are known to be associated with gold. The gold itself cannot be detected by XRD directly in the field (as with XRF), but minerals associated with gold can. Like XRF, XRD can be used as a fast and cheap way to identify areas with a chance of having gold that can be followed up by more expensive and time consuming (but accurate) methods of testing for gold. A recent successful example of this was demonstrated in a gold mine in Ghana.
XRD works by taking a sample, firing radiation at it and measuring how the radiation changes its angle as it passes through it or is reflected. Rock samples are made up of minerals and these minerals are mostly crystalline. They are not visible as nice big diamond-like crystals, but they are crystals all the same, just very small and smashed up. Mineral crystals each have a unique shape and geometry which reflect and refract light in an unique way. XRD in measuring this unique reflection signature can identify the mineral.
The technology is not new, but as with XRF, has been limited to the laboratory until relatively recently. One major drawback of XRD is that the sample needs to be pulverised before it can be analyzed.
ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) is a satellite that includes instruments, among others, for capturing multi-spectral images of the earth. Processed combinations of these images can be used to identify minerals on the surface of the earth over large areas.
In recent years ASTER imagery has been increasingly applied to mineral exploration, including gold, using the same principles of mineral association as XRD.