Satellite Imagery And Gold Exploration

By Leia Michele Toovey- Exclusive to Gold Investing News

The record-high price of gold, coupled with the increase in demand for the metal, as well as shrinking identified reserves is putting the pressure on explorers to discover new deposits. At the same time, gold explorers are faced with the challenge of locating a metal that is extremely rare, and hard to find in economically viable quantities. To increase their odds in finding gold, explorers are relying on the rapidly advancing field of remote sensing.

Since the launch of the first Landsat satellite in 1972, imaging sensor technology has undergone rapid advancements that have enabled explorers to collect increasingly more useful data. When the technology was in its primitive stages, geologists used the sensors to collect simple data, such as surface features, and used this data to provide clues to a potential mineral deposit beneath the surface. This surface data was also used as a tool in mapping.  Now, satellites fitted with “more advanced” sensors use the spectral properties of materials (what wavelengths of materials they absorb/reflect) to identify the materials without having to view them “in person.” This spectral data can be collected by sensors mounted on aircraft and/or satellites, and these sensors use infrared, near infrared, thermal infrared and short-wave technology to collect the data.

The sensors interpret the electromagnetic data in wavelengths that the human eye is unable to distinguish. The differences in absorption and reflection are analyzed and translated into assigned colors that are differentiated for each type of rock and each group of wavelengths. Other wavelengths can identify certain minerals of interest- such as clays and sulfides based on their absorption and reflection qualities. Geologists use data interpreted from satellite images to pick out rock units and seek surface clues such as alteration and other signs of mineralization to subsurface deposits of ore minerals, oil and gas, and groundwater.

The very first sensors used on satellites were problematic, mainly because of their poor spectral resolution, and inadequate spectral coverage. These limitations were rapidly changed in the early 1980's with the launch of Landsat 4 and 5. These new satellites carried the TM (thematic mapper) scanner. The TM system added coverage in the short-wave infrared and mid-infrared regions of the spectrum. Collecting data from these regions enabled the collection of data that could be used as a tool for identifying alteration mineralogy on the earth's surface potentially indicative of economic ore deposits. The thematic mapper is still routinely used as an exploration tool, however, since its introduction, other satellites were launched that had higher spectral resolution and could, therefore, provide more accurate data in determining surface mineralogy. The technology in satellite systems has advanced to the point where not only individual mineral species can be mapped, but chemical variations within the molecular structure of the crystal lattice of the mineral can also be detected. The resolution of the sensors on satellites can't compare to aircraft spectral remote sensors, however, satellite systems have the other advantages compared to aircraft, including the ability to collect more data, from greater areas, without having to fly an aircraft over the land in interest.