By Dan Oancea
Airborne hyperspectral remote sensing, a result of the integration of optical remote sensing and traditional spectroscopic technologies, could be defined as ‘airborne geochemistry’ because of its ability to differentiate the unique spectral signature of minerals that comprise the surface of the Earth.
All minerals reflect and absorb energy in both the visible and non-visible portions of the electro-magnetic spectrum. The hyperspectral sensors collect the individual reflectance spectra for each pixel element across an image, thus being able to mapping individual minerals of importance for mineral exploration (i.e. fingerprinting mostly alteration minerals as alunite, kaolinite, muscovite, pyrophyllite, chlorite, calcite and iron oxides).
The hyperspectral maps indicate a surface mineral abundance thus being the equivalent of a geochemical map (for more info check Canadian Space Agency's site).
The story began with the use of such sensitive devices by the military. The Northrop Grumman Corporation is the leading hyperspectral technology supplier to the U.S. military and at the same time the owner of the TWR Corporation.
Ekwan Technology Corporation, a private Canadian company, granted its 50% owned subsidiary, Ekwan-X Inc. (a publicly listed company) the rights to use their hyperspectral technology in the states of Nevada, New Mexico, Arizona, California, Colorado, and Utah. That means the rights to fly a wide swath instrument (256 m), which is owned by TWR.
Ekwan-X states that:
“The Ekwan-X-1 narrow swath (profiling) hyperspectral system consists of two down looking hyperspectral profiling sensors and one upward looking downwelling irradiance sensor. Each sensor records 366 contiguous spectral channels covering the 350 nm to 2500 nm wavelength range. The sensor simultaneously collects two parallel lines of contiguous pixels and downwelling irradiance data. The system is light weight and is easily installed on a variety of aircraft.
This imager has 384 contiguous spectral channels covering the 400 nm to 2500 nm wavelength range with a ground resolution capability between 0.8 m and 7 m and swath widths up to 2 km depending on altitude. With this instrument Ekwan-X has the most advanced hyperspectral imagery available in the world today.
Ekwan-X-1 is designed to be flown at low altitude on the same airborne platform with geophysical equipment (magnetometer, radiometrics, etc.). This allows the simultaneous acquisition of airborne hyperspectral and geophysical data.”
Further on, the company’s paper details a break-down structure of a hyperspectral field program:
“The first step in planning a Hyperspectral Survey Program is the selection of an area of interest based on the areas prospectivity and suitability for this type of survey. This is achieved by performing a comprehensive review of the available geological data. An assessment of the surface geology, topology, mineralogy, geophysical and geochemical data is conducted. A study of the logistics, weather patterns and sun angles should provide enough information to permit the selection of a large area where this technology will be most effective.
The next step requires laying out the area to be surveyed, followed by field trips to commence preliminary ground truthing on known mineral occurrences and to determine some immediate spectral data expectations. This will assist in adjusting and modifying the computer software for the survey.
Selecting a suitable aircraft, obtaining all necessary permits and then installing and testing of the Hyperspectral system are the next steps.
Once the above steps are completed, the airborne data collection can commence. Ekwan-X will conduct on-site data processing including calibration, ground truthing, quality control and analysis to insure high quality and accurately located data.”
To date, no mentioning of any exploration success based on the application of Ekwan’s technology on their site.
Back in 1997, Noranda and Falconbridge entered into an agreement with Earth Search Sciences Inc. (ESSI) to gain access to a high quality imaging spectrometer (Probe-1). The hyperspectral system flew over desert regions in northern Chile and over the Canadian Arctic proving to be a useful tool in defining exposed geology, alterations and gossans.
The ESSI provides airborne hyperspectral remote sensing services for a wide range of uses from exploration and monitoring of valuable natural resources to homeland security. At least on their page I could see a press release regarding a recent survey performed on behalf of El Capitan Precious Metals at their New Mexican El Capitan iron property. It was about making a quick decision regarding the mineral potential of the land claim block contiguous to the El Capitan deposit. Subsequently, the El Capitan’s geologist collected surface samples from hyperspectral anomaly areas; assay results showed that mineralization of a similar type and grade to the El Capitan deposit occurs at three locations marked by pronounced hyperspectral anomalies.
The Phoenix Matachewan Mines completed a major regional hyperspectral survey covering 1,115 sq km at the Bottle Creek mercury district of northwestern Nevada. No mentioning of the system used for data acquiring and analysis.
The hyperspectral method has certain advantages:
- It provides geological and mineral mapping capability at regional and project scale;
- Improves the target selection process;
- Lowers the cost of exploration.
It also has a few disadvantages:
- Mineral data can be efficiently acquired only over less covered regions (exposed geology terrains; i.e. desert, arctic and barren mountain ridges)
- Cost of the program is influenced by location, weather, and access to a suitable aircraft.
And sometimes is even easier: On a Google flight over the Andes you would see many targets that stand out because of their color patterns - e.g. Escalones, Carrizalillo, Relincho, or Vizcachitas. By analyzing a freely available Google Earth picture (visible light) a mineral deposit discovery might be just steps away. No sensors, filters, adjustments, software. Just your bare naked eyes and a prospector’s luck.
Wish that you’ll have it!