by Kathrine Moore
ASD INC. (Analytical Spectral Devices Inc.), a PANalytical company, based in Boulder, Colorado, has been researching and developing portable, analytical spectral devices for use in the field for 27 years. In an interview, Dan Shiley, Senior Application Chemist, for ASD and Manager of the SummitCAL Solutions team, discussed the hand held TerraSpec Halo used by majors and juniors alike.
The TerraSpec Halo is a handheld, infrared, mineral analyzer which Shiley says differs from similar products on the market in some impressive ways. According to Shiley, most other devices are XRF (X-ray fluorescence); they look at elemental composition whereas the Halo looks at the molecular characteristic of material. The system contains a spectrograph which goes from the visible range of 350 nanometers all the way up to 2,500 nanometers.
The 5.5 lb (with battery) Halo contains the same wavelength ranges as larger, backpack mounted instruments. Shiley explained that as most people don’t just look at a spectrum; they need some help to interpret what exactly the material is. “So we coupled the spectrum with a library of minerals and an automated search algorithm so that we can automatically produce up to seven min-erals identified in a complex natural mixture.”
The gathered data is interpreted right on the handheld device so the exploration geologist or his technician can look at the display screen and see which minerals are present. This is a big step change because with other devices the data gathered had to be taken back to the lab for interpretation.
Shiley said, “Those interpretations were somewhat dependent on the person looking at the information. Constancy among analysts was a big problem. With the Halo, it is all automated; there’s no question about someone interpreting a mineral as present or not present based on personal experience. It goes from being an art to being a science.”
The device can be used by most field workers and has two set-tings: one is for geologists with more data, as a geologist has a deeper understanding of geology and the geological environment he is in. There is also a technician setting with a higher threshold because technicians are less likely to have a complex understanding of the deposit. Scaler (numeric value) information is also provided allowing the geologist to understand the temperature, pressure or pH of the deposit at the time of mineral formation.
Shiley said the device works best with a dry sample. The best method he said “would be to measure material that is not weathered on the outside. The geologist would just use his rock hammer to break open a sample to measure inside of it. That way you get away from the surface crust which isn’t really representative of the minerals.”
The Halo has been thoroughly field tested and has been used in all sorts of environments. “We are always having customers ask about adding new minerals. ASD is continuously looking at adding new minerals and environments such as rare earth minerals and oil exploration. We have a suite of minerals that is tailored for the oil & gas industry. Right now our development library has around 4,500 spectra and currently there are 744 spectra representing 158 unique minerals on the Halo device. We are continuously evaluating mineral libraries and collections that might be appropriate to add to the device.” The Halo is most useful for identification of minerals from the following groups: amphiboles, carbonates, clays, epidote, iron hydroxides, micas, phyllosilicates, rare earth element minerals, zeolites and selected members of the silicate and sulfate groups.
Primarily, where ASD sees the device being used successfully in its maximum utility, are in clays and alteration minerals (minerals that are formed in an alteration event). Typically, said Shiley, those same minerals are the pathfinders that have been used for decades with our standard system. He concluded, “We believe that the mineral interpretations are more accurate than anything available from any other software or any other device. Major producers are using the device: BHP, Rio Tinto, and Freeport. All the major players are already using this technology.”