Measuring Mica Alteration

Identifying the alteration path from montmorillonite through smectite/illite, illite, sericite, muscovite to a potential ore zone can be a complicated process even for an experienced geologist. The SR-6500, RS-5400 and oreXpress field spectrometers with EZ-ID mineral identification software can identify these “white micas” and provide critical data for alteration mapping.

As the minerals alter from smaller to greater percentage of aluminum hydroxide, the change can be seen in spectral shifts at the 2200nm wavelength. White mica identification is shown in spectra primarily in an aluminum hydroxide absorption feature at 2200nm. The depth, breadth, and position of this feature can indicate the composition of the sample. Phengetic muscovite that is magnesium and iron rich can appear at 2207nm and have a longer wavelength, whereas muscovite at 2205nm has a shorter wavelength. The presence of acid in the mica pushes the identification toward muscovite; neutral pH is indicative of phengite.

With EZ-ID and access to more than 2600 mineral spectra in the USGS, SpecMIN and GeoSPEC mineral libraries, a geologist can examine the best matches to known samples of the minerals and accurately determine a vector to mineralization.

With an SR-6500, RS-5400 or oreXpress geological spectrometer and EZ-ID, the user can identify:

  • Montmorillonite
  • Smectite
  • Illite
  • Sericite
  • Muscovite
  • Phengite

Every oreXpress includes our DARWin SP Data Acquisition software and is available with EZ-ID and the Custom Library Builder Module. EZ- ID allows you to compare your target sample with a known library of mineral spectra. EZ-ID comes with the USGS spectral library and is available with the SpecMIN library from Spectral International and the GeoSPEC library. The USGS library contains 470 spectra for 314 minerals, while SpecMIN has 1528 spectra for 494 minerals and GeoSPEC has 688 spectra for 239 minerals. With all three libraries, a geologist has access to a wide range of possible matches for exploration projects.

EZ-ID features:

  • Fast and accurate identification of an unknown mineral to a known spectral library sample
  • Ease-of-use: take your scan using an oreXpress and see results in real-time
  • Simple, consistent user interface
  • USGS, SpecMIN and GeoSPEC libraries available
  • Weighted score for best matches
  • Include or exclude spectral regions of interest for optimal results

Using an oreXpress with EZ-ID delivers the following benefits for exploration geologists:

  • Quickly take a lot of samples
  • Cover more ground in less time
  • More accurate data provides a more complete picture of what you are looking at
  • Less time and expense than waiting for samples to come back from the lab
  • Less drilling – better results – quickly delivers a return-on- investment

In the field our spectreometers are  rugged, reliable, and designed for single user operation. Field collection of spectra is fast and accurate. In the core shack, a single geologist with a contact probe could log as much as 400 meters a day. And, since DARWin saves it all in an ASCII format, it’s easy to use the data with 3rd party software for mine mapping, mineral mapping and 3D imagery.

Sr-6500, RS-5400 and oreXpress field portable spectrometers are ideal for mineral identification

SPECTRAL EVOLUTION’S EZ-ID software has identified our target sample as muscovite using the USGS spectral library for reference. The shaded areas shown in the scan allow a geologist to concentrate on regions/wavelengths in the spectra of particular interest.