Identifying Chlorite with a Field Spectrometer

The identification of chlorite can be used to calculate distance from an ore body in porphyry deposits. Chlorite identification is a useful tool for exploration in propylitic alteration zones. Propylitic alteration can include several sub-zones:

  • Inner high temperature— actinolite, epidote, chlorite
  • Intermediate—epidote, chlorite, calcite
  • Distal—chlorite, calcite, hematite

Chlorite has distinctive absorption features around 2250nm by Fe-OH and 2340nm by Mg-OH. The specific wavelength position of Fe-OH absorption feature varies with Fe and/or Mg content. Mg-rich chlorite is generally between 2245 and 2255 nm, whereas Fe-rich chlorite tends to be around 2265 nm. The Mg-OH wavelength for chlorite rich in Mg is around 2330 nm and for Fe-rich chlorite is 2365 nm.

The depth of the absorption features at these wavelengths also varies. The deeper the absorption feature, the more Mg in the sample.

Chlorite can be identified in the field using an oreXpress oreXplorer and oreXpert spectrometer that covers the spectral range from 350-2500nm. The oreXpress offers high resolution/high sensitivity, the oreXplorer offers higher resolution, while the oreXpert is the highest resolution field instrument available. They are designed for field use with a rugged and durable chassis, battery power for a full day of scanning and a backpack for portability. They can be equipped with a 3mm spot size Miniprobe or a 10mm spot size contact probe to provide consistent illumination for scanning your samples. A benchtop probe with sample compactor is also available for chips and powder samples.