Can illite be used as a pathfinder mineral in uranium exploration?
In unconformity-type uranium deposits like those in the Athabascan basin, illite is often one of the clay minerals found along with sudoitic chlorite, dravite, dickite, and kaolinite. Illite can be considered a pathfinder mineral for uranium deposits.
Illite types can be diagenetic (coarse grained and platy) or hydrothermal (hairy/wispy). There is a small increase in aluminum (Al) content in hydrothermal illite relative to diagenetic illite. The shift to greater Al content can be more easily seen near 2200 nanometers using Spectral Evolution’s new ultra high resolution SR-6500 portable spectroradometer.
Resolution at FWHM for the SR6500 is:
- 1.5nm @ 700nm
- 3.0nm @ 1500nm
- 3.8nm @ 2100nm
Resolution is achieved using three high density solid state thermoelectrically cooled photodiode arrays:
- 1024 element TE-cooled silicon phtotodiode array detector (VIS-NIR)
- 512 element TE-cooled InGaAs photodiode array detector (SWIR 1)
- 512 element TE-cooled extended InGaAs photodiode array detector (SWIR 2)
Illite typically has two absorption peaks at 1400 and 2200nm.. The 1400 feature is derived from the OH-overtone stretching vibration while the 2200 feature is related to the Al-OH bending combined with OH stretching. To see the shift in illite associated with uranium deposits, the hydrothermal illite will have a small but higher concentration of Al as opposed to the diagenetic illite and will show absorption features at 2190 nm and 2200 nm as opposed to the diagenetic illite which will show the absorption feature at 2205, 2210, 2220 nm. By tracking the alteration changes in illite a geologist might get a better idea of how close an ore body might be.
SR-6500 ultra high resolution spectroradiometer can provide better resolution of key absorption features in mineral spectra.
With the higher resolution scans from the SR-6500 spectroradiometer, it is easier to see the subtle shift from hydrothermal illite to diagenetic illite.