Rock-type identification in a simulated underground environment using second-derivative thermal infrared reflectance spectra

This study investigates the usefulness of thermal infrared reflectance spectroscopy (TIR) to map rock faces in an underground environment. A laboratory Fourier transform infrared (FTIR) spectrometer was used to measure reflectance spectra (500-5000 [cm.sup.-1]) of freshly broken rock surfaces. A total of 37 samples covering 10 different rock types, including barren silicate rocks and rocks with disseminated sulfides, was collected from eight mines around the Sudbury Basin in Ontario. Freshly broken rock surfaces were measured wet and dry to address environmental conditions encountered underground. Spectral data were processed by the second-derivative approach and the spectral angle mapper algorithm (SAM) for rock-type identification. An average of 77% accuracy was achieved for all rock types. The success of this effort implies that hyperspectral analysis using second-derivative spectra is effective to remove the effect of liquid water, local geometry, and disseminated sulfides while preserving diagnostic rock spectral signatures between 700 and 1300 [cm.sup.-1]. Keywords: rock cores, spectroscopy, thermal, underground mining.