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

Jilu Feng^,1, Benoit Rivard^,1, E. Ann Gallie^,2, Arturo Sanchez-Azofeifa^#,3 and Helen Francis^,4

¹ Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada
² Department of Earth Sciences, Laurentian University, Sudbury, Ontario P3E 2C6, Canada
³ Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada
⁴ Mines Research, Inco Limited, Copper Cliff, Ontario P0M 1NO, Canada

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^–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 environmentalconditionsencounteredunder-ground. 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^–1.

Key Words: rock cores • spectroscopy • thermal • underground mining