Estimating sulphide ore grade in broken rock using visible/infrared hyperspectral reflectance spectra
The field of hyperspectral remote sensing has developed rapidly for widespread mineral mapping from airborne platforms. The purpose of the current study was to examine whether hyperspectral spectrometry (0.35-2.5 m) can be used in an underground mining environment for mapping the grade of sulphide ore in rock faces, hand specimens and core logging. Naturally broken samples of barren and ore-bearing rocks were collected from mines in the Sudbury Basin, Ontario, and dry and wet reflectance were measured. The sulphide minerals exhibit a one-sided absorption band at short wavelengths known as a conductance band. The hydroxyl-bearing silicates exhibit a triple absorption feature near 2.3 m. Two ratios, one describing the conductance band and one describing the hydroxyl band, can be used to separate high grade ores (>20-25% sulphides) from barren and lower grade rocks. The conductance band ratio can also be used to estimate the concentration of chalcopyrite alone, ±15% chalcopyrite, absolute. Errors are proportional to the concentration of pyrrhotite and pentlandite. Errors can be reduced if total sulphides are estimated by other means, which a parallel study indicates is possible using thermal reflectance wavelengths. The study indicates that there is a high potential to use hyperspectral tools to grade sulphide ores.