Laboratory reflectance spectra of hydrothermally altered carbonate facies, Pine Point mining camp, NWT, Canada

Abstract

This study uses reflectance spectroscopy to examine cores of hydrothermally altered carbonate facies within the North Trend, Pine Point mining camp. Four alteration types were constrained to specific facies in Pine Point, Sulphur Point, and Windy Point formations. These alteration types, each having a unique spectral signature, are: white dolomite, blue-grey dolomite, white calcite, and blue-grey calcite. The blue-grey calcite and dolomite signatures showed similarities in band positions between 0.8 μm and 1.1 μm, a spectral indicator for the presence of ferrous and ferric iron. The white calcite phase had an absorption feature at c . 1.73 μm likely due to organics. The spectral absorption bands for liquid water (1.4 and 1.9 μm) trapped in fluid inclusions were ubiquitous to all samples. Characterization of carbonates with respect to their timing of deposition (pre-, syn-, and post-mineralization) is complicated by lack of sulphides. Laboratory and field observations determined that blue-grey carbonates contain elevated sulphide concentrations compared to their white counterparts and commonly envelope Pb–Zn orebodies, and therefore this carbonate species may be directly associated with the ore deposition events. The carbonate alteration spectral signatures characterized by this study may be used to further the efficiency of airborne hyperspectral exploration in other Mississippi-Valley-Type districts.