HYPERSPECTRAL IMAGING OF MARBLE-HOSTED SAPPHIRE FROM THE BELUGA OCCURRENCE, BAFFIN ISLAND, NUNAVUT, CANADA

Hyperspectral imaging has been used to investigate spectral characteristics of the marble-hosted sapphire occurrence on Baffin Island, Nunavut, Canada. The Beluga corundum showing is hosted in the ~1.9 billion year old Lake Harbour Group of metasediments, and is associated with calc-silicate lenses within a larger marble package. Associated minerals include plagioclase, clinopyroxene, phlogopite, muscovite, calcite, graphite, nepheline, and scapolite among other rare phases. The Lake Harbour Group is also host to other gem occurrences such as lapis lazuli, diopside, tourmaline, pargasite and spinel, and several geologists have published on the high gem potential of these rocks (e.g., Gertzbein 2004, Butler et al. 2007, Sanborn-Barrie et al. 2008).

In total, 35 samples were studied using high spatial (~0.25 mm / pixel) and high spectral resolution (VNIR-SWIR, ~550 nm to 2500 nm). Hand samples and thin section offcuts were studied, allowing comparison between previous petrogenetic studies (e.g., Dzikowski 2013) and the new hyperspectral imaging datacubes.

Both academic and exploration work identified the importance of scapolite, nepheline and phlogopite in association with gem corundum mineralization. Each of these minerals was shown in this study to have distinct spectral responses readily distinguishable from the host calcite. This preliminary investigation of the hyperspectral images was able to successfully reproduce mineralogical and textural information relevant to gem mineralization that was extracted through conventional thin section petrography. However, hyperspectral remote sensing can be scaled up from the thin section scale to an outcrop or landscape scale.

Thus, early results from this research suggest that hyperspectral imaging can not only be useful in understanding mineralogical relationships of the rocks, but also be particularly useful via airborne surveys for gem exploration in areas with good outcrop exposure or excavations, such as in the Canadian North.

Future work is aimed at better understanding the relationship between gem corundum mineralization and its indicator minerals, such as scapolite, as well as the spectral responses of these indicator minerals.