Quantitative 3D shape descriptors of gold grains from Quaternary sediments: application to mineral exploration in glaciated terrain, Amaruq orogenic gold deposit (Nunavut, Canada)

Abstract

Native gold is malleable and deforms during glacial, fluvial and eolian sedimentary processes. Quantification of its morphology is used in mineral exploration to estimate a distance of transport from its primary source. However, this quantification depends on textural aspects, or on partial 2D measurements of gold grain shapes. In the glacial domain, the classification of the shape remains qualitative and subjective. Microtomography and photogrammetry using scanning electron microscope images are two methods used to reconstruct the gold grain shape in 3D and to quantify accurately grain shape parameters. Reconstructions are applied on gold grains ranging in size from 35 μm to 415 μm for the long axis and 2716 μm3 to 760,713 μm3 for the volume. Shape parameters such as particle length, volume, and surface area are estimated in order to compute 3D shape descriptors of roundness, sphericity, and convexity. This study integrates two new shape descriptors (the ellipticity shape descriptor and inscribed sphericity) in order to estimate the ellipticity and sphericity of gold particles. These descriptors can be used to evaluate a morphological change with the distance of transport in glacial sediments such as in the Amaruq gold deposit area.