Multi-method 2D and 3D reconstruction of gold grains morphology in alluvial deposits: a review and application to the Rivière du Moulin (Québec, Canada)
AbstractThe aim of this paper is to document and compare the 2D qualitative and semi-quantitative methods currently used to describe the shape of gold grains in fluvial environment to 3D quantitative methods using microtomography and SEM photogrammetry. These 3D methods are used to compute flatness, roundness, convexity, sphericity, and ellipticity shape descriptors of 13 gold grains from the Rivière du Moulin (Québec, Canada) in order to quantify the morphological change along 9 km of fluvial transport. Gold grains have moderate to high values of flatness, compactness, sphericity, and ellipticity indices that do not change significantly with distance of transport, whereas the roundness increases during transport. Gold grains are used to compare 2D and 3D methods and the results show small differences (< 8%) when shape descriptors are computed using image analysis software, whereas the difference (up to 70%) is more important for 2D measurements performed by a human operator. For application and characterization on a large set of gold grains, the 2D methods offer the advantage of speed, whereas, for a more detailed study on a limited number of gold grains, 3D methods enable estimation of the volume and yield more detailed shape descriptors changes during fluvial transport.