LINKING SECONDARY MINERAL FORMATION IN LATERITIC REGOLITH WITH PREFERENTIAL FLOW ACTIVITY

Preferential flow (PF), a non-uniform and fast movement of water and solutes through preferred pathways in soils, is well recognized to be a significant hydrological process that impacts soil formation and soil inhomogeneity. Here we present a case study of “garnierite”, a mixture of Ni-rich secondary minerals discovered from a serpentinite-derived lateritic regolith, providing several lines of evidences to illustrate the possible links between secondary mineral formation and PF activity. Our work indicates that: (1) the occurrence of garnierite is a typical non-uniform pattern, spatially associated with fractures, joints, and other macropores in the lower part of the soil profile that are commonly associated with PF activity; (2) garnierite shows a typical colloidal texture, indicating that the source of these minerals are originated from a weathering solution with colloidal nature, and the transport of such colloidal solution in the soil has been proved to be mainly driven by PF; and (3) garnierite demonstrates many comparable geochemical features with those PF domainated soils studied previously, especially higher organic matter concentration and lower soluble and exchangeable element speciation, which could be attributed to the effect of biological hot spot and soil-water interaction within the PF domain. These observations suggest that the garnierite is both spatially and genetically linked to PF, and it could be explained as a PF-driven weathering product due to improved leaching and precipitation processes within the PF domain. This study provides insight into the understanding of soil mineral formation from a hydrological perspective, especially for those secondary minerals with non-uniform occurrence.