Differences in Runoff, Leachate and Erosion, Generated By Rainfall on Slope Forming Materials from an Iron-Ore Mine, West Africa

摘要

Erosion and runoff can disrupt mining operations, make roads impassable and cause the off-site transport of contaminants. Managing this can become very expensive. Published data on the erodibility of slope forming materials (SFMs) at mine sites, including ore, soil and overburden are sparse, especially for African conditions. The physical and chemical properties of ten SFMs (comprising soil and non-soil samples) derived from an Iron-Ore Mine in West Africa were compared. Properties included organic carbon, CEC, pH, EC, density, particle size and dry-aggregate distribution, mineralogy and magnetic susceptibility. Leachate, runoff and eroded material were assessed under simulated tropical rainfall using SFMs at air-dry antecedent moisture conditions. Multiple-Regression Analysis was used to correlate SFM physical and chemical properties with runoff, leachate and erosion results. Differences in physical and chemical properties of the SFMs are not as clear cut as expected. Leachate processes are shown to be as important as runoff in terms of generating water flow and sediment on unconsolidated SFMs. No significant differences were observed between soil and non-soil SFMs in terms of leachate and runoff volumes, and erosion. Soil SRE and non-soils PHY-WEA and HRS generated runoff volumes and erosion rates that were at least double, if not several magnitudes greater than other SFMs. Soil LITH and non-soils COMB-WEA, NEW-WEA and RD generated leachate volumes and erosion rates significantly higher than the other SFMs The results provide a greater understanding of the erosion processes affecting soils and non-soil SFMs and have important implications for the management and design of rock-waste dumps, sedimentation ponds and water discharge facilities on mine sites. A more explicit classification system that distinguishes regolith or saprolitic non-soils from hard rock, non-soils would be useful in predicting runoff and leachate responses. This study shows that variables including magnetic susceptibility and mineralogy, which are not commonly assessed in erosion studies, are important in terms of erosion and leachate processes affecting SFMs. However, more research is required to determine how magnetic susceptibility and mineralogy affect rainfall-induced erosion processes.