Using Soil Magnetic Susceptibility Proxies to Estimate Overburden Thickness Overlying Ore of Lateritic Soils in Sulawesi Island Indonesia

Abstract

Sulawesi Island is one of the largest Ni ore producers in Indonesia. It is also expected to be a significant potential source of some critical metals (e.g., Co, Sc, rare-earth elements, and platinum-group elements). However, few studies show the post-mining impact on some heavy metal elements concentrated in this area. Therefore, improving the efficiency and effectiveness of soil organization and its effect on soil reclamation after mining is helpful. This study aimed to determine the accuracy in estimating the thickness of the overburden covering the nickel ore body profile from lateritic nickel post-mining areas by magnetic susceptibility measurements to discrepancy the overall laterite horizon, whereas χLF and χFD are used to distinguish the overburden zona and limonite and saprolite zone. The lateritic profile studied consists of soil formation of Fe-rich material in the Morowali, and Pomalaa block. We also evaluated the chemical element content of the soil and understood the relationship between the magnetic and geochemical properties of the soil. This study reveals the superparamagnetic (SP)-enriched soils indicated with the increase of the FD% values into the upward horizon, where the maximum values of FD are generally found at ranges 1 to 4m, indicating the overburden layers. Meanwhile, in the depth of 4m to 6m, the values of FD vary only slightly in the lower part initiated by the limonite layers, and then > 6m decreases sharply to the bottom, indicating the saprolite layers. The chemical element mobility trends indicate that Fe, Co, Cr, Mn, and Ti increase toward the layers, which is the same pattern as in FD. Due to this, parameters magnetics may also be a new geophysical approach for estimating the distribution of economically valued minerals on lateritic soils. The strong correlation of Co with Fe, Mn, and Cr in all layers indicates the influence of weathering o n these ultramafic rocks. This suggests an increasing trend toward prolonged pedogenesis.