Metal nanoparticles in soil: Indicators of concealed mineral deposits

Abstract

Nanogeology represents a cutting-edge scientific discipline characterized by its multi-disciplinary nature. This study provides an overview of the characteristics and behaviors of metal-bearing nanoparticles in soils above different ore deposits in China. It discusses the proposed origins, migration, and precipitation of these nanoparticles, as well as their applications in mineral exploration. Additionally, this study highlights the challenges and prospects of metal-bearing nanoparticles used in the mineral exploration.

Metal-bearing nanoparticles, which contain varying proportions of ore-related elements (e.g., Au, Ag, Cu, Pb and Zn) are rarely found in natural settings unrelated to ore bodies or mineral extraction. Due to the compositional similarity between metal-bearing nanoparticles in soil and likely link to concealed ore bodies, these nanoparticles can be effectively sampled in the soil, to understand the properties of the deeper concealed mineralization. Therefore, metal-bearing nanoparticles can serve as effective indicators of buried deposits. These nanoparticles may migrate from deep ore bodies to the surface through multi-process relay mechanisms, including geogas flow, atmospheric pressure pumps, electrochemical processes, and plant transpiration. They accumulate in fine-grained soil fractions with larger surface areas and adsorptive potential, such as clay minerals and organic matter, making fine-grained soil an important sink for metal-bearing nanoparticles. By separating fine-grained soil, the intensity of geochemical anomalies can be increased, thereby enhancing the accuracy of mineral exploration. Current research predominantly provides qualitative descriptions of nanoparticle characteristics, lacking quantitative analysis methods. Future efforts should focus on using high-resolution technologies such as Nano Scale Secondary Ion Mass Spectrometry (NanoSIMS), Atom Probe Tomography (APT), Focused Ion Beam Scanning Electron Microscopy (FIB-SEM), and synchrotron radiation to conduct detailed studies on the isotopic composition, internal structure, and elemental coupling relationships of nanoparticles. This approach will allow for better tracing of their origins and realize their potential in mineral exploration.