Characterization of metal-bearing nanoparticles observed in loess-covered terrain: Implications for prospecting

The recent depletion of mineral resources near the Earth's surface has led to a shift in mineral exploration toward concealed deposits in covered terrain. Consequently, significant attention has been directed toward metal-bearing nanoparticles in the soil above such deposits to gain insights into the composition of concealed ore bodies.

In this study, the characteristics (type, size, shape, chemical composition, and aggregation) of metal-bearing nanoparticles in ore samples of the Zhonghedi Ag-Pb-Zn polymetallic deposit and their overlying loess were systematically analyzed using transmission electron microscopy. Numerous nanoparticles containing Ag, Au, Cu, Pb, Zn, Fe, Mo, and other metallic elements were observed in the loess overlying the deposits as well as the ore samples. These nanoparticles exhibit a well-defined crystal shape, suggesting their primary particle nature. Moreover, the nanoparticles in the loess and ore samples share similarities in element distribution, size, and type, demonstrating their homologous nature. However, ore-related metal-bearing nanoparticles were not detected in samples collected from the background areas. Most metal-bearing nanoparticles in loess, excluding native particles, were oxides and sulfates, which may be attributed to oxidation of the native metal particles near the surface where oxygen fugacity increases. The elemental mapping of the nanoparticles showed that the ore-forming elements had the same distribution patterns and element assemblages to the ore material. These results indicate that metal-bearing nanoparticles in the loess have likely relationships with concealed ore bodies. Accordingly, the metal-bearing nanoparticles in the loess can provide information about concealed ore deposits, explain surface geochemical anomalies, and improve prospecting accuracy as a vector to mineralization.

Routinely finding nanoparticles in transported cover remains a challenge. However, this study shows it is viable and marks substantial progress in our knowledge and comprehension of metal-bearing nanoparticles in loess-covered terrain. Evidence of their presence and association with concealed ore bodies contributes significantly to our understanding of mineral exploration processes and offers new avenues for future research and practical applications.