Microscopic characterisation of metallic nanoparticles in ore rocks, fault gouge and geogas from the Shanggong gold deposit, China

Geogas prospecting is a potential method for exploring concealed ore bodies. However, a knowledge gap still exists regarding the relationship between metal-bearing nanoparticles (NPs) found in geogas and concealed ore bodies. In this paper, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were applied to study the occurrence of metal-bearing NPs in ore, gouge and geogas samples collected from a fault zone and a background area of the concealed Shanggong gold deposit. SEM observations of ore rocks showed that gold was mainly concentrated in microfractures and its distribution was correlated with that of Mo, S, Pb, and Co. According to the results of SEM, gold can coexist with pyrites in the form of sub-microscopic particles, as NPs or dispersed in a lattice. TEM analysis and in situ SEM observations of ore rocks suggested that gold and other metallic particles can form during the process of mineralization. After mineralization, it is hypothesized that NPs can be generated by faulting and weathering. Meanwhile, morphological and chemical composition analyses indicate that aggregation and biological activity can change the status of NPs occurrence in fault gouges. TEM showed that there were more particles in the ascending geogas collected in the fault zone than in the background area. In terms of composition, particle samples collected from the background area were primarily non-metallic oxides and aluminium silicate. More metallic NPs containing Zn, Cu, Cr and Ni were observed in geogas collected in the fault zone. As for morphology, while the NPs in the fault zone geogas showed various morphologies, spherical dominated in geogas from the background area. These results suggest that NPs in ore rocks and gouge can be rapidly channelled to the surface through faults. The driving forces of NP transportation may include of temperature and pressure differences and the earth's magnetic field. This knowledge consolidates the view that NPs in geogas can provide information about the deep Earth. This study increases our knowledge of NPs in gold deposits, fault gouges and geogas, and enhances our understanding of NP generation and migration mechanism sin fault systems. •Gold coexists with pyrites in the form of sub-microscopic particles in ore rocks from Shanggong gold deposit.•A fault can act as both a migration channel and a producer of NPs•Aggregation and biological activity can change the status of NPs occurrence in fault gouges.•Temper