Nanoparticles Observed by TEM from Gold, Copper-Nickel and Silver Deposits and Implications for Mineral Exploration in Covered Terrains

Geochemical exploration for concealed deposits covered by thick rocks overlying, transported soils present special problems. Geochemists conjectured that ultrafine metal particles or metal elements could be carried onto bubbles or micro-flow of geogas and migrate upward to the surface and ultrafine metal particles or metal elements transported to the surface by gases could be trapped by soil geochemical barriers. After years of study, ultrafine metal particles as nano-scale have been extensively observed in the geogas samples. In this study, nanoscale particles were observed in soils over three concealed ore deposits by using transmission electron microscope (TEM). The particle characteristics in sizes, shapes and chemical compositions are compared for study on the three types of Au, Cu-Ni, Ag Deposits. The results show that (1) nanoparticles of native metals or alloys widely occur in soils, geogas, and ores in the three mineral deposits; (2) nanocrystals occur in soils, geogas, and ores; (3) the sizes of nanoparticles are similar in diameter from 5 nm to 100 nm; (4) the particles tend to agglomerate into clustering forms; (5) the most obvious difference among nanoparticles collected from the three types of deposits is the chemical compositions that nanoparticles at Au and Ag-polymetallic deposits have Au element, while nanoparticles at Cu-Ni deposit have Ni and Cr elements; (6) nanoscale metal particles are not discovered in the samples collected from the background zone. The results indicate that nanoparticles of metals have good inheritance relationships with the deposits. The nanoscale particles of native metals or alloys from the ore body can migrate with the ascending flow of gases through structural fissures or rock pores upwards to the surface. On arriving at the surface, some of the particles persist in the soil, whereas gases and other particles are trapped by soil geochemical barriers. The discovery of nanoscale particles in geogas and soils over concealed ore bodies also provides direct observation evidence for deep-penetrating geochemistry using soil and geogas as sampling media to search for deeply concealed ore deposits.