Abstract
Mineral deposits concealed by thick cover sequences present special problems for geochemical exploration. A variety of penetrating geochemical methods have been developed in the last few decades to explore for buried deposits. The theoretical basis of the mechanism by which metals migrate upward from buried deposits through the cover to the surface is still not fully understood. One hypothesis is that metal particles or metal elements could be carried onto bubbles or micro-flow of geogas and migrate upward to the surface. After years of study, nano-scale metal-bearing particles have been widely observed in geogas samples from different kinds of concealed deposits. However, the occurrence of these metal-bearing particles carried by geogases in near-surface media, such as soil, has not been studied in detail. In this study, metal-bearing nanoparticles were observed in samples from soils and fault gouges over the Shenjiayao gold deposit. The results indicate that (1) the ore-forming elements in soils can only come from deep-seated ore bodies and they occur in nanoparticles in the study area; (2) there is an obvious relationship between metal nanoparticles in fault gouges and soils; (3) the metallic nanoparticles in fault gouges represent a transitional phase along the whole vertical migration process. In addition, the observation results show that the metal-bearing nanoparticles tend to be adsorbed on the surface of clay minerals, which provide theoretical support for using fine fraction soils as sampling media to carry out geochemical exploration in sediment-covered terrains. Based on the results and discussion, a simple migration model was built in this paper.
Highlights
As discoveries of world-class mineral deposits continue to decline, increased attention is being focused on geochemical exploration methods designed for terrains covered by thick regolith [1,2]
Two fault gouge samples were collected from a deep gully over the ore ore bodies in loess-covered the loess-covered soil samples collected the background area,three and bodies in the area,area, threethree soil samples werewere collected in theinbackground area, and three ore samples were collected in the underground mine
The scanning transmission electron microscope with high angle annular dark field (STEM-HAADF) image (Figure 3e) reveals that some smaller nanoparticles are attached on the surface of a big particle
Summary
As discoveries of world-class mineral deposits continue to decline, increased attention is being focused on geochemical exploration methods designed for terrains covered by thick regolith [1,2] These methods include partial extraction techniques, geogas analysis, electrogeochemistry, biogeochemistry, hydrochemistry, etc. Geogas is an effective method in the search for concealed deposits in covered terrains and has been used for mineral deposit exploration with satisfactory results [9,18,19,20,21,22,23,24,25] This method is based on the assumption that the geogas could carry ultrafine metal-bearing particles or metal elements in the form of tiny bubbles or micro-flow and migrate upwards to the surface [9,12,18,26,27,28,29]. The content of these ore-forming elements are usually lower than
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