Characterization of metal-bearing particles in groundwater from the Weilasituo Zn-Cu-Ag deposit, Inner Mongolia, China: Implications for mineral exploration

Abstract

Nanoparticles in groundwater have important implications for facilitating the transportation of metals in groundwater and, to a certain extent, can reveal the geochemical conditions of the groundwater. Therefore, there is an increasing interest in analytical techniques that allow for in-depth characterization of nanoparticles in the groundwater and utilize these characteristics for geochemical prospecting. Metal-bearing particles in groundwater samples from deep-lying orebodies (referred to as “deep groundwater”) of the Weilasituo Zn-Cu-Ag Deposit, Inner Mongolia, China and the groundwater from motor-pumped wells of a catchment basin around Weilasituo were chosen to study. Using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and transmission electron microscopy (TEM) coupled with energy dispersive X-ray spectrometer (EDS), individual particles were characterized. Based on the TEM compositional and structural investigation, Ag-, Pb-, Cu-, Zn-, Sn-, As- and Mo-bearing particles were observed in the groundwater samples collected in the deep ore and the catchment basin. These metal-bearing particles are compositionally and structurally similar to the ore mineral/metal-bearing particles observed in the ore bodies and can directly reflect the ore-forming elemental characteristics, e.g., metallogenic element assemblage and mineralization type, of the Weilasituo deposit. The result indicates that the metal-bearing particles originating from the concealed ore bodies migrate via the groundwater flow and discharge to the catchment basin. This finding implies that the metal-bearing particle phases have great significances in facilitating the transportation of ore-related species and forming the geochemical anomalies in the groundwater. This field-scale study demonstrates that, by applying the analytical transmission electron microscopy, the nanocharacteristics of metal-particles can be utilized to improve the accuracy and sensitivity for geochemical mineral exploration.