TEM observations of particles based on sampling in gas and soil at the Dongshengmiao polymetallic pyrite deposit, Inner Mongolia, Northern China

Abstract

Forty-two samples of particles that were carried by the ascending gas flow and forty-two corresponding soil samples were captured from Quaternary sediments overlying the Dongshengmiao polymetallic pyrite deposit in the Province of Inner Mongolia, North China. The category, size, shape, chemical composition and structure of these particles were analyzed by transmission electron microscopy (TEM) technique. The observations indicated that most of the particles carried by the ascending gas flow were sub-circular, elliptical or irregular in shape, with sizes ranging from 5nm to 400nm; their primary components were dominated by the metallogenic elements Fe, Cu, Zn and Pb, and their highest weight percentages were up to 80.2%, 82.5%, 49.1% and 59.6%, respectively. We determine that a large number of metal sulfides and oxides/hydroxides (such as PbS, Fe3O4, Sb3O2 and Fe(OH)3), native metal alloy (such as native vanadium–platinum–iron–cobalt alloy), nonmetallic oxides (such as SiO2), chlorides (primarily NaCl), nonmetallic hydroxides (such as KOH) and sulfate (primarily BaSO4) particles, as well as precious metal elements (such as Au and Pt) bearing particles and rare earth elements (such as Y) as observed in the samples, exhibited a good correspondence with the concealed ore bodies and the wall rock. A number of the particles that were carried by the ascending gas flow were found in elemental associations S–Cu, S–Zn, S–Pb, S–Mo, S–Fe–Zn, S–Fe–Cu, S–Fe–Cu–Mo, S–Fe–Zn–Pb and Cr–Mn–Fe, which were consistent with previous studies on the mineral assemblages of this deposit. The particles carried by the ascending gas flow and soil particles have a common origin, that is, the ore body. Different particles carried by ascending gas flows come from different types of deposits, without interference from the properties or thickness of the overlying layer, suggesting that geogas prospecting could be used to explore for different types of ore deposits. An analysis of the particles carried by the ascending gas flow along the 14th exploration line demonstrates a good spatial correlation with the known concealed ore bodies. Additionally, Pt-bearing and rare earth element bearing particles were first found in the ascending gas flow from the Dongshengmiao deposit.