TEM study on particles transported by ascending gas flow in the Kaxiutata iron deposit, Inner Mongolia, North China
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Metal migration processes, by means of gas-transported particles, from an iron magnetite skarn deposit beneath Quaternary transported overburden, to surface was studied at the Kaxiutata iron deposit. This study area is located in the desert of the Inner Mongolia region in northern China. Ascending gas-transported particles were collected using passive adsorption methods; a total of 50 samples were obtained over the known mineralization (30 within the mining area and 20 from the exploration area), and 15 samples were collected over background areas for comparison. The morphology, categorization, and chemical composition of particles in these samples were determined by transmission electron microscopy (TEM). In the mining and exploration area, the particles related to the subsurface mineralization (ore-bearing particles) are primarily Fe-, Cu-, Zn-, Pb-, and Bi-bearing, and particles show significant common characteristics. Sulphur is generally absent, or its content is notably low. However, based on the geological description of primary mineralization, Cu, Zn, and Pb occur mainly as sulphides, implying that the minerals were subjected to in situ or transport-associated oxidation. Most particles are actually aggregates of various smaller particles of diverse origin. Evidence of oxidation and agglomeration of particles may reflect the high porosity and gas permeability of the sandy overburden, which provides an oxidizing environment for gas-transported particles. The distribution of ore-bearing particles is correlated with the subsurface mineralization. Iron-rich particles (> 30% Fe) and Cu-, Zn-, and Bi-bearing particles collected above the mining area were also collected in the exploration zone, and these types of particles are likely indicators of underlying iron mineralization. Samples collected from the background zone revealed no Cu-, Bi-, Mo-, and Pb-bearing particles. The migration mechanism of gas-transported particles in the desert area is summarized and discussed based on this and previous studies.