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Zhang B.,China University of Geosciences | Zhang B.,Chinese Academy of Geological Sciences | Zhang B.,Key Laboratory for Geochemical Exploration Technology | Wang X.,Chinese Academy of Geological Sciences | And 9 more authors.
Journal of Geochemical Exploration | Year: 2016

Desert terrains are widespread in northwestern and northern China, and these areas present particular challenges for exploration. In recent years, partial extraction techniques have been proven to be effective in the search for concealed deposits in arid desert terrains in some cases. However, we still lack an understanding of the dispersion patterns of ore-forming elements in regolith. In this study, air reverse circulation drillings were used to create three-dimensional (3D) distribution patterns of elements in regolith over the Jinwozi gold deposit in China, which is covered by tens of metres of regolith, in order to trace the migration of elements and to understand the dispersion mechanisms. The 3D distribution maps of elements show that (1) coherent anomalies occur at different depths of transported cover over the ore body, (2) Au tends to be enriched in the top and bottom horizons and depleted in the middle horizon in the vertical direction, (3) the anomalous distribution of Au at the bottom is restricted to places at the interface of sediments and bedrock, and (4) the anomaly in the bottom sediments is confined to a width of tens of metres, whereas that in top soils is much wider and can extend up to several kilometres. In addition, close positive correlations were found between the As, Hg, and Au distributions. © 2015 Elsevier B.V. Source


Zhang B.,Chinese Academy of Geological Sciences | Zhang B.,China University of Geosciences | Zhang B.,Key Laboratory for Geochemical Exploration Technology | Wang X.,Chinese Academy of Geological Sciences | And 13 more authors.
Journal of Geochemical Exploration | Year: 2015

Geochemical exploration has focused on concealed deposits at the periphery of the Zijinshan Cu-Au mine, a volcanogenic hydrothermal-type deposit and one of the largest Au deposits in southeastern China. Recently, near the Zijinshan deposit, a concealed Ag-Au-U deposit was discovered below volcanic sequences in the Yueyang Basin to the east of Zijinshan and a blind porphyry Cu-Mo deposit was found in the Luoboling Basin to the west of Zijinshan. In this study, sampling of a soil profile was undertaken at a spacing of 25. m across the Yueyang Ag-Au-U mineralisation. Samples collected from the soil B horizon, generally at a depth of 5-30. cm, were then sieved to < 75. μm and analysed by near-total digestion (four-acid digestion) and selective leach partial digestion techniques in order to compare the effectiveness of the two methods. Later, additional geochemical research for concealed deposits was carried out across the Yueyang Ag-Au-U, Zijinshan Cu-Au, Wuziqilong Cu, and Luoboling Cu-Mo deposits. Sampling of soil profiles was undertaken at a spacing of 50-100. m. Samples were also sieved to < 75. μm and analysed by near-total digestion. The results show that (1) these two methods reveal similar geochemical anomalies and both effectively locate the concealed Ag-Au-U mineralisation in the Yueyang Basin, and (2) that the spatial distribution and suites of elements are consistent with the mineralisation types, i.e., Ag-Au anomalies occur above the Yueyang Ag-dominated polymetallic deposit, Cu-Au-Ag-As anomalies occur at the Zijinshan Cu-Au deposit, Cu-Ag-Au-As anomalies occur at the Wuziqilong Cu deposit, and Cu-Mo-W anomalies occur over the Luoboling Cu-Mo deposit. In addition, Au-Cu-bearing nanoparticles were observed in geogas from above a concealed Ag-Au mineralisation using a transmission electron microscope (TEM) equipped with energy dispersive spectroscopy. These results imply that fine-grained soils inherit minerals derived from in situ weathering of surface rocks and can adsorb mineralisation-related elements migrating from underlying deep-seated ore bodies. Total and partial analysis of fine-grained soils can be used for geochemical exploration to locate concealed deposits in areas covered by barren rock sequences. © 2015 Elsevier B.V.. Source

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