Delineation of geochemical blocks for undiscovered large ore deposits using deep-penetrating methods in alluvial terrains of eastern China

Many large ore deposits have been discovered in eastern China along the Circum-Pacific Rim. However, alluvium, which covers most of the terrain, prevents a complete assessment of the mineralization potential by geological and conventional geochemical approaches. Two deep-penetrating geochemical methods—collection of nanoscale metals in earthgas (NAMEG) and selective leaching of mobile forms of metals in overburden (MOMEO) have been used to investigate the possibility to delineate geochemical blocks generated from large ore deposits buried by alluvial terrains. A wide-spaced sampling was carried out in an area of approximately 250 000 km² at density of one sample per 400–800 km². The soil samples were subjected to MOMEO leaching and were analyzed for Au, Ag, Cu, Pb, Zn, Fe, and Mn by atomic absorption spectrometry (AAS). The earthgas samples were analyzed for 17 elements by INNA. The results show that water-extractable metals by MOMEO processing can give prominent expression to concealed deposits and can delineate large-scale geochemical anomalies in the alluvial terrains. The distribution of gold in earthgas is situated along the largest deep fault systems and the concentration centers distribute in the secondary faults on the both sides of the deep fault systems.