Deep-penetrating Geochemistry: Mechanism And Methods In Gobi Areas

The vast area of China's Gobi desert has a great potential for prospecting concealed ore deposits. This region is technically difficult for geochemical exploration due to dry climate and overburden covers. The objectives of the paper are to reveal mechanism of deep-penetrating geochemical anomalous formation of a concealed gold deposit in Gobi covering areas based on geochemistry, geology and geomorphology, and analysis of the landscape evoiution of Gobi desert, physical and chemical properties of covering regolith, to understand three-dimensional distribution of Au and associated elements in covering regolith by using overburden drilling, to improves the deep-penetrating geochemical methods. The main conclusions are as follows:1. The element anomalies in covering regolith layer have the obvious inheritance relationship in different depth over ore body and present contents of elements are higher in the top and bottom layers than those in the middle layer. Anomalies in the bottom of the covering layers are mainly concentrated near the altered zones and its surrounding lowlands. In the top layers, there are corresponding surface anomalies, but anomalous distribution area and concentrations are more than those in the bottom layers.2. The study area has experienced a complicated geological and weathering process from the ore formation, to the lateral dispersion under the process of pediplanation, the vertical migration, until to lateral dispersion at regolith surface. The eroded gold mineralization rocks were mechanically transported and deposited in the lowest places. The elements vertically migrate to the soil surface by earthgas extending and are captured by geochemical barrier such as clays in the fine-grained soils. After that the secondary lateral migration at soil surface formed a widely broad range of anomalies, which is the premise of low-density deep-penetrating geochemical methods to delineate regional targets in covered terrains. The laboratory research on geochemical migration finds that some high concentration of elements in the ore can migrate at least several meters every year. This means that at millions-of-years scale of the quaternary evolution history, elements quite have the ability to move hundreds of meters to the earth surface from the depth.3. A deep-penetrating geochemical procedure for different exploration stages from regional to local are proposed based on above-mentioned theoretical studies. In regional survey stage, the micro-particle measurement technique can be cost-effective to delineate regional targets. In local stage, combinations application of the micro-particle measurement, selective leaching of mobile forms, earthgas and electrogeochemical methods can be effective for location of ore body targets. Reverse circulation air drilling technology is an ideal choice for evaluating geochemical anomalies pinpointing ore bodies in covered area.