Deep-penetrating geochemistry for concealed sandstone-type uranium deposits: A case study of Hadatu uranium deposit in the Erenhot Basin, North China

摘要

Traditional geochemical exploration methods are not effective for locating concealed sandstone-type uranium deposits occurring at depths of hundreds of meters in sedimentary basins. In order to identify and trace the geochemical anomalous sources from the deposits in overburden regions, systematical luminescence intensity analyses have been carried out on mineral particles from both near-surface late Quaternary sediments and drillcore samples from the Hadatu sandstone-type uranium deposit in the Erenhot Basin. Luminescence intensity analyses yielded much older optically stimulated luminescence (OSL) ages for quartz minerals in late Quaternary sediments than their true depositional ages. In the same sedimentary layer, the apparent quartz OSL ages around the medium-grade borehole are particularly higher than those of the low-grade borehole. Therefore, the anomalies and the variations of these quartz OSL ages in late Quaternary sediments were ultimately controlled by concealed sandstone-type uranium deposits beneath. In contrast, the feldspar infrared stimulated luminescence (IRSL) signals of drill-core samples show no co-variations with deposits grade and sampling depth. Given the oversaturated luminescence signals on minerals from drill-core samples, they have no potential to unravel concealed sandstone-type uranium deposits. The strongly positive correlation between quartz OSL ages and previously published near-surface Rn anomalies in sediments confirms that the combination of OSL and areal Rn measurements is a cost-effective prospection approach for concealed sandstone-type uranium deposits.