Uranium deposits (In-situ leach projects)

Abstract

Sandstone-type uranium deposits are commonly located below the water table in weakly lithified or non-consolidated sands, and therefore they can be exploited using In-Situ Leach (ISL) technology. Such technology is based on dissolving uranium minerals directly in their host rocks (in-situ) by reactive solutions that are injected through drill holes, and then pumping the dissolved solution to the surface through some discharge drill holes. Estimation and reporting of uranium resources for ISL projects differ from hard rock mining projects. Uranium grade is determined by downhole geophysics, in particular the gamma-logging and the prompt fission neutrons logging coupled with sampling and assaying of the drill core. The main parameters which need to be considered are as follows: • grade and geometry of mineralisation are estimated with accuracy sufficient for supporting the remote mining • if grade is estimated using the gamma-logging technique secular disequilibrium should be studied and reported • hydrogeological confinement of the mineralised horizon • permeability of the mineralised horizon • composition of the host rocks, in particular the carbonate content, in order to estimate if uranium mineralisation is amenable to dissolution by acid or alkaline solutions • groundwater flow • aquifer salinity • rate of the in-situ dissolution of the uranium minerals. Hydrogeological and geotechnical information is obtained by testing the drill core samples and by using the pump tests and the downhole piezometers. Modifying factors for conversion resources to reserves are verified and corrected using field leach tests of uranium.