Uranium mineralisation in roll front deposits mined in Kazakhstan is due to the circulation of uranium bearing oxidized fluids. Deposition associated with permeability and redox properties of the host rocks, results in very complex deposit geometries, and high heterogeneity uranium grades.
In deep and low grades deposits, uranium is extracted by in situ recovery (ISR or ISL), via a network of drillholes which combine wells injecting acid solutions, and wells producing pregnant uranium solutions.
Stochastic simulation methods allow for the characterization of ore deposit uncertainties, by identifying parameters with the highest impact on the confidence level of reserves, and therefore it is a valuable aid to production planning.
This paper describes direct application of uncertainty assessments for drilling campaigns.
On completion of exploration drilling, the deposit is modelled in 3 dimensions with pluri-gaussian simulations to characterize the variability of lithology, redox context and ore body geometry. Several approaches are used and compared. The first is based on drill hole data and vertical proportion curves, whereas the second integrates the geological interpretation of the deposit through a 3D deterministic model. Uranium grades are then simulated in permeable mineralised rocks.
Simulation results are summarized using probability maps which are analysed to identify new areas of interest. Additional drilling is proposed to reduce the inherent uncertainties concerning ore geometry.
When ore limits are defined, borehole spacing inside exploitation limits is dictated by the uncertainty level assigned to the reserve estimation and mining plan.