The economic limits of in situ leach mining

Different technological procedures used for the chemical mining of uranium differ for one thing with a level of the deposit exploitation and for another with the expenditures. It is necessary to find out the highest acceptable value of the costs per unit of production - limit unit costs. This criterion serves both for selection of the minable parts of deposit, and for determination of the exploitation level of the deposit parts. The paper describes a calculation of the costs and their decomposition into the fixed and variable costs. An evaluation of the different variants of the deposit exploitation is based on the variable costs, expressed in the dependence on the parameters of technological procedure. These parameters are either primary, e.g. density of the wells or dosage of reagents, or secondary, e.g. the uranium production. A relation between primary and secondary variables is defined by the technological models. The first economic optimization calculations for uranium mining were carried out in Czech Republic in 1988. The Straz deposit uranium reserves were split into several categories and for each of them a set of different mining procedures (including economic evaluation) was calculated. For optimization of the exploitation three basic strategies were chosen: maximization of the production, minimization of the costs and maximization of the profit. Already this first calculation showed a necessity of higher differentiation in approach to different parts of the deposit - from very economical mining regimes to very sharp ones. An application of proposed arrangements brought great economies. In the beginning of the 90's a new generation of the technological and economic models was developed. These models have given a possibility to make the limit costs more precise under changed economic conditions of transformation of Czech Republic to the market economy. (author)