Simulation techniques are frequently used to solve various problems of operational research for the mining industry and more generally in earth sciences (hydrogeology, gravimetry, meteorology, etc.). First, the model to be simulated is characterized; for example, the spatial dispersion of grades in an ore body. Then a simulation technique is devised, which must be operational, particularly in terms of computer time. The efficiency of the simulation produced is obviously linked to the capacity of the model to fit the main characteristics of the revealed reality. One of the most important of these characteristics, namely the spatial autocorrelation of variables, is often ignored by the models commonly presented in classical literature.The originality of conditional simulation derives: (1) from the fact that these simulations meet the particular spatial autocorrelation function (covariance or variogram) which characterizes the reality observed; (2) from the conditionalization of the experimental data, i.e., the simulated values at data locations equal the experimental values; and (3) from the possibility of working in real three-dimensional space. The simulation technique proposed (turning-bands method) consists of simulating on lines (one-dimensional space) and then turning these lines in three-dimensional space. This procedure avoids the well-known explosion of computer time and memories involved in classical procedures extended to several dimensions. The originality of using conditional simulation techniques with regard to spectral analysis techniques is presented in the third point.