Evaluation of Tailings from a Porphyry Copper Mine based on Joint Simulation of Contaminants

Abstract

Tailings from porphyry copper mines contain environmentally harmful amounts of elements such as copper, molybdenum, lead and cobalt. Geostatistical simulation of contaminants at unknown locations can be helpful in taking preventive measures for tailings management. In the presence of spatially cross-correlated variables, cosimulation has been the traditional method of evaluation. However, application of cosimulation is cumbersome due to modeling so many auto/cross-variograms at once regarding Cauchy–Schwarz inequality. Moreover, cosimulation may face with an unsolvable system of equations in its algorithm. Then, application of joint simulation using minimum/maximum autocorrelation factors which gives reasonable results would be advantageous. In this study, nine spatially cross-correlated attributes of the Sungun porphyry copper deposit are transformed into orthogonal factors. Each factor is independently simulated by generating one hundred equiprobable realizations through the direct sequential simulation or the sequential Gaussian simulation method. The independent simulations are jointly back-transformed into the original data space using a rotation matrix. Test of the final simulations shows reasonable reproduction of data statistics such as the mean and variance values, cumulative distribution functions, cross-correlations and auto/cross-variograms. For each realization, contamination degrees of the blocks are calculated considering the simulated values of variables, the recovery percentage of contaminants in the tailings and the maximum permissible concentrations of the elements in soils. Blocks are categorized regarding the specified contamination degree thresholds and probabilities of occurrence of low, moderate, high and very high contaminations. Sulfide minerals of copper, antimony, arsenic, zinc, molybdenum and silver consist almost 96% of contaminants. All contaminants are sulfide minerals so that additional bulk flotation of the tailings is suggested for reducing their amounts.