The paper considers the main factors affecting the assessment and forecast of the environmental situation in the exploration and development of ore deposits. The data on the composition of soils, water and bottom sediments in some large mining areas (Norilsk, Komsomolsk, etc.) are presented. It is shown that the variability of mineral and chemical composition of ores and host rocks within the subsurface is one of the most important factors both for solving the problem of rational use of mineral deposits and for predicting the environmental consequences of their mining.