Deposits of gypsum developed in an open pit manner differ in a number of features of the geological structure, the main among which is their extremely high cavernous porosity. In the article, the method of generation the hypsometric maps of gypsum top based on determination of CaSO4×2H2O content in the blasting boreholes is offered. The hypsometric map constructed by this method entirely characterizes features of the geological structure of the blasting block. Filled with clay karst caverns in a roof of gypsum are distinctly allocated that allows reducing losses and impoverishment by proper planning of further extraction. Furthermore, the presented method allows more precisely determining the volume of gypsum and the impoverishing material within blasting blocks. Comparative analysis of currently used methods of calculation the quality gypsum volume shown that offered technique is capable to increase significantly the quality of the extracted gypsum and efficiency of its production.