For mining combustible minerals a plurality of boreholes are drilled in a gasifiable seam, e.g., in a coal bed, said boreholes 1 through 4 being intercommunicated by a number of gasification ducts. Then the combustible mineral is initiated to fire, and an oxygen-containing blast gas is blown through some of said boreholes into the gasification ducts, with the result that the generator gas is formed. Simultaneously a carbon- and/or hydrogen-containing blast gas is blown through other boreholes situated along the flow of the generator gas to enrich the latter with combustible ingredients. As a result some chemical reactions proceed under the effect of heat produced by the generator gas, whereby additional amounts of combustible elements are formed which add to the calorific value of the generator gas being withdrawn. The method is instrumental also in controlling the composition of the generator gas withdrawn by varying the ratio of the components of the blast gas enriching the generator gas.