Abstract：The geochemical block theory has been applied to analysis and processing of geochemical prospecting data from the whole province of Gansu, and a total of 173 geochemical blocks of 14 elements has been outlined, including 25 geochemical megaprovinces and 148 geochemical provinces. The authors have summarized the spatial distribution characteristics of geochemical blocks and traced the possible localities of occurrence of large to superlarge deposits through a study of the internal structure of the geochemical blocks. By using the metal reserves identified inside the blocks they have calculated the ore potentiality, predicted the metal resources of other elements or other areas, delineated ore prospect areas and determined seven ore targets of giant deposits. Based on a study of the relations between different ranks of geochemical blocks and the metallogenic regions and belts, important geochemical blocks and sub-blocks, metallogenic sub-belts and ore fields have been correlated and the potentials of regional mineral resources inside the geochemical blocks have been evaluated.