The deep structure is modeled for the crustal block in the Kolpakova River basin of the Kamchatka Peninsula. A technique for developing the 3D density model on the basis of the data derived from interpretation of gravity anomalies is described. The model is used for outlining the position and shape of the massive bodies in the upper crust, which are identified with intrusions of the Dukuk nickeliferous magmatic complex, with identification of areas promising with respect to metal deposits genetically associated with intrusive mafic and ultramafic magmatism. It is shown that the proposed technique represents an effective tool for the study of the inner structure in regions poorly studied by deep geophysical sounding methods or as yet completely lacking such data.