It is shown that the share of mantle, crustal and sedimentary substances in rocks and ore formations may be determined by isotope methods. On an example of Yakutian kimberlites a prove of mixing processes of mantle and crustal substances by means of strontium isotopes is delivered. Due to the high sensitivity of strontium to hydrothermal disturbances, the combined use of neodymium and strontium isotopes is believed to be a more perfect approach to the problem of determining the share of mantle substances. This is demonstrated by an application of isotopes to REE-minerals and alkaline rocks of Eastern Siberia and the Peoples Republic of Mongolia.