This project is to use negative thermal ionization mass spectrometry techniques to examine the 187Re-187Os isotope systematics of the Pechenga ferropicrites and associated Ni-Cu ores (Kola peninsula, USSR). The specific objectives of this research are: 1) to obtain information about the Os isotopic compositions of the mantle sources for these rocks, and constrain the geochemical behavior of Re and Os doing mantle melting and the subsequent crystal-liquid differentiation that produced these compositionally diverse suites, and 2) to utilize the Re-Os system as a tracer for determining the sources of noble metals contained in the Pechenga ores. Ultimately, because of the geochemical characteristics of Re and Os, the Re-Os system will provide new insights into the chemical evolution of the mantle and crust, and lead to a better understanding of noble metal ore formation.