New Data on the Composition of Plagioclase on the Western Flank of the Oktyabr’skoe Deposit: Evidence from the Data of IR Spectroscopy

Plagioclases from gabbroids of the Kharaelakh intrusion on the western flank of the Oktyabr’skoye deposit were studied using infrared spectroscopy. An analysis of 130 Fourier IR absorption spectra of plagioclases indicates a regular compositional change in the isomorphic series from andesine (1150 and 1096 cm –1 ) to anorthite (1142 and 1275 cm –1 ) depending on the degree of rock differentiation in the intrusion. The data of IR spectroscopy were verified by control X-ray microanalysis of the chemical composition. The Fourier IR spectra indicate that andesine is associated with olivine-bearing and olivine gabbro–dolerite. Anorthite is evenly distributed in gabbro–dolerite, but predominates in leucocratic gabbro. Analysis of Fourier IR spectra indicated the presence of iron and potassium among the impurities in the structure. Fe 3+ was recorded among the minor elements in plagioclases in the rocks confined to the intervals of ore disseminated mineralization (chalcopyrite, pyrrhotite, and pentlandite), such as picritic gabbro–dolerite, by absorption bands at 1580–1644 cm –1 . The new data we obtained is of great mineralogical significance. The revealed regularities in the distribution of minor elements in the section of ore and barren differentiates are recommended for use in the practice of geological exploration.