Interpretation of oxygen and carbon isotope compositions based upon the calculation of modal composition of rocks

The behavior of oxygen and carbon stable isotopes in granodiorites of the Berezitovoe deposit (the Amur Region northwest) affected by metasomatic processes has been studied. The isotope analysis of trace carbon in rocks (d13CPDB) and silicate oxygen (d18OVSMOW) was carried out at the Analytical Center of Far East Geological Institute FEB RAS, in Laboratory of Stable Isotopes using Finnigan MAT-253 massspectrometer. It was determined that quantity of (d18OVSMOW) and (d13СPDB) in metasomatic rocks was regularly varying from their front zones towards the back as follows: (d18OVSMOW) increased from +9.6‰ to +11.2‰ whereas (d13СPDB) decreased from -10.8 ‰ to -27.2. ‰. Based on the calculation of the modal composition of rock samples from the zones of metasomatc alteration, the change of isotope compositions may be linked to the increasing quartz and muscovite in the granite composition as well as to higher degree of reduction of metasomatic rocks relative to initial granites.