MINOR SULFIDE INCLUSIONS IN THE PLIOCENE- QUATERNARY VOLCANIC-ROCKS OF THE CAUCASUS

Plagioclase, orthopyroxene and some other phenocrysts from acidic and intermediate volcanics contain primary minor sulfide inclusions which consist of pyrrhotite, chalcopyrite and cubanite. MeS mole fraction in pyrrhotite varies from 0.94 to 0.99. Double-phase chalcopyrite (cuban ite) - pyrrhotite inclusions were formed as a result of monosulfide (F e, Cu)S + S-2 crystallisation. The formation of sulfides in a form of separate phases is considered as a result of basic and acidic magma mi xing and by local increase of sulfide activity at the front of plagioc lase crystallisation. Pyrrhotite inclusions formed as a result or magm a mixing were found Lo be enriched in Ni while those formed al the fro nt of plagioclase growth were poor in Ni.