SULFIDE GEOCHEMISTRY AND SOME GENETIC FEA TURES OF BAIKAL RIFT-ZONE BASALTOIDS

Pyrrhotite and monosulfide solid solution are the major sulfide phases in pyroxene nodules, phenocrysts and megacrysts of basaltoids from Ba ikal rift zone and Tokinsky Stanovik. Pyrite, pentlandite and chalcopy rite are the minor phases. The sulfides are crystallized at the differ ent stages of evolution of the basalt magmas. A clear-cut trend of sul fide composition ig observed on the Fe-Ni plot when changes from mantl e to near-surface rocks. Nicel content in the minerals studied changes from 0.03 to 21.26 wt% depending on conditions of formation. Nicel co ntents in sulfides from high-pressure mantle rocks (pyroxenite nodules and megacrysts) are higher than 1 wt%, whereas in that from different iated varieties and sulfides are lower, than 1 wt%. Composition nonuni formity was observed in sulfides from pyroxenite nodules. A fluid phas e take important part in formation of sulfides in the rocks of Baikal rift zone.