Nephelinites from Volcano Mountain, Yukon Territory, contain olivine, Ti-rich diopside, ulvospinel, nepheline, leucite, traces of calcite, and residual glass with varying compositions. Mass balance calculations suggest that these compositional differences are due to different fractionation paths; a conclusion consistent with the observed mineral abundances near the glasses. Pearce Element Ratios show that at least one of the lava flows sampled is not comagmatic with the others. Thermodynnmic modeling of silicate melts and textural observations indicate that the pressure-temperature path of fractionation was polybaric, and that the minimum depth of melt separation from the source rocks was 60 km. The volcanic rocks host dunite and lherzolite nodules consisting of diopside and hypersthene, olivine and chromian spinel. Deformation textures and mineral compositions are different from other occurrences in western North America. Geothermometry on the xenoliths provide temperature estimates between 930°C and 1350°C. The range of equlibrim pressures for the nodules is estimated from phase equilibria at 20 to 45 kilobars.
