In 1998, a new occurrence of emeralds was discovered in Finlayson Lake area, southeastern Yukon. Emeralds occur in the alteration selvages of quartz-tourmaline (-scheelite-muscovite-beryl) veins that cut biotite-chlorite metavolcanic schist in the metamorphic aureole around one of the area's largest bodies of mid-Cretaceous granite. In the area of the showing, the mafic schist, part of the widespread Upper Devonian Fire Lake unit, is meta-basalt of boninitic composition which overlies a thick, laterally tapering slab of variably serpentinized mafic and ultramafic meta-plutonic rocks. Using various geometric and geological criteria, this slab is inferred to be a sill, comagmatic with the Fire Lake unit, which intruded laterally from feeder dykes localized along a nearby synvolcanic fault.