Emerald at the Regal Ridge property in the Finlayson Lake district of southeastern Yukon is hosted within mid-Paleozoic mafic metavolcanic and metaplutonic rocks. These rocks overlie the shallowly dipping western edge of a 112 Ma quartz monzonite body, and aplite dykes associated with the intrusion locally contain beryl. Beryl-bearing aplites chemically differ from non-mineralized intrusions by having lower potassium and fluorine, and higher beryllium contents. The main host rocks for the mineralization are high-calcium boninites (high-magnesium basalt to andesite) with anomalously high chromium contents. Beryl occurs either within quartz-tourmaline veins or in highly altered schist zones adjacent to the veins. Several generations of syn- to late-tectonic quartz veins are present at Regal Ridge, and emerald appears to be mainly associated with the latest vein set, especially near the intersection between these and older veins. All of the quartz veining is thought to be related to progressive Cretaceous deformation and the relatively late emplacement of the quartz monzonite intrusions.