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The Tsa Da Glisza (Regal Ridge) emerald occurrence, Southeastern Yukon Territory, Canada : descriptive, genetic, and exploration models Neufeld, Heather Leah Douglas

Abstract

Emerald at the Tsa da Glisza property in the Finlayson Lake district of southeastern Yukon is hosted by mid-Paleozoic mafic metavolcanic rocks which overly the shallowly dipping western edge of a 112 Ma granite pluton. The main host rocks for the mineralization are high-Ca boninites (high-magnesium basalt to andesite) with anomalously high Cr contents. Beryl occurs within quartz-tourmaline veins, and in highly altered schist zones either adjacent to the veins, or near vein terminations. Several generations of syn- to late tectonic quartz veins are present at Tsa da Glisza, and emeralds are associated mainly with the latest vein set, especially near the intersection between these and older veins. The quartz veining is related to progressive Cretaceous deformation and to the relatively late emplacement of the granite intrusions. Aplite dikes associated with the intrusion locally contain beryl within quartz-rich segregations, and these beryl-bearing aplites differ chemically from non-mineralized intrusions by having higher Be and Na and lower K, Li, and F contents. The oxygen isotopic composition of the granite is distinct from that of the chlorite schist. The extent of homogenization of the two isotopic signatures can be tracked by the changing oxygen isotopic composition, and may be used to determine whether there was sufficient reaction between the veins fluids and host schist to produce emerald. 3 9Ar-4 0Ar geochronology confirms that mineralization occurred synchronous with regional deformation and metamorphism related to intrusion of the granite pluton from approximately 112 to 108 Ma. A genetic model for the emerald mineralization has been formulated: vein fluids were mixtures of fluids from both magmatic and local metasomatic sources. Beryllium derived from an adjacent Cretaceous granite was transported as both hydroxide and fluoride complexes within dominantly magmatic fluids. Emerald crystallized during cooling after the magmatic fluids mixed with hydrothermal fluids that had scavenged Cr from the surrounding mafic schist. Based on this genetic model, further exploration in the Finlayson Lake region, and the northern Cordillera, should focus on areas where permeable (schist rather than serpentinized ultramafic), high-Cr host rock is in close proximity to evolved felsic intrusive rocks.

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