The Teslin Crossing Pluton is a small (~75 km2), elliptical body which intrudes Jurassic Whitehorse Trough strata of Stikine Terrane. The pluton consists of a border phase, a lithologically and texturally complex central phase, and associated sills and dyke swarms. The border phase consists of a grey, crowded hornblende-plagioclase porphyry. The central phase consists of pink, medium to coarse grained, equigranular monzonite and syenite. Pyroxene and hornblende are essential constituents. Abundant accessory minerals include magnetite (up to 5%), titanite, apatite, rutile and zircon. Modal quartz is absent. Dykes and sills have compositions similar to the border phase. All phases contain a large amount of pea- to cobble-sized xenoliths including coarse-grained pyroxenite, coarse-grained gabbro and fine-grained diorite. The border phase also include sedimentary xenoliths. Locally there are zones of brecciation and potassic alteration.
Geochemically the pluton is alkalic with 3.1-3.4% K2O, 60-68% SiO2 and minor normative quartz. Most rocks are metaluminous but more evolved phases are slightly peraluminous. The pluton is classified as a slightly silica-saturated, pyroxenite-associated syenite. New and existing collections of macrofossils from the sedimentary rocks adjacent to the pluton indicate an age range of Pliensbachian to Aalenian, and provide a maximum age constraint for the pluton. A preliminary U-Pb date from the sill complex yields an age of approximately 175 Ma which is younger than the K-Ar ages of 181-186 Ma from the pluton. The Teslin Crossing pluton is an Early Jurassic alkalic plutonic complex in Stikine Terrane, and as such, is an excellent target for gold-rich porphyry copper mineralization.
