Petrology & geology of high level rhyolite intrusives of the Skukum area, 105 D SW, Yukon Territory

The Skukum area is located 58 km south-southwest of Whitehorse. It is an elliptical area of volcanic rocks, Tertiary in age, and surrounded by hypabyssal rhyolite intrusives. Field and petrographic evidence, fluorite and tourmaline stockwork, breccia pipes, roof pendants, miarolitic cavities and spherulites in the nine Skukum rhyolites suggest that they were emplaced at a high level. The intrusives vary in composition from rhyolite to dacite. The variation in texture within and between the intrusives can be explained by different rates of crystallization, temperature differences and compositional variability. Chemical data are in accord with the expected trends in a cogenetic suite of igneous rocks. Relatively low CaO and MgO, high SiO2 and anomalously low Sr concentrations indicate that the rhyolites were formed from a highly differentiated magma. Sr and Ba versus Al2O3 plots show that both k-feldspar and plagioclase were important fractionating phases. Rare earth element data further support this conclusion and also suggest that some accessory phase(s), such as monazite, allanite or fluorite help control the rare earth element behaviour. Partial melting of an already depleted…

Publisher

Government of Yukon

Resources

3

Catalogue metadata updated

2026-08-26