Asbestos in most Cordilleran deposits has been considered a product of fracturing, metasomatism and thermal metamorphism of ultramafic rocks by mesozoic intrusions. Such a history has been postulated for the exhausted asbestos deposit at Clinton Creek, 77 km northwest of Dawson City, Yukon. This report contains another interpretation of the mine geology. It is based on the premise that the ultramafic host rocks represent slices of oceanic crust thrust onto the North American craton during Mesozoic arc-continent collision. A critical fossil occurrence demonstrates that intensely deformed asbestos-bearing serpentinite and other cataclastic rocks are tectonically interleaved with weakly deformed Triassic and older (?) shale and sandstone of the younger, southwestern part of the Cordilleran miogeocline. Brittle fracturing, hydration and asbestos formation likely occurred during final emplacement of the ultramafic rocks onto the wet miogeoclinal strata.
