Results from an airborne gamma ray and magnetics survey in the Dawson Range in west-central Yukon indicate that the Pattison Creek pluton may be larger than currently mapped. Ground follow-up indicates that the pluton is approximately three times larger than originally shown. This pluton is a member of the Casino Intrusions - a unit identified as being genetically associated with copper-molybdenum mineralization and as such is considered a good exploration target. Examination of the pluton indicates that it is a highly fractionated, epizonal stock composed primarily of granite and alkali feldspar granite with later phases of peraluminous muscovite-bearing alaskite and aplite. Microthermometric and isotopic data indicate that mineralizing hydrothermal fluids are of low salinity, and depleted in deuterium and delta Oxygen-18 relative to values typical of magmatic waters. The gamma-ray survey shows it to have among the highest U and Th values in the survey area (> 3.0 and 15 ppm respectively).