The world-class Hemlo gold deposit is representative of an atypical mesozonal shear-hosted lode-gold deposit that is comprised of numerous lithologies. A contemporary classification scheme for the categorization of dyke lithologies that occur in the immediate Hemlo deposit is utilized by the mine geologists of Williams Operating Corporation at Barrick Gold’s Williams Mine. Although the deposit area has been studied extensively by myriad researchers, the physical and chemical properties of an intermediate intrusive lithology, designated as unit (11) in accordance with the Hemlo Geology Legend, are not well described. Nineteen samples representative of the (11) Intermediate Intrusive unit were obtained from varying localities throughout the Williams “C Zone” and “B Zone” sites, specific to the Hemlo deposit, within the Williams mine. Petrographic and geochemical analysis of these samples suggests that they are representative of a calc-alkalic magma series that evolved via the process of fractional crystallization in an island arc setting.