ORIGIN AND EVOLUTION OF THE SULFIDE-RICH, MAFIC IGNEOUS INTRUSION AT EAGLE MINE, UPPER PENINSULA, MI

The mafic Yellow Dog Intrusion of the Upper Peninsula, Michigan is host to a productive Cu,Ni sulfide-rich ore deposit at Eagle Mine. The origin of the ore and its relationship to its host intrusion are not well known. To better understand the processes responsible for the formation of the deposit, we collected a series of rocks from the mine that represent distinct crystallization phases of the intrusion. We use whole-rock major and trace element chemistry (derived from XRF analyses) and mineral chemistry (derived from EMP and SEM analyses) to document chemical evolution within the magma body. Petrographic observations reveal characteristic textural features associated with interaction of segregated liquids with the host crystalline framework. We show that the Yellow Dog parent magma likely experienced liquid immiscibility, such that conjugate Si-rich and Fe/S-rich liquids, with vastly contrasting densities, segregated within the host crystal mush. Our results bear on the origin of similar Cu,Ni magmatic ore deposits in northern MN and Ontario, CA.