Evaluation of Magnetite as an Indicator Mineral for Porphyry Cu Exploration: A Case Study Using Bedrock and Stream Sediments at the Casino Porphyry Cu-Au-Mo Deposit, Yukon, Canada

Abstract

The chemical composition of magnetite recovered from six local streams around the Casino high-grade porphyry Cu-Au-Mo deposit, west-central Yukon, is compared with igneous and magmatic-hydrothermal magnetite recovered from mineralized and unmineralized host rocks at the deposit. The aim is to characterize magmatic-hydrothermal magnetite associated with mineralization to discriminate between igneous and magmatic-hydrothermal magnetite from different sources in local streams as a potential exploration tool. Linear discriminant analysis of 12 variables (Mg, Al, Ti, V, Mn, Co, Cr, Ni, Cu, Zn, Ga, and Ge) and plots of Ti versus Ni/Cr are used to discriminate between magmatic-hydrothermal magnetite from the potassic alteration zone and igneous magnetite from granodiorite and quartz monzonite hosting the Casino deposit. Magmatic-hydrothermal magnetite with a chemical composition similar to that from the potassic alteration zone at the Casino deposit is identifiable in stream sediments draining the deposit. Detectable Cu in magmatic-hydrothermal magnetite, present in minute inclusions of sulfide minerals or substituted within the crystal lattice, is a strong indicator of Cu mineralization. We show that the chemical compositions of magnetite recovered from stream sediments can be used to explore for porphyry systems in Canada.