Garnet is a major repository of HREE, especially in prograde skarn, whereas LREE-enriched clinozoisite is the principal REE-host in retrograde skarn. REE distribution patterns define a pronounced partitioning of elements among the dominant coexisting minerals. Compositional variation between assemblages, and also within individual grains, defines an evolution from early feldspar-pyroxene skarn through main-stage calcic skarn to the ore-stage. A switch from a prograde, HREE-dominant signature to a LREE-enriched signature is observed in both retrograde and distal skarn. Zr-in-titanite geothermometry supports transition from magmatic to hydrothermal, skarn-forming processes at temperatures of ~ 660 掳C; the initiation of ore-stage is about 100 掳C lower.
Understanding REE distributions in all minerals within a complex, multistage ore system assists the development of vectoring tools that use trace element chemistry in exploration for similar IOCG deposits beneath regolith cover across the Olympic Province. Titanite and apatite show particular promise because of their characteristically distinct REE patterns in magmatic and hydrothermal stages, trace element responses to redox changes, and their widespread abundance throughout different lithologies in the area.