the mcfaulds lake area (commonly known as the ring of fire), has been the site of much recent exploration within northern ontario. the area represents a recently discovered archean greenstone belt which is host to world class chromite deposits along with significant cu-­‐zn vms, magmatic ni-­‐cu-­‐pge and fe-­‐ti-­‐v occurrences. much emphasis has been placed on the chromite mineralized ultramafic intrusions with little attention focused on the fe-­‐ti-­‐v mineralized ferrogabbroic intrusions. the butler and thunderbird intrusions represent the best described intrusions within the volumetrically significant ferrogabbroic suite within the mcfaulds lake area. these intrusions are characterized by a suite of well layered magnetite-­‐ilmenite rich rocks which are dominantly composed of gabbroic to anorthositic units with lesser stratigraphically conformable units composed of pure magnetite-­‐ilmenite. the fe-­‐ti oxide rich layers contain variable vanadium mineralization and low chromium contents within magnetite (up to 2.45 v2o5 wt. %, 0.99 % cr2o3 wt. %) and ilmenite (up to 0.57 v2o5 wt. %). the massive and semi-­‐ massive oxide layers occur as basal members of repeated cycles characterized by sharp lower contacts which grade upwards into oxide-­‐rich pyroxenite, followed by oxide-­‐bearing leucogabbros and/or anorthosites. the layers are believed to be caused dominantly by magmatic convection currents within a system which is at least partially open to oxygen. no evidence has been found to suggest multiple pulses of magma. oxide-­‐silicate liquid immiscibility is thought to only occur within the evolved, apatite-­‐bearing margins of the thunderbird intrusion; however, additional drilling may reveal further apatite mineralization. the ferrogabbroic intrusions are thought to have originated from a shallow depleted mantle source, possibly related to a plume event. the ferrogabbros have likely undergone a two stage differentiation to account for the extreme iron enrichments. the first stage is characterized by an anhydrous, tholeiitic melt, within the upper mantle (above the garnet stability field, <110 km) which underwent fe-­‐ti enrichment due to the crystallization of fe-­‐ poor phases (e.g., olivine, plagioclase, etc.) within a system closed to oxygen. the second stage is considered to be a very shallow intrusion within the mcfaulds lake mafic-­‐felsic volcanic rocks. this final stage is characterized by a system which was at least partially open to oxygen from an originally reduced magma (<qfm buffer). these magmas initially crystallized cr-­‐v-­‐rich magnetite-­‐ilmenite horizons and gradationally evolved into cr-­‐v-­‐poor, apatite-­‐bearing ferrogabbros. these ferrogabbros likely share a parental magma with the coeval cr-­‐ni-­‐pge-­‐ bearing ultramafic intrusions of the mcfaulds lake greenstone belt. additionally, spatial and geochronological evidence suggests that abundant vms-­‐style mineralization within the mcfaulds lake area may be a result of a thinned lithosphere during plume tectonics.