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Petrogenesis of the Ferrogabbroic Intrusions and Associated Fe-Ti-V-P Mineralization Within the McFaulds Greenstone Belt, Superior Province, Canada

出版	Lakehead University, 2016
URL	http://books.google.com.hk/books?id=9NvYzgEACAAJ&hl=&source=gbs_api

註釋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,