The Lithotectonic Setting and Paragenetic History of Deposit No.1, Mary River District, North Baffin Island
Master of Science
Dr. Norman Duke
Dr. Desmond Moser
Baffinland Iron Mines Corporation is currently extracting the highest grade BIF-hosted direct shipping iron ore in the world from their flagship Deposit No.1 on north Baffin Island. This deposit and several other prospects are hosted within the isoclinally folded Mary River Group, a Neoarchean greenstone belt terrane hosting Algoma-type BIF, ultramafics volcaniclastics and sediment. Mary River Group supracrustals are juxtaposed against Mesoarchean basement gneisses due to a regional Transhudson Orogen overprint, forming a regional dome-keel tectonic framework.
Detail mapping and core logging of Deposit No.1 combined with geochemistry and geochronology reveal the footwall rocks, previously interpreted as gneisses, volcanics and metasediments, to be mylontized and altered ~2900 Ma monzogranite. The footwall monzogranite has endured three stages of hydrothermal alteration during Paleoproterozoic extension, removing up to 40% SiO2. Stage 1 is the formation of epidote-carbonate-hornblende veins. Stage 2 involves the breakdown of feldspars and quartz to muscovite forming quartz-augen muscovite schist (QAMS). A low amphibolite facies metamorphic event follows stage 2 alteration, producing large cordierite porphyroblasts. Stage 3 further desilicifies QAMS by biotite alteration forming quartz-augen biotite schist (QABS) and biotite schist. Retrogression of biotite schist forms chlorite schist. Stage 3 schists are overprinted by a second low amphibolite facies metamorphic event, producing andalusite-staurolite-almandine and grunerite-almandine porphyroblastic assemblages. Temperatures and pressure of the second metamorphic event are calculated between 368-481°C at a max pressure of 3550 bars. Paragenetic sequencing of silica loss in monzogranite to form chlorite schist is identical to the formation of ore zone chlorite schist and therefore related to the formation of high grade iron ore. U-Pb dating of hydrothermal monazite in footwall QABS and ore zone chlorite schist bracket hydrothermal desilicification between 1873 ± 20 Ma and 1800 ± 12 Ma. Last, the paragenetic alteration-metamorphic history of Deposit No.1 is not fully consistent with previous metamorphic and gneiss dome models. A post-collsional model is presented to account for the paragenetic and metamorphic differences.
Fulcher, Sean A., "The Lithotectonic Setting and Paragenetic History of Deposit No.1, Mary River District, North Baffin Island" (2015). Electronic Thesis and Dissertation Repository. 2884.