| dc.description.abstract | The Mine Block Intrusion (MBI) is a 3 km by 1.5 km tear-shaped mafic complex that was emplaced along with
other mafic-ultramafic plutonic rocks of the South Lac des Iles Complex (LDIC) between 2,699 and 2,686 Ma
in the Marmion terrane of the Superior Province. The MBI consists of gabbronorite and magnetite-rich
gabbronorite, and a later series of noritic rocks and their metamorphosed altered equivalents.
Major element data of the MBI indicate that the rocks have a broadly gabbroic composition with protoliths
dominated by plagioclase, a predominance of orthopyroxenes over clinopyroxene, and titano-magnetite, which
is consistent with the petrographic observations. Magnetite gabbronorite rocks in the MBI were derived from
a metasomatized mantle, consistent with the arc setting proposed for the Lac des Iles Complex as a whole.
Plagioclase compositions decrease up the analyzed section, with no sharp change, suggesting a normal
fractionation process with no magma injection events. Plagioclase identified within the magnetite gabbronorite
of the MBI is labradorite-bytownite (An-number ranging from 0.58 to 0.75), which is less evolved than observed
in layered intrusions globally suggesting that saturation of Fe-Ti oxides occurred at an early stage of
differentiation compared with other mafic intrusions. [...] | en_US |
