pge–cu–ni sulfide mineralization of the mesoproterozoic escape intrusion, northwestern ontario
abstract
the escape intrusion is a tabular to bladed, mafic–ultramafic chonolith that hosts
economic concentrations of pge–cu–ni magmatic sulfide mineralization. the mesoproterozoic
intrusion is located about 50 km northeast of thunder bay, ontario, and with the current
intrusion makes up the thunder bay north intrusive complex (tbnic). the intrusive rocks of
the tbnic are part of the 1.1 ga midcontinent rift system (mrs) of north america and were
emplaced into the quetico basins during early stages of rift development. the fractionated hree
(gd/ybcn = 3.18–4.96) signature of the escape rocks suggests magma derivation from a deep
mantle source. primitive mantle-normalized trace element patterns of the escape intrusive rocks
are similar to ocean-island basalt, as well as multiple mrs-related mafic–ultramafic intrusions
(e.g., hele, disraeli, kitto), which is consistent with the mantle-plume hypothesis of mrs
formation.
the high-grade zone occurs within the (mostly wehrlitic) peridotite unit of the escape
intrusion, which lies below the weakly mineralized gabbro and hybrid units. the high-grade zone
within the escape intrusion is characterized by intercumulus sulfide mineralization that is nettextured at the core and disseminated at the margins. [...]