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. [...]