Sheree Hinz Honours thesis abstract

Thesis Title: 
Geochemistry of the Badwater Gabbro south of Armstrong, ON

The Badwater Gabbro south of Armstrong, Ontario is a Proterozoic mafic intrusion.  It is cut through by thin dikes of the Badwater Syenite and overlain by the Pillar Lake volcanics.  Through petrographic work, the intrusion was subdivided into six lithologies: altered mafic rocks, syenite, norite, gabbronorite, olivine gabbro/olivine gabbronorite, and gabbro.  The altered mafic rocks consist of metagabbro, metagabbronorite, serpentine-actinolite gneiss as well as talc-magnetite schist.  Much of the alteration is present in the form of hydrous alteration minerals.  This section is heavily altered and overprinted, likely the result of surficial weathering as well as hydrothermal alteration from extrusion of the Pillar Lake volcanics on top of the Badwater Gabbro.  The alteration minerals and textures seen throughout the intrusion could be the result of localized contact metamorphism caused by emplacement of the Nipigon sills at ~1.1 Ma.  Geochemically the Badwater Gabbro are similar to rocks derived from a mantel plume.  The Badwater Gabbro is characterized by high Gd/Yb ratios (2-7), indicating that the melt is sourced from within the garnet stability field.  The Badwater Gabbro was possibly emplaced along the lithospheric scale weakness of the Black Sturgeon fault zone.  The intrusion was likely affected by crustal contamination during emplacement; as suggested by the depletion of the HFSE on the trace element plots, indicating assimilation and enrichment of LREE relative to HFSE.