A note on the occurrence of nepheline syenite in Calvin Township, District of Nipissing, Ontario

Nepheline syenite occurs about 20 km southwest of Mattawa, Ontario, as an elliptical mass about 1 km by 1.5 km in size within an east-southeast-trending belt of metagabbro and mafic gneiss. Nepheline-free syenite extends 2 km farther to the east as a belt less than 100 m wide. The nepheline syenite is zoned from sodium-rich margins to a potassic core, but is bisected by a layer of amphibolitic gneiss similar to the surroundings. The syenite shows some mineralogical similarities to a huge massif of monzonitic rocks of granulitic affinity which lies a few kilometres to the west. All rocks have been strongly affected by two or more periods of deformation, but the nepheline syenite shows no obvious relation to this deformation. It appears to have been emplaced as a pluton subsequent to initial deformation, but prior to final assembly of the Grenville Province.