Rutter Pluton, French River, Ontario

For the second consecutive year, members of Wayne County Gem and Mineral Club joined with the Niagara Peninsula Geological Society for a several day trip to mineral sites in Ontario.  We thank Ashley Pollock for organizing the trip and I thank Ashley for writing this short summary of one of the sites we visited and allowing me to publish it in the September, 2017 WCGMC newsletter and also this this blog. 

It rained and then it stopped and then it rained again as we drove north to start our week long summer collecting trip.  But when we met our Wayne County Club friends at our first collecting stop along the French River south of Sudbury, the clouds had parted and the week of fun began.

The Rutter Pluton is a nepheline-syenite intrusion within/ straddling the border of the Grenville Front Tectonic Zone (GFTZ) of the Grenville Province.  The 10 km long, 2 km wide igneous body is dated at 975 million years.  Like much of the Precambrian terrain in Ontario, the igneous rocks have been metamorphosed to a gneissic texture.  Mineralogically, the pluton consists of nepheline, albite (plagioclase feldspar), potassium-feldspar, and biotite mica.  Quartz is absent.

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