The Ontario Geological Survey has issued a Guidebook on the Rocks of the Grenville Province near Renfrew, Ontario (OFR6331); and a Report on the Chenaux gabbro intrusion near Renfrew (OFR6299)

                           
I don’t often venture up the Ottawa valley to the Town of Renfrew or to Renfrew County, as there is so much to explore in Lanark County, southern Frontenac County and Carleton County.   However, on October 3, 2017 the Ontario Geological Survey released a field trip guide that might temp me to venture up the Ottawa valley (once the snow melts):

Duguet, M. and Easton R.M. 2017.
Tectonic and metamorphic architecture of the northeastern Composite Arc Belt and the Central Metasedimentary Belt boundary tectonic zone, Grenville Orogen: A geological guidebook; Ontario Geological Survey, Open File Report 6331, 115p.  
           
Three day-long  excursions are included in this guidebook.   The Abstract provides the following summary for the three ‘day trips’:

-“Day 1 focusses on the Black Donald domain, which is characterized by a distinctive lithotectonic package containing abundant garnetiferous migmatites and which was subjected to Shawinigan orogenic (circa 1190–1130 Ma) magmatic, metamorphic and deformational events.

- Day 2 focusses on the Mazinaw domain, which has many similarities to the Mazinaw domain rocks exposed in the Cloyne–Plevna area, albeit at much high metamorphic grades. Day 2 also includes a field trip stop in the Flinton Group near Renfrew.

-  Day 3 focusses on the geology of the Cobden map area. The first part of Day 3 focusses on metasomatic and Late Syenite suite intrusive rocks present in Bancroft terrane to the west of the Ross fault. The second half of Day 3 focusses on the lower grade marbles and gabbros present to the east of the Ross fault, as well as the northernmost slivers of Mazinaw domain rocks preserved along the west side of the Ross fault north of Renfrew.”

This is a field trip guide for those with a serious interest in the Grenville province of the Canadian Shield and an interest in metamorphic petrology.

A print copy of the field trip guide can be purchased from the Ontario Geological Survey’s Publication Sales office in Sudbury  for $26.80 (plus shipping charges and taxes) or downloaded free in pdf  format from
       
http://www.geologyontario.mndm.gov.on.ca/mndmaccess/mndm_dir.asp?type=pub&id=OFR6331       - Or -

http://www.geologyontario.mndm.gov.on.ca/mndmfiles/pub/data/imaging/OFR6331//OFR6331.pdf

Stop 32 on the field trip is an outcrop of coarse grained, bronzite-bearing, Chenaux gabbro, on County Road 653 north of the Town of Renfrew.  The field trip guide mentions that other outcrops record igneous layering in the Chenaux gabbro intrusion,  that “ The intrusion is interpreted to have formed within a primitive island arc”, and includes a reference to the following publication and map:

Azar, B. 2015.
Geology, geochemistry and mineral potential of the Chenaux gabbro, northeastern Central Metasedimentary Belt, Grenville Province; Ontario Geological Survey, Open File Report 6299, 87p.
http://www.geologyontario.mndmf.gov.on.ca/mndmfiles/pub/data/imaging/OFR6299//ofr6299.pdf

Azar, B. and Easton, R.M. 2015.
Precambrian geology of the Chenaux gabbro, Grenville Province; Ontario Geological Survey, Preliminary Map P.3781, scale 1:20 000.
http://www.geologyontario.mndmf.gov.on.ca/mndmfiles/pub/data/imaging/P3781//p3781.pdf

Bronwyn Azar’s Open File Report 6299 is worth a read if, like me, one has an interest in layered mafic intrusions.   She includes photos of igneous layering:
 - photo 8C at page 18 showing “ Primary igneous layering with alternating layers of leucogabbro (Unit 5c) and melagabbro (Unit 5b). Along Highway 17 south side in Horton Township looking east south (UTM 365323E 5044699N).” 
- photo 10D at page 20 showing “ Primary igneous layering with alternating metaleucogabbro and metamelagabbro layers. South side of Highway 17 near Cobden. Horton Township, ...looking south (UTM 365219E 5044804N).”

Map P.3781 shows the locations of the layering.

Christopher Brett
Ottawa