I was fortunate that I had paid trips to take me to Lac Saint Jean a few times both from Quebec City and From Trois Rivieres. I was working in Quebec as a steel inspector for some USA projects and I had one client who sent me to Alma, Lac Saint Jean QC once per month. The scenery on the way to Alma from Quebec City or Trois Rivieres was unforgettable. One Highway, Rt 175, traverses the Laurentide Mountains from Quebec toward Chicoutimi and the other Highway, Rt 155 follows the Mauricie River North through the mountains as well. There is gorgeous scenery in these mountains which are part of the Allochthonous Polycyclic Belt of the southern Grenvillian terrane. Off course I was looking at the road cuts, but the landscape was very photogenic as well. The Highway 175 from Quebec goes through some real boreal forest wilderness and transecting the Parc de Laurentides. From Quebec the route follows the Montmormency River for a while and the ascends through lake and mountain country until it arrives at the plains around Lac Saint Jean. This trip wil be another article. However this article is about a some locations on the Highway 155. As one takes Highway (Autoroute) 155 north from Trois Rivieres the route follows the Mauricie River which follows a fault at one point and widens after Shawinigan to a fiord like landscape. Later the route leaves the river northeastward, passing La Tuque until it arrives at Lac Saint Jean. Here is a view of Riviere Mauricie heading north about 12 miles north of Grande Mere.

I want to describe in this article some of the geology particularly a large cut exposed on route 155 in the Mekanic region. Both highways rout 175 and route 155 were in major constructions this year. Widening by stripping back forest and major blasting operations. I only wish I could have spent more time, but in passing back and forth I was able to do some collecting.
REGIONAL GEOLOGY
From what I have gleaned from the research, U-Pb zircon age and regional setting of the Lapeyrere gabbronorite, Portneuf-Mauricie region, south-central Grenville Province, Quebec , L. Nadeau and O. van Breemen, GSC Quebec, and the Geological Map of Quebec Edition 2002 DV 2002-07 Ressources Naturelles. This cut is in the Mekinac-Taureau Domaine of the Allochthonous Polycyclic Belt of the Grenvillian Terrane of Southern Quebec.
The Mekinac-Taureau Domaine is said to be a crustal-scale dome composed mainly of intermediate and felsic granulite. The cut was approximately 20 miles north of Grande Mere. This would be in Charnockitic gneiss and orthopyroxene bearing granitoids. Marble bands could appear in this metamorphized gneiss anywhere.
I passed a lot of blasted rock on both sides of this autoroute taken from this road cut.

I saw marble in the piles, which is always interesting in highly metamorphosed geology. This material was being used a fill in the widening of the highway and came from this newly blasted roadcut. The marble layer appears as the lighter colored band on the rock face. In the rock fill I saw rock with plagioclase, pyroxene and garnet, probably from the same cut outside the marble band, as well as pegmatite showing reddish feldspar and what might be allanite. However I concentrated on the marble skarn type rock. Here is a photo of the pegmatite where there is reddish feldspar, quartz and this tabular black mineral.

Some of the pegmatite had a brownish altered appearance with the same black tabular crystals. Sometimes the black mineral was around a olive brown mineral core.

There was coarsely crystalline white and orange calcite with accessory minerals. The white calcite specimens were taken and broken up and then allowed to dissolve in hydrochloric acid to expose the minerals.

Associated with the white coarsely crystallized calcite I collected some interesting finds. There was easily identified green prisms of apatite, which fluoresce lightly a bluish color. This is a close up of a crystal about 3 mm long.

Another specimen I broke out of a white calcite boulder contained a quartz crystal, apatite, a black mineral and a sulphide.

Here on the left is a terminated quartz xl (1/2”x1”) with a pyrrhotite next to it and an apatite xl (1/4x3/4) at the right. Disseminated through the calcite are black smaller prismatic crystals dispersed around.
Judging from the color and crystal form of the black mineral in this environment it probably is of the amphibole group. Perhaps edenite? Minerals in this mélange would require more testing. I found these black prisms in various sizes through out the calcite marble. Here is a close up.

It seems to be black, being translucent green in the thin corners.
The sulphide mineral has the bronzish color of pyrhottite. Here is a macro of the sulphide where you can see a twinning structure.

I found another specimen with what seems to be a hexagonal plate of pyrrhotite on ferruginous quartz crystals.
This was not in the calcite marble but the quartz crystallization occurred as a vein of ferruginous quartz in a black rockThis is the quartz crystallized in the vein opening. Also I noticed this platey assemblage of tan crystals. (perhaps barite?)

Returning to the white calcite scarn. I saw intimately associated with the black prismatic mineral, smaller dark green mineral and brown to resinous yellow crystals. The brown to yellow crystals seem to have the form and color of titanite. I am not sure of the dark green mineral.

This mineral I am also uncertain about. Perhaps diopside or vesuvianite? It appears to be more olive green that the other green mineral. It also occurs within the white calcite
And last two more minerals for the unidentified cache. One is grains of a rose colored mineral. I could geuss but that is all. The other purplish color.

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