The interpretation of Precambrian
and Paleozoic rocks in eastern Canada has considerably evolved over
the last few decades, thanks to a better understanding of geological
and tectonic processes. For instance, an updated subdivision of
geological provinces into subprovinces was developed. These subdivisions
evolve as new geochronological data is released, particularly in
the case of orogenic events that affected the Archean craton, which
is a major component of the Shield.
The Superior Province
(4 to 2.5 Ga) forms a large portion of the
North American continent, and covers a third of
Québec's landmass, i.e. a surface area
of 600,000 km². This
geological province forms the central part of
the Canadian Shield. It is world-renowned
for its numerous copper, gold, zinc, nickel and
silver deposits. More recently, it was also the
site of important discoveries of diamond occurrences.
Moreover, it is subdivided into
about a dozen subprovinces, half of which are
located in Québec. The most famous one
is the Abitibi Subprovince, the largest Archean
volcano-sedimentary belt in the world,
renowned for its copper, zinc, silver and gold
deposits. Rocks of the Superior Province are bounded
to the east by the Churchill Province, and to
the southeast by the Grenville Province.
The Churchill Province (2.1 to 1.75 Ga)
covers a surface area of about 150,000 km²
in the North part of Québec, northeast of the Superior Province. It
is characterized by four zones:
- The Ungava Orogen (Ungava
Trough), which borders the Superior Province to the north, and
is known for its nickel-copper deposits (namely the
Raglan mining camp);
- the Nouveau-Québec Orogen (Labrador Trough),
which borders the Superior Province to the east, and whose rocks
host important iron ore deposits as well as several deposits
of copper, nickel and platinum group elements (PGE);
- the Rae Province (or Far North craton), wedged
between the Nouveau-Québec and Torngat orogens, and which
contains Archean and Paleoproterozoic rocks (2.1 to 1.75 Ga)
and Mesoproterozoic plutonic rocks (1.7 to 1.1 Ga);
- the Torngat Orogen (2.1 to 1.75 Ga),
located east of the Rae Province, offers exploration potential
for diamond deposits.
The Grenville Province (1.2 Ga to 950 Ma)
also covers a surface area of 600,000 km².
It forms the southeastern margin of the Superior Province, and is
divided into three distinct belts. The Grenville Province is known
for its iron and ilmenite mines, its industrial mineral potential,
and less so for its base metal potential.
The St. Lawrence Lowlands (700 to 350 Ma)
developed at the end of the Proterozoic and during the Paleozoic,
with the formation of the St. Lawrence graben. The Lowlands are
divided into two platforms, the St. Lawrence Platform and the Anticosti
Platform. They overlie rocks of the Grenville Province. The dominant
mined resource is limestone. Two carbonatite intrusions, in Saint-Honoré
and Oka, host niobium deposits. Québec is the second producer
in the world for this rare metal.
South of the Grenville Province, the Appalachian
Orogen (650 to 350 Ma) developed along the margin of the
Canadian Shield during the Paleozoic. The Appalachian Orogen is
divided into three belts, and is bounded to the east by the Permo-Carboniferous
Magdalen Basin. Important asbestos resources and copper deposits
at Mines Gaspé are found in this geological province.
Extensive glaciation periods, dating back to the
Quaternary, affected Québec's landmass.
As a result, important glacial deposits cover
vast surface areas in the south part of the province,
and these deposits constitute important sources
of sand and gravel.