Background

Description

Deguisier Formation 1 (nAdg1): Basalt, Andesitic Basalt and Mafic Volcaniclastics

Deguisier Formation 2 (nAdg2): Basalt and Glomerophyric Volcaniclastics

Tholeiitic glomerophyric basalt is a special variety of massive to locally pillow basalt. It forms excellent marker horizons, extending from 500 m to 3 km with an average thickness rarely exceeding 100 m (Hocq, 1979). It is characterized by the presence of centimetric whitish clusters of feldspar crystals. This unit is particularly well displayed in Aiguebelle National Park (sheets 32D11 and 32D10; see Goutier and Melançon, 2003).

Deguisier Formation 3 (nAdg3): Felsic Volcanics and Volcaniclastics

This unit forms a large number of small felsic centres scattered throughout the Deguisier Formation (Dimroth et al., 1973; Hocq, 1979; Sanschagrin and Leduc, 1979; Leduc, 1981; Sanschagrin, 1981; Goutier, 1997; Pilote et al., 2009). These centres are 1 to 2 km long and do not exceed 500 m wide. The largest one intrudes at the junction of sheets 32D08, 32C05 and 32C12 (Pilote et al., 2009). The unit consists of massive to brecciated rhyolitic to dacitic flows, which belong to generally tholeiitic suites (Pilote et al., 2009). In addition, rhyolitic shell breccias are common at the eastern end of sheet 32D08.

Deguisier Formation 4 (nAdg4): Andesite and Intermediate to Mafic Volcaniclastics

This unit is located mainly in the southern and eastern parts of the Deguisier Formation (Dimroth et al., 1973; Hocq, 1979; Sanschagrin and Leduc, 1979; Leduc, 1981; Sanschagrin, 1981; Goutier, 1997; Pilote et al., 2009). It consists of massive to pillowed andesitic flows of thloeiitic affinity, the average thickness of which generally ranges from 7 to 10 m. The summital part of these flows is commonly brecciated along thicknesses ranging from 1 to 10 m. It should be noted that basaltic flows are uncommon in this unit.

Deguisier Formation 5 (nAdg5): Gabbroic Sill, Magnetite Basalt and Mafic Volcaniclastics

Over 90% of unit nAdg5 is represented by bulky gabbro sills. These sills can reach lengths exceeding 5 km and thicknesses ranging from 800 to 1200 m (Dimroth et al., 1973; Hocq, 1979; Sanschagrin and Leduc, 1979; Leduc, 1981; Sanschagrin, 1981; Goutier, 1997; Pilote et al., 2009). Units nAdg1 and nAdg5 alone represent the majority of the lithologies encountered in the Aiguebelle National Park (sheets 32D11 and 32D10; see Goutier and Melançon, 2003). Gabbros of unit Adg5 likely represent feeder pipes of many basaltic flows (Dimroth et al., 1973; Hocq, 1979; Sanschagrin and Leduc, 1979). They are similar in composition, but are distinguished by coarser grain size. Magnetite basaltic flows and mafic volcaniclastics are marginal parts of the Deguisier Formation.

Deguisier Formation 6 (nAdg6): Felsic to Intermediate Volcaniclastics, Medium to Coarse-Grained Matrix

Unit nAdg6 is present only in the central part of the Deguisier Formation in Aiguebelle National Park (sheets 32D11 and 32D10; see Hocq, 1979; Goutier and Melançon, 2003). It consists of thin volcaniclastic horizons that vary in composition from felsic to intermediate. These horizons are discontinuous and moderately long (500-3000 m) with thickness ranging from 100 to 500 m (Hocq, 1979; Sanschagrin and Leduc, 1979).

Deguisier Formation 7 (nAdg7): Felsic to Intermediate Volcaniclastics, Fine-Grained Matrix

Unit nAdg7 is very small and occurs in the central-eastern part of the Deguisier Formation (sheets 32D07 and 32D10). It forms relatively continuous marker horizons up to 3 km long and approximately 100 to 300 m wide. This unit consists of felsic to locally intermediate volcaniclastics with a fine-grained matrix (Hocq, 1979; Sanschagrin and Leduc, 1979).

Deguisier Formation 8 (nAdg8): Semi-Massive Sulphides, Exhalite, Volcaniclastics

Unit nAdg8 is located in the eastern part of the Deguisier Formation (sheet 32D08) and consists of mineralized zone observed at the Newcomex (Figuery Zone) showing. Mineralized horizons were defined by drilling. These are metric horizons rich in semi-massive sulphides (mainly zinc), exhalites and highly silicified volcaniclastics. The lateral extension of these units, according to the numerous drills carried out, does not exceed 500 m.

Deguisier Formation 9 (nAdg9):  Pyrrhotite-Pyrite Graphitic Claystone, Siltstone and Cherty Tuff

Unit nAdg9 was encountered in several drills located in the NE corner of sheet 32C05 and NW corner of sheet 32C06. It corresponds to important electromagnetic conductors (“INPUT” type anomalies) noted on geophysical surveys (GSC et al., 2009). This unit consists of graphitic mudstone, siltstone and cherty tuff for a total thickness of 2 to 30 m and a lateral extension of up to several kilometres. Sulphides (pyrrhotite and pyrite) are very common and vary in content (trace-5%). This unit is deformed and generally run by large longitudinal faults, giving it both a stratigraphic and structural marker (allowing position of some large faults to be clarified).

Thickness and Distribution

The Deguisier Formation is a package of generally E-W-oriented volcanic and intrusive lithologies with stratigraphic thicknesses ranging from 1 km to nearly 5 km, and affected by the Abijévis Synclinal (Dimroth et al., 1973; Hocq, 1979; Sanschagrin and Leduc, 1979; Leduc, 1981; Sanschagrin, 1981; Goutier, 1997). Various volcanic units belonging to this formation can be found in sheets 32D07, 32D08, 32D09, 32D10, 32D11, 32C05 and 32C12, north of the Porcupine-Destor Fault Zone.

Dating

Felsic flows and volcaniclastics (nAdg3) were dated 2719.4 ±1 Ma and 2718.1 ±1.3 Ma (McNicoll in Pilote et al., 2009; sheet 32D08). These ages indicate that the Deguisier Formation was emplaced in a relatively short period of time of ~2 Ma. 

Stratigraphic Relationship(s)

This formation marks the base of the Kinojévis Group. The Deguisier and Lanaudière formations are in fault contact (Aiguebelle Fault) throughout sheets 32C05 to 32D11 over more than 70 km. To the east of the intersection of the Abijévis Synclinal axial plane with the Aiguebelle Fault, volcanics of these two formations show opposite polarities. 

Paleontology

Does not apply.

References