GEOLOGY OF THE LAC AIGNEAU AREA (24E AND 24F/04). RG 2001-05, 2002. 44 pages and 2 maps.
BERCLAZ, A.., CADIEUX, A M.., SHARMA, K N M.., DAVID, J.., PARENT, M.., LECLAIR, A.



Abstract

The Lac Aigneau area (24E and 24F/04), mapped at a scale of 1:250,000 during the 1998 and 1999 field seasons, contains two lithodemic complexes and eleven intrusive suites, which were emplaced between ca. > 2.80 and < 2.67 Ga. These Archean units may be grouped into two major geological assemblages. They are cut by five families of younger dykes (ca. < 2.65 Ga; gabbro, diabase, ultramafic to mafic lamprophyre, carbonatized lamprophyre and carbonatite), and are bounded to the east by the Paleoproterozoic (2.0 to 1.8 Ga) New Québec Orogen. Volcani-sedimentary units, grouped in the Duvert and Qamaniq complexes, are the oldest rocks inventoried, and are penetratively transposed and affected by two phases of granulite-grade metamorphism. In the west part of the map area, the Duvert Complex is essentially enclaved in tonalites of the Suluppaugalik Suite (2805+9/-4 Ma). These tonalites are invaded by homogeneous intrusions of granodiorite (2725±5 Ma) and tonalite (2710 Ma) of the Rivière aux Feuilles Suite, by heterogeneous migmatitic granodiorites of the Monchy Suite, as well as by diatexites of the Rivière aux Mélèzes Suite (2671 Ma). In the south part of the map area, tonalites of the Suluppaugalik Suite are cut by diorites-tonalites-trondhjemites associated with diorites of the Coursolles Suite (dated at 2718+15/-9 Ma). Locally, within these suites, an early planar fabric (S2) oriented N-S, is preserved and interpreted as being related to a first phase of deformation (D2). This fabric is intersected in the south by a second planar fabric (S3) oriented E-W to ENE-WSW. All of these suites and structures are essentially outlined by regional negative magnetic anomalies, and form the extension of the Goudalie - La Grande Series. The northeastern half of the map area is underlain by the MacMahon Suite composed of two enderbitic units (dated at 2717±4 Ma and 2704±2 Ma) to which are associated bodies of mafic (orthopyroxene diorite, gabbronorite to anorthositic gabbro) and ultramafic rocks (pyroxenite, peridotite and hornblendite) as well as a synmagmatic metamorphic episode at the granulite facies. Laterally, this suite grades into clinopyroxene tonalites and diorites (Nallualuk Suite; 2698±3 Ma). These pyroxene-bearing suites are intruded by porphyritic monzogranites of the La Chevrotière Suite (ca. 2.717 and 2.686 Ga), as well as by late leucogranites of the Morrice (ca. 2682±4 Ma) and Dufreboy suites. These granites are the expression of a collisional process that is also responsible for regional metamorphism at the middle to upper amphibolite facies. Gabbro and diorite intrusions (Bacqueville Suite) are locally enclaved in the various granitic rocks. All these suites are bracketed between 2.717 and 2.671 Ga, and define an overall strongly positive magnetic gradient, outlined by a planar fabric oriented NW-SE to WNW-ESE (S4) and NNW-SSE to N-S (S5). The northeastern half of the Lac Aigneau area shares numerous similarities, namely gravimetric, magnetic, stratigraphic and tectono-metamorphic features, with units composing the Ashuanipi Subprovince, which suggests these two regions may form a single tectono-stratigraphic assemblage, the Utsalik-Ashuanipi Series. Mapping in 1998 and 1999 in the Superior Province helped uncover new economically significant mineral occurrences and showings. These occurrences were grouped into five metallogenic settings: iron formations associated with volcani-sedimentary belts (with Cu-Zn-Pb-Co±Ag±Au mineralization), ultramafic and mafic intrusions (with Cu-Ni±Co±Zn mineralization), quartz veins (with Cu mineralization), fault zones (with Cu-Zn-Ag±Au mineralization) associated with ultramafic to mafic lamprophyre dykes, carbonatized lamprophyre and carbonatite dykes, and finally, ultramafic lamprophyre dykes which seem to display some affinity with kimberlites.

Details

Document type

Document produced by the Ministère
Geological reports

Field of activity

General geology

Type of survey

Rock analysis
Geological survey

Cross-reference

Also see RG 2001-01

Document type

Document produced by the Ministère
Geological reports

Field of activity

General geology

Type of survey

Rock analysis
Geological survey

Cross-reference

Also see RG 2001-01