February 2012    Print this article

Geological surveys by the Bureau de l’exploration géologique du Québec: Impacts on Geological Knowledge and Mineral Potential in Québec

The geological surveys conducted in 2011-2012 by the Bureau de l’exploration géologique du Québec (or BEGQ) have helped improve our geological knowledge of Québec. The work has, in particular, located promising new geological units for mineral exploration, extended existing units and shed light on their three-dimensional geometry. It has also led to the identification of new regional, local and discrete exploration targets (PRO 2011-06) (PDF Format, 4,07 Mb).

We will present, as examples three projects that have had an impact on geological knowledge and mineral potential in Québec.

Mapping of the Kuujjuaq region

Isabelle Lafrance

To complete the 1:250 000 scale geological mapping of the Churchill Province core zone, cartographic work was launched in the summer of 2011, covering the NTS 24J and 24K sheets south of Ungava Bay.

Several targets of interest for mining companies were identified. Analysis of the results yielded five new indicators in the area mapped, in a range of contexts:

A new uranium indicator, Urani 22 (1205 ppm U, 332 ppm Y and 649 ppm REE) was also discovered outside the mapped area (NTS 24F16) after verification of a radiometric anomaly observed during an aerial geophysical survey carried out by the MRNF over the same period. This discovery led to the staking of 144 new claims when the work was presented at Québec Exploration 2011.

Mapping work on the core zone will continue to the south in 2012, covering sheet 24G and the eastern part of sheet 24F.

2011 James Bay project: Lac Nochet sector

Daniel Bandyayera, Jean Goutier and Pénélope Burniaux

As part of the James Bay project, a 1:50 000 scale geological survey covering four NTS sheets was carried out around lakes Corvette (33G/08), Semonville (33H/05), Nochet (33H12) and Tilly (33H/13), between the La Grande 3 and La Grande 4 reservoirs.

The main objective was to highlight the potential of a sector about which little is known, last covered by a regional mapping campaign in the 1950s and 1970s. Correlation with recent geology in the Lac Guyer area (Goutier et al., 2000; Bandyayera et al., 2010) enabled the volcanic-sedimentary units in the Guyer Group to be circumscribed, along with the boundary between the Opinaca and La Grande subprovinces, which in itself is an important exploration target for gold.

The main arguments for surveying the sector included:

The region is known for gold-bearing mineralizations associated with iron formations (such as the Eade and Orfée formations). To the north, porphyry Cu-Mo mineralizations are present, the largest of which is the Tilly deposit. To the south, several indicators of gold-bearing and poly-metallic mineralizations were also observed in the contact zone between the Opinaca and La Grande subprovinces. The best-know indicator is the gold-bearing Corvet Est deposit.

The new geological survey was carried out by a team of seven geologists and eight assistants, mainly travelling by helicopter. The mapping covered 2852 outcrops, and 386 new geochemical analyses were conducted.

The new geological and geophysical surveys were used to update the regional map. The Lac Nochet sector comprises volcanic-sedimentary and Archean plutonic rocks and paleoproteozoic sedimentary basins (Sakami formation), intersected by gabbroic, Archean and Proterozoic dyke swarms. The main results of the work are as follows:

Of the 17 samples collected from the intrusions, 3 were analyzed and showed indicial or anomal content of 1 g/t Pd and 3 g/t Au (1 analysis), 226 ppb Pd and 206 ppb Au (1 analysis) and 25% Cr2O3 (1 analysis).

Geological revision of the Matagami region

Pierre Pilote, Julie-Anaïs Debreil, Kenneth Williamson, Pierre Lacoste and Olivier Rabeau

The 2011 field campaign constituted the final phase in the Matagami project, a multidisplinary project launched in 2008 to review the geological and metallogenic understanding of the Matagimi mining camp (1960-2004 production: 4.6 Mt Zn; 0.494 Mt Cu). The geological revision work completed in the summer of 2011, at a scale of 1:20 000, covered the southern half of sheet NTS 32F13, the northern half of sheet 32F12 and the NE and SE parts of sheets 32E09 and 32E16 respectively (figure 1).

These areas together make up the mining camp. A 3D geometric model of the region was also produced to provide a better understanding of the area and predict extensions of specific stratigraphic units, structural elements (folds and faults) and the distribution of VMS-type mineralizations. The project was part of a larger partnership between the MRNF, researchers and students at INRS-ETE, UQAC and École Polytechnique de Montréal, the mining companies Xstrata Zinc and Donner Metals, and SOQUEM.

Click on image to enlarge





Figure 1 – Simplified geology of the Matagami region (Pilote et al., 2011)

Figure 2 – 3D geological model of the Matagami mining camp showing the position and differences in structure betweenthe North and South domains. The boundary between the two domains is shown in red. The North Domain is characterizedby numerous shear zones oriented 070° east-west, dipping steeply to the north. The South Domain has a relatively lowdeformation rate and two superposed fold phases (phase P1 oriented NNW and phase P2 oriented E-W), producinga dome-and-basin geometry.

The mapped region mainly belongs to the Abitibi subprovince. It is contains various volcanic and plutonic rocks, the Rivière Bell Complex (RBC - a vast subconcordant ultramafic to mafic layered intrusion dated at 2724.6 ± 2.5 Ma) and a narrow band of sedimentary rocks (the Matagami Group - MaG, <2700 Ma) in faulted contact with the Opatica Subprovince (OSP) to the north and volcanics to the south. These lithologies are crosscut by Proterozoic gabbro dykes. Two volcanic groups are present: the Lac Watson Group (WatG, 2725 à 2723 ± 2 Ma) and the overlying Wabassee Group (WabG). The WatG consists mainly of rhyolite, rhyodacite and dacite. It is this group that hosts the majority of volcanogenic massive sulphide deposits in the camp. The Key Tuffite, immediately overlying the WatG rhyolites, represents an important marker horizon for VMS mineralization in this mining camp. The WatG is intruded by the CRB. The Wabassee Group is dominated by andesites and pillowed basalts, either massive or brecciated. The group includes the Rivière Allard Formation (calc-alkaline to transitional affinity), the Rivière Bell Formation (tholeiitic affinity) and the Daniel Formation (calco-alcaline affinity).

Several geographical areas have been defined in the past in this vast region: the South Flank, the North Flank, the Central Camp, and the West Camp. Our work has led us to propose a new subdivision into North and South domains, with the boundary marked by three shear zones named “Rivière Allard”, “Rivière Waswanipi” and “Lac Matagami”, all oriented 070°. They represent reverse sinistral shears ranging from 50 m to more than 100 m thick, dipping steeply to the north with a stretching lineation plunging steeply to the east. The South Domain will now comprise the historically defined North Flank and South Flank, the Central Camp and the West Camp. Our work demonstrates, just as several researchers have suggested in the past, that the South Flank, Central Camp and West Camp share the same stratigraphy, oriented NW-SE with a gentle to quasi-horizontal dip, developed in a relatively consistent and predictable manner. Mapping also reveals that the South Flank and Central-West camps are affected by a weak S1 cleavage and by three major F1 fold axes (two synclines and one large anticline), also oriented NW-SE. An E- to ESE-oriented S2 schistosity crosscuts S1 cleavage. As for the North Flank, stratification is oriented 110° with a dip and general polarity to the north. An S2 schistosity oriented 090° to 110° affects the S0 surface and locally generated F2 folds. Shear zones, also oriented 110°, appear to repeat or truncate certain portions of the volcanic pile and the BRC. The resulting geometry of the juxtaposed North and South domains calls into question the existence of the Galinée Anticline and has serious implications for the VMS potential in the areas described above.

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