Jean Goutier

3D GIS as a support for mineral discovery

ABSTRACT Exploration for deep-seated mineral deposits in mature mining camps requires integration of large and heterogeneous spatial data-sets. Traditionally, geological, geochemical, and geophysical observations are acquired, processed and analysed independently within separate spatial contexts or more commonly, for geochemical data, in non-spatial feature space. Although methodological developments are still in progress, 3D GIS (geographic information system) technologies already provide powerful tools that can be used to integrate such heterogeneous data-sets to visualize, compare, and characterize geological relationships in a more supportive interpretive environment. Importantly, this technology provides better opportunities to embed all these properties in a more robust geometric framework in which structural history and palaeogeographic setting can be taken into account. We present 3D GIS applications that aid in interpreting relationship patterns amongst faults, folds and geochemical trends. Examples from the Noranda mining region, a classic VMS mining camp, demonstrate the applicability of 3D GIS to support the discovery of new mineral resources at depth.

Basaltic to andesitic volcaniclastic rocks in the Blake River Group, Abitibi Greenstone Belt: 2. Origin, geochemistry, and geochronology

In the Archean Blake River Group, mafic to intermediate fragmental units have controversially been proposed to have formed during the collapse of a giant submarine caldera. This paper describes and interprets these rocks, summarizing their physical characteristics, inferred origins, age relationships, and geochemical signatures. The widespread Stadacona member, south of Rouyn-Noranda, consists of several hundred meters of bedded volcaniclastic rocks interpreted to have been mostly deposited from aqueous density currents fed directly by explosive eruptions. The magmas involved in these eruptions were plagioclase-phyric tholeiitic to transitional basalts. The similarly widespread D’Alembert tuff, in the northern part of the Blake River Group, shares many physical characteristics with the Stadacona member and is thought to have a similar origin. However, the D’Alembert tuff is approximately six million years younger than the Stadacona member. It is composed mostly of transitional to calc-alkaline andesites and basaltic andesites with very distinct trace element profiles. Volcaniclastic rocks from other areas, such as Tannahill Township in Ontario and the Monsabrais area in Quebec, are interpreted to represent mostly in situ to remobilized hyaloclastite, with no explosive eruptions involved in their genesis. Our observations and interpretations are not compatible with models in which the volcaniclastic units are emplaced during a catastrophic event in relation with the collapse of a giant caldera. Instead, the fragmental rocks were produced by various mechanisms at many distinct times during the evolution of the Blake River Group.

Minto Large Igneous Province: A 2.00 Ga Mafic Magmatic Event in the Eastern Superior Craton Based on U‐Pb Baddeleyite Geochronology and Paleomagnetism

been obtained for the NNW trending Lac Shpogan dyke swarm of the James Bay area of the eastern Superior craton. Previously the age of the swarm was only constrained by its crosscutting relationship with the older but poorly dated (>2216 Ma) Sakami Formation quartz arenites. The new age confirms a link with the 1998 ± 2 Ma WWNW trending dykes of the Minto swarm (Buchan et al. 1998) located ~500 km to the north, a link which had been tentatively proposed on basis of similarities in geochemistry and paleomagnetism (Buchan et al. 2007). Both dyke sets likely belong to a single giant dyke swarm which may represent part of the plumbing system for a ca. 2.00 Ga large igneous province (LIP) with a wide distribution in the eastern Superior craton. Combining the paleomagnetic results from the two dyke sets yields an improved estimate of the paleopole for the eastern Superior craton at that time. The two most prominent Lac Shpogan dykes can each be traced for 150-300 km and appear to converge slightly to the north toward a focus in eastern Hudson Bay. Most of Minto dykes, including the dated Minto dyke, generally fit this convergent pattern, although each dyke is only exposed over a short distance. Maurice et al. (2009) include a wide swath of WNW trending dykes that are subparallel to the dated Minto dyke as part of the Minto swarm, although dating or paleomagnetic study is needed to confirm this interpretation. The most northeastern of the Minto dykes described by Buchan et al. (1998) has a welldefined NW trend which does not appear to fit the overall radiating Minto-Lac Shpogan pattern. It also has distinct geochemistry and opposite magnetic polarity from other Minto dykes and Lac Shpogan dykes (Buchan et al. 1998; Buchan et al. 2007). It is possible that this dyke is of a somewhat different age and not part of the Minto set. Both the Lac Shpogan and Minto paleomagnetic directions are likely primary because older ca. 2.22 Ga Senneterre and Maguire dykes from the same areas give consistent magnetic directions (Buchan et al. 2007) that are quite different from the Lac Shpogan and Minto directions. This demonstrates that no substantial magnetic overprinting has occurred since the emplacement of Lac Shpogan and Minto dykes. As noted by Buchan et al. (2007), the consistency of the Senneterre-Maguire paleomagnetic directions in the two areas also indicates that there has been no substantial post-2.22 Ga relative rotation. Given that the Lac Shpogan and Minto dykes are of identical age, that the paleomagnetic data for each are likely primary, and that no substantial rotation has occurred between the two areas where the dykes are found, we assume that any difference in paleomagnetic directions is most likely due to secular variation. Therefore, we have calculated an overall mean paleopole at 31.4N, 171.2E, A95=12 based on 9 dykes (6 Minto dykes and 3 Lac Shpogan dykes). We have excluded the NW dyke trending “Minto” dyke as it could be of a somewhat different age based on its distinct trend, geochemistry and reversed polarity compared to other Minto and Lac Shpogan dykes. The combined Minto-Lac Shpogan pole, which falls a few degrees south of the published Minto pole, is considered to be a better estimate of the pole for the eastern Superior craton at 2.00 Ga than was previously available based on only the Minto dykes. Several geological units in the eastern Superior craton and eastern Hudson Bay may be part of the Minto LIP based on geochronology, paleomagnetism or geochemistry. The Watts Group of the Purtuniq ophiolite in the Cape Smith Belt has been dated at 1998 ± 2 Ma (UMichael A. HAMILTON, Jean GOUTIER, Kenneth L. BUCHAN, 2016. Minto Large Igneous Province: A 2.00 Ga Mafic Magmatic Event in the Eastern Superior Craton Based on U-Pb Baddeleyite Geochronology and Paleomagnetism. Acta Geologica Sinica (English Edition), 90(supp. 1): 69-70.