DISCLAIMER: This English version is translated from the original French. In case of any discrepancy, the French version shall prevail.
|Author(s):||Gigon et al., 2013|
|Stratotype:||Outcrop 2013-JG-1351 (type locality)|
|Type area:||James Bay|
|Geological province:||Superior Province|
|Geological subdivision:||La Grande Subprovince|
|Lithology:||K-feldspar porphyritic hornblende-biotite-magnetite granodiorite|
The Pichi Pluton unit was introduced by Gigon et al. (2013) and was described in detail in the report by Gigon and Goutier (2017). This unit was associated with the Richardie Suite based on similar lithologies by Gigon et al. (2013) and Gigon and Goutier (2017). It should be noted that the Pichi River is well represented on the geological map of the Gigon and Goutier report (2017), but not on Figure 2 of that same report.
The Pichi Pluton consits of hornblende-biotite-magnetite granodiorite, K-feldspar porphyritic in its centre, and granite towards the edge with less K-feldspar phenocrystals. Granodiorite and granite are pinkish grey. They contain up to 20% ferromagnesian minerals consisting of biotite, hornblende and magnetite. Their abundance decreases towards the edge of the intrusion. Like rocks of the Richardie Suite, these rocks are characterized by the presence of 1-5% K-feldspar 1-3 cm long. Major minerals (>80%) are quartz and feldspar. Secondary minerals are sphene, hematite and epidote, while chlorite, sericite and apatite were observed in thin sections. These felsic rocks are massive, medium to coarse grained, and locally, pegmatitic. A slight foliation reflects the low degree of deformation that the rocks have undergone. Centimetric enclaves of hornblendite and diorite are common (Gigon and Goutier, 2017).
The lithology of outcrop 2013-JG-1351 is representative of the centre of the pluton. Samples from this outcrop were used for petrographic study, geochemical analysis and U-Pb isotopic dating.
Thickness and distribution
The Pichi Pluton has a rounded shape, with an area of 70 km² in sheet 33H03. The centre of the puton is located 8 km west of the Pichi River and 6 km north of Jacquelein Lake.
The Pichi Pluton was dated from a sample taken in the centre of the pluton (outcrop 2013-JG-1351). Most analyses on zircons gather on the concordia curve at an age of 2693 ±5 Ma (mean 207Pb/206Pb method, MSWD 0.9; Davis et al., 2018) which represents the best estimate of crystallization age.
|Unit||Sample||Isotopic System||Mineral||Crystallization Age (Ma)||(+)||(-)||Reference(s)|
|nAppi||2013-JG-1351A||U-Pb||Zircon||2699||5||5||Davis et al., 2018|
The Pichi Pluton is located in the contact zone between the La Grande and Opinaca subprovinces. No outcrops permit observation of the pluton’s stratigraphic relationships with surrounding rocks. The shape of the pluton and its concentric magnetic signature suggest that it is intrusive into rocks of the Laguiche Complex and Kamusaawach Intrusion. It is cut by two diabase dykes belonging to the Mistassini Dyke Swarm and the Lac Esprit Dykes.
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Publications available through SIGÉOM Examine
DAVIS, D W., LAFRANCE, I., GOUTIER, J., BANDYAYERA, D., TALLA TAKAM, F., GIGON, J., 2018. Datations U-Pb dans les provinces de Churchill et du Supérieur effectuées au JSGL en 2013-2014. MERN; RP 2017-01RP 2017-01, 63 pages. Disponible à https://gq.mines.gouv.qc.ca/documents/EXAMINE/RP201701.
GIGON, J., GOUTIER, J., 2017. Géologie de la région du lac Richardie, municipalité d’Eeyou Istchee Baie-James. MERN; RG 2016-04RG 2016-04, 45 pages, 2 plans. Disponible à https://gq.mines.gouv.qc.ca/documents/EXAMINE/RG201604.
GIGON, J., GOUTIER, J., CHARTIER-MONTREUIL, W., 2013. GEOLOGIE – LAC JACQUELEIN. MRN; CG-33H03-2013-01CG-33H03-2013-01, 1 plan. Disponible à https://gq.mines.gouv.qc.ca/documents/EXAMINE/CG33H03201301.
Ministère de l’Énergie et des Ressources naturelles (MERN). Pichi Pluton. Quebec Stratigraphic Lexicon. https://gq.mines.gouv.qc.ca/lexique-stratigraphique/province-du-superieur/pluton-de-pichi_en [accessed on Day Month Year].
Alban Duvernois, M.Sc. (redaction)
Mehdi A. Guemache, P. Geo., Ph.D. (coordination); Pierre Lacoste, P. Geo., M.Sc. (critical review); Simon Auclair, P. Geo., M.Sc. (editing); Céline Dupuis, P. Geo., Ph.D. (English version); Ricardo Escobar Moran (HTML editing).