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Pichi Pluton
Stratigraphic label: [narc]ppi
Map symbol: nAppi
 

First published: 23 July 2018
Last modified:

 

 

 

  DISCLAIMER: This English version is translated from the original French. In case of any discrepancy, the French version shall prevail. 

Informal subdivision(s)
Numbering does not necessarily reflect the stratigraphic position.
 
None
 
Author(s): Gigon et al., 2013
Age: Neoarchean
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
Category: Lithodemic
Rank: Lithodeme
Status: Formal
Use: Active
Related unit(s)
  • Richardie Suite
    Pichi Pluton

Background

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.

 

Description

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.

Dating

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

Stratigraphic Relationship(s)

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.

Paleontology

Does not apply.

References

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 2017-01, 63 pages.

GIGON, J., GOUTIER, J., 2017. Géologie de la région du lac Richardie, municipalité d’Eeyou Istchee Baie-James. MERN; RG 2016-04, 45 pages, 2 plans.

GIGON, J., GOUTIER, J., CHARTIER-MONTREUIL, W., 2013. GEOLOGIE – LAC JACQUELEIN. MRN; CG-33H03-2013-01, 1 plan.

Suggested Citation

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].

Contributors

First publication

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). 

 
 
9 août 2021