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.

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.