The Elson Complex was first named Bourdon Gneiss by Hammouche et al. (2011) in the Bonaventure Lake area. It was extended east in the Zeni Lake area by Hammouche et al. (2012). It was then renamed Elson Complex as part of the Southeastern Churchill Province synthesis (SECP; Lafrance et al., 2018) as the Bourdon Complex name was already in use in the Grenville Province. The unit defined by Hammouche et al. (2011) also included paragneiss, which was largely reassigned to the Zeni Complex (ApPzen3), and ultramafic rocks now assigned to the Pallatin Intrusive Suite (pPped1).

It takes its name from Elson Lake located in the SW portion of sheet 23I16.

The Elson Complex consists mainly of tonalitic gneiss (Aelo1) and granitic gneiss (Aelo2). Gneiss are highly deformed and folded; ptygmatitic folds and porphyroclasts are abundant. The complex locally contains highly deformed felsic and intermediate intrusions, and undeformed felsic intrusions, including pegmatitic granite.

Medium-grained quartzofeldspathic material, occurring as diffuse and irregular centimetric bands, cuts gneissic banding. This material appears to have resulted from rock migmatization (leucosome).

Gneiss displays sharp and regular banding, locally straight, which consists of alternating millimetric to centimetric grey and beige to pinkish bands. Centimetric to decimetric layers of dark grey or black diorite and amphibolite are also inserted in the sequence. Light bands are medium to fine grained and contain some biotite (<12%). They are mostly tonalitic in unit Aelo1. Dark bands are fine grained and contain a higher proportion of biotite (20-30%). Muscovite and hornblende are also present in minor amounts (<5%). Accessory minerals are clinopyroxene, sphene, opaque minerals and rutile. Slight sericite-epidote alteration is observed in thin sections.