Stevenson et al. (1969) mapped a kilometric subcircular mass in the Troie Lake area, the contours of which roughly correspond to the current Troie Complex, consisting of amphibolitic gneiss of pyroxene granodioritic composition. The Troie Complex was introduced by Madore et al. (1999, 2000) in the Peters Lake area (sheet 24M) to describe lithological assemblages corresponding to a strong subcircular magnetic anomaly within the Douglas Harbour Domain. Initially, the complex consisted primarily of orthopyroxene intrusive and metamorphic rocks (granulitic gneiss [Atie4], hornblende gabbronorite and biotite gabbronorite [Atie8]) and also included monzonite and porphyraceous monzonite to quartz monzodiorite (Atie9), gneissic granite (Atie6), migmatitic granite (Atie5), supracrustal rock klippes (granulitic metavolcanics [Atie3] and paragneiss [Atie2]) and iron formation layers (Atie1). Several of these assemblages were extended southward in the Dufreboy Lake area (sheet 24L). Simard et al. (2008) redefined the Troie Complex to retain only orthopyroxene rocks within the unit. Supracrustal rocks and iron formation layers have been assigned to the Arnaud Complex, granites to the Dufreboy Suite, and monzonite and quartz monzodiorite to the Belloy Suite.

The Troie Complex consists mainly of orthopyroxene orthogneiss and foliated to gneissic charnockitic intrusions consisting of enderbite, opdalite and a lesser amount of charnockite and hypersthene diorite, the whole interspersed with small hornblende or biotite gabbronorite intrusions (Madore et al., 1999, 2000; Simard et al., 2008; Simard, 2008). It was divided into three informal units (Simard, 2002, 2003; Leclair, 2003; MNRF, 2006a-c; Bilodeau et al., 2012a-c): gneissic to foliated orthopyroxene-clinopyroxene tonalite (nAtie1, formerly Atie4 [Madore et al., 1999, 2000]), hornblende gabbronorite and biotite gabbronorite (nAtie2, formerly Atie8 [Madore et al., 1999, 2000]) and charnockite (nAtie3, previously included in unit Atie4 [Madore et al., 1999, 2000]).

The main unit nAtie1 consists mainly of orthogneiss and foliated igneous rocks of felsic to intermediate composition. These granulitic rocks are characterized by the presence of orthopyroxene. They are enderbitic (hypersthene tonalite), opdalitic (hypersthene granodiorite) or, in lesser amounts, charnockitic (hypersthene granite; unit nAtie3) and dioritic. They contain enclaves of mafic rocks. The rock is heterogeneous, leucocratic to mesocratic and grey to greenish brown. It is migmatized and contains 10 to 60% pyroxene felsic mobilisate. In the most migmatized localities, the mobilisate is pervasive and accounts for >85% of the rock.

In thin sections, gneissic or foliated tonalite and its associated phases are granoblastic and medium grained (0.5-2.0 mm). Despite recrystallization, these rocks locally exhibit a more massive and coarser-grained (1-4 mm) relic texture of magmatic origin. In gneissic facies, ferromagnesian minerals tend to concentrate as porphyroblasts in dioritic bands. These ferromagnesian minerals are reddish biotite, clinopyroxene, orthopyroxene and green hornblende. Garnet porphyroblasts (<2%) are observed in a few places. Between 1 and 10% of opaque minerals, mostly magnetite, are disseminated in the rock. The most common secondary minerals are apatite and zircon.

Troie Complex 2 (nAtie2) : Hornblende Gabbronorite and Biotite Gabbronorite

A few small dark green to greenish beige gabbronorite intrusive bodies, not exceeding 20 km in diameter, are found mainly inside gneissic or foliated tonalite (unit nAtie1) as metric enclaves surrounded by felsic mobilisate, thus defining an agmatitic texture. Gabbronorite is also found as enclaves in granulitic rocks, indicating that gabbronorite intrusions can be of different ages. Based on petrographic and geochemical observations, two types of gabbronorite can be identified: hornblende gabbronorite and biotite gabbronorite. In thin sections, these rocks display a heterogranular granoblastic texture with grain sizes ranging from 1 to 5 mm. Locally, remnants of subophitic textures are observed, but primary igneous textures are usually replaced by recrystallization textures.

Both types of gabbronorite are mainly composed of clinopyroxene (10-35%), orthopyroxene (5-30%) and plagioclase (40-55%). Hornblende gabbronorite contains 15-30% green hornblende partially replacing pyroxenes and a small amount of biotite (1-5%). This first type of gabbronorite is usually deformed and displays a well-developed foliation. Biotite gabbronorite contains 5-15% biotite and <5% hornblende. This second type of gabbronorite is less deformed than the previous and locally forms dykesdisplaying  an igneous porphyraceous texture. In biotite gabbronorite, plagioclase locally forms zoned euhedral phenocrystals. Secondary minerals observed in both types of gabbronorite are apatite (1-3%) and quartz (1-2%). These rocks contain 5-15% disseminated opaque minerals, mainly magnetite and ilmenite.

Troie Complex 3 (nAtie3) : Charnockite

In southern Troie Complex (sheet 24L), a charnockite (hypersthene granite) unit was differentiated. The rock is brown to light brown, massive to foliated and porphyritic to megaporphyritic. It contains K-feldspar phenocrystals up to 5 cm long. In addition to orthopyroxene and plagioclase, charnockite is composed of biotite and, locally, hornblende and clinopyroxene. Unit nAtie3 contains opdalite (hypersthene granodiorite) locally.

Thickness and distribution

The Troie Complex is a subcircular unit, corresponding to a magnetic high, that covers a significant area within the Douglas Harbour Domain (Madore et al., 1999, 2000; Simard et al., 2008; Simard, 2008). It is >110 km by ≤90 km and covers three quarters of sheet 24M and the top quarter of sheet 24L.

Dating

U-Pb dating on zircons of a homogeneous charnockitic gneiss (nAtie1) yielded crystallization ages of 2741 ±8 and 2739 ±8 Ma (estimated) (David et al., 2009). Analysis of two individual monazites from the same sample yielded consistent ages of 2698 ±2 and 2706 ±2 Ma indicating a 2.70 Ga metamorphic event (David et al., 2009). U-Pb dating on zircons of another sample of biotite tonalitic gneiss collected in northern Troie Complex yielded a crystallization age of 2734 ±5 Ma (Percival et al., 2001). In comparison, U-Pb dating on zircons of a homogeneous coarse-grained gabbronorite (nAtie2) yielded crystallization ages of 2722 ±3 and 2726 ±14 Ma (estimated), as well as metamorphic ages of 2674 ±11 and 2675 ±2 Ma (David et al., 2009).