The first reports referring to geological aspects of this batholith were those produced by Bancroft (1912), Cooke et al. (1931) and Tremblay (1950). These reports were followed by several township-wide mapping campaigns (see Imreh 1984, 1991), studies and numerous exploration projects (Hawley, 1931; Norman, 1945; Derry, 1949; Rowe, 1953; Siroonian et al., 1959; Masterman, 1979). The first comprehensive studies encompassing this batholith, subdividing it into several lithologies, were those produced by Dawson (1954 and 1966). Subsequently came the work of Danis (1985), Bourne and Danis (1987), Boily et al. (1989, 1990), Rive et al. (1990), Boily (1992, 1995) and Mulja et al. (1995a, 1995b).

The La Corne Batholite is included in the vast Preissac-La Corne Plutonic Suite, which outcrops in the southern Abitibi Subprovince, about 40 km NE of the town of Val-d’Or (Tremblay, 1950; Dawson, 1966). It forms a synkinematic to late-kinematic intrusive complex intruded during the Archean (U-Pb dating 2681-2643 Ma; Feng and Kerrich, 1991) into volcanic rocks of the Malartic and Kinojévis groups, and into sedimentary rocks of the Caste Formation. Specifically, the La Corne Batholith consists of two distinct magmatic suites: 1) an early metaluminous dioritic to granodioritic suite (units nAlac4, nAlac3, nAlac5 and nAlac1), which contains many metasedimentary and metavolcanic xenoliths; and 2) a late peraluminous monzogranitic suite (unit nAlac2), moderately to non-foliated, xenolith-free, with associated pegmatitic aureole mineralized in Li, Be, Mo and Ta. These pegmatites are found in granitic parts, as well as in surrounding lithologies.

The La Corne Batholith is located in the eastern part of the Preissac-La Corne Plutonic Suite, it is elongated along a N-S axis. Tectonic foliation, marked by orientation of biotite and muscovite flakes, is evident on the margins of the batholith; however, this foliation becomes less pronounced in its centre. The whole batholith is surrounded by an aureole of lithium granitic pegmatites, mainly developed in the western and northern parts, and within which many mineralized zones and prospects have been recognized (see deposit records cited in Pilote [2018]; Dawson, 1966; Boily et al., 1989; Boily, 1995; Ste-Croix and Doucet, 2001; Pilote, 2018; Pilote et al., 2019). The Québec Lithium Mine, located on the northern contact of the La Corne Batholith, is part of this aureole. Lithium pegmatites also contain varying amounts (trace-2%) of colombo-tantalite, molybdenite and beryl. Brett et al. (1976) were the first to suggest that early hornblendite masses (unit nAlac4) located only in the western part of the batholith (sheet 32D08) be incorporated.

The work of Bourne and Danis (1987), carried out almost exclusively in the SW portion of the La Corne Batholith, proposed subdividing the early suite into two distinct plutonic facies. The first, called the inner zone (unit nAlac3), contains less than 5% modal quartz and has compositions ranging from brecciated biotite-hornblende gabbro to monzonite. The second facies, called the outer zone, contains more than 5% modal quartz and consists of biotite-hornblende quartz diorite (nAlac5) that progressively evolves towards biotite-hornblende granodiorite (nAlac1). The transition between each facies is relatively steep, but continuous. These two facies are reversely zoned, i.e. cores are mafic and margins are more felsic. A strip of metasomatized granodioritic rocks appears on contact with the outer suite and surrounding sedimentary rocks. This strip is characterized by myrmekitic plagioclase and plagioclase with albite margins, as well as higher quartz and biotite contents than other plutonic rocks in the outer zone.

The early dioritic to granodioritic suite covers almost all of this batholith. In particular, it outcrops along a N-S-oriented strip located between the villages of Vassan and La Corne on contact with surrounding volcano-sedimentary rocks. A few outcrops also appear on the eastern and western shores of Malartic Lake (sheet 32D08). In general, dioritic to granodioric intrusive masses consist of small, shallow outcrops with poor exposure compared to monzogranitic phases.

Combining all the observations made by Tremblay (1950), Brett et al. (1976), Dawson (1966), Bourne and Danis (1987) and Boily (1992), up to eight (8) distinctive lithologies have been recognized within this batholith, most of which show gradual contact. These are: 1) hornblendite or diorite-gabbro; 2) biotite-hornblende quartz diorite; 3) hornblende-biotite quartz monzodiorite; 4) hornblende-biotite monzodiorite; 5) hornblende monzonite; 6) hornblende-biotite monzonite; 7) hornblende-biotite tonalite; and 8) biotite-hornblende granodiorite.

For the purpose of simplification and in line with recent mapping in these areas (Pilote, 2017; Pilote and Lacoste, 2016; Pilote et al., 2016, 2017), the eight lithologies mentioned above have been renamed, grouped and distributed within five (5) units (nAlac1 to nAlac5). The early suite is represented by units nAlac4 (formerly hornblendite or diorite-gabbro), nAlac3 (formerly hornblende-biotite monzodiorite), nAlac5 (formerly biotite-hornblende quartz diorite; hornblende-biotite tonalite) and nAlac1 (formerly hornblende-biotite quartz monzodiorite); the late suite is represented by unit nAlac2 (formerly hornblende monzonite; hornblende-biotite monzonite; biotite-hornblende granodiorite).

The different units of the La Corne Batholith are described below in chronological order, from oldest to youngest: nAlac4, nAlac3, nAlac5, nAlac1 and nAlac2.

Unit nAlac4 is found south (sheet 32D08) and SE (sheet 32C05) of La Motte Lake. It is mainly composed of partially biotitized, chloritized and epidotized granular hornblende. The rock is black to greenish. Hornblende crystals range from 2 mm to 1 cm long. Feldspar content ranges from 10 to 70%. Altered pyroxenes are observed locally. Interestingly, Dawson (1966) interpreted this unit more as metamorphosed mafic volcanics. However, for Brett et al. (1976), this unit was interpreted as an early facies of the La Corne Batholith due to field cross-cutting relationships between different intrusive phases, and the presence of numerous amphibolite and sedimentary rock enclaves in hornblendite. Recent works (Boily, 1992; Pilote, 2018; Pilote et al., 2019) favour the latter interpretation.