Based on data from the regional mapping campaigns of Hocq (1975, 1985), a strip of leucocratic biotite ± hornblende gneiss partially aligned with the current map outline seemed to correspond to the MacLeod Batholith. The first works to mention the « MacLeod Granodiorite » were those of exploration companies (McAuley, 1990; Prior, 1991; Prior et al., 1991; Winter, 2008, 2011). Private companies mapped the extent of the Macleod Granodiorite because of its economic potential that was brought to light in 1988 with the discovery of the Lac MacLeod mineralized zone. Since then, several other Cu, Mo, Ag, Au and W mineralized showings have been discovered (Lac MacLeod-NE, Pointe Rocky, Pointe Richard, ML-06-128, ML-06-123, Windy Cible 4-3 and Cornu). They all have the unique feature of being spatially associated with the edge of the MacLeod Batholith.

Prior et al. (1991) divided the “MacLeod Granodiorite” into five (5) subunits. They used the hornblende/biotite ratio and rock texture (foliated or lineated) to distinguish facies, namely: 1) hornblende granofels, 2) hornblende-(biotite) granofels, 3) foliated hornblende-biotite granofels, 4) foliated biotite-(hornblende) granofels, and 5) foliated biotite granofels. The MacLeod Batholith (nAmcl) was formally introduced by Beauchamp (2020) to describe a large intrusive mass (25 km x 15 km) located in the Cadieux Lake area at the junction of sheets 33A02, 33A03 and 33A07. This batholith is regionally associated with a strong positive magnetic anomaly. No facies subdivision could be completed following the Ministère‘s mapping work.

In thin section, minerals observed are quartz, feldspars (plagioclase to K-feldspar rations of 2/1 to 3/1), hornblende and biotite. Accessory minerals are titanite (≤5%), epidote (pistachite, allanite), apatite, zircon and magnetite. Hornblende chloritization and plagioclase sericitization are commonly observed. The MacLeod Batholith is characterized by zoned alteration ranging from mild to intense. Potassic alteration (biotite, magnetite and K-feldspar in varying proportions) is present at the centre of the intrusion. Propylitic alteration (quartz, chlorite and epidote) and silicification are located at the edge of the intrusion. Later hematite and epidote-filled veinlets cut the S_n foliation and remobilize some of the Cu-Mo-Ag-Au-W mineralization hosted in the MacLeod Batholith and surrounding metasedimentary units.

The MacLeod Batholith is sharply cut by hematitized granite, which could represent a later magmatic intrusion within the batholith. Granite is massive to weakly foliated and is composed of biotite-hornblende ± magnetite. Magnetite forms centimetric clusters. The presence of hornblende in the granite may be a result of enclave contamination. The MacLeod Batholith contains numerous enclaves of mesocratic diorite and granoblastic hornblende gabbro that show a well-developed mineral lineation.

Type outcrop 18-LP-6149 consists of quartz monzodiorite and granodiorite. The rock is homogeneous and moderately foliated. The quartz content ranges from 18% to 25%. The sample collected contains 20% ferromagnesian minerals (predominantly hornblende ± biotite ± magnetite ± titanite) forming small lenticular millimetric aggregates parallel to the S_n foliation. The outcrop also contains small rounded diorite enclaves. Coarse-grained pinkish granite intrusions cut quartz monzodiorite.

Geochemical analyses of samples collected during the summer 2018 mapping work (Beauchamp, 2020) indicate that the MacLeod Batholith is a magnesian granitoid, generally calc-alkaline and type I (Maniar and Piccoli, 1989) metaluminous (Frost et al., 2001) . In the diagrams of Pearce et al. (1984), samples plot in the field of volcanic arc granites. The rare earth diagram normalized to CI chondrite (Palme and O’Neill, 2004) shows light rare earth enrichment over heavy rare earths. Negative anomalies in Nb, Ta, P and Ti, as well as positive anomalies in La, Ce and Nd characterize the spider diagram of this unit.