The intrusion was first described as the Barlow River Complex by Caty (1975) and Boudreault (1977), and later as the Barlow Pluton in subsequent publications (Racicot, 1979; Racicot et al., 1984).

According to Racicot et al. (1984, p. 189): “The Barlow Pluton is composed of two series of rocks, an outer shell of quartz monzodiorite and a core of leucotonalite. The transition between the two is relatively abrupt, but with the mutual dyking relationship typical of coeval intrusions. Structurally, the mass is surrounded by a relatively narrow envelope with a mylonitic texture which fades out into a more typically igneous foliation in the interior of the batholith. Structures are dominantly E-W, parallel to the elongation of the batholith and the regional structural trend. The outer quartz monzodiorite shell is variable in composition, showing primary banding, shown by a variation in the content of mafic minerals, and a variety of early or synchronous mafic dykes which are deformed or partly digested by the principal phases. The principal mineral components are plagioclase, An₂₄ (50-60%), quartz (10-15%), clinopyroxene and/or green hornblende (15%) with varying amounts of interstitial microcline (10-15%). The resulting rock is quite distinctive, and seems to occur only in masses in a similar structural position in the region. The leucotonalite core is a relatively monotonous rock, light grey, coarse-grained and composed of tabular crystals of plagioclase, An₂₄ (55-60%), with amoeboid quartz grains (25-30%) and biotite (0-5%). Late aplite dykes cutting the main phases are granodioritic in composition.”