The Pistolet Group is an autochthonous/parochthonous to allochthonous sedimentary unit belonging to the first cycle of the Labrador Trough (Clark and Wares, 2004). It is lithologically very heterogeneous and consists mainly of sedimentary rocks forming a passive continental margin platform (Dimroth, 1969, 1970, 1972, 1978; Clark and Wares, 2004). The Pistolet Group is distinguished from the underlying Seward Group by its distinctly marine character, the abundance of mudstone and the general absence of red rocks. The presence of a few dolomite beds in all Pistolet Group formations and most of their informal units distinguish it from the overlying Swampy Bay Group (Dimroth, 1969).

The sedimentary sequence of the Pistolet Group begins with mudstone, siltstone, fine-grained sandstone and dolomite, generally greenish to greyish, of the Lace Lake Formation. These rocks are thought to have been deposited in coastal or subcostal environments (Dimroth, 1972, 1978). In places, such as near Castignon and Romanet lakes (Dimroth, 1978; Chevé, 1985; Clark, 1986), rocks are dark green, dark grey or black and locally contain graphite (e.g. in the « central basin facies » of Dimroth, 1978), indicating a significant change in redox conditions early in the deposition of the group in these areas (Clark and Wares, 2004). Lace Lake Formation rocks are overlain by beds of stromatolitic dolomite, locally reefy, dolomitic sandstone and white quartzitic arenite of the Alder Formation (Dimroth, 1972, 1978). These red, green or white rocks were deposited in a shallow marine environment and exhibit characteristics indicative of transient oxidizing to reducing chemical conditions similar to those of the marginal facies of the Lace Lake Formation. The upper part of the Pistolet Group consists of a massive, non-stromatolitic, brown patina grey dolomite of the Uvé Formation. These rocks are thought to have been deposited largely in relatively still, deep water where conditions were locally reducing (Dimroth, 1972, 1978).

Formations of the Pistolet Group were divided by Dimroth (1969, 1972, 1978) into numerous informal units to allow detailed correlation between the various localities where this group was mapped. Dimroth (1972, 1978) also points out that the Alder and Uvé formations contain facies that are difficult to distinguish from those of the Lace Lake Formation. According to Dimroth (1972, 1978), the typical subdivision of the Pistolet Group into three formations can be applied to the Castignon Lake and Wheeler River areas and largely to the Granite Falls area (sheet 23N16). In the Luché and Girafe lakes area (Table 1; sheet 24C07), NW of Castignon Lake, Dimroth (1972, 1978) recognized particular facies of the group, which he described as a succession of white quartzitic arenite and dolomitic sandstone layers typical of the Alder Formation, and brown patina dolomite characteristic of the Uvé Formation. Dimroth (1972, 1978) mentions, however, that this succession is relatively unknown because of the limited number of outcrops.

Table 1: Characteristics of the Pistolet Group in the Luché and Girafe Lakes Area 

The Pistolet Group is the result of the development of a marine platform on the passive margin of the Archean continent (Dimroth, 1970, 1972, 1978). The source of the detrital material is thought to have been derived from terrain to the west and east of the Labrador Trough. Metamorphism is low in rocks of the Pistolet Group and increases from west to east, from sub-greenschist to greenschist facies (Dimroth and Dressler, 1978).

The Pistol Group contains nine informal units, numbered 1 to 15; numbers 7 to 11 and 13 are not used.

Unit pPpi2 is located between Luché Lake and Giraffe Lake, and west of Patu Lake (Dimroth, 1969, 1972, 1978; Dressler, 1973, 1979; Clark, unpublished). Dimroth (1972, 1978) estimates its thickness at 30 m. The unit consists of grey quartzitic, locally dolomitic arenite having a white alteration patina. The rock is massive and fine, medium or coarse grained (Dressler, 1979). According to Dimroth (1972, 1978), quartzitic arenite of unit pPpi2 is slightly tectonized and is indistinguishable from that of the Alder Formation. Arenite is in gradual contact with pink arkosic conglomerate (pPpi1) (Dimroth, 1972, 1978). In thin sections, arenite contains minor amounts of dolomite and feldspar (Dressler, 1979).

Pistolet Group 3 (pPpi3): Red, Green or Grey Siltstone, Mudstone and Fine-Grained Sandstone; Interbedded Purple Sandstone and White Quartzitic Arenite (« Quartzite »)