The Callbreath area is underlain by the Middle to Late Triassic Nightout pluton that consists of quartz diorite. Pegmatites occur along the north side of the intrusive about one kilometre south of its contact with Devonian to Permian sedimentary rocks of the Stikine Assemblage. These pegmatites range from dikes, consisting mainly of quartz, to those consisting mainly of pink orthoclase. Most of these dikes are less than 30 centimetres wide and the more siliceous carry some copper mineralization in small fissures.

Kerr (GSC Memoir 246, page 74) describes one such occurrence observed in an old trench near Nightout Mountain. A shattered zone within the granodiorite, and up to 30 centimetres wide, is filled with pegmatite carrying bornite and chalcopyrite in fractures within the quartz. Up to five per cent of this zone may consist of bornite.

Chalcopyrite and bornite were also found in fractures and in quartz veins within the granodiorite some 140 metres northeast of the pegmatites of Kerr's trench. Bart Mines Ltd explored their B and BM claims in the Nightout Mountain area in 1973 discovering this extension of the Callbreath showing and naming it the "Main Zone". The veins were reported to be up to five centimetres wide and occur in a zone that has a trend of 245 degrees (southwest toward the Callbreath trench). The granodiorite is chloritized and epidotized adjacent to these fractures. Potassium-feldspar also occurs in and adjacent to the fractures. The width of the Main Zone was reported to be approximately 15 metres. Visual estimates of the zone indicate a grade of 0.5 to 1.0 per cent copper. Rocks were taken for assay but not reported.

See Gran 15 South (104G 241) for details of related work history in the area.