The Three Sisters occurrences are hosted by Middle Jurassic (and/or Early Cretaceous?) intrusive rocks of the Three Sisters pluton and Late Triassic rocks of the Cake Hill pluton. The “Three Sisters” occurrences are named after the group of peaks on which the fine-grained mafic phase of the Three Sisters pluton is exposed (see Figure 3g, Fieldwork 2011).

The showings occur within the northern margins of the fine-grained mafic phase of the Three Sisters intrusions comprised of massive, equigranular to sparsely plagioclase porphyritic, hornblende quartz (?) diorite, and within the adjacent central felsic phase and leucocratic Cake Hill pluton which consists of equigranular hornblende quartz monzodiorite to quartz monzonite.

A brown-orange weathering zone, up to 200 metres wide and 2 kilometres long, is exposed within the Three Sisters central felsic phase close to contact with the fine-grained mafic phase (Figure 10, Fieldwork 2011). The zone contains abundant west-northwest striking and steeply north dipping goethite-coated fractures after pyrite, and pyrite is also disseminated throughout the hostrock. Three small exposures with quartz plus pyrite plus/minus chalcopyrite, plus/minus epidote veins and locally associated with in situ brecciation, are found several hundred metres to the south and southwest of this zone and are hosted in the fine-grained mafic phase. One assay sample from the latter location (11BVA32-241) assayed 0.35 per cent copper and slightly elevated gold (page 116 and Table 2, Fieldwork 2011). An assay sample from the gossanous pyrite zone (11BVA32-246) returned no anomalous values.

The Three Sisters showings were discovered during a 2011 fieldwork program completed by the BC Geological Survey. Two rock samples were collected, and the area was mapped.