Red Mountain is located near the western margin of the Stikine terrain in the Intermontane Belt. The Stikinia Belt comprises three primary stratigraphic elements: Middle and Upper Triassic clastic rocks of the Stuhini Group, Lower and Middle Jurassic volcanic and clastic rocks of the Hazelton Group, and Upper Jurassic sedimentary rocks of the Bowser Lake Group. Mineralogy suggests that the regional metamorphic grade is probably lower greenschist facies.
The age of intrusive rocks in the Red Mountain region range from Late Triassic to Eocene. Early to Middle Jurassic plutons, named the Goldslide Intrusions, appear to be closely related to the gold mineralization at Red Mountain. Eocene intrusions of the Coast Plutonic Complex occur to the west and south of Red Mountain and are associated with high-grade silver-lead-zinc occurrences.
Red Mountain lies along the western edge of a complex northwest trending structural culmination formed during the Cretaceous era. The Red Mountain mineral zones lie at the core of the Bitter Creek antiform, a northwest-southeast trending structure created during this deformation event (Greig, 2000). During the Tertiary era the area at Red Mountain was subject to extensional block faulting.
The Stuhini Group sedimentary rocks outcrop across approximately two-thirds of the mapped area. This group of rocks is the oldest of those found on the Red Mountain Gold Property and are comprised of Middle to Upper Triassic mudstones, siltstones, and cherts. The Stuhini Group rocks grade upward into Lower Jurassic Hazelton Group clastic and volcaniclastic rocks, which outcrop in the northeastern portion of the map area. Rocks of both groups are folded about axes that plunge towards 345° and dip steeply to the southwest.
The Goldslide intrusions underlying Red Mountain have been segregated into two phases, Goldslide (FHx) and Hillside (FHBp). Both phases have dioritic compositions. The Goldslide rocks have been noted to crosscut the Hillslide Porphyry suggesting the Hillslide Porphyry is the older phase (Sieb 1995).
The Hillside Porphyry occurs near the summit of Red Mountain and is a medium grained hornblende and plagioclase-phyric porphyry. The Hillside Porphyry contains rafts of the sedimentary rocks.
The Goldslide Porphyry is a hornblend-biotite quartz porphyry intrusion underlying most of the Red Mountain cirque.
Alteration is strong and widespread throughout the Property. All pre-Tertiary rocks have been hydrothermally altered. The sediments and intrusives display similar alteration assemblages. Alteration minerals observed include quartz, K-feldspar, tourmaline, sericite, chlorite, and pyrite. Red Mountain was named for an extensive rusty gossan covering 12 to 15 square kilometers of area.
Brittle faulting has affected all rock units at Red Mountain. Rhys et al. (1995) recognized two phases of faulting, northeast striking, steeply northwesterly dipping faults and north to northwest trending faults. Faults of the former group are those that offset the mineralized zones, such as the Rick Fault.