The East Ridge occurrence is located at an elevation of approximately 1680 metres and 1.2 kilometres east-northeast of Mount Graves.
The area is situated within a Mesozoic volcanic arc assemblage that lies along the eastern margin of the Intermontane Belt, a northwest-trending belt of Paleozoic to Neogene sediments, volcanics and intrusions bounded to the east by the Omineca Belt and to the west and southwest by the Sustut and Bowser basins. Permian Asitka Group crystalline limestones are the oldest rocks exposed in the region. They are commonly in thrust contact with Upper Triassic Takla Group andesite flows and pyroclastic rocks. Takla volcanics have been intruded by the early Jurassic granodiorite to quartz monzonite Black Lake Suite and are in turn unconformably overlain by or faulted against Lower Jurassic calc-alkaline volcanics of the Toodoggone Formation (Hazelton Group).
The dominant structures in the area are steeply dipping faults that define a prominent regional northwest structural fabric trending 140 to 170 degrees. In turn, high-angle, northeast-striking faults (approximately 060 degrees) appear to truncate and displace northwest-striking faults. Collectively these faults form a boundary for variably rotated and tilted blocks underlain by monoclinal strata.
The area is underlain by volcanics and volcaniclastics of the Jurassic Hazelton Group. These rocks form the eastern limb of a north-northwest–trending faulted anticline. Regionally, these rocks have been subdivided into four informal units (Forster, 1984) that, at the Mount Graves prospect, dip 50 to 80 degrees to the northeast. Welded and partially welded andesite pumice breccia, overlain by grey, green to orange hornblende porphyritic andesitic flows and pyroxene andesite flows; lesser thin discontinuous lenses of greywacke and laminated siltstone comprise lithologies of the Hazelton Group. Quartz monzonite dikes are found in the faulted core of the regional anticline and along northeast- and east-striking faults. A series of quartz feldspar porphyry rhyolitic dikes, striking northwest and dipping steeply, occur subparallel to bedding.
Locally, gossanous zones are associated with steeply dipping faults cutting moderately east-dipping andesite flows. Areas, up to 20 metres wide, of argillic alteration and silicification are associated with a main east-northeast–trending fault and host quartz-pyrite altered lenses. Calcite veining is also common in the area. Immediately downslope an agglomerate, up to 4 metres thick, is partially silicified and hosts minor disseminated pyrite and galena.
In 1987, a grab sample (L-319) over 0.25 metre from a quartz-flooded lens with disseminated pyrite assayed 0.290 gram per tonne gold and 55.6 grams per tonne silver (Assessment Report 17326).
In 1989, a rock sample (ER89R003) of andesite with trace disseminated pyrite near a fault assayed 0.09 gram per tonne gold and 12.2 grams per tonne silver (Assessment Report 19767).
Another zone of mineralization, located approximately 200 metres to the west of the previous zone and near the east side of the informally named ‘Square’ Lake, comprises a small outcrop of brecciated and altered andesite with quartz veinlets, blebs and replacements with minor pyrite and pyrrhotite. In 1996, a rock sample (R70) assayed 0.313 gram per tonne gold, 30.8 grams per tonne silver over 1.0 metre (Assessment Report 24993).
Also in 1996, a chip sample (R15) from a northwest-striking, quartz-feldspar porphyry rhyolite dike hosting minor pyrite and iron oxides, located on a ridge approximately 550 metres to the southeast, yielded 0.05 gram per tonne gold and 11.8 grams per tonne silver over 0.6 metre (Assessment Report 24993).
Work History
The area has been explored in conjunction with the nearby GWP (MINFILE 094E 087) occurrence and a completed exploration history can be found there.
