The Granduc property straddles the northerly trending South Unuk Shear Zone separating the upper greenschist to amphibolite facies metasedimentary and volcanic rocks of the Upper Triassic Stuhini Group from the lower greenschist grade metavolcanic and sedimentary rocks of the Hazelton Group. Large pretectonic to syndeformational elongate plutons and dikes of the Triassic John Peakes plutonic suite, including the Bucke Stock exposed north of the Granduc Mine, composed of hornblende diorite, monzonite, gabbro and syenite, intrude the Stuhini Group metasedimentary and metavolcanic rocks.

The volcanic rocks east of the Granduc orebodies are pillow lavas intercalated with graphitic siltstones, thin bedded lithic and crystal tuffs and volcanic sandstones. This sequence is overlain by the ore zone, graphitic siltstones, silty argillites, thin bedded lenticular gypsum-bearing limestones and quartz pebble and quartz cobble conglomerate lenses. These rocks underwent several periods of later deformation, intrusion, alteration, faulting and erosion, culminating in Tertiary time with Hyder plutonism. The ore deposit lies along part of the deformed, overturned west limb of a north trending anticlinal fold. The less deformed rocks to the east of the ore deposit include a complex volcanic-sedimentary sequence, which is considered to be part of the Lower-Middle Jurassic Hazelton Group.

Interest in the North zone was started by Newmont in 1977 and was continued by Esso in 1982, notably with the driving of the northern exploration drift from the main operating level of the mine. The drilling campaign by Esso in 1982 outlined two zones of copper mineralization, termed zone 1 and zone 2. Copper mineralization in the form of chalcopyrite in zone 1 occurs as coarse disseminations and local semi-massive sections within a magnetite iron formation/deep marine sediment-volcaniclastic host, which exhibits strong similarities to the main Granduc deposit. Zone 2 which lies east of zone 1 exhibits a different style of mineralization. Chalcopyrite, pyrite and pyrrhotite occur as disseminations and stringers in an altered biotitic, volcanic tuff host rock, mostly without magnetite. The style of mineralization exhibited by zone 2 possesses strong characteristics of a feeder zone, which may mean that the source of the Granduc deposit could be related to zone 2.

Mineralization was first intersected in surface drill hole 153-1 by Newmont Ltd. in 1977. Assays from this hole [over the intervals 529.5 metres to 540.0 metres and 558.3 metres to 566.85 metres were 1.39 per cent (10.14 metres true thickness) and 3.29 per cent (8.28 metres true thickness), respectively] were 1.39 per cent copper over 10.7 metres and 3.29 per cent copper over 8.7 metres (Assessment Report 35977). These intersections led to a surface diamond drilling program (approximately 7 620 metres in nine drill holes) by Esso Minerals Canada Ltd. in 1980 and 1982. Two separate mineralized zones were identified in the Upper Footwall series (Unit 2).

In 2012, the Granduc copper deposit comprised both a Main zone and a North zone. The Main zone consists of measured, indicated and inferred resources, and the North zone consists of an inferred resource. In 2012, On behalf of Castle Resources Inc., Tetra Tech estimated a new National Instrument 43-101 mineral resource for the Granduc copper deposit (Press Release, Castle Resources Inc., Dec.12, 2012 (also in Assessment Report 35977)). The Granduc copper deposit comprises both a Main zone (104B 021) and the North zone. The Main zone consists of measured, indicated and inferred resources, and the North zone consists of an inferred resource. Tetra Tech estimated and inferred resource for the North zone (at 0.8 per cent cut-off) of 14.11 million tonnes grading 1.49 per cent copper, 0.21 gram per tonne gold and 5.2 grams per tonne silver.

The Granduc area deposit types are volcanogenic massive sulphide (VMS) deposits of the Besshi-type.

Refer to Granduc (104B 021) for further geological and work history details.