The Whitehorse Copper Belt is located west of Whitehorse and contains 30+ mines, deposits and showings. By 1900, most of the important deposits had been discovered and the first small ore shipment was made that year. Many of the occurrences in the Copper Belt are skarns. The skarns form on or near the contact between the Whitehorse batholith and the Lewes River group. The Whitehorse batholith is commonly a grey coarse-grained hornblende granite and ranges from quartz monzonite to granodiorite to diorite. The Lewes River group contains numerous different rock types, most importantly of which is the limestone group, which is essential in the formation of skarns in the area.  A small number of occurrences within the Copper Belt are vein and/or replacement and occur within the Whitehorse batholith granite. 

The Reservoir Lake deposit is present within the Whitehorse batholith hornblende granite. The deposit presents itself as a vein style deposit where bornite is present in very thin veinlets along irregular cracks in the granite and is partly altered to malachite in surface exposures. The granite is generally fresh other than some silicification and development of epidote along fractures.