The Grag area is underlain by Upper Triassic Stuhini Group basaltic volcanics. The Stuhini Group rocks are intruded by quartz-monzonite stocks and associated feldspar-porphyry dikes of Tertiary age are genetically related to the Sloko Group volcanics (Geological Survey of Canada Map 1262A). Eocene Sloko Group andesitic rocks overlie the Stuhine rocks in the area.

On the property, the Stuhini Group volcanics have undergone lower greenschist facies metamorphism and host abundant chlorite, epidote, and minor calcite. They are well fractured and jointed and host dyke swarms which parallel the direction of jointing and faulting. The two preferred orientations are 020 to 030 degrees and 080 degrees with both sets steeply dipping.

Three types of sulphide mineralization occur on the property. The first is disseminated pyrite and pyrrhotite and very minor chalcopyrite in the monzonitic intrusives. The second type of mineralization is local sulphide lenses of disseminated pyrite, pyrrhotite, and minor chalcopyrite in the altered volcanic host rock.

The third and most important type of occurrence is sulphide mineralization associated with intrusive bodies and swarm dykes in contact with altered volcanics. The mineralization is found in highly silicified greenstone as disseminations, as fracture and joint fillings, and in quartz veining. The sulphides include pyrite, pyrrhotite, chalcopyrite, molybdenite with minor galena, and sphalerite. A large gossan with this type of mineralization was located just east of the claims (refer to Sue, 104K 051).

In the central area of the claim block, a mineralized zone hosting pyrite, pyrrhotite, and chalcopyrite is located within altered andesite which is cut by felsic swarm dykes. The zone is approximately 100 metres long and 8 metres thick. In 1979, a 50 metre composite chip sample assayed 0.3 gram per tonne silver, 0.0225 per cent copper, and 0.0102 per cent nickel (Assessment Report 7558). The highest concentrations of sulphide minerals were found in float along the north side of the glacier. The source has not been determined but may have come from the glacier valley to the east.

During September 1979, a 9 day reconnaissance geological and prospecting survey was conducted on the Grag 1 to 4 mineral claims for Northern Horizon Resource Corporation. Fourteen rock chip samples were taken on sulphide mineralized showings, and two of these showings were hand trenched. One stream sediment sample was taken on a major creek. Some of this work may have been done just east of the Grag claim boundary on the Sue claim where the most interesting in situ mineralization was found during the 1979 reconnaissance survey. Parts of the former Grag property were staked by DeCoors Mining Corp. in October 2006 and sold to Optima Minerals Inc in November 2006 and became part of the Taku Gold block of the Taku Property. The showing was not visited by Optima Minerals.