The Rapp Creek occurrence is located on a west facing slope in the northeastern head waters of Cottonwood Creek, approximately 1.5 kilometres south-southwest of Lomas Lake.

The area is underlain by chert and siliceous argillite of the Mississippian to Pennsylvanian Fourth Lake Formation (Buttle Lake Group), volcaniclastic rocks of the Middle to Upper Devonian Mclaughlin Ridge Formation (Sicker Group) and basaltic volcanic rocks of the Upper Triassic Karmutsen Formation (Vancouver Group). These have been intruded by quartz diorite and lesser granodiorite of Jurassic Island Plutonic Suite (Saanich Granodiorite).

Locally, a north west trending shear zone contains pyrite- and pyrrhotite-bearing quartz veins, up to 0.10-metre wide, in a volcanic host. The veins strike 143 degrees with a dip of 35 degrees to the north east and have been exposed for over 7 metres.

Another zone of mineralization, located approximately 200 metres up slope to the south east, comprises a limestone bed hosting several undulatory sulphide-rich horizons, varying from 2 to 25 centimetres in width, containing up to 75 per cent sulphides including pyrite, pyrrhotite and arsenopyrite.

In 1988, two chip samples (9978 and 9979) of the mineralized veins yielded 18.3 and 23.6 grams per tonne gold, with 5.2 and 5.6 grams per tonne silver over 2 and 3 metres, respectively, while samples from the sulphide-rich horizons yielded up to 20.6 grams per tonne gold and 4.3 grams per tonne silver (Harrington, E. (2010-10-22): Technical Report on the El Capitan Property).

The area has been explored in conjunction with the nearby El Capitan (MINFILE 092C 019) occurrence and a completed regional and property work history can be found there.