The Jewel Lake area is underlain by a complex of metamorphic rocks mostly of sedimentary and volcanic origin correlative with the Carboniferous or older Knob Hill Group, and a large granodiorite intrusion correlative to the Juro-Cretaceous Nelson Plutonic Rocks. Small dykes and sill-like bodies, feeders to nearby Tertiary lavas, pervade these units. Four north striking and one northwest striking quartz fissure-vein structures are known in the Jewel Lake camp, all of which have received some development.
Locally the northwest striking and steeply northeast dipping metamorphosed volcanic and sedimentary rocks are not always distingu- ishable, both being fine-grained and medium or dark coloured with primary structures such as bedding and flow banding being confused wit foliation or gneissosity. Generally the sedimentary rocks are brittle and quartz rich, however compositions vary and some biotitic varieties have the same competence as the amphibole-rich volcanic rocks. These rocks are locally called quartzites but few are true quartzites and more appropriate terms would be quartz wacke or lithic wacke. The massive character of the volcanic rocks is due to a combination of intense regional metamorphism and primary structures. Field and petrographic data indicate that at least some of the original rock formed as a result of massive accumulations of lava flows and pillow lava. Crosscutting feeder dykes and sills are significant and contribute to the massive aspect of the volcanic rocks. The metamorphosed schistose volcanic rocks are compositionally basalts. These metasedimentary and metavolcanic rocks form part of the Carboniferous (Pennsylvanian-Mississippian) or older Anarchist Group.
Igneous intrusions include a large Lower Cretaceous granodiorite pluton and a host of younger Lower Tertiary pulaskite and lamprophyre dykes. The granodiorite returned a K-Ar age date of 128 plus or minus 5 million years. The granodiorite is a homogeneous medium-grained grey body which intrudes the metavolcanic rocks along a northwest trending contact in the southwest part of the camp. Alteration is minor with some replacement of amphibole by epidote. The intrusive has produced little effect in both the metavolcanic and metasedimentary rocks. Granodiorite dykes occur and are compositionally similar to the main granodiorite body and are probably offshoots from it. Pulaskite dykes are numerically most important. Several types are evident including both quartz-bearing and undersaturated types.
On the Lakeside claim (L.1023), 381 metres northwest of the Dentonia vein structure (Minfile 082ESE055), a quartz vein occurs in a shear zone 0.7 to 1.2 metres wide. The vein ranges in width from 20 to 91 centimetres but averages 25 to 30 centimetres and is mineralized with pyrite and small amounts of galena and sphalerite. The vein attitude varies from 035 to 070 degrees and dips 68 degrees south.
