The Jewel Lake area is underlain by greenstones, pelitic schists and chert of the Upper Paleozoic Knob Hill Group; these are intruded by a large granodiorite intrusion (Wallace Creek pluton) 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.
The Jewel (Dentonia) quartz vein (082ESE055) is exposed over a length of approximately 1828 metres and can be traced from a point 457 metres north of the Ethiopia adit (Lot 932) and south a distance of 1371 metres to the Denero Grande workings (Lot 851). Essentially it follows a fracture zone which strikes south across the trend of the metamorphosed rocks. The fracture zone dips east to southeast at 30 to 60 degrees with variable strike, widths and amount of shearing. It has been developed on the Jewel (Lot 850), Enterprise (Lot 1022), Anchor (Lot 1021), Ethiopia (Lot 932) and most recently on the Denero Grande (Lot 851) claims.
Locally the northwest striking and steeply northeast dipping metamorphosed volcanic and sedimentary rocks are not always distinguishable, both being fine-grained and medium or dark coloured with primary structures such as bedding and flow banding being confused with 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.
Igneous intrusions in the Jewel Lake camp include a large Lower Cretaceous granodiorite pluton and a host of younger pulaskite and lamprophyre dykes. The granodiorite is a homogeneous medium-grained grey body intruding 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. Post-vein lamprophyre dykes as well as the pulaskite dykes are of probable Lower Tertiary age and cut all other major geological units.
The Dentonia quartz vein ranges widely in attitude with strikes varying from 000 to 050 degrees averaging about 020 degrees and dipping between 30 and 60 degrees southeast. The age of the Dentonia vein is bracketed by the granodiorite which lically hosts the vein and by crosscutting pulaskite and lamprophyre dykes. The dykes are correlated with petrographically similar Tertiary lavas of the summit of Mount Pelly and with volcanic rocks which occur to the west near Midway, dated at 49 plus or minus 2 million years. In general, the Dentonia vein cuts granodiorite in the south, metasedimentary rocks in the north and intervening metavolcanic rocks. Vein widths vary from an average of 0.9 metres to a maximum of 4.8 metres.
On the Ethiopia claim the Dentonia quartz fissure-vein is splayed into three sections across a distance of 48 metres. The vein dip varies from 35 to 45 degrees southeast. The Ethiopia adit explores the westernmost branch and central branch of the vein structure. The westernmost branch of the vein is irregular and discontinuous with widths up to 45 centimetres locally. The central branch is a shattered zone up to 45 centimetres wide containing irregular quartz veinlets and appears to be cut off by a pulaskite dyke. In general, the quartz vein widths range from 10 to 50 centimetres up to 1.2 metres. Mineralization is erratic and sparse and consists of pyrite, galena and chalcopyrite with the wide portions of the vein containing minor pyrite only.
