The Langara occurrence is one of a group of gold-silver showings which occur in a small area 10 kilometres west of the south end of Tatlayako Lake. Other showings in this group are covered by the Standard (092N 037) and Argo (092N 038) occurrences. Gold was discovered in 1911, although the area was not explored properly until the mid-1930's, and again in 1987 and 1988.
The area lies in the Gambier overlap assemblage, between the northeastern margin of the Jurassic to Tertiary Coast Plutonic Complex and the Tchaikazan fault to the northeast (Geological Survey of Canada Open File 1163, Map 1713A). It is located within a complex belt of folds and imbricated, gently southwest-dipping thrust sheets (Geological Survey of Canada Open File 1163, Papers 88-1E, 89-1E; Geology 1991). The thrusting took place in the Late Cretaceous because the thrusts are cut by a quartz diorite intrusion dated at 68 million years by the uranium-lead method on zircon (Geological Survey of Canada Papers 88-1E, 91-2).
The area of economic interest covers several square kilometres immediately south of a creek which flows east-northeast into Ottarasko Creek. The northern part of this area is underlain by a quartz diorite intrusion (which may be related to the 68 million year-old intrusion mentioned above). To the south of the intrusion are Lower Cretaceous siltstone, sandstone, greywacke and conglomerate (informally named the Cloud Drifter Formation in Geological Survey of Canada Papers 88-1E and 89-1E). These rocks contain isoclinal minor folds locally; bedding is obscure and rather irregular. The area also contains numerous, small mafic dykes.
The contact between the intrusion and the sedimentary rocks is irregular due to dyke-like projections and small stocks of quartz diorite, but generally it trends east-northeast for at least 3 kilometres. The adjacent sedimentary rocks have been strongly altered and hornfelsed by the intrusion for a width of 200 to 300 metres, and it is this zone that contains the most important mineral showings.
The hornfelsed and altered zone is characterized by silicification, pyritization and quartz veining. Fine pyrite and arsenopyrite are pervasive in trace amounts; chalcopyrite is less common. Locally oxidation has produced conspicuous limonitic zones. Quartz veins occupy fractures that cut both the quartz diorite and the sedimentary rocks. The veins are generally between 5 and 10 centimetres thick but may be up to 1.5 metres thick; some display epithermal textures. Some veins trend subparallel to the quartz diorite contact but these are much less mineralized than those that trend between northwest and north-northeast, which may be strongly mineralized with arsenopyrite and pyrite, with minor chalcopyrite and rare malachite.
The Langara occurrence is centred on 2 short adits which were cut (in 1935) to follow mineralized quartz-filled fractures in quartz diorite, close to its contact with silicified and hornfelsed greywacke and argillite (Minister of Mines Annual Reports 1934, 1935). The diorite is sericitized. Also present is a fine-grained intrusive rock, which is a marginal phase of the diorite. The fractures strike 150 degrees and dip about 60 degrees southwest, and are traceable for 120 metres. In addition, at least one vein strikes east and dips steeply south; this is up to 0.5-metre thick and is traceable for 90 metres.
A typical average assay of chip samples taken across the widths of veins or zones in the adits that are mineralized with arsenopyrite and pyrite is 6 grams per tonne gold and about 70 grams per tonne silver (Minister of Mines Annual Report 1934; Assessment Reports 16959, 17980). One quartz vein grab sample assayed 26.75 grams per tonne gold and 39.5 grams per tonne silver (Assessment Report 17980). Another grab sample assayed 2.52 per cent copper, 3.13 per cent zinc and 0.33 per cent lead, although high values of these metals are very sporadic (Assessment Report 16959).