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File Created: 24-Jul-85 by BC Geological Survey (BCGS)
Last Edit:  13-Jan-92 by Chris J. Rees(CRE)

Summary Help Help

NMI
Name STANDARD (L.1176), FEDERAL (L.1179), ARGO 1,3, LANGARA 1-7, ARGO (L.1177), MARY (L.1178) Mining Division Clinton
BCGS Map 092N047
Status Prospect NTS Map 092N07E
Latitude 51º 29' 02" N UTM 10 (NAD 83)
Longitude 124º 36' 04" W Northing 5704853
Easting 388827
Commodities Gold, Silver, Copper Deposit Types I02 : Intrusion-related Au pyrrhotite veins
Tectonic Belt Coast Crystalline Terrane Gambier, Plutonic Rocks
Capsule Geology

The Standard 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 Langara (092N 036) 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 Standard occurrence is centred on a short adit in silicified and mineralized siltstone and sandstone, although it is about 500 metres south of the main silicified and pyritized aureole of the quartz diorite intrusion. Arsenopyrite and pyrite mineralization is associated with quartz-filled fractures trending 160 degrees, or it is disseminated in the host rocks, and is traceable for 75 metres over a width of 1 to 2 metres. Some of the mineralization is massive and described as a replacement in argillite; this was assayed at 15 grams per tonne gold and 20.6 grams per tonne silver over 2 metres (Minister of Mines Annual Report 1935). A 4-centimetre thick quartz vein was analyzed at 19.2 grams per tonne gold and 9.8 grams per tonne silver; another sample contained 0.3 per cent copper (Assessment Report 17980).

Bibliography
EMPR AR *1934-F13; *1935-F33; 1937-F34
EMPR GEM 1974-219
EMPR EXPL 1988-C129
EMPR BULL 20 Part 4, p. 37
EMPR ASS RPT *16959, *17980
GSC OF 1163
GSC P 68-33; 88-1E, pp. 185-190; 89-1E, pp. 163-167; 91-2, pp.  109-113
GSC MAP 5-1968; 1713A
GSA GEOLOGY 1991, pp. 941-944

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