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File Created: 24-Jul-1985 by BC Geological Survey (BCGS)
Last Edit:  17-Dec-1991 by Chris J. Rees (CRE)

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NMI
Name PW, TWIST, KENO 1-4 Mining Division Clinton
BCGS Map 092N055
Status Prospect NTS Map 092N11E
Latitude 051º 35' 58'' UTM 10 (NAD 83)
Longitude 125º 03' 27'' Northing 5718494
Easting 357501
Commodities Molybdenum, Tungsten, Copper Deposit Types L05 : Porphyry Mo (Low F- type)
Tectonic Belt Coast Crystalline Terrane Plutonic Rocks
Capsule Geology

The PW occurrence is characterized by fracture-controlled molybdenite mineralization at the intersection of two fault systems in strongly altered intrusive rocks, 46 kilometres southwest of the community of Tatla Lake.

The area is underlain by a complex suite of gneisses and intrusions of the Klinaklini pluton of the Jurassic to Tertiary Coast Plutonic Complex (Geological Survey of Canada Open File 1163). The oldest rock is gneissic granite or granodiorite porphyry. This is intruded by biotite granite, the most abundant rock, and a 120 to 300- metre wide dyke-like body of coarse-grained biotite granite to granodiorite porphyry, which apparently emanates from a stock to the east. Several phases of dykes are also present, consisting of quartz-eye monzonite porphyry, andesite, aplite and monzonite.

Two main fault systems are present. A northwest-striking fault set, partly marked by dyke intrusion, generally separates the biotite granite from the granite-granodiorite porphyry to the northeast. A probably younger set of faults strikes north-northeast, and is also marked by dykes.

The main area of mineralization is at the intersection of these two fault systems, where there is much fracturing, dyke intrusion, and hydrothermal alteration. Alteration is primarily silicification, pyritization (usually about 3 per cent pyrite), oxidation, and leaching; there is also sporadic biotite, potassium feldspar and sericite. Oxidation has produced limonite and ferrimolybdite.

Mineralization is mainly hosted in the granite-granodiorite porphyry, which is locally capped by iron oxide and moderate to strong clay-silica alteration, and in narrow, randomly-oriented aplitic dykes. Significant molybdenite is present with minor pyrite in numerous quartz veins, 10 to 90 centimetres thick, hairline fractures, and vugs or fracture-fillings associated with quartz, biotite and potassium feldspar. Chalcopyrite-bearing fracture-fillings are also reported (Assessment Report 5494). A quartz vein about 300 metres east of the main mineralization contains scheelite; assay values of 0.09 per cent (oxide of) tungsten and 0.2 per cent molybdenum are reported (Assessment Report 9158).

Bibliography
EMPR EXPL 1975-E116; 1980-279
EMPR ASS RPT *5494, 9158
GSC OF 1163

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