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File Created: 24-Jul-85 by BC Geological Survey (BCGS)
Last Edit:  12-Jun-07 by Sarah Meredith-Jones(SMJ)

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NMI 092F14 Cu3
Name OYSTER, PYRRHOTITE CREEK, MWC 226 Mining Division Nanaimo
BCGS Map 092F074
Status Prospect NTS Map 092F14W
Latitude 49º 46' 49" N UTM 10 (NAD 83)
Longitude 125º 18' 03" W Northing 5516742
Easting 334363
Commodities Gold, Silver, Copper, Lead, Molybdenum Deposit Types H05 : Epithermal Au-Ag: low sulphidation
Tectonic Belt Insular Terrane Wrangell
Capsule Geology

The Mount Washington area is underlain by sediments of the Upper Cretaceous Nanaimo Group (Comox Formation), which unconformably overlie mafic volcanic rocks of the Upper Triassic Vancouver Group (Karmutsen Formation). Intruding both formations is an Oligocene quartz diorite stock of the Mount Washington Intrusive Suite, dated at 35 million years (+/- 6 million years). Several later breccias zones follow the Karmutsen-Comox unconformity and cut all rock units. They have recently been interpreted as stacked thrust faults or de- collements and have been mineralized by a later Tertiary epithermal gold-copper-arsenic event (see 092F 116).

The Karmutsen Formation comprises basaltic, massive and pillow lavas that are commonly porphyritic. The lavas grade into pillow breccias and aquagene tuffs. The overlying Comox Formation comprises fine-grained sandstone and greywacke, with interbedded siltstone. A basal conglomerate of the Comox Formation known as the Benson member consists of rounded clasts of Karmutsen Formation rocks.

The Tertiary quartz diorite stock is variably porphyritic and forms the core of Mount Washington. Several sills and dykes of quartz diorite and quartz diorite porphyry are related to the stock.

The Oyster breccia is a roughly circular feature that measures in excess of 350 metres in diameter and is thought to be a collapse breccia. The rocks surrounding the breccia "pipe" are mainly massive and/or amygdaloidal Karmutsen basalts. The breccia structure outcrops are composed mainly of Comox quartzite and minor porphyritic diorite. However, the fragment composition changes with depth from sediments to Karmutsen volcanics and intrusives. The matrix is often vuggy, the interstices lined with crystalline quartz and filled with limonite and fine fragments of limonitic quartzite.

A diamond-drill hole was put down on the centre of the zone in 1975 to a depth of 184 metres. This hole was deepened in 1988 to a depth of 542 metres. In the drill hole above 212 metres, the breccia is vuggy, bleached and intensely kaolinized. Below 212 metres, the breccia is very siliceous, glassy over short sections, with all interstices filled with quartz crystals and/or carbonate. The quartz matrix may also be lined with chlorite. The hole intersected small amounts of vein or matrix hosted molybdenite, arsenopyrite, and chalcopyrite, pyrite, realgar and orpiment is indicative of an epithermal overprint. Gold and silver content of core below 184 metres was negligible; assays for core above 184 metres were not reported.

The Pyrrhotite Creek breccia zone is an epithermal-type structure that occurs along a creek near the southern perimeter of the Oyster breccia. The structure consists of a lenticular zone of partially silicified and kaolinized bleached and brecciated basalt, mineralized across a width of about 1 metre and dipping toward the Oyster zone. Sulphide minerals present in decreasing order of abundance are pyrite, arsenopyrite, chalcopyrite, orpiment and realgar. The chalcopyrite sections of drill core were coincident with quartz veining and visible arsenopyrite.

A grab sample of silicified fault breccia assayed 14.50 grams per tonne gold, 31.88 grams per tonne silver, 1.04 per cent lead and 0.05 per cent zinc (Assessment Report 17193). A 43 centimetre section of core assayed 2.78 grams per tonne gold, 6.86 grams per tonne silver, 0.07 per cent copper and 3.67 per cent arsenic (Assessment Report 17193).

Bibliography
EMPR AR 1956-119; 1957-69; 1959-135; 1960-111; 1961-102; 1962-105;
1963-103; 1964-155,157; 1965-235; 1966-71; 1968-101
EMPR ASS RPT 839, 1120, 1142, 1145, 1691, 4471, 4505, 5146, 5267,
12605, 14085, 14705, 15228, 15395, 15526, 15776, 15825, 15826,
15857, 15765, 16762, 17123, 17181, *17193, *18473
EMPR EXPL 1975-E102; 1976-E116; 1977-E115; 1978-E131; 1980-175;
1983-209; 1984-166,168; 1985-C156; 1986-B29,C181,C184; 1987-
C156-158; 1988-C92,C93
EMPR EXPL REVIEW 1986, p. 70
EMPR FIELDWORK *1988, pp. 81-91
EMPR GEM 1969-212; 1970-281; 1973-236; 1974-183
EMPR PF (Various related reports located in Domineer file (92F 116))
EMR MP CORPFILE (Mount Washington Copper Company Limited; Noranda
Exploration Company; Qualicum Mines Limited; Cumberland Mining
Company Limited)
GSC BULL 172
GSC MAP 49-1959; 2-1965; 17-1968; 1386A
GSC OF 9; 61; 463
GSC P 66-1; 68-50, p. 39,42; 71-36; 72-44
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1987; Jan.19, 1988; Aug.3, Sept.12, 1989
W MINER Nov. 1965, p. 35; Nov. 1967, pp.35-40
Better Resources Limited (1987): Mount Washington Precious Metals
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Better Resources Limited, News Release Jan.16, 1987, Jul.26, 1988
Better Resources Limited, Annual Report 1987; Corporate Profile (not
dated); 1989 Snapshot Review; Statement of Material Facts dated
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Carson, D.J.T., (1960): Geology of Mount Washington, Vancouver
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Columbia
Carson, D.J.T., (1968): Metallogenic Study of Vancouver Island with
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Deposits, Ph.D. Thesis, Carleton University
McGuigan, P.J., (1975): Certain Breccias of Mount Washington
Property, Vancouver Island, B.Sc. Thesis, University of British
Mount Washington Copper Company Limited, (1971): Statement of
Material Facts dated May 26, 1971
Schroeter, T., EMPR District Geologist, Monthly Reports Jan.1987, Mar.
1988
Vancouver Market Report, February, 1987

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