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File Created: 24-Jul-1985 by BC Geological Survey (BCGS)
Last Edit:  15-Dec-1991 by Peter S. Fischl (PSF)

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Name ORONOCO (L.2158S), NO. 15 FRACTION (L.1598S), CUMONT Mining Division Similkameen
BCGS Map 092H038
Status Prospect NTS Map 092H07E
Latitude 049º 20' 44'' UTM 10 (NAD 83)
Longitude 120º 32' 10'' Northing 5468791
Easting 678957
Commodities Copper Deposit Types L03 : Alkalic porphyry Cu-Au
Tectonic Belt Intermontane Terrane Plutonic Rocks, Quesnel
Capsule Geology

The Oronoco prospect is on the east bank of the Similkameen River, 12.5 kilometres south of Princeton.

The region east of the Similkameen River is underlain by intrusive rocks of the Lost Horse Intrusions and the Smelter Lake stock (Copper Mountain Intrusions), both of Early Jurassic age, and volcanics of the Upper Triassic Nicola Group. The Nicola Group volcanics were previously included with the Wolf Creek Formation (Geological Survey of Canada Memoir 171). All units are unconformably overlain to the east by volcanics and sediments of the Eocene Princeton Group.

The prospect is hosted in the Lost Horse Intrusions, consisting of medium-grained porphyritic diorite, monzonite and syenite. The Lost Horse rocks exhibit intense albite-epidote alteration along the southern margin of the deposit. The altered rocks are pale green to light grey or nearly white and devoid of magnetite. The original plagioclase and pyroxene have been reduced to irregular, ragged patches of albite, plagioclase, sericite and epidote, and chlorite and epidote respectively. Pink orthoclase alteration, both along veins and pervasive, is widespread.

Mineralization consists of pyrite-chalcopyrite fracture-fillings and disseminations in Lost Horse rocks along the northeast-striking Honeysuckle break, and several subsidiary northeast-striking faults. This fault system also hosts the Duke of York prospect (092HSE007) to the west. Trenching has exposed copper mineralization over an area 120 metres long and up to 110 metres wide. A chip sample taken over the full length of a 12-metre long adit assayed 0.32 per cent copper (Geological Survey of Canada Memoir 171, page 37).

The deposit was initially explored by an adit excavated some time before 1934. Cumont Mines Ltd. completed 580 metres of trenching in about 1968. The deposit was also trenched and sampled by Similco Mines Ltd. in 1990.

EMPR AR 1917-453; 1968-207
EMPR BULL *59, pp. 74,75
GSC BULL 239, pp. 140,141
GSC MAP 300A; 888A; 1386A; 41-1989
GSC MEM *171-37; 243
GSC P 85-1A, pp. 349-358
GSC RPT 986 (1908)
GSC SUM RPT 1906, pp. 51,52
CIM BULL Vol. 44, No. 469, pp. 317-324 (1951); Vol. 61, No. 673, pp. 633-636 (1968)
CIM Trans. Vol. 18, pp. 192-201 (1915)
CJES Vol. 24, pp. 2521-2536 (1987)
Montgomery, J.H. (1967): Petrology, Structure and Origin of the Copper Mountain Intrusions near Princeton, British Columbia; unpublished Ph.D. thesis, University of British Columbia
EMPR PFD 21245