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File Created: 24-Jul-85 by BC Geological Survey (BCGS)
Last Edit:  04-Jul-08 by Mandy N. Desautels(MND)

Summary Help Help

NMI 092H5 Zn1, Cu1
BCGS Map 092H031
Status Past Producer NTS Map 092H05W
Latitude 49º 19' 01" N UTM 10 (NAD 83)
Longitude 121º 56' 42" W Northing 5463225
Easting 576674
Commodities Zinc, Copper, Lead, Silver, Gold Deposit Types G07 : Subaqueous hot spring Ag-Au
G06 : Noranda/Kuroko massive sulphide Cu-Pb-Zn
Tectonic Belt Coast Crystalline Terrane Harrison
Capsule Geology

The Seneca deposit is located on the east side of the Chehalis River on the west side of Harrison Lake, about 8 kilometres north of Harrison Mills, British Columbia.

The Seneca occurrence has been explored by mining companies since the 1920s. In the 1970s, Cominco Ltd. delineated a small Kuroko-type, stratiform, volcanogenic massive sulphide deposit. The property is currently owned by 493744 Ontario Ltd. and Metall Mining Corp.

The area of the Seneca deposit and its related occurrences, the Vent (092HSW139) and the Fleetwood/33 zones (092HSW165), are underlain primarily by volcanic rocks of the Lower-Middle Jurassic Harrison Lake Formation. In general, the strata on the property strike approximately northwest and are essentially flat lying or moderately east dipping. The stratigraphy has undergone very little deformation or metamorphism and retains pristine volcanic textures. Metamorphic grade in the area is zeolite facies.

McKinley et al. (Fieldwork 1994) have subdivided the property stratigraphy into three principal volcanic facies as follows: 1) Facies 1 - Lavas (vent-proximal facies) consist of basaltic to rhyolitic composition flows, domes and associated in situ hyaloclastites and autoclastic breccias. 2) Facies 2 - Volcaniclastic rocks (vent-proximal to distal facies) consist of juvenile to reworked, coarse volcanic breccia and tuffs to fine-grained siltstone. 3) Facies 3 - Synvolcanic intrusions consist of basaltic to rhyolitic sills and dikes that have intruded lavas and wet volcaniclastic sediments.

A fourth facies consists of an argillite that often contains flattened pumice clasts and is commonly in close proximity to mineralization. This fourth facies is restricted to the main Seneca deposit, also referred to as the Pit area, and does not correlate across the property.

Three types of mineralized zones are present in the Seneca area: 1) Conformable massive sulphide lenses. 2) Semimassive and disseminated sulphides associated with volcaniclastic rocks. 3) Stockwork and stringer mineralized zones.

Conformable, stratabound lenses of semimassive sphalerite, pyrite and chalcopyrite with lesser galena are exposed in the Pit area. The sulphides are hosted by fragmental rocks and occur as discontinuous pods that do not correlate between adjacent drillholes. Unlike the 33 zone, the massive sulphides in the Pit area are underlain by siliceous stringer and disseminated mineralization.

Massive to disseminated sulphides are hosted in the volcaniclastic 'ore zone conglomerate', tending to be restricted to the upper part of the unit. The 'ore zone conglomerate', part of Facies 2 and found only in the Pit area, varies from 1 to 15 metres in thickness. The unit consists of moderately silicified, mostly subrounded dacite lava clasts ranging from sand size up to 3 centimetres in diameter in a sandy or silty matrix. The unit can be matrix or clast supported, and also contains clasts and matrix that have been replaced and/or infilled by sulphides. A dacite lava clast breccia occurs stratigraphically below the 'ore zone conglomerate'. One of the better drillhole intersections (drillhole 85-03) cut 0.5 metre of massive pyrite, sphalerite and barite with lesser chalcopyrite, underlain by 3.5 metres of mostly semimassive pyrite. More commonly, the mineralization hosted by the 'ore zone conglomerate' consists of clasts that are partially replaced, or matrix that is partly infilled by pyrite and occasionally sphalerite. Some of the clasts are rimmed with later pyrite. Tetrahedrite has been microscopically recognized.

Faulting is evident in several directions and may have exerted some control on the mineralization.

Generally, most of the rocks at the Seneca occurrences are relatively unaltered, exhibiting pristine preservation of volcanic textures. Macroscopically recognizable alteration is restricted to the Vent and Fleetwood zones where it is characterized by intense silicification and sericitization associated with massive to flow banded and flow brecciated dacite porphyry. The volcanics are pyritized to varying degrees over much of the area.

In 1962, about 260 tonnes of ore was shipped from a small open pit that constituted the Lucky Jim (Seneca) prospect and shipped to the Britannia Mine (092GNW003). The ore graded 1.55 per cent copper, 8.15 per cent zinc, 154.28 grams per tonne silver and 4.11 grams per tonne gold (Assessment Report 23417).

Combined (drill indicated, possible and inferred) reserves at Seneca are 1,506,239 tonnes grading 3.57 per cent zinc, 0.15 per cent lead, 0.63 per cent copper, 0.82 gram per tonne gold and 41.13 grams per tonne silver. This reserve also includes 898,573 tonnes grading 1.09 grams per tonne gold, 55.53 grams per tonne silver, 0.84 per cent copper and 5.17 per cent zinc (undiluted) (Filing Statement 200/85, International Curator Resources Ltd.).

In 1985, a drillhole on the northeast side of the deposit intersected 0.6 metre of massive sulphides which assayed 5.97 grams per tonne gold, 246.85 grams per tonne silver, 10.1 per cent zinc, 0.36 per cent copper and 0.7 per cent lead. The deposit is considered still to be open in this direction.

In 1994, drillhole S-94-41 was drilled to test the Seneca horizon, 700 metres downdip of previous drillhole S-91-02, which intersected 0.24 per cent copper, 1.58 per cent zinc, 4.34 grams per tonne silver and 0.034 gram per tonne gold over 3 metres and which showed the most noticeable alteration to date. The hole also tested a mercury anomaly outlined and tested by Cominco Ltd. in 1972. The hole collared into dacite feldspar porphyritic flow and is underlain by dacitic feldspar phyric lapilli tuff. The dacitic package is underlain by a thick sequence of andesitic lapilli tuff and massive mafic flow and flow breccias. The hole, however, failed to find any significant mineralization and alteration.

The Vent zone (092HSW139) is 2 kilometres to the northwest along strike with the Seneca deposit. The Fleetwood and 33 zones (092HSW165), are about 1.5 kilometres northwest of the Vent zone. For further details on the Seneca deposits, readers are referred to the article by McKinley et al. (Fieldwork 1994).

In 1990, Metall Mining Corp. optioned the property to evaluate the Seneca deposit and the VMS potential for the remainder of the property. In 1991, the Fleetwood zone was discovered. In 1992, the 33 zone was discovered in the same area.

In 1995, International Curator Resources Ltd. conducted two days exploration work on the Dorothy 12 and 13 claims to determine the source of a coincident copper, lead, and zinc anomaly outlined by previous soil sampling. The area of these claims is underlain by a series of volcanic sediments, and rhyolitic to andesitic flows, tuffs and breccias that have been variable sericitized and silicified. Thirteen rock samples were taken from outcrops. The highest results were from sample JC-6, which yielded 0.07 per cent lead, 0.02 per cent zinc, 2.0 grams per tonne silver and 0.02 gram per tonne gold (Assessment Report 24318).

In 1997, Riverstone Resources Inc. drilled 6 holes (693.4 metres) on the IC claims.

EMPR AR 1897-578; 1898-1113; 1961-88; 1962-93
EMPR ASS RPT 2833, 2998, 5233, 5476, 5627, 6058, 6135, 6328,
17496, 18261, 20289, 21015, 22171, 22915, *23417, 24318, 25232
EMPR EXPL 1975-E62; 1976-E77; 1977-E122; 1978-E141; 1982-165;
1983-234; 1986-C201,202
EMPR FIELDWORK 1984, pp. 120-131; 1985, pp. 95-97; *1993, pp. 345-350
*1994, pp. 503-512
EMPR GEM 1971-265; *1972-102-114; *1973-125-128; 1974-102
EMPR MAP 65 (1989)
EMPR OF 1992-1; 1998-10; 1999-2
EMPR PF (International Curator Resources Ltd. (1988): Annual Report;
Riverstone Resources (1997): Prospectus, March 17, 1997; Notes on
Seneca Talk, D. Pearson, Nov.6, 1974; Notes on CIM District 6
Meeting, Kamloops, ~1984; Seneca Project, Monthly Report, Oct.
1986; Regional Geologist's notes, 1992; Photos, 1992)
EMR MIN BULL MR 223 B.C. 111
EMR MP CORPFILE (Zenith Mining Corporation Ltd.; Chevron Standard
GSC EC GEOL Vol.60, No.5 (1965), p. 955
GSC MAP 12-1969; 737A; 41-1989
GSC MEM 335, p. 276
GSC P 69-47, p. 67; 86-1B, pp. 715-720
CIM Special Volume 8, p. 101
CJES Vol.10 (1973), pp. 1688-1692
GAC Special Paper 3 (1966), p. 43; 6 (1970), p. 137
GAC Proceedings Vol.16 (1965), p. 63
GCNL #29,#144, 1976; #27, 1977; Dec.14, 1983; Jan.10,Mar.15,30, 1984;
#224, 1986; #116(Jun.15), 1990; #44(Mar.4),#157(Aug.15),
#186(Sept.26),#215(Nov.7), 1991; #72(Apr.10),#112(June 10), 1992;
#103(May29), 1997
GSA Vol.72 (1961), p. 1409
N MINER Mar.18,Jun.3, 1976; Feb.3,17,24, 1986; Aug.5, Sept.9, Oct.7,
1991; June 22, 1992
Arthur, A.J. (1987): Mesozoic Stratigraphy and Paleontology of the
West Side of Harrison Lake, Southwestern British Columbia, M.Sc.
Thesis, University of British Columbia
Chevron File
Crickmay, C.H. (1925): The Geology and Paleontology of the Harrison
Lake District, British Columbia, Ph.D. Thesis, Leland Stanford
Junior University, California, 140 pp.; (1962): Gross Stratigraphy
of the Harrison Lake Area, British Columbia, Evelyn de Mille Books,
Calgary, Alberta, p. 12
Mahoney, J.B. (1994): Nd Isotopic Signatures and Stratigraphic
Correlations: Examples from Western Marginal Basins and Middle
Jurassic Rocks of the Southern Canadian Cordillera; unpublished
Ph.D thesis, University of British, 289 pages
Matsukuma and Horikoshi, (1970): Kuroko Deposits of Japan, University
of Tokyo, Tokyo, Japan, 153 pp.
Pride, K.R. (1973): Mineral Graphic Study of Selected Sulphide
Samples from the Seneca Property near Harrison Mills, British
Columbia, unpub. B.Sc. Thesis, University of British Columbia
Ray, G.E. et al. (1985): Precious Metal Mineralization in
Southwestern British Columbia; Field Guides to Geology and
Mineral Deposits in the Southern Canadian Cordillera, GAC Section
Meeting, Vancouver, British Columbia, May 1985