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Ministry of Energy Mines and Responsible for Core Review

Trout Lake Area, Lardeau District (082K11)

 

NTS 082K12 & 13 location map (click for index map).

R. Pinsent (P.Geo.)
March 2004

KEYWORDS: Trout Lake, Beaton, veins, silver, Badshot Formation, Lardeau Group, Kootenay Arc, Silver
                     Cup Anticline

References


Introduction

The Trout Lake area (082K/11) is in the Lardeau district, in the West Kootenay region of southeastern British Columbia. It straddles the south end of Trout Lake and provides a cross section through the Badshot Range (Duncan Ranges) of the Selkirk Mountains. It also extends across the northern tip of Duncan Lake into the Purcell Mountains.

 

The layered rocks are folded but generally young from northeast to southwest. In the eastern part of the map sheet, in the Purcell Mountains and in the northeastern part of the Selkirk Mountains, they include Precambrian (Proterozoic) clastic strata of the Horsethief Creek and Hamill groups, and a thick early Cambrian limestone known as the Badshot Formation. The latter is a regionally extensive marker horizon throughout much of southeastern British Columbia. The southwestern Selkirk Mountains are almost entirely underlain by metasedimentary and metavolcanic strata of the Paleozoic Lardeau Group and the Lardeau Range, east of Trout Lake, is underlain by Lardeau rocks and those of the overlying, Late Paleozoic, Milford Group. Both units belong to the Kootenay Arc, which, at this latitude, is fault-bounded against Ancestral North American rocks at the Badshot limestone contact. The arc rocks are pericratonic and have undergone several phases of deformation. The presence of foliated clasts in conglomerates at the base of the Milford Formation speaks to deformation during the Devonian to Mississipian (Antler Orogeny), and the ubiquitous presence of tight northwest trending isoclinal folds with subhorizontal axes throughout the map area implies a significant amount of crustal shortening in the Late Jurassic (Columbian Orogeny). There are two major intrusions in the Trout Lake area. There is limited exposure of the Mesozoic Kuskanax, granite to monzonite, batholith in the extreme southwest corner of the map sheet and a similarly restricted area of the younger, but also Mesozoic Galena Bay, granodiorite, pluton in the northeast corner. The former appears to be syntectonic and, regionally, metamorphic grade decreases from southwest to northeast, away from its contact. The Kootenay Arc rocks lie in the hanging wall of the Columbia River Fault, a major zone of detachment that underwent significant dip-slip motion to the east during the Eocene. The hanging wall plate of the fault, known as the "Selkirk Allochthon", is composed of several, highly deformed, tectonic slices comprising parts of the Lardeau, Milford and Hamill Groups.

 

The Horsethief Creek and Hamill groups comprise a considerable thickness of mixed siliciclastic strata that accumulated on continental crust. Over time, arenaceous sediments became more argillaceous and calcareous, and there are several limestone bands in the Marsh Adams Formation, at the top of the Hamill Group. The Badshot Formation is a regionally significant marker that was referred to as the "lime dyke" by early prospectors. The Lardeau Group overlies, but is commonly in fault contact with, the Badshot. In the Trout Lake area, it is divided into six formations; the Index, Triune, Ajax, Sharon Creek, Jowett and Broadview. Of these, the Index and Broadview are of regional extent. The others are more local in distribution but are of considerable importance and value in delineating the structure of the Silver Cup Anticline, a faulted structure that hosts many of the larger deposits.

 

The Index Formation is at the base of what appears to be a simple stratigraphic sequence comprised of the six formations; however, the folded nature of the rocks makes for considerable local repetition and it is possible that the Index and Broadview may be the same unit. The Index Formation consists of a thick, mixed, sequence of grey, green and black phyllitic schist, siliceous argillite, calcareous phyllite and limestone, schistose metabasalt, mafic tuff and rare quartzite. It is (apparently) overlain by black siliceous argillite, chert and phyllite of the Triune Formation, and by massive quartzite of the Ajax Formation. The latter was referred to as the "Cromwell dyke" by early prospectors. The quartzite was overlain by the Sharon Creek Formation, another black siliceous argillite, chert and phyllite unit and that, in turn, was overlain by metamorphosed basalt, tuff and phyllite of the Jowett Formation. These volcanic rocks are covered by a similar sequence to that found below. The Broadview Formation includes grey, green and black phyllite, calcareous phyllite and limestone, siliceous argillite, gritty sandstone and schistose mafic volcanic rocks. The Lardeau Group is unconformably overlain by metaconglomerate, meta-sandstone and marble of the Milford Group.

 

The layered rocks are highly deformed and Fyles and Eastwood (1962) identified a major "N-shaped" fold structure east of Trout Lake. On its southwest side, the fold consists of the Silver Cup Anticline, which underlies much of Silver Cup Ridge. To the northeast of this anticline is the Finkle Creek syncline, the northeast limb of which is disrupted into a collage of fault-bounded fragments near the Badshot limestone. The folds are isoclinal and mimicked by numerous satellite structures. The axes are subhorizontal and there is a regionally extensive axial plane schistocity which is subparallel to bedding. The folds are disrupted by younger faults, some of which are close to axial in orientation and others are weakly to strongly discordant. These late faults, which include the Cup Creek Fault that cuts the Silver Cup Anticline, are important controls on mineralization.

 

There are 97 known occurrences in the area; of which 93 are metallic, 3 are industrial mineral and 1 is a placer occurrence. The area was first explored for hard-rock mineral deposits in the early 1890s as prospectors moved into the area from the Slocan and Kootenay Lakes areas. At that time, they identified three principal centres of gold and silver-lead mineralization and established mining camps at Camborne, east of Beaton, Ferguson, east of Trout Lake and Poplar, south of Trout Lake. The Ferguson camp, which includes both larger (Silver Cup [082KNW027], Nettie L. [082KNW100] and True Fissure [082KNW030]) and smaller-scale (Winslow [082KNW025], Ophir [082KNW032] and Wagner [082KNW212]) past-producing mines, is within the Trout Lake map sheet. The major mines were active in the early 1900s but had all ceased production prior to the 1950s. Most of the major deposits and showings are polymetallic, post-tectonic, epigenetic vein and/or replacements controlled by both structure and stratigraphy. However, in some localities (Winslow [082KNW025] and Ophir [082KNW032]), the veins are gold-rich and only weakly polymetallic. In some cases, surface gold values have clearly been enhanced by weathering.

 

Spatially, the majority of the deposits in the Trout Lake area fall into two major belts. In the northeast part of the map sheet there are numerous sulphide replacement and polymetallic vein deposits. The former include Mollie Mac [082KNW036], Index [082KNW038] and Silver Chief [082KNW039], which formed in siderite replacement zones in Index Formation (Lade, a.k.a. Mollie Mac) or Badshot limestone. The latter include Abbott [082KNW056], Badshot [082KNW033] and Mohican [082KNW035]. In these, the mineralization associated with the limestone is more obviously vein related. In the same general area, there are several occurrences in which the veins are in metasediment a short distance from the limestone (Wagner [082KNW212], Sheep Creek [082KNW050] and Princess Marie [082KNW225]). The second main belt of occurrences is the southeastern continuation of the Camborne Mining Camp, which is in NTS area 082K/13. Both lie along the axis of the Silver Cup Anticline. These occurrences, including the polymetallic veins at True Fissure [082KNW030], Nettie L. [082KNW100] and Silver Cup [082KNW027], have produced the bulk of the ore in the area. These occurrences are controlled by late structures that are concordant and highly discordant to the northwest trending regional fabric of the area. Other, lesser vein occurrences (Cromwell [082KNW058], Okanagan [082KNW024] and Alice [082KNW165]) that are also discordant commonly have a northeast trending strike and are notably enriched in gold.

 

The last major exploration push in the Trout Lake area occurred in the 1980s, in response to successful drilling on the Goldfinch [082KNW076] gold property in the Camborne camp. At that time, there was a significant amount of development work done on the Abbott [082KNW056] and Wagner [082KNW212] properties in the east, and on the Yuill [082KNW120] and Towser [082KNW028] properties (near Silver Cup) in the west.

 

Aspects of the geology of the area are described by many authors; however, the geology and metallogeny are best described by Emmens (1915), Gunning, Walker and Bancroft (1929), Fyles and Eastwood (1962) and Smith and Gehrels (1990). Fyles and Eastwood, in particular, delineate the stratigraphy and the structure of the Silver Cup anticline and Smith and Gehrels provide a modern, 1:25 000-scale, map of the mineralized area. The metallogeny of Camborne Mining Camp, in the adjacent Beaton map area (NTS 082K 12 & 13), is described by Church and Jones (1999) and much of what they say is applicable to the Trout Lake area.

 

References

Church, B.N. and Jones, L.D. (1999): Metallogeny of the Beaton – Camborne Mining Camp, Lardeau District (082K 12 & 13), British Columbia; British Columbia Ministry of Energy and Mines, Geological Fieldwork 1998, Paper 1999-1, pp193-222.

Emmens, N.W. (1914): The mineral resources of the Lardeau and Trout Lake Mining Divisions, British Columbia; British Columbia Bureau of Mines Bulletin #2.

Emmens, N.W. (1915): Lardeau Mining Division, in Ministry of Mines, Annual Report, 1914; British Columbia; British Columbia Ministry of Energy, Mines and Petroleum Resources Pages K245-283.

Fyles, J.T. and Eastwood, G.E.P. (1962): Geology of the Ferguson Area, Lardeau District British Columbia; British Columbia Department of Mines and Petroleum Resources, Bulletin 45, 91 pages.

Fyles, J.T. (1964): Geology of the Duncan Lake Area, Lardeau District, British Columbia; British Columbia Department of Mines and Petroleum Resources, Bulletin 49, 87 pages.

Read, P.B. (1973): Petrology and structure of the Poplar Creek map area, British Columbia; Geological Survey of Canada, Bulletin 193, 144 pages.

Read, P.B. (1975): Lardeau Group, Lardeau Map Area, West Half (82KWest Half), British Columbia, Geological Survey of Canada, Paper 75-1 Part A, pages 29-30.

Read, P.B. (1976a): Mineral Deposits of the Lardeau West Half Map Sheet: 1:125,000 Scale, Geological Survey of Canada, Open File 464.

Read, P.B. (1976b): Lardeau Map Area (82K West Half) British Columbia; Geological Survey of Canada, Paper 76-1A, pages 95-96.

Read P.B. and Wheeler J.O. (1976): Geology and Mineral deposits, Lardeau West Half, (082K/W); Geological Survey of Canada, Open File 432.

Smith, M.T. and Gehrels, G.E. (1990): Geology of the Lardeau Group East of Trout Lake, British Columbia (Silver Cup Ridge, Mount Wagner and Mount Aldridge areas; British Columbia Ministry of Energy, Mines and Petroleum Resources, Open File 1990-24.

Trettin, H.P. (1957): Regional framework and structural ore control of the Silver Cup mine, Lardeau, British Columbia; Unpublished M.Sc. Thesis, The University of British Columbia.

Walker, J.F., Bancroft, M.F and Gunning H.C. (1929): Lardeau Map Area, British Columbia, General Geology and Mineral Deposits; Geological Survey of Canada Memoir 161, 142 pages.

Wheeler, J.O. (1968): Lardeau (west half) map area, British Columbia (82K W1/2); in Report of Activities, Geological Survey of Canada, Paper 68-1A, pages 56-58.

BC Geological Survey Publications for NTS 082K