Cyclops zinc deposit, Summit Camp, Greenwood Mining Division, British Columbia, Canadai

Regional Level Types
Cyclops zinc deposit	Mine (Inactive)
Summit Camp	Mining Area
Greenwood Mining Division	Division
British Columbia	Province
Canada	Country

The past producing Cyclops zinc mine is located in the Summit Camp, south of the abandoned settlement of Eholt and about 13 kilometres north-west of Grand Forks, British Columbia, in the Greenwood Mining Division. Note that in the older literature, the area was within the Grand Forks Mining Division, which was later subsumed into the Greenwood Mining Division.
There is a description of the property, including regional geology, on the British Columbia “Minfile” site, current to 2020. This has a summary of the history of the property as well as a capsule description of the geology that is quoted below:
“The property is underlain by limestone, argillite and skarn of the Triassic Brooklyn Group [sic – Formation]. The skarn carries sphalerite, chalcopyrite, pyrite, magnetite and minor galena; the skarn has been silicified in places. Development work in the 1950's showed a mineralized zone to be up to 3.6 metres in width. A concordant body of gabbro, which post-date[s] the Triassic rocks, occurs to the south and southeast of the mineralized zone.”

Giles Peatfield comments:
The Triassic conglomerate/limestone/skarn package has been called the Brooklyn Formation by all workers in the area, up until 1986, when Church (1986), without offering any explanation, changed it to the Brooklyn Group. No justification was offered for this change, and indeed Fyles (1990) declined to accept it and continued to use Brooklyn Formation. Peatfield (1978) wrote that “The Brooklyn Formation is a mappable, heterogeneous unit, consisting of a large number of rocks types which lack lateral continuity. A distinctive feature of the formation is this internal heterogeneity.” The justification for this approach was by reference to the Code of Stratigraphic Nomenclature, as of 1970. The current Code (https://nacsn.americangeosciences.org/code/) covers this point as follows (Article 24 (b) Content): “A formation should possess some degree of internal lithic homogeneity or distinctive lithic features. It may contain between its upper and lower limits (i) rock of one lithic type, (ii) repetitions of two or more lithic types, or (iii) extreme lithic heterogeneity which in itself may constitute a form of unity when compared to the adjacent rock units.” With this in mind it would seem that Brooklyn Formation is a valid designation, and I for one will continue to use it.
There is a complication here with regard to claim names, in that older reports mention the Cyclops (Lot 1244), Mattie Davis (Lot 795) and Black Bess (Lot 1689), which are apparently no longer valid. These three Crown Granted (patented for US readers) Claims were dropped, perhaps for non-payment of taxes, and apparently replaced by located claims (Cyclops and Silver Chief) sometime prior to 1956 (see the claim map in Matthew (1956)). The Lancashire Lass (Lot 1687) at the southern end of the property appears to still exist as a Crown Grant. One must read the old reports with these changes in mind.
Hughes (1953) reported that “About 1,600 feet of diamond drilling was done in 1950, and several thousand tons of predominantly zinc ore was then indicated.” Matthew (1956) wrote that “Twelve-hundred feet south of the north boundary of the Cyclops, a small body of sphalerite with traces of chalcopyrite occurs in the limestone at the volcanics-limestone contact. This showing was examined by New Jersey Zinc and eight holes drilled to prove the extent. The drilling indicated the body to be shallow and to contain approximately 5,000 tons of 8 to 10% zinc.”
There has been a small amount of production of zinc ‘ore’ from the zone described above. Hughes (1953) wrote that “In July, 1952, a six-man crew started doing underground work and erecting surface buildings. An adit level was driven 130 feet in a southerly direction. At a point 100 feet from the portal a raise was driven 18 feet to connect with the bottom of an old shallow shaft. From this development work, 285 tons of ore was mined and trucked to the Providence mill at Greenwood for treatment. Owing to difficulties concerning disposal of the concentrates, it was decided to discontinue further development until satisfactory arrangements could be made for smelter treatment, and so underground work was stopped in October.” Official government records show production of 15,254 kilograms of zinc, based on the mined grade of 5.9 per cent zinc quoted in Hughes’ (1953) report.
This leads to the next point. The copper-silver skarn deposits in the Boundary District in general do not contain appreciable amounts of zinc, indeed in most of them sphalerite is not even reported. In a few of the smaller occurrences in the Brooklyn stratigraphy there are mentions of (probably) later quartz and calcite veins with small amounts of sphalerite and very rarely galena. Cyclops is unique, as far as is known, as a stratigraphically bounded deposit with enough sphalerite to constitute ore, and to be mined as such, albeit in very limited amounts.

Comments on the Minerals Reported:
Amphibole group: Gilmour (1982) wrote that “Overlying the zinc zone is a narrow unit of marble. The rocks are thinly bedded in places with marble and calc silicate altered argillaceous bands. Minor actinolite was noted.”, but with no analytical data.
Calcite: Gilmour (1982), describing a magnetite occurrence near the south end of the property, wrote “The magnetite bed containing minor calcite is 40 cm in width.”
Chalcopyrite: This is common in the skarn units, and is mentioned by several workers.
Epidote group: Matthew (1956) and Gilmour (1982) both mentioned ‘epidote’ but offered no specific mineral data.
Galena: Lucke and Paxton (1975) reported traces of galena in the zinc zone; Gilmour (1982) reported a small amount of lead in the zinc zone.
Garnet group: There are several references to ‘garnet’ in the skarn or calc-silicate rocks, but none with any compositional data. Peatfield (1978) reported on two samples from the Oro Denoro mine immediately to the north. These, based on crystal cell dimensions, were deemed to be indeterminate, between andradite and grossular.
Hematite: Gilmour (1982) wrote that “The calc silicate rock is green and occasionally [sic] brown, hard and massive. Garnet with epidote, calcite and hematite are the main constituents.”
Magnetite: Gilmour (1982) noted that “To the south [on the Lancashire Lass claim] by line 685 massive magnetite iron formation and minor copper mineralization occurs. The magnetite bed containing minor calcite is 40 cm in width.” This is reminiscent of a thin, continuous band of magnetite mapped by Peatfield (1978) in the old Oro Denoro pits.
Malachite: Gilmour (1982) noted several occurrences of malachite on his maps.
Quartz: Gilmour (1982) noted, on one of his maps, a quartz vein in calc-silicate rock.
Sphalerite: This is the mineral of primary interest on the Cyclops property. Matthew (1956) wrote that “Twelve-hundred [sic] feet south of the north boundary of the Cyclops, a small body of sphalerite with traces of chalcopyrite occurs in the limestone at the volcanics-limestone contact.” Gilmour (1982) described the zinc zone as follows: “Green sphalerite occurs as a distinctive bed and disseminated in limy argillaceous rocks.” Peatfield (1978) mapped, in a road cut near the northern boundary of the property, a small lens (about 2 by 6 metres) described as “massive banded light-coloured sphalerite”, at the contact of siliceous skarn and marble.
Comments on the rock types Reported:
Andesite: Matthew (1956) described the area of the property as follows: “The main rock type on the claims is a white crystalline limestone, which strikes N20°E and dips steeply west. To the east and in contact with the limestone is a basic andesitic volcanic. The contact is generally altered to an epidote-garnet skarn.” These andesitic rocks were considered by Peatfield (1978) to be probably of Jurassic age.
Breccia: Gilmour (1982) wrote that “On the Cyclops property recrystallized limestones (marble) of the Brooklyn Formation are the dominant Triassic rocks. The top of the sharpstone conglomerate [see note below] outcrops [sic] about 400 m to the west. Siliceous argillaceous bands up to 2 cm wide are interbedded with the limestones. A narrow sedimentary looking limestone breccia with a green matrix occurs northwest of the shaft.”
Conglomerate: The ‘sharpstone’ conglomerate [see note above] is a major member of the Brooklyn Formation on a regional basis. The unit was originally named by Seraphim (1956) in the Phoenix Mine area to the west, as “. . . a conglomerate formed from stones predominantly angular.” There has been much discussion over the years regarding the composition and origin of this stratigraphic unit (Peatfield, 1978). It is now generally accepted that the rock is of sedimentary origin rather than formed by hydrothermal processes – further discussion is beyond the terms of this review.
Diorite: Matthew (1956) noted that “. . . one small diorite outcrop is located to the east of the skarn zone near the north boundary of the Cyclops.”
Gabbro: Gilmour (1982) wrote at some length about this rock, as follows: “A sill-like body of gabbro about 400 m thick intrudes Brooklyn rocks adjacent to the mineralized zone. The rock is fine grained and a dark grey colour with a slightly coarser grained phase near the contact . . . . The gabbro had previously been mapped as tuff, andesite, diorite and basalt. The intrusion postdates the metamorphism of the Brooklyn Formation and in fact impinges a narrow hornfels zone on the calc silicate rocks.” This unit was originally defined by Church (1973), who called it the Cyclops Gabbro; it may be the same rock that Matthew (1956) called diorite.
Hornfels: See note above for gabbro.
Limestone: This is the principal rock on the property, and the host for mineralization. Gilmour (1982) noted that in places the unit is argillaceous.
Marble: Peatfield (1978) and Gilmour (1982) both noted that the Brooklyn limestone is locally converted to marble.
Skarn: Matthew (1956) wrote that “The three key claims, the Cyclops, the Silver Chief fraction and the Lancashire Lass are bisected by a contact, striking N20°E, between limestone on the west and volcanics on the east. The contact zone is altered to a garnet-epidote skarn and partially mineralized with sphalerite, minor chalcopyrite and magnetite.” Peatfield (1978) noted that in places the skarn is ‘siliceous’. Gilmour (1982) provided more data, writing that “The calc- silicate rock is green and occassionally [sic] brown, hard and massive. Garnet with epidote, calcite and hematite are the main constituents. This ‘skarn’ unit is generally stratigraphically controlled.”

Other Databases

Link to British Columbia Minfile:	082ESE122

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References