Red Dog copper-molybdenum deposit, Holberg, Nanaimo Mining Division, Vancouver Island, British Columbia, Canadai

Regional Level Types
Red Dog copper-molybdenum deposit	Deposit
Holberg	Community
Nanaimo Mining Division	Division
Vancouver Island	Island
British Columbia	Province
Canada	Country

The Red Dog copper-molybdenum deposit, which Minfile lists as a developed prospect, is located near the head of Holberg Inlet, about 7 kilometres north-northeast of the small settlement of Holberg, 37 kilometres west-northwest of the now mined-out Island Copper Mine, and 337 kilometres west-northwest of Nanaimo, British Columbia, in the Nanaimo Mining Division.
There is an extensive description of the deposit on the British Columbia “Minfile” site, current to 2022, to which interested readers are referred. The relevant portions pertaining to the geology of the region and deposit are presented here:
“Regionally, the area is underlain by northwest-trending belts of basaltic volcanics and carbonate sedimentary rocks of the Upper Triassic Karmutsen and Quatsino formations (Vancouver Group) and mafic volcanics and sediments of the Upper Triassic to Lower Jurassic Bonanza Group (Holberg volcanic unit, Nahwitti River wacke and Parsons Bay Formation). These volcanic and sedimentary rocks have been intruded by granodioritic rocks of the Early to Middle Jurassic Island Plutonic Suite.
Locally, andesitic to basaltic flows, bedded tuff, massive tuff, lapilli tuff and tuff breccia of the Bonanza Group are intruded by diorite, quartz diorite and quartz feldspar porphyry of the “Red Dog” porphyry stock (Island Plutonic Suite). On the northeast side of the property, the Bonanza rocks are metamorphosed to hornblende-biotite hornfels in contact zones with silicification and hydrothermal alteration in shear zones. On the southwest side, the Bonanza rocks have either been intensely silicified and brecciated or show alteration to pyrophyllite, pyrite, sericite, zeolite and kaolinite. Abrupt differences in alteration appear to be related to a series of east-orientated normal faults that down-step stratigraphy and alteration to the south.
Two zones of mineralization, referred to as the Red Dog and Slide zones, have been identified in altered Bonanza volcanics along the southern contact of the Red Dog porphyry stock. Alteration immediately south of the intrusive, over distances of 100 to 300 metres, varies from potassic to intermediate argillic and consists of biotite and hydrothermal magnetite with overprinting of chlorite and sericite. The alteration zone contains variable amounts of pyrite and chalcopyrite with minor bornite and molybdenite. Further to the south, potassic and intermediate argillic alterations are in contact with advanced argillic alteration containing pyrophyllite, dickite, silica and pyrite.
At the Red Dog zone, a quartz magnetite breccia hosted by Bonanza Group rocks and adjacent to feldspar porphyry dikes hosts sporadic chalcocite, bornite, chalcopyrite and molybdenite mineralization.
The Slide zone, located approximately 400 metres east of the Red Dog zone, is hosted by altered Bonanza Group rocks with biotite hornfels and local sericite-chlorite overprinting. Mineralization consists of disseminated and fracture-filling pyrite and chalcopyrite. Molybdenite occurs along joints, fractures and in quartz-sericite veins associated with shear zones. Northeast-trending, steeply dipping, late trachyte dikes cut the mineralization.”
There are no radiometric dates available for rocks in the immediate area of the Red Dog deposit. Muller et al. (1974) listed a large number of K-Ar ages for intrusive rocks of the Island Intrusions, which are intrusive into the Bonanza Group volcanic rocks. These ages, for intrusive bodies in the general region of the Red Dog deposit, ranged from 145±5 Ma to 169±6 Ma. Muller et al. (1974) also reported several whole rock ages for Bonanza volcanic rocks, ranging from 135±4 to 161±3 Ma (ignoring one younger age of 103±4 Ma). Further information is available in Muller et al. (1981), who wrote in summary that “Northcote and Muller (1972) earlier suggested that Island Intrusions and Bonanza volcanics are cogenetic. Possibly cooling of the batholith lagged somewhat after extrusion of the volcanics. On the basis of all available data the writers now conclude that Bonanza volcanism and plutonism of Island Intrusions occurred and ceased within Early Jurassic time.”
There are several recorded mineral resource estimates available for the Red Dog deposit. Pilcher and McDougall (1976) simply mentioned that the “Main Zone” was measured as 260 x 400 m[etres] but did not estimate tonnage and grade. Richards (1989) reported a deposit of 51.84 million tons (47 million tonnes) grading 0.32% Cu and 0.012 ounce/ton (0.41 gram/tonne) Au, with no mention of Mo. Crew Natural Resources Ltd. (1992) reiterated these numbers, quoting 47.7 million tonnes grading 0.3% Cu and 0.45 gram/tonne Au. Neither of the last two estimates would be regarded as National Instrument 43-101 compliant. Tahija et al. (2022) presented a compliant resource, quoted at several cut-off copper grades. Their totals for the 0.10% Cu cut-off were: Indicated – 54,490,000 tonnes grading 0.22% Cu, 0.31 gram/tonne Au and 0.004% Mo; additional Inferred – 2,979,000 tonnes grading 0.17% Cu, 0.25 gram/tonne Au and 0.002% Mo. Note that there do not appear to be resource estimates for the much smaller nearby Slide Zone. These resource estimates suggest that the deposit as presently known is too small and low grade to support a stand-alone operation, but that it might work as a satellite pit for the larger Hushamu deposit (Minfile No. 092L 240) about 12 kilometres to the east.
The Red Dog deposit is included in the USGS compilation by Singer et al. (2008). The information given by Singer et al. (2008) is incomplete.

Giles Peatfield comments on the minerals reported:
The reported mineralogy of the Red Dog property is complex, including a large number of alteration species. I have chosen to comment on all minerals reported, and provide some information regarding analytical techniques:
Alunite: This mineral was reported by McClintock (2015) on the basis of PIMA (Portable Infrared Mineral Analyzer) analysis. Tahija et al. (2022) wrote that alunite was detected by Vancouver Petro Graphics [sic – Petrographics] by TerraSpec spectral analysis.
Amphibole group: Northcote (1971) wrote that “On the northeast side of the property the Bonanza rocks are metamorphosed to hornblende (biotite) hornfels with some silicification and hydrothermal alteration in shear zones.” Tahija et al. (2022) wrote that “Within the contact metamorphic band, the andesite has been thermally altered to an assemblage of albite, actinolite, biotite and lesser chlorite.”
Ankerite?: Panteleyev and Koyanagi (1994) wrote that “Hostrocks to the silica-rich altered zones are themselves silicified and have albitic plagioclase, sericite and variable chlorite, epidote and ankeritic carbonate.”, but stopped short of a definite identification of ankerite.
Bornite: This is an important copper mineral, occurring in lesser amounts and generally fine-grained.
Calcite: Panteleyev and Koyanagi (1994) wrote that “Late fractures and veins with pink laumontite selvages and calcite filling are abundant around the margins of the deposit.”
Chalcocite: McClintock (2016), describing an attempt to drill to a deeper target, wrote that “The upper parts of RD16-04 is [sic] deeply weather[ed] and leached of sulphides in the upper 50 metres of the hole. At the base of the leach[ed] capping, is a 12 m thick zone of secondary copper enrichment consisting of chalcocite and lesser covellite.”
Chalcopyrite: This is the principal mineral of economic interest on the property.
Chlorite group: Most workers mentioned chlorite but gave no specific mineral data.
Copper: Muntanion (1983) described, at just below the base of overburden at 71 metres depth in Hole EC-141, smears of native copper with bornite.
Covellite: Panteleyev and Koyanagi (1994) reported that “In addition, fine-grained bornite and traces of (primary) covellite have been noted.”
Diaspore: This was reported regionally by Panteleyev and Koyanagi (1994) as X-ray confirmed, and at Red Dog by McClintock (2015) by PIMA analysis.
Dickite?: This was reported only by McClintock (2015) as possible by PIMA analysis.
Epidote: See note above for ankerite? Also McClintock (2016) wrote that “Propyllitic alteration on the property varies in composition depending on the host rock. It [sic - In] the Bonanza Group rocks is [sic - it] consists of extensive chloritization of the primary mafic minerals, epidote and pyrite generally occurring in cross cutting fractures.”
Feldspar group: Both orthoclase and plagioclase have been reported. More specifically, McClintock (2016) reported plagioclase as An30, An35 and An60.
Fluorite: McClintock (2016), describing a thin section of an altered lapilli tuff, reported that “Quartz also occurs in cross cutting veins and is accompanied by scattered grains of fluorite both in and adjacent to the veins.”
Hematite: Panteleyev and Koyanagi (1994) noted that “Hydrothermal alteration in the mineralized zone has produced silicified breccias and stockworks of dominantly crystalline quartz and magnetite ± pyrite or quartz with either pyrite or hematite.” McClintock (2016), describing the silicification of quartz-magnetite breccia, commented that “. . . accompanying the silicification, the magnetite was replaced by hematite and lesser chalcopyrite.”
Kaolinite: This was reported by Panteleyev and Koyanagi (1994), and by McClintock (2015) on the basis of PIMA analysis.
Laumontite: See note above for calcite.
Limonite: Although probably common here, limonite was mentioned specifically only by Northcote (1971), who noted that “In some stream beds limonite gossans several inches thick are formed.”
Maghemite?: Panteleyev and Koyanagi (1994), continuing the discussion of hematite, noted that “Some of the hematite is strongly magnetic, suggesting an intermediate Fe203 phase is present - maghemite (γFe203).”
Magnetite: This is major mineral at Red Dog, reported by all workers.
Malachite: Reports of malachite are restricted to a single mention by McClintock (2016) in drill core logging.
Mica group: Several species of mica have been reported at Red Dog. Northcote (1971) mentioned biotite and sericite. Panteleyev and Koyanagi (1994) added muscovite and illite to the list.
Molybdenite: This is a mineral of some economic interest here, mentioned by several workers. For example, Northcote (1971) wrote that “Molybdenite is most abundant on fracture surfaces and in quartz-sericite veins following shear zones.”
Pyrite: This is ubiquitous, mentioned by all workers.
Pyrophyllite: Panteleyev and Koyanagi (1994) wrote that “Crosscutting steeply dipping, east-trending fracture sets and altered bands contain quartz, pyrophyllite, sericite and kaolinite.” It was reported also by McClintock (2015) based on PIMA analysis.
Pyroxene group: The only mention of pyroxene was by McClintock (2016) who, describing a thin section of andesite porphyry, wrote that it had a “Porphyritic texture with plagioclase phenocrysts to 2mm, augite to 0.5mm or less and stilbite filled amygdules up to 2mm in a fine gained pilotaxitic matrix of plagioclase laths, biotite, epidote, augite, quartz and Kspar.”, but gave no more specific mineral data.
Quartz: This is ubiquitous, mentioned by all workers.
Rutile: This was reported regionally by Panteleyev and Koyanagi (1994) as X-ray confirmed, and at Red Dog by McClintock (2016) as an accessory in thin sections of andesite porphyry and quartz-magnetite breccia.
Scapolite: Tahija et al. (2022), describing hornfels facies alteration, noted that “Within the contact metamorphic band, the andesite has been thermally altered to an assemblage of albite, actinolite, biotite and lesser chlorite. Spectral analysis found minor amounts of scapolite.”
Stilbite: See note above for pyroxene group.
Titanite: McClintock (2016), describing a thin section of an andesite flow rock, mentioned titanite as an accessory with rutile and diaspore.
Topaz: McClintock (2016), describing alteration facies, noted that “Topaz and alunite are also noted.”
Zunyite: This was reported regionally by Panteleyev and Koyanagi (1994) as X-ray confirmed, and possible at Red Dog by McClintock (2015) by PIMA analysis. Based on the earlier analysis, I am prepared to accept this as valid at Red Dog.
In addition to the minerals listed above as occurring or possible at Red Dog, there are a number that were reported as X-ray confirmed by Panteleyev and Koyanagi (1994) in the region but not specifically mentioned at Red Dog. Some of these may in fact be present here, and it is worth listing them for general interest. They include: anhydrite, gypsum, meta-halloysite?, natroalunite, paragonite, schlossmacherite, smectite, sulfur and tridymite.
Giles Peatfield comments on the rock types reported:
The rock types listed are taken from several reports. I have chosen not to comment individually on the various units.
Giles Peatfield
BASc. (Geological Engineering) University of British Columbia 1966.
PhD Queen's University at Kingston 1978.
Worked for Texas Gulf Sulphur / Texasgulf Inc. / Kidd Creek Mines - 1966 to 1985.
Vancouver based consultant 1985 to retirement in 2016

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Link to British Columbia Minfile:	092LX200

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References