Chuchi porphyry copper prospect, Chuchi Lake, Omineca Mining Division, British Columbia, Canadai

Regional Level Types
Chuchi porphyry copper prospect	Prospect
Chuchi Lake	Lake
Omineca Mining Division	Mining Division
British Columbia	Province
Canada	Country

The Chuchi porphyry copper prospect is located about 9 kilometres north of Chuchi Lake, 93 kilometres north of Fort St. James, British Columbia, in the Omineca Mining Division.
There is an extended description of the property on the British Columbia “Minfile” site, current to 2015, to which interested readers are referred. Relevant portions pertaining to geology are quoted below:
“The Chuchi Lake showing is located at the approximate centre of an extensive zone (six square kilometres) of porphyry-style stockwork and disseminated mineralization. It includes both BP Resources Chuchi Lake property, the apparent centre of the porphyry system, and Rio Algom's Klaw property which occurs on the fringes of the alteration halo approximately 1.25 kilometres to the north.
The system is bounded to the east by a north-trending fault, and to the north by the fault in Klawdetelle Creek. Within it, crowded plagioclase porphyry monzonite stocks intrude the sedimentary horizon in the Lower Jurassic Chuchi Lake Formation (informal name) of the Middle Triassic to Lower Jurassic Takla Group, and blossom out into sill swarms. The sedimentary unit is of Pliensbachian age (Fieldwork 1991) [Nelson et al., 1992]. In many instances in drill core, hornfelsed sedimentary rocks show soft-sediment deformation, and are intimately intercalated with monzonite. The fine-grained, well-bedded sandstones, siltstones and tuffs grade downwards into massive coarse lapilli tuffs and agglomerates. In many cases, intrusive clasts form a large percentage of the fragmental material. Crowded plagioclase porphyry clasts with small blocky plagioclase crystals less than 2 millimetres across are common, and identical to the later porphyries that intrude the sediments. Clasts with pink secondary potassium feldspar, magnetite and epidote are also present.
In light of the geological evidence that sedimentation, intrusion and porphyry-style copper-gold mineralization were roughly coeval, the Early Jurassic (Pliensbachian) fossil ages of the sedimentary horizon would also date the Chuchi porphyry system (Fieldwork 1991) [Nelson et al. 1992].
Both the monzonite and the sediments at Chuchi Lake are extensively altered. Secondary potassium feldspar occurs in pink veinlets in the monzonite with magnetite, pyrite, and chalcopyrite. The sedimentary rocks show a strong biotite hornfels overprint, with subsequent mottling by potassic and propylitic alteration. Hairline veinlets with bleached selvages and magnetite veinlets and disseminations are also characteristic of alteration.
Copper-gold mineralization is accompanied by pervasive potassic and propylitic alteration and abundant secondary magnetite. The best grades fall within a northeast-trending zone that crosses the monzonite stock. This system was drilled extensively by BP Resources in 1990-91. The gold mineralization appears to be shear-zone hosted and is associated with pyrrhotite rather than pyrite or chalcopyrite (Faulkner, 1991) [there is no detailed reference for this publication, and I have not been able to find it].”
Giles Peatfield comments:
There have been two radiometric dates published for intrusive rocks in the general area of the property. Garnett (1978) reported a K/Ar age of 181±5 Ma, for biotite from medium-grained plagioclase syenite porphyry. He commented that the date was “partially reset by Unit 9 intrusion” but gave no further details. Unit 9 includes leucocratic granite, quartz syenite and alaskite. Nelson and Bellefontaine (1996) reported a U/Pb age of 188.5±2.5 Ma, on titanite from a crowded porphyritic monzonite.
Minfile reports that “A rough estimate of the geological resource at Chuchi Lake is 50 million tonnes with grades between 0.21 and 0.40 per cent copper and 0.21 and 0.44 gram per tonne gold (Press Release - Digger Resources Inc., October 17, 1991). This resource is not compliant with National Instrument (NI) 43-101 standards.”
The Chuchi porphyry prospect is included in the USGS compilation by Singer et al. (2008). The reference quoted in this report for Chuchi is Garnett (1974), except that the wording given for the title is incorrect and should be as in the reference list below. I know this to be correct as I have the original paper edition in my files. Another point of confusion is that the present Mindat posting refers to Singer et al. (2005) [USGS Open File 05-1060] rather than the more recent Open File as given in the reference list. To add to confusion, the mineral list given in Singer et al. (2008) is incomplete and in error as it includes scheelite. Nowhere in the original Garnett (1974) paper is this mineral mentioned, nor is it to be found in any other paper listed here. In any event, the environment is really not correct for scheelite. Was someone confusing this property with another occurrence?
The Chuchi porphyry prospect as presently known is relatively small and of sub-marginal grade. It is one of a number of similar occurrences and deposits in the general region, the largest and most important being the presently operating Mount Milligan mine (Minfile No. 093N 194), about 36 kilometres to the south-east. Work continues on the property – Pacific Ridge Exploration Ltd., in a press release dated 12 Dec. 2023, reported that recent geophysical surveys have outlined several promising target areas.

Giles Peatfield comments on the minerals reported:
The following comments, derived from several reports, give some details of the various minerals reported from the Chuchi copper prospect and immediately surrounding area.
Amphibole group: Heberlein et al. (1984) reported “green to black hornblende” in syenitic rocks. Harris (1985) reported pale green to olive brown amphibole in thin sections of several rock types. Wong (1990) reported “hornblende” in several rock types. Finally, Chadwick (2014) reported a coarse-grained biotite-actinolite hornfels in a distal alteration zone, quoting Nelson and Bellefontaine (1996).
Apatite: Harris (1985) found apatite as a prominent accessory in thin and polished thin sections of several rock types.
Bornite: This does not seem to be common in the Chuchi prospect. Chadwick (2014) reported bornite with chalcopyrite, generally in areas of more intense potassic alteration.
Calcite: Although probably common, the only specific mentions were by Wong (1990), who described a narrow zone of highly fractured and intensely altered rocks where “Quartz, Fe-carbonate and calcite form strong to intense pervasive alteration and veining.”, and by Wong and Barrie (1991, Part 2) who made several references to calcite in drill core logging.
Chalcopyrite: This is the principal mineral of economic interest and is noted by all workers.
Chlorite group: All workers have reported “chlorite” or chloritic alteration. Harris (1985) described many examples of chlorite as an alteration product of plagioclase, pyroxene or amphibole. There are no specific data available.
Epidote: This is common and reported by all workers, generally as an alteration product.
Feldspar group: There are numerous references to plagioclase and K-feldspar, but there are no specific data. Heberlein et al. (1984) reported “perthitic orthoclase” in syenite. Nelson and Bellefontaine (1996) reported secondary potassium feldspar. Most workers reported plagioclase, but again with no specific data except for Chadwick (2014) who mentioned “albite”.
Galena: Wong (1990) wrote that in hole 89-06, “At 193.6 m are two 1 cm wide subparallel carbonate-pyrite galena-chalcopyrite-sphalerite veins.” This is only mention of galena.
Gypsum: Wong (1990) found, near surface in hole 89-05, “Occasional fragment (xtal?) of gypsum.”, in an altered, pyritic fragmental rock.
Hematite: Wong (1990) mentioned, in drill core logs, numerous occurrences of hematite.
Limonite: Harris (1985) reported limonite as an alteration of pyrite. It is no doubt common here, just not reported.
Magnetite: This is common mineral here, mentioned by all workers.
Malachite: Again, this is probably common, but was only reported by Wong and Barrie (1991, Part A), in a brief section on mineralization and alteration, wrote that “The second type of mineralization, associated with the 070' fault, post-dates the porphyry-style mineralization. It consists of vuggy, narrow and discontinuous quartz veins and local stock-work within an envelope of sheared quartz, Fe-carbonate and sericite-altered intrusive and volcaniclastic rocks juxtaposed by the fault. While chalcopyrite and malachite are evident in this zone of shearing, it is probable that this represents a remobilization of the earlier porphyry-style mineralization.”
Mica group: There are many reports of micas from the deposit and surrounding area. Heberlein et al. (1984) reported both muscovite and biotite in syenitic rocks, and in describing an area of well mineralized hornblende diorite, wrote that “Here the hornblende diorite wallrocks are pervasively altered; the hornblendes to felted secondary biotite and feldspars to fine grained sericite.” Most other workers have noted both biotite and sericite. Nelson and Bellefontaine (1996) described “biotite hornfels” in the mineralized area. See also note above for hornblende.
Molybdenite: Wong (1990) noted, at 191.4 metres in hole 89-08, “Mo [molybdenite?] on one irreg low angle dry Fr [fracture] X-cutting Py-Cp-FF[?].” Wong and Barrie (1991, Part 2) noted several instances of traces of molybdenite on fractures in core.
Pyrite: This is ubiquitous and well reported.
Pyrrhotite: Wong and Barrie (1991, Part 2) reported a very few instances of pyrrhotite in their logging of drill core.
Pyroxene group: Heberlein et al. (1984) noted augite in basic volcanic flows and dyke rocks. Harris (1985) reported “pyroxene” in several thin and polished thin sections, but did not specify a species.
Quartz: There are numerous veins, often late stage, of quartz. Wong (1990) also described, at 35.2 metres in hole 89-05, a fragment in a crystal lithic tuff that was replaced by amethyst.
Rutile: Harris (1985) described a few occurrences of fine rutile needles in biotite.
Siderite?: Wong (1990) noted possible siderite in drill core logging. Wong and Barrie (1991, Part 1) reported “Fe carbonate”. Chadwick (2014) noted “iron carbonate”. One can assume this is siderite, but there are no definitive details.
Sphalerite: See note above for galena.
Titanite: Harris (1985) noted traces of sphene in thin sections of latite porphyry. See also note above in the Comments section, regarding radiometric dating.
Giles Peatfield comments on the rock types reported:
These rock names are derived from the several reports used in this review. Some may be alternate names for the same rock type, but I have chosen to list them all. Be aware that in most cases these are field names.

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:	093N 159

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References