Poison Mountain Cu-Au-Mo deposit, Poison Mountain, Clinton Mining Division, British Columbia, Canadai

Regional Level Types
Poison Mountain Cu-Au-Mo deposit	Deposit
Poison Mountain	- not defined -
Clinton Mining Division	Division
British Columbia	Province
Canada	Country

Posting prepared 04 December, 2025.
The Poison Mountain copper-gold-molybdenum porphyry deposit is located about 2 kilometres south-west of Poison Mountain, about 68 kilometres north-west of Lillooet, and 170 kilometres west-northwest of Kamloops, B.C., in the Clinton Mining Division.
There is a short description of the property on the British Columbia Minfile site, current to 2011. This includes a very brief summary of the history of the property as well as a description of the geology, which is quoted below:
“Mineralization at Poison Mountain is associated with two granodiorite to quartz diorite stocks (the Main and North porphyries) which intrude arkosic sandstones, conglomeratic sandstones and shales of the Lower Cretaceous Jackass Mountain Group. The stocks comprise relatively unaltered cores of hornblende-plagioclase porphyry which grade outwards into biotite-plagioclase porphyry in which the biotite is an alteration product of hornblende. The intrusion, potassic alteration and mineralization at Poison Mountain are about 59 to 56 Ma in age (Paleocene) as indicated by potassium-argon dating of hornblende and biotites from the mineralized system . . . .”
“The highest grade mineralization occurs within the biotite-altered border phases of the intrusions and adjacent biotite-hornfelsed sedimentary rocks. It consists mainly of pyrite, chalcopyrite, molybdenite and bornite, which occur as disseminations and fracture-fillings, and in veins associated with quartz. Calcite and gypsum also occur as hydrothermal minerals, and pyrite, together with magnetite and hematite, forms an irregular halo around the mineralized zone. Chlorite-epidote alteration occurs sporadically within Jackass Mountain Group rocks for several kilometres around the deposit.”
Giles Peatfield comments:
The Poison Mountain occurrence is a moderate sized porphyry copper deposit, with copper as the principal metal of interest and with possible by-product gold, silver and molybdenum. The grades appear, under present economic conditions, to be sub-economic. The deposit has a long history of exploration, by several major mining companies; as of late 2025 it appears to be in private hands, and there are no available reports of current work.
There has been no production from the Poison Mountain copper deposit. Holland (1950) listed the placer gold production from Poison Mountain Creek [sic - Poisonmount Creek] as 85 Troy ounces, for the period 1931-1940.
There have been several resource estimates published for the deposit, of which the most reliable would seem to be that provided by Brown (1995), who quoted in-house company calculations for “In-situ geological ore reserves at a 0.15% Cu sulphide (S) cutoff from block modelling . . . .”
For the “Oxide Zone”, the total was 40,211,000 tonnes grading 0.288% Cu (S), 0.127 gram per tonne Au, 0.007% Mo and 0.15% Cu (oxide).
For the “Sulphide Zone”, the total was 768,315,000 tonnes grading 0.232% Cu (S), 0.122 gram per tonne Au and 0.007% Mo.
Note that these are historical estimates, and would not be considered reliable in the present regulatory environment. They are presented purely for historical interest.
Regarding the age of the deposit, Glover et al. (1988) wrote that “Intrusive rocks in the vicinity of Poison Mountain consist of hornblende feldspar porphyry and hornblende-biotite-feldspar porphyry. They occur as three separate stocks which outcrop south, southwest and west of the summit. A fourth stock, which is dominantly feldspar-phyric, occurs 3 kilometres to the east. Porphyry copper-gold mineralization occurs within and adjacent to the outer portion of the south-western stock, where biotite partially replaces hornblende. Several potassium-argon dates obtained on biotite and hornblende from the mineralized stock give ages of 57 and 59 Ma (Late Paleocene to Early Eocene) (W.J. McMillan, personal communication, 1987).” Subsequently, Brown (1995) listed five potassium-argon dates on hornblende and biotite from intrusive rocks, ranging from 57.3±2.0 to 61.4±2.1 Ma, and a single date on biotite/hornblende from hornfels of 55.5±2.0 Ma.
Comments on the minerals reported:
The reports of minerals given here are from various papers on the deposit. For details of the rock types mentioned in this section, refer to notes below in the ‘Rock types reported’ section.
Acanthite: Brown (1995) reported that “Quartz and carbonate veinlets contain rare grains of sphalerite, galena, tetrahedrite and argentite.” “Argentite” was earlier mentioned by So (1988), presumably based on polished section work, although this was not specifically stated. The method of determination was not stated.
Amphibole group: Seraphim & Rainboth (1975) and Asch (2010) both reported ‘hornblende’; Brown (1995) reported ‘actinolite’.
Anhydrite: Asch (2010) reported numerous examples of anhydrite in drill core.
Apatite group: Brown (1995) noted trace amounts of ‘apatite’ in intrusive rocks, presumably in thin sections. There is no information regarding specific mineralogy.
Azurite: Brown (1995) described the secondary copper mineralogy as follows: “Oxidation of copper minerals occurs to depths of about 10 m in the inner hornfelsed greywacke zone and to depths of about 40 m in the BQDP and brecciated zone. Secondary minerals include azurite, malachite, native copper and cuprite, with jarosite, goethite, hematite and Ti-oxides (Grove, 1981). The secondary copper sulphides [sic], covellite, chalcocite and bornite, occur intimately associated with chalcopyrite.”
Bornite: See notes above for azurite and below for chalcopyrite.
Calcite: Numerous workers reported calcite.
Chalcocite: See note above for azurite.
Chalcopyrite: Brown (1995) described the sulfide mineralogy as follows: “Sulphide [sic] mineralization straddles the arcuate contact between BQDP [biotite quartz diorite porphyry] and hornfelsed greywacke. The principal sulphide [sic] minerals are pyrite, chalcopyrite, molybdenite and bornite. The highest copper grades are within BQDP and adjacent brecciated hornfels; the highest gold grades are within BQDP. Molybdenite is concentrated, albeit at low levels, within hornfels at the outer edge of the copper-gold zone.”
Chlorite group: Numerous workers reported ‘chlorite’, but no-one gave any further detail.
“Clay minerals”: Brown (1995) reported several instances of ‘clay’ as an alteration product, often with sericite, but gave no specific information.
Covellite: See note above for azurite.
Cuprite: See note above for azurite.
Digenite?: This species is listed here as being tentative. The present Mindat posting lists it, but Asch (1990) reported ‘digenite?’ in several places in drill logs, so this species must remain uncertain. This points out the danger of relying on third-party compilations and not getting back to original reports.
Epidote group: Brown (1995) reported several occurrences of epidote. For example, “Barren QDP [quartz diorite porphyry] stocks are located immediately east and 2 km east of the Poison Mountain deposit . . . , and are characterized by phenocrysts of feldspar (up to 12 mm diameter), biotite, and hornblende and by abundant secondary chlorite, epidote and carbonate . . . . Epidote is found in plagioclase phenocrysts, in fan-shaped aggregates and in the matrix.” A further example from Brown (1995) is “Propylitic alteration in the deposit area may be retrograde in nature, since the granodiorite, diorites and hornfelsed greywacke show minor amounts of carbonate, chlorite and epidote with trace amounts of actinolite, sericite and clay.”
Feldspar group: Brown (1995) reported both potash feldspar and plagioclase, but gave no specific information.
Galena: See note above for acanthite.
Goethite: See note above for azurite.
Gypsum: Brown (1995), describing weathering and oxide mineralization, wrote that “Both the granodiorite and the hornfels exhibit extensive phyllic-propylitic alteration envelopes on fractures and joints to an average of 70 m to 80 m depth, and a maximum observed depth of 140 m. Below this vertical extent, late stage veins of gypsum cross-cut both the BQDP [biotite-quartz-diorite porphyry] and hornfels.”
Hematite: See note above for azurite.
Ilmenite: Brown (1995) reported minor amounts of ilmenite in hornfelsed greywackes and in biotite quartz-diorite porphyry.
“Jarosite”: See note above for azurite. There is no information regarding the specific jarosite phase.
Kaolin: Grove (1981) wrote that “Exploration work [at Poison Mountain] since 1935 has shown the presence of pyrite, chalcopyrite, molybdenite, bornite, azurite, malachite, native copper, and cuprite, along with vein quartz, calcite, and gypsum with secondary sericite, chlorite. biotite, serpentine, kaolin, and hematite.”
“Limonite”: Although iron-oxide staining is doubtless common, the only specific mention of limonite seen was by Pegg (1980).
Magnetite: Seraphim & Rainboth (1975), describing the petrology of the intrusive rocks, wrote that “The grey matrix is composed of: quartz (up to 20 per cent of the total rock); sphene [titanite] (4 per cent); opaques, consisting predominantly of magnetite and/or ilmenite with minor pyrite (4 per cent); and minor amounts of apatite, chlorite, carbonate, muscovite, epidote and rutile.
Malachite: See note above for azurite.
Mica group: Various workers have referred to ‘biotite’, ‘sericite’ and ‘muscovite’, as rock-forming or alteration minerals.
Molybdenite: See note above for chalcopyrite.
Native copper: See note above for azurite.
Native gold: Poison Mountain creek is an historic placer mining creek. Richmond (1934) described the area in some detail, and specifically mentioned that “On the lower half of Poison Mountain creek the rocks exposed are principally coarse-grained feldspar “birds-eye” porphyry that are occasionally cut by narrow stringers and veinlets of quartz well mineralized with pyrite and containing gold in small amounts. Several such pyritized quartz veins of very narrow width have also been uncovered in several of the bed-rock cuts on the creek near its source.” It would appear that these veins are part of the overall mineralized system, and are most likely the source of the placer gold recovered in the creek.
Pyrite: See note above for chalcopyrite.
Quartz: Quartz is common, both as a rock-forming mineral and in the form of veins.
Rutile: The only reference to rutile is by Seraphim & Rainboth (1975), as traces in some intrusive rocks. So (1988) reported “Ti-oxides”, which may be what Seraphim & Rainboth (1975) were referring to – see note above for magnetite.
Serpentine: See note above for kaolin.
Sphalerite: See note above for acanthite.
Tenorite?: This species is listed here as being tentative. The reason it is included is that the present Mindat posting lists it, but a diligent search of reports from the property have failed to turn up any mention of the mineral, and it is not certain where the original poster found the reference to the mineral. That said, it is certainly possible in this environment.
Tetrahedrite sub-group: See note above for acanthite.
Titanite: See note above for magnetite.

Comments on the rock types reported:
1: Mindat list:
Biotite quartz diorite porphyry: Brown (1995) wrote that “Several quartz diorite porphyry (QDP) stocks intrude the sedimentary rocks in the Poison Mountain area, including a potasically [sic]-altered biotite quartz diorite porphyry (BQDP) with associated dikes, and two elongate granodiorite stocks.”
Biotite-quartz monzonite: Seraphim & Rainboth wrote that “The border zones [of the main intrusive mass] are very irregular and grade inward to the core and outward to the sedimentary host rocks. The parts which appear to be intrusive are biotite-quartz monzonite, consisting of a grey matrix in which are set irregular cream to grey plagioclase phenocrysts, up to 5 mm long, that occur locally in clusters up to 10 mm in diameter.” This is probably Brown’s (1995) BQDP unit.
Conglomerate: Brown (1995) wrote that “The sedimentary rocks of the Copper Creek area are massive, fine- to medium-grained feldspathic to lithic sandstones (greywacke) with thin bands of intercalated thin shale and pebble conglomerate. In the Fenton Creek area lenses of polymictic boulder conglomerate are interbedded with greywacke and shale that strike north-northwest and dip steeply to the east.”
Granodiorite: See note above for biotite quartz diorite porphyry.
Greywacke: Seraphim & Rainboth (1975), describing the host rocks of the intrusive bodies, wrote that “The greywackes and grits are grey to green, and some strata contain a relatively large amount of feldspar and chloritized mafic minerals. Locally, the greywacke approaches andesite in bulk composition.” Brown (1995) wrote that “The sedimentary rocks of the Copper Creek area are massive, fine- to medium-grained feldspathic to lithic sandstones (greywacke) with thin bands of intercalated thin shale and pebble conglomerate.”
Grit: See note above for greywacke.
Hornblende granodiorite: Grove (1981), describing the intrusive rocks on the property, wrote that “The oldest intrusion, a hornblende biotite granodiorite, extends northwesterly across the lower slope of Poison Mountain from Copper Creek to Fenton Creek. This pluton and the sedimentary country rocks are cut by a number of steep northerly trending hornblende biotite, porphyry dykes. These dykes are the birds-eye porphyry of MacKenzie (1920) [sic – Grove was mistaken here; the reference should be Richmond (1934)] and the Main, North, and East porphyry of Seraphim and Rainboth (1976). The presence of somewhat rounded inclusions of altered hornblende granodiorite in several of the porphyry dykes clearly demonstrates the sequence of intrusion.”
Hornblende-biotite granodiorite: See note above for hornblende granodiorite. This is possibly Brown’s (1995) BQDP unit.
Hornblende-biotite porphyry: See note above for hornblende granodiorite.
Hornblende quartz monzonite: Seraphim & Rainboth wrote that “The Main and North porphyry intrusions are separated by hornfels at the surface, but may be joined at depth. They are both zoned and consist of similar core and border phases. The cores are composed of hornblende-quartz monzonite porphyry.” This is possibly Brown’s (1995) BQDP unit.
Hornfels: See note above for hornblende quartz monzonite.
Quartz diorite porphyry: See note above for biotite quartz diorite porphyry.
Sandstone: See note above for greywacke.
Shale: See note above for conglomerate.
Siltstone: Seraphim & Rainboth (1975) wrote that “Several siltstone members are exposed within the explored area. The siltstone is commonly grey and black, and thin bedded, with beds averaging 2 centimeters thick.”

2: Varietal names for interest only:
'Big biotite porphyry':
'Bird's eye porphyry':
'Diorite':
'Feldspar hornblende porphyry':
'Laminated siltstone-mudstone':
'Mafic dike':
'Mafic-feldspathic breccia':
'Polymictic breccia':
'Polymictic conglomerate':
'Sandstone (feldspathic)':

Research by Giles Peatfield, Courtenay, British Columbia.
Edited by Doug Scott, Ottawa
Posting prepared 04 December, 2025.

Other Databases

Link to British Columbia Minfile:	0920 046

Other Regions, Features and Areas containing this locality

References