Mount Thomlinson molybdenum deposit, Mount Thomlinson, Hazelton, Omineca Mining Division, British Columbia, Canadai

Regional Level Types
Mount Thomlinson molybdenum deposit	Deposit
Mount Thomlinson	- not defined -
Hazelton	- not defined -
Omineca Mining Division	Mining Division
British Columbia	Province
Canada	Country

The Mount Thomlinson molybdenum deposit is located about 3 kilometres north of the peak of Mount Thomlinson, near the northern end of the Babine Range, 37 kilometres north-northeast of Hazelton, British Columbia, in the Omineca Mining Division.
There is an extended description of the property on the British Columbia “Minfile” site, current to 2020. The portion relative to geology is quoted below:
“Massive black argillaceous siltstones and argillites of the Middle Jurassic to Lower Cretaceous Bowser Lake Group have been intruded by a roughly circular stock (1400 metres diameter) of leucocratic quartz monzonite porphyry of the Eocene Babine Intrusions. Near the contact, the sedimentary rocks have been deformed and metamorphosed to medium or dark grey schists in a zone 91 to 152 metres wide. Stock contacts are sharp and biotite, muscovite, cordierite and andalusite have been formed in the contact aureole. The margins of the stock are foliated parallel to the contact and to the schistosity in the intruded rocks up to 100 metres from the contact. Much of the stock is a coarse-grained porphyry with potassium feldspar phenocrysts up to 5 centimetres long. In many areas, the stock is cut by narrow (2-10 centimetres [or locally up to 2 metres, see Kirkham (1965)]) aplite dikes. These dikes occur in swarms and occupy well-defined fractures. A potassium-argon age date from biotite from the stock resulted in an age of 54 Ma (Geological Survey of Canada Open File 2322).
Molybdenite, chalcopyrite and pyrite are associated with a system of quartz vein stockworks within the intrusive, along the contact hornfelsed zone with the argillaceous rocks. The quartz stockwork is best developed along this stock contact and post-dates the aplite dikes. The mineralized zone trends north-northeast (030 degrees) along the margin of the stock, and dips 58-65 degrees west. It is tabular and up to 100 metres wide. Molybdenite is most common as fine flakes in quartz veinlets and as smears along fracture planes. Locally it occurs as coarse flakes in quartz veins. Weathering of mineralization has been considerable, and in many areas extends from 60 to 91 metres below the surface. Limonite, ferrimolybdite, malachite and to a lesser extent, azurite, are the principal secondary minerals. Chalcopyrite, malachite and azurite also occur along fractures and veins. Although chalcopyrite is found in the same general areas as molybdenite, the two sulphides occur independently of each other. Pyrite (1-5 per cent) is found as disseminations, fracture-fillings and patchy crystalline concentrations in the intrusive and adjacent argillites. Minor amounts of magnetite, scheelite and pyrrhotite are also evident. The better grade rock lays [sic – lies] several metres from the contact within the intrusive rock. In general the mineralization extends farther into the intrusive than into sediments, and in many places the amount of mineralization drops off sharply at the contact.”
Giles Peatfield comments:
The property has a long exploration history, dating back to 1963 and continuing to at least 2010. The most significant work was by Southwest Potash Corporation (later AMAX), part of the American Metals Climax group of companies. This involved detailed surface activity, including trenching, and the drilling of nine diamond drill holes, during 1964 and 1965; results are contained in private company reports. In the period 1980 to 1982, Texasgulf Canada Limited (later Kidd Creek Mines) did surface work and drilled an additional five diamond drill holes (DeLancey, 1980, 1982; Bending, 1981). In later years several other concerns did mainly surface work and re-sampling of drill core, but no additional drilling was undertaken.
The radiometric age of 54 Ma quoted in the Geological Survey Open File (Richards, 1990) was originally reported by Carter (1981) as 53.8 Ma, on a sample (NC-68-13) supplied by R. V. Kirkham.
On the subject of “reserves”, Soregaroli and Sutherland Brown (1976) published (Table 3) a “Reserve” for Mount Thomlinson of 40.82 million tonnes grading 0.12 percent MoS2, which they stated was “measured, indicated and inferred” and “submarginal”. These numbers were derived from a report by AMAX (the successor of Southwest Potash Corporation), and as rightly pointed out by McMillan (2010) would not be considered a valid reserve, or even a resource, by modern regulatory standards. As further stated by McMillan, “These ‘reserves’ must therefore be considered unreliable by current standards. The reader is also cautioned on the validity of the ‘mineral reserve’ numbers. Under current NI [Canadian Regulatory National Instrument] 43-101 guide-lines the nine drill holes and five surface trenches are neither of sufficient density nor sufficient distribution to define a mineral resource. Therefore, none of the numbers published with respect to the amount of MoS2 or tonnes of ‘ore’ at Mount Thomlinson can be relied upon. They are presented here as information on the historical work on the property.” Note that these numbers have been included in the current (2020) Minfile write-up – again, be aware that they have no validity.
Giles Peatfield comments on the minerals reported:
All of the minerals listed, with the exception of calcite and pyrrhotite, were reported by Kirkham (1965), many identified by microscopy.
Some specific comments are justified:
Calcite: this was reported by Bending (1981) in drilling of weakly altered argillite to the west of the main mineralized zone.
Chlorite: Kirkham (1965) described “chlorite”, but gave no specific data. McMillan (2010) described “chloritic material”, again with no details.
Feldspar group: Kirkham (1965) described several feldspar species: in the core of the intrusive body he found “Coarse potash feldspar phenocrysts” and “plagioclase phenocrysts” these latter crystals he described as oscillatory zoned (An12-30). Further, he reported that “In the mineralized zone, . . . feldspar has been altered to carbonate and muscovite (sericite in places); and the quartzofeldspathic matrix of the porphyry has been recrystallized and has increased in grain size. Perthitic microcline is relatively fresh compared to other feldspars.”
Mica group: Kirkham (1965) reported biotite, which he regarded as a metamorphic product, and which gives the thermally altered argillite a brown colour. He also described muscovite and sericite (see comment above for feldspar group).
Pyrrhotite: This was reported by McMillan (2010). He noted that “Minor amounts of magnetite, scheelite and pyrrhotite are also present.” Unfortunately it is not clear from his report in which rocks these minerals occur.
Giles Peatfield comments on the rock types reported:
These rocks have been reported by all workers referenced here. Some specific comments are: Bending (1981) described the aplite as “felsic dykes”; McMillan (2010) described the thermally altered argillite as “hornfels”; Kirkham (1965) called the main intrusive rock “quartz monzonite porphyry”, whereas Bending (1981) described it as “granitic” and McMillan (2010) called it “leucocratic porphyry”.

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 1982 to retirement in 2016

Other Databases

Link to British Columbia Minfile:	093E 080

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References