Mastodon chrome-nickel deposit, Castle Mountain, Cascade, Greenwood Mining Division, British Columbia, Canadai

Regional Level Types
Mastodon chrome-nickel deposit	Deposit
Castle Mountain	- not defined -
Cascade	- not defined -
Greenwood Mining Division	Division
British Columbia	Province
Canada	Country

Research by Giles Peatfield, Courtenay, British Columbia.
Edited by Doug Scott, Ottawa
Posting prepared 21 November, 2025.



This property is located about 5 kilometres southeast of Cascade, B. C., on the southwest slope of Castle Mountain at an average elevation of 975 metres, immediately north of the US border. Cascade is about 17 kilometres east of the city of Grand Forks, in the Greenwood Mining Division. Note that the spelling “Mastodon” is deemed correct for the chrome portion of the property, while “Castle Mountain” refers to the nickel portion.
There is an extensive description of the property on the British Columbia “Minfile” site, current to 2008. This includes a summary of the history of the property as well as a comprehensive description of the geology, parts of which are quoted below:
“The area is predominantly underlain by Lower to Middle Jurassic Rossland Group massive greenstone, andesite, latite, agglomerate and volcanic breccia. Minor greywacke and interbedded limestone with lenses of silicified equivalents, also occur.
At the Castle Mountain Nickel deposit, a wedge-shaped ultramafic complex comprised of serpentinized dunite of the Carboniferous or older Anarchist Group has been tectonically emplaced against chlorite and carbonate altered Rossland Group greenstone breccias, tuffs, flows and metasedimentary rocks. The Rossland Group rocks surround the ultramafic body to the west, north and northeast while foliated monzonites of the Middle to Late Jurassic Nelson Intrusions, outcrop to the east and southeast. The contacts with these surrounding rocks are fault-bounded and commonly quartz-talc- carbonate altered. The serpentinite body has been mapped as an upthrust section of an ophiolite (J. Fyles, personal communication, 1989).
The faulted and sheared ultramafic body is 2440 metres long, 1220 metres wide and dips 38 degrees east. The rock is largely serpentinite and is composed of variably oxidized alternating layers of serpentinized dunite and gabbro or their equivalents. Locally unaltered dunite is present. Mesh textures in serpentine are absent, as are bastites, and there are no relict orthopyroxene grains which suggests the that protolith was massive dunite. The dunite and gabbro layers are intercalated with porphyritic dykes or sill-like bodies which constitute up to 30 per cent of the ultramafic rock mass. Predominant quartz-feldspar porphyry sills occur regularly throughout the body; crosscutting quartz porphyry dykes, diorite porphyry dykes and lamprophyre dykes are also common. Shearing and fracturing are pervasive throughout the ultramafic body with the zones commonly quartz-talc-carbonate altered.”
“Chromite occurs as disseminated grains, stringers and massive lenses. Disseminated chromite is ubiquitous; stringers of chromitite consisting of elongate trains of coarse crystals give the rock a "pebbly" texture with chromite forming 15 to 40 per cent of the rock. Pods of massive chromitite have been exposed in scattered workings across the serpentinite. The randomly located pods vary in size from 3 to 7 metres in length and 2 to 3 metres in width. Surface and underground development have shown that the chromite mineralization is structurally disrupted by a multitude of fractures and shears. Individual shears vary from 1 to 15 centimetres in width and can be grouped into zones up to 30 metres wide. Occasionally chromite is found to be concentrated along some of the shear planes. There is no specific orientation to the chromite mineralization but there has been some suggestion that it trends roughly northwest and dips subvertically. An adit and underground workings explored chromite lenses occurring in the hangingwall of a strong fault which strikes northeast and dips 50 degrees southeast. In 1918, about 725 tonnes of chromite ore, grading 38.5 per cent Cr2O3 was shipped from these workings.”
Giles Peatfield comments:
This is a somewhat unusual deposit, or better called deposit area, in that there are a number of small chromite lenses, from which there has been historical production, and a larger nickel-bearing zone which has been explored and has some very low-grade potential.
Regarding the production from the chromite lenses, Freeland (1919) wrote that “This group, including the Mastodon, Black Tail Fraction, Pan, Dominion Canyon, and Mammoth, is situated on Castle mountain at an elevation of 3,500 feet above sea-level and approximately 4,000 feet from the Canadian Pacific Railway bridge which crosses the Kettle river at Cascade. The outcrops of chromite were first located many years ago, but the low price of the mineral prohibited operations at that time. In 1917 the Stewart-Culvert Company, of Oroville, Wash., obtained a lease and bond for $5,000 on the property from Angus Cameron et al., of Laurier, Wash., and commenced development by stripping and sinking shallow shafts on the Mastodon claim, with the result that small lenses of chromite were uncovered, carrying from 30 to 50 per cent. Cr2O3. In 1918 the Stewart-Calvert Company graded half a mile of road from the claims to the end of a branch of the Deep Creek wagon-road, and commenced hauling chromite with teams to the Canadian Pacific Railway at Cascade, a distance of eight miles. From thence the ore was shipped to the Central States. The haulage costs were $7 a ton and railway freight approximately $17 a ton, with an excavation cost of $4.25 a ton. A total of 670 tons of chromite was shipped, averaging 38.5 per cent. Cr2O3.” Elsewhere in the Minister of Mine’s Annual Report for 1918, the tonnage shipped is given as ‘about 800 tons’, and the official records quoted on the British Columbia Minfile site are 799 tons, or 725 tonnes.
There has been no production from the nickel-bearing zone; nor does it seem likely that there will be. The British Columbia Minfile site lists an indicated resource, derived from a Statement of Material Facts 07/74, by Chromex Nickel Mining Ltd., of 354,676,100 tonnes grading 0.20% Ni. Grove and Johnson (1975) commented on this ‘resource’ as follows: “The Chromex report suggests that on the basis of the 1967-72 exploration a total of 391 million tons averaging 0.24% Nickel plus assorted by-products has been outlined. This assertion cannot be accepted or rejected without having the detailed calculations, drill logs, and analyses available for evaluation.”
As regards the characteristics of the mineralized material and possible methods of recovery, it seems relevant to quote Steiner (1977) at length as follows:
“It has been determined that the drilled-out portion of the ultrabasics carries about 5% magnetite and that about 45% of the total nickel present is in a solid solution directly associated with the magnetite. About 42% of the overall nickel content is in the form of, and associated with, sulphides and iron pyrites in the 5 to 80 micron range. Microprobe testing and examinations could not establish the form of the nickel balance.
Pentlandite is somewhat evenly distributed throughout the ultrabasics; in less altered dunite, which underlies the largest area, millerite predominates; and where more altered, heazelwoodite [sic] occurs.
Flotation tests, carried out on representative drill core rejects, in bulk and in the various Tyler mesh sizes, demonstrated that flotation is not a practical or economical method to be considered for concentration. It can be reasonably expected that advanced flotation practices can only effectively float that portion of the nickel sulphides from 50 microns up, with recovery of about 75 - 80% [of the sulfide-held Ni, not of the total Ni?].
Magnetic separation testing, carried out with laboratory Jones Wet Magnetic separators, has confirmed that in the 150 mesh Tyler sizing, a minimum of 80% of the magnetite could be concentrated with commercial units.
Chemical leaching tests, using ammonia in solution, at atmospheric pressure, indicate that nickel recovery, on a large scale operation is potentially possible. However, the economics of this method have not been sufficiently investigated, with regards to optimum particle size and heap versus tank methods. Ammonia can be synthesized very cheaply from natural gas. Thus, the close proximity of the natural gas pipe line enhances the value of the deposit.
Other methods of solvent extraction, ionic exchange concentration and metal recovery methods, researched, developed and presently being used by the writer, are also applicable to the recovery of nickel from the deposit described in this report.” Unfortunately, it is not clear where or how Mr. Steiner is in fact using these methods.
Grove and Johnson (1975) were asked “To examine and evaluate the geological, mineralogical and metallurgical data and processes submitted to Mr. John McMynn by Mr. M. Hretchka, Manager, Chromex Nickel Mines Ltd. Regarding the Castle Mountain Nickel deposit and the proposed means of beneficiation.”, concluding that “A large tonnage of low grade nickeliferous ultrabasic rock has been presented as a possible production venture using unproven metallurgical technology. The distribution of the nickeliferous mineralization has not been documented and the detailed mineralogy which must be known to discuss the metallurgy has also been omitted. The mineralization must at present be viewed as an unproven resource which could only become viable with the application of new or advanced technology.” Chromex had suggested some rather novel leaching method (see Steiner, 1977). Grove and Johnson (1975) pointed out that there were serious potential pollution problems with this method and cautioned against its use.
There has been some discussion regarding the possible presence of gold and platinum group elements in the deposit. Thomlinson (1920) reported on a small group of samples from the property; the results were mostly given as either ‘none’ or ‘trace’. A few samples gave results 0.01 to 0.06 Troy ounces per ton (0.34 to 2.06 grams per tonne) gold. Two samples gave results of 0.015 and 0.02 Troy ounces per ton platinum (0.51 to 0.69 grams per tonne). There are no reports of any better assays from samples from this deposit.
Comments on the Minerals Reported:
For details of the rock types mentioned in this section, refer to notes below in the ‘Rock types reported’ section.
Amphibole group: Dispirito et al. (1987) reported numerous occurrences of hornblende in various rock types, but there are no precise analytical data. The identity is regarded as most likely valid.
Arsenopyrite: Soux (1987) reported free particles of arsenopyrite in a polished section made from “Pan concentrate of sample CO 43 with ferromagnetic fraction removed.”
Calcite: Soux (1987) reported calcite in a polished section made from “Magnetic product at 0.5 Amp of panned concentrate from sample CG-9. Frantz [sic] isodynamic separator was used.” “Ilmenite is intimately intergrown with calcite displaying a mirmekitic texture. Calcite replaces ilmenite and magnetite.”
Chalcopyrite: Soux (1987) reported trace amounts of chalcopyrite in the “Ferromagnetic product of pan concentrate of sample CG-9.” “Pyrite is replaced by goethite and contains inclusions of chalcopyrite.” Chalcopyrite also occurs as free grains in a polished section of pan concentrate from sample CG-7.
Chlorite group: “Chlorite” was reported in several places by Dispirito et al. (1987), commonly as filling in vugs or amygdules, but they gave no further detail.
Chloritoid: Soux (1987) reported large amounts of chloritoid in several polished sections.
Chromite: Chromite is common on the property, and indeed was the subject of some production in the early years.
Chrysotile?: Dispirito et al. (1987), describing the serpentinized dunite unit, reported that “Crosscutting serpentinite veinlets are not common and traces of asbestos fibre were noted in only one locality.” I have assumed that this fibre is chrysotile, but there are no analytical details.
Feldspar group: Dispirito et al. (1987) reported numerous examples of “plagioclase” in various rock types, but there are no data to prove that these are plagioclase sensu stricto.
Garnet group: Dispirito et al. (1987), describing the agglomeratic andesite unit, reported that “Locally patches of skarn minerals were noted; these consist of garnet, deposed [diopside?], calcite, chalcopyrite and pyrite. They are thought to be metamorphosed limestone clasts.” They gave no analytical data regarding the garnet species.
Goethite: Soux (1987) reported several examples of polished sections where pyrite was partially replaced by goethite.
Heazlewoodite: The earliest reference to heazlewoodite was by Steiner (1972), who wrote that “Pentlandite is somewhat evenly distributed throughout the ultrabasics; in less altered dunite, which occupies the largest area, millerite predominates; and where more altered, heazelwoodite [sic] occurs.” Subsequently, Grove and Johnson (1975) wrote that “It may also be significant to record that a mineralogical study of the nickeliferous rock from the Mastadon [sic] by a Vancouver consultant indicated that Heazelwoodite [sic] (NiS - Ni = 72.13%, S = 22.16% +Fe) was the major Nickel [sic] bearing mineral.” Unfortunately, it is not possible to ascertain the name of the “Vancouver consultant”, and it is notable that Soux (1987), in examining polished sections, made no mention of heazlewoodite.
Ilmenite: See note above for calcite.
“Limonite”: Dispirito et al. (1987) note several examples of limonite as staining on surface exposures.
Magnetite: Magnetite is common on the property. See note above for calcite.
Marcasite: Soux (1987) reported marcasite in a polished section made from “Magnetic product at 0.5 Amp of panned concentrate from sample CG-7. Frantz [sic] isodynamic separator was used.”, writing that “Marcasite is intimately intergrown with pyrite and replaces it.”
Mica group: Dispirito et al. (1987) noted several examples of biotite in igneous rocks.
Millerite: Soux (1987), describing a “Pan concentrate of sample CG-43 with ferromagnetic fraction removed.”, noted several free particles of millerite. See also note above for heazlewoodite.
Native gold: Soux (1987) reported native gold in a polished section made from “Magnetic product at 0.5 Amp of panned concentrate from sample CG-7. Frantz [sic] isodynamic separator was used.”, writing that “Two particles of free gold and one intergrown with quartz were observed.”
Nickeline: Soux (1987), describing a “Pan concentrate of sample CG-12.” Wrote that “Niccolite [sic], chloritoid, and gangue are present mainly as free particles with no association to other minerals.”
Olivine: Steiner (1972) and Dispirito et al. (1987) wrote that olivine in altered dunite was invariably heavily serpentinized.
Pentlandite: See note above for heazlewoodite. Pentlandite was noted by Steiner (1972), by Grove and Johnson (1975), and by Steiner (1977), but interestingly not by Soux (1987).
Pyrite: See note above for marcasite.
Pyroxene group: Dispirito et al. (1987), described a grab sample as “Volcanic or metasediment, medium gray, finely crystalline. Skarn assemblage of minerals associated with fractures, minerals include garnet, diopside, calcite? Chalcopyrite [sic] and pyrite.” The identification of diopside was by field methods rather than formal analysis. They also mentioned augite as phenocrysts in a basalt porphyry dyke, again with no formal analytical identification.
Pyrrhotite: Soux (1987), describing a polished section of a pan concentrate of sample CG-12, noted pyrrhotite, in part replaced by goethite.
Quartz: This is common in some of the intrusive rocks on the property. See also note above for native gold.
Rutile: Soux (1987), describing a pan concentrate of sample CG-43 with the ferromagnetic fraction removed, noted that the gangue consisted mainly of quartz with inclusions of rutile and magnetite.
Talc: Hancock (1990), describing the massive serpentinzed dunite host of nickel mineralization, wrote that “Shearing and fracturing are pervasive throughout the body with the fractured zones commonly altered to quartz, talc and carbonate.”, but gave no further details.

Rock types reported:
The numerous rock types in the deposit and immediate surrounding area have been well described in the various reports on the property, most notably Dispirito et al. (1987) and Hancock (1990), among others. The names listed are based on field identification. Capsule descriptions are given in the comment section below.

Comments on the rock types Reported:
Agglomerate: Dispirito et al. (1987) wrote that “Andesites and andesitic agglomerates, as well as argillites and sandstones of the Jurassic Rossland Group surround the ultramafic body at Castle Mountain.”
Andesite: See note above for agglomerate.
Argillite: See note above for agglomerate.
Basalt: Dispirito et al. (1987) noted numerous examples of basalt dykes, and some basaltic flow rocks.
Breccia: Dispirito et al. (1987), describing the agglomeratic andesites, noted that “The rock type is characterized by a dark green fine grained groundmass which contains prismatic hornblende phenocrysts and quartz eyes as well as the distinctive breccia fragments which are comprised of the same material as the groundmass.”
Diorite: Dispirito et al. (1987) noted numerous examples of diorite dykes, and well as some larger intrusive bodies.
Dunite: Hancock (1990) wrote that “The hostrock to mineralization is a large block of massive serpentinized dunite of the Permo-Carboniferous Anarchist Group. The body extends approximately 2440 metres north from the international boundary and has a maximum width of 1220 metres. The rock is largely serpentinite but locally, unaltered dunite is present. Underground diamond drilling suggests that the body is interleaved with gabbro.”
Gabbro: See note above for dunite.
Granodiorite: Dispirito et al. (1987) noted that granodiorite of the Nelson Intrusions lies to the east of the mineralized area.
Lamprophyre?: Hancock (1990) mentioned lamprophyre dykes, referencing Steiner (1972); however, careful reading of Steiner’s paper shows no mention of lamprophyre. Such dykes are, however, shown on drill sections presented in Steiner (1977).
Limestone: Describing the agglomeratic andesite unit, Dispirito et al. (1987) wrote that “Near the western claim boundary this unit contains distinctive white limestone clasts . . . . Locally, patches of skarn minerals were noted; these consist of garnet, deposed [diopside?], calcite, chalcopyrite and pyrite They are thought to be metamorphosed limestone clasts.”
Peridotite: Grove and Johnson (1975) wrote that “The ultrabasic zone examined [by whom is not clear], including Dunite, Gabbro, and Peridotite and serpentinized, equivalents, . . . .”
Quartz-feldspar porphyry: Hancock (1990) wrote that “Crosscutting the serpentinite are dikes described as quartz feldspar porphyry, quartz porphyry, diorite and lamprophyre (Steiner, 1972) [sic – should be Steiner (1977)].”
Quartz-porphyry: See note above for quartz-feldspar porphyry.
Sandstone: See note above for agglomerate.
Serpentinite: See note above for dunite.
Skarn: See note above for limestone.

Other Databases

Link to British Columbia Minfile:	082ESE091

Other Regions, Features and Areas containing this locality

References