Canadian Rockhound: Gemstone Occurrences in B.C.

When one thinks of gems from British Columbia, jade and rhodonite are probably the first or only materials that come to mind. There are, however, many other gem species that have been found in B.C. Opaque gems and ornamental materials such as sodalite, dallasite, argillite and the quartz variety gems (e.g., agate, petrified wood and jasper) have been known for decades (Danner, 1976; Leaming, 1973). In addition, topaz, aquamarine, precious opal, star-sapphire, amethyst, peridot and hessonite have been discovered recently.

Because the geology of B.C. is very complex, it includes geological settings favourable for hosting a wide variety of gemstones. The potential for finding unusual or unique gem deposits is significant.

Volcanic rocks found throughout the province are host to occurrences of agate, amethyst, peridot and opal. Deposits of zircon, moonstone, sunstone, ruby and sapphire occur in similar rocks elsewhere (Johnston et al., 1991; Keller, 1990; Smith, 1988; Levinson and Cook, 1994), and hence could possibly be found in B.C.
High-grade metamorphic rocks are believed to be the source of some of the gems found in placer deposits in Sri Lanka (Keller, 1990). They are also host to many gem deposits in East Africa (Keller, 1992). Large areas of B.C. are underlain by similar high-grade metamorphic rocks; gemstones found to date include star-sapphire, zircon and red garnet. In addition, these rocks could potentially host deposits of sapphire, ruby, spinel, garnet in a variety of colours, cordierite (iolite), tourmaline, scapolite, kyanite and others.
B.C.'s abundant felsic plutonic rocks and associated granite pegmatites contain deposits of aquamarine, topaz, black tourmaline, red garnet, smoky and rose quartz, amethyst and phenacite. In addition, coloured gem tourmaline could be found in granite pegmatites.
Skarns, which are also abundant in B.C., are host to a variety of gems such as hessonite, vesuvianite, quartz and scheelite.

Previous publications dealing with B.C.'s gems are numerous and are cited throughout. Most of these deal with opaque gems and their localities; there are few descriptions of transparent gems. Consequently, this paper concentrates on transparent and less widely known gem materials. This article is based on a talk presented at the Canadian Gemmological Association's Gem Conference in Vancouver, 1995. A three-page table is added at the end of the article for quick reference.*

* Table is omitted in this edition -- Editor.

Amber

Amber has been reported from coal and lignite occurrences near Quesnel River, Nechako River (near Fort Fraser) and at Coalmont (Sabina, 1964). In addition, amber from the coal deposit at Hat Creek occurs as transparent, light yellow-orange grains weighing up to several grams.

Beryl (Emerald)

Emerald green beryl was discovered in 1989 in narrow quartz-calcite-pyrite veins that cut volcaniclastic rocks adjacent to a quartz monzonite intrusive on Red Mountain (near Stewart). Since then, several other specimens have been found in this area by geologists who were searching for gold. Microprobe analysis shows that this beryl is coloured green by trace amounts of vanadium (G. Robinson, pers. comm.). Although all of the crystals found so far have been small, fractured and opaque, their presence suggests that better quality emerald may occur elsewhere in the province.

Beryl (Aquamarine)

Aquamarine has been faceted from the following three locations: Mount Foster (near Bennett), the Horseranch Range (near McDame), and the B-Q Claims (near Passmore).

Aquamarine from Mount Foster (Figure 1) occurs in open spaces that represent formerly gas and/or fluid-filled voids in crystallizing granitic rocks (miarolitic cavities). Other gem-quality minerals occurring in these cavities include topaz, smoky quartz, phenacite, fluorite and microcline. The colour of the aquamarine ranges from colourless to light blue. The largest two stones cut to date weigh 8.63 and 2.99 carats, although the larger stone has many inclusions. Smaller stones that weigh under two carts are virtually flawless.

Aquamarine, Mount Foster
Fig 1. Faceted aquamarine gemstones from Mount Foster, near Bennett, B.C.

Beryl from the B-Q claims (Figure 2) was discovered in January 1993 during logging operations. Beryl, along with black tourmaline, smoky quartz and dark red garnet, occurs in miarolitic cavities in a granite pegmatite dyke that crosscuts the foliation of high-grade metamorphic gneiss. The largest aquamarine crystal discovered to date weighs 47.2 grams and measures 3.3 by 3.2 by 2.3 cm. Cut gems are a pale blue-green colour and tend to have numerous parallel planes of inclusions oriented perpendicular to the c-axis. The largest stone faceted so far weighs 5.26 carats.

Aquamarine, B-Q claim
Fig. 2 Aquamarine crystals from the B-Q Claims, near Passmore, B.C. The two large crystals are in their natural state. In between is a faceted aquamarine gem which weighs nearly 4 carats.

Beryl from the Horseranch Range occurs as euhedral crystals in granite pegmatite dykes that cross-cut high-grade metamorphic gneiss. Unlike the gem quality beryl from the B-Q claims and Mount Foster which occurs in miarolitic cavities, beryl from the Horseranch Range occurs embedded in the pegmatite host. Although most of the beryl is fractured and opaque, a few transparent fragments have been found. Cut stones are very pale blue to colourless; the largest weighs almost one carat.

The following five locations have produced aquamarine crystals which either have been cut or could be cut into tiny gems under 1/3 carat; Ash Mountain (near McDame), Skuckumchuck Creek (near Kimberley), Dunn Peak (near Barrier), Atlin area, and Prince George area.

Corundum (Star-Sapphire)

Star-sapphire (Figure 3) occurs on the Blu Starr claim (near Passmore) in the Slocan Valley, where claim owners discovered sapphire in a railroad cut that had been exposed since early this century. Until 1983, this corundum had gone unrecognized by geologists, prospectors and rockhounds. Anglo Swiss Inc., a Vancouver-based junior mining company, has acquired the claim and plans to do more exploration work on the property.

The sapphire occurs as opaque, black, brown or blue-grey hexagonal crystals in a high-grade metamorphic gneiss. Cut stones possess a sharp 6-rayed or rarely 12-rayed star when oriented correctly. Cabochons heavier than 11 carats have been cut.

Corundum also has been reported from river gravels in the Rossland area (Sabina 1964), but it is not known if this material is suitable for gems.

Star Sapphire, Blu Starr
Fig 3. Corundum crystal. The inset in the top left shows a cut star-sapphire. Star-sapphires are found on the Blu Starr claim near Passmore, B.C.

Garnet (Almandine)

Stepped trapezohedral crystals of deep red garnet up to 4 cm across occur along with aquamarine and tourmaline in the pegmatite at the B-Q claims near Passmore (Figure 4A). The largest crystals are not transparent throughout, but some of the smaller ones found loose in miarolitic cavities are. The largest stone cut to date weighs 4.04 carats. Larger stones, if cut, would likely be very dark and unattractive.

Small transparent crystals of dark red garnet up to 4 mm across occur within granite pegmatite in the Prince George region. I have seen transparent red garnets 5-6 mm across ostensibly from river gravels found along the Fraser River. Red garnet has also been found at several localities within high-grade gneiss near Kemano.

Garnet (Hessonite) and Vesuvianite

In 1992 hessonite (Figure 4B) was discovered within very narrow garnet-vesuvianite skarns adjacent to the beryl-bearing pegmatites of the Horseranch Range, near McDame. Some of this garnet possesses a rich orange colour, and when cut produces dazzling gems despite having some inclusions. The largest cut gem weighs 1.51 carats.

Some of the vesuvianite from this occurrence is transparent, and brown gems weighing 0.26 carat have been cut.

Garnet, B-Q claims
A.

Hessonite, Horseranch
B.

Fig 4. (A) Garnet from the B-Q Claims, Passmore. (B) Faceted hessonite (Garnet), from Horseranch Range, near McDame, B.C.

Jade and Rhodonite

B.C. is the world's largest producer of nephrite jade (Ward, 1996). While both jade and rhodonite are produced from many sites across the province, it is beyond the scope of this report to describe them. For information on jade and rhodonite refer to Danner (1976), Leaming (1966, 1973, 1978) and Ward (1996).

Malachite

Malachite is known to occur as a powdery weathering product on primary copper minerals from a number of sites throughout British Columbia (Traill, 1983), but only one site, the Lornex copper mine (near Logan Lake), has produced gem-grade material. Several small (up to 18 x 16 mm) attractive, banded green cabochons are known.

Opal

Opal is currently being produced near Vernon, by "Okanagan Opal". The opal occurs in seams and as vesicle fill in Tertiary volcanic rocks.

Yorke-Hardy (1994) describes the occurrence and nature of this opal, some of which has a strong and attractive play of colour (see Precious Opals in Canada in this issue). Colourful solid opal cabochons up to 3.5 carats have been cut (Yorke-Hardy, 1994). Because of the thin and irregular nature of the opal seams, some of this material is being fashioned as doublets and triplets.

Peridot and Pyroxene

Peridot is known from at least six localities in British Columbia. At five of these sites, rough peridot occurs in peridotite xenoliths contained within Tertiary and Quaternary basaltic volcanic rocks. At the sixth, Ruby Creek (near Atlin), peridot occurs as tiny, grass-green nodules in a placer gold mine. The nodules probably originated from Quaternary basalt that crops out immediately upstream from the gold mine. The Ruby Creek occurrence is of minor importance; the largest stone weighs only 0.16 carat.

Some of the volcanic rocks in the Dease Lake area contain volcanic bombs with abundant transparent pyroxene and olivine. All of the material found so far is small: cut peridot up to 0.60 carat and cut pyroxene up to 0.27 carat. The peridot is an attractive, medium yellow-green colour, while the pyroxene ranges in colour from rich dark green to muddy grey-green.

Peridot occurrences at Timothy Mountain (near Lac la Hache) and Big Timothy Mountains (near Hendrix Lake) have been described by Sabina (1964) and Leaming (1973). I have examined material only from Timothy Mountain - attractive grass-green gems weighing up to 2.13 carats have been cut.

In the Prince George area, an occurrence of Holocene volcanic rocks contains relatively abundant peridotite xenoliths. A very small number of these contain glassy olivine suitable for faceting. Most of these gems tend to be dark olive-green and are quite murky in appearance owing to abundant tiny mist-like inclusions. Several small gems, however, are light green and free of the inclusions. The largest cut stone I know of is 1.27 carats, although rough capable of producing a dark green stone of five carats or more exists.

Also occurring in these volcanic rocks are large (up to 5 cm across) anhedral crystals of very dark green, transparent orthopyroxene. These could be faceted into gems weighing two carats or more, but would be so dark they would appear black. A small cut stone weighing 0.19 carat appears dark green rather than black only when viewed under a strong light source.

Peridot from Lightning Peak (near Cherryville) (see Figure 5) has been mentioned by Leaming (1973), Sabina (1964) and Danner (1976). On Lightning Peak, peridotite xenoliths (some >30 cm across) are abundant in basaltic volcanic rocks. Most, however, contain sugary olivine not suitable for gem purposes. Very rarely, smaller glassy xenoliths contain gem-quality olivine. Peridot from Lightning Peak is apple green, and produces very attractive lively gems which represent the best quality among B.C. peridots. Stones as large as 3.52 carats have been cut. Inclusions in these gems are typical for peridot, consisting of "lily pads" and solid black inclusions (Cr-spinel?). Transparent, dark olive-green pyroxene is also present as subhedral phenocrysts within the volcanics. This pyroxene could yield very dark cut stones weighing more than a carat.

Peridot, Cherryville
Fig 5. Faceted peridot gemstones from Lightning Peak, near Cherryville, B.C. Peridot from Lightning Peak represent the best quality among B.C. peridots.

Quartz (Amethyst)

Amethyst has recently been discovered at several sites in the Slocan Valley (near Nelson). At one occurrence, the JLM Claim, colourless quartz, sphene and very rarely pale amethystine quartz crystals occur within fractures in high-grade gneiss. Pale purple gems that weigh up to 1.60 carats have been cut. Some of the colourless quartz displays magnificent Japan-law twinning and sceptred habits.

Lovely specimens of amethyst consisting of isolated centimeter-sized crystals upon a matrix of drusy quartz and barite are found on Lemon Creek (near Slocan). Cut stones range in colour from light to medium purple and weigh up to 1.5 carats.

Amethyst has been documented from near Penticton, and from the Kamloops area, near Monte Creek, Scottie Creek and Robbins Creek (Danner, 1976; Sabina, 1964; and Leaminig, 1973). I do not know how large this material is or if it is of gem quality. I have also seen rough from an undisclosed location near Slocan.

In the mineral collection of the M. Y. Williams Geological Museum at the University of British Columbia is a 10.19-ct, pale-coloured amethyst that is reported to have come from the Terrace area. This stone was donated in 1980 by the Burnaby Lapsmiths Club (J. Nagel, pers. comm.).

Rose Quartz

Rose quartz occurs in at least three pegmatites in B.C. Opaque, granular, medium pink quartz suitable only for cabochons occurs in a pegmatite along with beryl in the Horseranch Range, near McDame. On Mount Begbie, near Revelstoke, pale rose quartz occupies the core of a zoned pegmatite approximately one metre thick. Some of it is transparent enough to be faceted and could yield cut stones as large as 3-5 carats. The third rose quartz locality is near Slocan, from which pale bluish-pink stones up to 1.5 carats have been cut.

Colourless Quartz

Transparent, colourless quartz occurs in a wide variety of geological environments. B.C. localities are numerous and an attempt to document them all is beyond the scope of this article.

One noteworthy quartz occurrence is hosted in vugs in a copper-bearing skarn on Foley Mountain, near Agassiz (Wilson and Joyce, 1988). Some of the quartz contains a variety of attractive millimeter-sized mineral inclusion. Among these are a green acicular mineral (possibly actinolite), black hexagonal platelets (possibly hematite and/or biotite), irregular metallic grey sheet-like inclusions of pyrrhotite. Cut gems containing these inclusions are fascinating.

Smoky Quartz

Natural smoky quartz crystals found in B.C. most commonly occur in granite pegmatites and in miarolitic cavities in granitic rocks. I have documented four localities that have produced stones weighing over five carats. There are probably many more similar localities.

Most of the smoky quartz from Dunn Peak (near Barriere and the B-Q claims (near Passmore) tends to be fairly dark in colour, while material from Mount Foster (near Bennett) (see Figure 6) and Ash Mountain (near McDame) varies from light to very dark smoky. The largest cut stone of which I am aware comes from Mount Foster, is a light smoky colour, and weighs 80.75 carats.

Smoky quartz, Mount Foster
Fig 6. Faceted smoky quartz from Mount Foster, near Bennet, B.C. The smoky quartz from this locality varies from light to very dark smoky.

Topaz

East of Atlin, crystals of colourless topaz (Figure 7), smoky quartz, microcline, and beryl line the walls of miarolitic cavities that occur randomly throughout a small quartz monzonite stock. The largest stone cut to date weighs 4.01 carats, but if the largest crystal (65 carats) were cut, it would yield a clean stone weighing approximately 20 carats. After irradiation in a gamma-ray cell, a colourless piece of topaz from Atlin acquired a champagne colour.

Topaz, Atlin
Fig 7. Topaz from Atlin, B.C. Uncut and faceted examples shown.

Near Mount Foster, topaz crystals weighing up to 135 grams have been discovered in a similar geological environment. These topaz-bearing cavities are in close proximity to those that produced aquamarine crystals, but so far topaz and aquamarine have not been found in the same cavity. Topaz crystals found on surface are colourless, whereas those found below the surface are a champagne colour, suggesting that this colour is unstable, fading upon exposure to sunlight. The largest known crystal measures 6 by 5 by 4 cm, weighs 135 grams, and could yield champagne coloured gems as large as 5-10 carats. Only two stones have been cut so far, the heavier of which is 2.28 carats.

Topaz has been reported from elsewhere in the province, but it is not known if any of it is of gem quality (Sabina, 1964).

Tourmaline

Tourmaline occurs as jet-black crystals along with aquamarine on the B-Q claims (near Passmore). Some of these crystals are solid enough to be fashioned into attractive black cabochons with a high luster. This is exceptional considering that black tourmaline from most localities worldwide is highly fractured and will not hold together during cutting.

Zircon

High-grade gneisses on the Blu Starr claim contain small, light orange-brown grains of zircon, which have provided gems weighing up to 0.11 carat. A second occurrence is on Ruby Creek, near Atlin, where tiny zircons occur along with peridot and gold in a placer deposit.

Collector Gemstones

Many of the following materials are unsuitable for jewellery for reasons of low durability. However, most are sought after by collectors because of their rarity and great beauty when properly cut.

Barite

At the Rock Candy Mine near Grand Forks, transparent barite crystals coloured either grey or golden occur with purple and green fluorite in vugs within a fluorite vein that cross-cuts Tertiary syenite (Nagel, 1981). The largest faceted stone of which I am aware is a golden colour and weighs 58 carats.

Calcite

Transparent calcite is generally not rare, but I am aware of only two B.C. localities capable of producing calcite gemstones: the Boss Mountain Mine (near Hendrix Lake) and the Merry Widow mine (near Port McNeill). The only stone I have seen came from the Boss Mountain Mine. It weighs 5.58 carats and is a lovely amber colour. It is my understanding that other crystals found there might have cut slightly larger gems (A. Soregaroli, pers. comm.).

Dolomite and Magnesite

Cavities within the Mt. Brussilof magnesite mine (near Radium) contain magnificent crystals of magnesite, dolomite, quartz and a suite of very rare minerals. Transparent, colourless dolomite has been faceted, producing stones that weigh up to 21.66 carats. I have seen rough that could produce cut stones weighing 40 carats or more. Magnesite is colourless and tends to leave more inclusions than dolomite. Magnesite gems, with inclusions, have been cut, and weigh up to 10.58 carats.

Epidote

Crystals of epidote and quartz occur within Jurassic volcanic rocks on Vancouver Island, near Seward (J. Gorham, pers. comm.). Some of the epidote is transparent, and has been fashioned into dark green gems that weigh up to 0.12 carat.

Small transparent pieces of epidote also have been found in the Kemano area and if cut could yield stones as large as 0.1-0.2 carat.

Fluorite

Although fluorite is a relatively common mineral, large transparent pieces of rough are rare. Transparent fluorite comes from a number of places in B.C., but is probably best known from the Rock Candy Mine near Grand Forks. Gems tend to be grass green to blue green in colour, with a few inclusions, and can weigh as much as 27 carats.

Smaller fluorite gems come from the Vigilante Mine near Ainsworth (pale green, up to 2.77 carats), Ash Mountain near McDame (purple, up to 0.23 carat) and Mount Foster near Bennett (colourless, up to 1.40 carats).

Microcline

Sharp crystals of microcline with transparent, colourless microcline overgrowths, up to 4 mm thick were found in one of the miarolitic cavities at the Mount Foster aquamarine locality. Gems (with a few inclusions) up to 0.69 carat have been cut.

Natrolite

Sharp, colourless crystals of natrolite occur within the nepheline syenite of the Ice River plutonic complex near Field (Grice and Gault, 1981; Wight, 1992). Ice River natrolite has been fashioned into lively gems, the largest of which weighs 15.55 carats.

Phenacite

Phenacite, a rare beryllium silicate, has a hardness of 8 and lacks cleavage, so that it could be used safely in jewellery. Its lack of colour and extreme rarity, however, preclude its use in commonplace jewellery.

Small crystals of phenacite upon quartz crystals were found in one miarolitic cavity at the Mount Foster aquamarine locality. Colourless stones weighing up to 0.06 carat have been cut.

Scheelite

Etched crystals and fragments of scheelite were found in vugs associated with Japan-law twinned quartz crystals at Foley Mountain, near Agassiz (Wilson and Joyce, 1988). These vugs occur within a copper-bearing skarn. Cut scheelite ranges in colour from very light tan to colourless. The largest stone cut to date weighs 5.12 carats.

Sphene (Titanite)

Crystals of sphene with transparent sections have been found on the Itsall and JLM claim groups (both near Passmore). The sphene occurs with quartz and chlorite in open fractures that cross-cut high-grade gneiss. The sphene from both localities is usually dark brown in colour, and produces dark gems weighing over 3 carats when cut. Yellow-brown crystals occur very rarely on the Itsall claims; one of these was cut into a lively gem weighing 0.93 carat.

Summary

A wide variety of gem quality minerals is known from diverse geological environments in B.C. Deposits of jade, rhodonite and precious opal are currently being worked commercially, and occurrences of star-sapphire and aquamarine are the focus of on-going exploration. Coloured gemstone exploration in B.C. appears to be gaining interest.

B.C. possesses geology favourable for hosting more deposits of previously discovered gemstones, particularly peridot, precious opal and aquamarine, as well as for additional gemstones such as sunstone, sapphire and tourmaline. Tertiary and Quaternary volcanic rocks should be considered prime gemstone exploration targets, because they host occurrences of opal and peridot in B.C. and commercially viable deposits of sunstone, opal, and peridot in the western U.S.A. Deposits of sapphire and zircon are also possible in situ and in placer deposits derived from alkalic basaltic rocks. Granite pegmatites are abundant in B.C. and are favourable hosts for aquamarine, topaz, spodumene, spessartine, and coloured tourmaline. Gem-bearing pegmatites occur throughout the western cordillera in NWT, Yukon, Idaho, California, and Mexico, and B.C.'s potential for such pegmatites should also be considered high. B.C.'s high-grade metamorphic rocks, particularly those reaching upper amphibolite and granulite facies, are favorable targets for corundum, spinel, cordierite, garnet and other gem species.

To date, very little systematic exploration for transparent gemstones has taken place. Consequently, what has been documented here probably represents only a fraction of what could be discovered if more extensive exploration were undertaken. With B.C.'s large size and favourable geology, it seems overwhelmingly probable that significant new gemstone occurrences will be discovered.

References

Danner, W.R. (1976). Gem materials of British Columbia. Montana Bur. Mines and Geology, Spec. Pub. 74, p. 157-169.
Grice, J.D. and Gault, R.A. (1981). Edingtonite and natrolite from Ice River, British Columbia, Mineralogical Record, 12, p. 221-226.
Johnston, C.L., Gunter, M.E. and Knowles, C.R. (1991). Sunstone labradorite from the Ponderosa Mine, Oregon. Gems & Gemology, 27, p. 220-233.
Keller, P.C. (1990). Gemstones and their origins. Van Nostrand Reinhold, New York, 144 pp.
Keller, P.C. (1992). Gemstones of East Africa. Geoscience Press, Arizona, 144 pp.
Leaming, S.F. (1966). Rhodonite in British Columbia Canadian Rockhound, 10(1), p. 5-11.
Leaming, S.F. (1973). Rock and mineral collecting in British Columbia. Geological Survey of Canada, Paper 72-53, 138 pp.
Leaming, S.F. (1978). Jade in Canada. Geological Survey of Canada, Paper 78-19, 59 pp.
Levinson, A.A. and Cook, F.A. (1994) Gem corundum in alkali basalt: origin and occurrence Gems & Gemology, 30, p. 253-262.
Nagel, J. (1981). The Rock Candy Mine, British Columbia. Mineralogical Record, 12, p. 99-101.
Sabina, A.P. (1964). Rock and mineral collecting in Canada, Vol 1. Geological Survey of Canada, Misc. Report 8, 147 pp.
Smith, K.L. (1988). Opals from Opal Butte, Oregon. Gems & Gemology, 24, p. 229-236.
Traill, R.J. (1983). Catalogue of Canadian Minerals. Geological Survey of Canada Paper 80-18, 432 pp.
Wight, W. (1992). Check-list for rare gemstones-natrolite. Canadian Gemmologist, 13, p. 14-17.
Ward, F. (1996). Jade. Gem Book Publishers, Bethesda, Maryland, 64 pp.
Wilson, B.S. and Joyce, D.K. (1988). Japan-law twinned quartz crystals from Foley Mountain, British Columbia. Rocks and Minerals, 63, p. 459.
York-Hardy, R.W. (1994). Okanagan Opal. Canadian Gemmologist, 15, p. 43-45.

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The preceding article was first published in the Canadian Gemmologist, 1997, Volume 18, Number 3, Pages 74-86. Reprinted in the Canadian Rockhound with permission from the author and the editor of the Canadian Gemmologist. The Canadian Gemmologist is published by the Canadian Gemmological Association.