Hora, Z.D. (1997): Ultramafic-hosted Chrysotile Asbestos, in Geological Fieldwork 1997, British Columbia Ministry of Employment and Investment, Paper 1998-1, pages 24K-1 to 24K-4.
SYNONYMS: Quebec-type asbestos, serpentine-hosted asbestos, ultramafic-intrusion hosted asbestos.
COMMODITIES (BYPRODUCTS): Chrysotile asbestos (nephrite jade at Cassiar).
EXAMPLES (British Columbia (MINFILE #) - Canadian/International): Cassiar (104P 005), McDame (104P 084), Letain (104I 006), Ace (104K 025), Asbestos (082KNW075); Thetford Mines, Black Lake, Asbestos (Quebec, Canada), Belvidere Mine (Vermont, USA), Coalinga (California, USA), Cana Brava (Brazil), Pano Amiandes (Cyprus), Bazhenovo (Russia), Barraba (New South Wales, Australia), Barberton (Transvaal, South Africa).
CAPSULE DESCRIPTION: Chrysotile asbestos occurs as cross fibre and/or slip fibre stockworks, or as less common agglomerates of finely matted chrysotile fibre, in serpentinized ultramafic rocks. Serpentinites may be part of ophiolite sequence in orogenic belts or synvolcanic intrusions of Archean greenstone belts.
TECTONIC SETTINGS: Chrysotile deposits occur in accreted oceanic terranes, usually part of an ophiolite sequence, or within Alpine - type ultramafic rocks. They are also found in synvolcanic ultramafic intrusions of komatiitic affinity in Archean greenstone belts. In British Columbia the significant occurrences are found in the Slide Mountain, Cache Creek and Kootenay terranes.
DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: The serpentine host must have a nonfoliated texture and must be situated near a fault that is active during a change in the orientation of the regional stress from dip-slip to strike-slip fault motion. The serpentinite must be in the stability field of chrysotile when the change in orientation occurs. Subsequent deformation or temperature increase may destroy the fibre and result in a different mineralogy.
AGE OF MINERALIZATION: Precambrian to Tertiary. Deposits in British Columbia are considered Upper Cretaceous, deposits in southeastern Quebec formed during a relatively late stage of Taconic orogeny (late Ordovician to early Silurian), deposits in Ungava and Ontario are Precambrian. Chrysotile asbestos deposits are generally considered to be syntectonic and to form during the later stages of deformation.
HOST/ASSOCIATED ROCK TYPES: Serpentinite, dunite, peridotite, wehrlite, harzburgite, pyroxenite. Associated rocks are rodingite and steatite.
DEPOSIT FORM: In plan orebodies are equidimensional to somewhat oblate zones from 100 to 1000 metres in diameter within masses of serpentinized ultramafic rock. The vertical distribution of mineralized zones may be in the order of several hundreds of metres.
TEXTURE/STRUCTURE: Asbestos veins fill tension fractures in serpentinized ultramafic rocks or form a matrix of crushed and brecciated body of serpentinite. Usually, the orebodies grade from numerous stockwork veins in the centre to a lower number of crosscutting veins on the fringes. Cross-fibre veins, where the chrysotile fibres are at a high angle to the vein walls, are more abundant than slip fibre veins which parallel the vein walls. Individual veins are up to several metres in length and for the most part less than 1 cm thick, but may be up to 10 cm thick. In some deposits, powdery agglomerates of finely matted chrysotile form the matrix for blocks and fragments of serpentinite rock.
ORE MINERALOGY [Principal and subordinate]: Chrysotile.
GANGUE MINERALOGY [Principal and subordinate]: Gangue minerals in chrysotile veinlets are brucite and magnetite. Antigorite and lizardite may also be present in association with chrysotile veining.
ALTERATION MINERALOGY: Chrysotile and associated minerals are alteration products of ultramafic rocks. This process which starts as serpentinization, may be pervasive, but also fracture controlled and incomplete with serpentine surrounding peridotite (or other rock) cores. In relationship to changes in temperature, pressure and the fluid chemistry a variety of minerals from lizardite to talc and antigorite, or tremolite can be produced. Since the serpentinization of ultramafic rocks is frequently a multiple stage process, which can be either prograde or retrograde, many deposits contain minerals which do not form in the same stability field. Therefore, the alteration and gangue mineralogy are practically identical.
WEATHERING: In northern climates, only physical weathering of chrysotile and the serpentinized host rock takes place. Brucite and carbonates may be removed in solution and precipitated as hydromagnesite elsewhere. Lateritic soils should be expected in tropical climates.
ORE CONTROLS: Chrysotile veinlets are often best developed in massive serpentinite bodies with no schistose fabric. Chrysotile stability field; proximity to a fault that is active during change in the orientation of stress field; limited subsequent deformation and no subsequent medium to high grade metamorphism after the asbestos formation. Asbestos veins fill tension fractures in serpentinized ultramafic rocks or form a matrix of crushed and brecciated body of serpentinite.
GENETIC MODELS: Chrysotile asbestos deposits develop in nonfoliated, brittle ultramafic rocks under low grade metamorphic conditions with temperatures of 300 ± 50°C and water pressures less than 1 kbar. The chrysotile forms as the result of fluid flow accompanied by deformation where water gains access to partly or wholly serpentinized ultramafics along fault and shear zones.
ASSOCIATED DEPOSIT TYPES: Spatial association (but no genetic relationship) with podiform chromite deposits (M03) and jade (Q01) in ophiolitic sequences. Cyptocrystalline magnesite veins (I17), ultramafic-hosted talc-magnesite (M07) and anthophyllite asbestos deposits may be genetically related.
COMMENTS: Anthophyllite, a variety of amphibole, is another asbestiform mineral. Production of anthophyllite has been limited; Green Mountain mine in North Carolina is the only North American past producer.
GEOCHEMICAL SIGNATURE: None.
GEOPHYSICAL SIGNATURE: Magnetite, which is a product of both sepentinization and the formation of chrysotile, can produce well defined, magnetic anomalies. Gravity surveys can distinguish serpentinite from the more dense (~20%) peridotite.
OTHER EXPLORATION GUIDES: Asbestos fibres found in soils. Massive, brittle and unsheared ultramafic bodies which are partly or fully serpentinized in proximity to faults and shears.
TYPICAL GRADE AND TONNAGE: Total fibre content of commercial deposits is between 3 and 10%, the tonnage is between 500 000 to 150 million tons (in the asbestos industry fibre length is a critical parameter as well). In British Columbia, company reports indicate the Cassiar mine produced 31 Mt grading 7 to 10% fibre. There are however 25 Mt of tailings with 4.2% recoverable short fibre. Another 7.3 Mt geological reserves was left in the pit. The adjacent McDame deposit has measured reserves of 20 Mt @ 6.21% fibre and estimated geological reserves of 63 Mt. In the Yukon Clinton Creek produced 15 Mt @ 6.3% fibre. The following figures are from Duke (1996) and include past production plus reserves: Jeffrey, Quebec: 800 Mt @ 6% fibre, Bell-Wing-Beaver, Quebec: 250 Mt @ 6% fibre, British Canadian, Quebec: 150 Mt @ 6% fibre, Advocate, Newfoundland: 60 Mt @ 3% fibre. A relatively few deposits have been developed to mine agglomerates of finely matted chrysotile fibre which have much higher grades.
TYPICAL GRADE AND TONNAGE (continued): The very large Coalinga deposit in California has reported short fibre recoveries in the order of 35 to 74%. The Stragari mine in Serbia is recovering 50-60% fibre.
ECONOMIC LIMITATIONS: Fibre lengths may vary significantly within and between deposits; stockwork mineralization is typically more economically attractive if the proportion of longer fibres is higher. Typically, the fibre value starts at CDN$180/ton for the shortest grade and reaches CDN$1750 for the longest (Industrial Minerals, 1997).
END USES: Asbestos-cement products; filler in plastics; break lining and clutch facings; asbestos textiles; gaskets; acoustic and electric and heat insulation.
IMPORTANCE: Ultramafic-hosted chrysotile is the only source of asbestos in North America and considered the least hazardous of commercial asbestos minerals. During the 1980s the market for asbestos in many countries declined due to health hazard concerns.
Cogulu, E. and Laurent R. (1984): Mineralogical and Chemical Variations in Chrysotile Veins and Peridotite Host - Rocks from the Asbestos Belt of Southern Quebec; Canadian Mineralogist, volume 22, pages, 173-183.
Duke, J.M. (1995): Ultramafic-hosted Asbestos; in Geology of Canadian Mineral Deposit Types, Eckstrand, O.R., Sinclair, W.D. and Thorpe, R.I., Editors, Geological Survey of Canada, Geology of Canada, Number 8, pages 263-268.
Harvey-Kelly, F.E.L. (1995): Asbestos Occurrences in British Columbia; British Columbia Ministry of Employment and Investment, Open File 1995 - 25, 102 pages.
Hemley, J.J., Montoya, J.W., Christ, C.L. and Hosletter, P.B. (1977): Mineral Eqilibria in the MgO-SiO2-H2O System: I Talc-Chrysotile-Forsterite-Brucite Stability Relations; American Journal of Science, Volume 277, pages 322-351.
Hemley, J.J., Montoya, J.W., Shaw, D.R. and Luce, R.W. (1977): Mineral Equilibria in the Mgo-SiO2-H2O System: II Talc-Antigorite-Forsterite-Anthophyllite-Enstatite Stability Relations and Some Geological Implications in the System; American Journal of Science, Volume 277, pages 353-383.
Hewett, F.G. (1984): Cassiar Asbestos Mine, Cassiar, British Columbia; in The Geology of Industrial Minerals of Canada, Guillet, G.R. and Martin W., Editors, Canadian Institute of Mining and Metallurgy, Montreal, Quebec, pages 258-262.
Mumpton, F.A. and Thompson, C.S. (1975): Mineralogy and Origin of the Coalinga Asbestos Deposit; Clays and Clay Minerals, Volume 23, pages 131-143.
Nelson, J.L. and Bradford, J.A., (1989): Geology and Mineral Deposits of the Cassiar and McDame Map Areas, British Columbia; B.C. Ministry of Energy, Mines and Petroleum Resources, Paper 1989-1, pages 323-338.
O'Hanley, D.S. (1987): The Origin of the Chrysotile Asbestos Veins in Southeastern Quebec; Canadian Journal of Earth Sciences, Volume 24, pages 1-9.
O'Hanley, D.S. (1988): The Origin of the Alpine Peridotite-Hosted, Cross Fibre, Chrysotile Asbestos Deposits; Economic Geology, Volume 83, pages 256-265
O'Hanley, D.S. (1991): Fault Related Phenomena Associated With Hydration and Serpentine Recrystallization During Serpentinization; Canadian Mineralogist, Volume 29, pages 21-35.
O'Hanley, D.S. (1992): Solution to the Volume Problem in Serpentinization; Geology, Volume 20, pages 705-708.
O'Hanley, D.S., Chernosky, J.U. Jr. and Wicks, F.J. (1989): The Stability of Lizardite and Chrysotile; Canadian Mineralogist, Volume 27, pages 483-493.
O'Hanley, D.S., and Offler, R. (1992): Characterization of Multiple Serpentinization, Woodsreef, New South Wales; Canadian Mineralogist, Volume 30, pages 1113-1126.
O' Hanley, D.S., Schandl, E.S. and Wicks, F.J. (1992): The Origin of Rodingites from Cassiar, British Columbia, and their use to Estimate T and P(H2O) during Serpentinization; Geochimica et Cosmochimica Acta, Volume 56, pages 97-108.
Page, N.J. (1986): Descriptive Model of Serpentine-Hosted Asbestos; in Mineral Deposit Models, Cox, D.P. and Singer, D.A., Editors, U.S. Geological Survey, Bulletin 1693, pages 46-48.
Riordan, P.H., Editor (1981): Geology of Asbestos Deposits; American Institute of Mining and Metallurgical Engineers, New York, 118 Pages.
Virta, R.L. and Mann, E.L. (1994): Asbestos; in Industrial Minerals and Rocks, Carr, D.D., Editor, Society for Mining, Metallurgy and Exploration, Inc., Littleton, Colorado, pages 97-124.
Wicks, F.J. (1984): Deformation Histories as Recorded by Serpentinites. I. Deformation Prior to Serpentinization; Canadian Mineralogist, Volume 22, pages 185-195.
Wicks, F.J. (1984): Deformation Histories as Recorded by Serpentinites. II Deformation during the after Serpentinization; Canadian Mineralogist, Volume 22, pages 197-203.
Wicks, F.J. (1984): Deformation Histories as Recorded by Serpentinites: III. Fracture Patterns Development Prior to Serpentinization; Canadian Mineralogist, Volume 22, pages 205-209.
Wicks, F.J. and O'Hanley, D.S. (1988): Serpentine Minerals: Structures and Petrology; in Hydrous Phyllosilicates, Bailey, S.W., Editor, Reviews in Mineralogy, Mineralogical Society of America, Volume 19, pages 91-167.
Wicks, F.J. and Whittaker, E.J.W. (1977): Serpentine Textures and Serpentinization; Canadian Mineralogist, Volume 15, pages 459-488.
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by G.J. Simandl1 and D. Ogden2
1British Columbia Geological Survey, Victoria, B.C., Canada
2Omya Inc., Proctor, Vermont, USA.
Simandl, G.J. and Ogden, D. (1999): Ultramafic-hosted Talc-Magensite; in Selected British Columbia Mineral Deposit Profiles, Volume 3, Industrial Minerals, G.J. Simandl, Z.D. Hora and D.V. Lefebure, Editors, British Columbia Ministry of Energy and Mines.
SYNONYMS: Ultramafic-hosted magnesite/talc deposits, serpentinite-hosted talc.
COMMODITIES (BYPRODUCTS): Talc and magnesite (rarely nickel).
EXAMPLES (British Columbia - Canada/International): Rawhide (092ISW051), South Talc Lake Deposit (092ISW064), Gisby (092HNW002), J&J (092HNW047); Deloro magnesite-talc deposit (Ontario, Canada), Luzcan mine of Thetford township and Van Reet mine, Ponton township, (Quebec, Canada), Windham (Vermont, USA), Lahnaslampi mine (Finland).
CAPSULE DESCRIPTION: Ultramafic-hosted talc-carbonate deposits are located either along regional faults cutting ultramafic rocks or at contacts between ultramafic rocks and siliceous country rock. The ultramafic host rock is typically, but not necessarily of ophiolitic affiliation. Deposits related to regional fault systems cutting ultramafic host rock are commonly magnesite-rich. Deposits located within sheets of serpentinized peridotite, found along the periphery of ultramafic intrusions or near the borders of tectonically transported peridotite slices are typically talc-rich.
TECTONIC SETTINGS: These deposits are found typically in obducted, accreted or otherwise tectonically transported seafloor and ophiolite slices or lenses and in ancient greenstone belts. However, serpentinized ultramafic intrusions regardless of tectonic environment should be considered as a favourable host.
DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: Faulted and metasomatized ultramafic rocks and tectonically-transported serpentinites in contact with siliceous rocks; the deposits are younger than the ultramafic protolith.
AGE OF MINERALIZATION: Precambrian or younger. Post or syn-tectonic.
HOST/ASSOCIATED ROCK TYPES: Talc-carbonate-bearing serpentinite, steatite, talc schist, talc-magnesite-dolomite schist that may contain serpentine/chlorite schist, dunite and serpentinite with associated, commonly at least partially serpentinized gabbro, pyroxenite, harzburgite and websterite or meta-komatiiate sills and lavas. Because many of the talc-bearing rocks are allochthonous there is a wide variety of associated lithologies.
DEPOSIT FORM: The fault-related deposits are irregular bodies having their largest dimensions parallel to the faults. In some cases only the hanging wall of the faults is mineralized. Small ultramafic lenses are commonly entirely serpentinized, while larger lenses consist of peridotite cores surrounded by serpentinite. Steatite and talc schists are most likely to be found at the contact of the serpentinite with siliceous rocks, however they may also form tabular or irregular bodies.
TEXTURE/STRUCTURE: Ore is massive or schistose, talc is fine to coarse flakes.
ORE MINERALOGY [Principal and subordinate]: Talc, magnesite, rarely Ni-bearing minerals, such as pyrrhotite, pentlandite, melnikovite and bravoite.
GANGUE MINERALOGY [Principal and subordinate]: Dolomite, serpentine, chlorite, ankerite (Fe-rich dolomite), breunerite (Fe-rich magnesite), olivine, magnetite, quartz, pyrite, asbestos, rutile, calcite, chrome-mica.
ALTERATION MINERALOGY: N/A. Talc and magnesite are alteration (metasomatic) products.
ORE CONTROLS: Primary control is the presence of a magnesium-rich silicate rock to act as a source of magnesium. Permeable fault zones or serpentinite-siliceous rock contacts control the sites of talc formation.
GENETIC MODELS: These deposits are commonly magnesite-rich and are linked to CO2 and H2O metasomatism (carbonatization and hydration) of ultramafic rocks by fluids following faults and contacts. The following reactions 1, 2a and 2b and 3 illustrate the concept:
1) 18 serpentine + magnetite + 30 CO2 à 9 Talc + 30 breunerite + 27 H2O + 1/2 O2
2a) 2 olivine + 1 CO2 + H2O à 1serpentine + 1 magnesite
2b) 2 serpentine + 3 CO2 à 3 magnesite + 1 talc + 3 H2O
3) 1 serpentine + 2 quartz à 1 talc + H2O
The talc formed during metasomatism and/or regional metamorphism. Silica required for talc formation was derived from the country rock.
ASSOCIATED DEPOSIT TYPES: Chrysotile deposits (M06), magnesite veins and stockworks (I17) podiform chromite deposits (M03), famous "verde antique" dimension stone deposits and possibly, nephrite (Q01) and listwanite-related gold (I01) deposits.
COMMENTS: A similar origin has been proposed to explain the breunerite-talc assemblage in the Motherlode gold district in California. The hydration / carbonitization of ultramafic rocks differs from listwanite only by the lack of potassium metasomatism. Carbonitization products in some cases represent intermediate stage in formation of true listwanites (Halls and Zhao, 1995).
GEOCHEMICAL SIGNATURE: Talc is a relatively soft but inert mineral in most environments. It may be enriched in soils overlying talc-bearing zones. Ultramafic rocks are characterized by Mg, Fe, Cr, Ni, Co suite of elements. Under normal conditions, this signature may be reflected in soils, stream or lake sediments and in overburden.
GEOPHYSICAL SIGNATURE: Unserpentinized portions of the host ultramafic rocks commonly correspond to strong airborne and ground magnetic anomalies. Talc-rich zones corresponds commonly to airborne electromagnetic lows.
OTHER EXPLORATION GUIDES: Talc-rich zones coincide commonly with topographic lows and can be covered by lakes and swamps. Some deposits exhibit zoning from siliceous country rock (quartz-sericite-chlorite schist) into chlorite schist, then into the talc-bearing rocks (talc-carbonate-serpentine-bearing schists, steatite) with a serpentinite core. Deposits are located within sheets of serpentinized peridotite, along the periphery of ultramafic intrusions or thin, tectonically transported slivers, slices or lenses of peridotite. The ultramafic rocks and major faults may be detected by modern remote sensing technologies.
TYPICAL GRADE AND TONNAGE: The grade and size of these deposits is highly variable. The Deloro deposit consists of 54% magnesite and 28% talc. It is about 1800 metres in length, 300 metres wide and has been drilled to the depth of 120 metres. An underground talc mine of Cyprus Minerals Co., located at Windham, Vermont consists of lenses exceeding 230 metres in length and 100 metres in width. The Lahnaslampi orebody in Finland contains over 30 million tonnes exceeding 50% talc and 0.1 to 0.2% Ni. Nickel concentrate is produced from the tailings at Lahnaslampi. There is the opportunity that talc could be a by-product from listwanite-hosted gold mines. The metallurgical tests suggest that in some cases, it is technically possible to produce a magnesite concentrate as talc by-product. However, economics of the process and exact technical specifications of the potential product are not well documented.
ECONOMIC LIMITATIONS: Steatite contains more than 90% talc. Flotation is required for most deposits to produce high-quality fillers for paint and plastic applications, the ceramic and pharmaceutical industries, and crayons. Underground mining is economically feasible to depths exceeding 300 metres. FeO content of magnesite from these deposits varies from 0.5 to 7%. Research is underway to chemically reduce iron content of magnesite, in order to achieve refractory grade magnesia products. Current restrictions placed on asbestos-bearing materials makes the ores from asbestos-free deposits easier to market.
END USES: Talc from these deposits is commonly used in paper, ceramic, paint, plastic, roofing and electrical applications. Massive talc and soapstone are used in electric insulation, refractory applications, as carving stone or as raw material for laboratory sinks.
IMPORTANCE: Ultramafic-hosted talc-magnesite deposits are important source of talc.
Andrews, P.R.A. (1994): The Beneficiation of Canadian Talc and Pyrophyllite Ores: a Review of Processing Studies at CANMET; Canadian Institute of Mining and Metallurgy, Bulletin, Volume 87, Number 984, pages 64-68.
Anonymous (1993): The Economics of Talc and Pyrophyllite; 7th Edition; Roskill Information Services Ltd.,
London, England, 266 pages.
Bates, R.I. (1969): Geology of Industrial Rocks and Minerals; Dover Publications Inc., New York, 459 pages.
Blount, A.M. and Spohn, T. (1982): Mineralogy of Residual Soils Overlying a Talc Deposit; Mineralium Deposita, Volume 17, pages 17-21.
Griffis, A.T. and Griffis, R.J. (1984): Magnesite-talc Deposit in Southern Deloro Township, Ontario; in: The Geology of Industrial Minerals in Canada, Guillet, G.R. and Martin, W., Editors, Canadian Institute of Mining, Metallurgy and Petroleum, pages 122-124.
Halls, C. and Zhao, R. (1995): Listvenite and related rocks: Perspectives on Terminology and Mineralogy with Rerence to an Occurrence at Cregganbaun, C. Mayo, Republic of Ireland. Mineralium Deposita, Volume 30, pages 303-313.
Harris, M. and G.N. Ionides (1994): Update of a Market Study for Talc; B.C. Ministry of Energy, Mines and Petroleum Resources, Geological Survey Branch Open File 1994-24, 44 pages.
Hébert, Y. (1987): Géologie des Gîtes de Talc de l’Estrie; Ministère des Ressources naturelles du Québec, Exploration au Québec, DV pf-25, pages 7-11.
Isokangas, P. (1978): Finland; in Mineral Deposits of Europe, Volume 1, Northwest Europe; Bowie, S.H.U., Kwalheim, A. and Haslam, H.W., Editors, Institution of Mining and Metallurgy, The Mineralogical Society; pages 39-93.
MacLean, M. (1988): Talc and Pyrophyllite in British Columbia; British Columbia Ministry of Energy, Mines and Petroleum Resources, Open File 1988-19, 108 pages.
Morgan, J.H. (1957): Talc and Soapstone Deposits of Baker Talc Limited; in The Geology of Canadian Industrial Mineral Deposits, Proceedings of the 6th Commonwealth Mining and Metallurgical Congress, Canadian Institute of
Mining and Metallurgy, pages 235-239.
Piniazkiewicz, J., McCarthy, E.F. and Genco, N.A. (1994): Talc; in Industrial Minerals and Rocks, 6th Edition, Carr, D.D., Editor, Society for Mining, Metallurgy, and Exploration, Inc., Littleton, Colorado, pages 1049-1069.
Sims, C. (1997): Talc Markets - A World of Regional Diversity; Industrial Minerals, May 1997, pages 39-51.
Spence, H.S. (1940): Talc, Steatite and Soapstone; Pyrophyllite; Canada Department of Mines and Resources, Number 803, 146 pages.
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by G.J. Simandl1, T. Birkett2 and S. Paradis3
1British Columbia Geological Survey, Victoria, B.C., Canada
2SOQUEM, Québec City, Québec, Canada
3Geological Survey of Canada, Sidney, B.C., Canada
Simandl, G.J.; Birkett, T. and Paradis, S. (1999): Vermiculite; in Selected British Columbia Mineral Deposit Profiles, Volume 3, Industrial Minerals, G.J. Simandl, Z.D. Hora and D.V. Lefebure, Editors, British Columbia Ministry of Energy and Mines.
COMMODITY (BYPRODUCT): Vermiculite (± apatite).
EXAMPLES (British Columbia - Canadian/International): Joseph Lake (093K 100), Sowchea Creek vermiculite (093K 101); Libby (Montana, USA), Waldrop Pit, Enoreeq area (South Carolina, USA), Blue Ridge deposits (North Carolina, USA), Palabora deposit (Republic of South Africa).
CAPSULE DESCRIPTION: These near surface vermiculite deposits may also contain recoverable apatite. World-class vermiculite deposits occur mainly within zoned ultramafic complexes or carbonatites. Smaller or lower grade deposits are hosted by dunites, unzoned pyroxenites, peridotites or other mafic rocks cut by pegmatites and syenitic or granitic rocks.
TECTONIC SETTING: Deposits hosted by carbonatites and ultramafic complexes are commonly related to rifting within the continental platform or marginal to the platform in geosynclinal settings.
DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: Mafic and ulramafic igneous or metamorphic rocks exposed to intense weathering and/or supergene, low temperature alteration.
AGE OF MINERALIZATION: Most deposits are derived from rocks of Precambrian to Jurassic age. Deposits post-date emplacement of intrusive host and regional metamorphism. Their age may be linked to periods of intense weathering which show up as erosional surfaces, paleo-regolith or unconformities.
HOST/ASSOCIATED ROCK TYPES: For major deposits the main hosts are biotitites, pyroxenites, phlogopite-serpentine rock, phlogopite-diopside±apatite rock and peridotites. Associated rock types are magnetite pyroxenites, foscorite, carbonatites, and variety of serpentinites that are in contact with alkali granites, syenites, fenites or pegmatites.
For smaller or marginal deposits located in highly metamorphosed settings the typical host rocks are amphibolite and biotite schists in contact with pyroxenites or peridotite dykes or lenses, sometimes cut by pegmatites.
DEPOSIT FORM: Variable shapes, a function of the geometry of the favourable protolith and zone of fluid access. Semi-circular surface exposures found with deposits associated with ultramafic zoned complexes or carbonatites, usually near the core of the intrusion. Lenticular or planar deposits of vermiculite are found along serpetinized contacts between ultramafic rocks and metamorphic country rocks. Individual lenses may be up to 7 metres thick and 30 metres in length. Smaller lenses may be found along fractures and the margins of pegmatites crosscutting ultramafic lenses within high grade metamorphic terranes. The degree of alteration and vermiculite grade generally diminishes with depth. Vermiculite grades of economic interest rarely extend more than 40 metres below the surface.
TEXTURE/STRUCTURE: Vermiculite may be fine-grained or form books up to 20 cm across ("pegmatitic"). Serpentine can form pseudomorphs after olivine.
ORE MINERALOGY [Principal and subordinate]: Vermiculite ± hydrobiotite; ± apatite.
GANGUE MINERALOGY [Principal and subordinate]: Biotite, chlorite, phlogopite, clinopyroxene, tremolite, augite, olivine, hornblende, serpentine. In some of the deposits acicular tremolite and asbestos are reported.
ALTERATION MINERALOGY: Vermiculite is probably, in part, a low temperature alteration product of biotite.
WEATHERING: At least in some deposits, weathering is believed to play an important role in transformation of mafic minerals, mainly biotite, into vermiculite. Weathering also weakens the ore making blasting unnecessary; in extreme case it results in formation of semi- or unconsolidated, residual vermiculite deposits.
ORE CONTROLS: 1) The existence of a suitable protore, commonly dunite or pyroxenite rock containing abundant biotite or phlogopite which may be of late magmatic to hydrothermal origin. 2) Deposits occur mainly at surface or at shallow depths, but in some cases as a paleoregolith along an unconformity. 3) Vermiculite develops from periods of intense weathering or near surface alteration. 4) The maximum depth extent of the ore zone depends on the permeability, porosity, jointing and fracture system orientation which permit the circulation of meteoric fluids.
GENETIC MODELS: Vermiculite can form from variety of mafic minerals, but biotite or Fe-bearing phlogopite are deemed key components of the protore within economic deposits.
Most of the early studies suggest that vermiculite is a late magmatic, low temperature hydrothermal or deuteric alteration product. Currently, the most accepted hypothesis is that vermiculite forms by supergene alteration due to the combined effect of weathering and circulation of meteoric fluids.
ASSOCIATED DEPOSIT TYPES: Palabora-type complexes or other carbonatites (N01) contain vermiculite mineralization. Ultramafic-hosted asbestos (M06), ultramafic-hosted talc-magnesite (M07), nepheline-syenite (R13), Ni and platinoid showings, some sapphire deposits associated with so called "crossing line" pegmatites and placer platinoid deposits (C01 and C02) may be associated with the same ultramafic or mafic complexes as vermiculite deposits.
COMMENTS: In British Columbia, vermiculite is reported from surface exposures of granite, granodiorite and quartz diorite at the Joseph Lake and Sowchea Creek showings in the Fort Fraser/Fort St. James area (White, 1990). Low grades in combination with the preliminary metallurgical studies indicate that these occurrences are probably subeconomic (Morin and Lamothe, 1991). Similar age, or older, mafic or ultramafic rocks in this region may contain coarse-grained vermiculite in economic concentrations.
GEOCHEMICAL SIGNATURE: Vermiculite in soil.
GEOPHYSICAL SIGNATURE: Ultramafic rocks that host large vermiculite deposits are commonly characterized by strong magnetic anomalies detectable by airborne surveys. Since vermiculite is an alteration product of ultramafic rocks, vermiculite zones are expected to have a negative magnetic signature. However, no detailed geophysical case histories are documented.
OTHER EXPLORATION GUIDES: The largest commercial deposits usually form in the cores of ultramafic or alkaline complexes (mainly pyroxenites and carbonatites). The roof portions of these complexes have the best potential because they may be biotite-rich. Deposits derived from biotite schist are typically much smaller. All these deposits are commonly associated with some sort of alkali activity, be it only alkali granite or syenite dykes. Vermiculite deposits may have a negative topographic relief. A portable torch may be used to identify vermiculite in hand specimen since it exfoliates and forms golden flakes when heated. Therefore, an excellent time to prospect for vermiculite is after forest fires. Fenitization halos associated with alkaline ultramafic complexes and carbonatites increases the size of the exploration target. Horizons of intense paleo-weathering that exposed mica-bearing ultramafic rocks are particularly favourable.
TYPICAL GRADE AND TONNAGE: Deposits with over 35% vermiculite (<65 mesh) are considered high grade. Most of the economic deposits contain from few hundred thousand to several million tonnes; although clusters of small, high-grade, biotite schist-hosted deposits ranging from 20 000 to 50 000 tonnes were mined in South Carolina.
ECONOMIC LIMITATIONS: World vermiculite production in 1995 was estimated at 480 000 tonnes. Major producing countries were South Africa (222 000 tonnes, mainly from Palabora), USA (170 000 tonnes) and Brazil (41 500 tonnes). In the early half of 1996 the prices of South African vermiculite imported to USA varied from US$127 to 209 per tonne. Deposits must be large enough to be amenable to open pit mechanized mining. Large flake size (more than 65 mesh) is preferred. Both wet and dry concentrating methods are in use. Crude vermiculite is moved in bulk to exfoliation plants that are typically located near the markets. In commercial plants expansion of 8 to 15 times the original volume is typical, but up to 20 times may be achieved. The higher the degree of expansion (without decrepitation) the better the concentrate. The concentrates from those deposits where vermiculite coexists with asbestos or "asbestiform" tremolite are difficult to market because of the concerns over related health risks.
END USES: Agriculture 40%, insulation 23%, light weight concrete aggregate 19%, plaster and premixes 13%, other 5% (USA statistics). Other applications include carrier substrate for predatory mites in pest extermination, additive to fish feed, removal of heavy metals from soils and absorbent in poultry litter.
IMPORTANCE: Some vermiculite is derived from laterite-type deposits. Vermiculite may be substituted in concrete applications by expanded perlite or by expanded shale. Recently the use of vermiculite in cement compounds has reduced due to substitution by polystyrene. In agricultural applications it may be substituted by peat, perlite, sawdust, bark, etc. In ion exchange applications it may be substituted by zeolites.
Anonymous (1991): The Economics of Vermiculite, 6th edition, Roskill Information Services Ltd. London, 152 pages.
Anonymous (1997): Vermiculite; Metals and Minerals Annual Review, Mining Journal Limited, pages 95-96.
Bates, R.I. (1969): Geology of Industrial Rocks and Minerals; Dover Publications Inc., New York, 459 pages.
Boettcher, A.L. (1967): The Rainy Creek Alkaline-ultramafic Igneous Complex near Libby, Montana; Journal of Geology, Volume 75, pages 526-553.
Bush, A.L. (1968): Lightweight Aggregates; in Mineral Resources of the Appalachian Region, U.S. Geological Survey, Professional Paper 580, pages 210-224.
Bush, A.L. (1976): Vermiculite in United States; 11th Industrial Minerals Forum, Montana Bureau of Mines, Special
Publication 74, pages 146-155.
Hagner, A.F. (1944): Wyoming Vermiculite Deposits; Geological Survey of Wyoming, Bulletin 34, 47 pages.
Hindman, J.R. (1994): Vermiculite; in Industrial Minerals and Rocks, D.D. Carr, Editor, 6th Edition, Society for
Mining, Metallurgy, and Exploration, Inc., Littleton, Colorado, pages 1103-1111.
Morin, L. and Lamothe, J.M. (1991): Testing on Perlite and Vermiculite Samples from British Columbia; B.C. Ministry of Energy, Mines and Petroleum Resources, Geological Fieldwork 1989, Paper 1990-1, pages 265-268.
Palabora Geological and Mineralogical Staff (1976): The Geology and the Economic Deposits of Copper, Iron, and Vermiculite in the Palabora Igneous Complex: A Brief Review; Economic Geology, Volume 71, pages 177-192.
White, G.V. (1990): Perlite and Vermiculite Occurrences in British Columbia; B.C. Ministry of Energy, Mines and Petroleum Resources, Geological Fieldwork 1989, Paper 1990-1, pages 481-268.
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* Note: All BC deposit profile #s with an asterisk have no completed deposit profile. USGS deposit model #s with an asterisk had no published model in the late 1990s.
Examples of Ultramafic/Mafic Deposits
|BC Profile #
||B.C. Examples |
||Noril'sk (Russia), Duluth (Minnesota)
||Lynn Lake (Manitoba), Kluane (Yukon)
||Giant Mascot, Nickel Mountain |
||Josephine ophiolite (Oregon), Coto (Philippines), Elazig (Turkey)
||Castle Mountain, Scottie Creek |
||Methuen, Unfravile, Matthews-Chaffrey, Kingston Harbour (Ontario, Canada), Lac-du-Pin-Rouge, Lac Tio, Magpie (Quebec, Canada); Sanford Lake (New York, USA); Tellnes, Egersund (Norway); Smaalands-Taberg, Ulvno (Sweden)
||Red Mountain, Goodnews Bay (Alaska), Tin Cup Peak (Oregon)
||Tulameen Complex |
||Thetford Mines, Black Lake, Asbestos (Québec, Canada); Belvidere Mine (Vermont, USA), Coalinga (California, USA); Cana Brava (Brazil); Pano Amiandes (Cyprus); Bazhenovo (Russia); Barraba (New South Wales, Australia); Barberton (Transvaal, South Africa)
||Cassiar, McDame, Letain, Ace, Asbestos |
||Thetford & Magog (Québec), Deloro (Ontario)
||- - |
||Fort Fraser area |