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by G.J. Simandl1, T. Birkett2 and S. Paradis3

Ref: vermiculita, apatita, carbonatitos, ultra-máficas, complexos, intrusiva

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, Sowchea Creek vermiculite ; 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 contain vermiculite mineralization. Ultramafic-hosted asbestos, ultramafic-hosted talc-magnesite , nepheline-syenite (R13), Ni and platinoid showings, some sapphire deposits associated with so called "crossing line" pegmatites and placer platinoid deposits 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.

DEPÓSITOS - 30/04/2004 19:33:00

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