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Ministry of Energy Mines and Responsible for Core Review

M - Ultramafic/Mafic

BC Profile # Deposit Type Approximate Synonyms USGS Model #
M01* Flood Basalt-Associated Ni-Cu Basaltic subvolcanic Cu-Ni-PGE 5a/5b
M02* Tholeiitic intrusion-hosted Ni-Cu Gabbroid-associated Ni-Cu 7a
M03 Podiform chromite - - 8a/8b
M04 Magmatic Fe-Ti±V oxide deposits Mafic intrusion-hosted Ti-Fe deposits 7b
M05 Alaskan-type Pt±Os±Rh±Ir Zoned ultramafic, Uralian-type 9
M06 Ultramafic-hosted asbestos Serpentinite-hosted asbestos 8d
M07 Ultramafic-hosted talc-magnesite - - 8f*
M08 Vermiculite deposits - - - -

 

PODIFORM CHROMITE


M03
by Chris Ash
BC Geological Survey

 

Ash, Chris (1996): Podiform Chromite, in Selected British Columbia Mineral Deposit Profiles, Volume 2 - Metallic Deposits, Lefebure, D.V. and Hõy, T., Editors, British Columbia Ministry of Employment and Investment, Open File 1996-13, pages 109-112.

 

IDENTIFICATION

 

SYNONYMS: Alpine type; ophiolite hosted chromite.

 

COMMODITIES (BYPRODUCTS): Chromite (may contain platinum group elements Os, Ir and Ru).

 

EXAMPLES (British Columbia (MINFILE #) - Canada/International): Castle Mountain Nickel (082ESE091) and Scottie Creek (092INW001); Guleman ore field (Turkey); Kalimash - Kukes-Tropoje district, Bulquize and Todo Manco - Bater-Martanesh district (Mirdita ophiolite, Albania); Tiébaghi ophiolite and Massif du Sud (New Caledonia), Acoje and Masinloc-Coto (Zambales range/ophiolite, Luzon, Phillipines); Batamshinsk, Stepninsk, Tagashaisai and Main SE ore fields (Kempirsai massif, Southern Urals, Russia); Xeraivado and Skoumtsa mines (Vourinos ophiolite, Greece); Semail ophiolite (Oman); Luobusa, Donqiao, Sartohay, Yushi, Solun, Wudu and Hegenshan deposits (China) all > 1.5 Mt.

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Deposits of massive chromitite occur as pods, lenses or layers within ophiolitic ultramafic rocks.

 

TECTONIC SETTING: Obducted fragments of oceanic, lower crustal and upper mantle ultramafic rocks within accreted oceanic terranes.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: Formed as a primary magmatic differentiate during early olivine and chrome-spinel crystal fractionation of basaltic liquid at an oceanic spreading centre; (1) as massive to disseminated pods and lenses of chrome-spinel surrounded by a dunite envelope within depleted mantle harzburgite; or (2) as massive to disseminated cumulate layers in dunite at the base of the crustal plutonic section.

 

AGE OF MINERALIZATION: Mesozoic and younger.

 

HOST/ASSOCIATED ROCK TYPES: Variably serpentinized peridotite; residual mantle harzburgite; cumulate dunite.

 

DEPOSIT FORM: Podiform, tabular lenses, irregular masses, cumulate layers. Pods and lenses typically occur in clusters of variable size.

 

TEXTURE/STRUCTURE: Massive to disseminated, nodular (syn. leopard, grape, bean or shot ore), chromite net, occluded silicate, orbicular.

 

ORE MINERALOGY: Chromite.

 

GANGUE MINERALOGY (Principal and subordinate): Variably serpentinized olivine and orthopyroxene, magnetite, iddingsite.

 

WEATHERING: Black, no noticeable affects resulting from surface oxidation.

 

ORE CONTROLS: Proximity to the crust-mantle transition zone. Restricted to dunite bodies in tectonized harzburgite below this transition, or lower dunitic portions of ultramafic cumulate section above it.

 

GENETIC MODEL: Early fractional crystallization of chromite from a basaltic liquid either (1) just below the crust-mantle transition (syn. petrological MOHO) in small magma pockets or possibly conduits within the residual mantle harzburgite; or (2) immediately above the crust-mantle transition as cumulate layers within dunite at the base of the axial magma chamber. Pods and lenses in harzburgite obtain their diagonistic shape as a result subsolidus to hypersolidus ductile deformation due to mantle convection.

 

COMMENTS: Ophiolites of suprasubduction zone affinity with harzburgite mantle sections appear to be the only ophiolite type to host economic deposits of podiform chromite. A lack of any sizable chromite occurrence in British Columbia may reflect the fact that most ophiolitic complexes in the province are of mid- ocean ridge affinity. Occurrences of podiform chromite are found in ophiolitic ultramafic rocks in the Slide Mountain, Cache Creek and Bridge River terranes. Most of these known occurrences have been reviewed by Hancock (1990).

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Cr

 

GEOPHYSICAL SIGNATURE: Gravity anomaly.

 

OTHER EXPLORATION GUIDES: Found in rocks formed near or within the ophiolitic crust- mantle transition zone.

 

ECONOMIC FACTORS

 

TYPICAL GRADE AND TONNAGE: Grades range from 20 to 60% Cr2O3 and are a function of the texture of the chromite; i.e. amount of chromite relative to gangue serpentinite. Tonnages are variable, ranging from several thousand tonnes to several million tonnes.

 

ECONOMIC LIMITATIONS: The complex structure and irregular distribution make exploration and development difficult.

 

END USES: Chromium has a wide range of uses in the iron and steel industry which accounts for over 75% of its use. Chromite is also used in making refractory bricks for furnace linings.

 

IMPORTANCE: An important source of metallurgical-type chromite ores (45-60% Cr2O3: Cr/Fe = 2.8-4.3). Podiform chromite is the only source of refractory-type ore (min. 25% Al2O3: min. 60% Cr2O3 + Al2O3: max. 15% FeO). Historically podiform-type ore fields account for 57% of all chromite produced.

 

REFERENCES

 

Albers, J.P. (1986): Descriptive Model of Podiform Chromite; in Mineral Deposit Models, Cox, D.P. and Singer, D.A., Editors, U.S. Geological Survey, Bulletin 1693, page 34.

Christiansen, F.G. (1986): Structural Classification of Ophiolitic Chromite Deposits; in Metallogeny of Basic and Ultrabasic Rocks, Gallagher, M.J., Ixer, R.A., Neary, C.R. and Pichard, H.M., Editors; The Institution of Mining and Metallurgy, pages 279-289.

Duke, J.M. (1983): Ore Deposit Models 7. Magmatic Segregation Deposits of Chromite; Geoscience Canada, Volume 10, Number 1, pages 15-24.

Hancock, K.D. (1990): Ultramafic Associated Chrome and Nickel Occurrences in British Columbia; B.C. Ministry of Energy, Mines and Petroleum Resources, Open File 1990- 27, 62 pages.

Roberts, S. (1988): Ophiolitic Chromitite Formation: A Marginal Basin Phenomenon?; Economic Geology, Volume 83, pages 1034-1036.

Singer, D.A., Page, N.J. and Lipin, B.R. (1986): Grade and Tonnage Model of Major Podiform Chromite; in Mineral Deposit Models, Cox, D.P. and Singer, D.A., Editors, U.S. Geological Survey, Bulletin 1693, pages 38-44.

Singer, D.A. and Page, N.J. (1986): Grade and Tonnage Model of Minor Podiform Chromite; in Mineral Deposit Models, Cox, D.P. and Singer, D.A., Editors, U.S. Geological Survey, Bulletin 1693, pages 34-38.

Stowe, C.W. (1987): Evolution of Chromium Ore Fields; Van Nostrund Reinhold Co., New York, 340 pages.

Thayer, T.P. (1964): Principal Features and Origin of Podiform Chromite Deposits, and Some Observations on the Guleman-Soridag District, Turkey; Economic Geology, Volume 59, pages 1497- 1524.

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MAGMATIC Ti-Fe±V OXIDE DEPOSITS


M04

by G.A. Gross1, C.F. Gower2, and D.V. Lefebure3
1Geological Survey of Canada
2Newfoundland Department of Mines and Energy
3British Columbia Geological Survey

 

Gross, G.A., Gower, C.F., and Lefebure, D.V. (1997): Magmatic Ti-Fe±V Oxide Deposits, in Geological Fieldwork 1997, British Columbia Ministry of Employment and Investment, Paper 1998-1, pages 24J-1 to 24J-3.

 

IDENTIFICATION

 

SYNONYMS: Mafic intrusion-hosted titanium-iron deposits.

 

COMMODITIES (BYPRODUCTS): Ti, Fe

 

EXAMPLES (British Columbia - Canada/International): Bearpaw Ridge (093I 028); 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).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Ilmenite, hemo-ilmenite or titaniferous magnetite accumulations as cross-cutting lenses or dike-like bodies, layers or disseminations within anorthositic/gabbroic/noritic rocks. These deposits can be subdivided into an ilmenite subtype (anorthosite-hosted titanium-iron) and a titaniferous magnetite subtype (gabbro-anorthosite-hosted iron-titanium).

 

TECTONIC SETTING: Commonly associated with anorthosite-gabbro-norite-monzonite (mangerite)-charnockite granite (AMCG) suites that are conventionally interpreted to be anorogenic and/or extensional. Some of the iron-titanium deposits occur at continental margins related to island arc magmatism followed by an episode of orogenic compression.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: Deposits occur in intrusive complexes which typically are emplaced at deeper levels in the crust. Progressive differentiation of liquids residual from anorthosite-norite magmas leads to late stage intruions enriched in Fe and Ti oxides and apatite.

 

AGE OF MINERALIZATION: Mainly Mesoproterozoic (1.65 to 0.90 Ga) for the ilmenite deposits, but this may be a consequence of a particular combination of tectonic circumstances, rather than any a priori temporal control. The Fe-Ti deposits with titaniferous magnetite do not appear to be restricted in time.

 

HOST/ASSOCIATED ROCKS: Hosted by massive, layered or zoned intrusive complexes - anorthosite, norite, gabbro, diorite, diabase, quartz monzonite and hornblende pyroxenite. The anorthosites are commonly emplaced in granitoid gneiss, granulite, schist, amphibolite and quartzite. Some deposits associated with lower grade rocks.

 

DEPOSIT FORM: Lensoid, dike-like or sill-like bodies of massive ore, or disseminated in mafic host rocks. Some ore is disseminated as layers in layered intrusions. Typically the massive material has sharp, cross-cutting contacts with its anorthositic hosts, forming lenses tens to hundreds of metres wide and several hundred metres long. The massive ore may have apophyses cutting the host rock, be associated with intrusive breccias and contain anorthositic xenoliths. In layered deposits individual layers range in thickness from centimetres to metres and may be followed up to several thousand metres. Lean (disseminated) ore grades into unmineralized host rock. Lac Tio and Tellnes ore bodies are very large examples of the ilmenite subtype. Lac Tio is an irregular, tabular intrusive mass, 1100 m long and 1000 m wide. The Tellnes ore body, which is 400 m thick and 2.5 km long, is part of a 14 km long dike.

 

TEXTURE/STRUCTURE: Massive, disseminated or locally in layers. No zoning of ore minerals, but there may be variation in modal proportions of associated silicates. Medium or coarse grained, primary magmatic textures. Exsolution intergrowths of either ilmenite and hemo-ilmenite, or titanomagnetite, titaniferous magnetite or ilmenite in magnetite. Locally the massive ore, particularly near contacts with host rock, contains abundant xenoliths and xenocrysts derived from the associated intrusive.

 

ORE MINERALOGY (Principal and subordinate): Ilmenite, hemo-ilmenite, titaniferous magnetite and magnetite. Proportions of ilmenite and magnetite generally correlate with host rock petrology. Fe-sulphides such as pyrrhotite, pentlandite and chalcopyrite.

 

GANGUE MINERALOGY (Principal and subordinate): Silicate minerals, especially plagioclase, orthopyroxene, clinopyroxene and olivine, with apatite, minor zircon and pleonaste spinel. Orthopyroxene is rare to absent in the island arc-related titaniferous magnetite deposits.

 

ALTERATION MINERALOGY: Not normally altered.

 

WEATHERING: Rarely residual enrichment may occur in weathering zone.

 

ORE CONTROLS: The key control is the development of a late, separate Ti and Fe-rich liquid from a fractionating magma under stable conditions. Many deposits occur in elongate belts of intrusive complexes emplaced along deep-seated faults and fractures. Ilmenite deposits are associated with lower magnesian phases of anorthositic intrusions. Titaniferous magnetite deposits are commonly associated with magnesian, labradorite phases of anorthositic intrusions or gabbroic phases near the margins of the stock. In layered intrusions the titaniferous magnetite seams are commonly within the upper stratigraphic levels and in marginal zones of complex intrusive bodies.

 

GENETIC MODELS: Progressive differentiation of liquids residual from anorthosite-norite magmas leads to late enrichment in Fe and Ti. Typically plagioclase crystallization results in concentration of Fe and Ti in residual magmas which typically crystallize to form ferrodiorites and ferrogabbros. Layers form by crystal settling and accumulation on the floors of magma chambers and the disseminated deposits are believed to have formed in-situ. The origin of the discordant deposits, primarily associated with the Proterozoic anorthosites, is not well understood. Two genetic models have been suggested - remobilization of the crystal cummulates into cracks or fractures or emplacement as a Fe-Ti-oxide-rich immiscible melt with little silica.

 

ASSOCIATED DEPOSIT TYPES: Ni-Cu-Co magmatic sulphide deposits (M02), chromite deposits (e.g. Bushveld Complex), platinum group deposits (e.g. Stillwater Complex, Bushveld Complex), and placer ilmenite, magnetite, rutile and zircon (C01, C02).

 

COMMENTS: Titaniferous magnetite deposits associated with zoned ultramafic complexes in Alaska and British Columbia, such as Lodestone Mountain (092HSE034) and Tanglewood Hill (092HSE035), are included with Alaskan-type deposits (M05). Some authors would include them with magmatic Fe-TiV oxide deposits. In California in the San Gabriel Range occurrences of the ilmenite-subtype are hosted by anorthosite and ferrodiorite intrusions within a metamorphic complex composed of gneisses.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Ti, Fe, V, Cr, Ni, Cu, Co geochemical anomalies.

 

GEOPHYSICAL SIGNATURE: Magnetic or EM response, although if the deposit is particularly ilmenite-rich it may exhibit either a subdued or a strong negative anomaly. Sometimes the subdued response displays characteristic irregular patterns of negative and positive anomalies that show broad smooth profiles or patterns.

 

OTHER EXPLORATION GUIDES: Heavy mineral concentrations of ilmenite and titaniferous magnetite in placer deposits. Abundant apatite in some deposits. Association with anothosite and gabbro intrusive complexes along deep fracture and fault zones.

 

ECONOMIC FACTORS

 

GRADE AND TONNAGE: Both grade and tonnage vary considerably. The ilmenite deposits are up to several hundreds of millions of tonnes with from 10 to 75% TiO2, 32 to 45% Fe and less than 0.2% V. The Tellnes deposit comprises 300 Mt averaging 18% TiO2. The Lac Tio deposit, largest of 6 deposits at Allard Lake, contains more than 125 mt of ore averaging 32% TiO2 and 36% FeO. Titaniferous magnetite deposits can be considerably larger, ranging up to a billion tonnes with grades between 20 to 45% Fe, 2 to 20% TiO2 and less than 7% apatite with V contents averaging 0.25%.

 

ECONOMIC LIMITATIONS: The economic deposits are typically coarse, equigranular aggregates which are amenable to processing depending on the composition and kinds of exsolution textures of the Fe-Ti-oxide minerals.

 

USES: Titanium dioxide is a non­toxic, powdered white pigment used in paint, plastics, rubber, and paper. Titanium metal is resistant to corrosion and has a high strength­to­weight ratio and is used in the manufacturing of aircraft, marine and spacecraft equipment.

 

IMPORTANCE: Apart from placers, this type of deposit is the major source of TiO2. These deposits were an important source of iron (pig iron) in the former Soviet Union. They have been mined for Fe in Canada, however, the grades are generally lower than those in iron formations and iron lateritites. The only current iron production is as a coproduct with TiO2 in pyrometallurgial processing of ilmenite ore.

 

SELECTED BIBLIOGRAPHY

 

Ashwal, L.D. (1993): Anorthosites; Springer­Verlag, Berlin, 422 pages.

Force, Eric R. (1986): Descriptive Model of Anorthosite Ti; in Mineral Deposit Models, Cox, Denis P. and Singer, D.A., Editors, U.S. Geological Survey, Bulletin 1693, pages 32-33.

Force, E.R. (1991): Geology of Titanium-mineral Deposits; Geological Society of America, Special Paper 259, 113 pages.

Gross, G.A. (1965): General Geology and Evaluation of Iron Deposits; Volume I, in Geology of Iron Deposits in Canada, Geological Survey of Canada, Economic Geology Report 22, 111 pages.

Gross, G.A. and Rose, E.R. (1984): Mafic Intrusion-hosted Titanium-Iron; in Canadian Mineral Deposit Types: A Geological Synopysis; Geological Survey of Canada, Economic Geology Report 36, Eckstrand, O.R., Editor, page 46.

Gross, G.A. (1995): Mafic Intrusion-hosted Titanium-iron; 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 573-582.

Hammond, P. (1952): Allard Lake Ilmenite Deposits; Economic Geology, Volume 47, pages 634-649.

Hancock, K.D. (1988): Magnetite Occurrences in British Columbia, Open File 1988-28, B.C. Ministry of Energy, Minerals and Petroleum Resources, 153 pages.

Korneliussen, A., Geis, H.P., Gierth, E., Krause, H., Robins, B. and Schott, W. (1985): Titanium Ores: an Introduction to a Review of Titaniferous Magnetite, Ilmenite and Rutile deposits in Norway; Norges Geologiske Undersøkelse Bulletin, volume 402, pages 7­23.

Lister, G.F. (1966): The Composition and Origin of Selected Iron­titanium Deposits; Economic Geology, volume 61, pages 275­310.

Reynolds, I.M. (1985): The Nature and Origin of Titaniferous Magnetite­rich Layers in the Upper Zone of the Bushveld Complex: a Review and Synthesis; Economic Geology, volume 80, pages 1089­1108.

Rose, E.R. (1969): Geology of Titnaium and Titaniferous Deposits of Canada; Geological Survey of Canada, Economic Geology Report 25, 177 pages.

Wilmart, E., Demaiffe, D. and Duchesne, J.C. (1989): Geochemical Constraints on the Genesis of the Tellnes Ilmenite Deposit, Southwest Norway; Economic Geology, Volume 84, pages 1047-1056.

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ALASKAN-TYPE Pt+/-Os+/-Rh+/-Ir

M05
by Graham T. Nixon
British Columbia Geological Survey

 

Nixon, G.T. (1996): Alaskan-type Pt+/-Os+/-Rh+/-Ir, in Selected British Columbia Mineral Deposit Profiles, Volume 2 - Metallic Deposits, Lefebure, D.V. and Hõy, T., Editors, British Columbia Ministry of Employment and Investment, Open File 1996-13, pages 113-116.

 

IDENTIFICATION

 

SYNONYMS: Zoned ultramafic, Uralian-type, Alaskan-type.

 

COMMODITIES (BYPRODUCTS): Pt (Ir, Os, Rh, magnetite).

 

EXAMPLES (British Columbia - Canada/International): Tulameen Complex and associated placers; magnetite plus trace platinum group elements (PGE) -Lodestone Mountain (092HSE034), Tanglewood Hill (092HSE035); chromite - Grasshopper Mountain (092HNE011); olivine - Grasshopper Mountain Olivine (092HNE189); Red Mountain, Goodnews Bay (Alaska, USA), Tin Cup Peak (Oregon, USA), Ural Mountains and Aldan Shield (Russia), Fifield district (NSW, Australia).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Ultramafic intrusive complexes, commonly zoned, forming sills, stocks or intrusive bodies with poorly known external geometry. Subeconomic platinum group elements in lode occurrences are associated with: 1) thin (centimetre-scale), disrupted chromitite layers , 2) thick (metre-scale) concentrations of cumulus magnetite or 3) clinopyroxenite. Economic placer deposits appear to be derived predominantly from chromitite- hosted PGE occurrences.

 

TECTONIC SETTINGS: Traditionally subdivided into orogenic (unstable) and platformal (stable) environments. In British Columbia, Alaskan-type complexes were emplaced during an episode of Cordillera-wide, subduction-related arc magmatism followed by an episode of orogenic compression.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: Zoned to crudely layered ultramafic- mafic intrusive complexes with rarely preserved (or poorly documented) metamorphic aureoles. Intrusive margins are commonly faulted. Traditionally viewed as deep-seated cumulates diapirically re-emplaced at high levels in the crust. In British Columbia, at least, most intrusions appear to represent cumulate deposition in upper crustal (subvolcanic?) magma chambers and the diapiric re-emplacement model lacks definitive supporting evidence.

 

AGE OF MINERALIZATION: Precambrian to late Mesozoic; most Alaskan-type complexes in British Columbia appear to be mid-Triassic to late Early Jurassic in age.

 

HOST/ASSOCIATED ROCK TYPES: Predominantly dunite, wehrlite, olivine clinopyroxenite, clinopyroxenite, hornblende clinopyroxenite, clinopyroxene hornblendite, hornblende- and/or clinopyroxene-bearing gabbro/diorite. Minor lithologies include chromitite, magnetitite, olivine-hornblende clinopyroxenite, and hornblendite. Associated feldspar-bearing lithologies include gabbro/diorite, monzonite, monzodiorite and minor alkali-feldspar syenite and hornblende- feldspar ± quartz ± biotite pegmatite.

 

DEPOSIT FORM: Lode occurrences of PGEs are primarily controlled by magmatic cumulate stratigraphy:

1) chromitites are restricted to dunites where they form thin discontinuous layers or schlieren, pods and nodular masses seldom more than a metre in length;
2) magnetitites and concentrations of cumulus magnetite form well bedded, locally continuous layers up to six m thick intercalated with hornblende clinopyroxenite;
3) lenses and vein-like bodies of relatively coarse-grained or "pegmatoid", biotite and magnetite-poor, PGE-bearing clinopyroxenites are enclosed by finer grained, biotite and magnetite-rich, PGE-poor clinopyroxenites.

 

 

 

 

 

 

 

 

 

TEXTURE/STRUCTURE: Cumulus and intercumulus textures are most common; poikilitic textures may predominate locally, especially in hornblende-bearing lithologies. Comparatively rare macroscopic layering. Euhedral to subhedral chromite concentrations form networks around olivine or discrete wispy or thin layers in dunite. Chromitites typically form schlieren and nodular masses due to syndepositional remobilization. Magnetite-rich accumulations usually form thin to thick bedded layers in hornblende clinopyroxenite. Tectonic deformation, commonly in the form of ductile shear fabrics, is locally superimposed on magmatic textures, and is especially prevalent at intrusive contacts.

 

ORE MINERALOGY (Principal and subordinate): Three types of PGE mineral (PGM) associations are recognized in lode occurrences: 1) chromitite-PGM association, principally chromite and Pt-Fe(-Cu-Ni) alloys (e.g. tetraferroplatinum, isoferroplatinum, rare native platinum, tulameenite) and minor Os-Ir and Pt-Ir alloys, Rh-Ir sulpharsenides (hollingworthite-irarsite series), sperrylite (PtAs2), geversite (PtSb2), and laurite (RuS2); 2) magnetitite-PGM association (not well documented), principally magnetite (Ti-V-rich in certain cases) and Pt-Fe and Os-Ir alloys, and rare cooperite (PtS); 3) clinopyroxenite-PGM association (known from a single locality - Fifield, NSW, Australia), principally Pt-Fe alloys (isoferroplatinum-tetraferroplatinum), erlichmanite (OsS2), cooperite, and sperrylite-geversite. Minor amounts of base metal sulphides (chalcopyrite, pentlandite, pyrrhotite, pyrite, bornite, violarite, bravoite, millerite, heazlewoodite) generally accompany the PGM in all three associations.

 

GANGUE MINERALOGY (Principal and subordinate): The principal gangue minerals include olivine, chrome spinel, clinopyroxene, and hornblende in ultramafic rocks; hornblende, clinopyroxene and plagioclase in gabbroic/dioritic rocks; and hornblende, quartz (rare) and alkali feldspar in leucocratic differentiates. Orthopyroxene is characteristically absent as a cumulus phase but may form very rare intercumulus grains. Accessory magnetite and apatite are generally common, and locally abundant in hornblende clinopyroxenite; sphene and zircon occur in felsic differentiates; phlogopite-biotite is particularly widespread as an accessory phase in British Columbia.

 

ALTERATION MINERALOGY: Secondary PGM are minor and closely associated with the primary PGM alloys. Remobilization of PGE is believed to be extremely limited and may be commonly related to postmagmatic serpentinizaton processes acting during regional metamorphism and deformation.

 

WEATHERING: It has been argued by some that the PGE found in placer occurrences may owe their origin to the hydromorphic dispersion and precipitation of PGE during normal weathering processes. The debate continues, but it is clear from a variety of textural, mineralogical and isotopic (Re-Os) data that the common placer PGE occurrences are the products of mechanical degradation of magmatic lode occurrences and not surficial remobilization processes.

 

ORE CONTROLS: The PGM appear to be restricted to chromitite, magnetite-rich or clinopyroxenite layers which formed by primary magmatic crystallization processes. The chromite is typically associated with dunite whereas the magnetite is found with clinopyroxenite.

 

GENETIC MODEL: The origin of the PGE in Alaskan-type deposits is magmatic with very limited low-temperature remobilization. A low sulphidation, relatively high oxidation magmatic environment (subduction-related?) appears to be an important genetic control. The chromitites in dunite and, to a much lesser extent, the magnetite-rich layers in clinopyroxenite, appear to be the ultimate source of the placer PGE.

 

ASSOCIATED DEPOSIT TYPES: Placer deposits (C01, C02) are extremely important since they have been the only significant economically recoverable source of PGE associated with Alaskan-type complexes. Some lode deposits have been worked in Russia but their documentation is extremely poor.

 

COMMENTS: All of the world's most important Alaskan-derived placers appear to be related to concentrations of PGE in chromitites. Gold in these placers appears to have been derived from a separate source. Magnetite accumulations in clinopyroxenites of the Tulameen Complex have been explored for magnetite.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Primarily Pt, with subsidiary Os, Rh and Ir; other elements such as Cu, Ni, and Cr may be locally important. Geochemical pathfinder elements for PGE, such as As and Sb, may also be important.

 

GEOPHYSICAL SIGNATURE: Primarily magnetic; gravity may be important.

 

OTHER EXPLORATION GUIDES: Stream sediment sampling of heavy mineral concentrates for PGE is a key exploration tool; in favourable circumstances PGE geochemistry and platinum nugget mineralogy can uniquely distinguish an Alaskan-type heritage from all other common PGE environments.

 

ECONOMIC FACTORS

 

TYPICAL GRADE AND TONNAGE: PGE concentrations in grab samples from lode deposits are extremely spotty such that reliable tonnages and grades are not available. The associated placer deposits are likewise extremely variable. Maximum grade of Pt from the Goodnews Mining Company records, Alaska (1957) was approximately “$37 per cubic yard” at February 1993 prices. Placers in the Tulameen district reportedly yielded some 620 kg of impure platinum between 1889 and 1936. Some of the placer deposits in the former Soviet Union have yielded exceptional platinum nuggets of up to 11.3 kg.

 

ECONOMIC LIMITATIONS: The chromitite-PGE association appears to be the most important in British Columbia; without exception, all of these chromitite occurrences are small, dispersed throughout a dunite host, and all have been remobilized soon after deposition within the high-temperature magmatic environment. A small open pit operation appears to be the only potentially economic method of PGE extraction. The occurrence of the PGE as small micrometre-size inclusions in refractory chromite poses problems for processing.

 

END USES: PGE are primarily used as high-temperature catalysts in a variety of industries, perhaps the most familiar being platinum for automobile catalytic converters. Other uses include medical and electronic (fuel cells, thermocouples), and platinum is used in jewelry.

 

IMPORTANCE: PGE are classed as a strategic commodity. The most important producers are South Africa and Russia.

 

REFERENCES

 

Duparc, L. and Tikonowitch, M.N. (1920): Le Platine et les Gites Platiniferes de l'Oural et du Monde; Sonor, Geneve.

Hurlbert, L.J., Duke, J.M., Eckstrand, O.R., Lydon, J.W., Scoates, R.F.J., Cabri, L.J. and Irvine, T.N. (1988): Geological Environments of the Platinum Group Elements; Geological Association of Canada, Cordilleran Section Workshop, February 1988, Vancouver, 151 pages.

Johan, Z., Ohnenstetter, M., Slansky, E., Barron, L.M. and Suppel, D. (1989): Platinum Mineralization in the Alaskan-type Intrusive Complexes near Fifield, New South Wales, Australia Part 1. Platinum-group Minerals in Clinopyroxenites of the Kelvin Grove Prospect, Owendale Intrusion; Mineralogy and Petrology, Volume 40, pages 289-309.

Mertie, J.B. Jr. (1976): Platinum Deposits of the Goodnews Bay District, Alaska; U. S. Geological Survey, Professional Paper 938, 42 pages.

Nixon, G.T. (1992): Platinum-group Elements in Tulameen Coal, British Columbia, Canada - A Discussion; Economic Geology, Volume 87, pages 1667-1677.

Nixon, G.T. and Hammack, J.L. (1991): Metallogeny of Ultramafic-mafic Rocks in British Columbia with Emphasis on the Platinum-group Elements; in Ore Deposits, Tectonics and Metallogeny in the Canadian Cordillera, B.C. Ministry of Energy, Mines and Petroleum Resources, Paper 1991-4, pages 125-161.

Nixon, G.T., Cabri, L.J. and Laflamme, J.H.G. (1990): Platinum-group Element Mineralization in Lode and Placer Deposits associated with the Tulameen Alaskan- type Complex, British Columbia; Canadian Mineralogist, Volume 28, pages 503-535.

Page, N.J. and Gray, F. (1986): Descriptive Model of Alaskan PGE; in Mineral Deposit Models, Cox, Denis P. and Singer, D.A., Editors, U.S. Geological Survey, Bulletin 1693, page 49.

Rublee, V.J. (1986): Occurrence and Distribution of Platinum-group Elements in British Columbia; B.C. Ministry of Energy, Mines and Petroleum Resources, Open File 1986-7, 94 pages.

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ULTRAMAFIC-HOSTED CHRYSOTILE ASBESTOS


M06
by Z.D. Hora
British Columbia Geological Survey

 

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.

 

IDENTIFICATION

 

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).

 

GEOLOGICAL CHARACTERISTICS

 

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.

 

EXPLORATION GUIDES

 

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.

 

ECONOMIC FACTORS

 

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.

 

SELECTED BIBLIOGRAPHY

 

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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ULTRAMAFIC-HOSTED TALC-MAGNESITE


M06
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.

 

IDENTIFICATION

 

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).

 

GEOLOGICAL CHARACTERISTICS

 

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).

 

EXPLORATION GUIDES

 

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.

 

ECONOMIC FACTORS

 

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.

                   

REFERENCES

 

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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VERMICULITE


M08
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.

 

IDENTIFICATION

 

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).

 

GEOLOGICAL CHARACTERISTICS

 

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.

 

EXPLORATION GUIDES

 

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.

 

ECONOMIC FACTORS

 

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.

 

REFERENCES

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 # Global Examples B.C. Examples
 M01* Noril'sk (Russia), Duluth (Minnesota)  
 M02* Lynn Lake (Manitoba), Kluane (Yukon) Giant Mascot, Nickel Mountain
M03 Josephine ophiolite (Oregon), Coto (Philippines), Elazig (Turkey) Castle Mountain, Scottie Creek
M04 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) - -
M05 Red Mountain, Goodnews Bay (Alaska), Tin Cup Peak (Oregon) Tulameen Complex
M06 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
M07 Thetford & Magog (Québec), Deloro (Ontario) - -
M08 Enoree (USA) Fort Fraser area