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Ministry of Energy Mines and Responsible for Core Review

K - Skarn

BC Profile # Deposit Type Approximate Synonyms  USGS Model #
K01 Cu skarns - - 18a,b
K02 Pb-Zn skarns - - 18c
K03 Fe skarns - - 18d
K04 Au skarns - - 18f*
K05 W skarns - - 14a
K06 Sn skarns - - 14b
K07 Mo skarns - - - -
K08 Garnet skarns - - - -
K09 Wollastonite skarns - - 18g

 

Cu SKARNS


K01
by Gerald E. Ray
British Columbia Geological Survey

 

Ray, G.E. (1995): Cu Skarns, in Selected British Columbia Mineral Deposit Profiles, Volume 1 - Metallics and Coal, Lefebure, D.V. and Ray, G.E., Editors, British Columbia Ministry of Employment and Investment, Open File 1995-20, pages 59-60.

 

IDENTIFICATION

 

SYNONYMS: Pyrometasomatic and contact metasomatic copper deposits.

 

COMMODITIES (BYPRODUCTS): Cu (Au, Ag, Mo, W, magnetite).

 

EXAMPLES (British Columbia - Canada/International): Craigmont (092ISE035), Phoenix (082ESE020), Old Sport (092L 035), Queen Victoria (082FSW082); Mines Gaspé deposits (Québec, Canada), Ruth, Mason Valley and Copper Canyon (Nevada, USA), Carr Fork (Utah, USA), Ok Tedi (Papua New Guinea), Rosita (Nicaragua).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Cu-dominant mineralization (generally chalcopyrite) genetically associated with a skarn gangue (includes calcic and magnesian Cu skarns).

 

TECTONIC SETTING: They are most common where Andean-type plutons intrude older continental-margin carbonate sequences. To a lesser extent (but important in British Columbia), they are associated with oceanic island arc plutonism.

 

AGE OF MINERALIZATION: Mainly Mesozoic, but may be any age. In British Columbia they are mostly Early to mid-Jurassic.

 

HOST/ASSOCIATED ROCK TYPES: Porphyritic stocks, dikes and breccia pipes of quartz diorite, granodiorite, monzogranite and tonalite composition, intruding carbonate rocks, calcareous volcanics or tuffs. Cu skarns in oceanic island arcs tend to be associated with more mafic intrusions (quartz diorite to granodiorite), while those formed in continental margin environments are associated with more felsic material.

 

DEPOSIT FORM: Highly varied; includes stratiform and tabular orebodies, vertical pipes, narrow lenses, and irregular ore zones that are controlled by intrusive contacts.

 

TEXTURES: Igneous textures in endoskarn. Coarse to fine-grained, massive granoblastic to mineralogically layered textures in exoskarn. Some hornfelsic textures.

 

ORE MINERALOGY (Principal and subordinate): Moderate to high sulphide content. Chalcopyrite ± pyrite ± magnetite in inner garnet-pyroxene zone. Bornite ± chalcopyrite ± sphalerite ± tennantite in outer wollastonite zone. Either hematite, pyrrhotite or magnetite may predominate (depending on oxidation state). Scheelite and traces of molybdenite, bismuthinite, galena, cosalite, arsenopyrite, enargite, tennantite, loellingite, cobaltite and tetrahedrite may be present.

 

ALTERATION MINERALOGY: Exoskarn alteration: high garnet:pyroxene ratios. High Fe, low Al, Mn andradite garnet (Ad35-100), and diopsidic clinopyroxene (Hd2-50). The mineral zoning from stock out to marble is commonly: diopside + andradite (proximal); wollastonite ± tremolite ± garnet ± diopside ± vesuvianite (distal). Retrograde alteration to actinolite, chlorite and montmorillonite is common. In British Columbia, skarn alteration associated with some of the alkalic porphyry Cu-Au deposits contains late scapolite veining. Magnesian Cu skarns also contain olivine, serpentine, monticellite and brucite. Endoskarn alteration: Potassic alteration with K-feldspar, epidote, sericite ± pyroxene ± garnet. Retrograde phyllic alteration generates actinolite, chlorite and clay minerals.

 

ORE CONTROLS: Irregular or tabular orebodies tend to form in carbonate rocks and/or calcareous volcanics or tuffs near igneous contacts. Pendants within igneous stocks can be important. Cu mineralization is present as stockwork veining and disseminations in both endo and exoskarn; it commonly accompanies retrograde alteration.

 

COMMENTS: Calcic Cu skarns are more economically important than magnesian Cu skarns. Cu skarns are broadly separable into those associated with strongly altered Cu- porphyry systems, and those associated with barren, generally unaltered stocks; a continuum probably exists between these two types (Einaudi et al., 1981). Copper skarn deposits related to mineralized Cu porphyry intrusions tend to be larger, lower grade, and emplaced at higher structural levels than those associated with barren stocks. Most Cu skarns contain oxidized mineral assemblages, and mineral zoning is common in the skarn envelope. Those with reduced assemblages can be enriched in W, Mo, Bi, Zn, As and Au. Over half of the 340 Cu skarn occurrences in British Columbia lie in the Wrangellia Terrane of the Insular Belt, while another third are associated with intraoceanic island arc plutonism in the Quesnellia and Stikinia terranes. Some alkalic and calcalkalic Cu and Cu-Mo porphyry systems in the province (e.g. Copper Mountain, Mount Polley) are associated with variable amounts of Cu-bearing skarn alteration.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Rock analyses may show Cu-Au-Ag-rich inner zones grading outward through Au-Ag zones with high Au:Ag ratios to an outer Pb-Zn-Ag zone. Co-As-Sb-Bi-Mo-W geochemical anomalies are present in the more reduced Cu skarn deposits.

 

GEOPHYSICAL SIGNATURE: Magnetic, electromagnetic and induced polarization anomalies.

 

ASSOCIATED DEPOSIT TYPES: Porphyry Cu deposits (L04), Au (K04), Fe (K03) and Pb-Zn (K02) skarns, and replacement Pb-Zn-Ag deposits (M01).

 

ECONOMIC FACTORS

 

GRADE AND TONNAGE: Average 1 to 2 % copper. Worldwide, they generally range from 1 to 100 Mt, although some exceptional deposits exceed 300 Mt. Craigmont, British Columbia's largest Cu skarn, contained approximately 34 Mt grading 1.3 % Cu.

 

IMPORTANCE: Historically, these deposits were a major source of copper, although porphyry deposits have become much more important during the last 30 years . However, major Cu skarns are still worked throughout the world, including in China and the U.S.

 

REFERENCES

 

Cox, D.P. and Singer, D.A. (1986): Mineral Deposit Models; U.S. Geological Survey, Bulletin 1693, 379 pages.

Dawson, K.M., Panteleyev, A. and Sutherland-Brown, A. (1991): Regional Metallogeny, Chapter 19, in Geology of the Cordilleran Orogen in Canada, Editors, Gabrielse, H. and Yorath, C.J., Geological Survey of Canada, Geology of Canada, Number 4, page 707-768 (also, Geological Society of America, The Geology of North America, Volume G-2).

Eckstrand, O.R. (1984): Canadian Mineral Deposit Types: A Geological Synopsis; Geological Survey of Canada, Economic Geology Report 36, 86 pages.

Einaudi, M.T. (1982): General Features and Origin of Skarns Associated with Porphyry Copper Plutons, Southwestern North America; in Advances in Geology of the Porphyry Copper Deposits, Southwestern U.S., Titley, S.R., Editor, Univ. Arizona Press, pages 185-209.

Einaudi, M.T. and Burt, D.M. (1982): Introduction - Terminology, Classification and Composition of Skarn Deposits; Economic Geology; Volume 77, pages 745-754.

Einaudi, M.T., Meinert, L.D. and Newberry, R.J. (1981): Skarn Deposits; in Seventy-fifth Anniversary Volume, 1906-1980, Economic Geology, Skinner, B.J., Editor, Economic Geology Publishing Co., pages 317-391.

Meinert, L.D. (1983): Variability of Skarn-deposits: Guides to Exploration; in Revolution in the Earth Sciences - Advances in the Past Half-century, Boardman, S.J., Editor; Kendall/Hunt Publishing Company, pages 301-316.

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Pb-Zn SKARNS


K02
by Gerald E. Ray
British Columbia Geological Survey

 

Ray, G.E. (1995): Pb-Zn Skarns, in Selected British Columbia Mineral Deposit Profiles, Volume 1 - Metallics and Coal, Lefebure, D.V. and Ray, G.E., Editors, British Columbia Ministry of Employment and Investment, Open File 1995-20, pages 61-62.

 

IDENTIFICATION

 

SYNONYMS: Pyrometasomatic or contact metasomatic Pb-Zn deposits.

 

COMMODITIES (BYPRODUCTS): Pb, Zn, Ag, (Cu, Cd, W, Au).

 

EXAMPLES (British Columbia - Canada/International): Piedmont (082FNW129), Contact (104P 004); Quartz Lake (Yukon, Canada), Groundhog (New Mexico, USA), Darwin (California, USA) San Antonio, Santa Eulalia and Naica (Mexico), Yeonhwa-Ulchin deposits (South Korea), Nakatatsu deposits (Japan), Shuikoushan and Tienpaoshan (China).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Galena and/or sphalerite-dominant mineralization genetically associated with a skarn gangue.

 

TECTONIC SETTING: Along continental margins where they are associated with late orogenic plutonism. Pb-Zn skarns occur at a wide range of depths, being associated with subvolcanic aphanitic dikes and high-level breccia pipes, as well as deep-level batholiths. In British Columbia, some Pb-Zn skarns are found in oceanic island arcs where they form distally to larger calcic Fe or Cu skarn systems.

 

AGE OF MINERALIZATION: Mainly Mesozoic, but may be any age. In British Columbia, the 80 Pb-Zn skarn occurrences identified have a wide age range; over 40 % are Early to mid-Jurassic, 22% are Cretaceous, and a further 17% are Eocene-Oligocene in age.

 

HOST/ASSOCIATED ROCK TYPES: Variable; from high-level skarns in thick limestones, calcareous tuffs and sediment to deeper level skarns in marbles and calcsilicate-bearing migmatites. Associated intrusive rocks are granodiorite to leucogranite, diorite to syenite (mostly quartz monzonite). Pb-Zn skarns tend to be associated with small stocks, sills and dikes and less commonly with larger plutons. The composition of the intrusions responsible for many distal Pb-Zn skarns is uncertain.

 

DEPOSIT FORM: Variable; commonly occurs along igneous or stratigraphic contacts. Can develop as subvertical chimneys or veins along faults and fissures and as subhorizontal blankets. Pb-Zn skarn deposits formed either at higher structural levels or distal to the intrusions tend to be larger and more Mn- rich compared to those formed at greater depths or more proximal.

 

TEXTURES: Igneous textures in endoskarn. Coarse to fine-grained, massive granoblastic to mineralogically layered textures in exoskarn.

 

ORE MINERALOGY (Principal and subordinate): Sphalerite ± galena ± pyrrhotite ± pyrite ± magnetite ± arsenopyrite ± chalcopyrite ± bornite. Other trace minerals reported include scheelite, bismuthinite, stannite, cassiterite, tetrahedrite, molybdenite, fluorite, and native gold. Proximal skarns tend to be richer in Cu and W, whereas distal skarns contain higher amounts of Pb, Ag and Mn.

 

ALTERATION MINERALOGY: Exoskarn alteration: Mn-rich hedenbergite (Hd30-90, Jo10-50), andraditic garnet (Ad20-100, Spess2-10) ± wollastonite ± bustamite ± rhodonite. Late-stage Mn-rich actinolite ± epidote ± ilvaite ± chlorite ± dannermorite ± rhodochrosite ± axinite. Endoskarn alteration: Highly variable in development, and in many of the distal Pb-Zn skarns the nature of the endoskarn is unknown. However, Zn-rich skarns formed near stocks are often associated with abundant endoskarn that may equal or exceed the exoskarn (Einaudi et al., 1981). Endoskarn mineralogy is dominated by epidote ± amphibole ± chlorite ± sericite with lesser rhodonite ± garnet ± vesuvianite ± pyroxene ± K-feldspar ± biotite and rare topaz. Marginal phases may contain greisen and/or tourmaline.

 

ORE CONTROLS: Carbonate rocks, particularly along structural and/or lithogical contacts (e.g. shale-limestone contacts or pre-ore dikes). Deposits may occur considerable distances (100-1000 m) from the source intrusions.

 

ASSOCIATED DEPOSIT TYPES: Pb-Zn-Ag veins (I05), Cu skarns (K01) and Cu porphyries (L03, L04). In B.C., small Pb-Zn skarns occur distally to some Fe (K03) and W (K04) skarns.

 

COMMENTS: Pb-Zn skarn occurrences are preferentially developed in: (1) continental margin sedimentary rocks of the Cassiar and Ancestral North America terranes, (2) oceanic island arc rocks of the Quesnellia and Stikinia terranes, and (3) arc rocks of the Wrangellia Terrane. Their widespread terrane distribution partly reflects their formation as small distal mineralized occurrences related to other skarns (notably Cu, Fe and W skarns), as well as some porphyry systems. British Columbia is endowed with some large and significant Pb-Zn reserves classified as manto deposits (Nelson, 1991; Dawson et al., 1991). These deposits lack skarn gangue, but are sometimes grouped with the Pb-Zn skarns.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Pb, Zn, Ag, Cu, Mn, As, Bi, W, F, Sn, Mo, Co, Sb, Cd and Au geochemical anomalies.

 

GEOPHYSICAL SIGNATURE: Generally good induced polarization response. Galena-rich orebodies may be marked by gravity anomalies whereas pyrrhotite-rich mineralization may be detected by magnetic surveys. CS-AMT may also be a useful exploration system.

 

OTHER EXPLORATION GUIDES: Thick limestones distal to small granitoid stocks; structural traps and lithological contacts; exoskarns with low garnet/pyroxene ratios.

 

ECONOMIC FACTORS

 

GRADE AND TONNAGE: Pb-Zn skarns tend to be small (<3 Mt) but can reach 45 Mt, grading up to 15 % Zn, 10 % Pb and > 150 g/t Ag with substantial Cd. Cu grades are generally < 0.2 %. Some deposits (e.g. Naica (Mexico) and Falun (Sweden)) contain Au. The 80 British Columbia Pb-Zn skarn occurrences are generally small and have had no major metal production.

 

IMPORTANCE: Important past and current producers exist in Mexico, China, U.S.A (New Mexico and California), and Argentina. No large productive Pb-Zn skarns have been discovered in B.C.

 

REFERENCES

 

Dawson, K.M. and Dick, L.A. (1978): Regional Metallogeny in the Northern Cordillera: Tungsten and Base Metal-bearing Skarns in Southeastern Yukon and Southwestern Mackenzie; in Current Research, Part A, Geological Survey of Canada, Paper 1978- 1A, pages 287-292.

Dawson, K.M., Panteleyev, A. and Sutherland Brown, A. (1991): Regional Metallogeny, Chapter 19, in Geology of the Cordilleran Orogen in Canada, Gabrielse, H. and Yorath, C.J., Editors, Geological Survey of Canada, Geology of Canada, Number 4, page 707-768 (also, Geological Society of America, The Geology of North America, Volume G-2).

Eckstrand, O.R. (1984): Canadian Mineral Deposit Types: A Geological Synopsis; Geological Survey of Canada, Economic Geology Report 36, 86 pages.

Einaudi, M.T. and Burt, D.M. (1982): Introduction - Terminology, Classification and Composition of Skarn Deposits; Economic Geology; Volume 77, pages 745-754.

Einaudi, M.T., Meinert, L.D. and Newberry, R.J. (1981): Skarn Deposits; in Seventy-fifth Anniversary Volume, 1906-1980, Skinner, B.J., Editor, Economic Geology Publishing Co., pages 317-391.

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Fe SKARNS


K03
by Gerald E. Ray
British Columbia Geological Survey

Ray, G.E. (1995): Fe Skarns, in Selected British Columbia Mineral Deposit Profiles, Volume 1 - Metallics and Coal, Lefebure, D.V. and Ray, G.E., Editors, British Columbia Ministry of Employment and Investment, Open File 1995-20, pages 63-65.

 

IDENTIFICATION

 

SYNONYMS: Pyrometasomatic or contact metasomatic iron deposits.

 

COMMODITIES (BYPRODUCTS): Magnetite (Cu, Ag, Au, Co, phlogopite, borate minerals).

 

EXAMPLES (British Columbia - Canada/International): Tasu (103C 003), Jessie (103B 026), Merry Widow (092L 044), Iron Crown (092L 034), Iron Hill (092F 075), Yellow Kid (092F 258), Prescott (092F 106), Paxton (092F 107), Lake (092F 259); Shinyama (Japan), Cornwall Iron Springs (Utah, USA) Eagle Mountain (California, USA), Perschansk, Dashkesan, Sheregesh and Teya (Russia), Daiquiri (Cuba), San Leone (Italy).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Magnetite-dominant mineralization genetically associated with a skarn gangue (includes calcic and magnesian Fe skarns).

 

TECTONIC SETTING: Calcic Fe skarns: Intra and non-intraoceanic island arcs; rifted continental margins. Magnesian Fe skarns: Cordilleran-type, synorogenic continental margins.

 

AGE OF MINERALIZATION: Can be of any age, mainly Mesozoic to Cenozoic. Typically Early to mid-Jurassic in British Columbia.

 

HOST/ASSOCIATED ROCK TYPES: Calcic Fe skarns: Fe-rich, Si-poor intrusions derived from primitive oceanic crust. Large to small stocks and dikes of gabbro to syenite (mostly gabbro-diorite) intruding limestone, calcareous clastic sedimentary rocks, tuffs or mafic volcanics at a high to intermediate structural level. Magnesian Fe skarns: Small stocks, dikes and sills of granodiorite to granite intruding dolomite and dolomitic sedimentary rocks.

 

DEPOSIT FORM: Variable and includes stratiform orebodies, vertical pipes, fault- controlled sheets, massive lenses or veins, and irregular ore zones along intrusive margins.

 

TEXTURES: Igneous textures in endoskarn. Coarse to fine-grained, massive granoblastic to mineralogically layered textures in exoskarn. Some hornfelsic textures. Magnetite varies from massive to disseminated to veins.

 

ORE MINERALOGY(Principal and Subordinate): Calcic Fe skarns: Magnetite ± chalcopyrite ± pyrite ± cobaltite ± pyrrhotite ± arsenopyrite ± sphalerite ± galena ± molybdenite ± bornite ± hematite ± martite ± gold. Rarely, can contain tellurobismuthite ± fluorite ± scheelite. Magnesian Fe skarns: Magnetite ± chalcopyrite ± bornite ± pyrite ± pyrhhotite ± sphalerite ± molybdenite.

 

EXOSKARN ALTERATION (both calcic and magnesian): High Fe, low Mn, diopside- hedenbergite clinopyroxene (Hd20-80) and grossular-andradite garnet (Ad20-95), ± epidote ± apatite. Late stage amphibole ± chlorite ± ilvaite ± epidote ± scapolite ± albite ± K-feldspar. Magnesian Fe skarns can contain olivine, spinel, phlogopite, xanthophyllite, brucite, serpentine, and rare borate minerals such as ludwigite, szaibelyite, fluorborite and kotoite.

 

ENDOSKARN ALTERATION: Calcic Fe skarns: Extensive endoskarn with Na-silicates ± garnet ± pyroxene ± epidote ± scapolite. Magnesian skarns: Minor pyroxene ± garnet endoskarn, and propyllitic alteration.

 

ORE CONTROLS: Stratigraphic and structural controls. Close proximity to contacts between intrusions and carbonate sequences, volcanics or calcareous tuffs and sediments. Fracture zones near igneous contacts can also be important.

 

ASSOCIATED DEPOSIT TYPES: Cu porphyries (L03, L04); Cu (K01) and Pb-Zn (K02) skarns; small Pb-Zn veins (I05).

 

COMMENTS: In both calcic and magnesian Fe skarns, early magnetite is locally intergrown with, or cut by, garnet and magnesian silicates (Korzhinski, 1964, 1965;. Sangster, 1969; Burt, 1977). Some calcic Fe skarns contain relatively small pockets of pyrrhotite-pyrite mineralization that postdate the magnetite; this mineralization can be Au-rich. Byproduct magnetite is also derived from some Sn, Cu and calcic Pb-Zn skarns. Over 90% of the 146 Fe skarn occurrences in British Columbia lie within the Wrangellia Terrane of the Insular Belt. The majority of these form where Early to mid-Jurassic dioritic plutons intrude Late Triassic limestones.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Calcic Fe skarn: enriched in Fe, Cu, Co, Au, Ni, As, Cr. Overall Cu and Au grades are low (<0.2% Cu and 0.5 g/t Au). Magnesian Fe skarn: enriched in Fe, Cu, Zn, Bo.

 

GEOPHYSICAL SIGNATURE: Strong positive magnetic, electromagnetic and induced polarization anomalies. Possible gravity anomalies.

 

OTHER EXPLORATION GUIDES: Magnetite-rich float. In the Wrangellia Terrane of British Columbia, the upper and lower contacts of the Late Triassic Quatsino limestone (or equivalent units) are favorable horizons for Fe skarn development.

 

ECONOMIC FACTORS

 

GRADE AND TONNAGE: Grades are typically 40 to 50% Fe. Worldwide, calcic Fe skarns range from 3 to 150 Mt whereas magnesian Fe skarns can be larger (exceeding 250 Mt). In British Columbia, they reach 20 Mt and average approximately 4 Mt mined ore.

 

IMPORTANCE: Worldwide, these deposits were once an important source of iron, but in the last 40 years the market has been increasingly dominated by iron formation deposits. Nearly 90 % of British Columbia's historic iron production was from skarns.

 

REFERENCES

 

Burt, D.M. (1977): Mineralogy and Petrology of Skarn Deposits; Rendiconti, Societa Italiana di Mineralogia e Petrologia, Volume 33 (2), pages 859-873.

Cox, D.P. and Singer, D.A. (1986): Mineral Deposit Models; U.S. Geological Survey, Bulletin 1693, 379 pages.

Eckstrand, O.R. (1984): Canadian Mineral Deposit Types: A Geological Synopsis; Geological Survey of Canada, Economic Geology Report 36, 86 pages.

Einaudi, M.T. (1982): General Features and Origin of Skarns Associated with Porphyry Copper Plutons, Southwestern North America; in Advances in Geology of the Porphyry Copper Deposits, Southwestern U.S., Titley, S.R., Editor, Univ. Arizona Press, pages 185-209.

Einaudi, M.T., Meinert, L.D. and Newberry, R.J. (1981): Skarn Deposits; in Seventy-fifth Anniversary Volume, 1906-1980, Economic Geology, Skinner, B.J., Editor, Economic Geology Publishing Co., pages 317-391.

Korzhinski, D.S. (1964): An Outline of Metasomatic Processes (trans. M.E. Bergunker); International Geol. Review, Volume 6, pages 1713-1734.

Korzhinski, D.S. (1965): The Theory of Systems with Perfectly Mobile Components and Processes of Mineral Formation; American Journal of Science, Volume 263, pages 193-205.

Meinert, L.D. (1984): Mineralogy and Petrology of Iron Skarns in Western British Columbia, Canada; Economic Geology, Volume 79, Number 5, pages 869-882.

Meinert, L.D. (1992): Skarns and Skarn Deposits; Geoscience Canada, Volume 19, No. 4, pages 145-162.

Podlessky, K.V., Vlasova, D.K. and Kudrja, P.F. (1991): Magnetite-bearing Skarns of Mongolia; in Skarns - Their Genesis and Metallogeny, Theophrastus Publications, Athens, Greece, pages 265-298.

Ray, G.E. and Webster, I.C.L. (1991a): Geology and Mineral Occurrences of the Merry Widow Skarn Camp, Northern Vancouver Island, 92L/6; B. C. Ministry of Energy, Mines and Petroleum Resources, Open File Map 1991-8.

Ray, G.E., and Webster, I.C.L. (1991b): An Overview of Skarn Deposits; in Ore Deposits, Tectonics and Metallogeny in the Canadian Cordillera; McMillan, W.J., compiler, B. C. Ministry of Energy, Mines and Petroleum Resources, Paper 1991-4, pages 213-252.

Sangster, D.F. (1969): The Contact Metasomatic Magnetite Deposits of British Columbia; Geological Survey of Canada, Bulletin 172, 85 pages.

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Au SKARNS


K04
by Gerald E. Ray
British Columbia Geological Survey

 

Revised 1997

Ray, G.E. (1998): Au Skarns, in Geological Fieldwork 1997, British Columbia Ministry of Employment and Investment, Paper 1998-1, pages 24H-1 to 24H-4.

 

IDENTIFICATION

 

SYNONYMS: Pyrometasomatic, tactite, or contact metasomatic Au deposits.

 

COMMODITIES (BYPRODUCTS): Au (Cu, Ag).

 

EXAMPLES (British Columbia - Canada/International): Nickel Plate (092HSE038), French (092HSE059), Canty (092HSE064), Good Hope (092HSE060), QR - Quesnel River (093A 121); Fortitude, McCoy and Tomboy-Minnie (Nevada,USA), Buckhorn Mountain (Washington,USA), Diamond Hill, New World district and Butte Highlands (Montana,USA), Nixon Fork (Alaska, USA), Thanksgiving (Philippines), Browns Creek and Junction Reefs-Sheahan-Grants (New South Wales, Australia), Mount Biggenden (Queensland, Australia), Savage Lode, Coogee (Western Australia, Australia), Nambija (Ecuador), Wabu (Irian Jaya, Indonesia).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Gold-dominant mineralization genetically associated with a skarn gangue consisting of Ca - Fe - Mg silicates, such as clinopyroxene, garnet and epidote. Gold is often intimately associated with Bi or Au-tellurides, and commonly occurs as minute blebs (<40 microns) that lie within or on sulphide grains. The vast majority of Au skarns are hosted by calcareous rocks (calcic subtype). The much rarer magnesian subtype is hosted by dolomites or Mg-rich volcanics. On the basis of gangue mineralogy, the calcic Au skarns can be separated into either pyroxene-rich, garnet-rich or epidote-rich types; these contrasting mineral assemblages reflect differences in the hostrock lithologies as well as the oxidation and sulphidation conditions in which the skarns developed.

 

TECTONIC SETTINGS: Most Au skarns form in orogenic belts at convergent plate margins. They tend to be associated with syn to late island arc intrusions emplaced into calcareous sequences in arc or back-arc environments.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: Most deposits are related to plutonism associated with the development of oceanic island arcs or back arcs, such as the Late Triassic to Early Jurassic Nicola Group in British Columbia.

 

AGE OF MINERALIZATION: Phanerozoic (mostly Cenozoic and Mesozoic); in British Columbia Au skarns are mainly of Early to Middle-Jurassic age. The unusual magnesian Au skarns of Western Australia are Archean.

 

HOST/ASSOCIATED ROCK TYPES: Gold skarns are hosted by sedimentary carbonates, calcareous clastics, volcaniclastics or (rarely) volcanic flows. They are commonly related to high to intermediate level stocks, sills and dikes of gabbro, diorite, quartz diorite or granodiorite composition. Economic mineralization is rarely developed in the endoskarn. The I-type intrusions are commonly porphyritic, undifferentiated, Fe-rich and calc-alkaline. However, the Nambija, Wabu and QR Au skarns are associated with alkalic intrusions.

 

DEPOSIT FORM: Variable from irregular lenses and veins to tabular or stratiform orebodies with lengths ranging up to many hundreds of metres. Rarely, can occur as vertical pipe-like bodies along permeable structures.

 

TEXTURE/STRUCTURE: Igneous textures in endoskarn. Coarse to fine-grained, massive granoblastic to layered textures in exoskarn. Some hornfelsic textures. Fractures, sill-dike margins and fold hinges can be an important loci for mineralization.

 

ORE MINERALOGY (Principal and subordinate): The gold is commonly present as micron-sized inclusions in sulphides, or at sulphide grain boundaries. To the naked eye, ore is generally indistinguishable from waste rock. Due to the poor correlation between Au and Cu in some Au skarns, the economic potential of a prospect can be overlooked if Cu-sulphide-rich outcrops are preferentially sampled and other sulphide-bearing or sulphide-lean assemblages are ignored. The ore in pyroxene-rich and garnet-rich skarns tends to have low Cu:Au (<2000:1), Zn:Au (<100:1) and Ag/Au (<1:1) ratios, and the gold is commonly associated with Bi minerals (particularly Bi tellurides).

 

Magnesian subtype: Native gold ± pyrrhotite ± chalcopyrite ± pyrite ± magnetite ± galena ± tetrahedrite.

 

Calcic subtype:

 

Pyroxene-rich Au skarns: Native gold ± pyrrhotite ± arsenopyrite ± chalcopyrite ± tellurides (e.g. hedleyite, tetradymite, altaite and hessite) ± bismuthinite ± cobaltite ± native bismuth ± pyrite ± sphalerite ± maldonite. They generally have a high sulphide content and high pyrrhotite:pyrite ratios. Mineral and metal zoning is common in the skarn envelope. At Nickel Plate for example, this comprises a narrow proximal zone of coarse-grained, garnet skarn containing high Cu:Au ratios, and a wider, distal zone of finer grained pyroxene skarn containing low Cu:Au ratios and the Au-sulphide orebodies.

 

Garnet-rich Au skarns: Native gold ± chalcopyrite ± pyrite ± arsenopyrite ± sphalerite ± magnetite ± hematite ± pyrrhotite ± galena ± tellurides ± bismuthinite. They generally have a low to moderate sulphide content and low pyrrhotite:pyrite ratios.

 

Epidote-rich Au skarn: Native gold ± chalcopyrite ± pyrite ± arsenopyrite ± hematite ± magnetite ± pyrrhotite ± galena ± sphalerite ± tellurides. They generally have a moderate to high sulphide content with low pyrrhotite:pyrite ratios.

 

EXOSKARN MINERALOGY (GANGUE):

 

Magnesian subtype: Olivine, clinopyroxene (Hd2-50), garnet (Ad7-30), chondrodite and monticellite. Retrograde minerals include serpentine, epidote, vesuvianite, tremolite-actinolite, phlogopite, talc, K-feldspar and chlorite.

Calcic subtype:

 

Pyroxene-rich Au skarns: Extensive exoskarn, generally with high pyroxene:garnet ratios. Prograde minerals include diopsidic to hedenbergitic clinopyroxene (Hd 20-100), K-feldspar, Fe-rich biotite, low Mn grandite garnet (Ad 10-100), wollastonite and vesuvianite. Other less common minerals include rutile, axinite and sphene. Late or retrograde minerals include epidote, chlorite, clinozoisite, vesuvianite, scapolite, tremolite-actinolite, sericite and prehnite.

 

Garnet-rich Au skarns: Extensive exoskarn, generally with low pyroxene:garnet ratios. Prograde minerals include low Mn grandite garnet (Ad 10-100), K-feldspar, wollastonite, diopsidic clinopyroxene (Hd 0-60), epidote, vesuvianite, sphene and apatite. Late or retrograde minerals include epidote, chlorite, clinozoisite, vesuvianite, tremolite-actinolite, sericite, dolomite, siderite and prehnite.

 

Epidote-rich Au skarns: Abundant epidote and lesser chlorite, tremolite-actinolite, quartz, K-feldspar, garnet, vesuvianite, biotite, clinopyroxene and late carbonate. At the QR deposit, epidote-pyrite and carbonate-pyrite veinlets and coarse aggregates are common, and the best ore occurs in the outer part of the alteration envelope, within 50 m of the epidote skarn front.

 

ENDOSKARN MINERALOGY (GANGUE): Moderate endoskarn development with K-feldspar, biotite, Mg-pyroxene (Hd 5-30) and garnet. Endoskarn at the epidote-rich QR deposit is characterized by calcite, epidote, clinozoisite and tremolite whereas at the Butte Highlands Mg skarn it contains argillic and propyllitic alteration with garnet, clinopyroxene and epidote.

 

WEATHERING: In temperate and wet tropical climates, skarns often form topographic features with positive relief.

 

ORE CONTROLS: The ore exhibits strong stratigraphic and structural controls. Orebodies form along sill-dike intersections, sill-fault contacts, bedding-fault intersections, fold axes and permeable faults or tension zones. In the pyroxene-rich and epidote-rich types, ore commonly develops in the more distal portions of the alteration envelopes. In some districts, specific suites of reduced, Fe-rich intrusions are spatially related to Au skarn mineralization. Ore bodies in the garnet-rich Au skarns tend to lie more proximal to the intrusions.

 

GENETIC MODEL: Many Au skarns are related to plutons formed during oceanic plate subduction. There is a worldwide spatial, temporal and genetic association between porphyry Cu provinces and calcic Au skarns. Pyroxene-rich Au skarns tend to be hosted by siltstone-dominant packages and form in hydrothermal systems that are sulphur-rich and relatively reduced. Garnet-rich Au skarns tend to be hosted by carbonate-dominant packages and develop in more oxidising and/or more sulphur-poor hydrothermal systems.

 

ASSOCIATED DEPOSIT TYPES: Au placers (C01, C02), calcic Cu skarns (K01), porphyry Cu deposits (L04) and Au-bearing quartz and/or sulphide veins (I01, I02). Magnesian subtype can be associated with porphyry Mo deposits (L05) and possibly W skarns (K05). In British Columbia there is a negative spatial association between Au and Fe skarns at regional scales, even though both classes are related to arc plutonism. Fe skarns are concentrated in the Wrangellia Terrane whereas most Au skarn occurrences and all the economic deposits lie in Quesnellia.

 

COMMENTS: Most Au skarns throughout the world are calcic and are associated with island arc plutonism. However, the Savage Lode magnesian Au skarn occurs in the Archean greenstones of Western Australia and the Butte Highlands magnesian Au skarn in Montana is hosted by Cambrian platformal dolomites. Note: although the Nickel Plate deposit lies distal to the Toronto stock in the pyroxene-dominant part of the skarn envelope, the higher grade ore zones commonly lie adjacent to sills and dikes where the exoskarn contains appreciable amounts of garnet with the clinopyroxene.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Au, As, Bi, Te, Co, Cu, Zn or Ni soil, stream sediment and rock anomalies, as well as some geochemical zoning patterns throughout the skarn envelope (notably in Cu/Au, Ag/Au and Zn/Au ratios). Calcic Au skarns (whether garnet-rich or pyroxene-rich) tend to have lower Zn/Au, Cu/Au and Ag/Au ratios than any other skarn class. The intrusions related to Au skarns may be relatively enriched in the compatible elements Cr, Sc and V, and depleted in lithophile incompatible elements (Rb, Zr, Ce, Nb and La), compared to intrusions associated with most other skarn types.

 

GEOPHYSICAL SIGNATURE: Airborne magnetic or gravity surveys to locate plutons. Induced polarization and ground magnetic follow-up surveys can outline some deposits.

 

 

OTHER EXPLORATION GUIDES: Placer Au. Any carbonates, calcareous tuffs or calcareous volcanic flows intruded by arc-related plutons have a potential for hosting Au skarns. Favorable features in a skarn envelope include the presence of: (a) proximal Cu-bearing garnet skarn and extensive zones of distal pyroxene skarn which may carry micron Au, (b) hedenbergitic pyroxene (although diopsidic pyroxene may predominate overall), (c) sporadic As-Bi-Te geochemical anomalies, and, (d) undifferentiated, Fe-rich intrusions with low Fe2O3/FeO ratios. Any permeable calcareous volcanics intruded by high-level porphyry systems (particularly alkalic plutons) have a potential for hosting epidote-rich skarns with micron Au. During exploration, skarns of all types should be routinely sampled and assayed for Au, even if they are lean in sulphides.

 

ECONOMIC IMPORTANCE

 

TYPICAL GRADE AND TONNAGE: These deposits range from 0.4 to 13 Mt and from 2 to 15 g/t Au. Theodore et al. (1991) report median grades and tonnage of 8.6 g/t Au, 5.0 g/t Ag and 213 000 t. Nickel Plate produced over 71 tonnes of Au from 13.4 Mt of ore (grading 5.3 g/t Au). The 10.3 Mt Fortitude (Nevada) deposit graded 6.9 g/t Au whereas the 13.2 Mt McCoy skarn (Nevada) graded 1.5 g/t Au. The QR epidote-rich Au skarn has reserves exceeding 1.3 Mt grading 4.7 g/t Au.

 

IMPORTANCE: Recently, there have been some significant Au skarn deposits discovered around the world (e.g. Buckhorn Mountain, Wabu, Fortitude). Nevertheless, total historic production of Au from skarn (more than 1 000 t of metal) is minute compared to production from other deposit types. The Nickel Plate deposit (Hedley, British Columbia) was probably one of the earliest major Au skarns in the world to be mined. Skarns have accounted for about 16 % of British Columbia's Au production, although nearly half of this was derived as a byproduct from Cu and Fe skarns.

 

REFERENCES

 

Billingsley, P. and Hume, C.B. (1941): The Ore Deposits of Nickel Plate Mountain, Hedley, British Columbia; Canadian Institute of Mining and Metallurgy, Bulletin, Volume 44, pages 524-590.

Brookes, J.W., Meinert, L.D., Kuyper, B.A. and Lane, M.L. (1990): Petrology and Geochemistry of the McCoy Gold Skarn, Lander County, Nevada; in Geology and Ore Deposits of the Great Basin, Symposium Proceedings, Geological Society of Nevada, April 1990.

Ettlinger, A.D. and Ray, G.E. (1989a): Precious Metal Enriched Skarns in British Columbia: An Overview and Geological Study; B. C. Ministry of Energy, Mines and Petroleum Resources, Paper 1989-3, 128 pages.

Ettlinger, A.D., Albers, D., Fredericks, R. and Urbisinov, S. (1995): The Butte Highlands Project, Silver Bow County, Montana; An Olivine-rich Magnesian Gold Skarn; in Symposium Proceedings of Geology and Ore Deposits of American Cordilleran, Geological Society of Nevada, U.S. Geological Survey and Geological Society of Chile, April 10-13, 1995, Reno, Nevada.

Fox, P.E., and Cameron, R.S. (1995): Geology of the QR Gold Deposit, Quesnel River Area, British Columbia; in Porphyry Deposits of the Northwest Cordillera of North America, (editor) T.G. Schroeter, Canadian Institute of Mining, Metallurgy and Petroleum, Special Volume 46, Paper 66, pages 829-837.

Hammarstrom, J.M., Orris, G.J., Bliss, J.D., and Theodore, T.G. (1989): A Deposit Model for Gold-Bearing Skarns; Fifth Annual V.E. McKelvey Forum on Mineral and Energy Resources, U.S. Geological Survey , Circular 1035, pages 27-28.

McKelvey, G.E., and Hammarstrom, J.M. (1991): A Reconnaissance Study of Gold Mineralization Associated with Garnet Skarn at Nambija, Zamora Province, Ecuador, in USGS Research on Mineral Resources - 1991, Program and Abstracts. Editors E.J. Good, J.F. Slack and R.K. Kotra, U.S. Geological Survey, Circular 1062, page 55.

Meinert, L.D. (1989): Gold Skarn Deposits - Geology and Exploration Criteria; in The Geology of Gold Deposits; The Perspective in 1988; Economic Geology; Monograph 6, pages 537-552.

Mueller, A.G. (1991): The Savage Lode Magnesian Skarn in the Marvel Loch Gold-Silver Mine, Southern Cross Greenstone Belt, Western Australia; Part I. Structural Setting, Petrography and Geochemistry; Canadian Journal of Earth Sciences, Volume 28, Number 5, pages 659-685.

Orris, G.J., Bliss, J.D., Hammarstrom, J.M. and Theodore, T.G. (1987): Description and Grades and Tonnages of Gold-bearing Skarns; U. S. Geological Survey, Open File Report 87-273, 50 pages.

Ray, G.E. and Dawson, G.L. (1994): The Geology and Mineral Deposits of the Hedley Gold Skarn District, Southern British Columbia; B.C. Ministry of Energy, Mines and Petroleum Resources, Bulletin 87, 156 pages.

Ray, G.E. and Webster, I.C.L. (1997): Skarns in British Columbia;, B.C. Ministry of Energy, Mines and Petroleum Resources, Bulletin 101, 260 pages.

Ray, G.E., Ettlinger, A.D. and Meinert, L.D. (1990): Gold Skarns: Their Distribution, Characteristics and Problems in Classification; in Geological Fieldwork 1989, B.C. Ministry of Energy, Mines and Petroleum Resources, Paper 1990-1, pages 237-246.

Theodore, T.G., Orris, G.J., Hammarstrom, J.M. and Bliss, J.D. (1991): Gold Bearing Skarns; U. S. Geological Survey; Bulletin 1930, 61 pages.

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W SKARNS

K05
by Gerald E. Ray
British Columbia Geological Survey

 

Ray, G.E. (1995): W Skarns, in Selected British Columbia Mineral Deposit Profiles, Volume 1 - Metallics and Coal, Lefebure, D.V. and Ray, G.E., Editors, British Columbia Ministry of Employment and Investment, Open File 1995-20, pages 71-74.

IDENTIFICATION

 

SYNONYMS: Pyrometasomatic or contact metasomatic tungsten deposits.

 

COMMODITIES (BYPRODUCTS): W (Mo, Cu, Sn, Zn).

 

EXAMPLES (British Columbia - Canada/International): Emerald Tungsten (082FSW010), Dodger (082FSW011), Feeney (082FSW247), Invincible (082FSW218), Dimac (082M 123); Fostung (Ontario, Canada), MacTung (Yukon, Canada), Cantung (Northwest Territories, Canada), Pine Creek and Strawberry(California, USA), Osgood Range (Nevada, USA), King Island (Tasmania, Australia), Sang Dong (South Korea).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Scheelite-dominant mineralization genetically associated with a skarn gangue.

 

TECTONIC SETTING: Continental margin, synorogenic plutonism intruding deeply buried sequences of eugeoclinal carbonate-shale sedimentary rocks. Can develop in tectonically thickened packages in back-arc thrust settings.

 

AGE OF MINERALIZATION: Mainly Mesozoic, but may be any age. Over 70% of the W skarns in British Columbia are related to Cretaceous intrusions.

 

HOST/ASSOCIATED ROCK TYPES: Pure and impure limestones, calcareous to carbonaceous pelites. Associated with tonalite, granodiorite, quartz monzonite and granite of both I and S-types. W skarn-related granitoids, compared to Cu skarn- related plutonic rocks, tend to be more differentiated, more contaminated with sedimentary material, and have crystallized at a deeper structural level.

 

DEPOSIT FORM: Stratiform, tabular and lens-like orebodies. Deposits can be continous for hundreds of metres and follow intrusive contacts.

 

TEXTURES: Igneous textures in endoskarn. Coarse to fine-grained, massive granoblastic to mineralogically layered textures in exoskarn. Biotite hornfelsic textures common.

 

ORE MINERALOGY (Principal and subordinate): Scheelite ± molybdenite ± chalcopyrite ± pyrrhotite ± sphalerite ± arsenopyrite ± pyrite ± powellite. May contain trace wolframite, fluorite, cassiterite, galena, marcasite and bornite. Reduced types are characterized by pyrrhotite, magnetite, bismuthinite, native bismuth and high pyrrhotite:pyrite ratios. Variable amounts of quartz-vein stockwork (with local molybdenite) can cut both the exo and endoskarn. The Emerald Tungsten skarns in British Columbia include pyrrhotite-arsenopyrite veins and pods that carry up to 4 g/t Au.

 

ALTERATION MINERALOGY: Exoskarn alteration: Inner zone of diopside-hedenbergite (Hd60- 90, Jo5-20) ± grossular-andradite (Ad 10-50, Spess5-50) ± biotite ± vesuvianite, with outer barren wollastonite-bearing zone. An innermost zone of massive quartz may be present. Late-stage spessartine ± almandine ± biotite ± amphibole ± plagioclase ± phlogopite ± epidote ± fluorite ± sphene. Reduced types are characterized by hedenbergitic pyroxene, Fe-rich biotite, fluorite, vesuvianite, scapolite and low garnet:pyroxene ratios, whereas oxidized types are characterized by salitic pyroxene, epidote and andraditic garnet and high garnet:pyroxene ratios. Exoskarn envelope can be associated with extensive areas of biotite hornfels. Endoskarn alteration: Pyroxene ± garnet ± biotite ± epidote ± amphibole ± muscovite ± plagioclase ± pyrite ± pyrrhotite ± trace tourmaline and scapolite; local greisen developed.

 

ORE CONTROLS: Carbonate rocks in extensive thermal aureoles of intrusions; gently inclined bedding and intrusive contacts; structural and/or stratigraphic traps in sedimentary rocks, and irregular parts of the pluton/country rock contacts.

 

ASSOCIATED DEPOSIT TYPES: Sn (K06), Mo (K07) and Pb-Zn (K02) skarns. Wollastonite-rich industrial mineral skarns (K09).

 

COMMENTS: W skarns are separable into two types (Newberry, 1982): reduced skarns (e.g. Cantung, Mactung), formed in carbonaceous rocks and/or at greater depths, and oxidized skarns (e.g. King Island ), formed in hematitic or non-carbonaceous rocks, and/or at shallower depths. Late retrograde alteration is an important factor in many W skarns because, during retrogression, the early low-grade mineralization is often scavenged and redeposited into economic high-grade ore zones (e.g. Bateman, 1945; Dick, 1976, 1980). Dolomitic rocks tend to inhibit the development of W skarns; consequently magnesian W skarns are uncommon. In British Columbia they are preferentially associated with Cretaceous intrusions and hosted by calcareous, Cambrian age cratonic, pericratonic and displaced continental margin rocks in the Cassiar, Kootenay-Barkerville, Dorsay and Ancestral North American terranes.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: W, Cu, Mo, As, Bi and B. Less commonly Zn, Pb, Sn, Be and F geochemical anomalies.

 

ECONOMIC FACTORS

 

GRADE AND TONNAGE: Grades range between 0.4 and 2% WO3 (typically 0.7%). Deposits vary from 0.1 to >30 Mt.

 

IMPORTANCE: Skarn deposits have accounted for nearly 60 % of the western world's production, and over 80 % of British Columbia's production.

 

REFERENCES

 

Bateman, P.C. (1945): Pine Creek and Adamson Tungsten Mines, Inyo County, California; California Journal Mines Geology, Volume 41, pages 231-249.

Dawson, K.M., Panteleyev, A. and Sutherland Brown, A. (1991): Regional Metallogeny, Chapter 19, in Geology of the Cordilleran Orogen in Canada, Gabrielse, H. and Yorath, C.J., Editors, Geological Survey of Canada, Geology of Canada, Number 4, pages 707-768 (also, Geological Society of America, The Geology of North America, volume G-2).

Dick, L.A. (1976): Metamorphism and Metasomatism at the MacMillan Pass Tungsten Deposit, Yukon and District of MacKenzie, Canada; unpublished M.Sc. thesis, Queens University, 226 pages.

Dick, L.A. (1980): A Comparative Study of the Geology, Mineralogy and Conditions of Formation of Contact Metasomatic Mineral Deposits in the Northeastern Canadian Cordillera; Unpublished Ph.D. Thesis, Queen's University, 471 pages.

Eckstrand, O.R. (1984): Canadian Mineral Deposit Types: A Geological Synopsis; Geological Survey of Canada, Economic Geology Report 36, 86 pages.

Einaudi, M.T. and Burt, D.M. (1982): Introduction - Terminology, Classification and Composition of Skarn Deposits; Economic Geology; Volume 77, pages 745-754.

Einaudi, M.T., Meinert, L.D. and Newberry, R.J. (1981): Skarn Deposits; in Seventy-fifth Anniversary Volume, 1906-1980, Economic Geology, Skinner, B.J., Editor, Economic Geology Publishing Co., pages 317-391.

Kwak, T.A.P. (1987): W-Sn Skarn Deposits and Related Metamorphic Skarns and Granitoids; in Developments in Economic Geology, Volume 24, Elsevier Publishing Co., 445 pages.

Kwak, T.A.P. and White, A.J.R. (1982): Contrasting W-Mo-Cu and W-Sn-F Skarn Types and Related Granitoids. Mining Geology. Volume 32(4), pages 339-351.

Lowell, G.R. (1991): Tungsten-bearing Scapolite-Vesuvianite Skarns from the Upper Salcha River Area, East-central Alaska; in Skarns - Their Genesis and Metallogeny, Theophrastus Publications, Athens, Greece, pages 385-418.

Newberry, R.J. (1979): Systematics in the W-Mo-Cu Skarn Formation in the Sierra Nevada: An Overview; Geological Society of America, Abstracts with Programs; Volume 11, page 486.

Newberry, R.J. (1982): Tungsten-bearing Skarns of the Sierra Nevada. I. The Pine Creek Mine, California; Economic Geology, Volume 77, pages 823-844.

Newberry, R.J., and Swanson, S.E. (1986): Scheelite Skarn Granitoids: An Evaluation of the Roles of Magmatic Source and Process; Ore Geology Review, Number 1, pages 57- 81.

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Sn SKARNS


K06
by Gerald E. Ray
British Columbia Geological Survey

 

Ray, G.E. (1995): Sn Skarns, in Selected British Columbia Mineral Deposit Profiles, Volume 1 - Metallics and Coal, Lefebure, D.V. and Ray, G.E., Editors, British Columbia Ministry of Employment and Investment, Open File 1995-20, pages 75-76.

 

IDENTIFICATION

 

SYNONYMS: Pyrometasomatic or contact metasomatic tin deposits.

 

COMMODITIES (BYPRODUCTS): Sn (W, Zn, magnetite).

 

EXAMPLES (British Columbia - Canada/International): Only three in British Columbia - Silver Diamond, Atlin Magnetite, and Daybreak (104N069, 126 and 134 respectively); JC (Yukon, Canada), Moina, Mount Lindsay, Hole 16 and Mt. Garnet (Tasmania, Australia), Lost River (Alaska, USA).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Cassiterite-dominant mineralization genetically associated with a skarn gangue (includes calcic and magnesian Sn skarns).

 

TECTONIC SETTINGS: Late to post orogenic granites emplaced into thick and deeply buried continental margin sedimentary sequences, or sequences in rifted or stable cratonic environments.

 

AGE OF MINERALIZATION: Most economic deposits are Mesozoic or Paleozoic, but occurrences may be any age (the occurrences in British Columbia are Late Cretaceous).

 

HOST/ASSOCIATED ROCK TYPES: Carbonates and calcareous sedimentary sequences. Associated with differentiated (low Ca, high Si and K) ilmenite-series granite, adamellite and quartz monzonitic stocks and batholiths (of both I and S-type) intruding carbonate and calcareous clastic rocks. Sn skarns tend to develop in reduced and deep-level environments and may be associated with greisen alteration.

 

DEPOSIT FORM: Variable; can occur as either stratiform, stockwork, pipe-like or irregular vein-like orebodies.

 

TEXTURES: Igneous textures in endoskarn. Coarse to fine-grained, massive granoblastic to mineralogically layered textures in exoskarn; wrigglite skarns contain thin rhythmic and alternating layers rich in either magnetite, fluorite, vesuvianite or tourmaline. Some hornfelsic textures.

 

ORE MINERALOGY: Cassiterite ± scheelite ± arsenopyrite ± pyrrhotite ± chalcopyrite ± stannite ± magnetite ± bismuthinite ± sphalerite ± pyrite ± ilmenite.

 

ALTERATION MINERALOGY: Exoskarn alteration: Grandite garnet (Ad15-75, Pyralsp 5-30) (sometimes Sn, F, and Be enriched), hedenbergitic pyroxene (Hd40-95) ± vesuvianite (sometimes Sn and F-enriched) ± malayaite ± Fe and/or F-rich biotite ± stanniferous sphene ± gahnite ± rutile ± Sn-rich ilvaite ± wollastonite ± adularia. Late minerals include muscovite, Fe-rich biotite, chlorite, tourmaline, fluorite, sellaite, stilpnomelane, epidote and amphibole (latter two minerals can be Sn rich). Associated greisens include quartz and muscovite ± tourmaline ± topaz ± fluorite ± cassiterite ± sulphides. Magnesian Sn skarns can also contain olivine, serpentine, spinel, ludwigite, talc and brucite.

 

ORE CONTROLS: Differentiated plutons intruding carbonate rocks; fractures, lithological or structural contacts. Deposits may develop some distance (up to 500 m) from the source intrusions.

 

ASSOCIATED DEPOSIT TYPES: W skarns (K05), Sn ± Be greisens (I13), Sn-bearing quartz-sulphide veins and mantos (J02). In British Columbia, some of the Sn and W skarn-related intrusions (e.g. Cassiar batholith, Mount Haskin stock) are associated with small Pb-Zn skarn occurrences (K02).

 

COMMENTS: Sn skarns generally form at deep structural levels and in reduced oxidation states. However, wrigglite Sn skarns tend to develop in relatively near- surface conditions, such as over the cupolas of high-level granites. The three Sn skarn occurrences in British Columbia are all associated with an S-type, fluorine-rich accretionary granite, the Surprise Lake batholith. However, they are unusual in being hosted in allochthonous oceanic rocks of the Cache Creek Terrane.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Sn, W, F, Be, Bi, Mo, As, Zn, Cu, Rb, Li, Cs and Re geochemical anomalies. Borate-bearing magnesian Sn skarns may exhibit B enrichment.

 

GEOPHYSICAL SIGNATURE: Magnetic, induced polarization and possible radiometric anomalies.

 

ECONOMIC FACTORS

 

GRADE AND TONNAGE: Deposits can grade up to 1 % Sn, but much of the metal occurring in malayaite, garnet, amphibole and epidote is not economically recoverable. Worldwide, deposits reach 30 Mt, but most range between 0.1 and 3 Mt.

 

IMPORTANCE: Worldwide, Sn skarns represent a major reserve of tin. However, current production from skarn is relatively minor compared to that from placer Sn deposits and Sn-rich greissens and mantos. British Columbia has had no Sn production from skarns.

 

REFERENCES

 

Burt, D.M. (1978): Tin Silicate-Borate-Oxide Equilibria in Skarns and Greisens - The System CaO-SnO2-SiO2-H2O-B2O3-CO2-F2O-1; Economic Geology, Volume 73, pages 269- 282.

Cox, D.P. and Singer, D.A. (1986): Mineral Deposit Models; U.S. Geological Survey, Bulletin 1693, 379 pages.

Einaudi, M.T., Meinert, L.D. and Newberry, R.J. (1981): Skarn Deposits; in Seventy-fifth Anniversary Volume, 1906-1980, Economic Geology, Skinner, B.J., Editor, Economic Geology Publishing Co., pages 317-391.

Kwak, T.A.P. (1987): W-Sn Skarn Deposits and Related Metamorphic Skarns and Granitoids; in Developments in Economic Geology, Volume 24, Elsevier Publishing Co. 445 pages.

Kwak, T.A.P. and Askins, P.W. (1981): Geology and Genesis of the F-Sn-W (-Be-Zn) Skarn (Wrigglite) at Moina, Tasmania, Australia; Economic Geology, Volume 76, pages 439-467.

Mitrofanov, N.P. and Stolyarov, I.S. (1982): Comparative Description of Tin-bearing Skarns of the Ladoga Region and Central Asia; International Geology Revue, Volume 24, No. 11, pages 1299-1305.

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Mo SKARNS


K07
by Gerald E. Ray
British Columbia Geological Survey

 

Ray, G.E. (1995): Mo Skarns, in Selected British Columbia Mineral Deposit Profiles, Volume 1 - Metallics and Coal, Lefebure, D.V. and Ray, G.E., Editors, British Columbia Ministry of Employment and Investment, Open File 1995-20, pages 77-78.

 

IDENTIFICATION

 

SYNONYMS: Pyrometasomatic or contact metasomatic Mo deposits.

 

COMMODITIES (BYPRODUCTS): Mo (W, Cu, Pb, Zn, Sn, Bi, U, Au).

 

EXAMPLES (British Columbia - Canada/International): Coxey (082FSW110), Novelty
(082FSW107); Mount Tennyson (New South Wales, Australia), Little Boulder Creek (Idaho, USA), Cannivan Gulch (Montana, USA), Azegour (Morocco), Yangchiachangtze (China).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Molybdenite-dominant mineralization genetically associated with a skarn gangue (includes calcic and magnesian Mo skarns). Mo skarns are broadly separable into polymetallic and “molybdenite-only” types (see comments below).

 

TECTONIC SETTING: Late orogenic plutonism (derived from transitional crust) intruding continental margin carbonate sequences. Also, some are associated with Mo- bearing porphyry systems developed within intra-oceanic island arcs.

 

AGE OF MINERALIZATION: Mainly Mesozoic and Paleozoic, but may be any age. In British Columbia, they are mainly of Early to mid-Jurassic in age.

 

HOST/ASSOCIATED ROCK TYPES: Stocks and dikes of evolved, commonly leucocratic quartz monzonite to granite (some containing primary biotite and muscovite) intruding calcareous clastic rocks. Deposits tend to develop close to intrusive contacts. Some of the Mo skarns in British Columbia are associated with high- level intrusions that have explosive breccia textures.

 

DEPOSIT FORM: Irregular orebodies along, and controlled by, the intrusive contacts.

 

TEXTURES: Igneous textures in endoskarn; local explosive breccia textures. Coarse to fine-grained, massive granoblastic to mineralogically layered textures in exoskarn. Some hornfelsic textures.

 

ORE MINERALOGY (Principal and subordinate): Molybdenite ± scheelite ± pyrrhotite ± powellite ± chalcopyrite ± arsenopyrite ± pyrite ± pyrrhotite ± bismuthinite ± sphalerite ± fluorite. In rare instances also galena ± magnetite ± uraninite ± pitchblende ± cassiterite ± cobalite ± stannite ± gold.

 

EXOSKARN ALTERATION: Calcic Mo skarns: Hedenbergite pyroxene (Hd50-80, Jo1-3) ± low Mn grossular-andradite garnet (Ad40-95) ± wollastonite ± biotite ± vesuvianite. Magnesian Mo skarns: olivine (Fo96). Retrograde minerals: Calcic skarns: amphibole ± epidote ± chlorite and muscovite. Magnesian skarns: serpentine ± tremolite ± chlorite.

 

ENDOSKARN ALTERATION: Clinopyroxene, K-feldspar, hornblende, epidote, quartz veining, sericite, molybdenite.

ORE CONTROLS: Carbonate or calcareous rocks in thermal aureoles adjacent to intrusive margins.

 

ASSOCIATED DEPOSIT TYPES: Mo porphyries of quartz monzonite type (L05), Mo-sulphide veins, and Zn-sulphide veins (I05). Some Mo skarns in China are associated with distal, sphalerite-rich mineralization.

 

COMMENTS: Mo skarns are broadly separable into two types: polymetallic (containing molybdenite with other W, Zn, Pb, Bi, Sn, Co or U-rich minerals), and "molybedenite-only" (containing mainly molybdenite with no or few other sulphides). Over 85% of the 21 Mo skarns recorded in British Columbia occur in the Omineca Belt. More than 60% are hosted in cratonic, pericratonic and displaced continental margin rocks of the Kootenay, Cassiar and Ancestral North America terranes, and a further 19% are found in the Quesnellia Terrane.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Enriched in Mo, Zn, Cu, Sn, Bi, As, F, Pb, U, Sb, Co (Au).

 

GEOPHYSICAL SIGNATURE: Positive magnetic and induced polarization anomalies.

 

ECONOMIC FACTORS

 

GRADE AND TONNAGE: Worldwide, grades range from 0.1 to 2 % MoS2, and tonnages between 0.1 and 2 Mt. In British Columbia, the Coxey deposit produced 1 Mt of ore grading approximately 0.17 % MoS2. The Novelty and Giant are polymetallic Mo skarns near Rossland, British Columbia with unusually high grades of up to 47 g/t Au, 1.4 % Ni, 30.5 % As and 4.84 % Co.

 

IMPORTANCE: Mo skarns tend to be smaller tonnage and less economically important than porphyry Mo deposits.

 

REFERENCES

 

Einaudi, M.T., Meinert, L.D. and Newberry, R.J. (1981): Skarn Deposits; in Seventy-fifth Anniversary Volume, 1906-1980, Economic Geology, Skinner, B.J., Editor, Economic Geology Publishing Co., pages 317-391.

Theodore, T.G. and Menzie, W.D. (1984): Fluorine-deficient Porphyry Molybdenum Deposits in the Western North American Cordillera; Proceedings of the 6th Quadrennial IAGOD Symposium, Stuttgart, Germany, pages 463-470.

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GARNET SKARNS


K08
by Gerald E. Ray
British Columbia Geological Survey

 

Ray, G.E. (1998): Garnet Skarns, in Geological Fieldwork 1997, British Columbia Ministry of Employment and Investment, Paper 1998-1, pages 24I-1 to 24I-2.

 

IDENTIFICATION

 

SYNONYM: Pyrometasomatic or contact metasomatic garnet deposits.

 

COMMODITIES (BYPRODUCTS): Garnet (wollastonite, magnetite).

 

EXAMPLES (British Columbia - Canada/International): Mount Riordan (Crystal Peak, 082ESW102); San Pedro (New Mexico, USA).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Garnet-dominant skarn hosted by calcareous rocks generally near an intrusive contact.

 

TECTONIC SETTINGS: Virtually any setting.

 

AGE OF DEPOSIT: May be any age.

 

HOST/ASSOCIATED ROCK TYPES: Garnet is hosted by carbonate or altered calcareous mafic volcanic sequences that are intruded by relatively oxidized plutons.

 

DEPOSIT FORM: Irregular zones of massive garnet developed in exoskarn close to plutonic contacts. The shape of the deposit may be controlled partly by the morphology of the original conformable units.

 

TEXTURES: Coarse grained, massive granoblastic textures in exoskarn.

 

ORE MINERALOGY (Principal and subordinate): Abundant and massive, coarse grained garnet (grossular-andradite) ± wollastonite ± magnetite.

 

ALTERATION MINERALOGY (Principal and subordinate): Garnet, clinopyroxene, quartz, feldspar, calcite, sphene, apatite, axinite, vesuvianite and sericite.

 

OPAQUE MINERALOGY: Economically viable garnet deposits typically have very little or no sulphides.

 

ORE CONTROLS: Plutonic contacts and oxidized carbonate host rocks. The Mount Riordan garnet skarn lies proximal to the intrusion.

 

ASSOCIATED DEPOSIT TYPES: Cu, Fe, Au and wollastonite skarns (K01, K03, K04 and K09).

 

COMMENTS: The best industrial garnets (due to higher specific gravity and hardness) are almandine-pyrope composition. These generally occur in high grade metamorphic rocks and require secondary concentration in beach or stream placers to be mined economically. Examples include the Emerald Creek deposit located in Idaho, USA, and a 6 Mt beach-sand deposit situated near Geraldton, Western Australia that grades 35 per cent garnet. The Mount Riordan deposit is one of the largest and highest grade garnet skarns yet identified; its garnet is suitable for the production of sandblasting and other abrasive products that require high angularity and a wide range of grain sizes. In British Columbia, there have been intermittent attempts to process the garnet-rich tailings from the Iron Hill-Argonaut Fe skarn (092F 075).

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: May get very weak W, Mo, Zn and Cu geochemical anomalies.

 

GEOPHYSICAL SIGNATURE: Gravity and possible magnetic anomalies.

 

ECONOMIC FACTORS

 

GRADE AND TONNAGE: To be economic, garnet skarn deposits should be large tonnage (>20 Mt) and high grade (> 70% garnet). The Mount Riordan (Crystal Peak) deposit contains reserves of 40 Mt grading 78% garnet and San Pedro is a 22 to 30 Mt deposit with 85% andraditic garnet.

 

ECONOMIC LIMITATIONS: The garnet should be free of inclusions, possess a relatively high specific gravity and high angularity, and be present as discrete grains that can be processed easily by conventional benefication techniques. Economic concentrations of clean and industrially suitable grossularite-andradite garnet in skarn are rare. This is because skarn garnets tend to be relative soft and many contain fine-grained carbonate inclusions. Easy access, low cost transportation and a ready and reliable market for the product are essential features controlling the economic viability of a deposit.

 

END USES: Sandblasting, water-jet equipment and abrasives, such as sandpaper. Grossular-andradite garnets have more restricted uses than almandine.

 

IMPORTANCE: World production in 1995 of industrial garnet was approximately 110 000 tonnes, of which just under half (valued at $US 11 million) was produced in the U.S. Worldwide, most garnet is obtained from placer deposits or as a byproduct during hard rock mining of other commodities. The demand in North America for industrial garnet is growing; skarns are expected to be an important future source for the mineral.

 

SELECTED BIBLIOGRAPHY

 

Austin, G.T. (1991): Garnet (Industrial); in Mineral Commodity Summaries 1991, Department of the Interior, United States Bureau of Mines, pages 58-59.

Grond, H.C., Wolfe, R., Montgomery, J.H. and Giroux, G.H. (1991): A Massive Skarn-hosted Andradite Deposit near Penticton, British Columbia; in Industrial Minerals of Alberta and British Columbia, Canada, B.C. Ministry of Energy, Mines and Petroleum Resources, Open File 1991-23, pages 131-133.

Harben, P.W. and Bates, R.L. (1990): Garnet; in Industrial Minerals, Geology and World Deposits, Industrial Minerals Division, Metal Bulletin Plc., London, pages 120-12.

Hight, R.P. (1983): Abrasives; in Industrial Minerals and Rocks, 5th edition, American Institute of Mining, Metallurgy and Petroleum Engineers, Lefond, S.J., Editor, New York, pages 11-32.

Smoak, J.F. (1985): Garnet; Unites States Bureau of Mines, Bulletin 675, pages 297-304.

Ray, G.E., Grond, H.C., Dawson, G.L. and Webster, I.C.L. (1992): The Mount Riordan (Crystal Peak) Garnet Skarn, Hedley District, Southern British Columbia; Economic Geology, Volume 87, pages 1862-1876.

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WOLLASTONITE SKARNS


K09
by G.J. Simandl1, S. Paradis2, G.J Orris3 and G.E. Ray1
1British Columbia Geological Survey, Victoria, B.C., Canada
2Geological Survey of Canada, Sidney, B.C., Canada
3United States Geological Survey, Tucson, Arizona, USA

 

Simandl, G.J., Paradis, S., Orris, G.J. and Ray, G.E. (1999): Wollastonite Skarns; 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

 

COMMODITIES (BYPRODUCTS):  Wollastonite (in some cases garnet, clinopyroxene, high calcium carbonate, limestone, marble, Cu and possibly other metals).

 

EXAMPLES (British Columbia (MINFILE#):  Canada/International): Mineral Hill (092GNW052), Zippa Mountain (104B 384), Rossland wollastonite (082FSW341); Fox Knoll and Lewis (New York, USA), Lappeenranta (Finland), Khila (Belkapahar, India), Koytash (Uzbekistan, Commonwealth of Independent States).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Wollastonite deposits form irregular masses or lenses in metamorphosed calcareous rocks. Most form adjacent to or some distance from known igneous intrusions. Some deposits are located in medium to high grade metamorphic terrains and appear unrelated to intrusions.

 

TECTONIC SETTINGS: Magmatism associated with continental margin orogenesis and rifting; or intracratonic catazonal and/or magmatic settings.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING:  Exoskarns around granitic, syenitic, anorthositic or other intrusions in carbonate rocks. Epizonal to catazonal metamorphic environments. Some deposits are located in catazonal metasedimentary sequences lacking known intrusive bodies and are associated with mylonite zones that acted as channels for fluids. In these cases, it is difficult to determine if they are distal to the intrusions or related to the regional metamorphism.

 

AGE OF MINERALIZATION:  Typically Precambrian to Tertiary.

 

HOST/ASSOCIATED ROCK TYPES: Hosts are typically calcitic marble, limestone or calcite-rich siliceous metasedimentary rocks. The most common associated igneous rocks are felsic intrusives, charnockites, pegmatites and lithologies of the anorthositic suite including gabbros.

 

DEPOSIT FORM:  Irregular, lens-shaped or planar. Some deposits are several metres to tens of metres thick and can be traced for hundreds of metres.

 

TEXTURE/STRUCTURE:  Wollastonite crystals are accicular and may be porphyroblastic. They can form rosettes, fan-like textures, and millimeter to decimeter scale layering. Sometimes the wollastonite is massive. The wollasonite-rich rocks may contain remnants of the carbonate protolith.

 

ORE MINERALOGY (Principal and subordinate):  Wollastonite, sometimes garnet and clinopyroxene or calcite, rarely Cu and other sulphides.

 

GANGUE MINERALOGY (Principal and subordinate):  Garnet, clinopyroxene, calcite and quartz may be major constituents. Tremolite-actinolite, zoisite, clinozoisite, anorthite, prehnite, sulphides, oxides, graphite, vesuvianite and titanite may be minor constituents.

 

ALTERATION MINERALOGY:  Calc-silicate minerals in high grade metamorphic terrains are commonly affected by retrograde metamorphism. In some of these cases, retrograde clinozoisite, zoisite, prehnite and/or chlorite are present. Wollastonite crystal may be partially corroded and retrograded to quartz and/or calcite.

 

WEATHERING: Wollastonite commonly weathers with a positive relief in temperate regions.

 

ORE CONTROLS: Wollastonite often occurs at contacts of carbonate or siliceous calcareous rocks with igneous intrusions or within horses and roof pendants of carbonate rocks in intrusive bodies. Fracture and mylonite zones and hinges of folds and other zones of high paleo-permeability are extremely important, since an open system is the main pre-requisite for formation of high grade wollastonite deposits (Simandl, 1992; pages 265-277).

 

GENETIC MODEL:  Most wollastonite deposits are formed through contact metamorphism or metasomatism of siliceous limestone or other calcareous rocks. Typically fluids emanating from the intrusive rocks provide silica, alumina, iron and manganese which react with calcareous rocks to form skarn minerals. Introduction of silica under favorable physical and chemical conditions results in the formation of wollastonite according to the following reaction:

1 calcite + 1 SiO2 = 1 wollastonite + 1 CO2

 

Stability of the wollastonite is dependent on pressure, temperature and X(CO2) and X(H2O) of the ambient fluid.

 

The temperature required for wollastonite formation increases with increase in X(CO2) of the fluid and lithostatic

 

pressure. In some cases, the silica required for wollastonite formation may have been present as impurities within the limy sedimentary protolith. Some deposits in medium to high grade regional metamorphic settings are interpreted to form by interaction of metamorphic or metasomatic fluids with calcareous rocks along permeable zones such as saddle reefs, fracture or fault zones.

 

ASSOCIATED DEPOSIT TYPES: Cu-, Zn-Pb-, W-, Mo- and Au-bearing skarns (K01, K02, K05, K07, K04) and porphyry Cu (L04). Wollastonite rocks in catazonal environments may be in some cases be cut by crystalline graphite veins.

 

COMMENTS: Some W, Pb-Zn, or Cu skarn prospects are currently considered as potential sources of wollastonite.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE:  No direct chemical indicators are known for wollastonite, however associated metallic occurrences can be detected by geochemical methods.

 

GEOPHYSICAL SIGNATURE:  Electromagnetic and magnetic methods may be used to delineate intrusive contacts with calcareous rocks.

 

OTHER EXPLORATION GUIDES:  Commonly found in calcareous sediments cut by igneous rocks. Boulder tracing is a successfully used exploration method; boulders have a rotten wood-like appearance. Wollastonite usually has a positive relief relative to carbonate host rock. In some areas, greenish calcite porphyroblasts within calcitic marbles are common in proximity of wollastonite deposits located in catazonal metamorphic environments.

 

ECONOMIC FACTORS

 

TYPICAL GRADE AND TONNAGE: Highly variable. Wollastonite skarns vary from 0.1 million to 50 million tonnes. Grades vary between 20 and 80% wollastonite. Clinopyroxene and garnet are recovered from some deposits and calcite (limestone or marble) is recovered from others. In rare deposits Cu and wollastonite are recovered as co-products. Median tonnage is 1.3 million tonnes and median grade is 49% wollastonite (Orris, 1992).

 

ECONOMIC LIMITATIONS: Deposits that can supply high aspect ratio wollastonite products are highly sought after. The relative whiteness, brightness, color, aspect ratio of the particles, oil absorption, particle size, refractive index, pH of 10% slurry, specific gravity and type of impurities do determine possible applications. Specialized milling techniques and surface modification significantly increases the price of the wollastonite concentrate. Diopside and garnet may be separated by electromagnetic methods. If calcite is present and a high quality wollastonite concentrate is sought, then flotation is required. Flotation increases substantially the initial capital costs of the project. In glass and ceramic uses, a high iron content due to impurities, such as garnet, diopside, oxides and sulphides, can be a problem.

 

END USES: The major end uses of wollastonite are in ceramics, such as semi-vitreous bodies, heat insulators, acoustic tiles, electrical insulators, and fire-resistant products, such as interior or exterior construction boards, roofing materials, specialty refractors and glazes. It is also used as a functional filler in paint, coatings and plastics and metallurgical applications. Use of wollastonite as reinforcing agent in plastics and as asbestos substitute is increasing. High aspect ratio wollastonite (>15:1) with favorable physical properties is used mainly in plastic and paint as functional filler. Markets for low aspect ratio wollastonite are dependent mainly on the chemical composition and impurities and its end uses are in ceramics, fluxes, glass and limited filler applications.

 

IMPORTANCE:  These deposits are the only commercial sources of natural wollastonite. Competition from synthetic wollastonite is limited to specialty products in the low aspect ratio segment of the market.

 

REFERENCES

 

Anonymous (1994): The Economics of Wollastonite; Fifth Edition, Roskill Information Services Ltd, London, 138 pages.

Andrews, R.W. (1970):  Wollastonite; Monograph, Institute of Geological Sciences, Her Majesty’s Stationary Office, London, 114 pages.

Bauer, R.R., Copeland, J.R. and Santini, K. (1994): Wollastonite; in Industrial Minerals and Rocks, 6th edition; Carr, D.D. Senior Editor; Society for Mining, Metallurgy, and Exploration, Inc., Littleton Colorado, pages 1119-1128.

Fischl, P. (1991): Wollastonite and Tremolite Occurrences in British Columbia; B.C. Ministry of Energy, Mines and Petroleum Resources, Open File 1991-17, 52 pages.

Harben, P.W. and Bates, R.L. (1990): Industrial Minerals and World Deposits; Metal Bulletin, London, 312 pages.

Jain, P.M. (1993): Indian Wollastonite - A Success Story; Industrial Minerals, No. 315, pages 39-41.

Jaworski, B.J. and Dipple, G.M. (1996): Zippa Mountain Wollastonite Skarns, Iskut River Map Area; in Geological Fieldwork 1995, Grant, B. and Newell, J.M., Editors, B.C. Ministry of Energy, Mines and Petroleum Resources, Paper 1996-1, pages 243-249.

Orris, G.J. (1991): Descriptive Model of Wollastonite Skarn; in Some Industrial Mineral Deposit Models: Descriptive Deposit Models; U.S. Geological Survey, Open-File Report 91-11A, pages 5-6

Orris, G.J. (1992):  Grade and Tonnage Model of Wollastonite Skarns; in Industrial Mineral Deposit Models: Grade and Tonnage Models; U.S. Department of Interior, U.S. Geological Survey, Open File Report 92-437, pages 20-22.

Simandl, G.J. (1992):  Graphite deposits in the Gatineau Area, Quebec; Unpublished Ph.D. Thesis, Ecole Polytechnique de Montreal, Montreal (in French), 383 pages.

Simandl, G.J., Valiquette, G., Jacob, H.-L., Paradis, S. (1990):  Gîtes de Wollastonite, Province Tectonique de Grenville, Québec; Canadian institute of Mining and Metallurgy, Bulletin, Volume 83, Number 934, pages 101-107.

Simandl, G.J., Valiquette, G. and Martignole, J. (1989):  Genesis of Graphite-wollastonite Deposits, Grenville Geological Province, Québec; Geological Association of Canada and Mineralogical Association of Canada, General Program for Annual Meeting, Abstract, page A69.

Xian, Z.-M. (1996): Chinese Wollastonite; Industrial Minerals, Number 345, pages 59-63.

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Examples of Skarn Deposits

BC Profile # Global Examples B.C. Examples
K01 Mines Gaspé (Québec), Carr Fork (Yukon) Craigmont, Phoenix
K02 San Antonio (Mexico), Ban Ban (Australia) Piedmont, Contact
K03 Shinyama (Japan), Cornwall (Pennsylvannia) Tasu, Jessie, Merry Widow, HPH
K04 Fortitude, McCoy, and Tomboy-Minnie (Nevada, USA), Buckhorn Mountain (Washington, USA), Diamond Hill, New World district and Butte Highlands (Montana, USA), Nixon Forks (Alaska, USA); Thanksgiving (Phillippines); Browns Creek and Junction Reefs-Sheanan-Grants (New South Wales, Australia), Mount Biggenden (Queensland, Australia), Savage Lode, Coogee (Western Australia, Australia); Nambija (Ecuador); Wabu (Irian Jaya, Indonesia) Nickel Plate, French, Cante, Good Hope, QR-Quesnel River
K05 Cantung & Mactung (Yukon), Pine Creek (California) Emerald Tungsten, Dimac
K06 Lost River (Alaska), JC (Yukon) Daybreak
K07 Little Boulder Creek (Idaho), Mt. Tennyson (Australia) Coxey, Novelty
K08

San Pedro (New Mexico, USA)

Mount Riordan (Crystal Peak)
K09 Fox Knoll & Lewis (New York) Mineral Hill, Rossland