Varieties of carving stone often referred to as Soapstone.
Steatite is a massive and compact rock containing more than 90 % talc. The remainder consists of silicates (chlorite) and/or magnesium carbonates.
Soapstone is a massive, soft, impure talc rock that contains variable proportions of magnesian carbonates (dolomite and/or magnesite), serpentine, chlorite, tremolite and magnetite.
Pyrophyllite is a hydrated aluminum silicate. In contrast to talc, pyrophyllite is the product of hydrothermal alteration of felsic igneous rocks (rhyolite, dacite) and schists derived from metamorphosed volcanic ash. Nonetheless, its physical properties are identical to those of talc, and it therefore provides an ideal substitute for talc in a number of industrial applications.
Breunerite is ferroan (iron-rich) magnesite.
Talc is a soft hydrated
magnesium silicate that occurs as fine platelets that are inert
and hydrophobic. Industrial talc is widely used in many applications,
most notably in the production of ceramics and refractories.
Consumers that require high quality talc include the paint, paper
and plastics industries, which collectively represent almost
60 % of talc consumption in North America.
Deposits can be subdivided into four types according to the host rock:
Metamorphic rocks containing magnesian minerals;
Sedimentary rocks containing magnesian carbonates;
Talc deposits associated with metamorphic rocks
Regional or contact metamorphism of siliceous or sandy dolomites and talc-carbonate-bearing siliceous rocks produce dolomitic marbles containing tremolite, actinolite or diopside. These rocks can be transformed into steatite through interactions with silica-rich fluids. Contact metamorphism of dolomites and dolomitic limestone by granite or diabase intrusions may produce large bodies of high grade talc. These masses may be several hundred metres long by several metres wide. Hydrothermal fluid circulation may be locally intense enough to alter granite and other siliceous rocks into talc along the borders of the deposit. The most favorable sites for talc formation are the contact zones with igneous and sedimentary rocks, as well as zones marked by faulting and shearing. Deposits of this type can be found in the United States, Canada (Quebec, Ontario), Brazil, Italy, Slovakia, India, France, Australia and China.
Examples (British Columbia - Canada/International): Gold Dollar
, Red Mountain , Saddle Occurrences ; Henderson Talc Deposit
(Ontario, Canada), Treasure mine (Montana, USA), Gouverneur Talc
(New York State, USA) and Trimouns deposit (France).
Capsule Description: Most of the economic carbonate-hosted deposits are lenticular or sheet-like bodies and are concordant with surrounding dolomitic marbles, siliceous dolomitic marbles, dolomites, schists and phyllites. The massive or schistose ore consists mainly of talc ± dolomite, ± tremolite, ± calcite, ± magnesite, ± chlorite, ± serpentine, ± phlogopite.
Tectonic Setting: Protolith deposited mainly in pericratonic environments; in most cases the talc formed later within metamorphic, fold or thrust belts.
Depositional Environment / Geological Setting: Dolostones, dolomitic marbles or magnesite beds metamorphosed to greenschist facies or lower amphibolite facies represent a typical host environment. Upper amphibolite-grade marbles, where talc would not normally be stable, may contain retrograde talc zones.
Age Of Mineralization: Mainly Precambrian to Early Paleozoic but may be younger. In most cases syn- or post-metamorphic.
Host/Associated Rock Types: Dolomitic marbles and dolomites are the typical host, however some of the deposits are hosted by magnesite or mica schists. Phyllites, chlorite or mica schists, paragneiss and intrusive and metavolcanic rocks may be present adjacent to, or in the proximity of the talc deposits. Deposits may be crosscut by minor intrusions, such as diabase dikes.
Deposit Form: In most cases, podiform or deformed, sheet-like bodies oriented subparallel to the compositional layering within marbles and to geologic contacts. They commonly pinch and swell. Typical dimensions would be 2 to 20 m thick and tens to hundreds of m along strike and dip. Where fluids were the principal source of heat and/or silica, breccia zones and irregular deposits may occur near fault intersections.
Texture/Structure: Ore varies from fine-grained, massive or layered talc to coarse talc schists. Pseudomorphs of talc after tremolite are common in deposits that formed after the peak of metamorphism.
Ore [Principal and subordinate]: Talc and tremolite (in some ores and commercial products tremolite is a principal constituent).
Gangue Mineralogy [Principal and subordinate]: Dolomite, ± tremolite, ± calcite, ± magnesite, ± chlorite, ± serpentine, and ± phlogopite may be principal gangue minerals. Pyrite, ± graphite, ± mica, ± dravite, and ± anorthite are common accessory impurities.
Alteration Mineralogy: In some deposits at least a portion of talc is believed to have formed by retrograde reactions from tremolite. In some cases, there is a replacement of biotite by chlorite and feldspar by sericite or chlorite in the host rock.
Weathering: Talc-bearing zones may form ridges where chemical processes dominate and topographic lows where physical weathering and/or glaciation are most important.
Ore Controls: The main controls are the presence of dolomite or magnesite protolith, availability of silica and favourable metamorphic/metasomatic conditions. Talc deposits hosted by carbonate rocks may be divided into several subtypes according to the source of silica and geological setting:
a) contacts between carbonates, usually dolomitic marbles,
and silica-bearing rocks, such as biotite-quartz-feldspar gneisses,
schists, cherts and quartzites;
Genetic Model: Most carbonate-hosted talc deposits are believed to be formed by the reaction:
3 dolomite + 4 SiO2 + H2O = 1 talc + 3 calcite + 3 CO2
Silica may be provided either from adjacent quartz-bearing rocks, from silica layers within the carbonates, or by hydrothermal fluids. Absence of calcite in ores from several deposits indicates that talc may have formed in an open system environment and calcium was allowed to escape. The source of heat may be provided by regional metamorphism, contact metamorphism or by heat exchange from hydrothermal fluid. In environments where sedimentary-hosted magnesite deposits are known to occur, talc could have been produced by the reaction:
3 magnesite + 4 SiO2 + H2O = 1 talc + 3 CO2
In this second reaction calcite precipitation is not expected. This reaction takes place at lower temperature (given identical pressure and XCO2 conditions) than the dolomite reaction, therefore, magnesite may be almost completely converted to talc before dolomite starts to react.
Pseudomorphs of talc after tremolite and the presence of upper amphibolite grade, metamorphic assemblages in host rocks of some of the deposits indicate that talc post-dates the metamorphic peak and is probably of retrograde origin. Depending on the individual deposits, metamorphic or metasomatic (hydrothermal) characteristics may be predominant.
Associated Deposit Types: Chlorite deposits, marble (R04), high-calcium carbonate (filler-grade) and limestone (R09), dolostone (R10), sedimentary-hosted magnesite deposits (E09) and deposits such as Balmat, which is probably a metamorphosed sedex deposit (E14).
Talc deposits associated with magnesian carbonate rocks
Metasomatism or hydrothermal alteration of dolomitic rocks produces talc through interaction with silica- and magnesium-bearing fluids. The silica source may be sediments or hydrothermal solutions derived from various aluminous silicate rocks (schists, micaschists, pegmatites, granites) along strongly tectonized zones (faults, shears, fractures). This process creates high quality talc that is mainly found in veins that crosscut the dolomitic rocks. These lenticular talc veins may reach several hundred metres in length by several dozen metres in width. Dolomite, magnesite, chlorite and quartz are the principal impurities. Talc deposits and talc-chlorite schists are associated with dolomite, dolomitic limestone or magnesian rocks. This deposit type has been found in the United States, Germany, France, Austria, Russia, Finland, Australia, India and China.
Examples (British Columbia - Canada/International): Gold Dollar , Red Mountain , Saddle Occurrences ; Henderson Talc Deposit (Ontario, Canada), Treasure mine (Montana, USA), Gouverneur Talc (New York State, USA) and Trimouns deposit (France).
Most of the economic carbonate-hosted deposits are lenticular or sheet-like bodies and are concordant with surrounding dolomitic marbles, siliceous dolomitic marbles, dolomites, schists and phyllites. The massive or schistose ore consists mainly of talc ± dolomite, ± tremolite, ± calcite, ± magnesite, ± chlorite, ± serpentine, ± phlogopite.
Talc deposits associated with ultramafic rocks
Talc can be formed during serpentinization from ultramafic rocks like peridotite. The process is followed by carbonatization during which fluids containing more than 5 % CO2 are introduced and a talc-carbonate rock is formed (i.e., talc-magnesite). This rock may be further transformed into steatite through the interaction with silica-bearing solutions. The talc rock may replace lenses or large masses of serpentinite, but in most cases forms a layer or crust around such masses. The talc lenses may measure several hundred metres long by several hundred metres wide. The serpentinized ultramafic rocks that host asbestos deposits may also contain talc. These occurrences constitute the largest talc deposits but can contain more impurities, most notably asbestos minerals. Deposits associated with ultramafic rocks are found in the United States, Canada (Quebec, Ontario), Russia and Norway.
Examples (British Columbia - Canada/International): Rawhide , South Talc Lake Deposit , Gisby , J&J; Deloro magnesite-talc deposit (Ontario, Canada), Luzcan mine of Thetford township and Van Reet mine, Ponton township, (Quebec, Canada), Windham (Vermont, USA), Lahnaslampi mine (Finland).
Capsule Description: Ultramafic-hosted talc-carbonate deposits are located either along regional faults cutting ultramafic rocks or at contacts between ultramafic rocks and siliceous country rock. The ultramafic host rock is typically, but not necessarily of ophiolitic affiliation. Deposits related to regional fault systems cutting ultramafic host rock are commonly magnesite-rich. Deposits located within sheets of serpentinized peridotite, found along the periphery of ultramafic intrusions or near the borders of tectonically transported peridotite slices are typically talc-rich.
Tectonic Settings: These deposits are found typically in obducted, accreted or otherwise tectonically transported seafloor and ophiolite slices or lenses and in ancient greenstone belts. However, serpentinized ultramafic intrusions regardless of tectonic environment should be considered as a favourable host.
Depositional Environment / Geological Setting: Faulted and metasomatized ultramafic rocks and tectonically-transported serpentinites in contact with siliceous rocks; the deposits are younger than the ultramafic protolith.
Age Of Mineralization: Precambrian or younger. Post or syn-tectonic.
Host/Associated Rock Types: Talc-carbonate-bearing serpentinite, steatite, talc schist, talc-magnesite-dolomite schist that may contain serpentine/chlorite schist, dunite and serpentinite with associated, commonly at least partially serpentinized gabbro, pyroxenite, harzburgite and websterite or meta-komatiiate sills and lavas. Because many of the talc-bearing rocks are allochthonous there is a wide variety of associated lithologies.
Deposit Form: The fault-related deposits are irregular bodies having their largest dimensions parallel to the faults. In some cases only the hanging wall of the faults is mineralized. Small ultramafic lenses are commonly entirely serpentinized, while larger lenses consist of peridotite cores surrounded by serpentinite. Steatite and talc schists are most likely to be found at the contact of the serpentinite with siliceous rocks, however they may also form tabular or irregular bodies.
Texture/Structure: Ore is massive or schistose, talc is fine to coarse flakes.
Ore Mineralogy [Principal and subordinate]: Talc, magnesite, rarely Ni-bearing minerals, such as pyrrhotite, pentlandite, melnikovite and bravoite.
Gangue Mineralogy [Principal and subordinate]: Dolomite, serpentine, chlorite, ankerite (Fe-rich dolomite), breunerite (Fe-rich magnesite), olivine, magnetite, quartz, pyrite, asbestos, rutile, calcite, chrome-mica.
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
The talc formed during metasomatism and/or regional metamorphism. Silica required for talc formation was derived from the country rock.
Talc deposits associated with mafic rocks
1 - Lac Sunday-Se
2 - Mine Carter
3 - Lac Breeches-Est
4 - Collines Bisby
5 - Gilmont
6 - Wolfestown-Irlande
7 - Reed
8 - Lac Sunday-So
9 - Mine Clark (Talc)
10 - Petit Mont Ham
11 - Riv. Palmer-Est No 1
12 - Mine Du Mont St-Adrien
13 - Village-Des-Chutes
14 - Ste-Corinne No
15 - Monts Sutton
16 - Roundtop
17 - Eakins
18 - Knowlton-Sso
19 - Sutton Junction-Nord
20 - Carey Canadian (Zone D)
21 - Riv. Du Cinq
22 - Lac Nick
23 - Etang Chalmers
24 - Bolton Glen-So
25 - Etang Sallys
26 - Thompson Harbour
27 - Mine Asbestos Hill
28 - Mine Harvey Hill
29 - Umex-1
30 - Baie Indienne
31 - Montagne Du Neuf-Se
32 - Mine Rumpelville
33 - Riv. Palmer-Est No 3
34 - Riv. Palmer-Est No 2
35 - Mine Guillemette-Perron
36 - Jutras
37 - Mine Toussaint
38 - Labonte-Toussaint
39 - Mine Houle
40 - Mine Robertsonville Soapstone
41 - Mine Cyr (Talc)
42 - Megantic Talc
43 - Labbe Asbestos
44 - Collines Clapham
45 - Lac Du Huit
46 - Prospect Nicolet
47 - Mine Black Lake (Lac D'amiante)
48 - Mine Kitchener
49 - Briggs
50 - Mine Frontenac
51 - Mine Fraser
52 - Mine Montreal (Talc)
53 - Mine Riv. Nadeau
54 - Mine Riv. Palmer
55 - Mine Cyr (Steatite)
56 - Saint-Pierre-De-Broughton-Se
57 - Morin No 1
58 - Mine Pharo
59 - Mine Ives
60 - Lac Bonne-Allee
61 - Mine De Steatite D'eastray
62 - Brill-Nord
63 - St-Etienne-De-Bolton
64 - Lac Stukely-Ouest
65 - Mine Broughton
66 - Foy
67 - Nutbrown
68 - Lac Brompton-Nord
69 - Mine Baker
70 - Mine Tomifobia No 1
71 - Kateville
72 - Eastman-Sso
73 - St-Denis-De-Brompton-No
74 - Mine Van Reet (Baker Talc)
75 - Mine Bolton-Sud
76 - South Bolton
77 - Mine Marcoux
78 - Banfield
79 - Chartrot
80 - Mansonville-Nno
81 - Mansonville-Nord-Talc
82 - Red Hills
83 - Mine Pontbriand (National Asbestos)
84 - Mine Pontbriand-Sud
85 - Mine Federal
86 - Mine Cyr
87 - Rumpelville
88 - Mine Du Rang II, Lots 26-27
89 - Bras Au Saumon
90 - Trou, Lots 18-17-66