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Hora, Z.D. (1998): Sedimentary Kaolin,
in Geological Fieldwork 1997, British Columbia Ministry of Employment and
Investment, Paper 1998-1, pages 24D-1 to 24D-3.
IDENTIFICATION
SYNONYMS: Secondary kaolin deposits,
fireclay, underclays, high-alumina clay, china clay.
COMMODITIES (BYPRODUCTS) Kaolin (many
different grades for specific applications), ceramic clay, ball clay,
refractory clay (cement rock, bauxite, silica sand).
EXAMPLES (British Columbia (MINFILE #) -
Canada/International): Sumas Mountain (92GSE004,
92GSE024), Blue Mountain (92GSE028), Lang Bay (92F137), Quinsam (92F319),
Giscome Rapids (93J020); Cypress Hills (Alberta, Canada), Eastend, Wood
Mountain, Ravenscrag (Saskatchewan, Canada), Moose River Basin (Ontario,
Canada), Shubenacadie Valley (Nova Scotia, Canada), Aiken (South Carolina,
USA), Wrens, Sandersville, Macon-Gordon, Andersonville (Georgia, USA),
Eufaula (Alabama, USA), Weipa (Queensland, Australia), Jari, Capim (Brazil).
GEOLOGICAL
CHARACTERISTICS
CAPSULE DESCRIPTION: Beds, lenses and
saucer-shaped bodies of kaolinitic claystones hosted by clastic
sedimentary rocks, with or without coaly layers or coal seams. They
usually occur in freshwater basins filled with sediments derived from
deeply weathered, crystalline feldspathic rocks.
TECTONIC SETTINGS: Low-lying coastal plains
at continental edge; extension basins in orogenic belts; stable
continental basins; back arc basins.
DEPOSITIONAL ENVIRONMENT / GEOLOGICAL
SETTING: Clay beds are generally deposited in low energy environments
within freshwater basins. Temperate to tropical climatic conditions can
produce intensive kaolinitic weathering of feldspathic rocks of granitic
composition. The kaolin is then eroded and transported to estuaries,
lagoons, oxbow lakes and ponds.
AGE OF MINERALIZATION: Most of the world
class deposits are Upper Cretaceous to Eocene age. Some "fireclay" and "underclay"
deposits are Late Carboniferous.
HOST/ASSOCIATED ROCK TYPES: Kaolin beds are
associated with variably kaolinitic, micaceous sandstones within mudstone,
siltstone, sandstone and conglomerate sequences which often are
cross-bedded. Coal (sub-bituminous and liqnite) may be associated with
kaolin beds. Diatomite may also be present.
DEPOSIT FORM: Beds exhibit variable
thickness, usually a few metres; sometimes multiple beds have an aggregate
thickness of approximately 20 metres. Deposits commonly extend over areas
of at least several square kilometers.
TEXTURE/STRUCTURE: Kaolin is soft and
exhibits conchoidal or semiconchoidal fracture; it can be bedded or
massive. Most kaolins will slake in water, but some "flint" varieties
break into smaller angular fragments only. Depending on kaolin particle
size and presence of organic matter, some clays may be very plastic when
moist and are usually called "ball clays".
ORE MINERALOGY [Principal and
subordinate]: Kaolinite, halloysite, quartz, dickite, nacrite,
diaspor, boehmite, gibbsite.
GANGUE MINERALOGY [Principal and
subordinate]: Quartz, limonite, goethite, feldspar, mica, siderite,
pyrite, illmenite, leucoxene, anatas.
WEATHERING: The kaolin forms by weathering
which results in decomposition of feldspars and other aluminosilicates and
removal of fluxing components like alkalies or iron. Post depositional
weathering and leaching can produce gibbsitic bauxite. In some deposits,
post depositional weathering may improve crystallinity of kaolin particles
and increase the size of crystal aggregates.
ORE CONTROLS: The formation and
localization of clay is controlled by the location of the sedimentary
basin and the presence of weathered, granitic rocks adjacent to the basin,
particularly rapidly eroding paleotopographic highs.
GENETIC MODELS: Ideal conditions to produce
kaolinitic chemical weathering are high rainfall, warm temperatures, lush
vegetation, low relief and high groundwater table. The kaolin is eroded
and transported by streams to a quiet, fresh or brackish, water
environment. Post-depositional leaching, oxidation, and diagenesis can
significantly modify the original clay mineralogy with improvement of
kaolin quality.
ASSOCIATED DEPOSIT TYPES: Peat (A01), coal
seams (A02, A03, A04), paleoplacers (CO4), some bentonites (EO6),
lacustrine diatomite (FO6).
EXPLORATION GUIDES
GEOCHEMICAL SIGNATURE: None. Enrichment in
Al does not provide sufficient contrast with host sediments.
GEOPHYSICAL SIGNATURE: Apparent resistivity
and refraction seismic surveys can be used in exploration for fireclay
beds.
OTHER EXPLORATION GUIDES: Most readily
ascertainable regional attribute is sedimentary basins with Upper
Cretaceous and Eocene unconformities. Within these basins kaolin occurs
with sediments, including coal seams, deposited in low energy
environments.
ECONOMIC FACTORS
TYPICAL GRADE AND TONNAGE: Published data
on individual deposits are very scarce. Deposits in Georgia, USA contain
90 to 95% kaolinite. Individual Cretaceous beds are reported to be up to
12 m thick and extend more than 2 km while those in the Tertiary sequence
are 10 to 25 m thick and up to 18 km along strike. The Weipa deposit in
Australia is 8 to 12 m thick and contains 40 to 70% kaolinite. The Jari
deposit in Brazil is reported to contain more than 250 Mt of "good,
commercial grade kaolin". Over 200 Mt of reserves "have been proven" at
Capim deposit in Brazil. Ball clay deposits in Tennessee and Kentucky
consist of kaolin with from 5 to 30% silica; individual deposits may be
more than 9 m thick and extend over areas from 100 to 800 m long and up to
300 m wide.
ECONOMIC LIMITATIONS: Physical and chemical
properties affect end use. Physical properties include brightness,
particle size distribution, particle shape and rheology. Limonite staining
is a negative feature. The high level of processing required to meet
industry specifications and minimize transportation cost to the end user
are the main limiting factors for kaolin use. While local sources compete
for low value markets, high quality products may be shipped to users
several thousand km from the plant. Most production is from open pits;
good quality fireclay seams more than 2 meters thick are sometimes mined
underground. Typically, paper coating grade sells for up to US$120, filler
grade for up to US$92 and sanitary ceramics grade for $US55 to $65 per
short ton (Industrial Minerals, 1997). Refractory and ball clay prices are
within the same range.
END USES: The most important use for kaolin
is in the paper industry, both as a filler and coating pigment. A variety
of industrial filler applications (rubber, paints, plastics, etc.) are
another major end use. Kaolin's traditional use in ceramic products is
holding steady, but the refractory use has declined substantially in the
last two decades because of replacement by other high performance
products.
IMPORTANCE: One of the most important
industrial minerals in North America. Over 11 Mt is produced annually and
production is on a steady increase.
SELECTED BIBLIOGRAPHY
Bristow, C.M. (1987): World Kaolins -
Genesis, Exploitation and Application, Industrial Minerals, No.
238, pages 45-59.
Guillet, G.R. and Martin, W., Editors
(1984): The Geology of Industrial Minerals in Canada, Special Volume 29,
The Canadian Institute of Mining and Metallurgy, 350 pages.
Harben, P.W. and Bates, R.L. (1990):
Industrial Minerals and World Deposits, Metal Bulletin, London, 312
pages.
Malkovsky, M. and Vachtl, J., Editors
(1969): Kaolin Deposits of the World, A-Europe, B-Overseas Countries;
Proceedings of Symposium 1, 23rd International Geological Congress,
Prague, 1968, 460 pages.
Malkovsky, M. and Vachtl, J., Editors
(1969): Genesis of the Kaolin Deposits; Proceedings of the Symposium 1,
23rd International Geological Congress, Prague, 1988, 135 pages.
Murray, H.H. (1989): Kaolin Minerals: Their
Genesis and Occurrences, Hydrous Phyllosilicates, in Reviews in
Mineralogy, Bailey, S.W., Editor, Mineralogical Society of America,
Volume 19, pages 67-89.
Murray, H.H., Bundy, W.M. and Harvey, C.C.,
Editors (1993): Kaolin Genesis and Utilization, The Clay Minerals
Society, Boulder, Colorado, 341 pages.
Patterson, S.H. and Murray, H.H. (1984):
Kaolin, Refractory Clay, Ball Clay and Halloysite in North America,
Hawaii, and the Caribbean Region; U.S. Geological Survey,
Professional Paper 1306, 56 pages. |
