LCMR clay project: NRRI summary report
1990-10
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LCMR clay project: NRRI summary report
Published Date
1990-10
Publisher
University of Minnesota Duluth
Type
Technical Report
Abstract
Minnesota has a variety of clays and shales that have potential as industrial
clays. These clays are: 1) Precambrian clays; 2) Paleozoic shales; 3) pre-Late
Cretaceous primary (residual) and secondary kaolins; 4) Late Cretaceous ball clays and
marine shales; 5) Pleistocene glacial clays; and 6) Recent clays. Minnesota clays are
currently used for brick and as a portland cement additive. Other potential uses
include filler and coating grade kaolins, ceramic tile, refractory products, lightweight
aggregate, sanitaryware, and livestock feed filler.
Precambrian clays occur in the 1 .1 Ga Keweenawan interflow sediments of the
North Shore Volcanic Group, the Middle Proterozoic Thomson Formation and in the
Paint Rock member of the Biwabik Iron-Formation on the Mesabi Iron Range, all in
northeastern Minnesota. The Paint Rock clays have potential as red coloring additives
and glazes.
Paleozoic shales in southeastern Minnesota are primarily kaolinitic and illitic
shales that are interbedded with limestones. The Ordovician Decorah and Glenwood
Formations are marine shales that, in the past, have been used to make bricks, tile,
and lightweight aggregate. The thickness of these shales ranges from 10-90 feet.
The Decorah Shale has the lowest firing temperature with the best shrinkage and
absorption characteristics of all the Minnesota clays.
The pre-Late Cretaceous primary and secondary kaolins are found in the
western and central portions of Minnesota; the best exposures are located along the
Minnesota River Valley from Mankato to the Redwood Falls area and in the St. Cloud
area. The primary or residual kaolinitic clays are the result of intense weathering of
Precambrian granites and gneisses prior to the Late Cretaceous. Subsequent
reworking of these residual clays led to the development of a paleosol and the
formation of pisolitic kaolinite clays. Physical and chemical weathering of the
saprolitic kaolinite-rich rocks produced fluvial/lacustrine (secondary) kaolinitic shales
and sandstones. Recent exploration activity is concentrated in the Minnesota River
Valley where the primary kaolin thickness ranges from 0 to 200 + feet, and the
thickness of the secondary kaolins ranges from 0-45 + feet (Setterholm, et al, 1989).
Similar kaolinitic clays occur in other areas of Minnesota, e.g., St. Cloud and Bowlus
areas. However, less information is available on their thickness, quality, and areal
distribution due to varying thicknesses of glacial overburden. Cement grade kaolin is
extracted from two mines in the residual clays in the Minnesota River Valley, and a
third mine there yields secondary kaolinite-rich clays that are mixed with Late
Cretaceous shales to produce brick.
During the Late Cretaceous, Minnesota was flooded by the transgressing
Western Interior Sea, which deposited both non-marine and marine sediments. These
sediments are characterized by gray and black shales, siltstones, sandstones, and
lignitic material. Significant occurrences of Late Cretaceous sediments are found
throughout the western part of the state, with the best exposures located in Brown
County, the Minnesota River Valley, and the St. Cloud area. In Brown County, the
maximum thickness of the Late Cretaceous sediments is > 100 feet. These sediments
thicken to the west and can be covered by significant thicknesses ( > 300 ft.) of
glacial overburden in many areas. Current brick production comes from the Late
Cretaceous shales in Brown County. In the past, the Red Wing pottery in Red Wing,
Minnesota, used Cretaceous and some Ordovician sediments to produce pottery,
stoneware, and sewer pipe.
Glacial clays occur in glacial lake, till, loess, and outwash deposits, and these
clay deposits range in thickness from 5 to 100 + feet. Much of the early brick and
tile production (late 1800s and early 1900s) in Minnesota was from glacial clays. The
last brickyards to produce from glacial lake clays, e.g., Wrenshall in northeastern
Minnesota and Fertile in west-central Minnesota, closed in the 1950s and 1960s.
There has also been some clay production from recent (Holocene) fluvial and lake
clays that have thicknesses of 2-10 + feet. Both recent and glacial clays are
composed of glacial rock flour with minor quantities of clay minerals. Carbonates can
be a significant component of many of these clays. Glacial lake clays in northwestern
Minnesota (Glacial Lake Agassiz - Brenna and Sherack Formations) begin to bloat at
1830 ° F due to the presence of dolomite and smectite clays. These clays are a
potential lightweight aggregate resource.
Geochemistry, clay mineralogy, particle size, cation exchange capacity (CEC),
raw and fired color, and firing characteristics are useful in distinguishing different
potential industrial uses for Minnesota clays. These physical and chemical
characteristics help to distinguish potentially useful clays from those with less
desirable characteristics, e.g., high quartz or silica content, high shrinkage or
absorption upon firing, undesirable fired color, too coarse-grained, CEC of < 5
milliequivalents, etc. Certain clays, e.g., the bloating Decorah and Brenna Formation
clays, and the high alumina, refractory, pisolitic clays of the Minnesota River Valley,
have physical and chemical characteristics that indicate further exploration and
product research are necessary to fully evaluate the potential of these clays.
Description
Plates 1-7B mentioned in the report are also attached to this record. Disks 1-4 have not been located yet.
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Funding information
Natural Resources Research Institute, University of Minnesota Duluth, 5013 Miller Trunk Highway, Duluth, MN 55811-1442; Funded by the Legislative Commission on Minnesota Resources
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Suggested citation
Hauck, Steven A; Heine, John J; Zanko, Lawrence M; Power, B; Monson Geerts, Stephen D; Oreskovich, Julie A; Reichhoff, J. (1990). LCMR clay project: NRRI summary report. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/188505.
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