Mineral Resource Facts
by Robert M. McKay
The following economic minerals have been produced or explored
for in Iowa:
Construction Industry Resources
Clay and Shale
Clay and shale are produced in Iowa for use in Portland cement,
lightweight aggregate, common bricks, and for the ceramics
industry, including floor and wall tiles and pottery. Clay is
currently being produced from eight pits in Iowa by six
Crushed Stone (limestone)
Crushed stone is Iowa's leading mineral commodity, with a
production of 38 million tons, valued at $186 million, accounting
for almost 50% of the state's mineral value. The major use of
crushed stone is for road resurfacing, with the material also
used in cement manufacturing, bituminous surface aggregate,
agricultural limestone, and numerous other applications.
Currently, only limestone and dolostone are crushed in Iowa.
Dimension stone (flagging, veneer, and quarry blocks) of
limestone and dolostone is produced in Dubuque, Jackson, and
Jones counties. In Jones County, quarries in the Stone City area
have been producing dimension stone continuously since the 1880s.
This high quality rock, called Anamosa Stone, is marketed
throughout the midwest and as far as California.
In 1992 Iowa was the nation's second largest producer of gypsum,
mining over 2 million tons valued at $11.6 million. The two
primary gypsum producing areas in Iowa are in Webster County,
where it is produced from surface mines, and Des Moines County,
where it is extracted from an underground mine. Gypsum's primary
uses are for wallboard, plaster, and cement products.
Sand and Gravel
Sand and gravel resources represent one of Iowa's largest mineral
industries. Over 16 million tons of sand and gravel, valued at
over $58 million, were marketed by Iowa producers in 1992. These
resources are used primarily for maintenance of Iowa's road
system, for concrete aggregate, and subgrade road material. Most
of Iowa's mineable sand and gravel resources are stream-deposited
Agricultural/Chemical Feedstock Industries Resources
Lime: chemical feedstock, ag-lime, high-calcium limestone
Lime (calcium oxide) both as quicklime and hydrated lime are
manufactured in Scott County. It is produced by calcining
(burning under controlled conditions) high calcium limestone to
produce quicklime. Some of the quicklime is crushed and reacted
with water to produce hydrated lime. Lime is used by the chemical
industry in the production of paint and other products, and in
Peat is an unconsolidated material composed of partially
decomposed plant remains from a water-saturated environment such
as a bog or fen. Total peat production in Iowa is small and
limited to only a few sites. Last available production statistics
for Iowa were 1988 when 15,000 tons was mined, valued at
$433,000. Peat is primarily used as a soil conditioner.
Phosphate has never been produced in Iowa, however, the basal
portion of the Ordovician-age Maquoketa Formation in portions of
Dubuque County is moderately phosphatic. Although thin and
currently subeconomic, this interval is a potential source of
Iowa has extensive deposits of high purity, readily accessible
silica sand. This resource is present almost exclusively in the
St. Peter Sandstone (Ordovician) of northeastern Iowa. Most past
production was from underground mines near the Mississippi River
town of Clayton (Clayton County). Silica sand is used in the
foundry, glass, and chemical industries.
Iowa's coal resources have been estimated conservatively at 7.2
billion tons. Other estimates based on less rigorous criteria
range as high as 29.6 billion tons. All menial coal is
Pennsylvanian-aged occurring in the Cherokee, Marmot, and
view nomenclature for Pennsylvanian System of Iowa) with an
average rank of high volatile C bituminous. The coal occurs in
primarily nonmarine shales, sandstones, and siltstones with minor
interbedded marine limestones and shales. The Cherokee Group coal
beds themselves are characteristically variable in thickness and
extent while the younger coal beds are more persistent. High
sulfur and ash contents are common throughout. Historical
production information is available.
Methane is a by-product of coalification that has been produced
for fuel in many coal bearing regions. Recently,
"nonpetroleum" sources of natural gas have attracted
interest due to changes in the tax laws on natural gas
production. The gas is generated primarily in two phases during
coalification; first when the plant material is initially buried
and begins the process of anaerobic decay and later when the coal
makes the transition from C bituminous to B bituminous. This
latter change is brought about by continued application of heat
and pressure, usually due to burial.
The extensive area of Pennsylvanian-age strata in Iowa
includes significant coal resources. Much of these resources lie
at depths in southwestern Iowa where economic mining is
impossible. The coal in this area of the state and any associated
methane are a largely unknown resource.
Oil and Gas
Petroleum (oil and gas) is not currently produced in Iowa, and
exploration activities in Iowa have been historically low (with
only about 135 oil test wells drilled). Only two wells have
produced oil in Iowa, the W.F. Flynn P-1 and the CST #1 Bombei,
both drilled on the Keota Dome in Washington County, southeast
Iowa. The total production from both wells was less than 500
In addition to the southeast Iowa area, two other potential
provinces in Iowa offer the hope of potential petroleum
production. The Forest City Basin of southwestern Iowa and
adjacent states has produced significant amounts of oil in
Missouri and Kansas. Producing oil fields lie as close as 15
miles south of the Iowa border (at Tarkio, Missouri), but only
traces have been discovered in Iowa. Black shales associated with
the Precambrian age Midcontinent Rift System were the target of
exploration in the mid to late 1980s. A deep test well, the M.G.
Eischeid #1, was drilled in Carroll County in southwest Iowa in
1987 by Amoco Production Company. The well reached a total depth
of 17,851 feet, the deepest penetration of Midcontinent Rift
clastic rocks, but no petroleum detections were reported.
The Department Natural Resources administers Iowa's
oil, gas, and metallic minerals laws.
Uranium has never been mined in Iowa, however, in the mid 1980s a
short-term exploration program was initiated in Lyon County in
northwestern-most Iowa. This program targeted the base of the
Precambrian Sioux Quartzite for Olympic Dam type deposits.
Economic considerations halted activities before any exploration
drilling was conducted. Elsewhere in Iowa, high uranium values
are associated with Pennsylvanian black shales in southwest Iowa.
Chromite has never been mined in Iowa, however, in late 1964, New
Jersey Zinc drilled a series of exploration drill cores on an
aeromagnetic anomaly in Sioux and Lyon counties in northwest
Iowa. Later study of these cores revealed an altered Archean age
layered mafic pluton that included a serpentinized zone with
centimeter-thick chromite bands. Several exploration companies
have subsequently restudied the cores but have determined that it
was not an economic deposit. The drill cores are on file at the
Iowa Geological Survey's Oakdale Rock Library.
There are no outcroppings of gold-rich rocks in Iowa, however,
gold is scattered in small amounts in some of the glacial
materials that cover the state. The gold is concentrated in sands
and gravels in many of Iowa's rivers where it can be recovered in
small amounts by panning.
In 1853 an Eldora inn keeper named John Ellsworth reported a
discovery of gold on his farm along the Iowa River in Hardin
County. As news of the discovery leaked out, Iowa experienced its
own gold rush. As many as 3,000 would-be miners descended on the
Eldora area in search of instant wealth; all left disappointed.
In his 1904 report on the Geology of Fayette County, T.E.
Savage stated that $1.00 to $1.50 worth of gold could be panned
from Otter Creek in a day by a 'patient washer.' Today with the
value of gold at about $300 per ounce, that gold would be worth
Iowa's only historic iron production was from a Cretaceous-age
sedimentary iron deposit called Iron Hill near Waukon in
Allamakee County in northeast Iowa. The deposit was originally
explored in the 1870s and first mined in 1899. The mine operated
intermittently for 20 years between 1899 and 1918, and it is
estimated that about 67,000 tons of iron ore concentrate was
produced and shipped. Original reserve estimates of 10 - 12
million tons indicate that a substantial quantity of ore remains.
Lead and Zinc
The first mineral extraction of lead and zinc in Iowa was
probably before the year 1650 in the Dubuque area by early French
voyageurs and Indians. These early prospectors mined metallic
lead ores and initiated the lengthy history of mining of lead and
zinc ore in Iowa until 1910 when the Avenue Top Mine, the last of
the Dubuque area mines, was closed. Production figures for this
lengthy mining period are nonexistent to very incomplete,
however, lead production apparently peaked in 1848 and in 1854. A
reported 4,385 tons of lead was exported from Dubuque. By 1910,
the year the last mine ceased operation, combined annual
production of lead and zinc concentrates had declined to 270
tons. The industry's last production in Iowa occurred between
1911 and 1917 when ore concentrates, totaling less than 350 tons,
were processed from remnant dumps and tailings piles.
Manganese has never been mined in Iowa, however, in the late
1980s a U.S. Geological Survey-sponsored exploration program was
initiated around the Sioux (Quartzite) Ridge in South Dakota and
Minnesota. Although no exploration was conducted in Iowa, this
unit does extend into Lyon County, the northwestern-most Iowa
county. This program targeted the Cretaceous rocks and
Cannon-Force type sedimentary manganese deposits. A number of
drill cores were obtained, but no significant manganese
concentrations were discovered.
For additional information on mineral resources see