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Map Series No. 135
MINERAL RESOURCES OF HAMILTON COUNTY,
Steven M. Spencer, P.G. #319, Frank Rupert,
Ronald W. Hoenstine, and Ed Lane
FLORIDA GEOLOGICAL SURVEY
WALTER SCHMIDT, STATE GEOLOGIST AND CHIEF
DIVISION OF RESOURCE MANAGEMENT
DEPARTMENT OF NATURAL RESOURCES
In recent years, considerable attention has been focused on
Florida's rapid development, the accompanying population increase, and
their effect on the state's important mineral resources. Frequently, this
development occurred in areas underlain by known mineral deposits,
precluding extraction of the minerals. The economics associated with
these mineral resources represent substantial employment and income to
the private sector as well as taxes to county and state governments. One
response to this conflict between rapid population and urban growth, and
Florida's mineral resource development was in the form of legislation
enacted by the Florida Legislature in 1985 requiring each county to
establish a comprehensive land use plan. Additional guidelines and due
dates were established by the 1986 Florida Legislature.
In response to this legislation, and at the request of the North
Central Florida Regional Planning Council, the Florida Geological Survey
initiated this investigation of Hamilton County's mineral resources. Our
objectives were to identify potential mineral resource areas and to present
the results in a format appropriate for use by city and county planners.
This mineral resource assessment is general and is intended as a land-use
planning tool. A site-specific evaluation would require detailed research
beyond the scope of this r, .ii.-- i. ._11
A knowledge of Hamilton County's mineral resources is basic and
integral to the process of initiating, developing, and implementing an
effective comprehensive land use plan This information is essential to
planners and officials in their analyses of urban and rural development in
such areas as zoning, road construction and the establishment of waste
Resource evaluation for this report is based on a number of
sources including Florida Geological Survey reports and unpublished data,
core and well cutting descriptions, geological logs, field reconnaissance,
state and federal statistical data, company reports, questionnaires, and
discussions with mining company personnel and state and federal officials.
Although detailed information on company statistics is confidential,
information of a more general nature is readily available or can be
reasonably extrapolated from existing data. The diversity of sources as
well as their close association with the various aspects of resource
evaluation lends substantial confidence to the general assessments and
inferences of this report.
Metric Conversion Factors
For readers who prefer metric units to the U. S. units in this report,
the following conversion factors are provided.
Hamilton County is situated in the Northern (Proximal) Zone of
White (1970). This zone extends across the northern Florida peninsula and
westward into the Western Highlands of Florida's panhandle. Two major
geomorphic subdivisions of the Northern Zone occur in Hamilton County:
the Northern Highlands and the Gulf Coastal Lowlands (Figure 1).
The Northern Highlands incorporates the majority of Hamilton
County, being present in all but the extreme southwestern portion of the
county. Elevations generally range between 125 and 150 feet above mean
sea level (MSL). The topography here is characterized by gently sloping
hills and lowlands in the western half of the county and extensive swampy
lowlands in the eastern half. Lowland areas include Cypress Creek
Swamp, Bee Haven Bay, Buzzard Bay and Bird Bay. The majority of lakes
and large ponds are located in the Northern Highlands in northwestern
The southern boundary of the Northern Highlands is marked by a
relict marine escarpment named the Cody Scarp. This feature separates
the Northern Highlands from the topographically lower Gulf Coastal
Lowlands subzone. The Cody Scarp, which trends northwest-southeast in
Hamilton County, has been described by Puri and Vernon (1964) as the
most persistent topographic break in Florida (Figure 1). The toe of this
escarpment approximates an elevation of 100 feet above MSL in Hamilton
The Gulf Coastal Lowlands geomorphic subzone is a broad, flat-
lying marine erosional plain lying south of the Cody Scarp. It occupies
less than 20 percent of Hamilton County. This is an area of little relief with
elevations ranging from 100 feet above MSL at the toe of the Cody Scarp
to approximately 50 feet above MSL along the Withlacoochee and
Suwannee Rivers. The Gulf Coastal Lowlands of Hamilton County
incorporate portions of the Suwannee River State Park and several springs
including Morgans Spring and Adams Spring.
In addition to the above geomorphic features, two relict terraces
formed by ancient seas are present in the county. Healy (1975) identified
two terraces based on land surface elevations (Figure 2). In order of
descending elevation, they are: the Sunderland/Okefenokee Terrace (100-
170 feet above MSL), and the Wicomico Terrace (70-100 feet above MSL).
Hamilton County is underlain by siliciclastic sediments (quartz
sand, silt, clayey sand and clay). In turn, these sediments are underlain by
thick sequences of Cenozoic carbonates (limestone and dolomite) and
Mesozoic siliciclastics and carbonates measuring thousands of feet in
The near-surface geologic units include the Ocala Limestone which
was deposited during the Late Eocene (approximately 41 to 38 million
years before the present, BP) (Figures 3a-c). The lithology of this marine
limestone grades upward from alternating soft and hard, white to tan
fossiliferous and dolomitic limestone into white to pale orange, fossiliferous
limestone. The occurrence of the distinctive foraminifera genus
Lepidocyclina is common to abundant and is often used as an aid in
distinguishing this formation from the overlying Suwannee Limestone.
The Ocala Limestone, which occurs at depths ranging from 45 feet
to nearly 270 feet below land surface, forms an integral part of the Floridan
aquifer system in Hamilton County. Thickness of these carbonate
sediments averages 200 to 300 feet.
The Oligocene age (38 to 33 million years BP) Suwannee
Limestone, which represents the oldest geologic unit cropping out in
Hamilton County, unconformably overlies the Ocala Limestone. Outcrops
of this formation can be observed along the Suwannee River between
White Springs and Ellaville. Colton (1978) states that the Suwannee
Limestone was deposited in water between low tide level and a maximum
depth of approximately 100 feet. This unit comprises the upper portion of
the Floridan aquifer system in parts of western Hamilton County and in all
of the central and eastern portions of the county. The lithology of the
Suwannee Limestone in Hamilton County consists of a very pale orange,
finely crystalline, moderately to well indurated, fossiliferous, partially
recrystallized limestone (calcarenite) with moderate to good porosity.
Fossils include foraminifera, mollusks and echinoids. The top of this
formation is extremely variable and ranges from 20 to more than 150 feet
below land surface. Observed thicknesses range from approximately 10
feet to 150 feet (Figures 3a, 3b and 3c).
In northwestern Hamilton County, the Suwannee Limestone is
unconformably overlain by the St. Marks Formation. Deposited during the
Early Miocene (25 to 20 million years BP), the St. Marks Formation
averages 40 feet in thickness (Figure 3c) and is discontinuous in
distribution. The lithology of this formation is typically a white to very pale
orange, sandy, silty, clayey, calcilutitic, marine limestone. Fossils are few
and generally consist of mollusks and foraminifera. Where present, the St.
Marks Formation is the uppermost unit of the Floridan aquifer system.
The Hawthorn Group, which was deposited during the Early and
Middle Miocene (23 to 15 million years BP), unconformably overlies the
Suwannee Limestone or, where it is present, the St Marks Formation. It
is an important economic resource in Hamilton County, containing
abundant phosphate ore. It has a variable lithology ranging from
phosphatic dolomites and clayey sands to dolomitic silty clays. In general,
these sediments consist of pale olive to moderate yellow sandy, phosphatic
clays and sands.
The Hawthorn Group sediments can be observed intermittently
along the banks of the Suwannee River from State Highway 6 to the
confluence of the Alapaha River. The thickness of the Hawthorn Group
ranges from approximately 30 feet south of the Cody Scarp to as much as
150 feet in the northern and eastern portions of the county.
A veneer of Pleistocene to Holocene age (1.8 million years BP and
younger) sediments overlie the Hawthorn Group throughout Hamilton
County. The sediments, referred to as "Undifferentiated Sand and Clay,"
represent relict Pleistocene marine sands and Holocene aeolian and alluvial
deposits. Extremely variable in thickness, they range from a minimum
value of less than a foot to a maximum observed value of approximately
The following discussion of the economic geology of Hamilton
County is not intended to be a comprehensive investigation leading to
immediate industrial development because, in many cases, the data
represents information on a single outcrop, pit or mine. However, where
the data are favorable, they may indicate that certain areas warrant further
investigation. The Mineral Resources Map is designed to present an
overview of the major mineral commodities in an area Factors such as
thickness of overburden as well as the quality and volume of the deposit
will affect the mining of the mineral commodity at any specific site In
contrast, geologic cross sections are extrapolated from cores and well
cuttings to show the distribution and thickness of surface and near-surface
stratigraphic units (Figures 3b and 3c). Occasional variations between the
geologic cross sections and the Mineral Resources Map may occur The
following is a discussion of the clay, peat, phosphate, and sand resources
of the Hamilton County.
Most of the economic clay deposits in Florida are from the
Miocene age Hawthorn Group. Scott (1988) shows the Hawthorn Group
as present in northern and eastern Hamilton County. The clays are often
dolomitic, phosphatic, and very sandy. The clay minerals present in this
region are characteristically smectite, palygorskite, and illite (Scott, 1988).
Bell (1924) tested clay deposits from the White Springs region of
Hamilton County. Although results of these tests showed the clay to have
excellent plasticity and working qualities, samples had high air and fire
shrinkage, and a tendency to warp in firing. These clays were determined
to be unsuitable for fired products (Bell, 1924).
Alluvial clay deposits, belonging to the Bivans soil series, are
present along various portions of the Suwannee River (David Howell, U.S.
Soil Conversation Service (SCS), personal communication, 1991). The
SCS reports the alluvial clays contain up to 60 percent montmorillonite
(smectite) and extend to a depth of at least 81 inches.
A sandy clay to clayey sand, from scattered borrow pits located
throughout the county, is used as fill material by the county road
department. There is little potential for a structural clay products industry
in Hamilton County.
Peat is a product of partially decomposed organic materials which
accumulate when the depositional rate exceeds decomposition (Davis,
1946; Bond et al., 1986). In perennially wet areas organisms which
normally metabolize plant matter are inhibited, thereby allowing peat to
The United States Soil Conservation Service located two areas
containing the highly organic Dorovan Muck soil type in Hamilton County
(David Howell, SCS, personal communication, 1991). Dorovan Muck, the
most peat-like soil found in Hamilton County, is within the mining limits of
Occidental Chemical Corporation, Suwannee River Phosphate mine.
Florida produces approximately 80 percent of the nation's supply
of phosphate and roughly 25 percent of the world's supply (Florida
Phosphate Council, 1990). Phosphate is mined from two regions in
Florida: central peninsular Florida, primarily the Polk-Hillsborough County
region, and in Hamilton County in northern Florida. The phosphate mined
in eastern Hamilton County lies within the Georgia-Florida Phosphate
District (Sever et al., 1967). It is in this area that Occidental Chemical
Corporation operates two mines, the Swift Creek mine (multiple sections,
Township 1 S, Range 15 E), and the Suwannee River Phosphate mine
(multiple sections, Township 1 S, Ranges 15 and 16 E). Occidental began
processing land-pebble phosphate here in 1965.
Land-pebble phosphate (carbonate-fluorapatite) is present in the
Miocene age Hawthorn Group sediments. The phosphate is rounded to
subrounded, and varies from silt to pebble size. Its color ranges from
white, to tan, brown, or black with varying degrees of polish. Weathered
grains have a dull finish and are usually white or tan in color (Sever et al.,
1967). Phosphate at the Swift Creek mine averages 20 feet thick. It is
overlain by approximately 20 feet of sand and clayey sediments (Larry
Miller, Occidental Chemical Corporation, personal communication, 1991).
The economic deposit overlies a layer of phosphatic dolomitic clays, sandy
dolomite, sand or limestone.
FGS well data suggest that portions of north-central and
northeastern Hamilton County may contain phosphate deposits of
economic value (Mineral Resource Map). These wells (W-15121, W-12600,
W-12601, W-12773, and W-1039) contain up to 40 percent phosphate
(visual estimate) within 40 feet of land surface.
Phosphate mining in Florida is the open pit type and uses
draglines with capacities up to 70 cubic yards. Overburden is removed to
mined out areas or cuts. The draglines then remove the ore material to
pits where it is slurried using high water pressure and pumped to a
beneficiation plant (Campbell, 1986). The beneficiation process uses froth
flotation to separate the ore from the matrix material. This is usually a two
step flotation process where a reagent floats the phosphate, then in the
next stage, floats the waste material (Campbell, 1986). The two stage
flotation process recovers about 80 percent of the phosphate from the feed
material (Zellers-Williams, 1978). About 90 percent of the phosphate
produced in Florida goes into making agricultural fertilizer The remainder
is used in the production of livestock feed supplements, light bulb
filaments, cleaning supplies, bone china, soft drinks, vit,imins and other
goods (Florida Phosphate Council, 1990). The primary finished products
of Occidental's beneficiation process are diammonium phosphate and
phosphoric acid. A significant portion of Occidental's products are
transported to Jacksonville where they are shipped to foreign markets in
India, Italy, France, and China. However, the majority of their products are
transported via trucks, rail, and barge to the agricultural midwestern U.S.
In Hamilton County the Occidental Chemical Corporation employs over
1300 people and accounts for about 50 percent of all income earned (Ray
Kirkland, Occidental Chemical Corporation, personal communication,
1991). Occidential has substantial phosphate reserves and expects to
continue mining and processing through the year 2010.
Quartz sand is common in the near-surface and surface sediments
of Hamilton County. However, its occurrence with clays along with the
presence of other impurities, diminish its value as an economic commodity.
Surface grab samples from eastern Hamilton County were examined for
this investigation. The sediments were typically unconsolidated quartz
sands, yellowish gray to moderate yellowish brown in color, very fine to
coarse range, and subangular to subrounded (section 8, Township 2 S,
Range 16 E, and section 18, Township 1 S, Range 15 E). Accessory
constituents included variable amounts of clay, traces of heavy minerals
and iron staining, and minor amounts of organic
Much of Hamilton County has surface and near-surface sediments
made up of clayey sand, and organic muck. These undifferentiated
resources have extensive occurrences throughout the county. Although
the potential for large scale mining is minimal due to the heterogeneous
nature of these sediments, they may be valuable locally as fill material.
Bell, 0. G., 1924, A preliminary report on clays of Florida: Florida
Geological Survey Fifteenth Annual Report, 266 p.
Bond, P. A., Campbell, K. M., and Scott, T. M., 1986, An overview of peat
in Florida and related issues, report to the Florida
Legislature:Florida Geological Survey Special Publication 27, 151
Campbell, K. M., 1986, The industrial minerals of Florida: Florida
Geological Survey Information Circular 102, 94 p.
Colton, R. C., 1978, The subsurface geology of Hamilton County, Florida,
with emphasis on the Oligocene age Suwannee Limestone:
Masters Thesis, Florida State University, 185 p.
Cooke, C. W., 1939, Scenery in Florida as interpreted by a geologist:
Florida Geological Survey Bulletin 17, 120 p.
Davis, J. H., 1946, The peat deposits of Florida, their occurrence,
development and uses: Florida Geological Survey Bulletin 30, 250
Florida Phosphate Council, 1990, Phosphate Fact sheet-1989.
Healy, H. G., 1975, Terraces and shorelines of Florida: Florida Bureau of
Geology Map Series 71, scale 1:2,000,000.
Knapp, M. S., 1978, Environmental geology series-Valdosta Sheet: Florida
Bureau of Geology Map Series 79, scale: 1:250,000.
MacNeil, F. S., 1950, Pleistocene shorelines in Florida and Georgia. U. S.
Geological Survey Professional Paper 221-F, p. 95-107.
Puri, H. S and Vernon, R. 0., 1964, Summary of the geology of Florida
and a guidebook to the classic exposures: Florida Geological
Survey Special Publication 5 (revised), 312 p
Scott, T. M., 1988, The lithostratigraphy of the Hawthorn Group (Miocene)
of Florida: Florida Geological Survey Bulletin 59, 148 p.
Sever, C W., Cathcart, J. B, and Patterson, S. H, 1967, Phosphate
deposits of south central Georgia and north central peninsular
Florida: Georgia Department of Mines, Mining, and Geology,
Project Report 7, South Georgia Minerals Program, 62 p.
White, W A., 1970, The geomorphology of the Florida peninsula: Florida
Bureau of Geology Bulletin 51, 164 p.
Zellers and Williams, Inc., 1978, Evaluation of the phosphate deposits of
Florida u,.nq i r- n ,-,r,1il. i. 1 h. iii t ;, il-ern Final report prepared
for the U.S. Bureau of Mines, 196 p.
I NORTHERN HIGHLANDS
GULF COASTAL LOWLANDS
rr CODY SCARP
FIGURE 1. GEOMORPHOLOGY
(modified from White, 1970)
. . ...
100'-170' SUNDERLAND TERRACE (COOKE, 1939)
OKEFENOKEE TERRACE (MACNEIL, 1950)
70'-100' WICOMICO TERRACE
FIGURE 2. TERRACES AND SHORELINES
(modified from Healy, 1975)
0 4 MILES
0 6 KILOMETERS
SCALE FOR FIGURES
1,2, AND 3a
* WELL CUTTINGS LOCATION
0 CORE LOCATION
FIGURE 3a. GEOLOGIC CROSS SECTION LOCATIONS
0 --mSL - -
S 0 2 4 MILES
TD 1723' ,
0 3 6 KILOMETERS
SCALE FOR FIGURES 3b AND 3c
VERTICAL EXAGGERATION FOR FIGURES 3b AND 3c IS APPROXIMATELY 160 TIMES HORIZONTAL
FIGURE 3c. GEOLOGIC CROSS SECTION B-B'
Two well systems are used in this report. One uses the rectangular
system of section, township and range for identification. The well
number consists of six parts: W for well, county abbreviations, the
Township, Range, and Section, and the quarter/quarter location
within the section. The other system uses the Florida Geological
Survey sample repository accession number.
FIGURE 3b.GELGCCOSSCINA '