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MAP SERIES NO. 130
MINERAL RESOURCES OF
LEE COUNTY, FLORIDA
ED LANE, P.G.#141, THOMAS M. SCOTT,
RONALD W. HOENSTINE AND J. WILLIAM YON
FLORIDA GEOLOGICAL SURVEY
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, urban development has occurred in areas underlain by known
mineral deposits, which precludes future 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
growing conflict between rapid growth and development of the state's mineral resources
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 act and at the request of the Lee County Commissioners, the Florida
Geological Survey initiated a study of Lee County's mineral resources. The objective of this
report is to summarize and interpret geologic data (i.e., core and well cutting descriptions,
geophysical logs, and data derived from field reconnaissance) in a format appropriate for
use by city and county planners.
A knowledge of Lee County's mineral resources is basic and integral to the process of
initiating, developing and implementing an effective comprehensive land use plan. This
information and data are 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 disposal sites.
Factors used in evaluating the economic value of the county's known and potential
mineral resources are varied, changing, and in many instances interrelated, thus
complicating an accurate assessment. The evaluation process is inherently dependent on
an extensive exploration program, a necessary precursor to mining in order to determine
reserves, content and extent of specific mineral resources. In addition, such factors as
operating expenses, beneficiation, reclamation and capital costs of mining must be included
in the overall calculations.
Resource evaluation for this report is based on a number of sources including Florida
Geological Survey reports and unpublished data, field reconnaissance, county, state and
federal statistical data, company reports, questionnaires, and numerous 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 to the various aspects of resource evaluation lends substantial confidence
to the general assessments and inferences of this report.
METRIC CONVERSION FACTORS
In order to prevent the duplication of English and metric units in this report the following
conversion factors are provided.
White (1970) and Lane (1980) are the primary sources used in the following discussion of
the geomorphology of Lee County. White (1970) subdivided Florida into three geomorphic
zones and designated the southern part of the peninsula as the Southern or Distal zone,
which includes Lee County. Within this zone are several geomorphic features, including the
Immokalee Rise, the Caloosahatchee Valley, the Southwestern Slope, the Gulf Coastal
Lagoons and the Gulf Barrier Chain (Figure 1). Lee County is generally flat, sloping
gradually upward from sea level along the Gulf Coast to elevations between 20 to 30 feet
above mean sea level (MSL) at its eastern boundary.
The Immokalee Rise has the highest topographic elevations in the county, which range
from 25 to 42 feet MSL. Its boundary on Figure 1 is approximated by the 25-feet-elevation
contour. Surficial sediments associated with this feature are medium to fine sand and silt
overlying shell or limestone. Sand thickness generally increases with higher elevation,
which supports White's (1970) theory that the Immokalee Rise originated as a submarine
sand shoal when sea level stood higher than present, possibly during the Pleistocene.
North of and contiguous to the Immokalee Rise and the Southwestern Slope is a large
feature known as the Caloosahatchee Valley. This lowland extends as far east as Lake
Okeechobee and occupies most of the northern half of Lee County. It is underlain by
clayey sand and shell units and limestone. This valley generally has elevations less than 25
Another relatively large geomorphic feature present in the county is the Southwestern
Slope. This feature borders the Caloosahatchee Valley on the southwest and the Immokalee
Rise on the southeast. The Southwestern Slope varies in elevation from a maximum value of
25 feet MSL to sea level at the coast. The area is covered by a relatively thin veneer of sand
which is underlain at shallow depths by clay, shell and limestone units (Lane, 1980).
A nearly continuous sequence of barrier islands is present along the coast of Lee County.
These islands, known as the Gulf Barrier Chain, are separated from the mainland by the Gulf
Coastal Lagoons. Associated with these islands is a system of sand dunes that is seldom
more than one mile wide and 10-feet high (Lane, 1980). White (1970) speculated that these
barrier islands may have formed locally from sand eroded from headlands.
Several relict marine terraces are present in the county. These features were formed
during higher sea level stands that occurred in the Pleistocene Epoch. Based on elevation,
Healy (1975) recognized three terraces in Lee County (Figure 2). In order of descending
elevation, they are the Talbot Terrace (25 to 42 feet MSL), the Pamlico Terrace (8 to 25 feet
MSL) and the Silver Bluff Terrace (less than 10 feet MSL).
Lee County is underlain by a thick sequence of sedimentary rocks ranging In thickness to
at least 15,600 feet (Barnett, 1975; Arthur, 1988). Below the sedimentary sequence, Middle
Jurassic (mid-Mesozoic) igneous rocks (approximately 163 million years old) were
encountered. The igneous rock sample was recovered from an oil test well (W-10566) in
southeastern Lee County (section 14, Township 45 south, Range 27 east) from 15,618 feet
below MSL. These rocks, referred to as basement rocks, are overlain by more than 10,000
feet of primarily carbonate rocks (limestones and dolomites) with minor siliciclastic sediment
units (sand and shale). Carbonate deposition predominated from the mid-Jurassic through
the Oligocene (163 to approximately 25 million years ago). The post-Oligocene (Miocene
and younger) sediments consist of interbedded and mixed siliciclastics and carbonates.
Figure 3a is a map showing cross sections used in this report.
Eocene, Oligocene and some Miocene carbonate rocks form the Floridan aquifer system,
one of the world's most productive aquifers. The Floridan aquifer system in Lee County
consists of the Eocene Avon Park Formation and Ocala Group, the Oligocene Suwannee
Limestone and the lowest part of the Miocene-Pliocene Hawthorn Group. The major rock
types are limestones and dolomites with only a minor siliciclastic component. Water quality
in the Floridan aquifer system in Lee County Is poor due to high chloride, sulfate and total
dissolved solids (Wedderburn et al., 1982).
The Miocene-Pliocene Hawthorn Group occurs throughout the county, generally within
125 feet of the surface (Figures 3b and 3c). The Hawthorn Group consists of a lower
carbonate unit, the Arcadia Formation, and an upper sillciclastic unit, the Peace River
Formation (Scott, 1988). Phosphate is present in varying amounts throughout these
sediments. The Hawthorn Group's total thickness ranges from less than 500 feet in the
northwest to more than 700 feet in the east and southeast parts of Lee County. Wedderburn
et al. (1982) recognizes 850 feet of Hawthorn sediments in the northeastern corner of Lee
County. Since the majority of water wells in Lee County do not completely penetrate the
Peace River Formation of the Hawthorn Group, the Peace River Formation is the deepest
unit represented on the cross sections.
Sediments of the Hawthorn Group form the intermediate aquifer and confining system
including two main aquifers, the Sandstone and mid-Hawthorn aquifers, and three confining
zones, the lower, mid- and upper Hawthorn confining zones (Wedderburn et al., 1982). The
confining characteristics of the Hawthorn Group sediments also serve to confine the
Floridan aquifer system. Water from the producing zones In the Hawthorn Is better quality
than the underlying Floridan aquifer system (Wedderburn et al., 1982).
The Pliocene Tamiami Formation overlies the Hawthorn Group throughout the county and
is the oldest formation exposed in Lee County. During low water stages, the Tamiami
sediments are exposed along parts of the Caloosahatchee River in northeastern Lee County.
Many pits in the county expose the Tamiami Formation. The Tamiaml exhibits moderately
variable lithologic characteristics ranging from a poorly indurated, quartz sandy, clayey.
phosphatic, fossiliferous calcareous mud (often referred to as a "marld") to a well indurated,
quartz sandy, slightly phosphatic, fossiliferous limestone. In the northwestern portion of the
county, a very fossiliferous quartz sand with a clay and carbonate matrix occurs in the upper
Tamiami Formation. The thickness of the Tamiami Formation is variable in Lee County
ranging from less than 10 feet to more than 100 feet. In general it thickens in a north to
south trend. The top of the Tamiami ranges from approximately 20 feet above MSL to 40
feet below MSL.
The Caloosahatchee and Ft. Thompson Formations overlie the Tamiami Formation in
many areas of Lee County. The fossiliferous sands and carbonates of these units are often
less than 10-feet thick but exceed 60-feet thick in limited areas. Many mining operations
expose the Caloosahatchee and Ft. Thompson Formations. As the result of difficulties
separating Caloosahatchee and Ft. Thompson on a lithologic basis, the units are shown on
the cross sections as undifferentiated Caloosahatchee/Ft. Thompson Formation.
Undifferentiated Pleistocene-Holocene sediments overlie the Caloosahatchee-Ft.
Thompson sediments in Lee County. These sediments vary from unfossiliferous quartz
sands to very fossiliferous sands and shell beds, thin mart beds and organic-rich sediments.
The undifferentiated sediments generally occur as thin beds less than 10-feet thick.
However, along the coast these units can exceed 20-feet thick.
Sediments belonging to the Tamiami, Caloosahatchee and Ft. Thompson Formations and
the undifferentiated Pleistocene-Holocene sediments comprise the surficial aquifer system in
Lee County. Wedderburn et al. (1982) indicate that the surficial aquifer system ranges from
less than 15 feet to more than 125 feet in thickness. Water quality in the surficial aquifer
system while it is not exceptionally good, is better than that in the Intermediate aquifer and
confining system (Wedderburn et al., 1982).
The purpose of the following discussion is to provide information on the occurrence of
certain economic mineral commodities in Lee County. The information presented is not
intended to be an exhaustive investigation leading to immediate industrial development.
However, where the information is favorable it may indicate that certain areas warrant further
investigation. The Mineral Resources Map is designed to present a geographic overview of
the major economic mineral commodities identified in Lee County. Factors such as
thickness of overburden, quality, and volume of the deposit could affect the mining of the
mineral commodity at any specific site. In contrast, geologic cross sections have been
extrapolated from cores and/or well cuttings to show the distribution and thickness of
surface and near-surface stratigraphic units (Figures 3b and 3c). As a result, occasional
variations between the geologic cross sections and the Mineral Resources Map may occur.
The principal economic mineral commodities occurring in Lee County are limestone and
sand. In addition, a brief discussion of petroleum is included.
The extraction of limestone dominates the mining industry of Lee County. The
-commodity is present in the very near-surface sediments of eastern Lee County. Schmidt et
al. (1979) indicates that this limestone belongs primarily to the Pliocene Epoch Tamiami
Formation. It is comprised of tan to white or gray, poody to well Indurated, sandy, moldic
The limestone of the Tamiami Formation is mined by six companies in Lee County. These
companies are located east of the north-south trending Interstate Highway 75. They utilize
the open pit mining methods which are common to much of the southeastern United States.
Bulldozers clear away overburden which normally ranges up to 15 feet In thickness. The
limestone, once cleared, is fractured by heavy machinery or explosives. The broken rock is
then loaded by dragline or front-end loaders into trucks and transported to rock crushers for
processing. The water table is often encountered in the limestone pits. When this occurs,
draglines are used to extract the limestone under water to depths approaching 45 feet.
The Tamiami Formation mined in Lee County is primarily used as a base material in
roadway construction and as an aggregate grade rock for concrete and asphalt. Other
usages of limestone include riprap and drainfield aggregate. The fines (material remaining
after the production aggregate) are included as filler material in bituminous mixes used in
Quartz sand occurs on the surface and in the near-surface of Lee County. North and
west of the Caloosahatchee River, siliciclastic sediments as thick as 50 feet are present.
These sediments are comprised of clayey, shelly quartz sand, which is occasionally
cemented to form sandstone (Lane, 1980).
Although mining in Lee County is usually associated with limestone, there are a few
existing and abandoned operations which extract sand. The majority of these operations
are located in the northwestern part of the county in the vicinity of Burnt Store and Chiquita
Roads. This material is used locally as a source of fill material.
The Florida General Soils Atlas (Spielberger, 1975) rates soils as to their suitability as
sources of material for many categories. Materials suitable for two of these categories (sand
and roadfill) occur In Lee County. A soil, which Is labeled as a good source of sand, meets
the criteria of being at least three-feet thick. A soil rated as good for roadfill means that it is
well suited as embankment material when compacted and is easily removed from borrow
pits. Soils rated as good sand sources are most abundant In southeastern Lee County,
south of Immokalee Road and east of U. S. Highway 41. Small areas of good sand are also
found in the northwestern and northeastern portions of Lee County. The Lee County Land
Use Plan Map (1984) designates many of these areas as environmentally sensitive areas.
Approximately 90 percent of the county is rated as good for roadfill material by Splelberger
(1975) who considered only the uppermost 80 inches of the ground In preparing his report.
Two oil fields are located in Lee County (Mineral Resources Map). These fields (West
Felda and Lehigh Park Fields) were discovered in 1966 and 1974, respectively. The Upper
Cretaceous Sunniland Formation is the producing horizon for both oil fields and occurs at
depths of 11,890 feet below land surface for the Lehigh Park and 11,450 for the West Felda
Field. The Lehigh Park Field, through the end of 1985, produced 4,536,720 barrels of oil and
the West Felda Field, through 1985, produced 38,150,947 barrels of oil (Applegate and
Much of Lee County has surface and near-surface sediments comprised of clayey, shelly
sand, mad and organic muck. These undifferentiated resources have extensive occurrences
in the northeastern portion and the western half of the county. Any large scale economic
utilization is diminished by the heterogeneous nature of these sediments. However, they are
locally valuable as fill, since many areas are subject to flooding and require fill for building
and development purposes. In addition, these sediments have use as topsoil and roadfill.
Applegate, A. V. and Lloyd, J. M., 1984, Summary of Florida petroleum production and
exploration, onshore and offshore, through 1984: Florida Geological Survey Information
Circular 101, 69 p.
Arthur, J. D., 1988, Petrogenesis of Early Mesozoic tholeiilte In the Florida basement and an
overview of Florida basement geology: Florida Geological Survey Report of Investigation
97, 39 p.
Barnett, R. S., 1975, Basement structure of Florida and Its tectonic implications: Gulf Coast
Association of Geological Societies Transactions, v. 25, p. 122-142.
Healy, H. G., 1975, Terraces and shorelines of Florida: Florida Bureau of Geology Map
Series 71, scale 1:2,000,000.
Knapp, M. S., 1980, Environmental geology series, Tampa sheet: Florida Bureau of Geology
Map Series 97, scale 1:250,000.
Lane, E., 1980, Environmental geology series, West Palm Beach sheet: Florida Bureau of
Geology Map Series 100, scale 1:250,000.
Schmidt, W., Hoenstine, R. W., Knapp, M. S., Lane, E., Ogden, G. M., Jr., and Scott, T. M.,
1979, The limestone, dolomite, and coquina resources of Florida: Florida Geological
Survey Report of Investigation 88, 54 p.
Scott, T. M., 1988, The lithostratigraphy of the Hawthorn Group (Miocene) of Florida:
Florida Geological Survey Bulletin 59, 148 p.
Spielberger, A., (coordinator) 1975, The Florida general soils atlas with Interpretation for
regional planning districts IX and X: Florida Department of Administration, Division of
State Planning, Bureau of Comprehensive Planning, p. 27-28.
Sproul, C. R., Boggess, D. H., and Woodard, H. J., 1972, Saline-water intrusion from deep
artesian sources in the McGregor Isles area of Lee County, Florida: Florida Bureau of
Geology Information Circular 75, 30 p.
The Lee County Land Use Plan Map, 1984, Lee County Planning Department, Lee County,
Florida, no scale.
Wedderburn, L. A., Knapp, M. J., Waltz, D. P., and Burns, W. S., 1982, Part I Hydrogeologic
reconnaissance of Lee County, Florida: South Florida Water Management District
Technical Publication 82-1, 192 p.
White, W. A., 1970, The geomorphology of the Florida peninsula: Florida Bureau of Geology
Bulletin 51, 164 p.
\ CAPTIVA ISLAND
\W Le L.-45 -23E .. /
\ ISLAND / /
FIGURE 1 GEOMORPHOLOGY
0 4 Ml
FIGURES 1, 2, 3a
FIGURE 2 TERRACES AND SHORELINES
(modified from Healy 1975)
(PEACE RIVER FORMATION) TO 100
0 4 mi
TD 662 vertical exaggeration 420x horizontal
FIGURE 3b CROSS SECTION A-A'
TD 462 TO 770'
S CROSS SECTION LOCATIONS
FIGURE 3a CROSS SECTION LOCATIONS
The well and quarry system used in this report uses the
rectangular system of section, township and range for
identification. The well or outcrop number consists of six parts:
W for well or L for quarry, county abbreviation, the Township,
Range, and Section, and the quarter/quarter location within the
Fvertal eaGerationU420E horizontal
FIGURE 30 CROSS SECTION B-B'
(from White 1970, and Lane 1980)
DEPARTMENT OF NATURAL RESOURCES
FLORIDA GEOLOGICAL SURVEY
This public document was promulgated at a total cost of
$1,834.00 or a per copy cost of $2.44 for the
purpoM of disemlnatkng geologic data.