GEOLOGICAL SURVEY CIRCULAR 888

Phosphate-Rock Resources 

of the United States
Phosphate-Rock Resources 

of the United States

By JAMES B. CATHCART, RICHARD P. SHELDON, 

and ROBERT A. GULBRANDSEN

GEOLOGICAL SURVEY CIRCULAR 888

An analysis of phosphate-rock resources, 

based on past estimates and all available 

recent information, indicates that 

sufficient phosphate exists in the 

United States to meet domestic demands 

for the foreseeable future

1984
United States Department of the Interior 

WILLIAM P. CLARK, Secretary

Geological Survey

Dallas L. Peck, Director

Free on application to the Branch of Distribution, Eastern Region, U.S. Geological Survey, 604 South Pickett Street, Alexandria, VA 22304
CONTENTS

Abstract

Introduction .......................

Resource classification and nomenclature .......

Resource estimates based on certainty of existence 

Resource estimates based on feasibility of economic 

recovery ......................

United States phosphate resources ..........

Atlantic Coastal Plain phosphate province ....

Florida .....................

Identified resources ............

Hypothetical resources ..........

North Florida district ........

Northeast Florida district ......

East Florida district .........

South Florida district ........

Summary of phosphate resources of 

Florida ..................

Georgia .....................

South Carolina .................

North Carolina .................

Offshore .....................

Atlantic Coastal Plain .............

Northwestern Phosphate Province ........

Past resource studies .............

Data collection ...............

Resource assessments ...........

Ore thickness ...............

Phosphate grade ..............

Ore quality ................

Potential byproducts ...........

Page

9

9

9

13

13

15

16

17

17

18

19

19

19

19

20

21

21

22

22

22

23

23

United States phosphate resources Continued 

Northwestern Phosphate Province Continued 

Idaho ....................

Service and Coffman estimates . . . 

Garrand estimates ...........

Bauer and Dunning estimates . . . .

Gulbrandsen and Krier estimates . . 

Summary of estimates ........

Montana ...................

Swanson estimates ..........

Bauer and Dunning estimates . . . .

Summary of estimates ........

Wyoming ..................

Sheldon estimates ...........

Coffman and Service estimates . . . 

Bauer and Dunning estimates . . . .

Summary of estimates ........

Utah .....................

Coffman and Service estimates . . . 

Dames and Moore, Inc., estimates . 

Bauer and Dunning estimates . . . .

Unpublished Vernal area estimates . 

Summary of estimates ........

Northwestern United States .......

Other phosphate provinces ...........

Tennessee ..................

Other areas .................

Summary of U.S. phosphate resources ......

Future trends and problems ............

Glossary .......................

References cited ...................

ILLUSTRATIONS

Page

24

24

28

29

30

30

31

31

31

32

34

34

36

36

36

36

36

36

36

36

37

39

41

43

43

44

44

45

46

FIGURES 1-5. Diagrams showing:

1. Major elements of mineral resource classification .......................... 4

2. Reserve-base and inferred-reserve-base classification categories .................. 4

3. Southeastern phosphate resource category definitions, strippable resources ........... 5

4. Northwestern phosphate resource category definitions, strippable resources ........... 6

5. Northwestern phosphate resource category definitions underground resources ......... 7

Sketch map of Florida, with outlines of phosphate districts, location of significant drill holes, and areas

where the middle Miocene Hawthorn Formation and rocks of late Miocene age are missing .... 11 

Outcrops of the Permian Phosphoria Formation, localities sampled for phosphate, and large-scale geologic

mapping in Idaho .............................................. 25

Areas of phosphate resource assessment in Idaho ............................. 26

Depth categories of Northwestern Phosphate Province .......................... 27

Phosphate rock outcrops and sample localities in Montana ........................ 33

6.

7.

8.

9.

10.

11.

12.

Phosphate rock outcrops and sample localities in Wyoming ........................ 35

Phosphate rock outcrops and sample localities in Utah .......................... 38

in
TABLES

TABLE 1. Comparison of estimates of identified resources of phosphate rock in Florida ............... 10

2. Identified phosphate rock resources of Florida, estimated by various authors ............... 12

3. Summary of hypothetical phosphate rock resources of Florida, by county ................. 14

4. Summary of phosphate rock resources of Florida ............................... 18

5. Summary of phosphate rock resources, Eastern United States ....................... 20

6. USGS Circulars reporting phosphate stratigraphic data of the Northwestern Phosphate Province .... 21

7. Comparison of estimates of phosphate rock resources in Idaho ....................... 28

8. Comparison of phosphate rock resources in Montana ............................. 32

9. Comparison of phosphate rock resources in Wyoming ............................. 34

10. Comparison of phosphate rock resources in Utah ............................... 37

11. Phosphate rock resources of the Northwestern Phosphate Field ....................... 39

12. Other phosphate rock resources, United States ................................ 40

13. Phosphate rock resources of the United States ................................ 44

IV
Phosphate Rock Resources of the United States

By JAMES B. CATHCART, RICHARD P. SHELDON, and ROBERT A. GULBRANDSEN

ABSTRACT

In 1980, the United States produced about 54 million tons 

of phosphate rock, or about 40 percent of the world's production, of which a substantial amount was exported, both as phosphate rock and as chemical fertilizer.

During the kst decade, predictions have been made that easily minable, low-cost reserves of phosphate rock would be 

exhausted, and that by the end of this century, instead of being 

a major exporter of phosphate rock, the United States might 

become a net importer. Most analysts today, however, think 

that exports will indeed decline in the next one or two decades, 

but that resources of phosphate are sufficient to supply domestic needs for a long time into the future.

What will happen in the future depends on the actual availability of low-cost phosphate rock reserves in the United States 

and in the world. A realistic understanding of future phosphate 

rock reserves is dependent on an accurate assessment, now, 

of national phosphate rock resources.

Many different estimates of resources exist; none of them 

alike. The detailed analysis of past resource estimates presented in this report indicates that the estimates differ more 

in what is being estimated than in how much is thought to 

exist.

The phosphate rock resource classification used herein is 

based on the two fundamental aspects of a mineral resource 

(1) the degree of certainty of existence and (2) the feasibility 

of economic recovery.

The comparison of past estimates (including all available 

company data), combined with the writers' personal knowledge, indicates that 17 billion metric tons of identified, recoverable phosphate rock exist in the United States, of which about 

7 billion metric tons are thought to be economic or marginally 

economic. The remaining 10 billion metric tons, mostly in the 

Northwestern phosphate district of Idaho, are considered to 

be subeconomic, minable when some increase in the price of 

phosphate occurs.

More than 16 billion metric tons probably exist in the southeastern Coastal Plain phosphate province, principally in Florida 

and North Carolina and offshore in the shallow Atlantic Ocean 

from North Carolina to southern Florida. This resource is considerd to be hypothetical because it is based on geologic inference combined with sparse drilling data.

Total resources of phosphate rock in the United States are 

sufficient to supply domestic demands for the foreseeable future, provided that drilling is done to confirm hypothetical resources and the chemistry of the deposits is determined. Mining and beneficiation techniques will have to be modified or 

improved, and new techniques will have to be developed so 

that these deposits can be profitably exploited.

INTRODUCTION

The United States produced in 1980 about 54 

million metric tons of phosphate rock, which was 

40 percent of world production. About 59 percent 

of this production was exported, 26 percent as 

phosphate rock and 33 percent as manufactured 

fertilizers and chemicals. The remainder was used 

domestically, largely (88 percent) for fertilizer and 

animal feed supplement to produce agricultural 

products (U.S. Bureau of Mines, 1980). A significant portion of these agricultural products was exported, so the phosphate rock that went into that 

portion was exported indirectly. Thus, most phosphate is exported directly or indirectly, and its 

value contributes positively to the U.S. balance 

of international payments. Although the marketable value of the phosphate rock produced in 1980 

was only about $1.2 billion, the total value of the 

agricultural and chemical products depending on 

phosphate rock input is many times that. The continued ability of the U.S. phosphate industry to 

supply low-cost phosphate rock for export and 

domestic consumption is clearly of major importance to the Nation.

During the last decade, people have questioned 

whether the national endowment of phosphate 

rock in the ground is sufficient to support the national phosphate industry very far into the next 

century. A report by the U.S. Government Accounting Office in 1979, using information largely 

from producing companies and the U.S. Bureau 

of Mines, projected a significant decline in U.S. 

exports of phosphate by the mid-1980's and forecast that the Nation would become a net phosphate importing country in the first quarter of the 

next century. This decline, the report said, would 

be caused by the exhaustion of high-grade, easily 

mined, and beneficiated phosphate reserves in the 

Northwestern Phosphate Province in Idaho and 

adjacent States of Montana, Wyoming, and Utah,
and more importantly, in the Southeastern Phosphate Province from Florida to North Carolina. 

These two provinces presently produce about 97 

percent of the U.S. production and contain all but 

a minor portion of the Nation's phosphate resources.

A possible result of a significant decline in U.S. 

exports would be a greatly strengthened world 

market position and possible cartelization of a few 

phosphate exporting countries which have large 

resources of phosphate rock that could be 

exploited at low cost. This presumably would 

occur after the U.S. deposits that could be extracted at a low cost were exhausted. A rise in 

world phosphate prices could be expected, and the 

U.S. agricultural sector, forced to rely on imported high-priced fertilizer, would be weakened. 

In addition, some people fear that the very prospect of a weakened national phosphate-resource 

position might result in export restrictions on 

phosphate rock and phosphate products in the 

near future. Furthermore, a deteriorating phosphate industry would be in a weakening position 

in regard to allocation of railroad rolling stock, environmental regulations, severance taxation policies, and the like.

Analysts of the U.S. Bureau of Mines think that 

such a scenario is unlikely. Their current forecast 

(William Stowasser, written commun., 1981) is 

that exports of phosphate rock will decline during 

the decade of the 1980's. The reasons for the decline cited by analysts include the increasing cost 

of producing phosphate rock in the United States 

from lower quality deposits, the much higher cost 

of opening new mines, the high freight rates for 

shipping to European and Asian markets, and the 

competition from government-subsidized phosphate rock operations in foreign countries. The 

Bureau of Mines analysts anticipate that some of 

the lost export sales of phosphate rock will be 

made up by increased export sales of manufactured phosphate fertilizer and chemicals, that the 

United States will continue to export some phosphate rock, and that these factors will probably 

influence decisions to defer the construction of 

new phosphate mines in the 1980's. The domestic 

over-supply position forecast for the 1980's will be 

exacerbated by the decline in the export market 

demand for U.S. phosphate rock. The Bureau of 

Mines' analysts feel that none of the factors cited 

for the decline of exports appears to be reversible. 

For the long term, the phosphate industry probably will find it increasingly difficult to compete in 

international trade with phosphate rock, and as 

time progresses and North African and Middle 

East countries increase their manufacturing capacity for phosphate fertilizer, the competitive position of the U.S. producers of manufactured fertilizer will probably be eroded in international 

trade.

These Bureau of Mines analysts do not subscribe to the scenario that the United States will 

be importing phosphate rock from a cartelized 

world market, because the United States has adequate domestic resources and because most of the 

reasons cited for the decline of U.S. exports will 

also limit or prohibit importing phosphate rock 

into the United States.

What actually happens in the future to world 

phosphate rock prices and the U.S. position relative to the position of other phosphate exporting 

countries and when it happens will depend on the 

actual availability of low cost phosphate rock reserves in the United States and throughout the 

world. A realistic understanding of future phosphate rock reserves is dependent on an accurate 

assessment now of national phosphate rock resources.

Many estimates of phosphate-rock resources 

exist, no two of which are alike. Some view these 

different estimates as the result of a dispute 

among resource optimists and pessimists. However, detailed analyses of various estimates usually are due more to differences in what is being 

estimated than in how much is thought to exist. 

A large estimate may include rock that is only 

potentially economically available along with rock 

currently economically available; whereas, a lower 

estimate may include only the currently economically available rock. Differences in estimates may 

be due to differences in areas studied and price 

projections; to assumptions concerning mining 

techniques, ore processing techniques, and fertilizer manufacturing techniques; and finally to differences in the methods of assessment. Compatibility of resource estimates has been further hindered by technical language that may confuse specialists and nonspecialists alike.

A system of classifying phosphate rock resources is being devised by a joint subcommittee 

of the U.S. Bureau of Mines (USBM) and the U.S. 

Geological Survey (USGS) to give a single clear 

language to this complex subject and to permit 

real differences among estimates to be identified
and analyzed. This emerging phosphate rock resource classification is based on the principles of 

classification originally devised by V. E. McKelvey (1972) and modified by a joint committee of 

the U.S. Bureau of Mines and the U.S. Geological 

Survey, as U.S. Geological Survey Circular 831 

(USBM and USGS, 1981). This system will allow 

future resource estimates to be precisely stated. 

The classification is based on the two fundamental 

aspects of mineral resources (McKelvey, 1972): 

first, how well a resource is known and measured 

(degree of certainty of existence) and second, how 

feasibly a resource can be exploited with existing 

mining and processing technology at existing 

prices (feasibility of economic recovery). This system is illustrated in figures 1 and 2, in which the 

resource classes are named.

The system provides a format by means of 

which various estimates can be compared and significant differences can be identified. The comparison of past estimates is the subject of this part 

of this report.

RESOURCE CLASSIFICATION AND 

NOMENCLATURE

RESOURCE ESTIMATES BASED ON 

CERTAINTY OF EXISTENCE

Past published estimates of phosphate resources 

have not explicitly taken into account the degree 

of certainty of the existence of the resource. Mining companies of course are highly concerned with 

accurately estimating one category of resources, 

that is, their measured reserves prior to actual 

mining and their indicated reserves prior to trading or selling land. Reserves (fig. 1) can be measured by drilling on approximately an eighth-of-amile spacing, and reserves can be indicated with 

approximately a half-mile spacing. Such reserve 

estimates, however, are generally not published, 

although they may be reported on a confidential 

basis to the U.S. Bureau of Mines or the U.S. 

Geological Survey, either of which may publish 

aggregated reserve estimates. Publicly available 

estimates of the inferred reserve base are made 

by the U.S. Geological Survey or other geologic 

organizations, and the certainty of existence of the 

resource is based on geologic inference about the 

lateral continuity of the beds and the variability 

of their grade, thickness, and quality. (See p. 22 

for definitions.) Geologic judgment is used to determine what part of the resource is inferred reserve base and what part can be regarded as 

hypothetical undiscovered resource. This judgment usually varies among geologists and is the 

source of significant differences of estimates. A 

purely arbitrary definition of the criteria for assigning a resource to the inferred reserve base 

has been set up by the Bureau of Mines-Geological 

Survey Resource Classification Subcommittee 

based on the density of drill holes (figs. 3, 4, 5) 

(USGS, 1982). If drill holes are spaced at any distance less than 1 mile, the resource is regarded 

as an identified resource (inferred reserve base), 

but if drill holes are more than 1 mile apart, the 

resource is regarded as an undiscovered 

(hypothetical) resource, with the caveat that the 

spacing may be greater if justified by geologic inference. This arbitrary definition divides the resource classes efficiently and is understandable to 

all workers, but it cannot be regarded as an adequate substitute for an accurate, scientific assessment of resource class boundaries. An interesting 

theoretical approach to this problem is the statistical method called kriging, by which the statistical 

variability of physical parameters of a bed can be 

areally mapped (Davie, 1977). A parameter such 

as thickness or feet-percent P205 can be selected 

as an index of the resource quantity, and then an 

arbitrary limit of the statistical variance of that 

parameter may be chosen to express an acceptable 

geologic certainty of existence or measurement of, 

for example, inferred resources. In this case, the 

delineation of areas where the resource has a variance less than the limit would show the areas of 

inferred resources, and the areas where the variance was higher would show the areas of 

hypothetical resources. This method would overcome the deficiencies of setting resource boundaries by the arbitrary drill-hole spacing method. 

However, the methodology is not available at 

present because it has yet to be developed to the 

point where it can be routinely applied. In any 

event, past phosphate resource estimates have 

used neither method but have relied on unspecified geologic judgments, and, as a result, inferred resources and hypothetical resources have 

not been systematically separated.

RESOURCE ESTIMATES BASED ON 

FEASIBILITY OF ECONOMIC RECOVERY

The criteria for resource classes based on the 

feasibility of economic recovery include (1) bed 

thickness, (2) the phosphate content, (3) the con-
Cumulative 

Production

ECONOMIC

MARGINALLY 

ECONOMIC

SUBECONOMIC

IDENTIFIED RESOURCES

Demonstrated

Measured Indicated

Reserves

! T

Marginal Reserves

- -

Demonstrated 

Subeconomic Resources

Inferred

Inferred Reserves

Inferred 

Marginal Reserves

Inferred 

Subeconomic 

Resources

UNDISCOVERED RESOURCES

Probability Range 

 (or) 

Hypothetical Speculative

1

1

- + 

Other 

Occurrences Includes materials that are not considered a resource

FIGURE 1. Major elements of mineral resource classification. Column headings indicate degree of certainty of existence, row 

headings indicate possibility of economic recovery. From U.S. Geologicial Survey and U.S. Bureau of Mines (1981, p. 5).

Cumulative 

Production

ECONOMIC

MARGINALLY 

ECONOMIC

SUBECONOMIC

IDENTIFIED RESOURCES

Demonstrated

Measured Indicated

Reserve

Base

Inferred

Inferred

Reserve 

Base

UNDISCOVERED RESOURCES

Probability Range

 (or) 

Hypothetical Speculative

[- -+-

+

Other 

Occurrences Includes materials that are not considered a resource

FIGURE 2. Reserve-base and inferred-reserve-base classification categories. Column headings indicate degree of certainty of 

existence; row headings indicate possibility of economic recovery. From U.S. Geological Survey and U.S. Bureau of Mines 

(1981, p. 5).
o

5 

o

0

o

UJ

O

z

o

5

o

z

o

o

UJ

^

z

CDOC

2

0

5

0

0

o

UJ CO

D

(A

IDENTIFIED RESOURCES

DEMONSTRATED

c

INFERRED

"8 UJ «

UNDISCOVERED RESOURCES

HYPOTHETICAL

9 

3

 - c <" 5 = si a Ins

w "!s £ 8 1 g

» °-« £ SOT

UJ « co w co =

s |1 s fls

» fS Q ^S|

oc *o ~ oc -S = 9J> " C OC « £ W -? LLJ Q) ^ fc-

«2| - °S

Product: >29 percent P2O5, CaO/P2O5 1.55,

< 1.5 percent MgO, < 5 percent

Fe2O3 4- Al2O3

Ore: Thickness >2 ft, cubic yards overburden

and ore per ton of product <30

unconsolidated

Minimum size: 40 x 106 tons product

Mine depth: < 150 ft

SUBECONOMIC RESOURCES

Product P2O5; <29 percent; thickness 

<2 feet; mine depth 200 ft; 500 tons

I

SPECULATIVE

i

n o

=

 o 

o

*

*

piiwopiiaic piwiuwi pel O\«IG, \«uui\« yaiuo 

overburden and ore per ton of

phosphate product <40

(A

O

oc z

z oc

o 

0

Includes materials that are not considered a resource

FIGURE 3. Southeastern phosphate resource category definitions, strippable resources; present major industry economic

and technology.
u

ECONOM

D

ECONOMIC AN

_i

Z

o 

cc

u

3ECONOM

CO

IDENTIFIED RESOURCES

DEMONSTRATED

o

S UJ 0

INFERRED

"« UJ '

c «5 §c I S |j

UNDISCOVERED RESOURCES

HYPOTHETICAL

> >

!" 

2 u

< i- .£ > « .£ £

00 S i* cc « ** QJ 

 tt o £ g.°c

> 2 en tO co '~ 

^ 3 JJJ « .3 0

uj 9 =5 ^ 9 T> 'o> 

co _ 2 Q 2 ^

* «| i S|l

* C 111 (o C w

£^ z o^

>1 8 percent P2O5; <3 percent Fe2O3 + Al2O3; 

<1.5 percent MgO; thickness >5 ft;

 CaO/P2O5 <1 .55; ratio of cubic yards 

overburden per ton of ore <3.5:1; 

minumum size 20 x 106

SUBECONOMIC RESOUF

,

ICES

<15 percent P0OC ; thickness >3 ft; ratio

SPECULATIVE

of cubic yards overburden per ton of ore 9:1

UJ

o 

cc z

UJ UJ

Includes materials that are not considered e resource

FIGURE 4. Northwestern phosphate resource category definitions, strippable resources; present major industry economics

and technology.
IDENTIFIED RESOURCES UNDISCOVERED RESOURCES

DEMONSTRATED INFERRED HYPOTHETICAL SPECULATIVE

y

5 

o

o 

o

UJ

O

z

y

5 

o

o 

o

UJ

>-

O

oc

RESERVE BASE

Si

g «

"o =5

-£ 2

IS

o

c o 

o £ 

 g.2.0

2 TJ OS -c mo 

= « o

NONE

O 

2 

O

o 

o

UJ ffi 

W

SUBECONOMIC RESOURCES

>24 percent P2O& phosphate bed > 3 ft 

thick, < 1000 ft below entry level

(O

UJ

0

jE 1

°o

0

o

Includes materials that are not considered a resource

FIGURE 5. Northwestern phosphate resource category definitions, underground resources.
tent of chemical components deleterious to the fertilizer manufacturing process, (4) the ratio of the 

total amount of material that has to be moved 

(overburden and ore) to the amount of phosphate 

recovered, (5) the total depth of the strip mine, 

(6) the size of the deposit, and (7) the percentage 

of the phosphate in the ground recovered by mining. These criteria have been used in one way or 

the other, implicitly or explicitly, in past phosphate resource estimates and are indicated for 

each estimate of resources that follow.

The details of the phosphate resource class divisions are being studied, and class boundaries 

criteria are summarized in figures 3, 4, and 5 of 

the present report. Resources are classed according to economic feasibility of recovery into three 

classes: economic, marginally economic, and subeconomic. The divisions are primarily made on 

economic and technologic grounds, which differ 

from one deposit to another depending on the 

costs of the mining, processing, and transporting 

operations. Also, the variations of price of the 

product cause variations in the resource 

categories. In order to avoid continually changing 

amounts of resources within classes based on feasibility of economic recovery, the reserve-base and 

inferred-reserve-base classes were set up to include all the rock from which reserves and inferred reserves and marginal and inferred marginal reserves are derived (fig. 2). The reserve 

base is defined strictly on physical parameters and 

not on technologic or economic factors, although 

these factors influence the choice of physical parameters. It is important to note that the reserve 

base and inferred reserve base are made up of 

rock in the ground and do not take into account 

the fact that not all the ore is recoverable. The 

estimates of phosphate resources in this report are 

all of the reserve-base and inferred-reserve-base 

classes unless otherwise noted. Thus, they are not 

to be confused with reserves or inferred reserves, 

and they are larger than reserves by the amount 

of rock that cannot be recovered and is left in the 

ground. Also, the reserve base and inferred reserve base are liberally estimated; thus, they include some rock that will turn out to be subeconomic, although this overestimation is kept to 

a minimum by adopting as nearly as possible current mining parameters.

Two other factors unrelated to the resource 

classification problem are of critical importance for 

the comparison of resource estimates. The first is

areal coverage of the estimates. It is rare that 

any two estimates cover the same area. In some 

cases, this makes little difference because areal 

differences may be small or the resource excluded 

may be small, but in other cases it can be important. The second factor is the date of the estimate. 

Estimates are data dependent, and the amount of 

data available for an estimate increases over time. 

Usually, the latest estimates are more accurate 

for this reason. However, many estimates do not 

include a systematic display of the data used, so 

this factor is commonly difficult to analyze.

It was pointed out earlier that differences in estimates may relate in addition to the areal coverage and the date of estimate to differences in 

price assumptions or mining and processing in 

technology assumptions and also to the method by 

which the estimate has been made. Generally, 

such factors, although important in evaluating the 

estimate, are usually not explicitly stated so that 

resulting differences cannot be analyzed.

UNITED STATES PHOSPHATE RESOURCES

Phosphate is produced from three distinct types 

of deposits: (1) sedimentary phosphorites, (2) 

guano or guano-derived deposits, and (3) igneous 

apatite deposits.

Sedimentary phosphate deposits, or phosphorites, provide all of the phosphate used in the 

United States, as well as about 75 percent of the 

phosphate used in the world. Phosphorite occurrences are widespread throughout the United 

States, but phosphate is being produced today 

only from the Atlantic Coastal Plain Phosphate 

Province, the Northwestern Phosphate Province, 

and less importantly from Tennessee. Phosphate 

has been produced from many other States, and 

occurrences in these States are listed at the end 

of this report, but emphasis herein will be on the 

two major provinces just mentioned.

In the United States, guano or guano-derived 

deposits are very small; individual bat-cave deposits known from the arid Southwest contain up 

to a few thousand tons each, and small bird guano 

deposits are known from Florida and the Hawaiian 

Islands. These occurrences are not economically 

important and are not significant as sources for 

fertilizer phosphate.

Igneous apatites contribute about 20 percent of 

the total world production of phosphate. Deposits 

of igneous apatite are known in the United States

8
(for example, nelsonite deposits in Virginia; apatite-magnetite deposits in New York «md New Jersey; marginal apatite differentiates at Iron 

Springs, Utah; and apatite-rich iron ores at Pea 

Ridge, Missouri). No igneous deposits are being 

mined for phosphate, but some byproduct apatite 

was produced in the concentration of iron ore from 

the Pea Ridge deposits until several years ago. 

Production of apatite from igneous deposits will 

not be a significant factor in the supply of phosphate demands in the United States.

ATLANTIC COASTAL PLAIN 

PHOSPHATE PROVINCE

The largest phosphate resource of the United 

States is made up of the phosphate deposits of 

the Southeastern Coastal Plain States of North 

Carolina, South Carolina, Georgia, and Florida, including portions of their offshore continental 

shelves.

These phosphatic rocks were deposited over the 

shallow continental shelves of the region about 5- 

15 million years ago during the Miocene and Pliocene Epochs of the Tertiary Period. The deposition was in shallow bays and shelves when the 

sea level was higher than it is at present time. 

The phosphate deposits were not continuous over 

the whole region but occurred adjacent to the shallower parts of the shelf around local structural 

arches or platforms, and in some areas, particularly in deeper bays, phosphate was not deposited.

Subsequent lowering of the sea level caused 

some of the deposits to be reworked by waves 

and streams, concentrating the phosphate by removing lighter weight and finer grained material. 

During subaerial exposure, the deposits were 

weathered; light or moderate weathering continued to concentrate the phosphate, but intense 

weathering formed uneconomic aluminum phosphate minerals from the original calcium phosphate. Younger sediments, either marine or nonmarine, covered the phosphate deposits so that 

they are not exposed or are exposed only along 

streams. Drilling is needed to explore for and outline these deposits. The phosphate deposits consist 

of flat-lying unconsolidated pelletal phosphate 

grains, quartz grains, and clay minerals, and 

weakly consolidated phosphate pellets, quartz 

grains, and clay cemented by carbonate minerals.

Thus, the geologic distribution of the phosphate 

deposits of the Atlantic Coastal Plain Province is 

sporadic, and the thickness and quality of the deposits vary widely from place to place. The specific 

deposits and their resources are described in detail 

in the sections that follow.

FLORIDA

IDENTIFIED RESOURCES

Estimates of the resources of phosphate in 

Florida have been made repeatedly since the discovery of the deposits in the 1880's. It is not necessary to recapitulate all of the estimates; but in 

view of the differences that some perceived as discrepancies between the recent estimates of only 

reserves by the U.S. Bureau of Mines and of total 

resources by the U.S. Geological Survey, as reported by the General Accounting Office (GAO, 

1979), it seems appropriate to study the latest estimates and to recast these estimates into forms 

so that they can be readily compared. The most 

recent and complete resource estimates have been 

made by Zellars and Williams (1978), Fountain and 

Hayes (1979), and Mayberry (1981). The first two 

are estimates of total identified resources, 

whereas the last includes, in addition to identified 

resources, what we consider undiscovered 

(hypothetical) resources. Each report presents resources in a somewhat different manner, and these 

estimates are shown in table 1.

Zellars and Williams (1978, p. 7) stated: "For 

the Florida study, *C' deposits were identified as 

'active or projected,' *R' for other identified quantifiable deposits, and 'L' for identified unquantifiable deposits." The deposits are shown in figure 

6 as areas A and B and by the letters "R" or 

"L" for deposits that are isolated.

Summary of guidelines for the determination of 

identified resources (Zellars and Williams, 1978, 

table 19, p. 112) are

1. Deposit size greater than 5 million tons where 

the overburden is less than 20 feet, or greater than 10 million tons where the overburden 

is more than 20 feet, or greater than 15 million tons where the overburden is greater 

than 30 feet.

2. Grade of phosphate product greater than 27.5 

percent P205.

3. Grade of flotation feed greater than 4.6 percent P205.

4. There must be one ton of recoverable product 

for 10 yards of ore.

5. The ore zone must be greater than 5 feet thick.

6. Any product with more than 1.5 percent MgO 

will be separately classified.
TABLE 1. Comparison of estimates of identified resources of phosphate rock in Florida

[In millions of short tons]

Zellars and Williams (1978)

Identified resources

(C and R deposits, this report)

North

Florida

Central

Florida

South

and

East

Florida

Total or

average 

Tons

xlO6

1,398

890

1,862

4,150

P 2 o 5

(percent)

30.4

31.8

30.3

3U

Fountain and Hayes (1979)

"Estimated recoverable" resources

North

Florida

Central

Florida

South

Florida

East

Florida

Total 

Tons

x!06

1,764

1,129

3,050

2,662

8,605

P 2°5

(percent)

30+

31

30+

29+

30+

Mayberry (1981)

"Florida phosphate reserves"

Operating

mines and

mines planned

in next

20 years,

including

North

Florida.

Private

owners

(throughout

Florida).

"New

Discovery."

Total minable

with

conventional

technology.

Minable with

improved

technology.

Total 

Tons

x!06

2,900

500

1,400

4,800

5,200

10,000

, ?2<\

(percent)

31.1

30.7

30.2

30.7

30.2

30.4

Fountain and Hayes (1979) did not specify the 

criteria they used in determining resources, but 

their guidelines probably are similar to those of 

Zellars and Williams (1978). Fountain and Hayes 

(tables 2-12, p. 109) gave a figure for "total phosphate resources," and "total potential phosphate 

product," which is defined as 100 percent of the 

phosphate product in the ground. This number is 

reduced by excluding resources that underlie 

urban areas, roads, lakes, swamps, and rivers. 

After this reduction, a "potentially minable phosphate product" is shown, and this number is 

further reduced by a factor of 50-65 percent the 

recovery factor. The final number is what they 

call "estimated recoverable phosphate product," 

and this number is used in the tables in this report 

and should be comparable to the figures of Zellars 

and Williams.

Mayberry (1981) gave only broad data in a different form than the others but his text indicates 

that his numbers are for the recoverable phosphate product.

The numbers of Zellars and Williams (1978) and 

Fountain and Hayes (1979) for North Florida are 

similar (table 1). The numbers of Fountain and 

Hayes are slightly higher, but they include data 

for South Georgia which Zellars and Williams 

excluded. The numbers of these two estimates are 

also close for Central Florida, although Fountain 

and Hayes gave somewhat higher numbers than 

Zellars and Williams. However, for south and east 

Florida, the numbers of Fountain and Hayes are 

more than double those of Zellars and Williams. 

The higher numbers probably reflect differences 

in what is considered minable, but also the numbers reflect the increased prospecting in these 

areas after the report by Zellars and Williams was 

compiled. The numbers given by Mayberry (1981) 

are difficult to put into comparable categories because of different terms used, so the numbers 

shown in table 1 are modified only slightly from 

his original table. However, the total phosphate 

"minable with conventional technology" of 

Mayberry is about the same (4,800 million tons)

10
85°

__ 

N } \ ~ * r~'

LOCATION OF DRILL HOLES 

No phosphate present

Phosphate present in the 

middle Miocene 

Hawthorn Formation or 

in rocks of late Miocene' 

age; Data on tonnage 

and grade of phosphate

Middle Miocene Hawthorn 

Formation and rocks of late 

Miocene age are missing

APPROXIMATE AREA OF

KNOWN MINABLE DEPOSITS 

A, North Florida 

B, Central Florida

R,L LOCATION OF R AND L DEPOSITS OF 

ZELLARS AND WILLIAMS (1978)

APPROXIMATE AREA WHERE MIDDLE MIOCENE 

HAWTHORN FORMATION AND ROCKS OF 

LATE MIOCENE AGE ARE MISSING

OUTLINES OF PHOSPHATE DISTRICTS

1. North Florida

2. Northeast Florida

3. East Florida

4. South Florida

26°-

25°-

FIGURE 6. Sketch map of Florida east of long 85°W., with outlines of phosphate districts, location of significant 

drill holes, and areas where the middle Miocene Hawthorn Formation and rocks of late Miocene age are 

missing.

11
as the total of identified resources of Zellars and 

Williams (4,150 million tons). The category of 

"minable with improved technology" of Mayberry 

certainly includes at least a part of the high numbers of Fountain and Hayes for south and east 

Florida.

Tonnages in table 1 are in short tons of P205 

and were changed to metric tons of P205 and rearranged as shown in table 2 to fit them into the 

resource diagram of the USGS and USBM as 

shown in Circular 831 (1981). The numbers of Zellars and Williams for identified resources are arranged into the three categories (economic, marginally economic, and subeconomic) on the basis 

of their dollar figures. An economic resource is 

one where total production costs are less than 25 

dollars per ton; marginally economic is 25 to 35 

dollars per ton; and subeconomic is more than 35 

dollars per ton (Zellars and Williams, 1978, table 

22). These are all demonstrated measured resources. Zellars and Williams classified deposits 

as "C," "R," and "L." The "C" and "R" deposits 

are included in measured demonstrated resources,

but the "L" category is for deposits for which not 

enough data exist to compute measured resources. 

The "L" deposits may be considered as not technically feasible to mine. It is not possible to give 

an accurate figure for resources of "L" deposits, 

but the areas of these deposits in relation to the 

area of the "C" and "R" deposits is such that they 

may contain about 200 million short tons.

The data in Fountain and Hayes (1979) are for 

total "potentially minable" phosphate rock. The 

breakdown into economic, marginally economic, 

and subeconomic (table 2) was made using the percentages of these categories as derived from the 

data of Zellars and Williams. Thus, for the north 

Florida deposits, 66 percent was in the economic 

category, 32 percent in marginally economic, and 

only 2 percent in subeconomic. Percentages for 

each category for the deposits in Central Florida 

and south and east Florida were computed in the 

same way. All data in Fountain and Hayes are 

for identified demonstrated resources.

Mayberry's numbers are divided differently. His 

figures were not broken down by area, but he does

TABLE 2. Identified phosphate rock resources of Florida, estimated by various authors

[In millions of metric tons and millions of metric tons of P2O5; Tr., trace]

Economic

Marginally 

economic

Subeconomic

North

Central

South and 

East

North

Central

South and 

East

North

Central

South and 

East

Other occurrences 

(Minable with new 

technology)

Totals 

Average 

Zellars and Williams (1978)

Tons P205 Tons P 205 

xlO6 (percent) xlO6

845 30.4 260

780 31.8 250

1,000 30.3 300

404 30.4 120

25 31.8 10

527 30.3 160

20 30.4 Tr.

32 31.8 Tr.

166 30.3 50

180 30+ 60

3,979 1,210 

30.4

Fountain and Hayes (1979)

Tons P205 Tons P2°5 

xlO6 (percent) xlO6

1,056 > 30 320

884 > 31 280

3,052 > 30 920

512 > 30 160

31 > 31 10

1,600 30 490

33 > 30 Tr.

10 > 31 Tr.

500 > 30 150

No data

7,650 2,240 

30.6

Mayberry (1981)

Tons 

xlO6

1,270

1,820

1,270

4,700

9,060

P2°5 

(percent)

31.5

30.8

30.7

30.2

30.6

Tons P205 

xlO6

400

560

390

1,420

2,770

12
give dollar figures, and these were used to divide 

his numbers into the three categories economic, 

marginally economic, and subeconomic. 

Mayberry's numbers for "minable with improved 

technology" are put into "other occurrences" in the 

diagram.

HYPOTHETICAL RESOURCES

Hypothetical resources are deposits for which 

drilling information is sparse (less than one drill 

hole per section), or where only lithologic logs of 

drill holes are available, or where no drilling or 

outcrop data exist but where geologic inference 

indicates that deposits are present. These resources were estimated by us and are based on 

the latest available data. Tonnage and grade data 

are based on analyses of very sparse core samples 

and on geologic inference. Accordingly, all numbers (thickness, amount of recoverable phosphate, 

and area) are drastically reduced so that tonnage 

data are very conservative. In fact, numbers are 

so reduced that in some areas identified resources 

exceed hypothetical resources. For purposes of 

the following discussion of hypothetical resources, 

Florida has been divided into the following areas 

(fig. 6):

1. North Florida district, which includes all of 

Hamilton, Suwannee, Columbia, Baker, 

Union, and Bradford Counties, and parts of 

Clay, Alachua, Putnam, Marion, Lake, and 

Orange Counties.

2. Northeast Florida district, which includes all 

of Nassau, Duval, and St. John's Counties, 

and parts of Clay, Putnam, and Flagler 

Counties.

3. East Florida district, which includes all or most 

of Brevard, Indian River, Osceola, Highlands, St. Lucie, and Okeechobee Counties.

4. South Florida district, which includes all or 

parts of Hardee, DeSoto, Sarasota, Charlotte, Lee, Hendry, and Glades Counties.

The area on the east coast of Florida that is 

cross-hatched in figure 6 includes all of Volusia 

County, the south one-third of Flagler County, the 

northern part of Brevard County, and nearly all 

of Seminole County. Core samples from deep drill 

holes in this area had the same lithology and 

stratigraphy. The upper part consisted of loose 

sand of probable Holocene age underlain by 

slightly clayey sand containing some shell material 

(=Citronelle Formation of Pliocene age), which

rested on the Ocala Limestone of Eocene age. The 

Miocene Hawthorn Formation and Oligocene 

Suwannee Limestone are missing. Evidently, this 

was a structural high during the deposition of the 

Hawthorn Formation. This barren area forms a 

natural division between the deposits of northeast 

Florida and those of East Florida. Although the 

total number of data points is small, it is believed 

that on the scale of the map, the lines drawn are 

relatively accurate.

NORTH FLORIDA DISTRICT

The first estimates of the resources of the North 

Florida district were made by Mansfield (1942), 

who stated that there was a total of about 300 

million tons of known, probable, and possible reserves in Hamilton, Clay, Bradford, Lake, and 

Orange Counties. Resources tabulated in table 3 

are in the east half of Hamilton County, the north 

half of Columbia County, and small bordering 

parts of Baker and Union Counties (fig. 6).

Hamilton County. Mines and measured resources are in the east half of Hamilton County. 

Scattered data from the western half of the county 

indicate that the Hawthorn Formation is present 

but thin and that the resources are probably not 

large. Zellars and Williams (1978) have an L deposit in the western half of the county; resources 

for L deposits have been estimated, so no further 

resources will be tabulated for this county.

Columbia County. Known deposits are indicated by Zellars and Williams (1978) in the northern half of Columbia County. Scattered drilling in 

the southern half of the county intersects phosphate-bearing sand and clay of the Hawthorn Formation, and possibly some phosphates reworked 

into younger beds. The area that may be underlain 

by phosphate is about 150 square miles, and the 

amount of phosphate present in these sediments 

may average about 10 percent (a conservative figure based on hand lens examination of cuttings). 

The beds of phosphatic sand and clay range from 

3 to 13 m in thickness; if the average thickness 

is 3 m, these rocks contain about 2,000 tons per 

acre of phosphate particles. If one-fourth of the 

area is underlain by phosphate of this character, 

the hypothetical resources are about 50 million 

tons.

Baker County. Many prospect holes have been 

drilled in Baker County, most of them within the 

Osceola National Forest, but Zellars and Williams 

show an R deposit in the northern part of the

13
TABLE 3. Summary of hypothetical phosphate rock resources 

of Florida, by county

[Millions of metric tons]

County Tons

North Florida district

Columbia - 

Baker 

Union 

Bradford 

Clay 

Alachua 

Marion, Putnam, Lake,

and Orange 

Total 

50

 100

50

50

50

 200

 400

 900

Northeast Florida district

Nassau 150

Duval 100

St. John's 150

Clay 100

Putnam 100

Flagler 50

Total- 650

East Florida district

Brevard - 

Osceola 

Indian River 

Okeechobee - 

Highlands -

St. Lucie

Total-

- 1,000

- 1,000

- 100

- 100

-"scores of 

millions"

-"substantial, 

deeply buried"

- 2,200+

South Florida district

Hendry, Lee, Charlotte,

Tot al 

 150

50

 1,000

 100 

 125

Grand Total, 

hypothetical resources- -5,000+

county and an L deposit in the southern part of 

the county. The Hawthorn Formation underlies 

the entire county, is thick, and contains some 

phosphate throughout. Only the top clastic part 

of the Hawthorn may be minable; the lower carbonate part will require new technology. The area 

of the county for which resources have not been 

computed is about 200 square miles; the thickness 

of the clastic phosphate beds in the Hawthorn and 

younger formations ranges from 3 to 15 m, and

the amount of phosphate based on scattered samples is about 10 percent. Hypothetical resources, 

then, may be about 100 million tons.

Union and Bradford Counties. Zellars and 

Williams show C and L deposits across the boundary of Union and Bradford Counties, and prospecting data indicate thin overburden, 30 percent 

P205 , and about 15 percent acid insoluble. No 

prospect data exist for the western half of Union 

County, but all of the county is within the North 

Florida district, and the resources in this part of 

the county may be about 50 million tons. The eastern half of Bradford County is also within the district, and two deep drill holes show that the 

Hawthorn Formation is present and contains phosphate. Sparse data indicate that as much as 8 m 

of sandy and clayey phosphate rock are present 

under thin overburden. The few samples analyzed 

contained from 25 to 30 percent P205 , and the 

amount of phosphate pellets that may be recoverable is a few thousand tons per acre. The eastern 

half of the county is estimated to contain about 

50 million tons of phosphate.

Clay County. The western third of Clay 

County is within the boundary of the district. This 

area is about 100 square miles, and two deep wells 

in this part of the county indicate that the Hawthorn Formation contains, in the top clastic part, 

about 2,000 tons per acre of recoverable phosphate. Total tonnage, then, may be about 50 million tons.

Alachua County. Almost all of the eastern half 

of the county is within the district, and within this 

area there are a few prospect holes that have intersected potentially economic phosphate. An area 

in the northeastern part of Alachua County (fig. 

6) has an average of 7,000 tons per acre of phosphate pellets that contain about 28 percent P205 . 

This area is about 50 square miles in extent, so 

there may be as much as 100 million tons of resources, a figure that is comparable to the estimate of 30-50 million tons of "reserves" made by 

Pirkle (1957). In an area of about 1 square mile 

to the south and east of Gainesville, prospect data 

indicate about 7,000 tons per acre of pellets that 

contain about 29 percent P205 . The area may contain 25 million tons.

The total area of the county that is within the 

district is about 500 square miles, of which 

perhaps 125 may be underlain by shallow 

phosphatic sediments. On the basis of tonnage of 

about one-third of that in the prospected areas,

14
there is an estimated 100 million tons of phosphate 

as an additional resource. Total resources for the 

county, then, are 225 million tons.

Putnam, Marion, Lake, and Orange Counties. The western part of Putnam Couni/y, the 

extreme eastern part of Marion County, the northern part of Lake County, and the western part 

of Orange County are within the North Florida 

district. Zellars and Williams indicated an R deposit that is close to the juncture of Lake, Orange, 

and Seminole Counties, and drill data show that 

the area centered around Blackwater Creek doeL 

contain some phosphate near the surface. Data 

show that tonnages are as much as 10,000 tons 

per acre, but the average is closer to 2,500 tons 

per acre. Samples from several deep drill holes 

in the area show that phosphatic Hawthorn Formation is present, and recent drilling in the Ocala 

National Forest in Marion, Lake, and Putnam 

Counties has shown that the clastic upper part of 

the Hawthorn Formation contains abundant phosphate. Thicknesses of this upper unit range from 

1 to about 10 m; tonnages range from 2,500 to 

10,000 tons per acre, with an average of 28 percent P205. Overburden depths are from 20 to 35 

m.

The total area of these counties that is within 

the district is about 750 square miles. Total resources, then, might be about 400 million tons, 

assuming an average value of about 2,500 tons per 

acre (a conservative figure) and that only 20 percent of the total area is underlain by phosphate.

Suwannee County. Zellars and Williams reported that an L deposit of land-pebble type is 

present near Eridu, a small town in the northwest 

corner of the county. We have no data on this 

deposit, but we suspect that it may be reworked 

hardrock type phosphate in rocks of Pleistocene 

age. There may be other deposits of this type in 

the county, but drill data indicate that only "hardrock" deposits are present, particularly in the 

Steinhatchee district. We do not have enough data 

to give any hypothetical tonnages for this county.

NORTHEAST FLORIDA DISTRICT

The Northeast Florida district includes all of 

Nassau, Duval, and St. John's Counties, the eastern two-thirds of Clay County, the east half of 

Putnam County, and the northern two-thirds of 

Flagler County (fig. 6). Except for Flagler 

County, some drill data are available for all of 

these.

Nassau County. All of Nassau County lies 

within the district, and sample data from one drill 

hole indicate a total of about 4,000 tons per acre 

of phosphate pellets with about 27 percent P205. 

A deep well in the eastern part of the county intersects the phosphate-bearing Hawthorn Formation. The thickness of clastic Hawthorn is about 

10 m with 45 m of overburden (essentially barren 

of phosphate). The total area of the county is 

about 500 square miles, and except for the southeastern part of the county, all seems to be underlain by phosphatic Hawthorn Formation. Assuming an average of 2,000 tons per acre for about 

one-fourth of the area of the county, the amount 

of phosphate present would be 150 million tons.

Duval County. All of Duval County is within 

the Northeast Florida district. No sample data are 

available*, but six deep wells show that the entire 

county is underlain by the Hawthorn Formation. 

There are about 700 square miles in the county, 

but a large part of the county is within the urban 

area of Jacksonville; thus, it is likely that only 

about half of the total area may be available for 

mining. There are sample data for phosphate for 

a few holes in all of the counties surrounding 

Duval, and, projecting these data into the county, 

it is likely that the average phosphate amounts 

are 2,500 tons per acre and about 28 percent P205. 

Only the western third of the county (200 square 

miles) is available for mining, with total tonnages 

on the order of about 100 million tons.

St. John's County. All of St. John's County, 

an area of about 500 square miles is within the 

Northeast Florida district. Samples from three 

core holes and several deep wells show that all 

of the county is underlain by phosphatic Hawthorn 

Formation. The clastic phosphate deposits range 

in thickness from 1.5 to about 30 m and contain 

from 3,000 to 10,000 tons per acre, with 25-30 percent P205. About half the county either is along 

the Atlantic Coast or contains urban areas which 

must be removed from consideration as phosphate 

resource areas; the total tonnage in the remaining 

half of the county may be 150 million tons.

Clay County. The eastern two-thirds of Clay 

County is within the district. One core hole intersects phosphatic beds in the middle Miocene 

Hawthorn Formation, and an upper bed, which 

may be late Miocene in age, contains phosphate 

which is probably reworked from the Hawthorn. 

The upper bed is about 5 m thick and under 8 

m of overburden, and the underlying clastic beds

15
of the Hawthorn Formation are 16 m thick with 

variable amounts of phosphate. The total amount 

of recoverable phosphate pellets is about 6,000 

tons per acre, with 25-30 percent P205 . The 

amount of phosphate present in the county, using 

similar criteria as in the other counties, is about 

100 million tons.

Putnam County. The east half of Putnam 

County is within the Northeast Florida district. 

It is likely that this half of the county contains 

about as much phosphate as the west half (in the 

North Florida district), or about 100 million tons.

Flagler County. The northern two-thirds of 

Flagler County is within the district. The southern 

part of the county is within the area where the 

Hawthorn Formation is missing. There are no 

prospect holes within the county nor have we been 

able to locate any records of deep drilling. Data 

from adjacent counties in which the Hawthorn is 

present indicate that at least 2,000 tons per acre 

of phosphate pellets may occur in the formation, 

and about 50 million tons of phosphate pellets may 

occur in the northern part of the county.

EAST FLORIDA DISTRICT

The East Florida district includes the southern 

two-thirds of Brevard County, and all of Indian 

River, St. Lucie, Osceola, Highlands, and 

Okeechobee Counties.

Brevard County. The northern one-third of 

Brevard County is in the area where the Hawthorn Formation is absent; drill data show that 

this area has loose sand with shells overlying carbonate rock of the Eocene Ocala Limestone and 

contains no phosphate. Some drilling has been 

done in the county, particularly on the Deseret 

Ranch property. Results of this drilling are confidential, but Zellars and Williams (1978) considered 

this to be an R deposit, and the tonnage is combined with other tonnages for east and south 

Florida. Measured resources for this part of the 

county, then, are already listed. However, it 

seems likely that total resources in the county are 

extremely large. Mayberry (1981) has estimated 

the resources in Brevard County to be 3 billion 

short tons. Conservatively, then, there probably 

are at least 1 billion metric tons of hypothetical 

resources in this area.

Osceola County. All of Osceola County is within the East Florida district. A core hole in eastern

Osceola county (fig. 6) near the boundary with 

Brevard County had 6 m of phosphate rock under 

45 m of overburden, and about 8,000 tons per acre 

of phosphate pellets with an average content of 

30 percent P205. A drill hole in the northwestern 

part of the county penetrated the phosphate-bearing Hawthorn, and it is likely that the entire 

county is underlain by the Hawthorn Formation. 

Although it is difficult to calculate resources from 

such scattered data, it is possible that this county 

may contain about the same amount of phosphate 

as there is in Brevard County to the east, and, 

therefore, the total hypothetical resource is of the 

order of 1 billion tons.

Indian River County. One deep well has been 

logged in the eastern part of Indian River County 

(fig. 6). This well had about 30 m of phosphatebearing clastic rock of the Hawthorn Formation 

under about 40 m of overburden. The northwestern part of the county is adjacent to the Deseret 

Ranch area and probably contains phosphate. 

Total hypothetical resources in the county are conservatively estimated from these data to be about 

100 million tons.

Okeechobee County. Sparse drill data 

(lithologic logs only) indicate the presence of phosphate-bearing Hawthorn Formation throughout 

Okeechobee County. Again, with the very sparse 

data, it is very difficult to compute resources, but 

at least 100 million tons of hypothetical resources 

may exist in this county.

Highlands County. About half of Highlands 

County is within the East Florida district. Three 

deep drill-hole logs are known from the county; 

all describe phosphate-bearing sediments of the 

Hawthorn Formation. There are no chemical data, 

and the phosphate-bearing rocks are covered by 

thick overburden. Hypothetical resources cannot 

be adequately estimated, although it is likely that 

a few score million tons are present.

St. Lucie County. No drill-hole logs are known 

from St. Lucie County, but on the basis of data 

to the north and to the south, it is likely that the 

entire county is underlain by the Hawthorn Formation. The phosphate-bearing parts of the 

Hawthorn Formation are deeply buried, from 

perhaps 30 m in the western part of the county 

to as much as 160 m in the southeast. Resources 

cannot be adequately estimated, but substantial, 

deeply buried phosphate resources are present in 

this county.

16
SOUTH FLORIDA DISTRICT

The South Florida district is the southern 

extension of the classic land-pebble district. It includes parts of Hardee and Sarasota Counties and 

all of DeSoto, Charlotte, Hendry, Lee, and Glades 

Counties. Other counties in the southern part of 

Florida have not been included in this review, because, although phosphate-bearing rock of the 

Hawthorn Formation is present, the rock is deeply 

buried; one drill-hole log in Palm Beach County 

(fig. 6) has 300 m of overburden, and a hole in 

Bade County has 180 m of phosphate-bearing 

Hawthorn rocks under 100 m of overburden. The 

resources in these counties may be enormous, but 

they are so deep as to preclude mining, at least 

for the foreseeable future. They are, therefore, 

not considered any further in this summary.

Hardee and Manatee Counties. Abundant 

prospecting information exists, and Zellars and 

Williams (1978) indicated large areas of C deposits 

in Hardee and Manatee Counties. Areas not covered by prospecting or by C deposits do contain 

abundant phosphate. Resources in these counties, 

using 3,000 tons per acre and an area of about 

75 square miles, total about 150 million tons for 

Hardee County; resources for Manatee County 

may be about 50 million tons.

DeSoto County. All of DeSoto County is underlain by the Hawthorn Formation. Drilling data 

indicate that the formation may be divided into 

an upper clastic unit that contains abundant phosphate and into a lower carbonate unit, also with 

phosphate but unminable under present technology. The overburden thickness ranges from 18 to 

45 m; the upper clastic, phosphatic part of the 

Hawthorn is as much as 30 m thick. Zellars and 

Williams showed C deposits present in the northwestern part of the county, but data for the rest 

of the county have not been computed. A drill hole 

for which we have analytical data shows 10 m of 

clastic Hawthorn Formation that contains 13,000 

tons per acre of phosphate particles with an average of about 30 percent P205. The county is about 

450 square miles in area, and about 300 square 

miles are underlain by hypothetical resources. If 

the average tonnage is about 10,000 tons per acre, 

and if half the area is underlain by this type of 

material, total resources are about 1 billion tons 

a conservative figure.

Hendry, Lee, Charlotte, and Glades Counties. 

Phosphatic sedimentary rocks are known to be 

present close to the surface over a large area centered around the Caloosahatchee River in Hendry, 

Lee, Charlotte, and Glades Counties. We have no 

data on prospecting in this area; however, phosphate is present in the Hawthorn Formation, in 

unnamed sands of late Miocene age, in the Pliocene Tamiami Formation, in the Caloosahatchee 

Formation (Pliocene and Pleistocene), and in rocks 

of Pleistocene and Holocene ages.

The total area that may be underlain by shallow 

phosphate-bearing sediments is about 1,000 square 

miles, and if one-tenth of this area is underlain 

by 2,000 tons per acre of phosphate, total resources are 125 million tons. Much of the rock will 

probably contain calcite shells or cement.

Sarasota County. Only the eastern one-third 

of Sarasota County is within the district. This area 

is adjacent to areas in Hardee and DeSoto Counties that contain C deposits (Zellars and Williams, 

1978), and it is likely that the area is underlain 

by phosphate-bearing rock of the Hawthorn Formation. If the rock has 5,000 tons of phosphate 

per acre and if about 50 square miles of the eastern part of the county is underlain by this amount 

of phosphate, then total resources may be 100 million tons.

SUMMARY OF PHOSPHATE RESOURCES OF FLORIDA

The numbers used for identified resources for 

this report (table 4) are based on interpretation 

of the data of Zellars and Williams (1978), Fountain and Hayes (1979), and Mayberry (1981), plus 

our personal knowledge of the phosphate districts.

The total identified economic resources of North 

Florida are about 400 million metric tons, about 

equal to the figure of Zellars and Williams. The 

slightly higher figure of Fountain and Hayes includes deposits in south Georgia, which are not 

being considered here. Mayberry's numbers are 

comparable to the other two estimates.

For Central Florida, identified economic resources are estimated to be about 800 million metric tons, a number that is in between those given 

by Zellars and Williams and Fountain and Hayes.

For south and east Florida, we have used 2,000 

million metric tons, a figure between those of Zellers and Williams and Fountain and Hayes. 

Mayberry's total tonnage numbers are even larger 

than the numbers of Fountain and Hayes.

17
TABLE 4. Summary of phosphate rock resources of Florida

[In millions of metric tons]

Economic

Marginally 

economic

Subeconomic

Total 

Average 

IDENTIFIED RESOURCES

North

Central

South and 

East

North

Central

South and 

East

North

Central

South and 

East

Tons 

xlO6

900

800

2,000

450

20

1,000

20

10

400

5,600

P2°5 

(percent)

31.1

32.5

30.0

31.1

32.5

30.0

31.1

32.5

30.0

30.3+

Tons ?2 05 

xlO6

280

260

600

140

Tr.

300

Tr.

Tr.

120

1,700

HYPOTHETICAL RESOURCES

North 

Florida

Northeast 

Florida

South 

Florida

East 

Florida

Tons 

xlO6

900

650

1,425

2,200

5,175

P2°5 

(percent)

28+

30.1

28.0

29.5

29.0+

Tons P 20 5 

xlO6

250

200

400

650

1,500

Grand total of 

identified and hypothetical 

resources 10,775 million metric tons containing 29 percent P 2 05 = 3,200 million metric tons P2 0r

The reports of Zellars and Williams and Fountain and Hayes had the benefit of up-to-date information on what the phosphate companies consider 

reserves. Neither report considers any resources 

that were not, in effect, measured. Hypothetical 

resources are not considered, although the L deposit of Zellars and Williams might be considered 

hypothetical. Mayberry did list large tonnages 

that he said will be minable only with improved 

technology, and some of this material should probably be put into hypothetical resources.

Our figures for marginally economic and subeconomic categories were computed in the same 

way as being somewhere between the data of the 

other authors.

GEORGIA

Phosphate resources in southern Georgia (principally in Echols and Lowndes Counties) are in 

the Hawthorn Formation, and these deposits are

an extension of the North Florida district. A great 

deal of shallow drilling has been done in southern 

Georgia by many companies, but no leases have 

been executed. The amount of phosphate in tons 

per acre per foot of section is not high, and grades 

(in P205 content) are low. Resources are not 

known but are large, probably measured in hundreds of millions of tons, but reserves under present conditions are nil.

The phosphate deposit in the Savannah River 

area of north Georgia and southern South Carolina 

is in the Hawthorn Formation. Locally, the phosphate has been reworked, enriched, and concentrated in beds of late Miocene age (Furlow, 1969). 

The deposit is known to extend out to sea for at 

least 12 miles. Furlow (1969) indicated that the 

resource, on land, in Georgia is about 1 billion 

short tons of recoverable product that contains 

about 30 percent P205 (=about 300 million tons 

of P205). Total resources must be much greater.

18
Fountain and Hayes (1979) showed that the "estimated recoverable phosphate product" is 1.8 billion short tons (=about 500 million tons P205). 

Their data are for northern Georgia and southern 

South Carolina. This deposit is unminable because 

of environmental restrictions.

SOUTH CAROLINA

Phosphorite, probably of the Hawthorn Formation, is present in Jasper, Colleton, Hampton, and 

Beaufort Counties in southern South Carolina. 

This is an extension of the deposit in the Savannah 

River area in north Georgia. The resources in 

South Carolina are thought to be about 100 million 

metric tons of recoverable phosphate of about 31 

percent P205 or about 30 million tons of P205. 

Total resources are much greater. These data are 

based on unpublished company drilling reports.

The first sedimentary phosphate mined in the 

United States was from the Charleston phosphate 

district of South Carolina. Deposits are thin, are 

erratic in distribution, and are of Pleistocene and 

Holocene ages (Malde, 1959); but the deposits are 

reworked from phosphate deposited in the Hawthorn Formation or the Cooper Marl. No reserves, 

as such, are left in this district, and total resources 

of the Pleistocene reworked material are small, 

but large, very low grade resources may remain 

in the Cooper Marl of Eocene and Oligocene age.

NORTH CAROLINA

The phosphate deposit of the Miocene Pungo 

River Formation (Kimrey, 1965) is in a basin on 

the north flank of a small high associated with the 

Cape Fear arch. In the western part of the basin, 

the Pungo River Formation consists of a single 

bed of phosphorite that ranges in thickness from 

5 to about 25 m, but in the east, the Pungo River 

Formation thickens to about 75 m due to intercalation of beds of dolomite, sand, and clay. All beds 

contain some phosphate pellets; the basin is about 

600 square miles in extent; and the total amount 

of possibly recoverable phosphate is about 10 billion tons. Fountain and Hayes (1979) pointed out 

that the "estimated recoverable phosphate products" total 9.4 billion short tons, with 29-32 percent P205 , or a total of 2.8 billion tons of P205. We consider that most of this tonnage is subeconomic because of problems related to deep mining.

OFFSHORE

Phosphate pellets are known to occur offshore 

in the Atlantic Ocean from southern Virginia on 

the north to the southern tip of Florida. F. T. 

Manheim (written commun., 1978) stated that the 

phosphate deposits of the Blake Platform (fig. 6) 

are "* * * of larger magnitude than the Southern 

California offshore deposits." In a table in his report, he showed the tonnage of phosphate in the 

offshore California deposits as 2 billion tons.

Zellars and Williams (1979) showed that an area 

offshore from the Savannah River (12 miles 

offshore from Tybee Island; fig. 6) contains a deposit of 150 million short tons of recoverable phosphate product. This tonnage is conservative, but 

it represents that part of the deposit that might 

be minable today. Total resources are much 

larger.

A recent announcement by the National Science 

Foundation (newspaper reports, 16 February 

1981) stated that research by Dr. S. R. Riggs of 

East Carolina University and Dr. A. C. Hine of 

the University of South Florida has discovered 

large phosphate deposits 60 miles off the coast of 

North Carolina (fig. 6). The deposit covers hundreds of square miles, and the total tonnage must 

be very large.

On the basis of these data, then, offshore resources of phosphate are very large, and although 

the resource must be considered hypothetical 

rather than as identified, it is possible that large 

tonnages may be minable in the foreseeable future.

ATLANTIC COASTAL PLAIN

The economic or potentially economic phosphate 

deposits of the Atlantic Coastal Plain are in rocks 

of Miocene age or are in younger rocks in which 

the phosphate was derived from Miocene rocks.

Phosphate deposits are known to occur from the 

southern tip of Florida to northern North Carolina 

and offshore in the Atlantic Ocean from North 

Carolina to Florida. Deposits are poorly consolidated sand, clay, and carbonate rock (limestone 

and dolomite) and combinations of these 

lithologies all contain sparse to abundant phosphate nodules and pellets. The phosphate is concentrated at certain structural positions in basins 

or on the flanks of positive areas (anticlinal highs) 

that were rising at the time of deposition of the 

phosphate (Cathcart, 1968). The phosphate in the

19
rocks must be separated from the gangue minerals 

(quartz, clay, and carbonate) in order to produce 

an economic product.

The total amount of phosphate present in the 

Atlantic Coastal Plain is very large. Identified resources plus hypothetical resources total about 22 

billion metric tons (table 5).

NORTHWESTERN PHOSPHATE PROVINCE

The rich phosphate of the Northwestern Phosphate Province was deposited about 250 million 

years ago on the continental shelf of the North 

American continent at the edge of the ancient 

Pacific Ocean. The original accumulation of phosphatic sediment in the area now part of Idaho, 

Utah, Montana, and Wyoming was one of the 

largest known in all of geologic history. It contained at least l.TxlO12 metric tons of P205 , which 

is equivalent to 18 thousand billion metric tons of 

rock containing 9.6 percent P205 , the average 

phosphatic rock of the Northwestern Province. 

However, subsequent geologic events have removed much of the deposit from man's reach.

Younger sediments buried the phosphatic sediments as deep as 6 miles below the surface. Later, 

tectonic forces buckled and fractured the sedimentary rocks, including the phosphate, causing part 

to be uplifted and eroded away and part to be 

more deeply buried. Still later, lava flows in the 

central Idaho rift valleys further buried part of 

the phosphate rock.

The phosphate rock at depth is fresh and unweathered and consists of hard, black rock that 

is rich in organic matter and contains significant 

amounts of calcium and magnesium carbonate minerals. This phosphate rock makes up the major 

portion of the resource, but at present due to underground mining costs and the poorer grade and 

quality of the rock, it is not economic to mine. 

Thus, none of the deep underground fresh phosphate rock is included in the phosphate reserve 

of the Northwestern Province, with the exception 

of small underground mine reserves in Montana. 

Where the phosphate rock has been weathered, 

its grade has been increased due to the removal 

of calcium and magnesium carbonate minerals, 

some iron oxide, and organic matter all of which

TABLE 5. Summary of phosphate rock resources, Eastern United States

[In millions of metric tons; ( ) leaders, no data]

Florida

Georgia

South 

Carolina

North 

Carolina

Offshore 

Savannah R.

Blake 

Plateau

Onslow Bay 

(offshore, North 

Carolina)

Totals 

Averages 

Identified Resources

Tons

xlO6

5,600

1,000

 

1,000+

150

 

7,850

P2°5

(percent)

30.3

30+

 

30

30

 

30+

Tons P 2°5

xlO6

1,700

300

 

300

45

 

2,355

Hypothetical Resources

Tons

xlO6

5,175

1,000+

100+

8,000+

No data

P2°5

(percent)

29.0

30

30

30

must be very

Tons P205

xlO 6

1,500

300

30

2,400

large

Sparse data, must be very large

No data

14,275+

, must be very

29.7+

large

4,230+

Hypothetical resources were computed very conservatively so that the totals shown may be lower 

than the identified resources, which are based on company "reserves" data.

20
make the fresh rock uneconomic. The weathered 

rock, being close to or at the surface, can be easily 

mined and has the chemical and physical characteristics that make it a phosphate ore. This weathered phosphate makes up the reserves of the 

Northwestern Phosphate Field. These reserves 

are discussed in detail, by State, in subsequent 

sections.

PAST RESOURCE STUDIES

The phosphate deposits of the Northwestern 

Province for the most part occur on federally 

owned land, in contrast to those of the Southeastern Phosphate Province, which occur predominantly on privately owned land. Phosphate was discovered in 1889 in Cache County, Utah, and when 

it was realized that a significant and extensive deposit of bedded phosphate rock occurred on federally owned land, action was taken to withdraw the 

land from mineral entry. On December 9, 1908, 

the Secretary of the Interior established the western phosphate reserve by withdrawing from entry 

4,541,300 acres of land in Idaho, Utah, and Wyoming. Somewhat later, he withdrew additional land 

in Montana.

DATA COLLECTION

In response to these actions, a study by the 

U.S. Geological Survey was initiated to map the 

geology of the area and assess the phosphate deposits in order to classify the appropriate areas 

as phosphate land for public entry subject to the 

provisions of the Federal leasing law. This 

geologic study resulted in the publication of the 

monograph Geography, Geology, and Mineral Resources of part of Southeastern Idaho (Mansfield, 

1927). During and after World War II, the national need for vanadium and uranium stimulated 

an additional assessment of the phosphate deposits 

to determine their content of those trace elements. 

This resulted in the publication of a series of U.S. 

Geological Survey Circulars giving measured sections of the phosphatic beds in all of the four major 

States, as well as Nevada (table 6), publication 

of detailed geologic maps of much of the main 

phosphate area, and geologic analyses of the

TABLE 6. U.S. Geological Survey Circulars reporting phosphate stratigraphic data of the 

Northwestern Phosphate Province

State

Idaho

Montana

Years of data

collection

1947-48, Part I

1947-48, Part 2

1947-48, Part 3

1949, Part 1

1949, Part 2

1950-51

1947-48

1948

1949-50, Part 1

1949-50, Part 2

1951

Authors

McKelvey and others

McKelvey and others

O'Malley and others

Sheldon and others

Davidson and others

Smart and others

Swans on and others

Klepper and others

Cressman and others

Swanson and others

Peters on and others

Year of

publication

1953b

1953d

1953

1953

1953

1954

1953

1953

1953

1953

1954

uses

Circular

number

208

301

262

304

305

327

209

260

302

303

326

Wyoming 1947-48 

1949-50

1951

1952

McKelvey and others 1953c

Sheldon and others 1953

Cheney and others 1954

Sheldon and others 1954

210

307

324

325

Utah 1947-48 

1949-51

Smith and others 

Cheney and others

1952

1953

211

306

Montana, 

Idaho, 

and Utah 1953 Swanson and others 1956 375

21
stratigraphy of the deposits (Cheney, 1957; 

McKelvey and others, 1959; Sheldon, 1963; 

Cressman and Swanson, 1964). Subsequent additional detailed geologic mapping, which is still continuing, was initiated for the purpose of completing the classification of the phosphate lands according to the Federal leasing law and has resulted in collection of -dditional basic geologic data 

(Gere and others, 1966).

RESOURCE ASSESSMENTS

The data described in the preceding paragraph 

have been used for assessing the phosphate resources of the province. The U.S. Geological Survey has prepared assessments of Montana (Swanson, 1970, 1973), Wyoming (Sheldon, 1963), and 

Idaho (Gulbrandsen and Krier, 1980). The U.S. 

Bureau of Mines evaluated the western phosphate 

industry and its resources in Idaho, Montana, 

Utah, and Wyoming in a series of Reports of Investigations (Service and Popoff, 1964; Popoff and 

Service, 1965; Service, 1966; Coffhian and Service, 

1967; Service and Peterson, 1967). Assessments 

of surface phosphate resources in southeastern 

Idaho were made by Powell (1974) for the Idaho 

Bureau of Mines, and by the Garrand Corporation 

(1974), in part for the U.S. Forest Service. Under 

contract for the U.S. Bureau of Land Management, Dames and Moore, Inc. (1978), assessed the 

phosphate resources of Utah, including an analysis 

of the technology and economics of phosphate mining. Finally, Bauer and Dunning (1979), under 

contract to the U.S. Department of Energy, prepared a report on the uraniferous phosphate resources of the western phosphate field as part of 

the larger report on United States and world 

uraniferous phosphate deposits (De Voto and Stevens, 1979). This study also included an extensive 

analysis of the technologic and economic aspects 

of phosphate supply. The vast majority of the 

geologic data used in these assessments has been 

from the U.S. Geological Survey studies, although 

some additional data were collected by the various 

workers or were provided by industry.

The resource assessments noted have been 

based on the current technology of mining and 

processing phosphate rock. At present, mining in 

southeastern Idaho and Utah is by stripping of 

weathered surface deposits. Only in Montana is 

phosphate being mined underground. Phosphate 

mining and processing in both Utah and Montana

are parts of integrated operations in conjunction 

with sulfuric acid production from copper ore processing. They are not economically based on phosphate production alone and, therefore, might be 

subeconomic if not for the integrated system.

The mining parameters generally accepted by 

industry relate to mining thickness, stripping 

ratios, depth or bank slope, phosphate grade, combined iron and alumina content, magnesium oxide 

content, carbonate content, and potential byproducts. These are discussed in the following sections.

ORE THICKNESS

The generally accepted minimum strip mining 

thickness for phosphate rock is 5 feet. However, 

in southeastern Idaho, this is not a problem as 

the mined units are thicker.

Stripping ratios. Stripping ratios are measured in units of cubic yards of waste to short 

tons of ore and for present operations generally 

are less than 3.5 to 1. Garrand Corp. (1974) used 

this stripping ratio as the maximum for economic 

operations and used a ratio of 9 to 1 as a maximum 

for calculating the "ultimate (amount of phosphate 

rock) which may be mined from the area in the 

distant future." L. J. Garrand (oral commun., 

1981) believes that these ratios still apply today, 

although Breza and others (1979, p. 125) stated 

that the trend is one of increasing strip ratio.

Depth of Mining. A maximum depth of mining 

is not usually explicitly used; however, depth was 

defined by Powell (1974) as the downdip mining 

width, and he used a maximum of 250 feet for 

economic mining operations. Garrand Corp. (1974) 

used a 40° backslope for stripping resource calculations. In southeastern Idaho, where strip mining 

of the uniform phosphatic shale beds is carried out 

in steep terrain, the angle of backslope of the pit 

and the downdip width of the pit, combined with 

the stripping ratio, serve to limit the mining 

rather than the depth of the pit.

PHOSPHATE GRADE

The grade (P205 content) of the phosphate ore 

is critical to economic mining operations. The fertilizer industry originally required the phosphate 

rock feed to contain greater than 32 percent P205 

for their phosphoric acid process so that rock 

greater than 32 percent is known as acid grade 

phosphate. With the introduction of the electric 

furnace process for the production of elemental

22
phosphorus, which requires silica in the furnace 

mix to combine with the calcium of the phosphate 

mineral, apatite, phosphate ore with a silicate 

gangue of a grade between 24 and 32 percent P205 

could be used, and this is known as furnace grade 

phosphate rock. Rock of lower grade, between 18 

and 24 percent P205 , is not suitable for either the 

acid or the electric ftirnace process without beneficiation, and is known as beneficiation grade phosphate rock. Finally, rock between 10 and 18 percent P205 , generally not used in today's operations 

but commonly stockpiled for future use, is termed 

low-grade phosphate rock, and rock below 10 percent P205 is regarded as waste. These grade classes acid, furnace, beneficiation, and low are still 

used even though modern beneficiation technology, which treats all grades together to give a 

high-grade product, is beginning to make the classification outmoded. This trend seems likely to 

continue, and particularly when the presently subeconomic resources will have to be mined underground, different mining and processing technology will call for a reassessment of the grade 

boundaries. For this report, however, the old 

grade classification is used primarily because the 

published reports on northwestern phosphate have 

used this classification.

ORE QUALITY

The quality of northwestern phosphate rock ore 

depends on other compositional factors, including 

the contents of calcium and magnesium carbonate, 

combined ferric and aluminum oxide, magnesium 

oxide, and organic matter. Calcium and magnesium carbonates occur in the phosphate ore as calcite or dolomite, both of which are soluble in sulfuric acid and cause excess acid use in the process 

of making phosphoric acid. In the furnace process, 

calcite and dolomite are broken down at high temperature and combine with silica to form calcium 

and magnesium silicates, a reaction which wastes 

energy. Calcite or dolomite in phosphate ore increases the ratio between CaO and P205 , and usually if this ratio exceeds 1.55, the rock or beneficiation product is not economic. The amount of 

magnesium in the feed for the acid process is deleterious because it causes hygroscopic products 

to form which cake and clog filters and pipes. Magnesium oxide in the ore or beneficiation product 

in excess of 1.5 percent makes the material uneconomic. Ferric and aluminum oxide in the feed

for the acid process also cause the formation of 

hygroscopic products which hurt the processes so 

that if the combined Fe203 and A1203 content of 

the ore or beneficiation product is greater than 

5 percent, the material is uneconomic. The weathered phosphate rock that is presently being mined 

in the Northwestern Field generally contains little 

enough calcite, dolomite, and iron and aluminum 

minerals that these contaminants are not a problem; however, fresh underground rock, which will 

be mined in the future, contains significantly 

larger amounts of calcite and dolomite. Finally, 

the content of organic matter in the ore makes 

processing difficult due to the clogging of filters 

and pipes if it is not removed by calcining; or if 

it is removed by calcining and is too abundant, 

it serves as an additional fuel and causes excessive 

heating. No general economic limits have been set 

on the content of organic matter (or as it is reported by the chemist, loss on ignition), and in 

general the ore that is presently being mined in 

the Northwestern Field is weathered to the point 

that the organic matter is too low to cause trouble; 

however, fresh rock has a much higher content, 

and this problem will have to be dealt with in the 

future when mining goes underground.

POTENTIAL BYPRODUCTS

The technology of processing phosphate rock 

and manufacturing phosphate fertilizer is changing 

so that byproducts can be recovered, thereby increasing the value of the ore. Uranium is now 

being recovered in some plants, and if all the uranium present in phosphate rock that is presently 

being used in the acid process were recovered, 

it would amount to about 15 percent of the national uranium production for 1978 (Altschuler, 

1980a). Fluorine is being recovered as a byproduct 

of the manufacture of phosphoric acid. Other elements enriched in phosphorite and worth examining for byproduct recovery are vanadium, rare 

earths, silver, cadmium, chromium, molybdenum, 

arsenic, selenium, strontium, tellurium, and zinc 

(Altschuler, 1980b; Gulbrandsen, 1977). The organic content of the northwestern phosphate at 

the present time is considered a detriment except 

at those plants where it is counted on as a fuel 

for calcining to remove the organic matter and fluorine. It seems possible that future processing of 

fresh ore from underground mining will utilize the 

higher organic matter content for calcining the ore

23
to facilitate the removal of calcium and magnesium 

carbonate by solution or slaking, or in any event 

the organic material will be utilized for its energy 

value. An unusual feldspar buddingtonite which 

contains ammonium was found to occur in large 

quantities in the Phosphoria Formation (Gulbrandsen, 1974). At the present time, there is no 

use for this mineral, but the beds constitute a 

large volume of rock that is being mined as waste 

along with the phosphate rock, and it seems possible that the rock may have some potential for 

making an ammonium fertilizer.

IDAHO

The phosphate resources of Idaho have been assessed systematically by four different studies, 

which include those of (1) Service (1966), and 

Coffhian and Service (1967), (2) Garrand Corp. 

(1974), (3) Bauer and Dunning (1979), and (4) Gulbrandsen and Krier (1980). The common factor of 

all four of these studies, as was pointed out earlier, was that the preponderance of data on which 

all four were based were the earlier U.S Geological Survey stratigraphic and geologic map reports 

(fig. 7). However, areas of coverage (fig. 8), 

methodology of resource assessments, and resource parameters varied substantially between 

estimates so that no two can be compared directly. 

Each is discussed in this report.

SERVICE AND COFFMAN ESTIMATES

The major portion of phosphate lands in southeastern Idaho was assessed by Service (1966), 

which included all of the phosphate districts except for that portion of the Snake River district, 

which was included by Coffman and Service in a 

later volume (1967) of the series that covered 

Wyoming and Utah. Thus, between the two volumes, all of the phosphate resources of Idaho of 

any importance were covered (fig. 8). A few deposits of Permian phosphate are known in central 

Idaho, but stratigraphic and mapping studies have 

shown them to be insignificant. The active mining 

areas were not included in the Service and 

Coffman studies.

The limits to grade classes used by Service and 

Coffman conformed to earlier limits, and they 

were as follows:

Acid-grade greater than 31 percent P205 

Furnace-grade 24-31 percent P205 

Beneficiation-grade 18-24 percent P205 

Low-grade shale 10-18 percent P205

Service and Coffman did not use a minimum 

thickness for minable phosphate rock beds in 

southeastern Idaho, apparently because the 

economic zones of the phosphate beds there occur 

in excess of minimum mining thickness so that the 

problem never arises. However, in the fringe 

areas where economically minable zones thin 

greatly, a minimum thickness of 3 feet was used, 

in conformity with earlier studies.

The quality limits of the phosphate rock in Idaho 

also were not explicitly defined by Service and 

Coffman, probably because the rock in the minable 

zones generally contains smaller amounts than required of calcium or magnesium carbonate and 

iron and aluminum oxides.

Service and Coffman considered only the phosphate resource available by surface mining 

methods and the resource above and within 100 

feet below entry level (fig. 9). Service did not 

explicitly state whether or not his surface resources are included in resources above and within 

100 feet below entry level, and it can only be assumed that they are not from his discussion of 

them (Service, 1966, p. 10). The criteria for determining surface resources were not specified by 

Service other than to say that "reserves are based 

on economic mining depth, amount of overburden 

and favorable waste to ore ratio." This lack of definition makes it impossible to accurately compare 

his estimates of surface minable resources with 

other estimates of surface resources.

Finally, the estimates of Service and Coffman 

for Idaho do not take into account phosphate rock 

spoiled by tectonic structural crushing or thinning, 

or breaking of beds by faulting into such small 

blocks that they would be unsuitable for mining. 

Their estimates are not based on detailed correlations of phosphate beds and thus lack geologic control. No allowance was made for the effect of lowering of grade in unweathered, underground resources below that indicated from the sample data, 

which were almost exclusively collected from 

weathered surface rock. No documentation of calculations was published. For these reasons, the 

Service and Coffman estimates are difficult to 

evaluate and to compare with other estimates.

The Idaho resources of Service and Coffman 

have only been determined in broad categories of 

the resource system used in this report. The resource can be regarded as identified in Idaho, due 

to the well-developed lateral continuity of the 

phosphate beds within phosphatic members. Only

24
113°00 111-00'

American Fa/is / 

Reservoir i

EXPLANATION

OUTCROP OF PHOSPHORIA FORMATION

AREAS OF LARGE-SCALE GEOLOGIC 

MAPPING IN IDAHO

FIGURE 7. Outcrops of the Permian Phosphoria Formation, sample localities, and areas of large scale geologic mapping in Idaho.

the surface minable resources greater than 18 per- ered an estimate of the reserve base and inferred

cent P205 are considered to be economic. Because reserve base. The average grade of all rock higher

the Service and Coffman estimate is not of recov- than 10 percent P205 is 22.4 percent P205, assumerable phosphate, this material must be consid- ing that the average grades of each class are at

25
113°00' 30'

Sheldon, 1963

Service, 1966

Coffman and Service, 1967

Garrand, 1974

Gulbrandsen and Krier, 1980

FIGURE 8. Areas of phosphate resource assessment in Idaho.

26
Surface strippable resources

Meade Peak Member of 

Phosphoria Formation

~O (O

s 2

I '5 

FIGURE 9. Depth categories of Northwestern Phosphate Province.
the midpoint of the class; therefore, the phosphate 

between 10 and 18 percent P205 is included as subeconomic resource, because in the future, it could 

be blended with higher grade rock and still keep 

the average grade greater than 18 percent. The 

phosphate rock resource in the subeconomic identified resource class also includes phosphate rock 

higher than 24 percent P205 that occurs underground in the region from entry level to 100 feet 

below that level.

GARRAND ESTIAAATES

L. J. Garrand (Garrand Corp., 1974) assessed 

only the strippable resources (fig. 9) in the Soda 

Springs area of southeastern Idaho. This area (fig. 

8) essentially corresponds with the Peale Mountains. It should be noted that the area of Garrand's 

assessment does not include the Fort Hall, Chesterfield, Blackfoot River Reservoir, Mount Taylor, 

Swan Valley, and Snake River Range districts 

that were included, except for active mines, in the 

Service and Coffman assessments. However, the

Garrand assessment does include the most important part of the southeastern Idaho phosphate region.

Garrand did not use grade cutoffs to define the 

surface minable resources of the Soda Springs 

area. He selected 10 minable phosphate zones, calculated their average phosphate content, and 

broke these zones into high-, medium-, and lowgrade deposits and waste. He then calculated the 

weighted phosphate grade for each category. His 

data were combined into the two categories shown 

in table 7. His high-, medium-, and low-grade ore 

corresponds more or less with the acid, furnace, 

and beneficiation grades of earlier workers.

Garrand calculated resources using the actual 

thicknesses of the defined mining units. Because 

all units were over the commonly used minimum 

minable thickness of 3 feet, no minimum thickness 

was explicitly defined but was implicit in the assessment. Garrand assumed that all of these units 

could be selectively mined. The actual thicknesses 

used in the resource assessments were mining (or

TABLE 7. Comparison of estimates of phosphate rock resources in Idaho

[Resources in millions of metric tons; P^B in weight percent]

L

strippable resources

Underground 

resources

Material regarded not 

resource as 

Total

Reserve 

and 

inferred 

reserve 

base

Subeconomic

Above 

entry 

X level

o Below 

a entry 

"§ level to 

^ 1,000 ft 

below

1,000- 

5,000 ft 

below 

entry 

level

Greater 

than 5,000 

ft below 

entry 

level

Service (1966), 

C off man and 

Service (1967)

Tons 

xlO6

777

308

2,401

P 2°5 

(percent)

25.7

14

29.3

Garrand Corp. 

(1974)

Tons P 2 0 5 

xlO6 (percent)

1,038 24.5

681 24.5

Bauer and Dunning 

(1979)

Tons 

xlO6

5,235

111,805

177,650

294,690

P 2°5 

(percent)

27.0

24.6

27.1

Gulbrandsen and Krier/ Summary 

(1980) /

Tons 

xlO6

5,000

9,800

12,100

26,900

P2 o5

(percent)

28.0

27.7

27.7

Tons 

xlO6

1,038+

4,197-

2,401

7,397+

102,007

177,650

294,690

P 2°5 

(percent)

24.5

24.5

27.7

27.7

27.7

27.7

28
vertical) thickness rather than stratigraphic thickness.

A depth criterion was not considered by Garrand to be as important as surface mining criteria 

and hence was not used. The mining depth was 

defined as "the distance down dip along the contact between the limestone beds (which underlie 

the phosphatic beds) and phosphatic beds, beginning at the point in depth for which mining is expected to take place." The surface mining criteria 

used instead of depth criteria were as follows: The 

stripping ratio was defined as the cubic yards of 

waste to tons of ore. It was taken as 3.5 to 1 

for presently economically minable phosphate rock 

and as 9 to 1 to indicate phosphate rock which 

"ultimately may be mined from the area in the 

distant future." The maximum backslope on the 

mine pit was taken as 40°. Material that lies lower 

than 150 feet below water table was excluded.

Garrand's estimates exclude some areas because 

of their complex structure or the thinness of their 

phosphate-bearing beds, which would suggest 

complex structure. The geologic structure of the 

phosphate deposits was derived from a series of 

cross sections that were made from the existing 

geologic maps. All of his data, analyses, and calculations are presented in his report.

Garrand's resource assessment is the most detailed and meticulous made for the main phosphate 

field of Idaho. It superseded an earlier assessment 

made by Powell (1974), which was approximately 

of the same area and which used much the same 

approach.

For the present report, the high-, medium-, and 

low-grade phosphate resource delineated by Garrand with a less than 3.5 to 1 stripping ratio is 

taken to be equal to reserve base and inferred 

reserve base, because no attempt was made to assess the recoverability of the deposits even though 

some rock was excluded for structural and water 

table reasons. The phosphate in the Soda Springs 

area can all be assumed to be at least of the inferred category, but Garrand made no attempt to 

subdivide it. The additional resource of the same 

grade material available at a stripping ratio of 9 

to 1 was taken to be subeconomic identified resource.

BAUER AND DUNNING ESTIMATES

Bauer and Dunning (1979) assessed the phosphate resources of the Northwestern Phosphate 

Province broken down by State. The phosphate

resources of Idaho were estimated comprehensively for all of southeastern Idaho. The small deposits of south-central Idaho were not covered. 

The grade categories used by Bauer and Dunning 

were identical to those used by Service (1966). 

Thickness minima for phosphate resources were 

1 foot for surface mining, 3 feet for underground 

mining of high-, medium-, and low-grade phosphate rock and 6 feet for submarginal shale and 

waste shale. Three depth categories were used: 

(1) resources potentially amenable to surface mining methods and resources amenable only to underground mining, which were broken into two 

subcategories, (2) below surface resources and less 

than 5,000 feet below surface, and (3) more than 

5,000 feet below surface.

The surface minable criteria were a stripping 

ratio (cubic yards of waste per ton of phosphate 

ore) of 9 to 1. They pointed out that the then current ratio was about 5 to 1 and that the ratio of 

the three highest grade categories together was 

8.4 to 1.

The methodology of calculation of resources 

used by Bauer and Dunning was generally the 

same as that used by previous workers. The data 

are fully referenced or displayed in the publication, and the methodology is documented. Resource blocks were set up and defined by the area 

of influence of stratigraphic data, depth of the 

phosphate bed, geologic boundaries, State boundaries, and quadrangle boundaries. For large areas 

of no information, isopach and isopleth maps were 

made for data essential for resource calculation 

and projected into the areas of no information. 

Geologic maps, structure contour maps, structure 

sections, oil well tests, and stratigraphic information were used in these projections. The bias of 

resource estimates derived from the use of weathered, surface-sample analytical data was compensated for by using different specific gravities for 

calculating tonnages of unweathered rock of the 

various grades. This compensation corrects only 

for tonnage and not for grade categories, which 

are overestimated in the higher grades. No structurally spoiled rock was excluded.

The Bauer and Dunning estimates were 

categorized for this report as follows: The surface 

resources greater than 18 percent P205 were 

taken to be estimates of the combined categories 

of identified economic, marginally economic, and 

subeconomic resources, because the 9 to 1 stripping ratio was used and because no rock was

29
excluded due to tectonic spoilage. The underground resources were included in their estimates 

of rock greater than 18 percent P205 (the actual 

grade of this category was greater than 24 percent) below-the-surface deposits and above a plane 

5,000 feet below the surface, which would include 

rock that is subeconomic as defined in this study 

as well as phosphate rock that is not regarded as 

a resource. Thus, no clear definition of subeconomic resources of phosphate rock can be 

made. The Bauer and Dunning estimates of rock 

more than 5,000 feet below the surface are given 

in table 7 and are deposits not regarded as a resource in the frame of reference of the present 

report.

GULBRANDSEN AND KRIER ESTIMATES

Gulbrandsen and Krier (1980) assessed the phosphate resources of the Soda Springs area in southeastern Idaho in 1980. This area approximately 

corresponds to that assessed by Garrand (Garrand 

Corp., 1974). (See fig. 8.)

The primary concern of the Gulbrandsen and 

Krier assessment was the grade of underground 

rock, which has never been adequately sampled 

to make direct estimates, but which must be estimated from the sampling done on surface rocks. 

They analyzed the grade distribution of surface 

phosphate rocks from about 18 sections, and on 

the basis of two measured underground sections 

at mines, they made estimates of the grade of the 

unsampled underground rock. They discovered 

that the grade distribution of both surface and underground phosphatic rocks was bimodal with a 

distinct natural break at 20 percent P205. They 

calculated the resources of the rock with .greater 

than 20 percent P205. Because the zones of this 

rock occur in natural units of large enough thickness that their minability was no problem, no 

thickness criteria were used.

The depth classes of the resource used were (1) 

surface resources, (2) underground resources 

down to 600 m below the surface, and (3) underground resources 600 m or more below the surface 

(fig. 9). The surface resources were defined as 

those underlying outcrops of the Phosphoria Formation.

The Gulbrandsen and Krier estimates were 

categorized for this study in the following way: 

The surface resources would include rock with 

stripping ratios as large as 9 to 1 and would fall 

in the grade class with the P£05 value greater than

24 percent and therefore are classed as identified 

resources of all categories. The underground resources are greater than 24 percent P£05 and also 

are within 600 m of the surface, which is approximately equivalent to 1,000 feet below entry level. 

The Gulbrandsen and Krier estimates are difficult 

to compare precisely with the other estimates for 

reasons of difference of class parameters.

SUMMARY OF ESTIMATES

It is possible to derive a composite estimate of 

all the resource classes of phosphate rock in Idaho 

from the existing estimates. The classes are shown 

in the summary column in table 7.

No one has attempted to differentiate demonstrated resources from inferred resources, so all 

resources must be reported simply as identified. 

In the fringe areas of the main phosphate district 

of Idaho, data become sparse enough and stratigraphic correlations become uncertain enough that 

some of the resources probably should be classed 

as hypothetical resources of the unidentified class. 

However, these resources are certainly minor in 

comparison with those of the main districts of 

southeastern Idaho and can be included in identified resources for the present study.

Strippable resources of the economic and marginally economic classes make up the reserve base 

and the inferred reserve base and have been best 

estimated by Garrand (Garrand Corp., 1974). 

However, he did not estimate the strippable reserve base of Idaho other than in the Soda Springs 

area so that his estimates are minimal. The strippable identified resource for all of Idaho was estimated by Bauer and Dunning (1979), and by subtracting the reserve base and inferred base estimates of Garrand, a maximum estimate of the subeconomic identified strippable resources is obtained. The grade of the strippable resource is 

about 24.5 percent P£05 based on Garrand's work, 

which used minable units.

The underground resources, which are all subeconomic identified resources, can be broken into 

those above entry level and those below entry to 

1,000 feet below entry level. The estimates of Service (1966) of the phosphate rock containing more 

than 24 percent P205 give the former. When that 

is subtracted from the Gulbrandsen and Krier estimate of the resource from the surface to 600 m 

below the surface, a crude minimal estimate of the 

resource from entry level to 1,000 feet below entry 

level is obtained. This is quite crude because the

30
Gulbrandsen and Krier estimate is only for the 

Soda Springs area; whereas, the Service estimates 

are for all of Idaho. Also, the Gulbrandsen and 

Krier plane that is 600 m below the surface is only 

a very crude approximation of the plane 1,000 feet 

below entry level.

Thus, Idaho phosphate reserve base and inferred reserve base consist of at least 1,038 million 

tons of phosphate rock that averages about 24.5 

percent P205 . Of this resource, only a fraction will 

be recoverable due to spoilage of the rock by folding and faulting. The subeconomic identified resources of Idaho consist partly of strippable rock 

and partly of underground rock. The strippable 

rock amounts to less than 4,197 million tons and 

averages about 24.5 percent P205. It also would 

be only partially recoverable. The underground 

portion of subeconomic resources amounts to 

about 9,798 million tons of rock averaging about 

27.7 percent P205 . Of this, 25 percent is above 

entry level, where it could be mined with gravity 

stoping, and 75 percent is below entry level, 

where it would have to be raised a maximum of 

1,000 feet. Much phosphate rock exists below this, 

but in the foreseeable future, it seems unlikely 

that the energy costs of raising the rock more than 

1,000 feet would allow its economic recovery.

These composite estimates leave much to be desired, as they are not entirely compatible. However, without a major new effort to assess the 

resource, they are the best available, and they do 

give a general idea of the magnitude of phosphate 

resources of Idaho.

MONTANA

Two estimates have been made of phosphate resources in Montana based on the complete data 

set. They are Swanson (1970, 1973) and Bauer and 

Dunning (1979) (table 8). Popoff and Service (1965) 

made estimates based on Swanson's unpublished 

information for southwestern Montana, and their 

central-western Montana data were obtained from 

the very early literature on the subject, which was 

completely superseded by Swanson's work.

SWANSON ESTIMATES

The two works of Swanson (1970, 1973) present 

the basic stratigraphic and chemical analytical 

data on the phosphate resources of southwestern 

and central-western Montana (fig. 10), studies that 

include all of the known phosphate areas in Montana. Phosphate resources were reported in the 

following classes: plus 31 percent P205, plus 24 

percent, and plus 18 percent. In addition, the actual phosphate percentage was given for each 

class. The resources included only phosphate beds 

greater than 3 feet in thickness and were calculated above entry level, the first 100 feet below 

entry level, and the total block (fig. 9). The 

methodology of resource assessment was carefully 

and explicitly defined (Swanson, 1970). The resource blocks were conservatively defined and objectively presented in maps showing structure, 

contours, and faults.

Swanson's resource estimates are interpreted in 

this study as follows: The phosphate deposits containing more than 24 percent P205 and occurring 

above entry level are classed simply as resources, 

as they fall primarily in the identified class but 

also in the hypothetical class, and they include 

economic and marginally economic surface deposits, as well as subeconomic surface and underground deposits. The rock that contains more than 

24 percent P205 and lies beneath entry level is 

a subeconomic resource down to 1,000 feet below 

entry level, and material that is more than 1,000 

feet below entry level is not considered as a resource. Thus, the boundaries selected by Swanson 

for reporting phosphate resources do not conform 

to the boundaries adopted for this report, and his 

estimates cannot be broken down further than the 

general category of resources, with one large portion of phosphate rock containing both subeconomic resources and material not considered as

a resource.

BAUER AND DUNNING ESTIMATES

The Bauer and Dunning estimates (1979) for 

Montana cover the same area as the Swanson estimates but divide the deposits into surface deposits, underground deposits, and deep underground deposits, as discussed under the section 

on the Idaho resources. Their estimate is 

interpreted in this study as follows: The strippable 

surface deposits are simply resources as they are 

based on a stripping ratio of 9 to 1. Also, they 

include deposits that would probably be classed 

as hypothetical as well as inferred. The deposits 

occurring below the surface deposits down to a 

depth of 5,000 feet below the surface include both 

subeconomic underground resources and underground deposits not considered a resource. No 

further breakdown can be made.

31
TABLE 8. Comparison of phosphate rock resources in Montana

[In millions of metric tons]

0) CO

iH Q)

,e o

2. 3 

0- 0

 H CO 

M Q)

4-1 (_, 

C/]

round 

rces

M 3

M O

O) CO

 B Q)

^

 B

0) B

n) oj bC o

0) ^

M D

O

4-1 CO 

O Q)

C (-1

^ w

 H CO 

M «

0) 

4-1

S

Reserve and

inferred

reserve base

Subeconomic

Above entry

level

o H 

O

C

o

o Below entry

M

3 level to C/3

1,000 ft

1,000-

5,000 ft below

entry level

Greater than

5,000 ft below

entry level

Swanson (1970, 1973)

Tons

xlO6

437

7,168

P 2°5

(percent)

27.1

26.9

Bauer and Dunning

(1979)

Tons

xlO6

608

9,755

6,714

P 2°5

(percent)

24.3

27.8

29.0

Best estimates

(those used in

this report)

Tons

xlO6

608

9,755

6,714

P 2°5

(percent)

24.3

27.8

29.0

SUMMARY OF ESTIMATES

The phosphate resources of Montana reported 

in the Swanson and the Bauer and Dunning reports cannot be very well classified according to 

the criteria used in this report. The Bauer and 

Dunning estimate of surface resources of 608 million tons of phosphate rock containing 24.3 percent 

P205 is the best estimate of combined economic, 

marginally economic, and subeconomic strippable 

resources. Their underground phosphate rock estimate of 9,755 million tons of phosphate rock containing 27.8 percent P205 includes both subeconomic resources and material that is not considered as a resource. Their deep underground deposits also cannot be considered a resource. The

two estimates cannot be used to make a composite 

resource estimate as was done for the Idaho resources; however, the Bauer and Dunning estimate is the best for this report. It should be noted 

that the Bauer and Dunning estimates of total 

phosphate rock in the combined resource blocks 

of Montana are larger than the Swanson estimates 

for Montana. However, the difference is caused 

by more liberal boundaries of the resource blocks 

in the Bauer and Dunning study. Thus, the Bauer 

and Dunning estimate of 16,469 million tons of underground phosphate rock (combined underground 

and deep underground) include a large amount of 

hypothetical rock; whereas, the Swanson estimates are primarily made up of inferred rock. A

32
113° 112°

EXPLANATION

OUTCROP OF PHOSPHORIA FORMATION 

Dotted where questionable

 a I itu

\ 

\*«x') __ \ MONTANA

?-}' { I *> ~, IwYOMING 

N .*N I S^ I

FIGURE 10. Phosphate rock outcrops and sample localities in Montana.

33
difference between the two estimates that is hard 

to account for is that the Bauer and Dunning estimate of surface resources is larger than the Swanson estimate of rock above entry level. This problem could only be resolved by an extremely detailed comparison of the two estimates, which is 

beyond the scope of this study. The difference, 

at any rate, does not involve a major amount of 

phosphate resources.

WYOMING

Three resource assessments have been made of 

Wyoming (table 9, fig. 11). Sheldon (1963) assessed the phosphate resources in northwestern

Wyoming, exclusive of the westernmost ranges. 

Cofftnan and Service (1967) assessed the area of 

Wyoming not covered by Sheldon. Finally, Bauer 

and Dunning (1979) reassessed the complete State.

SHELDON ESTIMATES

Sheldon (1963) presented the basic stratigraphic 

and chemical analytic data on the resources of 

northwestern Wyoming exclusive of the Salt 

River, Sublette, and Tump Ranges of Wyoming. 

His methodology and class boundaries were standard, and he presented the estimates of acid, furnace, and beneficiation grades of phosphate rock. 

By depth, the classes were broken down into

TABLE 9. Comparison of phosphate rock resources in Wyoming

[In millions of metric tons]

v to

iH <U

f O

(0 )-i 

P. 3 

P. 0

 H to

)-J <U

C/3

T) 

§10 

(1) 

O 0

&SM O

<u to

T) tt)

^

T)

(1)

T)

(0 (1) bo o

V M

1-J 3

O

4-1 10

O <U

C )-i

"^ w

U (0

OJ 

4-1

S

Reserve

and

inferred

reserve

base

Subeconomic

Above 

£ entry 

^ level

cQ

^ Below

 g entry

w level to

1,000 ft

1,000-

5,000 ft

below

level

Greater

than

5,000 ft

below

entry

level

Sheldon (1963),

Coffman and Service

(1967)

Tons

xlO 6

1,470

767+

2,048

P 2°5

(percent)

28.2

28.2

28.2

Bauer and

Dunning

(1979)

Tons

xlO6

924

20,163

129,760

P 2°5

(percent)

23.4

27.5

27.3

Best estimates

(those used in

this report)

Tons

xlO6

924

1,165

767+

2,048

inf.

16,182

129,760

P 2°5

(percent)

23.4

28.2

28.2

28.2

27.5

27.3

34
111" 110° 109° 108°

43°

42°

;i

J Kemmerer

EXPLANATION

OUTCROP OF PHOSPHORIA FORMATIONDotted where questionable

Sample Locality

Flaming Gorge 

3 j Reservoir 50 MILES

INDEX MAP >V WYOMING ° 50 KILOMETERS

UTAH COLORADO

FIGURE 11. Phosphate rock outcrops and sample localities in Wyoming. Compiled and modified from Sheldon (1963).

above entry level, entry level down to 1,000 feet 5,000 feet below entry level was not estimated.

below entry level, and from 1,000 to 5,000 feet His grade classes greater than 24 percent P205

below entry level (fig. 9). Thus, the rock below and higher than 1,000 feet below entry level con35
stitute subeconomic phosphate resources. However, the portion above entry level would include 

surface-reserve-base and inferred-reserve-base resources.

COFFMAN AND SERVICE ESTIMATES

The Coffman and Service (1967) assessment covered that part of Wyoming not covered by Sheldon. The comments on the Coffhian and Service 

assessment made in the section on Montana phosphate resources apply to this section on Wyoming 

resources.

BAUER AND DUNNING ESTIMATES

The Bauer and Dunning assessment (1979) covered all of Wyoming and has been commented on 

earlier.

SUMMARY OF ESTIMATES

A composite of the estimates can be made from 

the three assessments (table 9). The Bauer and 

Dunning (1979) estimates of surface resources of 

924 million tons of phosphate rock containing 23.4 

percent P£05 are interpreted as identified and 

some hypothetical resources of all economic classes. The difference between the Bauer and Dunning (1979) estimates of surface resources greater 

than 24 percent P£05 (not shown in table 9) and 

the Sheldon (1963) and Coffman and Service (1967) 

estimates of resources above entry level give the 

underground resources above entry level. The 

Sheldon (1963) estimate of phosphate resources 

from entry level down to 1,000 feet below entry 

level is minimal because the westernmost ranges 

are excluded, and the Coffhian and Service (1967) 

estimates did not cover this depth class. The 

Bauer and Dunning (1979) estimate of underground rock down to 5,000 feet below the surface, 

after subtracting the resources above entry level 

and below entry level down to 1,000 feet below 

entry level, approximately gives the total rock between 1,000 and 5,000 feet below the surface. The 

approximation is due to the difference between the 

planes 1,000 feet below the surface and 1,000 feet 

below entry level. By subtracting the Sheldon 

(1963) estimate of rock between 1,000 and 5,000 

feet below entry level, which is for the most part 

inferred, from this, a rough estimate of the 

hypothetical rock is obtained. The rock deeper 

than 5,000 feet below the surface is given by 

Bauer and Dunning (1979).

UTAH

Three resource assessments have been published for Utah (table 10; fig. 12) and are those 

by Coffman and Service (1967), geologists of 

Dames and Moore, Inc. (1978), and Bauer and 

Dunning (1979).

COFFMAN AND SERVICE ESTIMATES

Coffman and Service (1967) assessed the phosphate resources of all of northern Utah east of 

Salt Lake Valley. Thus, the small deposits of 

western Utah were not included. The comments 

on the Coffman and Service (1967) assessment 

made on Montana phosphate resources apply to 

this section on Utah resources.

DAMES AND MOORE, INC., ESTIMATES

The estimates of phosphate resources made by 

Dames and Moore (1978) geologists covered the 

same region as the Coffman and Service (1967) 

estimates, and in fact they used the Coffman and 

Service (1967) estimates. They updated the 

Coffman and Service (1967) estimates and extensively analyzed the economic and technologic factors for phosphate production, concluding that underground mining would not be economic in the 

foreseeable future.

BAUER AND DUNNING ESTIMATES

The Bauer and Dunning assessment (1979) covered the same area of Utah as the two previous 

assessments. The parameters and methodology of 

the study have been discussed on page 29.

UNPUBLISHED VERNAL AREA ESTIMATES

The phosphate deposits near Vernal, Utah, on 

the southeast flank of the Uinta Range have been 

included in the estimates by Dames and Moore, 

Inc., and by Bauer and Dunning discussed in the 

last section; however, recent operations have 

shown them to be much larger than reported. 

Stauffer Chemical Company and Chevron Resources have indicated that the strippable reserves of phosphate rock are of the order of 500- 

700 million tons of rock (W. F. Stowasser, personal commun., 1981). The ore bed is about 20 

feet thick and averages about 20 percent P£05 . 

Bauer and Dunning estimated 275 million tons for 

the Vernal area, and the difference presumably 

is due to use of a different stripping ratio by indus36
TABLE 10. Comparison of phosphate rock resources in Utah

[In millions of metric tons]

Strippable resources

Underground 

resources

T3 

01 

T3 

(J 

OS 01 

bC 0

not reresoul

^ «

 H CO 

H <8 

0)

CO

Reserve and

inferred 

reserve base

Subeconomic

Above ent ry 

level

o H

C 

O

£j Below entry 

 £j level to 

w 1,000 ft

1,000-5000 ft 

below entry 

level

Greater than

5,000 ft

below entry 

level

C off man and

Service 

(1967)

Tons 

xlO6

268

P2°5 

(percent)

28.1

Dames and

Moore, Inc. 

(1978)

Tons 

xlO6

32

236

P2°5 

(percent)

28

28

Bauer and

Dunni ng 

(1979)

Tons 

xlO6

529

5,716

63,675

P2°5 

(percent)

24.9

27.5

30.1

Best estimates

(those used in 

this report)

Tons 

xlO6

^00

254

38

5,679

63,675

P 2°5 

(percent)

24.9

28.1

27.5

30

Corrected for industry reserve estimate of 600 million tons reserve in Vernal area.

try than by Bauer and Dunning. If the Utah estimates of Bauer and Dunning are increased to account for the average of this larger estimate of 

strippable deposits (600 million tons) of the Vernal 

area, they become 854 million tons, and this revised figure is used for the Bauer and Dunning 

estimates.

SUMMARY OF ESTIMATES

The three sets of resource estimates are all 

based on essentially the same set of data, that 

is, that of the U.S. Geological Survey. Each assessment used different resource boundaries, but

when assembled together, they can be put into 

a single, consistent set of resource estimates (table 

10). Strippable resources of both the reserve and 

inferred reserve bases and the subeconomic 

categories were estimated by Bauer and Dunning 

(1979) as 529 million tons of rock greater than 18 

percent P205. This compares to 32 million tons of 

subeconomic strippable resources estimated by 

Dames and Moore, Inc. (1978), who must have 

used a smaller stripping ratio. However, the revised figure of 854 million tons is used in this report. If the Coffman and Service (1967) estimate 

of 268 million tons of resources greater than 24 

percent P205 above 100 feet below entry level is

37
112° 111°

OUTCROP OF PHOSPHORIA FORMATIONDotted where questionable

SALT

LAKE{ SAtTLAKE 

CITY

40° 

FIGURE 12. Phosphate rock outcrops and sample localities in Utah. Recompiled and modified from Cl
correct, and if Bauer and Dunning's 1979 estimate 

of 230 million tons of strippable rock greater than 

24 percent P205 is subtracted from it, the subeconomic undergound resources above 100 feet 

below entry level would be 38 million tons. Subeconomic resources below this down to 1,000 feet 

below entry level are not possible to derive, but 

down to 5,000 feet below entry level are 5,679 million tons, using the Bauer and Dunning 1979 estimate and deducting the material above 100 feet 

below entry level. Tonnage of phosphate rock 

deeper than 5,000 feet below the surface is given 

by Bauer and Dunning (1979).

NORTHWESTERN UNITED STATES

The phosphate resource classes of the States of 

Idaho, Montana, Wyoming, and Utah cannot be 

added owing to different class boundaries. However, by apportioning, where necessary, the resource categories according to the ratios obtained 

in Idaho, an approximation of all of the resource 

categories can be obtained. These approximations, 

rounded to two figures, are shown in table 11, 

along with the average grade of the phosphate 

rock. This shows that more than 1,600 million tons 

of strippable economic reserve and inferred reserve base existed before mining began. It is difficult to say how much of the reserve base and inferred reserve base will actually be minable, but 

tectonic structural spoilage will probably be significant. If only half is minable, then 800 million tons 

would constitute the reserve. Approximately 140 

million tons of phosphate rock have been mined 

since the inception of mining to 1980, and 

8,117,000 tons was mined in 1979. Thus, about 660 

million tons of reserve might be available for the

TABLE 11. Phosphate rock resources of the Northwestern Phosphate Field

[In million of metric tons]

rippable 2sources

Underground 

resources

egarded 

rce

(-1 3 

0

4-) 01 

O CU c t-i

 a "

T3 S 0)

Reserve and

inferred

reserve base

Subeconomic

Above entry

o level H

0

cu 

-Q Below entry

w level to

1,000 ft

1,000- 

5,000 ft 

below entry 

level

Greater than 

5,000 ft

below entry

level

Tons 

xlO6

1,600+

6,000-

4,000

13,000

130,000

377,000

P2°5 

(percent)

24

24

28

28

28

28

39
TABLE 12. Other phosphate rock resources, United States

Rock unit and location. 

Description.

Estimated resources 

(metric tons)

Precambrian

Marquette Range Supergroup, Michigan.

Dense, black phosphate pebbles in quartzite 

Base of Proterozoic.

Spokane Formation, Belt Supergroup, Montana. 

Phosphate pellets in very thin beds.

Ocoee Supergroup, Tennessee.

Phosphate pellets in black shale and sandstone, 

Beds up to 1.3 m thick, up to 35 percent ?®'

20x10°

(25 percent

Very small.

No concrete data, 

individual deposits 

small about 1x10 

tons (about 25 

percent P^Oc).

Cambrian

Dunderberg Shale, Nevada.

Thin beds (max. = 50 cm., about 20 percent P 2°5)> wide 

distribution.

Milton Dolomite, Vermont.

Intraformational breccia zone

about 1.5 m thick may contain 5 percent

No data. Total 

resource may be 

large but reserves 

nil.

lOxlO6

(20-25 percent 

P 20 5 ).

Ordovician

Several formations, Nevada.

Shale, limestone, dolomite, with phosphate

pellets and nodules. 10 percent P2°5» maximum, thin beds.

Maquoketa Shale, Iowa, Wisconsin, Illinois. 

Sandy phosphorite and phosphatic dolomite. 

Beds up to 1.5 m, and up to 15 percent P°'

Cason shale, Arkansas.

Phosphatic shale, beds about 1 m, and up to 

20 percent P 20 5»

Decorah Formation and Galena Dolomite, Minnesota. 

Very thin beds (lag gravels at unconformity).

Nashville Group, Tennessee.

Hermitage, Bigby, Cannon, and Catheys Limestones of Nashville

Group and Leipers Limestone.

Phosphatic limestone, average about 5 percent P205-

Extends south into Limestone County, Alabama.

Lexington Limestone, Kentucky.

Phosphatic limestone, same as in Tennessee but 

not as extensive

Maravillas Chert, Texas.

Phosphatic nodules in shale: nodules, 23 percent ?2°5 ~ 

shale 1 percent P°«

No data, probably 

very small in 

individual deposits.

8xl0 6 (15 percent 

(P2°5 amenable to 

open pit mining near 

Dubuque. Total 

resources much 

larger.

20x1O6 .

Very small.

3 to 5x10*

tons of phosphate in 

these limestones 

(20 percent P 2°5)-

No tonnage data; 

may be about I/5th 

of Tennessee.

No data small?

40
TABLE 12. Other phosphate rock resources, United States Continued

Rock unit and location. 

Description.

Estimated resources 

(metric tons)

Silurian

Red Mountain Formation, Alabama.

Oolitic iron-ore deposits contain phosphate. 

When iron ores are treated by Bessemer process 

a "basic slag" containing about 8 percent P2°S is 

Phosphate is available to plants, good fertilizer

Unnamed formation, Nevada.

Dolomite, very thin beds (about 6 cm) contain 

up to 5 percent ?°'

No data.

No data, very 

small.

Devonian and Mississippian

Devonian Chattanooga and New Albany Shales and 

Mississippian Maury Formation. Alabama, 

Georgia, Tennessee, Kentucky, Ohio, Indiana, 

Arkansas, Oklahoma.

Sparse phosphate nodules in black shale. Nodules 

contain up to 30 percent P^Q^i black shale 2-3 percent

P 2°5*

Devonian Hardin Sandstone Member of Chattanooga Shale,

Tennessee, 

part of Chattanooga. So called "blue rock."

Thin beds 1 m, up to 25 percent Pj^5'

Devonian Sylamore Sandstone Member of Chattanooga 

Shale, Shale Arkansas, Oklahoma.

Basal Devonian, contains minor phosphate pellets

or nodules. No data on grade, beds thin.

Devonian Oriskany Sandstone. New York, Pennsylvania, Virginia. 

Basal bed of Oriskany in these states contains thin 

phosphorite bed, up to 25 percent P2°5-

Mississippian and younger Paleozoic

Tonnages have never 

been totaled, but 

because of very 

large outcrop area, 

the resource is very 

large.

SOxlO6 (20 percent 

P2°s) may be Basal 

greater.

No data, very 

small.

No data, small

Mississippian Brazer Limestone, Utah.

Basal member, phosphorite up to 2 m thick, as much 

as 33 percent ?2®5'

Mississippian to Permian Lisburne Group, Alaska. 

Black shale, calcareous phosphorite, 

4 m thick 16 percent P2°5'

Mississippian Fayetteville Shale, Arkansas 

Low P2^5 content, but individual, thin beds 

contain as much as 35 percent PoO,-.

SOOxlO

(20 percent

300x1 O

(16 percent

No data. Could be 

large 2-5 percent

P2 o5 .

future. At a linear rate of increase of production 

of 245,000 tons of rock a year, the rough average 

rate of increase from 1964 to 1980, these 660 million tons would be exhausted in about the year 

2018. At that point, an additional subeconomic resource of 6,000 million tons of strippable resources 

and 4,000 million tons of underground resources 

above entry level would be available for mining

if technology had been developed to economically 

mine it.

OTHER PHOSPHATE PROVINCES

Phosphate occurrences are known in the central 

interior of the United States from Texas in the 

south to Iowa and Wisconsin in the north, and 

in rocks that range in age from Ordovician through

41
TABLE 12. Other phosphate rock resources, United States Continued

Rock unit and location. 

Description.

Estimated resources 

(metric tons)

Mlssissippian and Pennsylvania!!

Several Pennsylvanian formations, eastern Kansas, 

and Oklahoma, and western Missouri. 

Coarse phosphate nodules in interbedded black 

shale and limestone. Nodules up to 30 percent P2°5 

shale 2-3 percent PO^S'

Pennsylvanian Macoupin Limestone, St. David Limestone 

Member, Cohn Coal Member, and Brereton Limestone 

Member, Illinois.

Sparse phosphate pellets and nodules 

in interbedded shale and limestone.

Mississippian Pitkin and Pennsylvanian Hale Formations, 

Arkansas.

Lenticular calcareous phosphorite at base of Hale 

Formation. Range from 0-7 m thick, up to 25 percent

Morrowan rocks, Texas.

Sandy phosphorite at base, may be lag gravel.

No data large 

in total.

No data.

5x1Ob (20

percent Po0 5^ 

(measured;, total 

greater.

40xl03 .

Very small (20 

percent P 9 0c).

Triassic

Shublik Formation, Alaska.

Black shaly phosphorite near base is 3-7 m

thick and up to 35 percent ?2°5 averaSe =12 percent,

5,000x10° 

(12 percent

Cretaceous

Several formations, Alabama, Georgia, Mississippi. 

Phosphate pellets in chalk, marl, and limestone. 

Phosphate pellets up to 30 percent ?2®5> total rock 

2-3 percent P2 °5*

Several formations, Texas, Colorado, North Dakota, 

South Dakota, California, same as above.

No data. Tons per 

acre very low, but 

total, because of 

because of large 

areal extent, large.

Do.

Eocene

Castle Hayne Formation, North Carolina.

Phosphate and glauconite in fossiliferous limestone.

Total ?2®5' about 2 percent, nodules may be up to 20 percent,

Tallahatta Formation, Georgia.

Phosphate pellets in sand. No analytical data. Phosphate 

pellets may be reworked from erosion of Cretaceous 

phosphate occurrences.

Midway and Claiborne Groups; Weches Greensand, Texas. 

Phosphate pellets in sand, limestone, glauconitic sand 

(greensand). Pellets up to 30 percent, individual, thin 

beds (50 cm) contain up to 10 percent ?®*

No data, smalli

Do.

No data. Tons 

per acre low, 

total tons 

probably large.

Eocene and Oligocene

Cooper Marl, South Carolina.

Sparse phosphate pellets in marl. P 2°5 content

of pellets up to 25 percent, but total rock contains

only 1-2 percent PoOc.

No data, 

large (?).

42
TABLE 12. Other phosphate rock resources, United States Continued

Rock unit and location. 

Description.

Estimated resources 

(metric tons)

Miocene

Monterey Formation, California.

Thick sequence of shale, siliceous shale, and 

phosphorite, but low (5-10 percent) in Po^S content. 

Mining may not be possible because of environmental 

restrictions.

Very large, 

hundreds of 

millions.

Pleistocene and Holocene

Reworked and secondary deposits

"River Pebble" (Florida and Georgia).

Coarse phosphate gravels, as bars and in flood 

plains along streams that are draining phosphate 

terranes. Low phosphate contact because of leaching 

by acid waters.

"Hardrock" (Florida and south Georgia) "Whiterock" 

(Tennessee).

Phosphate, in solution, derived from acid leaching 

of phosphorite, is precipitated on, or replaces 

underlying limestone. Very high P 2°5 content, very 

irregular deposits. Reworking after formation results 

in channel-like deposits (only in Florida).

Brown-rock deposits, Alabama, Kentucky.

High-grade phosphate residum left after acid weathering 

of phosphatic limestone. Deposits are erratic in 

distribution and individual deposits tend to be small.

"Landrock" and "River rock" Charleston area, South Carolina. 

Reworked from Miocene (Hawthorn?^ phosphorite in 

Pleistocene and Holocene. Small, erratic, low-grade 

deposits.

50x10°

(25 percent

Small in 

individual 

deposits, total 

may be large.

Small (15 percent

P 2o5 ).

Small.

Offshore deposits

Sea floor nodules, Pacific Coast.

Coarse-phosphate nodules on sea floor have been 

forming since Miocene. Resources may be large 

but tonnage per unit area is small. Nodules 

are high in P°-

Large.

Tertiary. Deposits are being mined presently only 

in Tennessee.

TENNESSEE

The brown-rock deposits of Tennessee are associated with the Nashville dome. The phosphate 

was deposited in rocks of Middle Ordovician age 

and is in the form of pellets and phosphatized fossil 

gastropods. The rocks are phosphatic only on the 

western flank of the Nashville dome. The phosphatic limestones have been weathered in modern 

time, carbonate has been removed, and the phosphate is concentrated as a residual deposit. The

deposits are covered by thin phosphatic soil and 

are economic because they are flat lying, poorly 

consolidated, and shallow. Reserves are only a few 

score millions of tons.

Mining is at the rate of a few million tons per 

year, and at the current rate, the reserves will 

be depleted sometime in the 1990's.

OTHER AREAS

A number of other small deposits are known 

throughout the United States and are listed in 

table 12, along with rough estimates of their magnitude.

43
SUMMARY OF U.S. PHOSPHATE 

RESOURCES

About 7 billion tons of phosphate concentrate 

that are economically or marginally economically 

feasible to mine and beneficiate by use of today's 

technology and prices are available for mining 

(table 13). Three-quarters of this resource occurs 

in Florida, and the rest is split about evenly between North Carolina and Idaho. This resource 

is being depleted by mining and will be exhausted 

in the next century; of course, the exact time of 

exhaustion is dependent on the rate of extraction.

In addition to these available resources, there 

exist an additional 24 billion tons of phosphate deposits classed as subeconomic resource, which are 

presently unavailable because mining and processing costs are too high relative to today's phosphate 

prices. Most of this subeconomic resource has been 

identified in the Northwestern Phosphate District 

of Idaho and adjacent States, where it consists 

of rock that must be mined by underground 

methods rather than by strip mining. Not only is 

the cost of underground mining higher than that 

of strip mining, but the rock has a different quality 

from rock now being mined and will require a different processing technology. Such a technology 

has not yet been developed.

More than 16 billion tons of additional phosphate

deposits probably exist but are not listed here because of insufficient drilling information. They are 

classed as undiscovered and are hypothesized to 

occur in the southeastern Coastal Plain province, 

particularly in Florida, North Carolina, and the 

shallow Atlantic offshore areas of the Blake 

Plateau, North Carolina, and the Savannah River, 

where detailed drilling is necessary to prove their 

tonnage and grade.

FUTURE TRENDS AND PROBLEMS

The United States phosphate industry will have 

to undergo major changes early in the next century if it is to continue to supply phosphate to 

domestic and world markets to meet projected demand. The present available reserve will be depleted, and the industry will have to turn to resources that are presently uneconomic to mine or 

unavailable. Several technologic opportunities 

exist that may make this possible. Valuable byproducts could be obtained, including uranium, vanadium, chromium, rare earths, and fluorine, and 

the value of these byproducts is sufficient to affect 

the economics of phosphate mining. The western 

underground phosphorites, in addition, contain 

significant quantities of organic matter, which constitutes an energy supply that could help alleviate 

processing costs. Large amounts of ammoniumTABLE 13. Phosphate rock resources of the United States

[In millions of metric tons of phosphate product or phosphate rock]

Identified recoverable resources Hypothetical 

resources

Remarks

Florida

Economic Marginal Subeconomic

3,700 1,470 430 5,000+ Recoverable.

North 

Carolina

1,000 Mostly economic.

Georgia (1,000) Unavailable due to

environmental restrictions.

Northwestern

U.S. 1,600- 23,000

Pre-mining resources 

in ground recoverable is 

considerably less.

Total U.S. 7,000- 23,430 15,000+ Georgia resources not included.

Additional 

identified 

rock not 

considered 

a resource

500,000

Occurs in northwestern field at 

depths too great for mining in 

foreseeable future.

44
rich feldspar (Gulbrandsen, 1974) presently are 

being mined as waste in phosphate mining in 

Idaho, and research on this material, which contains (NH4)20 in amounts up to 6 percent, might 

show that it could be utilized as special nitrogen 

fertilizer. Bore-hole hydraulic mining and slurry 

extraction hold some promise for mining the 

deeper subeconomic phosphate rock in the southeastern Atlantic Coast province. According to M. 

E. Zellars and J. M. Williams (written commun., 

1979) the costs of dredge mining of offshore phosphate deposits may be equal to projected onshore 

mining costs, in the late 1980's or early 1990's.

The phosphate resources that the Nation must 

turn to in the future are not well known. In the 

southeastern Atlantic Coastal Plain districts, only 

about a third of the resource has been explored 

to the point that its quantity and quality can be 

measured. The undiscovered portion promises to 

be large, and its quality will probably be similar 

to that of the identified deposits, but much uncertainty still exists. A similar situation exists for 

Idaho and the adjacent States. Although the deposits in the Northwestern United States are 

much more regular in geologic occurrence so that 

their existence and quantity can be better estimated, their quality is only poorly known. The 

rock that will have to be mined if the province 

is to continue to contribute to the Nation's phosphate supply is deep under the ground, and samples cannot be obtained without drilling. Meaningful research on processing technology to produce 

both phosphate and byproducts cannot be undertaken until the quality of the rock is better known.

The important phosphate resources of the Nation occur in areas where the land is needed for 

such uses as citrus groves, suburban development, 

forestry, and recreation. Much phosphate land is 

presently unavailable for exploitation because of 

these alternate uses. In addition, the effect of 

phosphate mining and processing on water, air, 

and land quality is significant, and considerable 

effort, much of which has been successful, has 

been made to prevent mining. These problems for 

phosphate development will have to be resolved 

if the Nation's phosphate resources are to be used 

to their full potential.

GLOSSARY

Back Slope. The back slope of a mine pit is the 

slope of the pit after mining the ore bed.

Economic. This term implies that profitable extraction or production under defined investment 

assumptions has been established, analytically 

demonstrated, or assumed with reasonable certainty.

Entry Level. The level of the entry to the mine 

that is used as a haulage road. The lowest entry 

level is where the ore bed intersects the lowest 

stream level and is the entry level which 

maximizes the amount of ore that can be mined 

by gravity stoping, which minimizes the energy 

costs of moving ore out of the mine.

Identified Recoverable Resources. Those phosphate resources whose tonnage and grade have 

been determined by drilling and chemical analysis and in which the phosphate product can be 

recovered using existent technology.

Inferred Reserve Base. The inplace part of an 

identified resource from which inferred reserves 

are estimated. Quantitative estimates are based 

largely on knowledge of the geologic character 

of a deposit and for which there may be no samples or measurements. The estimates are based 

on an assumed continuity beyond the reserve 

base for which there is geologic evidence.

Marginal Reserves. That part of the reserve base 

which, at the time of determination, borders on 

being economically producible. Its essential 

characteristic is economic uncertainty. Included 

are resources that would be producible given 

postulated changes in economic technologic factors.

Matrix. Term used by phosphate companies in 

Florida and North Carolina to designate the potentially minable material.

Phosphate Product. Deposits in the Atlantic 

Coastal Plain must be beneficiated. This is done 

by washing, screening, and froth flotation. The 

flotation concentrate (size range 0.1-1 mm) is a 

phosphate product. In the Florida deposits, the 

fraction greater than 1 mm, called pebble, is also 

a phosphate product.

Reserve Base. That part of an identified resource 

that meets specified minimum physical and 

chemical criteria related to current mining and 

production practices, including those for grade, 

quality, thickness, and depth. The reserve base 

is the inplace, demonstrated (measured plus indicated) resource from which reserves are estimated. It may encompass those parts of the resources that have a reasonable potential for becoming economically available within planning

45
horizons beyond those that assume proven technology and current economics. The reserve base 

includes those resources that are currently 

economic (reserves), marginally economic (marginal reserves), and some of those that are current subeconomic (subeconomic resources). The 

term "geologic reserve" has been applied by 

others generally to the reserve-base category, 

but it also may include the inferred-reserve-base 

category; it is not a part of this classification 

system.

Reserves. That part of the reserve base which 

could be economically extracted or produced at 

the time of determination. The term "reserves" 

need not signify that extraction facilities are in 

place and operative. Reserves include only recoverable materials; thus, terms such as "extractable reserves" and "recoverable reserves" 

are redundant and are not a part of this classification system.

Restricted Resources or Reserves. That part of 

any resource or reserve category that is restricted from extraction by laws or regulations. 

For example, restricted reserves meet all the 

requirements of reserves except that they are 

restricted from extraction by laws or regulations.

Subeconomic Resources. The part of identified 

resources that does not meet the economic 

criteria of reserves and marginal reserves. 

Undiscovered Resources. Resources, the existence of which are only postulated, comprising 

deposits that are separate from identified resources. Undiscovered resources may be postulated in deposits of such grade and physical location as to render them economic, marginally 

economic, or subeconomic. To reflect varying degrees of geologic certainty, undiscovered resources may be divided into two parts:

Hypothetical Resources. Undiscovered re^ 

sources that are similar to known mineral 

bodies and that may be reasonably expected 

to exist in the same producing district or 

region under analogous geologic conditions. 

If exploration confirms their existence and 

reveals enough information about their 

quality, grade, and quantity, they will be 

reclassified as identified resources. 

Speculative Resources. Undiscovered resources that may occur either in known 

types of deposits in favorable geologic settings where mineral discoveries have not

been made or in types of deposits as yet 

unrecognized for their economic potential. 

If exploration confirms their existence and 

reveals enough information about their 

quantity, grade, and quality, they will be 

reclassified as identified resources.

REFERENCES CITED

Altschuler, Z. S., 1980a, The bearing of geochemistry on the 

recovery of uranium and rare earths in phosphorites, in 

Impurity elements in phosphate rock and phosphoric acid: 

Proceedings, 2nd International Congress on Phosphorus 

Compounds, Institut Mondial du Phosphate, Paris, p. 605- 

626.

 1980b, The geochemistry of trace elements in marine 

phosphorites, Part I. Characteristic abundances and enrichment: Society Economic Paleontologists and 

Mineralogists Special Paper 29, p. 19-30.

Bauer, C. W., and Dunning, C. P., 1979, Uraniferous phosphate resources of the western phosphate field, in R. H. 

De Voto, and D. N. Stevens, eds., Uraniferous phosphate 

resources, United States and Free World: U.S. Department of Energy publication GJBX-110(79), p. 123-248.

Breza, H. M., and others, 1979, Phosphate mining and beneficiation, in R. H. De Voto, and D. N. Stevens, eds., Technology and economics of uranium recovery from phosphate 

resources, United States and Free World: U.S. Department of Energy publication GJBX-110(79), p. 39-174.

Cathcart, J. B., 1968, Phosphate in the Atlantic and Gulf 

Coastal Plains, in L. F. Brown, ed., Proceedings Fourth 

Forum on Geology of Industrial Minerals, University of 

Texas, p. 23-34.

Cheney, T. M., 1957, Phosphate in Utah and an analysis of 

the stratigraphy of the Park City and Phosphoria Formations, Utah: Utah Geological and Mineralogical Survey 

Bulletin 59, 54 p.

Cheney, T. M., Sheldon, R. P., Waring, R. G., and Warner, 

M. A., 1954, Stratigraphy: sections of the Phosphoria Formation in Wyoming, 1951: U.S. Geological Survey Circular 

324, 22 p.

Cheney, T. M., Smart, R. A., Waring, R. G., and Warner, 

M. A. 1953, Stratigraphic sections of the Phosphoria Formation in Utah, 1949-51: U.S. Geological Survey Circular 

306, 40 p.

Clabaugh, P. S., 1946, Map of Permian phosphate deposits of 

Montana, Wyoming, Idaho, and Utah: U.S. Geological Survey Preliminary Strategic Map 3-198.

Coffman, J. S., and Service, A. L., 1967, An evaluation of 

the western phosphate industry and its resources (in five 

parts), 4, Wyoming-Utah: U.S. Bureau of Mines, Report 

of Investigations 6934, 158 p.

Cressman E. R., and Swanson, R. W., 1964, Stratigraphy and 

petrology of the Permian rocks of southwestern Montana: 

U.S. Geological Survey Professional Paper 313-C, p. 

C275-C569.

Cressman, E. R., Wilson, W. H., Tandy, C. W., and Garmoe, 

W. J., 1953, Stratigraphic sections of the Phosphoria Formation in Montana, 1949-50, pt. 1: U.S. Geological Survey 

Circular 302, 23 p.

46
Dames and Moore, Inc., 1978, Inventory and market analysis 

of the phosphate resources of Utah: U.S. Bureau of Land 

Management, 86 p.

Davidson, D. F., Smart, R. A., Pierce, H. W., and Weiser, 

J. D., 1953, Stratigraphic sections of the Phosphoria Formation in Idaho, 1949, pt.2: U.S. Geological Survey Circular 305, 28 p.

Davie, Michel, 1977, Geostatistical ore reserve estimation: 

Elsevier Scientific Publishing Co., New York, 364 p.

De Voto, R. H., and Stevens, D. N., eds., 1979, Uraniferous 

phosphate resources, United States and free world: U.S. 

Department of Energy publication GJBX-110(79), v. 1, 724

PFountain, R. C., and Hayes, A. W., 1979, Uraniferous phosphate resources of the Southeastern United States, in R. 

H. De Voto, and D. N. Stevens, eds., Uraniferous phosphate resources, United States and free world: U.S. Department of Energy publication GJBX-110(79), p. 65-122.

Furlow, J. W., 1969, Stratigraphy and economic geology of 

the eastern Chatham County phosphate deposit: Georgia 

Geological Survey Bulletin 82, 40 p.

Garrand Corp., 1974, Phosphate study Caribou National 

Forest, Idaho: Unpublished report, U. S. Department of 

Agriculture, Contract 50-820.

Gere, W. C., Schell, E. M., and Moore, K. D., 1966, Stratigraphic sections and phosphate analysis of Permian rocks 

in the Teton Range and parts of the Snake River and Gros 

Ventre Ranges, Idaho and Wyoming: U.S. Geological Survey Open-File Report, 71 p.

Gulbrandsen, R. A., 1974, Buddingtonite, ammonium feldspar, 

in the Phosphoria Formation, southeastern Idaho: U.S. 

Geological Survey Journal of Research, v. 2, no. 6, p. 693- 

697.

 1977, By-product resources in phosphate ore of southeastern Idaho [abs]: Geological Society of America Bulletin 

v. 9, no. 6, p. 728.

Gulbrandsen, R. A., and Krier, D. J., 1980, Large and rich 

phosphorus resources in the Phosphoria Formation in the 

Soda Springs area, southeastern Idaho: U.S. Geological 

Survey Bulletin 1496, 25 p.

Kimrey, J. 0., 1965, Description of the Pungo River Formation 

in Beaufort County, North Carolina: North Carolina Division Mineral Resources, Bulletin 79, 131 p.

Klepper, M. R., Honkala, F. S., Payne, 0. A., and Ruppel, 

E. T., 1953, Stratigraphic sections of the Phosphoria Formation in Montana, 1948: U.S. Geological Survey Circular 

260, 39 p.

Malde, H. E., 1959, Geology of the Charleston phosphate area, 

South Carolina: U.S. Geological Survey Bulletin 1079, 105

PMansfield, G. R., 1927, Geography, geology, and mineral resources of part of southeastern Idaho: U.S. Geological Survey Professional Paper 152, 409 p.

 1942, Phosphate resources of Florida: U.S. Geological 

Survey Bulletin 934, 82 p.

Mayberry, R. C., 1981, Phosphate reserves, supply and demand, Southeastern Atlantic coastal states, 1980-2000 

A.D.: Preprint, Society of Mining Engineers, American 

Institute Mining Engineering, Denver, Colorado, 

November 1981, 21 p.

McKelvey, V. E., 1972, Mineral resource estimates and public 

policy: American Scientist, v. 60, no. 1, p. 32-40.

McKelvey, V. E., Armstrong, F. C., Gulbrandsen, R. A., and 

Campbell, R. M., 1953a, Stratigraphic sections of the 

Phosphoria Formation in Idaho, 1947-48, pt. 2: U.S. 

Geological Survey Circular 301, 58 p.

McKelvey, V. E., Davidson, D. F., O'Malley, F. W., and 

Smith, L. E., 1953b, Stratigraphic sections of the Phosphoria Formation in Idaho, 1947-48, pt. 1: U.S. Geological 

Survey Circular 208, 49 p.

McKelvey, V. E., Smith, L. E., Hoppin, R. A., and 

Armstrong, F. C., 1953c, Stratigraphic sections of the 

Phosphoria Formation in Wyoming, 1947-48: U.S. Geological Survey Circular 210, 35 p.

McKelvey, V. E., and others, 1959, The Phosphoria, Park 

City, and Shedhorn Formations in the Western Phosphate 

Field: U. S. Geological Survey Professional Paper 313-A, 

p. A1-A47.

O'Malley, F. W., Davidson, D. F., Hoppin, R. A., and Sheldon 

R. P., 1953, Stratigraphic sections of the Phosphoria Formation in Idaho, 1947-48, pt. 3: U.S. Geological Survey 

Circular 262, 43 p.

Peterson, J. A., Gosman, R. F., and Swanson, R. W., 1954, 

Stratigraphic sections of the Phosphoria Formation in 

Montana, 1951: U. S. Geological Survey Circular 326, 27

PPirkel, E. C., 1957, Economic considerations of pebble phosphate deposits of Alachua County, Florida: Economic Geology, v. 52, p. 354-378.

Popoff, C. C., and Service, A. L., 1965, An evaluation of the 

western phosphate industry and its resources (in five 

parts), 2. Montana: U.S. Bureau of Mines, Report of Investigations 6611, 146 p.

Powell, J. D., 1974, Evaluation of phosphate resources in 

southeastern Idaho: Idaho Bureau of Mines and Geological 

Information Circular No. 25, 33 p.

Service, A. L., 1966, An evaluation of the western phosphate 

industry and its resources (in five parts), 3. Idaho: U.S. 

Bureau of Mines, Report of Investigations 6801, 201 p.

Service, A. L., and Petersen, N. S., 1967, An evaluation of 

the western phosphate industry and its resources (in five 

parts), Trends and Outlook: U.S. Bureau of Mines, Report 

of Investigations 6935, 123 p.

Service, A. L., and Pdpoff, C. C., 1964, An evaluation of the 

western phosphate industry and its resources (in five 

parts), 1. Introductory Review: U.S. Bureau of Mines, Report of Investigations 6485, 86 p.

Sheldon, R. P., 1963, Physical stratigraphy and mineral resources of Permian rocks in western Wyoming: U.S. 

Geological Survey Professional Paper 313-B, p. 49-272.

Sheldon R. P., Cressman, E. R., Carswell, L. D., and Smart, 

R. A., 1954, Stratigraphic sections of the Phosphoria Formation in Wyoming, 1952: U.S. Geological Survey Circular 

325, 24 p.

Sheldon, R. P., Waring, R. G., Warner, N. A., and Smart, 

R. A., 1953a, Stratigraphic sections of the Phosphoria Formation in Wyoming, 1949-50: U.S. Geological Survey Circular 307, 45 p.

Sheldon, R. P., Warner, N. A., Thompson, M. E., and Pierce, 

H. W., 1953b, Stratigraphic sections of the Phosphoria 

Formation in Idaho, 1949, pt. 1: U.S. Geological Survey 

Circular 304, 30 p.

47
Smart, R. A., Waring, R. G., Cheney, T. M., and Sheldon, 

R. P., 1954, Stratigraphic sections of the Phosphoria Formation in Idaho, 1950-51: U.S. Geological Survey Circular 

327, 22 p.

Smith, L. E., Hosford, G. F., Sears, R. S., Sprouse, D. P., 

and Steward, M. D., 1952, Stratigraphic sections of the 

Phosphoria Formation in Utah, 1947-48: U.S. Geological 

Survey Circular 211, 48 p.

Swanson, R. W., 1970, Mineral resources in Permian rocks 

of southwest Montana: U.S. Geological Survey Professional Paper 313-E, p. 661-777.

 1973, Geology and phosphate deposits of the Permian 

rocks in central-western Montana: U.S. Geological Survey 

Professional Paper 313-F, p. 779-833.

Swanson, R. W., Carswell, L. D., Sheldon, R. P., and Cheney, 

T. M., 1956, Stratigraphic sections of the Phosphoria Formation, 1953: U.S. Geological Survey Circular 375, 30 p.

Swanson, R. W., Cressman, E. R., Jones, R. S., and Replogle, 

B. K., 1953a, Stratigraphic sections of the Phosphoria Formation in Montana, 1949-50, pt. 2: U.S. Geological Survey 

Circular 303, 21 p.

Swanson, R. W., Lowell, W. R., Cressman, E. R., and 

Bostwick, D. A., 1953b, Stratigraphic sections of the Phosphoria Formation in Montana, 1947-48: U.S. Geological 

Survey Circular 209, 31 p.

U.S. Bureau of Mines, 1980, Mineral Commodity Summaries 

1981.

U.S. Bureau of Mines and U.S. Geological Survey, 1981, Principles of a resource/reserve classification for minerals: U.S. 

Geological Survey Circular 831, 5 p.

U.S. Geological Survey, 1982, Sedimentary phosphate resource 

classification system of the U.S. Bureau of Mines and the 

U.S. Geological Survey: U.S. Geological Survey Circular 

882, 9 p.

U.S. General Accounting Office, 1979, Phosphates: a case study 

of a valuable, depleting mineral in America: Report to the 

Congress of the United States, EMD-80-21, November 

30, 52 p.

Zellars, M. E., and Williams, J. M., 1978, Evaluation of the 

phosphate deposits of Florida using minerals availability 

system: U.S. Bureau of Mines Open-File Report 112-78, 

106 p.

48

6 U.S. GOVERNMENT PRINTING OFFICE: 1984 776-041/4031 REGION NO. 8