Phosphate 

Deposits

GEOLOGICAL SURVEY BULLETIN 1252-D

Phosphate 

Deposits

By V. E. McKELVEY

CONTRIBUTIONS TO ECONOMIC GEOLOGY

GEOLOGICAL SURVEY BULLETIN 1252-D

A summary of salient features of the 

geology of phosphate deposits, their 

origin, and distribution

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1967
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

For sale by the Superintendent of Documents, U.S. Qovernment Printing Office 

Washington, D.C., 20402 - Price 15 cents (paper cover)
CONTENTS

Page

Abstract ______________________________________ Dl

Introduction _. _ ________________________________ 2

Mineralogy ________.________________________________ 3

Geochemical distribution and behavior ___________________ 4

Phosphate deposits ______________________________ 9

Apatite deposits of igneous origin __________________ 10

Sedimentary phosphorite and weathering derivatives ______ 10

Guano and related deposits ______________________ 13

Guides to prospecting ____________________________ 14

Beneficiation, processing, and use _______________________ 15

Production __________________________________ 16

Reserves ____________________________________ 16

References cited _____________________.._________ 17

ILLUSTRATIONS

Page

FIGURE 1. Diagram showing surface currents in an idealized

ocean and areas of ascending nutrient-rich water __ D6 

2. Map showing phosphate deposits and distribution of 

upwelling water and related phenomena in modern 

oceans ____________________________ 7

in

CONTRIBUTIONS TO ECONOMIC GEOLOGY

PHOSPHATE DEPOSITS

By V. E. McKELVEY

Abstract

The earth's crust contains an average of about 0.27 percent P20s, most 

of which occurs in species of apatite, Ca 10 (P04,COs)6(F,Cl,OH)2. Common 

igneous rocks contain 0.005-0.4 percent P205, but some of the less common 

alkalic rocks contain 1 percent or more.

Apatite is slowly soluble in neutral or alkaline waters, and its solubility 

increases with increasing acidity. It may survive rock weathering to form 

a phosphate-rich residuum, but it breaks down under prolonged exposure. 

The PCX content of most river and lake waters ranges from about 0.01 

to 0.5 part per million (ppm), but may be much higher in soft acid waters 

and highly saline alkaline lakes. About one-sixth of the phosphate carried 

to the sea by runoff is in dissolved form. The ocean as a whole is nearly 

saturated with phosphate, but its distribution within the ocean is not uniform; deep cold waters contain nearly 0.3 ppm PO*, but warm surface 

waters contain only 0.01 ppm or less. Oceanic circulation brings phosphaterich water to the surface in several environments, and phosphate may be 

precipitated either inorganically or biochemically, as the pH and temperature increase near the surface. Such nutrient-rich waters support abundant 

plant and animal life, including large colonies of fish-eating seafowl.

Minable concentrations of phosphate, containing from 5 to 35 percent 

PzOa, are formed in all phases of the phosphate cycle. Primary deposits 

include igneous apatites, sedimentary phosphorites, and guano; secondary 

deposits form from each of these as the result of weathering. Apatites of 

igneous origin include hydrothermal veins and disseminated replacements, 

marginal differentiations near the boundaries of intrusions, and pegmatites, 

but the largest deposits are intrusive masses or sheets associated with 

carbonatite, nepheline-syenite, and other alkalic rocks. Most of the world's 

phosphate production comes from marine phosphorites, many of which are 

associated with black shale and chert. Secondary processes including diagenetic phosphatization of calcium carbonate and .interstitial precipitation, 

reworking by waves and currents, and weathering have often played a 

prominent part in forming deposits of minable quality. Guano deposits consist of natural accumulation of the excrement of bats or, more importantly, 

seafowl, altered to various degrees through dehydration, oxidation, and

Dl
D2 CONTRIBUTIONS TO ECONOMIC GEOLOGY

leaching. Phosphate leached from guano phosphatizes the underlying rocks 

in some areas, forming apatite where the host rock is limestone and forming 

aluminum- or aluminum-iron-phosphate minerals where the underlying rock 

is a silicate. Individual deposits of both igneous apatite and marine phosphorite commonly contain hundreds of millions or billions of tons. 

Guano deposits and phosphatized rock derived from them are typically 

much smaller, but a few contain millions of tons. World resources total 

hundreds of billions of tons.

INTRODUCTION

Phosphorus is a vital component of every living cell, and it 

plays several fundamental parts in metabolic processes (Albaum, 

1952). It is required for the synthesis of starch, is an integral 

part of nucleic acids, may be essential to photosynthesis, is a 

major constituent of bone and teeth, and is important in the 

shell or shell-forming process of many organisms. Among the 

essential plant nutrients, phosphorus is one of the less abundant 

in most soils, and its availability is one of the most critical factors controlling plant growth.

Most virgin soils in temperate climates contain enough phosphorus to support good crop production, but many soils in tropical climates are naturally deficient in phosphorus because it is 

leached out during the advanced stages of chemical weathering. 

Phosphorus can be added to deficient soils in the form of natural 

or artificial fertilizers, and for sustained good yields it must be 

added to all soils when they are cropped heavily for long periods. 

Phosphate fertilizers are used extensively now in the developed 

countries, but in many of the less developed countries their use 

must be much increased to bring crop production to acceptable 

levels. Annual consumption of phosphate, for example, is about 

20-50 pounds per capita in western European countries, but is 

under 2 pounds per capita in most of the less developed countries. Deficiencies in plant nutrients, including nitrogen and 

potash as well as phosphate, are now the major factors limiting 

crop production in the less developed countries (Parker and Nelson, 1966), and fertilizers will play a key role in the war on 

hunger in the years ahead.

In the United States about two-thirds of the phosphate consumed is used for agriculture; the remainder is used as chemicals for detergents and other cleaning compounds, leavening 

agents, food preservatives, insecticides, and many other products.

World demands for phosphate are expected to double within the 

next decade. Although known supplies are adequate to meet world 

needs for many years, additional sources are needed in regions 

that contain no known minable deposits, for phosphate rock is a
PHOSPHATE DEPOSITS D3

low-value commodity and transportation costs may add substantially to its price at the point of final use. New sources are especially needed in many developing" countries that have neither 

known minable deposits nor the ability to pay for imports.

Unlike many other minerals, phosphate rock has not been intensively prospected for in the past; and because it resembles 

limestone and other common rocks in appearance, it has not 

always been recognized even where it has been uncovered in the 

course of other work. Opportunities for new discoveries are good, 

therefore, and the increasing knowledge about the origin and 

occurrence of phosphate deposits should aid in prospecting. The 

salient features of the geology of phosphate deposits are summarized here as background and orientation for those newly 

concerned with the problem.

MINERALOGY

About 200 minerals are known that contain 1 percent or more 

P2O5.1 Most of the phosphorus in the earth's crust, however, 

occurs in species of the apatite group, Cai0 (P04 ,C03 ) 6 (F,Cl,OH) 2 

(Palache and others, 1951, p. 877; Altschuler and others, 1958; 

Deer and others, 1962, p. 324). The structure of apatite favors a 

wide variety of minor substitutions (McConnell, 1938). For example, small amounts of V04 , As204, S02 , S04, or C03 may substitute for equivalent amounts of P04 ; the F position may be partly 

or completely occupied by F, Cl, or OH; and minor amounts of 

Mg, Mn, Sr, Pb, Na, U, Ce, and Y and other rare earths may substitute for Ca. Cationic replacements involving loss or gain of 

valence may be compensated for by anionic replacements of opposite nature. The composition of apatite deposits, therefore, may 

change on exposure to solutions of different composition from 

those from which they were deposited. One characteristic change is 

the substitution of fluorine for hydroxyl in teeth and bone, which 

results in a decrease in the solubility of apatite. It is this phenomenon that constitutes the basis for fluoridating water to prevent 

dental caries and that was utilized in demonstrating that the 

bones of "Piltdown Man" were of modern rather than ancient age 

(Oakley, 1955; Weiner and others, 1953).

Apatite is the principal primary mineral, but a number of others 

are common in deposits formed during weathering of phosphate

*In the trade the phosphate content of phosphate rock and fertilizer is commonly reported as Ca3(PO4 >2, known as bone phosphate of lime (B.P.L.). To convert PjOs to 

B.P.L., multiply percentage P2Os by 2.18. To convert to P, multiply percentage P2Os 

by 0.436.
D4 CONTRIBUTIONS TO ECONOMIC GEOLOGY

rock and guano.2 Examples are brushite (HCaP04 2H2 0), monetite (HCaP04 ), whitlockite (/3-Ca3 (P04 ) 2 ), crandallite (CaAL- 

(P04 ) 2 (OH) 5-H2 0), wavellite (A13 (OH) 3 (P04 )2-5H2 0), taranakite 

(K2A16 (P04 ) 6 (OH) 2 -18H2 0), millisite (Na,K)CaAl6 (P04 ) 4 (OH) s3H2 0), variscite (A1P04 -2H2 0), and strengite (FeP04-2H2 0).

GEOCHEMICAL DISTRIBUTION AND BEHAVIOR

The earth's crust contains about 0.27 percent P2 05 . Common 

igneous rocks, such as granite, diorite, gabbro, and peridotite, 

contain only from about 0.005 to 0.4 percent P2 05 , but some of 

the less common alkalic rocks, such as ijolite and turjaite, can 

contain more than 1 percent. Variations in phosphate content of 

igneous rocks generally parallel those of ilmenite and magnetite.

Apatite is slowly soluble in neutral or alkaline waters, and its 

solubility increases with increasing acidity, decreasing hardness, 

and decreasing temperature. Apatite may survive rock weathering for a time to form a phosphate-rich residuum, but it breaks 

down under prolonged exposure. Some of it may be redeposited 

locally. In high-calcium soils and rocks, apatite is again the mineral formed. Where the terrane consists of igneous rocks, aluminum or iron phosphates such as variscite or strengite are the 

secondary minerals (Hutchinson, 1952). In subtropical or tropical climates, where clay minerals and hydroxides are the end 

products of weathering, aluminum phosphates such as wavellite 

are formed.

Most phosphorus is carried to the sea as phosphate minerals 

or adsorbed on iron or aluminum hydroxides or clay, but some 

is carried in particulate or dissolved organic compounds, and 

about one-sixth of the total is carried in solution. The P04 content of most river and lake waters ranges from about 0.01 to 0.5 

part per million (ppm). Soft acid waters, such as those in parts 

of the Florida Peninsula, may contain a few parts per million, 

however, and the highly saline alkaline lake waters (such as 

Searles Lake, Calif.) contain 200-900 ppm.

The ocean as a whole is nearly saturated with phosphate, and 

an amount equivalent to that brought by rivers is precipitated 

almost continuously (Dietz and others, 1942; Kramer, 1964a, 

1964b; Roberson, 1966; Sillen, 1961; Smirnov and others, 1958).

2 The term "phosphate rock" is loosely applied to rocks of any origin that contain more 

than about 20 percent P2Os. The term "phosphorite" is equivalent in meaning, but is 

commonly applied only to phosphate rocks of marine origin. "Guano" is the term applied 

to accumulations of animal excrement, altered to various degrees through hydration, oxidation, and leaching.
PHOSPHATE DEPOSITS D5

The phosphate content of the ocean is by no means uniform, 

however; deep cold waters contain nearly 0.3 ppm PCX, but warm 

surface waters contain only 0.01 ppm or less. Oceanic circulation (mainly a reflection of atmospheric circulation, brought 

about by solar heating combined with the rotation of the earth) 

deep plows the sea and brings these phosphate-rich waters to 

the surface in several environments (Sverdrup and others, 1942, 

p. 140, 241, 246, 785; Brongersma-Sanders, 1948).

In an idealized ocean (see Fleming, 1957), the main elements 

of the current system consist of a large circulating gyral in each 

hemisphere (fig. 1); water cooled in polar latitudes moves toward 

the equator along the east side of the ocean, and water warmed 

in equatorial latitudes moves poleward along the west side. In 

this system, cold nutrient-rich waters are brought to the surface in four situations:

1. Where a current diverges from a coast, or where two currents 

diverge from each other such as along the equatorial currents and countercurrent (divergence upwelling). The effects 

of currents moving toward the equator in bringing cold phosphate-rich water along the coast are abetted by the seaward 

movement of coastal surface water that results from the combined effects of prevailing wind and Coriolis force; for as the 

surface water moves seaward, deep cold water wells up to 

replace it.

2. Where two currents meet to produce turbulence.

3. Along the west edge of poleward-moving density currents such 

as the Gulf Stream, where heavy and usually cold water lies 

to the left of the observer looking in the direction of flow in 

the northern hemisphere and lies to the right in the southern 

hemisphere (dynamic upwelling). In middle and northern latitudes, a cool coastal countercurrent, such as that along the 

Northeastern United States, is an accompanying feature (Sverdrup and others, 1942, p. 676).

4. In upper latitudes where highly saline water from the tropics

tends to sink as a result of winter cooling (convection). 

Each of these processes may take place in locations besides those 

shown in figure 1. For example, upwelling may take place wherever a prevailing wind or current moves surface water away 

from a coast, and some convection as a result of increase in density of surface water with winter cooling may take place wherever there are pronounced seasonal variations in temperature.
D6 CONTRIBUTIONS TO ECONOMIC GEOLOGY

30

Equatorial xn^_g_countercurrent > <»~»"

South equatorial current

90° 

EXPLANATION

x x

Turbulent mixing Upwellmg caused by divergence

Dynamically caused upwellmg

Mixing as a result of 

winter cooling

FIGURE 1. Surface currents in an idealized ocean, showing areas of 

ascending nutrient-rich water.

Pronounced climatic, biologic, and geologic effects accompany 

upwelling, especially where it is produced by divergence in coastal 

areas (fig. 2). The presence of cold waters along coasts produces
PHOSPHATE DEPOSITS D7

180° 160° 140° 120°100°80°60°40°20°0°20°40°60° 80° 10_0_° ._ 120° ^_ 140° 160° 180°

\ \ \ \ \ \ \

A Red water, no mass mortality "

X Red water, coinciding with mass mortality

A Mass mortality probably coinciding with red water

0 Diatom ooze or mud (broad bands of diatom

ooze in Arctic and Antarctic regions not

indicated)

... Upwellirg water 

._ Phosphate deposits

/80

180" 160° 140° 120°100°8Q° 60 040 0 20°0 0 20 0 40°60 0 80° 100° 120° 140° 160° 180°

FIGURE 2. Distribution of upwelling water and related phenomena in modern oceans. Modified from Brongersma-Sanders 

(1957) to include data on the distribution of phosphate deposits.

coastal fogs and humid-air deserts, such as those of northern 

Chile and southwest Africa. The nutrient-rich waters that lie 

alongside these deserts are the lushest gardens of the sea, for 

the upwelling cold waters there support tremendous quantities 

of organisms, with diatoms and other phytoplankton at one end 

of the food chain, and fish, whales, and fish-eating seafowl at the 

other. Blooms of dinoflagellates (red tides) and diatoms are 

characteristic biologic phenomena in upwelling areas, as are the 

mass mortalities of fish that accompany red tides and may be a 

consequence of them (Brongersma-Sanders, 1948, 1957). Most 

of the large accumulations of guano are formed by seafowl colonies feeding in these waters, and it is the extremely dry climate 

created by upwelling that makes the preservation of guano possible (Hutchinson, 1950).
D8 CONTRIBUTIONS TO ECONOMIC GEOLOGY

Concentrations of nutrients and accompanying organic 

growths are also found near the mouths of some large rivers, as 

well as in estuaries in which the outflow of surface water is replaced by a countercurrent of sea water. The decaying remains 

of organisms in such estuaries sink from outflowing surface 

water, and their decay products are trapped in the system by 

inflowing sea water; nutrients accumulate as a result of this 

process, and such estuaries often contain a higher phosphate 

content than adjacent river or sea water. The same process may 

also tend to enrich the nutrient content of upwelling waters 

(Redfield and others, 1963, p. 60-66).

The solubility of phosphate in upwelling waters decreases as 

the temperature and pH increase near the surface (Kazakov, 

1937; Kramer, 1964b; Roberson, 1966), and apatite may be precipitated by organic or inorganic processes. Organic skeletons 

and excrement contribute phosphate in concentrated form to the 

sea bottom, and organic tissues may carry phosphate to the bottom in moderately soluble organic compounds, from which it 

may be released before or after burial (van Vloten, 1955, p. 

141; Bushinski, 1964). Apatite, generally as carbonate-fluorapatite but under special conditions perhaps also as hydroxyapatite 

(Kramer, 1964b), may also be precipitated from sea water by 

inorganic processes; a common textural type of phosphorite composed of unaggregated microcrystalline apatite may have formed 

in this way (Gulbrandsen, 1960, p. 119).

Fossil shells, such as gastropods and pelecypods, that were 

nonphosphatic during the life of the organism, are sometimes 

found to be composed of apatite, giving clear evidence of replacement prior to or after burial. Apatite replacement of calcite has been demonstrated experimentally and has been suggested by Ames (1959) to be the main process .by which marine 

phosphorite is deposited. Evidence for its operation on a large 

scale, however, is lacking in most deposits. Interstitial accretion 

probably is a quantitatively more important diagenetic process 

and may be one of the processes by which the pellets and similar 

aggregates that are common in many phosphorites are first 

formed (Sheldon, 1957, p. 123; Bushinski, 1964; Cressman and 

Swanson, 1964, p. 375; D'Anglejan, 1967).

Although biologic processes are important in enriching the nutrient content of upwelling waters and in precipitating phosphate, they operate within and are basically controlled by the 

physical and chemical conditions of the system. The phosphorites and their lateral equivalents in the environment of strong 

upwelling black shale, chert, dolomite, limestone, and evapo-
PHOSPHATE DEPOSITS D9

rites are thus depositional products from moving masses of 

water that change in composition as the result of physical, chemical, and biologic processes (Gulbrandsen, 1960).

Submarine volcanism has been suggested as a local source of 

the fluorine, phosphorus, and silica of marine phosphorites (Taliaferro, 1933; Mansfield, 1940; Gibson, 1967). No doubt volcanic 

activity does contribute to the concentration of these and other 

elements in sea water, but their present distribution in sea 

water is not controlled by volcanic activity, and the processes 

described yield deposition from sea water of normal composition 

(McKelvey, Swanson, and Sheldon, 1953, p. 57; McKelvey and 

others, 1959, p. 27).

PHOSPHATE DEPOSITS

Minable concentrations of phosphate are formed in all phases 

of the phosphate cycle through the processes just described. Ordinarily these processes merely concentrate phosphorus a few 

times over its crustal average, but when they are permitted to 

operate under unusually favorable conditions, they may yield 

concentrations 100-125 times those of the crustal average. Particularly effective in forming rich deposits are two or more of 

these concentrating processes acting in sequence. For example, 

the oceanographic processes that result in upwelling bring phosphate-rich waters to the zone of photosynthesis where biologic 

or chemical processes may precipitate phosphate and form concentrations of a few percent P20S . Biologic, chemical, and 

mechanical processes may subsequently upgrade these deposits 

by oxidizing carbonaceous matter, forming pellets or nodules 

through diagenetic addition or reorganization of phosphatic material within the sediment, and winnowing away lighter and 

smaller particles, such as carbonaceous matter and clay (Altschuler and others, 1964). The phosphorites that result from 

these successive processes may contain as much as 25-30 percent P2OS . They, along with rocks containing lesser concentrations, may be upgraded still further by weathering; in fact, the 

bulk of the world's production of phosphate, particularly rock 

containing more than'30 percent P2 05 , comes from deposits that 

have been enriched by weathering.

The principal kinds of phosphate deposits (McKelvey, Cathcart, Altschuler, Swanson, and Buck, 1953), classed according to 

the process responsible for their primary localization, are igneous apatites, sedimentary phosphorites, and guano. Secondary 

deposits form from each of these as the result of weathering.
DIG CONTRIBUTIONS TO ECONOMIC GEOLOGY

APATITE DEPOSITS OF IGNEOUS ORIGIN

Apatite deposits of igneous origin occur as intrusive masses 

or sheets, as hydrothermal veins or disseminated replacements, 

as marginal differentiations along or near the boundaries of intrusions, or as pegmatites.

The intrusive masses are the largest of these deposits. They 

are commonly associated with alkalic igneous rock complexes, 

many of which such as those in Africa, Brazil, and Sweden 

are associated with rift valley structures. Carbonatite, ijolite, 

nepheline-syenite, and pyroxenite are common members of the 

rock assemblage. Many of these complexes have a ringlike structure, with carbonatite as the central core CPecora, 1956). Apatite or apatite-magnetite deposits occur as inclined sheets, in 

some places roughly interleaved around the core. Their thickness 

ranges from tens to hundreds of feet, and some are traceable for 

hundreds of feet or even a few miles. Their P205 content is as 

much as 36 percent, and lower grade deposits rich in magnetite 

are easily beneficiated. Deep weathering, as at Sukulu, Uganda, 

may yield a phosphate-rich residuum at the surface during decomposition of calcite, dolomite, and other more soluble minerals. 

Alkalic complexes known to contain apatite or to be favorable 

for its occurrence are much more numerous than was believed 

prior to World War II. Some of the largest deposits are found 

in the Kola Peninsula, U.S.S.R. (Fiveg, 1937), in eastern Uganda 

(Davies, 1947), and in Palabora in the Eepublic of South 

Africa (Russell and others, 1954).

Most of the other apatite deposits are either less extensive or 

lower in quality and hence of less economic importance. Examples include the disseminated deposits of hydrothermal apatiteilmenite (nelsonite) in Nelson County, Va. (Ross, 1941), the apatite veins in Norway, the apatite-magnetite marginal deposits 

associated with alaskite in the eastern Adirondacks, and the 

apatite-pegmatite deposits of southern Ontario.

SEDIMENTARY PHOSPHORITE AND WEATHERING DERIVATIVES

Most of the world's phosphate production comes from marine 

phosphorites. The richest and largest of these form at low latitudes (Sheldon, 1964b) in areas of upwelling associated with 

divergence, chiefly along the west coasts of the continents or, in 

large mediterranean seas, along the equatorial side of the basin. 

Lesser but significant concentrations form along the west sides 

of poleward-moving warm currents along the eastern coasts of 

continents (figs. 1, 2).

The rock assemblage in the cold-current environment is the 

product of deposition on a shoaling bottom over which shoreward
PHOSPHATE DEPOSITS Dll

moving waters are progressively warmed (Kazakov, 1937; Macpherson, 1945, p. 34-41). The typical lateral sequence of rocks, 

in a shoreward direction, consists of dark carbonaceous shale, 

phosphatic shale, phosphorite, and dolomite; chert or diatomite; 

several facies of carbonate rock; and saline deposits and red or 

light-colored sandstone or shale (McKelvey and others, 1959). 

These rocks were deposited synchronously, and they grade laterally into each other or intertongue. Because the environments in 

which these rocks are deposited shift laterally with epeirogenic 

movements of the sea bottom, the rocks are found in vertical 

sequence in nearly this same or reverse order. The thickest accumulations of phosphorite form in areas of geosynclinal subsidence, and in such areas phosphorite is generally associated with 

carbonaceous shale and chert (McKelvey, Swanson, and Sheldon, 

1953). The phosphorite is typically carbonaceous and pelletal, 

but nodules as well as skeletal matter and phosphatic shells may 

be present in lesser quantities. Individual beds may be several 

feet thick, can contain 30 percent or more P20S , and extend over 

hundreds of square miles. Phosphorites formed on adjacent 

platforms or stable areas are generally associated with cherty carbonate rock and light-colored sandstone or shale. The phosphorite is not appreciably carbonaceous and is likely to contain phosphatized shells as well as naturally phosphatic organic remains. 

It may consist largely of nodules, but phosphatic sandstone is 

a common textural type. Individual beds are generally only a 

few feet thick and contain less than 30 percent P205 . Thicker 

and richer deposits may occur locally but are highly lenticular. 

In Israel (Bentor, 1953) and Egypt (Youssef, 1965) such deposits are localized in synclines that evidently represented shallow depressions at the time of deposition. Examples of phosphorites deposited from upwelling associated with divergence are 

found in the Permian Phosphoria Formation in Idaho and adjacent States (Mansfield, 1927; Emigh, 1958; McKelvey and others, 1959; Sheldon, 1963; Cressman and Swanson, 1964), Miocene Monterey Formation of California (Gower and Madsen, 1964; 

Dickert, 1966), Mississippian and Triassic deposits of northern 

Alaska (Patton and Matzko, 1959), Jurassic La Caja and La 

Casita Formations in north-central Mexico (Rogers and others, 

1961), Miocene deposits in the Sechura Desert of Peru (Harrington and others, 1966), and extensive deposits of Cretaceous 

and Eocene age in western and northern Africa and the Middle 

East (British Sulphur Corporation, 1964). Phosphate deposits 

are abundant on the present sea bottom in most areas of upwelling; some of those off the California coast are being consid-
D12 CONTRIBUTIONS TO ECONOMIC GEOLOGY

ered for mining by dredging (Dietz and others, 1942; Emery, 

1960; Mero, 1965).

Phosphate deposits that formed in the warm-current environment along the eastern coasts of the continents generally consist 

of phosphatic limestone or sandstone. Chert, black shale, and salines are not associated with these deposits, and they are less 

extensive and lower in grade than the deposits formed from 

cold currents. In fact, only where these deposits have been either 

extensively reworked by submarine currents and (or) subjected 

to weathering are they rich enough to be mined, and even then 

most of them need to be beneficiated artificially. Examples include deposits in the Pliocene Bone Valley Formation of Florida 

(Cathcart, 1963; Altschuler and others, 1964), the Miocene of 

south-central Georgia and northern Florida (Sever and others, 

1967), the Miocene Pungo River Formation of North Carolina 

(Brown, 1958; Kimrey, 1965), and the Upper Cretaceous Gramame Formation near Recife, Brazil (Harrington and others, 

1966). Phosphate in this general environment may be the product 

of dynamic upwelling or the cool countercurrent associated with 

warm density currents (compare Gibson, 1967, p. 644), but the 

distribution of some of the deposits suggests estuarine deposition 

(Altschuler and others, 1964; Bushinski, 1964) and may have 

resulted from processes of estuarine circulation and nutrient 

enrichment (Redfield and others, 1963; Pevear, 1966).

Secondary processes have played a prominent part in concentrating the richest of the marine deposits. For example, the highest grade phosphate beds in the Phosphoria Formation appear 

to have been extensively washed by marine currents; in addition, leaching of carbonates and sulfides together with oxidation 

of carbonaceous matter has raised their P20S content from about 

27-30 percent at depths of a few hundred feet to 32-35 percent 

near the surface. Similarly, the Bone Valley deposits originated 

through submarine reworking of phosphatic residuum developed 

during deep weathering of phosphatic marls in the Miocene Hawthorn Formation; leaching related to recent weathering has upgraded some of the deposits still further (Altschuler and others, 

1964). The common occurrence of phosphorite at unconformities 

also reflects the combined effects of weathering and submarine 

reworking (Goldman, 1922).

Weathering in the present cycle accounts for the formation of 

enriched residual and replacement deposits from phosphatic deposits not otherwise minable. The Tennessee "brown rock" phosphate deposits consist of present-day residuum developed 

through decomposition of phosphatic limestones of Ordovician
PHOSPHATE DEPOSITS D13

age (Smith and Whitlatch, 1940). The "river pebble" deposits 

prominent in the early history of phosphate mining in Florida 

and South Carolina are mostly placers formed by alluvial concentration of phosphatic pebbles eroded from the phosphatic formations of the adjacent terrain.

The Tennessee "white rock" and Florida "hard rock" deposits 

were formed by redeposition of phosphate derived from the decomposition of apatite under more advanced weathering. The 

same decomposition-phosphatization process accounts for the formation of calcium aluminum phosphate and aluminum phosphate 

in the "leached zone" of the Bone Valley field and the deeply 

Weathered Cretaceous and Eocene deposits of west Africa (Capdecomme, 1953).

In addition to the marine phosphorites described above, carbonate-fluorapatite has been found recently in thin lake beds of 

Eocene age in Wyoming (Love, 1964), and noncommercial deposits of sodium phosphate minerals are found locally in or 

associated with saline deposits formed in the highly alkaline 

saline lakes (Fahey, 1962). Glauconite, associated with the marine phosphorites in many places, contains from 1 to 5 percent 

P2 05 , and because it also contains potash it has had some use 

as a fertilizer (Mansfield, 1922). Some sedimentary iron ores 

contain a few percent P2 05 (Geijer, 1962; Davidson, 1963), and 

the basic slag (Thomas meal) made from these ores (as well as 

that made from apatite-rich magnetite deposits of igneous origin) contains 8 percent or more P2 05 and is locally used as a 

fertilizer.

GUANO AND RELATED DEPOSITS

Most of the large accumulations of guano are formed at the 

surface by seafowl, but smaller quantities are formed by bats 

and to a lesser extent by other cave-dwelling mammals and birds 

(Hutchinson, 1950). The bat guanos are most abundant in the 

cave districts of temperate and tropical regions. Although many 

bat-guano deposits have been found and mined, most of them 

have been measured in hundreds or thousands of tons, and only 

sporadic production is obtained from them now. Seafowl deposits are mainly confined to islands and coastal regions in low 

latitudes. The largest lie along the west coasts of Lower California, South America, and Africa, and on islands near the equatorial currents. Many used to be several hundred thousand tons 

in size, and although most of the fossil accumulations have been 

mined out, production from the current crop is continuing in 

some areas.
D14 CONTRIBUTIONS TO ECONOMIC GEOLOGY

Fresh seafowl droppings contain about 22 percent N and 4 

percent P2 05 . Decomposition proceeds rapidly, and the phosphate content increases as the nitrogen (and total organic matter) decreases. Modern guano contains 10-12 percent P2O5, but 

leached guano contains 20-32 percent. The mineralogy of guano 

is complex. Slightly decomposed deposits contain soluble ammonium and alkali oxalates, sulfates, and nitrates, and a variety 

of magnesium and ammonium-magnesium phosphates. Largely 

decomposed guano consists chiefly of calcium phosphates (for 

example, monetite or whitlockite).

In areas where rainfall, however slight, is a normal event, 

the soluble phosphates of guano are carried to underlying rocks, 

where they may be deposited as cavity fillings or replacements. 

Through this process, phosphate from guano has accumulated 

over long periods of geologic time, and it has formed some comparatively large deposits. For example, reserves on Nauru, an 

island in the equatorial region of the western Pacific Ocean, were 

originally about 90 million tons of rock averaging about 39 percent P205 (Hutchinson, 1950, p. 221). The mineralogy of phosphatized rocks derived from guano depends on the composition 

of the host rock. Where it is limestone, as on many of the coral 

atolls, the phosphate mineral is apatite; but where the underlying rock is a silicate, as in islands of volcanic origin, the phosphate minerals are aluminum or aluminum-iron phosphates.

GUIDES TO PROSPECTING

The geologic relations described above provide the basis for 

prospecting for new deposits, at least to the extent of defining 

provinces and terranes worthy of .field reconnaissance. The relation of alkalic rocks to the rift zones helps focus on areas favorable for their occurrence, and the identification of individual 

alkalic complexes defines specific targets worthy of more detailed 

examination and exploration. The location of areas of modern 

up welling (and associated features) is a prime clue to the presence of phosphorite on the modern sea bottom and in adjacent 

coastal plain sediments. Probably not many nitrogenous guano 

deposits remain to be found, but known deposits and oceanographic features point to areas in which phosphatized rocks may 

occur. In older sedimentary rocks the presence of black shale and 

chert the companions of phosphorite in geosynclinal deposits 

are helpful clues. Other members of the phosphorite family (red 

beds and salines, for example) may be used to define favorable 

areas through regional lithofacies analysis, and, perhaps most 

important, the presence of phosphate even in small amounts may 

identify horizons that elsewhere contain richer primary or se-
PHOSPHATE DEPOSITS D15

condary deposits (McKelvey, 1963; Sheldon, 1964a). Paleogeographic and paleoclimatologic reconstruction, based on paelomagnetic and other studies, may make it possible to identify probable areas of upwelling in low latitudes and thus to define potential phosphogenic provinces (Sheldon, 1964b).

Because nearly all marine phosphorites contain from 0.005 to 

0.02 percent U, they are radioactive enough to be identified in 

gamma-ray well logging and, under favorable circumstances, by 

aerial radiometric reconnaissance. With experience, one can recognize the phosphate rock itself by its resinous luster and its 

white "bloom" on the surface of weathered outcrops or fragments. A few drops of concentrated hydrochloric acid on rocks 

containing more than 5-10 percent P2 05 will produce a white 

spot, the density of which is roughly proportional to the phosphate content (Gardner, 1944). A simple chemical test is also 

available for semiquantitative analysis in the field (Shapiro, 

1952).

BENEFICIATION, PROCESSING, AND USE

Because apatite is slightly heavier than some of the impurities commonly associated with it and because the "matrix" of 

many phosphorites is finer grained than the phosphatic particles, many impure phosphatic rocks can be upgraded by inexpensive washing or other hydraulic techniques. Noncarbonaceous 

deposits are effectively upgraded by flotation (Ruhlman, 1958; 

Service and Popoff, 1964).

A relatively small part of the phosphate mined is used directly 

as a fertilizer, and on acid soils in tropical or subtropical regions 

this may be the most efficient means of application. For most 

soils and for chemical uses, phosphate rock must be processed 

to a more soluble or purer state (Waggaman and Ruhlman, 

1960). Three basic methods are used for this purpose: acidulation, electric furnace reduction to the elemental state, and fusion. Rock containing 31 percent or more P2O5 is generally required in acid treatment; depending on the kind and amount of 

acid used, a wide variety of products are made by acidulation, 

including superphosphate (a mixture of phosphate rock and sulfuric acid containing 16-20 percent P2 05 ), phosphoric acid, triple 

superphosphate (a mixture of rock and phosphoric acid containing 42-48 percent P2 05 ), and ammonium and potassium phosphates (made by combining phosphoric acid with potash or ammonia). Feed for the electric furnace contains about 24 percent 

P2 05 ; the elemental phosphorus produced by this method is used 

mainly for chemicals, prominent among which are detergents 

and other cleansing products. Fusion methods combine high-
D16 CONTRIBUTIONS TO ECONOMIC GEOLOGY

grade phosphate rock with alkali salts, silica, or magnesium silicate and generally produce a partly defluorinated, moderately 

soluble slag usable as fertilizer without further treatment.

Most phosphate rock contains from 3 to 4 percent F; and much 

of it contains uranium, rare earths, and other minor elements 

(Davidson and Atkin, 1953; McKelvey and Carswell, 1956; Altschuler and others, 1958; Sheldon, 1959; Gulbrandsen, 1966; 

Altschuler and others, 1967). Some fluorine is now recovered, 

mostly for fluorosilicates used in insecticides, and processes are 

under development for manufacture of calcium fluoride. Uranium and vanadium have been recovered as a byproduct of phosphoric acid manufacture at times, and small quantities of other 

metals are recovered in ferrophosphorus, a byproduct of the production of elemental phosphorus. Some of the black shales associated with marine phosphorites contain potentially recoverable 

amounts of vanadium, zinc, and other metals (Gulbrandsen, 1960, 

1966; Love, 1961; Lotspeich and Markward, 1963).

PRODUCTION

United States production of phosphate rock in 1966 was 39 

million short tons, of which about 50 percent was used in agriculture, 25 percent in industry, and the remainder exported or 

stocked (Lewis, 1967). About 74 percent came from the Florida 

field, 11 percent from Tennessee, and 15 percent from Idaho and 

adjacent States. Some 40 countries in the same year contributed 

to world production, which totaled about 98 million tons. Of 

this, about 18 million came from Africa, 32 million from 

U.S.S.R. and Europe, 5 million from Asia, and 3 million from 

Oceania. Total production from Latin America, Asia and Africa 

(except Morocco, Senegal, Republic of South Africa, Togo, 

Tunisia, and Egypt) amounted to about 19 million tons, or less 

than one-fifth of the total.

About 74 percent of the world total was produced from marine 

phosphorites and their weathering derivatives, 24 percent from 

igneous apatite deposits, and 2 percent from guano or phosphatized rock derived from guano.

RESERVES

World reserves were estimated in 1953 (Jacob, 1953) to be 

on the order of 45 billion tons, but since then large deposits 

have been discovered in North Carolina, Georgia, Alaska, Baja 

California, Peru, Venezuela, Brazil, the Republic of South Africa, 

Uganda, several countries of west and north Africa, Israel, Jordan, China, and the U.S.S.R.; promising new prospects have also
PHOSPHATE DEPOSITS D17

been found in a number of other countries. Moreover, advances 

in beneficiation and processing technology now make it possible 

to recover economically many lower grade deposits that were 

formerly not considered minable. Although they are irregularly 

distributed, resources of phosphate rock in presently known deposits that are within reach of developed technology are probably 

on the order of hundreds of billions of tons.

REFERENCES CITED

Albaum, H. G., 1952, The role of phosphorus in the metabolism of plants, in

Wolterink, L. F., ed., The biology of phosphorus: East Lansing, Michigan

State Coll. Press, p. 37-75. 

Altschuler, Z. S., Berman, Sol, and Cuttitta, Frank, 1967, Rare earths in

phosphorites geochemistry and potential recovery, in Geological Survey

research 1967: U.S. Geol. Survey Prof. Paper 575-B, p. B1-B9. 

Altschuler, Z. S., Cathcart, J. B., and Young, E. J., 1964, Geology and

geochemistry of the Bone Valley Formation and its phosphate deposits:

Geol. Soc. America ann. mtg., Miami Beach 1964 Guidebook, field

trip 6, 68 p. 

Altschuler, Z. S., Clarke, R. S., Jr., and Young, E. J., 1958, Geochemistry

of uranium in apatite and phosphorite: U.S. Geol. Survey Prof. Paper

314-D, p. 45-90. 

Ames, L. L., Jr., 1959, The genesis of carbonate apatites: Econ. Geology,

v. 54, no. 5, p. 829-840. 

Bentor, Y. K., 1953, Relations entre la tectonique et les depots de phosphates

dans le Neguev Israelien: Internat. Geol. Gong., 19th, Algiers 1952,

Comptes rendus, sec. 11, pt. 11, p. 93-101. 

British Sulphur Corporation, 1964, A world survey of phosphate deposits

[2d ed.] : London, The British Sulphur Corp., Ltd., 206 p. 

Brongersma-Sanders, Margaretha, 1948, The importance of upwelling water

to vertebrate paleontology and oil geology: Koninkl. Nederlandse Akad.

Wetensch., Natuurk., Verh., 2d sec., pt. 45, no. 4,112 p. 

 1957, Mass mortality in the sea, in Hedgpeth, J. W., ed., Treatise

on marine ecology and paleoecology, v. 1, Ecology: Geol. Soc. America

Mem. 67, p. 941-1010.

Brown, P. M., 1958, The relation of phosphorites to ground water in Beaufort County, North Carolina: Econ. Geology, v. 53, no. 1, p. 85-101. 

Bushinski, G. I., 1964, On shallow water origin of phosphorite sediments, in

van Straaten, L. M. J. U., ed., Deltaic and shallow marine deposits 

Proceedings of the Sixth International Sedimentological Congress, The

Netherlands and Belgium 1963: Amsterdam, Elsevier Publishing Co.,

Developments in Sedimentology, v. 1, p. 62-70. 

Capdecomme, Laurent, 1953, Etude mineralogique des gites de phosphates

alumineux de la region de Thies (Senegal): Internat. Geol. Cong., 19th,

Algiers 1952, Comptes rendus, sec. 11, pt. 11, p. 103-117. 

Cathcart, J. B., 1963, Economic geology of the Plant City quadrangle,

Florida: U.S. Geol. Survey Bull. 1142-D, 56 p. 

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

the Permian rocks of southwestern Montana: U.S. Geol. Survey Prof.

Paper 313-C, p. 275-569.
D18 CONTRIBUTIONS TO ECONOMIC GEOLOGY

D'Anglejan, B. F., 1967, Origin of marine phosphorites off Baja California,

Mexico: Marine Geology, v. 5, no. 1, p. 15-44. 

Davidson, C. F., 1963, Phosphate deposits of Precambrian age: Mining Mag.,

v. 109, no. 4, p. 205-208.

Davidson, C. F., and Atkin, D., 1953, On the occurrence of uranium in phosphate rock: Internat. Geol. Gong., 19th, Algiers 1952, Comptes rendus,

sec. 11, pt. 11, p. 13-31. 

Davies, K. A., 1947, The phosphate deposits of the Eastern Province, Uganda:

Econ. Geology, v. 42, no. 2, p. 137-146. 

Deer, W. A., Howie, R. A., and Zussman, J., 1962, Rock-forming minerals,

v. 5, Non-silicates: New York, John Wiley & Sons, 371 p. 

Dickert, P. F., 1966, Tertiary phosphatic facies of the Coast Ranges, in

Bailey, E. H., ed., Geology of northern California: California Div. Mines

and Geology Bull. 190, p. 289-304. 

Dietz, R. S., Emery, K. O., and Shepard, F. P., 1942, Phosphorite deposits

on the sea floor off southern California: Geol. Soc. America Bull., v. 53,

no. 6, p. 815-848. 

Emery, K. O., 1960, The sea off southern California a modern habitat of

petroleum: New York, John Wiley & Sons, 366 p. 

Emigh, G. D., 1958, Petrography, mineralogy and origin of phosphate

pellets in the Phosphoria formation: Idaho Bur. Mines and Geology

Pamph. 114, 60 p. 

Fahey, J. J., 1962, Saline minerals in the Green River formation: U.S. Geol.

Survey Prof. Paper 405, 50 p. 

Fiveg, M. P., 1937, The apatite deposits of the Khibinian Tundras: U.S.S.R.,

Sci. Inst. Fertilizers and Insectofungicides Trans., no. 142, p. 8-21. 

Fleming, R. H., 1957, General features of the oceans, in Hedgpeth, J. W., ed.,

Treatise on marine ecology and paleoecology, v. 1, Ecology: Geol. Soc.

America Mem. 67, p. 87-108. 

Gardner, L. S., 1944, Phosphate deposits of the Teton Basin area, Idaho and

Wyoming: U.S. Geol. Survey Bull. 944-A, p. 1-36. 

Geijer, Per, 1962, Some aspects of phosphorus in Precambrian sedimentation:

Arkiv for Mineralogi och Geologi, v. 3, p. 165-186. 

Gibson, T. G., 1967, Stratigraphy and paleoenvironment of the phosphatic

Miocene strata of North Carolina: Geol. Soc. America Bull., v. 78, no. 5,

p. 631-650. 

Goldman, M. L, 1922, Basal glauconite and phosphate beds: Science, v. 56,

p. 171-173. 

Gower, H. D., and Madsen, B. M., 1964, The occurrence of phosphate rock in

California, in Geological Survey research 1964: U.S. Geol. Survey Prof.

Paper 501-D, p. D79-D85. 

Gulbrandsen, R. A., I960, Petrology of the Meade Peak Phosphatic Shale

Member of the Phosphoria formation at Coal Canyon, Wyoming: U.S.

Geol. Survey Bull. 1111-C, p. 74-146.

_____ 1966, Chemical composition of phosphorites of the Phosphoria Formation : Geochimica et Cosmochimica Acta, v. 30, p. 769-778. 

Harrington, J. F., Ward, D. E., and McKelvey, V. E., 1966, Sources of fertilizer minerals in South America, a preliminary study: U.S. Geol.

Survey Bull. 1240, 66 p. 

Hutchinson, G. E., 1950, The biogeochemistry of vertebrate excretion: Am.

Mus. Nat. History Bull., v. 96, 554 p.
PHOSPHATE DEPOSITS D19

Hutchinson, G. E., 1952, The biogeochemistry of phosphorus, in Wolterink, 

L. F., ed., The biology of phosphorus: East Lansing, Michigan State 

Coll. Press, p. 1-35.

Jacob, K. D., 1953, Phosphate resources and processing facilities, in Jacob, 

K. D., ed., Fertilizer technology and resources: New York, Academic 

Press, Agronomy Monographs, v. 3, p. 117-166.

Kazakov, A. V., 1937, The phosphorite f acies and the genesis of phosphorites: 

U.S.S.R., Sci. Inst. Fertilizers and Insectofungicides Trans., no. 142, 

p. 95-113.

Kimrey, J. O., 1965, Description of the Pungo River Formation in Beaufort 

County, North Carolina: North Carolina Dept. Conserv. and Devel. Div. 

Mineral Resources Bull. 79, 131 p.

Kramer, J. R., 1964a, Seawater Saturation with apatites and carbonates: 

Science, v. 146, no. 3644, p. 637-638.

_____ 1964b, Sedimentary phosphate facies [abs.]: Geol. Soc. America 

Spec. Paper 76, p. 95.

Lewis, R. W., 1967, Phosphate rock,m U.S. Bureau of Mines, Minerals yearbook 1966: Washington, U.S. Govt. Printing Office, v. 1 (in press).

Lotspeich, F. B., and Markward, E. L., 1963, Minor elements in bedrock, 

soil, and vegetation at an outcrop of the Phosphoria Formation on Snowdrift Mountain, southeastern Idaho: U.S. Geol. Survey Bull. 1181-F, 42 p.

Love, J. D., 1961, Vanadium and associated elements in the Phosphoria formation in the Afton area, western Wyoming, in Short papers in the 

geologic and hydrologic sciences: U.S. Geol. Survey Prof. Paper 424-C, 

p. 279-282.

_____ 1964, Uraniferous phosphatic lake beds of Eocene age in intermontane basins of Wyoming and Utah: U.S. Geol. Survey Prof. Paper 

474-E, p. 1-66.

McConnell, Duncan, 1938, A structural investigation of isomorphism of the 

apatite group: Am. Mineralogist, v. 23, no. 1, p. 1-19.

McKelvey, V. E., 1963, Successful new techniques in prospecting for phosphate deposits, in U.S. Dept. State, Natural resources Minerals and 

mining, mapping and geodetic control: Geneva, United Nations Conf. 

Application Sci. and Technology for the Benefit of Less Developed 

Areas, 1963, U.S. Papers, v. 2, p. 164-172; Australian Mining 1966, 

v. 58, no. 3, p. 8-13.

McKelvey, V. E., and Carswell, L. D., 1956, Uranium in the Phosphoria formation, in Page, L. R., Stocking, H. E., and Smith, H. B., compilers, 

Contributions to the geology of uranium and thorium by the United 

States Geological Survey and Atomic Energy Commission for the United 

Nations International Conference on Peaceful Uses of Atomic Energy, 

Geneva, Switzerland 1955: U.S. Geol. Survey Prof. Paper 300, p. 483-487.

McKelvey, V. E., Cathcart, J. B., Altschuler, Z. S., Swanson, R. W., and 

Buck, K. L., 1953, Domestic phosphate deposits, in Pierre, W. H., and 

Norman, A. G., eds., Soil and fertilizer phosphorus in crop nutrition: 

New York, Academic Press, Agronomy Monographs, v. 4, p. 347-376.

McKelvey, V. E., Swanson, R. W., and Sheldon, R. P., 1953, The Permian 

phosphorite deposits of Western United States: Internat. Geol. Gong., 

19th, Algiers 1952, Comptes rendus, sec. 11, pt. 11, p. 45-64.

McKelvey, V. E., Williams, J. Steele, Sheldon, R. P., Cressman, E. R., Cheney, 

T. M., and Swanson, R. S., 1959, The Phosphoria, Park City, and Shedhorn formations in the western phosphate field: U.S. Geol. Survey Prof. 

Paper 313-A, p. 1-47.
D20 CONTRIBUTIONS TO ECONOMIC GEOLOGY

Macpherson, E. O., 1945, Milburn-Clarendon phosphate deposits: New 

Zealand Dept. Sci. and Indus. Research Bull. 90, p. 1-43.

Mansfield, G. R., 1922, Potash in the greensands of New Jersey: U.S. Geol. 

Survey Bull. 727, 146 p.

_____ 1927, Geography, geology, and mineral resources of part of southeastern Idaho: U.S. Geol. Survey Prof. Paper 152, 409 p.

1940, The role of fluorine in phosphate deposition: Am. Jour. Sci.,

v. 238, no. 12, p. 863-879. 

Mero, J. L., 1965, The mineral resources of the sea: New York, Elsevier

Publishing Co., 312 p. 

Oakley, K. P., 1955, Analytical methods of dating bones, in Techniques in

archaeology: Adv. Sci., v. 12, no. 45, p. 3-8. 

Palache, Charles, Berman, Harry, and Frondel, Clifford, 1951, Dana's system

of mineralogy [7th ed.]: New York, John Wiley & Sons, v. 2, 1124 p. 

Parker, F. W., and Nelson, L. B., 1966, More fertilizers for more food, in

Harrar, J. G., chm., Prospects of the world food supply: Washington,

D.C., Natl. Acad. Sci., p. 78-84; Natl. Acad. Sci. Proc., v. 56, no. 2,

p. 382-388. 

Patton, W. W., and Matzko, J. J., 1959, Phosphate deposits in northern

Alaska: U.S. Geol. Survey Prof. Paper 302-A, p. 1-17. 

Pecora, W. T., 1956, Carbonatites a review: Geol. Soc. America Bull., v. 67,

no. 11, p. 1537-1556. 

Pevear, D. R., 1966, The estuarine formation of the United States Atlantic

Coastal Plain phosphate: Econ. Geology, v. 61, no. 2, p. 251-255. 

Redfield, A. C., Ketchum, B. H., and Richards, F. A., 1963, The influence of

organisms on the composition of sea-water, in M. N. Hill, ed., The sea,

v. 2: New York, Interscience, p. 26-77. 

Roberson, C. E., 1966, Solubility implications of apatite in sea water, in

Geological Survey research 1966: U.S. Geol. Survey Prof. Paper 550-D,

p. 178-185. 

Rogers, C. L., Cserna, Zoltan de, van Vloten, Rogelio, Tavera Amezcua,

Eugenio, and Ojeda Rivera, Jesus, 1961, Reconocimiento geologico y

depositos de fosfatos del norte de Zacatecas y areas adyacentes en

Coahuila, Nuevo Leon y San Luis Potosi: Mexico Consejo Recursos Nat.

no Renovables Bol. 56, 322 p. 

Ross, C. S., 1941, Occurrence and origin of the titanium deposits of Nelson

and Amherst Counties, Virginia: U.S. Geol. Survey Prof. Paper 198, 59 p. 

Ruhlman, E. R., 1958, Phosphate rock, pt. 1, Mining, beneficiation, and

marketing: U.S. Bur. Mines Inf. Circ. 7814, 33 p. 

Russell, H. D., Hiemstra, S. A., and Groeneveld, D., 1954, The mineralogy

and petrology of the carbonatite at Loolekop, eastern Transvaal: Geol.

Soc. South Africa Trans. and Proc., v. 57, p. 197-208.

Service, A. L., and Popoff, C. C., 1964, An evaluation of the western phosphate industry and its resources, pt. 1, Introductory review: U.S. Bur.

Mines Rept. Inv. 6485, 86 p. 

Sever, C. W., Cathcart, J. B., and Patterson, S. H., 1967, Phosphate deposits

of south-central Georgia and north-central peninsular Florida: Georgia

Dept. Mines, Mining, and Geology, South Georgia Minerals Prog., Proj.

Rept. no. 7, 62 p.

Shapiro, Leonard, 1952, Simple field method for the determination of phosphate in phosphate rocks: Am. Mineralogist, v. 37, nos. 3 and 4,

p. 341-342.
PHOSPHATE DEPOSITS D21

Sheldon, R. P., 1957, Physical stratigraphy of the Phosphoria formation in 

northwestern Wyoming: U.S. Geol. Survey Bull. 1042-E, p. 105-185.

 1959, Geochemistry of uranium in phosphorites and black shales of 

the Phosphoria formation: U.S. Geol. Survey Bull. 1084-D, p. 83-115.

 1963, Physical stratigraphy and mineral resources of Permian rocks 

in western Wyoming: U.S. Geol. Survey Prof. Paper 313-B, p. 49-273.

_____ 1964a, Exploration for phosphorite in Turkey a case history: 

Econ. Geology, v. 59, no. 6, p. 1159-1175.

1964b, Paleolatitudinal and paleogeographic distribution of phosphorite, in Geological Survey research 1964: U.S. Geol. Survey Prof.

Paper 501-C, p. 106-113. 

Sillen, L. G., 1961, The physical chemistry of sea water, in Sears, Mary, ed.,

Oceanography Invited lectures presented at the Internat. Oceanography

Cong., New York, 1959: Am. Assoc. Adv. Sci. Pub. 67, p. 549-581. 

Smirnov, A. D., Ivnitskaya, R. B., and Zalavina, T. P., 1958, Preliminary

results of a study of the CaO-PzOs-HzO system under conditions closely

approaching natural conditions: Gosudarstvennogo Nauchno-Issledovatel'skogo Inst. Gorno-Khim. Syr'ya Trudy, no. 4, p. 86-91; abs. in

Chem. Abs., 1961, v. 55, p. 15094. 

Smith, R. W., and Whitlatch, G. I., 1940, The phosphate resources of

Tennessee: Tennessee Div. Geology Bull. 48, 444 p. 

Sverdrup, H. U., Johnson, M. W., and Fleming, R. H., 1942, The oceans: New

York, Prentice-Hall, 1087 p. 

Taliaferro, N. L., 1933, The relation of volcanism to diatomaceous and

associated siliceous sediments: California Univ. Dept. Geol. Sci. BulL,

v. 23, p. 1-56. 

van Vloten, Roger, 1955, Geology of the border region between Coahuila and

Zacatecas, Mexico: Leidsche Geol. Mededelingen, pt. 19, p. 111-166. 

Waggaman, W. H., and Ruhlman, E. R., 1960, Phosphate rock, pt. 2, Processing and utilization: U.S. Bur. Mines Inf. Circ. 7951, 36 p. 

Weiner, J. S., Oakley, K. P., and Clark, W. E. Le Gros, 1953, The solution

of the Piltdown problem: British Mus. (Nat. History) Bull., Geology,

v. 2, p. 140-146. 

Youssef, M. I., 1965, Genesis of bedded phosphates: Econ. Geology, v. 60,

no. 3, p. 590-600.

O