Subsea Mineral Resources

U.S. GEOLOGICAL SURVEY BULLETIN 1689-A

Chapter A

Subsea Mineral Resources

By V. E. McKELVEY

US. GEOLOGICAL SURVEY BULLETIN 1689 

MINERAL AND PETROLEUM RESOURCES OF THE OCEAN
DEPARTMENT OF THE INTERIOR 

DONALD PAUL MODEL, Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

UNITED STATES GOVERNMENT PRINTING OFFICE: 1986

For sale by the Books and Open-File Reports Section, U.S. Geological Survey, 

Federal Center, Box 25425, Denver, CO 80225

Library of Congress Cataloging-in-Publication Data

McKelvey, V. E. (Vincent Ellis), 1916- 

Subsea mineral resources.

(U.S. Geological Survey bulletin ; 1689-A)

Bibliography: p. 95

Supt. of Docs, no.: I 19.3:1689-A

1. Marine mineral resources. I. Title. II. Series.

QE75.B9 no. 1689-A 557.3s 86-600199

[TN264] [553'.09162]
CONTENTS

Abstract 1 

Introduction 2

Concepts of reserves and resources 3 

Definitions 4 

Classification 4 

Summary 7

Geology of the continental margins and ocean basins 7 

Continental margins 7 

Deep-ocean basins 8

Plate tectonic processes in the origin of subsea geologic provinces 9 

Subsea minerals in relation to the continent-ocean framework 9 

Marine placers 9

Placer minerals 10

Geologic environments favorable for the formation of placers 10 

Placers in the marine environment 11 

World distribution of marine placer deposits 12 

Guides to prospecting for offshore placers 13 

Offshore sand, gravel, and calcium carbonate deposits 13 

Sand and gravel 17 

Shell 18

Other offshore sources of calcium carbonate 19 

Precious coral 20 

Phosphorite and guano 21

Mineralogy and goechemistry 22 

Origin 22 

Distribution 24 

Guides to prospecting 27

Subsurface hard-mineral deposits of the continental margins 27 

Metallic minerals 27 

Coal 28

Other nonmetallic minerals 28 

Manganese nodules and encrustations 29 

Chemical composition 30

World and ocean averages 30 

Relation to latitude 34 

Relation to water depth 35 

Metal-rich types of nodules 41 

Mineralogy 55 

Origin 56

Relation to water depth 57

Effects of direct precipitation from seawater in comparison with those

from diagenetic precipitation 57 

Relation to regional variation in sediment type, biologic productivity, and

physiography 59 

Distribution 61

The Clarion-Clipperton zone 62

Other areas containing nickel- and copper-rich nodules 67

Subsea Mineral Resources III
Cobalt-rich encrustations 68

Manganese- and iron-rich encrustations 71

Feasibility of commercial recovery 72 

Ferruginous and manganiferous sediments 73 

Metallic sulfide deposits 78

Red Sea metalliferous sediments 78

Sulfide deposits on the mid-ocean ridges of the east Pacific 80

Sulfide deposits associated with volcanic seamounts 83

Analogs on land 83

Feasibility of commercial recovery 85

Jurisdiction over exploration and production 86 

Red clays 86 

Radiolarian ooze 88 

Barite 88 

Seawater 89 

Energy in the oceans 89 

The Law of the Sea 91

Ocean regimes established by the Convention 92

Provisions affecting mineral resources 92

Consequences for the United States 94 

Acknowledgments 95 

References cited 95

FIGURES

1. Tectonic map showing active oceanic ridge systems of the deep-ocean floor with 

which hydrothermal systems are likely to be associated and where sulfide minerals may have been deposited 3 

2, 3. Diagrams showing:

2. Classification of mineral resources 5

3. Resource classification recommended by the UN group of 

experts 6

4. Idealized profile of a continental margin 8

5. Map showing world distribution of coastal placer deposits 12 

6-8. Maps showing heavy-mineral distribution on the:

6. Washington-northern Oregon shelf 14

7. Central Oregon shelf 15

8. Southern Oregon-northern California shelf 16 

9-12. Maps showing:

9. Distribution of gravel off the Northeastern United States 18

10. Gravel on the sea bottom off northern New Jersey 19

11. Sea-floor materials offshore Washington and northern 

Oregon 20

12. World distribution of precious coral 21 

13. Diagram showing surface currents in an idealized ocean 23 

14-16. Maps showing:

14. Distribution of subsea phosphorites 25

15. Distribution of phosphate deposits in the Southeastern United 

States 26

16. Manganese nodule stations in the Scripps Institution of Oceanography's Sediment Data Bank as of March 1980 31 

17-20. Plots showing relations between:

17. Manganese content in manganese nodules and their latitudes 36

18. Combined nickel and copper content in manganese nodules and 

their latitudes 37

IV Mineral and Petroleum Resources of the Ocean
19. Depth and combined nickel and copper content in manganese 

nodules 40

20. Depth and cobalt content in manganese nodules 41

21-23. Plots showing relations between depth and combined nickel and copper content in:

21. Pacific Ocean manganese nodules 42

22. Atlantic Ocean manganese nodules 43

23. Indian Ocean manganese nodules 44 

24-26. Plots showing relations between depth and cobalt content in:

24. Pacific Ocean manganese nodules 45

25. Atlantic Ocean manganese nodules 47

26. Indian Ocean manganese nodules 48 

27. Plot showing relation between depth and manganese content in manganese

nodules 49 

28-32. Maps showing distributions of:

28. Manganese nodules containing 1.8 percent Ni+Cu or more 50

29. Manganese nodules containing ^1.0 and <1.8 percent Ni+Cu 51

30. Manganese nodules containing 1.0 percent Co or more 52

31. Manganese nodules containing ^0.5 and <1.0 percent Co 54

32. Manganese nodules containing 35.0 percent Mn or more 55

33. Ternary plot of the principal mineral phases of manganese nodules at 107 stations 

for which all constituents have been analyzed 58

34. Map showing distribution of manganese nodules in the world ocean 62

35. Plot showing relation between depth and concentrations of manganese nodules 63

36. Map showing areas in the northeastern equatorial Pacific Ocean in which manganese nodules contain more than 1.8 percent Ni+Cu 64 

37-39. Maps showing distributions of:

37. Manganese nodules having high metal contents in the Pacific 

Ocean 68

38. Manganese nodules having high metal contents in the South 

Atlantic Ocean 69

39. Manganese nodules having high metal contents in the Indian

Ocean 70 

40-42. Maps showing target areas for exploration for:

40. Manganese nodules rich in combined nickel and copper in the central north equatorial Pacific Ocean 71

41. Manganese nodules rich in combined nickel and copper in the 

southeastern equatorial Pacific Ocean 72

42. Manganese nodules rich in combined nickel and copper in the central south equatorial Indian Ocean 73

43. Plot showing distribution of dissolved manganese and iron in the Black Sea 76

44. Schematic cross section of the Nikopol bedded manganese deposits in the Soviet

Union 77 

45, 46. Maps showing:

45. Hot brine deeps in the Red Sea 79

46. Mid-ocean ridge sites where active hydrothermal circulation and associated massive sulfide deposits have been observed 80

47. Geologic sketch map of the southern Juan de Fuca rift valley 81

48. Map showing regions of the ocean expected to provide areas geologically suitable 

for subseabed waste disposal 87

TABLES

1. Areas of subsea physiographic provinces 8

Subsea Mineral Resources V
2. Placer minerals 11

3. Composition of phosphorites from various submarine localities 26

4. World metal contents, nodule concentrations, and depths of manganese 

nodules 32

5. Comparison of the world average metal contents of manganese nodules listed 

in table 4 with the values reported by Cronan (1980) 32

6. Principal metal contents, nodule concentrations, and depths of manganese nodules in the Pacific, Atlantic, and Indian Oceans 32

7. Average principal metal contents of manganese nodules, by ocean 33

8. Other elements in manganese nodules of the world and of the Pacific, Atlantic, and Indian Oceans 33

9, 10. Principal metal contents, nodule concentrations, depths, and metal ratios of 

manganese nodules, grouped by latitude, in:

9. The northern hemisphere 35

10. The southern hemisphere 35

11-13. Average and maximum principal metal contents of manganese nodules, categorized by latitude, in:

11. The Pacific Ocean 36

12. The Atlantic Ocean 37

13. The Indian Ocean 38

14. Means of other elements in manganese nodules of the world, grouped by 

latitude 39

15. Metal contents, nodule concentrations, and depths of metal ratios in manganese 

nodules in water depths of less than 2,000 and more than 4,000 m 40

16. Principal metal contents of manganese nodules in water depths above and 

below 3,000 m 43

17. Means of other elements in manganese nodules in water depths above and

below 3,000 m 46

18-20. Metal contents, nodule concentrations, and depths of manganese nodules containing:

18. 1.0 percent Ni+Cu or more 48

19. 1.0 percent Ni+Cu or more outside the Clarion-Clipperton zone 49

20. More than 0.5 percent Co and more than 35 percent Mn 50

21. Other elements in manganese nodules of the world, grouped by combined 

nickel and copper, manganese, and cobalt contents 53

22. World means and ocean maximums of several other elements in manganese 

nodules that have exceptionally high concentrations 56

23. Metal contents, nodule concentrations, and metal ratios of manganese nodules 

in the C-C' area at stations where information on both is available 65

24. Metal contents and metal ratios of manganese nodules in the C-C' area 65

25. Metal contents, nodule concentrations, and metal ratios of manganese nodules 

in the C-C' area at stations where the nodule concentration is 5 kg/m2 or 

more 66

26. Partial composition of metalliferous sediments (excluding sulfide facies) of the 

Red Sea 74

27. Ferruginous and manganiferous sediments at or near oceanic spreading 

centers 75

28. Chemical analyses of the sulfide facies of Red Sea sediments 80

29. Estimates of typical grades and values per ton of contained metals for seafloor massive sulfide deposits, compared with typical ore from ophiolite massive sulfide deposits and deep-sea manganese nodules 82

30. Elements present in seawater in amounts greater than 1 ppm 89

VJ Mineral and Petroleum Resources of the Ocean
31. Allowable nickel production from deep-ocean nodules under the provisions of 

the Law of the Sea Convention and U.S. Bureau of Mines forecasts of growth 

in world demand for nickel 93

32. Comparison of Authority's 25-year income and contractor's internal rate of return from a manganese nodule operation under various assumptions 93

Subsea Mineral Resources VII

MINERAL AND PETROLEUM RESOURCES OF THE OCEAN

Subsea Mineral Resources

By V. E. McKelvey 

Abstract

About 20 nonpetroliferous minerals are produced from the 

continental margins. Sand and gravel, lime from shells and 

aragonite mud, precious coral, and placer minerals such as 

rutile, ilmenite, leucoxene, cassiterite, zircon, monazite, magnetite, gold, platinum, and diamonds are recovered by surface 

mining. Sulfur and salt are recovered by solution mining 

through drill holes. Barite is recovered by subsea quarrying. 

Coal and iron ore are mined underground from entry on adjacent land or from artificial islands. Potash is likely to be produced from subsea salt basins, and offshore production of 

phosphate is being considered in several areas.

The resources of the deep-ocean floor are yet to be developed. Those drawing the most interest are manganese nodules 

and encrustations, metallic sulfide deposits, and red clays.

Manganese nodules are composed chiefly of manganese and 

iron oxides, but, in places, they are relatively rich in nickel, 

copper, cobalt, molybdenum, and vanadium. Current commercial interest is focused on nodules having a combined 

nickel-copper content of 1.8 percent or more. The most prospective area thus far known for such deposits lies in the northeastern 

equatorial Pacific between the Clarion and the Clipperton fracture 

zones. The area is about 2.5 million square kilometers in size and 

contains about 2.1 billion dry metric tons of potentially recoverable nodules averaging 25 percent Mn, 1.3 percent Ni, 1 percent 

Cu, and 0.22 Co. Enough experimental work has been done to 

indicate that recovery of such deposits is technically feasible when 

economic conditions become favorable.

Cobalt-rich manganese oxide encrustations on bedrock are 

widespread on seamounts in the north-central Pacific Ocean 

and the Hawaiian Archipelago in water depths of 1,000 to 

2,500 m. They appear to average about 2 cm in thickness and 

about 0.9 percent Co, 0.5 percent Ni, 24 percent Mn, and less 

than 0.1 percent Cu. Although the feasibility of mining the 

crusts has yet to be demonstrated, several factors lead some to 

believe that their recovery is closer to being commercially 

feasible than that of the nodules.

Metallic sulfide deposits are associated with hydrothermal 

systems along ocean-floor spreading centers. The most promising deposits found thus far lie in a series of deep basins along 

the central rift valley beneath the Red Sea. The largest, the 

Atlantis II Deep, has an area of about 56 km2 . The upper 10 m 

of sediments are estimated to contain about 2.9 million tons of 

Zn, 1 million tons of Cu, 0.8 million tons of Pb, 45,0001 of Ag, 

and 45 t of Au, worth on the order of a few billion dollars. The 

Governments of Saudi Arabia and Sudan have been sponsoring

recovery research, and the deposits are expected to come into 

production during the latter part of this decade.

Sulfide deposits similar to those associated with ophiolite 

complexes on land have recently been found at seven ridge 

crest localities in the eastern Pacific. Qualitatively, their composition is similar to that of the Atlantis II deposits, although 

their zinc content is generally much higher (in the range of 

30-60 percent). Sulfide deposits have also been found on flank 

volcanoes near the crest of the East Pacific Rise. None of these 

deposits has been sampled enough to support meaningful tonnage estimates. Land analogs range from a few thousand to 

many millions of tons in size, and such a range can be expected 

for the subsea deposits also. The feasibility of their recovery has 

yet to be tested.

Red clays blanket about 30 percent of the deep-ocean floor, 

and several countries are seriously considering using them in 

situ for high-level radioactive waste storage. The extensive research in progress on this possibility has thus far not revealed 

any unfavorable elements and has identified many favorable 

ones.

Seawater itself is an important source of some chemicals and 

several forms of energy. Salt, magnesium compounds, and 

bromine are recovered now, and potassium, sulfur, boron, and 

uranium may be recovered in the future. Desalinated seawater 

is a valuable product in coastal desert areas. Of the ocean's 

enormous reservoir of energy, only a small amount of tidal 

energy is now being recovered, but research is underway on 

the recovery of ocean thermal energy, wave-generated energy, 

the energy in circulating current systems, and the energy represented by the large osmotic pressure difference between freshwater and saltwater.

The 1982 Law of the Sea Convention contains many provisions governing the development of subsea mineral resources. 

It assigns to coastal States the right to produce subsea minerals 

from their Exclusive Economic Zones, which extend 200 nmi 

seaward from their coasts, and also gives them jurisdiction over 

the mineral resources of most of their continental margins 

where they extend seaward of the Exclusive Economic Zones. 

Minerals beyond these limits of national jurisdiction are to be 

under the control of an International Sea-Bed Authority. The 

United States has not signed the Convention but has indicated 

that it will accept all of its provisions except those governing 

minerals beyond national jurisdiction.

Subsea Mineral Resources 1
INTRODUCTION

In 1876, Sir John Murray reported the discovery of metalrich nodules on the deep-sea floor during the voyage of 

H.M.S Challenger in 1873. Such nodules were of no commercial interest then, although small subsea mining operations had taken place near the shore in earlier times. For 

example, subsea mines were worked for lead and zinc in 

ancient Greece at Laurium and for tin and copper in Cornwall (Cruickshank and Siapno, 1985). A coal mine was 

developed from an artificial island off the coast of Scotland 

more than 350 years ago. In 1860, a concession was granted 

to a German firm to mine amber offshore in the Kurisches 

Haff in the Baltic Sea, an operation that lasted more than 30 

years (Beiersdorf, 1972; Glasby, 1982). And, of course, the 

production of salt by solar evaporation of seawater dates 

back many centuries. But the possibility of mining deep-sea 

nodules and other deep-water resources was not even imagined until the middle part of this century.

Three main series of events spurred interest in marine 

mineral resources. The first was the successful completion 

of an oil well in 8 m of water 1 mi offshore Louisiana in 

1938. It, as well as several subsequent wells off Louisiana 

and Texas in the early 1940's, was drilled from a rigid 

platform set on the ocean bottom, but the success of these 

wells pointed up the petroleum potential of the continental 

shelf and led to the 1945 Truman Declaration of U.S. sovereign rights over the mineral resources of the continental 

shelves. In 1947, completion of the first floating drilling 

platform extended offshore drilling to deeper water and 

opened a vast new domain to petroleum exploration and 

production.

The second series of events stimulating interest in marine 

minerals began with John Mero's publication of several 

papers and a small book from 1957 to 1965 calling attention 

to the considerable potential value of the metals (mainly 

manganese, nickel, copper, and cobalt) contained in the 

nodules and the probable feasibility of commerical production. Mero's works led several mining companies to investigate the nature of the resource and the technology required 

to develop it and at the same time aroused governmental 

interest in the question of who should own or control the 

rights to produce minerals from the seabed beyond the limits 

of national jurisdiction. Following a speech by Ambassador 

Arvid Pardo of Malta to the General Assembly of the United 

Nations in 1967, in which he proposed that such resources 

be considered the common heritage of all mankind, the 

United Nations established an Ad Hoc Committee on the 

Peaceful Uses of the Seabed and the Ocean Floor Beyond 

the Limits of National Jurisdiction. One of the early actions 

of that committee was to establish, largely on the initiative 

of the United States, an International Decade of Ocean Exploration. The U.S. contribution to this program, funded 

through the National Science Foundation, was substantial, 

as was resource-related research by other U.S. organizations

and those of other nations as well, notably the French Centre 

National pour 1'Exploration des Oceans, the P.P. Shirshov 

Institute of Oceanology of the Soviet Union, the Geological 

Survey of Japan, the Institute of Oceanography of New 

Zealand, and the Bundesanstalt fur Geowissenschaften und 

Rohstoffe of West Germany.

The third series of events stimulating interest in marine 

minerals was the research leading to the development in the 

early 1960's of plate tectonic theory, which postulates that 

the Earth's lithosphere is composed of about 20 moderately 

rigid, shell-like plates some 80 km thick that are in constant 

movement with respect to one another and that slide over a 

partially molten, plastic surface. Plates diverge along the 

mid-ocean ridge, where new oceanic crust is formed by 

volcanic and magmatic activity, and converge in the deepocean trenches, where cold oceanic crust moves downward 

beneath the adjacent continent or island arc and is destroyed 

at about the same rate at which new crust is formed. Plates 

also move past each other along strike-slip faults. Each of 

the six largest plates (the Eurasian, North American, South 

American, African, Indian-Australian, and Arabian plates) 

(fig. 1) includes continental masses and oceanic crust, 

which move together as a single plate and thus explain the 

past movements of the continents that led to the theory of 

continental drift advanced by Alfred Wegner in 1916 and by 

others before him. But most of the central evidence for this 

now widely accepted but still revolutionary theory came not 

from the continents but from the sea floor for example, 

Hess's (1948) observations that deep-sea trenches tend to be 

continuous along the island arcs and are clearly associated 

with strong seismic activity and volcanism in the adjacent 

land masses; Ewing and Heezen's (1956) discovery that a 

steep-walled linear valley occupies the crests of the midocean ridges, which are also the sites of many small earthquakes (Tarns, 1927) and high heat flow (Bullard and others, 1956); Heezen's (1960) recognition that the mid-ocean 

ridge system is worldwide and dynamic; and Mason and 

Raff's (1961) discovery of a linear pattern of magnetic 

anomalies on the sea floor off the western coast of the 

United States. The synthesis of plate tectonic theory that 

quickly followed these observations and others by Dietz 

(1961), Hess (1962), Vine and Matthews (1963), Wilson 

(1963), and others led to widespread recognition of the 

importance of marine geology in understanding a host of 

other phenomena ranging from mountain building to the 

origin of several kinds of mineral deposits. A deep-ocean 

drilling program soon won support, as did expanded marine 

geologic research worldwide.

As a result of these studies, knowledge about marine 

mineral resources and about the geology of the ocean basins 

has increased greatly during the last decade or so. Reports 

from oil and mining companies active in the marine environment indicate that much progress has also been made in 

mineral exploration and production technology. Oil and gas 

are now being produced from the continental shelves of

2 Mineral and Petroleum Resources of the Ocean
GLOBAL TECTONIC AND VOLCANIC ACTIVITY 

OF THE LAST ONE MILLION YEARS

Paul D Lawman Jr

Goddard Space Flight Center

April 1966

Van der Grmten Projection

Topography from "The Physical World," 1975

by the National Geographic Society

isform

LEGEND

.___._ Active ridges end continental extensions, n

faults generalized 

Total spreading rate, cm/year, (Minster and Jordan,

J Geophys. Res 83,5331,1°78); directions approximate 

Major active (cult or fault zone; dashed where nature or

activity uncertain

Normal fault or rift; hachures on downthrown side 

Reverse fault (subduction or overthrusl zone), barbs on

upthrown sirle 

Volconos active within the lost 1 million years,generalized

(some isolated basaltic centers omitted)

Figure 1. Tectonic map showing active oceanic ridge systems of the deep-ocean floor with which hydrothermal systems are 

likely to be associated and where, in places, sulfide minerals may have been deposited. Ridges where the spreading rates are 

approximately 6 cm/yr or faster appear to be the most favorable. (Reproduced courtesy of Paul D. Lowman, Jr., Goddard Space 

Flight Center, Greenbelt, Md.)

about 60 countries. Sand and gravel, lime in shells and 

aragonite mud, precious coral, and several placer minerals 

(notably, titanium sands, tin sands, zircon, monazite, staurolite, gold, platinum, diamond, and magnetite) are recovered mainly by dredging. Sulfur and salt are recovered by 

solution mining through drill holes. Barite is recovered by 

subsea quarrying. Coal and iron ore are mined underground 

from nearshore areas from entry on adjacent land or from 

artificial islands. Potash is almost certain to be produced 

from subsea salt basins. Preparation for the production of 

phosphorite off New Zealand is underway, and production 

off the shores of the Southeastern United States and southern 

California is being considered. No minerals have yet been 

produced commercially from the deep-ocean floor, but manganese nodules and the metalliferous muds of the Red Sea 

have been mined experimentally and are almost certain to be 

produced commercially before the end of this century. Polymetallic sulfide deposits, the first discovery of which took 

place in 1979, are also possible candidates for future production from the deep-ocean floor.

Exploration and development of marine mineral resources 

are only in their early stages, but it is plain that they will 

play an increasingly important role in satisfying the mineral 

needs of the future.

This report describes the nature, origin, distribution, and 

probable extent of all kinds of nonhydrocarbon mineral resources from and beneath the sea, beginning with those in 

the coastal environment and extending later to those in the 

deep-ocean basins. As background for these descriptions of 

marine mineral resources, I begin with some definitions and 

concepts of reserves and resources and follow with a brief 

description of the geology of the continental margins and 

ocean basins.

CONCEPTS OF RESERVES AND RESOURCES

Minerals are directly or indirectly the source of most of 

the materials and energy used by an industrial society. Increasing use of mineral resources has made possible the rise 

in level of living in both developed and developing

Subsea Mineral Resources 3
countries. As usage has increased, concern and controversy 

have arisen about the adequacy of resources to meet future 

needs. Much of both the concern and the controversy is 

caused by a lack of understanding of what mineral resources 

are and of how supplies are developed. It is especially important in considering marine mineral resources to know just 

what is meant by that term and to have in perspective the 

difference between mineral deposits that are producible now 

and those that have some potential for future production but 

are not yet within economic or technological reach. The 

discussion that follows begins with definitions of terms and 

basic concepts and extends to a brief description of the 

classification of reserves and resources.

Definitions

The term "mineral" has several connotations. As used by 

the mineralogist, it may refer to a naturally occurring, solid, 

inorganic substance that has distinctive physical properties 

and a composition that can be described by a chemical 

formula. As used by the mineral economist, it may refer to 

a commercially traded commodity derived from a naturally 

occurring, nonliving, organic or inorganic, solid, liquid, or 

gaseous substance. As used to describe resources, it refers 

to naturally occurring, nonliving, organic or inorganic, 

solid, liquid, or gaseous substances useful, or believed to be 

potentially useful, to man. Reference to the mineral resources of a country or region, for example, would likely be 

all encompassing and include its water resources, its energy 

resources (such as coal, gas, petroleum, uranium, and 

geothermal energy), and its potentially usable deposits of 

metallic and nonmetallic minerals, such as deposits of ferrous, base, and precious metals, phosphate rock, saline minerals, sand, gravel, and building stone. When specific aspects of mineral resources are discussed, the scope of the 

subject is generally limited to substances that are commercially traded. Water resources are thus treated separately, 

with the exception of brines containing commercially recoverable dissolved salts. Air is not commonly thought of as a 

mineral resource, but gases recovered commercially from 

the atmosphere (for example, argon, nitrogen, and oxygen) 

are counted as minerals in mineral production statistics.

The term "ore" refers to solid substances currently recoverable at a profit. Generally, it applies to explored and 

developed deposits of metallic minerals, but it is sometimes 

used to describe producible deposits of a few nonmetallic 

inorganic minerals such as phosphate or potash.

An important part of the concept of mineral resources is 

that they have a known or a conceived potential use. Estimates of resources thus do not represent permanently fixed 

quantities but may change over time as uses are found for 

naturally occurring substances previously thought to be worthless and as technologies are devised to recover valuable products from deposits once considered too lean, refractory, or

inaccessible to have any potential use. To prehistoric man, 

mineral resources thus would have been limited to flint, salt, 

water, and rocks that could be used for tools, weapons, or 

crude construction. By the end of the 19th century, about 30 

chemical elements were being used commercially; aluminum was known only in the laboratory, and deposits rich 

in that element would not have been considered a resource. 

Today, about 80 elements and 135 mineral commodities are 

being used commercially hi the United States, and mineral 

deposits that were once considered worthless, such as 

taconite (a hard, highly siliceous, iron-bearing rock), are 

now being produced commercially. Some important marine 

resources such as manganese nodules and sulfide deposits 

are prime examples of such "new" resources only recently 

recognized as having potential commercial value.

Mineral resources (excluding water) have been described 

as nonrenewable resources, hi contrast to renewable resources such as surface water and timber, which are or can 

be replenished naturally or artificially. The geologic processes by which most mineral deposits are formed take so 

long to complete that they cannot be expected to replenish 

deposits extracted from the ground and dispersed by use. 

But it is important to recognize that mineral resources can be 

extended by advancing technology that develops uses for 

substances not usable before, aids in the discovery of concealed deposits, improves recovery efficiency, or makes 

possible the mining and processing of deposits once thought 

to have no value. The life of mineral resources can also be 

extended by increased efficiency of use. For example, the 

card-sized calculator weighing 35 g and costing about $5 in 

1985 will perform more functions than the calculating machine of 1950 weighing 15 kg and costing $500 or more. 

Indeed, some of the advanced pocket calculators now available have more computing power than the computers of the 

early 1950's.

Classification

For many commercial and governmental purposes, it is 

desirable to know the magnitude of specific mineral resources at a mine site, in a region, in a country, and in the 

world at large. Over the years, diverse terms and classifications have been introduced in recognition of the need to 

indicate something about the degree of certainty involved in 

individual estimates of mineral resources. None of these 

terms or classifications has achieved universality in use, but 

the terms "proved," "probable," and "possible" and 

"measured," "indicated," and "inferred" are illustrative of 

attempts to indicate degrees of certainty in resource estimates. For many years, estimates were made only of known 

deposits believed to be recoverable at a profit, but, as advancing technology has lowered cutoff grades and shown 

the power of exploration in discovering new deposits and as 

mineral shortages have developed or threatened to develop,

4 Mineral and Petroleum Resources of the Ocean
interest has grown in the quantitative assessment of deposits 

that are as yet undiscovered or that are not profitably producible now but that may come within economic reach in the 

future. Figure 2 shows a classification based on the degree 

of certainty of the estimate (increasing from right to left) and 

the economic feasibility of recovery (increasing from bottom to top). A similar system was adopted by the U.S. 

Geological Survey (USGS) and the U.S. Bureau of Mines 

(USBM) in 1976 and modified somewhat in 1980 (U..S. 

Geological Survey and U.S. Bureau of Mines, 1980). A 

group of experts convened by the Secretary General of the 

United Nations in 1979 recommended an almost identical 

system (fig. 3), using letters and numbers for the various 

categories instead of names that may not be translatable into 

certain other languages (Schanz, 1980). Although there is 

not yet universal agreement on a classification system for 

mineral resources, publication of diagrams similar to figure 2, drawn from earlier versions of it (for example, 

McKelvey, 1972; Schanz, 1975), in many other countries 

indicates that its principles are widely accepted. The following discussion relates mainly to figure 2, but it is the principles of classification that are being emphasized rather than 

the terminology or the exact definition of the boundaries of 

individual categories.

The most important feature of the classification is that it 

distinguishes identified deposits that are recoverable with 

existing technology and at current prices from those that are

as yet undiscovered or, if known, are not yet within economic reach. In this classification, the term "reserves" is 

used only for identified deposits that could be produced 

commercially at the time that the estimate is made; the term 

"resources" is used for subeconomic and undiscovered categories and for the totality of all categories, including reserves, either for one mineral or for all minerals. Although 

resources may include undiscovered deposits that, even if 

found, are far from being economically recoverable, they 

include only those deposits conceived to be recoverable at 

some time in the future (the UN recommendations define the 

future as within the next two or three decades). Estimates of 

deposits not conceived to have such a potential would be 

classed as "other occurrences."

Another important distinction for some minerals, not selfevident from figure 2 but stressed in the UN report and, to 

a lesser extent, in the 1980 USGS-USBM system, is between recoverable and in situ quantities. Reserves in figure 2 would include only currently recoverable amounts, but 

some of the remainder might be shown in one or more of the 

subeconomic categories. Until recently, for example, crude 

oil recovery averaged only about 30 percent of that originally in place; higher prices and advancing technology make 

it reasonable to expect that the percentage will increase, 

perhaps to 60 percent or so, and that part of the oil originally 

in place (30-60 percent) could be classed as a "paramarginal 

resource" and the remaining part as a "subeconomic

TOTAL RESOURCES

Identified

Demonstrated

Measured Indicated Inferred

Undiscovered

Hypothetical 

(in known districts)

Speculative

(in undiscovered districts)

T

Reserves

Resources

+ +

1

Other 

occurrences Includes nonconventional and low-grade materials

Increasing degree of geologic assurance

Figure 2. Classification of mineral resources.

Subsea Mineral Resources 5
R

In situ resources quantities of economic 

interest for the next few decades

R-1

Known 

deposits 

reliable 

estimates

R-2

Extensions of 

known deposits 

and newly 

discovered 

depositspreliminary 

estimates.

R-3

Undiscovered 

deposits 

tentative 

estimates

R-1-E R-1-S R-2-E R-2-S

Economically Subeconomic Economically Subeconomic

exploitable exploitable

R-1-M 

Marginal economic

Figure 3. Resource classification recommended by UN group 

of experts. Although R denotes resources in situ, r expresses the 

corresponding recoverable resources for each category and 

subcategory, such as r-1-E.

resource." In the system recommended by the UN expert 

group, estimates of in situ versus recoverable resources 

would be reported separately, as they would be to some 

extent in the 1980 USGS-USBM scheme. However the distinction is made, it is an important one to make for those 

minerals for which current extraction practice leaves a substantial portion in the ground. At least some of the remainder is a resource, and an estimate of its amount establishes 

a target for advances in extractive technology or an indication of amounts that might become available at increased 

prices.

A good indication of the uncertainty that exists in estimates, even where discoveries have been made and some 

exploratory drilling completed, is seen in the National Research Council (NRC) of the United States (1976) report on 

gas reserve estimation for offshore producible shut-in leases 

in the Gulf of Mexico that is, leases on which a commercial discovery of oil or gas has been made but that are not 

yet in production. In 1974, because of concerns that Outer 

Continental Shelf Federal leases were deliberately shut in to 

raise gas prices, the Federal Power Commission (FPC) estimated the proved and probable reserves of the 168 leases 

then classified as producible shut in. The results, showing 

proved reserves of 4.7 and probable reserves of 3.3 trillion 

cubic feet of gas, were challenged as being much too conservative. Accordingly, the NRC was asked to make an independent estimate, using the same USGS data that the FPC 

had used. The NRC selected 33 leases as a representative

sample of the 168 leases and commissioned two consulting 

firms to make independent estimates of the gas reserves. 

Their results indicate that, rather than being too low, the 

FPC estimates may have been much too high. In the 33- 

lease sample, the FPC's estimate of both proved and probable reserves was 1.5 trillion cubic feet, in comparison with 

the two consultants' "best" estimates of 0.65 and 0.45 trillion cubic feet (the consultants also made "high" and "low" 

estimates that were 18-28 percent lower and 32-45 percent 

higher than their "best" estimates). The three groups' estimates of reserves in some individual reservoirs differed by 

more than an order of magnitude; with few exceptions, the 

FPC was generally the highest, consultant A generally the 

lowest, and consultant B generally in between. Because 

many of the reservoirs are structural traps associated with 

salt domes, differences in interpreting the extent of reservoirs at this early stage of exploration are understandable, 

but that such differences were not random indicates that 

differences in philosophy (possibly born from experience or 

the lack of it) were significant. In any case, the wide range 

in gas estimates in discovered and partly explored fields in 

the Gulf of Mexico made by experts using the same data is 

indicative of the great uncertainty that necessarily accompanies estimates of reserves, to say nothing of undiscovered 

resources. These "estimates" are fittingly described as such, 

with all the lack of precision implied by that term.

In light of such uncertainty, one may ask if estimates of 

reserves and resources serve any useful purpose. Obviously, 

they must be used with the understanding that they are only 

estimates, subject to a wide margin of error, and they they 

need to be continually updated as new information is acquired. But, with that understanding, they show (with respect to reserves) that there are or are not known deposits 

that can be mined with existing technology at current prices; 

they form the basis for commercial sale and purchase of 

mineral properties and guide plans for mineral development 

and production; and they provide governments with information bearing on the design of short-term supply policies. 

Estimates of identified subeconomic resources show 

whether there are known deposits large enough to justify 

technological research and development, valuable information for both industry and government. Estimates of undiscovered resources show whether there are targets for additional exploration, information as essential to government in 

formulating policy as it is to industry in laying plans to 

develop future supply.

Estimates made within the framework of the classifications illustrated in figures 2 and 3 help to emphasize that the 

development of mineral resources is a dynamic process 

(Schanz, 1977) and that the magnitude of usable resources, 

although limited by a finite Earth (a point that some would 

not concede, now that space exploration has begun), is not 

fixed but increases as technology and exploration advance 

and, of course, decreases through production. The mineral 

deposits being produced today were once in the category of

6 Mineral and Petroleum Resources of the Ocean
undiscovered subeconomic resources. For most minerals, 

the measured reserves of tomorrow will come from today's 

subeconomic or undiscovered categories; for some, they 

may come from today's other-occurrence category; for still 

others, they may come from unknown types of deposits that 

would not even have been listed in 1986 in the otheroccurrence category (DeYoung, 1978).

Marine mineral deposits fall into all of the classification 

categories shown in figures 2 and 3. Measured reserves exist 

for explored accumulations of oil and gas and several other 

minerals that are being mined now. The manganese nodules 

and marine sulfide deposits known on the deep-sea floor are 

classed as identified subeconomic resources. And, given the 

fact that subsea exploration for minerals has been small in 

comparison with the vastness of the area, undiscovered economic and subeconomic resources of all minerals are 

large for most minerals, probably larger than those already identified.

Summary

Mineral resources are naturally occurring solid, liquid, or 

gaseous substances useful, or believed to be potentially useful, to man. They are the source of most of the materials and 

energy used by an industrial society. Mineral resources include identified deposits producible under current economic and technological conditions (termed reserves), 

undiscovered deposits of the same quality (undiscovered 

economic resources), and known and unknown deposits 

that cannot yet be produced profitably (identified and 

undiscovered subeconomic resources). Estimates of the 

magnitude of mineral resources have low accuracy and 

can be expected to change over time as the result of further geologic exploration and technological advances that 

transform undiscovered and subeconomic resources into 

reserves.

All classes of mineral reserves and resources are represented in subsea oil and gas accumulations and other 

minerals under production, but the known deposits of the 

deep-ocean floor are in the subeconomic category. For 

most marine minerals, undiscovered deposits are probably far larger than deposits that have already been identified.

GEOLOGY OF THE CONTINENTAL MARGINS 

AND OCEAN BASINS

The solid Earth's surface is essentially composed of two 

great physiographic provinces the continents and the 

deep-ocean basins. The continents rise up to mean heights 

of 4,300 to 5,800 m above the deep-ocean floor. The ocean 

basins are filled with water, of course more than filled, in 

fact, for the oceans extend over the margins of the continents for distances of a few kilometers to more than 1,300

km. The boundary between the continents and the ocean 

basins lies beneath the sea at water depths of 2,000 to 

4,000m.

These physiographic provinces reflect the fundamental 

geologic differences between them. The crust forming the 

continents is richer in silica and the alkalis and poorer in iron 

and magnesium than the oceanic crust is. The continental 

crust averages about 35 km in thickness, in comparison with 

about 7 km for oceanic crust, and its density is less, an 

average of about 2.7 in comparison with about 3.0 for 

oceanic crust. The continents and ocean basins are in isostatic equilibrium with the underlying mantle; the lighter 

continents rise above the ocean basins, much as an iceberg 

does in the sea.

The configuration of the surfaces of these two great 

provinces reflects a further contrast in surface-shaping processes. Erosion is the dominant process on the continents, 

whereas sedimentation and volcanism are the dominant 

surface-shaping processes in the ocean basins.

Although the ocean basins are a great and distinct physiographic province when contrasted with the continents, they 

are themselves, like the continents, formed of several distinct physiographic features. The areas of the main subsea 

physiographic provinces are shown in table 1, and their 

character is briefly described in the following paragraphs.

Continental Margins

The submerged parts of the continents in most places 

consist of three main physiographic features (fig. 4). A 

continental shelf borders the land in most places. It is a 

gently seaward dipping surface that is a continuation of the 

coastal plain where one is present. The width of the shelf 

ranges from a few to several hundred kilometers and averages about 80 km. The edge of the shelf or shelf break, 

generally believed to be close to the lowest sea level during 

the Pleistocene glaciation, averages about 100 to 130 m in 

depth, but, at high latitudes, where it is believed that the 

shelves have not fully rebounded from the effects of ice 

loading, the depth of the shelf break may be at a depth of 

300 m or more. At the edge of the shelf, on which the 

sea-floor gradient is generally less than 1:1,000, the seabottom gradient steepens to 1:40 or more and falls along the 

continental slope to depths of 1,500 to 3,500 m or an average at the foot of the slope of about 3,000 m. The shelf and 

slope together are sometimes called the continental terrace. 

In some areas, such as offshore California, the continental 

terrace consists of a series of ridges and basins called the 

continental borderland.

There are two main forms of continental margins. In the 

Atlantic or passive type, the continental slope passes rather 

abruptly into the continental rise, an apron of erosional 

debris having a seaward gradient of 1:100 to 1:1,000 and a 

width of 100 to 1,000 km. In the Pacific or active type of

Subsea Mineral Resources 7
Table 1. Areas of subsea physiographic provinces 

[After Menard and Smith, 1966]

Province

Continental shelf and slope1 

Continental rise --------------

Abyssal hills and plains -------

Volcanic ridges and cones and 

other features. 

Trenches and associated ridges - - 

Total -------------------

Small ocean basins (included - - - 

above in continental rise 

and abyssal plains).

Area, 

xl06 km2

55.4 

19.2 

151.5 

118.6 

11.2

6.1 

362.0

7.5

Percentage of 

total area

15.3 

5.3 

41.8 

32.7 

3.2

3.7 

100.2 

2.1

'Menard and Smith (1966) estimated the area landward of the 200-m 

isobath (often taken as an approximation of the continental shelf) as 27.1 

(106 km2).

margin, the slope continues to the floor of a trench at a depth 

of 7.5 to 11.0 km. Off southern California, the margin 

consists of a series of ridges and basins called the continental borderland that are thought to be related to the San 

Andreas transform fault zone.

In some places, such as off the coasts of Maine and parts 

of Canada, the landward part of the continental shelf may 

consist of Precambrian or Paleozoic rocks, but the seaward 

part is generally underlain by Mesozoic or Cenozoic sedimentary rocks several kilometers or more in thickness. Particularly in the Atlantic and Indian Oceans, the continental 

rise, which receives most of the sediments eroded from the 

continents, also may be underlain by several kilometers or 

more of young sediments. Although the relief on the continental rise is generally low, it is cut in places by submarine 

canyons that extend upward into the slope and shelf.

The floor of semienclosed or marginal seas that lie between continents or between continents and island arcs is 

also a part of or is akin to the continental margin. Some of 

these basins have an abyssal plain below a depth of 2,000 m. 

Basins that border land areas having a large surface runoff 

have thick accumulations of sediments analogous to those of 

the continental rises.

Deep-Ocean Basins

The most prominent physiographic features of the deepocean basins are the ridges and rises, of which the midocean ridge, so named because it has a mid-ocean position 

in all the oceans but the Pacific, is most prominent. It is a 

nearly continuous (but branching) worldwide mountain 

chain broken by and in many places offset along crosscutting scarps termed "fracture zones." Its total length is 

80,000 km, and it ranges in width from 2,000 to 3,000 km 

or more. A steep-walled rift valley lies along the crest of the 

ridge. The ridge crests average about 2,500 km in depth, 

and the flanks extend downward to depths of 4,000 km or 

more. Rank gradients are relatively gentle, but local relief 

is commonly in the range of 100 to 1,000 m.

In most places, the mid-oceanic ridges are flanked by 

abyssal hills and abyssal plains. The abyssal hills are lower 

but less rugged parts of the ridges, and the abyssal plains are 

essentially flat areas adjacent to the continental rises where 

the ridge surface has been completely buried by sediments. 

They range from 3,000 to 6,000 m in depth.

Volcanoes and volcanic ridges are common on the deepocean floor. Seamounts are volcanoes that rise several

CONTINENTAL MARGIN

Figure 4. Idealized profile of a continental margin. 

8 Mineral and Petroleum Resources of the Ocean
hundred meters above the ocean floor. Some form islands. 

Volcanic ridges are generally formed by overlapping volcanoes. Guyots or tablemounts are subaerially planed-off volcanoes that have since subsided.

Much of the Pacific basin is rimmed by deep trenches, 

which are narrow troughs having steep slopes on their landward sides that range in depth from 7.5 to 11.0 km, in width 

from 40 to 120 km, and in length from 800 to 5,900 km. 

Most lie along the seaward sides of island arcs, but the 

longest (the Peru-Chile trench) lies along the western margin of South America.

Plate Tectonic Processes in the Origin of Subsea 

Geologic Provinces

The geologic provinces of the deep-ocean basins are the 

result of plate tectonic processes. The lithospheric plates 

mentioned earlier are pulling apart along the rift valleys at 

the crests of the mid-ocean ridges, and new oceanic crust is 

being formed there by the intrusion and extrusion of molten 

basaltic magma welling up from the mantle. A ridge crest is 

high relative to its flanks because it is hot and hence lower 

in density. As hot rock moves away from a spreading center, 

it begins to cool and contract, and its surface sinks as cooling and contraction progress. Because rock is a slow conductor of heat and because the plates are normally thick, the 

cooling process is a gradual one; about 80 Ma is required for 

oceanic crust to cool and sink to abyssal depths. The abyssal 

hills on the lower flanks of the ridges and the abyssal plains 

adjacent to some continental rises represent cooled and 

sunken oceanic crust buried beneath an accumulation of 

sediments.

The volcanic seamount chains on the ridge flanks and 

deep-ocean floor are the result of volcanic activity at hot 

spots (relatively stationary magma sources beneath the 

plates in the upper part of the mantle). Movement of a plate 

over such a stationary magma source produces a succession 

of extinct volcanoes such as those comprising the Hawaiian 

Islands chain. The extinct chain traces the movement of the 

plate through time, relative to the hot spot.

I mentioned earlier that trenches are the sites where cold 

oceanic crust plunges beneath another plate to be resorbed 

by the mantle at depth. Subduction, as the process is called, 

of oceanic crust beneath island arcs or convergent continental margins leads to volcanic activity of both basaltic and 

andesitic types and plays a major role in the accretion of new 

continental crust.

Convergence of two plates does not always result in subduction along a trench. Where a continental mass lies along 

the leading edge of converging plates, folded mountains 

may be the result. The Himalayas are examples of such 

mountains, formed by the collision of the Indian-Australian 

and Eurasian plates. Segments of oceanic crust and upper 

mantle, called ophiolite sequences in some places (in the

Alps, for example), have been incorporated in such mountains, and, in some places, oceanic crust has been obducted 

or thrust up on the edge of a continental mass instead of 

being subducted.

The widest continental margins are generally the Atlantic 

or passive type formed by plate divergence, and it is only 

along such margins that continental rises are formed. Active 

continental margins adjacent to a subducting oceanic plate 

are typically narrow. Where an oceanic plate subducts beneath another oceanic plate, an island arc eventually develops, mainly as the result of volcanic activity caused by the 

melting of the descending ocean slab and the mantle above 

it. The back-arc basin or marginal sea between the island arc 

and the mainland is thus also initially a product of plate 

tectonic processes and in time may become the site of another spreading center.

Subsea Minerals in Relation to the ContinentOcean Framework

Subsea mineral deposits relate in composition and diversity to the continent-ocean framework just as the physiographic and geologic features do. Potentially associated 

with the continental margins is the full variety of minerals 

found on the continents, even including those that are typically associated with mafic as well as felsic igneous rocks. 

Most such deposits probably would have to be mined by 

underground or quarrying methods, and it is unlikely that 

many of them can be produced economically in the foreseeable future. Much more promising are minerals typically 

associated with marine sediments. Subsea deposits already 

in production, such as oil, gas, sand and gravel, and others 

previously mentioned, are of this association; for them, the 

continental margins have a potential that may rival that of 

the land parts of the continents.

The minerals of the deep-ocean floor are of a much more 

limited variety mainly metalliferous deposits that are typically associated with mafic igneous activity. They include 

manganese nodules and encrustations, some of which have 

concentrations of nickel, copper, cobalt, and other metals; 

metallic sulfide deposits related to hydrothermal activity 

associated with volcanism along the mid-ocean ridges; and 

possibly radiolarian ooze and red clay. The metal-rich manganese nodules of the equatorial Pacific, the cobalt-rich 

manganese encrustations of the central Pacific, and the 

metalliferous sulfide muds of the Red Sea deeps are the only 

deep-sea deposits that seem to have a potential for commercial production during this century.

MARINE PLACERS

Placer deposits are economically valuable concentrations 

of heavy minerals (that is, minerals having specific gravities 

of 2.9 or more, heavier than those of common, rock-forming

Subsea Mineral Resources 9
minerals such as quartz and feldspar). They are residual 

minerals formed by the weathering of older rocks and separation from lighter clastic particles during transport by wind 

or water. In addition to being relatively heavy minerals, they 

are also resistant to chemical weathering and abrasion. 

Heavy minerals such as metallic sulfides that oxidize rather 

quickly are not present in most placer deposits, especially 

those far from their sources. Even magnetite, a mineral 

prominent in many placers and mined commercially in 

some, will not withstand long-distance transport, particularly in tropical or subtropical environments.

Placer Minerals

Twenty or so valuable heavy minerals are found in placers 

(table 2), but economically significant deposits are common 

for a much smaller number mainly gold, platinum, cassiterite, monazite, zircon, xenotime, staurolite, kyanite, diamond, and the titanium minerals rutile, ilmenite, and leucoxene (largely titanium oxide formed by the removal of 

iron from ilmenite by weathering). Production of gold from 

geologically young placers is thought to have contributed 

between one-quarter and one-third of the world total, and 

geologically old fossil placers, such as the Precambrian 

deposits of the Witwatersrand district of South Africa, have 

been the world's principal source of gold for some time 

(Simons and Prinz, 1973). Placer deposits also supply most 

of the world's tin production in the form of cassiterite 

(Sainsbury and Reed, 1973); they are the main source of 

monazite and other rare-earth minerals and the sole commercial source of zircon; and they are the source of about 

half of the world's production of titanium, including nearly 

all of its rutile (U.S. Bureau of Mines, 1982).

Most placer deposits yield more than one mineral, and 

some placer minerals, such as xenotime, monazite, kyanite, 

and staurolite, are rarely produced except as byproducts or 

coproducts of other minerals. A common assemblage consists of titanium minerals, monazite, zircon, and perhaps 

kyanite or staurolite; for many such deposits, commercial 

production would not be feasible without the recovery of 

several or all of the heavy minerals.

Geologic Environments Favorable for the 

Formation of Placers

All placer minerals are derived from igneous or metamorphic rocks or from mineral deposits formed as a result of 

hydrothermal activity associated with igneous processes. 

The immediate source for some placer deposits, however, is 

the reworking of a concentration of heavy minerals in older 

sediments, but, this exception notwithstanding, a prerequisite for the occurrence of placer deposits is a nearby crystalline terrane. Most gold placers are found within 15 km or 

so of their source, but placers containing tough minerals

such as ilmenite and rutile or diamond may be scores or even 

hundreds of kilometers from their sources. But, at least 

regionally, if not locally, a source terrane must be present. 

Tectonic setting broadly controls magmatic activity and 

the composition of intrusive and extrusive igneous rocks and 

associated mineral deposits; hence, it broadly controls the 

composition and distribution of placers. For example, calcalkaline volcanic igneous rocks are intruded and extruded in 

subduction-related arcs and are the source of the hydrothermal activity that leads to the formation of gold-bearing 

quartz veins. The tin-bearing granites of southeastern Asia 

are also the result of back-arc magmatic activity. Passive 

margins, on the other hand, are in many places the site of 

titanium and rare-earth mineral placers (Guild, 1974).

The formation of placers is especially favored by the deep 

chemical weathering of tropical and subtropical climates, 

which leads to the breakdown and destruction of most rockforming silicates and the concentration of the chemically 

resistant minerals. The degree of concentration that may be 

involved is illustrated by Van Overeem's (1960) description 

of the relation between the tin-bearing "Kaksa" (the name 

given to the layer in which cassiterite is concentrated in 

valley bottoms) and its source rock on the island of Billiton, 

Indonesia:

A not very rich Kaksa has a tin content of about 

3 percent. The overall tin content of the large 

block of basement rock enveloping the deep mine 

of Klappa Kampit is about 0.006 percent. Thus, if 

all the mineralization of Billiton would have been 

as intensive as in the Klappa Kampit complex 

(which is not the case), the rate of concentration 

would be in the order of 1:500. As the rate of 

mineralization of the Klappa Kampit area is an 

extreme one and taking into account the losses of 

fine-grained cassiterite which have undoubtedly 

taken place during the process of concentration in 

the valleys. . ., it can be said safely that thousands 

of cubic meters of basement rock were disintegrated and carried off to obtain one cubic meter of 

Kaksa layer.

When tin is selling for $6 or $7 a pound, a deposit containing 3 percent (60 Ib/ton) is a rich ore indeed, but the 

concentration of the valuable minerals in placers does not 

need to be large to make them economically recoverable. 

For example, primary ilmenite deposits must contain about 

10 percent Ti, more than 20 times its average abundance in 

the Earth's crust. Some of the Florida placers contain only 

about 0.4 to 0.6 Ti, a little less to a little more than its crustal 

average. Low-cost mining and beneficiation of unconsolidated sands plus coproduct recovery of other minerals make 

their recovery economic.

Although the occurrence of important placers in areas of 

present tropical or subtropical weathering is impressive (for 

example, Florida, Brazil, southwestern Africa, India, Ceylon, Indonesia, Thailand, and Australia), placers are also

10 Mineral and Petroleum Resources of the Ocean
Table 2. Placer minerals

Mineral Composition Specific gravity

Andalusite -------------------------------Al2SiO5

Cassiterite -------------------------------SnO2

Chromite -------------------------------- Fe+2Cr2O4

Columbite-tantalite ------------------------ (Fe, Mn) (Nb, Ta)2O6

Corundum -------------------------------A12O3

Diamond --------------------------------C

Euxenite ------------..--..--.......-.-.--(Y, Ca, Ce, U, Th) (Nb, Ta, Ti)2O6

Garnet (almandine) ------------------------ 3FeOAl2O3 -3SiO2

Gold ------------------------------------Au

Ilmenite --------------------------------- Fe+2TiO3

Kyanite ---------------------------------- Al2SiO5

Magnetite -------------------------------- FeOFe2O3

Monazite -------------------------------- (Ce, La, Nd, Th)PO4

Platinum --------------------------------- Pt

Rutile ----------------------------------- TiO2

Scheelite --------------------------------- CaWO4

Sillimanite ------------------------------- Al2SiO5

Staurolite -------------------------------- (Fe+2 , Mg, Zn)2Al9(Si, A1)4O22(OH)2

Topaz -----------------------------------Ar2SiO4(F, OH)2

Tourmaline-------------------------------H9A13 (B, OH)2Si4O19

Wolframite -------------------------------(Fe, Mn)WO4

Xenotime -------------------------------- YPO4

Zircon -----------------------------------ZrSiO4

3.16-3.20 

6.8-7.1 

4.6

5.3 -7.3 

3.95-4.1 

3.5

4.7-5.0 

4.25

15.6-19.3 

4.7 

3.23 

5.2

4.9-5.3 

14-19 

4.18-4.25 

5.9-6.1 

3.23

3.65-3.77 

3.4-3.6 

3.0-3.2 

5.0-5.5 

3.23 

4.2-4.86

found at higher latitudes. Some were derived during periods 

of deep weathering in the Tertiary. Important examples are 

the gold placers of California, which were derived from 

Eocene weathering when a subtropical climate prevailed 

there (Jenkins, 1935). At high latitudes, rapid physical rock 

disintegration accomplished through frost weathering is also 

effective in liberating minerals from source terrane. The 

great placers of British Columbia, Alaska, and eastern 

Siberia can be traced to this process. Glaciation, however, 

particularly continental glaciation, makes a negative contribution to placer formation, for it mixes and hence dilutes 

rich source materials with the lean on a vast scale. Workable 

placers, therefore, are rarely derived from drift or even 

glacial outwash (Jenkins, 1935).

Placers in the Marine Environment

Most of the foregoing observations about placers apply to 

both continental and marine placers. To focus now on placers in the marine environment, two sites are favorable for 

their occurrence beaches and drowned river channels.

Beginning with the formation of the great ice sheets during the Neogene, sea level has fallen and risen over a total 

range of about 200 m. During the last major buildup of the 

ice sheets about 18,000 years ago, sea level was about 

130 m below its present level. The transgression that took 

place with warming was relatively rapid until about 7 ka, at 

which time sea level was about 10 m lower than it is now;

its rise continues but very slowly (see Kennett's (1982) 

summary). As a result of these fluctuations, fossil beaches 

are found in many places both above and below the present 

level, and river channels are found submerged beneath the 

sea in many areas.

Beach placers are formed by sorting in the high-energy 

environment caused by waves breaking on the beach. Light 

minerals are selectively winnowed away from the heavy 

minerals. It has been long observed (Raeburn and Milner, 

1927) that high waves and a persistent wind direction are 

favorable for the development of placers on modern 

beaches. Although the beach environment is a narrow one, 

a transgressing sea can lead to the formation of a relatively 

wide deposit over time. The action of strong alongshore 

currents can lead to the development of beach placers a long 

distance from their source terrane. In the course of such 

transport, grain size is commonly reduced, and tough minerals such as rutile and zircon tend to be enriched as chemically or physically weaker minerals such as gold and magnetite are destroyed by abrasion, solution, or attrition.

Rivers and streams are probably the best sites for the 

concentration of heavy minerals (Emery and Noakes, 1968), 

particularly those that will not stand long-distance transport. 

The heavy minerals tend to be concentrated with coarse 

gravel at the bottom of the channel, in places trapped on the 

surface of bedrock, in cracks or cavities. Submerged river 

valleys are generally extensions of river valleys on land, 

but, of course, bottom topographic and perhaps seismic or

Subsea Mineral Resources 11
1(0 120 100 10 (0 40 20 0 20 40 10

\ \ \ \ \

EXPLANATION

 

Past or prtsent producer

A

Prospect, no known production 

Arrow points to offshore producer or prospect

\ \ \ \ \ \ \

ICO 140 120 100 »0 tO 40 20 0 20 40 10 10 100 ItO 140 l»0

Figure 5. World distribution of coastal placer deposits (from McKelvey and Chase, 1966). (Reproduced with permission from 

the Marine Technology Society.)

magentic surveys are required to determine their seaward 

course.

World Distribution of Marine Placer Deposits

The world distribution of marine placer deposits is shown 

in figure 5 (see also McKelvey and Wang, 1970; Rowland, 

1985). Probably the most valuable offshore placer production in total is that of cassiterite off Burma, Thailand, 

Malaysia, and Indonesia, mainly in drowned river valleys. 

Less valuable in aggregate production but more extensive 

and widespread geographically are beach and offshore deposits of what Emery and Noakes (1968) called the light 

heavy minerals, which have specific gravities in the range of 

4.2 to 5.3 (the titanium minerals, monazite and other rareearth minerals, zircon, and magnetite); coastal placers, in 

fact, are the principal sources of all these minerals except 

magnetite. Important deposits of these minerals, most of 

which contain several recoverable minerals, are found along 

the coasts of Brazil, Mauritania, Senegal, Sierra Leone, 

Kenya, Mozambique, Madagascar, India, Sri Lanka, 

Bangladesh, China, and the southwestern and eastern coasts

of Australia (see McKelvey and Wang's (1970) world map). 

Extensive deposits also occur off the eastern coast of Australia, but they cannot be mined economically (Morley, 

1981). Along the Konkin coast (west central) of India, 

ilmenite-rich sands, probably derived from the Deccan 

Traps (basalt), occur in beaches and bays over a distance of 

about 200 km (Siddiquie and others, 1979). Extensive deposits of light heavy minerals also containing potentially 

recoverable gold and cassiterite occur in beach deposits 

along Egypt's Mediterranean Sea coast (El Gemmizi, 1985). 

In the United States, Pleistocene beach placers of light 

heavy minerals have been mined from South Carolina and 

Georgia and are being mined now in northeastern Florida. 

The Florida deposits are in sand bodies as much as 25 km 

long, 2 km wide, and 10m thick that contain 2 to 4 percent 

heavy minerals (Pirkle and Yoho, 1970; Pirkle and others, 

1974, 1984). Recently, very extensive deposits containing 

an average of about 3.4 percent heavy minerals have been 

found offshore southern Virginia at water depths of 10 to 

50m (Grosz and Escowitz, 1983), on the basis of grab 

samples spaced at intervals of 15 min of longitude and 10 

min of latitude. Vibracores taken on a recent cruise show

12 Mineral and Petroleum Resources of the Ocean
that these deposits and similar ones off central Georgia 

extend to a depth of at least 10 ft (U.S. Geological Survey 

press release, June 28, 1985). In addition, Drucker (1983) 

has identified six zones of heavy-mineral concentration 

within the inner New York Bight as having heavy-mineral 

potential. In the eastern Gulf of Mexico, near Dauphin and 

Sand Islands, Stow and others (1976) estimated the presence 

of 23 million tons of light heavy minerals in deposits where 

they average 1.64 to 1.80 percent. On the Pacific coast, 

areas favorable for light heavy minerals have been identified 

by Phillips (1979) and Beauchamp and Cruickshank (1983) 

and include areas off Grays Harbor, Willapa Bay, and the 

Hoh River of Washington; the Columbia, Neholem, Siltcoas, and Umpqua Rivers of Oregon; and Crescent City, 

Calif, (see figs. 6, 7, 8).

As I mentioned previously, magnetite is destroyed early 

in the weathering process, particularly in tropical and 

semitropical climates, but titaniferous magnetite is more 

resistant to weathering. One such deposit containing 12 

percent titanium oxides and 56 percent Fe is being mined off 

the southern coast of Japan's Kyushu Island (Mero, 1965) in 

20 to 30 m of water in Ariaki Bay. Other large-scale deposits are known off the western coasts of New Zealand and 

Luzon (Philippines) and on the northern shore of the Gulf of 

St. Lawrence.

Diamonds have long been mined from raised beaches 

along the coast of Namibia, and they were discovered in 

gravels offshore in 1961. Mining there began a year or so 

later at water depths of 10 to 40 m but was suspended in 

1972 because the rough seas in that area made dredging 

costly and dangerous. Operations were resumed, however, 

in 1979 (Cronan, 1980). Dredging for diamonds has also 

been reported off Brazil (Archer, 1973).

Chromite-bearing beach sands along the southern coast of 

Oregon were mined during World War II. They are known 

to occur also on the continental shelf, and the U.S. Department of the Interior Outer Continental Shelf Mining Policy 

Task Force (1979) reported identified resources there containing 30 million tons of chromite, 6 million ounces of 

gold, and 0.35 million ounces of platinum. Chromite placers are extensive on beaches and the near offshore of 

Sulawesi in Indonesia, Luzon and Palawan in the Philippines, and New Caledonia, where they are derived from 

ultramatic rocks as the result of deep tropical weathering 

(B. Lipin, personal communication, 1983).

Gold has been mined from many beach placers (for example, along the coasts of California, Oregon, Washington, 

and Alaska). Very likely, beach-placer gold has been pretty 

well depleted, but the high price of gold is stimulating 

interest in offshore deposits, as the following U.S. Geological Survey (1982) report on current activities in Alaska 

indicated:

Three widely separated beach and offshore placer 

gold deposits are at various stages of development. About 20,000 acres in Golovinn Lagoon

approximately 65 miles east of Nome are being 

tested by Goodwin Resources, Ltd. A $500,000 

pilot recovery plant capable of handling 900 tons 

of sand a day is being built on the beach near 

Yakataga by Cusac Industries, Ltd., and Alaska 

Gold Mines, Inc. of Vancouver, British Columbia. Plans to use a large suction dredge to mine 

550 acres of tidal and offshore tracts near Point 

Woronzof in Cook Inlet adjacent to the Anchorage 

International Airport have been announced by 

Cook Inlet Exploration and Development. In the 

Nome area, State-issued prospecting leases and 

mining permits extend seaward to the 3 mile limit 

of State jurisdiction.

Moore and Welkie (1976) described potentially minable 

metal placers in the coastal Bering Sea, and Tagg (1979) 

identified nearshore areas on the western side of Kodiak 

Island; Yakataga, Yakutat, and Lituya Bay in the Gulf of 

Alaska; and the Bradfield Canal and Gastineau Channel in 

southeastern Alaska as meriting exploration for gold. Tagg 

also identified the Cape Prince of Wales area on the western 

Seward Peninsula as prospective for cassiterite and Good 

News Bay as prospective for platinum.

Guides to Prospecting for Offshore Placers

The best clues to identifying promising areas for the occurrence of offshore placer deposits are the presence onshore of alluvial or beach placers or the presence in the 

coastal region of igneous and metamorphic rocks, particularly in areas of deep chemical weathering. Most of the 

known offshore placer deposits (for example, the diamonds 

off Namibia, the cassiterite placers off Indonesia, and the 

rutile placers off the eastern coast of Australia) have been 

found on the basis of such clues, and it seems likely that 

many submerged beach or alluvial deposits remain to be 

discovered.

Prospecting within generally favorable areas can be aided 

by using seismic reflection surveys to define buried river 

valleys and fossil beaches. Magnetometer and radiometric 

surveys may help to identify buried placers rich in magnetite 

and radioactive minerals, respectively, although radioactive 

minerals must be within a few centimeters of the surface to 

be detectable (Force and others, 1983). Recently, ilmenite 

placers in Florida have been found to give a strong response 

to induced polarization (Wynn and Grosz, 1983). Sampling, of 

course, is necessary to determine the presence of heavy minerals, and drilling is essential to determine the grades, thicknesses, and extents of deposits being considered for mining.

OFFSHORE SAND, GRAVEL, AND CALCIUM 

CARBONATE DEPOSITS

Construction materials sand and gravel and lime in 

various forms account for the largest volume of nonfuel

Subsea Mineral Resources 13
124°W

Heavy mineral Opaque percent 

percent (average)

0.5

6.0

12.0

0-10

10-20

20-30

>30

Percent total "heavy" minerals on Washingtonnorthern Oregon continental shelf. Includes 

all "heavy" minerals, non-opaque and opaque 

(black sands) of sand fraction. Heavy minerals 

greater than 3.15 sp. gr.

Figure 6. Heavy-mineral distribution on the Washington-northern Oregon shelf (reproduced from 

Phillips, 1979).

mineral production offshore, just as they do on land. The 

main reason for this large offshore production is that land 

sources of these materials near coastal cities are becoming 

depleted. Because transportation costs are high, it is cheaper 

to turn to offshore sources than it is to attempt to develop

inland deposits. Environmental concerns about onshore 

quarrying and the growing competition between land users 

are additional incentives to offshore mining of construction 

materials. Inasmuch as these trends are likely to continue in 

the developed countries and to spread to the developing

14 Mineral and Petroleum Resources of the Ocean
124°W

Heavy mineral Opaque percent 

percent (average)

0-10

10-20

0.5

8.0

12.0

15.0

45'

Rock

Percent total "heavy" minerals on central 

Oregon continental shelf. Includes all 

"heavy" minerals, non-opaque (black sands), 

of sand fraction. Heavy minerals are greater 

than 2.96 sp. gr.

44'

43° N

Figure 7. Heavy-mineral distribution on the central Oregon shelf (reproduced from Phillips, 1979).

Subsea Mineral Resources 15
124°W

OREGON

Heavy mineral Opaque percent 

percent (average)

0-10

10-20

20-30

>30

Rock

0.5

8.0

12.0

15.0

Percent total "heavy" minerals en central 

Oregon continental shelf. Includes all 

"heavy" minerals, non-opaque (black sands), 

of sand fraction. Heavy minerals are greater 

than 2.96 sp. gr.

CALIFORNIA

Heavy mineral 

isopleth

< l f or no data

1-10

41

40° N»

Figure 8. Heavy-mineral distribution on the southern Oregon -northern California shelf (reproduced from 

Phillips, 1979).

16 Mineral and Petroleum Resources of the Ocean
ones, the offshore construction materials industry is likely to 

grow substantially.

Sand and Gravel

Continental runoff is the source of much sea sand, but, 

except where mountainous areas lie adjacent to the coast, 

most rivers do not transport gravel to the sea because their 

gradients are too low. Marine gravels are mainly derived 

from sea-cliff erosion and, at high latitudes, from glacial or 

fluvioglacial deposits. Where mountainous areas do lie adjacent to the coast, alluvial gravel may be an important source 

near river mouths and in submerged channels on the continental shelf. Although many offshore deposits were deposited on land when sea level was at a lower stand, strong 

currents can affect their distribution. For example, in the 

North Sea, where much is known about the distribution of 

sand and gravel because of an active offshore mining industry, the sea bottom tends to be exposed rock where currents 

are more than about 7.4 km/h. Where currents are between 

3.7 and 7.4 km/h, gravel deposits are common; where they 

are between 2.8 and 3.7 km/h, the bottom is made up of 

sand. Mud is the rule where currents are less than 2.8 km/h 

(Anonymous, 1980). Gravel is most common at depths less 

than 50 m, as are sediments having carbonate contents of 

more than 10 percent (Glasby, 1982).

World offshore production of sand and gravel much exceeds offshore production of other nonfuel minerals both in 

value and volume (Baram and others, 1978). The U.S. 

offshore sand and gravel industry is limited to State waters 

and is poorly developed in comparison with that in Europe 

and Japan, partly because land resources are still available 

in most areas and partly because regulations to govern leasing and production on the federally controlled Outer Continental Shelf have never been developed. Sand and gravel are 

being dredged in State-controlled waters off New Jersey, 

Connecticut, and Texas, and sand is being dredged off New 

York, Florida, Mississippi, and California.

Sand and gravel resources on the U.S. Outer Continental 

Shelf are enormous. Thus, the U.S. Department of the Interior Outer Continental Shelf Mining Policy Task Force 

(1979) estimated resources of sand and gravel off the Atlantic and Pacific coasts to be 830 and 29 billion cubic 

meters, 1 respectively; resources of sand off the gulf and 

Hawaiian coasts to be 269 and 19 billion cubic meters, 

respectively; and resources of sand and gravel off the coast 

of Alaska to be "large."

Gravel off the Atlantic coast is lagely restricted to the 

northeastern part (figs. 9, 10), where it is of fluvioglacial 

origin (Schlee and Pratt, 1970). Excellent deposits are 

known off central New Jersey in water depths of 30 m about 

75 km from New York City, in Massachusetts Bay at similar

! lm3 = ~2.lt.

depths only 20 km from Boston, and at an average depth of 

about 20 m on Nantucket Shoals 150 km from Providence, 

R.I. The sands of the Atlantic Shelf are quartz rich in the 

northeast and calcium carbonate rich (shelly) in the southeast.

The U.S. Department of the Interior Outer Continental 

Shelf Mining Policy Task Force (1979) listed numerous 

gravel deposits off the coast of California, including some 

in submerged river beds and beaches. Moore and Luken 

(1979) also identified numerous sand and gravel deposits off 

the coast of Washington and Oregon in water depths of less 

than 100 m (fig. 11). The gravel deposits off Washington 

are believed to be derived from glacial meltwaters during the 

Pleistocene. Most of the deposits off the coast of Oregon lie 

near submarine outcrops and are thought to have been 

formed by wave action at the lower sea levels prevailing 

during the Pleistocene.

An important use of gravel off the Beaufort Sea coast of 

Alaska and Canada (Pasho, 1985) will be to serve as artificial islands for oil and gas exploration and production platforms. The Department of the Interior Task Force reported 

the presence of extensive gravel deposits up to several tens 

of meters thick beneath an overburden of mud, sand, peat, 

and clay mixtures of variable thickness. About 5 million 

cubic meters of gravel is the amount estimated to be required 

for this purpose, and the task force believed that the offshore 

and nearby onshore deposits contain considerably greater 

amounts.

Sand and gravel are in short supply in Hawaii, but the task 

force reported a potential white sand supply on Penguin 

Bank off the western coast of Molokai 40 km from Honolulu 

at water depths of 50 to 60 m. Penguin Bank is a sunken 

coral reef, and the sand has been derived by erosion of its 

surface. The volume of sand there is believed to be in excess 

of 350 million cubic meters. Sand and gravel are also in 

short supply in many other Pacific islands. A group of 11 

island nations in the South Pacific (including the Cook Islands, Fiji, Guam, Conga, Samoa, Kiribati, the Solomon 

Islands, Vanatu, and Tuvalu) have asked the USGS for help 

in finding offshore supplies suitable for their construction 

industries (McCloy, 1984). In the Virgin Islands and Puerto 

Rico, where construction sands are in short supply, extensive offshore sources have been found recently that likely 

will dominate future production. Two of the deposits found 

offshore in Puerto Rico, for example, contain about 170 

million cubic meters, enough to supply Puerto Rico's construction industry for about 23 years at the current annual 

rate of consumption (Rodriguez, 1984).

The most extensive offshore sand and gravel industry is 

that of Japan. Approximately 1,000 small dredges there 

produce 60 to 70 million tons of sand and gravel a year, 

which is 20 percent of Japan's total production. The countries of northern Europe (in particular, the United Kingdom, 

the Netherlands, Denmark, and France) are also substantial

Subsea Mineral Resources 17
Figure 9. Distribution of gravel off the Northeastern United States (reproduced from Schlee and Pratt, 1970).

producers of offshore sand and gravel (Glasby, 1982; 

Padan, 1983). In total, they produced about 50 million tons 

in 1976. The leader among them, the United Kingdom, 

supplied about 15 percent of its own needs in 1980 (Tinsley, 

1983) and exported about one-fourth of its offshore production to the Netherlands, France, and Belgium (P. Webb, 

unpublished manuscript, 1983). In the North Sea, suction 

dredges mine at depths of up to 36 m. Sand and gravel are 

also mined offshore Thailand, Hong Kong, and Sydney, 

Australia.

Although dredging destroys bottom-dwelling organisms, 

dredges do leave behind undisturbed patches of sea floor 

between dredge tracks that serve as seeds for repopulation. 

A study of a dredged channel near Le Havre, France, 

showed that recolonization took place rapidly. Fish are not

harmed by dredging; in fact, fish reportedly follow along to 

i feed on sand fleas and worms that are uncovered by the 

disturbance at the draghead (Moore and Luken, 1979).

Shell

Offshore shell banks composed chiefly of calcium carbonate are an important source of construction aggregate, 

poultry grit, and lime in areas where limestone is scarce or 

lacking onshore. Iceland, for example, has no onshore 

source of lime and depends on a deposit of shell sand about 

10 mi off its western coast. The sea bottom to the west of 

the deposit is relatively shallow and rocky and has a rich 

growth of mollusks. During the winter months, storm waves 

break up the shells and carry them into a depression in Faxa

18 Mineral and Petroleum Resources of the Ocean
40° 00'

:m

:mt-

 C~ w <z^m% " '- . ". ".' ' '.'' ''

.^;^?X,::^.;; ::;::.x;;: sii;

l^ifSSKi

NEW JERSEY

+&&X ( $ma v^ XS^: M

 x;

Wxi '*?* : . . -: :: .

ItiH ISSilrSr

*:::;;;; ^V// X

7 4°30'

10 NAUTICAL MILLS

73 e OO'

EXPLANATION

Sample location

Sand

Pebbly Sand 

MAXIMUM PEBBLE SIZE

o

64-32mm

O

32- 16mm

O

16-8mm

O

8-4mm

Boundary of limonite 

stained sediment

 66 

Submarine contours 

showing depth in feet

Figure 10. Gravel on the sea bottom off northern New Jersey, delineated by John Schlee and others in joint studies undertaken 

by the U.S. Geological Survey and Woods Hole Oceanographic Institution, may find an important market in nearby urban areas 

(Schlee, 1964). (Reproduced with permission from Pit and Quarry.)

Bay, so that the deposit is self-renewing (Mero, 1965). 

Oyster shells have been dredged from San Francisco Bay in 

California for the manufacture of cement, and shell is also 

mined offshore Texas, Louisiana, Alabama, Florida, and 

the Netherlands. Extensive accumulations of shell are also 

known off California's Santa Cruz, Santa Rosa, and San 

Miguel Islands (U.S. Department of the Interior Outer Continental Shelf Mining Policy Task Force, 1979), off Washington and Oregon (Moore and Luken, 1979), and off the

Isle of Man in the Irish Sea (Cronan, 1980) and doubtless 

will be found in many other places if local needs stimulate 

prospecting.

Other Offshore Sources of Calcium Carbonate

Extensive deposits of high-purity aragonite mud and 

sand, possibly between 50 and 100 billion tons, occur on 

the broad shelf areas surrounding the Bahama Islands. One 

of the areas is the site of a dredging operation producing

Subsea Mineral Resources 19
124°00' 124°00'

Figure 11 . Sea-floor materials offshore Washington and northern Oregon (from Moore and Luken, 1979). Contours are in meters. 

(Reproduced with permission from Oregon Geology.)

several hundred thousand tons a year for export to the 

United States. It is 35 km long, 4 km wide, and about 6 m 

thick and contains about 1 billion metric tons (Baram and 

others, 1978). Lithothamnia, a calcareous algae, is dredged 

off northwestern France. Coral sands have been produced 

off Hawaii and Fiji. The coral reefs off the coasts of many 

tropical islands are a potential source of lime and aggregate 

and, for some, may be the only economic source of those 

materials.

Calcareous ooze, mainly Globigerina ooze, covers about 

128 million kilometers of the ocean floor at an average depth 

of 3,500 m (Mero, 1965). Although Mero pointed out that 

calcareous ooze would make a good cement rock and could 

be mined easily with a hydraulic dredge, it will be many 

years before serious consideration is given to deep-ocean 

mining of calcium carbonate, if ever.

Precious Coral

Several species of coral produce skeletons that have long 

been valued for their use in making jewelry. Unlike the soft

and porous coral that forms reefs, precious coral is dense 

and hard and takes a high polish. In ancient times, the 

principal source was the Mediterranean Sea, but it was discovered in Hawaii in 1957, and it has since been found off 

the Bonin Islands near Japan, off Okinawa, and in several 

other localities in the western Pacific (fig. 12). In Hawaii, 

black coral occurs at depths of about 30 to 100 m, and the 

pink, red, gold, and bamboo varieties range from depths of 

about 350 to 500 m. In the Mediterranean, red coral occurs 

at depths ranging from about 10 to 275 m (Grigg, 1979). 

The deep Hawaiian coral beds are harvested by a submersible; elsewhere, a dragnet has been used. Shallow beds 

are harvested by scuba divers.

Precious coral ranges in value from about $100/kg for 

black to about $l,500/kg for "angelskin" pink coral. Grigg 

(1979) estimated the output of the world precious-coral jewelry industry to be worth about $500 million a year and 

implied that the value of the raw coral itself would be about 

one-tenth that amount.

20 Mineral and Petroleum Resources of the Ocean
Shaded tint shows approximate 

area of reef-building coral

Known precious coral beds 

 Black coral 

o Bamboo coral 

x Red and pink corals 

A Gold coral

Figure 12. World distribution of precious coral (after Grigg, 1979). (Redrawn with permission of the National Geographic 

Society Cartographic Division.)

PHOSPHORITE AND GUANO

Phosphorus is an essential component of every living cell, 

and it plays several fundamental roles 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 the shell-forming processes 

of many organisms. Conversely, biologic processes influence the distribution of phosphorus and are responsible for 

its concentration in some deposits. Among the major 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 plant growth, but many soils 

in tropical climates are deficient in phosphorus because it 

has been leached out by advanced chemical weathering. 

Phosphorus can be added to deficient soils in the form of 

natural or artificial fertilizers; 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. 

Phosphorus is used in the manufacture of detergents and

many other chemicals, but, in the United States, about 87 

percent of its consumption is as fertilizers. Phosphate 

consumption has been growing steadily, more than 

tripling in the United States from 1958 to 1979, and is 

expected to continue to do so.

Phosphorus is concentrated in certain igneous processes, 

in particular in the intrusion of alkalic complexes, but more 

than 80 percent of world phosphate production comes from 

phosphorites or phosphatic sedimentary rocks. Phosphorites 

are marine sedimentary rocks rich in the mineral carbonate 

fluorapatite (Ca10 (PO4-CO3)6F2-3), also called francolite. 

Guano deposits are mainly accumulations of sea-fowl droppings on islands at low latitudes, although smaller quantities 

are formed by bats and other cave-dwelling mammals and 

birds.

Although phosphorite has been known subsea since it was 

dredged from the Agulhas Plateau off South Africa by the 

Challenger expedition in 1873 (Murray and Renard, 1891), 

mining it in the marine environment is just now beginning. 

Until now, of course, land deposits have been adequate to 

meet demands, but interest in subsea deposits is likely to 

increase as land deposits are depleted. Of particular interest 

will be unconsolidated nearshore deposits in shallow water 

that can be mined by existing dredging techniques and that 

are close to agricultural areas far removed from land deposits. Eventually, borehole mining may be used to mine

Subsea Mineral Resources 21
deeply buried deposits such as those off the Southeastern 

United States.

Mineralogy and Geochemistry

Phosphorus is the eleventh most abundant element in the 

Earth's crust. Because it averages only about 0.12 percent, 

however, it is classed as a trace element. Even so, it is a 

rock-forming element, both in the sense that it is a constituent of most rocks and in the sense that some rocks are 

composed mainly of phosphorus-bearing minerals.

About 200 minerals are known to contain 1 percent P2O5 

or more. Most of the phosphorus in the Earth's crust, however, occurs in species of the apatite group. The structure of 

apatite favors a wide variety of minor substitutions 

(McConnell, 1938). For example, small amounts of VO4 , 

As2O4 , SO2 , SO4 , or CO2 can substitute for equivalent 

amounts of PO4 , the F position can be partly or completely 

occupied by Cl or OH, or minor amounts of Mg, Mn, Sr, 

Pb, Na, U, Ce, and Y and other rare earths can substitute for 

Ca. The composition of apatite deposits, therefore, may 

change on exposure to solutions whose compositions are 

different from those from which they were deposited. One 

characteristic change is the substitution of fluorine for hydroxyl in teeth and bone. It was this phenomenon that was 

used to demonstrate that the bones of "Piltdown Man" were 

modern rather than ancient (Oakley, 1955).

Because phosphorus in the lithosphere occurs only in the 

quinquevalent state, its solubility is not affected by the redox potential of the environment. The solubility of apatite, 

however, is strongly influenced by pH; it is slowly soluble 

in neutral and alkaline waters below a pH of about 7 to 8, 

and its solubility increases with increasing acidity, decreasing hardness, and decreasing temperature. Apatite is less 

soluble than calcium carbonate and may form a residual 

concentrate on the weathering of a phosphatic limestone. In 

subtropical or tropical climates, apatite itself is eventually 

destroyed by weathering; some phosphorus may be redeposited in the form of aluminum phosphate minerals such as 

wavellite.

Fresh sea-fowl droppings contain about 22 percent N and 

4 percent P2O5 . Decomposition proceeds rapidly, and the 

phosphate content increases as the nitrogen and total organic 

matter content decrease. The mineralogy of partly decomposed guano is complex, but largely decomposed guano 

consists mainly of calcium phosphates such as monetite 

(HCaPO4) or brushite (CaHPO4 -2H2O) and contains 20 to 

32 percent P2O5 . In areas where rainfall occurs, the relatively soluble phosphates of decomposing guano are carried 

to underlying rocks, where they may be deposited as cavity 

fillings or replacements. The mineralogy of phosphatized 

rock depends on the composition of the host. Where it is 

limestone, as it is on coral atolls, the phosphate mineral is 

hydroxyapatite at first but changes to fluorapatite with time

as fluorine is picked up from sea spray or storm waves 

(Altschuler, 1973). Where the underlying rock is a silicate, 

as it is in islands of volcanic origin, the phosphate minerals 

are aluminum or aluminum-iron phosphates (for example, 

variscite (A1PO4 -2H2O) and strengite (FePO4 -2H2O)).

Most phosphorites containing more than 30 percent P2O5 

also contain 3 percent F or more and 0.01 percent U or 

more. Both elements are now recovered as byproducts in 

some places in the manufacture of phosphoric acid or other 

fertilizer chemicals. Some phosphorites also contain 0.1 to 

0.5 percent V2O5 , which is also recovered as a byproduct in 

some operations.

Origin

Most phosphorus is carried to the sea as phosphate minerals or adsorbed on iron or aluminum hydroxides or clay, but 

some is carried in paniculate or dissolved organic compounds, and about one-sixth of the total is carried in solution. The PO4 content of most river and lake waters ranges 

from about 0.01 to 0.5 ppm. Soft acid waters, such as those 

in parts of the Florida peninsula, may contain a few parts per 

million, however, and highly saline alkaline lake waters, 

such as those in Searles Lake, Calif., contain 200 to 900 

ppm.

The ocean as a whole is nearly saturated with phosphate, 

and an amount equivalent to what is brought by rivers is 

precipitated almost continuously (Dietz and others, 1942; 

Kramer, 1964a, b; Robertson, 1966; Sillen, 1961; Smirnov 

and others, 1961). The phosphate content of the ocean is by 

no means uniform, however; deep, cold waters contain 

nearly 0.3 ppm PO4 , 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) 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). Most of the early theories 

on the origin of phosphate developed from the study of 

ancient marine phosphorites exposed on land, beginning 

with Buckland (1829), who suggested that phosphorite was 

composed largely of fossilized coprolites. Other hypotheses 

of phosphorite origin also related it to some form of biologic 

activity (for example, the concentration of phosphate-rich 

skeletons, fecal matter, or the decay of carbonaceous matter).

In a remarkable paper, Kazakov (1937) discarded what he 

called the biolith theories and advanced the hypothesis of 

direct precipitation of apatite from seawater. He drew on 

geologic, oceanographic, and physical chemical evidence to 

support his hypothesis. For example, he observed that phosphorites are a sedimentary facies found only on the continental shelves and are not associated with deep-water sediments or with evaporite sequences. He observed that

22 Mineral and Petroleum Resources of the Ocean
phosphorite facies migrate laterally over time with marine 

transgressions and regressions. He distinguished the thin, 

nodular deposits generally associated with glauconite, 

which he called the platform facies, from the thicker pelletal 

deposits generally associated with black shale, which he 

called the geosynclinal facies. He noted that the P2O5 content of the present oceans increases with depth from a minimum in the zone of photosynthesis as the pH and temperature decrease and the partial pressure of CO2 increases. 

Supplementing such data with information on the areal distribution of P2O5 in the South Atlantic and with observations 

of his own on phase equilibria, Kazakov postulated that 

phosphate is chemically precipitated on shelving bottoms 

between depths of 50 and 200 m, where the pH of ascending 

cold waters rises as their temperature increases and the partial pressure of CO2 decreases. In this circulating system, 

the deep waters ascending the shelves on one side of a basin 

are largely depleted of phosphorus; when they circulate 

back into the upper levels of the sea, they yield no phosphate, largely because of biologic productivity, when 

they reach the other side of the basin. Although Kazakov 

did not use the term upwelling, it is clearly the process 

that he described.

In an idealized ocean (see Fleming, 1957), the main elements of the current system consist of a large circulating 

gyral in each hemisphere (fig. 13); water cooled in polar 

latitudes moves toward the equator along the eastern side of 

the ocean, and water warmed in equatorial latitudes moves 

poleward along the western 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, as they do along the 

equatorial currents and the countercurrent (divergence upwelling). The action of currents moving toward the equator in bringing cold, phosphate-rich 

water along the coast is 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 western edge of poleward-moving density currents such as the Gulf Stream, where heavy and usually cold water lies to the left of an observer looking 

in the direction of flow in the northern hemisphere 

and to the right in the southern hemisphere (dynamic 

upwelling). In middle and northern latitudes, a cool 

coastal countercurrent, such as the one 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).

90*

X X 

Turbulent mixing

Mixing as result of 

winter cooling

Upwelling caused by 

divergence

o 

Dynamically caused upwelling

Figure 13. Surface currents in an idealized ocean showing 

areas of ascending nutrient-rich waters (from McKelvey and 

Chase, 1966). (Reproduced with permission from the Marine 

Technology Society.)

Each of these processes can take place in locations besides 

those shown in figure 13. For example, upwelling can occur 

wherever a prevailing wind or current moves surface water 

away from a coast, and some convection resulting from 

increased surface-water density during winter cooling can 

take place wherever there are pronounced seasonal variations in temperature.

Pronounced climatic, biologic, and geologic effects accompany upwelling, especially where it is produced by divergence in coastal areas (fig. 13). The presence of cold 

waters along coasts produces coastal fogs and humid-air 

deserts, such as those of northern Chile and southwestern 

Africa. The desert environment minimizes continental 

runoff on the one hand and leads to evaporative conditions 

in restricted coastal water bodies on the other. The nutrientrich waters that lie alongside these deserts are the lushest 

gardens of the sea, for the upwelling cold waters there 

support tremendous quantities of organisms diatoms and 

other phytoplankton are at one end of the food chain, and 

fish, whales, and fish-eating sea fowl are 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

Subsea Mineral Resources 23
by sea-fowl colonies feeding in these waters; the extremely 

dry climate created by upwelling makes the preservation of 

guano possible (Hutchinson, 1950).

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 seawater. The decaying 

remains of organisms in such estuaries sink from outflowing 

surface water, and their decay products are trapped in the 

system by inflowing seawater; nutrients accumulate as a 

result of this process, and the phosphate contents of such 

estuaries often are higher than those of adjacent river water 

or seawater. 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 temperature and pH increase near the surface (Kazakov, 

1937; Kramer, 1964b; Robertson, 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 seawater by inorganic processes (Gulbrandsen and others, 1983); a common textural type of 

phosphorite composed of unaggregated microcrystalline apatite probably formed in this way, as did the concentrically 

layered oolites common in many ancient phosphorites (Gulbrandsen, 1960, p. 119; Ilyin and Ratnikova, 1981).

Fossil shells such as gastropods and pelecypods that were 

nonphosphatic during the life of the organism are sometimes 

found to be composed of apatite, clear evidence of replacement before 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 

has been demonstrated in the Peru-Chile (Manheim and 

others, 1975) and southwestern Africa (Birch and others, 

1983) offshore deposits. Interstitial accretion, however, 

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. E123; Bushinski, 1964; 

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

Emphasizing the importance of biologic and diagenetic 

processes in the origin of phosphorite, Baturin (1982, 

p. 228) believed that:

. . .the complete cycle of phosphorite formation 

on the ocean shelves includes five stages: (1) supply of phosphorus to the shelf zone in upwelling 

ocean waters; (2) consumption of phosphorus by 

phytoplankton and other organisms; (3) deposition of phosphorus on the bottom in biogenic detritus and accumulation of sediments with a high 

content of mobile biogenic phosphorus; (4) formation of gel-like, gradually hardening phosphate 

concretions in the sediments; (5) reworking of the 

sediments and residual concentration of the concretions.

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 evaporites) are thus the depositional products of 

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 in marine 

phosphorites (Taliaferro, 1933; Mansfield, 1940; Gibson, 

1967). Gulbrandsen's (1974) discovery of buddingtonite (an 

ammonium feldspar derived from the alteration of volcanic 

glass) in many beds of the Meade Peak Member of the 

Permian Phosphoria Formation supports this hypothesis 

(Burnett and Lee, 1980). No doubt, volcanic activity does 

contribute to the concentration of these elements and others 

in seawater, but their present distribution in seawater is not 

controlled by volcanic activity, and the processes described 

yield deposition from seawater of normal composition 

(McKelvey and others, 1953, 1959).

The origin of phosphorites illustrates the concatenation of 

processes that often take place in the formation of ore deposits of many kinds: (1) slight concentration of phosphorus 

in deep, cold water; (2) upwelling onto a shelving bottom 

and warming; (3) further concentration biologically or by 

direct precipitation or replacement; (4) diagenetic concentration; (5) reworking; and (6) weathering. Summerhayes 

and others (1973) reported that, although phosphorite off 

Namibia appears to be forming now, most of the phosphorite in that region is derived from the reworking of Tertiary 

deposits, and Burnett and Veeh (1977) found that four periods of phosphogenesis ranging from 0 to 10 to 130 to 140 

ka are represented in the deposits off Peru and Chile.

Distribution

Phosphorites on the present sea floor generally fit the 

distribution expected from the upwelling hypothesis (fig. 

14). They have been found on the shelves on the western 

sides of continents as a result of divergent upwelling; on 

submerged mountains in the Pacific, where they probably 

formed on seamounts as they were carried beneath equatorial upwelling by the northwestward-moving Pacific plate, 

or on since-submerged islands that were the sites of the sea24 Mineral and Petroleum Resources of the Ocean
Figure 14. Distribution of subsea phosphorites (redrawn from Bezrukov and Baturin, 1976). 1-4, Phosphorites on continental 

margins; 5-7, phosphorites on submerged mountains. 1, Holocene; 2 and 5, Neogene; 3 and 6, Paleogene; 4 and 7, Cretaceous.

fowl colonies that flourish in the equatorial countercurrent; 

and off the southeastern coasts of the United States and 

Australia, where they may be the result of dynamic upwelling. In spite of the numerous occurrences already 

known, only the deposits off the western coast of Mexico 

(Jahnke and others, 1983), off Chile, Peru, and Namibia 

(Baturin and Bezrukov, 1979; Baturin, 1982), and off the 

western coasts of South Africa (Birch and others, 1983) and 

Australia (O'Brien and Veeh, 1980) are of Holocene age. 

The other subsea phosphorites shown in figure 14 range in 

age from Neogene to Cretaceous (Baturin and Bezrukov, 

1979; Baturin, 1982).

None of the known Holocene deposits appears to compare 

in size or quality with many of the ancient phosphate deposits, and it thus appears that the Holocene was not an 

active period of phosphate deposition. Episodic deposition 

of phosphorite is demonstrated by the fossil records, which 

show that the major phosphogenic episodes took place during four intervals in the Proterozoic and one interval each in 

the Cambrian, Ordovician, Permian, Jurassic, Late Cretaceous, Eocene, and Miocene-Pliocene (Cook and McElhinney, 1979). Even within these periods, phosphate deposition evidently waxed and waned a number of times, for most 

of the large ancient deposits have two or even several 

phosphate-rich beds separated by weakly phosphatic or nonphosphatic beds. Sheldon (1980) recently postulated that 

(1) episodes of phosphogenesis occur at the onset of 

episodes of vertical mixing following periods of oceanic 

stability, during which the phosphorus content of the deep 

ocean had built up to high levels; (2) the major phosphogenic episodes of the Cretaceous to early Tertiary are due to

equatorial up welling at the time of high-level warm seas; 

and (3) the major phosphogenic episodes of the Cambrian, 

Ordovician, and Permian Periods and the Miocene Epoch 

are due to upwelling in the trade-wind belt at the time of 

transition from high-level warm oceans to low-level cold 

oceans related to glacial episodes. The underlying cause 

appears to be plate movements that reconfigure oceans and 

continents and modify climatic conditions. For example, the 

movement of Antarctica to its polar position during the 

Neogene led to the establishment of the circumpolar current, 

the initiation of glaciation, and a strong surge in deep-water 

circulation (Edgar, 1973).

Most of the phosphorites of Tertiary age and older being 

mined on land either contain more than 30 percent P2O5 in 

place or can be beneficiated to yield a concentrate containing more than 30 percent P2O5 . Most deposits of that quality, particularly those containing more than about 32 percent 

P2O5 , have been enriched by weathering. It is not to be 

expected, therefore, that subsea phosphorites will be as rich 

in P2O5 as the richest deposits found on land; table 3 generally supports this assertion. Some subsea phosphorites (for 

example, those offshore Namibia, Chile, and Peru) are associated with glauconite, a mineral not present in the old 

"geosynclinal" phosphorites. They are associated with diatomaceous ooze, which probably would become chert on 

lithifaction, and, although chert is a member of the geosynclinal phosphorite facies, the older geosynclinal deposits 

appear to have no known analogs on the present sea bottom.

The preceding does not mean that minable subsea deposits will not be found. A deposit that has recently come 

into production at Santo Domingo in Baja California is a

Subsea Mineral Resources 25
Table 3. Composition of phosphorites from various submarine localities (after Cronan, 1980)

[Localities 1-4, Agulhas Bank phosphorites, South Africa (from Parker, 1971; Parker and Siesser, 1972; Dingle, 1974); 5, Forty Mile Bank phosphorite, 

Baja California (from Mero, 1965); 6-10, northwest African continental margin phosphorites (from McArthur, 1974); 11, Peru-Chile continental margin, 

average from Burnett (1974); 12, sea off California, average of two samples from Burnett (1974); 13, Chatham Rise off New Zealand, average of two 

samples from Burnett (1974); 14, Blake Plateau phosphorite (from Burnett, 1974); 15, Necker Bank phosphorite (from Burnett, 1974)]

1 2 3

SiO2 ------ 6.20 3.45 15.30 

TiO2------ .06 .04 .10

A12O3 ----- 1.13 .92 2.14 

Fe2O3 ----- 1.40 25.80 5.58 

MnO----- .01 .06 .01 

MgO----- .97 1.49 1.34 

CaO ------ 47 02 33 42 37 04

Na2O----- .62 .34 .78

K20------ .43 .39 1.57

P2O5------ 14.82 10.26 17.89

S ._._ 31 91 Aft

F -------- 212 142 221

LOF4 ----- 25.52 23.24 16.15 

Organic C-------------------

'Quartz only. 

2Calcite only. 

3Pyrite sulfur only. 

4Loss on fusion (loss on ignition at

4 5

13.79 1 

.11 

2.12 

7.34 

.02 

1.45 

36.54 47.4 26 

.73 1 

1.51 

16.82 29.6 18 

.45 

2.03 3.3 

16.89

1,000 Tat localities

6

.8 1 

.019 

.37 

.54 

.01

.22 

.99 

.15 

.3

.443

.61

11-15)

7

2.01 

.016 

.36 

.77 

.09

8.02 

2.79 

.13 

26.2 

.563

.76

8

3.1 1 

.074 

1.95 

8.6 

.017

9.02 

1.96 

2.10 

16.5

.32

9

1.61 

.053 

1.12 

10.7 

.025

7.92 

1.82 

.41 

18.3

.21

10

4.61 

.087 

2.00 

8.7 

.016

6.72 

1.61 

1.75 

16.2

.34

11

22.13

5.15 

2.85

1.07 

33.93 

.85 

1.30 

22.61 

.16 

2.22 

8.78

12

8.93

1.38 

1.00

.71 

44.48 

.83 

.60 

30.63 

.35 

3.45 

9.34

13

0.95

1.83

.50 

52.29 

.55 

.64 

19.97 

.35 

2.47 

20.8

14

0.20

.51 

2.80

1.02 

51.33 

.58 

.45 

25.80 

.61 

3.25 

15.2

15

1.14

1.83 

50.73 

.46 

.15 

14.62 

.30 

1.38 

30.10

dune-beach-nearshore phosphatic sand formed when sea 

level was at a higher stand 10 to 27 ka (D'Anglejan, 

1967). It averages only about 4 percent P2O5 but is estimated to average about 20 m in thickness over an area of 

about 1,800 km2 and to contain about 1.5 billion tons of 

P2O5 . As an unconsolidated sand, it is easy to mine and 

beneficiate. Plans call for production of about 1.5 million 

metric tons of concentrate a year (Stowasser, 1982).

Relict phosphate deposits of Miocene age off southern 

California have attracted commercial interest but are not yet 

in production. They are estimated to contain approximately 

65 million metric tons of phosphate nodules and 52 million 

tons of phosphatic sand that average about 28 percent P2O5 

and occur at average water depths of over 200 m (U.S. 

Department of the Interior Outer Continental Shelf Mining 

Policy Task Force, 1979). Unevaluated phosphorite deposits are found at many other localities on the California 

borderland (Rowland and Cruickshank, 1983; Mullins and 

Rasch, 1985).

Phosphorite of Miocene age extends offshore Florida, 

Georgia, and South Carolina (fig. 15). A recent study (U.S. 

Department of the Interior Outer Continental Shelf Mining 

Policy Task Force, 1979) indicates the presence of about 1.3 

billion tons of phosphorite on the federally controlled Outer 

Continental Shelf in a 30-mi2 (18.6-km2) area at a water 

depth of about 14 m, from which a concentrate averaging 

about 30 percent P2O5 could be produced at costs that compare favorably with those of land-based operations. In the 

late 1960's, the Kerr-McGee Corporation considered offshore mining in State-controlled waters in the Savannah

MIOCENE UPLAND AREAS 

Shoreline = 0 Meter laopaeh of 

Pungo River end Hawthorn Sedlmentt

PHO8PHOQENIC PROVINCES 

Arrow* Indicate Regional Increase In 

Phoaphate Deposition. Actual 

Photphate Concentration la 

Determined by ««ond-JrM|D_CAROL|NA 

'Order Structural. PROVINCE

KNOWN MIOCENE 

PHOSPHATE DEPOSITS

1. AURORA. N.C.

2. ON8LOW BAY. N.C.

3. BLAKE PLATEAU

4. BEAUFORT. S.C.

6. CHATHAM-SAVANNAH. OA.

6. SOUTH OA.

7. NORTH FLA.

8. NORTH-CENTRAL FLA. *

9. OCALA HARD-ROCK

10. ST. AUGUSTINE. FLA.

11. EAST FLA.

12. CENTRAL FLA.

13. SOUTH FLA.

14. MIAMI TERRACE

16. POURTALES TERRACE

Figure T5. Distribution of phosphate deposits in the Southeastern United States (from Riggs, 1984). (Reproduced with 

permission from Science.)

26 Mineral and Petroleum Resources of the Ocean
district, but the project was cancelled because of public 

concern about the destruction of saltwater marshes and the 

possible contamination of freshwater aquifers. Environmental impacts of mining on the Outer Continental Shelf have 

not yet been carefully evaluated but appear to be minimal, 

except in coral reef areas and areas of touristic interest.

Phosphorite of Miocene age also occurs off North Carolina in the Aurora and Onslow Bay embayments (Riggs and 

others, 1982; Snyder and others, 1982) (fig. 15). The deposits in the Aurora outcrop area occur in 24 to 36 m of 

water. Two beds there are estimated to contain 3.75 billion 

metric tons of concentrate having an average P2O5 content 

of 29.2 percent (Riggs and others, 1985). Three beds in the 

northeastern Onslow Bay area, where the outcrop belt is in 

15 to 22 m of water, are also extensive and contain at least 

780 million metric tons of concentrate averaging 29.7 to 

31 percent P2O5 . Seismic surveys suggest that the Onslow 

Bay deposits extend seaward in the subsurface over a 

large area.

The Aurora area also contains surficial phosphatic sands 

of Holocene age, derived in part from the Miocene deposits 

but including some phosphate that formed about 100 ka 

(S.R. Riggs and M.D. Ellington, paper presented at 1983 

Geological Society of America Neogene Symposium; 

Riggs, 1984). They average about 0.6 m in thickness.

The Blake Plateau about 100 km off South Carolina contains about 2 billion tons of phosphorite nodules in an unconsolidated layer about 10 cm thick at a depth of about 300 

to 600 m (Manheim and others, 1980b). They average 20 to 

25 percent P2O5 . The Blake Plateau also has about 1.2 

billion tons of mixed manganese-phosphate nodule pavement, probably lag deposits of Miocene age.

Phosphatic sediments of probable Miocene-Pliocene age 

also occur off the northeastern, southeastern, and southwestern coasts of Florida (Cathcart and others, 1984; 

Gorsline and Milligan, 1963; Gould and Stewart, 1953). 

These deposits are extensive in the subsurface. It is possible 

that they, as well as other Atlantic Continental Shelf deposits, may become accessible through borehole mining 

(extracting the phosphatic sediment as a slurry through a 

drill hole) (McKelvey, 1985).

The Chatham Rise deposits east of New Zealand are 

residual nodules derived from the weathering of a middle 

Miocene limestone. They have been traced for a distance of 

some 480 km along the crest of the rise in a belt up to about 

40 km in width (Cullen, 1980). The nodules occur in a 

fine-grained glauconitic sand from which they could be easily separated, but the nodules themselves average only about 

20.0 to 21.5 percent P2O5 . An area of "207 km2 or 284 km2 

in the central part of the Rise at a water depth of about 400 m 

is estimated to contain 14 or 18 million tonnes of phosphorite nodules" (Kudrass and Cullen, 1982). Consideration is 

being given to mining the deposits for direct application as 

a fertilizer.

Dredge tests indicating the presence of significant 

minable deposits have recently been completed offshore 

Mataiva in French Polynesia.

Guides to Prospecting

The origin of phosphorite in areas of divergent and dynamic upwelling provides a basic guide to the selection of 

areas for further prospecting. As I have shown, it is not just 

areas of present upwelling that are of interest but also areas 

of upwelling in the past. From a practical standpoint, perhaps the best clues to favorable areas are the presence of 

Cretaceous or younger phosphorites in the onshore coastal 

region and, of course, reports of phosphate in offshore 

areas. As Riggs and others (1982) have shown, core sampling and seismic surveying may be necessary to find and 

appraise deposits that are largely concealed by surficial sediments even in their "outcrop" area.

SUBSURFACE HARD-MINERAL DEPOSITS OF 

THE CONTINENTAL MARGINS

Theoretically, any mineral resource mined on the continents can occur in the continental margins. The problems 

associated with bringing them into production are the difficulty of finding concealed deposits and the costs of extraction. In spite of these problems, however, underground mining of subsea-floor mineral deposits has a long history, 

going back at least to the previously mentioned underground 

coal mine operated more than 350 years ago off the coast of 

Scotland (Austin, 1967a). More than 100 subsea underground mines having shaft entry from land, islands, or artificial islands have recovered minerals such as coal, iron ore, 

nickel-copper ores, tin, gold, copper, mercury, and limestone off the coasts of Australia, Canada, Chile, Finland, 

France, Greece, Japan, Poland, Spain, Taiwan, Turkey, the 

United Kingdom, the United States, and other areas 

(Austin, 1967a, b, c). Some of the larger mines have working depths below sea level ranging from 30 to more than 

2,400 m and water cover of as much as 120 m and are as 

much as 8 km from shore (Cruickshank, 1969). Some minerals have been extracted through offshore wells by solution 

mining, and at least one mining operation is conducted by 

subsea quarrying.

Metallic Minerals

Many metallic mineral deposits within bedrock (such as 

tin ore, iron ore, nickel-copper ores, gold, and mercury) 

have been recovered from subsea underground mines in 

widely scattered areas. Off the Cornwall coast in the United 

Kingdom, for example, an early subsea underground tin 

mine was actively operated in the late 18th century until the 

shaft entry was accidentally hit by a ship and flooded. Geologic evidence indicates that the shelf off northwestern

Subsea Mineral Resources 27
Cornwall may be extensively mineralized and that the belt 

of granitic plutons, some of which may be tin bearing, is 

likely to extend westward to the Scilly Islands and possibly 

continue 160 km further offshore (Dunham, 1969; Dunham 

and Sheppard, 1969).

Subsea iron ore of commercial grade has been actively 

mined off Jussaro Island in Finland, off Elba Island in Italy, 

and off Cockatoo Island in the northwestern part of Australia. In Newfoundland, subsea iron-ore deposits, which 

were previously mined from shaft entries on Bell Island, are 

estimated to contain several billion tons of reserves (Pepper, 

1958).

Generally, any mineral that is worth more than $25 to $30 

a ton and extends offshore from the coast as a large, thick 

deposit (several hundred million dollars worth of reserves) 

beneath a cover of impervious rock may be economically 

recoverable by conventional underground mining. Solution 

mining through drill holes may have some potential in the 

future for the extraction of some metallic minerals from 

subsea deposits.

Not much prospecting has been undertaken as yet for lode 

deposits offshore, but areas favorable for their occurrence 

nearshore can be identified where mineralized terrane occurs along the coast. In southeastern Alaska, for example, 

John Mulligan and Thomas Pittman of the USBM (in a 1970 

letter referenced by Tagg (1979)) listed several places where 

they would expect to find sulfide deposits offshore.

Coal

Coal is the most important subsea-floor bedded deposit 

known to occur in large quantities in some of the ancient 

nonmarine sedimentary basins now buried beneath the continental shelves and beyond. Under certain geologic circumstances, portions of the coal-bearing basins might have subsided together with the underlying crustal blocks and now 

occur beneath the continental slope and adjacent areas. One 

new finding was coal in nonmarine Jurassic sedimentary 

strata in a hole at Orphan Knoll about 600 km off Newfoundland. A coal seam of Mesozoic age was also encountered in offshore petroleum drilling on the Grand Banks 

more than 300 km off Newfoundland (Emery and Uchupi, 

1972), and lignite of Late Cretaceous or early Tertiary age 

was found at a Deep Sea Drilling Project site on the Ninetyeast Ridge in the central Indian Ocean (Luyendyk, 1977).

Extensions of large coal fields have been delineated in 

many shelf areas of the world, and, for many years, coal has 

been produced from subsea underground mines off the 

United Kingdom, Japan, Turkey, Chile, and several other 

countries. In 1972, undersea coal production accounted for 

38 percent of total coal production in Japan and 10 percent 

in the United Kingdom; the world's annual subsea production was about 30 million tons.

In Japan, subsea coal mining dates back to 1860, when 

the Takashima coal mine was first extended off the coast of 

western Kyushu (Wang and McKelvey, 1976). To date, 

many subsea coal fields have been discovered off eastern 

Hokkaido and western Kyushu containing over 300 million 

tons of proven coal reserves recoverable under current economic conditions. The six existing subsea coal mines have 

been continually expanded and in 1972 produced a total of 

10.8 million tons (including 5.3 million tons of coking 

coal). The Miike mine, the largest subsea coal mine in 

Japan, has galleries extending more than 5 km off the coast 

and now employs more than 5,000 underground workers.

Offshore drilling in the United Kingdom has delineated 

large coal reserves beneath the North Sea off the Durham 

coast and has also indicated that enormous quantities of coal 

probably lie further offshore beneath the western flank of the 

North Sea Basin. Although deposits there may be beyond 

the present economic limit of subsea underground mining 

with entry from land, they might become recoverable by in 

situ gasification in the future. Exploration of the southern 

North Sea has shown that the coal measures extend to the 

Netherlands but at depths of 7,000 m and more (Kent, 

1980). The English Channel and the Celtic Sea are also 

likely to be underlain by coal.

Subsea coal deposits are widely known in many shelf 

areas of the world, including offshore Israel, Spain, the 

Arctic, the Soviet Union, northwestern Germany, Greece, 

Brazil, Japan, Argentina, Australia, Canada, and Alaska 

and possibly off New England, Washington, and Oregon 

(Tokunaga, 1967; McKelvey and others, 1969b). An appreciable portion of the increasing demand for coal may well be 

supplied by future subsea mines, since subsea underground 

mining is more environmentally acceptable and involves no 

serious environmental risk of surface subsidence above the 

mines. Continuing engineering research to develop new automated techniques of underground excavation and tunneling through hard rocks may eventually extend the economic 

limit of subsea mining of coal and other large deposits 

(beneath a cover of impervious rocks) to more than 35 km 

from the coasts and islands (Wang and Cruickshank, 1969). 

Moreover, the world's increasing demand for energy may 

accelerate development of in situ gasification and other new 

methods that would permit commercial in situ extraction of 

not only the offshore coal deposits presently beyond the 

limit of subsea underground mining but also the low-grade 

coal seams and organic-rich shales offshore as well as on 

land.

Other Nonmetallic Minerals

Most of the world's deposits of saline minerals (for example, sodium, potash, and magnesium salts) form by the 

evaporation of seawater, particularly during the early stages 

of continental rifting. They are thus widespread in the con28 Mineral and Petroleum Resources of the Ocean
tinental margins, but, because they are abundant in land 

sources, they have not been mined subsea. Huge potash 

deposits beneath the North Sea, however, can be accessed 

from vertical shafts at the Boulby mine near the coast of 

northeastern England (Woods, 1979; Smith and Crosby, 

1979). The deposits, consisting of sylvite (KC1) and carnallite (KMgCl3 -6H2O) associated with halite and anhydrite, 

occur in the Zechstein Basin of Late Permian age at a depth 

of about 1,100 m at the Boulby mine. The west-central edge 

of the basin underlies land, but most of it underlies the North 

Sea, which eventually will be the main site of production. 

Potash in the form of sylvite as well as the magnesium salts 

bischoffite (MgCl2 -6H2O) and tachyhydrite (CaCl2 -MgCl2 - 

12H2O) also occur onshore and offshore in the Congo Basin 

and its rifted part, the Sergipe Basin off the eastern coast of 

Brazil. The Congo deposits were mined from 1969 to 1977, 

when the mine was lost because of flooding (de Ruiter, 

1979). Several occurrences of potash are known to be associated with the Miocene salt beds in the Red Sea Basin, and 

an exploration program that will involve seismic surveys 

and drilling is being sponsored by the Saudi Arabian Government.

Common salt was produced by solution mining on the 

U.S. Outer Continental Shelf off Louisiana from 1960 to 

1979. Manheim (1979) estimated the rock salt present off 

the Atlantic and Gulf coasts to a depth of 1 km to total about 

70 trillion tons.

Native sulfur associated with salt-dome cap rock composed of anhydrite (CaSO4) has been produced offshore 

Louisiana by the Frasch process, in which superheated 

water is pumped into the deposit through drill holes to melt 

the sulfur and molten sulfur is pumped to the surface. 

Twenty-four of the 329 onshore and offshore salt domes in 

the U.S. coastal area of the Gulf of Mexico, 4 of the 41 salt 

domes in the Isthmus of Tehuantepec of Mexico, and the 

Challenger Knoll arising from the Sigsbee abyssal plain are 

overlain by cap rock that contains native sulfur (Davis and 

Kirkland, 1979). The origin of these salt domes is complex. 

The cap rock forms when the top of a salt diapir penetrates 

an aquifer; the halite dissolves and leaves a residue of relatively insoluble anhydrite. Sulfate-reducing bacteria in the 

presence of hydrocarbons oxidize organic matter, reduce 

sulfate, and emit carbon dioxide and hydrogen sulfide as 

waste products. The carbon dioxide reacts with calcium ions 

from the anhydrite to form calcium carbonate, and the hydrogen sulfide oxidizes to elemental sulfur. The reaction is

CaSO4+CH4

bacterial

action H2S+CaCO3+H2O

2H2S+O2 2S+2H20

Onshore native sulfur deposits are also associated with 

bedded deposits of anhydrite and gypsum in structurally

favorable settings, such as along faults or in structural highs, 

and there seems to be no reason not to expect similar deposits to occur offshore. Sulfur deposits tend to be much 

smaller than those of the saline minerals with which they are 

associated (in the range of millions or tens of millions of 

tons).

Sulfur is also recovered from offshore production of hydrogen sulfide contained in sour natural gas and in the refining of sulfur-bearing crude oil. Onshore, sulfuric acid is 

produced as a byproduct of the smelting of metal-bearing 

sulfide ores; if subsea sulfide deposits come into production, 

as at least the Red Sea deposits seem likely to do, byproduct 

recovery of sulfuric acid would almost certainly be required 

for environmental reasons.

Frasch mining of elemental sulfur deposits has declined 

since 1974 as known deposits are depleted and production 

from oil and gas increases (Bodenlos and Nelson, 1979). 

Even so, these deposits are still the largest source of sulfur 

production in the United States and the world and, in the 

United States, still account for about half of sulfur production.

A high-grade deposit of barite (BaSO4) first mined on 

Castle Island off southeastern Alaska has been mined by 

underwater blasting and dredging since 1969. The operation 

shows the feasibility of subsea mining of hard-rock deposits, but, at this stage of technological development, only 

high-grade deposits are likely to be amenable to this approach.

Amber, a fossil resin, occurs in marine glauconitic sands 

of early Tertiary age beneath the North Sea and the Baltic 

Sea and has been mined offshore and from beach deposits 

(Beiersdorf, 1972).

MANGANESE NODULES AND 

ENCRUSTATIONS

Black or dark-brown nodules and encrustations on rock 

surfaces composed of a variable mixture of manganese and 

iron oxides, phillipsite, and other silicate minerals are 

widely distributed in the deep-ocean basins and are found 

also in some parts of the continental margins, such as the 

Blake Plateau off the Southeastern United States (Manheim, 

1965). The nodules are of many shapes, ranging from 

roughly spheroidal to discoidal, and are generally 2 to 10 cm 

in diameter. Most are concentrically laminated about a nucleus of a fish tooth or bone, a rock fragment, or a fragment 

of a nodule (see Sorem and Fewkes (1977) and Haynes and 

others (1982) for extensive photographs and descriptions of 

manganese nodules). The encrustations are also generally 

laminated and may be several centimeters thick.

In several areas of the deep-ocean floor, the nodules contain 2.5 to 3.0 percent Ni+Cu+Co and, in recent years, 

have been the object of much research and technological 

development on the part of several mining organizations.

Subsea Mineral Resources 29
Although the nodules have yet to be produced commercially, they have been mined and processed experimentally, 

and it is likely that they will be within technologic and 

economic reach by the end of this century, if not before. 

Less attention has been given to the cobalt-rich encrustations, but Manheim and others (1982) pointed out that, at 

the metal prices prevailing in 1982, the value of these encrustations exceeds that of the nodules on the basis of both 

weight and unit of area; doubtless, the encrustations also 

will be considered for commercial exploitation.

Chemical Composition

Some 74 elements (Haynes and others, 1982, 1985) have 

been found to occur in manganese nodules and encrustations, but their chemical compositions are highly variable, 

both in nodules from a single dredge haul (Frazer, 1977) and 

from place to place. Their average composition varies from 

ocean to ocean and with latitude, water depth, and mineralogy. Over large areas of relatively uniform environment, 

averages based on several samples tend to be relatively 

constant.

World and Ocean Averages

The principal metal contents, concentrations, depths, and 

metal ratios from the 2,401 stations in the Scripps Institution 

of Oceanography's Sediment Data Bank as of March 1980 

(fig. 16) for which there are chemical analyses are summarized in table 4. Because the stations are irregularly distributed (McKelvey and others, 1983), even world averages 

must be regarded as only approximations. More than 400 

stations are located in the northeastern equatorial Pacific's 

Clarion-Clipperton zone, an area of about 2.5 million square 

kilometers in which nodules average 25.43 percent Mn, 

6.66 percent Fe, 1.27 percent Ni, 1.02 percent Cu, and 0.22 

percent Co (McKelvey and others, 1979). The disproportionate number of samples there biases the world averages. 

As the comparison in table 4 shows, excluding ClarionClipperton zone values from the world averages decreases 

somewhat the average nickel, copper, and manganese 

contents, increases the iron content, and has no effect on 

the cobalt content. The world averages estimated by Cronan (1980) (slightly revised from Cronan (1976, 1977)) 

are even lower in manganese, nickel, and copper and 

higher in iron and cobalt (table 5). Because more than 70 

percent of the stations outside of the Clarion-Clipperton 

zone are in the Pacific, the influence of Pacific samples 

on the world averges shown in table 4 is considerable. 

D. Z. Piper (personal communication, 1981) pointed out, 

however, that nodules in the Pacific Ocean are far more 

abundant than those in the Atlantic and Indian Oceans and 

that the number of Atlantic stations in the Sediment Data 

Bank (about 300, in comparison with about 300 Indian 

stations and nearly 1,800 Pacific stations) may give the 

Atlantic undue weight in the world average.

Mero (1962), Cronan and Tooms (1969), and Cronan 

(1977) called attention to the fact that the average manganese, nickel, and copper contents of Pacific nodules are 

higher than those of Atlantic and Indian nodules. These 

differences and others are shown in table 6. Even when 

the Clarion-Clipperton zone stations are eliminated, 

Pacific nodules contain 1.42 and 1.2 times as much manganese and 2.36 and 1.5 times as much combined nickel 

and copper as Atlantic and Indian nodules, respectively. 

As one might expect, these differences also show up in 

the maximum values; nodules from the Pacific Ocean 

contain as much as 50.3 percent Mn and 3.44 percent 

Ni+Cu in comparison with maximums of 40.9 and 32.3 

percent Mn and 2.3 and 3.24 percent Ni+Cu for the Atlantic and Indian Oceans, respectively. On the other 

hand, both the mean and the maximum iron contents are 

highest for Atlantic nodules 16.97 and 50.0 percent, 

respectively, in comparison with 14.23 and 39.63 percent 

for Indian nodules and 11.4 and 41.9 percent for Pacific 

nodules. Although the mean cobalt content is the same for 

nodules from the Pacific and the Atlantic, the maximum 

in Pacific nodules is 2.23 percent, in comparison with 

1.44 percent in Atlantic nodules and 0.94 percent in Indian nodules. The mean cobalt content of Atlantic nodules is more than twice the mean copper content and is 

nearly as much as the mean nickel content.

The metal ratios also differ considerably. Not only is 

the manganese-iron ratio much lower in Atlantic and Indian nodules, but the copper-nickel ratio in Atlantic nodules is also appreciably lower than the copper-nickel ratios in Pacific and Indian nodules. There is a moderate 

negative correlation between manganese and iron in 

Pacific nodules, a much weaker one in Indian Ocean samples, and essentially none in Atlantic nodules (McKelvey 

and others, 1983). A strong positive correlation between 

nickel and copper and a negative correlation between 

combined nickel and copper and iron are found in the 

Pacific nodules, but these correlations are weaker in Atlantic and Indian nodules. For comparison, table 7 shows 

the ocean averages previously estimated by Mero (1962), 

Goldberg (1965), and Cronan (1980) along with those 

from table 6.

The average depth of the nodule stations is about the 

same in the Pacific and Indian Oceans but is nearly 700 m 

shallower in the Atlantic Ocean. No data on concentration 

are available for the Atlantic; those for the Indian Ocean 

are sparse but, for what they are worth, average about the 

same as those for the Pacific.

The contents of other elements found in manganese 

nodules of the world and of the individual oceans are 

shown in table 8. 2 The world mean contents of sodium

2Although Haynes and others' (1982) data for the Pacific are much more 

extensive and cover more elements than the data in table 8 do, the table 8 

data are retained here because they were used in obtaining the world 

averages in tables 17 through 21.

30 Mineral and Petroleum Resources of the Ocean
80°N180°W. 150°W. 12(n/V. 90°W. 60°W. 30°W. 0° 30*E. 60°E. 90°E. 120°E. 150°E. 180°E.

60°N.

40°N.

80«S.

Figure 16. Manganese nodule stations in the Scripps Institution of Oceanography's Sediment Data Bank as of March 1980 (from 

McKelvey and others, 1983).

(1.97 percent), magnesium (1.57 percent), aluminum (2.70 

percent), silicon (7.69 percent), and calcium (2.23 percent) 

exceed 1.5 percent in the nodules; the sum of the oxides of 

these elements at their mean values is about 30 percent. In 

the ^0.1- to < 1.5-percent range are the means of carbon 

(0.327 percent), phosphorus (0.37 percent), sulfur (0.51 

percent), chlorine (0.83 percent), potassium (0.73 percent), 

titanium (0.69 percent), zinc (0.12 percent), and barium 

(0.23 percent). The means of 12 other elements (lithium, 

vanadium, strontium, yttrium, zirconium, molybdenum, 

tellurium, lanthanum, cerium, neodymium, and lead) are in 

the range of ^0.01 to <0.1 percent. Although the mean 

concentrations of these elements in nodules are all much 

lower than those in the deposits from which they are mined 

on land, many represent substantial geochemical concentrations. For example, in comparison with the averages estimated by Lee and Yao (1970) for oceanic crust, the mean 

for zinc in nodules is 10 times greater, that for lead is 93 

times greater, and that for molybdenum is 253 times greater. 

Even though their amounts are relatively small, some of

these minor metals for which the price is relatively high 

conceivably might be recovered as byproducts in the extraction of nickel and copper.

Analyses available for other elements are fewer than 

those available for the metals previously discussed. Given 

this limitation, regional variations nevertheless appear similar to variations observed for the principal metals occurring 

in the contents of some other elements. If only elements for 

which the station population in each ocean is 10 or more are 

considered, the means for phosphorus, calcium, and yttrium 

in Atlantic nodules are more than 20 percent higher than the 

world mean, and those for potassium and titanium are more 

than 20 percent lower (table 8). The means for silica, arsenic, and cerium in the Indian Ocean are more than 

20 percent higher than the world mean, and those for 

lithium, carbon, zirconium, potassium, molybdenum, and 

tin are more than 20 percent lower. Because stations in the 

Pacific are much more numerous than those in other oceans, 

they strongly influence the world mean for most elements,

Subsea Mineral Resources 31
Table 4. World metal contents (in percent), nodule concentrations (in kg/m2 ), and depths (in m) of manganese nodules 

[The Clarion-Clipperton zone is taken to be the area defined by lat 7° to 15° N., long 114° to 153° W.]

Mn --------------------

Fe ---------------------

Ni......................

Cu- -----------------

Ni+Cu -----------------

Co----- ---------------

Nodule concentration -----

FW>r»th

No. of 

stations

9 -I7O

_--_-.-2 374

O -30-J

2

1^CO

2

1 fr

_______7 284

__._.._ ------- 344 jt*t 

-------2,277

All stations

Mean

18.60 

12.47 

.66 

.45 

1.12 

.27 

10.89 

4,270

Stations outside the Clarion-Clipperton zone

Range

0.04-50.3 

.30-50.0 

.01-1.95 

.01-1.90 

.02-3.44 

.01-2.23 

.12-70.8 

46-7,280

No. of 

stations

1,979 

1,979 

1,977 

1,962 

1,960 

1,888 

291 

1,951

Mean

17.4 

13.6 

.55 

.34 

.90 

.27 

11.5 

4,182

Range

0.04-50.3 

.42-50.0 

.01-1.8 

.01-1.9 

.02-3.44 

.01-2.23 

.18-70.8 

46-7,280

Table 5. Comparison of the world average metal contents of manganese nodules listed in table 4 with the values reported by

Cronan (1980)

[All values in percent. The Clarion-Clipperton zone is here taken to be the area defined by lat 7° to 15° N., long 114° to 153° W.]

Element

Mn-----------------

PO

Ni ..................

Cu-----------------.

Ni+Cu -------------.

Co ------------------

World

-------------- 18.60

.-..--_._-._._ 12.47

.............. .66

..-----------. 45

.............. 1.12

.............. .27

Table 4 values

World, excluding 

Clarion-Clipperton 

zone

17.45

B

fi

.55

.34

.90

.27

World values 

reported by 

Cronan (1980)

16.174

15.608

/lOOO

O^<i1

7449

9007

Table 6. Principal metal contents (in percent), nodule concentrations (in kg/m2 ), and depths (in m) of manganese nodules in the

Pacific, Atlantic, and Indian Oceans

[The Clarion-Clipperton zone is here taken to be the area defined by lat 7° to 15° N., long 114° to 153° W.]

All Pacific Ocean stations

Pacific Ocean stations outside 

the Clarion-Clipperton zone All Atlantic Ocean stations All Indian Ocean stations

No. of No. of No. of No. of 

stations Mean Range stations Mean Range stations Mean Range stations Mean Range

Mn-------- 1,777 20.1 0.07-50.3 1,378 18.840.07-50.3 298 13

Fe- -------- 1,772 11.4 .3-41.9 1,377 12.77 .42 41.90 299 16

Ni--------- 1,784 .76 .01 1.95 1,378 .63 .01 1.80 297

Cu -------- 1,771 .54 .01-1.90 1,365 .41 .01-1.90 297 

Ni+Cu----- 1,770 1.30 .02 3.44 1,364 1.04 .02 3.44 296

/-i ITIl^k T7 J"k 1 'I T} \ *} \ A ^n J"\ 1 ^ T"> ^OC

Nodule con- 321 10.89 .12-70.80 268 11.61 .18-70.80 0 

centration.

rw»th------ 1 677 A. ^7Q 46 7 ">8n 1 TS1 A. ->7O 46 7 ->«n ">Q6 ^ 614

.25 0.04-40.9 303 15.25 0.60-32.30 

.97 1.54-50.0 303 14.23 1.33-39.63 

.32 .01-1.56 302 .43 .01-1.58 

.13 .01-.88 300 .25 .01-1.66 

.44 .03-2.3 300 .69 .03-3.24 

.27 .01-1.44 289 .21 .01-.94 

23 10.82 .40-43.2

-m 7 18f» mi A. ^Od. S6A 6 117

32 Mineral and Petroleum Resources of the Ocean
Table 7. Average principal metal contents of manganese nodules, by ocean

[The Clarion-Clipperton zone is here taken to be the area defined by lat 7° to 15° N., long 114° to 153° W.]

Pacific Ocean

Element

Mn-------

Fe--------

Ni--------

Cu-------

Ni+Cu---- 

Co-------

All table 6 

stations

- 20.1

- 11.4

- .76

- .54

- 1.30

- .27

Table 6 stations, 

minus ClarionClipperton zone

18.84 

12.77 

.63 

.41 

1.04 

.29

Mero 

(1962)

24.2 

14.0 

.99 

.53 

1.52 

.35

Goldberg

(1965)

19 

14 

.4 

.5 

.9 

.3

Cronan

(1980) 1

19.78 

11.96 

.634 

.392 

1.026 

.335

Atlantic Ocean

Table 6

13.25 

16.97 

.32 

.13

.44 

.27

Mero 

(1962)

16.3

17.5 

.42 

.20 

.62 

.31

Cronan 

(1980) 1

15.78 

.78 

.328 

.116 

.444 

.318

Indian Ocean

Table 6

15.25 

14.23 

.43 

.25 

.69 

.21

Cronan 

(1980) 1

15.10 

14.74 

.464 

.116 

.580 

.325

'Estimates made on the basis of detrital-free material.

Table 8. Other elements in manganese nodules of the world and of the Pacific, Atlantic, and Indian Oceans 

[ , no data]

Element

Li----------

f3~

C ---------

Na---------

Mg 

Al---------

Si--- .......

fft

Sc- fi --------

Ti------~-.

V---------.

Cr---------

Zn --------

n«

Ge--------

Ac

Rb--------

Si ---- . Y---------

Zr---------

Nb----..--

Mo--------

Ag------

Ci\ --------

No. of 

stations

----- 19

.-.__ 40

Of.

----- 75

----- 2

----- 410

----- 531

. . . . . 592

----- 509

----- 321

----- 106

----- 13

----- 490

i noa

if.

Qnn

- - - - - 437

- - - - - 274

----- 1,363

----- 57

..... 4

----- 63

----- 32

----- 369

. . . _ . H4

TOO

f.Q

QIC.

..... 7

----- 19Q

World

Mean, 

in percent

0.010

nni

.029

. 327 ~>4* i

T nn

1.97

1.57

2.70

7.69

.37

.51

O-3

.73

2.23

nns

.69

052

.V/V/ 007/

.12

001

004

.014

OO9

noc

.015

.057

OO7

n-jo

oni

nni

Range, 

in percent

0.00-0.060

.00-.010

nn9 non

033 1 50

a on ~\ nn

.30-6.55

02 5 39 . \J4* *J . J s

H o nn

94 98 8n

.02-6.03

.05-3.50

98 i ni

.11-3.70

n9 98 T\

00 9fS9 .W .^»U:7

m 8 on

oni snn

onn 9^1

ni o nn

ono on?

nnn_ nno

009 04R

nnn r\f\f.

nni 98^

009 nos

nn9 ~\fj[\

.001-.030

nn9 T>n

nnn_ nn9

nnn_ nn^

Pacific

mean, 

in percent

0.02

001

.030

342

3.0

2 05

1.50

2 75

7

CS)

98

32

O-3

89

1.96

nns

.73

.051

OOQ

.116

nni

nn4

.011

OO9

f\O A

.015

.061

nn?

041

nni

nni

Atlantic

mean, 

in percent

0.025

.77

1

O£

1.75

2 37

6.34

.91

1.34

.57

3.72

nn9

.42

.06

r\nf.

123

nni

.02

.094

f\^ A

.056

no4

.031

nni

Indian

mean, 

in percent

0.001

nni

nn?

.212

3.0

1.70

1.43

2

£*7

9.39

.37

o-j

.48

1.97

nni

£O

.054

nn9

.149

001

ni o

.079

.011

.034

nn?

.029

nni

Subsea Mineral Resources 33
Table 8. Other elements in manganese nodules of the world and of the Pacific, Atlantic, and Indian Oceans Continued 

[ , no data]

Element

Sn --------

Sb --------

Te --------

I---.---...

Ba--------

La --------

Ce --------

Nd--------

Sm--------

Eu --------

Tb--------

Yb ------

Lu --------

Hf --------

Ta --------

Hg -----

Tl---------

Pb --------

Th--------

No. of

stations

----- 141

----- 10

----- 17

..... 1

----- 463

----- 75

----- 72

----- 37

----- 38

----- 38

----- 36

----- 101

----- 32

----- 8

...-. 9

----- 22

.--.. i

----- 130

----- 1,246

----- 41

----- 121

World

Mean,

in percent

.008

.005

.022

250

.23

.021

.072

.026

.004

.001

.001

.003

.000

.001

.002

.010

.000

.016

.093

on?

.003

Range,

in percent

.000-.040

.004-.005

.017-.027

.000-2.14

.009-.070

.009-.300

.007-. 070

.002-.011

.000-.002

.000-.002

.001-.010

.OOO-.OOl

.OOO-.OOl

.000-.002

fina n/in

ftflfl c\f\\

.01-.75

nnn_ nno

.000-.013

Pacific

mean,

in percent

.010

.005

.022

25

.235

.022

.069

.027

.004

.001

.001

.003

.000

.001

.002

nos

.000

.017

.083

003

.003

Atlantic

mean,

in percent

.007

.004

.228

.023

.003

ni 8

.14

001

Indian

mean,

in percent

.001

.21

.018

.125

.011

.004

.001

.001

.001

.000

.012

fine

.101

ftftl

.003

and significant departures from the world mean are not to be 

expected in Pacific nodules. Even so, the mean for 

chromium in Pacific nodules is 28 percent higher than the 

world mean (and 4.5 times higher than that in Indian Ocean 

nodules), and sulfur is 37 percent lower.

Relation to Latitude

It has been known for some time that the subsea manganese nodules richest in nickel and copper are found hi the 

equatorial regions of the Pacific Ocean (Mero, 1962; Horn 

and others, 1972, 1973; Arrhenius, 1975; Piper and 

Williamson, 1977; Skornyakova, 1979; Cronan, 1980; 

Heath, 1981; Exon, 1983), although J.Z. Frazer (written 

communication, 1980) pointed out that, whereas nodules 

greatly enriched in copper occur only near the equator, 

nodules high in nickel occur in many different regions. 

Hutchinson (1947) also reported a latitudinal zonation of the 

iron-manganese ratio in surficial sediments of the Atlantic, 

and Goldberg (1954) found a pronounced dependence of 

this ratio on latitude in pelagic sediments of the Pacific (see 

also Skornyakova, 1965; Greenslate, 1975; Piper and 

Williamson, 1977). Tables 9 and 10 show that the relation 

between latitude and the metal content of the nodules extends to higher latitudes as well. The average manganese, 

copper, and nickel contents generally increase toward the

equator in both hemispheres, and iron decreases, although 

its high is in the 20° to 40° S. zone. Cobalt decreases slightly 

toward the equatorial region in the northern hemisphere but 

shows the opposite relation in the southern hemisphere. The 

increase toward the equator holds nearly as well for the 

maximum values of manganese, nickel, and copper. Curiously, however, the maximum values of iron and cobalt in 

both hemispheres are between latitudes 20° and 40°. Although the total metal content also increases toward the 

equatorial regions in both hemispheres, the difference between 20° groups is relatively small, except below latitude 

60°, where the total of the five metals considered is only 

about 25 percent, an indication that less than half of the 

nodules there are composed of iron and manganese minerals.

The latitudinal relations for manganese and combined 

nickel and copper are also shown in figures 17 and 18. 

These plots show well the increase in these metals toward 

the equator, but the graphs indicate that their contents decrease rather abruptly in the zone extending a few degrees 

north and south of the equator, as Piper and Williamson 

(1977) also showed. The graphs also show a rather curious 

decrease in manganese and combined nickel and copper 

between 20° and 30° S.

Although the average values for both nickel and copper 

generally increase toward the equatorial regions (the value

34 Mineral and Petroleum Resources of the Ocean
Table 9. Principal metal contents (in percent), nodule concentrations (in kg/m2), depths (in m), and metal ratios of manganese 

nodules in the northern hemisphere, grouped by latitude

Between 40° and 60° N. Between 20° and <40° N. Between 0° and <20° N.

Between 0° and <20° N.

outside the ClarionClipperton zone

No. of 

stations

Mn-------60

Fe- -------60

N1--------60

Cu-------60

Ni+Cu----60

Co-------60

Nodule---- 0

concentration.

Depth- - - - - 59

Mean

15.67

.31

.14

.45

3,395

Range

0.16-33.9

2

0 1 "ifi f\

.01-.72

.01 .49

.02-1.21

.01 1.01

972-7,231

No. of 

stations

474

474

463

418

19

465

Mean

18.1

n 64

.57

.32

.89

Tfi

5.43

3,753

Range

0.04-40.9

.42-50.0

.01-1.69

.01 1.10

.03-2.46

.23-17.6

64-6,401

No. of 

stations

913

907

925

f\^ A

924

231

827

Mean

22.1

9.2

.93

.73

1.67

l^S

9.7

4,617

Range

0.07-5P.3

.30-26.7

.02-1.95

.02 1.90

.08-3.44

.01 1.50

.12-56.4

46-7,180

No. of 

stations

514

512

519

CIO

518

509

178

501

Mean

20.41

11.17

.72

.55

1.27

Tfi

10.47

4,501

Range

0.07-50.30

1

-2 -a )/: if\

.02-1.60

09 1 QO

.08-3.44

.01 1.50

.20-56.40

46-7,180

Table 10. Principal metal contents (in percent), nodule concentrations (in kg/m2), depths (in m), and metal ratios of manganese 

nodules in the southern hemisphere, grouped by latitude

Between 0° and

No. of

stations

Mn-------322

Fe- ------- 324

Ni - -322

Cu-------319

Ni+Cu----319

Co- 312

Nodule---- 55

concentration.

Depth----- 319

Mean

1ST

1 3 fi

.55

.37

.91

.29

13.3

4,543

<20° S.

Range

0.21-42.3

83 34 0

.01-1.8

.01-1.66

.02-3.24

m l fifi

.18-62.0

119-7,280

Between 20° and

No. of

stations

361

361

 3CO

359

358

38

360

Mean

15.9

.20

.61

.29

17.3

4,266

<40° S.

Range

A H "2O A

01 1 73

m oo

.03-2.3

.01-2.23

1.2-70.8

800-6,715

Between 40° and <60° S.

No. of

stations

212

212

210

207

207

203

1

211

Mean

14.6

.45

.20

.65

.19

8.4

3,907

Range

0.20-36.0

1.1-30.6

.01-1.65

m oo

.03-2.49

.01-1.06

369-6,117

No. of

stations

35

35

34

33

0

35

>60° S.

Mean

9.4

14.9

.31

.19

.49

.19

4,183

Range

1.0 22.4

5.7 25.6

A-J 1 no

.02-.58

.06-1.58

.06-.57

232-5,051

for nickel between 40° and 60° S. is a slight departure from 

this trend), the copper-nickel ratios are not uniform (J.Z. 

Frazer, written communication, 1980). In the northern 

hemisphere, the copper-nickel ratio increases from an average of 0.49 between 40° and 60° N. to 0.8 in the equatorial 

region. In the southern hemisphere, the average is more 

erratic; the high average of 0.80 is south of 60° S. (where 

nickel and copper values are very low), and the low average 

of 0.59 is between 20° and 40° S. The latitudinal change in 

the percentages of nickel and copper contents is much 

greater than that of iron and manganese contents (Skornyakova, 1979).

The world averages are strongly influenced by the large 

number of Pacific stations, but somewhat similar latitudinal 

relations prevail in each ocean (tables 11, 12, 13).

The means of other elements in manganese nodules 

grouped by latitude are shown in table 14. The means for 

magnesium and lead decrease toward the equatorial region.

So do the means for boron, carbon, aluminum, silicon, and 

calcium in the overall, although they depart from the trend 

in one or more intermediate zones; the means for phosphorus, sulfur, chromium, and yttrium also decrease toward the 

equator in one hemisphere or the other. On the other hand, 

the means for potassium, titanium, vanadium, zinc, and 

molybdenum generally increase toward the equator, although there are some departures from the trend in intermediate latitudinal zones.

Relation to Water Depth

Many investigators have reported a relation between nodule composition and water depth (Menard, 1964; Mero, 

1965; Barnes, 1967; Cronan, 1967, 1977,1980; Cronan and 

Tooms, 1969; Piper, 1972, 1974; Horn and others, 1973; 

Skornyakova, 1976, 1979; Piper and Williamson, 1977;

Subsea Mineral Resources 35
UJ

U 

QC

55

50

45

40

35

30

UJ

Z 

O

UJ 

0) 

UJ

Z 20

< 

O

10

v; i.

>''. * *.* " 

 «

 ^>

80*S. 60°S. 40*S. 20°S. 0° 

LATITUDE

20°N. 40°N. 60°N. 80°N.

Figure 17. Relation between manganese content in manganese nodules and their latitudes at stations in the Scripps 

Institution of Oceanography's Sediment Data Bank (from McKelvey and others, 1983).

Table 11. Average and maximum (in parentheses) principal metal contents (in percent) of manganese nodules in the Pacific 

Ocean, categorized by latitude

Element

Mn--------

Fe- --------

Ni---------

Cu--------

Ni+Cu-----

Co--------

Total --

40°-<60° N. 

(30 stations)

15.71 (33.9) 

11.33 (26.0) 

.35 (.72) 

.19 (.49) 

.54 (1.21) 

.24 (.86) 

28.36

20°-<40° N. 

(355 stations)

19.72 (39.56) 

12.28 (41.90) 

.66 (1.69) 

.38 (1.10) 

1.04 (2.46) 

.28 (1.64) 

34.36

0°-<20° N. 

(885 stations)

22.39 (50.30) 

8.90 (26.7) 

.96(1.95) 

.76(1.90) 

1.72 (3.44) 

.26(1.50) 

34.99

0°-<20° S. 

(244 stations)

18.30 (42.3) 

14.17(34.0) 

.54 (1.80) 

.34 (1.54) 

.89(3.11) 

.31 (1.88) 

34.55

2o°-<40° S. 

(146 stations)

16.46 (38.02) 

16.93 (32.20) 

.47(1.73) 

.22 (.65) 

.69 (2.17) 

.35 (2.23) 

35.12

40°-60° S. 

(98 stations)

14.89 (36.0) 

14.13(28.20) 

.54(1.65) 

.24 (.84) 

.79 (2.49) 

.22(1.06) 

30.81

>60° S. 

(32 stations)

10.11 (22.40) 

15.57 (25.64) 

.32(1.00) 

.20 (.58) 

.52(1.58) 

.19 (.57) 

26.91

36 Mineral and Petroleum Resources of the Ocean
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 ^

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5' 3

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KJ

j;nU3^^

v>

r^

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3__

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ON Oz^

q 1°A

9 Z

KJOAZO1° A

KJ?O1° A

KJ 

°o

S" o

1° Ao^

1° A

ON°

tnV

ON

°o

?

ft) 3nw

OQ 

N' ^

CT

-<

ST

c 

o.

Z

Nd>

fs

/sn?

ft>3

Q. 3

ft>

X. 3

c 3

5'

~o 

ft>3

r^1

5' oT3'

£L3

2-

§Ln03

ST3

cr

5'

"^n

re3G

- ^

3 

ft>

3 

OQ 

ft) 3

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o>f/1

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^.

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ff

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& 0) w f^

COMBINED NICKEL AND COPPER CO

O

03 O 

0) 3

o 5' 

3 3

.31c

Q.

o
Table 13. Average and maximum (in parentheses) principal metal contents (in percent) of manganese nodules in the Indian 

Ocean, categorized by latitude 

[ , no data]

Element

Mn----------

Fe- ------

Ni-----------

Cu----------

Ni+Cu-------

Co----------

Total - - - -

0°-20° N. 

(28 stations)

---- 16.52(32.30)

---- 16.64(22.80)

-JO / 01\

---- .10 (.30)

---- .48(1.08)

. . . . 29 ( 93) '**' \-^-}> 

---- 34.41

0°-<20° S. 

(73 stations)

18.05 (32.25) 

11.92(19.70) 

.58 (1.58) 

.47(1.66) 

1.06(3.24) 

.20 (.94) 

32.28

20°-<40° S. 

(159 stations)

14.36 (26.50) 

15.47 (39.63) 

.37(1.19) 

.18 (.84) 

.55 (1.95) 

.22 (.62) 

31.15

40°-<60° S. 

(42 stations)

13.53 (24.57) 

12.25 (21.60) 

.48(1.43) 

.25 (.89) 

.72(2.13) 

.13 (.37) 

27.36

>60° S. 

(2 stations)

3.07 (3.93) 

8.94 (12.22) 

.04 

.02 

.06

12.13

Pautot and others, 1978; Frazer and Fisk, 1981; Andrews 

and others, 1980). High values of cobalt, for example, are 

found mainly on seamounts, and cobalt content tends to 

decrease with increasing depth. A moderate negative correlation of cobalt with depth is found (the correlation is 

weakly positive south of lat 60°, but the negative correlation 

is rather strong only in the group of samples from 40° to 60° 

N.), as is a weak positive correlation of combined nickel and 

copper with depth (McKelvey and others, 1983). Data on 

three groups of stations are summarized in table 15. The 

means for stations in water depths of less than 2,000 m are 

0.53 percent Co, 18.00 percent Mn, 14.81 percent Fe, and 

only 0.50 percent Ni+Cu. The means for samples from 

water depths of greater than 4,000 m are 18.6 percent Mn, 

11.7 percent Fe, 1.24 percent Ni+Cu, and only 0.24 percent Co. If Clarion-Clipperton zone samples are eliminated, 

the mean manganese value drops to 17.10 percent, combined nickel and copper decreases to 0.99 percent, iron 

increases to 13.01 percent, and the cobalt content remains 

unchanged.

Given the rather marked differences in the metal contents 

of these groups, one might expect the correlations of nickel, 

copper, and cobalt with depth to be stronger than tables 4, 

6, 9, and 10 indicate. The explanation of why they are not 

is found in figures 19 and 20, which show that the depth 

relation is not linear. Rather, there is a threshold depth of 

about 2,900 to 3,000 m, above which combined nickel and 

copper contents greater than 1 percent are rare and below 

which nodules containing cobalt in amounts greater than 

about 0.6 percent are rare. As figures 21 through 26 show, 

below the threshold depth for combined nickel and copper 

and above it for cobalt, the maximum metal contents rise to 

an optimum depth range and then decline. Nodules containing more than 3.0 percent Ni+Cu, for example, are found 

only in a depth range of about 4,450 to 5,450 m in the 

Pacific, and nearly all of them are in a range of 4,800 to 

5,200 m. No such values are found in the Atlantic, but the 

few samples containing more than 1.5 percent Ni+Cu occur 

in a depth range of about 4,850 to 5,200 m. In the Pacific, 

the optimum depth range for nodules containing more than

1 percent Co is about 800 to 1,850 m; in the Atlantic, it is 

about 1,000 to 1,650 m. No such high values have been 

found in Indian nodules, but one of the two highest values 

reported is from a depth of about 1,350 m. The rather 

substantial differences in the mean values of nickel, copper, 

iron, and cobalt above and below the 3,000-m depth are 

shown in table 16.

Cronan and Tooms (1969, p. 340) also noted the enrichment of nickel and copper in the deeper water nodules and 

observed that:

. . . 3000-4000 m is a critical depth for many of 

the elements. In the case of Co, Cu, Pb, Ba, and 

V, in particular, there is a sharp difference between the concentrations above and below 

3000 m. Those elements which are in higher concentrations in the shallower waters tend to 

increase gradually in concentration from 3000 m 

to the surface. A similar distribution is observed 

in the case of Cu although the highest average 

concentrations are recorded at the maximum 

depths.

(As I indicated above, the increase "to the surface" does not 

hold for cobalt.) Piper (1974) reported that the rare-earth 

composition of nodules also changes at the 3,000-m depth, 

and Piper and Williamson (1977) showed that the high values of the manganese-iron ratio as well as those of the nickel 

and copper ratios are below this depth.

As figure 27 shows, manganese shows little correlation 

with depth, although the data suggest a decrease in the 

maximum values and possibly an increase in the minimum 

values with increasing depth. No nodule analysis shows 

more than 32 percent Mn below depths of 5,300 m, and only 

one reports less than about 13 percent Mn below 6,000 m. 

The increase in the copper-nickel ratio with increasing 

depth reported by S.A. Mooreby (unpublished thesis, 1978, 

discussed by Cronan (1980)) for Indian Ocean nodules can 

also be seen by comparing the mean copper-nickel ratio with 

mean depths in the various populations analyzed in the 

tables here. Thus, at the mean depth of 1,266 m for samples 

from depths less than 2,000 m, the copper-nickel ratio is

38 Mineral and Petroleum Resources of the Ocean
Table 14. Means of other elements (in percent) in manganese nodules of the world, grouped by latitude 

[ , no data. Values set in italics are based on 10 stations or more]

Element

L ........

Be-------

C --------

F --------

Na-------

Mg-------

A1

Si--------

P ........

Cl--------

Ca -------

<sr

Ti--------

V-- ------

Cr--------

Zn -------

Ga-------

Ge -------

As -------

Rb-------

Sr--»- 

Y-- ------

Zr-- ------

Nb-------

Mo-------

Ag - 

Cd-------

Sn -------

Sb -------

Te -------

I-....-...

Ba-------

La -------

Ce -------

Nd-------

Sm ------ -

Eu -------

Tb-------

Yb-------

Lu -------

Hf -------

Ta -------

W--------

Hg -

Ti--------

Pb .......

Th-------

60°-40° N.

--- 0.000

ft9 8

 ")£

--- 1.64

--- 7.72

2

0 /

--- 72.75

.26

7-3

.57

--- 2.79

nni

.53

 --- .042

Ofld

.06

.002

.01

.003

f\O A

("19°.

.040

.005

.038

.000

.000

.297

.018

.053

.018

.004

.001

.001

.002

.000

.010

.720

nni

.008

40°-20° N.

--- 0.02

.000

/T>^C

.29

7.57

7.67

2.67

7 04 / .\j*t 

.50

.51

Of

.71

3.30

/r/n

.66

.055

.012

.12

.001

---- .004

.019

.003

.097

.076

.062

.009

.040

---- .001

.007

.005

---- .005

---- .022

.37

.02

.10

.027

.004

.001

.001

.003

.000

---- .001

_ _ _ _ 003 - - - - ,\j\jj

n is

.103

.\j\jj 003

.0021

20° N.-0°

0.001

.000

.02

.22

--- 3.0

1.84

1.57

2 CO

7.42

7S

.26

.74

1.87

023

64

046

.011

.11

.001

.009

.007

0<°2

.075

.\J*T4, 047

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.046

.001

.001

- - - - 25

.267

.027

.055

.034

.006

.001

.001

.003

.000

.076

.067

004

.0021

0°-20° S.

0.001

.001

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.30

2.30

1.40

2.56

7 CJ?

70

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2.07

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.000

.016

.001

.077

.075

.057

.070

.037

.001

.007

.004

.020

.773

.020

.065

.020

.003

.001

.001

.003

.000

--- .002

.077

--- .000

.076

.091

/T/19

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20°-40° S.

0.001

.022

.412

1 OO

7.96

1.42

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.073

.036

.004

.031

.002

.001

.070

.234

.020

.126

.020

.004

.001

.001

.003

.000

OOQ

.014

.121

/U19

.005

40°-60° S.

0.002

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too

2.37

7.55

2.46

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OjC

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98

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7.52

002

£^ 3

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.10

.001

.015

/1C9

.073

.072

.005

.037

.002

.009

.736

.017

.045

.030

.004

.001

.002

.003

.000

.012

.141

003

.004

60°-80° S.

1.96

2.64

 310

i-a oo

964

2.25

.639

041

.06

084

.073

.037

.005

.709

.161

Subsea Mineral Resources 39
Table 15. Metal contents (in percent), nodule concentrations (in kg/m2), and depths (in m) of metal ratios of manganese nodules

in water depths of less than 2,000 and more than 4,000 m

[The Clarion-Clipperton zone is here taken to be the area defined by lat 7° to 15° N., long 114° to 153° W.]

<2,000 m >4,000 m

Stations outside Clarion-Clipperton 

zone at >4,000 m

No. of No. of

stations Mean Range stations Mean

Mn--------------- 186 18.00 0.16-50.30 1,561 18.6 

Fe---------------- 186 14.81 .42-41.9 1,557 11.7

Ni---------------- 185 .41 .01-1.16 1,565 .71

Cu --------------- 174 .08 .01-.73 1,565 .52

Ni+Cu------------ 174 .50 .02-1.78 1,563 1.24

Co--------------- 170 .53 .01 2.23 1,530 .24

Nodule------------ 0 332 11.1

concentration.

Depth------------- 188 1,266 46-2,000 1,576 4,946 4

PERCENT

<kCJ 

Z

hZ

LUhCOPPER CON

Ni

0

Z

<

_J

LU 

CJ

Z

0

COMBIIS

D

1

' -" I/)

/ivi?' t » ** « *

No. of

Range stations Mean Range

0.04-42.30 1,249 17.10 0.04-42.30 

.3-50.0 1,249 13.01 .83-50.00 

.01-1.89 1,247 .58 .01-1.80 

.01-1.90 1,247 .41 .01-1.90 

.02-3.44 1,245 .99 .02-8.44 

.01-1.04 1,221 .24 .01-1.04 

.12-70.8 279 11.78 .18-70.8

,000-7,280 1,258 4,977 4,000-7,280

\ 

,.\

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» " ' .

It * " 

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- ' ".rAv-' >.;>. & $11$^: \ . 

,-: -^f \: ., «-^;::A^iVr.- -

..- ...>-.- -: .-« -: ? M-;..'..f ..;.,r, .

 . , '*'.*. »'* ' ..*'*.

1000 2000 3000 4000 5000

DEPTH, IN METERS

6000 7000 8000

Figure 19. Relation between depth and combined nickel and copper content in manganese nodules at stations in the 

Scripps Institution of Oceanography's Sediment Data Bank (from McKelvey and others, 1983).

40 Mineral and Petroleum Resources of the Ocean
LU 2

O 

QC 

UJ 

CL

z

UJ

K

o o

O 1

o

1000 2000 3000 4000 5000

DEPTH, IN METERS

6000 7000 8000

Figure 20. Relation between depth and cobalt content in manganese nodules in the Scripps Institution of Oceanography's Sediment Data Bank (from McKelvey and others, 1983).

0.196; at the mean depth of 3,395 m for samples between 

40° and 60° N., the ratio is 0.49; at the mean depth of 

4,379 m for all Pacific stations, it is 0.71.

Means of other elements in water depths above and below 

3,000 m are shown in table 17. If only those elements that 

have been analyzed at 10 stations or more in populations 

above and below the 3,000-m depth are compared, aluminum, silicon, potassium, scandium, and samarium are 

enriched in nodules below that depth, and boron, phosphorus, sulfur, calcium, vanadium, chromium, arsenic, strontium, yttrium, barium, cerium, and lead are enriched in 

nodules above it. Means for several other elements (for 

example, sodium, magnesium, zinc, zirconium, molybdenum, and lanthanum) are about the same in both groups.

Metal-Rich Types of Nodules

Three distinct, only rarely overlapping compositional 

types of possible economic interest can be recognized:

(1) nodules containing more than 1 percent Ni+Cu,

(2) nodules containing more than 0.5 percent Co, and

(3) nodules containing more than 35 percent Mn (although 

nodules in this group contain more than 0.5 percent Co only 

exceptionally, they do average nearly 1.1 percent Ni+Cu) 

(McKelvey and others, 1983). The metal contents of these 

types are summarized in tables 18, 19, and 20; the groups 

having high combined nickel and copper contents and high 

cobalt contents have been broken into two parts. These 

groups are similar to ones that Howarth and others (1977)

Subsea Mineral Resources 41
z

UJ

o 

cc

UJ *- 3

z

H

z

UJ

Z

o o

QC 

UJ 

Q. fe 2

O 

Q

<

UJ *

O

Q

I 1

002

O 

o

V'

I * * ' -#.V.

 v 7**. *

1000 2000 3000 4000 5000

DEPTH, IN METERS

6000 7000 8000

Figure 21. Relation between depth and combined nickel and copper content in Pacific Ocean manganese nodules at 

1,770 stations in the Scripps Institution of Oceanography's Sediment Data Bank (from McKelvey and others, 1983).

defined for the composition of Pacific nodules by using a 

nonlinear mapping technique. Their group 2, for example, 

averages 0.60 percent Co, 0.56 percent Ni+Cu, and 15.58 

percent Mn; their groups 3, 4, and 5 average 0.3, 0.27, and 

0.17 percent Co, 1.15, 1.97, and 2.74 percent Ni+Cu, and 

17.67, 22.07, and 26.99 percent Mn, respectively; their 

group 6 averages 0.06 percent Co, 1.05 Ni+Cu, and 

34.29 percent Mn.

Tables 18 and 19 show nodules high in combined nickel 

and copper worldwide and outside the Clarion-Clipperton 

zone. Mean combined nickel and copper contents of nodules 

within the Clarion-Clipperton zone seem to be slightly 

richer than those of nodules outside, but nodules rich in 

combined nickel and copper have essentially the same

chemical compositions wherever they are found. Given the 

depth and latitude relations already discussed, one would 

expect nodules rich in nickel and copper to occur at abyssal 

depths in low latitudes; tables 18 and 19 and figures 28 and 

29 confirm this expectation. Figures 28 and 29, however, 

show that nodules rich in nickel and copper also occur at 

higher latitudes. In both the Pacific and the Indian Oceans, 

nodules richest in nickel and copper are found mainly in the 

eastern parts (Cronan and Tooms, 1969; Tooms and others, 

1969; Cronan, 1980). Nodules containing 1.8 percent 

Ni+Cu or more are essentially absent from the Pacific west 

of 180° W., even at low latitudes, and none have been 

reported west of 75° E. in the Indian Ocean (fig. 28). Only 

a few samples containing 1.8 percent Ni+Cu or more have

42 Mineral and Petroleum Resources of the Ocean
UJ

o

DC 

UJ 

CL

Z 

O

o

cc 111

Q. 

Q. 

O 

O

UJ

o

Z

o

UJ

Z

m

O 

o

1000 2000 3000 4000 5000

DEPTH, IN METERS

6000 7000 8000

Figure 22. Relation between depth and combined nickel and copper content in Atlantic Ocean manganese nodules 

at 296 stations in the Scripps Institution of Oceanography's Sediment Data Bank (from McKelvey and others, 1983).

Table 16. Principal metal contents of manganese nodules in water depths above and below 3,000 m

Element

M

Fe-- ------------

Ni--------------

Cu -------------

Ni+Cu- ------

Co--- ----------

No. of stations

..._-----.-. 324

............ 324

 3 (\Q

irn

<3,000 m

Mean, in percent

17.16

1 C £.1

.39

.10

.50

.46

No. of stations

1,931

1,926

1,936

1 935

1 933

'

>3,000 m

Mean, in percent

18.60

12.17

.69

.49

118

.23

Subsea Mineral Resources 43
cc

UJ

I

O

u

O 

O

O

UJ

U

z

O

UJ

5

O 

O

; '.. "v vi*U ^v!^V.''j:

 , ** ' '< . ' ".*' ' * ' * *«

_j______\_____\______\-

1000 2000 3000 4000

DEPTH, IN METERS

5000 6000 7000

Figure 23. Relation between depth and combined nickel and copper content in Indian Ocean manganese nodules at 

300 stations in the Scripps Institution of Oceanography's Sediment Data Bank (from McKelvey and others, 1983).

been reported from the Atlantic, but the largest concentrations of samples containing > 1.0 to < 1.8 percent also lie on 

the eastern side of the basin (fig. 29).

Nodules containing >1.0 to <1.8 percent Ni+Cu are 

generally distinct from those in the cobalt- and manganeserich groups. In comparison with nodules containing 1.8 

percent Ni+Cu or more, they contain less manganese and 

more iron, and their copper-nickel ratio is appreciably 

lower.

Tables 18 and 19 indicate that the concentration of nodules on the sea floor is inversely related to combined nickel 

and copper content, both in the lower average concentration 

found in nodules containing 1.8 percent Ni+Cu or more in

comparison with those containing >1.0 to <1.8 percent 

Ni+Cu and in the maximum nodule concentrations in each 

group. This relation was previously reported by Menard and 

Frazer (1978) and Frazer and Fisk (1981) for the entire 

Pacific but was found to be weak in the Clarion-Clipperton 

zone (McKelvey and others, 1979).

The manganese content of nodules high in cobalt (table 

20) is similar to that of nodules high in combined nickel and 

copper, but the iron content is much higher. These cobaltrich nodules are low in combined nickel and copper, and 

their copper-nickel ratio is also low. Comparison of the 

>0.5- to < 1.0-percent group shows that, in the > 1.0- 

percent group, manganese is appreciably higher, iron is

44 Mineral and Petroleum Resources of the Ocean
UJ

o

QC

z 

O

o

GO 

O 

O

1000 2000 3000 4000 5000

DEPTH, IN METERS

6000 7000 8000

Figure 24. Relation between depth and cobalt content in Pacific Ocean manganese nodules at 1,710 stations in the 

Scripps Institution of Oceanography's Sediment Data Bank (from McKelvey and others, 1983).

slightly lower, the copper-nickel ratio is lower, and the 

average depth is about 1,000 m less. Figures 30 and 31 

suggest, along with previous observations (Mero, 1962; 

Menard, 1964; Cronan and looms, 1969; Piper and 

Williamson, 1977; Calvert, 1978), that, although cobaltrich nodules occur over a wide range of latitudes and longitudes, those containing more than 1 percent or even more 

than 0.5 percent Co are relatively more populous in the 

central and western Pacific. The > 1.0-percent cobalt group 

is, in fact, essentially of the same composition, as are the 

encrustations reported by Craig and others (1982) from the 

Hawaiian Archipelago and by Manheim and others (1982) 

on mid-Pacific seamounts 1.0 percent Co, 0.5 percent Ni, 

25.0 percent Mn, and <0.1 Cu in the crusts, according to

Manheim and others, in comparison with means of 1.25 

percent Co, 0.55 percent Ni, 26.02 percent Mn, and 0.094 

percent Cu for the same metals in the > 1.0-percent Co 

nodules shown in table 20. It is possible that some samples 

reported as nodules in the Sediment Data Bank may actually 

be encrustations.

Nodules containing more than 1.0 percent Co have not 

been reported in the Indian Ocean, but those containing 0.5 

percent Co or more are confined to the western side of that 

basin. The number of samples in the ^ 1.0-percent Co group 

is only 27, perhaps not enough to justify much confidence 

in the observations made about them here.

Nodules high in manganese (table 20) also have been 

found at only 27 stations, again too few to support much

Subsea Mineral Resources 45
Table 17. Means of other elements in manganese nodules in water depths above and below 3,000 m 

[ , no data]

<3,000 m

Element

L--.- .....

Be ---------------

C ----------------

Na--- ------ 

Mg ---- .

A1

Si-. - .....

P -_...._........_

o

d- -------------- _.

Ca ............ ....

<5r

Ti-- ...............

V-----------------

Pr

Zn -----.------.--.

Ga---------------

Ge----- - ---- .

As ---------------

Rb---. ............

Si-------- -----

Y--- -.- ....

Zr----------------

Nb----------------

Mo---------------.

Ag --------

Cd----------------

Sn ----------------

Sb ----------------

Te ----------------

I----.....-........

Ba - --- 

La ----------------

Ce ----- - 

Nd----------------

Sm----------------

Eu ----------------

Tb ----------------

Yb----------------

Lu ----------------

Hf ----------------

Ta ----------------

W-----------------

Hg--~- ----- 

n- . - ....

Pb ----------------

Th- - -----

No. of stations

....-----..... 5

.............. 10

.-..----...--. 33

.............. 2

.............. i

.............. 98

.....---...... 125

.............. 103

.....-------.. 94

.............. 51

.............. 12

....--.-...... o

.............. 119

.............. igg

.............. 21

1 1£.

f.0

.............. 52

.............. 188

....-..-.-.... 15

.............. o

.............. 14

.............. o

.............. 77

1£i

-____-----__._ Af\

.............. 15

.............. us

.............. o

.............. 23

.....-.--..... 19

.............. i

.............. o

.............. o

.............. 63

.............. 33

.............. 15

.............. 13

.....---...... 13

.............. 13

.............. n

.............. 36

.............. 13

.............. o

.............. o

.............. o

.....---..-... o

.............. 24

.............. 197

.............. 9

.............. 13

Mean, in percent

0.001

.001

.vtU040

.91

3 00

1.83

1.61

1.72

5.07

1.148

oc

.47

4.65

ftftl

.76

.071

.015

.11

.001

_

.020

.122

.024

.057

.005

.045

.001

.004

.004

.34

.022

.087

.021

.003

.001

.001

.004

.000

_

ni 8

.14

,\j\j£ 002

.002

>3,000 m

No. of stations

14

30

52

£Q

1

310

403

478

399

O£«

92

13

1£Q

883

54

748

1£.1

221

1,118

41

4

47

32

290

239

52

710

7

102

122

8

17

1

398

42

57

24

25

25

25

64

19

8

9

22

1

101

1,029

31

105

Mean, in percent

0.013

.001

.022

.311

3 on

2.02

1.553

2 95

8 0Q

.22

A 1

0-3

01

1.72

Oft?

£Q

049

006

.12

.001

.004

.012

.002

.075

.012

057

.008

.037

.001

.001

.009

.005

.022

 25^ J

.22

.021

.068

.028

.005

.001

.001

.002

.000

.001

.002

.010

.000

.016

.08

001

.003

46 Mineral and Petroleum Resources of the Ocean
UJ

O 

QC

UJ

CL

O

o

00

O 

U

1000 2000 3000 4000 5000

DEPTH, IN METERS

6000 7000 8000

Figure 25. Relation between depth and cobalt content in Atlantic Ocean manganese nodules at 285 stations in the 

Scripps Institution of Oceanography's Sediment Data Bank (from McKelvey and others, 1983).

generalization about them. The data, however, indicate that 

they are relatively low in iron (some are very low); the mean 

manganese-iron ratio is 16.12, in comparison with 4.43 for 

nodules of the 1.8-percent Ni+Cu type. The mean combined nickel and copper content, 1.08 percent, falls in the 

lower range of the sl.O- to < 1.8-percent Ni+Cu group. 

Halbach and Fellerer (1980) found, for nodules from the 

southeastern Pacific, that combined nickel and copper increases as the manganese-iron ratio increases up to about 5 

and decreases as that ratio increases further.

Although the number of samples shown in figure 32 is 

small, all but two of them occur in the eastern and north 

equatorial Pacific (see also Mero, 1962; Cronan and Tooms, 

1969; Skornyakova, 1979; Cronan, 1980; Heath, 1981).

Only one sample is in the Atlantic, and none have been 

found in the Indian Ocean. Whereas the nodules especially 

rich in manganese are found along the eastern margin of the 

Pacific Basin, Skornyakova (1979) reported that those rich 

in iron are from its western margin, where they have concentrations as high as 70 percent Fe2O3 and manganese-iron 

ratios of less than 1 (see also Price and Calvert, 1970).

Other elements in manganese nodules classed by metal 

type are shown in table 21. Examining the distribution of 

other elements hi nodules typed by their high contents of 

combined nickel and copper, manganese, and cobalt (table 

21) indicates that several other elements follow these metals 

in their variations. The mean values of magnesium, aluminum, silicon, potassium, scandium, chromium, and zinc

Subsea Mineral Resources 47
Z 

UJ 

O 

DC 

UJ 

Q.

Z 

UJ

O 

O

00

O

O

1000 2000 3000 4000

DEPTH, IN METERS

5000 6000 7000

Figure 26. Relation between depth and cobalt content in Indian Ocean manganese nodules at 289 stations in the 

Scripps Institution of Oceanography's Sediment Data Bank (from McKelvey and others, 1983).

Table 18. Metal contents (in percent), nodule concentrations (in kg/m2 ), and depths (in m) of manganese nodules containing 1.0 

percent Ni+Cu or more

>1.8 percent Ni+Cu

Mil-------"--" ---.

Co

Ni-- -- - -" . Cu - Ni+Cu-- . Co - 

Nodule concentration

Depth - - 

No. of 

stations

----- 557

. . . . . 554

----- 561

----- 561

----- 561

. . . . . 527

----- 141

fftf.

Mean

26.17 

6.89 

1.29 

1.05 

2.34 

.21 

5.9 

4,720

Range

14.02-45.6 

.3-16.92 

.56-1.95 

.33-1.90 

1.81-3.44 

.01-.63 

12 27 25

2,660-6,401

>1-<1.8 percent

No. of 

stations

459 

457 

465 

465 

465 

444 

76 

423

Mean

20.4 

10.2 

.85 

.54 

1.39 

.23 

9.3 

4,668

Ni+Cu

Range

7.11-45.5 

1.0-22.2 

.24-1.43 

.06-1 .22 

1.0-1.8 

.01-1.0 

.18-30 

1,116-6,965

48 Mineral and Petroleum Resources of the Ocean
55

50

45

^ 40

UJ

U 

<r

a! 35

2 30

UJ

Z 

8 25

UJ 

CO

UJ

20

15

10

1000 2000 3000 4000 5000

DEPTH, IN METERS

6000 7000 8000

Figure 27. Relation between depth and manganese content in manganese nodules at stations in the Scripps Institution 

of Oceanography's Sediment Data Bank (from McKelvey and others, 1983).

Table 19. Metal contents (in percent), nodule concentrations (in kg/m2), and depths (in m) of manganese nodules containing 1.0

percent Ni+Cu or more outside the Clarion-Clipperton zone

[The Clarion-Clipperton zone is taken here to be the area defined by lat 7° to 15° N., long 114° to 153° W.]

Mn-------------------

fta

^i.... .................

Cu-------------------

Ni+Cu----------------

Co --------------------

Depth- ----------------.

No. of 

stations

*^£.1

O£1

. . . _ . 264

. . . . . 264

. . . . . 264

T30

----- 90

. . _ . . 259

>1.8 percent Ni+Cu

Mean

26.10 1 

7.72 

1.24 

.98 

2.23 

.19 

5.08 

4,652 3

>1.0-<1.8 percent Ni+Cu

Range

4.02-45.60 

3.23-16.92 

.56-1.80 

.33 1.90

1.81-3.44 

.01-.49 

.20-20.0 

,160-6,401

No. of 

stations

367 

365 

370 

370 

370 

350 

74 

356

Mean

20.61 

10.78 

.84 

.52 

1.36 

.22 

9.44 

4,640

Range

7.11-45.50 

1.10-22.20 

.24-1.43 

.06-1.22 

1.00-1.80 

.01-1.00 

.18-30.0 

1,116-6,965

Subsea Mineral Resources 49
180°W. 150°W. 120-W. 90°W.

8CTN. r

60-W. 30-W. 30°E. 60°E. 90°E. 120"E. 150°E. 180°E.

60°N.

60°S.

80"S.

Figure 28. Distribution of manganese nodules containing 1.8 percent Ni+Cu or more (from McKelvey and others, 1983).

in the > 1.8-percent Ni+Cu group are appreciably higher 

than those in the >0.5- to < 1.0-percent Co group. The 

highest means for magnesium (1.87 percent), scandium 

(0.018 percent), and chromium (0.013 percent) are in the 

^ 1.8-percent Ni+Cu group, which also has the lowest

mean values for sulfur (0.22 percent), calcium (1.59 percent), strontium (0.06 percent), lanthanum (0.013 percent), 

cerium (0.035 percent), and lead (0.048 percent); the mean 

for vanadium (0.043 percent) in this group is also appreciably lower than that in the >0.5-percent Co groups but is

Table 20. Metal contents (in percent), nodule concentrations (in kg/m2), and depths (in m) of manganese nodules containing more 

than 0.5 percent Co and more than 35 percent Mn

^ 1.0 percent Co >0.5-<1.0 percent Co >35 percent Mn

Mn-------------

Fe-------------

Ni-------------.

Cu ---- --.

Ni+Cu---------.

Co------------.

Nodule ---------

concentration. 

Depth----- ------

No. of 

stations

--- 27

--- 27

--- 27

--- 27

--- 27

--- 27

... o

--- 23

Mean

26.02 

15.6 

.55 

.094 

.64 

1.25

1,764

Range

18.83-50.3 

9.5-20.3 

.3-1.25 

.03-. 36 

.33-1.5 

1.0-2.23

795-5,192

No. of 

stations

155 

154 

155 

150 

150 

155 

4

152

Mean

20.0 

16.54 

.44 

.16 

.60 

.64 

17.2

2,791

Range

6.3-45.5 

4.2-26.0 

.11-1.47 

.02-1.50

. 17 £.O

.5-.91 

1.8-30

64-5,775

No. of 

stations

27 

27 

27 

27 

27 

24 

1

27

Mean

38.68 

5.74 

.69 

.38 

1.08 

.24 

3.6

3,467

Range

35.12-50.3 

.65-15.8 

.05-1.74 

.01-1.37 

.06-3.11 

.01-1.5

260-5,276

50 Mineral and Petroleum Resources of the Ocean
80°N180«W. 150°W. 120°W. 90*W. 6(TW. 30°W. 0° 3(TE. 60°E. 90T. 120°E. 15CTE. 1WE.

60°N.

40°N.

20°N.

20°S.

40°S.

60°S.

BO'S.

Figure 29. Distribution of manganese nodules containing >1.0 and <1.8 percent Ni+Cu (from McKelvey and others, 1983).

about the same as that in the ^35.0-percent Mn group. The 

^0.5-percent Co groups have the highest means for phosphorus (0.531 percent), calcium (2.83 percent), titanium 

(1.07 percent), vanadium (0.069 percent), strontium (0.14 

percent), yttrium (0.031 percent), zirconium (0.072 percent), lanthanum (0.027 percent), cerium (0.133 percent), 

and lead (0.26 percent) and the lowest means for magnesium 

(1.337 percent), aluminum (0.71 percent), silicon (2.00 percent, at only six stations, however), potassium (0.32 percent), and zinc (0.07 percent). The >35.0-percent manganese group has the highest means for sodium (2.77 

percent, at only nine stations) and barium (0.423 percent) 

and the lowest means for phosphorus (0.120 percent, at only 

seven stations), titanium (0.253 percent), and vanadium 

(0.041 percent at only eight stations). The mean for silicon 

(4.68 percent) in this group is appreciably lower than that in 

the high combined nickel and copper groups, and it is lower 

also than the silicon mean in the ^0.5- to < 1.0-percent Co 

group (5.18 percent).

Although the covariance of other elements with the principal metals in manganese nodules supports the idea that the

metal groups described are geochemically distinct, the metal 

groups do not include the maximum values for several other 

elements namely, titanium (8.9 percent), phosphorus 

(6.03 percent), sulfur (3.50 percent), potassium (3.70 percent), calcium (28.73 percent), scandium (0.269 percent), 

vanadium (0.5 percent), zinc (9.00 percent), molybdenum 

(0.220 percent), barium (2.14 percent), lanthanum (0.07 

percent), cerium (0.30 percent), yttrium (0.095 percent), 

neodymium (0.07 percent), and lead (0.75 percent). Because many of these maximums are larger than the means by 

an order of magnitude or more, one might suspect that they 

are simply erroneous. That this explanation may not be 

valid, however, is suggested by the fact that their maximums in each ocean are also much higher than the world 

mean (table 22). For example, the world maximum for 

titanium (8.90 percent) comes from the Pacific, but the 

highest values in the Atlantic and Indian Oceans are 2.03 

and 1.76 percent, respectively. The maximum for zinc (9.0 

percent) is from the Indian Ocean, but the high values in the 

Atlantic and Pacific Oceans are 8.0 and 7.0 percent, respectively. It seems possible, then, that types of metal-rich nodSubsea Mineral Resources 51
80°N.

180°W. 150°W. 120*W. 90°W. 60*W. 30°W 30°E. 60°E. 90°E. 120°E. 150°E. 180*E.

60°S.

80°S.

Figure 30. Distribution of manganese nodules containing 1.0 percent Co or more (from McKelvey and others, 1983).

ule groups other than those discussed here may exist and that 

some of them may have potential economic value.

The Sediment Data Bank had no analyses for platinum 

metals and gold in manganese nodules as of March 1980. In 

1932, however, V.M. Goldschmidt and C. Peters (see 

Goldschmidt, 1954) reported 0.5 ppm Pt, 0.2 ppm Pd, and 

0.2 ppm Rh in a nodule from Challenger Station No. 286 in 

the southeastern Pacific (133°22' W., 33°29' S.). Harriss 

and others (1968) determined palladium, iridium, and gold 

values in several nodules and found ranges of 0.24 to 9.25 

ppb Pd, 0.90 to 23.1 ppb Ir, and 0.21 to 8.28 ppb Au. 

Although individual analyses thus vary considerably, the 

averages for each metal in both Atlantic and Pacific nodules 

are similar, and no correlation with any other major and 

trace metals was found.

Recently, P.J. Aruscavage (see Flanagan and Gottfried, 

1980) determined platinum, palladium, and ruthenium values for the two nodule samples used by the USGS as standard samples. The one from the Clarion-Clipperton zone (at 

124°28' W., 14°50' N.) contains 123 ppb Pt, 5.6 ppb Pd, 

and 4.7 ppb Ru, and the one from the Blake Plateau (at

78°22' W., 31°02' N.) contains 453 ppb Pt, 2.5 ppb Pd, and 

18 ppb Ru. Analyses of 12 other nodules from the western 

Atlantic (Manheim and others, 1980a) show that ironenriched nodules from seamounts have the lowest platinum 

values, the maximum being 120 ppb. Elements best correlated with platinum in these samples are nickel and cadmium. The rhodium content of these samples ranges from 2 

to 30 ppb. Halbach and others (1984) recently found that 

platinum concentrations in ferromanganese seamount crusts 

from the central Pacific range from 0.14 to 0.8 ppm, older 

crust generally being richer (~0.6 ppm) than younger crust 

(~0,3 ppm Pt). The shallower the water, the higher the 

platinum content. The platinum contents correlate positively 

with nickel and with the manganese-iron ratio.

Because so few samples have been analyzed for precious 

metals, nothing can be said about their geographic or geochemical distributions. If the few data available are reliable, 

they do suggest that the concentrations of silver in the nodules and of the metals that are commonly associated with 

gold in its ores (antimony, tellurium, and bismuth) are geochemically remarkable, even though the actual amounts are

52 Mineral and Petroleum Resources of the Ocean
Table 21 . Other elements in manganese nodules of the world, grouped by combined nickel and copper, manganese, and cobalt

contents

[ , no data]

a 1.8 percent

Ni+Cu

Element

L-------

R*

r .......

F .-.---.

Ma ....

Mg------

A1-------

Si-------

p .......

SI ...----

Q .......

Ca ------

Sc- ------

Ti-------

V-------

Cr-------

Zn------

Ga ------

Ge ------

As ------

DU

Sr-------

Y-------

Zr-------

Nb------

Mo------

f* j

Sn ------

Ol_

Te ------

Ba------

T a - - -

Ce ------

Nd------

Sm------

Fu ------

T*!*

V1»

Lu ------

TJf

Ta ------

No. of 

stations

4

-- 6

-- 15

-- 15

-- 0

46

78

ion

-- 111

-- 61

07

4

-- 73

07Q

-- 16

-- 169

-- 69

-- 371

-- 10

0

-- 19

18

-- 55

-- 33

A !*> 43

7

1 Q£

0

-- 29

6

4

5

1

78

-- 11

-- 22

4

5

5

5

-- 17

2

4

n

Mean, 

in percent

0.018 

.0002 

.02 

.23

2.02 

1.87 

2.65 

6.98 

.21

.22 

.86 

.79 

1.59 

.018

.47 

.043 

.013 

.14 

.002

.008 

.002 

.06 

.011

.049 

.007 

.05

.002

.010 

.004 

.024 

.25 

.288

.013 

.035 

.021 

.003 

.001

.001 

.002 

.000 

.001

>1.0-<1.8 percent

Ni+Cu

No. of 

stations in

5 

12 

20 

22

1

67 

91 

111 

111 

70

32 

5 

80 

191 

19

169 

95 

55 

267 

16

1 

14 

8 

80 

32

55 

17 

175 

3 

28

26 

4 

9 

0 

101

15 

15 

7 

10 

10

10 

22 

7 

4 

n

Mean, 

percent

0.020 

.000 

.027 

.321 

3.00

1.97 

1.57 

2.96 

8.26 

.288

.319 

.860 

.86 

1.73 

.001

.58 

.05 

.001 

.14 

.001

.000 

.012 

.001 

.077 

.012

.050 

.007 

.039 

.001 

.001

.009 

.005 

.021

.224

.019 

.066 

.023 

.004 

.001

.001 

.002 

.000 

.001

>35.0 percent

Mn

No. of 

stations

0 

0 

6

1 

0

9 

9 

11 

11

7

3 

0 

10 

14 

3

16 

8 

5 

11

4

0

1 

0 

8 

5

6

1 

13 

0 

0

1 

0 

0 

0 

10

1 

0 

0 

0 

0

0 

5 

0 

0 

n

Mean, 

in percent

0.016 

.93

2.77 

1.67 

2.09 

4.68 

.120

.547

.72 

1.64 

.001

.253 

.041 

.001 

.08 

.001

.002

.070 

.007

.033 

.001 

.056

.009

.423 

.018

.002

&1.

No. of 

stations

0 

0 

5 

0 

0

7 

8 

12 

6

4

1 

0 

8 

11

4

16 

9 

3 

12 

1

0 

1 

0

7 

5

6 

1 

11 

0 

1

2 

0 

0 

0 

8

6

2 

2 

2 

2

1 

6 

2 

0 

n

0 percent 

Co

Mean, 

in percent

0.041

1.99 

1.47 

.71 

2.00 

.32

1.2

.32 

2.72 

.001

1.07 

.069 

.002 

.07 

.002

.027

.14 

.031

.072 

.007 

.060

.000 

.022

.333

.024 

.133 

.032 

.005 

.001

.000 

.005 

.001

*0.5-<

No. of 

stations

2 

6 

9 

2 

1

37 

47 

46 

39 

23

3 

0 

43 

81 

8

80 

34 

28 

85 

4

0

7 

3 

27 

14

18 

7 

63 

0 

15

5 

0 

1 

0 

39

13 

10 

5 

4 

4

4 

12 

4 

0 

n

C1.0 percent 

Co

Mean, 

in percent

0.000 

.001 

.032 

.080 

3.0

1.80 

1.337 

1.81 

5.18 

.531

1.199

.49 

2.83 

.001

1.01 

.064 

.001 

.14 

.001

.016 

.001 

.119 

.021

.061 

.006 

.048

.001 

.004 

.021 

.286

.027 

.098 

.034 

.006 

.001

.001 

.004 

.000

Subsea Mineral Resources 53
Table 21 . Other elements in manganese nodules of the world, grouped by combined nickel and copper, manganese, and cobalt 

contents Continued 

[ , no data]

2:1.8 percent

Ni+Cu

Element

W-------

Hg------

O

Tl-------

Pb ------

ft:

T*U

No. of 

stations

1

0

-- 25

-- 301

1

39

Mean, 

in percent

.003

.02 

.048 

.001 

.002

>1.0-<1.8 percent

Ni+Cu

No. of 

stations

2 

0 

24 

229 

9 

24

Mean, 

in percent

.004

.013 

.071 

.002 

.003

> 3 5.0 percent >1.0 

Mn

No. of 

stations

0 

0 

1 

19 

0 

1

Mean, 

in percent

.000 

.09

.005

No. of 

stations

0 

0

2 

12 

2 

1

percent 

Co

Mean, 

in percent

.037 

.26 

.003 

.001

>0.5-<1.0 percent 

Co

No. of 

stations

0 

0 

15 

95 

4 

10

Mean, 

in percent

.020 

.17 

.003 

.003

small. The world means for silver, antimony, tellurium, and 

bismuth in the nodules (table 17) are 0.001, 0.005, 0.022, 

and 0.003 percent, respectively, and represent concentration 

factors above the averages in oceanic crust (according to Lee 

and Yao, 1970) of 110, 55, 250,000, and 200 percent, 

respectively.

Interest in recovering metals from subsea manganese nodules has thus far focused on nickel, copper, cobalt, and (on 

the part of a few companies) manganese. It seems possible, 

however, that some other elements (molybdenum and vanadium, for example) may also prove to be recoverable as 

coproducts, particularly if hydrometallurgical processes are 

used to concentrate the metals.

80*N180*W. 15CTW. 120-W. 90*W. 60-W. 30°W. 3<TE. BO-E. 90°E. 120°E. 1WE. 180°E.

60*N

ears.

80*S

Figure 31. Distribution of manganese nodules containing >0.5 and <1.0 percent Co (from McKelvey and others, 1983). 

54 Mineral and Petroleum Resources of the Ocean
80°N180°W. 150°W. 120*W. 90°W. 60*W. 3(n/V. 0° 30°E. 60°E. 90°E. 120°E. 150°E. 180°E.

60°S.

80°S.

Figure 32. Distribution of manganese nodules containing 35.0 percent Mn or more (from McKelvey and others, 1983).

Mineralogy

Many of the variations in the chemical compositions of 

nodules are reflected in their mineralogy. Mineralogical 

studies are difficult because most component particles, are 

submicroscopic, but much progress has been made, beginning with the pioneering X-ray diffraction studies of Buser 

and Grutter (1956). They described three manganese oxide 

minerals in nodules by identifying their X-ray patterns as 

those of synthetic analogs and named then 10-A manganite, 

7-A manganite, and AMnO2 . They also identified the ferric 

oxyhydroxide mineral goethite as a component of the nodules. Subsequent workers (Straczek and others, 1960; 

Hewett and others, 1963; Manheim, 1965; Cronan and 

Tooms, 1969) correlated the 10-A manganite with todorokite and the 7-A manganite with birnessite. Controversy 

has developed over the terminology used to describe the 

manganese minerals and indeed over the question of 

whether they are valid minerals (see Burns and Burns (1977) 

for a review), but there seems to be no disagreement over 

the existence of the three phases. Most authors, following

the recommendations of Burns and Burns (1977), have referred to them as todorokite, birnessite, and AMnO2 . 

Chukhrov and others (1979), however, recently proposed 

that the AMnO2 phase be called vernadite. Burns and Burns 

(1979) accepted that proposal, and that usage is adopted 

here. Haynes and others (1982), in addition to the three 

main manganese oxide minerals, listed 11 other manganese 

oxide minerals as having been identified, though rarely, in 

manganese nodules.

Although goethite (alpha FeOOH) has been reported by 

some investigators, the iron phase is generally believed to be 

amorphous hydrated ferric oxide (Burns and Burns, 1977; 

Bischoff and others, 1981). Haynes and others (1982) listed 

eight other iron oxide minerals as having been identified in 

the nodules; of these, they said that lepidocrocite (gamma 

FeOOH) and feroxyhyte (delta FeOOH) are the most commonly observed.

All three main manganese minerals can be present in 

individual nodules, and it appears that vernadite is present 

in most of them. Birnessite is less common and generally 

occurs only if the other two are also present (Barnes, 1967;

Subsea Mineral Resources 55
Table 22. World means and ocean maximums (in percent) of several other elements in manganese nodules that have exceptionally high concentrations 

[ , no data]

Element

p ........_.....

c

Ca- ---------

Ti--------------

Sc- ------

V --------

Cr- -

Zn -------------

Y--------------

Mo - 

Ba-------------

La -------------

Ce -------------

Nd-------------

Pb -------------

World mean

---------- 037

.......... .51

..-_---_.. 73

----..--.. 2.23

.....---.. .69

rjn«

---------- 052

----- 007

.......--. .12

---------- .015

---------- .038

.......... .23

.......... .021

.......... .072

...-.---.. .026

---------- .093

Pacific

5 12

1.90

3.70

24.0

S on

.269

. JW500

231

7.00

095

.220

1.65

.070

.300

.070

.46

Maximum

Atlantic

6 m

2 501

2.71

28.73

2 03

0041

.15

.017

8.00

.07 1 1

.177

.800

.033 1

.40

Indian

4.42

3.50

.65

14.93

1.76

001 1

.102

.013

9.00

.038 1

.066

2.14

.0291

.3001

.015 1

.75

'Based on fewer than 10 samples.

Piper and others, 1979; Bischoff and others, 1981). The 

vernadite phase is extremely fine grained, and, when it 

occurs in nodules, it contains admixed amorphous iron hydroxide and extremely fine grained silicate minerals (Usui, 

1979; Halbach and Ozkara, 1979), including some of extraneous origin. Recently, Bischoff and others (1981) have 

shown that the mineral phillipsite (K, Na, Ca)^ (Si, 

A1)8O16 -H2O, according to Fleischer (1980) is also ubiquitous in the nodules and forms in place on the growing 

nodules, as the manganese minerals and amorphous iron 

hydroxide do. Bischoff and his coworkers suggested, in 

fact, coupled and mutually catalytic reactions in which the 

alteration of phillipsite from volcanic glass locally raises the 

pH and stimulates the oxidation of Mn+2; this process, in 

turn, releases the hydrogen required in the formation of 

phillipsite. Haynes and others (1982) listed 34 accessory 

minerals as having been identified in the nodules; a few of 

these minerals are authigenic, but most are elastics accidentally incorporated in the growing nodules.

Origin

Early interest in the origin of manganese nodules focused 

on the source of the manganese. Sir John Murray postulated 

its release from ocean-floor basalt by submarine weathering 

(Murray, 1877), but his coauthor in the Challenger reports, 

A.M. Renard, favored a seawater source, the manganese 

presumably being derived from continental runoff (Murray 

and Renard, 1891). K.W. vonGumbel, however, proposed 

a subsea hydrothermal source (Berger, 1986). Although the 

importance of the hydrothermal source of metals in the

deep-sea environment is recognized to a much greater extent 

now than it was in von Gumbel's time, the other sources 

identified by Murray and Renard also contribute. Interest in 

the origin of the nodules in recent years has focused more on 

the factors controlling their deposition, composition, and 

distribution.

Abundant evidence has accumulated to show that variations in the metal contents of these minerals are reflected in 

variations in bulk nodule chemical composition. The structure of todorokite (Mn+2 , Ca, Mg)Mn+4O7 -H2O (Fleischer, 1980) includes sites in which small divalent cations, 

such as nickel, copper, magnesium, and zinc, can replace 

Mn+2 and other sites that will accommodate large cations, 

such as potassium. Birnessite Na4Mn14O27 -H2O (Fleischer, 1980) apparently has somewhat similar properties 

(Burns and Burns, 1977). It is the nodules rich in todorokite 

and birnessite that are rich in nickel and copper and the other 

minor metals previously described as most abundant in the 

> 1-percent Ni+Cu type (Burns and Fuerstenau, 1966; 

Barnes, 1967; Cronan and Tooms, 1969; Tooms and others, 

1969; Margolis and Burns, 1976; Piper and Williamson, 

1977; Calvert and Price, 1977; Halbach and Ozkara, 1979; 

Usui, 1979; Piper and others, 1979; Cronan, 1980; Bischoff 

and others, 1981). It is also the todorokite-rich nodules that 

have a manganese-iron ratio greater than 1.5 (Margolis and 

Burns, 1976; Piper and Williamson, 1977; Calvert and 

Price, 1977; Halbach and Ozkara, 1979). On the basis of 

microprobe analyses of individual layers of todorokite and 

the AMnO2 (vernadite) phase (including the amorphous 

iron) in nodules from the north-central Pacific, Usui (1979) 

found several of the elements that he examined to be parti56 Mineral and Petroleum Resources of the Ocean
tioned between the two phases by grade, such that concentrations of manganese greater than 30 percent, of both copper and nickel greater than 0.8 percent, of magnesium 

greater than 0.8 percent, of potassium greater than 0.6 percent, and of sodium greater than 0.5 percent are in the 

todorokite phase and concentrations below those values are 

mostly, if not entirely, in the vernadite phase. Amounts of 

iron greater than 4 percent and of silica greater than 1.2 

percent are restricted to the AMnO2 phase (vernadite). 

Cobalt has about the same range in both phases, but most of 

the concentrations greater than 0.3 percent are in the 

AMnO2 phase, and most below that value are in todorokite.

Although a number of authors have reported a positive 

correlation between cobalt and iron, Usui found a positive 

correlation between cobalt and manganese and concluded 

that trivalent cobalt is substituting for manganese in the 

vernadite phase and that some divalent cobalt may substitute 

for manganese in the todorokite phase (10-A manganite 

phase in his terminology). Burns (1976) made a similar 

proposal and suggested that the formula for AMnO2 (vernadite) should be (Mn, Co+3)Mn6O13 -H2O. Halbach and 

Ozkara (1979) reported similar findings in studies of nodules from an area within the Clarion-Clipperton zone. Nodules consisting mainly of todorokite contain 23 to 32 percent 

Mn, 2 to 3.2 percent Ni+Cu, 0.1 to 0.2 percent Co, and less 

than 7 percent Fe; those consisting mainly of vernadite contain 16 to 24 percent Mn, 1.0 to 1.6 percent Ni+Cu, 0.25 

to 0.40 percent Co, more than 1 percent TiO2 , and more 

than 9 percent Fe and have an manganese-iron ratio of 2.5 

or less.

Bischoff and others (1981) believed that titanium, phosphorus, and some silica are associated with the amorphous 

iron phase, and Calvert and Price (1977) showed a similar 

correlation of arsenic, yttrium, lead, strontium, and cobalt with iron. Even though amorphous iron hydroxide is 

physically a part of the vernadite phase in the nodules, its 

content varies independently of the vernadite content. Variations in the chemistries of the nodules are thus best understood as variations in their contents of authigenic todorokitebirnessite, vernadite, amorphous iron hydroxide, and 

phillipsite, along with clay and other siliceous minerals of 

extraneous origin. To illustrate compositional variations in 

the authigenic components of nodules, Bischoff and others 

(1981) used a ternary diagram in which all of the manganese 

phases are lumped together and plotted against the phillipsite and amorphous iron phases. Figure 33 follows this design and shows an almost complete gradation of mineral 

composition within the ranges of about 4 to 55 percent 

manganese oxide phases, 7 to 37 percent amorphous iron 

phase, and 7 to 60 percent phillipsite phase.

Given the mineralogy of the nodules, it is easy to understand the concentration of so many of the chemical elements. Not only does the structure of todorokite favor the 

incorporation of many elements, but also both iron and 

manganese oxides are well known for their abilities to scavenge other metals from seawater by physical adsorption 

(Goldberg, 1954). It is also easy to understand variation in 

metal content as a function of mineralogy, at least in large 

part. But to what factors do variations in the proportion of 

mineral phases relate?

Relation to Water Depth

Barnes (1967), Cronan (1967), Cronan and Tooms 

(1969), and Piper (1972) found that the relation between 

metal content and water depth is also a function of the 

mineralogy of the nodules, todorokite being more abundant 

in deeper water nodules and vernadite being dominant in 

nodules from shallower depths. The three manganese oxide 

phases represent different degrees of oxidation of manganese, and Cronan and Tooms (1969) concluded that variations in the mineralogy of nodules with depth may reflect 

variations in the degree of oxidation of the environment of 

deposition. Piper and Williamson (1977) found support for 

this theory in the fact that the few nodules containing more 

than 0.5 percent Co and occurring in water depths greater 

than 3,000 m are from the area immediately west of the Line 

Island Ridge, where there is a major intrusion of highly 

oxidizing antarctic bottom water. Halbach and Manheim 

(1984), however, pointed to the presence of an oxygen 

minimum in the central Pacific, where the seamount deposits are richest in cobalt, and suggested that cobalt enrichment in these waters rather than oxidizing environmental 

conditions account for the elevated cobalt concentrations.

Cronan (1980) related the increase in the combined nickel 

and copper content of nodules that takes place at a depth of 

about 3,000 m to the lysocline, the depth at which calcium 

carbonate inorganic remains begin to dissolve and to liberate 

metals (particularly copper) concentrated by organisms. Because copper is more concentrated in the skeletons of many 

organisms than nickel is (Halbach and others, 1979), this 

process would also explain the fact that copper-nickel ratios 

in shallow-water nodules are lower than those in deep-water 

nodules. (Heath (1981) has reviewed the importance of surface plankton in the concentration of metals.)

Effects of Direct Precipitation from Seawater in Comparison 

with Those from Diagenetic Precipitation

Another factor that may explain differences in nodule 

mineralogy involves the source and manner of deposition of 

their components. Rabb (1972) found that many nodules 

have a smooth upper surface and a gritty, lumpy bottom. 

Separate analyses of tops and bottoms showed that the tops 

are high in iron, cobalt, and lead and low in copper, nickel, 

molybdenum, zinc, and manganese and that the reverse is 

true for the bottoms. Calvert and Price (1977), Halbach and 

Fellerer (1980), Piper and others (1979), and Usui (1979) 

have suggested that the upper surfaces of such nodules 

(shown to be composed of vernadite) represent precipitate 

derived directly from seawater and that the bottoms (todorokite) represent a diagenetic precipitate derived by leaching

Subsea Mineral Resources 57
of the underlying sediment. Concentrations of manganese, 

copper, nickel, cobalt, and zinc in the interstitial water of 

deep-sea sediments have been found to be higher than those 

in deep seawater, and Lynn and Bonatti (1965) and others 

(Bender, 1971; Menard, 1976) proposed than Mn+4 in the 

sediments is reduced to Mn+2 under low Eh conditions (perhaps created in part by the oxidation of buried organic matter, as Price and Calvert (1970) suggested), dissolved, carried upward, and precipitated under the oxidizing conditions 

prevailing at or near the surface. Nickel and copper also go 

into solution in this process (Piper and others, 1979). In the 

redox potential range in the sediment, the solubility of iron 

oxide is not affected, and it remains in the sediment 

(Borchert, 1970, referred to by Halbach and Ozkara, 1979; 

Cheney and Vredenburgh, 1968, referred to by Usui, 1979). 

The sediment thus represents the residue resulting from diagenesis (Piper and others, 1979).

Some nodules (Halbach and Ozkara's (1979) type A and 

Usui's (1979) type B) contain little or no vernadite and are 

explained as having formed within the sediment just beneath 

the surface. Halbach and Ozkara also found nodules (their

type B) composed entirely of vernadite on the flanks of a 

seamount within the area that they studied. They found that, 

in contrast to the todorokite nodules, in which the nucleus 

is generally a fragment of a preexisting nodule, the vernadite 

nodules generally have a rock nucleus. They translated the 

findings of Heye and Marchig (1977) that nodule growth 

rate increases with increasing manganese, nickel, and copper contents to conclude that the growth rates of todorokite nodules and layers are 10 to 15 times greater than those 

of vernadite (see also Piper and Williamson, 1977), which 

both they and Usui believed is deposited from a colloidal 

form in near-bottom seawater rather than from an ionic 

solution of Mn+2 , as todorokite is.

Lyle (1981), confirming Heye and Marchig's (1977) finding, observed an inverse ratio between nodule growth and 

iron content and suggested that, in areas of very low productivity, growth is slow and is controlled by precipitation from 

seawater. In areas of oxic diagenesis, the rate of growth 

increases with increasing biologic productivity in surface 

water. "As the rate of input of organic debris increases to the 

level at which anoxic diagenesis begins ... the mobilization

MnO + MgO + NiO + CuO AI2O3 +K2O + Na20 + SiO2

Figure 33. Ternary plot of the principal mineral phases (normalized to total 100 percent) of manganese nodules at the 

107 stations in the Scripps Institution of Oceanography's Sediment Data Bank for which analyses of all the constituents 

shown have been made (from McKelvey and others, 1983). Compositions shown for metal types are based on means.

58 Mineral and Petroleum Resources of the Ocean
of Mn under anoxic conditions results in rapid nodule 

growth that virtually swamps the input of other metals, 

leading to lower Cu and Ni contents" (Heath, 1981, p. 757). 

This process, Heath believed, explains the high manganese 

content of nodules in the hemipelagic sediment along the 

eastern margin of the Pacific.

The three types of nodules described by Halbach and 

Ozkara are all from within a relatively small area in which 

the water depths range from 4,600 m at the summit of a 

seamount to 5,200 m on the surrounding ocean floor. The 

presence of both todorokite and vernadite in the same nodules indicates that both minerals may form in the same 

macroenvironment. Halbach and Ozkara believed that the 

type formed is governed by topography, the availability of 

rock fragments to serve as nuclei, local sedimentation rate, 

and bottom-current activity. Vernadite forms as nodules or 

crusts on rock surfaces where no sediment has accumulated 

or on the tops of nodules exposed to seawater, and todorokite forms at or near the surface of the sediment, which is 

largely radiolarian ooze in the southern part of the ClarionClipperton zone and red clay in the northernmost part. Nodules containing adjacent laminae of both minerals (the A 

type of Usui and the AB type of Halbach and Ozkara) reflect 

merely a change in the nodule's exposure to seawater (for 

example, burial by sediment to deposit todorokite on top of 

vernadite or a winnowing away of enough sediments to 

uncover a nodule forming near the bottom surface). Local 

variations in nodule content within the Clarion-Clipperton 

zone, in which the todorokite-vernadite nodules are most 

common (Halbach and Ozkara, 1979), may thus reflect differences in the todorokite contents of the nodules as a result 

of local variations in their exposure to seawater. Cronan 

(1977), however, suggested that, although the presence of 

todorokite is a probable prerequisite for the enrichment of 

nickel and copper in the nodules, it is not the only factor, for 

some todorokite-rich nodules outside the North Pacific have 

lower contents of these metals.

The great concentration of manganese with respect to iron 

in Clarion-Clipperton zone nodules is thus explained as a 

diagenetic mobilization of manganese in sediments in which 

the iron, although it is several to many times more abundant 

than manganese, remains fixed. More puzzling is the fact 

that, in the vernadite-amorphous iron phase apparently 

formed by colloidal precipitation from seawater, the 

manganese-iron ratio, although averaging only about 1.5 

according to Usui's analyses, is the reverse of what it is in 

seawater. For whatever reason, proportionately more iron 

than manganese leaves seawater in some other way.

This fact leads to other interesting questions. Why do the 

iron and manganese phases occur together, and why do they 

commonly occur as nodules? As Halbach and Ozkara (1979) 

and others indicated, they occur as encrustations on bedrock 

where nucleating grains are absent. The tendency for extremely fine grained particles to form aggregates is common 

with many other kinds of materials; Ramberg (1952) attributed this tendency to differences in surface energy that 

lead to a lower free energy in clusters rather than in disseminated form. The scarcity of iron-manganese minerals indicates that iron and manganese have little chemical affinity, 

but Burns and Burns (1977, p. 246) pointed out that: 

. . .although AMnO2 and Fe OOHxH2O consist 

of very small disordered crystallites, both phases 

contain cations in octahedral sites of hexagonally 

closed packed oxygen layers. Therefore, these 

two phases in manganese nodules are highly susceptible to epitaxial intergrowth (that is, oriented 

intergrowth of one phase on the other where lattice parameters or interplanar spacings are similar) 

which probably initiates nucleation and leads to 

the intimate association of manganese and iron 

oxide phases.

As I mentioned earlier, Bischoff and others (1981) thought 

that the other main constituent of manganese nodules, 

phillipsite, may form as a coupled reaction with the manganese oxides. It thus appears that there are good reasons for 

these chemically distinct phases to occur together in the 

nodules.

Because both todorokite and vernadite phases can form in 

the same macroenvironment, it would seem that, of the 

factors previously proposed as affecting the composition of 

the nodules, hydrostatic pressure (Barnes, 1967), dissolved 

oxygen (Cronan and Tooms, 1969), and pH-Eh conditions 

within the abyssal aqueous environments (Crerar and 

Barnes, 1974) do not control the deposition of todorokite 

versus vernadite or the ratio between the two. Such physiochemical factors, however, may influence their minorelement contents. The enrichment in the cobalt contents of 

nodules from shallow depths, for example, has been ascribed to oxidation from Co+2 to Co+3 under the highly 

oxidizing conditions prevailing on seamounts and similar 

features (Goldberg, 1961; Burns, 1965; Cronan and Tooms, 

1969; Piper and Williamson, 1977), and Goldberg (1965) 

suggested a similar effect with respect to lead. Halbach and 

Manheim (1984), however, attributed the high cobalt content in central Pacific seamount deposits to cobalt enrichment in those waters, another possible factor in metal enrichment. The wide variations in the nickel and copper 

contents of todorokite (Usui, 1979) may be due in part to 

variations in physicochemical factors.

Relation to Regional Variation in Sediment Type, Biologic 

Productivity, and Physiography

Because of the importance of sediment diagenesis in the 

formation of todorokite, which has a high manganese-iron 

ratio and generally high nickel and copper contents, regional 

variations in sediment character should be examined as a 

possible source of regional variations in nodule composition. Piper and Williamson (1977) found that, in the Pacific, 

the relation between the manganese-iron ratio of nodules 

and latitude is almost the reverse of the relation between the

Subsea Mineral Resources 59
manganese-iron ratio of sediments and latitude (sediment 

data from Skornyakova, 1965). Manganese-iron ratios in 

nodules are in the range of 6 to 9 near 10° N. and 10° S. 

and diminish to about 2 in the equatorial region and to 

less than 1 north and south of the 20° parallels. The high 

manganese-iron ratio in sediments is about 0.7 in the 

equatorial region, and the lows of 0.01 to 0.03 are in the 

10° N. and 10° S. regions. On the basis of a comparison 

with Lisitzin's (1972) map showing sedimentation rates 

for the Pacific, Piper and Williamson suggested that nodules having high manganese-iron ratios tend to occur in 

areas where sediment accumulation is slow.

Although Skornyakova (1979) found no correlation between the manganese, nickel, copper, and cobalt contents 

of nodules and associated sediment, she broadly related 

changes in nodule composition to sediment lithology. Following Horn and others (1973), she observed that nodules 

in the northern Pacific having the highest average manganese, nickel, copper, and zinc concentrations are associated with the radiolarian ooze of the equatorial belt and 

decrease successively in the adjacent zones of miopelagic 

clay, eupelagic clay, and calcareous ooze. She attributed 

the differences in the iron and manganese contents of 

nodules on the eastern and western sides of the Pacific to 

differences in primary manganese contents during sedimentation; sediments on the west are initially poor in 

manganese, and those on the east are richer because of 

the presence of only a thin oxidized layer of sediment. 

Skornyakova related the composition of nodules in the 

equatorial belt to the high organic productivity associated 

with the equatorial currents, which cause the diagenetic 

migration of the metals as buried organic matter oxidizes, 

and to slow deposition of sediment 

because of high-velocity bottom currents. Heath (1981) also 

related the metal content of the nodules to sediment type 

and, in turn, to biologic productivity in the overlying 

waters.

The zone of highest organic productivity in the equatorial 

region of the Pacific lies 50 to 100 km south of rather than 

above the zones in which nodules are richest in nickel and 

copper. Exon (1981, p. 61) suggested that this zone is a 

result of northwestward movement of the Pacific plate in 

this region at a rate of about 100 km/Ma: "Assuming that the 

high productivity zone has not moved much (relative to the 

equator) in the past 10 million years, the time during which 

the nodules probably formed, they would have been beneath 

the high productivity zone for much of their growth."

Several other investigators (Arrhenius, 1975; Greenslate 

and others, 1973; Margolis and Burns, 1976; Piper and 

Williamson, 1977; Cronan, 1977) also have suggested that 

organic productivity plays an important role in concentrating some of the nodule metals and transporting them to the 

bottom and, when such metals are buried by sediment, in 

creating the reducing environment that leads to their diagenetic mobilization and subsequent deposition at the surface.

According to Glasby (1981, p. 4), "On a regional scale, the 

most important factor controlling the composition of South 

Pacific abyssal nodules is the biological productivity of the 

overlying surface sea water." Nodule abundance in that 

area, he reported, is inversely related to sedimentation rate, 

a factor that Piper and others (1982) considered to be of 

primary importance in the distribution of nodules over the 

Pacific Basin as a whole (see also Menard, 1976).

Greenslate (1975), Wendt (1974), and Margolis and 

Burns (1976) reported the widespread presence of sessile 

arenaceous foraminifera on the nodules. Margolis and Burns 

found that, whereas foraminifera are present on nodules 

from all latitudes, they are most abundant and most diverse 

on nodules from the Clarion-Clipperton zone. The iron, 

titanium, and cobalt contents of foraminiferal tubes are 

higher than those of the nodule surface on which they are 

growing, and the manganese, nickel, and copper contents 

are lower. Margolis and Burns did not believe that the 

foraminifera actually precipitate manganese, copper, and 

nickel, although they deposit iron oxide as a cementing 

agent, but they did "feel that the large number of these 

animals. . .on the nodules from the copper-nickel rich zones 

of the northeastern equatorial Pacific, are somehow linked 

to the unique chemical composition of nodules from this 

area" (Margolis and Burns, 1976, p. 259), perhaps as a part 

of the high biologic productivity of the area. They asked, 

however, why, if high productivity of the surface layers of 

the ocean is the critical factor in trace-metal concentration in 

the manganese nodules, are nodules from other areas of 

oceanic upwelling and high productivity (the diatom ooze 

beneath the Antarctic convergence at about 55° S., for example), not also so enriched? As a possible reason, they 

suggested dilution by terrigenous sediment in those areas. 

Nodules from high southern latitudes differ from those in the 

equatorial region not only in their lower metal content but 

also in their low manganese-iron ratios. Cronan (1977, 

p. 37) suggested that high detrital sedimentation rates 

"could lead to low Mn/Fe ratios in view of the greater 

amounts of releasable Fe relative to Mn in the products of 

continental weathering," and he suggested that higher detrital sedimentation rates in the Atlantic as compared with 

those in the Pacific may explain the differences in their 

manganese-iron ratios.

However, many of the stations outside the ClarionClipperton zone in the Pacific, where nodules are high in 

combined nickel and copper (fig. 28), as well as many 

stations where the nodules contain 35 percent Mn or more 

(fig. 32) do, in fact, lie seaward of areas of coastal upwelling along the eastern side of the Pacific Basin, close 

enough, perhaps, to receive some of the organic debris 

generated by coastal upwelling. But such a relation is not 

evident in the central South Pacific, where the nodules are 

also high in combined nickel and copper (figs. 28, 29).

60 Mineral and Petroleum Resources of the Ocean
Many of the regional variations in nodule metal content 

relate to the physiography of the ocean basins as it controls 

depth, organic productivity, and sediment type. Cronan's 

(1977) analysis of variations in nodule metal contents from 

different environments brings out, for example, the high 

cobalt content of nodules from seamounts and other submarine elevations, the high manganese content of nodules 

from continental borderlands, and the high combined nickel 

and copper contents of abyssal nodules.

In summary, many factors may play a part in the origin 

of subsea manganese nodules and the variations in their 

compositions: (1) the rate of deposition of sediment and its 

content of terrigenous and biogenous matter, (2) the redox 

potential of the environment and the extent to which diagenetic processes are locally operative, (3) the local availability of the various metals, (4) the local availability of nucleating materials, (5) the bottom topography and water depth 

and the bottom-current activity and character, and (6) the 

biologic productivity of surface waters, which is, in turn, 

related to oceanic circulation and its effects in locally bringing nutrient-rich waters into the photic zone.

Combinations of these factors seem to explain, at least 

partly, some of the features of nodule distribution and composition. For example, the high concentrations of cobalt in 

western Pacific nodules relate to the highly oxidizing, essentially nondepositional environment prevailing on the extensive seamounts and plateaus in that area. The asymmetrical concentrations of the principal metals in nodules on the 

eastern sides of the oceans versus those on the western sides 

and their latitudinal variations may be a function of slow 

sedimentation at abyssal depths and oceanic circulation. The 

main elements of oceanic circulation are (1) two large circulating gyrals, one in the northern hemisphere moving 

clockwise and one in the southern hemisphere moving 

counterclockwise, (2) an eastward-flowing equatorial 

countercurrent between them, and (3) areas of high organic 

productivity where cold, nutrient-rich waters well up in 

coastal areas along the eastern sides of the basins in each 

hemisphere and along the equatorial countercurrent. These 

elements combine to create a widespread blanket of sediments on the abyssal floor; this blanket varies regionally in 

character, depending on whether biogenous, pelagic, or terrigenous sediments are dominant, and is generally below the 

lysocline, where metals are liberated from organic matter 

and where diagenetic processes are active in mobilizing and 

partitioning metals.

The differences in the average compositions of nodules 

from ocean to ocean may reflect the major differences in 

their geology and morphology. The Atlantic Ocean, for 

example, recieves much more terrigenous matter per unit of 

area than the Pacific does, its abyssal plains and areas covered by noncalcareous pelagic sediments are proportionally 

much smaller, and its mean depth is nearly 10 percent less 

all factors that would help to account for the lower average

contents of manganese, nickel, and copper in Atlantic 

nodules.

But such broad controls are not much help in explaining 

many aspects of the regional trends for example, the continuation of the poleward decrease in manganese, nickel, 

and copper contents of nodules to high latitudes, even in 

areas of high organic productivity; the area of the central 

South Pacific in which the content of these metals is high; 

the apparent localization of the manganese-rich (35 percent 

or more) nodules on the eastern side of the Pacific Basin and 

the northeastern equatorial region east of the ClarionClipperton zone and their lower nickel and copper contents; 

the higher iron content of nodules on the western side of the 

Pacific; and the anomalously high local content of some 

normally minor metals such as tellurium, lead, and zinc. 

Given the large number of factors that can affect the composition of the nodules, it is not surprising that it is difficult to 

determine their interplay in accounting for specific variations. But, plainly, a greater understanding of ocean processes and regional oceanography is needed to explain all the 

variations observed in the compositions of subsea manganese nodules. If the reasons for these variations do come 

to be understood, they may facilitate, on one hand, 

prospecting for economically valuable deposits; on the other 

hand, the local composition of nodules may serve as an 

indicator of locally prevailing environmental conditions.

One final question concerning the origin of manganese 

nodules deserves mention namely, why are they not 

buried by sediment instead of remaining at the surface? 

Their growth rate of 3 to 50 mm/Ma is much less than the 

rate of deposition of the sediment on which they accumulate. Hence, it might be thought that their slow growth rate 

would not allow them to remain at the surface. In fact, the 

nodules are generally older than the sediment on which they 

lie. Some have suggested that they are kept at the surface as 

the result of the movement of animals, but this theory does 

not seem reasonable. Not all nodules are at the surface; 

some have been buried by sediment, for they have been 

found in cores, and bottom photographs in some places 

show them to lie beneath a light blanket of sediment.

Distribution

The world distribution of manganese nodules is shown in 

figure 34, taken from Cronan's (1980) reduction of Rawson 

and Ryan's (1978) compilation. More detailed compilations 

of nodule distribution have not been made for the Atlantic 

and Indian Oceans, but Piper and others (1982, 1985) have 

mapped their distribution in the Pacific on the basis of percentage of the bottom covered as seen on bottom photographs and reported in core samples. Piper and others (1982) 

showed that:

In the northeast quadrant of the Pacific Ocean, 

three areas exhibit a sea floor coverage that comSubsea Mineral Resources 61
::::: Areas of nodule coverage JJJ Areas where nodules are particularly abundant

Figure 34. Distribution of manganese nodules in the world ocean (after Rawson and Ryan, 1978, as modified by Cronan, 1980). 

(Copyright 1980 by Academic Press.)

monly exceeds 50 percent. One area lies between 

the Clarion and Clipperton fracture zones. A second is in the Central Pacific basin, and a third is 

in the vicinity of the Musician Seamounts. Correlation of hiatuses in sedimentation during the Neogene, with these areas of high nodule coverage, 

suggest that a low rate of sediment accumulation 

is of primary importance.

Another area where the nodule coverage is 50 percent or 

more lies in the eastern part of the southwestern Pacific 

Basin. Areas where the nodule coverage is 25 percent or 

more are in the vicinity of the Jane Seamount in the northwestern Pacific, the south-central Pacific, the Peru Basin, 

and the southeastern Pacific Basin (Piper and others, 1985). 

Coverage is less than 1 percent over large areas of the 

Pacific, perhaps three-quarters of it in the aggregate.

The publicly available data on concentration (that is, 

weight per unit of area) of manganese nodules are insufficient, especially outside of the Pacific, to support any firm 

conclusions, but, in figure 35, all but one of the stations 

having more than about 13 kg/m2 of nodules occur at depths 

greater than about 3,700 m. Analysis of hundreds of freefall grab samples collected by the Centre National pour 

1'Exploration des Oceans-Societe le Nickel and the Association Frangaise pour 1'Etude et la Recherche des Nodules 

Polymetalliques led Pautot and Melguen (1979) to conclude

that the greatest concentrations of nodules are restricted to 

an interval of 300 to 400 m, the lower limit of which varies 

from basin to basin but falls within the range of 4,350 to 

5,200 m, close to the carbonate compensation depth in each 

basin. Skornyakova (1979) also reported that the highest 

concentrations of nodules are confined to depths below the 

carbonate compensation depth.

Although available evidence thus indicates that the greatest concentrations of nodules occur at abyssal depths, the 

encrustations, which average 2 cm in thickness over large 

areas, reported by Halbach and Manheim (1984) and Commeau and others (1984) on mid-Pacific seamounts at depths 

between 2,500 and 1,200 m represent a far greater concentration of metalliferous oxides per unit area than the nodules 

do, except in their rarest concentrations. In fact, the average 

concentration of manganese oxide crust of 33 kg/m2 implied 

by Manheim and others (1982) is four times the average of 

8.33 kg/m2 dry weight in nodules of the Clarion-Clipperton 

zone, the area of greatest current commercial interest for 

nodule mining.

The Clarion-Clipperton zone

Figure 36 shows the approximate limits of areas in the 

northeastern equatorial Pacific within which publicly available analyses indicate that manganese nodules contain more

62 Mineral and Petroleum Resources of the Ocean
1C 80

IS

UJ

5 

UJ

< 70 

O

GC 

UJ°- 60

GC 

<D 

O

UJ

O 

O

UJ (/)

50

40

CD

20

Z 

O

I 10

UJ

O

 ;:

8 2500 3000 3500 4000 4500 5000

DEPTH, IN METERS

5500 6000 6500

Figure 35. Relation between depth and concentration of manganese nodules at stations in the Scripps Institution of 

Oceanography's Sediment Data Bank (from McKelvey and others, 1983).

than 1.8 percent Ni+Cu. The existence of high-grade nodules in this region has been known for many years. Mero 

(1965) included this region as part of a broader one in which 

nodules are high in copper; Menard (1964, p. 186) identified 

part of the region as containing nodules high in nickel. 

Subsequently, Horn and others (1972, 1973) referred to the 

area between the Clarion and Clipperton fracture zones and 

120° and 155° W. as having unquestionably the best economic potential for nodules rich in nickel and copper and 

showed that the distribution of the rich nodules corresponds 

to that of siliceous sediments of Miocene age. Cronan 

(1972), Skornyakova (1976, p. 206-207), Margolis and 

Burns (1976), Bezrukov (1976, p. 252), and Piper and 

Williamson (1977) also roughly delineated the area as one 

containing nodules high in nickel and copper, and several

authors (Archer, 1976, 1978; Holser, 1976; Pasho and 

Mclntosh, 1976; Frazer, 1977; Bastien-Thiry and others, 

1977) have recently attempted to estimate the magnitude of 

the resources in the general region and the number of potential mine sites that it might contain. The region has been the 

focus of studies sponsored by the National Science Foundation in support of the International Decade of Ocean Exploration (Frazer and Arrhenius, 1972; Horn and others, 1972, 

1973), by the Federal Republic of Germany's ship Valdivia 

(Schultz-Westrum, 1973; Friedrich and others, 1974), a 

French group (Bastien-Thiry and others, 1977), and the 

Deep Ocean Mining Environmental Study sponsored by the 

National Oceanic and Atmospheric Administration (see 

Piper and others, 1979; Sorem and others, 1979; Bischoff 

and Piper, 1979). The Deepsea Ventures, Inc., "claim" is

Subsea Mineral Resources 63
ieo°w 110PW

Figure 36. Areas in the northeastern equatorial Pacific in which manganese nodules contain more than 1.8 percent Ni+Cu (from 

McKelvey, 1980). Numbers represent the average percentage of combined nickel and copper of samples in 1° squares where 

analyses are available at five stations or more. The rectangles outline the Deepsea Ventures, Inc., "claim" (DSV) and the Deep 

Ocean Mining Environmental Studies program sites (A, B, C). (Copyright 1980 by the American Association for the Advancement 

of Science.)

within the high-grade area between the Clarion and Clipperton fracture zones, as are other sites selected by deep-sea 

mining consortia for prospecting and experimental mining 

and the three sites judged by the USBM to have the best 

potential for economic mining (Hillman, 1983). Nodules 

containing more than 1.8 percent Ni+Cu are known in other 

parts of the world (Rawson and Ryan, 1978; McKelvey and 

others, 1983), but the area between the Clarion and Clipperton fracture zones (hereafter referred to as the C-C' area) 

shown in figure 36 is clearly the one of greatest current 

interest with regard to the possible recovery of manganese 

nodules.

The metal content and concentration of nodules at stations 

within the C-C' zone, where data on both are available, are 

shown in table 23. The data show a correlation coefficient 

between combined nickel and copper content and concentration of -0.24 at the 98-percent confidence level, weak 

enough to suggest that, in this area only, a slight positive 

bias would result from treating grade and abundance as 

independent variables. On the basis of this assumption, the 

grade of all available samples has been averaged in table 24. 

The results are only slightly different from those shown in 

table 23, with the exception of molybdenum.

Because only six molybdenum analyses are available for 

the stations represented in table 23, in comparison with 93 

for those in table 24, the average shown in table 24 must be 

considered more reliable, although the difference is slight. 

Table 25 has been added on the assumption that it may be

possible to restrict operations to areas containing higher 

concentrations of nodules.

The slight differences in the average metal contents of 

C-C' nodules shown in tables 23, 24, and 25 indicate a basis 

for high confidence in their validity. They confirm, in fact, 

Hein's (1977) report of almost identical averages for the 

several thousand samples collected from the C-C' zone by 

the Centre National pour 1'Exploration des Oceans 

(namely, 25.56 percent Mn, 6.40 percent Fe, 1.25 percent 

Ni, 1.05 percent Cu, and 0.24 percent Co), and they also 

correspond almost exactly to the averages of Haynes and 

others (1982) (namely, 25.4 percent Mn, 6.9 percent Fe, 

1.28 percent Ni, 1.02 percent Cu, and 0.24 percent Co). 

The average concentration of nodules in the C-C' area, 

however, is much more uncertain than the average metal 

content, partly because the determinations are fewer but also 

because the measurement itself is less certain. Bastien-Thiry 

and others (1977) considered that the error in concentration 

estimates ranges from 20 to 50 percent.

The weak inverse relation between grade and nodule concentration in the C-C' area can be seen by comparing tables 

23 and 25. These tables show a decrease of approximately 

5 percent or 0.15 wt percent in the mean content of nickel 

plus copper in comparison with an increase of approximately 41 percent in mean concentration from 8.45 to 11.94 

kg/m2 . The low-grade nodules in the high concentrations 

shown in table 25, however, contain more nickel plus

64 Mineral and Petroleum Resources of the Ocean
Table 23. Metal contents (in percent), nodule concentrations (in kg/m2 ), and metal ratios of manganese nodules in the C-C' area 

at stations where information on both is available 

[ , not enough stations for a meaningful value]

Mn ----------------------

Fe -----------------------

Ni .......................

Cu -----------------------

Ni+Cu -------------------

Co -----------------------

Mo ----------------------

Nodule concentration -------

Mn/Fe--------------------

Ni/Mn--------------------

Cu/Mn -------------------

(Ni+Cu)/Mn --------------

Co/Mn -------------------

Mo/Mn -------------------

Cu/Ni --------------------

No. of

stations

..........90

..........90

..........90

..........90

..........90

..........60

.......... 6

..........90

..........90

..........90

.......... 90

..........90

..........60

.......... 6

..........90

Mean

27.15

7.25

1.40

1.06

2.45

.24

.06

8.45

4.24

.052

.039

.091

.009

.002

.75

Range

7.30-35.50

3.31-12.51

.52-1.91

.26-1.64

.78-3.50

.09-. 39

.03-.07

.20-27.25

1.30-9.70

.026-. 148

.013-.114

.039-.261

.003-.027

.002-.002

.49-1.04

Standard

deviation

4.92

2.17

.31

.30

.58

.05

.02

6.14

1.84

.013

.011

.022

.004

.000

.12

Correlation

coefficient

-0.241

-.642

.772

.802

.822

.0092

 

.832

Between nickel plus copper and concentration. 

2Between the respective metals.

copper per unit area (0.27 kg/m2) than the high-grade nodules but low concentrations shown in table 23 (0.21 kg/m2). 

Previous estimates of the potentially recoverable resources in the C-C' area were for the region as a whole, 

reduced to an area considered minable on the basis of, for 

example, the percentages of samples considered to be above 

some "cutoff grade and concentration. Archer (1976) estimated that the area contains 23 to 27 potential mine sites, 

each capable of producing an average of 3 million metric 

tons of dry nodules per year for 25 years. Holser (1976, fig. 

4) showed approximately 20 "first-generation" mine sites 

for the Clarion-Clipperton area, each averaging 75 million 

metric tons for its lifetime production. For the northeastern

equatorial Pacific, bounded by lat 0° N. and long 100° W. 

and 170° E. and excluding the Mid-Pacific Mountains in the 

region north of 20° N. and west of 160° W., Pasho and 

Mclntosh (1976) estimated a 95-percent chance that there 

are at least 5 mine sites capable of producing 3 million 

metric tons a year for 20 years, a 50-percent chance that 

there are more than 30 such sites, and a 5-percent chance 

that there are more than 140 sites that may become commercially exploitable before the year 2000. Pasho (1977) later 

refined this estimate to indicate a probable range of 10 to 95 

mine sites. In the northern equatorial Pacific, Frazer (1977) 

identified an area of 3.3 million square kilometers in 11 5°

Table 24. Metal contents (in percent) and metal ratios of manganese nodules in the C-C' area

Element

Mn -------.--..-----.

Fe -------------------

Ni --------------.-.--

Cu-------------------

Ni+Cu ---------------

Co-------------------

Mo ------------------

Mn/Fe ----------------

Ni/Mn ----------------

Cu/Mn ---------------

(Ni+Cu)/Mn ----------

Co/Mn ---------------

Mo/Mn ---------------

Cu/Ni ----------------

No. of

stations

.............362

.............359

.............366

.............366

.............366

.............323

............. 93

.............359

.............362

.............362

.............362

.............319

............. 93

.............366

Mean

25.43

6.66

1.27

1.02

2.29

.22

.05

4.38

.05

.04

.09

.009

.002

.80

Range

2.50-36.43

.50-15.31

.11-1.91

.11-1.66

.22-3.51

.05-.56

.02-.08

.30-57.00

.02-. 15

.Ol-.ll

.04-.26

.003-.027

.001-.004

.44-1.34

Standard

deviation

4.98

1.99

.27

.28

.52

.07

.01

3.41

.01

.01

.02

.004

.000

.14

Correlation

coefficient 1

-0.30

.75

.70

.77

.028

.59

.79

'Between the respective metals.

Subsea Mineral Resources 65
Table 25. Metal contents (in percent), nodule concentrations (in kg/m2) 

at stations where the nodule concentration is 5 kg/m2 or more 

[ , not enough stations for a meaningful value]

and metal ratios of manganese nodules in the C-C area

Mn -----.-------...----..

Fe -------.-.------..---..

Ni .......................

Cu----------------------

Ni+Cu ..-...-..--........

Co ....._.................

Mo ----------------------

Nodule concentration -------

Mn/Fe --------------------

Ni/Mn--------------------

Cu/Mn -------------------

(Ni+Cu)/Mn --------------

Co/Mn -------------------

Mo/Mn -------------------

Cu/Ni --------------------

No. of

stations

...... ....58

----------58

......_...58

..........58

..........58

..........38

.......... 4

...-....-.58

---------58

..........58

..........58

..........58

..........38

...-..._.. 4

...... ...58

Mean

26.68

7.85

1.34

.96

2.30

.25

.07

11.94

3.82

.050

.035

.085

.010

.002

.71

Range

16.20-33.50

3.31-12.51

.52-1.88

.26-1.43

.78-3.21

.15-.39

.07-.07

5.50-27.25

1.58-9.70

.026-.068

.013-.047

.039-. 109

.007-.019

.002-.002

.49-.92

Standard

deviation

4.28

2.17

.33

.28

.59

.05

.00

4.80

1.69

.007

.007

.012

.003

.000

.11

Correlation

coefficient

0.061

-.762

.882

.91 2

.922

-.052

 

.882

'Between nickel plus copper and concentration. 

2Between the respective metals.

squares between 5° and 20° N. and 110° and 155° W., 38 

percent of which she predicted contain enough nodules for 

first-generation mining. She estimated nodule resources for 

this area comparable to 26 mine sites, each capable of producing 75 million dry metric tons over its lifetime. She 

identified two additional mine-site equivalents in the South 

Pacific, and, allowing for error by a factor of two, she 

expressed her final total estimate as 14 to 56 mine-site 

equivalents.

On the basis of extensive surveys conducted between the 

Clarion and Clipperton fracture zones by the French, 

Bastien-Thiry and others (1977) estimated that an area of 

2.25 million square kilometers3 presumably essentially 

the same as the area outlined in figure 36 contains 7.75 

billion wet metric tons of nodules in place or 5 to 10.6 

billion wet metric tons averaging 2.25 percent Ni+Cu and 

0.24 percent Co measured as dry weight. At a "cutoff 

nodule concentration of 5 kg/m2 and an assumed 20-percent 

recovery, Bastien-Thiry and his colleagues estimated that 

the recoverable tonnage would be 670 million wet metric 

tons averaging 2.5 percent Ni+Cu, enough to support 8 to 

11 mining operations each producing 3 to 4 million wet 

metric tons for 20 years. The concentration of nodules is 

reported to average 3.45 kg/m2 (including sites where they 

are absent), significantly less than the concentrations shown 

in tables 23 and 25. Bastien-Thiry and others reported that 

their results are based on grid surveys involving 262 localities where 1,844 sampling stations were established. If concentration measurements were made at all of these sites,

their data base would be much more reliable than that 

formed by the publicly available information analyzed here. 

Because of the paucity of the publicly available data, 

particularly on nodule concentration, not much accuracy can 

be claimed for estimates of nodule resources in the C-C' 

area, but a rough estimate confirms the general order of 

magnitude indicated by the previous estimates. Of the nodule concentrations reported in table 23, 36 percent are less 

than 5 kg/m2 , which can be taken as the minimum average 

concentration for mining. As I previously indicated, nodules 

are reported to be absent at 22 percent of the stations shown 

or, if they are present, to cover less than 20 percent of the 

ocean bottom. On the assumption that these two percentages 

can be combined to indicate how much of the area does not 

contain minable resources, the minable area would be 1.25 

million square kilometers averaging (rounded from table 25) 

11.9 kg/m2 of nodules containing about 1.3 percent Ni, 

1 percent Cu, 25 percent Mn, 0.22 percent Co, and 0.05 

percent Mo. If we assume that only 20 percent of the nodules would be recoverable and that the moisture content is 

30 percent, the C-C' area would contain about 2.1 billion 

dry metric tons of potentially recoverable nodules,4 enough 

to support about 28 mining operations, each producing an 

average of 75 million metric tons of nodules over its lifetime 

(McKelvey and others, 1979). Halbach and Fellerer (1980) 

estimated recoverable nodules in the northeastern Pacific 

nodule belt to be 2.7 billion tons. For the Pacific as a 

whole, including the nodule belt, they estimated a total of 

8.1 billion tons of recoverable nodules.

3The size actually given in the report is "2.25-million-sq.-m," but other 

parts of the same report suggest that "m" is probably a typographical error.

4In the resource classification system adopted by the U.S. Geological 

Survey and the U.S. Bureau of Mines (1980), the nodules in this area 

would be classed as identified marginal resources.

66 Mineral and Petroleum Resources of the Ocean
Estimates based on other plausible assumptions would be 

higher or lower but of the same order of magnitude. When 

we consider the paucity and uncertainty of the concentration 

data and the fact that data stations are not randomly distributed, it is readily conceivable that the size of the minable 

area could range from one-half to twice the size estimated, 

with proportionate effects on the estimates. If the distribution of the nodules is found to be locally irregular, a minimum average concentration may not be adopted in mining; 

as a result, the potentially recoverable resource may increase somewhat, although the percentage of the resources 

recoverable would initially be reduced. If the percentage of 

recoverable nodules is increased as a result of technological 

advances over time, then potentially recoverable tonnage 

and the number of average-sized operations that such tonnage would support would increase proportionately. It 

seems clear, however, that this most promising area now 

known contains potentially recoverable manganese nodule 

resources adequate to support not more than several tens of 

the average-sized operation postulated.

The three areas within the C-C' zone selected by the 

USBM as having the best potential are estimated to have 67 

million dry tons of recoverable nodules containing 1.3 percent Ni, 1.0 percent Cu, and 0.21 percent Co; 66.9 million 

tons containing 1.45 percent Ni, 1.24 percent Cu, and 0.25 

percent Co; and 148.8 million tons containing 1.33 percent 

Ni, 1.04 percent Cu, and 0.26 percent Co (Hillman, 1983).

Other Areas Containing Nickel- and Copper-Rich Nodules

The Clarion-Clipperton zone is the largest and most 

promising area known to have nodules rich in nickel and 

copper; in fact, at this stage, it seems likely that no other 

area of comparable size containing nodules of comparable 

quality and concentration will be found. Nevertheless, analysis of the data on the 2,401 stations in the Sediment Data 

Bank shows that several other areas appear to contain metalrich nodules, including some that might be high enough in 

combined nickel and copper (that is, 1.8 percent or more) to 

justify exploration for sites suitable for first-generation mining.

For this analysis, the locations of stations falling into the 

metal types described in the preceding section were plotted 

on a world map (parts of which are reproduced here) as a 

basis for selecting areas in which nodules might contain 

1 percent Ni+Cu or more and that therefore seemed to deserve further study. The results give some indication of 

areas that seem favorable for further exploration. Because 

data on concentrations outside of the Clarion-Clipperton 

zone are few, no attempt has been made to estimate tonnage 

in other areas. The detailed information on nodule deposits 

in the Peru Basin between lat 8° and 5° S. and long 90° and 

92° W. was reported by Halbach (1984; Halbach and others, 

1980) from a cruise of the R. V. Sonne in 1979. The nodule

density shows mean values ranging from 7 to 14 kg/m2 for 

different locations, some peak values being 30 kg/m2 . The 

nodules average 1.1 to 1.2 percent Ni, 0.5 to 0.7 percent 

Cu, and 22 to 38 percent Mn.

Estimates of average grade and of size are given for 

several other areas, but, because the data are sparse, these 

estimates must be taken as only a rough indication of what 

may be present in areas that, at this time, are merely targets 

for exploration. Nor should it be concluded that the areas 

identified as warranting further study are the only ones that 

deserve further exploration. As the maps show, many other 

areas contain high-quality nodules, and further sampling 

might show some of these areas to be of minable size.

No consideration has been given here to further identifying exploration areas for nodules rich in cobalt or manganese. The data shown in figures 30, 31, and 32 do suggest, however, that there may be large areas in which such 

nodules might be found. One of the striking results of this 

analysis as well as of other analyses is that there appears to 

be considerable continuity in the combined nickel and copper contents of manganese nodules over large areas, and this 

continuity may hold also for nodules rich in cobalt and in 

manganese. The data suggest, for example, that one or more 

such areas in which nodules contain more than 1 percent Co 

may be found in the north-central Pacific between 158° and 

180° W. This region is the one within which Manheim and 

others (1980b) reported cobalt-rich manganese oxide encrustation covering "nearly the entire exposed surface of the 

seamounts studied" between depths of 2,500 and 1,200 m. 

Samples containing more than 35 percent Mn that have been 

reported along the eastern side of the Pacific Basin (fig. 32) 

may be indicative of large areas of manganese-rich nodules, 

although the data assembled by Piper and others (1985) on 

sea-floor nodule coverage indicate that the concentration of 

nodules there is very likely to be low.

Several areas in which nodules have high combined 

nickel and copper contents have been selected for further 

analysis; these areas are shown in figures 37, 38, and 39, 

along with the average combined nickel and copper contents 

for all stations within each area. These averages range from 

0.72 percent Ni+Cu in the South Atlantic to 1.56 percent in 

the central south equatorial Indian Ocean. Figures 40, 41, 

and 42 are enlarged maps of the same areas within which are 

delineated smaller areas of nodules containing more than 

1.0 percent and more than 1.8 percent Ni+Cu. Nodules 

containing lesser amounts have been included in these 

smaller areas where the average of a particular station and 

the stations adjacent to it is above the cutoff. It must be 

emphasized that areas thus delineated are significant only as 

targets for further exploration.

Subsea Mineral Resources 67
30°N

15°N.

15°S.

30°S.

45eS.

Figure

others,

EXPLANATION

10.861 Area selected for further study. + 3=1.8 percent Ni + Cu 

Number is average Ni + Cu ««..-,« *. * ^ 

percentage at stations within study x 1 «°- 1 -79 Percent Nl + Cu 

area o SB 1.0 percent Co

A 3=35.0 percent Mn

37. Distribution in the Pacific Ocean of manganese nodules having high metal contents (from McKelvey and 

1983).

As figures 40, 41, and 42 show, fairly large target areas 

for nodules containing more than 1.8 percent Ni+Cu can be 

identified in the central north equatorial Pacific Ocean, the 

southeastern equatorial Pacific Ocean, and the central south 

equatorial Indian Ocean. If nodule mining becomes possible, the rich resources of the Clarion-Clipperton zone will 

probably be large enough to support production for several 

decades. Some time in the distant future, however, it may 

be feasible to mine lower grade nodules; looking to that 

possibility, one can identify even larger areas in which the 

nodules contain ^1.0 to <1.8 percent Ni+Cu.

As I have already mentioned, those target areas identified 

on the maps should not be thought the only ones worth 

considering. Others can be picked out from figures 28, 32, 

and 37. For example, a fair-sized target for nodules containing more than 1.8 percent Ni+Cu appears to lie at long 154°

to 160° W., lat 1° to 3° S. in the South Pacific (McKelvey 

and Wright, 1980); on the basis of recent samplings, Exon 

(1982) identified this area and other areas in the central 

South Pacific between lat 1° and 7° S. as containing nodules 

of potential economic significance. The large area at long 

124° to 160° W., lat 0° to 18° S. would be a target for 

nodules containing more than 1.0 percent Ni+Cu. Of 

course, further sampling may disclose other promising areas 

now unknown.

Cobalt-Rich Encrustations

Cobalt-rich encrustations of manganese oxides on six 

submarine terraces in the Hawaiian Archipelago at depths

68 Mineral and Petroleum Resources of the Ocean
60«W. 40°W. 20«W. 20*E. 40°E.

20°S.

40»S.

60°S.

EXPLANATION

Area selected for further study. 

Number is average Ni + Cu 

percentage at stations within study 

area

+ 3=1.8 percent Ni + Cu

X 1.0-1.79 percent Ni + Cu

n 3*1.0 percent Co

Figure 38. Distribution in the South Atlantic Ocean of manganese nodules having high metal contents (from McKelvey 

and others, 1983).

ranging from 5 to 1,200 m have been described by Craig and 

others (1982). The encrustations are most prevalent on the 

two deepest terraces and range up to 50 mm thick; thickness 

increases northwestward as the age of the bedrock increases, 

such that the growth rate approximates 2.5 mm/106 yr. Their 

metal contents vary considerably but average about 1.15 

percent Co, 0.35 percent Ni, and 0.05 percent Cu. They are 

composed of vernadite and amorphous FeOOH and are very 

likely formed by deposition of ferromanganese floes from 

seawater, as Toth (1980) suggested.

The cobalt-rich encrustations of manganese oxides reported by Manheim and others (1982), Halbach and others 

(1982), Halbach and Manheim (1984), Commeau and 

others (1984), and Hein and others (1986) from seamounts 

in the Mid-Pacific Mountains and the vicinity of the Line 

Islands in water depths of 1,200 to 2,500 m are apparently 

extensive but have not yet been delineated regionally. An 

indication of their extent, however, can be seen from the

distribution of cobalt-rich nodules shown on figure 30, some 

or most of which may actually be encrustations. Areas in 

that region that are enclosed by the 2,500-m contour can be 

considered favorable for the occurrence of cobalt-rich encrustations.

The encrustations described by Manheim and others 

(1982) contain about 1.0 percent Co, 0.5 percent Ni, 25 

percent Mn, and less than 0.1 percent Cu, almost the same 

as the Hawaiian Archipelago encrustations described by 

Craig and others (1982) and as the means of the high cobalt 

nodules shown in table 16. Higher values have been found; 

for example, a crust sample from a seamount midway between Honolulu and American Samoa contains 2.5 percent 

Co, 0.8 percent Ni, and 32 percent Mn (Hein and others, 

1985).

These cobalt-rich encrustations are up to 9 cm thick and 

are thought by Manheim and others to average about 2 cm. 

Substrates are dominantly Middle Tertiary phosphorite,

Subsea Mineral Resources 69
20°N.

40°E. 60°E. 80°E. 100°E. 120°E. 140°E

0°

20°S.

40°S.

60°S.

1.56

1.22

X X

EXPLANATION

Area selected for further study. 

Number is average Ni + Cu 

percentage at stations within study 

area

-I- 3=1.8 percent Ni + Cu 

X 1.0-1.79 percent Ni + Cu

Figure 39. Distribution in the Indian Ocean of manganese nodules having high metal contents (from McKelvey and 

others, 1983).

basalt, and altered basalt. According to Manheim and others 

(1982) (see also Halbach and Manheim, 1984):

Photographic and other evidence suggest that 

crusts cover nearly the entire surface of the 

seamounts studied. A preliminary economic evaluation. . . yields a processed metal value of $5.2 

to $6.2/m2 for Line Island and Mid-Pacific Mountains seamount areas sampled. This figure contrasts with $1.63/m2 estimated for prime deepwater nodules. A single seamount with an average

area of about 300 km2 between the 2,500 and 

1,000 m isobaths could yield more than 4 million 

tons of dry ferro-manganese crust if 40 percent of 

the area contained accessible and recoverable 

crusts. Thus, if engineering recovery is feasible, 

seamount crusts appear to have significant economic potential.

Assuming an average crustal thickness of 2 to 2.5 cm, an 

areal coverage of 40 percent, and an average metal content

70 Mineral and Petroleum Resources of the Ocean
180-W 

20°N.

170°W. 160-W.

10°N.

H~ 

X

D

EXPLANATION 

*1.8 percent Ni + Cu 

1.0-1.79 percent Ni + Cu 

3*1,0 percent Co 

0.5-0.99 percent Co 

<1.0 percent Ni + Cu, <0.5 percent Co

Area within which Ni + Cu* 1.8 percent 

(240,000 km3 ; 27 stations; average 2.0 

percent Ni + Cu)

Area within which Ni + Cu*1.0 percent

Figure 40. Target areas for exploration for manganese nodules rich in combined nickel and copper in the central north 

equatorial Pacific Ocean (from McKelvey and others, 1983).

of 0.9 percent Co, 0.5 percent Ni, 0.06 percent Cu, and 

24.7 percent Mn, Clark and others (1984) estimated that the 

more favorable areas within the 200-mi Exclusive Economic 

Zones (EEZ) of the Hawaiian Archipelago and the JohnstonPalmyra Islands region contain 6.9 million metric tons of 

cobalt, 3.9 million metric tons of nickel, 0.5 million metric 

tons of copper, and 189.2 million metric tons of manganese. 

Assuming that prime areas (where the crusts average 4 cm 

thick and 1.0 percent Co, 0.5 percent Ni, 0.06 percent Cu, 

and 24.7 percent Mn and cover 60 percent of the area) make 

up 7.5 percent of the permissive areas in these regions, they 

estimated that the prime areas contain 0.628 million metric 

tons of cobalt, 0.314 million metric tons of nickel, 0.039 

million metric tons of copper, and 15.523 million metric 

tons of manganese. They believed that, in some areas, the 

crusts are so weakly bonded to bedrock that they can be 

scraped off easily, and, because they occur in much shallower water, they may pose less difficult problems for mining than the nodules do. These advantages, together with the 

facts that the value of the crusts is higher than that of the 

nodules and that large tonnages of the crusts occur in areas 

under national jurisdiction where the terms for mining may 

be more attractive than those in the area beyond national 

jurisdiction and under the Law of the Sea Convention, led 

Clark and his coworkers to believe that the crusts "will 

prove to be closer to commercial viability than deep-sea 

nodules."

It should be noted, however, that the most abundant component in the crusts is cobalt, the producer price of which for 

most of 1982 and 1983 was $12.50/lb, in comparison with 

the pre-1976 price of $3.00 to $4.00/lb. Spot prices during 

that period were half the producer price or less, an indication 

of price weakness. Substantial production from the subsea 

nodules or encrustations or another new source might result 

in a much reduced price for cobalt, which would inject 

uncertainty into the near-term value of the cobalt-rich manganese oxides.

Manganese- and Iron-Rich Encrustations

Encrustations of manganese-rich oxides on basalt have 

been reported from several localities along the rift valleys at 

active spreading centers. Examples are the Mid-Atlantic 

Ridge at lat 23°, 26°, and 36° N., the East Pacific Rise near 

the equator (the Galapagos spreading center) and at lat 8° S., 

and the Gulf of Aden near lat 12° N. These encrustations are 

of hydrothermal origin and consist of todorokite, birnessite, 

or pyrolusite. They contain 30 to 58 percent Mn. In that 

respect, they resemble the manganese-rich nodules in composition, but they contain much less iron (less than 1.0 

percent in some deposits), nickel, copper, and cobalt than 

the nodules do (Rona, 1978, 1984; Cronan, 1980).

Iron-rich manganese-poor encrustations have also been 

found in subsea hydrothermal environments (for example, 

the East Pacific Rise at lat 8° S.) (Bonatti and Joensuu,

Subsea Mineral Resources 71
100"W. 90°W. 80°W.

10°S

20°S

EXPLANATION

 j" 5*1.8 percent Ni + Cu

X 1.0-1.79 percent Ni + Cu

A 3535.0 percent Mn

O 0.5-0.99 percent Co

<1.0 percent Ni + Cu, 

<35.0 percent Mn, 

<0.5 percent Co

Area within which Ni + Cus*1.8 percent 

(815,000 km2 ;12 stations; average 2.11 

percent Ni + Cu)

Area within which Ni + Cus«1.0 percent

Figure 41. Target areas for exploration for manganese nodules rich in combined nickel and copper in the southeastern 

equatorial Pacific Ocean (from McKelvey and others, 1983).

1966). Cronan (1980) attributed the rather clean separation 

of iron and manganese in the subsea hydrothermal environment to early precipitation of iron oxides and silicates as 

ascending hot, low Eh solutions begin to cool and oxidize as 

they enter the marine environment, manganese oxide being 

precipitated later in the process.

Feasibility of Commercial Recovery

The commercial feasibility of mining a given mineral 

deposit means that the operation has or can meet several 

prerequisites: technical feasibility of mining and processing; 

environmental acceptability; profitability; and legal authorization. Only a successful operation can demonstrate conclusively that all of these requirements have been met. Because full-scale mining of manganese nodules and crusts has 

not been attempted, judgments about its commercial feasibility at this stage are necessarily speculative. Even so, they 

are indicative of the near-term outlook.

Although the results of the extensive research and development activities undertaken by several nodule mining consortia are held as trade secrets, several of these groups have 

announced success in their attempts to lift nodules from the 

bottom and in the development of methods to recover the 

metals. More research and development may be required in 

advance of full-scale operations, but there is little doubt now 

that the mining and processing of the nodules will be technically feasible (Chung, 1985).

The environmental effects of experimental mining activities have been monitored by the National Oceanic and Atmospheric Administration, which has also published (National Oceanic and Atmospheric Administration, 1981) a 

programmatic environmental impact statement on nodule 

mining and has sponsored much environmental research 

related to both mining and processing (see Tweedt (1985) 

for a summary). Nodule dredging totally destroys the bottom fauna but leaves it unharmed in adjacent undredged 

areas, which provide the seed for repopulation. Adverse 

effects are therefore short lived. Other environmental effects

72 Mineral and Petroleum Resources of the Ocean
70°E. 80°E.

10°S.

20°S.

+ 

X

EXPLANATION 

3*1.8 percent Ni + Cu 

1.0-1.79 percent Ni + Cu

<1.0 percent Ni + Cu, <0.5 percent Co, 

<35.0 percent Mn

Area within which Ni + Cus*1.8 percent 

(270,000 km2 ; 12 stations; average 2.3 

percent Ni + Cu)

Area within which Ni + Cus* 1.0 percent

Figure 42. Target areas for exploration for manganese nodules rich in combined nickel and copper in the central south 

equatorial Indian Ocean (from McKelvey and others, 1983).

appear to be negligible. Further activities need to be monitored, but, at this stage, it seems that nodule mining and 

processing can be undertaken without adverse environmental effects.

The cost of nodule mining and processing has been estimated in several publicly available studies (for example, 

Arthur D. Little, Inc., 1977; Nyhart and others, 1978; 

Flipse, 1982; Andrews and others, 1983; Antrim and Sebenius, 1983; Hillman, 1983). Capital costs in these estimates 

range from about $0.6 to $1.7 billion, and estimates of the 

internal rate of return (IROR) range from about 2.7 to 18.1 

percent, the higher costs and less profitable returns being the 

most recent ones. Even though the estimates range widely, 

they tell the same story: nodule mining will require huge 

capital outlays and is not prospectively profitable enough to 

warrant undertaking now. Although most manufacturing 

companies have an IROR in the range of 13 to 15 percent, 

it is generally recognized that the prospective IROR for 

high-risk ventures such as the first deep-seabed mining projects 

should be of the order of 30 percent to warrant investment.

As I will discuss more fully later, considerable uncertainty exists now as to the legal authorization for mining 

beyond the limits of national jurisdiction. Combined with 

the low prospective profitability, this uncertainty casts 

doubt on the feasibility of commercial nodule mining for 

some years to come.

As I mentioned previously, cobalt-rich manganese oxide 

crusts are more valuable than nodules at current prices. 

Because extensive deposits lie within the EEZ, the legal

uncertainty about their availability for mining may be much 

reduced and perhaps eliminated, depending on the actions of 

national governments. On these counts, the prospects for 

their commercial production are better than those for the 

nodules. The technical feasibility of mining the crusts has 

yet to be established, although preliminary ideas are already 

being considered (Paul, 1985). But, until methods for mining the crusts are developed and tested, the feasibility of 

producing them commercially will be uncertain.

FERRUGINOUS AND MANGANIFEROUS 

SEDIMENTS

The hot brine deeps in the median valley of the Red Sea 

are underlain by several types of metalliferous sediments 

namely, sulfides, oxides, carbonates, and silicates. Although iron is an important component of the sulfide facies, 

which will be discussed in the next section, it is also an 

important component of the other facies, as table 26 shows. 

These facies are the products of a hydrothermal system 

arising from the circulation of seawater through evaporites 

and hot basalts along the Red Sea spreading center. According to Shanks and Bischoff (1977), the several mineral 

facies represent a fractionation as the temperature of the 

brine decreases after it emanates from the sea bottom and the 

pH and Eh rise. The sequence of precipitation of the facies 

on cooling is sulfides, iron silicates, iron oxides, and manganese oxides; manganese precipitates later than iron oxides

Subsea Mineral Resources 73
Table 26. Partial composition (in percent) of metalliferous sediments (excluding sulfide facies) 

of the Red Sea (from Bignell, 1975)

Fe Mn Zn Cu

Silicate facies

Atlantis II Deep:

Ferroan nontronite ------------------------ 9.72 0.06 0.69 0.18

Green smectite---------------------------21.50 .22 .52 .28

Brown montmorillonite -------------------- 8.90 1.15 .21 .16

Iron oxide facies

Limonite facies:

Kebrit Deep ----------------

Gypsum Deep --------------

Vema Deep ----------------

TTiAtic rV»f»n

Atlantis II Deep ------------

Lepidocrocite facies: 

Atlantis II Deep -------------

^tff»1Y*l 1 C T~^f*f*T> 

Thetis Deep ----------------

Gypsum Deep --------------

Hematite facies, Atlantis II Deep ---

\Aytonf^t iff* "FQf*if*c Ttiffic T^ffr%

.......-....--30.80

. ---------- .--50.70

.............-57.70

.._...._--.... 54.60

..--.. -------- fid 50

/;i i/j

..-.........--51.43

._..- _-_--.-_ 35 00

..............60.47

.---_-.------. 54 35

.----------.-- 35 79

£S1 TC

0.17 

.35 

.05 

.45 

.98 

.26

.36 

2.00 

1.28 

.19 

.29 

.21

0.10 

.24 

.10 

.66 

.20 

.15

.08 

.10 

.17 

.18 

.12 

.13

0.03 

.01 

.001 

.006 

.09 

.01

.004 

.08 

.40 

.03

.74 

.47

Manganite facies

Thetis Deep --------------------

Chain Deep B -----------------.

..............20.50

..............30.75

..--_-._--.-_- 12 93

-i on

15.48 

17.85 

35.37 

15.56

0.75 

1.32 

1.22 

.21

0.09 

.04 

.13 

.01

Carbonate facies

Rhodochrosite, Atlantis II Deep ----.............. 6.49

CO C£i

9.41

.25

0.23 

.16

0.02 

.04

because of its slower rate of oxidation and its solubility at a 

higher pH (Krauskopf, 1957; Cronan, 1980). Although the 

iron in some ferruginous sediments in the Red Sea deeps is 

as rich or richer than that in most iron ores being mined on 

land, the recovery of iron from these sediments is not currently contemplated.

Ferruginous and manganiferous sediments (both lithified 

and unlithified) have also been found in the Gulf of Aden. 

The manganiferous sediments, a mixture of todorokite and 

birnessite, contain 34 to 42 percent Mn, 1.3 to 6.4 percent 

Fe, 14 to 900 ppm Ni, 8 to 203 ppm Cu, and 2 to 75 ppm 

Co (Cann and others, 1977). Crerar and others (1982) believed that the Gulf of Aden deposits and similar ones near 

the Galapagos rift are the modern analogs of manganese and 

manganiferous chert deposits in the Franciscan Complex of 

California, which in turn are similar to manganese deposits 

associated with ophiolite complexes elsewhere, such as 

those described in the Apennines by Bonatti and others 

(1976b). Typically, the Franciscan deposits are lens shaped,

as much as 30 m thick (but averaging only 1 m), and as 

much as 300 m in diameter (but most commonly only 15m). 

Although these deposits may contain 30 to 50 percent Mn, 

their tonnage is too small to make modern analogs attractive 

for exploration and mining by themselves; it is conceivable, 

however, that they might be recovered as a part of a mining 

operation directed at sulfide deposits, with which they may 

be associated vertically or laterally.

Ferruginous and manganiferous sediments have been 

found in numerous localities at other oceanic spreading centers and as basal sediments as much as 20 m thick overlying 

basalt in many drill holes in both the Atlantic and Pacific 

Ocean Basins (Bostrom, 1970; Von der Borch and Rex, 

1970). The sediments were evidently deposited as a result of 

hydrothermal activity on newly formed basaltic crust in or 

near the axial zone of spreading and brought to their present 

positions as a result of continued sea-floor spreading. As 

table 27 shows, iron is considerably more abundant than 

manganese in these sediments, and, among the minor

74 Mineral and Petroleum Resources of the Ocean
Table 27. Ferruginous and manganiferous sediments at or near oceanic spreading centers (from Rona, 1978) 

[DSDP, Deep-Sea Drilling Project. , no data]

Range of composition

Location

Basal sediment overly

Mineralogy

f ing-- Goethite, iron-rich smecFe, 

in percent

2.3-10.5

Mn, 

in percent

0.3-.7

Ni, 

in ppm

20-370

Cu, 

in ppm

25-167

Co, 

in ppm

Zn, 

in ppm

62-267

basalt in several DSDP 

holes in North Atlantic 

Basin.

tite, manganese hydroxides.

Basal sediment overlying - - Siderite and other minerbasalt in several DSDP als. 

holes in east Atlantic 

Basin.

1.1-1.6 .02-7.3

Bauer Deep Smectite, goethite, 

todorokite.

9-18 2-7 410-1,700 710-1,200 90-330 110-680

Basal sediment overlying-- Goethite, iron-rich smec- 21.1-27.8 5.7-7.6 570-800 800-1,490 55-110 480-690 

basalt in several DSDP tite, manganese hyholes in north-central droxides. 

Pacific Basin.

East Pacific Rise crest ---- Goethite, iron-rich smecbetween lat 12° and tite, manganese hy14° S. droxides.5.7-22.6 .6-8.8 250-1,200 510-1,800 75-280 190-530

Basal sediment overlying-- Goethite, iron-rich smec- 2.1-30.6 

basalt in several DSDP tite, manganese hyholes on East Pacific droxides. 

Rise between lat 10° 

and 15° N.

.4-9.6 62-1,680 220-1,814 10-183 33-518

Basal sediment overlying-- Goethite, iron-rich smecbasalt in several drill tite, manganese hyholes on the East droxides. 

Pacific Rise between 

lat 9° and 13° S.

4.7-23.3 .2-9.5 270-805 270-1,700 18-290 220-1,050

Indian Ocean Ridge 

between lat 16° and 

40° S.

.03-7.0 .1-2.0

metals, copper is more abundant than nickel in many areas, 

the reverse of their relation in nearly all subsea manganese 

nodules.

Similar sediments are found in the Bauer Deep between 

the East Pacific Rise and the Galapagos Rise. Sediments 

there average 15 percent Fe, 4 percent Mn, 0.12 percent Cu, 

0.1 percent Ni, 0.02 percent Co, and 0.04 percent Zn 

(Bischoff and others, 1979). The Bauer Deep is about 

3.9 million square kilometers in size and contains about 360 

trillion tons of such sediment on a dry salt-free basis 

(J.L. Bischoff, personal communication, 1978). At 1983 

prices, the four minor metals together would be the equivalent of about 15 Ib/t Cu, which is within the range of the

grade of porphyry copper deposits now being mined on 

land. Even so, the sediments in the Bauer Deep and similar 

sediments elsewhere cannot be thought to be minable in the 

foreseeable future (Field and others, 1981).

Iron and manganese oxide precipitates have also been 

found associated with subsea hydrothermal activity in other 

areas besides the mid-ocean spreading centers. Zelenov 

(1964) reported iron and manganese oxide precipitates 

around hydrothermal vents on the submarine Banu Wuhu 

volcano of Indonesia. Deposits associated with hot springs 

in New Britain's Matupi Harbor contain 44 percent Fe, 

0.034 percent Mn, 52 ppm Zn, and 47 ppm Cu (Ferguson 

and Lambert, 1972). Sediments in the inner exhalation zone

Subsea Mineral Resources 75
of the Santorini caldera in the Cyclodes volcanic arc in the 

eastern Mediterranean contain 40 percent Fe and 0.02 percent Mn; in the outer exhalation zone, they contain 7 percent 

Fe and 0.55 percent Mn (Smith and Cronan, 1975; Cronan, 

1980).

All of these deposits are of hydrothermal origin, although 

Cronan (1980) suggested that the sediments of the Bauer 

Deep are deriving some of their metals from the decay of 

organic matter and perhaps by the adsorption from seawater 

of iron and manganese oxides. Together with the sulfide 

deposits to be described in the next section, these deposits 

are the products of a hydrothermal system in which seawater 

circulating in fractures along the ridges is heated by contact 

with freshly intruded basalt, leaches metals from it, and 

emanates from the sea floor from hydrothermal vents. Cronan (1980) believed that the iron-rich manganese-poor deposits and the rarer manganese-rich iron-poor deposits are 

products of a basically similar hydrothermal system in 

which sulfides precipitate first (possibly subsurface), followed by silicates, iron oxides, and manganese oxides, the 

same sequence described for the Atlantis II deposits.

An ironstone crust containing as much as 47 percent Fe 

has been found at the surface of the bottom at many locations in the Gulf of Mexico (Pequegnat and others, 1972), 

and thin ferruginous layers of sediment have been found also 

in many cores in the Gulf of Mexico (Watson and Angino, 

1969). Ferruginous crusts at the sea floor have also been 

found at a number of localities in the western equatorial 

Atlantic by McGeary and Damuth (1973), who believed that 

these crusts were formed at or near the end of the Pleistocene, when the postglacial sea-level rise shut off the supply of terrigenous sediment to the deep-ocean floor: 

Geochemical and stratigraphic evidence seem to 

indicate that the iron-rich crust was formed when 

decaying organic material reduced the iron and the 

terrigenous minerals. The reduced iron dissolved 

in the interstitial water, which was then expressed 

upward during sediment compaction. Upon reaching the sediment-water interface, the iron was oxidized and reprecipitated, forming an ironcemented crust that has been varied by post glacial 

pelagic sediments.

But, whereas the known iron- and manganese-rich sediments on the present sea floor are the products of hydrothermal activity and are spatially linked to hydrothermal systems, the most important and extensive fossil marine iron 

and manganese ores bear no direct relation to hydrothermal 

activity. According to Force and others (1983) and Cannon 

and Force (1983), about three-fourths of the world production of manganese ore comes from shallow marine sedimentary deposits for which there are as yet no known large 

analogs on the present sea bottom. They believed that fossil 

deposits formed during high sea-level stands that corresponded to stratified and stagnant oceans. Manganese is 

more than 100 times more soluble in anoxic seawater than

it is in oxygenated seawater, and Cannon and Force believed 

that manganese oxides precipitated where deep anoxic water 

welled up toward the surface and became oxygenated. A 

present-day analog is the Black Sea, where deep anoxic 

water has an Eh of -0.15, a pH of 7.6, and dissolved CO2 

and H2S; above a depth of 200 m, the water has an Eh 

greater than 0, a pH of 8.0 to 8.3, and dissolved oxygen. 

The dissolved manganese in the anoxic water is about 500 

times greater than that in the oxygenated surface water (fig. 

43). Manganese nodules forming on a shallow-water shelf 

in the northwestern part of the Black Sea may be the result 

of upwelling anoxic water mixing with oxygenated surface 

water. A similar process may account for manganese nodules in the Baltic Sea, where silled anoxic basins are rimmed 

with manganese nodules (Manheim, 1965). Cannon and 

Force (1983) believed that the large bedded manganese oxide and carbonate deposits of the Nikopol and Chiatura 

districts in the Soviet Union and the Varna district in Bulgaria were deposited during the Oligocene, when anoxic 

conditions occurred in the paleo-Black Sea.

The ore in the Nikopol district overlies a glauconitic sandstone and is 2 to 3 m thick over an area about 25 km wide 

and over 150 km long (Maynard, 1983, summarized from 

Varentsov and Rakhmanov, 1977, 1980, and others). The 

ore changes from oxides in the north to mixed oxides and 

carbonates and then to carbonate in the south, a reflection of 

increasing water depth at the time of deposition (fig. 44).

+200

CONCENTRATION (ppb) 

100 300 500

5 -500

-1500 L

Approximate 

shelf break

Fe

Figure 43. Distribution of dissolved manganese and iron in the Black Sea (after Brewer 

and Spencer, 1974).

76 Mineral and Petroleum Resources of the Ocean
LANDWARD

XXX

100 m

Some pre-Oligocene sediments 

present but not shown

Carbonate ore 

Sand

Clay

Glauconitic sand 

Oxide ore 

Crystalline rocks

Figure 44. Schematic cross section of the Nikopol bedded manganese deposits in the Soviet Union (from Cannon and Force, 

1983). (Reproduced with permission from the Society of Mining Engineers.)

The Groote Eylandt manganese deposit in Australia is 

another marine giant. It was deposited during midCretaceous time, and Frakes and Bolton (1984) proposed 

that it was formed when dissolved manganese was concentrated in relatively anoxic waters of the intracratonic basin 

during a marine transgression and precipitated as oxides and 

carbonates during a regression.

Again, no true analogs of these deposits are known on the 

sea floor today, but Calvert and Price (1970) have described a mixed manganese oxide-manganese carbonate deposit in the nearshore waters of Loch Fyne extending over 

an area of about 10 km2 in water depths of 180 to 200 m; the 

deposit is about 0.2 m thick and contains 5 to 10 percent 

Mn.

Some 90 percent of the world's production of iron ore 

also comes from marine sedimentary deposits that have no 

known true subsea analogs now (Maynard, 1983). About 

75 percent of the world production comes from banded ironformations of the Lake Superior type, nearly all of which are 

of Precambrian age, and 15 percent from oolitic ironstones, 

most of which are of Phanerozoic age.

It is generally believed that the banded iron-formations 

formed as a result of the oxidation of upwelling anoxic water 

containing perhaps a few parts per million of dissolved iron 

in a reduced form reacting with low concentrations of ambient free oxygen in near-surface waters (Holland, 1973; 

Walker and others, 1983). The oxygen content of the Precambrian atmosphere was substantially lower than it is now, 

of course, and such extensive deposits are not to be expected 

in the present ocean.

According to Van Houten and Bhattacharya (1982), most 

of the oolitic ironstones of Phanerozoic age were deposited 

during two episodes Early Ordovician to Early Devonian 

time and Early Jurassic to middle Cenozoic time (times of 

warm climate and extensive transgression). Chamosite 

(Fe+2 , Mg, Fe+3)5Al (Si3Al)O10(OH, O)8) proto-ovoids are 

forming, however, on muddy distributary banks of the 

Mahakam delta in Kalimantan, Borneo (Alien and others, 

1979), and ferric oxide proto-ovoids and chamosite pellets 

are forming in shallow sediments in the Niger and Orinoco 

deltas (Porrenga, 1965) and the Ogooue delta off Gabon 

(Giresse, 1969). Glauconite (K, Na)(Fe+3 , Al, Mg)2(Si, 

A1)4O10(OH)2 , which is associated with many Phanerozoic 

oolitic ironstones and some marine manganese deposits, has 

been found at many localities (for example, off the coasts of 

California, South Africa, eastern Australia, New Zealand, 

and eastern North America (Mero, 1965)). It is largely restricted to water depths of 400 to 600 m and to areas where 

sediment deposition is slow. Glauconite is not an iron ore 

(although it has been used as a fertilizer and water purifier), 

but it contains about 25 percent Fe2O3 . Thick glauconite 

beds thus represent large accumulations of iron.

Many theories have been advanced for the origin of the 

banded iron-formations and the oolitic ironstones, but, as 

Maynard (1983) suggested in his excellent review, none is 

without drawbacks. There seems to be wide agreement on 

their shallow-water marine origin, however, which is possibly related to changes in the Eh, pH, and temperature of 

upwelling waters, as Cannon and Force (1983) have postulated for the marine bedded manganese deposits. Even

Subsea Mineral Resources 77
though iron and manganese are partitioned in their precipitation, as previously described, it is not uncommon to find 

iron and manganese deposits in close association in the same 

vertical sequence (for example, in the Francevillian basin of 

Gabon, in Urucum in Mato Grosso, Brazil, and in Nsuta in 

West Africa), and it seems possible that at least some iron 

and manganese deposits (perhaps glauconite deposits also) 

are lateral time equivalents.

The present oceans are not anoxic, of course, and thus are 

not widely favorable for the formation of the huge iron and 

manganese deposits of the past. But that unfavorability does 

not rule out the possibility of the local existence of such 

deposits in restricted environments. Even if such deposits 

were present, however, they are not likely to be of economic 

interest in the foreseeable future.

METALLIC SULFIDE DEPOSITS

Concentrations of base-metal sulfide deposits were first 

discovered on the deep-ocean floor in the Atlantis II Deep 

of the Red Sea by a Woods Hole Oceanographic Institution 

expedition in 1965 (Degens and Ross, 1969), and they were 

first reported in a mid-ocean ridge crest in 1974 when 

Bonatti and others (1976a) found small amounts of iron and 

copper sulfides in the equatorial Mid-Atlantic Ridge. Beginning with the 1977 discovery by Lonsdale (1979) of small 

amounts of iron, copper, and zinc sulfides in the rift valley 

in the Gulf of California and the discovery by the C YAMEX 

expedition in 1978 of sizable sulfide deposits in the East 

Pacific Rise at 21° N. (Francheteau and others, 1979), several sulfide deposits have been found along the axes of 

Pacific spreading centers. These sea-floor discoveries were 

preceded by recognition that the massive sulfide deposits 

associated with volcanic rocks were deposited in similar 

submarine environments. Thus, since the late 1950's, it has 

been recognized that the massive sulfide deposits associated 

with ophiolite complexes on land were formed on the deepocean floor (for reviews, see Anderson, 1969; Sillitoe, 

1972; Sawkins, 1976; Solomon and Walshe, 1979; Franklin 

and others, 1981). And, beginning in the 1960's with the 

discovery of metalliferous sediments along mid-ocean ridge 

crests (Bostrom and Peterson, 1966) and of high heat flow 

there (Elder, 1965), several geologists predicted the occurrence of sulfide deposits in association with hydrothermal 

systems in the spreading center environment (Sillitoe, 1972; 

Bonatti and others, 1976a).

Sulfide deposits have also been found on seamounts a few 

kilometers from the East Pacific Rise crest at lat 13° N. 

(Hekinian and others, 1981) and near lat 20° N. (Lonsdale 

and others, 1982a). Rona (1984) listed a total of 21 occurrences of sulfide minerals on the sea floor in all environments, including some in fracture zones. Most are of scientific interest only.

Red Sea Metalliferous Sediments

The Red Sea occupies a rift valley at a divergent plate 

boundary. Seventeen deep basins (Shanks, 1983) lie along 

its median valley (fig. 45). Most of them contain hot, highly 

concentrated brines, and some contain metalliferous sediments. Of these, the sediments of the Atlantis II Deep are 

the most promising for commercial production, and they 

have been the object of extensive scientific studies and exploration.

The Atlantis II Deep lies at a depth of about 2,000 m. It 

is elongate and parallel to the axis of the median valley and 

has an area of about 56 km2 . It has two layers of hot brine. 

The lower layer had temperatures of 56 °C and 60 °C in 1966 

and 1972, respectively, and a salinity of 25.7 percent. The 

upper layer had a temperature of 44 °C to 60 °C in the same 

years and a salinity of 13.5 percent. A layer of sulfide muds 

about 1 m thick is extensive (table 28). Except in the southwestern basin of the deep, where it is cut by veins and 

otherwise modified by epigenetic processes (Zierenberg and 

Shanks, 1983), the sulfide mud is finely laminated. It is 

overlain by 7 to 8 m of iron oxide and iron silicate muds that 

also contain small quantities of other metals (Bischoff, 

1969). The principal minerals of the sulfide mud are pyrite 

(FeS2), chalcopyrite (CuFeS2 ), and sphalerite (ZnS2). 

Bischoff and Manheim (1969) estimated that the upper 10m 

of sediment in the Atlantis II Deep averages 29 percent Fe, 

3.4 percent Zn, 1.3 percent Cu, 0.1 percent Pb, 54 ppm Ag, 

and 0.05 ppm Au. Contemplating recovery of all these 

metals except iron, they estimated that the upper 10 m of 

sediment in the Atlantis II Deep would contain about 2.9 

million tons of zinc, 1 million tons of copper, 800,000 t of 

lead, 4,500 t of silver, and 45 t of gold. Hackett and 

Bischoff (1973) later revised the estimates for zinc and 

copper to 3.2 million and 0.8 million tons, respectively. A 

more recent estimate (Nawab, 1984) is 2 million tons of 

zinc, 0.4 million tons of copper, 4,000 t of silver, and 80 t 

of gold (see also Guney and others, 1984). At mid-1983 

metal prices, the total in-place value of these metals for 

these estimates would be in the range of about $3.8 to $5.1 

billion, about 40 to 25 percent of which would be in the 

value of silver and gold.

As I discussed previously, the Red Sea deeps contain 

several distinct facies of metalliferous sediments seen in 

both vertical and lateral variations, in some places over short 

distances (Bischoff, 1969; Bignell, 1975). These facies include (1) the mixed sulfide facies already described; (2) a 

pyrite facies; (3) several silicate facies in which smectite 

(Al2O3 -2SiO2) and other clay like minerals dominate and 

among which an iron-rich smectite is the most widespread; 

(4) several oxide and hydroxide facies in which limonite 

(2Fe2O3 -3H2O), goethite (Fe2O3 -H2O), lepidocrocite 

(Fe 2 O 3 -H2O), magnetite (Fe 3 O4 ), or manganite 

(Mn2O3 -H2O) dominate; (5) carbonate facies in which

78 Mineral and Petroleum Resources of the Ocean
X Deeps with brines 

D Deeps with hydrothermal sediments 

A Hydrothermally influenced sediments 

1,000m

Figure 45. Hot brine deeps in the Red Sea (modified from Mustafa and Amann, 1980) 

(from McKelvey, 1980). Deeps shown are those containing the most highly metalliferous 

sediments. (Copyright 1980 by the American Association for the Advancement of 

Science.)

siderite (FeCO3) and rhodochrosite (MnCO3) are present; 

(6) sulfate facies composed of anhydrite (CaSO4) and gypsum (CaSO4 -2H2O). Buried saline deposits are also extenThe Red Sea metalliferous sediments are the products of 

a still-active hydrothermal system along a slow-rate spreading center in which seawater of normal composition (Craig, 

1969) circulating through subsurface halite, anhydrite, and 

gypsum attains a high salinity. Contact with recent basalt in 

the rift area raises the water temperature to more than 200 

°C and allows it to leach metals from the basalt. On

Subsea Mineral Resources 79
Table 28. Chemical analyses of the sulfide facies of Red Sea sediments (from Bignell, 1975) 

[ND, not detected; N/D, not determined]

Facies Ca, 

in percent

AI 203 , 

in percent

Fe, Mn, 

in percent in percent

Zn, Cu, Ni, Co, 

in percent in percent in ppm in ppm

Mixed sulfide facies:

Atlantis II Deep (SU2) ------------------ 3.70 2.81 15.74 1.11 10.92 2.22 130 185

Atlantis II Deep (SU^ ------------------ 9.70 1.72 20.31 2.81 5.31 1.34 94 125

Atlantis II Deep------------------------ 5.70 1.74 25.71 .17 11.40 .83 60 260

(sulfide-silicate facies). 

ErbaDeep --------------------------- 10.64 4.11 16.60 .61 .34 .06 45 40

Pyrite facies:

Gypsum Deep ------------ ............ 29.10 .18 19.10 .09 .05 .67 13 45

discharge and cooling at the surface, the metals precipitate, 

beginning with chalcopyrite, galena, sphalerite, and pyrite 

and followed successively by iron silicates, iron oxides, and 

manganese oxides as the temperature decreases and the pH 

increases (Shanks and Bischoff, 1977; Krauskopf, 1957). 

Although two of the deeper lakes in the East African rift 

valley show evidence of hydrothermal mineralization and 

although a small deposit of iron and manganese oxides in the 

Afar rift bordering the Red Sea may also be of volcanicsedimentary origin (reviewed by Maynard, 1983), no other 

large brine pool deposits are known. It seems unlikely that 

any will be found in the open ocean. Deposits having the 

same lithologic association are not known in the fossil 

record, either, but, because evaporites are a common 

product of the early stages of continental rifting, it would 

not be surprising if similar deposits were found in ancient 

rift systems.

Sulfide Deposits on the Mid-Ocean Ridges of the 

East Pacific

Since the 1978 CYAMEX discovery of sulfide deposits at 

lat 21° N. on the East Pacific Rise (Francheteau and others, 

1979; Crane and Ballard, 1980; Hekinian and others, 1980; 

Zierenberg and others, 1984), such deposits have been 

found at seven other ridge crest localities in the east Pacific 

(fig. 46): (1) the Juan de Fuca Ridge (Normark and others, 

1982, 1983, 1984; Normark, 1983;Koski and others, 1982, 

1984); (2) the Gorda Ridge (Rowland and others, 1983); 

(3) the Guaymas Basin in the Gulf of California (Lonsdale 

and Becker, 1985; Lonsdale and others, 1980; Lonsdale, 

1984); (4) the East Pacific Rise at lat 13° N. (Hekinian and 

others, 1981, 1983); (5) the East Pacific Rise at lat 21° N.; 

(6) the Galapagos rift (Corliss and others, 1979; Malahoff, 

1981, 1982a; Law and others, 1981; Malahoff and others, 

1983); and (7) the East Pacific Rise at lat 20° S. (Ballard and 

others, 1981). The deposits are all associated with active or 

inactive hydrothermal vents. Associated with the active

vents are unique assemblages of large clams, mussels, and 

tube worms, the food for which comes from microbial 

chemosynthesis using energy from the reaction of sulfides in 

heated seawater (Grassle, 1982). The hydrothermal fluids 

are at temperatures of up to 380 °C or so, and they contain 

about 100 ppm Fe and a few parts per million of zinc and

I20°W 90°W

30°N

0°

25°S

Figure 46. Mid-ocean ridge sites (solid circles) where active 

hydrothermal circulation and associated massive sulfide deposits have been observed (from Normark and others, 1983). 1, 

Juan de Fuca Ridge; 2, Gorda Ridge; 3, Guaymas Basin; 4, East 

Pacific Rise, lat 21° N.; 5, East Pacific Rise, lat 13° N.; 6, 

Galapagos rift; 7, East Pacific Rise, lat 20° S. Open circles 

indicate numbered Deep-Sea Drilling Project sites where similar sulfide deposits have been recovered at depth.

80 Mineral and Petroleum Resources of the Ocean
Cd, Pb, Hg, K, Mg, Ag, Mo, V, Ga, Sn, Ti, Sr, Ba, Li, Sc, 

in ppm in ppm in ppb in percent in percent in ppm in ppm in ppm in ppm in ppm in ppm in ppm in ppm in ppm in ppm

430

200

320

80

1,850 3,100

1,090 1,140

1,430 3,140

90 N/D

0.8 0.6 120 330 140 58 42 460 480 1,700 11 4

.7 .8 75 85 68 23 22 580 1,100 4,000 44 6

.9 .7 100 130 71 32 6 97 110 380 12 9

55 

45

120 N/D 

145 155 .1 .2 ND 2 32 ND ND 58 2,700 430 35 3

*

Is

edge of rift valley

central depressiondashed where Inferred 

approximate depth in meters

sheet and lobate flows

pillow flows

talus

X VJ hydrothermal vent

&! v) » "' " '<*

rffi> hydrothermal plume

9 acoustic transponder

* -

 /, » 

Figure 47. Geologic sketch map of the southern Juan de Fuca 

rift valley (from Normark and others, 1983).

copper (concentrations 108 times the amount found in ordinary seawater) (Edmond and Von Damm, 1983). The deposits occur as mounds, chimneys (coalesced in places) 

(Malahoff, 1982b), and encrustations. In some areas, they 

have been found to occur intermittently along the rift valley 

over a width of 100 m or so and a length of several kilometers (fig. 47). With one exception, the deposits found thus 

far lie on basalt. In the Guaymas Basin (the exception), they 

are forming on sediments that overlie basalt at depth (Lonsdale and others, 1980; Lonsdale, 1984).

Associated with the deposits in some areas are iron oxides 

that might represent gossan that is, decomposed sulfide 

minerals resulting from submarine oxidation, a process that 

might take place rapidly if the deposits are not buried by 

sediments or lava flows.

Malahoff (1982b) suggested that individual sulfide bodies 

form rather rapidly, perhaps in a period of decades or less, 

and that, because they are and have been forming continuously along the axis of rift systems, they can be considered 

to be renewable resources.

All of the deposits except those on the Galapagos rift have 

zinc as their main metal and sphalerite (ZnS2) and wurtzite 

(Zn, Fe)S as their main minerals. Anhydrite (CaSO4), barite 

(BaSO4), opal (SiO2), and pyrite (FeS2) are common associates (Edmond, 1984). At the lat 21° N. site, Oudin (1983) 

identified a total of 33 minerals, many of them rare and 

most, except for those just named, occurring only in small 

quantities.

The composition of the east Pacific deposits is qualitatively similar to that of the sulfide deposits of the Atlantis II 

Deep, although their zinc content is 10 times higher or more 

(30-60 percent or so). The Galapagos deposits contain less 

than 1 percent Zn but 5 to 10 percent Cu, mainly in the form 

of chalcopyrite. According to Malahoff (1982a), the sulfide 

body is about 1,000 m long, 200 m wide, and at least 35 m 

thick and possibly amounts to 20 million tons. It contains 

about 85 percent pyrite plus marcasite (FeS2), and those

Subsea Mineral Resources 81
Table 29. Estimates of typical grades and values per ton of contained metals for sea-floor massive sulfide deposits, compared with 

typical ore from ophiolite massive sulfide deposits and deep-sea manganese nodules (from Bischoff and others, 1983) 

[ , not determined]

Sulfides, Iat21° N. and 

Juan de Fuca Ridge

Element

Zn ------

Cu------

Ni ------

Co------

/"* A

Mo -----

AAe S -----

Pb ------

Mn -----

Ge ------

Total

Metal values, 1 

in $/kg

O OQ

------ 1.46

------7.1

 3« r>8

_-_--. 2 22

1 8 87

 ice 90

....... .44

-------.40

-- 1,060.0

Typical 

grade,2 

in percent

30

.5

.07

.02 

.30

.01

Value 

per ton, 

in dollars

267.0 

7.30

1.55

71.06 

1.32

(106.0) 

---348 236

Sulfides, 

Galapagos rift

Typical 

grade,3 

in percent

0.2 

5.0

.02 

.017

Value 

per ton, 

in dollars

1.78 

73.0

7.01 

3.20

84.9

Sulfide ore, 

Cyprus4

Typical 

grade,4 

in percent

0.2

2.5

Value 

per ton, 

in dollars

1.78 

36.50

38.28

Deep-sea 

manganese nodules

Typical 

grade, 5 

in percent

0.13 

.99 

1.22

.23

.018 

28.8

Value 

per ton, 

in dollars

1.16 

14.45 

86.62 

80.69

9.05

(115.20)

191.97 

(307. 17)7

'Prices from Metals Week, December 6, 1981. Mn as ferromanganese, others as pure metals.

Approximate average from Bischoff and others (1983, table 5).

3Taken from Bischoff and others (1983, table 3, sample 9).

4Typical ore from Skouriotissa mine reported by Constantinou and Govett (1972).

5Average for Clarion-Clipperton prime zone reported by McKelvey and others (1979).

6Excluding Ge because its recovery at such a concentration likely would not be profitable.

'Including Mn.

minerals are also present (but in much lesser amounts) in the 

zinc-rich deposits (Bischoff and others, 1983).

None of these deposits has been sampled enough to make 

meaningful estimates of average composition, but Bischoff 

and others (1983) have developed "typical" compositions of 

the zinc- and copper-rich sulfide deposits and compared 

them with Cyprus sulfide ore and with manganese nodules 

from the Clarion-Clipperton zone (table 29) (Broadus and 

Bowen, 1983). As the table shows, Bischoff and others 

considered zinc, copper, cadmium, silver, and lead to be 

potentially recoverable from the zinc-rich deposits, 77 percent of the total value being made up by zinc and 20 percent 

by silver. They considered copper, zinc, cobalt, and molybdenum to be the potentially recoverable metals in the 

copper-rich deposits, 86 percent of the value being made up 

by copper. Their total values of $348/t and $85/t for the 

zinc- and copper-rich deposits, respectively, compare with 

about $38/t for Cyprus ore and $192/t for Clarion-Clipperton zone manganese nodules if manganese is not recovered 

and $307/t if it is. Very likely, sulfur would also be recovered, but its potential value has not been estimated.

All of the ridge sulfide deposits found thus far are in areas 

where the spreading rates are medium or fast (that is, greater 

than about 5 cm/yr). Iron and manganese oxides of hydrothermal origin have been found in many other ridge

systems, including the slow-spreading'Mid-Atlantic Ridge, 

but, with the exception of a rare find (Bonatti and others, 

1976a) of disseminated grains of pyrite or chalcopyrite in 

basalt, sulfide deposits have not been found in ridges having 

slow spreading rates. However, the largest subsea sulfide 

deposit found thus far (the Atlantis II) is forming at a slowrate spreading center; in fact, on theoretical grounds, Rona 

(1984) believed the probability for the formation of large 

deposits on slow-spreading centers to be greater than that on 

fast-spreading centers. In the Pacific and Indian Ocean 

Basins, medium- or fast-spreading ridge systems have a 

total length of approximately 40,000 km (Bischoff and others, 1983). The fact that all Pacific Ridge expeditions since 

1978 have discovered sulfide deposits indicates that they are 

widespread, as the following discussion of the analogous 

deposits already mined and explored on land will show, but 

it is not to be supposed that a continuous sulfide deposit 

exists along the entire mid-ocean ridge.

As with the Red Sea deposits, the mid-ocean ridge sulfide 

deposits are the result of seawater circulating through hot 

basalt and leaching metals from it. Bischoff and others 

(1983) estimated that the deposition of the silver in 1 g of 

sulfide required the leaching of about 2,500 g of basalt, if 

all of its silver were removed.

82 Mineral and Petroleum Resources of the Ocean
Sulfide Deposits Associated with Volcanic 

Seamounts

Hekinian and others (1981) reported iron-rich (pyrite and 

marcasite) sulfide (and some chalcopyrite, rare zinc sulfide, 

and local concentrations of cobalt) on the flanks of a volcanic seamount 6 km southeast of the axis of the East Pacific 

Rise near lat 13° N., where zinc-rich sulfides are found in 

the axial zone at about 30 sites over a distance of about 15 

km. Hekinian (1984) said that, "A first approximation indicates that the deposit has a volume of material 10 times as 

great as all the combined sulfide deposits distributed along 

the 20-kilometer segment of the adjacent axis of the East 

Pacific Rise." He considered seamounts to be "favoured 

sites for the formation of mineral deposits."

Lonsdale and others (1982) found deposits of pyrite and 

chalcopyrite on Green volcano (so named for bright-green 

secondary copper minerals found in places) about 20 km 

west of the sulfide deposits in the axial zone of the East 

Pacific Rise at lat 21° N. They occur in three environments the caldera floor, on the walls of the caldera and pit 

craters, and on the summit benches around the caldera and 

craters. Outcrops of massive sulfides formed about 5 percent of a 10,000-m2 area of crater wall, and Lonsdale and 

others speculated that they might be projections from a 

continuous sulfide deposit mostly blanketed by a finegrained iron oxide veneer. They believed that sulfide deposits on flank volcanoes such as this one are most likely to 

form during the geologically brief period when the magma 

chamber is freezing and thus creating fractures that give 

access to circulating fluids.

Flank volcanics are carried away from the ridge axis by 

plate movement and become extinct before they have moved 

very far. Lonsdale and others (1982) thought that they might 

be far more numerous than anyone had previously realized. 

Unless sulfide deposits formed on the surfaces of these 

volcanics are quickly buried, however, they are likely to be 

destroyed rather quickly by oxidation. If seamount deposits 

prove to be large enough and rich enough to be of commercial value, targets for exploration would be flank volcanoes 

near the ridge crest.

Analogs on Land

Strata-bound sulfide deposits associated with submarine 

volcanic rocks are found in many parts of the world. Known 

as a part of the generic group of volcanic-associated massive 

sulfide deposits, they have been defined by J.M. Franklin 

and D.F. Sangster in a comprehensive review (Franklin and 

others, 1981) as sulfide accumulations normally composed 

of at least 60 percent sulfides in their stratiform portions; 

pyrite is generally the dominant sulfide, and chalcopyrite,

sphalerite, or galena is the principal economic mineral. 

Franklin and Sangster said (Franklin and others, 1981) that 

at least 420 deposits of this type have been recorded (although information on occurrences of this type in the Soviet 

Union and the People's Republic of China is scant) and that: 

. . .virtually every major tectonic domain that has 

submarine volcanic rocks has at least minor representation of this deposit type. From our compilation of tonnage and grade data (production and 

reserves) these deposits collectively contain at 

least 3.7X107 metric tons of copper, 8.6xl07 

metric tons of zinc, 2.2x 107 metric tons of lead, 

6.3X1010 g of silver, and 2.2xl09 g of gold. 

These are obviously minimum figures. 

All of these deposits were formed on the sea bottom 

(some overlie a stringer system of discordant veins) as the 

result of hydrothermal systems associated with submarine 

volcanism, possibly in areas where the bottom waters were 

anoxic and where they were thus preserved until burial 

(Force and others, 1983). Not all of them, however (perhaps 

not even half), were formed in the mid-ocean ridge environment in association with basaltic volcanic activity. The volcanic rocks associated with many of them are wholly felsic 

in composition (rhyolites, dacites, or andesites). Felsic extrusives are not unknown in mid-ocean ridge volcanoes 

(some are found in Iceland, for example), but, if present at 

all, they are a minor component. The domains in which they 

are dominant are continental crust overlying subduction 

zones in island arcs or near the edges of continental masses. 

Thus, the volcanoes forming the "ring of fire" around the 

Pacific are dominantly felsic. The massive sulfide deposits 

in which the associated volcanoes are mainly felsic, as they 

are in the famous Kuroko deposits of Japan, likely were 

formed in submarine basins in an island arc setting. Qhmoto 

(1978) suggested that they were deposited on submarine 

resurgent calderas. Although many of their characteristics 

are similar to those formed in a ridge setting, they are of 

interest not as analogs of the recently discovered east Pacific 

deposits but as examples of sulfide deposits that may be 

found in other subsea environments yet to be identified in 

the present ocean.

Also known on land are syndiagenetic sulfide deposits 

associated with marine sedimentary rocks not in the immediate vicinity of volcanic rocks. Examples are the silverlead-zinc deposit at the Sullivan mine in British Columbia 

(Sawkins, 1976, 1982); the lead-zinc deposits at Mac Arthur 

River in Australia (Maynard, 1983); and the recently discovered Red Dog zinc-lead-silver deposit in the Delong 

Mountains of northwestern Alaska (G.E. McKelvey, personal communication, 1984). These deposits are clearly of 

subsea hydrothermal origin; for example, Alexander Malahoff found tube worms associated with the Red Dog deposit. 

Sawkins (1976, 1982) believed that these deposits and other

Subsea Mineral Resources 83
similar ones are related to rifting, and that view was shared 

by Mitchell and Garson (1981) as well. Thus, these deposits 

may be near analogs of the Guaymas Basin (Edmond and 

Von Darnm, 1983) and the Red Sea deposits, although, as 

Sawkins (1976) pointed out, none of the known land deposits has the lithologic setting of the Red Sea deposits. 

Lonsdale (1979) speculated that barite deposits forming by 

hydrothermal discharge along the San Clemente strike-slip 

fault in the southern California borderland may be underlain 

at depth by sulfide deposits that would be depositional counterparts of the Kuroko deposits.

The land analogs of the ridge sulfide deposits are in sequences of basalt flows and dikes and other mafic and ultramafic rocks known as ophiolites. They generally include 

some deep-sea sediments such as radiolarian chert or metalliferous sediment arid are widely recognized as representing 

segments of oceanic crust that have been thrust up (obducted) onto a continent rather than carried beneath it (subducted), as oceanic crust usually is. A classic example is the 

Troodos massif of Cyprus, where a sheeted basaltic dike 

complex represents the feeder system to overlying pillow 

basalts deposited at an oceanic ridge crest. At the base or the 

top of the uppermost pillow lava in places are lenticular 

massive sulfide deposits locally capped by an ochre layer, 

interpreted as the product of submarine weathering of sulfides before burial. The uppermost part of the sequence 

consists of sedimentary rocks, including (1) manganiferous 

iron-rich sediment (called umber) similar to the metalliferous sediments found near ridge crests and first described by 

Bostrom and Peterson (1966), (2) red jasper, and (3) radiolarian chert. Many of the deposits are adjacent to steep 

normal faults and are underlain by a stringer zone extending 

hundreds of meters below the sulfide deposits and containing veinlets of sulfide minerals. Some of the Cyprus deposits may be associated with ancient volcanoes (Ohmoto, 

1978).

Although the Troodos ophiolite is generally taken as the 

classic analog of the mid-ocean ridge assemblage (Maynard, 

1983; Sawkins, 1982), Schminke and others (1983) subdivided its lavas into a:

. . .lower, differentiated andesite to dacite series 

resembling evolved island-arc tholeiites and an 

upper series of picrite, mafic basalt, and basaltic 

andesite very low in TiO2 , K2O, P2O5 , Nb, Rb, 

and Ba. The highly depleted basalt and basaltic 

andesite resemble lavas formed from oceanic crust 

near island arcs the occurrence of fractionated 

lavas at the base and primitive lavas at the top 

suggests a broad zone of accretion located above 

a subduction zone.

Moores and others (1984) also did not believe that these 

ophiolites and others represent typical oceanic crust formed 

at mid-ocean spreading ridges.

Even though the Troodos deposits may not be the very 

close analog of the mid-ocean ridge deposits that they were

thought to be, they are the products of submarine volcanic 

activity and as such tell several important things about what 

can be expected of similar deposits beneath the present 

ocean. Far from being a single continuous orebody, the 

Troodos deposits are localized in 15 districts 1 or 2 to 30 km 

apart. Each district has several orebodies; in one example 

cited by Franklin and others (1981), the seven that have 

been mined have an average size of 220,000 t. Only six of 

the districts contain more than 1 million tons of ore, and the 

largest has 15 million tons. Although they are mined chiefly 

for copper and pyrite, they are variable in composition. 

One, for example, averages 6.52 percent Cu and 8.44 percent Zn, whereas the largest contains about 4 percent Cu and 

only 0.5 percent Zn; cobalt is erratically distributed but 

reaches 0.35 percent in one district.

As another example of the size and frequency of sulfide 

deposits in ophiolites, the Semail ophiolite in Oman should 

be mentioned. It is 500 km in length and contains many 

small sulfide deposits. As yet, however, only three significant deposits (in the range of 1-7 million tons) have been 

found (Coleman and others, 1979). Haymon and others 

(1984) reported the presence of fossilized tube worms in a 

matrix of zinc and iron sulfide minerals at one locality there. 

These features are similar to those found in other ophiolite 

sequences. The deposits are localized and locally variable in 

composition, and most are measured in hundreds of thousands or millions of tons. As many other kinds of minerals 

are, however, most of the ore may be contained in larger 

deposits in the range of a few tens of millions to perhaps 

100 million tons in the rare supergiant.

The implications of these features for subsea exploration 

are several. The deposits are likely to be localized, and some 

will probably be too small to be recoverable, particularly if 

they are isolated from other deposits. The deposits are likely 

to be locally variable in composition and concealed by gossan or younger basalt flows or sediments. Because of these 

characteristics, detailed exploration, including at least shallow drilling, will be required to evaluate the deposits and to 

guide mining. And, although no sulfide deposits have yet 

been identified in areas of active subsea hydrothermal activity associated with island arcs, they are nonetheless targets 

for prospecting. In discussing such prospects, Sillitoe 

(1982) said:

The most obvious example is in the northern offshore extension of the Taupo volcanic zone, New 

Zealand. . .where currently resurgent calderas are 

a distinct possibility. Suitable submarine calderas 

might also exist adjoining southeast Sumatra, 

along the offshore extensions of the Semangka 

transform fault within Semangka Bay and southeastward to Krakatoa; in southern Kyushu, Japan, 

where the Quaternary Aira and Ata calderas collapsed beneath Kagoshima Bay, a volcanotectonic graben that may be a northeastern extension of the Okinawa back-arc basin; and in the

84 Mineral and Petroleum Resources of the Ocean
southern Aegean, where Holocene caldera collapse (for example, Santorini) was in a tensional 

back-arc setting linked to northward subduction. 

Rona (1982) considered the marginal seas of the western 

Pacific, where spreading centers occur in back-arc basins 

between the volcanic island arcs and the 'mainland, to be 

generally favorable for their occurrence. Using abiogenic 

methane in surface water as a tracer for submarine hydrothermal systems, Kim and others (1983) believed that 

they have identified sites of hydrothermal activity in the 

Mariana Trough and at Loihi Seamount, the youngest of the 

Hawaiian volcanoes.

Feasibility of Commercial Recovery

Only the Atlantis II Deep has been explored enough to 

justify an estimate of its tonnage and potential value; on the 

basis of publicly available information, even such estimates 

must be regarded as tentative and subject to major revision. 

With that caveat, the Atlantis II deposit has been estimated 

by Bischoff and Manheim (1969) to contain about 85 million tons of the composition already indicated. It thus ranks 

among the supergiants of known sulfide deposits, although 

it is lower in grade than many of them. Even so, at current 

prices and on the assumption of about 85 percent recovery, 

the potential value of its contained metals would be roughly 

$3.2 to $4.3 billion.

In 1974, the Governments of Saudi Arabia and Sudan 

formed the Red Sea Commission to undertake joint research 

and development studies on the Red Sea deposits. Work has 

been proceeding steadily, mainly through a contract with the 

German firm Preussag AG. All phases of the recovery, 

processing, and tailings disposal systems have been tested 

(Mustafa and Amann, 1980; Nawab, 1984), and, although 

some pilot-scale testing remains to be done, production is 

expected to begin in the latter part of this decade.

Given the metal compositions estimated by Bischoff and 

others (1983) for "typical" east Pacific ridge deposits and 

shown in table 29, the value of these deposits in place would 

range from $85/t to $348/t. No speculations have even been 

made public as to the cost of mining the mid-ocean ridge 

deposits. It is possible that the experimental lifting technology already used for manganese nodule mining might be 

suitable for the sulfides, and processing technology is already well established. How the mining itself would be done 

is the problem (Cruickshank and Zippin (1983) and Kaufman (1985) have discussed the possibilities). Some of the 

rock might be soft enough to be dredged with a towed or 

self-propelled miner, but, if the rock is hard enough to 

require blasting, the added cost would be considerable. Another required technology not transferable from nodule research and development is that of detailed exploration, including drilling.

Neither the feasibility nor the profitability of subsea sulfide mining can be assessed now. A useful question at this 

stage, however, is whether the targets appear to be large 

enough to warrant further investment in exploration and 

research and development. A crude approach to finding an 

answer is to look at the targets for nodule mining. It has been 

generally accepted that a reasonable model for a manganese 

nodule operation would be one producing 3,000,000 t/yr of 

nodules for 25 years. Estimates of whether the revenues 

from such an operation would be sufficient to warrant the 

large investment required have varied considerably, but it is 

significant that a target of that magnitude has led several 

consortia of members from several countries to invest many 

tens of millions of dollars in exploration and research and 

development on nodule mining. The value of the metals in 

75 million tons of nodules is about $13.4 billion if only 

nickel, copper, and cobalt are recovered and $23 billion if 

manganese is recovered also. Notwithstanding the fact that 

the target justifying research and development on the Red 

Sea muds (where the discovery had already been made and 

where the hurdles anticipated in developing the technology 

were lower than those seen here for the ridge sulfides) was 

only about $6 billion, it would appear that the target justifying exploration and research and development on the ridge 

sulfide deposits would have to be of the order of $15 billion 

or possibly more. A roughly similar assumption has been 

made by Cruickshank and Zippin (1983), who speculated 

that a viable operation on the Gorda Ridge would produce 

a total of 30 million tons of ore over 20 years; at the value 

of $348/t calculated by Bischoff and others (1983) for the 

nearby Juan de Fuca deposits, such an operation would 

represent a total value of about $10.5 billion.

Is it likely that such targets exist? The $15 billion translates into about 43 million tons or so of the Juan de Fuca 

tenor not necessarily in a single deposit or even in one 

closely spaced cluster of deposits but at least in an area small 

enough that a mining organization can hope to control it. On 

the basis of the land analogs discussed previously, the answer would seem to be, "Yes, there are some, and, if one 

could expect to control a sulfide-bearing ridge crest of the 

length of the Troodos massif (that is, 90 to 100 km), there 

are probably a lot more."

Even if such targets do exist, the feasibility of mining 

subsea sulfide deposits has yet to be demonstrated. Crawford and others (1984) have made some preliminary studies 

of the geotechnical engineering properties of the subsea 

sulfides (their density, porosity, durability, hardness, compressive strength, and cutting properties). They concluded 

that "the most feasible method for mining would be some 

type of cutter head and hydraulic lifting system," but, as yet, 

such a system has not even been designed, much less tested. 

At this stage, one cannot assume that the deposits will become economically recoverable (Broadus and Bowen, 

1984).

Subsea Mineral Resources 85
Jurisdiction Over Exploration and Production

Much of the mid-ocean ridge lies seaward of 200 nmi 

from the coastal baselines from which the breadth of the 

territorial sea is measured. Under the provisions of the Convention adopted by the Law of the Sea Conference on 

April 30, 1982, coastal States would have jurisdiction over 

the 200-mi EEZ and over the part of the continental margin 

that extends beyond that distance. Its language is somewhat 

ambiguous in stating that "the outer limits of the continental 

shelf. . .either shall not exceed 350 nautical miles from the 

baselines from which the breadth of the territorial sea is 

measured or shall not exceed 100 nautical miles from the 

2500 meter isobath," but, notwithstanding these provisions, 

"on submarine ridges the limits of the continental shelf shall 

not exceed 350 nautical miles from the base lines from 

which the breadth of the territorial sea is measured," perhaps 

an implication that, on an oceanic ridge, the limit might be 

as much as 350 mi if the bathymetry would carry it that far. 

This implication is clearly negated, however, by an earlier 

provision defining the continental margin, over which 

coastal States are to have jurisdiction, as including the shelf, 

slope, and rise but not "the deep-ocean floor with its oceanic 

ridges."

Beyond the EEZ, then, the mid-ocean ridge would be a 

part of the area under the control of the International SeaBed Authority. The Convention provides no detailed regulations governing the mining of minerals other than manganese nodules, but a provision added during the eleventh 

session of the conference requires that the Council (the 

Authority's executive body), acting by consensus, would, 

on request, promulgate rules and regulations governing the 

mining of other minerals. If the parallel system were applied 

to the sulfide deposits, as it is to the nodules, an aspiring 

contractor would have to identify two areas containing deposits of estimated equal value much more of a burden on 

a sulfide miner than it would be on a nodule miner in view 

of the probable requisite deposit size just discussed.

The ridge area that would be under coastal State jurisdiction would not be nearly as large as that under international 

jurisdiction, but, because of the area's proximity to shore 

and because the operator might not have to bear the burden 

of the parallel system, it seems likely that commercial interest in ridge sulfide deposits would focus initially on areas 

within the EEZ. Examples of ridge areas that would fall 

within the EEZ include the northern part of the Juan de Fuca 

Ridge (Canada), the northern part of the Gorda Ridge 

(United States), the Guaymas Basin (Mexico), parts of the 

East Pacific Rise (Mexico and Chile), and part of the Galapagos Ridge (Ecuador). Also within the EEZ would be most 

of the areas that are promising for the occurrence of subsea 

sulfide deposits associated with felsic volcanic rocks.

Although many areas in the EEZ can be identified as 

likely to attract commercial interest, none of the countries 

involved has regulations in place governing the exploration

and development of such deposits. Serious commercial exploration is therefore not likely to develop soon.

RED CLAYS

Deposits of red or brown clay blanket about 30 percent 

(100 million square kilometers) of the ocean floor (Hollister 

and others, 1981). They are largely of terrigenous or volcanic origin, and the regional variations in their mineralogical compositions reflect climate and continental input. The 

illite that generally forms more than 50 percent of the clay 

in the northern hemisphere and 20 to 50 percent in the 

southern hemisphere reflects continental input. Chlorite is 

much more abundant in polar areas than it is in tropical seas, 

where it weathers to kaolinite, which is much more 

abundant in tropical regions. Montmorillonite (smectite) is 

an alteration product of volcanic ash and is much more 

abundant in the Pacific and Indian Oceans than it is in 

the Atlantic, which is less active volcanically (Kennett, 

1982).

The average grain size of red clay is generally less than 

5 (X. Red clay is generally found away from plate boundaries 

in open ocean areas at depths greater than 4,000 m. Its rate 

of accumulation is on the order of 0.1 to 10 mm/ka. Because 

of this slow rate, coupled with a continuously renewed oxygen supply, the red clays are oxidized and generally low in 

organic carbon (generally less than 1 percent) (Hollister and 

others, 1981). Because they lie below the carbonate compensation depth, red clays contain little or no calcium carbonate, and, because of the great sorptive power of the 

clays, they contain many minor elements; Goldberg and 

Arrhenius (1958) reported the presence of 19 elements in 

addition to silica and alumina, including manganese, nickel, 

copper, cobalt, vanadium, and lead.

Mero (1962) speculated that these minor elements might 

be recoverable, particularly if the manganese oxide grains, 

with which several of them are probably associated, just as 

they are in the manganese nodules, could be separated from 

the clay; he also speculated that the clay might be used for 

ceramics. Neither of these possible uses is likely to become 

economic for many decades, if ever, but one potential use 

is being seriously considered by several countries namely, 

in situ use for the storage of high-level radioactive waste. 

Canada, the Commission of European Communities, 

France, Japan, the Netherlands, the United Kingdom, the 

Federal Republic of Germany, and the United States are 

members of a Seabed Working Group under the auspices of 

the Organization for Economic Cooperation and Development's Nuclear Energy Agency conducting research on the 

feasibility of storing solidified high-level radioactive waste 

in canisters emplaced 25 to 50 m beneath the surface within 

the red clay blanket.

It is generally agreed that a safe site for the disposal of 

high-level radioactive wastes, whether on land or beneath

86 Mineral and Petroleum Resources of the Ocean
the sea, must have a low probability of seismic or volcanic 

activity, must remain unaffected by climatic change (such as 

a return to a glacial period), and must provide a strong 

barrier to the movement of fluids. In addition, the characteristics being sought for a subseabed repository are a long, 

uninterrupted sediment depositional history, a capacity for 

strong sorption of nuclides by the sediments, a low permeability, good elastic properties, no degradation of properties 

under thermal stress, absence of gases within the sediments, 

and low or no natural pore-water circulation. The site should 

also not be in areas characterized by bad weather, should not 

be near shipping lanes or strong surface currents, should not 

be at high latitudes (Hinga, 1982), and should not be in 

areas where abyssal storms are likely to erode the bottom 

(Hollister and others, 1984). It should also be possible to 

recover the canisters containing the waste.

Several regions in the Pacific and Atlantic Oceans are 

being evaluated as potential subseabed waste-disposal sites 

(fig. 48), and the properties of the red clay and its probable 

reactions to possible stresses are being studied (Anderson, 

1979; Hollister and others, 1981; Laine and others, 1983; 

McConnell and Shephard, 1983). The studies are incomplete, and none of the investigators is ready to draw final

conclusions about the suitability of the red clay. Thus far, 

however, no unfavorable elements have Been encountered; 

to the contrary, many favorable elements have been identified (Hollister and others, 1981). For example, although the 

clay is extremely cohesive, it has elastic properties that will 

allow easy penetration by a canister through either free fall 

or drilling, and yet the emplacement hole can either self-seal 

or be easily sealed artificially. It has extremely low permeability and the highest sorption capacity for radionuclides of 

any geologic medium yet tested, so it can be expected to 

contain the waste after the canisters have decayed. Acording 

to Hollister and others (1981):

Initial estimates suggest that for a 1.5 kw decaying heat source (i) a water molecule will be transported by thermally induced movement approximately 0.3 m in 1,000 years (after which, 

effectively, all of the heat is gone), and (ii) a 

radionuclide with a distribution coefficient of 103 

to 106 ml/g, a half-life of less than 500,000 years, 

and a burial depth of 15 m or more in the sediment 

will not reach the benthic boundary layer at the 

surface of the sediment before it has decayed essentially to zero concentration.

IN 121 141 IN IN IN 149 in IN N N 41 21 I 21 41 N N

Figure 48. Regions of the oceans expected to provide areas that are geologically suitable for subseabed waste disposal (large 

boxes) (from Hinga, 1982). The smaller boxes are locations surveyed by the Sea-Bed Working Group nations. (Copyright 1980 

by the American Geophysical Union.)

Subsea Mineral Resources 87
Although the ocean itself is not considered to be a barrier to 

the leakage of radioactive waste, it certainly can dilute and 

disperse to low levels any radioactive nuclides that might 

escape, in spite of the improbability of their doing so. 

Abyssal waters are also very cold (about 2 °C) and constitute 

a huge heat sink for any heat that might be generated by the 

waste (McConnell and Shephard, 1983).

The red clay environment meets well the requirements of 

tectonic stability and protection from the effects of climatic 

change such as glaciations. A 25-m piston core from the 

north-central Pacific, for example, shows continuous red 

clay sedimentation extending back 70 Ma (McConnell and 

Shephard, 1983). Another advantage of the red clay environment is that most of it is devoid of other resources. Much 

of it is a biological desert because of the absence of nutrients, and, although manganese nodules may be present on 

the sea floor, their metal content over large areas is too low 

to be of commercial interest (Anderson, 1979). Hinga 

(1983) believed that, even if mining operations were conducted over a repository, they would not jeopardize the 

containment of radioactive wastes. Still another advantage 

is that the water-saturated red clay is an excellent medium 

for the propagation of sound, so that the lateral and vertical 

characters of the repository can be accurately established by 

seismic reflection techniques, calibrated with sediment 

cores (Hollister and others, 1981). The north-central Pacific 

also appears to be free of abyssal storms that might scour 

bottom sediments (Hollister and others, 1984).

Several kinds of rocks (salt, granite, basalt, shale, and 

tuff) are being investigated as possible repositories on land 

for high-level radioactive waste (Kerr, 1979), but, if levels 

of containment assurance are assumed to be equal and satisfactory, the abyssal red clay environment has several advantages over land sites. For one thing, some nuclear nations 

may not have suitable disposal sites within their borders. For 

another, the abyssal environment in areas containing no 

resources of commercial value helps to ensure that the area 

will be safe from human intrusion.

The U.S. Seabed Disposal Program projects 1988 as the 

time when it will be possible to judge the merits of seabed 

emplacement (Hinga, 1982). If it is considered to be desirable, engineering development would take several years. 

Even more time consuming might be the development of a 

suitable regulatory regime to authorize and manage subseabed disposal.

Disposal of high-level radioactive waste in the ocean is 

prohibited by the 1973 London Dumping Convention and 

the U.S. Marine Protection, Research, and Sanctuaries Act 

of 1972. However, the International Atomic Energy Agency 

recognized in 1973 that subseabed disposal is not the same 

as ocean dumping, so those prohibitions would not apply 

(McConnell and Shephard, 1983). What probably would 

apply, however, would be provisions of the 1982 Law of the 

Sea Convention, particularly article 137, which states that 

"No State shall claim or exercise sovereignty or sovereign

rights over any part of the Area or its resources. ..." "Area" 

means the seabed and subsoil beyond the limits of national 

jurisdiction, and resources are defined in article 133 as "all 

solid, liquid or gaseous mineral resources in situ in the Area 

or beneath the seabed." Subseabed emplacement of waste 

would constitute the in-place use of a resource, for it is the 

physical and chemical properties of the clay that are being 

counted on for containment.

The United States and some Western countries have not 

signed the Law of the Sea Convention and might claim not 

to be under its prohibitions. They are, however, signatories 

to the 1958 convention on the high seas, article 2 of which 

states that"... no State may validly purport to subject any 

part of [the high seas] to its sovereignty." Committing an 

area of the seabed to waste disposal for a million years is 

likely to be considered as a claim of sovereignty over the 

area. It seems likely, then, that international regulations will 

be required. The Law of the Sea Convention does not now 

provide for the recovery or use of resources other than the 

manganese nodules, but one of its provisions requires that 

rules and regulations governing mining of other minerals be 

developed on request.

It is conceivable that a suitable abyssal clay site might be 

found north of the Hawaiian Islands within the U.S. EEZ. 

Use of such a site would come under U.S. regulations alone, 

but, of course, such regulations would have to be developed.

RADIOLARIAN OOZE

The manganese nodules in the Clarion-Clipperton zone in 

the northeastern equatorial Pacific lie on a substrate of clay 

and radiolarian ooze. Arrhenius (1977) has suggested that 

an associated product of nodule mining might be radiolarian 

silica. Diatomite, also composed of silica and otherwise 

similar to radiolarite, is mined on land for a variety of uses 

ranging from filtration to light-weight aggregate. Its price 

averaged $175/t in 1982; if comparability is assumed, radiolarian silica would be a valuable product. The extremely 

high moisture content of the ooze, however, poses difficult 

transport and processing problems. Moreover, most of the 

ooze is admixed with red clay. For these reasons, its commercial recovery does not seem likely.

BARITE

Barite (BaSO4) has been found as nodules, crystals, and 

microcrystalline aggregates on the deep-ocean floor in many 

parts of the world. It has already been mentioned as part of 

the mineral assemblage associated with hydrothermal vents, 

and it is possible that hydrothermal waters may be the source 

of barite concentrations away from the vents.

Arrhenius and Bonatti (1965) reported that widespread 

barite in the southeastern Pacific makes up 5 to 10 percent

88 Mineral and Petroleum Resources of the Ocean
of the sediments in an area about 15° in width, centered 

roughly on the 110° E. meridian and extending from the 

equator to about lat 40° S. Localized occurrences of barite 

concretions containing up to 75 percent BaSO4 have been 

found in many parts of the world (see Mero (1965) and 

Cronan (1980) for summaries), but thus far no extensive 

high-grade deposits have been reported subsea. Their possible presence should not be ruled out, however, for thick and 

extensive bedded deposits of marine origin containing as 

much as 95 percent BaSO4 are known on land in many parts 

of the world (see Brobst's (1973) summary).

SEAWATER

Nearly all the chemical elements are present in seawater, 

most of them in trace quantities only. Excluding hydrogen 

and oxygen, only 12 are present in amounts greater than 

1 ppm (table 30).

Only a few products are recovered from seawater commercially. Salt is produced in many parts of the world by 

solar evaporation in shallow seaside pans. Only a few percent of the salt produced in the United States come from this 

source, but about one-third of the total world salt production 

is so derived (Shigley, 1968). Magnesium compounds are 

recovered from the bitterns remaining after the salt precipitates, and about one-third of U.S. production comes from 

this source. Magnesium metal is also produced from seawater by electrolysis, and most of that produced in the 

United States is so derived. Chlorine is recovered in this 

process but is reacted with methane and water to make 

hydrochloric acid, which is used to make the magnesium 

chloride feed for electrolysis. Much of the world production 

of bromine comes from seawater plants in Australia, 

France, India, Italy, Japan, and Spain; it has been produced 

from seawater in the United States also, but current producTable 30. Elements present in seawater in amounts greater 

than 1 ppm (after Shigley, 1968)________________

Element

Amount, 

in ppm

d -----------..-...----.--..-......--.--..---18,980

Na-------------------------------------------10,561

Mg -------------------------------------------1,272

S --------------------------------..--------.----884

Ca -------------------------------------------.--400

K ----------------------------------------------380

Br -----------------.-----------..-.--------------65

C------------------------------------------------28

Sr -----------------------------------------------13

B---------------------------------.---------------4.6

Si -------------------------------.------------.02-4.0

F -------------------------------------------------1.4

tion comes entirely from underground brines in Michigan 

and Arkansas.

Potash and iodine were produced from seaweed in times 

past in many places, including the United States, but are 

produced now more cheaply from other sources (Armstrong 

and Miall, 1950). Potassium, sulfur, and boron have been 

said to be recoverable from seawater, but they cannot yet 

compete commercially with other sources. Extensive research on the recovery of gold from seawater, present in the 

amount of 4 parts per trillion, has not been successful. The 

Dow Chemical Company did recover some (0.09 mg, worth 

about 10 cents, from 15 t of seawater).

Desalinated seawater has come to be an important product 

in many coastal areas. In 1976, 1,382 desalting plants (including 346 in the United States) were producing 594 million gallons of freshwater per day, mainly, though not entirely, from seawater (Miller, 1979). Several processes are 

available for desalting ion exchange or electrodialysis to 

remove the salts or distillation, freezing, or reverse osmosis 

to remove the water and leave the salts behind. Most large 

desalination plants use a multistage distillation process that 

removes only about half the water. Nearly all of the plants 

have been built since 1950, and nearly 90 percent of those 

have been built since 1966, when only 153 were in operation 

(Shigley, 1968). Even though desalinated water is expensive to produce, additional capacity will be added to satisfy 

the growing needs of coastal cities in areas where water is 

in short supply.

ENERGY IN THE OCEANS

The ocean is a potential source of energy in several forms, 

the largest being nuclear. Seawater contains an average of 

17 ppm deuterium for a total of 25 trillion tons in the ocean 

(in the fusion reaction, equivalent to an unimaginable 

7,500xl024 Btu) (Cambel, 1965). The ocean also contains 

about 20 billion tons of lithium 6, which could be used to 

breed tritium for use in a proposed deuterium-tritium reactor. Although seawater contains only about 0.03 ppm U, 

methods for its possible recovery are being explored. The 

Japanese Government is said to be developing a new method 

for extracting uranium from seawater, said to be 20 times as 

effective as any current method and believed by Japanese 

scientists to be price competitive with other sources (Anonymous, 1981).

Tidal energy is enormous but extremely difficult to recover, because, in most places, the tidal range is small, and 

funneling large quantities of water through a generator 

would be impossible. Moreover, power generation must 

necessarily be intermittent. Although tidal water wheels 

have been used in a few places in Europe and the United 

States to generate power for grinding grain, the only major 

tidal electric plant ever built is at France's La Ranee estuary 

in Brittany, where the maximum tidal range is 44 ft. The

Subsea Mineral Resources 89
installation consists of a dam near the mouth of the estuary, 

a powerplant equipped with turbines that can operate on 

both inflow and outflow and with blades that can turn the 

turbines into pumps to accelerate the buildup and lowering 

of the basin level, locks for navigation, and sluice gates to 

accelerate the filling and emptying of the basin. Its maximum output is 240 MW, but, because its power generation 

is not constant, its output is only about one-third of that. But 

is is assured production, not subject to droughts.

A mean tidal range of 5 m or more is considered necessary for an economic operation. More than 30 sites around 

the world meet this requirement (Couper, 1983). Potentially 

suitable sites in the United States are Cook Inlet in Alaska 

and Pasamaquoddy and Cobscock Bays in Maine. In other 

countries, the most promising areas are the upper Bay of 

Fundy in Nova Scotia, where a plant under construction at 

Annapolis Royal was expected to go onstream in August 

1983 (Arpin, 1982); the Gulf of Mezen in the Soviet Union; 

the Bay of Mont St. Michel in France; the Severn River 

estuary in England; the Walcott Inlet in Australia; San Jose, 

Argentina; and Asan Bay in South Korea, where a plant is 

also under construction(?). Tidal possibilities worldwide 

have been estimated to have a potential energy output of 

635,000 GW, the equivalent of more than a billion barrels 

of oil a year (Ryan, 1979).

Wind-generated wave energy incident on the coastlines of 

the world has been estimated to be 2 to 3 x 1012 W, a significant fraction of world power consumption (Newman, 

1979). Because of the prevalence of westerly winds, the 

eastern edges of the oceans are the most favorable for wave 

power. The western coasts of Norway and Scotland have 

received the most attention, but the western coast of North 

America is comparably promising. Mean values of the wave 

power in such areas are 10 to 1,000 kW/m of coastline. 

Many devices are being investigated for the recovery of 

wave power, particularly in Japan, the United Kingdom, 

and Norway. Newman (1979) believed that, if the cost of 

conventional power generation continues to escalate, waveenergy conversion may become economic within a decade.

Among the largest reservoirs of solar energy are the 

ocean-circulating current system, or gyres, in both hemispheres. Because of the Earth's spin, these currents are 

strongest on the western sides of the oceans. The Florida 

current 30 km off Miami Beach contains 50 times more 

energy than all the rivers in the world (Lissaman, 1979). In 

1973, W.A. Mouton proposed what he called the Coriolis 

concept, the idea of manufacturing electric power from the 

installation of giant turbines in the Florida current. Feasibility studies have been underway since then, supported by the 

U.S. Department of Energy since 1978. Results have been 

generally encouraging. Development of a prototype unit has 

not yet begun but may take place within a few years. The 

concept calls for an array of turbines that would deliver 

10,000 MW of power to Miami, about 10 percent of the 

energy needs of the State of Florida. Such an extraction of

energy would reduce the speed of the Gulf Stream by only 

about 1 to 2 percent, much less than its natural fluctuation. 

Many believe that the cost of producing electricity from this 

resource may be lower than that of producing it from fossil 

fuels or nuclear powerplants "at the same site, particularly in 

the Pacific islands (Craven, 1984).

The large temperature difference (171 °C-221 °C) between surface and deep-ocean water in the tropics has stimulated interest in ocean thermal energy conversion. Warm 

surface water would be used to vaporize liquid ammonia at 

high pressure. The vapor would drive a turbine and generate 

electricity. Cold water pumped from the bottom would cool 

and liquify the vapor for reuse. Nutrients brought up in the 

cold water might enhance organic productivity, and fish 

might be a byproduct of electric power (Cohen, 1979). A 

conversion plant might also be used to desalinate seawater. 

One-third of the energy generated would have to be used for 

pumping up the cold water (a 100-MW plant would require 

a cold water throughput equal to the flow at Boulder Dam), 

and economic means of transporting the electricity to land 

have yet to be worked out. Another alternative would be to 

use the electricity at the site for electrolyzing water to make 

hydrogen. Other options are also possible (Craven, 1984).

Another large store of solar energy in the oceans is in the 

form of salinity; the salinity gradient between river water 

flowing into the sea represents an osmotic pressure difference of 24 atm, equivalent to a 240-m waterfall. Wick 

(1979) estimated that, if it were possible to convert the 

salinity gradient of one-half the flow of the Columbia River 

into electricity at only 30-percent efficiency, 2,300 MW 

would be produced. He estimated that the potential salinitygradient power of global runoff is 2.6X1012 W, about 

10 percent of present global power demands. The technology for the recovery of salinity-gradient power is not yet 

available, but Wick described several methods that he believed could be commercially successful.

The artificial culture of biomass (not a mineral resource 

but a potential form of ocean energy also of solar origin) is 

receiving serious consideration as a possible source of energy (Ryther, 1979). Seaweed is cultured now in the Far 

East for hydrocolloids and other products and yields as 

much as 20 dry t/acre/yr (deciduous and evergreen forests 

yield about 5 and 10 dry t/acre/yr, respectively); under carefully controlled experimental conditions, Ryther has obtained as much as 40 dry t/acre/yr. Beginning in the mid1970's, a research and development program for the design 

and development of an ocean energy farm to culture kelp, 

covering 100,000 acres 100 mi off the coast of southern 

California, was begun under the auspices of the U.S. Energy 

Research and Development Administration, the National 

Science Foundation, the American Gas Association, and 

other public and private organizations. The anticipated harvest would be the equivalent of about 15 dry t/acre/yr, 

8 dry t of which would be organic biomass. Energy conversion by wet anerobic digestion would yield natural gas that

90 Mineral and Petroleum Resources of the Ocean
would be piped to shore. Considering the magnitude of the 

research and development that lie ahead, Ryther (1979) 

believed that "open-ocean energy farming of sea weeds 

must be regarded as a long-term prospect that cannot be 

realized in a time frame of less than tens of years."

Hydrothermal vents on the ocean ridges and subsea volcanoes complete the catalog of ocean energy sources. The 

temperature of the water at these vents is about 350 °C, and, 

if they were on land, they would be of commercial interest. 

One possible way to recover energy from such sources 

would be to locate an ocean thermal energy conversion plant 

on or near a vent. Inasmuch as the cold water for the system 

could be obtained nearby, the lengthy cold-water pipe required for a surface conversion plant could be eliminated 

(Couper, 1983).

THE LAW OF THE SEA

The Law of the Sea has been a topic of international 

concern for centuries, but the UN Law of the Sea Conferences date back to President Harry S. Truman's 1945 declaration claiming sovereign rights over the mineral resources 

of the continental shelf. This pronouncement followed the 

completion of the first producing oil well offshore Louisiana 

and the recognition that the technology for offshore production was in hand. Several other countries, at first interested 

in fish rather than in minerals, soon declared sovereignty 

over territorial seas up to 200 mi in width, leading to international concern over extensions of national jurisdiction.

The United Nations convened the First Law of the Sea 

Conference in 1958; representatives of 86 States were in 

attendance. After only 9 weeks of negotiations, the conference concluded the 1958 Geneva Conventions on the Territorial Sea and Contiguous Zone, the High Seas, Fishing and 

Conservation of the Living Resources of the High Seas, and 

the Continental Shelf. The Continental Shelf Convention 

gave coastal States sovereign rights over nonliving resources of the seabed and subsoil of the continental shelf, 

which it defined as ". . .the submarine areas adjacent to the 

coast but outside the area of the territorial sea, to a depth of 

200 meters or, beyond that limit, to where the depth of the 

superjacent waters admits of the exploitation of the natural 

resources of the said areas."

The 1958 Territorial Sea Conference failed to reach 

agreement on the breadth of the Territorial Sea. A second 

conference focused on that topic in 1962 also failed to reach 

any agreement.

In setting limits to the continental shelf on the basis of 

exploitation, the conferees plainly did not think that the 

resources of the deep-ocean floor would ever be exploitable. 

In 1959, however, John Mero began publishing papers, 

followed by a book in 1965, calling attention to their potential value and the feasibility of their recovery and thus 

sparked interest in deep-ocean mining on the part of mining 

companies and politicians.

In 1966, U.S. Ambassador James Roosevelt spoke to the 

UN Economic and Social Council about the potential value 

of deep-sea resources; in the same year, President Lyndon 

B. Johnson referred to them as the "legacy of all human 

beings." This concept was elaborated by Ambassador Arvid 

Pardo of Malta in a 1967 speech to the UN General Assembly describing resources of the areas beyond national jurisdiction as the common heritage of mankind and calling for 

the establishment of an international regime under which 

those resources could be developed for the benefit of all 

mankind. A Committee on the Seabeds and Ocean Floor 

Beyond the Limits of National Jurisdiction was then established and held the first of many meetings in June 1968.

Although the initial focus of the committee was on the 

breadth of the Territorial Sea, the limits of national jurisdiction, and seabed resources in international areas, its scope 

gradually expanded to include nearly all aspects of the Law 

of the Sea, which became the scope also of the Third UN 

Law of the Sea Conference, which began in 1974. If the 

formation of the United Nations can be thought of as the 

world's first giant step toward world government, this Law 

of the Sea Conference can be thought of as the second giant 

step in that direction, for it prescribed an international 

regime over about 50 percent of the solid Earth to deal with 

the allocation of mineral resources, the collection of revenues from their production, the protection of the environment, and the settlement of disputes. The conference also 

defined the nature and extent of national jurisdiction over 

the rest of the ocean and prescribed some of the things that 

must be accomplished or addressed under national regimes.

On April 30, 1982, after 8 years of difficult negotiations, 

the Third UN Law of the Sea Conference voted 130 to 4 

(with 17 abstentions) to adopt the new Convention. At a 

signing ceremony held in Jamaica on December 10, 1982, 

117 nations signed the Convention, and several others have 

signed since. The Convention will enter into force 12 

months after 60 States have signed and ratified it. A 

Preparatory Commission entrusted with broad responsibilities to draw up rules and regulations governing mineral 

exploration and mining in the area beyond national jurisdiction was formed early in 1983 and is meeting for several 

weeks at a time twice a year.

The United States is one of four countries that voted 

against adoption of the Convention. On July 9, 1982, President Ronald W. Reagan announced that the United States 

will continue to participate at a "technical expert level" but 

that it will not sign the Convention because of objections to 

provisions related to deep-sea mining. Several other industrialized countries have already signed, including Australia, 

Canada, Denmark, France, Japan, the Netherlands, Norway, Sweden, the Soviet Union, China, Belgium, and Italy. 

The Federal Republic of Germany and the United Kingdom 

joined the United States in not signing because of objections 

to the deep-seabed mining provisions. The following

Subsea Mineral Resources 91
sections will outline the major provisions of the Convention, 

on the assumption that it will enter into force with at least 

some industrialized countries as parties to it, and the probable implications for the United States and other countries 

that do not accede to it.

Ocean Regimes Established by the Convention

The Convention consists of some 320 articles and 8 annexes, accompanied by 4 resolutions. The text is divided 

into 17 parts, 9 of which deal with the regimes to be established over various parts of the oceans; the remaining 8 deal 

with topical matters. Two of the regimes the High Seas 

and the Area (that is, the deep-ocean floor in which the 

exploration and exploitation of nonliving resources are to be 

under international control) are beyond the limits of national jurisdiction, but the others spell out the rights and 

obligations of coastal States in areas where they have some 

jurisdiction. The main elements of the regimes are:

1. A Territorial Sea 12 nmi in breadth adjacent to the 

coastal State which has sovereignty over it but with the 

right of innocent passage for ships of other nations and 

a 12-nmi Contiguous Zone in which the coastal State 

has certain rights related to the enforcement of its laws 

and regulations in the Territorial Sea.

2. An Archipelagic regime in which an archipelagic State 

would have rights over waters within baselines joining 

the outermost points of its islands equivalent to the 

rights of a coastal State over its Territorial Sea but 

guaranteeing freedom of navigation and overflight in 

specified sealanes.

3. An International Straits regime giving all States the right 

of transit passage (that is, continuous and expeditious) 

for ships (including submerged vessels) and aircraft 

through and over straits used for international navigation but giving adjacent States the right to enforce 

international safety and pollution regulations.

4. An EEZ extending up to 200 nmi from the baselines from 

which the Territorial Sea is measured, within which the 

adjacent coastal State has sovereign rights over living 

and nonliving resources and from which consent must 

be obtained for the conduct of marine scientific research but where freedom of navigation and overflight 

is preserved.

5. A Continental Shelf regime in which the coastal State has 

sovereign rights over sedentary species and nonliving 

resources over most of the continental margin where it 

extends beyond the EEZ but must make payments on 

production of nonliving resources starting 5 years after 

production has begun at each site. Coastal State consent is required for the conduct of marine scientific 

research related to seabed resources, but consent may 

not be withheld except in specific areas in which mineral exploitation is or will soon be taking place.

6. A regime of Habitable Islands beyond the 200-nmi EEZ 

for which jurisdiction over the adjacent sea and its 

resources is determined by the same provisions that 

apply to other land territory.

7. A regime of Enclosed or Semi-Enclosed Seas for which 

no special delimitation provisions are defined but 

within which bordering States are supposed to cooperate in the management, conservation, and exploitation 

of living resources, in the protection of the marine 

environment, and in the conduct of scientific research.

8. The High Seas beyond the 200-nmi EEZ, where the 

activities of nationals, although required to conform to 

internationally agreed rules, are under the control of 

their flag States.

9. The Area of the seabed beyond the limits of the continental shelf or the EEZ where the shelf extends less than 

200 nmi offshore in which exploration and exploitation 

of nonliving resources are under the control of an International Sea-Bed Authority under conditions specified 

in the Convention.

Other parts of the Convention deal with protection of the 

marine environment, scientific research, development and 

transfer of marine technology, and settlement of disputes. 

Although coastal States would have jurisdiction over 

some or most activities in all of the ocean regimes except the 

Area, those acceding to the Convention would be required 

to do many things. For example, they are obligated to protect the marine environment; to take all measures necessary 

to prevent, reduce, and control pollution of the marine environment from any source; to adopt laws and regulations to 

prevent, reduce, and control pollution from land-based 

sources, from seabed activities, from dumping, from vessels, and from or through the atmosphere and to enforce 

such laws and regulations; and to cooperate in the conservation and management of the living resources of the High 

Seas.

Provisions Affecting Mineral Resources

The 200-nmi EEZ would put under coastal State jurisdiction most of the minerals of the continental margins and, in 

some areas, those of the deep-ocean floor. For example, Isla 

Clarion (Mexico) might have manganese nodules within its 

EEZ, Mexico and Ecuador have the sulfide deposits of part 

of the East Pacific Rise, the United States has the deposits 

of part of the Gorda Ridge, and Saudi Arabia and Sudan 

have the Red Sea sulfide deposits. The Continental Shelf 

(note that the term is used in the Convention with a juridical 

meaning far broader than that of the geomorphic usage) 

regime would give coastal States jurisdiction over resources 

of the continental margin where it extends beyond the EEZ 

to a line connecting fixed points not more than 60 nmi apart. 

At each of these points, the thickness of sedimentary rocks 

is at least 1 percent of the shortest distance to the foot of the

92 Mineral and Petroleum Resources of the Ocean
continental slope or not more than 60 nmi from the foot of 

the slope, except that these points shall not exceed either 

350 nmi from the Territorial Sea baselines or 100 nmi from 

the 2,500-m isobath. A Commission on Limits of the Continental Shelf would be established to review the boundaries 

proposed by each State and make recommendations concerning them. The effect of these provisions would be to put 

the world's producible hydrocarbon resources under coastal 

State jurisdiction if all of those States were to accede to the 

Convention.

In the Area beyond the limits of national jurisdiction, 

exploration and exploitation of seabed resources would be 

licensed through the International Sea-Bed Authority, governed by an Assembly and a Council and assisted by a 

Secretariat and an associated operating organization called 

the Enterprise, to explore and exploit minerals from the 

Area in parallel with other operators. A number of provisions have been devised to allow States that are party to the 

Convention or their nationals to carry out exploration and 

exploitation of mineral resources of the Area and at the same 

time, and presumably at the same pace, to enable the Authority, through the Enterprise, to develop seabed resources 

as the agent of mankind as a whole and especially of the 

developing countries. Under this parallel system, as it is 

called, aspiring contractors will bring to the Authority a 

description of two mine sites of estimated equal value. The 

Authority will reserve one site for exploration and exploitation by the Enterprise alone or in joint arrangements with 

others. The international community (largely the industrialized countries) will furnish funds for one initial commercialscale project by the Enterprise, although it might use those 

funds in several joint ventures. The funds will be evenly 

divided between interest-free loans and guaranteed interestbearing loans. During the first 10 years after the Enterprise 

begins operations, contractors will be obliged to sell mining 

technology to the Enterprise on "fair and reasonable commercial terms and conditions" if the Enterprise finds that it 

is not available in the open market. Governments will also 

provide assistance in obtaining processing technology if the 

Enterprise finds that it is not otherwise available. To protect

Table 31. Allowable nickel production from deep-ocean nodules under the provisions of the Law of the Sea Convention and 

the U.S. Bureau of Mines forecasts of growth in world demand 

for nickel

[3.5-percent growth in nickel production from 1975 to 1984 and startup of 

nodule production in 1988 are assumed (L.A. Antrim, personal communication, 1980)]

Table 32. Comparison of Authority's 25-year income and contractor's internal rate of return from a manganese nodule operation under various assumptions

[Taken from UN Third Conference on the Law of the Sea, A/Conf. 62/ 

WPlO/Rev. 2, 1980. IROR, internal rate of return]

Average annual growth 

in world demand,

Allowable nickel production, 

in thousands of metric tons

in percent

22 -----

3.4 ................

\ 8

1985

.-.----164 2

...-..-175.0

1 TO £.

1990

170.1

235 9

199.7

1995

242.0

399.5

459.9

2000

279.7

503.1

592 0

Single system 

of payments

Case

A1 ---

B2 ---

C3 ---

D4 ---

E5 ---

p6 ...

Income, 

in millions 

of dollars

..... 527

<;io

-----599

8O7

----1 312

----1 312

IROR, 

in percent

5.1 

7.9 

13.9 

20.1 

20.9 

25.0

Mixed system 

of payments

Income, 

in millions 

of dollars

258 

429 

574 

1,015 

1,791 

1,964

IROR, 

in percent

6.2 

8.5 

13.8 

19.5 

20.2 

23.9

1 Low-profit situation; high costs and low-grade nodules.

2Same as case A; metal prices increasing 1 percent/yr.

3Baseline case in the study by the Massachusetts Institute of Technology 

(MIT) (Nyhart and others, 1978).

4MIT baseline case at mid-1979 prices.

5MIT baseline case; costs increased by 25 percent and prices increasing 

2.5 percent/yr.

6MIT baseline case; prices increasing 2.5 percent/yr.

the markets of land-based producers of nodule metals, the 

Convention limits the amount of nickel that can be produced 

from the Area over the first 20 years after production begins 

to the sum of all growth in world nickel consumption in the 

5 years before the beginning of commercial production plus 

60 percent of the projected annual growth thereafter. The 

allowable nickel production under these provisions and the 

projected growth in world demand are shown in table 31.

Four kinds of payments will be required of nodule producers: (1) an application fee of $500,000; (2) an annual 

fixed charge of $1 million before production commences 

(after production starts, the contractor will pay either a fixed 

fee or a production charge, whichever is larger); and either 

(3) a production charge (5 percent of the market value of 

processed metals during the first 10 years of commercial 

production and 12 percent during the next 10 years (called 

the single system of payment)); or (4) a share of the net 

proceeds attributable to the mining part of the operation (35 

to 50 percent) plus a production charge (2 percent) during 

the first period of commercial production and a larger profit 

share plus a production charge (50-70 and 4 percent, respectively) during the second period (called the mixed system of payments. Table 32 compares the two systems. The 

details are complicated, but the most important features of 

the mixed system are that both the percentage of the profit 

share to be paid and the time when the second period begins 

are tied to the rate of return on the investment.

One of the accompanying resolutions pertains to the 

rights to be granted to pioneer investors who had spent $30 

million or more on seabed activities before January 1, 1983 

(developing countries had until January 1, 1985, to qualify).

Subsea Mineral Resources 93
The number of pioneers permitted to qualify is limited to 

eight, plus an unspecified number from developing countries; six of these eight are identified as existing consortia 

from industrialized countries. Each consortium is limited to 

one site not larger than 150,000 km2 , half of which would 

have to be relinquished by the end of 8 years and reserved 

for the Enterprise. Each investor would have to be registered 

with the Preparatory Commission by a "certifying State" 

that had signed the Convention. All of the States whose 

companies are members of a consortium must be parties to 

the Convention. Each pioneer would pay a $250,000 fee to 

the Preparatory Commission for registration, plus $250,000 

to the Authority when it applied for approval of its work 

plan. Work obligations would be specified by the Preparatory Commission. Certifying States would have to ensure 

before applications are submitted that claims for individual 

areas do not overlap. Pioneer investors would be guaranteed 

approval of their plans for exploitation if those plans were 

submitted within 6 months of the Convention's entry into 

force. Each pioneer would also be given the right to produce 

up to a specified amount of minerals within the production 

limitation formula provided in the Convention; the Enterprise would be guaranteed production authorization for two 

mine sites.

During its last session, the conference guaranteed a seat 

on the Council to the largest consumer of seabed minerals, 

which was expected to be the United States.

The Convention calls for a review conference to convene 

15 years after commercial production begins to consider 

whether the system of exploitation has achieved its aims. If, 

after 5 years, the conference has not agreed on the system 

of exploitation, it may decide to adopt amendments to the 

existing system by a three-fourths majority vote; these 

amendments would enter into force for all State parties 12 

months after accession by two-thirds of the State parties. 

Although the detailed regulatory provisions of the Convention are clearly directed to the mining of manganese nodules, the Authority would have the right to regulate the 

exploration and exploitation of other minerals, and, under a 

provision added in the last session of the conference, the 

Council (the Authority's executive body), acting by consensus, would have to promulgate, on request, rules and regulations governing such mining.

Consequences for the United States

Even if the United States does not accede to the Convention, it may benefit from some provisions that might come 

to be recognized as customary international law. President 

Reagan, for example, has already declared U.S. jurisdiction 

over a 200-nmi EEZ and has announced a policy encouraging the development of its mineral resources. The U.S. 

Minerals Management Service is responding to this policy 

by developing a leasing program for nonenergy minerals in

the EEZ, including the cobalt-rich crusts and the sulfide 

deposits (Smith and others, 1985). The U.S. EEZ comprises 

3.9 billion acres, the largest of any country in the world. An 

indication of its resource potential has been presented by 

Rowland and McGregor (1984).

Beyond the limits of national jurisdiction, the United 

States is planning to authorize mining as a high-seas freedom and to protect the interests of its nationals by reciprocal 

agreements with other States. Under the Deep Seabed Hard 

Mineral Resources Act of 1980, an American entity can 

obtain a license for exploration and a permit for exploitation 

of seabed mineral resources beyond the limits of national 

jurisdiction. Such a license or permit would exclude other 

American entities from conducting exploration or exploitation in the same area. There is also a provision for reciprocal 

recognition of such rights issued by other countries that 

establish compatible ocean mining programs. Six other nations (the Federal Republic of Germany, France, Japan, the 

United Kingdom, the Soviet Union, and Italy) have also 

passed deep-seabed mining legislation.

In August 1984, the United States signed an agreement 

with Belgium, France, the Federal Republic of Germany, Italy, Japan, the Netherlands, and the United Kingdom designed to avoid conflicts over mine sites. The United 

States subsequently issued licenses to four consortia authorizing them to undertake exploration in their respective 

areas.

Some of the States that signed the August agreement have 

also signed the Convention (France, Japan, Belgium, the 

Netherlands, and Italy). If the Convention enters into force, 

these States would not be permitted to recognize any future 

claims by U.S. nationals, for article 137 of the Convention 

provides that "No state or natural or juridical person shall 

claim or acquire or exercise rights with respect to the minerals recovered from the Area except in accordance with this 

part. Otherwise no such claim shall be recognized."

Ambassador Tommy Koh, the last president of the Law 

of the Sea Conference, has said with respect to the U.S. 

intention to establish a separate mining regime, "An alternate to the Law of the Sea Convention is unacceptable 

because it would take resources that are a part of the common heritage of mankind. . . .If the United States does 

engage in seabed mining through an alternate regime, I will 

challenge it by bringing an action to the International Court 

of Justice" (Van Dyke, 1985). In response, Brian Hoyle of 

the U.S. Department of State argued ". . .that it is in the 

interest of both those nations that have signed the Convention and those that have not to allow some International 

Court of Justice. . . .But the fact is there would still be a 

cloud on title if a nation continued to grant a license outside 

the Convention. The ICJ's decision is not going to be dispositive as far as a banker is concerned" (Van Dyke, 1985).

Security of tenure is a cardinal requirement for the development of a mine site anywhere. Until that security can be 

assured for deep-seabed sites beyond the limits of national

94 Mineral and Petroleum Resources of the Ocean
jurisdiction, mining is not likely to take place there, even if 

economic conditions become favorable.

ACKNOWLEDGMENTS

Parts of this report are updated and revised versions of 

previous publications prepared in collaboration with my colleagues, Livingston Chase, Frank F.H. Wang, Nancy A. 

Wright, Robert W. Rowland, and Roger W. Bowen. Their 

fine efforts are gratefully acknowledged. Much appreciated 

also are the helpful suggestions received from reviewers 

Michael J. Cruickshank, N. Terence Edgar, and Frank T. 

Manheim and editor Kathie R. Fraser.

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106 Mineral and Petroleum Resources of the Ocean D.S. GOVERNMENT PRINTING OFFICE: 1986 - 491-405 - 226/40015