Data of Geochemistry

' *

Chapter W. Chemistry of the Iron-rich 

Sedimentary Rocks

GEOLOGICAL SURVEY PROFESSIONAL PAPER 440-W
Data of Geochemistry

 

MICHAEL FLEISCHER, Technical Editor

Chapter W. Chemistry of the Iron-rich 

Sedimentary Rocks

By HAROLD L. JAMES

GEOLOGICAL SURVEY PROFESSIONAL PAPER 440-W

Chemical composition and occurrence of 

iron-bearing minerals of sedimentary rocks, 

and composition, distribution, and 

geochemistry of ironstones and iron-formations

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1966
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

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

Washington, D.C. 20402 - Price 45 cents (paper cover)
CONTENTS

Abstract. _ _______________________________

Introduction. _________ ___________________

Iron minerals of sedimentary rocks __ ______

Iron oxides __ _______________________

Goethite (a-FeO (OH) ) and limonite _ 

Lepidocrocite (y-FeO(OH) )________

Hematite (a-Fe2O3) _ _ _ __ ___. _ _

Maghemite (7-Fe2 03) __ __________

Magnetite (Fe3O4 ) ________ _ ___

Iron silicates

Greenalite. ________________________________

Glauconite____ _____________________________

Chlorite (excluding chamosite) _______________

Minnesotaite. ______________________________

Stilpnomelane_ _____________________________

Iron sulfides __ _ ______________________________

Pyrite (FeS2)___-__.__ _ ___________________

Marcasite (FeS2) _-_.--_----__-___-_-_____-__

Hydrotroilite and tetragonal FeS_ ____________

Melnikovite and greigite __ _________________

Classification and facies_____________________________

Major subdivisions ___ _____ _ __________________

Facies___ ______________________________________

Geochemical aspects. _______________________

Natural associations ___ ___________________

Role of organic activity ___ _______________________ __

Chemistry of iron-rich rocks, according to groups and 

facies __ _________________________________________

Oxide facies____ ________________________________

Oolitic limonite ironstone____________________

Hematitic rocks of Mesozoic and Paleozoic agePage 

Wl

1

2

2

2

3

3

3

3

3

4

4

6

6

7

8

9

9

9

10

10

11

11

11

12

12

15

16

17

17

17

18

Face

Chemistry of iron-rich rocks, etc. Continued 

Oxide facies Continued

Hematitic iron-formation of Precambrian age__ W18 

Magnetite-rich rocks of Mesozoic and Paleozoic 

age___________-__-._____________ 19

Magnetite-rich iron-formation of Precambrian

age._____-__---____--_---_-------------_ 21

Silicate facies_________________________________ 21

Chamositic ironstone____--_-_-__----_-_---_- 21

Silicate iron-formation of Precambrian age_____ 22

Glauconitic rocks__-_-____--------__-------- 23

Carbonate facies______-_-_-___-------_---------- 23

Sideritic rocks of post-Precambrian age._______ 24

Sideritic iron-formation of Precambrian age____ 24

Sulfide facies___________________________ 25

Blackband and clayband siderite_____ _________ 26

Distribution of deposits in space and time.____________ 28

Tertiary________________________________ 28

Mesozoic.______--_____-_---_--_-----------_-_- 28

Paleozoic.__________________----____---_-___- 30

Precambrian- ___ _ _____-___--_----__------------ 34

Iron in natural waters------------------------------- 39

Iron in solution..____________---_-__--_-_------_ 39

Iron in suspension_____-_-_-_-_-_-___----------- 40

Iron as a constituent of transported or suspended

clays.__-___-__________---_-___-__-----__---_ 40

Conclusions-______-_____-____-__-___--___------ 40

Iron in present-day sediments___--_----__-_-___------ 41

Bog iron deposits-_-______-_-----------___------ 41

Minor elements___________________________________ 42

Differences between ironstone and iron-formation.--.--- 46 

Origin________________-_--___--__----___-_-__------ 47

References _________________________________________ 51

Index.____________________________________________ 61

ILLUSTRATIONS

Page 

FIGURE 1. X-ray diffraction patterns of four types of glauconite___________________-_______-_-_-__----_-_----- W7

2. Eh-pH diagram showing relations between anhydrous iron compounds at 25° C., 1 atm. pressure._________ 13

3. Eh-pH stability fields for iron minerals with carbonate equilibria as in "normal sea water" and total dissolved

sulfur as in "average river and lake water" at 25° C_______-__-______--------_-_-_----------------- 14

4. Eh-pH relations of iron oxides, sulfide, and carbonate with total dissolved sulfur = 10~6M and total dissolved

carbonate = 1M, at 25° C.___________________________________---_----- 14

5. Schematic section showing relations between ironstone facies and physico-chemical conditions.____________ 15

6. Generalized stratigraphic successions of Precambrian rocks of the Lake Superior region. ________________ 38

7. Activity of dissolved iron in equilibrium with total sulfur at activity 10~3 and total carbonate at activity

5X10-3__ .-_-----_-_-.______-__..-_-__.__-____--. _._.____..__-_-___-_--____-____-_-_-_---_ 39
IV CONTENTS

TABLES

TABLES 1-4. Analyses of 

1. Separated limonite (goethite) 

ooliths from two Mesozoic 

ironstones.------- ___________

2. Siderite__________________

3. Chamosite___-_________.______

4. Greenalite __________________

5. Selected analyses of glauconite.________

6. Analyses of minnesotaite, stilpnomelane, 

thuringite, and bavalite_ _________

7. Values for free energy (AF°) for species 

of importance to the iron system, at 

standard conditions.________________

8-19. Analyses of 

8. Oolitic limonite (goethite) ironstone. _____________________

9. Hematite-rich sedimentary rocks 

of Paleozoic and Mesozoic

age.

10. Hematite-rich rocks of sedimentary origin, Precambrian age_

11. Magnetite-rich sedimentary 

rocks of Mesozoic and Paleozoic age__________________

12. Magnetite-rich ironstones of 

Precambrian age__________

13. Chamositic ironstones _________

14. Silicate iron-formation, mostly 

Precambrian_____________

15. Glauconitic rocks (greensand)

16. Siderite rocks of post-Precambrianage____________

17. Sideritic iron-formation, Precambrian-._______________

Pag« TABLES 8-19. Analyses of Continued Page

18. Sulfide-rich rocks__. . W27

19. Blackband and clay-ironstone 

W3 siderite____ 27

4 20-22. Occurrences of iron-rich sedimentary

5 rocks 

6 20. Tertiary age.___- 28 

8 21. Mesozoic age_-___------- _ 29

22. Paleozoic age--_---____------- 31

8 23-25. Occurrences of iron-rich beds of Precambrian age 

23. North and South America,. 34 

14 24. Europe and Asia__--___--_- 36

25. Australia and South Africa 37 

26-28. Iron, manganese, and minor-element con18 tents of 

26. Bog iron ores from deposits in

Finland__________-_._ 43

19 27. Some iron-rich rocks.-.-------- 43

28. Average of contents for iron-rich

20 rocks, U.S.S.R_______.. 44 

29. Contents of Cu, As, V, Ni, Ti, and Zn in

minette ironstone of Luxembourg _ 44

20 30. Minor-element contents of glauconitic, 

chamositic, and sideritic ironstone of

21 Lias (Jurassic) age of southern Sweden. 44

22 31. Spectrographic analyses of ironstone of 

the Clinton Formation and Group

23 (Silurian) and Martin Formation

24 (Devonian), U.S.A__ 45 

32. Minimum and maximum concentrations

25 of minor elements given in tables 8-19 

and 27-31 as compared with crustal

26 abundance___________-_-_. ... 45
DATA OF GEOCHEMISTRY

CHEMISTRY OF THE IRON-RICH SEDIMENTARY ROCKS

By HAROLD L. JAMES

ABSTRACT

The iron-rich sedimentary rocks, defined as those containing 

15 percent or more iron of depositional or diagenetic origin, have 

a wide range of physical and chemical properties, in part because 

of gradations into more common sedimentary types and in part 

because of the wide variety of iron minerals possible. The iron 

may be in the form of goethite (limonite), hematite, and magnetite; siderite, with a substantial range in amounts of manganese, magnesium, and calcium in solid solution; chamosite, 

greenalite, and glauconite (which upon slight metamorphism 

may be converted into thuringite and other chlorites); minnesotaite, and stilpnomelane; and pyrite and marcasite. Many of 

these minerals may be preceded by metastable species of uncertain status, such as ferric hydroxide and hydrotroilite. Other 

minerals, of rare occurrence, are lepidocrocite, maghemite, the 

tetragonal iron sulfide, greigite, smythite, and pyrrhotite.

By custom, the noncherty and generally oolitic iron-rich rocks, 

most of which are of post-Precambrian age, are referred to as 

ironstone (including the "minette type"), whereas the chertbanded rocks, most of which are of Precambrian age, are called 

iron-formation. Both ironstones and iron-formations may be 

divided into four major facies oxide, silicate, carbonate, and 

sulfide on the basis of the dominant iron mineral. This facies 

classification has a theoretical base established by the distribution of stability fields of the iron species, expressed most effectively in terms of redox potential (Eh) and pH. Examples of 

stability-field diagrams show that at given anion concentrations 

almost any combination of oxides, silicates, carbonates, and 

sulfides of iron can exist stably at some geologically reasonable 

value of Eh and pH. The dominant aspect, however, is one of 

sequential appearance of stable fields for oxide, carbonate, and 

sulfide with decrease in Eh. In an idealized restricted basin in 

which iron sediments are being formed, this corresponds to 

progressive decrease in available oxygen in the bottom environment. The facies, therefore, are a direct reflection of depositional environments.

Chemical analyses of the iron-rich rocks are organized and 

presented according to facies and in part according to age 

(Precambrian and post-Precambrian), and the distribution in 

space and time is summarized in a series of tables. The major 

differences in bulk compositions are inherent in the classification as in the ratio of FeO to Fe20s and the content of COa 

the silicate facies being significantly higher in Al2 0s. The 

SiOa content varies chiefly according to the relative amounts of 

clastic quartz (in ironstone) or chert (in iron-formation).

Data on minor-element content are relatively scarce. The 

information available shows the amounts to be generally low in 

comparison with crustal abundance. Differences between facies 

are slight, except for higher chromium and vanadium in

chamositic rocks, and commonly are submerged by local differences related to the geochemical nature of the terrain adjacent 

to basins of deposition.

The origin of the iron-rich sedimentary rocks remains a matter 

of speculation, as no modern-day examples exist. A few deposits, exemplified by the ironstone of the Lahn-Dill district of 

Germany and the Helen iron-formation of the Michipicoten 

district of Canada, appear to have a genetic relation to volcanic 

and igneous activity and may be classed as "exhalative-sedimentary." The more typical and more extensive ironstones 

and iron-formations, however, are entirely lacking in volcanic 

and igneous associations; for these the iron seemingly must be 

derived by weathering of exposed land, although the large 

chemical and physical differences between ironstone and ironformation imply some significant difference in the nature of the 

process. It is suggested, by analogy with bog-iron deposition, 

that for both types the iron is extracted and transported by 

ground waters of low pH, and that this process was more effective 

in Cambrian and pre-Cambrian time, possibly because of a 

significantly higher content of C02 in the earth's atmosphere.

INTRODUCTION

Iron, which is estimated to make up about 4.7 percent 

of the earth's crust, is present in significant amounts in 

almost all sedimentary rocks. The average sandstone, 

including graywacke, contains 1.7 percent Fe2O3 and 

1.5 percent FeO (Pettijohn, 1963, p. 15); the average 

shale contains 4.2 percent Fe2O3 and 2.45 percent FeO, 

and the average limestone 0.54 percent combined 

Fe2O3 and FeO (Clarke, 1924, p. 25, 564). Each of 

these rock types, however, ranges in composition into 

facies in which the iron content is 20 percent or more. 

The iron-rich sedimentary rocks, here defined as those 

containing 15 percent or more Fe of primary origin 

(depositional or diagenetic), in part therefore can be 

considered a family of end members of the sedimentary 

series. These rocks commonly are referred to as ironstone or iron-formation.

The iron-rich rocks have a great range of physical and 

chemical characteristics. In part this is due to gradations from the common sedimentary rocks sandstone, 

shale, limestone, chert with retention of attributes of 

the parent stem. In larger part, however, the diversity 

is due to the extraordinary ability of iron to form difWl
W2 DATA OF GEOCHEMISTRY

ferent minerals in response to different conditions of the 

bottom and diagenetic environment. Iron may precipitate as ferric oxide or hydrate (hematite, maghemite, 

goethite, lepidocrocite), as a ferrous-ferric oxide (magnetite), as a ferric-ferrous silicate (glauconite), as a 

ferrous-ferric silicate (greenalite, chamosite), as a carbonate (siderite), or as a sulfide (pyrite, marcasite, or 

less stable precursors). Inasmuch as the classification 

of the iron-rich rocks is based in large part on the 

mineralogy of the iron, the character, composition, and 

occurrence of the iron minerals found in sedimentary 

rocks are reviewed in the following section. The discussion will deal only with those aspects of importance to 

the problem at hand; more complete data on the optical, 

structural, and chemical properties of the pure minerals 

are available in standard texts and references.

IRON MINERALS OF SEDIMENTARY ROCKS 

IRON OXIDES

Goethite (limonite), hematite, and magnetite are 

found as important constituents of the iron-rich sedimentary rocks; lepidocrocite and maghemite have been 

observed but are rare.

Hydrogoethite, hydrohematite, turgite, and other 

reported oxide-hydrates have questionable status as 

minerals, and have not been identified in mineralogical 

studies supported by X-ray examination. The "hydrogoethite" of Tula, central Russia, has been shown to be 

lepidocrocite with adsorbed water (Palache, Berman, 

and Frondel, 1944, p. 644) and it is likely that more 

recently described occurrences, such as reported by 

Tochilin (1952) are of similar material. Hydrohematite 

and turgite probably represent mixtures of hematite 

and goethite or hematite with adsorbed water (Posnjak 

and Merwin, 1919). Akaganeite C8-FeO(OH)), recently 

described by Mackay (1962), has not yet been recognized in the iron-rich sedimentary rocks, but Mackay 

states (p. 278-279), "The colloidal properties of /3-FeO(OH) 

are shown to be of considerable complexity and undoubtedly will have a bearing on the formation of 

deposits of hydrated iron oxides."

Both ferrous and ferric hydroxides can, of course, be 

readily precipitated in the laboratory, and they may 

well be transitory species in natural chemical precipitates. The development of stable phases of iron oxides 

from original hydrates is discussed by Garrels (1959, 

p. 29-30), who considers the first precipitate to be 

Fe2O3 -7iH2O, with a solubility product of 10~37 (as compared with 10~*2 for hematite).

Structural data for the oxides and hydroxides of iron 

are given by Bernal, Dasgupta, and Mackay (1959, p. 

17).

GOETHITE (a-FeO(OH)) AND LIMONITE

Goethite is the principal constituent of the postPrecambrian deposits of such sedimentary iron oxide 

ores as those of the Jurassic of Europe (Correns and 

Engelhardt, 1941; Taylor, 1949; Correns, 1952a). The 

"limonite" of the iron-rich sedimentary rocks consists 

of goethite intimately mixed with other materials and 

commonly has appreciable adsorbed additional water. 

Caill&re and Kraut (1953) and others have suggested 

that goethite, as well as other iron minerals in the 

sedimentary ores, develop diagenetically from an original iron hydroxide gel, which may well be true, but no 

direct evidence is available. According to Correns 

(1952a) the goethite may contain appreciable amounts 

of alumina with contraction of the unit cell constants 

a0 and 60 :

Percent

AIO(OH)

1.5

4.5

11.2

Percent

FeO(OH)

98.5

95.5

88.8

Cell dimensions, in A

a

4.59

4.53

4.48

6

9.97

9.88

9.82

c

3.02

2.99

3.00

Bernal, Dasgupta, and Mackay (1959, p. 17) give the 

dimensions of (presumably) pure goethite as: a=4.587, 

6=9.937, c=3.015.

The goethite of the sedimentary ores characteristically occurs in the form of ooliths built of successive 

shells of the oxide or of alternating shells of iron oxide 

and chamosite in a matrix that may be chamosite, 

clay, siderite, or calcite; rarely or never is it a matrix 

to ooliths of different composition. The compositions 

of separated limonite (goethite) ooliths from two 

English ironstones of Mesozoic age are given in table 

1. The excess water is characteristic, and the ooliths 

quite evidently contain admixed silicate, phosphate, 

and carbonate.

The absence of goethite in the Precambrian sedimentary ores, and the dominance of hematite in most 

of the lower Paleozoic oolitic ores strongly suggests 

a progressive development of hematite from original 

goethite (or a more primitive hydrate). The generalization is not absolute, however, as hematite is present 

in some of the Mesozoic rocks (see Harder, 1951, for 

description of Lias-y hematite oolite), and some lower 

Paleozoic ironstones are goethitic the Mayville ore of 

the Neda Formation of Wisconsin, for example (Hawley 

and Beavan, 1934). Certainly both hematite and 

goethite are stable at low temperatures, but according 

to Smith and Kidd (1949) goethite in neutral solutions 

decomposes to hematite above 125° ±15° C.
CHEMISTRY OF THE IRON-RICH SEDIMENTARY ROCKS W3

TABLE 1. Analyses of separated limonite (goeihite) ooliihs from 

two Mesozoic ironstones

SiOa.... . ... ... .... .

AlaOs..... ............

FeO.._ . 

MnO. ...... . ...

MgO.. . 

CaO..__ 

KjO... . .........

NaaO... 

H»0+..-. . 

A

5.15

4.49

69.93

.95

.48

1.05

.57

on

.01

11.89

B

5.53

4.62

69.50

.56

.20

.68

.53

.14

.01

12.32

Ha O-_ .

TiO»__ . 

PtOs-.. .-. 

COi. 

C. ....................

FeSa._ __ -. .........

(Co, Ni)0~_ . 

A

2.07

1.05

1.23

.48

.41

.03

100. 11

B

3.44

.71

.95

.43

.37

.20

.05

100.24

A. Frodingham Ironstone, England (Hallimond, 1925, p. 79). Ooliths occur in

matrix mostly of chamosite and siderite. 

B. Claxby ironstone, Lincolnshire, England (Hallimond, 1925, p. 79). Ooliths

occur in matrix mostly of clay (altered chamosite?) and carbonate.

LEPZDOCROCITE (r-FeO(OH))

Lepidocrocite is rare or absent in most sedimentary 

ironstones, but is reported by Correns (1952a) as 

a constituent in the oolitic ores of Kladno Nucic, 

Czechoslovakia.

HEMATITE

Hematite is only locally an important ^constituent 

of the Tertiary and Mesozoic ironstones and is virtually 

absent from many. It is, however, a dominant mineral 

in some (though not all) of the lower Paleozoic oolitic 

ironstones such as those in the Clinton Group or Formation of New York (Ailing, 1947) and of the Birmingham district, the Wabana ores of Newfoundland (Hayes, 

1915), and the Bliss Sandstone of New Mexico (KeUey, 

1951). Hematite is the principal mineral in Precambrian iron formations of every continent, in which rocks 

it is interbedded with quartz ("chert").

MAQHEMITE (y-FeiOs)

Maghemite, the strongly magnetic isometric dimorph 

of hematite, is of rare occurrence in the sedimentary 

ironstones, though it is abundant in some laterites. 

Crystallographically it is very similar to magnetite, 

and the cell dimensions a0 of the two minerals are nearly 

identical, so that even with X-ray techniques it is 

difficult to distinguish the two. In polished section 

the mineral is isotropic, gray to blue with brownish-red 

internal reflections.

Correns and Engelhardt (1941) describe maghemite 

and magnetite in the Mesozoic ironstones of Germany, 

although later work by Harder, reported by Correns 

(1952a), casts doubt on the determinations of the maghemite. Recently, however, Deudon (1957) used a 

combination of X-ray, magnetic-separation, and chemical analysis to show that one bed 10 to 20 cm thick in 

the "Couche Grise" of the Ottange basin of Lorraine 

and Luxembourg contains about 40 percent maghemite, 

20 percent hematite, 20 percent magnetite, and 20 

percent geothite plus calcite.

MAGNETITE (FesCh)

Magnetite is an abundant iron oxide in the Precambrian iron formations, in which it may be either of

diagenetic or metamorphic origin. It is not common in 

the younger ironstones, but is by no means rare. It is 

a constituent in the Jurassic ores of Lorraine, Luxembourg, and Germany (Berz, 1922; Caillere and Kraut, 

1946; Hoehne, 1955). Hoehne describes the magnetite 

as occurring both as isolated crystals and as a constituent of individual ooliths; the characteristic crystal 

form is shown by Ramdohr (1955a) to be the cube. 

Magnetite occurs locally in ooliths in the unmetamorphosed Northampton sand ironstone of England, in 

places as shells between chamosite and limonite 

(Taylor, 1949); it is locally abundant in the Jurassic 

beds of Yorkshire, in sideritic chamosite oolite, where 

it occurs as octahedra 0.002 mm to 0.012 mm diameter 

in chamosite ooliths (Rastall and Hemingway, 1949).

In the iron-formations of Precambrian age, magnetite 

most commonly occurs as impure layers alternating 

with chert (quartz); magnetite-bearing itabirite of 

Brazil may contain as much as 20 percent dolomite 

(Dorr, 1958, p. 62).

SIDERITE

Siderite is one of the most important constituents of 

sedimentary ironstones, including those of the Precambrian. In Sweden it is the principal mineral in 

ironstones of the Lias (Lower Jurassic), 12 beds of which 

have an aggregate thickness of 60 meters in a sequence 

of clastic and coaly sediments 1,000 meters thick 

(Hadding, 1933; Palmqvist, 1945); in England it is a 

dominant mineral in the Cleveland ironstones of 

equivalent age (Whitehead and others, 1952), and in 

the slightly younger Northampton ironstone (Taylor, 

1949). In these rocks it is typically associated with 

chamosite, less commonly with limonite (goethite) and 

calcite; the Swedish rocks are characterized also by the 

presence of detrital sand and clay. The so-called 

"blackband ores" are thin layers of massive siderite that 

are particularly abundant in the Paleozoic coal measures 

of Europe and the United States; according to Tyler 

(1950), 75 beds occur in the lower coal measures of 

Wales. Siderite also is common as concretionary 

masses in clays and marls, as for example in the Lower 

Cretaceous beds of the Atlantic coastal plain (Singewald, 1911). Some of the principal Precambrian ironformations of the Lake Superior region those of the 

Mesabi, Gogebic, Marquette, Cuyuna, and Iron RiverCrystal Falls districts are in large part composed of 

interbedded siderite and chert.

Analyses of six sedimentary siderites are given in 

table 2.

Most of the siderite in the sedimentary rocks is so 

very fine grained and intimately mixed with other materials that chemical and optical properties are not 

easily determined, although in many ironstones more
W4 DATA OF GEOCHEMISTRY

TABLE 2. Analyses of siderite

Si02 -.-_. ..........

A12 03 --. _

FejOa 

FeO .

MnO. ..________..._

MgO._. ............

CaO.... ............

H2 0+ ...........

H8 0-._. ...........

TiOs ....... ..

P2 06 . . ... ..... .

C02 .. ..............

Insol. residue .......

C-.. .-- . .._

8. . .. . ..

A

0.9

1.3

.4

46.89

.13

3.37

4.66

12.0

.25

35.36

4.57

99.8

B

1.5

2.6

1.5

47.92

.18

2.46

3.71

12.4

.43

33.33

3.06

99.4

O

1.2

1.6

.6

45.83

.18

3.68

5.10

12.1

.33

35.20

3.74

99.6

D

0.65

46.7

8.2

4.2

1.1

} .09

.00

.64

38.0

.20

.06

99.84

E

0.09

46.0

5.0

5.2

3.5

.12

.00

2.4

36.4

1.5

.02

100.23

F

0.53

49.0

4.2

4.8

2.2

.10

.00

1.4

37.4

.38

.03

100. 04

i Calculated from loss on ignition; includes organic matter.

A. Northamptonshire, England. Sphaerosiderite from Northampton sand ironstone (Taylor, 1949, p. 48). Analyst: C. 0. Harvey.

B. As above. From oolitic chamosite-siderite rock, Northampton sand ironstone 

(Taylor, 1949, p. 48). Anayst: C. O. Harvey. Total includes 0.3 percent OdO.

O. As above. From siderite mudstone, Northampton sand ironstone (Taylor, 1949, 

p. 48). Analyst: C. O. Harvey.

D, E, F. Iron River, Michigan. Thin layers of carbonate in Riverton Iron-Formation. Analyses by H. F. PhiUips, P. L. D. Elmore, and P. W. Scott, U.S. 

Geological Survey. Laboratory numbers 138255, 138258, and 138260. All 

samples contain small amounts of phosphate, free carbon, quartz, and pyrite.

coarsely crystalline siderite occurs as spherulitic aggregates, and as diagenetic replacements particularly of 

chamosite ooliths. The composition of the siderite 

can be expressed in terms of four components FeCO3 , 

MnCO3 , MgCO3 , and CaCO3 that are in solid solution. For three separated and analyzed siderites 

(table 2, analyses A, B, C) from the Northampton sand 

ironstone, Taylor (1949, p. 48-50) gives calculated 

compositions in weight percent, together with measured 

properties. The data in table 2, with compositions 

converted to mol percent (weight percent in parentheses), are given in columns A, B, C, below. For 

comparison, the composition of siderite of the Lias-7 of 

Germany as calculated by Harder (1951, p. 458), is 

shown in column D. Cohen (1952, p. 470-471) using 

a microradiograpkic technique in which the X-ray beam 

is passed through thin sections to produce a shadow 

photograph that reveals distribution of iron finds that 

at least the larger siderite crystals in Taylor's material 

are zoned, which accounts for the range of observed 

indices.

FeO03 ... ................

MnC03._.. _ --------..-

MgCOs.- __ . ___ ...-

CaCOs ..... 

A

79.1 (82.60)

3

( OA\

10.2 (7.74)

10. 4 (9. 40)

1. 730-1. 845

1.813

3.60

B

co c (oa i Q\

.4 (.40)

7. 5 (5. 66)

1. 775-1. 838

1.816

3.62

C

77 9 (81 39)

.4 (.38)

10.4 (7.98)

11.3 (10.25)

1.789-1.837

1

(210

3.58

D

Q9 /QK\

3

/o\

13 (10)

2

/o\

1. 834-1. 842

1 84

The siderite in the Precambrian iron-formations of 

Lake Superior typically occurs interlayered and to 

some extent intimately mixed with chert (see James, 

1954, for review of occurrence). Analyses of individual 

layers, less than % inch thick, of nearly pure carbonate

from the Riverton Iron-Formation of the Iron River 

district of Michigan are given in table 2, analyses 

D, E, and F. X-ray examination has shown the carbonate to be a single phase, with calculated molecular 

proportions as follows (weight percent given in parentheses) :

FeCOs -

MnCOs --.. ...... ....

MgCOs . -- 

OaCOa- ......... ..... .........

D

76.4

13.7

9.1

.8

78. 5)

14 01

fi 8)

.7)

E

77.9 (80.7)

8.9 (9.1)

11.9 (9.0)

1.3 (1.2)

F

81.2 (83.8)

7.2 (7.4)

10.7 (8.0)

.9 (.8)

Huber (1959, p. 93) has calculated from rock analyses 

the composition of carbonate from the Gogebic district 

of Michigan and other districts of the Lake Superior 

region. Representative examples are as follows (weight 

percent in parentheses):

FeCOj . 

MnCOs -- 

OaCOa . -- 

Ghgebic 

(Midi.)

76.8 (80.9) 

3.9 (4.1) 

17.0 (12.9) 

2.3 (2.1)

Qunflint 

(Minn.)

75.8 

.5 

16.4 

7.3

80.2)

12.6) 

6.7)

Marquette 

(Mich.)

85.7 (89.0)

12.5 (9.4) 

1.8 (1.6)

IRON SILICATES

The only iron silicates definitely of primary origin and 

of importance in the iron-rich sedimentary rocks are 

chamosite, glauconite, and greenalite. Thuringite (bavalite), minnesotaite, and stilpnomelane are of common 

occurrence, however, and are described here. These 

minerals probably are derived by low-grade metamorphism of preexisting silicates, though a diagenetic 

origin cannot be ruled out entirely. In any case, the 

primary sedimentary composition of rock containing 

them probably has not been significantly altered, as 

it may be in higher metamorphic zones in which 

grunerite, garnet, and fayalite are developed.

CHAMOSITE

Chamosite (including "berthierine") is the most 

abundant primary iron silicate of ironstones other than 

those of Precambrian age, and is a dominant constituent of many. It typically occurs as ooliths of dark 

green material in a matrix of siderite or calcite, and 

often is associated with ooliths of goethite; quite commonly ooliths are constructed of alternating shells of 

chamosite and goethite, as in the Northampton sand 

ironstone (Taylor, 1949) and in the ironstones of 

Lorraine (Cayeux, 1909).

The mineralogical classification of chamosite is still 

in question, but it seems evident that the term has 

been and probably will continue to be applied to 

materials that are not mineralogically identical and to 

some that probably are mineralogically heterogeneous.
CHEMISTRY OF THE IRON-RICH SEDIMENTARY ROCKS W5

Hallimond (1939) and later Engelhardt (1942) showed 

that differences existed between the structure of the 

studied chamosites and of accepted chlorite, although 

Engelhardt computed a formula on the basis of a 

chlorite structure. Orcel, He'nin, and Caillere (1949) 

examined a number of chamosites by thermal and 

X-ray techniques and found distinct differences between 

the materials from different localities. Brindley (1951) 

and Brindley and Youell (1953) tentatively concluded 

that chamosite (in a restricted sense) is closely related 

to the kaolin-type structure rather than to chlorite; 

and the critical feature is the presence of a 7 A basal 

reflection in the X-ray diagram, rather than the 14A 

reflection typical of chlorite.

Caillere and Henin (1951) also divide the chamositic 

materials into two main groups on the basis of characteristic 14A and 7A spacings, but relate the 7A variety 

to an antigorite structure (comparable to greenalite) 

rather than to a kaolin structure. The silicate of the 

Lias-gamma beds of Gottingen (Germany) is shown by 

Harder (1951) to contain both chamosite of 7A structure and chamosite with a 14A chlorite structure; the 

latter Harder attributes to groundwater alteration of 

original chamosite. The chamosite of the Saint-Barbe 

Lias (Lorraine) also has a 7A structure, according to 

Deudon (1955). Protich (1955) studied the chamosites 

from 3 localities of Cretaceous strata in Yugoslavia; 

that from GlediS, with an unusually high Fe2O3 content 

(see table 3, analysis E), and that from Poustenck are 

of the 7A type, whereas that from VlakSa is of the 14A 

chlorite type.

TABLE 3. Analyses of chamosite

SiO2 ...... ..... .......

AlsOs-. .... ...

FesOa- _ . . ... 

FeO.. _--..-..... ..

MnO.. ......... . ......

MgO... ... ....... ..

CaO . ......... ...

NasO.. .... .........

KaO.. ...... ...........

H20+.................

HsO-. ........ .........

TiO2 . 

PS0{...................

CO2 ...... ..............

A

30.07

17.26

3.66

37.61

.02

1.69

.44

.16

| 9.01

.12

100.04

B

22.43

14.27

11.98

37.63

.02

3.42

.00

.22

.04

9.70

.19

99.90

C

22.47

21.82

.22

39.79

.03

2.82

.38

10.07

Tr.

.00

2.04

99.75

Ci

23.81

23.12

.23

39.45

2.72

10.67

100. 00

D

26.65

16.14

6.69

34.43

4.47

f 11.42

I .08

99.88

E

21.50

20.12

14.89

21.90

.98

1.92

1.18

11.68

3.92

99.14

F

20.62

11.96

5.11

25.98

.30

3.07

11.50

.09

8.36

2.56

.72

5.11

3.94

100. 34

A. Chamosentze, Switzerland (Dgverin, 1945, p. 31); analyst, J. Jakob. From 

chamosite-calcite bed in Middle Jurassic (Dogger). Indices of refraction 

7=0=1.63.

B. Windgalle, Switzerland (Dgverin, 1945, p. 89); analyst, J. Jakob. From chamosite-calcite bed in Middle Jurassic.

O. Corby, Northamptonshire (Brindley and Youell, 1953, p. 61); analyst, R. F. 

Youell. From oolitic chamosite-limonite-siderite rock in Northampton sand 

ironstone (Middle Jurassic). Total contains 0.11 percent SOs.

Oi. As above, corrected for calculated impurities (Brindley and Youell, 1953, p. 61).

D. Schmiedefeld, Germany. Analysis by Jung, quoted by Engelhardt (1942, p. 

149). From thuringite-bearing ironstone in the Lower Silurian.

E. Gledie, Yugoslavia (Protich, 1955). From chamositic bed of Cretaceous (Aptian) 

age. Total contains 1.05 percent NiO.

F. Island of Raasay, Scotland (MacGregor, Lee, and Wilson, 1920, p. 197-198). 

Hand-picked ooliths from bed of Jurassic age. Total includes 0.06 percent 

(Co,Ni)O, 0.71 percent FeSs, 0.25 percent O. Total given as 100.35 percent in 

original.

777-130 65 2

Nelson and Eoy (1954, p. 344) report the important 

discovery of complete polymorphism between chlorites 

characterized by 7A and 14A basal spacings; they write 

(p. 337): "The 7A chlorites formed during sedimentation may be converted into 14A chlorites in one case 

or remain as 7A chlorites in another as a result of postdepositional history * * *." They propose the term 

"septechlorite" (and septechamosite) for the 7A mineral, a designation accepted by Deer, Howie, and 

Zussman (1962, p. 164). It seems evident that chamosite proper, characterized by the 7A spacing and 

exemplified by the unaltered iron silicate in the Mesozoic ironstones of England and Lorraine, is readily 

transformed by slight metamorphism to a chlorite 

(thuringite-bavalite) characterized by the 14A spacing. 

Hallimond, in printed discussion of the paper by 

Caillere and Henin (1951) cites textural evidence that 

suggests reconstitution of the "chamosite" of Chamoson 

and states (p. 136) that it would not be surprising if 

this, the original chamosite, turned out to be bavalite, a 

view supported by Taylor in the same discussion.

Chamosite, because of its very fine grain size and 

intimate mixture with other materials, is very difficult 

to separate for analysis, and even the most carefully 

prepared materials are impure; furthermore, for many 

published analyses doubt exists as to the specific 

mineralogic identity. Of those listed in table 3, only 

C, D, and E are certainly of the 7A structural type; as 

previously mentioned, the chamosite of the type 

locality (analysis A) may actually be a 14A chlorite. 

The most typical chamosites are essentially ferrous, 

but the mineral may be oxidized without loss of structure; Brindley and Youell (1953) have prepared ferric 

varieties by heat treatment of ferrous chamosite, and 

some natural chamosites have a significant content of 

ferric iron.

The reported optical properties of chamosite are of 

course of questionable validity in view of the uncertainty of mineralogic classification of the particular 

materials. The chamosite ooliths of the unaltered 

chamositic rocks of the Mesozoic of England (Hallimond, 1925; Taylor, 1949), such as represented by 

analysis C in table 3, are built of very fine flakes, pale 

to dark green, arranged tangentially, so that the oolith 

shows a dark extinction cross under crossed nicols. 

The flakes have positive elongation, mean indices of 

refraction that range from 1.62 to 1.66, and birefringence that ranges from zero to about 0.03. Crystalline 

chamosite in the same rocks occurs as cores to ooliths 

and as scattered flakes in the chamositic mudstones; 

this chamosite is uniaxial or nearly so, optically negative, pleochroic in shades of yellow and green, with a 

prominent fibrous cleavage; mean indices of refraction 

are as for the oolitic material. The Schmiedefeld
W6 DATA OF GEOCHEMISTRY

chamosite (Engelhardt, 1942 see analysis D, table 3) 

has higher indices: 7=18=1.668, and those for the 

Gledic chamosite (analysis E, table 3), according to 

Protich, are 7=1.679, a = 1.671. It is apparent that 

the increase in index and birefringence is directly 

related to ferrous-ferric ratio.

Chamosite from most localities has been shown to 

have a specific gravity of 3.0 to 3.4, but that from the 

Northampton sand is reported by Taylor (1949, p. 41) 

to have a specific gravity of 2.7 to 2.9, possibly because 

of admixture with submicroscopic kaolinite.

Youell (1958) has shown that the degree of disorder 

of chamosite at different stratigraphic horizons in the 

Northampton sand ironstone is a distinctive feature of 

particular beds.

GREENAUTE

Greenalite, a common and abundant primary iron 

silicate in the Mesabi and Gunflint districts of the Lake 

Superior region, was described and named by Leith 

(1903, pp. 101-115). The mineral was further described by Jolliffe (1935), and by Gruner (1936), who 

defined it as a ferrous analogue of antigorite. It has 

been synthesized by Flaschen and Osborn (1957, p. 926). 

The mineral, which probably is more closely related 

structurally to chamosite than to antigorite is classed 

as a septechlorite by Deer, Howie, and Zussman (1962, 

p. 167). Steadman and Youell (1958) report the 

following structural data:

do=5.54A 

60=9.59A 

c0=7.19A 

0=90°

A partial chemical analysis by Leith (1903, p. 108), as 

computed by Gruner (1946, p. 16), is given in table 4 

(analysis A); for nearly 60 years this was the only 

analysis available. Recently, however, Cochrane and 

Edwards (1960) have described a late Precambrian 

greenalite-bearing iron-formation from northern Australia. The analysis of separated greenalite is given as 

analysis B in table 4, and the computed formula is 

9(Fe,Mn,Mg)0.2(Fe,Al) 2O3 .8SiO2 .8H2O (Cochrane and 

Edwards, 1960, p. 16). Chemical data on greenalite given by Jolliffe (1935) are of uncertain value 

because of the probable mixture of the material with 

minnesotaite, which at that time had not been defined.

Greenalite, in contrast to chamosite and glauconite, 

occurs in quantity only in rock of Precambrian age, 

although it has been reported in the Ordovician of 

southern Scotland (Kennedy, 1936) and in Mesozoic 

sandstone of Sweden (Hadding, 1929, pp. 235-236). 

Like glauconite, it occurs as rounded to subangular 

isotropic light- to dark-green pellets; rarely do the

pellets have the concentric structure characteristic of 

chamosite. It typically is associated with magnetite. 

The granules have a range in density of 2.85 to 3.15 

(Jolliffe, 1935, p. 414), with an aggregate index of 

refraction of about 1.670.

TABLE 4. Analyses of greenalite

SiOt ... ..........

A1SO3 .. _ ... . 

FejOa- ~ - 

FeO -. _- .

MnO.. - ...........

MgO__._-.... __ ..

CaO_. ._.... .._. -

A

32.02

1.01

22.95

29.15

5.34

B

32.27

3.03

14.83

36.00

.87

2.11

Tr.

NajO _. - 

KjO .- .-

HjO+ -._-.-_. .-_

H2O- ... ..

Ti02._ ................

P,05 ...

A

} 9.52

99.99

B

.14

.10

f 8.71

\ 2.37

.05

.01

100.49

A. Greenalite from Biwabik Iron-Formation, Mesabi district, Minnesota. Composition as computed by Gruner (1946, p. 16) from analysis given by Leith (1903, 

p. 108).

B. Roper Bar, Australia (Coehrane and Edwards, 1960, p. 17). P. J. J. Sinnott, 

analyst. Greenalite separated from greenalite-magnetite rock. Total given as 

100.35 in original.

GIjAUCONITE

Glauconite is a common though not especially abundant material in ironstones younger than the Precambrian, and in a few places it forms deposits of considerable thickness. It is rare, but not unknown, in rocks of 

Precambrian age; glauconite has been identified in 

strata of the Sinian System of Asia (see, for example, 

Kazakov and Polevaya, 1958, p. 383-384). Glauconite 

is an established mineral species, but, as with chamosite, 

the term is applied to mixtures of minerals of particular 

form and mass-aggregate properties. It typically 

occurs as bright-green pellets, which may accumulate as 

beds tens of feet in thickness containing 75 percent or 

more glauconite (Mansfield, 1920; Hutton and Seelye, 

1941), but it also occurs as intergranular fillings and 

disseminations, as crustifications, as replacements of 

other materials, and as canal fillings in organic debris 

(Cloud, 1955, p. 484), and the color may range from 

yellow to nearly black. The pellets range in size from 

about 0.01 in diameter to about 0.5 mm (Burst, 1958b, 

p. 484).

Burst (1958a, 1958b) divides natural glauconites into 

four classes:

1. Well-ordered, nonswelling, high-potassium micatype lattice, with well-defined X-ray reflections at 

3.3A and 10A. Closely approaches group 1M of 

the mica polymorphs.

2. Disordered, nonswelling, low-potassium mica-type 

lattice. Can be assigned to group iMd of the 

mica polymorphs.

3. Extremely disordered, expandable, low-potassium 

montmorillonite-type lattice.

4. Mixtures of two or more clay minerals, such as

kaolinite and illite.

Characteristic X-ray diffraction diagrams of oriented 

material of these four classes are shown in figure 1.
CHEMISTRY OF THE IRON-RICH SEDIMENTARY ROCKS W7

10(A) 4.48 10(A)

(Inter.layered) 

3

(Mineral mixture) 

4

FIGURE 1. X-ray diffraction patterns of four types of glauconite, according to Burst's 

classification (Burst, 1958b):

1. Franconia Sandstone, Cambrian, Wisconsin; well-ordered, nonswelling, 

high-potassium, mica-type lattice;

2. Burditt Marl of Adkins (1933), Cretaceous, Texas; disordered, nonswelling, low-potassium, mica-type lattice;

3. Byram Formation, Oligocene, Mississippi; extremely disordered, expandable, low-potassium, montmorillonite-type lattice;

4. Wilcox Formation, Eocene, Texas; mixtures of two or more clay minerals 

as normal pellet constituents.

The first class corresponds to the mineral glauconite, 

the structure of which was defined by Gruner (1935), and

* * * retreating from this end point on gradual steps of diminishing potassium content are materials which less and less resemble 

glauconites and more and more resemble montmorillonites. 

(Burst, 1958b, p. 492.)

A somewhat similar scheme by Smulikowski (1954), 

based on the relations between interlayer cations (K, 

Na, Ca), Al4, and Al6, requires chemical analysis and 

formula calculation for classification.

Glauconite is a constituent of modern sediments in 

many parts of the world (Cloud, 1955). It has been 

found in sandy sediments at depths ranging from that 

of near-shore shallows to 14,400 feet, but its most common locale is 60 to 2,400 feet. Glauconites are essentially ferric (ferric-ferrous ratio typically about 

7:1) and the material does not form in strongly 

reducing environments. Burst (1958b, p. 482) concludes, "Decaying organic material * * * creates a 

local reducing environment which sufficiently counteracts the over-all oxidizing marine environment * * *." 

Under such conditions glauconite can form as direct 

accretions or as replacements of preexisting material. 

Modern glauconites characteristically are deficient in 

potassium, which fact has been interpreted by some 

to indicate lower potassium content of present seawater as compared with that of previous eras. More

likely, however, it reflects "immaturity" of the glauconitic material, which after diagenesis will attain a 

more ordered structure with fixation of additional 

potassium. Both Burst (1958a, 1958b) and Hower 

(1961) stress progressive reactions in the development 

of glauconite.

Glauconite is a very fine-grained material and, by 

virtue of its mode of origin, may contain considerable 

admixtures of other material. A large number of 

analyses have been reported in the literature, but many 

are of dubious value; many have been made on samples 

treated with acids or alkalis or separated by use of 

inorganic liquids such as Thoulet's and Clerici's 

solutions, with resultant significant ion exchange. 

The selected analyses listed in table 5, except for A 

and B, in general typify the mineral glauconite; the 

material glauconite has a far greater range in composition, as indicated in column I. The only consistent 

relations between composition and age or type of 

enclosing rock is the lower content of K2O in recent 

glauconites as compared with those of older age, and 

the higher A1203 content of glauconite from limestone.

CBLLOKITE (EXCLUDING CTTAMOSITE)

The chlorite of the iron-rich rocks is typified by the 

iron-rich variety, thuringite, the occurrence and habit 

of which are described here. Chlorite of similar character but of somewhat lesser iron content is not uncommon; Hunter (p. 26),l for example, classes the 

nonchamositic chlorite of the Clinton as daphnitebrunsvigite.

Thuringite is an abundant mineral of the Lower 

Silurian ironstone of Thuringia, Germany, where it 

forms ooliths in a matrix of quartz and magnetite. 

Engelhardt (1942) established that thuringite has the 

structure of an orthochlorite, and also established the 

virtual identity of bavalite with thuringite, and the 

distinction of both from chamosite. Analyses are given 

in table 6, E and F. The bavalite studied by Engelhardt was from Devonian strata of Brittany, France, 

where it occurs in oolitic form in association with magnetite and siderite(?). Thuringite is also reported from 

the lower Paleozoic oolitic chamositic ironstones of 

North Wales, where it occurs in association with magnetite and stilpnomelane (Pulfrey, 1933).

Thuringite and bavalite are optically negative; 

2F=0° or very small; they are pleochroic in shades of 

green and greenish yellow; and have low birefringence. 

Indices of refraction for analyzed material listed in 

table 6 are:

Thuringite (sample E, table 6): 7=0=1.672 

Bavalite (sample F, table 6): 7=0=1.681

i Hunter, R. E., 1960, Iron sedimentation of the Clinton Group of the central 

Appalachian Basin: The Johns Hopkins University [Baltimore], unpublished 

Ph. D. thesis, 416 pp.
W8 DATA OF GEOCHEMISTRY

TABLE 5. Selected analyses of glauconite 

[Except for A and B, these glauconites probably would belong to Burst's class 1 (ordered mica-lattice) and class 2 (disordered mica-lattice) Burst, 1958b]

Si02 ____ ________ ______

A12 03 ___ ----- _______

Fes08 _____ ---_----_-_

FeO __ __.__-_.___-__

MnO _______ _______

MgO_._______________

CaO __ ________ _____

Na2 0_-______________.

K2 0__________________

H2 0+_____ _ __._

H2 0-

Ti02 ___-___.______-__

P2 05 -__________._____

Sp. gr______ _ 

A

46.90

4.06

27.09

3.60

.70

.20

1.28

6.16

| 9.25

99.24

B

54.58

7.17

18.27

2.86

2.95

1.86

1.23

5.34

. oo

inn 7Q

c

52.64

5.78

17.88

3.85

Tr

3.43

.12

.18

7.42

/ 5.86

\ 2.83

.16

.18

1 on ^

2.708

D

49,89

7.52

18.93

3.00

3.75

.25

.11

7.52

6.11

2.34

.05

.22

99 69

2.772

E

50.58

6.72

19.50

2.96

4.10

.34

.04

8.26

I 1 >7C

f 7. <D

.27

100. 83

F

49.07

10.95

15.86

1.36

Tr

4.49

.07

.13

7.51

6.63

3.66

.15

.19

100. 20

2.687

G

49.13

9.96

16.67

1.29

3.01

.95

.49

8.87

5.03

4.34

99.74

2.825

H

48.66

8.46

18.80

3.98

.01

3.56

.62

.00

8.31

4.62

1.94

.10

.12

99.18

2.855

I

41. 0-56. 0

1. 5-22. 2

6. 2-28. 0

1.3- 8.6

. 6- 4. 8

. 1- 4. 0

.0- 3.0

3. 7- 9. 3

j 4.8-13.5

A, B. Recent sediments:

A. Recent greensand from Agulhasbank, near Agulhas, South Africa.

Analyst Gumbel (Smulikowski, 19S4, p. 38). 

B. Recent glauconite from Aomori Bay, Japan. Analyst, Takahashi

(Smulikowski, 1954, p. 36). 

C-E. Greensand or sandstone:

C. Glauconite from Tertiary greensand at Makerewau Creek, New Zealand.

Analyst, Seelye (Huttoii and Seelye, 1941, p. 596). 

D. Glauconite from lower Oligocene sandstone, Tysmienica, Carpathian

Mountains. Analyst, Szubartowski (Smulikowski, 1954, table 3,

No. 26). 

E. Glauconite from Upper Cretaceous greensand, Sewell, New Jersey,

U.S.A. Analyst Bailey (Mansfield, 1920). Total includes COs 0.30

percent.

The structural formula for the thuringite (sample E 

in table 6) is given by Engelhardt (1942) as:

(Si4. 8 A13 .2) (MgMFeJSFef.Alj.7) (OH) 16 . 0020.o; 

that for bavalite (sample F in table 6):

(Si^AU (Mg,Fe«Fe.+_' M..) ((OH) 13. 9 0.2)020. 0

Thuringite is very similar in composition to chamosite, and it is likely that it is the product of mild metamorphism of originally chamositic rocks. Probably 

much of the difficulty in establishing the mineralogical 

identity of chamosite is due to development of thuringite 

in varying amounts from the original silicate. ACTABLE 6. Analyses of minnesotaite, stilpnomelane, thuringite, 

and bavalite

SiO2 - ... .._. ._

AhOs 

FesOs.. ..........

FeO ..- _ MnO....... ..__.._.

MgO...............

CaO._.. ..__.__._.__

Na2O_._.. ._._____ .

K80.... ............

H20-K . 

H2O-_._. ..........

TiOs ___ .

A

11 90

.61

2.00

33.66

.12

6.26

.00

.08

.03

5

F.A

.24

.04

99.87

B

48.03

6.48

i 19

22.88

2.67

.83

.00

.83

6 90

2.64

23

100. 55

C

44 77

16.38

15.08

1.15

C QQ

nn

.84

1 79

7.17

1

QQ

.18

100. 23

D

42.42

6.71

33.24

QC

2.27

5.20

00

o oo

1.45

100. 47

E

on QO

17.64

8 7fl

37.96

a IP;

10.31

.07

Tr.

99.65

F

21.71

91 Q^

S9

43.01

.05

2

00

.16

\ 0.

r . OO

10.10 .11

.08

100. 07

A. Minnesotaite. From Biwabik Iron-Formation, Mesabi district, Minnesota

(Gruner, 1944a). R. B. Ellestad, analyst. 

B. Stilpnomelane. From Otago Schist, New Zealand. C. O. Hutton, analyst

(Hutton, 1938). 

O. Stilpnomelane. From Mont Chemin, Wallis, Switzerland. J. Jakob. analyst

(Jakob, 1927). 

D. Stilpnomelane. Iron County, Michigan (Ayres, 1940). V. L. Ayres and B. Park.

analysts.

E. Thuringite. From Schmiedefeld, Thuringia, Germany. (Jung and K6hler, 1930). 

F. Bavalite. Bas-Vallon, Brittany, France. (Orcel, 1923).

F-H. Limestone:

F. Glauconite from glauconitic limestone, Milburn Quarry, Otago, New 

Zealand. Analyst, Seelye (Hutton and Seelye, 1941, p. 596). Analysis 

total includes CrsOs 0.07 percent and S 0.06 percent. 

G. Glauconite from Lower Ordovician limestone, Berg, Sweden. Analyst,

Palmqvist (Hadding, 1932, p. 124).

H. Glauconite from Upper Cambrian Bonneterre Dolomite. Analyst, 

Brown (Specific gravity given by Gruner, 1935, p. 708). This is the 

material for which Gruner developed the structural formula of glauconite as (OH) 8 K2 (Mg, F+2) 3 (Fe+s, Al) 6 (Sin A18) O«. 

I. Maximum and minimum of 40 analyses in Hendricks and Ross (1941, p. 692-693).

cording to Hallimond (1925, p. 28), thuringite is 

distinguished from chamosite in thin section or fine 

powders by the hexagonal habit of the scales, retention 

of green color in fine powders (chamosite is grayer), 

and bluish-green rather than green pleochroism parallel 

to the base.

MrNNBSOTATTE

Minnesotaite, the iron analogue of talc, is a rockforming mineral in some Precambrian iron-formations. 

In 1927, Bicharz (1927) recognized that some of the 

"amphibole" reported in rocks from the Mesabi 

district of Minnesota could not be an amphibole and 

suggested the term "crystallized greenalite" for the 

material. Jolliffe (1935), in a study of greenalite, 

describes a "mineral x" from the Gunflint Iron-Formation of Ontario and Minnesota and gives a partial 

chemical analysis and optical properties. The problem 

was finally resolved by Gruner, who defined the 

structure of the mineral and named it minnesotaite 

(Gruner, 1944a). Further data on occurrence in the 

Lake Superior region are given by Gruner (1946), 

Tyler (1949), James (1954, 1955), and by Huber 

(1959), and by Harrison (1952, 1953) for the QuebecLabrador iron belt of Canada. Because of its characteristic extremely fine grain size, the mineral probably 

has gone unrecognized in many iron-rich rocks of other 

parts of the world. It is generally associated with one 

or more of the following minerals: greenalite, stilpnomelane, siderite, magnetite, and quartz. Gruner (1946, 

p. 12) believes it to be a primary constitutent of the
CHEMISTRY OF THE IRON-RICH SEDIMENTARY ROCKS W9

rocks; Tyler, James, and Harrison believe it to be a 

low-grade metamorphic product.

Minnesotaite is greenish gray in hand specimen, with 

a waxy luster. As seen under the microscope it is in 

aggregates of very fine plates and fibers, colorless or 

pale green; it strongly resembles talc, sericite, and 

pyrophyllite, but commonly forms tiny rosettes or 

sheafs. Optically negative, 2V less than 5°, positive 

elongation, slightly pleochroic (7=|3=pale green; a 

colorless or very pale yellow); indices 7=1.615, a= 1.580 

(7 Q:=0.035). The mineral has been synthesized 

(Flaschen and Osborn, 1957, p. 926). The formula 

proposed by Gruner (1944a, p. 370) is:

(OH) n (Fe+2, Mg) u (Si, Al, Fe+2) 16O37.

The analysis is given in table 6, A. In simplified form 

the formula may be written as (Fe, Mg) 3Si4Oio(OH) 2.

STUJPNOMELANB

Stilpnomelane, a so-called "brittle mica", is a common constituent of many iron-rich rocks. In the ironformations of the Lake Superior region it is a rockforming mineral (Gruner, 1944b, 1946; Tyler, 1949; 

James, 1954); it also occurs as thin veins of coarsely 

crystalline material cutting stilpnomelane-bearing rock 

(Grout and Thiel, 1924; Ayres, 1940), and as a metamorphic mineral near dikes and sills (Tyler, 1949). 

Stilpnomelane occurs in North Wales as a secondary 

mineral adjacent to dikes in oolitic chamosite rock of 

Ordovician age (Hallimond and Enos, 1924; Hallimond, 

1925, p. 29), and in the iron-rich rocks of the Lahn-Dill 

district of Germany (Holzner, 1933).

Stilpnomelane is very similar in appearance to biotite 

and doubtless has gone unrecognized in many rocks as a 

result. In veins, as in the Cuyuna district of Minnesota, it forms foliae as much as several centimeters in 

diameter, olive green to nearly black. As a rock-forming mineral in ironstones it occurs as microscopic 

needles and plates, rarely more than a few tenths of a 

millimeter in length, with very strong pleochroism and 

absorption. The color ranges from olive green to dark 

brown, depending on the ferrous-ferric ratio. Density 

ranges from about 2.8 to 2.9. It is optically negative, 

and 2V is very small or zero. Indices show large ranges 

that can be related to ferric-ferrous ratio (Button, 1938, 

1945, 1956) ;a=1.55 1.63; 7=0=1.68 1.74. On the 

basis of X-ray studies, Gruner (1937; 1944b, p. 296) 

concludes that Stilpnomelane is fundamentally a talc 

structure with layers "stacked in such a manner that 

the hexagonal rings more or less fit on each other as in 

micas". Al and Mg are essential constituents. The 

general structural formula developed by Gruner is:

(OH) 4 (K, Na, Ca) 0 -i(Fe, Mg, Al) 7_8Si 8O23 _24 -(H2O) 2 -4 .

The three analyses of Stilpnomelane given in table 6 

(B, C, D) show the range in FeO and Fe2O3 .

IRON SULFIDES

Pyrite and marcasite. the latter relatively scarce, 

are the only sulfides of quantitative significance in 

lithified iron-rich sedimentary rocks. As with the 

oxides, however, these minerals may have been preceded in certain sedimentary environments by less 

stable materials of primary origin and transitory 

existence. The terms hydrotroilite and melnikovite 

have been used by many authors to apply to amorphous black sulfides present in unlithified sediments of 

Recent and Tertiary age, but definition as true mineral 

species has been lacking. Recently, however, the 

existence of a tetragonal form of FeS has been established, which Berner (1962, 1964) believes to be the 

main mineral component of hydrotroilite, and Skinner 

and his coworkers (1964) have isolated and defined 

the new mineral greigite (Fe3S4) that appears to be the 

main component of melnikovite. The two pairs 

hydrotroilite and tetragonal FeS and melnikovite and 

greigite are therefore discussed separately under these 

headings below.

Smythite (rhombohedral Fe3S4) and pyrrhotite 

(Fei_xS) occur as authigenic minerals in some sedimentary rocks Erd, (Evans, and Richter, 1957), but both are 

very rare. Pyrrhotite is also produced by metamorphism of pyrite (see, for example, Neumann, 1950).

PYKITB CFeSs)

Pyrite, the most common sulfide of the sedimentary 

ironstones, generally occurs as scattered isolated 

crystals that clearly are of diagenetic origin. It is 

a dominant mineral in the Sulphur Bed of the Cleveland 

ironstone of England and in the middle part of the 

Dominion Bed of Wabana, Newfoundland; at these 

places it forms layers as much as a foot thick and is in 

in the form of pellets, spherules, and replacements of 

shell fragments. The graphitic Wauseca Pyritic Member of the Dunn Creek Slate, a 50-foot Precambrian 

unit of the Iron River district, Michigan, contains 

35 to 40 percent pyrite as crystals about 0.003 mm 

diameter (James, 1951). Pyrite of extraordinary 

occurrence is described by Tyler and Barghoorn 

(1963) in chert of the Precambrian Gunflint IronFormation of Ontario; the crystals appear to have 

moved bodily in the chert, leaving a marked trail.

The occurrence of microspheres of pyrite in Recent 

muds as well as ancient rocks has been extensively 

investigated in recent years. Shales and muds may 

contain 10,000 or more spheres per cubic millimeter of
W10 DATA OF GEOCHEMISTRY

rock. They are described by Love (1962b, p. 122) as 

follows:

The spheres range in diameter between 3 and 30 microns, commonly being 7-10 microns and are composed of large numbers 

of minute euhedral sulfide crystals, each generally %-1 microns 

in size * * *.

Chemical analysis by Vallentyne (1962) of a 450-mg 

concentrate from a Recent lake sediment yielded the 

following results, in weight percent:

Fe -_--_--__-_-_-----____________-_ 46. 59

S_ __.-__--_.__.___--____.________ 53. 16

Si______________________________ . 13

C____________________________ .009

Isolation of pyrite spheres from rocks of early Paleozoic 

to Recent age and dissolution in acid have yielded 

organic residues of distinctive aspect; these forms 

have been named "Pyritosphaera barbaria" by Love 

(1957, 1962a). Vallentyne (1962, p. 145) suggests 

that the spheres may be "secondarily biogenic" that 

is, that the pyrite formed as a result of reactants produced by the organism rather than as accretion around 

living cells.

In a few areas, notably Meggen, Germany, and 

Mount Isa, Australia, pyrite of similar habit to the 

microspheres is a major rock constituent (see Schouten, 

1946; Baker, 1960; Love and Zimmerman, 1961). 

Whether the pyrite in these rocks is of sedimentary or 

later origin has been debated at length. Baker (1960) 

suggests that the microsphere form may be the product 

of either hydrothermal or sedimentary processes.

MAJRCASITE (FeSj)

Marcasite, rare or absent in most ironstones, is the 

characteristic sulfide associated with "black band" 

siderite ores of coal-bearing strata, where it occurs as 

nodules, partings, and thin layers. Newhouse (1927) 

describes marcasite layers in the Carboniferous of the 

Appalachians a few inches thick that cover square 

miles. Edwards and Baker (1951) consider deposition 

of marcasite in coaly deposits to be a reflection of an 

acid environment, in contrast to the neutral or alkaline 

environment of marine deposits characterized by 

presence of pyrite.

HYDROTROZLITE AND TETRAGONAL FeS

The term hydrotroilite was used by Arkhangelskii 

(1933) and previous authors to describe the unstable 

amorphous iron sulfide fraction of bottom sediments of 

the Black Sea. The material was distinguished by its 

black color and by generation of H2S upon treatment 

with hydrochloric acid. As Berner (1964) has observed, the term pervades the sedimentologic literature, 

including that of recent date, even though justification 

as a definite mineral species has been lacking and the 

composition is uncertain. Although the composition

generally is assumed to be FeS'^H2O, Volkov (1959, 

p. 398) concludes that the common ferrous sulfide of 

Black Sea muds is hydrotroilite with a composition 

FeS'ftH2S, and Korolev (1958, p. 460) suggests that 

there exists a series of transitional phases between 

hydrotroilite and stable pyrite or marcasite.

Detailed study of natural hydrotroilite has been 

hampered by its instability and extremely fine grain 

size. By designing an experiment to simulate to some 

degree the natural environment Berner (1962) synthesized tetragonal FeS; he also recognized this compound in sediment from the highly contaminated Mystic 

River of Massachusetts, U.S.A. In a later study 

(Berner, 1964) the nature and occurrence of tetragonal 

FeS are more completely discussed; the mineral is 

shown to be essentially identical with mackinawite, 

which has been found in sulfide ore deposits (Evans and 

others, 1964; Kouvo and Vuorelainen, 1963), and with 

the informally named kansite, a product of steel-pipe 

corrosion (Myers and others, 1958). Berner shows 

further that X-ray data published by Volkov (1961) for 

a sulfide concretion from Black Sea bottom muds are 

consistent with those of tetragonal FeS plus a lesser 

amount of greigite (Fe3S4 , see next section).

The calculated specific gravity of synthetic tetragonal 

FeS is 4.29. The cell dimensions are c0 =5.047 ± 

0.002A; OQ= 3.679±0.002A. In natural occurrence 

that is, as "hydrotroilite" the mineral may contain 

"absorbed or nonessential water" (Berner, 1964), so that 

the formula of FeS-?iH2O would apply.

Arkhangelskii (1933) reported that where "hydrotroilite" was present in abundance, it was in part 

converted to marcasite, and Ostroumov and Shilov 

(1956) report similar transition in deep-sea deposits of 

the north Pacific. In most sediments, however, the 

only positively identified crystalline sulfide is pyrite or 

marcasite. (See Tageeva and Tikhomirova, 1957, for 

further data on Black Sea muds; Brodskaya and Martova, 1957, for Sea of Okhotsk; Shepard and Moore, 

1955, for Gulf of Mexico.)

A recent study of isotopic compositions of sulfur 

compounds of bottom sediments in four basins off the 

southern California coast (Kaplan, Emery, and Rittenberg, 1963) has thrown considerable light on the complex process of sulfide formation. The sulfur is present 

in five forms: pyrite (dominant), acid-volatile sulfide 

("hydrotroilite"), elemental sulfur, organic sulfur, and 

sulfate sulfur (in interstitial solutions). The bacterial 

reduction of sulfate results in strong enrichment in the 

lighter isotope (S32) in precipitated materials. Kaplan, 

Emery, and Rittenberg (1963, p. 319) state:

Using the isotope data, a series of diagenetic reactions can be 

traced beginning with sulphate and ending with pyrite * * * 

the greatest fractionation in the reduced entities exists in the
CHEMISTRY OF THE IRON-RICH SEDIMENTARY ROCKS Wll

surface sample and that the S32 enrichment there is similar for 

all compounds * * * must mean formation from a large sulphate 

reservoir. With increase in depth, all reduced components 

become less enriched in S32, free sulphide showing the greatest 

change and pyrite the least. The changes become apparent 

after burial and isolation from the infinite sulphate reservoir. 

Under such conditions the first sulphide evolved must be the 

lightest, later sulphide becoming more enriched in S34 as the 

sulphate is depleted. The trends * * * indicate that the 

earliest formed sulphide is converted first into acid volatile 

sulphide and then to pyrite. The isotopic variation of elemental 

sulphur with depth and its 5 S34 values between those of free and 

acid volatile sulphide suggest that (a) it is continually being 

formed and destroyed and (b) its formation probably occurs 

through oxidation of free sulphide. These findings support 

earlier hypotheses * * * that pyrite forms by the direct 

reaction of hydrotroilite and elemental sulphur:

FeS+S-»FeS2 .

MKLNIKOVTTB AND GREIGITE

Doss (1912 and earlier papers) described melnikovite 

as an amorphous black magnetic iron sulfide, which was 

found in clays of Miocene age in Samara, Russia. The 

material was reported to have a hardness of 2 to 3 

and a density of 4.2 to 4.3, to be soluble in dilute 

HC1, and to have the composition Fe5S7 . Berz (1922), 

however, concluded that the material was a mixture of 

magnetite and pyrite, and subsequently the terms 

melnikovite-pyrite or melnikovite-marcasite were used 

for fine-grained mixtures of pyrite and marcasite 

(Ramdohr, 1955b). In 1957 Lepp synthesized a 

sooty magnetic sulfide (or sulfide hydrate) with a 

distinctive X-ray pattern and properties similar to the 

melnikovite of Doss (Lepp, 1957), but his data were 

not adequate for complete chemical and mineralogical 

definition. Material also referred to as melnikovite 

has been produced experimentally by Korolev (1958), 

but the X-ray properties are significantly different 

from those given by Lepp. As a mineral species, 

therefore, the status of melnikovite has remained unclarified.

Iron sulfide similar to the melnikovite of Doss 

recently has been found in lacustrine sediments of 

Tertiary age in San Bernadino County, Calif. (Skinner, 

Erd, and Grimaldi, 1964). The HCl-soluble magnetic 

iron sulfide has the composition Fe3S4 (spinel structure) 

and has been named greigite, a polymorph of smythite. 

It is sooty black and occurs with marcasite in grayish 

black laminae in the sediment. The unit cell dimension is 9.876 ±0.002A, with a calculated density of 

4.079±0.003. Skinner, Erd, and Grimaldi conclude 

that greigite formed by the action of anaerobic bacteria 

in bottom sediments of an alkaline lake.

The X-ray properties of "cubic magnetic iron sulfide" 

synthesized by Berner (1964) are essentially identical 

with those of natural greigite and conform to the

"melnikovite" synthesized by Lepp (1957). As mentioned in the previous section, Berner shows that the 

X-ray properties of the melnikovite of Volkov (1961; 

see also Volkov and Ostroumov, 1957), which occurs 

in hard black concretions at depths of 335-337 cm in 

Black Sea bottom muds, can be accounted for by a 

mixture of tetragonal FeS with the cubic iron oxide 

(greigite). Berner also suggests that Doss' melnikovite 

was a mixture of elemental sulfur with one or more of 

the magnetic iron sulfides (pyrrhotite, smythite, 

greigite).

CLASSIFICATION AND FACIES

MAJOR SUBDIVISIONS

Two major groups of the iron-rich sedimentary rocks 

are recognized: (1) the "ironstones", which are noncherty and largely of post-Precambrian age, and (2) 

the "iron-formations", which are typically laminated 

with chert and largely (but not exclusively) of Precambrian age. Use of the two terms in this manner is 

entirely the result of custom, not prior definition or 

logic, but it is continued as it provides ready distinction between dissimilar rocks. "Ironstone" appears 

to have no synonym, other than the commonly used 

"iron ore", whereas the rock here referred to as ironformation is known also as itabirite (Brazil,) banded 

hematite quartzite (India), iron-bearing formation and 

taconite (U.S.A.), and quartz-banded ore (Scandinavia). 

Only in South Africa, where the term "banded ironstone" is used for Precambrian cherty iron-formation 

is there overlap in usage of the two terms.

With minor exceptions, both ironstone and ironformation probably have originated as chemically 

precipitated marine sediments. The younger rocks 

commonly contain marine fossils often replaced by 

iron oxides and the older iron-f ormations occur within 

typically marine sequences of strata. A nonmarine 

origin for the Precambrian iron-formations has been 

suggested, however, most explicitly by Hough (1958). 

Hunter 2 (p. 212, 229) has produced evidence to 

indicate that the Clinton ores of eastern United States 

were deposited in marginal marine waters of less-thannormal salinity. The best documented example of a 

nonmarine sedimentary ironstone appears to be that of 

Oligocene age in northern Turgai, U.S.S.R., where 

oolitic ironstone contains fresh-water molluscs (Davidson, 1961).

Three other groups of iron-rich rocks of lesser 

importance can be defined: (1) theblackband and clayband ores, most of which are diagenetic or postdiagenetic deposits of siderite, often with associated marcasite or pyrite, found in coal measures and in some

*See footnote, p. W7.
W12 DATA OF GEOCHEMISTRY

clays; (2) the "bog iron ores" found in many bogs and 

small lakes in higher latitudes; and (3) surficial accumulations, known as canga in Brazil, derived from nearby 

outcrops of iron-rich rocks. These accumulations, of 

considerable extent and importance in some areas, have 

much in common with lateritic deposits and with 

residual-transported deposits of bauxite and therefore 

are not discussed in this chapter. The blackband and 

clayband ores, though not strictly or sedimentary 

origin, are included here because they occur in sedimentary rocks and because they share common factors 

in chemistry of origin with the marine deposits.

Still another group consists of iron-rich sedimentary 

rocks that grade into manganese-rich beds, such as 

those of the Kazakh region of the U.S.S.R. (Maksimov, 

1960). This class of deposits, commonly associated 

with volcanic rocks, is noted in passing here but is not 

treated in detail.

FACIES

Of greater significance to problems of genesis and 

distribution than the groupings given above is a classification according to the nature of the dominant iron 

mineral oxide, silicate, carbonate, or sulfide. Geochemical facies based on mineralogy are suggested or 

established both in relation to the geochemistry of iron 

(Teodorovich, 1947; Krumbein and Garrels, 1952; 

Huber and Garrels, 1953; Krauskopf, 1957; Huber, 

1958; Garrels, 1960), and to geologic occurrence 

(Harder, 1919; Tyler, 1950; James, 1954; Borchert, 

1952, 1960a, 1960b; Strakhov, 1959).

GBOCHEMICAL ASPECTS

The relations among the various compounds of iron 

are most effectively illustrated by the showing of 

stability fields in diagrams of oxidation potential (Eh) 

versus hydrogen-ion concentration (pH). Stemming 

in considerable part from the work on corrosion of iron 

by Pourbaix (1949 and earlier papers), the use of 

stability-field diagrams in application to geology has 

developed rapidly in recent years. A series of papers 

by Garrels with his colleagues and students (Castano 

and Garrels, 1950; Krumbein and Garrels, 1952; 

Garrels, 1953; Huber and Garrels, 1953; Huber, 1958), 

all of which deal in part or specifically with the problem 

of iron sedimentation, culminated in the publication of 

a book (Garrels, 1960) in which the method and the 

application to iron equilibria are discussed fully. 

Krauskopf (1957) has used Eh-pH diagrams to analyze 

the behavior of manganese and iron, and Hem (1960a, 

1960b) and Hem and Cropper (1959) have utilized the 

Eh-pH approach to define the stability fields of iron in 

solution.

The field boundary between any two molecular 

species, or between two ionic species in solution, is

established from the Nernst equation, expressed as

(1)

where

Eh=oxidation potential (redox potential), 

E°=potential of the reaction under standard conditions, 

R=universal gas constant, 0.00198 kcal/degree mole, 

T= temperature, degrees Kelvin, 

n number of electrons involved in the reaction, 

F=Faraday constant, 23.06 kcal per volt-gram

equivalent,

In k= natural logarithm of the equilibrium constant of the 

reaction;

and from the relation

where

E°= nF' (2)

A F° standard free energy of the reaction.

To establish the Eh-pH relation between a pair of 

compounds such as hematite and magnetite, write the 

electrode reaction:

2F3O4+H2O=3Fe2O3+2H++2e

The standard free-energy change of the reaction is 

obtained by subtracting the free energy (values in 

kcal given in table 7) of the reactants from those of 

the products:

AF°=(3X -177.1) + (2X0)-(2X242.4) -(-56.69) 

= + 10.2 kcal

then from (2)

_fl0.2 

2X23.06

= 0.221 volt

Substituting in (1), at 25° C or 298.16° K, and converting to logic,

Eh= 0.221 +

.00198X298.16 

2X23.06

Noting that the activities of Fe2O3, Fe3O4, and H2O 

are unity by convention, and that pH= log H+, the 

Eh-pH equation for the reaction is the straight line

Eh= 0.221-0.059 pH (3)

At fixed concentrations of carbonate species in 

solution (CO3~ 2; HCO^ 1 ; H2CO3) or sulfur species (H2S; 

S~2 ; HS" 1 ; HSO^ 1 ; SO<T 2), similar equations can be derived for equilibrium relations between oxides and 

siderite, siderite and sulfide, or oxides and sulfide.
CHEMISTRY OF THE IRON-RICH SEDIMENTARY ROCKS W13

Values of free energy of formation, AF°, for species of 

importance to the sedimentary iron system are listed 

in table 7. Equilibrium constants for significant 

reactions are given by Latimer (1952), from which 

source part of the data given in table 7 is derived.

0.7

Figure 2 is from Krauskopf (1957, p. 64). On the 

diagram the field boundaries are based on total carbonate =0.002M, which is the aqueous concentration 

at pH 8 in equilibrium with the atmosphere; total 

sulfur =0.1M; and total silica =0.002M, which is the

-0.5

10

FIGUEK 2. Eh-pHdiagramshowlngrelations between anhydrous Iron compounds at 25° 0, latm pressure (from Krauskopf, 1957, p. 64).

Solid lines are boundaries of stability fields, as labeled. Cross-bars on short vertical lines show the intersection of field boundary at 

low concentrations of carbonate, sulfide, and silica. Dashed lines are theoretical limits of water stability. Dash-dot lines are isoconcentration lines, drawn through points where concentration of FeM in equilibrium with oxides is 0.5 ppm and 5 ppm. Question marks 

along FeaOi-FeO boundary indicate that FeO is unstable with respect to Fe and FeaOt

Other conditions are specified in text. 

777-130 «8 8
W14 DATA OF GEOCHEMISTRY

TABLE 7. Values for free energy (AF°) for species of importance

to the iron system, at standard conditions

State: aq, species in solution; s, solid; I, liquid; c, crystalline

[From compilations by Garrels (I960)]

Species

Fe . .... ... -

Fe« - - 

Fe+1-. 

FeO-... ....... 

FesOi..... 

Fe(OH)+2... .. ......

Fe(OH) 2 -. - 

Fe(OH) 2+.. .........

Fe(OH)s.. -

FeO2H-. 

FeCOs. - 

FeSiOj... -. 

COs-* 

State

aq

aq

aq

Free 

energy 

(kcal)

0.0

-20. 30

-2.53

-58.4

-177. 1

-242.4

-55.91

-115. 57

-106.2

-166. 0

-90.6

-23.32

-36.00

-161. 06

257.0

-126. 22

Species

HCOr ~ 

HjCOa -

C/U2 .-

H+_... ...........

OH-.. ..............

H2O ________ ..

HiOi..--_-_..-_-_-..

H8SiO4-- -.. 

BUSi04 - ...

SiO2 (quartz) ........

s-»._ ____ -

H,S... - ... 

HS-~ ... ... ...

HSOr... . .. ..

SOr2 _ - _____

State

aq

aq

aq

Free 

energy 

(kcal)

-140. 31

-149.00

-92. 31 

.0

-37. 595

-56.690

-31. 47

-286. 8

-300. 2

-192.4

22.1

-6.54

3.01

-179.94

-177.34

amount soluble in water (chiefly as H4SiO4) at 25° C. 

Figure 3, from Huber (1958, p. 134), shows "blocked0.4

0.2

0.0

>-0.2

-0.4

-0.6

-0.8

6 7 

PH

10

FIGTJEK 3. Eh-pH stability fields for iron minerals with carbonate equilibria as in 

"normal sea water" and total dissolved sulfur as in "average river and lake water" 

(about 3.2 X10-8M), at 26° C. (From Huber, 1968, p. 134.) Dashed lines indicate 

field boundaries for sulfur as in normal sea water (about 102 -2 times concentration 

of river and lake water).

out" fields for the compounds; it is based on total 

carbonate as in "normal sea water" (activities not 

specified, but from Sverdrup, Johnson, and Fleming, 

1942, pp. 195-202); total sulfur as for "average river 

and lake water" 17.7 ppm SO";2 and salinity 146 ppm, or 

about 3.2X10-8 M. Figure 4, from Garrels (1960, p. 

157), shows field boundaries at relatively low concentration of dissolved sulfur and very high concentration 

of dissolved carbonate.

The three diagrams illustrate the wide range of 

thermodynamically stable associations possible; virtually any combination of oxides, silicate, carbonate, 

and sulfide is stable at standard temperature and

o

FIGTJEB 4. Eh-pH relations of iron oxides, sulfide, and carbonate with total dissolved sulfur = lO-'M and total dissolved carbonate = 1M, at 26° C. (From Garrels, 

I960, p. 167.) Heavy lines are field boundaries. Light line shows position of isoconcentrations of Fe in solution, at activity of 10-*. Dot-dash lines indicate theoretical limit of water stability.

pressure under some geologically reasonable values of 

Eh, pH, and ionic concentrations. Notable, however, 

is the restricted field of siderite at all but very high 

carbonate concentration, and the remarkable persistence of the pyrite field at very low sulfur concentration (fig. 4). The stability realm of magnetite shown 

on figures 3 and 4 is wiped out by assuming an appreciable amount of silica in solution, as indicated on figure 

2 by the Fe2O3-FeSiO3 field boundary. The formation 

of the sedimentary ores, in all their variety, clearly 

requires a variety of special conditions; as stated by 

Garrels (1960, p. 162), "* * * it is obvious that a 

siderite facies can be obtained by having a high dissolved CO2 and by removing sulfide sulfur from the 

system; a silicate facies by removing sulfur and a 

high CO2 content, while preserving enough silica to 

yield chert; a magnetite facies by reducing sulfur, 

CO2 , and maintaining silica at a value under-saturated 

with respect to amorphous silica."

The Eh-pH diagrams are extremely helpful in appraising the significance of natural assemblages, but a 

number of factors seriously restrict the direct applica-
CHEMISTRY OF THE IRON-RICH SEDIMENTARY ROCKS W15

tion to the geologic problems. Chief among these 

are that the compounds used in the thermodynamic 

calculations do not correspond exactly to the natural 

phases and that metastable phases are not accounted 

for. Natural siderite in the sedimentary ores is not 

FeCO3 ; it is a complex (Fe, Mn, Mg, and Ca)-bearing 

carbonate. The silicate is not FeSiO3 ; it is the far 

more complex chamosite, greenalite, or glauconite. 

The original oxide is not Fe2O3 ; it is limonite or some 

more primitive hydrate. The primary sulfide may not 

be pyrite, but a metastable phase such as tetragonal 

FeS. The natural occurrence of these phases indicates 

that they have larger stability (or metastability) fields 

than do the compounds being considered. Furthermore, the thermodynamic analysis indicates only 

theoretical phases; whether or not a particular phase 

will form may depend on other factors the presence 

of a catalyst, for example. In spite of the difficulties 

involved in their application, however, Eh-pH diagrams 

do indicate equilibrium associations under specified 

condition. Much more rigorous analysis of natural 

associations will be possible with the gradual accumulation of free-energy values for the more complex 

materials, coupled with greater understanding of the 

role of metastable phases and with more specific data 

on the natural environmental ranges of Eh, pH, and 

ionic concentrations.

NATURAL ASSOCIATIONS

That the iron-rich sedimentary rocks fall into natural 

groups based on the dominance of oxide, silicate, carbonate, or sulfide has long been recognized (for example, 

see Harder, 1919). The concept of sedimentary or 

geochemical facies based on mineralogy and reflecting 

sedimentary environments has been given explicit definition by Teodorovich (1947) and particularly by 

Borchert (1960a, 1960b) for the younger ironstones, and 

by James (1954) for the Precambrian iron-formations. 

The general relations as visualized by Borchert are 

shown unequivocally in figure 5. Strakhov (1959, p. 

765) presents a somewhat similar generalization, with 

two important differences: (1) all the iron minerals 

except the oxides are considered of diagenetic origin, 

and (2) the relative positions of siderite and chamosite 

are reversed that is, the shore-to-depth sequence is 

oxide-silicate-carbonate-sulfide. This sequence also is 

proposed for the Precambrian iron-formations (James, 

1954), with the addition of a magnetite-bearing facies 

and substitution of greenalite (plus stilpnomelane and 

minnesotaite) for chamosite.

No example is known of a complete array of major 

facies grading laterally one into the other as indicated 

diagrammatically in figure 5. The main reason for this 

is that the shore-to-depth profile is merely a device for 

indicating a range in environmental conditions, particularly oxygen availability. Nevertheless, to quote from 

an earlier paper (James, 1954, p. 242),

Although it is doubtful if the pattern of precipitation indicated is 

ever actually obtained in nature because of complicated relationships between depth of basin, height of barrier, and details of 

circulation, the facies relationships between the various mineralogies are valid.

Detritus from

Sea level

02 zone

CO, zone

pH: 7.2-8.5

Eh:+0.05 to+0.4

Most important agents: 

02 ,C02 , Cl- 1 . S04 -2, 

C03-2, HC03-i,

pH; 6-7.5

Eh: +0.05 to-0.2

H 2 S zone 2

^L pyrite sapropel rna^

Without benthos 

Abundant bacteria

Most important agents: 

HCOg-'.CI-i, S04 -2, 

P04 ~3 , N02-»

n . Eh: -0.2 to -0.5

Most important agents: 

H 2 S, Cx H y 02 , 

C x Hy , NH 4OH

FIGURE 5. Schematic section showing relations between ironstone facies and physico-chemical conditions. (From Borchert, 1960b, p. 34.)
W16 DATA OF GEOCHEMISTRY

Partial facies arrays that is, time-equivalent gradations from one facies into adjoining ones have been 

described for many areas: oxide to chamosite in the 

Clinton (Hunter,3 figs. 66, 69); chamosite to siderite in 

the Northampton sand ironstone (Taylor, 1949, fig. 1); 

magnetite-greenalite to carbonate in the Gunflint 

(Goodwin, 1956, figs. 3 and 6); hematite to magnetite 

to silicate and carbonate in the Labrador trough 

(Gastil and Knowles, 1960, p. 1249).

A valuable analysis of relations within the oxide 

facies is provided by Plaksenko (1959), in his study 

of relations between hematitic and magnetitic phases of 

iron-formation in the Kursk district, U.S.S.R. From 

west to east, dominantly hematitic iron-formation gives 

way to rocks in which magnetite is dominant, and this 

transition is accompanied by a considerable increase 

in the amount of interbedded metashale. In a typical 

vertical section (thicknesses range from 120 m to 

nearly 500 m), metashale is succeeded first by magnetite 

iron-formation and then by hematite iron-formation, 

and this sequence is repeated several times. Plaksenko 

relates the cyclic aspect to transgression and regression, 

and concludes that the normal shore-to-depth sequence 

is shale, magnetite, hematite. This reversal of the 

idealized relative position of hematite and magnetite is 

to be expected if a significant amount of clastic material 

is being contributed from the land, especially if the 

clastic material is clayey, with an organic component; 

it is particularly to be expected during regressive cycles. 

White (1954) shows that in the Mesabi district of 

Minnesota the initial transgression produced a normal 

pattern, with hematite grading into clean sand (Pokegama Quartzite) on the shoreward side, and into 

magnetite in the deeper part of the basin; during regression sideritic and even pyritic rock accumulated in near 

shore positions and these graded seaward into magnetite 

and silicate facies.

Mixed assemblages and small-scale alternations between facies are common. These multiphase rocks owe 

their character to one or any combination of several 

factors:

1. Clastic accumulation of iron minerals that were 

formed initially in separated environments. This 

process is typified by many oolitic ironstones, 

which may contain chemically heterogeneous assemblages of limonite ooliths, chamosite ooliths, 

ooliths of alternating chamosite and limonite, partly 

replaced fossil fragments and clastic grains, and 

phosphate pellets.

2. Precipitation of iron minerals at boundary conditions 

between facies, so that the minerals of each facies 

are in equilibrium.

»See footnote, p. W7.

3. Precipitation in overlapping stability fields. Little 

is known of the true stability field of chamosite, for 

example, but its occurrence is controlled in part by 

available alumina and the stability field may overlap that of other iron minerals.

4. Periodic changes in bottom environment, due to 

seasonal effects or longer-range shifts in water 

currents, which result in small-scale interlamination of dissimilar facies.

5. Incomplete mineralogic response to changes in environment because of slow reaction rates or inadequate capacity of the system. This effect is 

particularly to be expected in diagenesis: the 

commonly observed partial replacements of chamosite and limonite ooliths by siderite, for example, 

doubtless are due to reactions below the depositional interface, and these reactions may be halted 

by depletion of CO2 in the burial environment.

6. Post-diagenesis metamorphism, again with incomplete reactions due to low capacity of the system 

or to sluggish reaction. The development of 

hematite in Paleozoic and Precambrian rocks is 

probably a metamorphic process, one which has 

gone to completion in many rocks whereas in 

others (the Mayville ore of Wisconsin, for example) both goethite and hematite are present. 

The partial development of thuringite from chamosite is another example.

Textural relations provide the most significant 

guides as to which factor or combination of 

factors is to be invoked to explain a specific 

assemblage, particularly if considered in the 

light of theoretical possibilities set up by EhpH diagrams and known differences in natural 

environments. It is to be expected, however, 

that diagenetic modifications will be in the direction of decreasing state of oxidation; studies of 

recent bottom sediments show that the Eh below 

the water-sediment interface is generally lower 

than that of the depositional environment (Zobell, 

1946; Bruevich, 1938a, 1938b).

The interrelationships between ooliths and 

matrix, arising principally from physical mixing 

of materials deposited in separated environments plus diagenetic modifications, have led 

Braun (1964) to define, for minette-type ironstone, 14 classes within the framework of the 4 

main facies. Each is illustrated by chemical 

and modal analyses.

ROLE OF ORGANIC ACTIVITY

A number of organisms are known to cause the precipitation of iron (see Harder, 1919, for a thorough 

review), but the true importance to the accumulation
CHEMISTRY OF THE IRON-RICH SEDIMENTARY ROCKS W17

of iron-rich rocks is difficult to assess. The subject 

will be only briefly surveyed here, as actual data significant to the question are few.

Three general situations may be considered;

1. The organism acts essentially as a catalyst that 

is, it causes or speeds up precipitation of a compound that is thermodynamically appropriate 

to the environment. The well-known abundance 

of bacterial populations in natural precipitates of 

iron oxides, as in emerging ground waters, is an example; in effect, the organism derives energy for 

growth from the oxidation of metastable ferrous 

iron. The products of biochemical precipitation 

will be mixed with inorganic precipitates of the 

same character. In a sense, the organism is of 

only incidental importance; it flourishes by taking 

advantage of the slow rate at which equilibrium 

is reached by wholly inorganic processes.

2. The organism selectively accretes a compound as 

part of its cell wall or skeletal structure, as in the 

familiar example of silica secretion by radiolaria. 

This accretion may or may not be in harmony with 

the inorganic aspects of the system; a diatom, for 

example, can secrete and maintain a silica test in 

an environment greatly undersaturated with 

respect to silica. However, with the possible 

exception of Pyritosphaera barbaria (see under 

"Pyrite"), no organism is known to secrete an 

iron compound as a principal constituent of its 

hard parts.

Foraminifera, and possibly some other organisms, are known to extract particulate iron 

oxide from sea water; foraminiferal tests are 

reported by Correns (1937) to contain 0.16-0.65 

percent Fe2O3 . As has previously been mentioned, 

this concentration, followed by death of the organism and return of CaCO3 to solution, probably 

is the main reason for the high content of iron in 

deep-sea sediments (Wakeel and Riley, 1961). 

A somewhat similar process is suggested by 

Strong (1956), who has isolated iron bacteria in 

rock salt of Devonian and younger age; he 

suggests (p. 585) that bacterially precipitated 

iron "* * * provide[s] material for certain deposits of iron oxide by solution of salt and aqueous 

redeposition of haematite."

3. The organism significantly modifies the physicochemical nature of the environment through its 

life processes. Reducing conditions that is, low 

Eh are created by bacterial action on included 

organic detritus in sediments, which results in 

consumption or displacement of oxygen, reduction 

of sulfate to produce H2S or to directly precipitate 

iron sulfide, and liberation of H2S by destruction

of proteins. Berner (1963) has shown that direct 

measurements on black muds show a good fit to 

the theoretical curve Eh=0.4850+.0295 pS~2. 

In such an environment, the iron is the main 

poising element in the system (Zobell, 1946). 

Whether by precipitating material directly or by 

creating the appropriate environment, microorganisms 

almost surely play a dominant role in the formation of 

many sulfide-rich sediments. They also may create 

reducing microenvironments in the vicinity of organic 

particles in an otherwise oxidizing regime. Glauconite 

probably is formed in such localized environments, in 

which the Eh is appreciably lower than in the surrounding medium.

In general, however, it seems fair to conclude that, 

except for the sulfide-rich rocks, organisms have not 

been of first-order importance in the concentration of 

iron to form the ironstones and iron-formations, even 

though they may have been involved with the actual 

process of precipitation.

CHEMISTRY OF IRON-RICH ROCKS, ACCORDING TO 

GROUPS AND FACIES

Tables 8 to 19 present selected analyses of iron-rich 

rocks, grouped according to facies and to some extent 

according to age, and some of the more significant 

aspects of each group are given in summary fashion 

below. The separation according to age is to permit 

isolation of differences between the Precambrian ironformations and the younger ironstones; these differences are discussed in a later section.

Except where otherwise stated, the analyses are 

known or believed to be of representative samples of 

particular rock types in general of hand specimen 

size or somewhat larger.

OXIDE FACIES

The oxide facies of the normal iron-rich sedimentary 

rocks comprises the oolitic limonitic and hematitic 

ironstones of post-Precambrian age, banded hematitic 

iron-formation of Precambrian age, and magnetiterich rocks of both Precambrian and younger age. 

In the tables these are grouped according to subf acies 

for example, limonitic ironstone and according to age 

(Precambrian and post-Precambrian).

OOLITIC UMONITE IRONSTONE

The oolitic limonites are very largely restricted to 

ironstones of Tertiary and Mesozoic age. An exception 

is that of the Mayville ore of Ordovician age (table 8, 

analyses Q-R).

The rocks typically consist of oolitic or pelletal 

grains of limonite, many with cores of clastic material, 

in a matrix of chamosite or calcite. Some consist of 

mixtures of chamosite and limonite ooliths, with the
W18 DATA OF GEOCHEMISTRY

chamosite either partly altered to limonite or containing 

limonite in alternating layers with chamosite. The 

rocks are chemically heterogeneous and doubtless are 

the products of a primary chemical precipitation 

followed by mechanical transport and sorting of the 

ooliths. Siderite, present in quantities of as much as 

10 percent or more, is of diagenetic origin.

Chemically the rocks are marked by a wide range in 

composition that is related in considerable part to 

the rudely inverse relation between quartz and calcite 

content, and to the amounts of chamosite and of secondary siderite. The P2O5 content is generally high, 

reflecting the presence of pelletal cellophane.

HEMATTTIC BOCKS OF MESOZOIC AND PALEOZOIC AGE

Most of the hematitic ironstones listed in table 9 

are oolitic rocks similar in physical character to the 

oolitic limonites and with similar associations and origin. 

As in the limonites, an inverse relation between CaO 

and SiO2 reflects the dominance of either clastic quartz 

or clastic or interstitial calcite. Chemically the chief 

difference is hi the lesser H2O content, represented 

mineralogically in the dominance of hematite.

Two analyses, L and M, are of ironstone of the 

"Lahn-Dill" type, as contrasted to the "minette" type. 

The Lahn-Dill ironstone is a type example of the socalled exhalative-sedimentary class (Borchert, 1960b, 

p. 25; Oftedahl, 1958), produced by sedimentary deposition of materials derived from submarine volcanic and 

fumarolic activity. The Lahn-Dill ironstone, which 

includes both quartz-rich and calcite-rich varieties, has 

a distinctly lesser content of P2O5, A12O3 , and MgO than 

do ironstones of the normal minette type.

Two analyses, Q and R, are quartz-banded ores of 

the Dunderland belt of Norway. These rocks, which 

consist chiefly of interlayered quartz and crystalline 

iron oxides, are of early Paleozoic age and have been 

metamorphosed. Physically and mineralogically they 

are very similar to many of the Precambrian ironformation rocks.

HEMATITIC IRON-FORMATION OF PRECAMBRIAN AGE

The hematitic variety (or subf acies) of the oxide f acies 

(table 10) is one of the more common types of Precambrian iron-formation, though in some places there 

is some question as to the primary nature of the hematite. Edwards (1936) and Miles (1941), in discussing 

the now dominantly hematitic rocks of South and 

Western Australia, for example, note that much of the 

hematite is secondary after magnetite; according to 

Johnson (1962, p. 31), residual magnetite is present

TABLE 8. Analyses of oolitic limonite (goethite) ironstone

SIOz .. ....

AliOi.. ........

FeO..._ 

MnO. 

MgOCaOH2 0+___ _ 

H2O-...._ 

TiO2 

P205 -_ 

CO2... 

S_ .........

Subtotal .

Less O for S _ .

Total. 

A

8.60

3.72

35.82

9.57

on

2.10

15.90

} 6.84

1.67

15.10

.18

99 89

.09

QQ ftO

B

17.75

3.38

47.36

7.37

.45

1.72

5.25

8.23

2.20

6.08

.04

99.83

.02

99.81

C

25.03

4.60

41.61

7.46

39

2.10

4.85

7.68

1.88

4.67

.07

100 34

.03

100. 31

D

5.39

40.45

8.72

.36

1.63

15.13

7.20

.17

1.67

15.00

.04

* 100. 18

.02

4 100. 16

E

8.64

4 8Q

35.07

12.02

00

1.95

14.05

7.16

1.86

13.84

.07

QQ fiS

.03

QQ ft*

F

8.44

5.27

36.78

14.27

9fi

1.94

11.30

7.78

2.06

12 04

.05

100. 19

.02

100. 17

G

7.83

d fi9

43.14

8.23

34

o in

10 7«

7.94

1 Q^

12.00

.07

100. 97

.03

1AA QJ.

H

10.40

7 SQ

50.48

93

1.47

7.67 ( 11. 64

19

2.35

9 H9

i QO 89

& QQ 89

I

6.55

6.91

62.88

.18

00

1.10

6.06

10.24

1.83

3

00

.004

99 46

99.46

J

3.45

3.56

36.40

.18

.31

.58

27.08

6.56 2 1.60

1.05

20.64

.009

QQ 89

QQ 89

K

10.45

5.28

39.00

.28

.33

.41

20.07

7.59 2 1.72

1.10

.045

QQ R7

.02

QQ fi^

L

23.85

7.57

39.46

8.78

9Q

1.95

4.91

8.23 2 1.85

.96

3.26

.25

99.51

.12

99.39

M

14.32

5.20

43.22

1.31

.36

1.03

14.66

7.99 2 1 64

1.35

10.32

.032

QQ 70

.02

99.77

N

3.90

3.34

19.4

11.31

1.58

1.3

26.3

.77

.41

O

9.25

4.6

24.86

10.66

1.4

1.83

21.1

.85

.27

P

13.77

4.77

38.71

6.56

.167

2.92

11.18

0)

.917

» 20. 13

.055

99.18

.03

99.15

Q

6.90

4.72

60.50

.604

.20

2.97

6.70

7.06

.95

3.33

5.86

.048

99.84

.02

99.82

R

5.12

3.25

72.34

.44

.61

5.98

4.90

.32

3.73

3.60

100.29

100. 92

i Included under CO2.

^ Not included in total. Reported as "hydration grad" in original reference.

'Includes H2 O.

* Total includes 0.08 percent V2 Os, 0.02 percent As.

' Total includes 2.24 percent SOs, 0.13 percent V2 Oe, 0.01 percent NiO, 0.08 percent C.

A-G. Minette ores of the "Grise," "Noire," and "Verte" horizons of LandresAmermont basin, Lorraine: A-C from Coche and others, 1954; D-G from 

Cocke and others, 1955, analyses credited to Ecole de Mines, Nancy. Calculated modes as follows:

Goethite- .....

Siderite. .........

Chamosite .......

Calcite ...........

Other............

A

(Couche 

Grise)

40.9

10.3

2.1

14.9

23.2

4.0

3.7

.9

B

(Couche 

Noire)

54.1

9.2

9.9

5.9

15.2

5.0

.6

C

(Couche 

Verte)

47.6

5.5

1.0

19.5

4.5

17.6

4.1

.5

D

(Couche 

Grise)

43 76

13.17

14.22

22.71

1.45

5.67

1.40

E 

(Couche 

Grise)

39.8

Q 9

20.9

23.4

2.0

4.4

.1

F 

(Couche 

Grise)

37.0 in ^

29.1

17.5

.7

4

0

.3

G

(Couche 

Grise)

45.4

8 7

19 4

19 1

9 O

4.3

1.1

H. Ore from the Lias-y horizon, north GSttingen. Germany, between Harz and 

Soiling (Harder, 1951, p. 465). H. Harder, analyst. Calculated mode- calcite, 

4.9 percent, gypsum 4 8 percent, apatite 5.5 percent, goethite (with minor chamosite 

and siderite) 84 percent.

I-M. Minette ores of Luxembourg, stratlgraphically assigned as follows: I, Rotes 

Haupt Lager 3: J, Gelbes Neben Lager 2a; K, Gelbes Haupt Lager 2; L, Braunes 

Lager I; M, Rotes Lager I, Separate values given in original reference for quartz 

and combined SiOs. Quartz content of samples as follows: I, 0.05 percent; J, 0.11 

percent: K, 6.46 percent; L, 11.46 percent; M, 8.90 percent. From Lucius (1945, 

table B); analyses by technical laboratory of Konzerns A.R.B.E.D.

N-O. Partial analyses of unweathered "* * * chamosite-siderite mudstone * * * 

crowded with limonite ooliths"; from Frodingham ironstone. North Lincolnshire, 

England. N is from "Appleby bore 2": O is from Yarborough Pit. Analysis of 

separated limonite ooliths from this bed given in table 1, this report. Hallimond 

(1925, p 78); analyses by Frodingham Iron Co., Ltd.

P. Limonite oolite of Jurassic age (Corallian Berts), from East Kent, England 

(Lamplugh, Wedd, and Pringle, 1920, p. 225). Sample from drill core: analysis 

credited to E. O. Forster Brown.

Q-R. Mayville Ironstone from the Neda Formation of Ordovician age. Mayvllle, 

Wisconsin (Hawley and Beavan. 1934. p. FQ5). 0 is composite analysis of run-ofmine ore, made in 1925 by E. J. Wechter and Mayville Iron Co; R. by E. J. Beavan, 

analyst. Ore chiefly goethite and calcite, with a wide variety of other minerals in 

minor quantity.
CHEMISTRY OF THE IRON-RICH SEDIMENTARY ROCKS W19

TABLE 9. Analyses of hematite-rich sedimentary rocks of Paleozoic and Mesozoic age

SlOi.... 

AhOs -

FesOi.-. . ....

FeO.... _._

MnO._ .........

MgO... _ -_ 

CaO. ...... .....

NajO-.. ._

KjO._..._ ....

HjO-K... .... 

H,0---.. .

TiOi ..... .

Pj05 - .. ........

COj - 

S... .... ...

SO»._ ....... .

C-.. 

^ Subtotal..

Total.. 

A

11.51

6.85

29.90

12.08

.058

1.82

16.97

.019

.30

4.15

.30

.39

1 97

11.97

.10

1.90

.38

* 100. 13 

.05

4100.08

B

13.36

7.89

29.62

2.69

.33

.93

21.90

.014

.50

1.85

1.48

.45

2.35

14.59

.32

1.05

.33

599. 93 

.16

4 no 77

c

10.94

3.72

42.88

7.67

.29

5.90

10.80

.05

.02

1.76

.12

.14

.71

14.98

.00

« 100. 03 

.03

8100.00

D

4.21

4.38

37.72

7.27

.18

1.68

22.49

.01

.00

1.98

.21

.12

1.00

18.62

.00

.00

99.87

99.87

£

11.98

5.13

75.90

0)

.23

.21

2.71

U.86

9 ff>

.03

100. 07 

.02

100.05

P

12.59

5.71

75.12

W

.06

.42

1.49

22.17

.52

.27

1.63

.00

99.98

99.98

G

9.85

3.23

67.79

10.03

0.37

2.42

2.35

.32

.40

2.26

1.05

100.07

100.07

H

4.66

3.05

52.08

91 17

.78

1.14

2.88

1 79

.27

.28

2.11

10.78

100.92

100.92

I

15.29

9.63

44.17

19.38

.26

1.45

1.54

.46

.08

5.80

.83

1.07

.43

100.39

100.39

J

8 on

2 7Q

66.55

1 1^1

1 13

1.39

9.40

.15

.43

} 2.12

1.02

5.73

1.31

8.38

102.43

102.43

K

52.83

.81

5.70

14.61

4.75

.32

18.14

.32

«1.30

98.78

98.78

L

2.59

.75

52.56

.88

.11

.21

22.40

.05

.03

f 1.12

1 .21

.084

18.50

.31

.009

.08

100.12 

.15

'99.97

M

4fi 7Q

.25

50.80

.40

.01

.02

.80

.05

.04

.27

.08

.05

.12

.06

.028

.17

.09

8100.14 

.01

8100.13

N

13.60

5.17

55.56

.23

.14

1.49

10.26

.07

1.22

1.88

.80

.22

1.80

7.36

.03

.00

99.83 

.02

99.81

0

30.82

10.33

43.13

.45

.21

1.01

2.16

.07

2.36

4.78

2.05

.34

1.34

.10

.02

.00

99.17 

.01

99.16

P

19.08

4.45

55.48

.18

.15

2.05

7.14

.07

1.05

1.87

.67

.20

1.41

6.02

.03

.00

99.85 

.02

99.83

Q

34.35

3.73

50.41

1.17

.39

.20

3.85 }"

} .50

.23

.46

2.9

.04

99.33

.02

99.31

B

36.32

4.58

43.47

2.35

.35

2.66

4.25

1.7

.64

.32

.55

2.8

.19

100.18 

.10

100.08

1 All iron reported as FejOa.

1 Reported as "loss on igition"; includes COj.

» "Organic matter".

i Total includes 0.116 percent V2O5 , 0.001 CoO, 0.05 NiO.

» Total includes 0.28 percent VsOj.

 Total includes 0.05 percent F.

' Total includes 0.05 percent VjOs, 0.08 percent BjOj.

«Total includes 0.015 percent VjOs, 0.1 percent B2Oi.

A-B. Oolitic hematite in chamosite-siderite matrix, from the Lias (Lower Jurassic) 

of north Gottingen (Harder, 1951, p. 463-464); analyses by H. Harder. Calculated modes as follows, in percent:

Siderite. _____ __ 

Pyrite ___________ -

A

46

24.83

15

12.52

3.00

4.09

.17

.65

B

54

32.09

4

1.25

5.53

2.27

.60

.56

C. Oolitic hematite of Westmorland bed of the Clinton Group (Silurian), Kirkland,

N.Y. Rock is dominantly hematite and calcite. Analysis by Paula M. Buschman, U.S. Geological Survey. Sample F-2640, collected by R. P. Sheldon.

D. Hematitic ironstone, from base of Keefer Sandstone of Clinton Group (Silurian)

age. Sample F-2635, collected by R. P. Sheldon from road cutl mile south of

Allenwood, Pennsylvania; analysis by Paula M. Buschman, U.S. Geological

Survey. Sample consists of hematite, calcite, dolomite, minor quartz.

E-F. Dominion bed (Lower Ordovician), Wabana, Newfoundland. Analysis E by

Nova Scotia Steel and Iron Co.; analysis F by T. G. McFarlane. Reported

as analyses C and D in Hayes (1915, p. 45), from "average" samples of Zone

2. Specific gravity of No. F is 4.10. Average mode for analyses E and Fin

percent: hematite 65.5 percent; chamosite 23.9 percent; phosphate (shell 

fragments) 4.4 percent; quartz 6.0 percent (Hayes, 1915, p. 47).

G-H. Ore bed of zone 4, Wabana, Newfoundland. Analysis G of lower part of ore 

zone 4, specific gravity 4.23; analysis H is of upper part of ore zone 4. A. V. 

Seaborn, analyst, as reported by Hayes (1915, p. 52-53).

I. Ore bed of zone 4 (lower part), Wabana, Newfoundland. C. O. Hayes (1915, p. 63), 

analyst. Oolitic hematite and chamosite.

J. Rhubina hematite (Carboniferous), South Wales. Analysis made in laboratories 

of Geological Survey of Great Britain; quoted by Hallimond (1925, p. 85). Oolitic 

hematite with abundant shell fragments. As given by Hallimond, analysis is 

divided into two parts. The first is of the "soluble part," with 10.36 percent 

reported as insoluble residue; the second is of the ignited insoluble residue. The 

total for the first (including 10.36 percent insoluble) is 101.72 percent; the total 

for the second is 11.07 percent.

K. Cheadle hematite (Carboniferous), Froghall, North Staffordshire, England. 

Massive hematite with calcite and dolomite. Partial analysis made in laboratory of Geological Survey of Great Britain; reported by Hallimond (1925, p. 86). 

Total includes 0.04 percent insoluble.

L. Hematite-calcite ore (Devonian), Koenigszug mine, Lahn-Dill region, Germany 

(Harder, 1954, p. 60). H. Harder, analyst. Sample contains about 0.001 percent 

NiO, and less than 0.0005 percent CoO.

M. Hematite-quartz ore (Devonian), Constanze mine, Lahn-Dill region, Germany 

(Harder, 1954, p. 61). H. Harder, analyst. Sample contains about 0.005 percent 

NiO, less than 0.0005 percent CoO.

N. Oolitic hematite with chamosite, calcite, dolomite, and quartz. From the Martin 

Formation of Devonian age, Gila County, Ariz. (Willden, 1961). Sample F-2726, 

analysis by Paula M. Buschman, U.S. Geological Survey. Sample represents 

the upper 6 feet of the bed (see also Willden, 1960, p. B21-B23).

O. As above. Sample G-2892; represents lower foot of the ore bed; may be slightly 

oxidized.

P. As above. Sample F-2727, representing 6.2 feet of beds.

Q. Quartz-banded hematite ore, Ortrann mine, Dunderland, Norway (Bugge, 1948, 

table 1, borehole sample 115/11). Late Cambrian or Early Ordovician age. 

Rock contains 48.6 percent hematite, 3 percent magnetite. Analysis made in 

laboratories of Rana Gruber A/S (Company).

R. Quartz-banded hematite ore, same locality, reference, and analyst as for Q, borehole sample 122/III. Rock contains 38.8 percent hematite, 7 percent magnetite.

in some of the dominantly hematitic rocks of the Gaud 

Itabirite of Brazil.

The hematitic iron-formation consists of thin layers 

or laminae of hematite alternating with those of 

recrystallized chert. In the Lake Superior region, at 

least, the layers pinch and swell to give rise to "wavy 

bedded" iron-formation. Oolitic textures are typical 

of such rock (James, 1954) and are preserved even in 

areas of moderate to strong metamorphism (James 

and others, 1961, p. 44-15).

Chemically, the rock is remarkable in its simplicity; 

SiO2 and Fe2O3 generally account for all but a small 

percentage of the total. In contrast to hematitic and 

limonitic rocks of younger age, the phosphorus content 

is very low rarely as much as 0.1 percent.

MAGNETITE-RICH ROCKS OF MESOZOIC AND PAUEOZOIC

AGE

Magnetite-bearing facies are not common in rocks of 

post-Precambrian age, but they have been described as

minor rock types in several unmetamorphosed ironstones. The characteristic occurrence of magnetite in 

ironstones of the minette type (table 11, analyses A to 

G) is as fine granules or small crystals of diagenetic 

origin, clustered within limonite or chamosite ooliths. 

As Taylor (1949, p. 83) states with respect to magnetite 

in the Northampton sand ironstone (analysis G):

Clearly it was not formed normally as a result of the alternation 

between oxidizing and reducing conditions. This is shown by 

its complete absence between concentric skins of chamosite and 

limonite in the ooliths.

Magnetite in the chloritic ironstones of early Paleozoic 

age in Brittany, Normandy, and Wales (represented 

by analysis H) may be a metamorphic mineral, the byproduct of conversion of an original iron-rich chlorite 

to chlorite of lower iron content (Pulfrey, 1933).

Analyses I and J are from the same district as 

analyses Q and R (table 9), the Dunderland belt of 

Norway. As in the hematitic rocks of that area, the
W20 DATA OF GEOCHEMISTRY

TABLE 10. Analyses of hematite-rich rocks of sedimentary origin, Precambrian age 

[All rocks have been moderately metamorphosed]

S10» . 

AljOa 

Fe2Os __ -- __ ____ _____ _______ -

FeO- ... ... ... ... .... ........ ...

MnO _ 

MgO.. ... . ... _ 

OaO ... .............

Na»O _.. ...........-

KjO... .. .. .....................

H|0+.... ... ... ... ... ... ... ... ... ... ... ... ... ... ...

H»0-_ 

TiOa

P»05 . 

CO»__. ......... 

8--- . ..............................

SO».- 

Total. .................... . . ....

A

AA Q(\

.37

53.08

.71

Tr

.07

OQ

\ 12

/ - 12

04

.03

.07

99.57

B

on 79

A.t\

58.58

1.03

00

.07

.03

.07

.28

.02

Tr

.02

.40

.03

a 100. 70

C

46.81

40

46.91

5 03

Tr

.36

.14

f .13

I .03

OQ

04

Tr

3 100. 22

D

V7 U

an

50.41

10.17

.00

.19

Tr

} .03

.26

.02

Tr

.03

.58

.02

100.05

El

40.1

g

50.1

1.6

.2

2.0

1.4

.07

2.6

.009

98.9

FI

28.30

3.86

63.39

2.57

.00

.56

»fi

.72

.00

.085

100. 34

G

if, 04

.00

51.00

1.41

.02

.00

Tr

. uu

.68

.00

.39

100.44

H

51.56

Tr

47.48

on

.00

.00 {----

99.94

I

56.23

.45

34.96

5.67

.07

1.13

.81

.15

.12

.49

.03

.02

05

.06

100.24

J

39.3

<.5

60.1

.3

<.l

<.l

.3

.03

K

El A

<.5

47.8

.4

<.l

<.l

.1

.12

1 Samples dried at 100° C. before analysis. 

s Given as 100.60 in original reference. 

8 Given as 100.19 in original reference.

A-B. Banded specularite iron-formation, Krivoi Rog Series, Ukraine, TJ.S.S.R. 

(Semenenko and others, 1956, p. 95). Analysis A by S. A. Panchenko; analysis 

B made in laboratories of Ukranian Geologic Administration.

C-D. Hematite-magnetite iron-formation, Krivoi Rog Series, Ukraine, U.S.S.R. 

(Semenenko and others, 1956, p. 101). Analysis C by P. P. Makhovka; 

analysis D made in laboratories of Ukranian Geologic Administration. 

B. Hematite iron-formation, Menominee district, Michigan. Composition as 

recast by James (1954, p. 260; error in P2 O5 content corrected) from commercial analysis. Representative of shipment of 13,417 tons. Sample dried at 

100° C. before analysis. Approximately 47 percent hematite, 40 percent 

quartz, 5 percent dolomite, 5 percent magnetite, 3 percent kaolin and chlorite. 

F. Banded ironstone ("calico rock") of the Swaziland System, Umhlatuzi Valley

Zululand, South Africa (Wagner, 1928, p. 71). Name of analyst not given.

G. "Hematite quartzite", Camel Hill, Middleback Ranges, Australia (Edwards, 

1953, p. 468). Edwards(?), analyst.

H. Banded ironstone of the Hospital Hill Slate Zone, Witswatersrand System. 

Johannesburg, South Africa (Wagner, 1928, p. 73). Name of analyst not 

given.

I. Specularite-magnetite iron-formation, Atlantic City district, Wyoming 

(Bayley, 1963, p. 10). Chip sample taken from about 200 feet of outcrop. 

Dorothy F. Powers, analyst, U.S. Geological Survey.

J-K. Banded chert-specularite, Cau6 Itabirite, Minas Gerais, Brazil. (J. V. N. 

Dorr II, written communication of December 12, 1963). Samples are composites of 25-75 chip samples; dried at 110° C. before analysis. Selected from 

10 analyses, which show SiOz range of 36.3 to 51.4 percent (average 44.2), 

FesOj range of 47.8 to 63.6 percent (average 54.9). M. B. J. Fernandes, 

analyst.

TABLE 11. Analyses of magnetite-rich sedimentary rocks of Mesozoic and Paleozoic age

Si03 __ 

AliOa .................. 

FejOa. 

FeO.. .... ... ...

MnO. __ .............. ... ..

MgO. ................... ... . ... ....... .

CaO__ _ .... _ . _ ..

Na»O.__

K2O__ ............... ......

HsO+ _ _ __ _

HjO- _ . 

Ti02 . .... ...

PiOa. 

COj_ .............. ....... .............. ..... ...........

S... ....................... ... ............. ...... ... . .

SOa-. . ... _ . ....

C. ............. _ ..... _ . . . ..... . . ..

Subtotal. ____________ _________ ____ .

LessO..... ____ .. .... .. __ ...... _ _ . _ .. ...

Total _____________ _____________ ... ...

A

3.2

2.2

30.3

38.3

19

2.1

4.6

| Tr

1 Q 1

/ 3' 1

1.14

13.0

.55

1.1

99.91

.28

a 99. 63

B

3.4

3.2

20.9

18.8

.31

1.0

28.2

I:::::::::

. 1

1.4

19.2

99.51

99.5

C

4.8

4.7

44.1

24.9

.21

1.2

6.4

9.4

2.1

1.0

98.81

98.8

D

7.03

7.13

32.56

25.92

.22

1.82

2.84

f 4.88

I 6.20

1.57

9.38

.02

.56

100. 13

.01

100.12

E

8.20

4.77

14.90

33.69

.32

1.80

12.45

J 5.60

1.72

15.80

.42

99.67

.21

99.46

F

15.63

7.92

16.21

32.82

.25

2.62

f 7.82

1.55

6.33

8.33

.17

99.65

.09

99.56

G

6.2

5.9

18.2

34.8

.3

2.4

4.6

4.6

1.3

1.8

19.0

.10

.04

99.24

.05

99.2

H

U2.90

3.66

34.14

32.90

1. 00

5.00

* f . W

2.25

.25

100.00

.13

99.87

I

35.6

4.76

32.73

14.84

.26

2.17

4.84

\ 1 2

/ L2

.50

.38

.44

1.86

.08

99.66

.04

99.62

J

35.94

4.49

34.46

14.99

.31

3.04

3.55

.32

.55

1.12

.23

100.90

.12

100. 78

1 Reported as "clay and silica."

3 Reported as "Loss on ignition (carbonic acid, organic matter, etc.)."

8 Total includes 0.05 percent As, 0.05 percent Zn, 0.03 percent V.

A-C. Magnetite oolite in minette ores of Jurassic age of the Lorraine basin, France 

(Hoehne, 1955). Sample A from Angevillers; samples B and C from Amermont.

D. Magnetite ironstone of Jurassic age (Upper Lias, Dogger Seam), West Rosedale, 

Cleveland district, England. Quoted by Lamplugh and others (1920, p. 

60) as an average of many analyses of the Dogger, or Top, Seam. 

E. Magnetite-siderite ironstone, Couche Grise, of Aalenien (Jurassic) age, Lorraine, France. Mode: Quartz <1 percent, siderite 25.1 percent, magnetite 

21.6 percent, phosphate 3.8 percent, calcite 14.3 percent (Deudon, 1955, p. 

478). Analysis made in mineralogical laboratory, Facultes des Sciences de 

Toulouse.

F. Calcitic chamosite-magnetite-siderite ironstone of Dogger (Middle Jurassic) 

age. Analysis by C. Schmidt. Erzegg-Planplatte region, Switzerland 

(Deverin, 1945, p. 42). Specific gravity 3.24.

G. Siderite-magnetite-chamosite, Northampton sand ironstone, Middle Jurassic 

age. Easton Neston, England (Taylor, 1949, p. 60). Calculated mode: 

Sideritic carbonate 48.5 percent, magnetite 26.4 percent, chamosite 18.9 

percent, phosphate 4.0 percent (Taylor, 1949, p. 63). Analyst, C. O. Harvey, 

Geological Survey of Great Britain.

H. Oolitic magnetite ironstone of Cambrian age. Gareg-fawr mine, Carnarvonshire, Wales (Strahan and others, 1920, p. 24): analysis made by "Dr. Price 

of Newport."

I. Banded magnetite-quartz rock, Late Cambrian or Early Ordovician age, 

0rtvann mine, Dunderland, Norway (Bugge, 1948, table 1, borehole sample 

131/11). Rock contains 47 percent magnetite, 0.6 percent hematite. Analysis represents 2.5 m of core. Analyst not specified; analysis presumably 

made in laboratories of Rana Gruber A/S (Company).

J Banded magnetite-quartz rock, same locality as sample I (Bugee. 1948, table 

1, borehole 123). Rock contains 48 percent magnetite, 1.5 percent hematite. 

Analysis represents 9 m of core. Analyst not specified; analysis presumably 

made in laboratories of Rana Gruber A/S (Company).
CHEMISTRY OF THE IRON-RICH SEDIMENTARY ROCKS W21

magnetite-rich rocks are interlayered with quartz and 

are more like Precambrian iron-formation than they 

are like the normal minette type.

Except for the quartz-banded ores (analyses I and J), 

the rocks are not different chemically in any significant 

respect from the hematitic ironstones, other than in 

ferrous-ferric ratio.

MAGNETITE-RICH IRON-FORMATION OF PRECAMBRIAN

AGE

The magnetite-banded rocks, as represented by 

analyses A, B, D, E, F, G, and L in table 12, are one of 

the major types of Precambrian iron-formation. They 

consist of layers alternately quartz-rich and magnetiterich. Both chemically and mineralogically the magnetite f acies is more complex than the hematite f acies with 

which it commonly is associated. The rock generally 

contains appreciable quantities of siderite and an iron 

silicate (greenalite, minnesotaite, stilpnomelane, chlorite), reflected chemically in the significant content of 

CO2, MgO, and to a lesser degree, A12O3 . The rocks are 

notably lower in A12O3 , CaO, and P2O5 than magnetitebearing rocks of younger age (table 11).

Analyses H to K are of South African rocks from 

stratigraphically widely separated positions in the Precambrian. Of interest and importance is the occurrence 

of chamositic rocks (particularly analyses J and K), 

physically and chemically more closely allied to the 

post-Precambrian magnetite facies than to the more 

typical cherty rocks of the Precambrian. The age of 

the Pretoria Series of the Transvaal System, in which 

chamositic rocks occur, is believed to be about 2,000 

million years (Nicolaysen, 1962, p. 580, 582).

SILICATE FACIES

The silicate facies comprises those rocks in which the 

primary silicates chamosite, greenalite, and glauconite 

are dominant, plus those in which minnesotaite, ironrich chlorite, or stilpnomelane probably metamorphic 

in origin are major constituents.

CHAMOSITIC IRONSTONE

The chamositic rocks are one of the most characteristic facies of the post-Precambrian ironstones (table 13). 

In some districts they grade into or are interbedded 

with limonite (or hematite) oolite; in others they grade 

into or are interbedded with sideritic rocks.

The rocks typically are oolitic, but most do not 

exhibit chemical heterogeneity to the degree shown by

TABLE 12. Analyses of magnetite-rich ironstones of Precambrian age

Si02 

A12 03 -- 

FeO._ 

MnO__ 

MgO... .

CaO-... 

Na20

K2 0__ 

HaO+____ 

H2 0-_ ....... ... 

Ti02 _ __

P2 06 -

COi 

s

S03 -- - --

c

Less O

Total.. 

A

34.44

.85

30.54

22.06

.21

2.30

1.72

.00

.13

.44

.17

.02

.07

7.36

.01

.00

.04

100 36

.01

100.35

B

35.86

1.57

20.26

.16

1.74

.51

} .02

.60

.06

.04

.14

.60

.17

100. 29

C

2.56

6.20

21.54

26.57

.04

6.95

1.85

f .60

I 1.10

5.66

.53

.27

3.99

QQ Qfi

99.86

DI

51.52

.08

35.37

10.24

.20

.02

1.48

0

.060

1.06

inn n^i

100. 03

El

45.66

.28

19.16

21.28

2.73

1.04

1.54

0)

.085

7.54

.12

QQ AA

99.44

FI

39.50

.44

29.21

18.51

.12

2.00

2.71

0

.040

6.22

.129

8.017

4 QS QO

.06

98.84

GI

22.70

.31

22.07

23.20

1.06

3.88

4.49

0)

.014

21.18

.005

8.016

98.92

H

42.10

4.65

22.15

17.83

3.35

2.25

1.00

\ 7*

/ " 75

.15

.05

4.90

.10

*99.28

.05

99.23

I

50.90

6.25

20.00

14.40

.85

2.00

.85

1.30

.30

.05

1.10

.15

e 98. 15

.08

98.07

J

19.05

6.60

41.30

22.70

.25

1.25

1.25

f 5.50

I .65

.15

.20

.60

.25

99.75

.13

99.62

K

5.84

4.40

42.03

34.35

.90

.90

1.50

2.90

.28

.26

1.19

4.75

.08

99.38

.04

99.34

L

47.2

1.6

38.5

10.1

1.3

.8

2 .22

.007

99.7

99.7

1 Samples dried at 100° C. before analysis.

2 Calculated from 0.088 P. 

' "Organic C."

4 Given as 99.90 in original reference.

5 Given as 99.30 in original reference. 

« Given as 97.85 in original reference.

A. Banded magnetite iron-formation, Ironwood Iron-Formation, Gogebic district, 

Michigan (Huber, 1959, p. 100); Lucile N. Tarrant, U.S. Geological Survey, 

analyst. Calculated mode: Magnetite 44.3 percent, quartz 31.3 percent, 

sideritic carbonate 17.5 percent, minnesotaite 6.0 percent, excess constituents 

1.3 percent. Sample represents 11 feet of drill core.

B. Banded magnetite-quartz rock with minor chlorite, siderite, and cummingtonite. Saksagan (Krivoi Bog) Series, Ukraine, U.S.S.B. (Semenenko 

and others, 1956, p. 105); O. I. Dokhlenko, analyst.

C. Magnetite-stilpnomelane rock, with minor cummingtonite and carbonate, 

middle suite of Krivoi Hog Series. From northern part of Saksagan band, 

U.S.S.K. (Aleksandrov and Zmeenkova, 1958, p. 79); A. V. Zmeenkova, 

analyst.

D-E. Banded magnetite chert from the Lower Cherty division of Biwabik IronFormation, Mesabi district, Minnesota (Gruner, 1946, p. 58-59); analyses by 

Mines Experiment Station, University of Minnesota; W. E. Apuli, chief 

chemist. Analysis D is one of 5 given by Gruner of magnetite-rich rock cut 

by drill hole near Aurora; sample represents 30 feet of core. Analysis E 

is one of 6 given by Gruner for magnetite-rich rock cut by drill hole near 

Hibbing; sample represents 20 feet of core. Books mostly magnetite and 

quartz, with siderite and iron silicates (greenalite, minnesotaite, stilpnomelane) in lesser amounts. 

F-G. Magnetite chert member of Temiscamie Iron-Formation, Lake Albanel

777-130 65 4

district, Quebec, Canada (Quirke, 1961, p. 312; see also Quirke, Goldich, and 

Krueger, 1960). Each sample represents 58 feet of core from drill hole. 

Analysis of major elements by Cleveland-Cliffs Iron Co; C02 and C by 

Mines Experiment Station, University of Minnesota.

H. Magnetite-siderite slate, South Africa. From uppermost part of Pongola 

beds, Swaziland System (Wagner, 1928, p. 69); analyzed in the Government 

Chemical Laboratory, Johannesburg. Sample is composite of 37 taken 

across 40-foot bed in southeastern Transvaal. Keported to contain some 

chamosite. Specific gravity 3.41.

I. Shaly magnetite ironstone, same locality as H but stratigrapMcally 40 feet 

higher (Wagner, 1928, p. 69). Analysis is of a composite sample representing 

a 20-foot thickness. Analyzed in the Government Chemical Laboratory, 

Johannesburg.

J. Arenaceous oolitic magnetite-chamosite ironstone (Wagner, 1928, p. 85). 

From "Magnetic Quartzite Iron Horizon," Pretoria Series. Sample from 

core of hole drilled near Pretoria, S. Africa; H. G. Weall, analyst. Calculated mode (main constituents): quartz 11.2 percent, magnetite 35.2 percent, hematite 17.0 percent, chamosite 28.6 percent, calcite 1.4 percent 

(Wagner, 1928, p. 86).

K. Oolitic magnetite-chamosite-siderite ironstone (Wagner, 1938, p.92). From 

"Clayband Horizon," Pretoria Series. Sample from core of hole drilled 

near Pretoria, S. Africa. Calculated mode (main constituents): magnetite 

60.9 percent, chamosite 22.0 percent, siderite 12.5 percent, phosphate 0.6 

percent (Wagner, 1928, p. 93). Major elements determined in "laboratory 

of the Gutehoffnungshutte"; COj and HaO determined by Government 

Chemical Laboratory, Johannesburg.

L. Magnetite-quartz rock (Krishnan, 1952, p. 524), average of "large number of 

samples." From Kanjamalai deposit, Madras State, India.
W22 DATA OF GEOCHEMISTRY

TABLE 13. Analyses of chamositic ironstones 

[See also chamositic siderites]

SiO» ............

AhOs _______ _ _.

FejOj-. ..... __ . -

FeO . 

MnO . ... . ___ . __ . __

MgO. _______ - _____ . ....

CaO___ ... ... .... ___ ... _.

Na«O.. _ .

KjO ... ... ... 

HjO+ 

HiOTlOj. 

P»0« 

COj.. 

S 

BO» 

C 

Total _______ . .......

A

21.78

10.67

6.20

22.70

.08

3.61

12.25

.08

09

8.36

1.01

.53

1.62

8.45

1.47

.50

* 99. 96

.11

<99.85

B

16.24

8.09

5.10

15.12

.26

2.41

24.15

.32

.024

6.00

.51

.75

1.53

18.04

.59

.01

.63

« 99. 99

.30

' 99. 69

C

49.64

8.82

8.71

16.70

.23

3.19

2.10

5.09

(9

.91

5.15

.72

101. 36

.36

101. 00

D

42.76

7.82

12.47

16.29

.091

.61

1.44

.12

.63

7.23

5.66

.50

.30

3.37

2.043

.98

100.31

.02

100.29

E

13.4

7.4

8.5

31.9

2.5

6.1

4.9

3.6

2.8

17.4

.5

99.0

.3

98.7

F

13.70

9.04

15.15

36.47

2.26

6.48

6.31

(0

.62

1.75

8.95

100. 73

100.73

G

6.60

5.27

24.76

23.34

.97

19.60

\ 52

t va

4.27

(I) ,

.31

1.21

13.32

100. 17

100. 17

H

26.00

14.50

2.03

29.03

3.67

7.30

/.._. 

L

9.68

(')

.87

1.34

485

99.27

99 27

I

26.20

15.71

3.70

28.45

1.67

1.36

6.50

} 7.90

.10

3.93

3.00

«1.39

99.91

99.91

J

41.80

16.18

4,28

24.28

1.86

.43

1.00

8.44

.05

1.12

.00 '.56

100.00

100.00

K

16.22

7.65

2.99

35.38

3.12

1.84

4.01

f 2.61

\ .78

.61

4.91

16.64

96.76

96.76

L

15.60

6.96

2.24

18.25

.56

8.83

17.64

.01

.02

3.38

.14

.18

.80

24.99

.00

« 99. 96

.15

99.81

M

32.04

13.24

2.01

24.32

.13

2.78

8.26

.05

.23

5.60

.37

.70

.97

8.42

.00

? 99. 56

.19

99.37

1 Samples apparently dried before analysis.

* Reported as 82. 

»FeSs.

* Total includes 0.23 percent VjOs, 0.05 percent BjOa, 0.06 percent NiO. 

«Total includes 0.17 percent VjOs, 0.04 percent NiO, 0.004 percent CoO.

* Includes 0.36 percent F. 

' Includes 0.44 percent F.

A. Chamosite ironstone from the Lias (Lower Jurassic) of north Gottingen, Germany 

(Harder, 1951, p. 460-462). Rock contains about 72 percent chamosite, 16 percent calcite.

B. Calcitic chamosite ironstone, same locality and reference as above. H. Harder, 

analyst. Rock contains about 53 percent chamosite, 39 percent calcite.

C. Arenaceous chamosite ironstone of the " Couche Noire" of Middle Jurassic (Aalenian) age, Landres-Amermont basin, Lorraine, France (Coche and others, 1954). 

Analysis by laboratory of Ecole des Mines, Nancy. Rock contains about 38 

percent chamosite ("ehlorite")> 37 percent clastic quartz, 10 percent siderite, 

10 percent limonite.

D. Arenaceous green chamosite oolite of Early Jurassic (Lias) age, RSdingeberg, 

Sweden (Palmqvist, 1935, p. 69). Sven Palmqvist, analyst. SiOa value 

divided into "sand" 28.79, percent, SiOa (sol.)" 12.38percent, "SiO2" 1.59percent; 

AljOs value divided into "AljOs" 6.46 percent, "AUOa (clay)" 1.36 percent.

E. Chamosite oolite, Northampton sand ironstone, of Middle Jurassic (Inferior 

Oolite) age, (Taylor, 1949, p. 60). G. A. Sergeant, analyst, Geological Survey of 

Great Britain. From Lodge Pit, near Irchester, Northamptonshire, England. 

Rock contains about 36 percent chamosite, 10 percent goethite, remainder 

mostly sideritic carbonate.

the limonitic and hematitic oolitic ironstones. Nevertheless, they have a wide range in mineralogic and 

chemical makeup, attributable in part to the amount 

of clastic material mostly quartz, calcite, or dolomite and in part to extensive diagenetic modifications 

such as development of siderite and magnetite. The 

rocks are dominantly ferrous, but the chamosite ooliths 

themselves often contain concentric skins of oxidized 

material that represent interludes of higher Eh of the 

bottom environment during accumulation. As is to 

be expected, the AlgOs content is higher than in most 

other types of ironstone, and to a considerable degree 

the chamosite can be considered a product of sea-bottom 

reactions between ferrous iron in solution with detrital 

clay particles. The replacement of clastic material by 

chamosite indicates, however, that the process of formation was not simply that of clay diagenesis. In the 

Northampton sand ironstone the process of iron enrichment of clay to produce chamosite was locally reversed, 

with the production of kaolinite that partly retains the 

oolitic form of chamosite (Taylor, 1949, p. 32).

SIUCATE IRON-FORMATION OF PRECAMBRIAN AGE

Most of the analyses listed in table 14 are of rocks 

that have been metamorphosed to some degree. Of

F-H. Chamosite oolite, Chamosentze, Switzerland, of Middle Jurassic (Dogger) 

age (Deverin, 1945, p. 24). C. Schmidt, analyst. Average mode for 3 

analyses includes chamosite 40 percent, magnetite 14 percent, quartz 13 

percent, siderite 11 percent, calcite 10 percent.

I. Oolitic ironstone, quarry near Llangoed, Anglesey, Wales (Strahan and others, 

1920, p. 14; see also Pulfrey, 1933, for mineralogic descriptions). E. J. Morris 

and W. E. Williams, analysts. Ordovician. 

J. Oolitic ironstone, Bonw, Mynydd-y-Garn, Anglesey, Wales (same analysts as

samples F-H; Strahan and others, 1920, p. 15). Ordovician. 

K. Oolitic chamosite, Zone 4, Scotia bed, Wabana, Newfoundland (Hayes, 1915,

p. 58). A. O. Hayes, analyst. Ordovician. Specific gravity of rock 3.50. 

L. Oolitic chamosite, uppermost 6 inches of Westmoreland bed of Clinton Group 

(Silurian), Westmoreland, New York. Sample F 2639, collected by R. P. 

Sheldon; analysis by Paula M. Buschman, U.S. Geological Survey. Modal 

analysis given in Hunter, 1960, p. 104 (see footnote, p. W7) as follows: Hematite 

and masked chamosite 9.9 percent; chamosite 36.8 percent; calcite, dolomite, 

siderite 45.9 percent; pyrite 1 percent; quartz 6.0 percent; cellophane 0.4 

percent.

M. Oolitic chamosite, uppermost 6 Inches of Keefer Sandstone of Clinton (Silurian) 

age, Piato, Allegheny County, Maryland. Sample F 2642, collected by R. P. 

Sheldon; analysis by Paula M. Buschman, U.S. Geological Survey. Modal 

analysis given in Hunter, 1960, p. 104 (see footnote, p. W7), as follows: 

Chamosite 48.4 percent; Calcite, dolomite, siderite 22.8 percent; pyrite 0.2 

percent; quartz 11.6 percent; argillaceous matrix 17.0 percent.

the Precambrian rocks, only that from the Roper River 

(analysis H) can be considered to be essentially in 

unaltered form; those from the Mesabi district (analyses A-C) are weakly metamorphosed, with the partial 

conversion of greenalite to minnesotaite and stilpnomelane; that from the Gogebic district (analysis F) is 

slightly more metamorphosed, with complete loss of 

original greenalite. Grunerite- and garnet-bearing 

rocks, representing a higher degree of metamorphism, 

are arbitrarily excluded in the tabulations.

Most of the rocks consist of quartz (recrystallized 

chert) in layers alternating with silicate-rich layers that 

generally contain significant amounts of magnetite and 

siderite. An exception is represented by analyses D 

and E, in which quartz, chlorite, siderite, and magnetite 

occur as fine-grained intergrowths in a laminated rock. 

The rock, though rich in iron, does not resemble normal 

iron-formation, and the bulk chemistry can be matched 

by that of some of the younger chamositic ironstones.

Aside from analyses D and E, the Precambrian silicate 

rocks are strikingly different in chemical composition 

from the chamositic ironstones of younger age. Most 

notable is the much higher content of SiO2 (original 

chert) and much lower contents of A12O3 and P2O6.
CHEMISTRY OF THE IRON-RICH SEDIMENTARY ROCKS W23

Also included in the tabulation is the analysis of an 

unusual greenalite-chert rock of Ordovician age 

(analysis L).

GLAUCON1TIC ROCKS

Glauconite, (see table 15) though of widespread 

occurrence as a minor constituent of ironstones, rarely 

forms discrete deposits with ironstone associations. 

An exception is the Seend ironstone of England, represented by analysis I. Most of the larger glauconite 

deposits (greensands), such as those of New Jersey, 

have been studied as sources of potash rather than iron. 

Nevertheless, in the ironstone districts, glauconite as a 

disseminated mineral bears definite facies relation to 

other iron minerals. The oolitic hematite-chamosite ironstones of the Clinton Group, for example, are shown by 

Hunter (See footnote p. W7) to grade to the east into 

semicontinental hematitic sandstone and to the west 

into glauconite-bearing marine strata.

The compositions of the glauconitic rocks (table 15) 

have a wide range, in considerable part due to the variable proportions of clastic material, interstitial calcite, 

and secondary siderite. Though glauconite, like chamosite, probably in large part originates by reactions 

between solids and sea water, the actual accumulation 

into deposits is accomplished by transport and deposition of granules and pellets, along with more usual 

clastic components. The typical glauconite is dominantly ferric and depending upon its "maturity" 

with a substantial content of K2O (see table 5). The 

compositions of the Gulf Coast greensands (analyses 

E-H, table 15) are therefore unusual, in that the rocks 

are more ferrous than normal glauconitic rocks and 

have a very low content of K2O. In part the ferrous 

aspect is due to secondary siderite, but this can account 

only partially for the relatively low ferric-ferrous ratio. 

The rocks are also high in A12O3 . Evidently the pelletal 

material making up these greensands is far removed 

from the ordered mica structure of ideal glauconite; 

quite possibly it includes some chamosite. The association glauconite-chamosite is nob particularly common, 

but it has been described. Chillingar (1956) reviews 

several occurrences of glauconite and chamosite in the 

U.S.S.R. Of interest is the extremely low content of 

K2O (0.14 percent) of a chamosite-bearing glauconite 

of Mesozoic age (Chillingar, 1956, p. 495).

CARBONATE FACIES

Aside from the "blackband" and "clayband" siderites, 

which are discussed later, the rocks included in the 

carbonate facies are divided into those of Precambrian 

and post-Precambrian age. These groups are strikingly different in chemical composition and physical 

character, but they bear entirely comparable facies

TABLE 14. Analyses of silicate iron-formation, mostly Precambrian

SiOs--. 

AlsOa... . 

FeO __________ . ____________

MnO 

MgO_ . 

CaO _______________________

Na2 0-._ 

K2O.__.. . 

n3o+. .................................... .

^o-. .................................... .

TiO2 

PiOi.. ......................................

COa 

B. ..........................................

C.. .........................................

Total _________________ . ...

A

60.96

1.09

6.01

30.37

.00

5.26

.04

.00

.00

6.41

.75

.00

.00

Tr

.21

100.10

100. 10

B

42.48

.53

6.63

33.76

4.29

4.80 (2)

7.44

98.93

98.93

C

65.42

.08

4.19

23.63

2.45

4.16

«

Tr

99.93

99.93

D

61.18

11.95

8.09

12.16

2.71

2.42

1.12

2.12

1.86

1.19

.07

.61

.54

3.70

99.61

99.61

E

48.11

3.27

13.62

16.69

3.27

2,91

.80

.24

2.32

1.74

.44

.52

.44

5.62

99.99

99.99

F

29.35

.70

4.41

39.61

1.02

3.81 9 in

.00

.00

2.79

.06

.01

.14

16.37

.06

.08

100. 41

.03

100. 38

G

38.51

2.70

13.57

21.47

1.81

3.53

3.55

.01

.09

.144

12.70

.005

.027

98.12

98.12

H

30.26

2.26

16.47

37.00

.78

2.09

Tr

.16

.14

8.73

2.15

.03

.01

Tr

100.08

100.08

I

62.18

3.08

18.30

16.68

4.36

2.90

\ B8

{ '*

} >.94

.28

(')

3.32

99.62

99.62

J

38.85

2.23

13.20

26.58

.67

2.02

2.09

t - 11

i .11

| .59

.15

.23

13.52

.37

* 100. 87

.19

100. 68

K

45.10

2.16

17.41

20.83

.47

1.81

2.66

\ 12 / - 12

.67

.10

.18

8.52

.59

» 100. 85

.28

100. 57

L

71.08

.55

.78

18.53

.00

.18

Tr i

i

} 6.40

.13

.44

98.09

98.09

iLoss on ignition, presumably includes COa.

2 Samples dried at 100° C. before analysis.

»SOa.

«Includes 025 percent SOi. Total given as 100.69 in origina reference apparently 

corrected O for S.

«Includes 0.23 percent SOi. Total given as 100.56 in original reference apparently 

corrected O for S.

A. Greenalite rock, Biwabik Iron-Formation, Mesabi district, Minnesota (Leith, 

1903, p. 108). Analysis by George Steiger, U.S. Geological Survey.

B. "Taconite consisting of about 8.6 percent quartz, 19 percent carbonate, and 

71 percent minnesotaite and greenalite" (Gruner, 1946, pp. 56-57). From 

"Lower Slaty division," Biwabik Iron-Formation, Mesabi district, Minnesota. Analysis by Mines Experiment Station, University of Minnesota; 

W. E. Apuli, chief chemist.

C. "Taconite consisting of about 28 percent quartz and 72 percent minnesotaite" 

(Gruner, 1956, pp. 66-67). From "Lower Cherty division," Biwabik IronFormation, Mesabi district, Minnesota. Analysis by Mines Experiment 

Station, University of Minnesota, W. E. Apuli, chief chemist. 

D-E. Laminated chlorite-siderite-magnetite-quartz rock, Stambaugh Formation, 

Iron River district, Michigan (James, 1954, p. 271). Analyses by Leonard 

Shapiro and W. W. Brannock, U.S. Geological Survey.

F. Sideritic silicate iron-formation, Gogebic district, Michigan (Huber, 1959,.p

91). Calculated mode: minnesotaite 46.3 percent sideritic carbonate 40.8

percent, magnetite 6.4 percent, quartz 5.8 percent, excess constituents 1.0

percent. Represents 14 feet of drill core. Lucile N. Tarrant, analyst, U.S.

Geological Survey. 

G. "Upper argillite" member, Temiscamie Iron-Formation, Lake Albanel range,

Quebec (Quirke, 1961, p. 306; also Quirke, Goldich, and Krueger, 1960).

Main elements determined in laboratories of Cleveland-Cliffs Iron Co.,

Owen Hassett, chief chemist; C and COa by Mines Experiment Station,

University of Minnesota. 

H. Magnetite-bearing oolitic greenalite rock, Roper River, Northern Territory,

Australia (Cochrane and Edwards, 1960, p. 17; also Edwards, 1958). F. J. J.

Sinnott, analyst. 

I. Stilpnomelane-actinolite-magnetite-quartz rock, Krivoi Rog Series (Semenenko and others, 1956, p. 374). Verkhtsevskovo region, U.S.S.R. Analyzed

in laboratories of Ukrainian Geologic Administration. 

J-K. Thuringite-magnetite-siderite-quartz rocks, Krivoi Rog Series (Semenenko

and others, 1956, p. 387). Verkhtsevskovo region, U.S.S.R. Analyzed in

laboratories of Ukrainian Geologic Administration. 

L. Black cherty rock with granules of greenalite, Ordovician in age (Kennedy,

1936, p. 435). From near Glenluce, Wigtownshire, Scotland. W. J. Skilling,

analyst.
W24 DATA OF GEOCHEMISTRY

TABLE 15. Analyses of glauconitic rocks (greensand) 

[Values in parentheses reported separately; not Included in total]

SiOi _- _______ 

AliOS --. 

FejOs - - 

FeO 

MnO--_ - -- - --- -- - --- - 

MgO

CaO 

NajO 

KjO--... -- ----- -- - - 

HjO-K... - -- -- - . 

HjO-....- - - - - -- 

TiOj.. 

PsOs 

COj . 

FeSs

Total--.---.--- ..

A

R9 Qfi

3.52

8.91

1.52

1.90

2.10

.82

3.56

} 7.68

1.05

1.00

( 911

100.96

B

50.74

1.93

17.36

3.34

3.76

2.86

1.53

6.68

9.08

1.79

.88

(.16)

99.95

C

51.83

6.23

17.15

2.93

3.66

.52

.76

6.60

9.98

.31

.36

(.24)

» 100. 33

D

50.32

7.53

18.38

3.02

3.82

.65

.22

7.88

8.58

.34

.15

(.07)

100.89

E

29.40

7.46

5.60

14.54

2.88

20.00

Tr

3.41

12.20

Tr

14.80

100.29

F

32.10

15.54

12.71

20.39

5.20

1.98

2.37

3.62

15.20

Tr

4 100. 09

G

28.67

16.80

8.41

20.74

.11

1.55

.45

.03

.70

11.76

.30

.25

10.03

(2)

99.80

H

27.21

18.87

9.32

18.55

.12

1.49

.38

.11

.43

13.12

.42

.31

9.85

(2)

100.18

I

21.61

5.82

17.48

25.69

.52

.59

2.88

.14

.83

1" 3.05

\ 2.59

.25

.96

16.68

.50

.79

100. 38

1 Includes organic matter.

2 Reported as "present."

3 Given as 100.42 in original reference. 

* Total included 0.98 percent SO8 .

A-D. Greensand from Eocene Manasquan Formation (A) and Paleocene Hornerstown Sand, New Jersey (Mansfield, 1922, p. 124). R. K. Bailey, analyst; 

organic matter by E. T. Erickson (reported separately on p. 130).

E. Greensand,Texas (Schock, 1918, p. 170). Eocene. Analyst's name not given.

F. Greensand marl of Eocene age, Texas (Schock, 1918, p. 170; see also Baker,

1935) L. E. Magnenat, analyst.

G-H. Greensand, Weches Greensand Member of Mount Selman Formation, Texas; 

of Eocene age (Eckel, E. B., 1938, p. 25). J. J. Fahey, analyst.

I. Glauconite-limonite oolite from Seend ironstone, Wiltshire, England (Hallimond, 1925, p. 89). Lower Cretaceous. Analyzed in laboratories of Geological Survey of Great Britain.

relations to silicate and oxide rocks in their respective 

associations.

SEDERITIC ROCKS OF POST-PRECAMBRIAN AGE

The range of physical and chemical characters of 

sideritic ironstone is exceptionally well displayed in the 

Northampton Sand ironstone, as described by Taylor 

(1949, especially pp. 23-29, 33-35) and represented in 

part by analyses B-G, table 16. In the more common 

varieties of the Northampton Sand, the siderite may 

form a groundmass for chamosite or limonite oolite, 

typically with considerable diagenetic replacement of 

the ooliths; it may occur in fine-grained sideritic mudstone with sandy and argillaceous material; it may occur in limestone as matrix and partial replacements of 

shell fragments and calcite ooliths, or replacements of 

matrix calcite; or it may occur as "sphaerosiderite" 

rounded masses and nodules in chamositic or kaolinitic 

ironstone. Of these several varieties, probably only 

sideritic mudstone represents a primary sediment. 

This rock generally is fine grained and massive. In 

the other varieties the bulk of the siderite is diagenetic, 

as shown by textural relations to other rock components; 

it is commonly more coarsely grained; and it has greater 

range in relative molecular proportions of FeO, MgO, 

and CaO.

As with other ironstone types, the sideritic rocks 

have a considerable spread in chemical composition 

only in part reflected by the selected analyses in table 

16 as a result of gradations into chamositic and 

limonitic facies and into normal mudstone, sandstone, 

limestone, and dolomite. Granules of cellophane and 

phosphatized organic debris occur in the varieties 

containing ooliths of chamosite or limonite; the content

of P2O5 ranges from low « 0.2 percent) to high (> 2 

percent), approximately in direct relation to the oolitic 

component.

SIDERITIC IRON-FORMATION OF PRECAMBRIAN AGE

The typical sideritic iron-formation (see table 17) 

is a thinly bedded or laminated rock made up almost 

wholly of alternating layers of dominantly chert and 

dominantly iron-rich carbonate, in roughly equal proportions by volume. It may grade into or be interbedded with pyritic facies, on the one hand, as in the 

Iron River district of Michigan (James, 1951) and the 

Michipicoten area of Ontario (Goodwin, 1962), and 

into silicate or silicate-magnetite facies, on the other, 

as in the Mesabi district (Gruner, 1946; White, 1954), 

the Gogebic district of Wisconsin and Michigan (Huber, 

1959), the Gunflint district of Ontario (Goodwin, 1956), 

and the Labrador trough (Harrison, 1953; Gas til and 

Knowles, 1960). The transitions into silicate or silicatemagnetite are well illustrated by analyses D to G in 

table 17 and analysis F in table 14, and accompanying 

modes of rock from the Gogebic district, in which the 

silicate is minnesotaite.

Chemically, the greatest range is in the SiO2 :(FeO + 

CO2) relation, reflecting the variable proportions of 

chert and siderite. As in most Precambrian ironformation, the alkali content is very low or actually 

zero. In rocks containing carbonaceous material or 

associated with pyritic facies the carbonate is notably 

higher in Mn content (analyses A-C, M-N) and the 

P2O5 content is distinctly higher than in rocks with 

silicate association. Sideritic iron-formation from the 

Cuyuna district, Minnesota, contains as much as 12.9 

percent MnO (Schmidt, 1963, p. 21).
CHEMISTRY OF THE IRON-RICH SEDIMENTARY ROCKS W25

TABLE 16. Analyses of siderite rocks of post-Precambrian age

SiOa. 

Ala03 

FeaOs-. ~ -

FeO... ._.. . ...

MnO._ ..... ....

MgO._. ._ 

CaO.... ..... ...

NaaO .

EjO .. 

H20+..... .... ...

HjO- . 

TiOa. - 

PiOj.. 

COi. 

s

FeSa-- -

C __ ...... .....

Total... 

A

7.56

4.10

1.83

43.86

.13

3.92

2.90

.11

1.13

.81

.28

.18

.11

32.84

799.82

03

' 99. 79

B

9.20

8.95

2.64

39.53

.05

2.06

6.73

4.32

2.70

23.01

036

99.23

.02

99.21

C

8.03

8.86

23.76

27.58

.17

3.13

4.65

3.95

1.84

17.35

.014

99.33

.01

99.32

D

4.42

5.40

45.14

.18

3.69

6.03

.108

33.06

.111

99.48

.06

99.42

E

4.88

3.38

1.20

49.32

.37

1.51

3.46

2.33

filft

32.70

QQ SQ

.06

99.83

F

12.73

9.10

7.12

32.62

.16

4 V7

8.70

44

2

10

21.78

.216

QQ 49

.11

QQ 11

G

2 Q

1.3

1.4

23.4

2 A

9S 7

Q

.2

Q

38.8

.4

100.1

.2

QQ Q

H

8

C1

1.77

36 91

.42

3.75

K CA

.05

03

4.05

10.00

.36 1 30

9ft 7ft

.05

.27

8 99 96

.03

8 99 93

I

1Q e

1ft 9

q A

00 K

.7

3.5

5 A

2 90

8 Oft

.3

1.0 19 0

100.0

.1

99 9

J

qo 71

5.54

2 CO

oe 17

.46

2.30

3 97

.72

i ftfl

1.62

s 1.33

QQ *V7

99.57

K

7.75

8.35

1.71

35.61

.37

4.03

10.53

\ 18 ; - 18

4.15

(2)

.18

25.25

.102

6.36

99.85

.05

99.80

Li

12.70

4.65

16.83

27.93

.76

4.34

5 QS /. \

4.73

0)

1.53

20.80

.11

9100.36

.06

9 100.30

MI

18.60

5.31

21.47

23.06

.76

3.26

4.47

5.77

G)

.60

16.30

.21

1° 99. 81

.11

10 99. 70

N

9.09

7.11

7.34

44.90

.20

.53

2.37

.01

.34

3.73

.80

2.44

.81

19.78

4.013

.28

99.74

99.74

O

8.20

5.84

3.25

42.72

.36

.84

3.94

.05

.51

1.78

1.43

.39

.21

29.41

4.19

.62

99.74

.10

99.64

P

3.77

4.57

43.23

.84

.33

4.97

.12

.70

2.11

.77

.24

.39

29.91 4.16

.61

100.08

.08

100. 00

Q

13.5

.7

1.8

43.8

1.5

1.7

3.1

1 9

J ' 9

.03

2.45

29.6

11 99. 08

"99.1

~R

18.63

5.90

42.10

.61

1.58

QQ

.58

.28

.33

324.31

.44

96.97

.22

96.75

1 Sample dried before analysis. Moisture content ("hydratationgrad") of L 

reported as 2.49 percent; that of M as 2.38 percent.

2 Sample dried at 212°F before analysis. Moisture loss reported as 6.48 percent. 

8 Reported as loss on ignition in analysis of acid-soluble fraction.

4 Reported as 82.

5 "Coaly matter."

9 "Carbonaceous matter."

7 Contains 0.06 percent F.

8 Total includes 0.03 percent CraOs, 0.08 "V. oxide," 0.02 As. 

» Total does not include 0.60 reported as insoluble. 

i° Total does not include 0.80 reported as insoluble. 

» Contains 0.0005 percent VaO5 .

A. Siderite bed in upper 6 feet of Brassfleld Dolomite of Silurian age. Rose Run 

pits, Owingsville, Bath County, Ky. Analysis F2641 by Paula M. Buschman, U.S. Geol. Survey, of sample collected by R. P. Sheldon. Subtotal 

contains 0.06 percent F. Analysis also shows zero 80s.

B-G. Sideritic rocks from the Northampton Sand ironstone, Middle Jurassic age 

(Taylor, 1949. pp. 60-61). B, described as "ooliths of chamosite in siderite 

matrix"; C, ''Ooliths of limonite and subordinate chamosite in siderite 

matrix"; D, "fine-grained siderite mudstone": E, "fine-grained siderite mudstone [with] scattered chamosite ooliths"; F, siderite mudstone with chamositic cement and local calcareous debris;" G, "siderite granules scattered 

through calcite groundmass" (Taylor, 1949, p. 58). Calculated mineral 

compositions given in original reference. Analyses B-F by Stewarts and 

Lloyds, Ltd.; Analysis G by G. A. Sergeant, Geological Survey of Great 

Britain.

H. Cleveland ironstone (Middle Jurassic), Eston, England (Hallimond, 1925, 

p. 51). Main seam. Rock contains about equal amounts of siderite and 

chamosite (34 percent each). J. E. Stead, analyst.

I. Cleveland ironstone (Middle Jurassic), Cleveland, England (Hallimond, 1925, 

p. 51). Main seam. Rock contains approximately equal amounts of siderite 

and chamosite (about 30 percent each). J. E. Stead, analyst.

J. Cleveland ironstone, "Pecten Seam" (Whitehead and others, 1952, p. 61; 

analysis quoted from older report). From Glaisdale Mine, Yorkshire, 

England.

SULFIDE FACIES

Although sulfide, principally pyrite, is a constituent 

of many or most iron-rich sedimentary rocks, rarely 

does it assume major proportions. As a facies, the 

sulfide rocks (see table 16) are distinctly subordinate 

to those of the oxide, carbonate, and silicate, and the 

defining mineral is almost wholly of diagenetic origin. 

With a few exceptions, such as the previously noted 

thin pyritic beds of the Cleveland district of England 

and at Wabana, Newfoundland, the heavily pyritic 

rocks are black shales or their equivalents, with a large 

content of organic matter or carbon. The absence of 

direct precipitates, the scarcity of rocks of this facies, 

and the typical association with organic shales are all 

to some degree reflections of the extraordinarily slow 

rate at which sulfate in natural solutions is reduced, 

even in the thermodynamically stable realms of sulfide, except when catalyzed by biochemical agents. 

Viewed differently, it may also be said that the presence 

of organic matter, which permits the development of

K. Cleveland ironstone, "Two-foot Seam" (Whitehead and others, 1952, pp. 59- 

60). Analysis by J. and H. S. Pattison, Newcastle upon Tyne.

L. Minette ore from Luxemburg, Jurassic (Aalenian) in age. From upper part 

of "Grunes" horizon, Lager IV (Lucius, table B). Quartz content reported 

separately as 1.14 percent, included in total SiOa. Analysis by laboratory 

of Konzern, A.R.B.E.D.

M. Minette ore from Luxemburg, Jurassic (Aalenian) in age. From near base of 

"Schwarzes" horizon, Lager III (Lucius, table B). Quartz content reported 

separately as 9.48 percent, included in total SiO2. Analysis by laboratory 

of Konzern, A.R.B.E.D.

N. Ilmenite-bearing gray oolite, chamositic, from Kurremolla, southern Sweden 

(Palmqvist, 1935, p. 53). Jurassic (Lias) age. Analysis by Sven Palmqvist. 

SiOa is total of values for "sand" 3.10 percent, "SiOa (sol.)" 5.70 percent, 

"SiOa" 0.29 percent. AljOs is total of values for "AljOs" 6.86 percent, and 

"AlsOs (clay)" 0.25 percent.

O. Greenish-gray, dense siderite rock, locality as for N (Palmqvist, 1935, p. 58). 

Analysis by Sven Palmqvist. SiOj is total of values for "sand" 1.41 percent, SiO2 (sol.) 1.71 percent, and SiOa 5.08 percent. AlzOs is total of 

values of "AlaOs" 1.49 percent, and "AkOa (clay)" 4.35 percent.

P. Light-gray, dense siderite rock, locality as for N (Palmqvist. 1935, p. 89.) Analysis by Sven Palmqvist. SiOz is total of values for "sand" 0.15 percent, 

"SiOa (sol.)" 3.03 percent, and "SiOj" 4.18 percent. AljOa is total of values 

for "AlaOj" 0.25 percent, and "AlaOs (clay) ' 3.52 percent.

Q. Siderite rock ("Weisseisenerzen"), Auerback, Germany (Harder, 1955, p. 516); 

Analysis by H. Harder. Cretaceous. Contains 0.0005 percent VaOs.

R. Siderite rock from western Bashkiria, U.S.S.R., of Devonian age (Florensky, 

V. P., and Balshina, B. V., 1948, p. 690; sample 702/4). Analyst, B. V. 

Balshina. Associated with chamositic ironstone. Analysis is total of two 

parts, acid-soluble, and acid-insoluble (26.36 percent), given in original 

reference. All T102, AlaO3 , and FeaOs is in "acid-insoluble" fraction, as is 

all but 0.39 percent of the SiOa. Calculated mode as follows (ibid., p. 691): 

detrital material 26.36 percent, siderite 67.27 percent, calcite 0.43 percent, 

magnesite 2.19 percent, pyrite 0.82 percent, apatite 0.78 percent, other 2.58 

percent.

anaerobic sulfate-reducing bacteria, commonly is necessary to create the requisite low Eh for sulfide formation 

in sedimentary environments.

In table 18 are tabulated chemical analyses of a 

variety of sulfide-rich sedimentary rocks. The only 

complete analysis available (analysis A) is of a 50- 

foot bed of graphitic pyritic slate, the Wauseca Pyritic 

Member of the Dunn Creek Slate, which underlies the 

sideritic Riverton Iron-Formation in the Iron River 

district of Michigan (James; 1951, 1958). The pyrite 

occurs mostly in separated grains of about 3 microns 

diameter, and most show crystal outlines. The content of pyrite is nearly constant over a known strike 

length of about 20 miles. The fine-grained matrix is 

black with scattered fine flakes of mica and particles of 

quartz. Similar concentrations of pyrite in slate are 

known elsewhere, most notably at Mount Isa, Australia 

(Love and Zimmerman, 1961), and other localities in 

Australia (Skinner, 1958; Baker, 1960); lesser but still 

significant concentrations occur in units such as the
W26 DATA OP GEOCHEMISTRY

TABLE 17. Analyses of sideritic iron-formation, Precambrian

SiOa _______ -

AljOs..............

FeO. _____ . _

MnO __ ..

MgO_.-.__..._...

CaO...-..-_._ 

NaaO...- .....

KjO..............

HsO+_... .....

HjO-... __ .....

Ti02._ ...........

P2 05 .... 

C03 ..............

S.................

FeS... ...........

C-._._-.__-.._.__.

Subtotal _ 

Less O ...

Total... .

A

24.25

1.71

.71

35.22

2.11

3.16

1.78

.04

.20

.00

.21

.00

.91

27.60

1.96

99.86

99.86

B

18.11

.18

.34

40.68

2.56

3.59

1.31

.06

.04

.05

.09

Tr

.47

.06

1.41

99.47 

.03

QQ dd

C

99 Q7

1.08

3

KQ

33.17

6.77

2.02

1 dS

.06

.10

.00

.17

.10

.62

26.50

2.02

100.65

100.65

D

39 26

2.88

.63

24.94

1.23

d ff>

4.62

.00

.00

1.23

.11

.07

.11

20.46

.04

.07

100.27 

.02

100.25

E

40.09

2

00

Q Qfi

25.84

1.25

2 79

.03

.40

.56

.23

10

14.38

.01

.05

6 100. 26 

.01

5 100. 25

F

on 07

2.46

1.33

3

KO

.62

.00

.00

1 69

28

.27

.09

on Od

.09

d>;

100.29 

.05

100.24

G

°.fi fi9

.41

.46

34.50

Q9

4.41

1.45

.00

00

.02

fw

.02

.10

27.03

.07

flfi

100.11 

fid

100.07

H

1.30

2 ^1

OQ 77

90

1 QQ

fifi

} .09

.51

.10

.03

9ft 9H

100. 22

100 22

I

46.46

.24

64

9A 9Q

.21

3 in

1 Q7

{:::;:,::

.07

Tr

1°.

19.96

».ll

100. 22

100. 22

J

45.4

i ft

21.1

1.7

1 Q

1.1

.05

.07

\ t* OUW

.03

.41

1 fi "7

99.16

QQ 9

K

48.10

.47

ft 7Q

99 °.ft

9 Ql

.74

f 1.80

1 (2)

087

1 K Q9

.40

98.98

QQ QQ

L

27.439°.

1 fid

Ort oo

.77

5.04

6 * 64

OQ f\O

.016

100.08

100.08

M

30.15

.40

O1 *M

. 9 KQ

4.77

1 9*

(2)

.02

.665

24.65

101.40

101.40

N

1O Ql

3 9Q

OQ fiO

1 7°.

5

«0

4.34

.94

.45

1.30

.10

.09

9<?

97 nfi

<8.43

99.84

99 84

O

QQ CO

^ 97

4 90

28.07

.04

.47 1 79

.39

.12

Ql

1.76

.03

19 02

99.25

QQ 9*

p

68.22

dS

2.40

20.90

.01

44

I

qo

.27

.04

.50

2.26

.02

13.00

99.87

QQ ft"7

»Reported as MtijOj. 

' Sample dried at 100° C. before analysis. 

»Given as FeSs.

4 Reported as 5.08 percent Fe, 3.35 percent S, with text notation that sulflde is 

mainly pyrrhotite (8.31 percent) with minor pyrite (0.12 percent). 

«Total contains 0.01 percent VjOj.

A. Banded chert-carbonate rock, Riverton Iron-Formation, Iron River district, 

Michigan (James, 1951, p. 257); analyst, Leonard Shapiro, U.S. Geol. Survey. 

Sample represents 3 feet of drill core.

B-C. Carbonate-rich layers in Riverton Iron-Formation, Iron River district, Michigan, (James, 1951, p. 257). Analysis B by Leonard Shapiro; analysis C by 

Charlotte Warshaw, U.S. Geol. Survey.

D-G. Banded chert-carbonate from the Ironwood Iron-Formation, Gogebic district, 

Wisconsin-Michigan (Huber, 1959, p. 91). Analyses D and G, by Lucile 

N. Tarrant, analyses E and F by Lucille M. Kehl, U.S. Geol. Survey. 

Analyses D, E, F, and G represent, respectively, 17, 12,14, and 12 feet of drill 

core. Calculated modes in percent, as follows:

D

49.6

31.8

14.5

.9

3.4

E

35.9

34.7

10.2

14.4

5.0

F

52.4

29.5

6.5

6.9

5.0

G

67.2

29.7

1.7

.7

.7

H. Carbonate iron-formation, Negaunee Iron-Formation, Marquette district, Michigan (Van Hise and Bayley, 1897, p. 337). Analyses given separately for acidsoluble and acid-insoluble fractions. George Steiger, analyst.

I. Carbonate iron-formation, Gunflint Iron-Formation. From north side Gunflint 

Lake, Gunflint district, Ontario (Irving and Van Hise, 1892, p. 192; see also 

Goodwin, 1956). T. M. Chatard, analyst.

J. Chert-siderite rock, Welch mine, Florence County, Wis. Sample 150004, collected by C. E. Dutton; analysis by P. L. D. Elmore, S. D. Botts, M. D. 

Mack, U.S. Geol. Survey, using "rapid analysis" methods described in U.S. 

Geol. Survey Bull. 1036-C.

K. Siderite-rich bed in "Lower Slaty division", Biwabik Iron-Formation, Mesabi 

district near Hibbing, Minn. (Gruner, 1946, p. 59). Sample represents 15 feet 

of drill core. Analysis by Mines Experiment Station, University of Minnesota; W. E. Apuli, Chief Chemist.

L. Upper sideritic chert member, Temiscamie Iron-Formation, Lake Albanel range, 

Quebec (Quirke, 1961, p. 308). Sample represents 10 feet of drill core. Major 

elements determined in laboratory of Cleveland-Cliffs Iron Co.; organic O 

and COj by Mines Experiment Station, Univ. of Minnesota.

M. Siliceous iron carbonate rock from the Kennedy mine, Cuyuna district, Minnesota (Harder and Johnston, 1918, p. 120-121). Analyst: J. H. McCarthy, 

Mines Experiment Station, University of Minnesota.

N. Lowermost member of iron-formation at Helen mine, Michipicoten district, 

Ontario (Collins, Quirke, and Thomson, 1926, p. 69; see also Goodwin, 1962).

O. Quartz-siderite rock, Krivoi Rog Series, Ukraine, U.S.S.R. (Semenenko and 

others, 1956, p. 147); S. A. Panchenko, analyst.

P. Quartz-rich siderite iron-formation, Krivoi Rog Series, Ukraine, U.S.S.R. 

(Semenenko and others, 1956, p. 149); analyses by laboratories of Ukraine 

Geologic Administration.

Chattanooga Shale of the United States (about 11 

percent, according to Bates and Strahl, 1957), the Upper 

Cambrian "alum shale" of Sweden (about 12 percent 

in the Peltura zone, written communication from V. E. 

McKelvey), and the Kupferschiefer of Germany and 

its equivalent, the Marl Slate of England. The 

pyritic deposit of Meggen, Germany, is thought by 

some to be of sedimentary origin (Lindgren, 1933, p. 

269), and by others to be epigenetic; Ehrenberg, 

Pilger, and Schroder (1954) conclude that it formed as 

a result of submarine exudation of magmatically 

derived fluids that is, it is of "exhalative-sedimentary" 

origin. In several of these units notably the Mount 

Isa rock and the Kupferschiefer the pyrite is accompanied by a variety of other sulfides.

Analyses G to H, table 18 are of a Precambrian 

pyritic slate in Minnesota that has been metamorphosed to yield some pyrrhotite a hydrothermal 

origin for the sulfides, as proposed by Thiel (1924), 

seems very unlikely. Analysis F represents a thick 

unit of pyritic rock as much as 120 feet thick, with 

associated pyrrhotite, siderite, magnetite, and quartz 

of the Michipicoten district of Ontario; according to

Goodwin (1962) the rock is the product of sedimentation 

of materials derived from submarine hot spring and 

fumarolic activity that is, it is of the "exhalativesedimentary" type. A similar origin is suggested for 

pyrrhotite-pyrite bodies at Samreid Lake, Ontario 

(Friedman, 1959).

The occurrence of sulfide as diagenetic replacements 

in limestone is well known, particularly because of the 

spectacular preservation of fossils converted entirely 

to pyrite. In a few places the pyritic replacements 

assume major proportions as rock constituents; analyzed 

samples of a 4-foot bed in the Greenhorn Limestone of 

the Black Hills, for example, contain as much as 25.2 

percent pyrite (Rubey, 1930, p. 8).

BLACKBAND AND CLATBAND SIDERITE

The so-called blackband and clayband (or clayironstone) siderites (table 19) occur in clays and shales 

as thin layers rarely more than a foot or so thick, 

or as disconnected lenses and nodules. They consist 

of fine-grained siderite for the most part, with variable 

amounts of clastic material sand and clay and 

organic matter. Spherulitic structure is common.
CHEMISTRY OF THE IRON-RICH SEDIMENTARY ROCKS W27

TABLE 18. Analyses of sulfide-rich rocks

[Values given in percent] 

Sample A. Complete analysis

SiOi.. . . 

AhOa 

FeO_ ... .... ..

MnO... 

MgO -.... -

CaO . - 

36.67

6.90

2 OK

.002

.65

.13

TManf)

KjO - -

HjO+ -

HsOTiOi. ..

Pa05 

Vj05 

0.26

1.81

1.25

.55

.39

.20

.15

FeSi.... 

SO3 . ___ . _ -

C._.. 

Total.. __

38.70

2.60

>7.60

100.21

Samples B-H. Partial analyses

SiOj __ ... _ .....

AliOs 

Fe- .... 

Mn-_ ..................

MgO. _ ........ ......

OaO.. ..-........ ...

PiOl.- ..--.-. -..-

P............. ... ...

s

SO»_ . 

CuO... ...... ..........

PbO. ...............

Ni, Co.... ....... ... ...

HiO. . _.

B

9 01

35.18

.54

.35

34.46

0

29.00

25.00

.015

14(1

.11

D

13.20

28.60

2.80

.52

24.58

E

31.10

25.70

F

4.69

.56

42.1

1.0

1.90

3.87

32.6

G

42.11

8.72

18.88

.75

.20

.19

.063

14.8

16.24

H

36.57

5.28

27.84

.16

1.69

1.70

.119

15.6

10.96

1 Includes organic matter.

A. Pyritic graphitic slate, Iron Eiver district, Michigan. Precambrian (James,

1951). Charlotte M. Warshaw, analyst. 

B. Oolitic pyrite, Wabana, Newfoundland (Hayes, 1915, p. 49). Ordovician.

A. V. Seaborn, analyst. 

O. "Sulphur band" of Cleveland ironstone, Cleveland district, England (Hallimond. 1925, p. 54). Middle Jurassic. J. E. Stead, analyst.

D-E. "Sulphur band" of Cleveland ironstone (Lamplugh, Wedd, and Pringle, 

1920, p. 53). Analysis D by A. A. Street, analysis E by Eidsdale and Co., 

Middlesbrough.

F. Pyritic member of Precambrian iron-formation of Michipicoten district, 

Goodreau A deposit, Ontario (Goodwin, 1962, p. 577). J. H. Dann, analyst. 

G-H. Sulflde-bearing graphitic slate (Precambrian), Aitkin County, Minn. (Pennington and Davis, 1953, p. 9, 14). Sulfldes are pyrite, pryrrhotite, and 

marcasite. Sample G represents 66 feet of drill core; sample H represents 70 

feet. Analyses by Lerch Bros., Orosby, Minn.

The typical occurrence is in rocks associated with 

coal beds, notably those of Carboniferous or Permian 

age. They are abundant in the Appalachian coal 

field (see, for example, Stout, 1944; Singewald, 1911), 

and they are reported to occur at 75 horizons in the 

lower coal measures of Wales (Tyler, 1950, p. 518). 

In the U.S.S.R., in the foreland of the Urals in the general 

vicinity of Perm, siderite forms irregular and lenticular 

beds as much as several meters thick over a region 

of thousands of square miles (Belousov, 1933; Miropolskaya, 1949).

The rocks tend to be higher in FeO relative to MnO, 

CaO, and MgO than the marine siderite facies. The 

FeCO3 content of the carbonate commonly is 90 percent or more. The calculated molecular composition 

of siderite from the coal measures of the Lvov basin of 

the U.S.S.R., for example, in molecular percent is 

95.07 percent FeCO3 , 2.15 percent MnCO3 , and 2.77 

percent CaCO3 (Vartanova, Artemenko, and Galkina, 

1950, p. 302). The blackband ores are significantly 

higher in C or organic content than those of the clayband variety and commonly contain several percent 

marcasite.

Much of the blackband and clayband siderite is of 

diagenetic origin, but some of the more continuous 

layers may represent primary sediments, deposited in 

brackish waters or marine swamps in the presence of 

abundant vegetal matter.

TABLE 19. Analyses of blackband and clay-ironstone siderite

SiOa.. ____ . ._.. ____ . ___________ . ________

A1303 ._. .__ _ ___._

Fe203 . . .. . .__. . . ....

FeO.. _____ .___. ___________ . _______ . ____ ..

MnO... ____________________________ . .........

MgO.. .--.- ... __ ....__ _________ ..... __ _

CaO.... ___________________________ . _____

NajO. . .._ _ . .... .....

K20._. . _ .. ..... __ ..

H3 0+ . _ ______________. _ __

H8 0- . .

TiOj.. ....... ...... .___ .... 

PsO5 - . . . . - - . ..... _ ... ...

C0a . . . .. . 

S ____ _ _____ _

SO3 . __________________________________

FeSj. . _.. .._._ _ 

C. . __ .._.._.

Subtotal ______________________________

LessO ___ _________________________

Total... _____ . _________________

A

5.10

2.35

.00

50.92

.58

.30

.70

} 2.70

V*

31.80

.18

5.00

QQ Qfi

.09

QQ 87

B

6.46

2 64

C OK

d9 HR

2

09

1.76

o 0*7

( Tr

I .15

.21

.65

QO 7n

.20

.11

100.00

100.00

C

13.50

i °.n

QQ 07

1 °.fi

2 77

2 19

10

1 91

CQ

.69

OQ J7

Trfii»

QQ HQ

09.09

D

10.04

5.57

1 49

07 QQ

1.51

3.37

4.59

.55

1 47

.74

on

9Q Q9

Tr

31.42

QQ CO

QQ C9

E

12.86

6.16

.39

AQ Q1

.98

1.15

1.67

.42

1.32

.54

.83

28.22

Tr

on

3.88

99.53

99.53

F

6.83

2.85

.43

51.45

.54

.42

2.13

.16

.54

.19

.23

33.31

.02 3.67

99.77

99.77

G

13.35

5.79

.41

41.03

.55

3.36

3.00

.86

1.36

.57

.70

28.49

3.07

99.54

99.54

H

0.48

.37

1.18

41.37

.89

4.00

4.53

} 4.10

.02

1.87

31.34

.30

1.28

»8.25

» 100. 00

100.00

I

8.67

4.47

.42

43.11

2.07

2.09

5.15

( J.25

\ 2.12

1.176

32.74

.178

100. 44

.09

100. 35

J

10.72

4.45

1.11

38.08

1.06

3.75

5.19

.12

.19

1.10

.77

.22

1.83

30.20

.02

.42

<1.04

100.27

100. 27

Water and organic matter."

* "Moisture."

3 "Organic matter."

* Total of carbon, organic 0.92 percent, and hydrogen, organic 0.12 percent. 

« Total includes 0.02 "arsenic acid."

A. Siderite ironstone ("blackband"), Prestwick Mine, Natal, South Africa (Wagner, 

1928, p. 127-128). R. R. Walton, analyst. Associated with coal beds of Karoo 

System (Carboniferous to Triassic). Calculated mode: quartz 2.33 percent, 

"clay substance" 7.82 percent, siderite 83.24 percent, calcite 0.48 percent, apatite 

0.76 percent, pyrite 0.34 percent, carbon 5.00 percent. Some of "clay substance" 

is chamosite.

B. "Clay ironstone," Ashburnham Sussex, England (Lamplugh, in Lamplugh, 

Wedd, and Prince, 1920, p. 227). Bed in Wadhurst Clay (Cretaceous). Analysis by R.R. Tatlock and Thomson, Glasgow.

O. "Clayband ironstone," Pargate. Yorkshire (Gibson, in Strahan and others (1920). 

Bed of siderite nodules in Coal Measures (Carboniferous). Analysis reported 

here is total of acid-soluble and ignited acid-insoluble residue. All SiOj is in 

insoluble portion. Analyst not known.

D. Siderite ironstone, Brown Rake, Butterley, Derbyshire, England (Gibson, in 

Strahan and others, 1920, p. 52). Bed in Coal Measures (Carboniferous). Analysis reported here is total of acid-soluble and ignited acid-insoluble residue.

Analyst not known. 

E. Brooch ironstone, Corngreaves, Staffordshire, England (Gibson, in Strahan and

others, 1920, p. 62). Thin layer in Coal Measures (Carboniferous). Analysis

reported here is total of acid-soluble and ignited acid-insoluble residue. Analyst

not known. 

F. Sideritic ironstone ("Crawstone"), Madeley Wood, Shropshire, England (Dewey,

in Strahan and others, 1920, p. 93). Irregular masses in fine-grained sandstone

of Coal Measures (Carboniferous). Specific gravity 3.68. Analysis reported

here is total of acid-soluble and acid-insoluble residue. Analyst not known. 

G. Clay ironstone, Rosser Vein Mine, Dowlais, South Wales (Strahan, in Strahan

and others, 1920, p. 114). Bed in Coal Measures (Carboniferous). Analyst

not known. 

H. Blackband ironstone, Dundonald Colliery, Fifeshire, Scotland (MacGregor,

Lee, and Wison, 1920, p. 142). Analysis by Lochgelly Iron and Coal Co. Layer

4-6 inches thick above coal bed of early Carboniferous age. 

I. Blackband ore, Holmes County, Ohio (Stout,1944. pp. 168-169). Nodular siderite

in Pennsylvanian strata. Analysis by Ohio Geological Survey. 

J. Blackband ore, Tuscarawas County, Ohio (Stout, 1944, p. 172). Nodular siderite

above Lower Kittanning coal (Pennsylvanian). D. Schaaf, analyst.
W28 DATA OF GEOCHEMISTRY

DISTRIBUTION OF DEPOSITS IN SPACE AND TIME

The size, position, and duration of basins of deposition, the dimensions of the deposits, and the facies 

relations both within the iron-rich sedimentary rocks 

and other rocks formed contemporaneously all these 

are of importance to the geochemistry of iron sedimentation, particularly with respect to problems of genesis. 

Though volumetrically of minor proportions, the ironrich rocks throughout the world have been studied 

extensively, both because of intrinsic interest and 

economic value. The literature on the subject is immense (see Luttrell, 1955, for a partial bibliography). 

Fortunately, three compendia of relatively recent 

vintage are available: "Die Eisenerzvorrate der Welt" 

(Einecke, 1950); "Symposium sur les gisements de fer 

du monde" (edited by Blondel and Marvier, 1952); 

and "Survey of World iron resources" (United Nations, 

1955). These are excellent source books.

In the succeeding paragraphs and accompanying 

tables, the occurrence and character of iron-rich sedimentary rocks are summarized briefly. The time aspect 

can be delineated accurately only for deposits of postPrecambrian age; for the Precambrian, assignments of 

age can be made in a relative sense within some individual regions but absolute age is not readily 

established.

DEPOSITS OF TERTIARY AGE

Deposits of Tertiary age (see table 20) are widespread 

in northern Europe, northern Africa, and southern 

United States, but most are of minor dimensions. The 

only unit of significant size is that of the Kerch district of the Crimea. The rock mostly limonitechamosite oolite was deposited in a Pliocene embayment of the Black Sea, in an area of about 150 by 50 

km. The iron deposits were formed in/the central part 

of the embayment and grade laterally into sands and 

clays (see facies map in Markevich, 1960, p. 370).

DEPOSITS OF MESOZOIC AGE

The principal Mesozoic deposits (see table 21) are 

those of Jurassic age in northern Europe. These include the famous minette beds of eastern France, 

Luxembourg, Belgium, and western Germany, the major

TABLE 20. Occurrences of iron-rich sedimentary rocks of Tertiary age

Pliocene.. ________

Miocene _ _ _______

Oligocene _ _ _____

Eocene___________

Locality

Kerch Basin,

U.S.S.R. 

Gelrode, Belgium____

Vogelsberg, Germany.

Caucasus, U.S.S.R __

East side of Urals,

U.S.S.R. 

Tunisia_________

Algeria __ ____ _

Kandi region,

French W. Africa. 

Kressenberg, Germany. 

Weald, England ____

India_______. _____

Colombia _ _ _ ____

Texas, U.S.A. ______

Mississippi, U.S.A. _

Character

chamosite. 

Sandy glauconite.. .

hematite. 

Siderite ____________

chamosite (?).

__.__do_____________

-__-do_____________

__._-do_____________

Siderite beds and

nodules (clay 

ironstone) .

stone) .

and clays. 

Siderite. ___________

Thickness

< 22m______.

-= 15 m _____

3.5 m__ ______

8-15m_______

Few meters. __

2-6 m __ --_

< 100 ft_____

Remarks

Youngest major ironstone. Deposited in 

embayment of 

Black Sea. Lateral 

gradation into ferruginous sands and 

clays.

May be Oligocene in

age. 

Weches Greensand

Member of Mount 

Selman Formation. 

Wilcox Formation and

Ackerman Formation (Wilcox age) .of 

former usage.

Key References

Konstantov and

others, 1933; 

Putzer, 1943; 

Malakhovsky, 

1956 and 1959; 

Markevich, 1957.

Ancion, 1952.

Blondel and others,

1955. 

Mahmoudi, 1952.

Arkhangelskii and

Kopchepova, 1934. 

Davidson, 1961.

Gottis, 1952.

Betier, 1952.

Blondel, 1952.

Gudden and others,

1952.

Krishnan, 1952.

Colombia, 1952,

Hubach, 1953. 

Eckel, 1938.

Vestal, 1954; Lowe,

1914.
CHEMISTRY OF THE IRON-RICH SEDIMENTARY ROCKS W29

ironstones of England (Northampton, Cleveland), and 

others of lesser importance. At first glance, the 

picture would appear to be one of simultaneous deposition of iron over broad areas, in a transgressive 

epicontinental sea bordering the deep Tethys seaway 

to the south. In detail, however, this breaks down, 

and it becomes apparent that the present deposits 

reflect dozens of separated basins, few of which exceeded 50 miles in maximum dimension. Furthermore, even for those formed within the same stage 

the Aalenian, for example, which is the age of the major 

deposits the iron-rich beds in adjoining basins may 

not be stratigraphically equivalent (see fig. 9 in Lucius,

1945, for the relations between the Esch and Differengen basins). At any one time, therefore, there 

existed at most perhaps one or two basins of modest 

size within which iron-rich rocks were being laid down 

surely less than 1 percent of the total area of the epicontinental sea. This fact, not readily apparent 

because of the relatively coarse units of time normally 

dealt with, emerges as a result of the extraordinarily 

detailed stratigraphic analysis made possible by the 

rich fossil record; it is a fact of major importance to 

bear in mind in appraising the geochemical processes 

involved in the deposition of these and other much less 

accurately dated ironstones.

TABLE 21. Occurrences of iron-rich sedimentary rocks of Mesozoic age

Cretaceous: 

Upper... ___ __

Lower _ _ _____

Cretaceous undivided.

Jurassic: 

Upper (Malm) . _

Locality

Salzgitter, Germany.

Gross Iselde, Peine,

Damme, West 

Hannover, Germany. 

Scania, Sweden __

Mugai, Khoper

districts, Russia.

New Jersey, U.S.A. _

New Jersey ___ _

Alberta, Canada _____

Claxby, England. ...

Wassy, Point Varin,

Metabief, Sommevoire, France. 

Maryland, U.S. A __

Moravia, Czechoslovakia. 

Carpathia, Poland. __

Agbaja plateau,

Nigeria. 

Udi plateau,

Nigeria.

Giphorn, Wessergebiet, Germany.

Character

Oolitic and pisolitic

limonite. 

Siliceous limonite---.

Glauconitic sandstones. 

Limon ite oolite __

Glauconite _ ___ _

Clay iron stone ______

Oolitic limonitechamosite. 

Oolitic limonite,

glauconite. 

Oolitic limonite.

Clay ironstone. _ _ _

Arenaceous siderite __

Clay iron stone _ _____

Oolitic limonite _

"Rubbly" ironstone.

nite and limestone. 

Limonite oolite, in

part.

Thickness

<100m _ ...

<30m_______

1-2 m. _______

<40ft _______

<30ft ___ _

6 m aggregate

>40ft_._____

2-28 ft_..____

<4m________

<9m._.-_.__

Remarks '

Much rock is clastic,

derived from erosion 

of older ironstones 

on diapiric uplifts. 

In part of pre- Cretaceous age.

Thick.. ___ _ ________

Area 50 by 20km_____

In several formations;

area 160 by 16 km. 

Hornerstown sand

(now considered to 

be Paleocene). 

Areal extent not yet

defined.

Arundel Formation

(now considered to 

be Upper Cretaceous) .

Chamosite and siderite,

minor magnetite 

found in deeper 

drill holes. 

Probably clastic

deposit.

Oxf ordian age _ _

Key references

Kolbe, 1952; Blondel

and others, 1955; 

Seitz and others, 

1952.

Seitz and others,

1952. 

Hadding, 1932.

Arkhangelskii and

Kopchenova, 1934.

1943; Nassim, 

1950; Attia, 1954. 

Mansfield, 1922.

Mansfield, 1922.

Mellon, 1962.

Hallimond, 1925.

Blondel and others,

1955. 

Singewald, 1909.

Roth and Matejka,

1953. 

Einecke, 1950.

Jones, 1958.

Hazell, 1958.

N6th, 1952.

Seitz, Hoffman, and

Preul, 1952.

See footnote at end of table.

777-130-^65 5
W30 DATA OF GEOCHEMISTRY

TABLE 21. Occurrences of iron-rich sedimentary rocks of Mesozoic age Continued

Middle (Dogger) _ _ 

Lower (Lias)____ _

Triassic.___ __ __

Locality

Chamoson,, Erzegg, 

Fricktal, Switzerland. 

Hungary. _._ ___ _

"Minette" beds of 

eastern France, 

Belgium, Luxemburg, Western 

Germany.

Northampton, 

England.

Cleveland, England __

East Midland, 

Banbury, England.

Northern G6ttingen__

Fredericke Basin, 

Germany.

Vares, Yugoslavia. __

Frodingham, 

England.

Scania, Sweden __ __

No denosits of sianific

Character

Limonite, chamosite 

oolite.

Oolitic limonite and 

chamosite, 

mainly.

Chamosite and 

limonite oolite; 

siderite.

Sideritic chamosite 

oolite.

Sideritic chamosite 

oolite (Marlstone 

ironstone) .

Hematite oolite and 

hematitechamosite oolite. 

Oolitic limonite and 

chamosite, 

mainly.

Siderite and 

hematite, locally 

oolitic. 

Mainly limonite 

oolite.

Sandy siderite, some 

chamosite and 

limonite oolite, 

ance known.

Thickness

l-2m _ _ __

To 9 m _ ___.

To 25feet____

Main seam

2J4-5 feet.

To 25 feet.. __ 

4-5 m _ _ _ _

Beds few 

meters 

thick.

To 60m ___ _

To 32 feet_-__

Many 

meters.

Remarks »

Separate beds of 

Callovian and 

Bathonian age.

Aalenian in age. As 

many as 12 beds in 

several basins within region 120 by 40 

km.

Aalenian (lower 

Dogger) age. 

Original basin 100 

by 20 miles. 

Uppermost middle 

Lias in age. Four 

separate beds.

Same age as Cleveland 

ironstone. With 

Cleveland, deposited in individual 

basins about 30 by 

15 miles in region 

250 by 30 miles. 

Lias-T age, equivalent 

to Pliensbachian.

Lias-a-3 age, 

equivalent to lower 

Sinemurian. Four 

beds. 

Considered to be of 

"exhalativesedimentary" type. 

Lower Lias age 

(approximately 

Sinemurian) .

Oldest Jurassic ironstone in Europe.

Key references

Deverin, 1945.

Panto, 1952. 

Cayeux, 1909; Coche, 

Dastillon and 

others, 1954, 1955; 

Bichelonne and 

Angot, 1939; 

Lucius, 1945; and 

many others. 

Taylor, 1949.

Whitehead and 

others, 1952; 

Rastall and Hemingway, 1949. 

Whitehead and 

others, 1952.

Harder, 1951. 

Kolbe, 1952.

Latal, 1952.

Whitehead and 

others, 1952.

Kern, 1952. 

Palmqvist, 1935; 

Hadding, 1929, 

Hadding, 1933.

i Nomenclature of Jurassic stages follows Kolbe (1953). It diflers from French usage 

(Cusset, de Torcy, and Maubeuge, 1952, p. 147), which places the Malm-Dogger 

boundary above the Oxfordian and places the Aalenian in the Lias. It also diflers

from British usage (Arkell, 1956, p. 10-11) which includes the Aalenian with the 

Bajocian, the Domerian with the Pliensbachian, and the Lotharingian with the 

Sinemurian.

The Triassic Period, one of widespread aridity during which continental areas stood high and the oceans 

were confined largely to the major basins, is the most 

barren interval of post-Precambrian tune insofar as iron 

sediments are concerned. Clearly such conditions are 

not favorable for sedimentary concentration of iron, 

as the known deposits are of trivial size.

DEPOSITS OP PALEOZOIC AQE

The Carboniferous and the Permian, marked by 

major coal beds in many parts of the world, are also 

marked by extensive development of the blackband 

siderite, but ironstones of normal character are relatively scarce. The strata of middle and lower Paleozoic age (see table 22), in contrast, contain many ironrich units. Two types are of particular interest: 

the Lahn-Dill type of Devonian age, associated with volcanic rocks and believed to represent sedimentary deposition of the products of submarine volcanic and 

fumarolic activity (the "exhalative-sedimentary" ores); 

and the somewhat comparable deposits formed in eugeosynclinal (orthogeosynclinal) tracts, as typified by the 

Ordovician ironstones of northwest France, Wales, 

Portugal, and Spain. The latter deposits generally are 

characterized by the presence of abundant thuringite 

and magnetite.

The youngest rocks of "iron-formation" aspect 

that is, with interbedded chert are of Paleozoic age. 

The outstanding example is that of the Lesser Khingan 

range of Manchuria, the age of which is established 

by the presence of an Early Cambrian brachiopod 

(Modioloides prisons Walcott). The iron-formation, 65 to 

80 feet thick, consists of banded hematite-chert and magnetite-chert (Chebotarev, 1958); itis underlain bya 25-foot bed
CHEMISTRY OF THE IRON-RICH SEDIMENTARY ROCKS W31

of manganese carbonate which grades into the overlying 

iron-formation through a transitional zone of braunitehematite. The unit is traced for a strike length of 60 

km and, according to Chebotarev, there is no evidence 

of igneous activity during the period of deposition. A 

second major example, as yet incompletely described 

in available literature, is in the Snake River region 

between the Yukon and Northwest Territories, Canada. 

According to C. D. A. Dahlstrom (oral communication 

to the Annual Convention of the Canadian Institute

of Mining and Metallurgy, Montreal, Canada, April 

1964), a jasper-hematite iron-formation several hundred feet thick is overlain by fossiliferous rocks of 

Middle Cambrian age and underlain by an evaporitebearing sequence that is correlated with nearby strata 

of Early Cambrian age. Other iron-formation units of 

possible or probable Paleozoic age are those of Morro 

do Urucum, Brazil; Relun, Chile; and the Mandi district of northern Pakistan and the Chisapani Garhi 

area of south-central Nepal (O'Rourke, 1962).

TABLE 22. Occurrences of iron-rich sedimentary rocks of Paleozoic age 

[Locality names given in brackets are according to the Columbia Lippincott Gazetteer of the World (1961)]

Permian.. _______

Carboniferous ___.

Devonian. _ _ _____

Locality

Desert Basin,

Australia. 

Szechwan, China. __

Kiangai, China _ ___

Opaczna and Ostrawice, Poland. 

Perm, Russia. ____ _

Karroo beds, South 

Africa and Southern Rhodesia.

Wyoming, U.S.A____

-___.do-_ ___________

England, Wales,

Scotland. 

Lvov Basin,

U.S.S.R. 

Shansi and Hunan

provinces, China. 

Appalachian region

U.S.A. 

Lahn-Dill district

Germany. 

Thuringia, Harz,

and Westfalen, 

Germany.

Ribera area, Spain _

Belgium.. _ _ _____

Lanschakogel,

Austria. 

Macedonia, Yugoslavia.

Dielette, 1'Hermitage-Lorge, and 

Trelon, France. 

Camdag-Ferizla area,

Turkey.

Character

possibly chamositic. 

Pisolitic hematite

shale.

Chamositic ironstone. 

Siderite (clay ironstone) . 

Blackband siderite. 

Chamosite reported locally.

glauconite, also 

shale with "buckshot ore".

hematitic shale.

band siderite. 

--_._do______. ______

_____do_____________

-____do_____________

chamosite, siderite, magnetite.

Oolitic hematite and

chamosite (or 

orthochlorite), 

siderite. 

Bedded hematite __ _

Bedded limonite ____

Oolitic chamosite, 

siderite, minor 

magnetite.

magnetite, 

quartz. 

Oolitic oxides, siderite, chlorite.

Thickness

<30ft.______

2-4m__.____-

1-5 m_______-

Lenticular. _ _ _

Beds< 16 m

thick. 

2 m __ __.

<4m__ ______

Beds 1-20 m._

Lenses "< 25 m

thick.

Remarks

stone and shale.

In quartzite____ _ ___

Locally manganif erous _

Associated with coal 

beds. Some layers 

many square miles 

in area. 

Three thin beds in

Amsden Formation.

tion of C. C. Branson, Wind River 

Mts. 

Thin layers and lenses

occur at many 

horizons in Coal 

Measures. 

Thin layers and lenses

associated with coal 

beds. 

Thin layers and lenses

associated with coal 

beds.

associated with coal 

beds.

halative-sedimentary" class of 

ores, believed related to volcanism.

Lahn-Dill type. __ _ __

Middle and Early 

Devonian age. 

Thin beds _______

Three or more beds in 

phyllite in area of 

60 by 30 km. 

Thin beds-. ___ _. _

Fossiliferous- _____ __

Key references

Edwards, 1958.

Krishnan, 1955.

Do.

Einecke, 1950.

Miropolskaya, 1949;

Belousov, 1933. 

Wagner, 1928; 

Tyndale-Biscoe, 

1952.

Wanless, Belknap,

and Foster, 1955; 

Branson, 1939.

son, 1941. 

Strahan and others,

1920; MacGregor 

and others, 1920.

Bartonova and

others, 1950. 

Juan, 1946.

Stout, 1944; Singewald, 1911. 

Kolbe, 1953;

Borchert, 1960b; 

Harder, 1954.

Von Gaertner, 1952;

Beyschlag, Krusch, 

and Vogt, 1915; 

Hesemann, 1952.

Kern, 1952.

Page, 1958.

1957; Blondel, 

1955.
W32 DATA OF GEOCHEMISTRY

TABLE 22. Occurrences of iron-rich sedimentary rocks of Paleozoic age Continued

Devonian Con_ _ _

Ordo vician * ______

Locality

Rates, Portugal.

Volga-Ural region,

U.S.S.R. 

Bashkira and Tatar

republics, U.S.S.R.

Algeria. 

Arizona, U.S.A__--_-

Nova Scotia, Canada. 

Hunan, Kiangsi,

Hupeh provinces, 

China.

Sierra Grande, Argentina. 

Eastern U.S. A _ __

Aroostook County,

Maine, U.S.A. 

Sardinia, Italy ____

China. 

Thuringia, Germany.

Holoubkha [Holoubkov], Czechoslovakia. 

Zdice and Krusna

Hora [Krusne 

Hory], Czechoslovakia. 

Nucitz [Nutschitz],

Czecholsovakia.

Einodtal, Austria. 

Anjou, France ______

Normandy, France __

North Wales _ _.

Southern Highlands,

Scotland.

Character

bedded siderite 

and limonite. 

Oolitic ironstone.. ___

-_ _do__ _____ -__

hematite, "green 

silicate", quartz. 

Oolitic hematite_____

Pyrite __ _ _ ______

Oolitic hematite

(Clinton iron 

ores) .

siliceous carbonate. 

Oolitic thuringitechamosite with 

siderite and magnetite. 

Oolitic hematite. __ _

Oolitic chamositethuringite, magnetite.

and hematite. 

_-__do_--_-_____-_-

____.do ____________

lite; oolitic.

Fe-chlorite; oolitic. 

Oolitic chlorite_--___

Thickness

5-7ft_ 

<2m___..___

4 m __ ______

30 ft max. in

Ala.

A tfffTfrfFft t.f*

150 ft. 

15m___._ _ _

Aggregate

g25m.

^22 m _______

<> 6 m. ______

^6 m_.______

Remarks

Thin beds. _ ._ __ _

Lower Frasnian in age.

Many beds.

Three lenticular beds

known. 

Upper part of Martin

Formation.

Several beds. _._

Grades into baritic

rock, also into limestone; may not be 

sedimentary. 

In sequence of "Devonian to Carboniferous" age. 

Sporadic occurrence

from New York to 

Ala. generally four 

beds.

Manganiferous. _ - _ ___

Three beds. Arenig

age. 

Tremadoc age _ ______

Arenig age _ ____ ___

Caradoc age. Can be

traced for 40 km. 

Tremadoc age _ ___

Arenig age, metamorphosed. 

Arenig-Llandeilian

age. 

Several beds of Arenig

and younger age.

Key references

De Jesus and Cotelo

Neiva, 1952. 

Strakhov and others,

1959. 

Miropolsky, 1949.

Matheron, 1955.

WUlden, 1960, 1961.

Hayes, 1919.

Juan, 1946; Krishnan, 1955. 

Lindgren, 1933: Bergeat, 1914; Ehrenberg, H. and others, 

1954. 

Argentina, 1952.

Burchard, Butts, and

Eckel, 1910; Burchard, 1913; Newland and Hartnagel, 1908; Ailing, 

1947; Lesure, 1957; 

Hunter, 1960 (see 

footnote p. W7) . 

Pavlides, 1960,

1962. 

Penta, 1952.

Krishnan, 1955.

Von Gaertner, 1952;

Engelhardt, 1942. 

Blondel, 1955.

Do.

Beyschlag, Krusch,

and Vogt, 1915. 

Einecke, 1950.

Troger, 1950; Hoenes

and TrQger, 1945. 

Do.

Strahan and others,

1920; Pulfrey, 

1933. 

Kennedy, 1936.

See footnote at end of table.
CHEMISTRY OF THE IRON-RICH SEDIMENTARY ROCKS W33

TABLE 22. Occurrences of iron-rich sedimentary rocks of Paleozoic age Continued

Ordovician ' Con.

Cambrian ________

Paleozoic (?) _ ___

Locality

Quadranail,

Portugal.

Cova, Portugal.

Siljan district,

Sweden.

French West Africa...

French Morocco. __

Wabana, Newfoundland.

Nova Scotia,

Canada. 

Mayville, Wis.

U.S.A.

Dunderland, Norway. 

Georgia, U.S.A__ _ _

Virginia, U.S. A _

Talladega, Ala.

U.S.A. 

New Mexico, U.S.A__

Lesser Khingan

Range, eastern 

U.S.S.R.

Relun, Chile_-,_____

Morro do Urucum

Brazil.

Character

Oolitic chamosite,

siderite.

corvo); magnetitequartz. 

Magnetite, thuringite, siderite; 

oolitic. 

Oolitic limonite,

chamosite, minor 

glauconite.

Hematite and red

jasper.

oolitic.

Oolitic chamosite 

and hematite.

_____do______-_-___-

Oolitic limonite ___ -

Banded quartz-magnetite, quartzhematite.

Oolitic hematite. _ -

Siliceous specular

hematite.

quartz. 

Arenaceous oolitic

hematite, minor 

glauconite.

Banded cherty ironformation.

Banded hematitejasper with manganese beds.

Thickness

< 9m..._.._

Several

meters. 

2 m-8 m___ _

< 25 m_ ____

Beds 5-30 ft__

< 8ft. .__-._

< 55ft______

TTpw rnpf.PTci

 < 50ft_____-

1-3 ft________

< 6ft___ _ _

< 50 ft. 

< 15 ft... _

20-25 m __ _

20m _ ____

300m _ . __

Remarks

Approx. Arenig age____

_____do_______________

Similar beds found in

Estonia, Latvia, and 

Gotland. 

Ordovician and Cambrian age. 

In schist. _________ _

Llandeilian age; 41

localities known.

12 or more beds in 5 

zones in sandstone 

and shale of Arenig 

age.

In Neda Formation;

also noted in 

Illinois (Workman, 

1950). 

Widespread unit_ ___ _

Several beds at two

horizons 3,000 ft 

apart in marbleschist-quartzite sequence. Some manganiferous beds. 

In Shady Formation. _

In shale and quartzite.

Found over lateral

distance of 100 

miles; occur in Bliss 

Sandstone. 

Underlain by manganiferous bed. 

Contains Lower 

Cambrian brachiopod. 

Area 8 by 15 km _____

Key references

Cotelo Neiva, 1953.

Do.

Rechenberg, 1956.

Hessland, 1949.

Hadding, 1932.

Blondel, 1952.

Agard, Destombes,

Naudet, and van 

Leckwijck, 1952; 

Percival, 1955. 

Hayes; 1919, 1929.

Haves, 1919.

Hawley and Beavan,

1934. 

Argentina, 1952.

Bugge, 1948; Foslie,

1949; Carstens, 

1955.

Kesler, 1950.

Harder, 1908.

Reed, 1949; Pallister,

1953. 

Kelly, 1951.

Nalivkin, 1960;

Chebotarev, 1958; 

O'Rourke, 1961.

Nef, 1952, Valdes,

1955. 

Dorr, 1945; Dorr,

Guild, and 

Barbosa, 1952.

1 In much of French and German literature, the Silurian comprised both Ordovician and Silurian of British and American usage; by some, it included the Cambrianas well. Where stage names are given, these have been converted into standard 

American usage; where they are not, the original terminology is retained.
W34 DATA OF GEOCHEMISTRY

DEPOSITS OF PRECAMBRIAN AGE

Every shield area of the world has been found to contain beds of iron-formation, much of it only weakly 

metamorphosed. The principal occurrences are summarized in tables 23, 24, and 25, according to area and 

for those of the Canadian Shield and South Africa to 

some degree according to relative stratigraphic position. 

The only region not included in the tables is that of 

central Africa, where iron-formation is known to be 

present in thick beds at many places (see for example, 

Woodtli, 1961) but for which published data are as yet 

too fragmentary to present a coherent picture.

The iron-formations of South Africa, Brazil, India, 

and the Krivoi Rog-Kursk areas of the U.S.S.R. all are

of imposing thickness and extent, but probably the most 

impressive assemblage is to be found in the Canadian 

Shield. Here, in a discontinuous chain surrounding a 

northeastward-trending core area of older and more 

highly metamorphosed rocks, is a remarkable series of 

"ranges" of rudely equivalent age. The Belcher IslandNastapoka Island area is on the northwest flank of this 

block, the Labrador-Quebec "trough" is on the northeast end, the Lake Albanel range is on the southeast 

flank, and the Marquette, Menominee, Gogebic, Gunflint, Mesabi, and Cuyuna districts are on the south 

margin. The principal iron-formation units are bracketed in age between about 1,800 million years and 2,500 

million years (Lowdon and others, 1963; Goldich and 

others, 1961).

TABLE 23. Occurrences of iron-rich beds of Precambrian age in North America and South America 1

Region

Canadian shield:

ly Animikie (or 

Huronian)

a era ««&G.

Locality

Falls district, 

Mich.

Amasa Oval and

West Marquette, 

Michigan.

Islands, Canada. 

Labrador trough,

Labrador-Quebec.

Mistassini district, Quebec. 

Mesabi-Gunflint

range, MinnesotaOntario.

Cuyuna district, 

Minnesota.

Gogebic, Marquette, 

and Menominee 

districts, Wisc.- 

Mich.

Character

tion, mostly siderite facies.

Chert-magnetite,

chert-hematite, 

chert-siderite.

tion; oxide, silicate 

(greenalite), siderite facies. 

Cherty iron-formation; oxide, silicatesiderite facies.

tion ; oxide, silicate, 

siderite facies. 

Cherty iron-formation ; oxide, silicate, 

siderite facies.

Mostly silicatesiderite ironformation.

Cherty iron-formation; oxide, silicate 

siderite facies.

Thickness

< 600 ft ______

<800 ft __..

270ft ________

< 600 ft ______

<700ft ______

<800 ft ______

Several hundred feet.

< 2,000 ft, 

Marquette 

district.

Remarks

Riverton Iron-Formation; youngest ironformation of Animikie Series.

In Animikie Series,

but younger than 

major iron-formation units. Four 

separate units 

(Mansfield, Bird, 

Fence River and 

Amasa of Amasa 

Oval: Bijiki of West 

Marquette).

Sokoman Formation;

Wabash Lake IronFormation. Belt 

600 miles long, 60 

miles wide.

Biwabik Iron-Formation; Gunflint IronFormation. Total 

length 200 miles, 

interrupted by 

Duluth Gabbro 

Complex. 

Manganiferous. Possibly correlative 

with Biwabik IronFormation. 

Ironwood Iron-formation (Gogebic) ; 

Negaunee Iron-Formation (Marquette); 

Vulcan Iron-Formation (Menominee). 

Probably correlative 

but deposited in 

separate basins.

Key references

James, 1951, 1954,

1958; James and 

others, 1959.

Leith, Lund, and

Leith, 1935; Gair 

and Wier, 1956; 

Bayley, 1959; 

James, 1958.

Moore, 1919.

Harrison, 1952; Westervelt, 1957; 

Auger, 1954; Gastil 

and Knowles, 1960.

Quirke, Goldich, and

Krueger, 1960; 

Quirke, 1961. 

Gruner, 1946; White,

1954; Goodwin, 

1956.

Grout and Wolff, 

1955; Schmidt, 

1963.

Leith, Lund, and 

Leith, 1935; 

Huber, 1959; 

James, 1958.

See footnote at end of table.
CHEMISTRY OF THE IRON-RICH SEDIMENTARY ROCKS 

TABLE 23. Occurrences of iron-rich beds of Precambrian age in North America and South America ' Continued

W35

Region

Canadian shield 

Continued 

Pre-Animikie 

age.

Rocky Mountain. _

South America

Locality

Michipicoten district, Ontario.

Vermilion district, 

Minnesota.

Skunk Creek belt,

Mich. 

Southwest MontanaAtlantic City, Wyo__

Wyo. 

Arizona-New MexicoGuiana Shield, 

Venezuela.

Mato Grosso, Brazil,

and Santa Cruz, 

Bolivia. 

Minas Gerais, Brazil 

(Quadrilatero 

Ferrif ero) .

Minas Gerais, Brazil.

Character

Helen Iron-Formation: chert, siderite, pyrite.

Lower iron-formation: chert-magnetite, cherthematite.

Mostly chert-hematite, chert-magnetite.

Banded magnetitequartz-silicate. 

Banded quartz-magnetite, mostly.

Banded quartz-magnetite, 

do __

Banded jasper-magnetite.

Banded magnetitequartz, hematitequartz.

hematite. 

.....do...... _.__

Banded quartz-hematite (itabirite).

Siderite iron-formation.

Thickness

Siderite beds 

to 350 ft; 

pyrite beds 

to 120 ft. 

Lenticular, 

typically to 

300ft 

thick, 3,000 

ft long. 

Few hundred 

feet or less.

100 ft_____.__

Beds ^50ft_. 

150 ft... _ __

<300ft ___ .

^30 ft, lenticular.

^700 ft 

(Cerro 

Bolivar). 

75m_. ____ .

<300m

(Morro do 

Urucum). 

To 1000 m; 

average 

about 250 

m.

Lenses to 50 

ft.

Remarks

Helen Iron-formation 

considered to be of 

exhalative-sedimentary type.

Soudan Iron-Formation, underlain by 

Ely Greenstone 

(lower Precambrian). 

In Dickinson Group. _.

Many occurrences, 

probably not correlative.

In Jerome area, Arizona, interbedded 

with dacite flows.

Includes El Pao, Cerro 

Bolivar, Santa 

Barbara areas.

Manganiferous; possibly Paleozoic in age.

Gaud Itabirite, of 

Minas Series; original extent probably 

more than 10,000 

square miles. 

In pre- Minas Rio das 

Velhas Series.

Key references

Goodwin, 1962.

Grout and others, 

1951; Goldichand 

others, 1961.

James and others,

1961. 

DeMunck, 1956; 

James and Wier, 

1961, 1962. 

Bayley, 1963.

Levering, 1929.

Burchard, 1931; 

Anderson and 

Creasey, 1958; 

Bertholf, 1960. 

Stam, 1963, Ruckmick, 1963.

Dorr, Guild, and

Barbosa, 1952. 

Dorr, 1945; Dorr,

Guild, and Barbosa, 1952. 

Dorr, Guild, and 

Barbosa, 1952; 

Johnson, 1962; 

Guild, 1957; Dorr 

and Barbosa, 1963. 

Gair, 1962.

>Not a complete list. Does not Include some highly metamorphosed rocks In Canada, nor some recent discoveries for which information is scant.
W36 DATA OF GEOCHEMISTRY

TABLE 24. Occurrences of iron-rich beds of Precambrian age in Europe and Asia 1

Area

U.S.S.R____ _ ._.

China.... _ . __

India. _____ _ ___

Locality

others, Norway; 

Stripa and others, 

central Sweden; 

Porkonen and 

Jussaari, Finland.

Ukraine.

netic anomaly).

Zaporozh'ye 

region.

Southern Urals. ...

Eastern Siberia 

(Bakal upland) .

northern China.

Southern Manchuria 

and adjacent areas 

of Korea.

adjoining areas of 

Bonai and Keonjar. 

Bailadila, Rowgat,

and adjacent deposits of Madhya 

Pradesh. 

Hyderabad. _______

Mysore State. _____

Salem-Trichinopoly 

district, southern 

India.

Character

hematite, quartzmagnetite.

tion; oxide, silicate, carbonate 

facies.

hematite, quartzmagnetite.

hematite.

mation.

shale and limestone. 

Hematite- j asper. _ _ _ _

(minette type).

Banded hematitequartz, magnetitequartz.

jasper.

magnetite, quartzhematite.

quartz-hematite 

schist.

quartz.

Banded magnetitequartz.

Thickness

Generally few

tens of 

meters or

less.

<200 m ___

<500 m. ...

<500 m __ _

be thick. 

Lenses <60

m.

Lenses in 

zone 200 

m thick.

4 TYi nt* IPCJQ

^400 m (at 

Miao Erh 

Kou).

^3,000 ft

(possible 

fold repetition) . 

< 1,500 ft_ -__

<150ft _ __.

<200ft__. _

Beds to 100 

ft.

Remarks

Strongly metamorphosed in most 

places.

Tightly folded belt

250 km long.

with several hundred 

meters of Paleozoic 

and younger strata. 

Stratigraphy similar

to both Krivoi Rog 

and Kursk.

Part of Burzyansk

Series (Riphean).

Classed as exhalativesedimentary.

with sandstone and 

shale. Shows stromatolitic structures. 

In middle Precambrian Wu-t'ai-shan 

System.

Area of 40 by 25

miles.

In Dharwar System

("Archean"). 

In Dharwar System. __

At least 3 beds known. _

Key references

Norway: Bugge,

1953; Poulsen, 

1952. Sweden: 

Geijer, 1938; 

Geijer and Magnussen, 1948, 

1952. Finland: 

Marmo, 1952. 

Svitalsky, 1937;

Semenenko and 

others, 1956; 

Belevtsen, 1957. 

Plaksenko, 1959.

Alexandrov, 1962.

Polovinkina and

Rozina, 1956 (as 

reported in published annotated 

bibliographies) . 

Starostina, 1959.

Pavlosky and Belichenko, 1958.

Tegregen, 1921;

Krishnan, 1955; 

Matsuzawa, 1953.

Tegregen, 1921; 

Tsuro, 1931; 

Murakami, 1922; 

Asano, 1953; 

Krishnan, 1955. 

Krishnan, 1955

Spencer and Percival, 1952.

Krishnan, 1955.

Krishnan, 1952.

Krishnan, 1952

Radhakrishna, 

1951. 

Krishnan, 1952.

J Not a complete list. Includes iron-rich beds of major thickness and (or) significance. Grouped deposits, as in India, may include formations not stratigraphically 

equivalent.
CHEMISTRY OF THE IRON-RICH SEDIMENTARY ROCKS W37

TABLE 25. Occurrences of iron-rich beds of Precambrian age in Australia and South Africa

Australia

Locality

Roper Bar, northern Australia. _ _ __ _

Constance Range, northern Australia ___

Yampi Sound, northwestern Australia. ___

Western Australia _ __ _ _ _ _

Middleback Ranges, South Australia _ _

Character

Oolitic hematite and

greenalite; magnetite, siderite.

Oolitic hematite and

greenalite (?) ; 

siderite.

Banded hematitequartz, magnetite-quartz. 

__-do __ _--_- .

__do

Thickness

Beds <40ft__

<30ft______-

<130ft ______

Many thin

beds. 

< 200 ft ___

Remarks

Three beds separated

by sandstone and 

shale. "Upper 

Proterozoic."

Two beds separated

by sandstone. 

"Upper Protero- zoic." 

"Middle Precam- brian." 

Widespread in occurrence ("jasper 

bars"). "Archean."

formations.

Key references

Edwards, 1958;

Cochrane and 

Edwards, 1960.

Edwards, 1958.

Canavan, 1953.

Miles, 1953.

Rudd and Miles,

1953; Percival, 

1955b; Edwards, 

1953; Miles, 1954.

South Africa

Locality

Transvaal System 

of Transvaal.

Transvaal System 

of Cape Province.

System of 

Transvaal and 

adjacent areas.

of Transvaal, 

Natal, Zululand, Northern 

Cape Province; 

also Southern 

Rhodesia.

Stratigraphic position

Pretoria Series, 5 

horizons: 

1. Waaikraal. _..

2. Daspoort ___

3. Clayband... _

4. Pisolitic

ironstone.

quartzite 

(lowest unit). 

Dolomite Series, 

Thabazimbi. 

Pretoria Series, 

Griquatown 

Stage: Postmasburg belt (Gamagara Rand).

one in Hospital 

Hill Slate Zone.

horizons.

Character

Magnetite and

silicates. 

Oolitic hematite

and chamosite. 

Magnetite-chamosite-siderite oolite.

tite chamosite.

tite-chamosite 

oolite. 

Banded quartzhematite. 

Banded chert, magnetite, silicates, 

siderite.

hematite, quartzmagnetite.

magnetite, quartzhematite; magnetite-chamositesiderite in places.

Thickness

<12ft_______

Av. 3ft __ __

<4ft _ _____

<6ft___-____

<27ft_______

200-260 m____

2,500 ft in 

south, 

1,000 ft in 

north.

several 

hundred ft.

20-100 ft.

Remarks

\ Crop out in belts

partly encircling 

Bushveld Complex.

 Magnetic quartzite 

(Timeball Hill

horizon) can be 

, traced for 300 miles.

Strati graphically below 

Pretoria Series. 

Belt 320 miles long____

Key references

Wagner, 1928.

Du Preez, 1945.

Wagner, 1928; 

Cilliers and 

others, 1961; 

Cullen, 1963.

Wagner, 1928.

Do.
W38 DATA OF GEOCHEMISTRY

GOGEBIC-KEWEENAWAN 

DISTRICTS, MICH.-WISC.

MENOM.NEE DISTRICT 

MICH.-WISC.

LITHOLOGlC SYMBOLS

s of volcanic Rocks of sedimentary 

origin origin

Sandstone and 

quartz ite

Greenstone tuff 

and breccia Conglomerate, congiom- 

, ^ ^ . eratic sandstone, and 

[^r_rwv.[ arkose

Greenstone, in part with j-^r-- -=1 

preserved pillow \ r ' ^\ 

structures Graywacke, shale, argilt-,- -=\ lite, slate, and schist

Amphibolite of basaltic 

composition

Iron-formation

Schist. Probably includes some rocks of 

volcanic origin

Crystalline rocks, mostly 

of igneous origin

Gebbro and granite of 

post-middle Keweenawan age

Granitic rock of 

post-Animikie age

Gneissic granite of late 

pre-Animikie age

Granitic gneiss of known 

or probable early preAnimikie age

FIQUEE 6. Generalized stratigraphic successions of Precambrian rocks of the Lake Superior region, showing occurrence of iron-formation units (modified from

James, 1960).

The iron-rich rocks of the Canadian shield attain 

maximum thickness and complexity on the south side 

of Lake Superior (fig. 6). The main iron-formation 

unit of the Animikie Series (unit B of fig. 6, which 

represents the Vulcan, Negaunee, Ironwood, Biwabik, 

and Gunflint Iron-Formations of the various districts) 

attains a thickness of 2,000 feet in the Marquette 

district. In the Menominee and Iron River-Crystal 

Falls districts and adjoining areas, the main ironformation is succeeded by at least four other units 

having thicknesses of 100 to 800 feet; in column 4, in 

ascending order, these are the Mansfield and Bird 

Iron-bearing Members of the Hemlock Formation 

(C,D), the Amasa Formation (E), and the Riverton 

Iron-Formation (F). The aggregate thickness of the 

Animikie Series in the area illustrated by column 4 

(fig. 6) is about 50,000 feet, of which iron-formations in 

maximum thickness comprise about 4,000 feet. All 

the facies of iron-formation are represented sulfide, 

carbonate, silicate, and oxide (both hematite and 

magnetite varieties). Of particular interest are the 

local development of algal structures in the Biwabik 

Iron-Formation (unit B'), as described by Grout and 

Broderick (1919) and by Gruner (1946), and the 

magnificent preservation of algal forms in basal chert of

the Gunflint Iron-Formation of Ontario (Barghoorn, 

1957).

Also shown in figure 6 are the pre-Animikie ironformation units of Minnesota and Michigan (units A 

and A7 )- Unit A', in particular the Soudan IronFormation of the Vermilion district is representative 

of "Keewatin-type" iron-formation, of common occurrence in the pre-Animikie mafic volcanic rocks 

elsewhere in the Shield. The Soudan is more than 

2,500 million years old (Goldich and others, 1961), and 

is separated from the Animikie Group by two profound 

unconformities.

The main iron-formations of the Lake Superior 

region appear to be approximately equivalent in age to 

those of Krivoi Rog and Kursk in Russia, which have 

been assigned an age of 1,800-2,000 million years 

(Semenenko, 1959), and to the Transvaal System of 

South Africa, which contains the major iron-formations 

of that region and which is estimated to be about 2,000 

million years in age (Nicolaysen, 1962). The Gaud 

Itabirite of Brazil, which was thought to be bracketed 

between 500 and 1,350 million years (Herz and others, 

1961), is now believed to have an age between 2,600 

and 1,300 million years (P. W. Guild, written communication, March 19, 1964). In India the rocks associated 

with iron-formation of the Singhbhum district yield
CHEMISTRY OF THE IRON-RICH SEDIMENTARY ROCKS W39

apparent ages of about 1,500 million years (Pichamuthu, 

1962). The oldest iron-formation units known are 

those of "Keewatin-type" in the Swaziland System of 

South Africa, the age of which is believed to be in 

excess of 3,100 million years (Nicolaysen, 1962). 

IRON IN NATURAL WATERS

Iron is held and transported in natural waters in 

three forms: (1) as dissolved iron, mainly ferrous; (2) 

in suspension as a colloid or particulate form; and (3) 

as a constituent of clastic particles.

IRON IN SOLUTION

The solubility product of Fe(OH) 3 , which is the 

stable (or metastable) species of iron in the Eh-pH 

range of most natural surface waters, is extremely low. 

Published values range from 10~36 to 10~40 (Hem, 1960a, 

p. 53). Consequently the amount of iron that theoretically can be held in true solution is vanishingly small 

except at abnormally low values of pH (5 or below), or 

in equilibrium with abnormally high concentrations 

of S04~2 or Cl~] certain oilfield brines and volcanic 

waters (see White, Hem, and Waring, 1963, p. 32, 44). 

The low theoretical solubility of iron in the normal 

environmental range is indicated by figure 7, which is 

one of a family of Eh-pH diagrams that can be drawn 

for specified anionic concentrations (Hem, 1960b, p.

? 0.2

Solid-phase Fe minerals 

relatively stable

-o.o

-0.2 -

-0.4

-0.6 -

-0.8

0

Figure 7. Activity of dissolved iron in equilibrium with total sulfur at activity 

10-' (equivalent to 96 ppm SOr2 and total carbonate at activity 5X10-' (equivalent 

to 305 ppm HCOri). (From Hem, 1960b).

69). As Hem states, the usefulness of such diagrams 

is restricted by the arbitrary selection of anionic values 

and by the implicit assumptions of equilibrium and 

absence of unspecified complex ions.

According to Lewis and Goldberg (1954), the average 

content of soluble iron in the ocean is 0.0034 mg/1 both 

at surface and at depth (mg/1=ppm, in water of unit 

density). Dobrzhanskaia and Pshenina (1958) record 

the soluble iron content of the Black Sea as zero at the 

surface and at depth in most places, but locally in the 

"deep layer", at 1,000-2,000 m in depth, the concentration is as high as 0.020 mg/1. The content of soluble 

iron of ground waters in common rocks generally is less 

than 1 ppm, but values of as much as 5 ppm are not 

rare (White, Hem, and Waring, 1963). The higher 

values doubtless reflect the presence of ferrous iron 

in water of either low pH or low Eh, or both. According 

to Hem and Cropper (1959, p. 16) iron concentrations 

of as much as 50 ppm are stable in natural ground 

waters. The redox potentials of such waters will be 

raised in near-surface environments by contact with 

oxygen, with consequent precipitation of ferric iron. 

Hem notes, however, that ferrous iron commonly is 

present in emerging natural waters and attributes its 

preservation to lack of equilibrium. The dissolvediron content of stream waters generally is low; the 

average for streams of the world has been computed to 

be 0.73 ppm (Strakhov, 1948). 4

Iron may also be in solution as organic complexes, 

including chelates, many of which are well known in 

laboratory procedures (Bjerrum, Schwarzenbach, and 

Sillen, 1957). Information on such possible complexes 

in natural environments is scant, but the complexes 

of tannic acid have been investigated experimentally 

by Hem (1960c). The complexing of ferrous iron was 

noted to be particularly strong in fairly concentrated 

solutions of tannic acid (500 ppm, or about 1.5X10"3 

molarity); colored complexes were formed over a pH 

range of 2 to 9, with Fe concentrations after a month's 

time of 10 to 2 ppm. Hem (1960c, p. 94) concludes that 

the mechanism may be effective in solution and tansport of iron in forested regions. Hutchinson (1957) 

discusses at some length the relation between iron content and organic matter in lake waters, noting that 

some lakes in northern Sweden contain as much, as 

2,500 mg Fe m~3 (p. 711). He concludes (p. 714) that

* * * apart from particulate iron compounds in organisms and 

perhaps in suspended silt, the main forms of iron in lake water 

are ferric hydroxide in particulate form or adsorbed to particles 

of microscopic dimensions, and an organic iron complex or series 

of complexes.

* Some uncertainty exists as to the validity of Strakhov's values. In the published 

discussion accompanying the paper, A. P. Vinogradov expresses the view that the 

division made between soluble and suspended iron seemed arbitrary and that in 

fact the amount of iron in true solution is much lower.
W40 DATA OF GEOCHEMISTRY

Shapiro (1964) also notes that iron is present in many 

natural waters in vastly greater quantity than that 

predicted by physicochemical argument, and he shows 

experimentally that much of this excess iron must be in 

the form of ferric colloid peptized by organic acids. 

As previously mentioned, certain waters of volcanic 

association may contain large amounts of iron in 

equilibrium with SO4~2 or Cl" 1 . White, Hem, and 

Waring (1963, p. 44) record values of as high as 5,100 

ppm. A particularly interesting example is the ironrich water of hot springs related to Ebeko volcano, 

Paramushir Island, and its transport to the Okhotsk 

Sea (Zelenov, 1958). For the main stream carrying 

iron-rich waters to the sea, the data are as follows:

Distance below confluence of hot-spring waters

0 -- --

700-800 m_... _ ...

1700-1800 m.. 

Mouth of stream (~* 3km)

pH

1.3 

1.4

1.6

1.4 

l.R

Iron content 

(mg/1)

Fe+s Fe«

150 120 

20 200 

10 320

5 320 

220

The discharge is 1.8/m3/sec, and the total iron delivered to the sea is 400-500 gms/sec or 35-50 tons per 

day. The iron-rich waters extend into the sea as a 

colored band a few hundred meters wide and several 

kilometers long. The band is divided into three 

zones: (1) a near-shore zone of poisonously green 

water out to 50-80 m from the river mouth; (2) a 

zone about 1.5 km long colored yellow by precipitation of yellow iron oxides, and (3) a zone out to the 

open sea of bluish-yellow water without precipitated 

iron oxides. The pH increases steadily from 1.7 in 

the surf zone to 7.6 in the normal sea water. The 

content of iron decreases steadily to 1 mg/1.

IRON IN SUSPENSION

Ferric hydroxide readily forms colloidal suspensions, 

which are fairly stable and have a positive charge. 

Iron sols are reportedly stabilized by organic colloids; 

Moore and Maynard (1929, p. 375) state, "Natural 

streams, therefore, in which the content of organic 

matter is at least 4.5 ppm, will have no difficulty in 

transporting 30 ppm colloidal silica and 10 ppm colloidal ferric oxide.* * *" Iron in particulate form, 

which is defined by Lewis and Goldberg (1954) to be 

that of plus 5-micron dimensions, is present in considerably greater amounts than dissolved iron in sea 

water and displays much greater range 0.0045 mg/1 

in deep waters (more than 500 m) and as high as 3.25 

mg/1 in shoal water. The maximum amount of particulate iron in the Gulf of Panama is 0.863 mg/1. in 

near-shore positions (Schaefer and Bishop, 1958).

Plankton such as diatoms absorb particulate ferric 

hydroxide, and Harvey (1932-33) comments that there 

is "* * * little more ionic iron in a cubic metre of water 

than found in a diatom of moderate size."

Strakhov (1948 table 7), in his extensive study of 

suspended iron in natural waters, shows that for 

streams in the U.S.S.R. the ratio of suspended iron to 

dissolved iron which here appears to include particles 

of true colloidal dimension ranges from about 1:1 

to 100:1. It must be noted, however, that for some 

streams the amount of suspended iron was computed 

from the turbidity of the water and the Fe content of 

the total load; this would include iron carried on or 

chemically as part of clay minerals.

IRON AS A CONSTITUENT OF TRANSPORTED OR 

SUSPENDED CLAYS

Iron is associated with clays as an essential ion in 

the clay structure, as in nontronite, or as surface films 

of oxides on the clay micelles (Carroll, 1958). Of these 

two principal modes, the surface films on oxides appear 

to be quantitatively the more important; the iron-bearing clays are relatively scarce in occurrence. As quoted 

by Carroll (p. 4), the average ferric oxide content of 

the colloid fraction of 162 soils in the United States is 

10.3 percent. Presumably, an appreciable fraction of 

this is as separated particles, rather than clay-bound, 

which would separate from the clay host during erosion 

and transportation; nevertheless, although quantitative data are few, there seems little doubt but that 

much iron is transported as oxide films on clays. If 

the clay fraction is accumulated in an environment of 

low Eh, the oxide iron may return to solution and 

redeposit as glauconite, chamosite, siderite, or sulfide 

(Carroll, 1958, p. 24; Strakhov, 1948).

Iron also of course may be transported in coarser 

clastic fractions as an essential constituent of such 

minerals as pyroxene or hornblende or of volcanic 

materials, and similarly can be recycled through seabottom reactions a process labelled "halmyrolse" by 

Hummel (1922). This mobilization of iron from clays 

and other clastic materials may take place both on seabottom or below the depositional interface. Bruevich 

(1938b) describes such mobilization and reconcentration of iron (and manganese) in bottom deposits of the

Barents Sea.

CONCLUSIONS

The amount of iron in true solution in the oceans and 

most natural bodies of water is extremely small, and is 

controlled by the very low (= 10~38) solubility-product 

of Fe(OH) 3 . Concentrations typically are about 0.003 

mg/1 in ocean water and considerably less than 1 mg/1 in 

most streams and ground waters. The only natural 

waters carrying significantly large quantities of iron
CHEMISTRY OF THE IRON-RICH SEDIMENTARY ROCKS W41

(to 10 mg/1) in solution are certain bicarbonate or 

bicarbonate-sulfate ground waters and rare hot springwaters in some volcanic areas (to 5,000 mg/1). Some 

natural fresh waters may also contain relatively large 

concentrations of iron as an organically peptized ferric 

colloid, or, to a lesser degree, as organic complexes.

The bulk of the iron produced by present-day erosion 

is transported to the ocean as colloidal ferric hydroxide, 

as adhering oxide on clay, or as chemically bound ions in 

clastic mineral particles. This iron may be remobilized 

by sea-bottom reactions to form local concentrations, 

such as concretions, fossil replacements, and perhaps 

glauconite pellets, but in general it must remain associated with, and be much subordinate to, the dominantly clastic deposits; it is not a likely source of iron 

for the main deposits of ironstone and iron formation.

IRON IN PRESENT-DAY SEDIMENTS

With the exception of "bog ores" in lakes of higher 

latitudes (see next page), there is no example in presentday environments of deposition of material approaching 

in composition the iron-rich units of past eras. Hematite-coated quartz grains and hematite oolite dredged 

from the North Sea have been regarded as contemporary 

formation of iron oolite (Pratje, 1930), but there is 

considerable doubt as to the interpretation; the material 

may be reworked from older beds, and certainly the 

North Sea is not the site of modern-day ironstone 

deposition.

The general sedimentation pattern of present-day 

marine regions is that of relatively iron-poor sediments 

near the coasts and progressive increase in iron content 

toward the deeps, the highest iron content being found 

in the red clays far from shore. In a chemical and 

mineralogical study of deep-sea sediments, Wakeel and 

Riley (1961, p. 125) write:

With the exception of the highly calcareous sediments, the iron 

content of the deep-sea sediments, calculated as Fe2O3, on a 

carbonate and water-free basis, is surprisingly uniform. This 

is particularly true of the argillaceous samples, which contain 

average concentrations of 8.23 percent total Fe203 (7.04 percent Fe203 and 1.13 percent FeO on original clay). [In table 

3 in Wakeel and Riley, the average Fe2 03 content of argillaceous sediments, on a carbonate and water-free basis, is given 

as 8.93 percent rather than 8.23 percent. H.L.J.} The mean 

iron contents of the sediments of the three oceans are similar, 

but those from the Pacific are slightly higher * * *.

Certain of the highly calcareous samples from the Atlantic 

(Nos. 2, 6, and 11) and their acid-insoluble residues have Fe203 

contents (on a water- and carbonate-free basis) considerably 

higher than the argillaceous sediments. This effect has been 

observed previously by Revelle (1944) who found that sediments containing less than 30 percent of carbonates contained 

on the average about 7.0 percent of Fe2 03 (on a water- and carbonate-free basis), whereas those containing over 80 percent of 

carbonates had much greater concentrations of Fe2Os amounting 

to as much as 16 percent in some cases. This excess iron over

that contained in the argillaceous sediments is probably derived from globigerina or other organisms, the highly insoluble 

iron oxide or hydoxide content of which remains after their calcareous parts have dissolved away during sedimentation.

The relating of iron content to organisms had been proposed by Correns (1937, 1952b), who noted that 

foraminiferal tests contain 0.16 to 0.65 percent Fe203 . 

Correns also noted that the far-reaching deltaic deposits of the Amazon River, which is higher in Fe 

content than most major streams, are not enriched 

in iron, doubtless because of dilution by a heavy 

clastic load.

The pattern of iron distribution in bottom deposits 

of lakes and seas has been studied by many. In 

general, however, the total amount of iron is relatively 

moderate less than that of the deep-sea deposits 

and much less than that of the sedimentary ironstones. 

Tabulations by Strakhov (1959, table 4) for bottom 

deposits of the Black Sea, for example, show total iron 

to range from 3.07 percent to 4.94 percent of which a 

quarter to a half is in detrital material. The exceptionally high iron content (to 11.11 percent) found 

locally in the bottom sediments of the Okhotsk Sea, 

particularly near the Kurile Islands, doubtless is related to incorporation and dissolution of volcanic 

materials (Ostroumov, 1955).

A submarine iron-rich deposit similar to that being 

deposited off Paramushir Island (see p. W40) is reported 

to be present near Santorin, Greece. According to 

Harder (1960), the deposit, the extent of which is not 

specified, consists mainly of ferrous and ferric hydroxides and is related to recent volcanic or fumarolic 

activity. The chemical composition of the deposit is 

as follows, in weight percent:

Si02

FeaO, 1 --

A12 03 ________-

P205 _-._

V205~ -

Mn0 2 ________

18

_______ 58

_______ .05

._ ___ .3

___---- .0

_______ .15

Ti02-___--____

Mn02 ___-_ __

CaO._. _______

MgO_________

H20_____---_-

_______ 0.01

_______ .1

_______ .15

_______ .2

__._.__ 21

i Presumably total iron given as FeaOs. 

aAs given.

BOG IRON DEPOSITS

The so-called bog iron ores including "lake ore", 

"meadow ore"; "raseneisenstein" are found in many 

swamps and lakes in recently glaciated regions, notably 

in North America, northern Europe, and northern Asia. 

Prior to about 1900 these deposits were significant 

sources of iron ore and were studied by many investigators, particularly in Europe, but modern literature on 

the subject is scarce. Nevertheless, as Lindgren (1933, 

p. 263) says, "* * * the easily traceable processes of 

their formation gives us a most welcome key to the 

origin of other and more obscure deposits." The most 

significant work of relatively recent years is that of
W42 DATA OF GEOCHEMISTRY

Ljunggren (1953, 1955a, 1955b), on the bog ores of 

Sweden; and that of Strakhov (1948) and Krotov (1950) 

on the bog ores of the U.S.S.R.

The ores exhibit a wide range of characters in 

composition (manganiferous to nonmanganiferous), in 

occurrence, and in physical properties. Harder (1919, 

p. 53) divides them into two general groups on the basis 

of occurrence: (1) those formed in agitated or flowing 

water at lake margins, and (2) those formed in marshes, 

bogs, or other shallow depressions.

Type 1, lake ore, is found most abundantly between 

depths of 1 to 5 m and rarely at depths of as much as 

10 m. The ores consist of oolitic or pisolitic grains, 2 to 

7 mm in diameter, commonly cemented into discs 

ranging in diameter from an inch or so the "pennyore" of Sweden to a foot or more. These grains and 

discs, together with fragments of similar material and 

clastic detritus, coalesce to form more or less continuous 

masses generally less than 1 m thick. Krotov (1950) 

reports the alternation of iron and manganese oxides, 

locally with chamositic chlorite, in some of the concretionary forms in Russian lakes.

The bog ores of type 2 occur as thin layers of earthy 

to pisolitic yellow to black oxides, both at the surface 

and below as much as several feet of porous soil or peat. 

Much of the material is cemented sand and encrusted 

plant remains. These ores commonly contain nests of 

white fine-grained siderite, and in places the siderite is 

the major iron mineral; the analyses given by Clarke 

(1924, p. 538) of "raseneisenstein" from the Netherlands show as much as 37.70 percent FeCO3 . Vivianite 

also is a common mineral, in amounts to several percent 

or more.

The chemical compositions of "lake ores" have considerably greater range in manganese and lesser range 

in phosphate (and carbonate) than the bog ores of 

type 2. Many analyses are quoted by Beyschlag, 

Krusch, and Vogt (1909); those of Finnish lake ores 

show the following range:

Percent

Fe2O3 ________ 20. 5-69. 5 

MnO2 ________ 3. 3-40. 3 

SiO2 _________ 7.1-19.3 

A12O3 _______.- .9-3.2

Percent

CaO_________ 0.4- 0.8 

MgO_______.____ Tr.-.3

P2O5 _________ 0.45-1.25 

Loss on ignition. __ 12. 9-21. 9

Further analyses of Finnish ores, giving Fe and Mn 

contents together with minor elements, are presented 

in table 26. In many of the deposits, layers of ironrich material alternate with, are encrusted by, or grade 

into manganese-rich ore.

"" Goethite is the only identifiable iron oxide of the bog 

ores. In a differential thermal and X-ray study of the 

Swedish ores, Ljunggren (1955b) finds that the soft 

earthy ores yield diffuse patterns in X-ray powder 

photographs, only the major reflections of goethite 

being identifiable, whereas the hard varieties of lake

ore are much better crystallized. The DTA curves 

are significantly different from standards of any of the 

crystalline iron oxides, probably owing to the presence 

of oxide and oxide hydrate gels. The manganese 

mineral associated with the Swedish ores probably is 

mainly delta-Mn02 , but the identification is not 

certain (Ljunggren, 1955b, p. 145-146). The manganiferous ores are enriched in minor elements and have 

higher radioactivity than the predominantly iron ores 

(Ljunggren, 1955a).

The distribution of the deposits appears to have 

little relation to the nature of bedrock, nor do the deposits in bogs and lakes have any necessary relation to 

tributary streams. On the basis of a study of bog 

iron deposits in Finland, Aarnio (1920) concluded that 

the deposits were found only in or adjacent to waterpermeable ground, usually sand, in areas of humous 

podzolic soil. These soils are strongly acid; iron 

(and manganese) are leached in the A-horizon 

and are removed, probably as soluble humates or 

bicarbonate. Formation of bog ores occurs when the 

subsoil water enters water courses, lake shallows, or 

more aerated ground (Ljunggren, 1955a; Aarnio, 1920; 

Strakhov, 1948; Borchert, 1960a). In general, the 

precipitation is in response to the predictable rise in 

Eh when the waters become aerated, and the increase 

in pH with loss of CO2.

Bog ores of quite different origin are present in areas 

of recent or present-day volcanic activity in Japan. 

According to Zelenov (1960, p. 50), one deposit is 2,000 

m long, 30-200 m wide, and as much as 20 m thick. 

The iron in these deposits apparently has been precipitated from emerging thermal waters.

MINOR ELEMENTS

The systematics of minor-element distribution in 

the iron-rich sedimentary rocks are poorly known, for 

three principal reasons: (1) relatively few rocks have 

been analyzed; (2) most investigations have covered 

only a few of the minor elements and these are different 

from one study to another; and (3) the values obtained 

by different methods, or by different laboratories, are 

not necessarily comparable. Reason 3 may be illustrated by reference to the published values for boron 

content of Finnish lake ores, as determined by highly 

reputable analysts: Goldschmidt (1954, p. 286-87) 

reports that of 12 samples analyzed, 9 had no boron, 

2 contained 5 ppm, and only one contained as much as 

10 ppm, whereas Landergren (1948; see table 26 in this 

report) finds boron to be present in all analyzed samples 

of entirely similar ore, with amounts in the range of 

20 to 40 ppm.

For reasons 2 and 3 above, it is not feasible to present 

a single tabulation of available analyses, nor is it feasible
CHEMISTRY OF THE IRON-RICH SEDIMENTARY ROCKS W43

TABLE 26. Iron, manganese, and minor-element contents of bog iron ores from deposits in Finland 1 

[Adapted from Landergren, 1948. Values are given In weight percent]

Element »

Name

Fe.._ -._-._.-

Mn....-....__-

B __ 

Be ___--__-.

Co.. -__--__-.

Cr.__ -._._._._

K... ...-..-

Li...... .........

Mg... .......

Mo... ........

Ni...... .........

Rb.. .........

Ti_..-_--._-.__._

V ______ -

W.. ....

Estimated 

error 

(percent)

±25 

±25 

±30 

±20 

±15-20 

±10-15 

±20 

±10 

±15 

±40 

±25 

±20

1

18.8 

14.1

0.003 

<.001 

.01 

<.001

.004 

.1 

<.005 

.003 

<.001 

<.001 

<.01 

<.01

2

34.8 

5.9

0.003 

<.001 

.02 

<.001

.0005 

.1 

<.005 

.006 

<.001 

.01 

<.001 

<.01

3

12.0 

8.9

0.003 

<.001 

.008 

<.001 

.06 

.001 

.5 

.006 

.002 

.001 

1.0 

<.001 

<.01

4

31.0 

12.0

0.003 

.001 

.01 

<.001 

.04 

.0006 

.1 

.005 

.01 

<.001 

.03 

<.001 

<.01

5

49.9 

.6

0.003 

<.001 

.03 

<.001 

<.04 

<.0005

<005 

.001 

<.001 

<.01 

<.001 

<.01

6

26.1 

16.7

0.002 

.001 

.008 

<.001 

.05 

<.0005

<!005 

.004 

.001 

.03 

<.001 

<.01

7

44.22 

1.65

0.003 

<.001 

.01 

<.001

.004 

.3 

<.005 

.001

.15 

<.001 

<.01

8

33.43

1.10

0.002 

<.001 

.006 

<.001 

.07

.0005 

.2 

<.005 

.001 

.001 

.08 

<.001 

<.01

9

44.22 

.89

0.003 

.001 

.008 

<.001

<.005

<005 

.004 

<.001 

.10 

<.001 

<.01

10

26.35 

2.92

0.003 

<.001 

.008 

<.001

<.0005

<005 

<.001

<.01 

<.001 

<.01

11

42.44 

.83

0.003 

<.001 

.02 

<.001

<.6505 

< !

<.005 

<.001

.03 

<.001 

<.01

12

25.4 

23.3

0.004 

.001 

.007 

<.001 

.05 

.0005 

.09 

<.005 

.008 

.001 

.20 

<.001 

<.01

13

28.27 

15.35

0.003 

.0008 

.02 

<.001 

.004 

.0007 

.66 

<.005 

.01 

.001 

.20 

<.001 

<.01

14

40.4 

.20

0.002 

<.001 

.01 

<.001

<.0005

<005 

.003

.02 

<.001 

<.01

Average*

32.7 

7.45

0.0029 

.0007 

.013 

<.001

.001

.004 

.008 

.15 

<.001

» Samples numbered as in Landergren (1948). From collection by B. H. Kranck. 

a Fe and Mn determined "in Helsingfors;" uams of analyst not given. Ti determined chemically and other elements spectrographically by 8. Landergren in laboratories of Geological Survey of Sweden; estimated errors as given by Landergren. 

1 As given by Landergren, 1948, p. 108,110.

TABLE 27. Iron, manganese, and minor-element contents of some iron-rich rocks. 

[Adapted from Landergren, 1948. Values in weight percent]

Element '

Element

Fe.. _ .....

Mn. 

B. ... .......

Be. ... ...

Co. 

Cr.. ........

K ....

Li...........

Mg 

Mo..........

Ni.. ........

Rb... __ ...

Ti.... 

V.. ...... ...

w_ 

Estimated error 

(percent)

±25 

±25 

±30 

±20 

±15-20 

±10-15 

±20 

±10 

±15 

±40 

±25 

±20

Sideritic ironstone

A

38.9 

.2

0.01 

<.001 

.04 

.001 

.4 

.01 

.04 

<.001 

.01 

.001 

.2 

.01 

<.03

B

53.4 

.1

0.001 

.002 

.008 

.01 

nd 

.004 

.7 

<.003 

.01 

<.001 

.09 

.05 

.03

Chamositic ironstone

C

35.3

.05

0.01 

<.001 

.02 

.01 

.06 

.003 

1.2 

<.001 

.01 

<.001 

.3 

.05 

<.03

D

(*) 

0.1

0.002 

.001 

.01 

.003 

.2 

.004 

.9 

<.001 

.01 

.002 

.2 

.05 

<.03

E

35.7 

.2

0.005 

.001 

.03 

.03 

.11 

.02 

.4 

<.001 

.03 

<.001 

.3 

.06 

<.03

F

nd 

1.2

0.001 

<.001 

.03 

.02 

nd 

.003 

1.0 

<.001 

.04 

<.001 

.05 

.05 

.1

Limonitic 

ironstone

G

nd 

0.5

0.01 

.001 

.005 

.03 

.07 

.01 

2.1 

<.001 

.02 

.001 

.10 

.03 

<.03

Hematitic 

Iron-formation

H

52.0 

.09

<0. 001 

.007 

.005 

.008 

.2 

.001 

4.8 

<.003 

.001 

.001 

.02 

.02 

<.03

I

52.2 

.3

0.001 

<.001 

<.003 

.001 

nd 

<. 0005 

.8 

<.001 

.003 

<.001 

.02 

.003 

<.03

Magnetite 

iron-formation

J

46.6 

.08

<0. 001 

<.001 

<.003 

.005 

.32 

.002 

1.48 

<.003 

.001 

.01 

.08 

.002 

<.03

K

nd 

0.25

<0. 001 

<.001 

<.003 

.001 

nd 

<.0005 

1.0 

<.001 

.01 

<.001 

.02 

.004 

<.03

Averages *

Oolitic ironstone *

L

31 

.16

0.0073 

.001 

.02 

.024

.012

.02 

.0007 

.39 

.05

Sideritic ironstone

M

38

.26

0. 0028 

.001 

.03 

.002

.01

.005 

.0005 

.20 

.007

Quartzbanded 

ore, 

Sweden

N

52 

.12

0.0006 

.0029 

.0027 

.005

.0006

.002 

.0006 

.01 

.0085

i Fe and Mn determined in laboratories of Geological Survey of Sweden. Ti determined chemically and other elements spectrographically by S. Landergren in laboratories of Geological Survey of Sweden; estimated errors as given by Landergren.

2 Dominantly chamositic ironstone.

* As given by Landergren, 1948, p. 108,110.

* Given as 5.4 percent by Landergren; probably a typographical error.

EXPLANATION OF SAMPLES

A. Unweathered sideritic mudstone, Northampton, England Northampton Sand

ironstone. No. 3 in tables 44, 45, 46 in Landergren, 1948.

B. Mlnette ore, gray bed. Luxembourg. No. 5 in tables 53, 54, 55 in Landergren, 1948 

C. Unweathered chamosite oolite oolites of chamosite and subordinate limonite in

sideritic groundmass Northampton, England. No. 1 in tables 44, 45, 46 in

Landergren, 1948. 

D. Gray green chamosite ore, Frodingham ironstone, Lincolnshire, England. No. 6

in tables 44, 45, 46 in Landergren, 1948. 

E. Marlstone ironstone, Oxfordshire, England. Average of 7 analyses 8a to 8g, in

tables 44, 45, 46 in Landergren, 1948. 

F. Minette ore, green bed, Luxembourg. No. 8 in tables 53, 54, 55 hi Landergren,

1948.

G. Minette ore. brown bed, Luxembourg. No. 6 in tables 53, 54, 55 in Landergren,

1948. Rock is assumed to be a limonite oolite. 

H. Quartz-hematite ore. banded; from the Stripa mine, Sweden. No. 24 in tables 15,

23, 27 in Landergren 1948.

I. Jaspilite, Marquette, Michigan. No. 32 in tables 53, 54, 55 in Landergren, 1948. 

J. Quartz-magnetite ore, from the Strassa mine, Sweden. No. 27 in tables 15, 23, 27

in Landergren, 1948.

K. Quartz-banded magnetite ore, South Varanger, Norway. No. 1 In tables 53,54,55 

in Landergren, 1948.

to separate them according to the schemes of classification used for the bulk analyses given in previous tables. 

Instead, on the assumption that most results will have 

a fair degree of internal consistency, some of the available data on minor elements are presented in separate 

tables, each of which represents the results from a single

investigator or a single laboratory. Table 27 is a 

selection of analyses from the tremendous work of 

Landergren, which is unparalleled both in volume and 

in the clarity with which the methods, estimated errors, 

and results are presented. Table 26, previously referred to, also is drawn from this work. Table 28 con-
W44 DATA OF GEOCHEMISTRY

tains analyses from a tabulation of average values for 

some Russian deposits, as given by Arkhangelsk!! and 

Kopchenova (1934). The results were based on an extensive analytical project carried out at the Institute of 

Geology and Mineralogy (Moscow); the methods of 

analysis (colorimetric) and individual values are reported in a separate publication (Arkhangelskii and 

Kopchenova, 1935).

TABLE 28. Average contents of iron, manganese, and minor elements l of some iron-rich rocks from U.S.S.R.

[Adapted from Arkhangelskii and Kopchenova, 1934.2; nd., not determined; Tr., 

trace. Values in weight percent]

Fe.. 

Mn......

As.......

Co.......

Or.......

Cu...... .

Ni.......

P ....

Ti _ . _

V........

Bog ore; 

Karelia 

and 

Moscow 

districts

A

37.66 

.84 

.01 

0 

.01 

.004 

0 

1.57 

.22 

.03

Chamositelimonite 

oolite, 

Kerch, 

Pliocene

B

39.83

1.88 

.08 

.019 

.17 

.002 

.008 

1.12 

.16 

.06

Limonite oolite, 

Cretaceous

Mugai

C

28.80 

.37 

.01 

nd 

Tr. 

.011 

Tr. 

.45 

nd 

.08

Khoper

D

42.21 

1.21 

0 

Tr. 

Tr. 

Tr. 

.007 

1.21 

.11 

.03

Clay ironstone, 

Caucasus

Oligocene

E

33.94 

4.17 

Tr. 

0 

0 

.003 

0 

.51 

.13 

0

Jurassic

F

42.17 

.79 

Tr. 

0 

0 

.003 

Tr. 

.11 

.07 

0

Ironformation, 

Kursk, Precambrian

G

47.46 

.13 

Tr. 

0 

Tr. 

.01 

0 

.12 

.08 

0

1 Qualitative analyses for Pb, W, Zn, Mo, and Sn contents also reported for individual samples. Results generally negative, but W present in trace amounts in 

samples from Kerch and Kursk, and Pb present "in appreciable amounts" in one 

Kursk sample.

2 The seven average compositions selected are from a table containing 14, including 

some for deposits of questionable origin. The 14 averages are reported to be based on 

analyses of about 200 samples.

Table 29 gives the contents of six metals from the 

eight separated minette ironstone beds of Luxemburg, 

assembled by Lucius (1945) from the work of R. 

Stumper; it is one of the few compilations available for 

stratigraphic units within a single basin. Table 30 

presents a few analyses from the Liassic beds of southern 

Sweden, arranged according to lithologic character of 

the ironstone by Palmqvist (1935); the work was done 

in V. M. Goldschmidt's laboratory at the University of 

Gottingen. Table 31 contains semiquantitative data 

by the U.S. Geological Survey on 11 samples from the 

ironstones of the Clinton Group of New York and 

Pennsylvania and the Martin Formation of Arizona. 

These data, though suitable for statistical analysis, 

must be used with caution; individual values may or 

may not be significant. Finally, in table 32, the 

maximum and minimum values of the assembled data 

are compared with crustal abundance.

An extensive study by Hegemann and Albrecht (1954) 

of the oxide ores of iron provides a valuable comparison 

of minor-element contents of the sedimentary ores as 

compared with those of magmatic or hydrothermal 

origin. Individual analyses are not given the results 

are grouped and assembled in graphic form but it is 

evident that in general the minor element content of the 

sedimentary types is low. The ores of the Lahn-Dill

type ("exhalative-sedimentary") are considered to be 

distinctly higher in Zn and Cu, and possibly Ag, Pb,. 

and Mo, than the normal ironstones. The results also 

show a several-fold enrichment over crustal abundance 

of Ni, Co, and V in the minette ores of Lorraine, which 

confirms the results reported by Lucius (1945) presented 

hi table 29.

TABLE 29. Contents of Cu, As, V, Ni, Ti, and Zn in minette 

ironstone of Luxembourg

[As quoted in Lucius (1945, p. 159, adapted from work of R. Stumper). Values in 

weight percent]

Stratum 1 and location

A 

B

C 

D

E 

F 

G 

H

Layer 3b, St. Miehel

Layer 3a, St. Miehel 

(Middle red). ......

Layer 3, Landergrund

Layer 2, Mont-Rouge,

Layer 1, Mont- Rouge 

(Gray) .... ...... ...

Layer I, Mont-Rouge

Layer II, Mont-Rouge 

West (Black) 

Layer III, Mont- Rouge, 

Enclave (Green) ......

Cu

0.0068 

.0061 

.0040 

.0048 

.0051 

.0051 

.0057 

.0051

As

0.019 

.019 

.020 

.020 

.019 

.026 

.023 

.023

V

0.060 

.062 

.056 

.059 

.060 

.070 

.059 

.070

Ni

0.0060 

.0069 

.0061 

.0059 

.0078 

.0095 

.0102 

.0110

Ti

0.116 

.118 

.111 

.093 

.099 

.111 

.126 

.113

Zn

0. 0147 

.0145 

.0100 

.0157 

.0182 

.0212 

.0239 

.0230

1 Units arranged in relative stratigraphie position (A is youngest, H is oldest).

TABLE 30. Minor element contents of glauconitic, chamositic, and 

sideritic ironstone of Lias (Jurassic) age of southern Sweden

[Adapted from Palmqvist, 1935. Analyst: Cl. Peters, Mineralog. Inst., Gottingen, 

using spectrographic methods. Results (expressed as oxides) given in tables 5-11 

in Palmqvist, 1935. Values in weight percent]

As-. ..

B. ........

Co. .-.

Or.. -----

Ge

Ni....... .

V.. .......

Zn.-.....-

A

Glauconite, 

Baldringe 

Road

nd

0.03

0

.07

.0004

.0008

.007

nd

B

Brown 

cement, 

Baldringe 

Road

nd

0.016

.0008

.0007

.0004

.04

.03

.008

C

Oolite 

(chamosite?), 

Baldringe 

Road

nd

0.016

.0008

.0035

.0004

.04

.7

.008

D

Siderite, 

Kurremola, 

locality 2

nd

0. 016-0. 003

nd

nd

.0004

nd

nd

0

E

Oolite with 

siderite and iron 

silicate, Kurremola, locality 5

0.013

0. 016-0. 003

nd

nd

nd

nd

nd

.004

A commonly held view is that the iron-oxide sediments are enriched in minor elements because of assumed origin as a positively charged colloid, able to 

adsorb other elements (Goldschmidt, 1954), or because 

ferric iron can form insoluble vanadate, arsenate, 

chromate, or selenate (Goldschmidt, 1954; Krauskopf, 

1955). The concept of sedimentary iron oxides as 

scavengers for minor elements in natural environments 

does not seem to be borne out by the available data on 

the oxide ironstones, though it certainly appears true 

for the manganese-iron oxide concretions of present 

sea bottoms.

Except for phosphorus, the distribution and occurrence of which has been discussed in relation to major 

rock components, the minor-element content of ironstones is surprisingly low, with maximum concentrations 

no greater than or considerably below those of shale.
CHEMISTRY OF THE IRON-RICH SEDIMENTARY ROCKS W45

TABLE 31. Spectrographic analyses of ironstone of the Clinton Formation and Group (Silurian) and Martin Formation (Devonian),

U.S.A.

Analysts; Nancy M. Conklin (analyses A-E, I-K) and Paul R. Barnett (analyses F-H) ,TT.S. Geol. Survey. Laboratory numbers are given at heads of columns. Values in

weight percent]

Ba . ___. 

Be . .

Ce ...........................

Co. _ _ 

Cr............. ..................

Cu. .. ...........................

Qa.. ........ . ._.______ .

La . _ _._ _

Mo.. ........ ....... .............

Nb. .............................

Nd ... ....- .-..-.

Ni... ........................ ...

Pb.. ............................

fie. ... ..... _____ ...

Sr.

V. ...................... ...

Y. ........................ ......

Yb. ................. .

Zt. ........................ ......

CLINTON i

A

(oolitic 

chamosite)

F2639

0.0007 

.0003 

0 

.0015 

.007 

.015 

.0003 

0 

<.002 

nd 

0 

.003 

0 

.0015 

.007 

.03 

.007 

.0007 

.003

B

(oolitic 

hematite)

F2640

0.007 

0 

0 

0 

.007 

.0003 

.0003 

.007 

<.002 

nd 

0 

.003 

0 

0 

.007 

.03 

.007 

.0007 

.007

C 

(siderite)

F2641

0.0015 

0 

0 

<.0015 

.0007 

.0003 

.00015 

0 

0 

nd 

0 

.0007 

0 

0 

.0007 

.0015 

0 

nd 

0

D

(oolitic 

chamosite)

F2642

0.003 

.00015 

0 

.003 

.015 

.015 

.0015 

.007 

<.002 

.0015 

.015 

.007 

0 

.003 

.015 

.07 

.007 

.0015 

.07

E

(hematite)

F2635

0.0015 

0 

0 

0 

.007 

.0003 

.0007 

0 

<.002 

0 

0 

.0015 

0 

.0007 

.03 

.015 

.007 

.0007 

.007

MARTIN 2

[Oolitic hematite with glauconite]

F

F2726

0.007 

0 

0.03 

.0015 

.007 

.0007 

.0007 

.015 

0 

.0015 

.015 

.0015 

.0015 

.0007 

.03 

.015 

.003 

.0007 

.003

G

F2727

0.007 

0 

0.03 

.0015 

.007 

.0003 

.0007 

.015 

0 

.0015 

.015 

.0015 

.0015 

.0007 

.03 

.015 

.003 

.0007 

.007

HS

F2728

0.003 

0 

.03 

.0015 

.007 

.0003 

.0007 

.007 

0 

.0015 

.015 

.0015 

.0015 

.0007 

.03 

.007 

.003 

.0007 

.007

I

G2892

0.03 

.0003 

.03 

.003 

.007 

.0015 

.0007 

.015 

<.005 

.0015 

.015 

.003 

.003 

.0015 

.03 

.03 

.007 

.0007 

.015

J3

G2893

0.015 

.0003 

.03 

.003 

.007 

.0007 

.0003 

.015 

<.005 

.0015 

.015 

.003 

.003 

.0015 

.03 

.03 

.007 

.0007 

.007

KS

G2894

0.007 

. 00015 

.03 

.003 

.007 

.0015 

.0007 

.015 

<.005 

.0015 

.015 

.003 

.003 

.0015 

.03 

.03 

.007 

.0007 

.007

i For chemical analyses, description, and location for A, see table 13, No. L; B, 

table 9, No. C; C, table 16, No. A, D, table 13, No. M, E, table 9, No. D.

3 For chemical analysis, description, and location fr F, G, I, see table 9, Nos. N, 

P, O, respectively.

a Specific locations given in Willden, 1960,1961.

NOTE. Values, in percent, are reported to nearest number in the series 3,1.5, 0.7, 

 0.3, 0.15, 0.07, ....... These numbers represent midpoints of group data on a

geometric scale. Comparisons of this type of semiquantitative results with data 

obtained by quantitative methods, either chemical or Spectrographic, show that the 

assigned group includes the quantitative value about 60 percent of the time. Also 

looked for but not found: Ag, As, Au, Bi, Cd, Dy, Er, Eu, Gd, Ge, Hf, Hg, Ho, In, 

Ir, LI, Lu, Os, Pd, Pr, Pt, Re, Rh, Ru, Sb, Sn, Sm, Ta, Tb.Te, Th, Tl, Tm. U, W. 

and Zn. B reported in barely detectable amounts in several samples (limit of 

detection 0.002 percent).

TABLE 32. Minimum and maximum concentrations of minor 

elements given in tables 8-19, 27-31 as compared with crustal 

abundance

[Values in weight percent]

Element

As........ 

B_ .

Ba.. ...

Be. 

Ce-_ 

Co-. 

Cr._ ...

Cu .... .

<Ja ...

<Je .

La. .

LiMo.. .

Nb.. ._

NLP. 

Pb 

Rb _ -

Sc 

Ti 

V.-. 

W... ...

Y_._. _ ..

Yb 

Zn.. ......

Zr .....

Crustal 

abundance 

(from 

Mason, 

1958, p. 44)

0. 0002 

.0003 

.0400 

.0002 

.0046 

.0023 

.0200 

.0045 

.0015 

.0002 

.0018 

.0030 

.0001 

.0024 

.0080

.1180 

.0015 

.012 

.0005 

.4400 

.0110 

.0001 

.0040 

.0003 

.0065 

.0160

Concentration from 

tables in this report

Minimum

0 

0 

.0007 

0 

0 

0 

.0007 

.0003 

. 00015 

0 

0 

0 

0 

0 

.0007

0 

0 

0 

0 

.02 

.0015 

0 

0 

.0007 

0 

0

Maximum

0.026 

.03 

.03 

.007 

.03 

.04 

.17 

.015 

.0007 

.0004 

.015 

.02 

<.003 

.0015 

.04

2.62 

.003 

.01 

.003 

1.91 

.7 

.1 

.007 

.0015 

.0239 

.07

Reference for maximum

Table

29 

30 

31 

27 

31 

27 

28 

31 

31 

30 

31 

27 

27 

31 

1 27 

J 30 

11 

31 

27 

31 

11 

30 

27 

31 

31 

29 

31

Analysis

F 

A 

I 

H F-K 

A 

B 

A, D E-K 

A-C 

G-K 

E 

B, H, J 

D, F-K 

F 

B, C 

F 

p,K

D 

F 

C 

F 

A, B, D, E, I, J, K 

D 

G 

D

i Excluding Ti-rich siderites of Sweden, which contain abundant clastic ilmenite.

With respect to copper, Goldschmidt (1954, p. 185) 

states:

A concentration of copper in marine oxidate sediments, such as 

in ferric hydroxides and the higher oxides of iron and manganese, 

is well established even if adequate average data cannot be given.

The analyses now available, however, indicate the 

copper content commonly is less than crustal abundance. Again, Goldschmidt (p. 286-287) reports 

boron in the marine ferric ores, in amounts "* * * usually 

ranging from 50 to 500 ppm B2O3 , sometimes reaching 

1,000 ppm, and rarely as low as 30 ppm," and the 

Scania (Sweden) ironstone was found to contain 100 

to 1,000 ppm B2O3 by Palmqvist (1935), who, like 

Goldschmidt, attributed the high content to a marine 

environment of origin. In striking contrast, however, 

is the absence of boron in the ironstones of the Clinton 

(see table 31). Quite evidently the boron content in 

itself is not a reliable criterion of marine versus nonmarine origin, particularly in view of the previously 

noted content of 20 to 40 ppm in the definitely nonmarine bog ores (table 26); the "very marked" difference 

noted by Goldschmidt does not appear to exist.

Goldschmidt (1954, p. 473) reports "conspicuous 

concentration" of arsenic, to 700 ppm, in marine ores 

of Mesozoic age, and the oolitic ores of the Kerch basin 

of Russia are very much enriched in this element. 

In a detailed discussion, accompanied by many analyses, 

Vasyutinsky and Nevoysa (1961) show the mean content of As of the Kerch ores to be 0.10-0.12 percent, 

the greatest concentration (to 0.29 percent) being 

in the iron oxide ooliths; the amount in siderite and 

chlorite (chamosite) is much less. The arsenic content
W46 DATA OF GEOCHEMISTRY

of the mineralogically similar minette of Luxembourg 

(table 29) is about an order of magnitude lower than 

that of Kerch, and the ironstones of the Clinton Formation and Group and the Martin Formation (table 31) 

have a zero content.

On an deductive basis, a definite relation is to be 

expected between the pattern of minor-element distribution and the facies of ironstone. Analysis of these 

probable relat: ons is difficult, however, because of 

scarcity of suitable data and because of the influence of 

local factors. The lack of data is particularly acute 

with respect to the Precambrian iron-formations, except for those of Sweden. The effect of local differences in the environment of deposition specifically 

the geochemical aspect of the surrounding terrain 

may be large and may in fact submerge differences due 

to the chemistry of precipitation. For example, in 

table 29 data for several metals are given for the several horizons of minette ironstone in Luxemburg. The 

8 beds represented vary widely in mineralogic character; they include oxide, silicate, and siderite facies. 

The contents of Cu, As, V, Ni, Ti, and Zn all are 

relatively high and astonishingly similar from one 

horizon to another; the total range of each is scarcely 

greater than what might be expected in a single bed. 

Another example is that of the high lanthanide content 

(particularly La, Ce, and Nd) in the ironstone of the 

Martin Formation of Arizona (see table 31), which 

probably reflects a distinctive aspect of the region at 

the time of deposition; mineralogically similar facies of 

the Clinton have virtually no lanthanide content.

Arkhangelskii and Kopchenova (1934) conclude that 

significant differences in minor-element content exist 

between bog ores, limonite oolite, and clay ironstone, 

although the differences, as indicated by the average 

values listed n table 28, are not impressive. Landergren (1948, p. 91) notes the greater enrichment of Cr 

and V in chamositic ores of Great Britain as compared 

with sideritic rocks. This trend also is evident in the 

Russian ores (table 28) and to some degree in the 

Clinton ironstone (table 31). The chamositic rocks are 

generally higher in Al-content than other ironstones, 

and the increased amounts of Cr and V probably stem 

from an initial clay constituent.

Though data are still scarce except for Sweden, the 

Precambrian iron-formations doubtless are very much 

lower in minor-element content than the younger ironstones. Landergren (1948, p. 163) notes the remarkable deficiency of the ferrides titanium, vanadium, 

chromium, manganese, cobalt, and nickel in the 

banded ores of Sweden.

DIFFERENCES BETWEEN IRONSTONE AND IRONFORMATION

Both ironstone and iron-formation have a wide range 

in characteristics and associations, but it seems worth 

while to summarize the differences that exist between 

the more abundant deposits that may be classed as 

typical of the two groups, namely ironstone of the 

minette type, and iron-formation of the Lake Superior 

type.

1. Age. Ironstone: Pliocene to middle Precambrian. 

Principal beds are of lower Paleozoic and of 

Jurassic age. Oldest known occurrence is in 

strata with approximate age of 2,000 million years 

(Transvaal Series, South Africa); youngest unit 

of significant size is of Pliocene age (Kerch basin, 

U.S.S.R.). Iron-formation: Cambrian to early Precambrian. Principal formations in the U.S.S.R., 

South Africa, and North America have an age of 

about 2,000 million years. "Keewatin-type" ironformation, generally associated with volcanic rocks, 

occurs in the oldest known Precambrian strata 

of several shield areas of the world. Youngest 

proved age for iron-formation is Cambrian.

2. Thickness. Ironstone: major units a few meters to 

a few tens of meters. Iron-formation: major 

units 50 meters to 600 meters.

3. Original areal extent. Ironstone: individual basins 

of deposition probably rarely more than 100 miles 

in maximum dimension. Iron-formation: difficult 

to determine, but at least some units had continuity over linear distances of many hundred 

miles.

4. Physical character. Ironstone: massive to poorly 

banded; silicate and oxide facies oolitic. Iron-formation: thinly bedded; has layers of dominantly 

hematite, magnetite, siderite, or silicate alternating 

with chert that makes up about half the rock by 

volume; oolitic structure relatively rare except in 

hematitic and silicate facies of some areas.

5. Mineralogy. Ironstone: dominant oxide is goethite; 

hematite is fairly common, magnetite relatively 

rare; chamosite is primary silicate, glauconite 

(chlorite and stilpnomelane in metamorphosed 

ironstone) is minor; calcite and dolomite common 

constituents; pelletal collophane relatively abundant in some rocks. Iron-formation: no goethite; 

magnetite and hematite about equally abundant; 

primary silicate is greenalite, with minnesotaite, 

stiipnomelane, and chlorite in rocks of slightly 

higher metamorphic grade. Quartz (chert) a 

major constituent; dolomite present in some units
CHEMISTRY OF THE IRON-RICH SEDIMENTARY ROCKS W47

but calcite rare or absent. Pelletal phosphate, 

chamosite, glauconite absent.

6. Chemistry. Ironstone: except for high content of 

iron, no distinctive aspects. Iron-formation: remarkably low content of Na, K, Al, and minor 

elements; phosphorus content generally much 

lower than in ironstone (Geijer, 1962); Mn/Fe 

ratio believed by some to be higher (Lepp, 1963).

7. Associated rocks. No distinctive differences. Both 

ironstone and iron-formation typically are interbedded with shale, sandstone, or graywacke, or 

their metamorphosed equivalents. Carbonate 

rocks limestone and (or) dolomite in the ironstone sequences and dolomite in iron-formation 

sequences not rare but subordinate to clastic 

rocks in immediately associated strata.

8. Relative abundance of facies. No gross differences 

apparent. Probable order of abundance for 

ironstone: oxide, silicate (chamosite), siderite, 

sulfide; for iron-formation, order is similar but 

siderite facies may be more abundant than 

silicate facies. Within oxide facies, however, 

magnetite is far more abundant hi iron-formation 

than in ironstone.

Some of the differences hi the above summary can be 

ascribed to greater degree of metamorphism or simple 

"aging" of the (generally) older rocks, which result in 

change of goethite to hematite, chamosite to chlorite, 

and possibly glauconite to stilpnomelane, but many 

features remain as distinctive to iron-formation. Chief 

among them are the notably greater abundance in the 

Precambrian, the greater dimensions, the interlayered 

chert, and the extremely low content of the alkalis, 

alumina, phosphorus, and minor elements.

ORIGIN

The lack of modern-day examples of ironstone and 

iron-formation deposition makes the subject of origin a 

fertile one for speculation. Furthermore, the question 

is not a simple one: it has many facets, some interrelated and some for the most part independent. 

Fairly definite conclusions can be drawn as to the 

distribution patterns and basic chemistry of iron 

deposition: both ironstone and iron-formation were 

formed as chemical sediments in marine or brackishwater basins of restricted circulation, or in marginal 

seas of modest extent, the mineralogy of the iron 

precipitates being governed principally by relative 

availability of oxygen, carbon dioxide, and sulfur. 

Beyond this, many major and minor problems remain 

unsettled. Chief among them are the source and mode 

of transport of iron (and, for the iron-formation, also 

silica) and the relation between ironstone and ironformation.

The various mechanisms that have been proposed for 

derivation of the iron are as follows:

1. Iron is derived from weathering of land masses 

under humid tropical or subtropical conditions 

(Gruner, 1922; Gill, 1927; Moore and Maynard, 

1929; Taylor, 1949; Sakamoto, 1950; Alexandrov, 

1955; Hough, 1958); under arid conditions (Woolnough, 1941); or by weathering under an atmosphere of lower oxygen and higher C02 content 

than at present (MacGregor, 1927; Tyler and 

Twenhofel, 1952).

2. The iron is derived from sea-bottom reactions on 

chiefly clastic materials (Strakhov, 1959; Borchert, 

1960a; Braun, 1964), and concentrated by solution 

and selective sea-bottom precipitation (Borchert), 

or mainly by diagenetic reactions (Strakhov).

3. The iron (and also silica in the iron-formations) is 

derived from processes related to contemporaneous 

volcanic and igneous activity (Van Hise and 

Leith, 1911; Moore, in Moore and Maynard, 1929; 

Goodwin, 1956; Oftedahl, 1958; Gruner, 1959, 

written communication, a reversal of views published in 1922; Harder, 1963).

Each of these mechanisms other than that calling 

for atmospheric modification can be either observed 

or reasonably inferred on a small-scale basis at the 

present. For example, the bog iron deposits represent leaching of iron from surface and subsurface 

materials and lateral movement to sites of deposition 

essentially a weathering process; sideritic concretions 

and some glauconite concentrations surely represent 

mobilization of iron from surrounding sediments by 

sea-bottom or diagenetic reaction; present-day deposition of iron related to volcanism is known from at 

least a few localities. None of the processes are 

mutually exclusive; the question is one of scale and of 

which process is dominant. Of the three possibilities, 

it would seem to the present writer that the second 

sea-bottom or diagnetic reactions is quantitatively 

inadequate, particularly with respect to the ironformations, unless the chemistry of seawater differed 

profoundly from that of today. If this judgment is 

accepted, then only two major possibilities need to 

be considered: derivation of iron by weathering processes, and derivation of iron by processes related to 

volcanism and igneous activity.

Assessment of the role of volcanism and related 

processes to iron deposition is not easily made, as it 

depends largely upon inferences drawn from associated 

rocks. Nevertheless, a close and probable genetic 

relation seems reasonably proved for a few ironstones 

and iron-formations for example, the Devonian ironstone of the Lahn-Dill district of Germany, and the 

"Keewatin-type" Precambrian iron-formations, ex-
W48 DATA OF GEOCHEMISTRY

emplified in the Michipicoten district of Canada. 

Another well-documented example is that of Meggen, 

Germany (Ehrenberg, Pilger, and Schroder, 1954), 

where pyritic beds of Devonian age grade laterally 

into barite. In others, such as the deposits of Kazah, 

U.S.S.R. (Maksimov, 1958), the iron-rich strata 

interfinger with and grade into manganese-rich beds. 

These various deposits, which have been classed as 

exhalative-sedimentary, typically exhibit rapid changes 

in thickness and lithic facies, and all have close spatial 

relations to volcanic rocks or other evidence of volcanic 

and igneous activity.

For most of the major ironstone units of younger 

age, however, for which time-equivalent relations 

can be established with other rocks so that contemporaneous volcanic or igneous activity in surrounding 

regions can be excluded derivation of iron by weathering processes, or at least nonvolcanic processes, seems 

certain. Typical of the deposits of nonvolcanic 

association are the many ironstone beds of Jurassic 

age of northern Europe, which were deposited in 

isolated or semi-isolated marine basins on the order 

of several tens of miles in maximum dimension, marginal 

to or within an epicontinental sea. The iron seemingly 

can only have been derived from weathering of adjoining land areas, as concluded by Taylor (1949) for 

the Northampton Sand ironstone of England.

Most of the major iron-formations of the world 

similarly are devoid of apparent volcanic associations, 

although the possibility of a relationship cannot be as 

readily dismissed, at least for units of Precambrian 

age, in view of the great difficulty or perhaps (at 

present) impossibility of establishing true time-equivalence between dissimilar rocks of separated areas. 

Nevertheless, sufficient information on the enclosing 

geology of these areas is at hand to show that the 

relationship, if it existed, was not an immediate one; 

the iron and silica were not derived from thermal 

waters of volcanic or igneous source within the basins 

of deposition.

Deposition of both ironstone and iron-formation 

of nonvolcanic affiliation requires a more efficient 

means of transporting iron to the site of deposition 

and of separation from other materials than that now 

evident in dominant surface processes, in which the 

bulk of the iron is transported in the form of colloidal 

iron oxide and is inextricably tied up with the clastic 

fraction.

For the ironstones of nonvolcanic origin, with ages 

as young as Pliocene, significant atmospheric or biospheric modification seems an unlikely possibility: 

the range of environmental conditions in the Pliocene 

could not have differed greatly from those of the present 

except in relative importance. The only process now

yielding iron concentrations, other than by volcanic 

contributions, is that of bog-ore formation, which 

involves shallow subsurface leaching of iron from 

permeable sands, and transportation in bicarbonate 

ground waters of low Eh and pH. It does not seem 

unreasonable to invoke this process on a much larger 

scale. The process and general setting may be visualized as follows: during a period of widespread and 

dominantly clastic sedimentation in a shallow epicontinental sea, local warping resulted in emergence of 

low broad island areas separated by shallow and generally interconnected basins. Climatic conditions 

probably warm and humid permitted development 

of a thick cover of deeply rooted vegetation on the 

emergent blocks of permeable and weakly lithified 

sediments. Deep penetration of ground waters rich 

in CO2 and organic acids the CO2 content augmented 

by subsurface production from root processes resulted 

in leaching of fine-grained iron oxides and iron sulfides 

in near-surface zones, with the products of leaching 

being transported by acid ground waters to bordering 

seas via subsurface routes. If the sites of debouchement of the ground waters were fully open to oceanic 

circulation, then most of the dissolved material was 

dispersed, but if the site was a relatively small basin 

with restricted circulation, then the iron could be 

trapped and ultimately precipitated according to the 

Eh-pH conditions prevailing. Clastic components 

sand and clay and associated clastic rocks would 

represent contribution and periodic influx of surfacetransported materials, which would be interlayered 

and in part intermixed with the products of chemical 

precipitation.

For several reasons the process suggested for deposition of ironstone appears inadequate to explain 

deposition of iron-formation. Chief among these are 

the far greater dimensions of the depositional units, 

the more complete separation of iron from constituents 

other than silica, and the presence of interbedded 

chert. Most layers within iron-formation are finely 

laminated, with thicknesses of laminae being on the 

order of 0.1 mm. If these represent yearly precipitations, an iron-formation 200 m thick would take 

about a million years to accumulate, even assuming no 

breaks in sedimentation. It is more likely that the 

laminae represent longer time intervals, and that 

sedimentation was not continuous, so that a thick ironformation may well have taken some tens of millions of 

years to accumulate. Maintenance for such a long 

period of time of topographic conditions appropriate 

for continued groundwater flow of the type outlined 

seems improbable. Furthermore, in pre-Devonian 

time the landscape would not be covered with deeply 

rooted vegetation, if indeed it was covered at all.
CHEMISTRY OF THE IRON-RICH SEDIMENTARY ROCKS W49

Finally, the ground water hypothesis would offer no 

obvious explanation for the interbedded chert.

Neither the dual occurrence of ironstone and ironformation in strata at least as young as Cambrian, nor 

the fact that ironstone could be deposited both in 

Pliocene time and in a period far back in the Precambrian, eliminates the possibility of a significant 

relation between evolution of the earth's atmosphere 

and origin of iron-formation. An atmosphere appreciably different from that of the present could have 

persisted at least into early Paleozoic time. Strong 

limits on this speculation are imposed, however, by 

evidence from within the iron-formation units and their 

associated rocks. Any proposed system must permit 

or account for the following facts:

1. Depositional environments for iron had comparable 

ranges in Eh to those inferred for younger ironstone. This fact is derived from the observed 

range in facies (oxide to sulfide), from the relative 

abundance of facies types, and from the relation 

of the facies to physical features of the rocks that 

give independent evidence on environment of 

origin. Oolitic structure, for example, which 

surely in part reflects deposition in shallow and 

turbulent and therefore well-aerated water, is 

confined to oxide and silicate facies, as it is in 

younger ironstone; never is it present in sideritic 

facies.

2. The precipitation of calcium, magnesium, and minor 

elements was strongly repressed during the ironformation cycles.

3. Chert rarely occurs as separate units in strata 

associated with iron-formation. Furthermore, 

within iron-formation the amount of chert varies 

systematically with the facies defined by iron 

minerals. The implication, therefore, is that 

precipitation of silica was not independent of 

that of iron.

4. Thick units of dolomite are present in strata associated with some units of iron-formation. The 

dolomite actually interbedded with or adjacent to 

iron-formation commonly contains magnetite, but 

the principal units as much as 2,000 feet thick 

contain no more iron than dolomites of younger 

age.

5. Associated clastic rocks, such as quartzite, graywacke, and argillite, are quite similar in mineralogy and chemistry to equivalent rocks of younger 

age. Clastic feldspar is common in the quartzites 

and graywackes, which indicates that chemical 

breakdown of rocks during erosion was not entirely 

dominant over physical processes. 

A number of workers have suggested that the earth's

atmosphere during the time of iron-formation deposition was higher in CO2 than during later eras. The 

existence of thick and widespread oxidic facies seemingly 

eliminates the possibility that an actual reducing atmosphere prevailed, but it does not eliminate the possibility 

that the partial pressure of CO2 was significantly 

greater. If, for example, in a dominantly oxidizing 

atmosphere, though perhaps much lower in oxygen than 

today, the partial pressure of CO2 were 0.03 atmosphere, 

instead of the present 0.0003 atmosphere, the equilibrium pH of surface waters would be reduced from 

8.17 to about 6.1 (Rubey, 1951, p. 1129). If the total 

volume of surface waters were less than at present, the 

pH would be still lower. Surface waters would then 

to some degree have similar chemical attributes, 

particularly the capacity to leach and transport iron, 

that is now characteristic of acid ground waters. 

Furthermore, if the pH of marine water in fact was 

much lower than at present, either because of the direct 

equilibration with CO2 of the atmosphere or because of 

higher concentration of some other constituent 

chlorine, for example then an additional important 

factor is introduced: namely, that the sea itself could 

have been a major reservoir for iron in solution.

The validity of this model is open to some question. 

Revelle and Fairbridge (1957, p. 246) conclude that the 

present CO2 content of the atmosphere is an approximate equilibrium value, controlled in large part by 

carbonate precipitation and silicate weathering. The 

specific situation analyzed, however, is that of a sudden 

increase in partial pressure of CO2 and its effects on 

seawater equilibrium, with the implicit assumption of 

element concentrations similar to those of present 

oceans. This assumption is not necessarily an acceptable one; conceivably, for example, seawater at the 

time of iron-formation deposition might have been 

much undersaturated with respect to elements such as 

calcium. Cloud (1965) questions the existence of an 

oxygen-bearing atmosphere in early and middle Precambrian time, as do Lepp and Goldich (1964). Cloud 

develops the concept of photosynthetically generated 

oxygen to provide local oxidizing environments. The 

concept is a valuable one, but whether local generation 

of oxygen is quantitatively adequate for precipitation of 

thick oxidic sediments remains to be demonstrated.

It is clear, however, that an increase in the partial 

pressure of CO2 to relatively modest levels would have 

profound effect on the cycle of iron, and vastly increase 

the efficiency of iron extraction and transport. Accepting this as a probable condition, and considering 

the limiting factors previously outlined, the proposition 

is here presented that 

1. The earth's atmosphere has been dominantly oxidizing since at least mid-Precambrian time that 

is, for the past 2 billion years and that oxygen,
W50 DATA OF GEOCHEMISTRY

perhaps locally generated by photosynthesis, was 

available even at the time of formation of the 

oldest known stratified rocks (3 billion years or 

more in age).

2. During mid-Precambrian time, the atmosphere contained a considerably greater amount of CO2 

than at present, and that this relatively high 

CO2 content persisted but in diminishing amounts 

until at least early Cambrian tune.

3. The iron-formations typically were deposited adjacent to long-exposed low-lying land masses 

during intervals in which clastic contributions to 

the sea were almost nil. Reduction of the land 

surface during the iron-formation cycle was almost 

entirely by deep chemical weathering, with complete chemical breakdown of silicates so as to 

yield abundant iron and silica in solution.

4. An important event leading to the deposition of 

major iron-formations was the formation of shallow restricted troughs or basins, marginal to the 

old landmass, in which the products of chemical 

weathering could be accumulated, and in which 

abnormal bottom conditions, particularly of Eh, 

could exist. Some units of iron-formation consisting only of oxide facies, however, could have 

been deposited in the relatively unrestricted 

shallows of low-sloping continental shelves.

5. The precipitation of such elements as Ca, Mg, K, 

and Na was inhibited by the low pH of the sea 

water, possibly also by low concentrations; whereas 

iron, transported as bicarbonate, and silica, derived from breakdown of silicates and transported 

as monomeric H2SiO4 (Siever, 1962), reached 

saturation levels. The intimate association of 

iron minerals and chert, therefore, is due to the 

manner in which the elements were extracted from 

the landmass and trapped: the breakdown of 

silicates to yield the necessary amounts of iron in 

solution would at the same time place large 

amounts of silica in solution. The fractionation 

of iron and silica from other elements was not 

accomplished at the source, but rather during the 

precipitation process.

6. The rhythmic layering so characteristic of ironformation is due to some periodic, perhaps seasonal 

change in environment. Sakamoto (1950) suggests 

that this change is one of alternating wet and dry 

seasons, with consequent effect on the pH of 

waters tributary to the basin of deposition; Hough 

(1958), by analogy to present-day lakes, concludes 

that the layering is due to seasonal overturn. It 

is here proposed that the layering is due to explosive growth of silica-secreting organisms in 

response to periodic (seasonal?) increase in either

the nutrient content or the temperature of surface 

waters in the basin of deposition. According to 

this concept, iron would be precipitated at a slow 

and nearly constant rate, whereas the silica-rich 

layers would represent relatively brief interludes 

during which organically precipitated silica was 

showered down from near-surface levels in the 

water.

7. Periodic influx of clastic material, now represented by 

rocks such as graywacke and quartzite, represent 

intervals of structural disturbance during which 

chemical weathering became subordinate to physical disintegration of the land surface. During 

these periods the supply of iron and silica in solution was greatly reduced, so that iron-formation 

and clastic sedimentary rocks, in general, now are 

mutually exclusive.

8. Thick units of iron-free dolomite, which, if present 

in the iron-formation sequences generally are 

separated by some distance stratigraphically from 

the main iron-formation units, were formed either 

before the restriction on open-sea circulation was 

established or during periods when it was destroyed. During these intervals the iron and 

silica being contributed were lost to the open sea, 

whereas the carbonate rock could have been precipitated from water not significantly different in 

composition from that of the oceanic reservoir, in 

response to some special conditions such as those 

now prevailing on the Bahama Banks.

9. The time of maximum development of iron-formation, 

about 2,000 million years ago, was near or at the 

close of a very long and perhaps world-wide period 

of stable structural conditions. In the Canadian 

Shield, at least, to judge from the geochronologic 

data now available, this structural stability had 

lasted for about 500 million years. In this, the 

region of greatest iron-formation occurrence, the 

formation of the necessary marginal basins was the 

earliest stage of what was to develop into a 

eugeosynclinal and erogenic cycle of major 

proportions.

Both ironstone and iron-formation, therefore, may 

have been formed by essentially similar processes 

extraction of iron by weathering from adjacent land 

areas and precipitation in (generally) restricted basins. 

The great differences between the rocks could be 

ascribed to primarily two factors: (1) the greater efl&- 

ciency of the weathering process in Precambrian time, 

which would permit the close association of abundant 

iron and abundant silica in solution; and (2) the far 

lengthier periods of structural stability, two of which 

had durations as long as from the Cambrian to the 

present approximately from 2,500 to 2,000 million
CHEMISTRY OF THE IRON-RICH SEDIMENTARY ROCKS W51

years and from 1,000 to 500 million years ago. The 

lesser, though by no means insignificant, amount of 

iron-formation of Cambrian age could be due to a diminished COg content of the atmosphere.

These suggestions for origin of ironstone and ironformation should be taken for what they are that is, 

plausible speculations. They are offered to provide 

targets for further research, by means of which specific 

aspects can be either verified or rejected; most surely 

they are not final answers.

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CHEMISTRY OF THE IRON-RICH SEDIMENTARY ROCKS W55

Hem, J. D., 1960b, Some chemical relationships among sulfur 

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 1954, Sedimentary facies of iron formation: Econ. 

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James, H. L., and Wier, K. L., 1961, Geologic and magnetic

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James, H. L., and Wier, K. L., 1962, Geologic and magnetic maps

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W56 DATA OF GEOCHEMISTRY

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CHEMISTRY OF THE IRON-RICH SEDIMENTARY ROCKS W57

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CHEMISTRY OF THE IRON-RICH SEDIMENTARY ROCKS W59

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INDEX

Akaganeite___________________

Alumina, in goethite..____________

Analyses, bavalite_______________

blaekband and clayband siderite___-.....

bog iron ores_____________ __ 

brown cement.. ___________ 

chamosite..___...__________ 

chamosite-limonite oolite________... 

ehamositic ironstone___________... 

clay ironstone. ______________ 

Cretaceous iron-formation_______ 

glauconite._.__________.......

glaueonitic rocks.....___________

greenalite___________________ 

hematite.....__ __ __...___

hematitle iron-formation___________

Lahn-Dill type of ironstone_______ 

limonite___.__.___,____ 

limonite oolite__ __ _____. .. 

limonitic ironstone_______________

magnetite _ _.__

magnetite iron-formation______ _. 

minnesotaite___.____________ 

minette ironstone .__.___. ___ 

oolite (chamosite?)-___________ 

oolite with siderite and iron silicate___ 

quartz-banded ore, Sweden__ ____ 

siderite__________________ 

sideritie iron-formation of Preeambrian

sideritie ironstone...__ __ __. 

sideritie rocks of post Preeambrian agesilicate iron-formation..._______. 

stilpnomelane--. .. .... . . 

sulfide-rieh rocks..________.__. 

thuringite_______________. 

See also under Spectrographie analyses.

Berthierine. See under Chamosite. 

Blaekband siderite_____________. 

Bog iron deposits._____________.

Page

W2

2

8

27

43,44 

44 

5 

44

22,43

44

44

8,44

23

6

19,20 

43 

18 

3,18 

44 

43

20,21 

43 

8

18,44

44

44

43

4,44

Carbonate facies of iron-rich rocks.. _____ 23 

Chamosite__.__..___________ 2,4 

Chamositic ironstone...___________ 21 

Chlar-te-. --_ -- -- .- -. 7

Classification of the iron-rich sedimentary

rocks....__.___________.. 11

Page 

Clayband siderite..._______..__ ... W26

Dissolved iron._______________... 39

Earth's crust, percentage of iron in___._ 1 

Eh and pH relations..____________ 13,14,39

Faeies of the iron-rich sedimentary rocks 12

Glauconite- 2

Glauconitie rocks. -_______-___._ 23 

Goethite containing alumina, contraction of

unit-cell constants_ __ _ 2

Goethite (limonite)- _____________ 2,3

Greenalite.. 2

Grelgite_ _ ... - 11

Hematite.. __. . . 2,3

Hematitle rocks of Mesozoie, Paleozoic, and

Preeambrian age... ... 18 

Hydrogoetblte......__._ . .... 2

Hydrohematite__.... 2

Hydrotroilite __ _ 10

Iron, mechanisms for derivation ____ __ 47 

Iron associated with elays. ... .... 40 

Iron content of natural waters. _.. 39 

Iron-formation and ironstone, deposition.._ 47,49 

differences between_ 46 

Iron in present-day deposits___... _. 41 

Iron oxides, development of stable phases..._ 2 

Iron silicates.... . 4 

Iron sulfldes____.___._ _...__ 9 

Ironstone facies, relation to physico-chemical

conditions__.__ _ __ 15 

Ironstone. See also under Iron-formation.

Lahn-Dill type of ironstone. .... 18

Lepidocrocite. 2,3

limestone, average, percent iron in_ .... 1

Maekay, A. L., quoted 2 

Maghemite. .. 2,3 

Magnetite...__..__ 2,3 

Magnetite-rich rocks of Mesozoie, Paleozoic,

and Precambrian. 20,21 

Marcasite. 2,10 

Melnlkovlte-. .... . - - 11

Page 

Mesozoie deposits of iron-rich sedimentary

rocks___.... . W28

Minette type of ironstone.. . .......

Minnesotaite. 

Minor elements, concentrations compared with 

crustal abundance .......

distribution in iron-rich rocks______

Mixed assemblages, factors influencing character. _ 

Organic activity in precipitation of iron. 

Oxide faeies of iron-rich rocks. .

18

45

42

16

Paleozoic deposits of iron-rich sedimentary

rocks_______.________ 30

Precambrian deposits of iron-rich sedimentary

rocks_______._________ 34

Pyrite_-_.__ 2,9

Pyrttosphaera barbaria, secretion of iron. _ _ 17

Sandstone, average, percent iron oxide in__ 1 

Shale, average, percent iron in_._ __.._.. 1 

Siderite.. __ ,____ __ ___ 2,3,4 

Sideritie iron-formation of Precambrian age... 24 

Sideritie rocks of post-Preeambrian age 24 

Silicate facies of iron-rich rocks. _ 21 

Silicate iron-formation of Precambrian age. 22 

Speetrographie analyses, ironstone . 45 

Stilpnomelane. . 9 

Stratigraphic succession, Precambrian rocks.. 38 

Strong, M. W., quoted, on baeterially precipitated iron_________.... 17 

Sulflde faeies of iron-rich rocks . 25 

Suspensions of iron__... 40

Taylor, J. H., quoted, on magnetite content

in Northampton sand ironstone.. 19

Tertiary deposits of iron-rich sedimentary

rocks______________ 28

Tetragonal FeS._ 10

Turgite... 

Volcanic activity, relation to derivation of

iron._______________ 47

Weathering, derivation of iron by... 47

W61