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 Page Face Abstract. _ _______________________________ Wl Chemistry of iron-rich rocks, etc. Continued Introduction. _________ ___________________ 1 Oxide facies Continued Iron minerals of sedimentary rocks __ ______ 2 Hematitic iron-formation of Precambrian age__ W18 Iron oxides __ _______________________ 2 Magnetite-rich rocks of Mesozoic and Paleozoic Goethite (a-FeO (OH) ) and limonite _ 2 age___________-__-._____________ 19 Lepidocrocite (y-FeO(OH) )________ 3 Magnetite-rich iron-formation of Precambrian Hematite (a-Fe2O3) _ _ _ __ ___. _ _ 3 age._____-__---____--_---_-------------_ 21 Maghemite (7-Fe203) __ __________ 3 Silicate facies_________________________________ 21 Magnetite (Fe3O4) ________ _ ___ 3 Chamositic ironstone____--_-_-__----_-_---_- 21 3 Silicate iron-formation of Precambrian age_____ 22 Iron silicates 4 Glauconitic rocks__-_-____--------__-------- 23 4 Carbonate facies______-_-_-___-------_---------- 23 Greenalite. ________________________________ 6 Sideritic rocks of post-Precambrian age._______ 24 Glauconite____ _____________________________ 6 Sideritic iron-formation of Precambrian age____ 24 Chlorite (excluding chamosite) _______________ 7 Sulfide facies___________________________ 25 Minnesotaite. ______________________________ 8 Blackband and clayband siderite_____ _________ 26 Stilpnomelane_ _____________________________ 9 Distribution of deposits in space and time.____________ 28 Iron sulfides __ _ ______________________________ 9 Tertiary________________________________ 28 Pyrite (FeS2)___-__.__ _ ___________________ 9 Mesozoic.______--_____-_---_--_-----------_-_- 28 Marcasite (FeS2) _-_.--_----__-___-_-_____-__ 10 Paleozoic.__________________----____---_-___- 30 Hydrotroilite and tetragonal FeS_ ____________ 10 Precambrian- ___ _ _____-___--_----__------------ 34 Melnikovite and greigite __ _________________ 11 Iron in natural waters------------------------------- 39 Classification and facies_____________________________ 11 Iron in solution..____________---_-__--_-_------_ 39 Major subdivisions ___ _____ _ __________________ 11 Iron in suspension_____-_-_-_-_-_-___----------- 40 Facies___ ______________________________________ 12 Iron as a constituent of transported or suspended Geochemical aspects. _______________________ 12 clays.__-___-__________---_-___-__-----__---_ 40 Natural associations ___ ___________________ 15 Conclusions-______-_____-____-__-___--___------ 40 Iron in present-day sediments___--_----__-_-___------ 41 16 Role of organic activity ___ _______________________ __ Bog iron deposits-_-______-_-----------___------ 41 Chemistry of iron-rich rocks, according to groups and Minor elements___________________________________ 42 facies __ _________________________________________ 17 Differences between ironstone and iron-formation.--.--- 46 Oxide facies____ ________________________________ 17 Origin________________-_--___--__----___-_-__------ 47 Oolitic limonite ironstone____________________ 17 References _________________________________________ 51 Hematitic rocks of Mesozoic and Paleozoic age- 18 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 Pag« TABLES 8-19. Analyses of Continued Page 1. Separated limonite (goethite) 18. Sulfide-rich rocks__. W27 ooliths from two Mesozoic 19. Blackband and clay-ironstone ironstones.------- ___________ W3 siderite____ 27 2. Siderite__________________ 4 20-22. Occurrences of iron-rich sedimentary 3. Chamosite___-_________.______ 5 rocks 4. Greenalite __________________ 6 20. Tertiary age.___- 28 5. Selected analyses of glauconite.________ 8 21. Mesozoic age_-___------- _ 29 6. Analyses of minnesotaite, stilpnomelane, 22. Paleozoic age--_---____------- 31 thuringite, and bavalite_ _________ 8 23-25. Occurrences of iron-rich beds of Pre­ 7. Values for free energy (AF°) for species cambrian age of importance to the iron system, at 23. North and South America,. 34 standard conditions.________________ 14 24. Europe and Asia__--___--_- 36 8-19. Analyses of 25. Australia and South Africa 37 8. Oolitic limonite (goethite) iron­ 26-28. Iron, manganese, and minor-element con- stone. _____________________ 18 tents of 9. Hematite-rich sedimentary rocks 26. Bog iron ores from deposits in of Paleozoic and Mesozoic Finland__________-_._ 43 age. 19 27. Some iron-rich rocks.-.-------- 43 10. Hematite-rich rocks of sedimen­ 28. Average of contents for iron-rich tary origin, Precambrian age_ 20 rocks, U.S.S.R_______.. 44 11. Magnetite-rich sedimentary 29. Contents of Cu, As, V, Ni, Ti, and Zn in rocks of Mesozoic and Paleo­ minette ironstone of Luxembourg _ 44 zoic age__________________ 20 30. Minor-element contents of glauconitic, 12. Magnetite-rich ironstones of chamositic, and sideritic ironstone of Precambrian age__________ 21 Lias (Jurassic) age of southern Sweden. 44 13. Chamositic ironstones _________ 22 31. Spectrographic analyses of ironstone of 14. Silicate iron-formation, mostly the Clinton Formation and Group Precambrian_____________ 23 (Silurian) and Martin Formation 15. Glauconitic rocks (greensand) 24 (Devonian), U.S.A__ 45 16. Siderite rocks of post-Precam- 32. Minimum and maximum concentrations brianage____________ 25 of minor elements given in tables 8-19 17. Sideritic iron-formation, Pre­ and 27-31 as compared with crustal cambrian-._______________ 26 abundance___________-_-_. ... 45 DATA OF GEOCHEMISTRY CHEMISTRY OF THE IRON-RICH SEDIMENTARY ROCKS By HAROLD L. JAMES ABSTRACT chamositic rocks, and commonly are submerged by local differ­ The iron-rich sedimentary rocks, defined as those containing ences related to the geochemical nature of the terrain adjacent 15 percent or more iron of depositional or diagenetic origin, have to basins of deposition. a wide range of physical and chemical properties, in part because The origin of the iron-rich sedimentary rocks remains a matter of gradations into more common sedimentary types and in part of speculation, as no modern-day examples exist. A few de­ because of the wide variety of iron minerals possible. The iron posits, exemplified by the ironstone of the Lahn-Dill district of may be in the form of goethite (limonite), hematite, and mag­ Germany and the Helen iron-formation of the Michipicoten netite; siderite, with a substantial range in amounts of manga­ district of Canada, appear to have a genetic relation to volcanic nese, magnesium, and calcium in solid solution; chamosite, and igneous activity and may be classed as "exhalative-sedi- greenalite, and glauconite (which upon slight metamorphism mentary." The more typical and more extensive ironstones may be converted into thuringite and other chlorites); minne- and iron-formations, however, are entirely lacking in volcanic sotaite, and stilpnomelane; and pyrite and marcasite. Many of and igneous associations; for these the iron seemingly must be these minerals may be preceded by metastable species of uncer­ derived by weathering of exposed land, although the large tain status, such as ferric hydroxide and hydrotroilite. Other chemical and physical differences between ironstone and iron- minerals, of rare occurrence, are lepidocrocite, maghemite, the formation imply some significant difference in the nature of the tetragonal iron sulfide, greigite, smythite, and pyrrhotite. process. It is suggested, by analogy with bog-iron deposition, By custom, the noncherty and generally oolitic iron-rich rocks, that for both types the iron is extracted and transported by most of which are of post-Precambrian age, are referred to as ground waters of low pH, and that this process was more effective ironstone (including the "minette type"), whereas the chert- in Cambrian and pre-Cambrian time,