UNITED STATES MINERAL RESOURCES 



IRON 



By Harry Klemic, Harold L. James, and G. Donald Eberlein 



CONTENTS 



Abstract of conclusions 291 



Introduction 292 



Exploitation 294 



Byproducts and coproducts 296 



Environmental problems 296 



Geologic environment 297 



Ore minerals 297 



Classification of deposits 297 



Bedded sedimentary deposits 298 



Banded iron-formations 298 



Ironstones 299 



Miscellaneous sedimentary deposits 299 



Deposits related directly to igneous activity- 300 



Magmatic segregations 300 



Pyrometasomatic deposits 300 



Deposits formed by hydrothermal solutions.. 301 

 Replacement deposits in nonferruginous 



rocks 301 



Enrichments of preexisting ferruginous 



rocks 301 



Deposits produced by surface or near-surface 



enrichment 302 



Laterites 302 



Enrichments of preexisting low-grade 



ores 302 



Summary of types of deposits 302 



Resources 302 



Identified reserves and resources 302 



Hypothetical resources 304 



Speculative resources 304 



Exploration 304 



Problems for research 305 



Selected references 306 



FIGURES 



33-38. 



Graphs : 



33. Steel production in the United 



States, 1951-71 



34. World production and world trade 



in iron ore since 1951 



Page 



292 

 293 



33-38. 



Graphs — Continued : 



35. U.S. iron-ore consumption, produc- 

 tion, and imports for consumption 

 in the period 1951-71 



Sources and amounts of iron ore im- 

 ported to the United States, 1961- 

 71 



Value of United States imports and 

 exports of iron ore, 1951-71 



Iron-ore production in the United 

 States and in the Lake Superior 

 region of the United States, 1875- 

 1971 



36. 



37. 



38. 



TABLES 



57. 

 58. 

 59. 

 60. 



Principal features of the iron-formation facies- 

 Summary description of categories of iron ore_ 



World iron-ore resources 



The identified iron-ore resources of the United 



States 



ABSTRACT OF CONCLUSIONS 



293 



294 

 294 



295 



Page 



298 

 303 

 303 



304 



Iron is the principal metal employed in modern industrial 

 civilization and is indispensable to everyday living. Annual 

 world production of iron ore is approximately 750 million 

 long tons. The United States produces more than 80 million 

 tons of iron ore per year, of which about 80 percent is from 

 the Lake Superior region. World trade in iron ore is nearly 

 300 million tons per year and is highly competitive. The 

 United States has sufficient reserves and potential resources 

 of iron ore to meet its needs for many decades but imports 

 about one-third of the iron ore it consumes. Most of the im- 

 ports are from Canada and South America. 



The principal iron-ore minerals are the iron oxides — mag- 

 netite, hematite, and goethite. Bedded sedimentary deposits 

 of these minerals in Precambrian banded iron-formations 

 containing 30 percent or more of iron are the principal 

 sources of iron ore. The six major continents contain vast 

 known iron-ore resources. Identified world resources of iron 

 ore, including reserves, exceed 780,000 million tons. Iron-ore 

 reserves in the United States are about 9,000 million tons, 

 and total identified U.S. iron-ore resources, including re- 

 serves, are 100,600 million tons. These are mainly in the 



U.S. GEOL. SURVEY PROF. PAPER 820 



291 



