Chapter 28 

 SEDIMENTARY IRON DEPOSITS 



Stanley A. Tyler 



Professor of Geology 



University of Wisconsin 



Madison, Wisconsin 



GENERAL STATEMENT OF PROBLEM 



Iron is the second most abundant metallic element in the earth's 

 crust. It occurs combined wifeh other elements to form a large variety 

 of iron-bearing minerals. Most sedimentary rocks contain some iron, 

 but only those that show an unusual concentration (10 percent Fe or 

 more) are included here under the term sedimentary iron deposit. 

 The wide distribution of sedimentary iron deposits throughout geo- 

 logic time from pre-Cambrian to Tertiary serves to emphasize the im- 

 portance of the sedimentary processes in which iron participates. 



More than 90 percent of the world's production of iron ore is derived 

 from sedimentary iron deposits. Thus a thorough knowledge of sedi- 

 mentation is a prerequisite for those who wish to specialize in this 

 field. 



The primary interest of the geologist or engineer who studies iron 

 deposits from a commercial point of view is to discover large, high- 

 grade bodies of iron ore. It is true that practically every type of iron 

 deposit has been exploited at some time or other in the past, but with 

 the enormous tonnage requirements of the modern steel industry of 

 today we find that only deposits that contain extremely large tonnages 

 of desirable material can be utilized economically. This in effect has 

 practically limited commercial development to the residual deposits 

 formed on or within siliceous iron formations and to the marine oxide 

 deposits. The laterite deposits contain large tonnages of relatively 

 high-grade material, but the presence of undesirable impurities limits 

 their use. 



A knowledge of sedimentation is helpful in solving many of the 

 practical problems associated with iron deposits. The problems usu- 

 ally center around variations in iron content, the stratigraphic position, 



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