296 



UNITED STATES MINERAL RESOURCES 



direct-shipping ores or of ores that had been bene- 

 ficiated by simple washing techniques (Button, 

 1955). As a result of continued large-scale produc- 

 tion, resources of direct-shipping ore were rapidly 

 becoming depleted, and efforts were made to obtain 

 alternate sources of ore. Imports were increased 

 rapidly during the 1950's. Since 1964 imports have 

 exceeded 40 million tons per year, as shown in 

 figure 36. 



During the 1950's, however, the Lake Superior 

 iron mining industry underwent a technological 

 revolution with the development of processes for 

 large-scale treatment of low-grade material to pro- 

 duce high-grade agglomerates. The agglomerates, 

 principally in the form of pellets, are ideal furnace 

 feed. The net result has been displacement of direct- 

 shipping ore by pelletized concentrates produced 

 from low-grade ores. Jet-drilling, autogenous ore- 

 grinding, magnetic concentration and flotation, and 

 pelletizing now are common practice not only for 

 low-grade ores but also for those of higher grade. 

 The successful research that led to these develop- 

 ments has vastly increased the reserves of minable 

 ore not only in the Lake Superior region but also 

 throughout the world. 



BYPRODUCTS AND COPRODUCTS 



The banded iron-formations that make up the 

 bulk of the iron resources of the world generally do 

 not contain significant amounts of byproduct or co- 

 product other than manganiferous iron ore. 



Other types of iron deposits, however — particu- 

 larly those related to igneous activity, some deposits 

 related to surface and near-surface enrichment, and 

 iron-rich placer deposits — commonly contain recov- 

 erable or potentially recoverable materials in addi- 

 tion to iron (Button, 1955; United Nations, 1970). 

 These are gold, silver, copper, cobalt, titanium, tin, 

 manganese, chromium, nickel, vanadium, zinc, sul- 

 fur, phosphates, rare earths, aluminum, fluorine, 

 beryllium, uranium, thorium, and zirconium. In the 

 United States, gold, silver, copper, and cobalt are 

 recovered from iron ore in Pennsylvania and tita- 

 nium from deposits in New York; phosphate min- 

 erals are potentially recoverable from iron deposits 

 in New York and Missouri. Some of these phosphate 

 minerals also contain rare earths, uranium, and 

 thorium. Titanium is recovered from iron sands in 

 Japan, vanadium from iron deposits in South Africa 

 and Peru, and phosphates from deposits in Sweden. 

 Tin may be recoverable from iron deposits in Malay- 

 sia and nickel, chromium, and aluminum from 

 lateritic deposits in several tropical areas. Iron has 

 been recovered from nickel ores in Canada and from 



sulfide-rich copper deposits in the Western United 

 States. Zircon and associated titanium minerals have 

 been recovered from iron-rich sands in Italy. 



In addition to the metal and mineral byproducts 

 and coproducts, the waste rock from mining and the 

 tailings from ore beneficiation plants are valuable 

 resources in some areas such as the Northeastern 

 United States. They are used for road metal and for 

 fill for construction purposes, and sand- and gravel- 

 sized materials from some of these plants have been 

 used in making concrete. 



ENVIRONMENTAL PROBLEMS 



The mining and processing of iron, as with other 

 metals required to sustain the economy, have un- 

 desirable environmental consequences. Those spe- 

 cifically associated with iron are chiefly factors of 

 scale: the mines and recovery plants are huge, 

 transportation systems are complex, and furnaces 

 and steel mills are major industries in themselves. 



Most of the iron ore produced in the United States 

 is extracted from open pits, which in the Mesabi 

 district are a mile or more wide, many miles long, 

 and several hundred feet deep. The tonnage of 

 waste material produced in stripping operations 

 commonly is two to three times that of the ore 

 mined, and this mass must be disposed of. In the 

 past, most of the waste has simply been accumulated 

 in great unsightly piles adjacent to the mining op- 

 eration. This spoil could, however, either be returned 

 to mined-out areas or distributed in a beneficial 

 manner. Part of the waste may be processed as 

 low-grade ore. 



The pits themselves, after mining ceases, have 

 the potential for environmental enhancement, since 

 most will fill with water and thus become manmade 

 lakes. To make these lakes usable for recreational 

 and other purposes, however, the bounding walls 

 would have to be reduced to a stabilized configura- 

 tion to protect against hazardous slumping and to 

 provide access. The cost would be substantial, and 

 careful planning before and during the mining 

 operation would be necessary. The added cost would 

 place the domestic industry at a competitive dis- 

 advantage with less restrained foreign producers, 

 but at the national level it would yield lasting bene- 

 fits to the present and future population of the 

 country. 



Perhaps a more diflicult problem is posed by dis- 

 posal of the large amounts (more than 50 million 

 tons per year) of finely ground waste (fines) pro- 

 duced in the United States in the extraction process 

 whereby taconite containing about 30 percent iron 

 is concentrated to a product containing 60 percent 



