IRON ORE Iron is smelted from several oxidized minerals occurring in abundance in the earth's crust. In order of commercial import ance these minerals are hematite (Fe203), magnetite
li monite (hydrated iron oxide) and the carbonate siderite (FeCO3). Great deposits of these minerals in relatively pure state, close enough to the surface to be mined easily, are in many regions. They are so common that an iron and steel industry will be devel oped whenever and wherever a population of machinery-using humanity accumulates. Iron deposits located in sparsely settled countries are potential ores of the future ; for present uses an ore must be so situated and of such a nature that it can be mined, smelted by methods now known, and transported to market at a profit. Proximity to cheap fuel will enhance the value of ore—in Great Britain inland furnaces smelt local ores containing as low as 23% iron. The enormous ore deposits near Lake Superior in North America are a thousand miles from coking coal and an iron-consuming population, but intensive production and cheap water transport on the Great Lakes enables them to dominate the American market. On the other hand Brazil has huge untouched reserves of iron too far inland to export and with no home de mand. The Continent depends upon the minette ores of Lorraine —ores which until the beginning of this century were valueless for steel making because no way was known to eliminate a high percentage of harmful phosphorus.
The most productive iron ore region in the world is in very old (pre-Cambrian) strata surrounding Lake Superior, on the border between United States and Canada. Sev eral long narrow areas called ranges contain the workable ores, which are hematites. Data on these ranges follow (shipments in long tons of 2,24o lb.) : The deposits in the Mesabi range are flat, thick and close to the surface, and are therefore mined in open cuts by steam shov els. Underground mining is the rule in the others, the veins being fairly steep and worked to 3,00o ft. depth. The wealth of these ranges is such that ores of various analyses and textures are available. One-fourth the output is Bessemer ore, suitable for acid steel, containing on the average 55% iron and 0.04 phosphorus. The Cuyuna ore contains notable amounts of manganese. Basic or non-Bessemer ores from the ranges are higher in phosphorus and averaged 51.5% iron in 1937, with silica forming the principal impurity.
In view of the tremendous annual production of the Mesabi range, it may be questioned how long it will be before the region is worked out. The average iron content of all lake ores dropped from
in 1902 to 514% in 1910, and has been maintained since then only by mining increasing amounts of high grade ore, and washing, screening, or drying one-third of the remainder. Minnesota is estimated by the State geologist to have demon strated reserves of 1,250 million tons of recoverable ore. Unless these reserves are increased by new discoveries the Mesabi range will be worked out by 1975 or 2000, depending on whether the pre-depression or the post-depression rate is figured. But any prediction about the age of a mining district must prophesy also the state of the future art of ore concentration—lean rock today may be workable ore tomorrow. In fact, this region contains an unlimited tonnage of magnetite-bearing strata just outside the classification of ore, as defined by conditions in 1937.
While seven-eighths of American ore comes from the Lake ranges, the balance of about eight million tons is taken from many ore occurrences in the Clinton formation in the Appalachian mountains, an uplift which parallels the Atlantic coast from north to south. In the northern region the ores are predominantly mag netites ; at the southern end in the State of Alabama, deposits of a low-grade red hematite with an easily fusible gangue are found near extensive coal measures. All these deposits are mined by underground methods ; among them are mines which have pro duced continuously since the earliest iron smelting in America.
Ore beds second in importance only to those in the Lake Superior region occur in strata of Mesozoic age near the Franco-German border, extending northward into Lux embourg and Belgium. They are of recent commercial develop ment. While only 830,00o tons were produced in 1897, they are now the chief ores for the French, Belgian, German and Luxem bourg blast furnaces which together in 1937 produced 3o% of the world's pig iron. Mining is done in three principal basins, Longwy near the Belgian border, Briey, and Nancy at the south. Previous
to the World War much of this area was GerTnan territory, and practically all of the rest was promptly overrun and occupied by the invading army. Possession of this all but essential region was thereafter one of the aims of the contending Powers. Great dam age was done during the occupation and the retreat, and not until 1926 did the area approach the productivity of 1913. While the output of the region exclusive of Belgium and Luxembourg was about 4o million tons in 1913, equally divided between France and Germany, the French department of Meurthe-et-Moselle was able to hoist only 5 million tons in 192o. Recovery of the reunited provinces has been so rapid, however, that the output of ore reached 37 million tons in 1926. The ore beds occur in flat strata 6o to 120 ft. thick, from 30o to 75o ft. below the surface. The iron is contained in tiny nodules of hematite, cemented with a calcareous or a siliceous gangue. It is only necessary to combine these two to procure a self-fluxing, easy smelting mixture, very desirable commercially even though its iron content is quite low. Representative analyses, after driving off 8 to 12% moisture, are as follows: Phosphorus is strikingly uniform, being 1.7 to 1.9% of the iron contained, and the Lorraine pig iron must therefore be used in basic steel making, as later to be explained.
Since the rich blackband, clay iron stone and brown hematites of the Carboniferous strata have been almost exhausted, 8o% of the iron ore mined in Great Britain is now taken from leaner strata, averaging only 271%, which are a continuation of the Lorraine beds. Workable deposits extend in a broad strip from the coast of Yorkshire south-west to that of Dorset and are estimated to contain 3,400 million tons of work able ores. The beds are nearly horizontal, and consequently have broad outcrops in gently rolling ground, thus permitting them to be mined by quarrying operations. As a rule the individual de posits are small, and do not warrant the powerful excavating machinery installed in the great Mesabi pits. A maximum work ing face is 3o ft. Such "marlstones" (or simply "stone") contain the iron in tiny ooliths like the Lorraine ore, but near the surface the iron has been oxidized and hydrated to limonite, and at depth is a carbonate. Gangue materials are either calcareous or siliceous. These deposits have been longest mined at Cleveland, and here a limited area has produced 51 million tons a year since 1875. All mining is underground in carbonate ores sometimes as deep as 600 ft.; 9 to 12 ft. beds are reckoned excellent. A governmental survey made in 1918 found only 200 million tons of recoverable ore here in reserve. An average analysis follows: Cleveland ores therefore are suitable for basic steel Making, wrought iron manufacture or general iron foundry work. Except for the several post-war years of acute industrial depression, Great Britain's ore demands have been about stationary since the turn of the century. Each year Cleveland hoists 51 million tons, other regions dig 9 million tons and 6 million tons are imported, principally low-phosphorus ore from Spain and Sweden.
Whether there is any likelihood of exhausting the available iron ore is a question which has occupied some minds. From the above remarks, it may appear that certain regions, such as the Mesabi range and the Cleveland beds, may be exhausted in the near future. However there is little to fear but that other deposits, only slightly less favoured, will supply the gap. Conservative estimates by economic geologists indicate that there are now about 3o billion tons of ore in reserve, which at the present annual consumption of i oo to i25 million tons, should last Zoo years. Of this huge tonnage, two-thirds is located in the Western hemisphere ; Brazil and United States possess most of this, but Newfoundland and Cuba both have notable deposits ; France has half the balance, and the rest is scattered about in readily accessible locations. All such computations assume a cer tain state of metallurgical art in order to define ore. But metallur gical art is constantly advancing. Since so large a proportion of the earth is iron, it is safe to say that in the future, as in the past since before history began, the mind of man will always find means to win from mother earth this most useful metal, in supply ample for his current needs.