The Pumping Job
The opening of the deposits will be facilitated by the fact that depth of water
and overburden in certain places is not great. It will not be necessary to pump every gallon out of the lake in order to get at the ore. The overburden is compact clay, mud, gravel and silt, and the thicknesses of it can be noted above. When the level of water is reduced to disclose the bottom of the lake, however, the over
burden will be removed hydraulically or by suction dredges and mining can begin, while other parts of the orebody surface which are deeper under water can be attacked later. Engineers estimate that ore shipments can begin 11 months after the pumping starts.
High Grade of Ore
The grade of ore proven by drilling is, of course, important because on the high average iron content and exceptional purity depends the future industrial importance of these deposits. Steep Rock ore is remarkably high in grade and regularly consistent in metallic content. The grade is calculated to run from 61 iron per cent dry analysis or 57 iron per cent natural as shipped taken as conservative for an average. Such ore, lacking as it does penalizing quantities of phosphorus, sulphur and silica, commands a premium in the steel making industry. That premium may run from 20 per cent to 30 per cent of the base price of iron ore at the head of the lakes.
The Opinion of Experts
The following extracts taken from the report of Roberts and Crago, recognized
iron ore consultants of Duluth, will serve to emphasize the importance of the deposit:
"The iron ore producers of the United States are straining every resource. The production from the Lake Superior region in 1941 was 81,210,606 long tons. Efforts are being made to produce 90,000,000 tons in 1942, which is about double the normal production. While there are large known reserves in the Lake Superior region, such tremendous annual productions are exhausting the immediately available iron ore very rapidly. Many of the largest open pit mines on the Mesabi Range are actually scraping bottom. It is not possible to increase at once the production of underground mines to a large extent.
"The underground mines that produce the high-grade lump ores required in the final stages of making open hearth steel are being pushed to the limit; there has never been an overabundance of this ore in the Lake Superior region. The war demand has caused the mines to resort to many expedients to obtain lump ore, much of which has not been satisfactory; developed reserves on the American side are rapidly approaching depletion. On the other hand, at Steep Rock, all of the evidence from the past two winters' drilling indicates that at least 25 per cent of the ore that will be produced there is of high-grade, desirable, lump ore variety.
"The Steep Rock ores are not only of Bessemer grade (containing as they do 60.64 per cent iron, .020 per cent phosphorus, 3.43 per cent silica and .017 per cent sulphur dried) but they are extremely low in phosphorus; so low is this phosphorus content that each ton of Steep Rock ore can be mixed with ordinary non-Bessemer ore to produce two or three tons of Bessemer ore. More important, even though it be true that there are large reserves of ore in the Lake Superior region, it is becoming increasingly difficult to produce ores of the average silica content required in the blast furnace, i.e. about 8 per cent.
In view of the extraordinary expansion of production during wartime, this is particularly so as regards immediately available ore. In contrast, the Steep Rock ores are very low in silica, averaging less than 3.5 per cent. It is therefore apparent that one ton of this low silica ore may be utilized by mixing with siliceous ore and thus a suitable silica content may be obtained in the resulting product. The siliceous ore so mixed would otherwise not be available unless subjected to some form of treatment requiring construction of plant and increased cost."
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