Bulletin No. 17. The Magnetite Deposits of the Eastern Mesabi Range Minnesota

Abstract

The Mesabi range is a belt of iron-bearing formation about 100 miles long, located about 80 miles north of Duluth, which is situated at the west end of Lake Superior. The trend of the belt is east-north- east. The iron-bearing formation, commonly called taconite, is largely drift covered throughout the main range and has few of the topographic features of a "range." It is called a range because iron-bearing formations in other districts form ranges; and at the east end of the Mesabi district there are some rocky hills rising 200 to 400 feet above the general level. This report is a discussion of the eastern end of the range-that part which lies between the town of Mesaba and Birch Lake, a distance of about 20 miles. This portion of the range is commonly called the "east Mesabi." It is distinguished from the rest of the range by several features, besides the topography above mentioned. In this area, outcrops are numerous; most of the iron is in magnetic form; recrystallization has increased the size of grain and reduced the porosity; there has been very little leaching or enrichment; and in places the beds are more highly tilted. These several peculiarities make the east Mesabi a logical unit for separate study. The field work was done in the summer of 1917, by Frank F. Grout and T. M. Broderick. The Mesabi Syndicate (D. C. Jackling, and Hayden-Stone and Company) were at that time actively exploring certain parts of the area and Mr. W. G. Swart, in charge at the Duluth office, made the work much more effective by rendering many drill records accessible to the Survey. A large number of samples have been assayed in their laboratories.