MAGNETIC ANOMALIES AND MAGNETIZATIONS OF THE BIWABIK IRON‐FORMATION, MESABI AREA, MINNESOTA

Abstract

In a study of the relationship of magnetic anomalies to the magnetite content and structure of layered Precambrian iron‐formations, the effective induced and remanent magnetizations of the Biwabik iron‐formation were determined by analyses of aeromagnetic anomalies recorded 1,000 ft above the Biwabik in areas of known geology. The induced magnetization along the layers is relatively insignificant because the formation is almost perpendicular to the earth’s magnetic field. For the relatively unmetamorphosed iron‐formation of the Main Mesabi district, the dominant magnetization was found to be across the layers, about 0.012 gauss, and most likely induced. For the strongly metamorphosed iron‐formation of the East Mesabi district, the dominant magnetization was found to be along the layers, about 0.100 gauss, and remanent. These values are used as bases for explaining aeromagnetic anomalies from correlatives of the Biwabik iron‐formation in the Gunflint, Cuyuna, and Gogebic districts.