From Compass to Drone: The Evolving Role of Magnetics in Mapping the Geology and Ore Deposits Of the Lake Superior Region: 1830-2022
2022
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From Compass to Drone: The Evolving Role of Magnetics in Mapping the Geology and Ore Deposits Of the Lake Superior Region: 1830-2022
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2022
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Minnesota Geological Survey
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Report
Abstract
The Lake Superior region, the “Birthplace of North American Precambrian Geology,” is noted for
its world-class mineral resources, especially its native copper and iron ore deposits, and its classic
bedrock of Archean and Proterozoic orogenic belts and the exposures of rocks of the Midcontinent
Rift System. The magnetic method of mapping the region’s ore deposits and bedrock geology has
been used for nearly two centuries because of limitations in the exposure of the Precambrian
bedrock in the region. For the first century magnetic mapping was directed primarily at the
identification of regions favorable for iron and copper ore deposits using simple magnetic needle
instrumentation. Initially instrumentation was limited to the use of the dial (sun) compass and used
mainly for exploration of hard, magnetite-rich iron ore deposits. With the introduction of the dip
needle, a counterbalanced magnetic needle oscillating vertically in the magnetic meridian, to the
Lake Superior region likely in 1865 by T.B. Brooks, magnetic mapping was no longer restricted
to the difficult to interpret magnetic field angular variations.
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