PALEOMAGNETIC EVIDENCE ON THE ORIGIN OF THE MARQUETTE AND STEEP ROCK HARD HEMATITE AND GOETHITE DEPOSITS

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Abstract
Hard hematite ore is mined at the Cliff-Shaft mine, Marquette Range, Michigan, and hard goethite ore is mined at the Caland and Steep Rock mines. Steep Rock Range, Ontario. A paleomagnetic study was made on 67 samples from the ore horizons and associated rocks of these deposits. Alternating-current demagnetization and other standard paleomagnetic procedures were used. Geologists have proposed several theories to explain the genesis of these iron deposits of direct-shipping grade. Both ore deposits have a prefolding remanence that differs in age from any of the associated rock units. This indicates that both deposits were formed as laterites resulting from the oxidation and leaching of primary iron formation by meteoric solutions. The hard hematite ore was derived from the primary magnetite-banded oxide facies of iron formation which underlies the ore at the Cliff-Shaft mine, and the hard goethite ore was derived from the primary pyrite facies at the Caland or Steep Rock mines. The laterites were subsequently buried, folded, faulted, and intruded, but the mineralogy, structure, and texture of the ores were essentially unchanged during these events.