The Duluth Complex.
The Duluth Complex, the related Beaver Bay Complex, and the associated North Shore Volcanic Group are rock formations which comprise much of the basement bedrock of the northeastern part of the U.S. state of Minnesota in central North America.
The Duluth Complex is a composite intrusion of troctolite and gabbro derived from periodic tapping of an evolving magma source. In the waning stages of rifting, the principal rock types deposited in the Midcontinent Rift System shifted gradually from magmatic to sedimentary; among the sedimentary sequences are those for which alluvial-fan, fluvial braid-plain, aeolian, and lacustrine depositional environments may be inferred.
The Duluth Complex is one of the largest intrusions of gabbro on earth, and one of the largest layered mafic intrusions known. It covers an area of 4715 km2. The lower portion of the intrusion along the northwestern margin consists of ultramafic cumulates with associated segregations of nickel, copper and platinum group elements. The upper differentiated portions include ilmenite bearing labradorite anorthosites.
Babbitt is one of the 8 low grade Ni-Cu and that are distributed in an interval of 35 Km in a lower region of the Duluth Complex.