Title
Geology and Structure of a Portion of the Partridge River Intrusion: A Progress Report
Other titles
Natural Resources Research Institute Technical Report
Publisher
University of Minnesota Duluth
Abstract
Studies of the basal contact of the Partridge River intrusion, as deduced
by compilation of all drill hole data and relogging of 37 drill holes, has
indicated more structμre than previously recognized. Structure contour maps of
the footwall rocks have been prepared showing the nature of the basal contact,
the top of the Biwabik Iron-Formation, and the thickness of the Virginia
Formation beneath the Partridge River intrusion. These data indicate that preexisting
folds in the basement rocks at both Minnamax and Dunka Road exerted a
strong control over the form of the base of the intrusion. Several northeasttrending
normal faults and northwest-trending strike-slip(?) faults were al so
delineated in this study which supports the half-graben model proposed by Weiblen
and Morey (1980). A northeast~trending pre-Keweenawan fault has also been
located in the Wetlegs area. Along this fault an inferred window of Biwabik Iron
Formation is in direct contact with the Partridge River intrusion. Three oxidebearing
ultramafic bodies {Longnose, Longear, and Section 17) are exposed at the
surface along this zone. The spatial location of oxide-bearing ultramafics to
areas where the iron formation is in direct contact with the Duluth Complex
suggests that they may be genetically related.
At least five major units within the basal portion of the Partridge River
intrusion have been delineated for the Wetlegs area. They are present in 23
drill holes at Wetlegs and extend northeast into the Dunka Road Cu-Ni deposit
and southwest into the Wyman Creek Cu-Ni deposit. From the base up, these units
are characterized by: sulfide-bearing augite troctolite {175-1570 ft. thick);
troctolite with abundant layers of picrite (melatroctolite), peridotite and
dunite (450 ft. thick); a 250 ft. thick, fine-grained, mottled-textured
troctolitic anorthosite ("marker bed" for the area); augite troctolite (400 ft.
thick); and augite-bearing anorthositic troctol ite (250 ft. thick). To the
northeast and southwest of Wetlegs, most of these units are present but the
omission of particular units in either direction indicates an irregular stacked
pattern. Establishment of an internal stratigraphy has provided an excellent
opportunity to: 1) study the nature of any structural discontinuities present
within the intrusion, 2) determine the extent and variability of intrusive
lithologic units, 3) more fully understand any background geochemical variations
that may be present within and between the l i tho logic units, and 4) better
understand the origin of the Partridge River intrusion, the various Cu-Ni, CuNi-
Ti and Fe-Ti deposits and their relationship to the origin of the Duluth
Complex.
Series/Report Number
NRRI Technical Report;
NRRI/GMIN-TR-88-08
Funding information
Natural Resources Research Institute, University of Minnesota Duluth, 5013 Miller Trunk Highway, Duluth, MN 55811-1442
Suggested Citation
Severson, Mark J.
(1988).
Geology and Structure of a Portion of the Partridge River Intrusion: A Progress Report.
University of Minnesota Duluth.
Retrieved from the University of Minnesota Digital Conservancy,
https://hdl.handle.net/11299/188503.