The petrology, petrogenesis, and metallogeny of the South Kawishiwi intrusion in the Nokomis deposit area, Duluth Complex, northeastern Minnesota.

Abstract

A recent flurry of minerals exploration in northeastern Minnesota has legitimized the Duluth Complex as one of the largest deposits of base and precious metals in the world. These activities have facilitated both the need and the means for academic studies geared toward developing and defining the numerous Cu-Ni-PGE resources in the Duluth Complex. This study focuses on Duluth Metals‟ Nokomis deposit, taking advantage of huge volumes of new drilling and associated data to examine previous work conducted by Severson (1994), and Peterson (2001) with regard toward the petrology, stratigraphy, and genesis of the South Kawishiwi intrusion in the Nokomis deposit (formerly known as Maturi Extension) area. Through the examination of recently drilled core, and bedrock mapping in the study area Severson‟s (1994) igneous stratigraphy was evaluated and largely adopted with several additions and minor modifications. Analyses of geochemistry allowed for confirmation of several stratigraphic attributes alluded to by Severson (1994). Whole-rock, major-element geochemistry showed progressive re-charge trends through the upper parts of the intrusion, while whole-rock, major-element geochemistry and mineral chemistry data seemed to show order through chaos in the basal contact area of the intrusion. Major-element, whole-rock geochemistry also confirmed a large block of exotic rocks within the intrusion. As such, the intrusion has been broken into several major zones (basal contact zone, and upper zone) with a third zone consisting of a large block of remnant anorthositic series rocks (anorthositic inclusion block). iv Testing Peterson‟s (2001) open versus confined style mineralization model for the South Kawishiwi intrusion was the prime objective of this study. Petrographic and chemical analysis of samples collected from recently drilled core, as well as the analysis of available whole-rock and assay geochemical data led to the exploration and development of answers to several questions related to Peterson‟s (2001) model. Analyses geared toward testing for lateral flow in the basal contact area of the intrusion ultimately led to the determination that magma flow was likely prominent in the basal contact area of the South Kawishiwi intrusion, and that channelized flow may have resulted in significant upgrading of metals. This study ultimately results in the presentation of several petrogenesis and metallogenesis models for the South Kawishiwi intrusion in the Nokomis deposit area, which are largely founded on Peterson‟s (2001) mineralization model, and Severson‟s (1994) ideas regarding petrogenesis of the South Kawishiwi intrusion.