Precambrian Research Center

Students supported by the
Precambrian Research Center

A primary objective of the PRC is to provide financial and advisory support to graduate and undergraduate students conducting field-based research on the Precambrian geology of the Lake Superior region. This support comes in the form of graduate research assistantships, which are limited to UMD graduate students, and research grants, which are available to undergraduate or graduate students from any school. The extent to which the PRC can provide such support will vary based on the annual level of Corporate and Individual Membership contributions.

Student: Tom Johnson
Status: 2nd year MS candidate at UMD
Primary Advisors: Vicki Hansen, George Hudak

PRC Support: 1/2-time graduate research assistantship for the 2008-09 academic year

Thesis title: Structural, Kinematic, and Hydrothermal Fluid Investigation of the Murray Shear Zone, northeastern Minnesota with Implications for Gold Mineralization

Research Description: Last summer, I conducted research in the Murray Shear Zone of northeastern Minnesota to investigate its architecture and kinematic history with respect to fluid migration as a catalyst for gold mineralization.  My research involved transect mapping through the Murray Shear Zone, which originates near Tower, MN and continues eastward through Eagle’s Nest Lake.  In the middle to late 1980s, Newmont Mining Corporation discovered subeconomic gold mineralization (12.5 ppm) along the northern margin of the Murray Shear Zone.  Exploratory drill holes intersected anomalous gold in the area but it was believed that economic mining was not feasible (Peterson and Patelke, 2003).  Models of Archean gold deposits have since enabled a deeper understanding with which to base exploration in Archean shear zones.  Sibson (1992) noted that in mesothermal environments (~ 10 km deep), within the brittle/ductile transition at the base of the lithospheric seismogenic regime, a process of intermittent high-pressure hydrothermal fluid release known as fault-pressure-activated valves is responsible for fluid movement up-dip of high-angle structures, mineralization, and hydrothermal self-sealing.  These sub-vertical structures may be present within the Murray Shear Zone as preliminary field data indicate dominant dip-slip features.  The objective of my study is to determine if indeed the Murray Shear Zone is an eroded and exposed mesothermal gold system.  Methods for a thorough investigation include field mapping, drill core logging, thin section study, and whole rock geochemistry.  This research will help to better understand the architecture of the Murray Shear Zone with implications for an economic gold deposit.

References
Peterson, D. M., Patelke, R. L., 2003.  National underground science and engineering laboratory (NUSEL): geological site investigation for the Soudan Mine, northeastern Minnesota.  Economic Geology Group, National Resources Research Institute, University of Minnesota Duluth: Technical Report NRRI/TR-2003/29.
Sibson, R. H., 1992.  Earthquake faulting, induced fluid flow, and fault-hosted gold-quartz mineralization.  In:  Bartholomew, M. J., Hyndman, D. W., Mason, R., Mogk, D. W., (Eds.), Basement Tectonics 8:  Characterization and Comparison of Ancient and Mesozoic Continental Margins—Proceedings of the 8th International Conference on Basement Tectonics (Butte, Montana, 1988) Kluwer Academic Publishers, Dordecht, The Netherlands, pp. 603-614.

Student: Chris White
Status: 2nd year MS candidate at UMD
Primary Advisor: Jim Miller
Co-advisors: John Goodge, Dean Peterson

PRC Support: 1/2-time graduate research assistantship for the 2007-08 academic year

Progress (9/08): Chris took a full time job in May, 2008 as a geologist with Duluth Metals Ltd. in Ely, MN. He is well into the writing phase of his dissertation and expects to defend his thesis some time in early 2009.

Thesis title: The Magmatic Evolution and Cu-Ni-PGE Mineralization of the Northern South Kawishiwi Intrusion, Duluth Complex, Northeastern Minnesota

Research Description: My thesis work focuses on understanding the igneous petrology and sulfide mineralization of a portion of the 1.1 Ga South Kawishiwi intrusion (SKI), which occurs along the northwestern margin of the Duluth Complex in northeastern Minnesota, Previous studies of the SKI (Severson, 1994) show it to have formed by multiple injections of tholeiitic magma to produce a complex igneous stratigraphy.  Economic grades of Cu-Ni-PGE enriched sulfide occur along the <100m-thick basal zone of the 2+km-thick intrusion and several deposit areas are presently being evaluated for development by various mineral exploration companies.  My work will focus on the Maturi and Nokomis deposits, which occur in northern part of the SKI and are under lease by Duluth Metals, Inc..  Two general styles of mineralization are noted in these deposits: a low-grade, large volume type called open-style and a higher-grade, lower-volume type called confined style (Peterson, 2001).  A major objective of my thesis is to better characterize these contrasting mineralization styles and to test a model proposed by Peterson (2001) that explains the two styles as reflecting different hydrodynamic conditions of sulfide-bearing magma flow under and around a large inclusion block of older gabbroic anorthosite.  My methods of investigation will involve field mapping, drill core logging, petrographic observations, microprobe analysis, and whole rock geochemistry.  This research will result in a more detailed characterization of the igneous stratigraphy and sulfide mineralization and which will in turn lead to a better understanding of the magmatic and metallogenic evolution of the South Kawishiwi intrusion.

References
Peterson, D.M., 2001, Development of a conceptual model of Cu-Ni-PGE mineralization in a portion of the South Kawishiwi intrusion, Duluth Complex, Minnesota: Society of Economic Geologists, Second Annual PGE Workshop, Sudbury, Ontario.

Severson, M.J., 1994, Igneous stratigraphy of the South Kawishiwi Intrusion, Duluth Complex, northeastern Minnesota: NRRI/TR-93/34, 210 p.

2008 Grantees

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