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Precambrian Research Center

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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.

Aubrey on OC

Graduate Research Assistantships

2011-2012 : Ben Brooker, Matt Chaffee, Chris Goscinak

2010-2011 : Dan Foley

2008-2009 : Tom Johnson

2007-2008: Chris White

Graduate Research Assistantships

2011-2012 Academic Year

Student: Ben Brooker
Status: 2nd Year MS candidate at UMD
Primary Advisor: Jim Miller

Support: PRC graduate research assistantship for the 2011-12 academic year, USGS EDMAP grant ($5340), PRC research grant ($1000), and UMD block grant ($1000)

Thesis Title: Geology and Petrology of a Mesoproterozoic Intrusion in portions of the Brule Lake and Cherokee Lake 7.5’ Quadrangles, Northeastern Minnesota

Research Description: My research focuses on gaining a better understanding of the petrology and magmatic evolution of the 1.1 Ga Midcontinent Rift-related Sawbill Lake Intrusion. The Sawbill Lake Intrusion makes up the westernmost component of the Brule Lake- Hovland gabbro in northeastern Minnesota and has not been mapped in detail.
In the summer of 2010, I attended UMD’s Precambrian field camp to fulfill my undergraduate requirement for a six-credit field camp at Illinois State University. I also chose this camp to become familiar with the geology of the Duluth Complex, which I was considering studying for my MS research at UMD. In the fifth week of the field camp, I participated in a “capstone” mapping project with four other students that focused on mapping part of an as yet unnamed mafic layered intrusion in the Boundary Waters Canoe Area Wilderness (BWCAW). I found the geology interesting and the experience in the BWCAW left me craving more time in the lakes of northeastern Minnesota. During the capstone project, Jim pitched an idea for a thesis project that would involve integrating our 2010 mapping with capstone mapping conducted in 2007 and 2009 by other Precambrian field camp students. Collectively, these three, week-long capstone mapping projects covered about 11 square miles of the intrusion, however, many areas of the intrusion remain to be investigated. Therefore, with support from a USGS EDMAP grant, I conducted three weeks of additional mapping in the summer of 2011. The new areas will be integrated with previous mapping to create a 1:24,000 scale bedrock geologic map of the northern half of the intrusion (the southern half is not well exposed).
The main objective of this project is to document the igneous stratigraphy of the Sawbill Lake mafic layered intrusion by conducting detailed mapping, a petrographic study, and mineral chemical analyses. The overall goal of this study is to understand the emplacement and crystallization history of the intrusion. One of its more interesting aspects, which petrogenetic models must explain, is that it is composed of a well differentiated sequence of lower troctolite cumulates and upper oxide gabbroic cumulates that are separated by a screen of abundant volcanic and sedimentary hornfels inclusion all along its 15 kilometer strike length. Stay tuned.

Student: Matt Chaffee
Status: 2nd year MS candidate at UMD
Primary Advisors: Jim Miller (UMD) and Pete Hollings (Lakehead)

Support: Graduate research assistantship for the 2011-12 academic year, summer employment, and all analytical costs fully funded by Magma Metals (Canada) Limited, Thunder Bay, Ontario ($40,800)

Thesis Title: Petrographic and Geochemical Study of the Hybrid Rock Unit Associated with the Current Lake Intrusive Complex, Magma Metals’ Thunder Bay North Property

Research Description: The focus of my research consists of characterizing the mineralogical, textural and geochemical attributes of intensely altered and contaminated intrusive rocks associated with the Current Lake Intrusive Complex (CLIC). Discovered in 2001, the CLIC is one of several recently discovered ultramafic to mafic intrusions associated with the 1,1 Ga Midcontinent Rift (MCR) that host Ni-Cu-PGE deposits (Heggie, 2005; Ware et al., 2008; Rossell, 2008; Goodgame et al.2010; Goldner, 2011: Foley, 2011). The CLIC is intruded into Archean granites and high-grade schists of the Quetico subprovince. Largely unexposed in the Current Lake area about 50 kilometers northeast of Thunder Bay, Ontario, the CLIC was discovered when glacially transported ultramafic boulders, containing disseminated sulfide, were located along the shores of Current Lake. This eventually lead to the initiation of an ongoing drilling project (MacTavish and Smyk, 2010, Goodgame et al., 2010). The first drill hole intersected 10.5 meters of disseminated mineralization averaging 1.4 g/t Pt, 1.3 g/t Pd, 0.5% Cu, and 0.3% Ni.
Over the course of drilling, it was discovered that a heterogeneous intrusive rock unit commonly occurs at the margins of the mineralized ultramafic intrusion. This unit came to be termed the Hybrid Rock Unit (HRU). The close spatial relationship between the HRU and the CLIC raises the obvious question as to whether these two intrusions are also petrogenetically related. My research will employ core logging, petrographic studies, mineral chemistry and lithogeochemical analysis, and geochemical modeling in order to characterize the mineralogical, textural, and geochemical attributes of the HRU. The results of this study will address the question of the HRU’s petrogenetic relationship to the CLIC, as well as to understand the origin of its heterogeneity.

References Cited
Foley, D. J., 2011, Petrology and Cu-Ni-PGE Mineralization of the Bovine Igneous Complex, Baraga County, Northern Michigan. M.S. thesis. University of Minnesota Duluth, Duluth, MN, 83p.
Goldner, B.D., 2011, Igneous petrology of the Ni-Cu-PGE mineralized Tamarack intrusion, Aitkin and Carlton Counties, Minnesota. M.S. thesis. University of Minnesota Duluth, Duluth, MN, 155p.
Goodgame, V.R., J.R. Johnson, A.D. MacTavish, W.E. Stone, K.P. Watkins and G.C. Wilson, 2010, The Thunder Bay North Deposit: Chonolith-Hosted Pt-Pd-Cu-Ni Mineralization Related to the Midcontinent Rift. 11th International Platinum Symposium, Abstract Volume, Sudbury, Ontario. Ontario Geological Survey, Miscellaneous Release–Data 269.
Heggie, G.J. 2005, Whole rock geochemistry, mineral chemistry, petrology and Pt, Pd mineralization of the Seagull intrusion, northwestern Ontario. M.Sc. thesis, Lakehead University, Thunder Bay, ON.
MacTavish, A. and Smyk, M.C., 2010, Thunder Bay North Project, Magma Metals Limited. In Miller, J.D., Smyk, M.C. and Hollings, P.N. (eds.).Cu-Ni-PGE deposits in mafic intrusions of the Lake Superior region: A field trip for the 11th International Platinum Symposium; Ontario Geological Survey, Open File Report 6254, 166p.
Rossell, Dean, 2008, Geology of the Keeweenawan BIC intrusion: Institute of Lake Superior Geology. 54th Annual Meeting, Marquette, MI, Proceedings and Abstracts, p. 181-199.
Ware, A., Cherry, J., and Ding, X., 2008, Geology of the Eagle project: Institute of Lake Superior Geology. 54th Annual Meeting, Marquette, MI, Proceedings and Abstracts, p. 87-111.

Student: Christopher Goscinak
Status: 2nd year MS candidate at UMD
Primary Advisor: Vicki Hansen

Support: PRC graduate research assistantship for the 2012 spring semester

Thesis title: Quartz Fabric Analysis and Interpretation of Archean Shear Zones: Vermilion District, NE Minnesota

Research Description: Two suites of end-member hypotheses have been proposed to explain the formation of granite-greenstone terrains which make up large tracts of Archean (3.8-2.5 Ga) crust. 1) Volcanic arc-accretion likens Archean tectonic processes to modern day subduction and arc-accretion systems dominated by horizontal displacements (e.g., Percival and Williams 1989; Card, 1990; Cawood, 2006). 2) Sagduction-diapirism likens Archean tectonic processes to a gravity inversion of less dense felsic plutonic material diapirically rising with respect to the sinking (sagduction) of more dense mafic volcanic material with dominantly vertical displacements (e.g., McGregor, 1951; Anhaeusser et al., 1969; Collins et al., 1998; Bedard et. al, 2003; Van Karendonk et al., 2004; Chardon et al., 2008). Structural fabrics within the Vermilion district of northeastern Minnesota have lead to studies advocating both hypotheses. Studies concluding dextral transpression, supportive of volcanic arc-accretion, interpret dextral shearing perpendicular to the lineation due to oblique convergence (Hudleston et al., 1988; Schultz-Ela and Hudleston, 1991) Other studies, interpreting shearing parallel to the lineation more supportive of the sagduction-diapirism hypothesis (Goodman, 2008; Karberg, 2009; Johnson, 2009; Erikson, 2010). Although examining similar structural data, these studies differ on their interpretations of the motion plane and shearing direction relative to the lineation. Shear sense interpretations must be conducted on the plane of highest asymmetry, the motion plane. Within the Vermilion district, the motion plane can be ambiguous due to the small grain-size of deformed mineral grains.
To gain insight on how the L-S tectonites formed my research employs fieldwork, microstructure kinematic analysis, and quartz crystallographic fabrics analysis. Fieldwork consists of mapping and determining the extent of a small-unstudied shear zone near the town of Pleya, MN. Microstructure work on will yield a kinematic interpretation of the shear zone. Quartz crystallographic fabrics results in crystallographic preferred orientation (CPO) diagrams and will be analyzed on samples from the Kawishiwi Shear Zone in addition to the Pleya Shear Zone. This kind of structural analysis has yet to be applied to this area and will prove useful, for it confronts first-order issues such as ductile flow direction and orientation of the vorticity vector and motion plane. This will document if flow is parallel, or perpendicular, or at some angle to lineation.

References Cited:
Anhaeusser, C.R., Mason, R., Viljoen, M.J., Viljoen, R.P., 1969. A reappraisal of some aspects of Precambrian shield geology. Geological Society of America Bulletin vol. 80, 2175-2200.
Card, K.D., 1990. A review of the Superior Province of the Canadian Shield, a product of Archean accretion. Precambrian Research, vol 48, 99-156.
Cawood, P.A., Kroner, A., Pisarevsky, S., 2006. Precambrian Plate tectonics: criteria and evidence. GSA Today, vol. 16, 4-11.
Collins, W.J., Van Kranendonk, M.J., Teyssier, C., 1998. Partial convective overturn of Archaean crust in the east Pilbara craton, Western Australia: driving mechanisms and tectonic implications. Journal of Structural Geology vol. 20, 1405-1424. Erikson, E., 2010. Structural and kienematic analysis of the Shagawa Lake shear zone, Superior Province, northen Minnesota: implications for the role of vertical versus horizontal tectonics in the Archean. Canadian Journal of Earth Sciences, vol. 47, 1463-1479.
Goodman, S., 2008. Structural and Kinematic Analysis of the Kawishiwi Shear Zone, Superior Province. M.S. Thesis, University of Minnesota Duluth, MN.
Hudleston, P.J., Schultz-Ela, D., Southwick, D. L., 1988. Transpression in an Archean greenstone belt, northern Minnesota. Canadian Journal of Earth Sciences, vol 25, 1060-1068.
Johnson, T., 2009. Structural, Kinematic and Hydrothermal Fluid Investigation of the Gold-Bearing Murray Shear Zone, Northeastern Minnesota. M.S. Thesis, University of Minnesota Duluth, MN.
Karberg, S M., 2009. Structural and Kinematic Analysis of the Mud Creek Shear Zone, Northeastern Minnesota. M.S. Thesis, University of Minnesota Duluth
Macgregor, A.M., 1951. Some milestones in the Precambrian of Southern Rhodesia. Transactions of the Geological Society of South Africa. 54, 27-71.
Percival, J.A., and Williams, H.R. 1989. Late Archean Quetico accretionary complex, Superior province, Canada. Geology, vol. 17 (1). 23–25.
Schultz-Ela, D.D., Hudleston, P.J., 1991. Strain in an Archean greenstone belt of Minnesota. Tectonophysics, vol. 190, 233-268.
Van Kranendonk, M.J., Collins, W.J., Hickman, A., Pawley, M., 2004. Critical tests of vertical vs. horizontal tectonic models for the Archaean East Pilbara Granite-Greenstone Terrane, Pilbara Craton, Western Australia. Precambrian Research vol. 131, 173-211.

2010-2011 Academic Year

Student: Dan Foley
Status: Completed MS degree, July 2011
Primary Advisor: Jim Miller

Support: PRC graduate research assistantship for 2011 spring semester

Thesis title: Petrology and Cu-Ni-PGE Mineralization of the Bovine Igneous Complex, Baraga County, Northern Michigan

Research Description: My research focuses on gaining a better understanding of the petrology and magmatic evolution of the Midcontinent Rift-related Bovine Igneous Complex. First discovered in the early nineties in northern Michigan by Rio Tinto, this intrusion has since been extensively drilled in hopes of discovering significant nickel, copper, and PGE reserves (Rossell 2008). Although only minor mineralization has been observed, a handful of well mineralized early ultramafic rift related intrusions similar to BIC have been discovered in Northern Michigan, Northern Minnesota, and Canada and thus have become increasingly popular exploration targets (Hollings et al. 2007). The recent successful discovery of several similar mineralized intrusions raises the question as to what differences led to the formation of the poorly mineralized BIC as compared to the better-mineralized intrusions located throughout the rift? The principal objective of my research is to characterize the igneous stratigraphy, cumulate phase layering, sulfide mineralization, cryptic mineral variation, and bulk geochemical variations of the Bovine Igneous Complex. Consisting of core logging, field mapping, petrographic studies, and chemical analysis, the result of the research may be a better understanding of what processes are important to the evolution of a poorly versus strongly mineralized intrusion.

References
Hollings, P., Hart, T., Richardson, A., MacDonald, C., A., 2007. Geochemistry of the Mesproterozoic intrusive rocks of the Nipigon Embayment, northwestern Ontario: evaluating the earliest phases of rift development. Canadian Journal of Earth Science, 44, pp. 1087-1110.
Rossell, D., 2008. Geology of the Keweenawan BIC Intrusion. 54th Annual Institute on Lake Superior Geology, Field Trip Guidebook, v.54, pp. 181-193.

Dan at BIC

2008-2009 Academic Year

Student: Tom Johnson
Status: Completed MS degree July, 2009
Primary Advisors: Vicki Hansen, George Hudak

PRC Support: PRC 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.

Tom Johnson

Tom and Dean

2007-2008 Academic Year

Student: Chris White
Status: Completed MS degree June, 2010
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.

Chris and Benedek at Maturi

Chris at Omaday Lake