Browsing by Subject "Precious metals"

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    The petrology, petrogenesis, and metallogeny of the South Kawishiwi intrusion in the Nokomis deposit area, Duluth Complex, northeastern Minnesota.
    (2010-08) White, Christopher Reed
    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.
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    Precious Metals (Pt-Pd-Au-Ag) in Three Copper-Nickel Deposits in the Duluth Complex
    (University of Minnesota Duluth, 1989-11) Hauck, Steven A
    The research work on the precious metals in the three copper-nickel deposits centered on: 1) defining the lateral and vertical extent of the precious metals; and 2) the controls on mineralization, e.g., lithology, structure, etc. While these objectives were the same for each deposit, the methods of investigation at each deposit were dependent upon the amount and quality of previous data available.
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    Regional Till Geochemical Survey of the Western Vermilion Greenstone Belt, Minnesota
    (University of Minnesota Duluth, 2004) Larson, Phillip C
    This report presents results of a reconnaissance-scale fine-fraction (silt and clay; -250 mesh, <63μm) till geochemical survey of the western Vermilion Greenstone Belt (VGB). Survey results provide information on the background concentrations of a suite of precious, base metal, and pathfinder elements in till. The survey has identified a number of areas with elevated to anomalous precious and base metal concentrations in till associated with bedrock mineralization in the greenstone belt. The dataset provides a framework for interpretation of the significance of results of future regional and property-scale till geochemical surveys. The survey has identified a number of areas with anomalous precious and base metal concentrations. A prominent zinc anomaly (up to 266 ppm) is present down-ice of Fivemile Lake, underscoring the potential for significant undiscovered zinc mineralization in this area. Highly anomalous copper (314 ppm), gold (54 ppb), molybdenum (26 ppm), and zinc (368 ppm) are present in till in near Needleboy and Armstrong Lakes, suggesting the presence of significant mineralization in an essentially unexplored area. Anomalous gold concentrations suggest significant unidentified gold mineralization exists within the greenstone belt, most notably in the Bass Lake sequence between the Mud Creek shear zone and Vermilion Fault, where gold values up to 940 ppb were identified. Using the results of this survey as a baseline, higher density follow-up till sampling promises to more clearly define and determine the significance of anomalies, as well as determine the location of potential source rocks. Interpretation of mixing of exotic granitic with local greenstone lithologies indicate that over 50% of the fine-fraction material has been transported less than 3 km. Flow direction, transport distance, and probability sector data indicate most geochemical anomalies identified by this survey are correlative with previously identified areas with high potential for bedrock mineralization. This survey demonstrates that till composition in the VGB systematically reflects both bedrock composition and economic mineralization. Results suggest drift exploration methods in general and fine-fraction till geochemical surveys in particular, can be successfully incorporated into an integrated exploration program in the VGB. Higher density sampling is recommended to determine the significance of anomalies and more precisely define source rocks. Further work is recommended to test the applicability till geochemistry to property-scale investigations and of heavy mineral surveys.