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Item Characterization of precious metal mineral occurrences in the NorthMet deposit of the Partridge River Intrusion, Duluth complex, Minnesota, USA.(2011-08) Cervin, Daniel O.The NorthMet deposit is a Cu-Ni-PGE magmatic sulfide ore body located along the northwestern margin of the Partridge River Intrusion (PRI), which is part of the 1.1 Ga Duluth Complex. PolyMet Mining Company is currently seeking a permit to develop an open pit mine at the site, which is about 7 miles south the town of Babbitt, MN. During pilot-plant test runs by PolyMet, approximately 75% of the total mass of precious metals (75% is the average recovery of Pd, Pt, and Au) known to exist from assay data were recovered; total sulfide recovery was 90%. In a sulfide flotation beneficiation process, it is assumed that precious metals are contained within sulfide minerals as small (micron-sized) platinum group minerals (PGM), as Au-Ag minerals, or in solid solution. The 75% recovery implies that some precious metal mineral (PMM) phases may not be hosted by sulfide minerals. This study seeks to characterize the mineralogical and textural occurrences of PMM in the NorthMet ore feed and concentrates. This information is not only of importance to the beneficiation of NorthMet ores, but also to the understanding of the metallogenesis of PGE-Au in magmatic sulfide deposits. The energy dispersive spectrometer-equipped scanning electron microscope at University Minnesota Duluth was used in backscatter electron composition mode (BEC) to conduct detailed compositional scanning of polished thin sections to locate PMM. As the 75% precious metal recovery would predict, NorthMet PMM primarily occur in association with sulfide minerals. Of the 346 PMM investigated in this study, 267 (77%) were hosted by sulfide minerals (mostly chalcopyrite and pentlandite), either as inclusions or at sulfide grain boundaries. The remaining 23% (79) of PMM were found in a variety of primary silicates, secondary silicates, and apatite. Forty-eight percent of sulfide-hosted PGM are located at sulfide grain boundaries, 52% occur as inclusions in sulfide. 1) The lower recovery rate of precious metals relative to base metals in NorthMet ores is largely due to the textural and mineralogical occurrence of Au-Ag minerals, of which 55% are hosted by silicates and apatite. Furthermore, most Au-Ag minerals do not appear to be strongly attached to and intergrown with sulfide host minerals either as inclusions or at grain boundaries and are likely lost to tailings prior to introduction to sulfide flotation systems. 2) Platinum group minerals have a strong sulfide association: at least 90% are hosted in sulfide minerals. PGM occur in secondary silicates (7%) and in association with apatite (3%) in contact with, or close to sulfides. PGM primarily occur at sulfide grain boundaries in sulfide halo textures, usually in plagioclase. PGM do not occur as inclusions in primary silicate minerals. Sulfide boundary PGM are often intimately intergrown with adjacent silicate minerals. 3) An orthomagmatic model is invoked to explain the genesis of NorthMet ores. The strong sulfide association of PGM, the indirect sulfide association of Au-Ag, the general paucity of hydrous, secondary minerals in PGM-bearing sulfide halo textures, and the mostly well-preserved primary igneous textures indicate that magmatic processes formed the NorthMet ore body.Item Genesis of sulfide mineralization within the granite footwall of the maturi deposit of the South Kawishiwi intrusion, Duluth complex, NE Minnesota(2014-10) Steiner, Ronald AlexanderThe Maturi Cu-Ni-PGE deposit occurs along the basal zone of the SKI where it is in contact with granitic rocks of the Archean Giants Range Batholith (GRB) composed of plagioclase rich monzonite to monozodiorite. Generally Cu-Ni-PGE-enriched sulfides are disseminated throughout a 50-150m-thick basal mineralized zone (BMZ) and locally may be semi-massive to massive sulfide. Several researchers have noted significant sulfide disseminated to massive sulfide mineralization resultant from S originating from the BMZ. The mechanism of mineralization was unconfirmed. The goal of this study is to determine the mechanism of mineralization using petrography, traditional lithogeochemical analysis, and isocon geochemical modeling. Petrographic observations are consistent with pyroxene hornfels metamorphism by the presence of charnokites and partial melted indicated by the presence of quartz-feldspar aggregates, mortar texture, lattice dislocations in feldspars, and sieve texture in feldspars. Often those characteristics of partial melting are closely associated with magmatic sulfides. Isocon modeling indicates that incompatible elements were lost from the system which is often coincident with the gain in sulfide components based on a best-fit isocon of Mg-Mn-Cr. Petrographic and geochemical lines of evidence are interpreted to result from the dense sulfide liquid displacing the less dense partial melt from the GRB thereby penetrating into the footwall and resulting in the mineralization of below the Maturi Deposit.Item The geochemical evolution of the Sonju Lake intrusion: assimilation and fractional crystallization in a layered mafic intrusion near Finland, Mn.(2011-08) Dayton, Ryan N.The Sonju Lake Intrusion, located within the Beaver Bay Complex near Finland, MN, is the most completely differentiated intrusion related to the Midcontinent Rift System (Stevenson, 1974; Wieblen, 1982). The Sonju Lake intrusion exhibits a cumulate stratigraphy consistent with closed system differentiation of tholeiitic magma by fractional crystallization (Stevenson, 1974; Miller et al., 1993; Miller and Ripley, 1996). The Finland granite, composed of micrographic-textured ferromonzonite to leucogranite, forms the hanging-wall to the Sonju Lake intrusion and has geochemistry consistent with the Finland granite being a late stage felsic differentiate of the Sonju Lake intrusion (Miller and Green, 2002; Miller and Ripley, 1996). However, geophysical modeling of gravity and aeromagnetic data implies a volume of granophyre that approaches that of the Sonju Lake intrusion and therefore greatly exceeds the volume of felsic material that could be accounted for by differentiation of a mafic body of that size (Miller et al., 1990). Miller and Ripley (1996) suggested that the Finland granite was emplaced first and acted as a density barrier to the upward movement of the mafic Sonju Lake magma. Since underplating of the mafic magma would be expected to cause melting in the lower portions of the Finland granite, the lithologically and chemically gradational contact between the two bodies might instead represent a mixing zone between the mafic magma of the upper Sonju and the partially melted base of the Finland granite. The major and minor element geochemistry of the Finland granite resembles an extreme differentiate of the Sonju Lake intrusion and precludes using lithogeochemical data to evaluate the extent of mixing between mafic and felsic magmas. The Finland granite and Sonju Lake intrusion have distinct and identifiable isotopic compositions of Nd. Samples from the leucogranite range from -3 to -3.6 εNd at 1096 Ma with an average of -3.4 εNd for five samples (Vervoort and Green, 1997, Vervoort et al., 2007, this study). Samples from the Sonju Lake intrusion, below the cumulus arrival of apatite, range from 1.47 to -1.62 εNd. The rocks above and including the uppermost cumulate layer of the Sonju Lake intrusion consistently exhibit decreasing values of εNd with increasing stratigraphic height closer to the Finland granite. If the consistent isotopic signature of the leucogranite (-3 to -3.6 εNd) is taken as the initial εNd of the Finland granite as a whole, it is clear that the underlying quartz ferromonzodiorite, with εNd compositions of -1.7 to -2, contains a more radiogenic Nd component attributable to the Sonju Lake intrusion. The quartz ferromonzodiorite may be a late-stage differentiate of the Sonju Lake intrusion that assimilated non-radiogenic Nd from the Finland granite. An assimilation-fractional crystallization model is presented to evaluate Nd isotopes in the upper portions of the Sonju Lake intrusion and overlying Finland granite. From this model it is estimated that the Sonju Lake intrusion assimilated an amount of Finland granite equal to approximately 1-1.5% of the total mass of the Sonju Lake intrusion. Anomalously negative εNd values for samples from the SLI-1 core that profiles the felsic-mafic contact west of the main exposure area are enigmatic.Item A geophysical investigation of dewatering structures in Western Lake Superior.(2012-02) Gustafson, Daniel JayIrregular ring shaped depressions are widely developed on the floor of Lake Superior. They are typically between 200 and 300 meters across. The troughs that define these rings are typically 10 to 30 meters wide and up to five meters deep. High resolution multibeam bathymetric data show that the lake floor rings are actually chains of individual bathymetric pocks. In Lake Superior bathymetric pocks have been observed as isolated features, irregular polygonal rings, and closely grouped ring networks. The Lake Superior basin contains sediments deposited during the last deglaciation of the basin. The glacial and post-glacial sediments sit atop Precambrian basement rocks. These bathymetric ring features have not been commonly reported elsewhere. Pockmarks, however, have been observed globally and are typically the result of expelled fluids or gases. A series of high resolution, single-channel seismic data sets were collected in addition to high resolution multibeam bathymetry to test the working hypothesis that Lake Superior’s rings are the result of sediment dewatering. The vast depth of the Thunder Bay trough provides an ideal location to study these features, protected from wave base erosion. The results confirm the existence of three types of dewatering structures associated with the lake floor rings. These features include two deep-sourced and one shallow dewatering structure(s). The evidence suggests that the rings were produced by the expulsion of fluid from the lake floor at, or close to, the termination of glaciolacustrine deposition in the basin. This places the formation of these unusual features around the time of the last eastward overflow from Lake Agassiz directly into Lake Superior. Abrupt lake level change linked to the Agassiz overflow is believed to have triggered basin wide expulsion of pore water leading to the formation of the lake floor rings.Item Igneous petrology of the Ni-Cu-PGE mineralized Tamarack intrusion, Aitkin and Carlton Counties, Minnesota(2011-03) Goldner, Brian DavidThe Tamarack intrusion is an unexposed mineralized cumulate ultramafic intrusion located near the town of Tamarack, about 80 kilometers west of Duluth, Minnesota. Rio Tinto Exploration (previously Kennecott Exploration) has been conducting exploration drilling of the Tamarack intrusion for Cu-Ni-PGE sulfide deposits since 2001. The intrusion was emplaced into black slates of the Paleoproterozoic Animikie Basin during the early magmatic stage of the 1.1Ga Midcontinent Rift. A new U-Pb baddeleyite age reported here yields an age of 1105.6 ± 1.2 Ma and confirms its association with the Midcontinent Rift. Drilling and geophysical data indicate that the Tamarack intrusion has a tadpole-like shape that is about 13 km long and is between 1 and 4 km wide. The narrow tail area of the intrusion, which is the site of greatest exploration drilling, is composed exclusively of ultramafic rock types. The wider “body” area at the southeastern end of the intrusion is composed of a wider variety of rock types ranging from lherzolite to granophyric gabbronorite. Core logging, petrographic observations, mineral chemical analyses, lithogeochemical analyses, and XRF scanning of drill core were employed on four drill cores from the Tamarack intrusion to evaluate its emplacement and crystallization history. Core logging and petrography show that the lherzolitic cumulates of the tail area can be subdivided into two texturally and modally distinct units – a lower Feldspathic Lherzolite Unit characterized by coarse olivine primocrysts, and an upper Lherzolite Unit characterized by medium-grained olivine. The contact between the two lherzolite units was investigated in three cores. In one core, the contact occurs across a zone of intense alteration; in another, it shows the two lherzolite lithologies irregularly interlayered; and in a third, the feldspathic lherzolite contains gabbroic inclusions of unknown origin. In the drill core from the body area, a lherzolite similar to the upper Lherzolite Unit of the tail area grades upsection to an intergranular olivine websterite, and then to a gabbronorite, which locally contains interstitial to irregular segregations of granophyre. Disseminated Ni-Cu-PGE sulfide mineralization is present throughout most of the lithologies studied here, but is particularly abundant in the tail area at the basal contact of the Feldapathic Lherzolite unit and in a zone straddling the contact between the two lherzolite units. Whereas mineral compositions and whole rock chemical analysis within the Feldspathic Lherzolite and Lherzolite Units found in the tail of the intrusion show little cryptic variation, the chemical attributes of lithologies in the body areas show evidence of extreme differentiation. Olivine composition ranges from Fo84 in the lowermost lherzolite and becomes progressively evolved to Fo10 in the uppermost granophyric gabbronorite. Other mineral and whole rock data both show smooth gradations from the lherzolite to the gabbronorite which are consistent with these lithologies having formed from a single mafic parental magma by fractional crystallization in a closed system. The main petrologic conclusions of this study are: 1) The two lherzolitic units in the tail area formed from a similar high-Mg olivine tholeiitic parent magma. The composition of this parent magma is estimated from subtracting 30% Fo89 olivine phenocryst composition from a chilled margin found at the basal contact of the Feldspathic Lherzolite unit. The resulting composition is comparable to other picritic basalt compositions found at the base of the MCR-related Mamainse Point Volcanics. 2) The emplacement of the lower feldspathic lherzolite preceded that of the upper lherzolite in the tail area. The differences in texture and modal mineralogy between the two lherzolite units are attributed to more rapid cooling of the earlier feldspathic lherzolite, creating an orthocumulate in contrast to the more adcumulate upper lherzolite. 3) The sulfide mineralization straddling the lherzolite contact in the tail area is attributed to country rock assimilation and sulfur contamination in the leading edge of the lherzolite parent magmas during the two main emplacement episodes. The sulfide mineralization in the upper part of the Feldspathic Lherzolite is thought to be related to downward infiltration of sulfide liquid from the overlying Lherzolite unit magma upon its emplacement into the semi-molten core of the Feldspathic Lherzolite. 4) Finally, the well differentiated lithologic sequence comprising the body area is interpreted to have resulted from closed-system fractional crystallization of the second magma pulse that created the upper Lherzolite Unit in the tail area.Item Incipient vegetation recovery and its effect on braided channel morphology at Mount Pinatubo, Philippines.(2011-06) Dunn, Emily O"DonnellBraided channels are characterized as being dynamic geomorphic agents whose behavior is somewhat unstable and unpredictable. Vegetation can provide stability to this unstable behavior, constraining lateral migration rates and providing resistance to flow. In this thesis I investigate the relationship between vegetation and braided channels to better understand what controls braided versus meandering channel morphology. More specifically, I am interested in the effects of vegetation including roughness and cohesion, how much vegetation is required to have an influence, and the effect of aggradation to predict the future of the braidplain on the Pasig-Potrero and Sacobia Rivers at Mount Pinatubo, Philippines. The eruption of Mount Pinatubo in 1991 deposited 5-6 cubic kilometers of pyroclastic flow deposits onto the flanks of the volcano. I am studying the Pasig-Potrero and Sacobia Rivers on the east flank of Mount Pinatubo as vegetation becomes re-established in the braidplain. Vegetation was absent in the valley bottom for the first decade following the eruption due to extremely high sediment transport rates and rapid reworking of the braidplain. In the last three years vegetation has begun to persist in the braidplain through the rainy season. Research procedures included a combination of field work and cellular numerical modeling. Field work was comprised of 76 1x1 meter plots to characterize vegetation growth, 181 root strength measurements, 15 root density samples, 52 Wolman pebble counts, and surface sediment samples for grain size analysis. A fiber bundle model, RipRoot, devised by Pollen and Simon (2005) was utilized to obtain values for added cohesion due to roots present on streambanks. Roughness was quantified for different vegetation growth scenarios. A cellular numerical model was devised, based on Murray and Paola (2003), to test field data and gain more understanding of the relationship between vegetation and channel dynamics. Water and sediment were routed through a 200x42 cellular matrix based on slope and stream power, respectively. Vegetation was added as an impedance to sediment transport, which can also be thought of as an increase in bank strength. Both braidplains range in with from 300-500 meters, with an average of 10-50 braids, 0.1-20.0 meters wide, in cross-section. Vegetation growth occurs in patterns categorized as sparse, dense and clumpy comprised of a mix of grasses, vines, forbs and woody trees. Both stem diameter and height increased from sparse to clumpy to dense vegetation, with an average diameters of 5.25 mm in sparse to 9.92 mm in dense plots and average stem heights from 0.72 m in sparse to 2.44 m in dense plots. Roughness calculations show that vegetation decreases flow velocities by an estimated 3-12%. Values obtained from RipRoot show that dense vegetation adds 8.21-12.31 kPa of cohesion to streambanks while sparse vegetation adds 0.13-0.29 kPa. This added cohesion creates stable streambanks, which otherwise are considered unstable. Cellular model results run with the effect of vegetation show more organization of flow, seen as a decrease in total channel width and an increase in channel depth. Channel width decreases with increasing vegetation density. Channel width increases with increasing sediment transport rates, lending the idea of a sediment transport threshold that must be overcome for vegetation growth to occur on the braidplain. This observation is compatible with field observations showing a lack of vegetation growth in the braidplain while fluvial aggradation rates were high. In all, field data and observations, coupled with model results show that vegetation increases bed roughness and increases bank strength, effects that are consistent with evolution to a single-thread channel pattern.Item Mineralogy, spatial distribution, and isotope geochemistry of sulfide minerals in the Biwablk Iron Formation(2011-10) Theriault, Stephanie AnnThe Biwabik Iron Formation (BIF), which is located along the Mesabi Range in NE Minnesota, was deposited in the near shore environment of the Paleoproterozoic Animikie Basin. Although mined for natural ore and taconite, it does contain measurable amounts of sulfide minerals, as pyrite and pyrrhotite. This study is part of a larger study to evaluate whether sulfur from waste rock piles and tailings basins along the Mesabi Range are contributing to sulfate in the St. Louis River Watershed (SLRW). The primary objective of this study is to characterize the mineralogic and lithologic occurrence, spatial distribution, and sulfur isotope geochemistry of both primary and secondary sulfide minerals in the BIF in order to better establish their variation and understand their origin. Previous isotopic studies conducted on sulfides in Animikie Basin sediments have focused largely on primary (syn-depositional) sulfides in order to determine the chemistry of ocean water at the time of deposition. These studies concluded that primary sulfides were the result of bacterial reduction of Paleoproterozoic seawater sulfate. Consistent with previous studies, primary sulfides appear as small anhedral “blebs” with δ34S values of -5.4‰ to +12.4‰. Secondary sulfides display a wide range of morphologies (cubes, framboids, veins, and anhedral masses), geographic and stratigraphic distribution, and δ34S values (+80.37‰ to -36.11‰). These secondary occurrences are largely attributed to metamorphic effects of the mafic Duluth Complex or to oxidation and desilicification processes attending the formation of natural iron ores. A secondary objective of this study is to evaluate the source of sulfur to the SLRW. Sulfur isotope values from sulfates collected in the SLRW near mining operations yielded δ34S results of +4‰ to +9‰. This range is similar to the δ34S of primary sulfides in the BIF. However, it was determined that the average δ34S value of all 72 sulfide occurrences analyzed in this study is 8‰. Therefore, it is more probable that the entire range of primary and secondary sulfide are contributing to sulfate in the SLRW, rather than one specific occurrence of sulfide.Item A multiproxy record of Asian monsoon variations during the last 15,000 years from Peiku Co, Tibetan plateau.(2012-05) Du, MiaoKnowledge of Asian monsoon variations will help extend our understanding of global atmospheric circulation. Numerous studies on the Tibetan Plateau have demonstrated the great potential of lake sediment records as indicators of monsoon induced climatic changes during the Holocene. This study focuses on a multi-proxy record from Peiku Co, including XRF elemental composition, carbon isotopes of biomarkers, and GDGT indicies (TEX86, BIT, MBT/CBT), providing a paleoenvironmental history of this region on the southern Tibetan Plateau. The study shows that the climate of the Peiku basin transitioned to wetter conditions after 15 ka BP, but the wetter phase was followed by an arid event between 13 ka and 11.5 ka BP that likely correlated to the Younger Dryas. The early- to mid-Holocene climate was wetter, while drier climate prevailed after 6.7 ka BP. The climate of the late- Holocene returned to wetter conditions, probably due to stronger SW monsoons. The cold event at 8.2 ka BP and a widespread event at 4.2 ka BP could not be distinctively identified in all the proxy records from Peiku Co. The application of the BIT index indicated a constantly high amount of soil organic matter input to the lake, which biased the mean annual lake surface temperature as reconstructed by TEX86. Most Tibetan lakes are greatly influenced by riverine supply, resulting in high BIT values. Further study of the GDGT distribution in soil, water column and lake sediments are needed for a better regional calibration of lake surface temperature and air temperature.Item New evidence of Proterozoic high P-T metamorphism in East Antarctica from thermobarometry and in-situ U-Pb age dating of monazite in metamorphic glacial clasts, central Transantarctic Mountains, Antarctica(2014-11) Nissen, Chelsea I.The East Antarctic shield (EAS) is a key component in the study of early crustal evolution due to its ancient geologic history and involvement in the amalgamation and break-up of major supercontinents. The EAS has documented affinities with the cratons of Africa, India, and Australia based on limited coastal outcrop, but an ice cap up to 4 km thick prevents direct access to the interior bedrock of the EAS. Additionally, thermomechanical effects of the Ross Orogeny (~500 Ma) obscure the Precambrian history in rarely-exposed crystalline basement. Metamorphic rock clasts from glacial moraines near the central Transantarctic Mountains were studied for petrologic, geochemical, and isotopic characteristics in order to further understand the geologic history of the EAS. These clasts were presumably eroded from the interior of the EAS and may provide unique natural samples of the ice-covered basement. Metamorphic rock clasts selected in this study are semi-pelitic gneisses with high-pressure mineral assemblages, as well as accessory minerals including monazite and zircon. New in-situ SHRIMP U-Pb analysis of monazite yielded Paleoproterozoic to Neoproterozoic ages in six clasts. Among these, two clasts from Lonewolf Nunataks, at the head of Byrd Glacier, gave previously unrecognized ages of ~1900-1700 Ma, with one having a Mesoproterozoic overprint at ~1200 Ma. Lonewolf Nunataks clasts preserve evidence of high-pressure granulite-facies metamorphic conditions associated with Proterozoic crustal convergence and thickening during orogenic activity. Clasts sampled from moraines near the Miller Range yielded Neoproterozoic U-Pb ages; one clast yielded ages of ~660 and ~590 Ma, whereas other clasts gave ages of ~570- 545 Ma. Neoproterozoic samples conducive to thermobarometric analysis record high P-T conditions comparable to previously documented Ross Orogen activity in reactivated Precambrian crystalline rocks of the Nimrod Group. Together, the clast ages coupled with P-T analysis record previously unknown Paleoproterozoic tectonometamorphic events in central East Antarctica, overprinted by younger Mesoproterozoic metamorphism. Clasts from Lonewolf Nunataks may reflect a Paleoproterozoic event within the EAS related to development of the Nuna supercontinent (~1870-1900 Ma), overprinted by a Mesoproterozoic orogenic event, possibly related to the final amalgamation of Rodinia (~1200 Ma). One clast with a metamorphic age of ~660 Ma may record rift-margin activity associated with supercontinent breakup. Neoproterozoic ages of ~590-545 Ma from some of the clasts are demonstrably older than Ross Orogen ages known from Nimrod Group metamorphic basement; these older ages may therefore provide evidence that Ross orogenic activity was initiated earlier than previously thought, and that its metamorphic overprint extends farther inboard of the Transantarctic Mountains.Item Petrology and Cu-Ni-PGE mineralization of the Bovine Igneous Complex, Baraga County, Northern Michigan.(2011-07) Foley, Daniel JayThe Bovine Igneous Complex (BIC), located 8 kilometers southeast of the town of L’anse, Michigan, is a small basin-shaped mafic/ultramafic intrusion emplaced in the southwestern part of the Paleoproterozoic Baraga Basin. Although age dating of the BIC intrusion has so far been unsuccessful, the intrusion was very likely emplaced during the early magmatic stage of Midcontinent Rift development, given its similarities to other mineralized early stage intrusions, such as Tamarack and Eagle. Targeted by Kennecott as a Cu-Ni-PGE prospect, the intrusion has undergone extensive exploration drilling since 1995. To date, the intrusion has been found to be only weakly to moderately mineralized with Cu-Ni-PGE sulfides. Metal tenors provided by initial drilling averaged less than .5% Cu and Ni, and less than 350 ppb Pt and Pd (Rossell, 2008). Preliminary evaluation of field mapping, core logging and geochemical data by Rossell (2008) interpreted the intrusion to be a layered ultramafic/mafic body with an igneous stratigraphy composed of a basal wehrlite, overlain by a clinopyroxenite, and capped by a gabbro. This study was undertaken to further refine the igneous stratigraphy of the BIC, specifically its phase layering and cryptic variation, toward the goal of better understanding its emplacement, crystallization, and mineralization history. For this study, two drill cores (BIC01-01 and 08BIC-044) that profile the BIC were investigated for their petrographic attributes, cryptic mineral compositions, and whole rock lithochemistry. In addition, a detailed (1:6,000) re-mapping of the BIC was conducted. This study has found that the lithostratigraphy of the main intrusion is generally similar to that found by Rossell (2008), but when mineral modes and textures are factored in, the cumulate stratigraphy of the BIC is found to progresses from an olivine cumulate with intercumulus augite and plagioclase (feldspathic wehrlite unit), to an augite+olivine cumulate with intercumulus plagioclase (feldspathic olivine clinopyroxenite unit), to an augite+oxide±olivine cumulate with intercumulus plagioclase (oxide clinopyroxenite unit), and finally, a plagioclase+augite+oxide cumulate (oxide gabbro unit) at the top. Complimenting this cumulate phase layering is a smooth cryptic variation of upward decreasing mg# in olivine and augite composition. While this cumulate stratigraphy of Ol #1; Ol + Aug #1; Ol + Aug + Ox #1; Aug + Pl + Ox – Ol #1; Aug + Pl + Ox is evident in the field exposures and in the BIC01-01 drill core, a lower ultramafic zone was discovered in the longer 08BIC-044 core. This lower ultramafic zone is composed of feldspathic wehrlite unit (Ocp cumulate) and overlying feldspathic olivine clinopyroxenite unit (COp cumulate). Although generally similar to the same units composing the lower part of the main intrusion (called the upper ultramafic zone), there are subtle differences in mode, texture and composition that indicate that the lower ultramafic zone is a separate intrusive component of the BIC. The emplacement model is proposes that the system begins with the injection of a small pulse of magma through the Archean gneisses and into the base of the Michigamme Formation. This small pulse fractionally crystallizes from the base up, a feldspathic wehrlite followed by a feldspathic olivine clinopyroxenite. The conduit is then reopened and a second larger magma pulse is intruded above the first pulse and fractionally crystallizes producing the cumulate stratigraphy seen in outcrop and drill core BIC01-01. Due to the collinear nature of trace element and rare earth geochemistry from the lower ultramafic, upper ultramafic, and gabbro zones it is concluded that the two magma pulses came from the same parent magma source. This parent magma was determined to be a high magnesium low aluminum tholeiitic basalt with an Mg# between 68 and 70. These estimates were derived by the manipulation of geochemistry obtained from a sample located in the basal chill. Chalcophile element geochemistry suggests the BIC underwent three episodes of sulfur saturation. The first event occurred as the initial pulse, which formed the lower ultramafic zone, was injected into the surrounding country rock. Next, as the second pulse of magma injected above the first, the magma became oversaturated leading to a spike in metal tenors at the base of the upper ultramafic zone. The BIC reached sulfide saturation for a third time in passive event caused by progressive fractional crystallization.Item The petrology, petrogenesis, and metallogeny of the South Kawishiwi intrusion in the Nokomis deposit area, Duluth Complex, northeastern Minnesota.(2010-08) White, Christopher ReedA 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.Item Physical volcanology and hydrothermal alteration of the Rainy River Gold Project, northwest Ontario.(2011-07) Wartman, Jakob MichaelThe Rainy River Gold Project (RRGP) is located 75km northwest of Fort Frances, Ontario, within the Rainy River Greenstone Belt. This advanced stage exploration project has a NI43-101 compliant gold resource of 6.6 Moz indicated and inferred and 14.7 Moz indicated and inferred silver (from Rainy River Resources Press Release, February 2011) represented by low grade (<2g/t), low-moderate grade (2-10g/t), and high grade (>10g/t) gold mineralization. The nature of the gold mineralization in this deposit has been the subject of controversy, and several competing models have been proposed to explain its genesis. Initial exploration in 1967 suggested that the deposit was a shear zone-hosted resource. However, recently completed exploration drilling has now defined large, diffuse zones of gold mineralization in dacitic volcanic and volcaniclastic rocks, suggesting, in part, a syn-genetic genesis for the gold mineralization. While previous studies have examined structural regimes and timing of gold mineralization, this research focuses on the physical volcanology and hydrothermal alteration associated with the deposit. Field mapping is difficult due to a paucity of outcrop, and geological correlations are complicated by polyphase deformation, hydrothermal alteration, and both regional, and locally contact, metamorphism. This study included comprehensive fieldwork involving mapping of all available outcrops and compiling them at a 1:25,000 scale and exploration drill core logging along three sections totaling ~9000 m of core. Fieldwork, supplemented with petrographic studies of 210 thin sections and lithogeochemical investigations comprising 69 samples, has enabled distinction of stratigraphy, volcanic facies, and hydrothermal alteration assemblages, and enabled processes associated with hydrothermal metasomatism to be evaluated. Drill core is locally intensely altered and deformed, resulting in many of the units having false pyroclastic textures (Allen, 1988). Despite this, strata associated with the RRGP contain some well-preserved primary textures. These primary textures indicate that the volcanic facies in the deposit include coherent dacitic flows and associated synvolcanic intrusions with autoclastic breccias, hyaloclastites, peperites, and syn- to postdepositional resedimented volcaniclastic deposits. The coherent dacitic flows are massive, range in thickness up to 150 m, and in lateral extent for 2500 meters. Coherent dacite flows grade into a heterogeneous facies, characterized by pods and lobes of coherent dacite, enveloped by autoclastic breccia and hyaloclastite. Flows are interspersed with strongly altered volcaniclastic sediments that are locally punctuated by peperites. Volcanic facies reconstruction indicates the presence of lobe-hyaloclastite dome/flow complex fed, and locally intruded by, synvolcanic dacite hypabyssal intrusions. An apparent feeding fissure is centered to the west of the main area of mineralization. Hydrothermal alteration is widespread throughout the deposit and is marked by silicification, chloritization, sericitization, and carbonitization (as well as minor epidote and local biotite alteration). Quartz, sericite and chlorite are ubiquitous in the deposit. The isocon method developed by Grant (1986) and the box plot method developed by Large et al. (2001) were utilized to quantify the chemical alteration resulting from the hydrothermal alteration in RRGP rocks. Alteration assemblages are dominantly stratabound, and their distribution is related to original rock permeability, with flow tops, autoclastic breccias, and volcaniclastic sediments being most strongly altered. Shearzones also preserve stronger alteration intensities. Gold mineralization appears to have initially occurred within a synvolcanic, lowsulfidation (Simmons et al., 2005) epithermal system. Elevated gold values are strongly correlated with highly permeable units and increased alteration intensity, suggesting enhanced mineralization in areas that experienced higher water: rock ratios. Postvolcanic remobilization of the gold appears to have occurred, as the highest gold values in the deposit are spatially related to shear-zones and associated quartz-carbonate-epidote veins.Item Sediment budgets indicate Pleistocene base level fall drives erosion in Minnesota's greater Blue Earth River basin(2015-01) Bevis, MartinMinnesota River (MNR) tributaries are some of the most turbid in the state; many are impaired for turbidity under the Clean Water Act. Suspended sediment affects ecology and economics from headwater streams to Lake Pepin, where much of it is deposited. This project created sediment budgets for the greater Blue Earth River basin (GBERB), a group of MNR tributaries with some of the highest sediment loads. A sediment budget is a way to understand the movement of sediment though a watershed that can help landowners, land managers and other interested parties allocate resources to effectively reduce sediment loads. Our budgets use historic aerial photos and lidar-derived digital elevation models to delineate source extents and measure bluff and channel erosion rates in ArcGIS; these data were combined with upland and ravine erosion rates measured in the Le Sueur watershed. We explored sediment budget sensitivity to adjustments for sediment storage, bluff vegetation state, sedimentology, erosion rate extrapolation methods and higher-precision bluff extent delineations. Tributaries of the Minnesota River are adjusting to a profound (70m) base level fall at the end of the Pleistocene. About half of the GBERB sediment load comes from reaches below knickpoints where response to base level fall drives erosion of near-channel features like bluffs. Budgets are not sensitive to bluff erosion rate extrapolation techniques and we found no statistically significant correlations between decadal bluff retreat rates and parameters such as bluff vegetative cover, slope, size, aspect, sediment texture or stream power. There is little in-stream sediment storage in the GBERB: accommodation space primarily occurs on floodplains and in lakes, but these features are scarce due to base level fall and agricultural practices. Surficial sediment in the GBERB is composed primarily of homogeneous glacial tills and load estimates have little sensitivity to adjustments for the different bulk density and texture of glaciolacustrine and glaciofluvial sediments. It is important to construct an accurate inventory of bluff extents: A poorly-managed but plausible inventory increased the sediment budget by about 15%. These results will be useful in constructing sediment budgets for other MNR tributaries and in managing the GBERB. Shapefiles and data used in this project are available through the University of Minnesota Digital Conservancy.Item Seismic stratigraphy of Thunder Bay and the Isle Royale region of Lake Superior.(2010-08) Voytek, Emily BeachGlacial Lake Agassiz was the largest of the proglacial lakes to have formed in North America during retreat of the Laurentide Ice Sheet. The extent of Lake Agassiz was controlled by a combination of factors including topography, ice position and degree of isostatic rebound. Most changes in the outlet location of the lake involved a catastrophic release of water. Evidence for some of these catastrophic floods are visible in both terrestrial and sub‐lacustrine records. An influx of freshwater from Lake Agassiz to the North Atlantic from such floods has been suggested as a possible trigger for the initiation of the Younger Dryas cold interval. A series of airgun single‐channel seismic‐reflection profiles from Thunder Bay and the adjacent Isle Royal Trough of Lake Superior suggest that water from Glacial Lake Agassiz did not catastrophically release into Lake Superior at this locality, as has been previously suggested. Seismic surveys from a region further north within Lake Superior identified features of a younger catastrophic release of water. The features associated with the younger event include bedrock scour and large debris fans, neither of which are present in the Thunder Bay area. Given the similarity in geomorphic conditions at the two locations, similar features are expected if the same type of event occurred. Therefore, the absence of such features suggests that Lake Agassiz did not drain catastrophically through Thunder Bay. Instead of catastrophic outflow features in the seismic records, a thick package of distinct units occur in the Isle Royale trough, which suggest a complex history of ice retreat and readvance. Trough parallel profiles show a massive seismic package, which grades into more individually distinguishable units in the direction of general ice retreat.Item Statistical analysis of the spatial and temporal distribution of acid deposition in the West Midlands, England, United Kingdom.(2012-01) Cota-Guertin, Avery RoseThe burning of high sulfur coal during the Industrial Revolution of England resulted in air quality deterioration. Anthropogenic emissions are linked to health problems and environmental degradation. The implementation of environmental emission control legislation of the 1970s resulted in a significant decrease in sulfur dioxide (SO2) and nitrogen oxide (NOx) emissions. Acid deposition, as a result of industrialization, spatially and temporally varies throughout the West Midlands of England. This study seeks to quantify the effects of acid deposition as a result of the Industrial Revolution of the West Midlands using leadlettered marble gravestone corrosion as a proxy for environmental degradation. Prior to the implementation of environmental legislation corrosion values were 0.78 mm/100yrs and following legislation values decreased to 0.54 mm/100yrs indicating the efficacy of environmental clean-up efforts. Within individual cemeteries considerable variability exists. Factors that may contribute to this variability include: tree cover, orientation of stones, algae/lichen cover, gravestone texture, and local elevation differences. Statistical analysis of cemetery variables indentified tree cover, gravestone texture, gravestone color (algae/lichen cover), and local elevations differences to be significant with p-values ≤ 0.5. Tree cover and gravestone texture were used to adjust corrosion measurements. Adjusted cemetery corrosion rates mapped in ArcGIS® suggest spatial and temporal variability across the study area. Areas associated with high industrial and/or residential activity correlate to high corrosion rates.Item Surface boulder concentrations of the Late Wisconsinan Rainy lobe, Minnesota, USA(2015-01) Berthold, Angela JeannineSurface boulder concentrations on the surface of till sheets are ubiquitous features of the Late Wisconsinan Rainy lobe. They occur irrespective of topography or position on the landscape and are commonly found littering the surface of uncultivated pastures and wooded areas within the Wadena and Brainerd drumlin fields of central Minnesota and the Toimi drumlin field and the Rögen moraine of northeastern Minnesota. Previous work in these locations noted the occurrence of surface boulders but dismissed them as an erosional lag or resulting from periglacial processes. Characterizations of boulder lithologies, the composition and texture of the underlying till, and mean transport length suggest that this is not the case, and that surface boulder concentrations are primary features of till deposition. We present models for surface boulder deposition in both lodgement till and deforming bed regimes.Item Tephrochronology of the Lake Malawi Drill cores: a feasibility study.(2012-07) Chorn, BenjaminThe Lake Malawi Drilling Project recovered sediment cores from two sites on Lake Malawi in 2005: one in the northern basin (site MAL05-2 at 9°58'56.60"S, 34°11'9.17"E) and one in the central basin (site MAL05-1 at 11°17'39.60"S, 34°26'9.00"E). These cores have been studied extensively for paleoenvironment and paleoclimate conditions. Uncertainty still exists in stratigraphic correlations between cores, and the age model is becoming more refined. Cores from hole 2A and 2B contain several tephra layers, and 17 visible tephra layers were examined to correlate between the two sites. Tephra layers were sampled and analyzed for chemical composition using both electron microprobe analysis with wavelength-dispersive spectrometry (EMPA-WDS) and on a scanning electron microscope through energy-dispersive spectrometry (SEM-EDS). SEM-EDS was found to produce results that were not sufficiently accurate to make correlations and did not accurately reflect the chemical composition of samples. Because of the higher counting time and current used in SEM-EDS, alkali elements experienced migration and thus had lower perceived concentrations. Other elements such as MnO and MgO had abundances at the detection limit of SEM-EDS (0.2 wt.%) and thus varied greatly from EMPA-WDS results. Four visible tephra layers could be correlated between holes 2A and 2B, based on EMPA-WDS compositions using single linkage Euclidean distance statistical analysis of geochemical data. The correlations established that identical tephra layers in holes 2A and 2B differed in burial depth by as much as 0.9 mblf (meters below lake floor). A 23 m segment of drill site 1C was also examined for visible tephra layers and cryptotephra layers. Tephra from 23.72 to 46.29 mblf were examined in search of ash from the Youngest Toba Tuff (YTT) eruption (~74 ka). This depth corresponds to ~55 ka to ~85 ka based on the current age model for the drill site. The discovery of YTT ash would provide an isochronous marker and would improve the age model for this drill site. Three visible tephra layers were found and examined for chemical compositions, however only two possibly correlate with ash from site 2 and none correlated to the YTT. Three cryptotephra were found using a density separation method. Sediment was extracted and the fraction larger than 25 μm was density separated using sodium pentatungstate. Tephra was then identified based on optical properties and counted using a petrographic microscope, and converted to a count of shards/g. Each cryptotephra layer was analyzed using EMPA-WDS. Cryptotephra layers were also examined by X-ray fluorescence (XRF) to evaluate the utility of this rapid, non-destructive, and inexpensive approach. A phonolitic to trachytic cryptotephra layer (~1,000 shards/g), a rhyolitic cryptotephra layer (~3,000 shards/g), and a thin visible layer (phonolitic to trachytic, ~0.1 cm thick, >15,000 shards/g) were scanned with XRF. Three different XRF scanning resolutions were attempted (0.5 cm, 0.2 cm, and 0.05 cm). The cryptotephra layers were not detected at any scanning resolution; however the thin visible layer was detected at all scanning resolutions. The cryptotephra layers were all analyzed by EMPA-WDS to determine chemical composition. Of the three cryptotephra layers found in hole 1C, two were phonolitic to trachytic (typical of the Rungwe Volcanic Province eruptions) and one was rhyolitic. The rhyolitic layer, found at 28.10 mblf, correlates to the YTT eruption. One other cryptotephra layer correlates to layers from site 2, and the other layer does not correlate using geochemical data and cluster analysis (single linkage Euclidean distance). The rhyolitic cryptotephra layer correlates to the YTT (~74 ka) based on the geochemical results from EMPA-WDS. The cryptotephra layer matches the chemical composition of YTT ash published in Smith et al., 2011. This is a significant discovery because the depth at which the cryptotephra layer was found, 28.10 mblf, corresponds to an age of ~60 ka using the model by Scholz et al. (2011) and therefore indicates the need for a revised age model for this portion of the drill core. This discovery also extends the distal extent of the YTT ash from its source in the Indonesian archipelago to ~7,300 km. The most distal known extent prior to this discovery was ~4,300 km from Toba in the Arabian Sea (Schulz et al., 2002). The presence of YTT ash in Lake Malawi more than doubles the known area of YTT ash, and creates strong evidence for finding the YTT ash in other areas of East Africa.Item Timing and pattern of valley excavation, Le Sueur River, south-central Minnesota, USA(2012-05) Johnson, Andrea LynneStrath terraces of the Le Sueur River, south central Minnesota, preserve the record of river incision. A combination of airborne LiDAR (light detection and ranging) and terrace dating through optically-stimulated luminescence (OSL) and radiocarbon methods were used to construct a conceptual model of valley excavation during the Holocene and late Pleistocene from lateral and vertical incision. The river is responding to approximately 70 meters of base level fall that occurred 13,400 years ago (11,500 radiocarbon years before present), when glacial River Warren carved the Minnesota River valley. The carving of the Minnesota River valley led to widespread incision on Minnesota River tributaries as knickpoints propagated upstream from the main stem Minnesota River. As the knickpoint moved up the Le Sueur River, hundreds of terrace surfaces were formed. These terraces are strath terraces carved into glacial tills, with alluvial deposits overlying planed-off till surfaces. Observations from dating terrace alluvium indicate that the river underwent relatively continuous incision, which is ongoing today. The incision model derived from terraces ages was coupled with valley geometry measured from LiDAR data to determine how valley excavation rates have changed through time. Results from this conceptual model indicate that valley excavation has been relatively constant through time. When this background valley excavation rate was compared with the modern sediment load, it was determined that the modern sediment load is 4-5 times greater than the average Holocene sediment load. This demonstrates that the post-settlement load is greater than the pre-settlement load and should guide the management of this basin to focus on the anthropogenic changes to the basin.