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Browsing by Subject "Master of Science in Geology"

Now showing 1 - 20 of 130
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    210Pb Geochronology in Lake Superior Sediments: Sedimentation Rates, Organic Carbon Deposition, Sedimentary Environments, and Post-Depositional Processes
    (1980-07) Evans, James Erwin
    210Pb geochronology is used to determine sedimentation rates, 210Pb flux rates, and organic carbon deposition rates from 17 sediment box cores in Lake Superior, U.S.A. These data, in conjunction with organic carbon, PCB, trace metal, benthic organism, and sedimentary structure data, are used to investigate depositional and postdepositional processes. Sedimentation rates vary from 0.01-0.20 cm/yr in Lake Superior. A dynamic model is presented which emphasizes: (1) very high (greater than 0.15 cm/yr) sedimentation rates in marginal bays, (2) moderate to very high (0.07-0.19 cm/yr) open lake sedimentation rates in regions adjacent to marginal bays, these regions are affected by plumes of suspended sediment that originate in marginal bays by wave-stirring of bottom sediments, and enter the open lake, (3) moderate to high (0.05-0.11 cm/yr) sedimentation rates adjacent to the Red Clay Area, where shoreline recession rates are high, (4) moderate to high (0.05-0.12 cm/yr) sedimentation rates in the deepest portions of the Lake Superior Troughs region, with downslope sediment movement off the adjacent shoals and into the troughs, (5) low to moderate (0.04-0.05 cm/yr) sedimentation rates from cores with current bedding features in the Keweenaw Current region, and (6) very low (0.01-0.03 cm/yr) sedimentation rates in the central lake basins due to isolation from sediment sources. Organic carbon deposition rates (K) range from 0.0001 to 0.0032 g Carbon/cm2/yr, and K varies as a power function of sedimentation rate W (g/cm2/ yr) such that K = 0.04 W1.03. This result may imply that higher sedimentation rates favor organic carbon preservation with rapid removal from the oxidizing conditions at the sediment-water interface through burial. However, the exponent is very close to 1.00, which implies that a constant proportion of organic matter is deposited with sedimentation at any site. Calculations using primary productivity measurements and average K values indicate that about 77-87% of primary production carbon is oxidized in the water column during deposition. The 210 Pb flux rate P (dpm/cm2/ yr) is directly related to the organic carbon deposition rate, such that K = 4 x 10-4P. This indicates that the main transfer mechanism for 210Pb through the water column is via association with organic particles. Organic carbon concentrations (C) decline exponentially with increasing sediment age from surficial values of 1-5% to "background" values of 0.5% in 9,000 year old sediment. The decay phenomena can be described by C = C0 e-λt, with values for the decay constant (λ) ranging from 0.2 to 1.7 x 10 -2/yr. These decay constants are 2 to 3 orders of magnitude higher than the oceans, probably due to the presence of younger and more chemically reactive organic components in Lake Superior sediments. The sedimentation rate (W) is inversely related to the decay constant (λ), such that λ = 5.33 x 10 -4 w -0.53. This may indicate that rapid burial promotes organic matter preservation. Independent evidence for biological mixing of Lake Superior sediments includes surficial zones of constant 210Pb activity, the presence of PCB substances below the sediment horizon corresponding to its first usage in commercial quantities, benthic organism studies, and lack of lamination in the upper portions of cores on x-radiographs. Oligochaete displacement rates are calculated which equal or exceed sediment accumulation rates in many cores. This indicates that oligochaetes cause significant sediment mixing at some sites. At other sites, additional mixing by burrowing amphipods may increase sediment mixing. Mixing is considered as a mechanistic analogue to diffusion phenomenon, and mixing (eddy diffusion) coefficients are calculated (Db = 0.002-10.54 cm2/yr). The highest of these compare to other studies from lakes and nearshore marine regions, while the lowest compare to rates from abyssal regions. Zones of constant 210Pb activity at depth in the sediment correspond to the time intervals 1900-1910, 1910-1920, and 1940-1950. These are interpreted as storm deposit layers, and may correspond to major storms which occurred in the Lake Superior region during November 27-28, 1905, November 22-24, 1918, and November 10-12, 1940. Diagenetic horizons are described from the sediments, these include 1-2 mm thick black laminations, 1.0-1.5 cm thick orange-colored "crusts", and layers 3-5 cm thick of many 1-2 mm diameter micronodules. The available evidence indicates that the black laminations are Mn enrichments and the orange-colored crusts may be Fe enrichments.
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    Archean Geology of an area between Knife Lake and Kekekabic Lake, eastern Vermilion district, northeastern Minnesota
    (1978-09-27) Vinje, Steven Paul
    Sedimentary and volcanic rocks of the Kekekabic Lake area, which is located within the eastern Vermilion district, northeastern Minnesota, comprise a portion of the Lower Precambrian Knife Lake Group and lie in three of Gruner's (1941) structural segments. The dominant lithology within the Knife Lake greenstone segment is arkose. The arkose is largely composed of plagioclase feldspar, is approximately 250 feet thick, and underlies the Amoeba Lake member of the Knife Lake Group. Interbedded with the arkose is black slate. Rocks within the Knife Lake greenstone segment trend N 74°E and dip 60° to the southeast. The dominant lithology within the Spoon Lake segment is graywacke. The graywacke samples studied are equally divided between the lithic and feldspathic subtypes. Rock fragments within the lithic graywackes are predominantly andesite and dacite. Plagioclase is the predominant feldspar within the feldspathic graywackes. Interbedded with the graywackes are green slates, mafic (basalt or andesite) crystal tuffs, volcanogenic conglomerate, and very minor iron-formation. The rocks within the Spoon Lake segment are approximately 800 feet thick, and have been deformed into a syncline which trends S 45W and plunges 35° to the southwest. The dominant lithology within the Kekekabic Lake segment is graywacke. The graywacke samples studied are equally divided between the lithic and feldspathic subtypes. Lithic and feldspathic graywackes of the Kekekabic Lake segment are similar petrographically to lithic and feldspathic graywackes of the Spoon Lake segment. However, the graywacke samples of the Kekekabic Lake segment, in general, contain more detrital K-feldspar (although it is still a minor component) and hornblende grains than those of the Spoon Lake segment. Interbedded with the graywackes of the Kekekabic Lake segment are green slates, mafic (basalt or andesite) and felsic (trachyte to latite) crystal tuffs, and very minor ironformation. Graywackes and associated interbedded rocks of the Kekekabic Lake segment are approximately 1000 feet thick, and have been deformed into a syncline which trends S 50°W and plunges 30° to the southwest. The graywackes and associated interbedded rocks contained in both the Spoon Lake and Kekekabic Lake segments comprise the Amoeba Lake Member of the Knife Lake Group (Gruner, 1941). The eastern portion of the Kekekabic Lake syncline is occupied by three subaerial flows. The oldest of these flows, stratigraphically, is a porphyritic green augite-hornblende andesite which is exposed at the nose of the syncline and is approximately 225 feet thick. To the west, the augite-hornblende andesite is conformably overlain by a red porphyritic hornblende andesite which is approximately 300 feet thick. The red hornblende andesite is overlain conformably, to the west, by a green porphyritic hornblende basalt which is approximately 300 feet thick. The three subaerial flows apparently plunge under a green hornblende-rich tuff and agglomerate unit. The tuff is composed exclusively of hornblende grains and is bedded and cross-bedded. The agglomerate clasts are accidental lamprophyre rock fragments. The hornblende-rich tuff and agglomerate is approximately 200 feet thick. The tuff and agglomerate and the three subaerial flows comprise the Kekekabic Lake Member of the Knife Lake Group (Gruner, 1941). Turbidite sequences within the Kekekabic Lake area are characteristic of distal turbidites, and correspond to facies associated with the depositional lobe of the mid-fan portion of a submarine fan (Walker and Mutti, 1973). Two periods of deformation have occurred in the Kekekabic Lake area along with broad folding and longitudinal and transverse faulting. The first period of deformation produced isoclinal folds, trending S 45°-50°W, with vertical to overturned fold axes that plunge to the southwest. The second period of deformation produced a pervasive N 62°-70°E cleavage throughout the area. Subsequently, broad folding warped the beds of the eastern Vermilion district on an axis trending N 60°W. Following folding, longitudinal faulting divided the Kekekabic Lake area into three distinct segments. Concurrent with or subsequent to longitudinal faulting, transverse faulting locally offset rock contacts. Sedimentary and volcanic rocks of the Kekekabic Lake area are representative of the middle portion of a calc-alkaline basalt-andesite-rhyolite volcanic pile accumulation which presumably developed within an island arc or continental orogenic system.
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    The Bedrock Geology of a Portion of the Cramer 15' Quadrangle, Lake County, Minnesota
    (1980-01) Lehman, George Albert
    The area studied consists of sections 20 - 29 and 32 - 36 of T60N, R6W of the Cramer, Minnesota 15' quadrangle. Units exposed include the anorthositic "series," troctolitic "series," and felsic "series" of the Duluth Complex, volcanic rocks of the North Shore Volcanic Group, melagabbroic-gabbroic intrusive rocks, diabasic rocks, and a hypabysal intrusive. Bedrock units are locally covered by a variety of glacial deposits related to the Rainy Glacial Lobe of the Wisconsin Ice Age. Troctolites and gabbros of the troctolitic series of the Duluth Complex display cummulate textures and regular cryptic (chemical) variation in the anorthite content of plagioclase (An78 to An58), the forsterite content of olivine (Fo70 to Fo50), and in the FeO/FeO+MgO ratio in augite (22 - 40). Orientations of igneous laminations as well as the areal distribution of rock types and cryptic variations strongly suggest the troctolitic series is a sill-like intrusion which differentiated in place as the result of crystal settling.
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    Chemostra Tigraphy and Climatostra Tigraphy of the Paleoproterozoic Snowy Pass Supergroup, Wyoming and Its Application for Correlation with Other Sequences in North America
    (1998-02) Bekker, Andrey
    The early Paleoproterozoic ocean and atmosphere experienced significant changes in climate and chemical composition. A global glaciation was followed by climatic amelioration. Chemical composition of the ocean, namely, carbon isotope values, changed dramatically during this time. Collected data support a glacial origin for the Headquarters and Vagner and possibly for the Campbell Lake Formations. Stable isotope values of limestones of the Vagner and Espanola Formations are similar, thereby strengthening correlation of the underlying glacial units. The Nash Fork Formation, based on carbon isotope values, was deposited at the end of the carbon isotope excursion. Study of carbonates of the Chocolay and Cobalt Groups showed similar carbon isotope values of the Gordon Lake Formation and the Kona Dolomite, supporting their correlation. Other carbonate units of the Chocolay Group that were considered correlative with the Kona Dolomite appear to have different carbon isotope systematics and are interpreted to be older.
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    The Colvin Creek Body, a Metavolcanic and Metasedimentary Mafic Inclusion in the Keweenawan Duluth Complex, Northeastern Minnesota
    (1996-02) Patelke, Richard Lee
    The Northern Colvin Creek body (CCB) within the 1100 Ma Duluth Complex (Complex), northeastern Minnesota, is a very large, rotated inclusion of Keweenawan basalt and sedimentary rock metamorphosed to pyroxene hornfels facies by immersion in the Complex. The inclusion is about 2500 m in strike length with a stratigraphic thickness of 800 m. Volcanic and sedimentary features indicate a stratigraphic top to the northwest; strike is about N60°E and dips are 70° to 90° to the northwest. Previously the CCB has been interpreted as an oxidized, metamorphosed basalt of the North Shore Volcanic Group (Tyson 1976) and by Severson and Hauck (1990) as an intrusive unit of the Partridge River intrusion (PRI). The body consists of two metavolcanic units and an overlying metasedimentary unit. One of the metavolcanic units is cut by a sill. The stratigraphic package is bounded to the north by a weakly recrystallized olivine gabbro and to the south and east (?) by a poorly exposed, moderately metamorphosed, oxide-rich, fine-grained augite troctolite that shows local assimilation of the margins of the inclusion; both of these igneous units are parts of the Partridge River Gabbro Complex of the PRI. In the two volcanic units mineralogy consists of plagioclase-augite-olivine-orthopyroxene-magnetite-ilmenite. Concentrations of augite replace amygdules that are round, sheeted, and pipe-like; recrystallized piagioclase phenocrysts are locally present. Grain sizes in these units range from very fine- to locally medium-grained, averaging fine-grained. Thin, discontinuous, irregular augite veins are common. Metasedimentary rocks are anorthositic gabbro to gabbroic anorthosite in mineralogical and chemical composition and are of relatively constant proportions of plagioclase-diopside-orthopyroxene-magnetite-ilmenite, with lesser hematite, hercynite, geikielite and apatite. Sedimentary features include millimeter to centimeter scale density-graded modal layering and cross-beds. Texture is fine-grained with very uniform grain size throughout the unit. The contact between the volcanic and overlying sedimentary rocks is a thin (0-2 m) interval of ferrosalite pyroxene- and plagioclase-rich rock with locally abundant cordierite, garnet, biotite, and hercynite. The inclusion is associated with a magnetic high similar to many others in the Partridge River Gabbro Complex. It is uncertain if the rocks of the Colvin Creek body are the cause of this magnetic high, or simply overlie a buried anomaly. Geochemical work has confirmed the unit subdivisions established in the field. It has indicated essentially isochemical metamorphism and has given evidence that the metavolcanic units are probably equivalent to intermediate olivine tholeiites of the North Shore Volcanic Group. The metasedimentary rocks are more problematic; they are not analogous to any of the typical interflow sandstones of the North Shore Volcanic Group as described by Jirsa (1980, 1984). At about 350 m they are as thick as the total measured section of North Shore Volcanic Group interflow sedimentary rocks, show no rock fragments, no quartz, no conglomeratic horizons, and no intercalated volcanic rocks. These metasedimentary rocks, however, appear to match a Keweenawan sandstone exposed near Phantom Lake, north of Two Harbors. The similarities include: both rocks are strongly magnetic, bedded and cross-bedded; plagioclase-rich and quartz-poor; and of uniform fine grain-size. Neither of these units can be strictly correlated with any other in the Keweenawan system.
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    A Comparison of Two Archean Ultramafic Pyroclastic Rock Units from the Superior Province, Northwestern, Ontario
    (1989-12) Schaefer, Stephen Jon
    Two Archean komatiitic pyroclastic rock units occur on opposite sides of the Quetico Fault in northwestern Ontario. The eastern unit, the Dismal Ashrock is located 3 km north of Atikokan, Ontario on the northern side of the Quetico fault within the Wabigoon Subprovince of the Superior Province. It is part of a supracrustal sequence (the Steep Rock Group) that overlies an Archean unconformity. The Grassy Portage Bay Ultramafic pyroclastic rock unit (GUP) is located 100 km to the west on the south side of the Quetico fault, and is part of an overturned succession comprising mafic metavolcanic rocks, GUP and metasedimentary rocks. The Quetico Fault is a dextral fault with a history of transpressive tectonics. The Dismal Ashrock is steeply inclined, little deformed and has undergone greenschist facies metamorphism, and it is divided into komatiitic lapilli tuff, komatiitic volcanic breccia, komatiitic volcaniclastic rocks and a mafic pillowed flow. The GUP outcrops form an arcuate fold interference pattern. The GUP is strongly deformed and has undergone amphibolite facies metamorphism. It is divided into komatiitic lapilli tuff and komatiitic volcanic breccia. The Dismal Ashrock and the GUP contain cored and composite lapilli - unequivocal evidence for explosive volcanism. Locally some of the lapilli fragments are highly vesicular (up to 30% by volume) - greater than reported for any other komatiites. Other fragments show no vesicularity. The low vesicularity of some of the pyroclasts and association with pillowed lava flows in the case of the Dismal Ashrock indicate phreatomagmatic volcanic activity. Explosive water-magma interaction was probably initiated by modified eruption characteristics produced from exsolving volatiles. The Dismal Ashrock and GUP are similar in chemical composition and plot on the border between peridotitic and basaltic komatiites on a Jensen AFM diagram. They are high in MgO, Cr and Ni; however, they are unusually enriched in Fe, Ti, Zr, Mn, P, Ba, Nb, Rb and Sr compared to other komatiites. Several lines of evidence indicate that this unusual composition could not have been caused by alteration or assimilation, and an enriched mantle source region is the likely cause. Many of the characteristics that Dismal Ashrock and GUP share are rare or unique on a global scale, indicating that the Dismal Ashrock and GUP are correlative in some manner.
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    Contact Metamorphism Adjacent to the Laramie Anorthosite Complex, Albany County, Wyoming
    (1996-05) Xirouchakis, Dimitrios
    The 1440 Ma old Laramie Anorthosite Complex, in SE Wyoming, intrudes Archean granitic gneisses and supracrustal rocks. In the central part of the complex, gneisses of pelitic and granitic composition are intruded and metamorphosed by the central anorthositic dome and the southwestern-most parts of the Maloin Ranch Pluton. The pelitic rocks exhibit field and microtextural features that suggest partial melting. Disruption of the foliation, subhedral to euhedral cordierite, orthopyroxene and oikociystic feldspars are commonly observed. Textural relations between phases suggest reactions between a mixture of crystals and silicate melt during cooling. The migmatites lack any evidence of prograde metamorphism. The granitic gneiss lacks any evidence of melting and contains garnet near the Anorthosite, and the Maloin Ranch Pluton. Pressure conditions of 3.25 (±0.5) kb were calculated from the displacement of the reaction Orthopyroxene + Sillimanite = Hercynitic Spinel + Cordierite, in the pelites. Garnet-biotite geothermometiy, in pelitic assemblages, gives temperatures that range from 620° to 800° C. The garnet-cordierite geothermometer, from pelitic assemblages, yields temperatures that range from 630° to 750° C. Garnet-biotite compositions from the granitic gneiss are within or close to the limits of the experimental calibration. Calculations yielded a peak metamorphic temperature of 850° C and lower retrograde conditions of 760° C. South of the southern anorthositic dome, mafic pyroxene hornfelses and problematic quartzrich metasediments(?) are encountered. In the enigmatic metasediments the textures indicate recrystallization during cooling. This unit does not retain any evidence of prograde metamorphism. In contrast, the mafic pyroxene hornfelses appear to reflect peak metamorphic conditions. The displacement of the reaction Oinopyroxene + Plagioclase = Gamet + Quartz in the metasediments, gives pressure conditions of 3.25 (±1.9) kb. Pyroxene and Fe-Ti oxide geothermometry, from both units, yields temperatures that range from 730° to 840° C. The 1400 Ma Sherman Granite intrudes the Anorthosite Complex and its aureole. The retrograde assemblages observed in the metamorphic rocks, and their areal distribution suggest that the granitic intrusion occurred while the aureole was cooling at 0.5-3 kb and about 600° C.
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    Contact Metamorphism of the Virginia Formation in the Minnamax Deposit St. Louis County, Minnesota
    (1979-10) Kirstein, Mark H
    The Middle Precambrian Virginia Formation, cut by diabase dikes, was intruded and contact metamorphosed by the Late Precambrian Duluth Complex near Babbitt, Minnesota. Sulfide mineralization of magmatic origin, with minor amounts formed by hydrothermal replacement, is concentrated at the irregular contact zone between the Virginia Formation and the Duluth Complex. Five miles south of Babbitt this mineralization constitutes the Minnamax Copper-Nickel Deposit, which is being investigated and evaluated underground by AMAX Exploration, Inc. The Virginia Formation consists of pelitic hornfels, calc-silicate pods, and "reaction" rims around the pods. The pelitic hornfels is dark gray, fine-grained, massive, and composed of plagioclase, hypersthene, and cordierite with local occurrences of orthoclase, biotite, and graphite. The calc-silicate pods are light gray, fine- to coarse grained, are spherical to ellipsoidal and range from 4 inches to 8 feet across. There are three types of pods; homogenous types with no mineral zones developed, layered types with mineral layers developed, and concentric types with mineral zones developed. The primary minerals are diopside, grossular garnet, plagioclase, sphene, wollastonite, and possibly some calcite, and quartz. From strikes and dips of relict bedding in pelitic horn.fels and from the broken, fra.ctured, and jumclad nature of calc-silicate pods deformation of the Virginia Formation appears intense. The "reaction" rims are dark gray, fine-grained, and up to 3 inches wide. They are composed of plagioclase, hypersthene and poikiloblastic clinopyroxene giving a composition intermediate between the pelitic hornfels and calc-silicate pods. The protolith of the pelitic hornfels appears to be a calcareous argillite and the calc-silicates a siliceous dolomitic limestone. The pods are believed to have originally been calcareous concretions in argillite with some being pieces brought up from the calcareous zone at the top of the Biwabik Iron Formation. The "reaction" rims developed after deformation took place, as they surround broken and fractured pods, and formed from diffusion of calcium from the pods into the pelitic hornfels. The metadiaba.se dikes are dark gray, fine-grained, and massive. They are composed of lathy plagioclase, augite, and hypersthene. A relict ophitic texture is evident and relict plagioclase phenocrysts have been resorbed. Sulfides consist of pyrrhotite, exsolved pentlandite, and chalcopyrite in pelitic hornfels and chalcopyrite with exsolved cubanite in calc-silicate pods. Minor ilmenite and magnetite is present in the sulfides. Alteration consists of uralitization of pyroxenes and sericitic and kaolinitic alteration of plagioclase. Quartz, calcite, apophyllite, anhydrite, fluorite, heulandite, laumontite, and prehnite are gangue minerals. This emplacement occurred after the main metamorphic event and formed by hydrothermal replacement. Based on the primary mineral assemblages present, the rocks fall in the pyroxene hornfels facies. The presence of plagioclase and wollastonite in the calc-silicate pods give a minimum temperature of 600 degrees Celsius at 2 kilobars pressure, and a mole fraction of CO2 in the vapor phase less than 0.25. An increase of albite in plagioclase can lower the temperature of the reaction forming plagioclase and wollastonite, and could cause the plagioclase and wollastonite to disappear with quartz and calcite stableo From the presence of laumontite, an upper limit of 350 degrees Celsius at 2 kilobars pressure can be given for the sulfides e:mplaced hydrothermally. A bottom temperature ranging from 250 to 300 degrees Celsius can be given by the presence of exsolved cubanite in chalcopyrite.
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    Deformation in the Archean Knife Lake Group, Vermilion District, Northeastern Minnesota
    (1989-01) MacArthur, James
    Finite strain analysis and detailed mapping of structures in Archean volcanic and sedimentary rocks in the eastern Vermilion District of northern Minnesota reveal three deformational events, the first of which appears to be responsible for the measured strain. D1 produced regional isoclinal folds with approximately E-W trending, gently plunging axes, and approximately vertical axial planes. A strong penetrative foliation occurs parallel to the axial planes of these folds and clasts in conglomerates and volcanic rocks have been strongly flattened in the plane of the foliation. D2 was a dextral simple shear event with the shear plane oriented approximately E-W which produced sigmoidal tension gashes and rotational microstructures. Kink bands indicative of EW shortening may also have been produced in an EW compressive component of this event. D3 was another simple shear event with the shear plane oriented E-W, dipping 60S with a sinistral sense of movement reflected on east-facing vertical planes or a north-side-up movement in plan view. Rotational microstructures and a local SC foliation were produced in the D3 event. Finite strain analysis reveals flattening strains consistent with D1 kinematics. Variations in measured strain are interpreted to be due to competence contrasts between strain markers and matrix. Analysis of the effects of competence contrast on apparent strain recorded by various lithologies reveals significant variations. Strain analysis using conglomerate clasts of several lithologies as well as lithic lapilli as markers thus gives an approximation of finite strain but is not sufficiently sensitive to reflect D2 and D3 strains in the study area.
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    Development of a Copper-Nickel Industry in Northeastern Minnesota
    (1973-06) Saremba, Scott P
    Many factors and problems must be considered in the developing of a copper-nickel operation in the Duluth Complex of Northeastern Minnesota. Exploration studies in the Complex reveal large volumes of low-grade copper-nickel sulfides (65 billion tons) and relatively small quantities of high-grade material (in excess of one percent). The Duluth Complex has not been extensibly explored and large areas of the Complex remain to be studied for their mineral potential. The known copper-nickel deposits are in a favorable geographic location with respect to labor, transportation, electrical power, water resources, and needed ancillary operations. The known deposits are found along the base of the Duluth Gabbro, and it is believed that most of the mineralized material will be found along the base. The deposits are found on Federal, state, and private lands, and therefore, the acquisition of these lands to prospect and permit to mine is different in each case. Federal and state mineral rights are leased, but private mineral interests may be bought or sold. Mineral land environment must be considered, as exploration and mining will affect the land, water, and air in varying degrees. Exploration can be carried out with no lasting effect on the environment, but actual mining can produce lasting effects. The degree to which the environment will be affected will depend on advanced planning, statutory authority to regulate the impact of mining on the environment, mineland reclamation plans, and the extraction method used or not used. Because most of the copper-nickel deposits are within the Superior National Forest, prospecting and mining must follow the rules and regulations of the Forest Service and Department of Interior. Part of the Duluth Gabbro is in the Boundary Waters Canoe Area, but a court decision has terminated all attempts to explore the area and prevents future mining in the BWGA. Public opinion is against mining in the BWCA because of the effects that are feared it will have on the wilderness character. Although, geological studies could be carried out without having any detrimental effect on the area. At the present, there is an oversupply of copper and nickel on the world market, but a projected demand is expected to substantially exceed supply in the future (10-20 years). Therefore, the United States will become more and more reliant on foreign sources. The prediction clearly indicates that additional U.S. copper-nickel operations will be needed. This report indicates the probability of success of such an operation in Northeastern Minnesota.
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    Differentiated Mafic-Ultramafic Sills in the Archean Vermilion District, Northeastern Minnesota
    (1974-02-01) Schulz, Klaus Jurgen
    Detailed mapping of part of the Newton Lake Formation north of Ely, Minnesota has shown the presence of numerous sill-like mafic-ultramafic intrusions in the Archean volcanic sequence. Three types of intrusions have been found: layered, differentiated mafic-ultramafic sills ranging from 400 to 1500 feet thick and at least 4 miles long; gabbroic sills of variable thickness and e xtent; and ultramafic lenses ranging from 75 to 300 feet thick and up to 3000 feet long. The layered sills were studied in detail. They have a well-developed internal stratigraphy which consists of a lower chilled-margin, peridotite, pyroxenite, bronzite gabbro, and gabbro units and an upper chilled-margin. Petrographic studies indicate that the units formed by gravitational accumulation of mineral grains, The stratigraphic succession reflects the general order of crystalization: 1) chromite, 2) chromite + olivine, 3) clinopyroxene + orthopyroxene, 4) clinopyroxene + orthopyroxene + plagioclase, 5) clinopyroxene + plagioclase. Microprobe analyses of cumulus pyroxenes has shown cryptic variations exist between units. The gabbroic sills are generally similar to the upper gabbroic parts of the layered sills. The ultramafic lenses consist of a central peridotite unit surround by a complex chilled-margin. Textural and structural features of the ultramafic lenses suggest intrusion of an olivine bearing liquid, with flowage differentiation forming the peridotite unit and rapid chilling of a crystal free liquid forming the chilled-margin. Differentiation trends of whole rock samples and calculated liquid compositions of the layered intrusions are generally in close agreement and show a general iron but minimal alkali enrichment with differentiation. Chemical analyses of chilled-margins are low in Al2O3 (10 wt%) and high in MgO (11 wt%) with a high CaO/Al2O3 ratio (0.85). The calculated bulk composition is distinctly ultrabasic in nature (MgO = 17 wt%). Mixing calculations utilizing least square methods suggest that the magma was partially differentiated at the time of intrusion. The bulk composition for the layered sills is very similar to high-MgO basalts from the Archean of Western Australia. An inital magma temperature for the layered intrusions of between 1200°C and 1100°C is inferred from element partitioning between coexisting mineral phases. Textural relations and phase equilibria suggest that crystallization of both sills and lenses probably did not take place under pressures greater than about 1 kb. (2.7 km) and may have been even lower. Metamorphism of the lower grades of the greenschist facies has affected all rocks of the Newton Lake Formation. The ultramafic rocks are serpentinized to varying degrees with olivine often the only altered phase. Serpentinization appears to have occurred along small microfractures which cut the peridotite. The mafic rocks typically have actinolite, sausseritized plagioclase, chlorite, epidote, and rare sphene. Relict grains are common in both ultramafic and mafic units suggesting that metamorphic reactions were retarded perhaps by low H2O and CO2 availability and pressure, The layered sills and lenses of the Newton Lake Formation apparently formed penecontemporaneously with the surrounding basic volcanic rocks. The layered sills probably formed as high level synvolcanic intrusions, some of which may have also acted as magma chambers for gabbroic liquids which formed sills and/or flows. The ultramafic lenses could be smaller injections of the same magma which formed the larger layered sills.
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    Drift Lithology in Relation to Bedrock Geology, Long Island Lake Quadrangle, Cook County, Minnesota
    (1977-06) Everson, Curtis I
    Lithologic studies in northeastern Minnesota suggest that drift prospecting is a useful tool for mapping drift-covered bedrock. A detailed study of till clasts composition in the Long Island Lake Quadrangle revealed a significant relationship between drift lithology and bedrock geology. The Long Island Lake Quadrangle is a suitable area for this study for the following reasons: (1) outcrops are numerous enough to have allowed the construction of a detailed geologic map; (2) the area contains eight distinctive rock units; (3) the local bedrock experienced glacial erosion, indicated by the existence of glacially abraded and quarried outcrops. The distribution of glacial sediments, mainly till and outwash, were mapped and one hundred and one samples of drift were collected along traverses parallel to ice flow (perpendicular to strike of the bedrock). Both till and outwash contain a large quantity of local bedrock clasts in the size ranges greater than 1mm in diameter. Clasts smaller than 1mm are mainly minerals, and therefore not so diagnostic of local bedrock. As a test, boulders greater than 1 meter in diameter were used in the field for inferring bedrock contacts. These contacts were found to be within 60 meters (200 ft.) of contacts placed by outcrop mapping. Lack of local bedrock clasts in the smaller size fractions indicate either high resistance of local bedrock to crushing, or lack of opportunity for crushing because of short residence time in the glacial system (short distance transport). In either case, the fine-grained fraction therefore represents a contribution to the glacial load from more distant sources and the coarse-grained fraction represents a contribution form local sources.
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    Early Precambrian Bedrock Geology of the Northwest Angle, Lake of the Woods County, Minnesota
    (1979-07) Zamzow, Craig Edward
    The Northwest Angle is located in northwestern Minnesota, bounded by the Lake of the Woods, Manitoba, and Ontario. About 4 km2 of outcrop scattered over 250 km2 area was investigated, during ten weeks of field work. The Northwest Angle contains four major rock units: a supracrustal unit; a tonalitic unit; a granitic unit; and a mafic dike unit. The supracrustal rocks show evidence of amphibolite prograde metamorphism; they are well foliated, and lineated. The foliation is given by compositional banding while the lineation is caused by the alignment of hornblende prisms in the plane of foliation. Tonalitic rocks show evidence of amphibolite grade metamorphism, the degree of foliation is variable. The granitic and mafic dike rocks show evidence of deuteric alteration; most outcrop areas contain massive rock, but two of the granite outcrop areas, both in the northwest part of the peninsula are foliated. The supracrustal rocks appear to be composed of intermediate-mafic, calc-alkalic and tholeiitic volcanics mafic to ultra mafic hypabysal intrusions, and sediments which are mineralogically similar to the volcanics. The plutonic rocks of the area show varied metamorphic effects, but maintain an igneous texture overall. The structure of the area is complex. The predominate structural grain is northeast - southwest and is produced by foliations found in the supracrustal, and tonalitic units. The granite and supracrustal rocks which crop out in the northwest part of the peninsula have foliations trending northwest to southeast. It appears that northeast trending isoclinal folding of the supracrustal rocks is responsible for the northeast trending structural grain; northwest trending structural features are attributed to detachment, or rotation of large crustal blocks, during plutonic emplacement. The apparent order of geologic events is: (1) deposition of supracrustal rocks; (2) isoclinal folding of supracrustal rocks along a northeast trend; (3) emplacement of tonalitic intrusives; (4) emplacement of granitic intrusives; (5) emplacement of large mafic dikes. Isoclinal folding of the supracrustal rocks may be comtemporaneous with tonalitic emplacement.
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    Effects of Free Flowing Saline Wells on Water Quality in a Surficial Aquifer
    (1999-12) Knoke, Kevin Lyle
    For over a century there has been concern over the adverse effects that the water from the Dakota Aquifer has on the unconfined Sheyenne Delta aquifer of North Dakota. High concentrations of NaCl and Na2SO4 often render water of the Dakota Aquifer unfit to drink. The purpose of this thesis was to gain a better understanding of the physical and chemical processes influencing ground water chemistry at a site in which mixing of waters from both the Dakota and the Sheyenne Delta aquifers has occurred. Located in the northwest corner of Ransom County of southeastern North Dakota, the research site centers around a free flowing Dakota Aquifer well that is impacting the surficial Sheyenne Delta Aquifer. The areal extent of the contaminant plume (mixed Dakota and Sheyenne Delta Aquifer water) was determined using electrode resistivity after which monitoring wells were installed. Groundwater samples were collected and submitted for analysis of major cations and anions. Following statistical analysis of samples for quality control measures, the distribution of major cations and anions was evaluated by contour concentrations. The USGS geochemical modeling software NETPATH was used to determine the amount of evaporative concentrations of Dakota Aquifer water prior to infiltration into the Sheyenne Aquifer and the degree of dilution with fresh water is evaporatively concentrated 2.35 times as it infiltrates. Concentrations of chloride Cl- and sulfate SO42-, as well as other major ions, show that the plume of brackish water is concentrated near the water table at and a short distance down gradient from the infiltration point. With continued transport distance, the plume mixes vertically with water of the surficial aquifer and is diluted. The average change in concentration is 79.29 mg/l per meter of linear distance from the infiltration point.
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    Eskers and Heavy Mineral Prospecting, Northeastern Minnesota
    (1988-01) Brown, Timothy Reed
    Mineral exploration in heavily glaciated terrain is difficult because a mantle of glacial drift generally covers the bedrock. Eskers and the heavy minerals they contain were studied to (1) determine their potential use as a prospecting tool, and (2) better understand the dynamics of esker formation. Studies emphasized paleohydraulics, origin of esker sediment, lithology, and mineralogy. 'IWo main types of eskers are recognized in northeastern Minnesota on the basis of their morphology, sedimentology, and origin. Continuous eskers form as a single, continuous segment when an ice sheet is stagnant, or nearly stagnant. Meltwater flowing through an ice tunnel deposits sediment in both the tunnel and onto an adjacent outwash plain. Melting of the tunnel walls induces inflow of the ambient ice which leads to the influx of rock debris. Seasonal fluctuations of meltwater discharge leave a sedimentary sequence characterized by a wide variety of grain sizes (medium-grained sand to boulders) and bedforms (climbing ripples, massive beds, and planar, trough, and graded cross beds). Be2ded eskers are a series of consecutive segments, or beads, that are separated by swamps or lakes, and whose trends follow the low ground between the drumlins of the Toimi Drumlin Field. A limited range of bedforms (massive beds and trough cross beds) and grain sizes (mostly bouuders) are exposed in the beaded eskers. Other sedimentary features may be present, but they are covered by the surrounding swamp deposits and not exposed. Individual segments of the beaded esker system probably form at the margin of an actively retreating ice sheet as an annual deposition event. Average distances between successive bead crests imply an annual retreat rate of 1200 feet (365 m) per year. Stone counts, X-ray diffraction, and petrographic examinations of heavy mineral mounts were evaluated as drift prospecting tools. Similar results between stone counts in eskers and in the surrounding till indicate that the esker material is most likely derived from the basal ice debris. Concentration of the heavy mineral population by fluvial processes makes eskers and outwash better locations for sampling than till. A small split from each of the 97 bulk samples was analyzed by X-ray diffraction. As no more than 5 or 6 minerals could be identified from the charts, it does not appear to be an efficient method for prospecting. In contrast, petrographic examination of heavy mineral mounts gave a much better indication of minerals present. However, no economic indicator minerals were identified with either method. The petrographic studies were useful in differentiating glaciofluvial material deposited by the various lobes of ice. The St. Louis sublobe deposits, with a higher percentage of garnets, can be distinguished from the Rainy lobe and Superior lobe deposits, whose heavy mineral populations reflect the mafic bedrock over which the ice moved.
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    An Evaluation of Anthropogenic Trace Metals in the Western Basin of Lake Superior
    (1998-01) Niendorf, Christopher Ronald
    Lake Superior sediment cores were collected and analyzed for a suite of trace metals in the solid and aqueous phase. There have been few prior studies of redox chemistry of trace metals and the effects of early diagenesis on metal in Lake Superior. In this study, redox chemistry of Fe, Mn and Co is examined, in addition to the sediment profiles of Cu, Pb, Zn and Ba. The interaction between the solid and aqueous phase redox elements is consistent with those found in other studies. The redox elements show a classic distribution, a distinct solid phase peak with a corresponding rapid increase in aqueous phase concentration. Historical events are discerned in the sediment record: the beginning of Cu mining in Michigan; and the rise and fall of alkyl lead consumption in the U.S. A mathematical model is used to predict early diagenetic concentrations of the redox elements (Fe, Mn and Co) in solid and aqueous phase assuming simple one-dimensional diffusion. The results of the model are compared to the actual vertical profiles of these metals. Trace metal fluxes of Cu and Zn into and out of the sediments are calculated. The net flux of Zn shows significant regeneration and release into the water column. Sedimentation rates and core chronologies are based on 210Pb analyses. The 100-year average sedimentation rates range between 0.011 and 0.018 g/cm2/yr (0.046 to 0.059 cm/yr), and are compared to others reported for Lake Superior. X-ray diffractometry is used to identify the presence or absence of taconite tailings and the general clay lithology at each site. Three of seven sites are affected by taconite mining. Taconite tailings were discharged into the lake beginning in 1956, therefore the first appearance of tailings in the sediment column can be used to calculate a rudimentary sedimentation rate, which ranged between 0.085 and 0.098 cm/yr.
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    Genesis of Mylonite and Structure of Francis Peak, Wasatch Mountains, Utah
    (1990-11) Dunlap, William James
    This thesis focuses on progressive deformation and mylonite formation from three common protolith rock types, layered gneiss, amphibolite and granitic rock. Protolith rock types and deformed equivalents were sampled in · the Farmington Canyon Complex on Francis Peak in the northern Wasatch Mountains of Utah. Genesis of mylonitic foliation and lineation was promoted by grain-scale processes such as recrystallization, strain, solution transfer, metamorphic reaction and fluid influx. Despite the extreme textural transition that takes place during mylonitization, protolith rock type can often be identified even after complete recrystallization. Geometric and kinematic field data were used to constrain the tectonic history of the rocks and to construct a model for the development of structures associated with the mylonites. Mylonitization probably took place during an obscure Proterozoic deformation or the Cretaceaous Sevier Orogeny, although kinematic data suggest that the former is more likely.
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    Geologic Processes and Hazards in High-Relief Terrain
    (1977-07) Berner, Heinz
    The content of this paper summarizes the principles of glacial processes and some aspects of mass movement in mountain regions such as the Alps. Especially avalanche formation and protective measures as practiced in Switzerland shall be discussed. The purpose of this report is to review some surficial geologic processes in high-relief terrain and see how they affect human developments and activities. It is thus, too, a practical exercise in environmental geology, particularly as it relates to land use planning. Furthermore, it is a library research paper required for graduation.
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    The Geology and Economic Petrology of the Archean Newton Lake Formation Boulder Bay Area, St. Louis County, Minnesota
    (1984) Yeomans, Bruce Wyatt
    The Boulder Bay area is located one and a half miles west of Ely, Minnesota, near the western shore of Shagawa Lake. This one square mile area is underlain by part of the Archean Newton Lake Formation. Eight rock types were mapped in the area and include metabasalt flows, gabbro intrusions, banded iron formation, muscovite phyllite, schistose metagreywacke, rhyolite intrusions, a granodiorite with associated apophyses, and dacite dikes, in addition to quartz veins. All rocks are metamorphosed to greenschist facies and show varying degrees of cataclasis. Two periods of deformation are recognized in the Boulder Bay area. The first is indicated by a prominent east-northeast strike of steeply dipping volcanic and sedimentary units, which is parallel to the strike of rocks present throughout the Vermilion District. Folds of this deformation are isoclinal. Six high-angle east-northeast trending faults of unknown displacement are recognized. The second period of deformation, with a major axis roughly at right angles to the first deformation, is indicated by west-northwest trending open folds in the limbs of the isoclinal folds and by locally abundant crenulations in rock cleavage. In the central portion of the area, an epizonal syntectonic (Algoman orogeny, 2.7 b.y.) granodiorite stock intrudes metabasalt flows. A narrow contactmetamorphic aureole surrounds the stock. Zoned alteration accompanied the development of gold and sulphide-bearing quartz veins in the granodiorite. Ore minerals occur as fracture fillings in these veins which were subjected to repeated periods of shearing. Similarities between Boulder Bay mineralization and ore in various gold mines in the Canadian Shield suggest a low to moderate temperature mineralizing fluid. Sulphide and gold deposition may have occurred from hydrothermal fluids migrating from depth and along deep seated fault zones. Rock types in the Boulder Bay area are typical of part of an Archean metavolcanic-metasedimentary pile and were probably deposited under subaqueous conditions. Whole rock analyses indicate the majority of the rocks are tholeiitic. The similarity of rock chemistry in the Boulder Bay area to that in other portions of the Superior Province suggests a continental orogenic or island arc origin for the area.
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    Geology and Exploration Geochemistry of the Glacial Deposits of Northeastern Itasca County, Minnesota
    (1983-09) Steinmaus, Karen
    Late Wisconsinan glaciation produced two lobes of the Laurentide ice sheet in northeastern Minnesota: the Rainy Lobe and St. Louis Sublobe of the Des Moines Lobe. In Itasca County, deposits of the St. Louis Sublobe of the Des Moines Lobe have come in contact with, and have overridden deposits of the Rainy Lobe. The Rainy Lobe ice advanced from the northeast across the Precambrian Shield, depositing a brown sandy non-calcareous till. Deposits of the Rainy Lobe in the area are referred to as Nashwauk Drift. As the ice moved in a southwesterly direction over the crest of the Giants Range, it incorporated a large percentage of granite cobbles and boulders into its drift. Other rock fragments include metavolcanic and metasedimentary rocks of local origin, with minor basalt, gabbro and granophyre. The St. Louis Sublobe entered Minnesota from the northwest, overriding the deposits of the Rainy Lobe. St.Louis Sublobe drift, referred to as Caribou Drift, consists of a thick supraglacial accumulation of calcareous sand and gravel. The till facies is a silty, calcareous flow till containing abundant granitic and metamorphic clasts, with Paleozoic carbonate and Cretaceous shale. Groundwater, lake water and lake sediment were sampled and analyzed for Co, Cu, Ni, Zn, Fe, Mn, Ca, Mg, K, and Na, to chemically characterize the surf icial deposits. Specific conductivity, pH, and depth were also measured at each site. Multivariate statistical procedures were used to differentiate the samples, then characterize each group. Cluster analysis successfully separated the samples into two groups, which correspond to the two drift types. The dominant influence on the chemistry of the samples is the drift lithology, not climate, bedrock lithology or vegetation. Results of discriminant analysis and t-tests show that pH, Ca, Mg, Na, Fe, Mn, Cu and Zn, are the variables that best distinguish the drift types. Ca, Mg, Mn, and pH are enriched in the St. Louis Sublobe samples, with Fe, Cu, Zn, and Na enriched in Rainy Lobe samples. The composition of the drift is a result of processes operating in the surficial environment, e.g., oxidation-reduction, organic complexing, and bedrock interactions. The chemical differences detected in the analysis suggest not only that both drift types are favorable for the migration of metal ions, but that the dominant influence on the chemistry of the two systems is the drift lithology. The inhibiting factor in the success of their use as geochemical sampling media is thought to involve their physical rather than chemical nature. Rainy Lobe deposits, thin occurrences of locally derived basal till appear to be chemicalaly and physically amenable to exploration geochemistry. The great thickness of the supraglacial sediments making up the Caribou Drift is thought to act as an effective barrier to circulating and oxidizing groundwaters.