• Geochemistry Of The Late Devonian 'Punctata' Event In The Western Canada Sedimentary Basin

      Sliwinski, Maciej Grzegorz; Whalen, Michael; Newberry, Rainer J.; Trainor, Thomas P.; Severin, Kenneth P. (2012)
      Carbonate deposits straddling the Early-Middle Frasnian (Late Devonian) transitional interval at the isolated Miette carbonate platform in the Western Canada Sedimentary Basin were studied geochemically to better understand the paleoceanographic changes that had taken place regionally during the global 'punctata Event' Earth-system perturbation, characterized by the short-term (<0.5 M.y.) yet wide-spread eutrophication of epeiric environments and the deposition of organic carbon-rich facies. This event occurred while the evolution of terrestrial forests entered a rapid, near exponential phase of diversification and expansion, thus altering nutrient-cycling between the terrestrial and marine realms through a transient increase in the intensity of pedogenic weathering. I've attempted a reconstruction of the chemostratigraphic variance of (1) bioproductivity, paleoredox and detrital elemental proxies, of (2) isotopic records (delta13C (carb & org); delta15Norg), and of (3) related parameters, including TOC, magnetic susceptibility (MS) and the abundance and mineralogy of acid-insoluble carbonate residues, and interpreted these within the context of regional sequence stratigraphy and paleogeography against the background of global geobiological events. Analytical methods and standards were developed for measuring low (<10 ppm) concentrations of crucial proxies in carbonates (down to 1-2 ppm) by WD-XRF, and were verified by a diversity of statistical tests and analyses. Evaluation of chemostatigraphic trends revealed that eutrophication and geochemical anomalies associate strongly with a 3rd-order transgression (IIc1) and increased detrital input in the lower punctata Zone. Factor analyses were thus applied to constrain the influence of 1) siliciclastic input vs. 2) the development of benthic anoxia (explaining 55 and 35% of total variance, respectively) on trace element excursions, but also to 3) assess the extent to which MS records within the stratigraphy track the clastic input. Mineralogical controls on MS variance were determined by XRD analyses of acid-insoluble limestone residues, and a multivariate linear regression model was found to account for 97.7 % of total variance as a function of variable admixing of illite, pyrite, quartz and feldspars, in turn variably diluted by the total carbonate content.
    • Geodatabase development and GIS based analysis for resource assessment of placer platinum in the offshore region of Goodnews Bay, Alaska

      Oommen, Thomas (2006-12)
      Goodnews Bay, southwest Alaska, is known for extensive Pt reserves that have their source in the neighboring Red Mountain. The reserves potentially extend offshore into the Bering Sea. This study aims at developing a geodatabase to integrate all offshore platinum related data collected by researchers and agencies in the past, with the intent to identify data gaps. Based on these data gaps 49 new areas were sampled for Pt and geophysical data were collected in summer 2005. Spatial distribution map for offshore Pt was created using a new Multiple Regression Pattern Recognition Technique (MRPRT) that gave an R²=0.76, a significant improvement from standard GIS based geospatial techniques. Four potential Pt exploration areas were delineated, including one area where drowned ultramafics and buried alluvial channels co-occur. Coastal currents influenced the surficial platinum accumulations, and no clear relation between Pt distribution and sand bars in the far offshore could be established.
    • Geographic distribution of genetic variation in ten species of North American forest birds: island endemism and transcontinental ranges

      Topp, Carrie M. (2008-05)
      Comparative genetic studies of geographically co-occurring species can lend insight into current and historic relationships among populations and species. This enables examination of similarities and differences among species and provides information about historic processes leading to current genetic and geographic distributions. I used this approach to study two different types of avian co-distribution: island endemism and transcontinental ranges. The Queen Charlotte Islands (QCI), Canada, have many endemic subspecies; historically it may have been a glacial refugium. I used genetic analyses to determine subspecies uniqueness and to identify units of conservation for five species, four with endemic QCI subspecies. I found that QCI populations were genetically differentiated from mainland populations, although each species had a different isolation history, and that QCI is an important area for avian conservation and management. East-to-west genetic splits across North America are seen in vertebrates and may be the result of Pleistocene glacial cycles. Five migratory thrushes successfully colonized northern North America. They have overlapping transcontinental ranges and similar ecological niches in woodland communities. I used genetics to determine how these thrushes established continent-wide ranges. Despite their ecological and distributional similarities these five thrush species had different patterns of colonization across North America.
    • The geography of isolation: nineteenth century science, exploration and the conception of the Aleutian Islands

      Watson, Annette (2000-12)
      The purpose of this thesis is threefold: first, to follow the early history of Alaska from the point of view of the Aleutian Islands; second, to follow how the history of science intersects with this history. Third, to show how nineteenth century science and scientists conceived of the Aleutians, and how their conceptions translated to public perceptions of landscape. The Aleutian Islands went from being the center of the newly-purchased Alaska in 1867--to an isolated chain of islands stretching beyond the margins of the map. Tracing the progression of this isolation demonstrates how landscape--an amalgamation of physical experience and myth--is the product of one's identity.
    • A geohydrologic analysis of an upland-bedrock aquifer system: applications to interior Alaska

      Youcha, Emily K. (2003-05)
      Ester Dome, an upland-dome bedrock aquifer system, located nearby Fairbanks, Alaska, was studied to identify important geohydrologic processes occurring in Interior upland aquifer systems. The ground-water dynamics at Ester Dome are complex due to the fractured nature of the aquifer system. The geology at Ester Dome consists of metamorphic and igneous rocks. Valley bottom deposits include gravels and loess. The flow pattern of the dome aquifer system is radial. Ground-water flows from a central high elevation recharge area and discharges into lakes, streams, and wetlands in the valley bottoms. The primary form of recharge to the bedrock aquifer is from spring snowmelt. Snow water equivalent and snow depth increases with elevation. Ground-water levels were observed at fifty sites on Ester Dome for two years. Water levels in wells at high elevations or locations with no silt or permafrost coverage show seasonal fluctuations. However, ground-water levels in the valley bottoms show little seasonal fluctuations, except wells that penetrate gravel deposits and have no overburden. A ground-water flow model was developed to aid in the understanding of these geohydrologic processes. The ground-water flow model shows recharge and bedrock hydraulic conductivity as the most sensitive parameters.
    • Geologic description and reservoir modeling of a Jurassic aged, low permeability, light oil reservoir, northern coastal plain, Alaska

      Newell, Jack Robert (2001-05)
      The objectives of the study include the analysis of the geologic description and reservoir modeling of a Jurassic aged, low permeability, light oil reservoir on the northern coastal plain of Alaska. The methodology of the study was to use a reservoir simulation model to evaluate the performance and cumulative recovery of the reservoir under primary depletion and a water injection process. Results of the simulation showed a primary recovery of 15.9 %OOIP of oil by solution gas drive. The results of thee simulation by a water displacement process showed that 41.9 %OOIP oil could be recovered with a production of 38.5 %HCPV of the injected water. This study has an application in determining estimates of the design paramaters for surface facilities required for the development of the field.
    • Geologic setting of the Central Alaskan hot springs belt: Implications for geothermal resource capacity and sustainable energy production

      Kolker, Amanda M.; Eichelberger, John; Newberry, Rainer; Larsen, Jessica; Colt, Steve (2008-12)
      The Central Alaskan Hot Springs Belt (CAHSB) is a vast stretch of low-temperature hydrothermal systems that has the potential to be a geothermal energy resource for remote communities in Alaska. Little exploration has occurred in the CAHSB and the resource is poorly understood. A geothermal power plant was installed in 2006 at Chena Hot Springs (CHS), one of the 30-plus hot springs in the CAHSB. This, in addition to the multiple direct use projects at CHS, could serve as a model for geothermal development elsewhere in the CAHSB. This dissertation evaluates the geologic setting of the CAHSB and explores the implications for resource capacity and sustainable energy production. The local geology and geochemical characteristics of CHS are characterized, with a focus on identifying ultimate heat source responsible for the hot springs. A radiogenic heat source model is proposed and tested for the entire CAHSB, wherein the anomalously radioactive plutons that are associated with nearly every hot spring are providing the source of heat driving the geothermal activity. This model appears to be feasible mechanism for the observed heat transfer. This implies that CAHSB “reservoir” fluids are probably low-temperature. It also suggests that individual hydrothermal systems are small-scale and localized features, unlike the types of hydrothermal systems that are conventionally exploited for energy (i.e., those that derive their heat from magmatic or deep crustal sources, which have higher reservoir temperatures and larger spatial extent). In this context, the individual capacity of several CAHSB resources close to communities is assessed, and a preliminary evaluation of the sustainability of the power production iii iv scheme at CHS is given. As another approach to the question of sustainability, this dissertation explores the ways in which external benefits of geothermal energy can influence the economics of a project. In sum, producing geothermal energy from CAHSB resources is somewhat risky at the present time, though it may be less risky than continued use of diesel fuel. The risks of geothermal development could be greatly reduced by rapid and immediate exploration efforts to collect much-needed data about CAHSB geothermal resources.
    • Geological modeling and reservoir simulation of Umiat: a large shallow oil accumulation

      Oraki Kohshour, Iman; Dandekar, Abhijit; Hanks, Catherine; Ahmadi, Mohabbat; Dandekar, Abhijit (2013-05)
      Current high oil price and availability of new technologies allow re-evaluation of oil resources previously considered uneconomic. Umiat oil field is one such resource: a unique, shallow (275-1055 feet), low-pressure (200-400 psi) reservoir within the permafrost zone located north of the Arctic Circle, 80 miles west of Trans Alaska Pipeline System (TAPS) with an estimated 1.5 billion barrel of oil-in-place. This thesis presents a reservoir model that incorporates recently identified permeability anisotropy patterns within the Cretaceous Nanushuk sandstone reservoir to evaluate various potential mechanisms such as horizontal wells and immiscible gas injections. The simulation model focuses on the Lower Grandstand which is identified as a better reservoir rock. The reservoir temperature is assumed at 26 OF and gas is injected at the same temperature to maintain equilibrium with the permafrost and prevent any well integrity problems. An optimum horizontal well length of 1500 ft was found and applied for all simulation cases. The simulation results show that with 50 years of lean gas injection, recovery factors for the base case and case of 600 psi injection pressures are 12% and 15%, respectively, keeping all other parameters constant.
    • Geology and gold mineralization of the Nyac district, southwest Alaska

      Wenz, Zachary John (2004-08)
      The Nyac district, southwest Alaska, contains multiple felsic to mafic plutons and dikes intruding the volcano-sedimentary package of the Nyac terrane. Dated plutons and dikes in the Nyac terrane record Early Cretaceous ages; other plutons in southwest Alaska are Late Cretaceous and Tertiary. The Nyac district contains high-temperature and low-temperature gold mineralization. The age of high-temperature mineralization is concordant with plutonism and the low-T mineralization is younger, possibly Tertiary. The high-temperature mineralization occurs in the Bonanza Pluton and associated grey granodiorite porphyry dikes. Bonanza Pluton mineralization consists of gold-bearing quartz veins with pyrite-chalcopyrite-magnetite-bismuthinite-molybdenite. Fluid inclusions from mineralized quartz veins record trapping temperatures up to 560⁰ C and salinities up to 60 wt% NaCl. Mineralization in the grey granodiorite porphyry dikes consists of gold-bearing quartz veins with tellurobismuthite-tetradymite-chalcopyrite. Fluid inclusions from mineralized quartz veins record trapping temperatures up to 370⁰ C, salinities up to 5 wt% NaCl, and CO₂ concentrations up to 80 vol%. Both types display sericite-chlorite-albite alteration, and the Bonanza Pluton also displays potassic alteration. The low-temperature mineralization occurs at the Bonanza Creek Color Anomaly and along high-angle faults. This type contains anomalous Au and Hg. The alteration assemblage is sericite-kaolinite, indicating low temperature (<240⁰ C) and acidic fluids.
    • Geology and gold mineralization of the Richardson district, East-Central Alaska

      Graham, Garth E. (2002-12)
      The Richardson district contains multiple granitic units intruding gneiss and schist. The Bald Knob prospect contains gold-bearing quartz veins with the assemblage Bi-̊ Au-̊ hedleyite and high methane fluid inclusions. These features indicate very low fs₂-f₀₂ conditions, lower than any reported for 90 Ma interior Alaska gold systems, including the nearby Democrat and Buckeye prospects. The Bald Knob and Democrat Lode prospects returned ⁴⁰Ar/³⁹Ar ages of 1̃04 and 9̃0 Ma, respectively. Peraluminous dikes possess collisional tectonic signatures and interpreted age of 114 Ma. Younger dikes and 3 km² granite pluton possess arc-type compositions and yield ⁴⁰Ar/³⁹Ar ages of 9̃0 Ma. Garnet-biotite geothermometry on metamorphic rocks indicates low-P regional metamorphism (550-600C; 3-4 kb) and vertical movement between adjacent fault blocks. Highest temperatures are in the fault block hosting the Bald Knob prospect, suggesting it represents the deepest mineralization exposure in the area and is most proximal to a causative pluton.
    • Geology and origins of the Mike Lake (Skarn Ridge) gold-copper skarn deposit, Yukon Territory, Canada

      Mrozek, Stephanie Anne (2012-08)
      The Mike Lake (Skarn Ridge) deposit has an elemental suite of Cu-Au-Bi-As-Sn and a mineralogy dominated by scapolite, clinopyroxene, and pyrrhotite, with lesser garnet and Fe-axinite (a Ca-borosilicate). This study is the first published description of the deposit. The deposit was studied with techniques including drill core logging and detailed surface mapping (1:5,000 scale), combined with petrographic examination of polished thin sections, X-ray fluorescence and X-ray diffraction analyses, electron microprobe analysis of major minerals, and ⁴⁰Ar/³⁹Ar dating. Ore mineralization styles include vein-controlled, disseminated, and net-textured replacements of clinopyroxene and calcite by electrum, chalcopyrite, pyrrhotite, and arsenopyrite, with variable native bismuth and bismuth tellurides. A strong Au:Bi correlation (R² = 0.74) indicates the two elements were transported and deposited together; however a poor Au:Cu correlation (R² = 0.23) suggests different mineralization events or different modes of Au-Cu transport. The virtual absence of retrograde alteration provides an ideal opportunity to examine metal- and silicate-zoning patterns apparently associated with prograde alteration. Using the ⁴⁰Ar/³⁹Ar dating method, I have determined that the adjacent Mike Lake pluton is younger than the skarn, and hence, genetically unrelated. Through analysis of samples from surface and 72 drill holes, I show systematic zoning in skarn mineralogy and mineral compositions suggesting deposit derivation from an unknown pluton to the southeast at depth.
    • Geology and origins of the peak gold-copper-silver skarn deposit, Tok, Alaska

      Illig, Peter Edward; Newberry, Rainer; Mezger, Jochen; Layer, Paul (2015-12)
      The distal Peak Au-Cu skarn deposit was discovered in 2012 on Tetlin native lands 15 miles southeast of Tok, Alaska. The deposit contains anomalous Au-Cu-Bi-Ag-Mo-Fe-Te-As-Pb-Co-W-Cd-Ni. At the time of drilling deposit style, mineralization and origin were not understood. Upper Paleozoic and older metamorphic rocks had been previously mapped in the area; however, no igneous or metasomatic rocks had been recognized. To better understand the deposit I created a 1:25,000 scale geologic map of the 25 km² exploration area; employed approximately 682,500 assays for metal ratios; described textures and minerals in 138 polished thin sections; employed approximately 3,000 meters of new core logging to produce a cross-section and long-section; acquired microprobe compositions of skarn amphibole, pyroxene and garnet; analyzed 122 rocks by X-ray fluorescence analysis; had Pb isotopic ratios determined for 3 galena samples; and had 5 rocks dated by ⁴⁰Ar/³⁹Ar and U-Pb techniques. Based upon this data, I define Peak as a distal amphibole-rich Cu-Au skarn. The skarn's plutonic source remains undiscovered, and is likely NE of, and well below the deposit. Based radiometric dating and trace element analyses of plutonic and volcanic rocks, the immediate area experienced intrusive and extrusive activity at 70-75 Ma in a volcanic arc setting.
    • Geology and timing of zinc-lead-silver mineralization, northern Brooks Range, Alaska

      Werdon, Melanie Beth; Newberry, Rainer J. (1999)
      The north-central and northwestern Brooks Range of Alaska hosts widespread Carboniferous Zn-Pb-Ag +/- Ba shale-hosted massive sulfide (Sedex) deposits, and Zn-Pb-Ag +/- Cu vein-breccia and disseminated sulfide occurrences. The Sedex deposits are hosted by black carbonaceous shale and siliceous mudstone of the Mississippian to Pennsylvanian Kuna Formation and are spatially associated with minor (e.g. Red Dog) to locally abundant (e.g. Drenchwater) volcanic and hypabyssal intrusive rocks. The vein-breccia and disseminated sulfide occurrences show no obvious igneous association and are hosted by a deformed but only weakly metamorphosed package of Upper Devonian to Lower Mississippian mixed continental and marine elastic rocks (the Endicott Group). Textural, mineralogical, isotopic, chemical, and fluid inclusion data indicate that sulfides, quartz, and lesser carbonates in the Kady vein-breccia and disseminated sulfide prospect were deposited from slightly acidic, low salinity, carbon-destructive, relatively oxidized, low temperature (<250�C) hydrothermal fluids, under evolving chemical conditions (i.e. decreasing temperature and pressure, and increasing pH, fo2, fs2). The lack of known Sedex mineralization in the north-central Brooks Range and the presence of sulfide mineralization within the Endicott Group suggests that Kady represents the hydrothermal fluid pathway below a failed or non-existent Sedex system. Trace element analyses of volcanic rocks and 40Ar/ 39Ar laser step-heating ages indicate the following geologic history for the north-central and northwestern Brooks Range: within-plate alkaline volcanic rocks at Red Dog and Drenchwater were emplaced from approximately 344 Ma to 336 Ma in a continental extensional environment. This presumably set up an elevated geothermal gradient, which heated basinal fluids. Sedex mineralization is estimated to have formed between 337 and ~314 Ma by basinal dewatering. 40Ar/39Ar ages of recrystallized white mica in Upper Devonian sandstone adjacent to large sulfide-bearing vein-breccia zones fall within the independently estimated time frame for Sedex mineralization. Tholeiitic gabbro magmatic activity occurred around 276 +/- 15 Ma. The transition with time from within plate alkaline to tholeiitic magmatism suggests progressive episodic extension in a continental basin.
    • Geology of the boundary area, Eagle A-1 and Tanacross D-1 quadrangles, east-central Alaska

      Flynn, Roy L. (2003-05)
      Structural relationships and tectonic events in the Boundary area of east-central Alaska shed light on the generally obscure tectonic history of the Yukon-Tanana Upland region. This study used detailed mapping of 160 km², with supporting petrography, geochemical analyses, and ⁴⁰Ar/³⁹Ar dating to define the geology and tectonic history of the Boundary area. A major thrust zone juxtaposes lithotectonic assemblages of metamorphic rocks in the Boundary area, with the Fortymile River assemblage (approximately middle amphibolite facies) thrust over the Nasina and Klondike series (middle to upper greenschist facies), and ultramafic rocks and metagabbro (lower greenschist facies) and epidote-amphibolite-facies gneiss and schist imbricated along the thrust faults. Final thrust imbrication postdates cooling from peak metamorphism in amphibolite-facies lithologies, which appears to be Early Jurassic age. The thrust zone is exposed partially rimming a broad, dome-shaped anticline that encompasses the entire map area. Thermally reset ⁴⁰Ar/³⁹Ar ages in the Boundary area appear to be the result of a short-lived, probably igneous, Mid-Cretaceous reheating event, with widespread and locally variable effects, contemporaneous with intrusion of the Crag Mountain pluton south of the map area. Numerous later high-angle, presumably strike-slip faults transect the Boundary area, with apparently associated latest Cretaceous to Miocene volcanic rocks.
    • Geology of the Caribou Creek area, Big Delta quadrangle, east-central Alaska

      Lessard, Richard R. (2006-12)
      The Caribou Creek area, in the Big Delta C4 Quadrangle, East-Central Alaska, is known for significant placer gold, but no lode source. I present a new 200 km² area geologic map utilizing ground based mapping, airborne geophysical surveys, and follow-up laboratory investigations. Mapping and petrography delineate 10-20 km² blocks containing contrasting rock units and mineral assemblages. Amphibolite facies blocks contain abundant post-kinematic andalusite, with central blocks containing partially replaced kyanite, and blocks to the southeast and west containing post-kinematic sillimanite. Geothermobarometry shows that the amphibolite-facies blocks experienced pressures/temperatures of 11.5 kbars/650°C, followed by a collisional event associated with low-P/variable T post-kinematic recrystallization. The distribution of alumino-silicates suggests the central blocks were down dropped relative to adjacent blocks. Gold occurrences are found in west to northwest trending, steeply dipping quartz veins with stibnite ± arsenopyrite. Located in the central blocks, they are separated from a barren granodiorite pluton by a sinistral, northeast trending, high-angle fault. This study has shown the existence of major faults with significant vertical and horizontal movement, making gold source determination difficult. Future lode gold exploration in the area must take the high-angle faulting into consideration.
    • The geology of three extrusive bodies in central Alaska Range

      Albanese, Mary; Turner, Don; Swanson, Samuel; Gilbert, Wyatt; Kienle, Juergen; Stone, David (1980-05)
      The Buzzard Creek basalt, Jumbo Dome, and Sugar Loaf Mountain occur in the Central Alaska Range. The purpose of this study is to determine the age, nature, geothermal potential, and possible genetic relationships between these igneous bodies. The areas were investigated by mapping, radiometric dating, and petrologic studies. The Buzzard Creek basalt appears to have formed by a maar eruption about 3,000 years ago. Seismic evidence suggests this basalt may be related to current subduction in the area. Jumbo Dome consists of calc-alkaline andesite and is probably Pleistocene in age. Sugar Loaf Mountain is composed of Mid-Tertiary rhyolite. Geochemistry suggests that the Sugar Loaf Mountain rhyolite and Jumbo Dome andesite may also be subduction-related. Differences in age and geochemistry indicate there is no genetic relationship between the rocks of the three areas. The ages, type of volcanic features', and snow melt patterns suggest that these three areas have low geothermal potential.