• Gaussian process convolutions for Bayesian spatial classification

      Best, John K.; Short, Margaret; Goddard, Scott; Barry, Ron; McIntyre, Julie (2016-05)
      We compare three models for their ability to perform binary spatial classification. A geospatial data set consisting of observations that are either permafrost or not is used for this comparison. All three use an underlying Gaussian process. The first model considers this process to represent the log-odds of a positive classification (i.e. as permafrost). The second model uses a cutoff. Any locations where the process is positive are classified positively, while those that are negative are classified negatively. A probability of misclassification then gives the likelihood. The third model depends on two separate processes. The first represents a positive classification, while the second a negative classification. Of these two, the process with greater value at a location provides the classification. A probability of misclassification is also used to formulate the likelihood for this model. In all three cases, realizations of the underlying Gaussian processes were generated using a process convolution. A grid of knots (whose values were sampled using Markov Chain Monte Carlo) were convolved using an anisotropic Gaussian kernel. All three models provided adequate classifications, but the single and two-process models showed much tighter bounds on the border between the two states.
    • Gene by environment interactions between three candidate genes for obesity and omega-3 polyunsaturated fatty acids

      Pasker, Renee Leigh; Boyer, Bert; Wolf, Diane E.; Tiwari, Hemant (2008-12)
      Multi-factorial diseases, like obesity, are caused by genetic and environmental factors. Few studies examine potential interactions between genetic and environmental factors. Understanding these interactions can lead to better disease prevention. One important environmental factor related to obesity is omega-3 fatty acids. Yup’ik Eskimos consume a high amount of two omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). This study examined 10 single nucleotide polymorphisms (SNPs) in three genes: ADIPOQ, PPARG, and PPARGC1A. Also, 7 obesity phenotypes were examined: BMI, percent body fat, waist circumference, sum of skin-folds, plasma adiponectin, plasma triglycerides, and HDL cholesterol. Associations between these SNPs and phenotypes in 981 related Yup’ik Eskimos were examined using mixed models. Interactions were investigated with these SNPs and δ15N, a biomarker used to determine intake of EPA and DHA. The results showed that EPA and DHA modify the expression of all three genes. Additionally, SNPs in all three genes were associated with one or more obesity phenotypes. The most statistically significant results were with two SNPs in ADIPOQ and plasma adiponectin. This study supports the role of these genes in the etiology of obesity. Finally, this study demonstrates that these genes are influenced by EPA and DHA.
    • Gene-By-Diet Interactions And Obesity Among Yup'ik People Living In Southwest Alaska

      Lemas, Dominick; Boyer, Bert B.; O'Brien, Diane M.; Schulte, Marvin K.; Tiwari, Hemant K. (2012)
      BACKGROUND: Molecular approaches have expedited the discovery of human obesity genes, however the heritability explained by these loci remains low (<2%). Gene-by-environment interactions may partially account for the "missing heritability" attributed to variation in obesity phenotypes. OBJECTIVE: The specific aims of this dissertation were to (i) identify genetic polymorphisms associated with obesity-related phenotypes in Yup'ik people and (ii) evaluate how n-3 polyunsaturated fatty acid (n-3 PUFA) intake modifies associations between genetic polymorphisms and obesity-related phenotypes in a population with widely varying intake of n-3 PUFAs. APPROACH: We genotyped genetic polymorphisms in (1) candidate genes with a strong physiological role in obesity pathophysiology; (2) candidate genes identified in obesity whole-genome linkage studies that were regulated by n-3 PUFAs; and (3) candidate genes reproducibly implicated in obesity genome-wide association studies (GWAS). DATA & ANALYSES: We used Center for Alaska Native Health Research (CANHR) data collected between 2001 and 2008. We estimated dietary intake of n-3 PUFA using nitrogen stable isotope ratios (delta15N) of red blood cells (RBC) and obesity-related phenotypes were obtained by trained staff. Genotype-phenotype analyses used generalized linear models that accounted for familial correlations. RESULTS: Our analyses of candidate genes based on physiology revealed a polymorphism called P479L in carnitine palmitoyltransferase 1A (CPT1A) that was associated with elevated fasting HDL-cholesterol and all obesity phenotypes. Our investigation of candidate genes that are regulated by n-3 PUFAs and implicated in obesity whole-genome linkage studies demonstrate that polymorphisms in stearoyl CoA desaturase (SCD) and steroyl regulatory element binding protein (SLC2A4) were associated with obesity-related phenotypes; however n-3 PUFA intake did not modify associations between SCD and SLC2A4 polymorphisms and obesity phenotypes. Finally, our investigation of candidate genes reproducibly implicated in obesity GWAS demonstrated that genetic predisposition to obesity is associated with adiposity and that interactions with n-3 PUFA intake accounted for more than twice the phenotypic variation in adiposity. CONCLUSION: Taken together, results from this dissertation suggest that selecting candidate genes based on large-scale genomic analyses, such as linkage analyses and GWAS, has the potential to identify gene-by-environment interactions that partially account for the "missing heritability" attributed to obesity.
    • Genetic Ancestry Modeling And Performance Association In The Alaskan Sled Dog

      Huson, Heather Jay; Runstadler, Jonathan; Hundertmark, Kris; Ostrander, Elaine; Bailey-Wilson, Joan (2011)
      Alaskan sled dogs present us with the unique opportunity to study the development of a population of dogs produced from the selective breeding of high performance athletes. I establish that sled dogs are a genetically distinct population of dogs that segregate into two sub-groups based on their racing style of "sprint" or short distance and "distance" or long distance. The practice of interbreeding Alaskan sled dogs with various purebred dogs over the past century has allowed us to investigate the impact of these domestic breeds on the sled dog genome and their potential contribution to athletic performance. Here, I establish genetic profiles of both the sprint and the distance racing dogs using microsatellite-based markers, single-nucleotide polymorphism (SNP) arrays, and ancestry modeling. Population structure is assessed using clustering and principle component analyses. Inbreeding patterns are examined through population structure, inbreeding statistics, estimations of linkage disequilibrium, and autozygosity. Purebred breed components and their potential role in influencing performance attributes of Alaskan sled dogs were determined through genetic breed identification. Ancestry modeling was used to localize genomic regions of specific breed selection. These breeds were then analyzed for their genetic contribution to regions experiencing selection within the sprint or distance racing dogs. I determined regions of selective sweep and genome-wide association to the sprint or distance racing dogs. A genome-wide association analysis of heat tolerance performance in sprint dogs identified SNPs potentially regulating the MYH9 gene. This was the first genetic assessment of ancestry, inbreeding, and performance genes attributed to racing Alaskan sled dogs.
    • Genetic and phenotypic divergence within and between cinnamon teal (Anas cyanoptera) and blue-winged teal (A. discors)

      Wilson, Robert E.; McCracken, Kevin G.; Lindberg, Mark S.; Winker, Kevin; Sorenson, Michael D. (2011-08)
      Spatial heterogeneity in selection pressures can lead to extensive morphological variation and differences at functional genes between populations across a species' range without corresponding genetic variation at neutral loci. Divergent selection among populations may thus lead to intraspecific variation and in many cases speciation. Phenotypic and genetic structure within and between Cinnamon Teal (Anas cyanoptera) and the closely related Blue-winged Teal (A. discors) was assessed using body size measurements and neutral genetic markers in conjunction with a functional locus, hemoglobin. Cinnamon Teal are composed of five subspecies corresponding to distinct ecogeographic regions in North and South America. Subspecies and geographic regions differed significantly in overall body size, with the largest subspecies and the largest individuals found at high elevations in the central Andes (A. c. orinomus) and at high latitudes in southern Patagonia (A. c. cyanoptera). South American populations showed strong positive correlations with latitude and elevation while the migratory subspecies in North America (A. c. septentrionalium) showed few significant correlations with elevation and no relationship between latitude and body size. In addition, plumage differences were restricted to between North and South America as there was extensive variation observed within continents. Cinnamon Teal highland and lowland populations showed strong divergence in body size (Pst=0.56) and exhibited frequency differences in one non synonymous [alpha]-globin amino acid polymorphism (Asn/Ser-[alpha]9; Fst = 0.60), despite considerable admixture of reference loci. Selection pressures imposed by the hypoxic highland environment have likely resulted in asymmetric gene flow from the highlands into the lowlands following a highland colonization event from the lowlands. Cinnamon Teal and Blue-winged Teal show distinct but paraphyletic mitochondria) DNA ... and broadly shared nuclear alleles. Unlike South American Cinnamon Teal, North American Cinnamon Teal and Blue-winged Teal are characterized by high genetic diversity, large effective population size, and recent population expansion. Haplotypic and allelic sharing across continents is likely because of incomplete lineage sorting rather than ongoing gene flow. Within-continent estimates yielded higher migration rates consistent with hybridization. However, Cinnamon Teal and Blue-winged Teal are similar in body size; differences in plumage coloration may reduce hybridization events.
    • Genetic And Phenotypic Divergence Within And Between Cinnamon Teal (Anas Cyanoptera) And Blue-Winged Teal (A. Discors)

      Wilson, Robert E.; McCracken, Kevin; Sorenson, Michael D.; Winker, Kevin; Lindberg, Mark S. (2011)
      Spatial heterogeneity in selection pressures can lead to extensive morphological variation and differences at functional genes between populations across a species' range without corresponding genetic variation at neutral loci. Divergent selection among populations may thus lead to intraspecific variation and in many cases speciation. Phenotypic and genetic structure within and between Cinnamon Teal (Anas cyanoptera) and the closely related Blue-winged Teal (A. discors) was assessed using body size measurements and neutral genetic markers in conjunction with a functional locus, hemoglobin. Cinnamon Teal are composed of five subspecies corresponding to distinct ecogeographic regions in North and South America. Subspecies and geographic regions differed significantly in overall body size, with the largest subspecies and the largest individuals found at high elevations in the central Andes (A. c. orinomus) and at high latitudes in southern Patagonia (A. c. cyanoptera). South American populations showed strong positive correlations with latitude and elevation while the migratory subspecies in North America (A. c. septentrionalium) showed few significant correlations with elevation and no relationship between latitude and body size. In addition, plumage differences were restricted to between North and South America as there was extensive variation observed within continents. Cinnamon Teal highland and lowland populations showed strong divergence in body size (PST = 0.56) and exhibited frequency differences in one non-synonymous alpha-globin amino acid polymorphism (Asn/Ser-alpha9; FST = 0.60), despite considerable admixture of reference loci. Selection pressures imposed by the hypoxic highland environment have likely resulted in asymmetric gene flow from the highlands into the lowlands following a highland colonization event from the lowlands. Cinnamon Teal and Blue-winged Teal show distinct but paraphyletic mitochondrial DNA (phiST = 0.41) and broadly shared nuclear alleles. Unlike South American Cinnamon Teal, North American Cinnamon Teal and Blue-winged Teal are characterized by high genetic diversity, large effective population size, and recent population expansion. Haplotypic and allelic sharing across continents is likely because of incomplete lineage sorting rather than ongoing gene flow. Within-continent estimates yielded higher migration rates consistent with hybridization. However, Cinnamon Teal and Blue-winged Teal are similar in body size; differences in plumage coloration may reduce hybridization events.
    • Genetic consequences of ice ages for a holarctic rodent: phylogeography and post-glacial colonization of the tundra vole, Microtus oeconomus, in Beringia

      Galbreath, Kurt Egan (2002-08)
      Periodic glacial advances during the Pleistocene fragmented and displaced populations, while lowered sea levels permitted a biotic interchange between Asia and North America via the Bering Land Bridge. The tundra vole (Microtus oeconomus), a recent colonizer of North America, is a good model for studying the genetic consequences of these events. Variation in Mitochondrial (cytochrome b and control region) and nuclear (ALDH1) markers were examined within the context of Beringia's paleoclimatic history to examine the role of glaciations in driving differentiation and structuring patterns of genetic diversity. Genealogical relationships among genetic lineages were also assessed to elucidate probable paths of transberingian gene flow and post-glacial colonization. A deep phylogeographic break in western Beringia separates Beringian and Central Asian clades and may have been initiated by glacial vicariance. Population genetic structure within the Beringian clade has largely been determined by an historical reduction in genetic diversity and subsequent local differentiation. Serial bottlenecking during post-glacial colonization had minor effect, if any. Female-mediated gene flow among populations has been minimal since the last glacial maximum, but affinities among populations in Siberia and Alaska suggest two latitudinally partitioned routes of gene flow across the Bering Land Bridge. Also, post-glacial colonization of heavily glaciated southcoastal Alaska probably proceeded along coastal routes from the west after glacial recession.
    • Genetics and sex expression in Alaskan populations of Silene acaulis

      Klaas, Amber (2004-12)
      Gynodioecy, the coexistence of hermaphrodites and females within plant populations, is often caused by an interaction between maternally-inherited cytoplasmic male sterility (CMS) genes and nuclear male fertility restorer genes. Previous population studies have found cytoplasmic alleles associated with femaleness. We analyzed the spatial distributions of mitochondrial and chloroplast alleles and the sexual phenotype of individuals within five Alaskan populations of Silene acaulis. Sex ratios were variable between two mountain ranges in this study, possibly due to differences in the frequencies of CMS genes. Clustering of mitochondrial alleles, but not sex, was found within two populations at a scale <̲ 2 m. This result may be because maternally-inherited mitochondrial genes are locally spread through seed, but nuclear restorers are spread through pollen and seed. We also investigated sex ratios and CMS genes temporally and did not find patterns of changing sex ratios or mitotypes across size classes. This does not support the theory that females and the mitotypes they carry have been selected against over time, implying that female clusters were not broken-up due to pollen limitation. Patterns of mitochondrial and chloroplast alleles suggest either non-maternal inheritance of cytoplasmic markers or multiple reversals in the evolutionary history of cytoplasmic markers.
    • The genome of a saxitoxin-producing cyanobacterium

      Krohn, Andrew Lee (2005-08)
      Saxitoxin, the causative agent of paralytic shellfish poisoning, is produced by dinoflagellates and cyanobacteria, the latter being a far simpler organism at the genomic level. In order to establish a baseline for future research into saxitoxin biosynthesis, we sought to determine the genomic complexity of the saxitoxin-producing cyanobacterium, Anabaena circinalis strain ACBU02, relative to the published genome of its non-toxic analogue, Anabaena sp. PCC 7120. Total conservation of genomic organization was represented in less than 10 percent of end-sequenced DNA clones from restriction digestion libraries. Ninety percent of sequences contained highly homologous regions indicating a high degree of conservation among genome content. The genome size of A. circinalis strain ACBU02 was also estimated to be significantly smaller than that of Anabaena sp. PCC 7120. These data provide a solid foundation for the development of new strategies for isolation of the genes responsible for biosynthesis of saxitoxin and its chemically similar congeners from saxitoxin-producing cyanobacteria.
    • Geo-referenced and documented red squirrel (Tamiasciurus hudsonicus) midden sites from 2016 and 2017 in a highly used forest area behind the University of Alaska, Fairbanks

      Huettmann, Falk; Robold, Richard; Adams, R. (EWHALE Lab, University of Alaska Fairbanks, 2017)
      This dataset consists out of 29 presence points of red squirrel (Tamiasciurus hudsonicus, Taxonomic Serial No.: 180166) midden sites. Data was collected in a highly human-used forest area behind the University of Alaska, Fairbanks for summer 2016 (n= 29) and winter/spring 2017 (n=20).The data set consists of an ESRI shapefile for each year. Data was collected in two consecutive years (2016-2017). The first set of data points (summer 2016) was collected with a land cruising survey design and recorded with a GPS unit, based on an opportunistic course project work by R. Adams. The second data collection campaign took place in spring 2017 to check whether the squirrel midden sites from 2016 are still in use (data collected by R. Robold). The coordinate system is decimal degree (5 decimals) and with a geographic projection NAD_1983_Alaska_Albers. The excel sheet has five columns (site ID, a short description of the vegetation, latitude, longitude, and one if the middens are still used in 2017); the excel document (midden_data_with_control.xlsx) size is 10 KB (2017). The map is a JPEG-file (Midden_sites_2016-27_RR) with a size of 3MB and the shapefiles have an overall size of ca. 50 KB each. This data set is the basis for ongoing study on squirrels in the boreal forest and urban areas.
    • Geochemical studies of fumarolic systems in the eastern Aleutian Volcanic Arc: Applications for understanding magmatic and volcanic processes

      Kodosky, Lawrence Gerard; Keskinen, Mary; Newberry, Rainer; Kienle, Juergen; Keith, Terry; Layer, Paul (1992)
      Geochemical studies of active and fossil fumaroles were conducted at Mount St. Augustine and the Valley of Ten Thousand Smokes (VTTS) to investigate fumarolic systems for providing information on volcanic and magmatic processes. Gases and condensates collected from high-temperature rooted fumaroles at Mount St. Augustine in 1979, 1982, and 1984 are characterized by systematic long-term trends in gas composition and stable isotopes that can be best explained by progressive magmatic outgassing coupled with increasing proportions of seawater in the fumarolic emissions. Seawater-magma interaction may initiate some of the early explosive phases of Mount St. Augustine eruptions. The distribution and morphology of rootless fumaroles formed on pyroclastic flows and a lava flow emplaced during the 1986 eruptive cycle of Mount St. Augustine were controlled by pre-eruption drainage and topography, as well as by the thickness, compaction, and settling of the flow deposits. The majority of chemical components present in encrustations collected from these active fumaroles were derived by acidic condensate leaching of the eruptive deposits. Trace-element distribution apparently followed a pattern of isomorphic substitution in the encrustation phases. A reconnaissance survey of surface Hg$\sp\circ$ contents in the VTTS supports the presence of a shallow intrusion beneath the dome-like feature known as the Turtle. Based on the Hg$\sp\circ$ data, the preferred model of the 1912 Novarupta vent is one generated by collapse of supporting vent walls into a cored-out explosive vent after the major eruptive phase. Vent morphology is funnel-like with subsidence concentrated in the narrow funnel center. The magnitude of the Novarupta Basin Hg$\sp\circ$ anomalies implies that a shallow ($\approx$1 km depth) incipient hydrothermal system has developed beneath the vent.
    • 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.
    • 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.
    • 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.
    • 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.