The Mount Nansen gold-silver deposit,Yukon territory,Canada

The Mount Nansen ore deposit consists of a system of narrow steeply dipping veins in metamorphic rocks of Precambrian to Paleozoic age, andesitic volcanics and granodioritic to granitic intrusives of Mesozoic age, and Cretaceous to early Tertiary dacitic porphyries.Pyrite, arsenopyrite, sphalerite, galena and freibergite are the main constituents of the sulphide ore which has been mined for its gold and silver content. In parts of the mine the sulphide minerals are altered to a complex association of secondary minerals. No supergene enrichment zones have formed, suggesting very limited transport during alteration as a possible result of the existing permafrost conditions. Statistical evaluations of gold and silver assay data indicate a down-dip decrease of the silver content and a more uniform gold distribution.Two possible metallogenetic explanations are given: 1. a hydrothermal origin of the deposit as a final phase of the Cretaceous-early Tertiary magmatic episode 2. a source horizon concept with the metal content of the ore deposit having been derived from the surrounding country rocks.

---

Zusammenfassung Die Mount Nansen Lagerstätte setzt sich aus einem System geringmächtiger, steil einfallender Gänge zusammen. Diese durchsetzten präkambrische bis paläozoische Gesteine, mesozoische, andesitische Extrusiva und granodioritische bis granitische Intrusiva sowie kretazische bis frühtertiäre dazitische Porphyre.Pyrit, Arsenkies, Zinkblende, Bleiglanz und Freibergit sind die Hauptbestandteile des sulfidischen Erzes, welches seines Gold- und Silbergehaltes wegen abgebaut wurde. Die Sulfidmineralien wurden in gewissen Abschnitten der Mine zu einer komplexen Vergesellschaftung sekundärer Erze umgewandelt. Die Abwesenheit einer supergenen Anreicherungszone kann auf die herrschenden Permafrostbedingungen zurückgeführt werden, welche nur einen limitierten Stofftransport während der Verwitterung zuließen. Die statistische Auswertung der zahlreichen Gold- und Silberanalysenresultate lassen eine Abnahme des Silbergehaltes nach der Teufe und eine eher gleichmäßige Verteilung des Goldgehaltes erkennen.Zwei metallogenetische Deutungen werden für das Lager diskutiert. Erstens eine hydrothermale Herkunft als abschließende Phase des kretazischen bis frühtertiären Magmatismus, und zweitens eine pseudohydrothermale Herkunft (source horizon concept), wobei das umliegende Nebengestein als Quelle für die Metallgehalte des Lagers betrachtet wird.

     

Limnology of the Klutlan moraines,Yukon Territory,Canada

Lakes of the Klutlan moraines originate by down-melting of stagnant ice under a mantle of rock debris and vegetation ranging from scattered herbs and shrubs on the younger moraines to multiple-generation closed spruce forest on the oldest moraines, which are 600–1200 yr old. Lakes on the youngest moraines are temporary, turbid with glacial silt, and marked by unstable ice-cored slopes. On older moraines most lakes have clear water and stable slopes. On the oldest moraines many lakes have brown water caused by dissolved humic materials derived from the thick forest floor, but even here some slopes are unstable because of continued melting of buried ice. Morainic lakes contain bicarbonate waters of moderate alkalinity and conductivity and low levels of nutrients. The highly diverse phytoplankton is dominated by chrysophytes and cryptomonads, with few diatoms. Extremely low values for phytoplankton biomass place most of the lakes in an “ultraoligotrophic” category. Zooplankton is dominated by copepods, which were found even in ice ponds only a few years old, and by the cladoceran Daphnia pulex. Surface-sediment samples contained a total of 16 species of chydorid Cladocera. Of these, Alonella excisa and Alona barbulata are apparently the pioneer species in the youngest lakes. Chydorus sphaericus only appears in lakes of the oldest moraines. A successional pattern is not conspicuous, however, partly because some of the lakes on the older moraines originated by recent collapse over buried ice. Lakes on the upland outside the dead-ice moraines yielded 39 species in the zooplankton. The distinctive assemblage on upland lakes may relate more to different water chemistry than to age.     

Wastage of the Klutlan ice-cored moraines,Yukon Territory,Canada

A series of ice-cored Neoglacial moraines at the terminus of the Klutlan Glacier covers an area of 90 km². Studies were made to determine empirically how long ice persisted in the Klutlan moraines and to develop models that can accurately predict wastage rates under current climatic conditions. A meltout curve based on climatological data reflects the sum of three melting processes: surficial melting, melting by lake water, and melting by geothermal heat. About 950 yr are required to melt 180 m of ice with a debris concentration of 1%, or about 1200 yr for a 1.5% debris load. Another meltout curve, based on seismic data, suggests total meltout in about 875 yr. When all geologic factors are considered, the empirical meltout curve is remarkably similar to that derived by considering the major heat-flux parameters. Meltout rates can be predicted if (1) the fundamental climatic parameters can be ascertained, and (2) the sediment concentration in the ice is known.     

Statistical analysis of stream sediment data from the Ife-Ilesha area of Southwest Nigeria

Statistical treatment of geochemical exploration data in the Ife-Ilesha area has not been fully utilized as a tool in their interpretation. The results of 176 stream sediment samples from an area of 1800 km² analyzed for Cu, Zn, Mn, Ni, Co and Cr after hot extraction were treated with both simple and sophisticated (R-mode factor) statistical analytical methods. All the elements were found to have density distributions closely approaching lognormal or a mixture of two lognormal populations.They all show strong positive correlations with correlation coefficient values ranging from 0.5 between Mn and Ni to 0.84 between Mn and Co, all considered to be real at 5% level of significance.R-mode factor analysis produced a three-factor model which accounts for 82.0% of the total variance in the data. Factor 1 (Cu-Co-Ni) correlates spatially with the area underlain by the amphibolite complex, thus reflecting the parent rock as dominant influencing factor. Factor 2 (Mn-Co) and the strong positive correlation between Mn and Co are interpreted as resulting from the influence of Co-adsorption by Mn-oxides. Factor 3 (Zn) is probably a mineralization factor.     

Fungal remains in Pleistocene ground squirrel dung from Yukon Territory, Canada

Fungi in dung of the Arctic ground squirrel (Spermophilus parryii) collected near Dominion Creek, Yukon Territory, Canada, have a radiocarbon age of 12,200 ± 100 yr B.P. Most of the fungal remains are assignable to modern taxa, and most of these are either widespread saprobes or nonspecific coprophiles. However, specimens identified as Chaetomium simile and Thecaphora deformans represent fungi that may be more characteristic of rodent dung than that of other animals, inviting consideration of dung fungi as a potential source of paleontological data.     

Postglacial climates inferred from a lake at treeline,southwest Yukon Territory,Canada

Pollen, chironomid, and ostracode records from a lake located at alpine treeline provide regional paleoclimate reconstructions from the southwest Yukon Territory, Canada. The pollen spectra indicate herbaceous tundra existed on the landscape from 13.6–11 ka followed by birch shrub tundra until 10 ka. Although Picea pollen dominated the assemblages after 10 ka, low pollen accumulation rates and Picea percentages indicate minimal treeline movement through the Holocene. Chironomid accumulation rates provide evidence of millennial-scale climate variability, and the chironomid community responded to rapid climate changes. Ostracodes were found in the late glacial and early Holocene, but disappeared due to chemical changes of the lake associated with changes in vegetation on the landscape. Inferred mean July air temperature, total annual precipitation, and water depth indicate a long-term cooling with increasing moisture from the late glacial through the Holocene. During the Younger Dryas (12.9–11.2 ka), cold and dry conditions prevailed. The early and mid-Holocene were warm and dry, with cool, wet conditions after 4 ka, and warm, dry conditions since the end of the Little Ice Age.     

The true sample catchment basin approach in the analysis of stream sediment geochemical data

The Sample Catchment Basin Approach (SCBA) is one of the techniques widely employed in the analysis of stream sediment geochemical data and delineation of anomalous catchments. However, this method fails to take into account the real catchment basin boundaries of each sample by incorporating only the incremental area between two adjacent samples. In other words, the SCBA incorrectly assumes that the geochemistry of every sample catchment within a drainage is independent from upstream sample catchment(s) feeding into this drainage. The chemical composition of sediment at the basin outlet originates from the whole basin upstream and not the incremental area as postulated in the SCBA. Consequently, the calculated background values for various lithologies and the background value for the element of interest at the basin outlet might be far from reality.This study used a True Sample Catchment Basin Approach (TSCBA), that reflects the true catchment boundary of every stream sediment sample, and in which all calculations are carried out on the premise that this boundary and the true area affect the composition of each sample. The results obtained from the application of both the SCBA and TSCBA to a gold endowed study area in western Iran clearly illustrated the superiority of the TSCBA over the SCBA. In addition, this study demonstrated the advantage of using the modified dilution correction equation of Mokhtari and Garousi Nezhad (2015), as compared to the existing Hawkes’s equation commonly used for dilution correction of residual values.     

Landform development on moraines of the Klutlan Glacier,Yukon Territory,Canada

The landform evolution of the Klutlan moraines is described and explained primarily with respect to processes that cause voids in which debris is deposited. Morainal deposits of different ages provide examples of landforms at different stages of development, so that continuous ideal evolutionary sequences can be inferred. Specific features are classified as those on material of the same depositional age that develop mostly in a vertical direction with numerous topographic reversals, and those cross-cutting materials of different depositional age that develop primarily in a horizontal direction. The evolution of slopes is often terminated by their destruction as the underlying ice melts, but former slopes on morainal debris are traceable to ice-ridge slopes on the original glacier surface. The general process of evolution is one of downwasting by surficial icemelt, in which a grand topographic reversal takes place as the original ice mass with a gently convex surface melts to leave a basin floored by a concave mantle of morainal debris. The primary glacial process of melting differs from the primary karst process of solution, but many minor glacial processes and major glacial forms are similar to minor karst processes and major karst forms.     

Paleoecology of Beringian “packrat” middens from central Yukon Territory, Canada

Rodent middens from ice-rich loess deposits are important new paleoenvironmental archives for Eastern Beringia. Plant macrofossils recovered from three middens associated with Dawson tephra (ca. 24,000 ¹⁴C yr B.P.) at two sites in Yukon Territory include diverse graminoids, forbs, and mosses. These data suggest substantial local scale floristic and habitat diversity in valley settings, including steppe-tundra on well-drained soils, moist streamside meadows, and hydric habitats. Fossil arctic ground squirrel burrows and nesting sites indicate that permafrost active layers were thicker during Pleistocene glacial periods than at present on north-facing slopes.     

Late Holocene moisture balance variability in the southwest Yukon Territory,Canada

Analyses of sediment cores from Marcella Lake, a small, hydrologically closed lake in the semi-arid southwest Yukon, provides effective moisture information for the last ∼4500 years at century-scale resolution. Water chemistry and oxygen isotope analyses from lakes and precipitation in the region indicate that Marcella Lake is currently enriched in ¹⁸O by summer evaporation. Past lake water values are inferred from oxygen isotope analyses of sedimentary endogenic carbonate in the form of algal Charophyte stem encrustations. A record of the δ¹⁸O composition of mean annual precipitation at Jellybean Lake, a nearby evaporation-insensitive system, provides data of simultaneous δ¹⁸O variations related to decade-to-century scale shifts in Aleutian Low intensity/position. The difference between the two isotope records, Δδ, represents ¹⁸O-enrichment in Marcella Lake water caused by summer effective moisture conditions. Results indicate increased effective moisture between ∼3000 and 1200 cal BP and two marked shifts toward increased aridity at ∼1200 and between 300 and 200 cal BP. These prominent late Holocene changes in effective moisture occurred simultaneously with changes in Aleutian Low circulation patterns over the Gulf of Alaska indicated by Jellybean Lake. The reconstructed climate patterns are consistent with the topographically controlled climatic heterogeneity observed in the coastal mountains and interior valleys of the region today.     

Paleolimnology of two lakes in the Klutlan Glacier region,Yukon Territory,Canada

Lakes developed on progressively younger end moraines of the Klutlan Glacier were initially assumed to have originated shortly after moraine emplacement and to have persisted to the present. Limnological differences between lakes on old vs young moraines were thought to result from limnological maturation within the lakes and ponds themselves and in response to the development of soils and vegetation on moraine surfaces. This study represents a paleolimnological test of this hypothesis. If true, the first-formed sediments of lakes on old moraines should be comparable to sediments presently forming in lakes on young moraines. Geochemical and paleontological studies of surface sediment to a series of lakes on progressively older moraines provide baseline information for comparing successive levels of lake sediment cores from older moraines. Results indicate that the time of lake initiation seldom reflects moraine age. Even on the oldest moraine (Harris Creek), lake basins are presently forming. Their sediment character more closely relates to the rapidity of basin formation due to melting of buried ice than to age of the lake itself or of the moraine on which it is situated. Vegetation and soil development play an important but secondary role in determining the character of lake sediments; rapid subsidence can convert humic-water lakes surrounded by second-generation spruce forests into turbid-water lakes with unstable, slumping margins. A detailed paleolimnological study of two lakes, one on the unglaciated upland and another in an outwash channel penetrating the oldest moraine, revealed progressive limnologic changes through time, suggesting that their basins were stable for 1200 and 400 yr, respectively. The changes in diatom stratigraphy of these lakes appear to relate to natural limnological changes associated with lake maturation and accumulation of nutrients as well as to changes in the surrounding vegetation and soils.     

Formation of the Neoglacial surge moraines of the Klutlan Glacier,Yukon Territory,Canada

The Klutlan Glacier is a valley glacier 82-km long emerging from the Icefield Ranges of the St. Elias Mountains. It is one of at least 200 surging glaciers identified in western North America. During about the past 1200 yr, the glacier has deposited at its terminus a series of at least 7 surge-related Neoglacial ice-cored moraines. Lithologic characteristics of the Klutlan moraines suggest that they have resulted principally from the surging of the tributary Nesham Glacier, which periodically injects a lobe of medial and lateral moraines and the underlying ice into a more slowly moving Klutlan ice stream. Subsequent surges of the main ice carry the Nesham surge lobes to the Klutlan terminus as discrete geomorphic features. For the past 400 yr a Nesham lobe has reached the Klutlan terminus at approximately 80-yr intervals.     

Temperatures of the past 2000 years inferred from lake sediments,southwest Yukon Territory,Canada

Lake sediments from four sites in the southwest Yukon Territory, Canada, provided paleotemperature records for the past 2000 yr. An alpine and a forest site from the southeastern portion of the study area, near Kluane Lake, and another alpine-forest pair of lakes from the Donjek River area located to the northwest yielded chironomid records that were used to provide quantitative estimates of mean July air temperature. Prior to AD 800, the southwest Yukon was relatively cool whereas after AD 800 temperatures were more variable, with warmer conditions between ~ AD 1100 and 1400, cooler conditions during the Little Ice Age (~ AD 1400 to 1850), and warming thereafter. These records compare well with other paleoclimate evidence from the region.     

Soil development on recent end moraines of the Klutlan Glacier,Yukon Territory,Canada

Data on soils with six Neoglacial moraines of the Klutlan Glacier have been compared with those from moraines at the warm, moist coastal site of Glacier Bay, 160 km south. Percentage organic matter increases rapidly for the first 100 to 150 yr of soil development and then continues to rise gradually for the next 100 yr. Soil pH falls from 8.0 in recent till to approximately 6.0 in 200-yr-old soils. Nitrogen levels in the mineral soil increase from near zero in recent tills to 0.7% in soils 175–200 yr old; organic horizons of soils associated with spruce forests in later successional stages contain approximately 1% nitrogen. Concentrations of certain inorganic phosphate ions in the different-aged soils increase continually throughout the succession. Data for nine chemical variables were subjected to a principal components analysis; the major pattern in the data reflects the differences between soils of low organic content and high pH present in early successional stages, and nutrient-rich soils with high organic content and low pH present after succession has progressed toward the spruce forest. These trends in soil development with time are strikingly similar to those reported from Glacier Bay, except that the changes in soil properties appear to be delayed by 50–100 yr at the Klutlan terminus. Although numerous signs of nitrogen deficiency have been identified in plants growing on new soils at Glacier Bay, none was observed visually in living plants or in nutrients measured in samples of foliage from three plant taxa (Epilobium latifolium, Salix spp., and Populus balsamifera) taken from the Klutlan moraines. Concentrations of nitrogen and other nutrients (Ca, Mg, K, total P) in the foliage samples show no clear trends with increasing soil development. Low temperatures, a short growing season, and very low mean annual precipitation probably limit plant growth and account for the delayed soil development on the Klutlan moraines.     

Holocene paleoenvironmental changes inferred from diatom assemblages in sediments of Kusawa Lake, Yukon Territory, Canada

The southwest Yukon Territory, Canada, is an important region for recovering sensitive records of Holocene paleoclimatic change. More information is needed, however, to constrain the timing of the major Holocene climatic transitions, and to understand associated impacts on different ecosystems. For example, paleolimnological studies have focused on small lakes and ponds, but the history of large lakes has received little study. We analyzed diatom assemblages, species richness, valve concentrations, and biogenic silica, in the sediments of Kusawa Lake (60°16.5'N; 136°10.9'W; 671 m a.s.l.) to reconstruct the responses of this large (surface area = 142 km²), deep (Z_max = 135 m) freshwater ecosystem to Holocene climatic transitions. Diatoms colonized the lake soon after ice retreat, around 11,000 cal yr BP; assemblages throughout the record were dominated by planktonic types. Diatom concentrations and biogenic silica were high during the Holocene Thermal Maximum between 10,700 and 7300 cal yr BP, then began to decrease in response to cooling associated with orbitally driven reductions in insolation. Diatom assemblages shifted towards taxa with lower surface water temperature optima after 8300 cal yr BP, perhaps in response to abrupt and progressive cooling. Our study confirms that diatom assemblages in large lakes are sensitive to regional-scale paleoclimatic changes.     

Natural acid rock drainage associated with black shale in the Yukon Territory,Canada

Investigated herein are water and sediment geochemistry, and metal attenuation processes associated with natural acid rock drainage originating from black shale formations in the Macmillan Pass area, Clear Lake prospect and Engineer Creek by the Dempster Highway in the Yukon Territory, Canada. The most metalliferous water having pH 3.0, 150 mg/L Zn, 39 mg/L Ni, 2.8 mg/L Cu and 9.1 mg/L As was found in a tributary stream of Engineer Creek with no known mineral deposits occurring in the vicinity. For all three study areas, the water and sediment geochemistry is significantly affected by the local lithology and prevailing metal attenuation processes. Despite their anomalous acidity and metal contents, the natural acid streams contribute only a small fraction of the contaminant loadings to the major water courses because of their low flows. Dilution, neutralization, sorption and co-precipitation are identified as the major mechanisms attenuating aqueous transport of potentially deleterious metals. However, microbial mediation in metal attenuation is also evident in low-flow systems. The wide variation of water and sediment geochemistry along a flow path renders the establishment of background metal values difficult. In assessing environmental impacts, it may be more practical to consider metal loadings on a watershed scale than to rely on a comparison with operationally defined background concentrations.     

Full-glacial paleosols in perennially frozen loess sequences, Klondike goldfields, Yukon Territory, Canada

Perennially frozen loess deposits in the Klondike goldfields include paleosols formed in full-glacial environments, correlated by Alaskan distal tephra with Marine Isotope Stages (MIS) 2 and 4. Patterns of organic and inorganic carbon and clay distribution, microstructures, and profile morphologies indicate that soil formation occurred in a base-rich environment in which organic matter accreted predominantly as root detritus. At sites approximately 20 km apart, the expression of cryoturbation and ice wedge development decreases in strength upward in loess-paleosol sequences correlated with MIS 4, suggesting increasing aridity. Configurations of cryoturbation features and ice-wedge thaw unconformities, the presence of numerous ground squirrel burrows, and an absence of peat accumulation suggest that these substrates were predominantly well-drained, with active layers of equal or greater thickness than in modern soils on similar sites in the west-central Yukon. Some characteristics of these paleosols are similar to those of modern steppe and tundra soils, consistent with plant macrofossil evidence for local ecological diversity during full-glacial conditions in eastern Beringia.     

The Dublin Gulch intrusion-hosted gold deposit, Tombstone plutonic suite, Yukon Territory, Canada

The Dublin Gulch intrusion is a member of the Tombstone plutonic suite, a linear belt of middle Cretaceous intrusions that extend across the Yukon Territory. Like many of the intrusions in this suite, the Dublin Gulch intrusion is associated with several different zones of gold and tungsten mineralization, within and immediately adjacent to the intrusion. The Eagle zone (50.3 Mt @ 0.93 g/t gold), located in the southwestern part of the Dublin Gulch intrusion, hosts the most significant concentration of gold in the area. The gold occurs in a broadly east-west-striking, steeply south-dipping series of sheeted veins. The veins consist of early quartz-scheelite-pyrrhotite-pyrite-arsenopyrite, and are associated with K-feldspar-albite alteration envelopes. These grade out to and are overprinted by sericite-carbonate-chlorite alteration. The same assemblage also occurs in veinlets that refracture sheeted quartz veins and contain the majority of the gold. The gold occurs with molybdenite, lead-bismuth-antimony sulfosalts, galena, and bismuthinite. Gold correlates strongly with bismuth (r²=0.9), a relationship common to several intrusion-related gold deposits, but has a poor correlation with all other elements. Tungsten and molybdenum have a weak inter-element correlation (r²=0.55) and paragenetically pre-date the majority of gold precipitation. Lead, zinc, copper, silver, antimony, and arsenic have moderate to strong inter-element correlations (0.58 to 0.93). The change from tungsten-bearing mineralization through to gold-bismuth-rich ores with elevated syn- to post-ore lead, zinc, copper, silver, antimony, and arsenic can be grossly correlated with a change in hydrothermal fluid composition. Early scheelite-bearing quartz contains primary CO₂-rich fluid inclusions, which are post-dated by secondary inclusions with higher salinities (up to 15 wt% NaCl equiv.) and less CO₂. These latter inclusions are interpreted to coincide with the later gold-bismuth and base metal mineralization. The favored genetic model is one in which early CO₂-rich fluids exsolved from a magma with an initially high CO₂ content, but progressively became more saline and H₂O-rich as the system evolved.     

Primary alkaline magmas associated with the Quaternary Alligator Lake volcanic complex,Yukon Territory,Canada

The Alligator Lake complex is a Quaternary alkaline volcanic center located in the southern Yukon Territory of Canada. It comprises two cinder cones which cap a shield consisting of five distinct lava units of basaltic composition. Units 2 and 3 of this shield are primitive olivine-phyric lavas (13.5–19.5 cation % Mg) which host abundant spinel lherzolite xenoliths, megacrysts, and granitoid fragments. Although the two lava types have erupted coevally from adjacent vents and are petrographically similar, they are chemically distinct. Unit 2 lavas have considerably higher abundances of LREE, LILE, and Fe, but lower HREE, Y, Ca, Si, and Al relative to unit 3 lavas. The ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd isotopic ratios of these two units are, however, indistinguishable. The differences between these two lava types cannot be explained in terms of low pressure olivine fractionation, and the low concentrations of Sr, Nb, P, and Ti in the granitoid xenoliths relative to the primitive lavas discounts differential crustal contamination. The abundance of spinel lherzolite xenoliths and the high Mg contents in the lavas of both units indicates that their compositional differences originated in the upper mantle. The Al and Si systematics of these lavas suggests that, compared to unit 3 magmas, the unit 2 magmas may have segregated at greater depths from a garnet lherzolite mantle. The identical isotopic composition and similar ratios of highly incompatible elements in these two lava units argues against their differences being a consequence of random metasomatism or mantle heterogeneity. The lower Y and HREE contents but higher concentrations of incompatible elements in the unit 2 lavas relative to unit 3 can be most simply explained by differential partial melting of similar garnet-bearing sources. The unit 2 magmas thus appear to have been generated by smaller degrees of melting at a greater depth than the unit 3 magmas. The contemporaneous eruption of two distinct but volumetrically restricted primary magmas from adjacent vents at the Alligator Lake volcanic complex suggests that volcanism in this region of the Canadian Cordillera is controlled by localized, small batch processes.