Fine-grained gold in stream sediments of east-central Lemhi County, Idaho

1990 ◽  
Author(s):  
G.A. Desborough ◽  
W.H. Raymond ◽  
K.V. Evans
Keyword(s):  
Stream Sediments ◽  
East Central ◽  
Fine Grained

Seismic deformation analysis of Tuttle Creek Dam

2012 ◽  
Vol 49 (3) ◽  
pp. 323-343 ◽  
Author(s):  
Timothy D. Stark ◽  
Michael H. Beaty ◽  
Peter M. Byrne ◽  
Gonzalo Castro ◽  
Francke C. Walberg ◽  
...  
Keyword(s):  
Constitutive Model ◽  
Constitutive Models ◽  
Deformation Analysis ◽  
East Central ◽  
Fine Grained ◽  
Upstream Slope ◽  
Downstream Slope ◽  
Soil Constitutive Models ◽  
Seismic Deformation

To facilitate the design of seismic remediation for Tuttle Creek Dam in east central Kansas, a seismic finite difference analysis of the dam was performed using the software FLAC and the UBCSAND and UBCTOT soil constitutive models. The FLAC software has a key advantage because it can use calibrated site-specific constitutive models. Earlier deformation analyses using a hyperbolic constitutive model for the foundation fine-grained materials did not properly represent the modulus and strength reduction and predicted extremely large permanent deformations. Cyclic triaxial laboratory tests using high-quality samples and in situ vane shear tests were used to calibrate the FLAC constitutive model herein. The resulting FLAC analysis of the unremediated dam predicted an upstream slope toe deformation of about 0.6 m, a crest settlement of about 0.6 m, and a downstream slope toe deformation of about 1.5 m using the design ground motion. Based on the estimated permanent deformations and other factors, it was decided that the anticipated upstream slope and crest deformations were tolerable and only the downstream slope had to be remediated to protect the downstream seepage control system.

The morphology, mineralogy, and behavior of u "fine-grained" gold from placer deposits of Alberta: sampling and implications for mineral exploration

1986 ◽  
Vol 23 (11) ◽  
pp. 1662-1672 ◽  
Author(s):  
L. Giusti
Keyword(s):  
Mineral Exploration ◽  
Sampling Procedure ◽  
Stream Sediments ◽  
Shape Factors ◽  
Athabasca River ◽  
Fine Grained ◽  
The North ◽  
Placer Deposits ◽  
Routine Sampling ◽  
And Behavior

The morphology of a large number of gold grains from stream sediments of the North Saskatchewan River and the Athabasca River was studied, together with the partitioning of the placer gold between various size fractions.Two major morphological varieties of gold were observed: (1) flaky, scaly gold, with folded and hammered edges, and with crystals or crystal faces still visible on the surface; and (2) "sandwiched," droplike particles, sometimes toroidal. About 5% of both types of gold were found to be coated with "new," secondary gold.The size of the majority of the gold grains studied varies between 0.500 and 0.010 mm. The most frequent size range in the North Saskatchewan River is 0.125–0.250 mm, whereas in the Athabasca River it is 0.063–0.125 mm. An important fraction of the gold from both rivers is smaller than 0.063 mm.The average Corey shape factor (CSF) of the gravity-recovered gold increases as the particle size decreases, whereas the gold grains lost to the tailings indicate very low average shape factors (i.e., high degree of flattening). This apparent increase in CSF for the smallest fractions recovered when using mechanical techniques is due to the fact that the flaky gold particles are more difficult to recover than the more spherical ones. Moreover, the presence of a gold-rich rim on all the gold grains increases their hydrophobicity.The sampling procedure to be adopted in Alberta and, more generally, in glaciated terrains is discussed. In particular, the use of the −63 μm fraction for routine sampling of stream sediments is suggested.

Early Holocene pinyon (Pinus monophylla) in the northeastern Great Basin

1990 ◽  
Vol 33 (1) ◽  
pp. 94-101 ◽  
Author(s):  
David B. Madsen ◽  
David Rhode
Keyword(s):  
Great Basin ◽  
Late Quaternary ◽  
Early Holocene ◽  
Hunter Gatherers ◽  
Pinus Monophylla ◽  
East Central ◽  
Lake Bonneville ◽  
Fine Grained ◽  
Pine Nut ◽  
Human Use

AbstractFine-grained excavation and analysis of a stratigraphic column from Danger Cave, northeastern Great Basin, suggests prehistoric hunter-gatherers were collecting and using singleleaf pinyon (Pinus monophylla) near the site for at least the last 7500 yr. Human use of the cave began after the retreat of Lake Bonneville from the Gilbert level, shortly before 10,000 yr B.P. In stratum 9, culturally deposited pine nut hulls appear in the sequence by about 7900 yr B.P. and are continuously present thereafter. A hull fragment in stratum 10 is directly dated to 7410 ± 120 yr B.P. These dates are at least 2000 yr earlier than expected by extrapolation to macrofossil records from the east-central and central Great Basin, and necessitate some revision of current biogeographical models of late Quaternary pinyon migration.

The Erskine Field, Block 23/26, UK North Sea

2003 ◽  
Vol 20 (1) ◽  
pp. 523-535 ◽  
Author(s):  
R. N. Coward
Keyword(s):  
Lacustrine Environment ◽  
East Central ◽  
Shallow Marine ◽  
Western Margin ◽  
Permeability Characteristics ◽  
Fine Grained ◽  
Delta Plain ◽  
Porosity And Permeability ◽  
Shale Formation ◽  
High Temperature High Pressure

AbstractThe Erskine Field is a high temperature, high pressure (HTHP), gas condensate accumulation located on the western margin of the East Central Graben. The field was discovered in 1981 by the 23/26a-3RE well and subsequently delineated by six appraisal wells. Development approval was granted in 1995 and to date five development wells have been drilled. In December 1997, Erskine Field became the first HTHP field in the UKCS to achieve production. Hydrocarbons are produced from three separate Jurassic reservoirs. In order of decreasing importance, these are: the Late Oxfordian Erskine Sandstone (Puffin Formation), the Middle Jurassic Pentland Reservoir, and the Late Oxfordian Heather Turbidite Reservoir.The Erskine Sandstone is very fine to fine-grained highly bioturbated, shaley sandstone. The sandstones represent shallow marine progradational sequences, deposited predominantly in the offshore transition zone. Within the majority of the Erskine Sandstone, porosity is high (20-25%) but with relatively poor associated permeability (0.1-10mD). However, the tops of the coarsening upward sequences (E30 and E70 zones) have appreciably better permeability and are thought to be the major conduits for fluid flow. The E30 and E70 zones would not have been identified, had it not been for the extensive coring programme undertaken in the development wells.The Pentland Reservoir is a regionally extensive sequence of interbedded sandstone, shales, coals and siltstones, deposited in a fluvial-lacustrine environment in a delta plain setting. Permeability in the Pentland reservoir (0.1 mD-1 D) is in general far superior to the values observed in the Erskine Sandstone. The main control on the observed variability in porosity and permeability characteristics is grain size, that in turn is controlled by facies.The Heather Turbidite Reservoir occurs within two thin predominantly fine-grained turbidite sandstone beds in the Heather Shale Formation. This reservoir is restricted to the Alpha Terrace region in the SW of the field, and is drained by a single development well.Total Erskine Field reserves are estimitated at approx 400 BCF of gas and 66 MMBBL of condensate.

scholarly journals Chemical weathering trends in fine-grained ephemeral stream sediments of the McMurdo Dry Valleys, Antarctica

Geomorphology ◽  
2017 ◽  
Vol 281 ◽  
pp. 13-30 ◽  
Author(s):  
Kristen R. Marra ◽  
Megan E. Elwood Madden ◽  
Gerilyn S. Soreghan ◽  
Brenda L. Hall
Keyword(s):  
Chemical Weathering ◽  
Stream Sediments ◽  
Mcmurdo Dry Valleys ◽  
Dry Valleys ◽  
Ephemeral Stream ◽  
Fine Grained

scholarly journals A generalized photon-tracking approach to simulate spectral snow albedo and transmissivity using X-ray microtomography and geometric optics

2021 ◽  
Author(s):  
Theodore Letcher ◽  
Julie Parno ◽  
Zoe Courville ◽  
Lauren Farnsworth ◽  
Jason Olivier
Keyword(s):  
Optical Properties ◽  
Coarse Grained ◽  
East Central ◽  
X Ray ◽  
Fine Grained ◽  
Potential Applications ◽  
Visible Wavelengths ◽  
Tracing Techniques ◽  
Bidirectional Reflectance Distribution ◽  
Snow Samples

Abstract. A majority of snow radiative transfer models (RTM) treat snow as a collection of idealized grains rather than a semi-organized ice-air matrix. Here we present a generalized multi-layer photon-tracking RTM that simulates light transmissivity and reflectivity through snow based on x-ray microtomography, treating snow as a coherent structure rather than a collection of grains. Notably, the model uses a blended approach to expand ray-tracing techniques applied to sub-1 cm3 snow samples to snowpacks of arbitrary depths. While this framework has many potential applications, this study's effort is focused on simulating light transmissivity through thin snowpacks as this is relevant for surface energy balance applications and sub-nivean hazard detection. We demonstrate that this framework capably reproduces many known optical properties of a snow surface, including the dependence of spectral reflectance on snow grain size and incident zenith angle and the surface bidirectional reflectance distribution function (BRDF). To evaluate how the model simulates transmissivity, we compare it against spectroradiometer measurements collected at a field site in east-central Vermont. In this experiment, painted panels were inserted at various depths beneath the snow to emulate thin snow. The model compares remarkably well against the spectroradiometer measurements. Sensitivity simulations using this model indicate that snow transmissivity is greatest in the visible wavelengths and is limited to the top 5 cm of the snowpack for fine-grained snow, but can penetrate as deep as 8 cm for coarser grain snow. An evaluation of snow optical properties generated from a variety of snow samples suggests that coarse grained low density snow is most transmissive.

Sedimentology of proglacial rivers in eastern Scotland during the Late Devensian

2001 ◽  
Vol 92 (2) ◽  
pp. 149-171 ◽  
Author(s):  
Philip M. Marren
Keyword(s):  
Flood Events ◽  
East Central ◽  
Fine Grained ◽  
High Magnitude ◽  
High Stage ◽  
Discharge Regime ◽  
Depositional Architecture ◽  
The Relationship ◽  
Depositional Elements

ABSTRACTThis paper reconstructs the characteristics of rivers which deposited proglacial fluvial sediments in east-central Scotland during the Late Devensian. Sediment depositional architecture and geometry, together with the relationship between high-stage and falling and low-stage depositional elements, were used to relate the proglacial sediments to the glacial meltwater discharge regime. The proglacial river systems studied were dominated by ‘normal’ ablation controlled discharge, rather than by high magnitude flood events. Consequently there is a great deal of spatial and vertical variability. Deposition occurred during short intervals of rapid aggradation, so that relatively fine-grained falling-stage sediments, as well as coarser, bar-core sediments are well preserved. Models relating the characteristics of the final deposit to the nature of the river are presented. These emphasise the role of stage changes and aggradation rates in controlling sediment architecture in braided fluvial deposits.

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