Primary distribution of silver and copper in native gold from six deposits in the Western United States

Electron-microprobe analyses and mineragraphic studies of native gold demonstrate considerable variations in the primary intergrain and intragrain distribution of silver. The gold grains have from 1–55 weight percent silver; copper is present in grains from only one locality and ranges from 0.1–0.6 weight percent. Some gold grains have strong zoning of silver whereas others have no detectable zoning. Gold grains from some deposits show remarkable intergrain homogeneity of silver and/or copper content, but others exhibit extreme heterogeneity. We believe that the inhomogeneities and variations in silver content recognized and emphasized here are features of primary deposition. We also recognize low-silver rims with sharp boundaries bordering many of the grains examined but believe these are developed in a relatively oxidizing, low-temperature environment and are not primary lode features. Opaque mineral inclusions of primary origin in gold grains are common in some deposits, scarce in many, and virtually absent from others. These inclusions may be of value in characterizing some gold deposits. For the majority of gold crystals from Copper Basin, Arizona, the lowest silver content observed was in the central portion of each grain and the highest silver content was in the rim. This is believed to be due an increase in the proportion of silver to gold in solution during growth of the crystals. Analysis of sized fractions of 331 gold grains from Pennsylvania Mountain, Colorado, shows no systematic correlation of grain size with silver content. Electron microprobe step-scanning of gold from Alder Gulch, Montana, suggests more than one mineralization event took place. Pyrite and acanthite inclusions less than 0.05 mm in the largest dimension, are present in some grains from this deposit. Inclusions of pyrite, pyrrhotite, chalcopyrite, and an isotropic Co-As-S mineral are present in the low-silver, copper-bearing gold from Ninemile Creek, Montana. The presence of copper and the low silver content in this gold is not typical of the gold-quartz-pyrite association which is common in the Western United States.

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Zusammenfassung Untersuchungen von Zusammensetzungen von Einzelkörnern und benachbarten Körnern mit der Mikrosonde und durch erzmikroskopische Studien an gediegenem Gold weisen beträchtliche Variationen in der primären Verteilung von Silber auf. Die Goldkörner enthalten von 1–55 Gewichtsprozent Silber; Kupfer ist gegenwärtig in Körnern von nur einer Gegend zwar in Mengen von 0,1–0,6 Gewichtsprozent. Manche Goldkörner sind stark zonar mit Silber während andere keine bemerkbaren Zonen aufweisen. Goldkörner aus einigen Ablagerungen zeigen eine bemerkenswerte Homogenität von Silberund/oder Kupfergehalt, andere aber sind durch extreme Inhomogenität gakennzeichnet. Wir glauben, daß die festgestellten Inhomogenitäten und Variationen des Silbergehaltes Merkmale von primären Ablagerungen sind. Zusätzlich wurden an vielen von den von uns untersuchten Körnern scharfbegrenzte Randzonen mit niedrigem Silbergehalt beobachtet. Wir glauben, daß sich die Randzonen in einer verhältnismäßig oxidierenden Umgebung von niedriger Temperatur entwickelten und daß sie nicht Merkmale primärer Erzadern sind. Opake Mineraleinschlüsse von primärem Ursprung in Goldkörnern kommen in manchen Ablagerungen vor, selten in vielen und sind virtuell abwesend in anderen. Für einige Goldablagerungen können diese Einschlüsse als charakteristische Kennzeichen von Wert sein. Der niedrigste Silbergehalt für die meisten Goldkristalle, aus dem Copper Basin, Arizona, war in der Mitte der Körner und der höchste Silbergehalt war in den Randzonen der Körner gegenwärtig. Es wird angenommen daß dieses auf eine Zunahme in den Proportionen von Silber zu Gold in der Lösung während des Wachstums der Kristalle zurückzuführen ist. Analysen von Größensortierungen von 331 Goldkörnern aus den Pennsylvania Mountain, Colorado, zeigen keine systematische Korrelation der Korngrößen mit den Silbergehalten. Mikrosonde — Scanninganalysen an Gold aus dem Alder Gulch, Montana, weisen auf mehr als einen Mineralisationsvorgang hin. Pyrit- und Akanthiteinschlüsse von weniger als 0,05 mm in den größten Dimensionen sind in einigen Körnern dieser Ablagerung enthalten. Einschlüsse von Pyrit, Pyrrhotin, Chalcopyrit und von einem isotropen Co-As-S-mineral finden sich in dem silberarmen, kupferhaltigen Gold von Ninemile Creek, Montana. Der Kupfergehalt und der niedrige Silbergehalt in diesem Gold sind nicht typisch für die in dem westlichen Teil der USA übliche Gold-Quarz-Pyrit Assoziation.

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Publication authorized by the Director, U. S. Geological Survey.     

A simple method for obtaining a continuous record of the presence and type of clouds in the sky during the day

Summary A photovoltaic cell or solar cell suitably mounted to look at a small portion of the sky and connected to a sensitive recorder yields considerable information as to the condition of the sky. The author has used such a simple device for many years and it is found that familiarity with the type of trace, which is in response to the changes in reflected light from clouds, will permit a good estimate of the type of clouds that are present. The presentation of such cloud information on a standard potentiometer or galvanometer type recorder is very convenient when correlating cloud conditions with other variables being recorded on similar types of recorders.     

Periglacial geoarchaeology at the Dog Creek site,Northern Yukon

The Dog Creek archaeological site (NcVi‐3), located in the northern Yukon, provides evidence of complex site transformational processes related to microclimatic conditions occurring since the mid‐Holocene. Geoarchaeological research at Dog Creek sought to interpret site formation processes in order to understand the relationship between surficial artifacts, buried artifacts, and stratified sediments. It also attempted to reconstruct the periglacial processes that were active in transforming the site and their relationships to microclimatic conditions. Sedimentology and fabric analysis show that artifacts were buried by solifluction and disturbed by frost heave and cryoturbation. Radiocarbon dating and pollen analysis demonstrated that solifluction took place approximately 5200–2000 years ago when a spruce forest existed at the site. This evidence suggests an onset of cooling conditions that continues to the present. After the mid‐Holocene, the spruce treeline began to move south toward its present position. © 2001 John Wiley & Sons, Inc.     

Pb‐isotope compositions of the Tasik Chini volcanic‐hosted massive sulfide deposit,Central Belt of Peninsular Malaysia: Implication for source region and tectonic setting

Lead isotope data of sulfides and host volcanic rocks from the Bukit Botol and Bukit Ketaya deposits, the two representative deposits of the Tasik Chini volcanic‐hosted massive sulfide (VHMS) deposit, Central Belt of Peninsular Malaysia, are reported. Lead isotope compositions of the associated sulfide minerals and volcanic rocks from the Bukit Botol deposit exhibit homogeneous and less radiogenic values (²⁰⁶Pb/²⁰⁴Pb showing a range of composition from 18.14 to 18.20, ²⁰⁷Pb/²⁰⁴Pb between 15.52 and 15.59 and ²⁰⁸Pb/²⁰⁴Pb from 37.96 to 38.35). Similarly, the Pb isotopic compositions of the host volcanic rocks from the Bukit Ketaya deposit yielded a narrow range to those of the sulfide samples (²⁰⁶Pb/²⁰⁴Pb from 18.04 to 18.20, ²⁰⁷Pb/²⁰⁴Pb between 15.43 and 15.57 and ²⁰⁸Pb/²⁰⁴Pb of 37.96 to 38.30). The uniform Pb‐isotope compositions of the sulfides in the ore horizon and the host volcanic rocks from both deposits suggest a derivation from a similar source reservoir and mineralization processes. In the framework of the tectonic model for the Central Belt of Peninsular Malaysia, both deposits display a range of lead isotopic compositions originated from mixing of bulk crust/juvenile arc and minor mantle sources, which are typical for VHMS deposits in an island arc–back arc setting.     

Recent occurrence of large jökulhlaups at Lake Tuborg,Ellesmere Island,Nunavut

The varved sediment record from glacially-fed Lake Tuborg, Ellesmere Island, Nunavut, shows that only three large jökulhlaups have occurred there in the last millennium: 2003, 1993, and 1960. Detailed analyses of sediment microstructure and particle size, combined with in-situ hydrometeorological and limnological process studies, allowed jökulhlaup facies identification and discrimination from deposits from other processes. Deposits from large jökulhlaups are anomalously thick, typically lack internal structure, have sharp bases, and fine upwards. The ice-dammed lake above Lake Tuborg (the source of the jökulhlaups) likely changed its drainage style in 1960, from ice-dam overtopping to ice-dam flotation and glacial tunnel enlargement by melt widening, which allowed the lake to drain completely and catastrophically. Complete drainage of ice-dammed lakes by ice-dam flotation is rare in the region is due to the pervasiveness of cold-based ice. Twentieth century warming is likely responsible for some combination of dam thinning, lake expansion and deepening, and changing the thermal regime at the base of the dam. Anomalously thick individual varves were periodically deposited beginning in the nineteenth century, and their thickness increased with time. This likely reflects a combination of increased ice dam overtopping, subaqueous slope failures, sediment availability and rising air temperature. The varve record presented here significantly correlates with a previous, shorter record from Lake Tuborg. However, generally weak correlations are found between the new varve time series, regional records of air temperature, and glacial melt from ice cores on the Agassiz Ice Cap. It is hypothesized that on short timescales, sedimentation at the coring location reflects a complex and varying integration of multiple hydroclimatic, geomorphic and limnologic influences.     

The effect of carbon dioxide cooling on trends in the F2-layer ionosphere

The effect of carbon dioxide (CO₂) cooling on trends of h_mF₂ and N_mF₂ are investigated using a coupled thermosphere and ionosphere general circulation model. Model simulations indicate that CO₂ cooling not only causes contraction of the upper atmosphere and changes of neutral and ion composition but also changes dynamics and electrodynamics in the thermosphere/ionosphere. These changes determine the altitude dependence of ionospheric trends and complex latitudinal, longitudinal, diurnal, seasonal, and solar cycle variations of trends of h_mF₂ and N_mF₂. Under the CO₂ cooling effect, trends of N_mF₂ are negative with magnitude from 0% to −40% for doubled CO₂, depending on location, local time, season, and solar activity. The corresponding trends of h_mF₂ are mostly negative with a magnitude from 0 to −40 km, but can be positive with a magnitude from 0 to 10 km at night, with maximum positive trends occurring after midnight under solar minimum conditions.     

Radar Detection of Near-Earth Asteroids 2062 Aten, 2101 Adonis, 3103 Eger, 4544 Xanthus, and 1992 QN

We describe Doppler-only radar observations of near-Earth asteroids 2062 Aten, 2101 Adonis, 3103 Eger, 4544 Xanthus, and 1992 QN that were obtained at Arecibo and Goldstone between 1984 and 1996. Estimates of the echo spectral bandwidths, radar cross sections, and circular polarization ratios of these objects constrain their pole-on breadths, radar albedos, surface roughnesses, taxonomic classes, rotation periods, and pole directions. Aten's bandwidth is consistent with its radiometrically determined diameter of 0.9 km. Adonis has a rotation periodP≤ 11 h and an effective diameter (the diameter of a sphere with the same projected area as the asteroid) between 0.3 and 0.8 km. The radar properties of Adonis suggest it is not a member of taxonomic classes C or M. The effective diameter of Xanthus is between 0.4 and 2.2 km with a rotation periodP≤ 20 h. Echoes from 1992 QN constrain the asteroid's pole-on breadth to be ≥0.6 km and probably exclude it from the C and M taxonomic classes. The strongest Eger echoes are asymmetric with bandwidths that set lower bounds of 1.5 and 2.3 km on the minimum and maximum breadths of the asteroid's pole-on silhouette. If Eger is modeled as a 1.5 × 2.3 km biaxial ellipsoid, then its effective diameter for an equatorial view is 1.5 km end-on and 1.9 km broadside or pole-on, implying a geometric albedo smaller than published values but still consistent with a classification as an E-type object. The near-unity circular polarization ratios of Adonis, Eger, and 1992 QN are among the highest values measured for any asteroid or comet and suggest extreme near-surface roughness at centimeter to meter scales.     

Analysis of Radionuclide Releases from the Fukushima Dai-Ichi Nuclear Power Plant Accident Part I

Part I of this publication deals with the analysis of fission product releases consecutive to the Fukushima Dai-ichi accident. Reactor core damages are assessed relying on radionuclide detections performed by the CTBTO radionuclide network, especially at the particulate station located at Takasaki, 210 km away from the nuclear power plant. On the basis of a comparison between the reactor core inventory at the time of reactor shutdowns and the fission product activities measured in air at Takasaki, especially ⁹⁵Nb and ¹⁰³Ru, it was possible to show that the reactor cores were exposed to high temperature for a prolonged time. This diagnosis was confirmed by the presence of ¹¹³Sn in air at Takasaki. The ¹³³Xe assessed release at the time of reactor shutdown (8 × 10¹⁸ Bq) turned out to be in the order of 80 % of the amount deduced from the reactor core inventories. This strongly suggests a broad meltdown of reactor cores.     

Estimates of sediment and nutrient loads in 10 major catchments draining to the Great Barrier Reef during 2006-2009

The Great Barrier Reef (GBR) catchment area has been monitored simultaneously for sediment and nutrient exports from 10 priority catchments discharging into the GBR lagoon between 2006 and 2009. This allows GBR catchment-wide exports to be estimated and spatially compared within a discrete time-frame. Elevated levels of sediment and nutrient exports were recorded in all monitored catchments as compared to pre-European estimates, but vary around previous estimates of mean annual loads. During the period of monitoring, the Burdekin and Fitzroy catchments contributed the highest sediment and nutrient exports, however when loads were normalised for area, these catchments produced the lowest unit yields. In contrast, the highest yields were produced in the wetter and proportionately more intensively cultivated Johnstone, O'Connell, and Pioneer catchments particularly for dissolved nitrogens. This assessment offers the necessary scientific foundation for future monitoring, assessment, and management of sediment and nutrient loads entering the GBR.