Seasonal variation of gold and arsenic in biogeochemical samples from a disseminated gold deposit in the Northern Cordillera

An orientation survey was conducted over the Quartz Mountain, Oregon, hot-spring type disseminated gold deposit to address three questions critical to successful exploration of the area: What is the relationship between bedrock geology and the trace-element content of trees and soils; do these relationships change seasonally; are these relationships similar in the two tree species which discontinuously blanket the area?Twig, needle and wood samples were collected four times during the year from both ponderosa pine (Pinus ponderosa) and white fir (Abies concolor). Soils were collected once. All samples were analyzed for Au and As and the wood samples were analyzed also for Sb.Arsenic was the best pathfinder element, having little analytical, spatial, or seasonal variation in the twig and needle samples. Anomalous levels were 150 μg/g (ppm) As in pine and 30 μg/g in fir. Gold showed analytical variation of 20–30%, sample duplicate variation up to 90%, spatial changes, and seasonal variation ranging from winter-summer background [10–20 ng/g (ppb) Au] to anomalies of 300–400 ng/g (ppb) Au in pine and 100 μg/g (ppb) Au in fir in the spring and fall. Antimony could not be completely evaluated as a pathfinder element because it was only determined in wood samples.Needles and twigs from both species proved to be viable sample media for exploration of the area. Wood was not a suitable medium because of low, erratic values, perhaps due in part to analytical technique. Needles had 2 to 20 times higher As concentrations than did twigs. Twigs had a slightly higher Au content [25 ng/g (ppb)] than did needles. The pine samples were higher in both elements than were the fir samples. The data, normalized by species, could be treated as one homogeneous data base.The soil Au and As data outlined the mineralization clearly with a central Au anomaly [100 ng/g (ppb) and greater] surrounded by As anomalies [100 μg/g (ppm) and greater] over a distance of 594 m. Neither spring nor fall tree Au anomalies were coincident with the soil Au anomaly. Consistent throughout the year, tree As anomalies coincided with the soil As anomalies, but covered a smaller area. Both the Au and As anomalies in trees appeared to be related to bedrock contact zones rather than to the soil the trees were growing in.     

Spatial Diffusion of Wal-Mart: Contagious and Reverse Hierarchical Elements

In its 30 years of existence, Wal-Mart Stores, Inc. has grown to become the largest retailer in the United States in terms of sales volume. This paper describes and analyzes the geographic expansion of Wal-Mart from its origin in northwest Arkansas. During its early years the firm grew slowly and opened stores primarily in small towns. In recent years it has expanded into metropolitan areas in order to serve more completely the U. S. market. The firm's expansion pattern has been characterized by elements of both neighborhood contagious diffusion and reverse hierarchical diffusion.     

Gravitational microlensing of planets: the influence of planetary phase and caustic orientation

Recent studies have demonstrated that detailed monitoring of gravitational microlensing events can reveal the presence of planets orbiting the microlensed source stars. With the potential of probing planets in the Galactic bulge and Magellanic Clouds, such detections greatly increase the volume over which planets can be found. This paper expands on the original studies by considering the effect of planetary phase on the form of the resultant microlensing light curve. It is found that crescent-like sources can undergo substantially more magnification than a uniformly illuminated disc, the model typically employed in studying such planets. In fact, such a circularly symmetric model is found to suffer a minimal degree of magnification when compared with the crescent models. The degree of magnification is also a strong function of the planet's orientation with respect to the microlensing caustic. The form of the magnification variability is strongly dependent on the planetary phase and from which direction the planet is swept by the caustic, providing further clues to the geometry of the planetary system. As the amount of light reflected from a planet also depends on its phase, the detection of extreme crescent-like planets requires the advent of 30-m class telescopes, while light curves of planets at more moderate phases can be determined with today's 10-m telescopes.     

Mapping the human record in the British early Palaeolithic: evidence from the Solent River system

The lithic record from the Solent River and its tributaries is re‐examined in the light of recent interpretations about the changing demography of Britain during the Lower and early Middle Palaeolithic. Existing models of the terrace stratigraphies in the Solent and its tributary areas are reviewed and the corresponding archaeological record (specifically handaxes) for each terrace is assessed to provide models for the relative changes in human occupation through time. The Bournemouth area is studied in detail to examine the effects of quarrying and urbanisation on collection history and on the biases it introduces to the record. In addition, the effects of reworking of artefacts from higher into lower terraces are assessed, and shown to be a significant problem. Although there is very little absolute dating available for the Solent area, a cautious interpretation of the results from these analyses would suggest a pre‐Marine Isotope Stage (MIS) 12 date for the first appearance of humans, a peak in population between MIS 12 and 10, and a decline in population during MIS 9 and 8. Owing to poor contextual data and small sample sizes, it is not clear when Levallois technology was introduced. This record is compared and contrasted to that from the Thames Valley. It is suggested that changes in the palaeogeography of Britain, in particular land connections to the continent, might have contributed to differences in the archaeological records from the Solent and Thames regions. Copyright © 2009 John Wiley & Sons, Ltd.     

The Influence of Land Cover on Shuttle Radar Topography Mission (SRTM) Elevations in Low‐relief Areas

The Shuttle Radar Topography Mission (SRTM), the first relatively high spatial resolution near‐global digital elevation dataset, possesses great utility for a wide array of environmental applications worldwide. This article concerns the accuracy of SRTM in low‐relief areas with heterogeneous vegetation cover. Three questions were addressed about low‐relief SRTM topographic representation: to what extent are errors spatially autocorrelated, and how should this influence sample design? Is spatial resolution or production method more important for explaining elevation differences? How dominant is the association of vegetation cover with SRTM elevation error? Two low‐relief sites in Louisiana, USA, were analyzed to determine the nature and impact of SRTM error in such areas. Light detection and ranging (LiDAR) data were employed as reference, and SRTM elevations were contrasted with the US National Elevation Dataset (NED). Spatial autocorrelation of errors persisted hundreds of meters spatially in low‐relief topography; production method was more critical than spatial resolution, and elevation error due to vegetation canopy effects could actually dominate the SRTM representation of the landscape. Indeed, low‐lying, forested, riparian areas may be represented as substantially higher than surrounding agricultural areas, leading to an inverted terrain model.     

XMM–Newton observations of the Seyfert 1 AGN H 0557−385

We present XMM–Newton observations of the Seyfert 1 active galactic nucleus (AGN)  H 0557 − 385  . We have conducted a study into the warm absorber present in this source, and using high-resolution Reflection Grating Spectrometer (RGS) data we find that the absorption can be characterized by two phases: a phase with log ionization parameter ξ of 0.50 (where ξ is in units of erg cm s⁻¹) and a column of  0.2 × 10²¹ cm⁻²  , and a phase with log ξ of 1.62 and a column of  1.3 × 10²² cm⁻²  . An iron Kα line is detected. Neutral absorption is also present in the source, and we discuss possible origins for this. On the assumption that the ionized absorbers originate as an outflow from the inner edge of the torus, we use a new method for finding the volume filling factor. Both phases of  H 0557 − 385  have small volume filling factors (≤1 per cent). We also derive the volume filling factors for a sample of 23 AGN using this assumption and for the absorbers with  log ξ > 0.7  , we find reasonable agreement with the filling factors obtained through the alternative method of equating the momentum flow of the absorbers to the momentum loss of the radiation field. By comparing the filling factors obtained by the two methods, we infer that some absorbers with  log ξ < 0.7  occur at significantly larger distances from the nucleus than the inner edge of the torus.     

A locally conservative variational multiscale method for the simulation of porous media flow with multiscale source terms

We present a variational multiscale mixed finite element method for the solution of Darcy flow in porous media, in which both the permeability field and the source term display a multiscale character. The formulation is based on a multiscale split of the solution into coarse and subgrid scales. This decomposition is invoked in a variational setting that leads to a rigorous definition of a (global) coarse problem and a set of (local) subgrid problems. One of the key issues for the success of the method is the proper definition of the boundary conditions for the localization of the subgrid problems. We identify a weak compatibility condition that allows for subgrid communication across element interfaces, a feature that turns out to be essential for obtaining high-quality solutions. We also remove the singularities due to concentrated sources from the coarse-scale problem by introducing additional multiscale basis functions, based on a decomposition of fine-scale source terms into coarse and deviatoric components. The method is locally conservative and employs a low-order approximation of pressure and velocity at both scales. We illustrate the performance of the method on several synthetic cases and conclude that the method is able to capture the global and local flow patterns accurately.     

Heavy metal distribution in karst soils from Croatia and Slovakia

With the use of the optimised three-step BCR sequential-extraction procedure it was possible to assess the mobility of selected elements in soil profiles from Croatian and Slovakian karst terrains. The soils in the Croatian karst were enriched in Cr, Ni, V, Mn, Cu, Cd and Mo, while soils from the Slovak Karst had high Pb and Zn concentrations. It was determined that the elements were most readily mobilised from the topsoil and the degree of mobility decreased with depth. Cr and Ni were mainly bound to the residual fraction, and Pb in the oxidisable fraction. Cu mobility was high in samples treated with agrochemicals throughout the soil profile.     

4D seismic for oil-rim monitoring

In the central North Sea ‘Gannet‐A’ field, a 50 ft oil rim is overlain by a gas cap of variable thickness. Oil is produced from horizontal wells which initially produced dry oil, but as the field became more mature, a significant water cut was seen in several wells. A dedicated 4D seismic monitor survey was acquired in order to assess the remaining distribution of oil reserves. By forward modelling the synthetic seismic response to parameters such as contact movement and residual saturations (using 2D and 3D wedge models), and comparing the results with real seismic data, we are able to decipher the contact movements across the field. It is shown that, in one part of the field, the increased water cut is caused primarily by the vertical displacement of the entire oil rim into the initial gas cap. This oil‐rim displacement produces a very different 4D seismic response from the case of a static gas–oil contact and rising oil–water contact (normal production). As a result of these observations, we are able to optimize field production by both re‐perforation of existing wells and by drilling sidetracks into the displaced rim: a brown‐field development opportunity that might otherwise be missed.