Integrated geophysics for mineral exploration in drift-covered volcanic terrains: examples from northern Vancouver Island,Canada     

C. Lowe  M.E. Best  P.T. Bobrowsky  D.A. Seemann 《Geophysical Prospecting》1998,46(3):201-225

Known mineral occurrences in northern Vancouver Island are typically hosted in volcanic units of the Bonanza Group. At a local scale, the mineralization is associated with advanced argillic bedrock alteration and is often intimately related to porphyry intrusions. On a larger scale, faults are thought to exert the most significant control on the distribution of mineralized host rocks. Poor exposures and a complex glacial history limit the use of traditional methods of geological mapping and mineral exploration in this region and to date geophysical methods have been under-utilized. Here we present findings from four standard geophysical (gravity, magnetics, electromagnetics and seismic refraction) methods, recently deployed here to elucidate the subsurface geology, as well as to identify new targets for base metal exploration. Results at two different sites show that the integrated interpretation of geophysical data, constrained by physical rock property measurements, yields detailed images of the subsurface at a fraction of the cost of drilling. At one site, east of Rupert Inlet, the final subsurface model shows that the Bonanza Group is not nearly as extensive as previously presumed. An extension of the Holberg Fault is identified some 50 km east of the visibly mapped outcrop and an extensive zone of alteration around the fault is recognized. Furthermore, a number of the methods provide support for the existence of a porphyry dike at this site. At the second site, north of Rupert Inlet, magnetic and electromagnetic data prove effective at mapping alteration and locating shear zones beneath a relatively thin drift cover. Together, these results help outline a strategy for exploration in drift-covered terrains and show that a redirection of exploration effort is warranted in the case of northern Vancouver Island.  相似文献   

Deep radio observations of 3C 324 and 3C 368: evidence for jet–cloud interactions     

P. N. Best  C. L. Carilli  S. T. Garrington  M. S. Longair  & H. J. A. Ro¨ttgering 《Monthly notices of the Royal Astronomical Society》1998,299(2):357-370

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Dissolved oxygen as a physico-chemical supporting element in the Water Framework Directive   总被引：1，自引：0，他引：1  

Best MA  Wither AW  Coates S 《Marine pollution bulletin》2007,55(1-6):53-64

For transitional and coastal waters the Water Framework Directive identifies 5 "General chemical and physiochemical elements supporting the biological elements". The five elements are transparency, thermal conditions, oxygenation conditions, salinity and nutrient conditions. "Supporting" in the context of the directive means that the values of the physicochemical quality elements are such as to support a biological community of a certain ecological status, recognising the fact that biological communities are products of their physical and chemical environment. Physicochemical and hydromophological aspects fundamentally determine the type of water body and habitat, and hence the type specific biological community. The directive does not intended that these supporting elements should be used as surrogates for the biological elements in monitoring. The monitoring and assessment of the physical and physicochemical quality elements will support the interpretation, assessment and classification of the results arising from the monitoring of the biological quality elements. This paper considers the challenges involved in the development of oxygen standards for the directive, their relationship to the biological elements and normative conditions of the directive and to regulatory requirements.  相似文献   

0.5 Mpc-scale extended X-ray emission in the z= 2.48 radio galaxy 4C 23.56     

O. Johnson  O. Almaini  P. N. Best  J. Dunlop 《Monthly notices of the Royal Astronomical Society》2007,376(1):151-156

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On the evolution of the black hole: spheroid mass ratio     

R. J. McLure  M. J. Jarvis  T. A. Targett  J. S. Dunlop  P. N. Best 《Monthly notices of the Royal Astronomical Society》2006,368(3):1395-1403

We present the results of a study which uses the 3C RR sample of radio-loud active galactic nuclei to investigate the evolution of the black hole:spheroid mass ratio in the most massive early-type galaxies from  0 < z < 2  . Radio-loud unification is exploited to obtain virial (linewidth) black hole mass estimates from the 3C RR quasars, and stellar mass estimates from the 3C RR radio galaxies, thereby providing black hole and stellar mass estimates for a single population of early-type galaxies. At low redshift  ( z ≲ 1)  , the 3C RR sample is consistent with a black hole:spheroid mass ratio of   M _bh/ M _sph≃ 0.002  , in good agreement with that observed locally for quiescent galaxies of similar stellar mass  ( M _sph≃ 5 × 10¹¹ M_⊙)  . However, over the redshift interval  0 < z < 2  the 3C RR black hole:spheroid mass ratio is found to evolve as   M _bh/ M _sph∝ (1 + z )^2.07±0.76  , reaching   M _bh/ M _sph≃ 0.008  by redshift   z ≃ 2  . This evolution is found to be inconsistent with the local black hole:spheroid mass ratio remaining constant at a moderately significant level (98 per cent). If confirmed, the detection of evolution in the 3C RR black hole:spheroid mass ratio further strengthens the evidence that, at least for massive early-type galaxies, the growth of the central supermassive black hole may be completed before that of the host spheroid.  相似文献   

Architecture and evolution of a fjord‐head delta,western Vancouver Island,British Columbia     

Jeffrey E. Gutsell  John J. Clague  Melvyn E. Best  Peter T. Bobrowsky  Ian Hutchinson 《第四纪科学杂志》2004,19(5):497-511

The architectural framework and Holocene evolution of the Zeballos fjord‐head delta on west‐central Vancouver Island was established through a multidisciplinary field‐based study. The Zeballos delta is a composite feature, consisting of an elevated, incised, late Pleistocene delta and an inset Holocene delta graded to present sea level. Both deltas have a classic Gilbert‐type tripartite architecture, with nearly flat topset and bottomset units and an inclined foreset unit. Time domain electromagnetic (TDEM) and ground‐penetrating radar (GPR) surveys, borehole data, and gravel pit exposures provided information on the internal form, lithologies and substrate of both deltas. Both sets of deltaic deposits coarsen upward from silt in the bottomset unit to gravel in the topset unit. The TDEM survey revealed a highly irregular, buried bedrock surface, ranging from 20 m to 190 m in depth, and it delineated saltwater intrusion into the deltaic sediments. Late Quaternary sea‐level change at Zeballos was inferred from delta morphology and the GPR survey. The elevated, late Pleistocene delta was constructed when the sea was about 21 m higher relative to the land than it is today. It was dissected when sea‐level fell rapidly as a result of glacio‐isostatic rebound. Relative sea‐level reached a position about 20 m below the present datum during the early Holocene. Foreset beds that overlap and progressively climb in a seaward direction and topset beds that thicken to 26 m landward imply that the delta aggraded and prograded into Zeballos Inlet during the middle and late Holocene transgression. Sea‐level may have risen above the present datum during the middle Holocene, creating a delta plain at about 4 m a.s.l. Remnants of this surface are preserved along the valley margins. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Deep spectroscopy of z∼ 1 6C radio galaxies – II. Breaking the redshift–radio power degeneracy     

K. J. Inskip &#;  P. N. Best  H. J. A. Röttgering  S. Rawlings  G. Cotter  M. S. Longair 《Monthly notices of the Royal Astronomical Society》2002,337(4):1407-1416

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The X-ray properties of optically selected z > 0.6 clusters in the European Southern Observatory Distant Cluster Survey     

O. Johnson  P. Best  D. Zaritsky  D. Clowe  A. Aragón-Salamanca  C. Halliday  P. Jablonka  B. Milvang-Jensen  R. Pelló  B. M. Poggianti  G. Rudnick  R. Saglia  L. Simard  S. White 《Monthly notices of the Royal Astronomical Society》2006,371(4):1777-1792

We present XMM–Newton observations of three optically selected   z > 0.6  clusters from the European Southern Observatory (ESO) Distant Cluster Survey (EDisCS), comprising the first results of a planned X-ray survey of the full EDisCS high-redshift sample. The EDisCS clusters were identified in the Las Campanas Distant Cluster Survey as surface brightness fluctuations in the optical sky and their masses and galaxy populations are well described by extensive photometric and spectroscopic observations. We detect two of the three clusters in the X-ray and place a firm upper limit on diffuse emission in the third cluster field. We are able to constrain the X-ray luminosity and temperature of the detected clusters and estimate their masses. We find that the X-ray properties of the detected EDisCS clusters are similar to those of X-ray-selected clusters of comparable mass and – unlike other high-redshift, optically selected clusters – are consistent with the T –σ and   L _X–σ  relations determined from X-ray-selected clusters at low redshift. The X-ray determined mass estimates are generally consistent with those derived from weak-lensing and spectroscopic analyses. These preliminary results suggest that the novel method of optical selection used to construct the EDisCS catalogue may, like selection by X-ray luminosity, be well suited for identification of relaxed, high-redshift clusters whose intracluster medium is in place and stable by   z ∼ 0.8  .  相似文献   

Deviations from passive evolution – star formation and the ultraviolet excess in z∼ 1 radio galaxies     

K. J. Inskip  P. N. Best  M. S. Longair 《Monthly notices of the Royal Astronomical Society》2006,367(2):693-708

Galaxy colours are determined for two samples of 6C and 3CR radio sources at z ∼ 1, differing by a factor of ∼6 in radio power. Corrections are made for emission-line contamination and the presence of any nuclear point source, and the data analysed as a function of both redshift and the radio source properties. The galaxy colours are remarkably similar for the two populations, and the ultraviolet excess evolves with radio source size similarly in both samples, despite the fact that the alignment effect is more extensive for the more powerful 3CR radio galaxies. These results seem to suggest that the alignment effect at these redshifts does not scale strongly with radio power, and is instead more closely dependent on galaxy mass (which is statistically comparable for the two samples). However, it is likely that the presence of relatively young (≲several times 10⁸-yr-old) stellar populations has considerably contaminated the K -band flux of these systems, particularly in the case of the more powerful 3CR sources, which are ∼0.5 mag more luminous than the predictions of passive evolution models at z ∼ 1. The higher luminosity of the 3CR alignment effect is balanced by emission at longer wavelengths, thereby leading to comparable colours for the two samples.  相似文献   

Environmental dependence of active galactic nuclei activity in the supercluster A901/2     

R. Gilmour  M. E. Gray  O. Almaini  P. Best  C. Wolf  K. Meisenheimer  C. Papovich  E. Bell 《Monthly notices of the Royal Astronomical Society》2007,380(4):1467-1487

We present XMM data for the supercluster A901/2, at   z ∼ 0.17  , which is combined with deep imaging and 17-band photometric redshifts (from the COMBO-17 survey), two degree field (2dF) spectra and Spitzer 24 μm data, to identify active galactic nuclei (AGN) in the supercluster. The 90 ksec XMM image contains 139 point sources, of which 11 are identified as supercluster AGN with   L _{X(0.5−7.5 keV)} > 1.7 × 10⁴¹ erg cm⁻² s⁻¹  . The host galaxies have   M _R < −20  and only two of eight sources with spectra could have been identified as AGN by the detected optical emission lines. Using a large sample of 795 supercluster galaxies, we define control samples of massive galaxies with no detected AGN. The local environments of the AGN and control samples differ at ≳98 per cent significance. The AGN host galaxies lie predominantly in areas of moderate projected galaxy density and with more local blue galaxies than the control sample, with the exception of one very bright type I AGN very near the centre of a cluster. These environments are similar to, but not limited to, cluster outskirts and blue groups. Despite the large number of potential host galaxies, no AGN are found in regions with the highest galaxy density (excluding some cluster cores where emission from the intra-cluster medium obscures moderate luminosity AGN). AGN are also absent from the areas with lowest galaxy density. We conclude that the prevalence of cluster AGN is linked to their environment.  相似文献