The geochemistry of arsenic and its use as an indicator element in geochemical prospecting

The geochemistry of arsenic is reviewed, and the use of the element as an indicator in geochemical prospecting for various types of mineral deposits is outlined.Arsenic is a widespread constituent of many types of mineral deposits, particularly those containing sulphides and sulpho-salts. In these and other deposits arsenic commonly accompanies Cu, Ag, Au, Zn, Cd, Hg, U, Sn, Pb, P, Sb, Bi, S, Se, Te, Mo, W, Fe, Ni, Co, and Pt metals. Under most conditions arsenic is a suitable indicator of deposits of these elements, being particularly useful in geochemical surveys utilizing primary halos in rocks, and secondary halos and trains in soils and glacial materials, stream and lake sediments, natural waters, and vegetation. Some of the natural arsenic compounds (e.g., arsine, dimethylarsine) are volatile, but methods utilizing gaseous arsenic halos for geochemical prospecting have not yet been developed.     

The 2dF QSO Redshift Survey – VIII. Absorption systems in the 10k catalogue

We examine the highest signal-to-noise ratio spectra from the 2dF QSO Redshift Survey (2QZ) 10k release and identify over 100 new low-ionization heavy-element absorbers: damped Lyman α (DLA) candidates suitable for higher-resolution follow-up observations. These absorption systems map the spatial distribution of high- z metals in exactly the same volumes as the foreground 2QZ QSOs themselves sample and hence the 2QZ gives us the unique opportunity to compare directly the two tracers of large-scale structure. We examine the cross-correlation of the two populations to see how they are relatively clustered, and, by considering the colour of the QSOs, detect a small amount of dust in these metal systems.     

Plastic deformation of metamorphic pyrite: new evidence from electron-backscatter diffraction and forescatter orientation-contrast imaging

Application of new scanning electron microscope techniques to the study of deformed metamorphic pyrite reveals evidence for plastic deformation not readily recognised by more traditional methods. Specifically, use of forescatter solid-state detectors in conjunction with tilted polished specimens of pyritic ore produces high quality crystallographic orientation contrast images, which map the distribution of deformation domains within grains. Use of electron-backscatter diffraction allows quantification of the crystallographic misorientations shown by the orientation contrast images. Combination of these techniques shows that the pyrite studied deforms by slip on {100} and more rarely {110} systems. Slip is often associated with distributed rotation of up to 20° about <100> and more rarely <110> axes. Pyrites may have simple histories involving rotation about a single <100> axis, or more complex histories involving rotation about different <100> axes, and more rarely <110>, in different domains of the same pyrite grain, or sequential rotations about quite different systems, typically distributed rotation about <100> followed by discrete rotation about a non-crystallographic axis. Received: 25 June 1997 / Accepted: 14 May 1998     

Lyα absorption in the nearby Universe: the sightline to Q1821+643

We present the first results of a survey designed to understand the origin of Lyα-forest absorption systems at low redshift. Using the WYFFOS and HYDRA multifibre spectrographs on the William Herschel and Wisconsin Indiana Yale NOAO (WIYN) telescopes, we have identified 51 galaxies brighter than b _j := :18.5 within 30 arcmin of the sightline of the QSO 1821+643. We find three galaxies within 500 h ⁻¹ kpc of the QSO sightline; the nearest galaxy is 104 h ⁻¹ kpc away from the line of sight, and is at the same redshift as a strong ( W _r :=:0.63Å) Lyα absorption line. The remaining two galaxies have no corresponding absorption to extremely low equivalent width limits (< 0.05 Å). Beyond 500 h ⁻¹ kpc, Lyα absorption lines are found at redshifts similar to those of several galaxies, but we show that these coincidences are likely to be accidental.   Half of the Lyα systems for which we could have found at least an L ^* galaxy have no galaxies at the redshifts of the absorbers. For the majority of the remainder, we show that any apparent association with galaxies is probably coincidental. These Lyα systems are characterized by their weak equivalent widths ( W _r :<:0.2Å), and we conclude that this population of absorbers is uncorrelated, or at best weakly correlated, with galaxies.     

Public housing as a barrier to long-distance migration

The relationship between migration and housing tenure in Britain is explored, with particular reference to those living in subsidized housing provided by local councils. "In this study, data have been extracted from the 1991 Sample of Anonymised Records to assess the impacts of tenure on long-distance migration compared with short-distance migration. Logit models are used to control for the effects of a wide range of socio-economic variables, allowing the independent impact of tenure to be identified. It is shown that long-distance migrants are less likely to move into council housing than other tenures, but it is argued that this does not support the assumption that the sale of council housing will necessarily increase labour mobility."     

The 2dF-SDSS LRG and QSO Survey: the spectroscopic QSO catalogue

We present the final spectroscopic QSO catalogue from the 2dF-SDSS LRG (luminous red galaxy) and QSO (2SLAQ) survey. This is a deep,  18 < g < 21.85  (extinction corrected), sample aimed at probing in detail the faint end of the broad line active galactic nuclei luminosity distribution at   z ≲ 2.6  . The candidate QSOs were selected from SDSS photometry and observed spectroscopically with the 2dF spectrograph on the Anglo-Australian Telescope. This sample covers an area of 191.9 deg² and contains new spectra of 16 326 objects, of which 8764 are QSOs and 7623 are newly discovered [the remainder were previously identified by the 2dF QSO Redshift Survey (2QZ) and SDSS]. The full QSO sample (including objects previously observed in the SDSS and 2QZ surveys) contains 12 702 QSOs. The new 2SLAQ spectroscopic data set also contains 2343 Galactic stars, including 362 white dwarfs, and 2924 narrow emission-line galaxies with a median redshift of   z = 0.22  .
We present detailed completeness estimates for the survey, based on modelling of QSO colours, including host-galaxy contributions. This calculation shows that at   g ≃ 21.85  QSO colours are significantly affected by the presence of a host galaxy up to redshift   z ∼ 1  in the SDSS ugriz bands. In particular, we see a significant reddening of the objects in   g − i   towards the fainter g -band magnitudes. This reddening is consistent with the QSO host galaxies being dominated by a stellar population of age at least 2–3 Gyr.
The full catalogue, including completeness estimates, is available on-line at http://www.2slaq.info/ .     

黔西南Au-As-Hg-Tl矿化区毒害金属元素的水地球化学

研究了黔西南典型Ａｕ－Ａｓ－Ｈｇ－Ｔｌ矿化区内毒害金属元素在采矿活动和自然状态影响下的水地球化学特征及其环境效应。结果表明,已开采的Ｈｇ－Ｔｌ矿区地下水和地表水中均有很高的毒害金属元素,煤采区地下水中亦表现出类似的特征,而Ｈｇ－Ｔｌ矿区外围地下水中金属元素保持在较低的水平。Ｈｇ－Ｔｌ矿区地素水中Ａｓ和Ｔｌ的分布模式表明,其含量的变化受矿区地下水排泄和尾矿淋滤作用的控制。在尚未开采的金矿区,浅层地下     

Dissolved vanadium in rivers and estuaries

New measurements of dissolved vanadium in a variety of rivers and estuaries are presented here. The data indicate that the average concentration of dissolved vanadium in major rivers entering the ocean is 15 nmol/kg. Weathering rate and type of source rock, rather than solution chemistry or anthropogenic influences, appear to be the important factors in determining fluvial dissolved vanadium concentrations. Laboratory experiments suggest that in oxic waters vanadium is found predominantly in its most oxidized, anionic form (V(V)). Complexation with organic matter and formation of large colloidal species appear to be unimportant. Adsorption also appears to be a less important influence for vanadium than for some other trace elements such as zinc.In estuaries, vanadium behaves as a bioactive element, showing a close correspondence with the distribution of phosphate. The extent of estuarine vanadium removal is presently uncertain but may be low due to rapid remineralization of this element. Based on the river flux, the oceanic residence time for dissolved vanadium is estimated to be 100,000 years.