Malariological and sociological significance of ‘tanka’ and ‘beri’ in the Thar Desert, Western Rajasthan, India     

B. K. Tyagi  S. P. Yadav 《Journal of Arid Environments》1996,33(4):497-501

Both ‘tanka’ and ‘beri’, the well-like structures made for storing drinking water fetched from distant places or superficially charged from the runoff water of the monsoon rains, are considered integral components of rural communities in the Thar Desert of Rajasthan State in north-western India.A. stephensi, the confirmed malaria vector in desert regions, breeds in these structures predominantly.  相似文献   

Tolerance and Rejection: The Vote on Colorado's Amendment Two     

Richard K. Ormrod  David B. Cole 《The Professional geographer》1996,48(1):14-27

Coloradoapos;s 1992 vote on Amendment Two was the first meaningful, broad-based test of attitudes on gay rights within the United States. Analysis of voting results distinguishes places of tolerance from places of rejection. Social differences separating these places reflect typical contrasts between “traditionalists” and “modernizers” found in cultural conflicts at the national level. Places showing support for gay rights are recreational-based mountain communities, urban areas, and university communities. Those showing opposition are rural, agriculturally based communities. Suburban areas produced a more ambivalent vote.  相似文献   

Preliminary seismic hazard maps of Slovenia     

J. K. Lapajne  B. SŠket Motnikar  P. Zupancčicč 《Natural Hazards》1996,14(2-3):155-164

The preparation of the preliminary seismic hazard maps of the territory of Slovenia has been based on an expansion of the basic approach laid out by Cornell in 1968. Three seismic source models were prepared. Two of them are based mainly on the earthquake catalogue using the Poissonian probability model. A map of seismic energy release and a map of earthquake epicenter density are used to delineate seismic sources in these models. The geometry of the third model which is based on a rough estimate of seismotectonic setting is taken from the probabilistic seismic hazard analysis of a nuclear power plant in Slovenia. Published ground motion attenuation models based on strong motion records of recent strong earthquakes in Italy are used. Test maps for variable and uniform b-values are presented. The computer program, Seisrisk III, developed by the U.S. Geological Survey is used.  相似文献   

Phase relations of osumilite and dehydration melting in pelitic rocks: a simple thermodynamic model for the KFMASH system     

T. J. B. Holland  E. V. S. S. K. Babu  D. J. Waters 《Contributions to Mineralogy and Petrology》1996,124(3-4):383-394

 Thermodynamic modelling of (1) osumilite solid solutions and (2) dehydration melting in pelitic compositions within the KFMASH system is quite successful in reproducing the invariant and univariant reactions determined in experimental studies. Even though rather preliminary, such melt thermodynamic models may be very useful in interpolating and extrapolating the limited information available from a small number of experimental runs. These methods allow the compositions of all phases to be monitored as a function of pressure, temperature and equilibrium phase assemblage for any desired bulk composition. Locating the higher variance phase fields (e.g. quadrivariant, quinivariant) is often difficult or impossible by inspection, but is made relatively easy using thermodynamic software such as thermocalc. In the KFMASH system the calculated partition of Fe and Mg between osumilite, garnet, cordierite, orthopyroxene and biotite are shown to be in good agreement with experimental and natural data and allow reliable calculation of mineral compositions coexisting with quartz-saturated and H₂O-undersaturated melts for a variety of bulk compositions. These phase diagram calculations allow quite tight limits to be placed on the pressure, temperature and water activity conditions which accompanied metamorphism of natural osumilite occurrences in Nain, Namaqualand, and Rogaland. At fixed bulk composition, the initial melting of pelites by dehydration of biotite can occur via univariant, divariant or trivariant equilibria depending upon pressure of metamorphism. Of particular interest is that, for low pressures or more magnesian bulk compositions, fluid-absent melting begins by generating liquid from the high-variance assemblage biotite+cordierite+K-feldspar+ quartz. This type of modelling allows investigation, at least qualitatively, of the fine scale details of melt production as a function of changes in pressure, temperature and bulk composition. Received: 29 November 1995 / Accepted: 22 April 1996  相似文献   

The thermodynamic properties of H2O in magnesium and iron cordierite     

G. B. Skippen  Avril E. Gunter 《Contributions to Mineralogy and Petrology》1996,124(1):82-89

 The equilibrium water content of cordierite has been measured for 31 samples synthesized at pressures of 1000 and 2000 bars and temperatures from 600 to 750° C using the cold-seal hydrothermal technique. Ten data points are presented for pure magnesian cordierite, 11 data points for intermediate iron/magnesium ratios from 0.25 to 0.65 and 10 data points for pure iron cordierite. By representing the contribution of H₂O to the heat capacity of cordierite as steam at the same temperature and pressure, it is possible to calculate a standard enthalpy and entropy of reaction at 298.18° K and 1 bar for, (Mg,Fe)₂Al₄Si₅O₁₈+H₂O ⇄ (Fe,Mg)₂Al₄Si₅O₁₈.H₂O Combining the 31 new data points with 89 previously published experimental measurements gives: ΔH ^° _r =–37141±3520 J and ΔS ^° _r =–99.2±4 J/degree. This enthalpy of reaction is within experimental uncertainty of calorimetric data. The enthalpy and entropy of hydration derived separately for magnesian cordierite (–34400±3016 J, –96.5±3.4 J/degree) and iron cordierite (–39613±2475, –99.5±2.5 J/degree) cannot be distinguished within the present experimental uncertainty. The water content as a function of temperature, T(K), and water fugacity, f(bars), is given by n _H2O=1/[1+1/(K ⋅ f _H2O)] where the equilibrium constant for the hydration reaction as written above is, ln K=4466.4/T–11.906 with the standard state for H₂O as the gas at 1 bar and T, and for cordierite components, the hydrous and anhydrous endmembers at P and T. Received: 2 August 1994/Accepted: 7 February 1996  相似文献   

Book reviews     

G. M. Steed  B. F. Windley  R. Lisle  K. Nicholson 《Mineralium Deposita》1996,31(1-2):140-141

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Feasibility and cost of creating an iron-phosphate coating on pyrrhotite to prevent oxidation     

Z. J. Georgopoulou  K. Fytas  H. Soto  B. Evangelou 《Environmental Geology》1996,28(2):61-69

 Acid mine drainage (AMD) occurs when sulfide minerals are exposed to an oxidizing environment. Most of the methods for preventing AMD are either short-term or high cost solutions. Coating with iron phosphate is a new technology for the abatement of AMD. It involves treating the sulfide with a coating solution composed of H₂O₂, KH₂PO₄, and sodium acetate as a buffer agent. The H₂O₂ oxidizes the sulfide surface and produces Fe³⁺ so that iron phosphate precipitates as a coating on the sulfide surface. Experiments performed under laboratory conditions prove that an iron phosphate coating can be established on pyrrhotite surfaces with optimal concentrations of the coating solution in the range of: 0.2M/0.01M H₂O₂, 0.2M KH₂PO₄, and 0.2M sodium acetate NaAc, depending on the experimental scale. Iron phosphate coating may be a long-term solution to the problem of AMD. The method would be easy to implement; the reagent cost, however, is not low enough, although it is lower than the conventional treatment with lime. Received: 30 March 1995 · Accepted: 6 September 1995  相似文献   

Characterisation of brown coal humic acids and modified humic acids using pyrolysis gcms and other techniques     

W. R. Jackson  G. D. Bongers  P. J. Redlich  G. Favas  Y. Fei  A. F. Patti  R. B. Johns 《International Journal of Coal Geology》1996,32(1-4)

It has been proposed that Victorian brown coal can be considered as a two-component structure — a lignocellulosic “host”, containing various amounts of weakly bound or entrapped “guest” material together with very small amounts of inorganic and/or mineral matter. The latter predominantly consists of wax esters and/or terpenoid material. In this paper we describe attempts to gain structural information regarding the more complex, “host” component of the coal. Our initial model compound has been humic acid that can be readily obtained from the coal by alkaline extraction. It has been found that “pure” humic acid, free from material associated with the “guest” components of the coal, can be obtained by a highly selective, low-yielding alkaline extraction. This humic acid has been studied by nmr spectroscopy and pyrolysis gas chromatography-mass spectroscopy (py-gc/ms). The products arising from py-gc/ms have been compared with those obtained from similar pyrolysis of whole coals. Alkylation of humic acids using alkyl halides in the presence of base has been successfully carried out and reactivity of the resulting materials compared with those of the parent coal and humic acid.  相似文献   

Characteristics and origin of sediment-hosted disseminated gold deposits: a review   总被引：4，自引：0，他引：4  

Greg B. Arehart 《Ore Geology Reviews》1996,11(6):383-403

Sediment-hosted disseminated gold (SHDG) deposits comprise a major portion of the gold production and reserves in the US. Although presently known to be common only in western North America, SHDG deposits are a significant source of world gold production. These deposits are characterized by extremely fine-grained disseminated gold, hosted primarily by arsenian pyrite. Other metals show very little enrichment although in addition to As, anomalous concentrations of elements such as Sb, Hg, Tl and Ba are utilized as exploration tools. The host rocks are dominantly silty carbonates, but ore concentrations are also present in siliceous and silicified rocks as well as intrusive rocks. Alteration consists of decarbonatization, silicification (jasperoid formation) and argillization, which are arranged both spatially and temporally in that order. Argillic alteration is zoned from kaolinite-dominated cores to sericite-dominated margins. The deposits commonly exhibit significant structural (faults) and stratigraphic (composition/permeability) controls. Until the last few years, SHDG deposits were considered as near-surface, epithermal type deposits in origin. Because of their fine-grained nature and the lack of macroscopic features such as veins, it has proven quite difficult to extract geochemical data that are clearly related to their genesis. However, fluid inclusion data indicate pressures corresponding to depths of 2–4 km under lithostatic conditions. Temperatures are constrained by fluid inclusions and phase equilibria to near 225°C. Stable isotope data from alteration minerals and fluid inclusions indicate that the ore fluids were dominated by meteoric waters, some of which had clearly exchanged oxygen with wallrocks during their passage through the crust. Although the data vary, most ore fluids probably had δD values near −150‰ and δ¹⁸O values ranging from −10 to +5‰. Sulfur isotope values reported from SHDG deposits span a wide range, from −30 to +20‰ (sulfides) and 0 to >45‰ (sulfates). Ore-related sulfides (pyrite, realgar) fall at the upper end of the range reported for sulfides. The alteration and mineral assemblage indicate the ore fluids were probably near neutral and gold was likely carried as a bisulfide complex. The depositional mechanism(s) probably included mixing, cooling and oxidation. These mechanisms are consistent with the observed alteration features, i.e. quartz precipitation, calcite dissolution and sericite-kaolinite coexistence. It also explains the presence of both siliceous ores containing native Au and sulfide ores containing Au in pyrite. The extreme variations in sulfur isotopes as seen at Post and fluid inclusion data from Carlin may be indicative of some phase separation (‘boiling’), but such relations have not been documented in other deposits and the importance of phase separation to gold deposition appears minimal.  相似文献   

Continental break-up and collision in the Neoproterozoic and Palaeozoic — A tale of Baltica and Laurentia     

T.H. Torsvik  M.A. Smethurst  J.G. Meert  R. Van der Voo  W.S. McKerrow  M.D. Brasier  B.A. Sturt  H.J. Walderhaug 《Earth》1996,40(3-4):229-258

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