The sources and evolution of mineralising fluids in iron oxide–copper–gold systems, Norrbotten, Sweden: Constraints from Br/Cl ratios and stable Cl isotopes of fluid inclusion leachates     

S.A. Gleeson  M.P. Smith 《Geochimica et cosmochimica acta》2009,73(19):5658-5672

We have analysed the halogen concentrations and chlorine stable isotope composition of fluid inclusion leachates from three spatially associated Fe-oxide ± Cu ± Au mineralising systems in Norrbotten, Sweden. Fluid inclusions in late-stage veins in Fe-oxide–apatite deposits contain saline brines and have a wide range of Br/Cl molar ratios, from 0.2 to 1.1 × 10⁻³ and δ³⁷Cl values from −3.1‰ to −1.0‰. Leachates from saline fluid inclusions from the Greenstone and Porphyry hosted Cu–Au prospects have Br/Cl ratios that range from 0.2 to 0.5 × 10⁻³ and δ³⁷Cl values from −5.6‰ to −1.3‰. Finally, the Cu–Au deposits hosted by the Nautanen Deformation Zone (NDZ) have Br/Cl molar ratios from 0.4 to 1.1 × 10⁻³ and δ³⁷Cl values that range from −2.4‰ to +0.5‰, although the bulk of the data fall within 0‰ ± 0.5‰.The Br/Cl ratios of leachates are consistent with the derivation of salinity from magmatic sources or from the dissolution of halite. Most of the isotopic data from the Fe-oxide–apatite and Greenstone deposits are consistent with a mantle derived source of the chlorine, with the exception of the four samples with the most negative values. The origin of the low δ³⁷Cl values in these samples is unknown but we suggest that there may have been some modification of the Cl-isotope signature due to fractionation between the mineralising fluids and Cl-rich silicate assemblages found in the alteration haloes around the deposits. If such a process has occurred then a modified crustal source of the chlorine for all the samples cannot be ruled out although the amount of fractionation necessary to generate the low δ³⁷Cl values would be significantly larger.The source of Cl in the NDZ deposits has a crustal signature, which suggests the Cl in this system may be derived from (meta-) evaporites or from input from crustal melts such as granitic pegmatites of the Lina Suite.  相似文献   

The carbonate-hosted willemite prospects of the Zambezi Metamorphic Belt (Zambia)     

Maria Boni  Rosario Terracciano  Giuseppina Balassone  Sarah A. Gleeson  Alexander Matthews 《Mineralium Deposita》2011,46(7):707-729

Zambian willemite (Zn₂SiO₄) deposits occur in the metasedimentary carbonate rocks of the Proterozoic Katangan Supergroup. The most important orebodies are located around Kabwe and contain both sulphides and willemite in dolomites of low metamorphic grade. The Star Zinc and Excelsior prospects (Lusaka area), discovered in the early 1920s, occur in the metamorphic lithotypes of the late Proterozoic Zambezi Supracrustal sequence, which were deposited in a transtensional basin formed during the oblique collision of the Kalahari and Congo cratons. The deposits are hosted by the limestone and dolomitic marbles of the Cheta and Lusaka Formations. Structural analysis indicates that several fracture sets host the deposits, which may be genetically related to the Pan-African Mwembeshi dislocation zone (a major geotectonic boundary between the Lufilian Arc and the Zambezi Belt). In both prospects, willemite replaces the marbles and is found along joints and fissures with open-space filling textures and locally may develop colloform and vuggy fabrics as well. Silver as well as traces of germanium and cadmium have been detected within the willemite ore, and lead or zinc sulphides are scarce or absent. Calcite locally replaces willemite. Willemite is associated with specular hematite and franklinite and post-dates the Zn-spinel gahnite in the paragenesis. Genthelvite [Zn₄Be₃(SiO₄)₃S] occurs as a minor phase in irregular aggregates. The willemites from the Lusaka area, though Mn-poor, show green cathodoluminescence colours and bright green fluorescence in short-wave UV (as the high-temperature willemites in USA). Thermometric analyses of primary fluid inclusions in willemite yield homogenization temperatures that range from 160°C to 240°C and salinities of 8–16 wt.% equiv. NaCl. The homogenization temperatures suggest a hypogene–hydrothermal origin for the willemite concentrations. The geochemistry of fluid inclusion leachates suggests that the hydrothermal fluids were brines derived from highly evaporated seawater. Precise age constraints are currently lacking for the Lusaka area deposits, though the deposits are not deformed, indicating that they post-date the Lufilian orogeny (~520 Ma). The possibility of precursor ores exists; the gahnite–franklinite–willemite deposits could have been derived from a metamorphosed primary sulphide (or even nonsulphide) concentration that has subsequently been completely destroyed. However, there is no real evidence of such a primary source for the willemite mineral association. The Lusaka zinc ores may have been produced by an extensive hydrothermal system, with fluids discharging along basinal fracture zones controlled by the pre-Pan-African rifting stage. A paragenesis similar to that of the Lusaka prospects has been proposed to be a vector towards massive sulphide ores in several parts of the world; therefore, it is possible that these small willemite showings in Zambia may be part of a much bigger, and still unexplored, zinc province.  相似文献   

Mineralogical characterization of the Nkamouna Co–Mn laterite ore, southeast Cameroon     

G. Lambiv Dzemua  S. A. Gleeson  P. F. Schofield 《Mineralium Deposita》2013,48(2):155-171

The Nkamouna property is an oxide laterite deposit developed on serpentinized peridotite in southeast Cameroon. It is enriched in Co and Mn, has sub-economic Ni grades and will be mined primarily for Co. The ore zone is ca. 10 m thick and comprises the lower breccia (～3 m thick) and ferralite (7–8 m thick) units sandwiched between an 8-m-thick ferricrete overburden and a barren hydrated Mg–silicate saprolite. The ore mineral assemblage includes Mn oxyhydroxides, magnetite, maghemite, ferritchromite, goethite, hematite, kaolinite and gibbsite. Lithiophorite is the most common Mn mineral and is the main host of Co, Mn and a significant proportion of Ni. It occurs as coatings in pores and on other mineral grains and as concretions and impregnations in the matrix. It is invariably associated with gibbsite in the lower breccia and with magnetite and ferritchromite in the ferralite. Although ore in the lower breccia is volumetrically less important than the ferralite, it has the highest grade and Co/Ni ratio. The lithiophorite in the ore zone is authigenic, and its formation was enhanced by influx of Al³⁺ from the overlying ferricrete. Magnetite and ferritchromite in the ferralite are relicts and contributed to mineralization by enhancing the permeability of the ferralite and providing substrates for the precipitation of the Mn oxyhydroxides. The structure and mode of occurrence of the lithiophorite makes Nkamouna ore amenable to physical beneficiation, producing a concentrate with Co grades 2.3–4.5 times higher than the run-of-mine ore.  相似文献   

On the equation of transport for cosmic-ray particles in the interplanetary region     

G. M. Webb  L. J. Gleeson 《Astrophysics and Space Science》1979,60(2):335-351

In this paper we provide two new alternative derivations of the equation of transport for cosmic-ray particles in the interplanetary region. Both derivations are carried out by using particle positionr and timet in a frame of reference fixed in the solar system, and the particle momentump is specified relative to a local frame of reference moving with the solar wind. The first derivation is carried out by writing down a continuity equation for the cosmic rays, taking into account particle streaming and energy changes, and subsequently deriving the streaming and energy change terms in this equation. The momentum change term in the continuity equation, previously considered to be due to the adiabatic deceleration of particles in the expanding magnetic fields carried by the solar wind, appears in the present analysis as a dynamic effect in which the Lorentz force on the particle does not appear explicitly. An alternative derivation based on the ensemble averaged Liouville equation for charged particles in the stochastic interplanetary magnetic field using (r, p,t) as independent coordinates is also given. The latter derivation confirms the momentum change interpretation of the first derivation. We also provide a new derivation of the adiabatic rate as a combination of inverse-Fermi and betatron deceleration processes.  相似文献   

Cyclogenesis in the Mediterranean region     

Thomas A. Gleeson 《Meteorology and Atmospheric Physics》1953,6(2):153-171

A statistical study is made of cyclones originating in the Mediterranean region in the months October through May from 1929 to 1939 and 1945 to 1952. The following features are summarized: synoptic type, points of origin, monthly and geographic frequencies, relation of displacement to topography and deepening, 24-hr deepening, isobar direction at 3 km at time and place of origin, relation between 3-km isobar direction and cyclone trajectory, and relation between vertical temperature distribution and central pressure.

---

Zusammenfassung Es wird eine statistische Untersuchung der Zyklonen durchgeführt, die sich während der Perioden 1929 bis 1939 und 1945 bis 1952 (jeweils in den Monaten Oktober bis Mai) im Mittelmeergebiet gebildet haben. Dabei wird über folgende Gesichtspunkte zusammenfassend berichtet: Synoptische Wetterlage, zyklogenetische Ursprungsstellen, monatliche und geographische Häufigkeitsverteilung Beziehung zwischen Verlagerung einerseits und topographischen Einflüssen und Vertiefung anderseits, Depressionsvertiefung innerhalb 24 Stunden, Isobarenrichtung in 3 km Höhe im Zeitpunkt und Ort der Zyklonenentstehung, Beziehung zwischen der Isobarenrichtung in 3 km und der Zyklonenbahn, Beziehung zwischen der vertikalen Temperaturverteilung und dem Luftdruck im Zyklonenzentrum.

---

Résumé Il s'agit d'une étude statistique des dépressions formées en Méditerranée pendant les périodes 1929–1939 et 1945–1952, d'octobre à mai. L'auteur considère les points de vue suivants: situation météorologique générale, régions cyclogénétiques, distribution des fréquences par mois et par régions, relation entre le déplacement et les influences topographiques et le creusement, creusement en24 heures, direction des isobares à 3 km d'altitude au moment et au lieu de formation, relation entre cette même direction et la trajectoire dépressionnaire, relation entre la répartition verticale de la température et la pression au centre de la dépression.

---

---

With 20 Figures.

---

Contribution to a research project sponsored by the Geophysics Research Directorate of the Air Force Cambridge Research Center under Contract No. AF 19 (122)-466.  相似文献   

A New Assessment Framework for Transience in Hydrogeological Systems          下载免费PDF全文

Matthew Currell  Tom Gleeson  Peter Dahlhaus 《Ground water》2016,54(1):4-14

The importance of transience in the management of hydrogeologic systems is often uncertain. We propose a clear framework for determining the likely importance of transient behavior in groundwater systems in a management context. The framework incorporates information about aquifer hydraulics, hydrological drivers, and time scale of management. It is widely recognized that aquifers respond on different timescales to hydrological change and that hydrological drivers themselves, such as climate, are not stationary in time. We propose that in order to assess whether transient behavior is likely to be of practical importance, three factors need to be examined simultaneously: (1) aquifer response time, which can be expressed in terms of the response to a step hydrological change (τ_step) or periodic change (τ_cycle); (2) temporal variation of the dominant hydrological drivers, such as dominant climatic systems in a region; (3) the management timescale and spatial scale of interest. Graphical tools have been developed to examine these factors in conjunction, and assess how important transient behavior is likely to be in response to particular hydrological drivers, and thus which drivers are most likely to induce transience in a specified management timeframe. The method is demonstrated using two case studies; a local system that responds rapidly and is managed on yearly to decadal timeframes and a regional system that exhibits highly delayed responses and was until recently being assessed as a high level nuclear waste repository site. Any practical groundwater resource problem can easily be examined using the proposed framework.  相似文献   

Energy losses of galactic cosmic rays in the interplanetary medium     

I. H. Urch  L. J. Gleeson 《Astrophysics and Space Science》1973,20(1):177-185

Using realistic models of cosmic-ray propagation in interplanetary space we present, for electrons, protons and helium nuclei of a given energy near Earth, calculations of their distribution in energy before entering the solar cavity and their mean energy loss. Interplanetary conditions appropriate for the epochs 1965 and 1969 have been used. Cosmic-ray energies in the range of 20 MeV/nucleon to 1000 MeV/nucleon have been considered.  相似文献   

Energy losses and modulation of galactic cosmic rays     

L. J. Gleeson  I. H. Urch 《Astrophysics and Space Science》1971,11(2):288-308

Numerical solutions of the cosmic-ray transport equation for the interplanetary region and including the effects of diffusion, convection, and energy loss, have been obtained for a galactic differential number-density spectrum of gaussian form, central kinetic energyT ₀, and a width at half height maximum of 0.1T ₀. These solutions have been used to show the redistribution in energy, and the reduction in number density, within the solar cavity. The mean energy loss is shown to be usefully approximated by the force-field potential when /T ₀1/2. The principal finding is that galactic cosmic-ray protons and helium nuclei, with kinetic energies less than about 80 MeV/nucleon, virtually, are completely excluded from near Earth by convective effects. As a result of this exclusion, it is found that it is not possible to demodulate the proton and helium-nuclei spectra, observed in 1964–65, to obtain information about low-energy galactic cosmic rays.  相似文献   

Cosmic-ray streaming and anisotropies     

Miriam A. Forman  L. J. Gleeson 《Astrophysics and Space Science》1975,32(1):77-94

The principal result of this paper is the demonstration that in interplanetary space the electric-field drifts and convective flow parallel to the magnetic field of cosmic-ray particles combine as a simple convective flow with the solar wind. In addition there are diffusive currents and transverse gradient drift currents. With this interpretation direct reference to the interplanetary electric-field drifts is eliminated and the study of steady-state and transient cosmic-ray anisotropies is both more systematic and simpler. Following a discussion of our present knowledge of the diffusion coefficient in the interplanetary medium, the theory is applied to steady-state anisotropies near Earth in the kinetic energy (T) range 7.5 MeV<T<20 GeV. First the theory of the diurnal variation atT>-2 GeV is examined and it is suggested that the azimuthal streaming associated with the observations be regarded simply as proof that there is no significant net radial flow of cosmic rays at these energies. Second, it is predicted that, near Earth, the radial anisotropy will have a (+?+) variation with energy and this prediction is very insensitive to the precise values of the parameters used: intensity spectrum, solar wind speed, radial density gradient, and diffusion coefficient. Then, third, the small and radial steady-state anisotropies reported by Raoet al. (1967) in the intervals 7.5<T<45 MeV and 45<T<90 MeV are re-examined and it is found that the gradients and diffusion coefficients required to produce the reported anisotropies in 7.5<T<45 MeV are inconsistent with those expected from other data.  相似文献   

On the direct observation of cosmic-ray energy losses     

L. J. Gleeson  I. D. Palmer 《Astrophysics and Space Science》1971,12(1):137-146

During the decay of solar cosmic-ray events cosmic-rays with kinetic energies of about 1 MeV are convected outward with the solar wind. It is shown that, with currently available observations it should be possible to demonstrate directly the energy losses which are occurring. Observations from two spacecraft on the same heliocentric radial line are required. In this paper observations from Venera-4 and Imp-F have been used. A simple and direct demonstration would be provided by the observation of nearly mono-energetic pulses convected between the two spacecraft, but no such pulses were found to be present. A second method depends upon observing the ratio of the integral fluxes at the two spacecraft and comparing this with the value predicted by theory. The relevant theoretical analysis has been given. It is shown that in order to discriminate between energy-loss processes the spacecraft must be well separated. For spacecraft at Earth's orbit and the orbit of Venus the integral-flux ratio predicted with energy loss due to adiabatic deceleration is a factor of three higher than that predicted with no energy loss. Comparisons of integral-flux ratios for two events observed on spacecraft separated by approximately 0.1 AU gave inconclusive results. In view of the importance of energy-loss processes in the propagation of cosmic rays it is suggested that others with access to relevant data might continue this investigation.  相似文献