Architecture and emplacement of the Nebo–Babel gabbronorite-hosted magmatic Ni–Cu–PGE sulphide deposit,West Musgrave,Western Australia

The Nebo–Babel Ni–Cu–platinum-group element (PGE) sulphide deposit in the West Musgrave Block, Western Australia, is the largest nickel sulphide discovery in the last 10 years. The deposit is hosted within a concentrically zoned, olivine-free, tube-like (chonolithic), gabbronorite intrusion associated with the, approximately, 1,078-Ma Giles Complex-layered intrusions in the Warakurna large igneous province. Emplaced into sulphide-free amphibolite facies orthogneiss, the fault-offset Nebo–Babel chonolith extends for 5 km and has a cross-section of 1 × 0.5 km. Igneous mineralogy, fabrics, and textures are well preserved. The lithostratigraphy includes variably textured leucogabbronorites (VLGN) that form an outer shell around mineralised gabbronorite (MGN), with barren gabbronorite (BGN) and oxide–apatite gabbronorite (OAGN) in the middle and lower parts of the chonolith. Mineral and whole-rock geochemistry indicate that the units become progressively evolved in the order: VLGN, MGN, BGN, and OAGN, and that incompatible trace-element concentrations increase downwards within the MGN and BGN. The mineralisation, which is confined to the early, more primitive units (VLGN and MGN), occurs as massive sulphide breccias and stringers and as disseminated gabbronorite-hosted sulphides. The massive sulphides were emplaced late in the intrusive sequence, have different PGE chemistry and Cu tenor to the disseminated sulphides, and have undergone sulphide fractionation. The distribution of disseminated sulphides, which are primary magmatic in origin, is related to chonolith geometry and magma flow regimes, rather than to gravitational settling. Sulfur-bearing country rocks are absent in the Nebo–Babel deposit area, and thus, local crustal S addition was unlikely to have been the major mechanism in achieving sulphide immiscibility. The Nebo–Babel intrusion is part of an originally continuous magma chonolith with multiple and related magma pulses. The parental magma was medium- to low-K tholeiite with 8–9 wt% MgO. The initial magma pulse (VLGN), the most primitive and sulphide saturated, was probably emplaced along a linear weakness in the country rock. After crystallisation of VLGN, marginally more fractionated, sulphide-saturated magma was injected through the thermally insulated core of the conduit, forming the MGN. Successive pulse(s) of more fractionated magma (BGN) were emplaced in the core of the intrusion. After magma flow ceased, closed system crystal fractionation produced consistent mineral and chemical fractionation trends within BGN and OAGN. After crystallisation, the intrusion was overturned and then offset by the Jameson Fault resulting in the apparent ‘reverse’ chemical and mineral trends in Nebo–Babel.     

Microwave Mode Coupling Above Active Regions as a Coronal Density Diagnostic

It is well recognized that the phenomenon of depolarization (the conversion of polarized radio emission into unpolarized emission) of microwaves over solar active regions can be used to infer the coronal electron density once the coronal magnetic field is known. In this paper we explore this technique using an active region for which we have excellent radio data showing depolarization at two frequencies, and for which we have an excellent magnetic field model which has been tested against observations. We show that this technique for obtaining coronal densities is very sensitive to a number of factors. When Cohen's (1960) theory where depolarization is due to magnetic field rotation alone is used, the result is particularly sensitive to the location of the surface on which the magnetic field is orthogonal to the line of sight. Depending on whether we take into account the presence of electric currents in the photosphere or not, their extrapolation into the corona can result in very different heights being deduced for the location of the depolarization strip, and this changes the density which is then deduced from the depolarization condition. Such extreme sensitivity to the magnetic field model requires that field extrapolations be able to accurately predict the polarity of magnetic fields up to coronal heights as high as 10⁵ km in order to exploit depolarization as a density diagnostic.     

The dangerous border of the 5:2 mean motion resonance

After discovering that asteroid (2953) Vysheslavia, a Koronis family member, has a typical dynamical lifetime of the order of 10 Myr only against “falling” into the 5:2 Kirkwood gap and ending up in a hyperbolic orbit (Milani and Farinella, 1995. Icarus 114, 209–212), we decided to repeat the same study for two other asteroids, 1991 UA₂ and 1993 FR₅₈, lying also very close to the outer edge of the same resonance. The orbital elements of these bodies were not yet accurate enough and we appealed to observers, both professional and amateur, to obtain more astrometric data. Eight groups in three different countries carried out observations, and as a result the Minor Planet Center could derive updated, accurate orbits for both objects. Here we report on the preliminary results of our study. Whereas the long-term behavior of 1991 UA₂ looks fairly regular and stable, 1993 FR₅₈ exhibits a typical “stable chaos” behavior; nevertheless, it does not end up in the resonance within a time span of 50 Myr. On the other hand, its fictitious clones, placed just 3–4 × 10⁻³ AU closer to the resonance, undergo large irregular semimajor axis changes, fall into the resonance and escape on a timescale <1 Myr.     

Secular variations of major planets' orbital elements

The secular variations of the orbital elements of principal planets are calculated by means of classical Lagrange's method. The terms of the second order with respect to mass, introduced by Hill (1897) and Brouwer and van Woerkom (1950), have been taken into account as well. The best contemporary values of planetary masses and mean elements (Bretagnon, 1982) served as the starting data set for this calculation. Considerable differences with respect to previous solutions of the same type (Brouwer and van Woerkom, 1950: Sharaf and Boudnikova, 1967) were found in the coefficientsA ₅₅,A ₅₆, andA ₆₆ of the system of equations of variation of elements and in the roots (frequencies)r ₅ andr ₆. Results are compared with some higher order/higher degree solutions and their accuracy discussed. It is confirmed that the solutions like that of Brouwer and van Woerkom, although not being completely inferior to all higher order/higher degree ones, can be considered as the first approximation only. Hence, they should be replaced by more accurate ones (Duriez, 1979: Bretagnon, 1984: Laskar, 1984) in the future applications.     

A Simple Method of Estimating Scalar Fluxes Over Forests

A simple aerodynamic-variance method is proposed to fill gaps in continuous CO₂ flux measurements in rainy conditions, when open-path analysers do not function. The method requires turbulent conditions (friction velocity greater than 0.1 ms^–1), and uses measurements of mean wind speed, and standard deviations of temperature and CO₂ concentration fluctuations to complement, and at times replace, eddy-covariance measurements of friction velocity, sensible heat flux and CO₂ flux. Friction velocity is estimated from the mean wind speed with a flux-gradient relationship modified for the roughness sublayer. Since normalised standard deviations do not follow Monin-Obukhov similarity theory in the roughness sublayer, a simple classification scheme according to the scalar turbulence scale was used. This scheme is shown to produce sensible heat and CO₂ flux estimates that are well correlated with the measured values.     

利用火箭技术进行云催化的自动化系统

介绍了一个用多普勒或非多普勒雷达装备的新的自动化防雹雷达中心。该系统实现了从雷达采集云信息到发射装有催化剂火箭这一整个过程的自动化,从而提高了雷达中心的效能。系统包括雷达视频信号的数字化处理系统、天线控制子系统和专家信息系统。自动化防雹系统的应用范围广泛,例如:防雹作业,气象研究,降水测量和短期预报等。     

The statistical characters of PM10 in Belgrade area

The concentrations of air pollutants depend on meteorological conditions and pollutant emission level. From the statistical properties of air pollutants the number of times the daily average concentrations exceed the assigned air quality standard (AQS) can be estimated, as well as the level of reduction of particle matter emission sources required to meet the AQS. In this paper three statistical distributions (lognormal, Weibull and type V Pearson distribution) were used to fit the complete set of PM₁₀ data for the Belgrade urban area during a three-year period (2003–2005). The method of moments and the method of least squares were both used to estimate the parameters of the three theoretical distributions. The type V Pearson distribution represented the PM₁₀ daily average concentration most closely. However, the parent distributions sometimes diverged in predicting a high PM₁₀ concentration and therefore asymptotic distributions of extreme values were used to fit the high PM₁₀ concentration distribution more correctly. This method can successfully predict the return period and exceedances over a critical concentration in succeeding years. The estimated emission source reduction of PM₁₀ to meet the assigned standard varied from 53% to 63% in the Belgrade urban area. The results provide useful information for air quality management and could be used to examine the similarities and differences among air pollution types in diverse areas.     

Genetic model of uranium mineralization in the Permo-Triassic sedimentary rocks of the Stara Planina eastern Serbia

One deposit and four occurrences of uranium minerals in the Permo-Triassic sedimentary rocks of the Stara Planina in eastern Serbia were ascertained using data from years of multidisciplinary geological research. The minerals are the fissure-filling type, and were assigned to the exogenic mineralization group, being mostly epigene in nature. Relevant geological information was used to derive a genetic model of uranium mineralization in the Permo-Triassic sedimentary rocks of the Stara Planina. The model explains the formation of Permo-Triassic rocks and three stages of the complex process of U mineralization. The genetic model treats: (1) the primary sources of the uranium; (2) the mobility of uranium; and (3) accessory metals from the parent rocks to their deposition in host rocks and the postmineral change in ore bodies. A geochemical barrier zone was identified in the sedimentary rocks that contained uranium mineral ore. This geochemical barrier area included crescent-shaped, flat-lens, or vein-like ore bodies. The U-containing mineral described is comparable with those from the relatively common fissure-filling uranium minerals found around the world.