A mathematical model of concentrate solids content for the wet drum magnetic separator

Low concentrate density from wet drum magnetic separators in dense medium circuits can cause operating difficulties due to inability to obtain the required circulating medium density and, indirectly, high medium solids losses. The literature is almost silent on the processes controlling concentrate density. However, the common name for the region through which concentrate is discharged—the squeeze pan gap—implies that some extrusion process is thought to be at work. There is no model of magnetics recovery in a wet drum magnetic separator, which includes as inputs all significant machine and operating variables.A series of trials, in both factorial experiments and in single variable experiments, was done using a purpose built rig which featured a small industrial scale (700 mm lip length, 900 mm diameter) wet drum magnetic separator. A substantial data set of 191 trials was generated in this work. The results of the factorial experiments were used to identify the variables having a significant effect on magnetics recovery.It is proposed, based both on the experimental observations of the present work and on observations reported in the literature, that the process controlling magnetic separator concentrate density is one of drainage. Such a process should be able to be defined by an initial moisture, a drainage rate and a drainage time, the latter being defined by the volumetric flowrate and the volume within the drainage zone. The magnetics can be characterised by an experimentally derived ultimate drainage moisture. A model based on these concepts and containing adjustable parameters was developed. This model was then fitted to a randomly chosen 80% of the data, and validated by application to the remaining 20%. The model is shown to be a good fit to data over concentrate solids content values from 40% solids to 80% solids and for both magnetite and ferrosilicon feeds.     

Isotopic constraints on growth conditions of multiphase calcite–pyrite–barite concretions in Carboniferous mudstones

Carbonate concretions in the Lower Carboniferous Caton Shale Formation contain diagenetic pyrite, calcite and barite in the concretion matrix or in different generations of septarian fissures. Pyrite was formed by sulphate reduction throughout the sediment before concretionary growth, then continued to form mainly in the concretion centres. The septarian calcites show a continuous isotopic trend from δ¹³C=?28·7‰ PDB and δ¹⁸O=?1·6‰ PDB through to δ¹³C=?6·9‰ PDB and δ¹⁸O=?14·6‰ PDB. This trend arises from (1) a carbonate source initially from sulphate reduction, to which was added increasing contributions of methanogenic carbonate; and (2) burial/temperature effects or the addition of isotopically light oxygen from meteoric water. The concretionary matrix carbonates must have at least partially predated the earliest septarian cements, and thus used the same carbonate sources. Consequently, their isotopic composition (δ¹³C=?12·0 to ?10·1‰ PDB and δ¹⁸O=?5·7 to ?5·6‰ PDB) can only result from mixing a carbonate cement derived from sulphate reduction with cements containing increasing proportions of carbonate from methanogenesis and, directly or indirectly, also from skeletal carbonate. Concretionary growth was therefore pervasive, with cements being added progressively throughout the concretion body during growth. The concretions contain barite in the concretion matrix and in septarian fissures. Barite in the earlier matrix phase has an isotopic composition (δ³⁴S=+24·8‰ CDT and δ¹⁸O=+16·4‰ SMOW), indicating formation from near‐surface, sulphate‐depleted porewaters. Barites in the later septarian phase have unusual isotopic compositions (δ³⁴S=+6 to +11‰ CDT and δ¹⁸O=+8 to +11‰ SMOW), which require the late addition of isotopically light sulphate to the porewaters, either from anoxic sulphide oxidation (using ferric iron) or from sulphate dissolved in meteoric water. Carbon isotope and biomarker data indicate that oil trapped within septarian fissures was derived from the maturation of kerogen in the enclosing sediments.     

Cenozoic tectonic events at the border of the Paraná Basin, São Paulo, Brazil

In the last decade, even in areas that had been considered tectonically stable, a great amount of Cenozoic, including the Quaternary period, structural data have been collected throughout Brazil. The main goal of this study is to describe the Cenozoic structures and tectonic evolution of an area that is located at the border of the Paraná Basin in the state of São Paulo.The research methods consisted of the analysis of: (1) brittle structure data, mainly conjugate fractures and fault slip data; (2) lineaments traced on air photos and TM Landsat and radar images; and (3) a second-order base surface map.The study area, during the Cenozoic, has been affected by five strike–slip tectonic events, which generated mainly strike–slip faults, and secondarily normal and reverse ones. The events were named, from the oldest to the youngest, E1-NE, E2-EW, E3-NW, E4-NS, and E5-NNE; and the maximum principal stresses σ1 strike approximately NE–SW, E–W, NW–SE, N–S, and NNE–SSW, respectively. Event E2-EW seems to have been contemporaneous with the deposition of the Rio Claro Formation, the most important Cenozoic deposit of probable Neogenic age, and also to have controlled the distribution of its deposits. Event E3-NW was the strongest one in the area, as is pointed out by structural data, and the maximum principal stress σ1 of event E5-NNE is partially concordant with the orientation of σH-max of well break-out data in the Paraná Basin, suggesting a Neotectonic activity for this event. Finally, discontinuities parallel and correlated to the directions of strike–slip faults of the Cenozoic events seem to have actively controlled the sculpturing of the relief in the study area.     

Olivine in ultramafic lamprophyres: chemistry,crystallisation, and melt sources of Siberian Pre- and post-trap aillikites

We studied olivines from the Devonian pre-trap (the Ilbokich occurrence) and the Triassic post-trap (the Chadobets occurrence) carbonate-rich ultramafic lamprophyres (UMLs) in the southwestern portion of the Siberian craton. On the basis of detailed investigations of major, minor, and trace-element distributions, we have reconstructed the main processes that control the origins of these olivines. These include fractional crystallisation from melt, assimilation, and fractional crystallisation processes with orthopyroxene assimilation, melt-reaction diffusive re-equilibration, alkali enrichment, and CO₂ degassing of the melt. Furthermore, we inferred the composition of the sources of the primary UML melt and their possible correlations with proto-kimberlitic melts, as well as the influence of the Triassic Siberian plume on the composition of the lithospheric mantle. The main differences between olivines from the Ilbokich and the Chadobets aillikites were that the olivines from the former had more magnesium-rich cores (Mg# = 89.2?±?0.2), had Mg- and Cr-rich transition zones (Mg# = 89.7?±?0.2 and 300–500 ppm Cr), had lower Ni (up to 3100 ppm) and Li (1.4–1.5 ppm), and had higher B (0.8–2.6 ppm) contents, all at higher Fo values (90–86), relative to the olivines from the latter (Mg# = 88–75; 200–300 ppm Cr; up to 3400 ppm Ni; 1.4–2.4 ppm Li; 0.4–2.2 ppm B). The Siberian aillikite sources contained a significant amount of metasomatic material. Phlogopite-rich MARID-type veins provided the likely metasomatic component in the pre-trap Devonian Ilbokich aillikite source, whereas the Triassic Chadobets aillikitic post-trap melts were derived from a source with a significant carbonate component. A comparison of UML olivines with olivines from the pre-trap and post-trap Siberian kimberlites shows a striking similarity. This suggests that the carbonate component in the aillikitic source could have been produced by evolved kimberlite melts. The differences in the lithospheric metasomatic component that contributed to pre-trap and post-trap aillikitic melts can be interpreted as reflections of the thermal impact of the Siberian Traps, which reduced phlogopite-bearing metasomes within the southwestern Siberian sub-continental lithospheric mantle.     

Emulating the OPAL equation of state

The equation of state for the structure of the Sun and stars has to be precise to allow comparisons with observations, i.e., helioseismic inversions of thermodynamic quantities. Among the two of the most popular formalisms are (1) the OPAL equation of state developed at Livermore and (2) the Mihalas-Hummer-Däppen (MHD) equation of state. While OPAL has a solid theoretical foundation, and matches the observational data better, the MHD formalism is more intuitive, easy to realize, and has the possibility of adjustable parameters. Furthermore, it an open-source product in contrast to the proprietary OPAL. Recently a version of MHD has been obtained by including the so-called “Plank-Larkin partition function” and by adding scattering-state terms. The resulting formalism matches OPAL rather well. Here, we report on the next logical step, the implementation of this MHD upgrade into the simple and popular CEFF equation of state. Such an implementation will make it a flexible and convenient tool, allowing an approximative on-line implementation of OPAL in solar and stellar models.     

Stable Atmospheric Boundary-Layer Experiment in Spain (SABLES 98): A Report

This paper describes the Stable AtmosphericBoundary Layer Experiment in Spain (SABLES 98),which took place over the northern Spanish plateaucomprising relatively flat grassland,in September 1998. The main objectives of the campaign were to study the properties of themid-latitude stable boundary layer (SBL).Instrumentation deployed on two meteorologicalmasts (of heights 10 m and 100 m)included five sonic anemometers, 15 thermocouples,five cup anemometers and three propeller anemometers,humidity sensors and radiometers.A Sensitron mini-sodar and a tetheredballoon were also operated continuously. Atriangular array of cup anemometers wasinstalled to allow the detection ofwave events. Two nocturnal periods analysedon 14–15 and 20–21 September are used toillustrate the wide-ranging characteristics of the SBL.     

On the validity of the Permian bivalve family Pachydomidae Fischer 1887

Australian bivalve genera referred to the Family Pachydomidae Fischer (1887) and Newell (1956) are compared in details of dentition and ligament with genera placed in the Edmondiidae King (1850). It is found that the hinges of Myonia Dana (1847) and Pachymyonia Dun (1932) are edentulous like those of Edmondia de Koninck (1844). Megadesmus Sowerby (1838) ( = Pachydomus Morris 1845) has a rudimentary tooth in the right valve, but its anterior retractor connected to the adductor by the protractor resembles the musculature of Myonia and Pachymyonia, and the internal ligament is in between that of Edmondia unioniformis and E. josepha, so that the differences are scarcely of subfamilial and probably not of familial rank. Other genera referred to the Pachydomidae differ more. Pyramus, Notomya, and Globicarina have a well‐defined tooth in the right valve and a discrete anterior retractor, and Astartila has a tooth in each valve, and a discrete anterior retractor. Astartila appears to be close in its dentition to the Early Carboniferous genus Scaldia de Ryckholdt (1852). Thus, whilst the present study is incomplete because of the uncertain nature of the hinge and musculature of some edmondiid genera of the European Carboniferous, it appears that the Family Pachydomidae is polyphyletic, with several generic lineages, of which at least two can be traced back to Early Carboniferous members of the Family Edmondiidae.     

Coastal Habitat Use and Residency of Juvenile Atlantic Sharpnose Sharks (Rhizoprionodon terraenovae)

Coastal habitat use and residency of a coastal bay by juvenile Atlantic sharpnose sharks, Rhizoprionodon terraenovae, were examined by acoustic monitoring, gillnet sampling, and conventional tag–recapture. Acoustic monitoring data were used to define the residency and movement patterns of sharks within Crooked Island Sound, Florida. Over 3 years, sharks were monitored for periods of 1–37 days, with individuals regularly moving in and out of the study site. Individual sharks were continuously present within the study site for periods of 1–35 days. Patterns of movement could not be correlated with time of day. Home range sizes were typically small (average?=?1.29 km²) and did not vary on a yearly basis. Gillnet sampling revealed that juvenile Atlantic sharpnose sharks were present in all habitat types found within Crooked Island Sound, and peaks in abundance varied depending on month within a year. Although telemetry data showed that most individuals remained within the study site for short periods of time before emigrating, conventional tag–recapture data indicates some individuals return to Crooked Island Sound after extended absences (maximum length?=?1,352 days). Although conventional shark nursery theory suggests small sharks remain in shallow coastal waters to avoid predation, juvenile Atlantic sharpnose sharks frequently exited from protected areas and appear to move through deeper waters to adjacent coastal bays and estuaries. Given the high productivity exhibited by this species, the benefit gained through a nursery that reduces predation may be limited for this species.