Platinum-group mineralization at the margin of the Skaergaard intrusion, East Greenland

This is the final version of the article. Available from Springer Verlag via the DOI in this record.Two occurrences of platinum-group elements (PGEs) along the northern margin of the Skaergaard intrusion include a sulfide-bearing gabbro with slightly less than 1 ppm PGE + Au and a clinopyroxene-actinolite-plagioclase-biotite-ilmenite schist with 16 vol% sulfide and 1.8 ppm PGE + Au. Both have assemblages of pyrrhotite, pentlandite, and chalcopyrite typical for orthomagmatic sulfides. Matching platinum-group mineral assemblages with sperrylite (PtAs2), kotulskite (Pd(Bi,Te)1–2), froodite (PdBi2), michenerite (PdBiTe), and electrum (Au,Ag) suggest a common origin. Petrological and geochemical similarities suggest that the occurrences are related to the Skaergaard intrusion. The Marginal Border Series locally displays Ni depletion consistent with sulfide fractionation, and the PGE fractionation trends of the occurrences are systematically enriched by 10–50 times over the chilled margin. The PGE can be explained by sulfide-silicate immiscibility in the Skaergaard magma with R factors of 110–220. Nickel depletion in olivine suggests that the process occurred within the host cumulate, and the low R factors require little sulfide mobility. The sulfide assemblages are different to the chalcopyrite-bornite-digenite assemblage found in the Skaergaard Layered Series and Platinova Reef. These differences can be explained by the early formation of sulfide melt, while magmatic differentiation or sulfur loss caused the unusual sulfide assemblage within the Layered Series. The PGEs indicate that the sulfides formed from the Skaergaard magma. The sulfides and PGEs could not have formed from the nearby Watkins Fjord wehrlite intrusion, which is nearly barren in sulfide. We suggest that silicate-sulfide immiscibility led to PGE concentration where the Skaergaard magma became contaminated with material from the Archean basement.The authors are grateful for logistical support from Platina Resources Ltd., Geological Survey of Denmark and Greenland, and members of the 2011 Skaergaard field team. JCØA was supported by grants from Helford Geoscience LLP and the Camborne School of Mines Trust. CT was supported by the Danish Natural Research Council and the Carlsberg Foundation, and CEL was supported by the US National Science Foundation (EAR-1019887). Samples were sectioned and prepared by Steve Pendray at Camborne School of Mines. The QEMSCAN is a registered trade mark of FEI Corporation

Toward an understanding of disequilibrium dihedral angles in mafic rocks

[1] The median dihedral angle at clinopyroxene-plagioclase-plagioclase junctions in mafic rocks, Θcpp, is generally lower than equilibrium (109° ± 2°). Observation of a wide range of mafic bodies demonstrates that previous work on systematic variations of Θcpp is incorrect in several important respects. First, the spatial distribution of plagioclase compositional zoning demonstrates that the final geometry of three-grain junctions, and hence Θcpp, is formed during solidification (the igneous process): sub-solidus textural modification in most dolerites and gabbros, previously thought to be the dominant control on Θcpp, is insignificant. Θcpp is governed by mass transport constraints, the inhibiting effects of small pore size on crystallization, and variation in relative growth rates of pyroxene and plagioclase. During rapid cooling, pyroxene preferentially fills wider pores while the narrower pores remain melt-filled, resulting in an initial value of Θcpp of 78°, rather than 60° which would be expected if all melt-filled pores were filled with pyroxene. Lower cooling rates create a higher initial Θcpp due to changes in relative growth rates of the two minerals at the nascent three-grain junction. Low Θcpp (associated with cuspate clinopyroxene grains at triple junctions) can also be diagnostic of infiltration of previously melt-free rocks by late-stage evolved liquids (the metasomatic process). Modification of Θcpp by sub-solidus textural equilibration (the metamorphic process) is only important for fine-grained mafic rocks such as chilled margins and intraplutonic chill zones. In coarse-grained gabbros from shallow crustal intrusions the metamorphic process occurs only in the centers of oikocrysts, associated with rounding of chadacrysts

Water Adsorption on AnO2 {111}, {110} and {100} Surfaces (An = U, Pu); A DFT+U Study

The interactions between water and the actinide oxides UO2 and PuO2 are important both fundamentally and when considering the long-term storage of spent nuclear fuel. However, experimental studies in this area are severely limited by the intense radioactivity of plutonium, and hence, we have recently begun to investigate these interactions computationally. In this paper, we report the results of plane-wave density functional theory calculations of the interaction of water with the {111}, {110}, and {100} surfaces of UO2 and PuO2, using a Hubbard-corrected potential (PBE + U) approach to account for the strongly correlated 5f electrons. We find a mix of molecular and dissociative water adsorption to be most stable on the {111} surface, whereas the fully dissociative water adsorption is most stable on the {110} and {100} surfaces, leading to a fully hydroxylated monolayer. From these results, we derive water desorption temperatures at various pressures for the different surfaces. These increase in the order {111} < {110} < {100}, and these data are used to propose an alternative interpretation for the two experimentally determined temperature ranges for water desorption from PuO2

High energy solar neutrinos and p-wave contributions to ^3He(p,\nue^+)^4He

High energy solar neutrinos can come from the hep reaction ^3He(p,\nue^+)^4He with a large end point energy of 18.8 MeV. Understanding the hep reaction may be important for interpreting solar neutrino spectra. We calculate the contribution of the axial charge transition $^3P_0\to ^1S_0$ to the hep thermonuclear S factor using a one-body reaction model involving a nucleon moving in optical potentials. Our result is comparable to or larger than previous calculations of the s-wave Gamow Teller contribution. This indicates that the hep reaction may have p-wave strength leading to an enhancement of the S factor.Comment: 4 pages, 1 ps figure, very minor changes, Phys. Rev. C in pres

The Thickness of the Mushy Layer on the Floor of the Skaergaard Magma Chamber at Apatite Saturation

We present a novel way of constraining the thickness of the crystal mush in fractionated layered intrusions using detailed microstructural analysis. The results are combined with geochemical data to create a snapshot of the crystal mush on the floor of the Skaergaard magma chamber in the period immediately before and after the saturation of the bulk liquid in apatite (the UZa–b boundary). The step-change in the fractional latent heat (that part of the total enthalpy budget associated with crystallization) accompanying the arrival of a new liquidus phase is recorded by a step-change in the median clinopyroxene–plagioclase–plagioclase dihedral angle, Θcpp, in fully solidified cumulates. Dihedral angles are formed during the last stages of solidification and hence the change of Θcpp associated with apatite-in marks a point close to the base of the mushy layer at the moment the bulk liquid became saturated in apatite, whereas the first appearance of abundant, homogeneously scattered, cumulus apatite crystals in the stratigraphy marks the top of the mushy layer at this moment. Comparison of the offset between these two markers in five widely spaced drill cores through the Skaergaard Layered Series suggests that the mushy layer was only a few metres thick at the UZa–b boundary in the centre and east of the floor, whereas it was ∼100 m thick on the floor near the western margin. There is no correlation between the efficiency of liquid expulsion (as recorded by bulk-rock P2O5 concentrations and the stratigraphic distribution of reactive symplectites) and the recorded mush thickness at the moment of apatite saturation, suggesting that existing models of adcumulate formation that depend on mush thickness need to be reconsidered.M.B.H. and C.T. acknowledge support from a Royal Society Joint International Grant. M.B.H. was supported by the Natural Environment Research Council (grant numbers NE/F020325/1 and NE/J021520/1). C.T. was supported by the Carlsberg Foundation, the Danish Council of Independent Research, and the Danish National Research Foundation

A whole-rock data set for the Skaergaard intrusion, East Greenland

We report a compilation of new and published whole-rock major and trace element analyses for 646 samples of the Skaergaard intrusion, East Greenland. The samples were collected in 14 stratigraphic profiles either from accessible and well-exposed surface areas or from drill core, and they cover most regions of the intrusion. This includes the Layered Series, the Upper Border Series, the Marginal Border Series and the Sandwich Horizon. The geochemical data were obtained by a combination of X-ray fluorescence and inductively coupled plasma mass spectrometry. This data set can, for example, be used to constrain processes of igneous differentiation and ore formation.

High temperature oxidation resistance in titanium-niobium alloys

Titanium alloys are ideally suited for use as lightweight structural materials, but their use at high temperature is severely restricted by oxidation. Niobium is known to confer oxidation-resistance, and here we disprove the normal explanation, that Nb5+ ions trap oxygen vacancies. Using density functional theory calculation, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) we show that Nb is insoluble in TiO2. In fact, the Ti–Nb surface has three-layer structure: the oxide itself, an additional Nb-depleted zone below the oxide and a deeper sublayer of enhanced Nb. Microfocussed X-ray diffraction also demonstrates recrystallization in the Nb-depleted zone. We interpret this using a dynamical model: slow Nb-diffusion leads to the build up of a Nb-rich sublayer, which in turn blocks oxygen diffusion. Nb effects contrast with vanadium, where faster diffusion prevents the build up of equivalent structures

Estimation of efficiency of the use of financial resources on enterprises

Стаття присвячена дослідженню теоретичних та практичних питань аналітичного забезпечення управління використанням фінансових ресурсів підприємств. Запропоновані комплексні показники оцінки даного процесуThe article is devoted to research of theoretical and practical questions of the analytical providing of management the use of financial resources of enterprises. The complex indexes of estimation of this process are offere