Fe-isotope fractionation in magmatic-hydrothermal mineral deposits: a case study from the Renison Sn-W deposit, Tasmania

We present 50 new iron isotopic analyses of source granite and mineral separates from the Renison tin deposit in western Tasmania. The aim of the study is to characterise the composition of minerals within a tin deposit associated with a reduced, S-type magma. We have analysed bulk samples of granite, and separates of pyrrhotite, pyrite, arsenopyrite, magnetite, chalcopyrite and siderite by multi-collector inductively coupled mass spectrometry. The isotopic compositions of mineral separates are consistent with theoretical predictions of equilibrium fractionation based on Mössbauer spectroscopy and other parametric calculations. Mineral-mineral pairs yield temperatures of formation that are in agreement with prior detailed fluid inclusion studies, but are spatially inconsistent with declining fluid temperatures with distance from the causative intrusion, limiting the use of Fe isotopes as a potential geothermometer, at least in this case. Comparison of our data with published data from other deposits clearly demonstrates that pyrite, magnetite and chalcopyrite from the hottest ore fluids (>300-400. °C) at Renison are isotopically heavier than minerals sampled from a deposit formed at similar temperatures, but associated with a more oxidised and less differentiated intrusion.Christine M. Wawryk, John D. Fode

Non-Fermi liquid behavior in a fluctuating valence system, the filled skutterudite compound CeRu_{4}As_{12}

Electrical resistivity $\rho$, specific heat C, and magnetic susceptibility $\chi$ measurements made on the filled skutterudite CeRu_4As_{12} reveal non-Fermi liquid (NFL) T - dependences at low T, i.e., $\rho$(T) $\sim$ T^{1.4} and weak power law or logarithmic divergences in C(T)/T and $\chi$(T). Measurements also show that the T - dependence of the thermoelectric power S(T) deviates from that seen in other Ce systems. The NFL behavior appears to be associated with fluctuations of the Ce valence between 3^+ and 4^+ rather than a typical Kondo lattice scenario that would be appropriate for an integral Ce valence of 3^+.Comment: 18 pages, 5 figure

Fe isotopes and the contrasting petrogenesis of A-, I- and S-type granite

Abstract not availableJohn Foden, Paolo A. Sossi, Christine M. Wawry

Power spectral analysis of heart rate variability in children and adolescents with IDDM

ObjectiveTo investigate power spectral analysis (PSA) of heart rate variability (HRV) in children and adolescents with IDDM, its relationship with other measures of HRV and standard cardiovascular responses, and factors associated with reduced HVR.Research design and methodsA total of 130 subjects with IDDM aged 12.8 +/- 3.2 years and 108 healthy control subjects were studied. Power spectra were analyzed from supine electrocardiograph (ECG) recordings by processing into consecutive R-R intervals and analysis using fast Fourier transformation. Standard cardiovascular responses to deep breathing and standing were performed.ResultsIDDM subjects had a reduction in total power including both low-frequency (0.05-0.14 Hz; P = 0.0001) and high-frequency (0.14-0.40 Hz; P = 0.0002) components. These changes were seen from diagnosis. Other measures of HRV, coefficient of variation (CV) and standard deviation (SD) of mean resting heart rate, were also significantly lower in IDDM. All 20 (15%) of the 130 IDDM subjects with total power less than the 5th percentile in control subjects also had reduced HRV when measured by CV of heart rate. There was an independent relationship between age and the high-frequency component in IDDM subjects and control subjects. Total power correlated with mean heart rate (r = -0.56; P ConclusionsChanges in HRV are a sensitive and reproducible measure of early autonomic dysfunction in childhood. In this age-group, PSA appears no more sensitive a measure of reduced HRV than other closely correlated measures of HRV.Andrew M Wawryk, David J Bates, and Jennifer J Coupe

Symmetry of order parameters in multiband superconductors LaRu4_4As12_{12} and PrOs4_4Sb12_{12} probed by local magnetization measurements

International audienceThe temperature dependencies of the lower critical field Hc1ðTÞ of several filled-skutterudite superconductors were investigated by local magnetization measurements. While LaOs4As12 and PrRu4As12exhibit the Hc1ðTÞ dependencies consistent with the single-band BCS prediction, for LaRu4As12 (thesuperconducting temperature Tc ¼ 10.4 K) with a similar three-dimensional Fermi surface, we observe asudden increase in Hc1ðTÞ deep in a superconducting state below about 0.32Tc. Remarkably, a rapid rise ofHc1ðTÞ at approximately the same reduced temperature 0.27Tc is also found for the heavy-fermioncompound PrOs4Sb12 (Tc ≃ 1.78 K), in fair accord with the earlier macroscopic study. We attribute theunusual Hc1ðTÞ dependencies of LaRu4As12 and PrOs4Sb12 to a kink structure in their superfluid densitiesdue to different contributions from two nearly decoupled bands. Whereas LaRu4As12 is establishedas a two-band isotropic s-wave superconductor, nonsaturating behavior of Hc1ðTÞis observed for PrOs4Sb12,indicative of an anisotropic structure of a smaller gap. For this superconductor with broken time-reversalsymmetry, our findings suggest a superconducting state with multiple symmetries of the order parameters