Chris Ballhaus (chrisb@nwz.uni-muenster.de)1, Marian Tredoux2 & Andreas Spaeth2
1 Institut für Mineralogie, Universität Muenster, 48149 Münster, Germany
2 Department of Geology, University of Cape Town, Rondebosch 7700, South Africa
Liquidus experiments were performed in the sulfide system Fe-Ni-Cu-S to determine the partition coefficients of Ni, Cu, Ir, Ru, Rh, Pt, and Pd between monosulfide solid solution (mss) and sulfide melt at three different S2-fugacities. The PGEs were added at trace concentration levels to the charges (total 500 ppm PGEs) and measured with laser-ablation ICP-MS. S2-fugacity was controlled internally by fixing the metal/S atomic ratio of the starting mix.
We present an internally consistent set of mss-melt partition coefficients for Fe, Ni, Cu, Ir, Ru, Rh, Pt, and Pd, determined over a wide range of temperatures and S2-fugacities. The DPGE were determined for the first time at concentration levels within the validity of Henry's law. It is shown that all elements are either highly compatible (Ir, Ru, Rh) or incompatible with mss (Cu, Pt, Pd), regardless of S2-fugacity. Ni is the only exception. DNi changes from moderately incompatible with mss at low S2-fugacity (0.5 ± 0.1) to compatible with mss at high S2-fugacity (up to 2.4).
The experiments revealed a hitherto unreported miscibility gap in the Fe-Ni-Cu-S system. Several starting compositions separated into two immiscible sulfide melt fractions well above liquidus temperature. The conjugate melts differ markedly in terms of metal/S ratio, Cu content, and possibly melt structure. Careful analysis of the conjugate compositions, both with EPMA and LA-ICP-MS, shows that the miscibility gap is closed, i.e. has the shape of a "loop" in T-X space that is bordered by single phase fields both toward its low and high temperature sides.
The data are applied to bulk sulfide ore analyses of the Sudbury Igneous Complex, to derive primary sulfide melt compositions and fractionation paths.
Serge Balyshev (balyshev@gpg.crust.irk.ru) & Vitaly Lashkevitch
Institute of the Earth's Crust SB RAS, Lermontov str.,128, 664033 Irkutsk, Russia
Computational thermodynamic modelling of metasomatic processes were carried out by means of the program complex "Selector-C" [Karpov et al., 1997]. As a subject for modelling we used rocks of ultrabasic (peridotites), basic (amphibolites) and middle (diorites) composition, which after interaction with fluids were changed to granitic rocks. Deep fluids bring in rocks granitizing components (SiO2, K2O, Na2O) and after interaction take out CaO, MgO, FeO. In our models we considered the temperature 600-700°C and the pressure 4-5 kbar. The comparison of volumes and energetic characteristics of processes of acid metasomatism revealed the following: the peridotites volume increased in 3.6 times intensively than diorites and in 2.1 - than amphibolites ones. The volume increase in diorites is about linear character and contrasts to nonlinear in amphibolites and peridotites. This nonlinearity was caused by contrast changing in mineral composition (especially by quantity of hydro-minerals: Amf, Bt, Mu). The character of enthalpy increase is linear in all modelled systems, but more heat emanates from ultrabasic and basic rocks. The summary heat emanated from peridotites is 10.5% of primary enthalpy (6.1% and 3.7% for amphibolite and diorite respectively). This heat is sufficiently for example (preliminary calculation for 1 kg amphibolites) to warm about 5 kg of surrounding rock up to 100°C. This work is supported by RFBR (grant #99-05-65636).
Karpov IK, Chudnenko KV & Kulik DA, Amer. J. Sci, 297, 767-806, (1997).
Sandra Barboni (paris@camserv.unicam.it)1, Eleonora Paris, Gabriele Giuli & Claudia Romano2
1 Dipartimento di Scienze della Terra and INFM, Università di Camerino, Camerino, Italy
2 Dip. di Scienze Geologiche, Terza Università di Roma, Roma, Italy
In this study we present structural data on Vanadium in silicate glasses of interest in the field of Earth Sciences. Although usually considered as network-modifiers in the melt structure, transition elements like Vanadium can be present in minerals (i.e. in crystalline structures) both in tetrahedral and octahedral coordination. X-ray absorption spectroscopy can give useful information on the coordination number of these elements as well as on the cation-anion (i.e. oxygen) bond-length and T-O-T bond angles. The V K-edge XANES (X-ray Absorption Near Edge Structure) spectra have been collected at LURE (F) Synchrotron Radiation Center. We have synthesized at high temperature glasses of chemical composition analogue of major rocks, like basalts and granites. These samples have been added with variable amounts of Vanadium. The aim of this procedure is to: 1: valuate the structural behaviour of Vanadium in different glass types; 2: determine the influence of an increased concentration of Vanadium on its structural behaviour; 3: compare the results obtained for each type of glass to clarify the influence of glass composition on the element; 4: determine the effect of a very high alkalis content by comparison with a sodium disilicate glass composition. Several crystalline samples with this element present in a variety of oxidation states and polyhedral geometry have been used as reference materials and allow to evidence: a- V5+ is the predominant form of Vanadium in our synthetic glasses and is present in a tetrahedral environment, therefore Vanadium may be referred to as network-forming element; b- comparison between glasses with same composition but increasing Vanadium content shows that the local environment does not change as a function of its content for the chosen range of composition.
Ivan Bazhan (ibazhan@uiggm.nsc.ru) & Yuriy Seryotkin (yuvs@uiggm.nsc.ru)
Koptuyg Pr.3, Novosibirsk 630090, Russia
The aim of this work was to investigate the influence of ion-molecular filling on the properties of narrow-porous zeolites. Ion-exchanged forms were obtained from natural analcime Na1.88[Al1.88Si4.12O12]H2O (a=13,729 Å, b=13,686 Å, c=13,710 Å, V=2576 Å3, Ibca) (Bakakin et.al., 1994) in LiNO3 and NaNO3 salt melts. The dehydration of (Na,Li)-analcime with the lithium content from 30% to 70% gave rise to two phases. Phase I contained mainly sodium and phase II lithium. Phase I underwent minor compression (V"-3%) and phase II considerable compression (V"-9%) under dehydration. The near-linear dependence of the phase concentrations on the exchange degree (Fig.1) indicates that the composition of phases are fixed. Phase I included about 25% of Li and 75% of Na, and phase II about 65% of Li and 35% of Na. Ion-exchanged samples were studied by high temperature X-ray diffraction method. The (Na, Li)-analcime with the exchange degree 65%, at heating, showed two structural transformations. The first transition was at 350oC. Pseudocubic unit cell transformed to pseudotrigonal one with reduction of the parameter a and increase of the angle (alpha) (Fig. 2).
Fig. 1. The phase concentrations depending on the lithium concentration in the analcime.
Fig. 2. The changes of unit cell parameter a and angle (alpha) on the heating.
At the temperature rises parameter a increased and angle (alpha) decreased back to 90o. The second structural transformation was observed at 610oC. This transformation was associated with the transition of unit cell from pseudotrigonal to pseudocubic. Only one phase occurred at the exchange degree of 70% and over. With rising Li content the compressibility of a sample at dehydration decreased. The anomalous behavior of (Na,Li)-analcime structure was interpreted as a result of Na migration from S to W sites. Decreasing compressibility with increasing lithium content was explained by tolerance of lithium to coordination environment and lithium ability to triple coordination.
Bakakin VV, Alexseev VI, Seryotkin YuV, Belitsky IA & Fursenko BA, Dokl. Akad. Nauk, 339, 520-524, (1994).
Index of EMPG VIII Volume
Further EMPG VIII Information
Index of the Journal of Conference Abstracts
Cambridge Publications Home Page