Trace element fractionation between biotite, allanite, and granitic melt

<jats:title>Abstract</jats:title><jats:p>The partitioning of a large suite of trace elements between biotite and water-saturated granitic melt was measured at 2 kbar and 700—800 ˚C. To reach equilibrium and to grow biotite crystals large enough for analysis, runs usually lasted from 30 to 45 days. In every charge, a few trace elements were initially doped at the 0.1—0.5 wt. % level and analyzed by electron microprobe after the run. First-row transition metal ions are highly compatible in biotite with D<jats:sup>biotite/melt</jats:sup> of 17 for Ti, 35 for V, 47 for Co, 174 for Ni, and 5.8 for Zn. A very notable exception is Cu with D<jats:sup>biotite/melt</jats:sup> < 0.9. This is likely one of the reasons why Cu is enriched together with Mo (D<jats:sup>biotite/melt</jats:sup> = 0.29) in porphyry deposits associated with intermediate to felsic plutons, while the other transition metals are not. Both Nb and Ta are mildly compatible in biotite with D<jats:sup>biotite/melt</jats:sup> being larger for Nb (3.69) than for Ta (1.89). Moderate (15—30%) biotite fractionation would be sufficient to reduce the Nb/Ta ratio from the chondritic value to the range observed in the continental crust. Moreover, the strong partitioning of Ti into biotite implies that already modest biotite fractionation suppresses the saturation of Ti-oxide phases and thereby indirectly facilitates the enrichment of Ta over Nb in the residual melt. The heavy alkalis, alkaline earths, and Pb are only mildly fractionated between biotite and melt (D<jats:sup>biotite/melt</jats:sup> = 3.8 for Rb, 0.6 for Cs, 0.6 for Sr, 1.8 for Ba, 0.7 for Pb). The rare earth elements are generally incompatible in biotite, with a minimum for D<jats:sup>biotite/melt</jats:sup> of 0.03–0.06 at Gd, Tb, and Dy, while both the light and heavy rare earths are less incompatible (e.g. D<jats:sup>biotite/melt</jats:sup> = 0.6 for La and 0.3 for Yb). This behavior probably reflects a partitioning into two sites, the K site for the light rare earths and the octahedral Mg site for the heavy rare earths. There is no obvious dependence of the rare earth partition coefficients on tetrahedral Al in the biotite, presumably because charge balancing by cation vacancies is possible. Allanite was found as run product in some experiments. For the light rare earths, D<jats:sup>allanite/melt</jats:sup> is very high (e.g. 385 to 963 for Ce and Nd) and appears to increase with decreasing temperatures. However, the rather high solubility of allanite in the melts implies that it likely only crystallizes during the last stages of cooling of most magmas, except if the source magma is unusually enriched in rare earths.</jats:p&gt

An experimental study on the behaviour of copper and other trace elements in magmatic systems

1. Distribution of trace elements between biotite and hydrous granitic melt. The synthetic system haplogranite-anorthite-biotite-H2O, doped with a suite of trace elements (V, Cr, Co, Ni, Cu, Zn, Rb, Cs, Sr, Ba, Mo, W, Nb, Ta, REE, Pb and Zr) was experimentally investigated over the temperature interval of 700-800°C at 200 MPa (H2O) to study the distribution of trace elements between biotite and coexisting hydrous melt. The starting materials were a series of volatile-free synthetic glasses obtained by heating a mixture of appropriate reagent grade chemicals (oxides, carbonates or hydroxides) corresponding to ~76 wt% haplogranite (35 wt% SiO2, 40 wt% NaAlSi3O8 and 25 wt% KAlSi3O8), ~8 wt% anorthite, ~15 wt% biotite (with a 1:1 molar ratio of Mg/Fe) and ~1 wt% total trace elements, so selected as to avoid peak interference during microprobe analysis. Experiments were carried out under water-saturated conditions in cold-seal autoclaves with run durations of between 35 and 45 days. The oxygen fugacity was close to the Ni-NiO buffer. Run products were analysed by electron microprobe. Besides biotite, run products contained other phases including amphibole (hornblende), clino-pyroxene, plagioclase, magnetite, allanite and glass. Measured partition coefficients indicate that most alkalis, alkaline earth metals and transition metal elements favoured biotite over the melt (e.g. DRb ~ 2.6, DCs ~0.6, DBa ~1.8, DSr ~0.6, DCo ~34, DNi ~84, DZn ~8.1, DV ~26, DCr ~15, and DTi ~10). The converse is, however, true for the REEs, with D-values decreasing from DLa ~0.6 to DGd ~0.04 and again rising to DLu ~0.4. The variation of trace element partition coefficients with ionic radius was described by an elastic strain model. The alkalis (Cs+, Rb+, and Na+) and alkaline earths (Ba2+, Sr2+, and Ca2+), including Pb2+, follow K+ into the largest interlayer site of the biotite crystal, each group fitting onto separate parabolic curves. Most of the other trace elements, including 2+ (Ni, Co, Zn, Cu, and Fe), 3+ (V and Cr), 4+ (Ti and Zr), 5+ (Nb and Ta), and 6+ cations (W and Mo) follow Mg2+ into the M2 site, in 6-fold co-ordination, with each group following its own parabolic curve. However, only the divalent group, with more than two trace elements, has been treated onto the elastic strain model with fit parameters ~90, ~6850 kbar and ~0.67 Å. The REEs show a partitioning pattern, which cannot be explained by substitution onto a single lattice site. They apparently partition into two crystallographic sites of the biotite (i.e. K and M1). The LREEs predominantly partition into the K-site, the MREEs show mixed partitioning character in both the K and M1 sites and the HREEs predominantly partition into the M1 site. The measured partition coefficients, therefore, fit onto two parabolic curves. The accessory mineral allanite was found in run products belonging to some samples doped with REEs in the starting mixtures. The REEs are highly compatible in allanite with their partitioning behaviour possibly being influenced by temperature (e.g. DCe ~390, DPr ~340, DNd ~290, DEr ~40, at 800°C and DPr ~650, DNd ~630, DEr ~60, at 775°C). Brice model fit-curves show that all REEs partition into the octahedral Ca-site of the allanite crystal. Biotite is an early crystallising mineral in magmatic systems and tends to fractionate a greater proportion of the compatible trace elements from the melt, rendering them unable to form viable ore deposits. On the other hand, incompatible trace elements are progressively enriched in the melt with increasing crystallisation and fractionation of biotite, with the result that at fluid saturation, a good proportion of these elements will be extracted from melt by exsolved and migrating hydrothermal fluids, to be later concentrated and deposited to form ore deposits. Allanite-melt partition coefficients for REEs are so high that a very small fraction of crystallisation and fractionation of allanite may drastically deplete the melt of its REE content close to zero. 2. Speciation and oxidation state of copper in silicate melts The oxidation state of copper in silicate melts of variable composition was studied at 1 bar at temperatures of between 1250 and 1400°C under controlled oxygen fugacity. Synthetic silicate glasses (each doped with 1 wt% Cu, as CuO) of haplogranites, tholeiite, alkali-basalt and andesite were prepared from appropriate amounts of reagent-grade oxides, carbonates and hydroxides. With regard to the haplogranites, a series of 4 separate glasses were prepared with varying molar ratios of [Na2O+K2O]/Al2O3 (i.e. 0.6, 0.93, 1.42 and 1.75) but keeping the SiO2 content and the molar ratio Na2O/K2O relatively constant, to represent a range of naturally occurring melts, including peraluminous, subaluminous, and peralkaline varieties. Experiments were conducted using a gas-mixing technique to investigate the effect of oxygen fugacity on the redox ratio of copper (Cu2+/Cu+) in silicate melts, at various equilibrium temperatures (1250-1400°C). Oxygen fugacity inside the furnace (1 bar total pressure) was imposed by pure CO2 and CO2/H2 gas mixtures with varying ratios. A Y- doped ZrO2 oxygen sensor assembly was installed in the furnace as a means of monitoring the imposed oxygen fugacity inside the furnace. A Bruker IFS 125 HR Fourier-Transform-Spectrometer (FTIR) was used to measure absorbance due to crystal field bands of Cu2+ in the run product glasses. The Cu+ content in the glasses was determined as the difference between the total Cu determined by electron microprobe and the Cu2+ measured by optical spectroscopy. Glass standards containing only Cu2+ were also prepared under high oxygen partial pressure generated by the decomposition of PtO2 in sealed Pt/Rh capsule at 1250°C. The extinction coefficients e (l/mol/cm) in glass standards were calculated to be 12.8 for alkalibasalt, 16.8 for tholeiite, 11.6 for andesite, 7.26 for haplogranite with the molar ratio (Na + K)/Al = 0.6, 33.2 for haplogranite with (Na + K)/Al = 0.93, 15.6 for haplogranite with (Na + K)/Al = 1.42 and 15.4 for haplogranite with (Na + K)/Al = 1.75. Peraluminous haplogranite glass with molar ratio (Na+K)/Al = 0.60 entirely contained Cu+ ions, which could not be converted into Cu2+ ions even under the most oxidising conditions using PtO2. For a given glass composition under the same gas atmosphere, absorbance (A), colour intensity and ratio Cu2+/Cu+, increase with decreasing run temperatures. On the other hand, if temperature is kept constant and gas atmosphere varied, absorbance (A), glass colour intensity and the ratio Cu2+/Cu+, increase with increasing oxygen fugacity. Generally the maximum absorption band due to Cu2+ ions at any run temperature appeared at ~ 13000 cm-1 (wavenumber) for andesite, alkalibasalte, and tholeiite glass and ~ 12500 cm-1 for haplogranite glasses. For a silicate melt of a given composition, plots of log (Cu2+/Cu+) against log fo2 at any run temperature exhibit a linear relationship, with graphs for different temperatures trending almost parallel to each other with slopes in the range of 0.239 to 0.256. The lowest and highest temperature curves lie uppermost and lowermost, respectively. At a fixed run temperature T, plots of log (Cu2+/Cu+) against log fo2 for a silicate melt of any given composition exhibit a similar linear relationship, with curves for the granitic , dioritic and basaltic melts lying upper-most , intermediate and lowest, respectively. ?H for the oxidation of Cu+ to Cu2+ was estimated to be -531.3, -392.8, -386.9, -394.3, -473.9 and -521.9 kJ/mol, for tholeiite, alkali-basalt, andesite, haplogranite with (Na + K)/Al = 0.93, haplogranite with (Na + K)/Al = 1.42 and haplogranite with (Na + K)/Al = 1.75, respectively. The redox ratios Cu2+/Cu+ for granitic and dioritic magmatic systems that often crystallise at temperatures in the range 700 - 800°C, under oxygen fugacities between those of QFM (quartz-fayalite-magnetite), Ni-NiO, and H-M (hematite-magnetite) was estimated. The results show a predominance of Cu2+ in granitic and dioritic plutons, i.e. the ratio Cu2+/Cu+ is always greater than one. Basaltic melts, however, seem to behave differently. They crystallise in the temperature range (1100 - 1200°C), under oxygen fugacities between those of QFM and Ni-NiO buffer systems, with a predominance of Cu+ over Cu2+ ions in their melts, i.e. with very low ratios of Cu2+/Cu+ (usually less than one). 3. Solubility of copper in common rock-forming minerals A range of synthetic systems was experimentally investigated (in two options) at isobaric and isothermal conditions (2 kbar and 600-700°C) to determine the solubility of copper in some common rock-forming minerals (muscovite, phlogopite, orthoclase, and albite) which crystallized from hydrothermal solutions in equilibrium with excess metallic Cu and Cu2O. Samples for option one experiments were prepared simply by mixing reagent grade chemicals corresponding to ~65 wt% mineral and ~ 35 wt% Cu2O, whereas samples for option two experiments consisted of mixtures corresponding to ~90 wt% mineral and ~ 10 wt% hypothetical Cu-bearing mineral (e.g. for the mineral muscovite 90 wt% KAl2 [AlSi3O10] [OH]2 + 10 wt% Cu+Al2(AlSi3O10)(OH)2). Experiments were carried out in cold seal bombs at 600 - 700°C with run durations of 15 - 20 days using capsules made of pure copper. Depending on the composition of the starting mixtures, different copper solubilities were observed as different mixtures stabilised different mineral assemblages. For instance, the solubility of Cu (as wt% Cu2O) in orthoclase (CuOr) is in the range 0.863-0.049 and 0.089-0.049 in run products of option 1 (Or1) and 2 (Or2) mixtures, respectively. In albite, CuAb ranges from 1.175-0.630 in Ab1 and 0.041 in Ab2. In muscovite, CuMu ranges from 0.965-0.634 in Mu1 and 0.08 in Mu2. In phlogopite, CuPhl ranges from 1.142-0.555 in Phl1. In quartz, CuQtz ranges from 1.336-1.173 in Qtz1 and 0.054-0.049 in Qtz2. The upper and lower values of the solubility ranges correspond to 600 and 700°C, respectively. Many other phases crystallised in the run products of both experimental options remain to be identified whilst others simply exist in very low proportions. So there is seemingly still more work left to be done. In principle, once the experimental samples are fully characterised, the results obtained in these experiments can be combined with those of copper solubility studies in hydrothermal fluids, available from thermodynamic data bases, to calculate partition-coefficients of copper between fluid and minerals existing in equilibrium.1. Die Verteilung von Spurenelementen zwischen Biotit und wasserhaltiger granitischer Schmelze Das synthetische System Haplogranit-Anorthit-Biotit-H2O dotiert mit einer Reihe von Spurenelementen (V, Cr, Co, Ni, Cu, Zn, Rb, Cs, Sr, Ba, Mo, W, Nb, Ta, REE, Pb und Zr) wurde experimentell untersucht im Temperaturbereich von 700-800°C und bei einem Druck von 200 MPa (H2O) um das Verteilungsverhalten von Spurenelementen zwischen Biotit und der koexistierenden Schmelze zu erforschen. Die Ausgangsmaterialien waren eine Reihe von synthetischen Gläsern mit der Zusammensetzung von ungefähr 76 wt% Haplogranit (35 wt% SiO2, 40 wt% NaAlSi3O8 und 25 wt% KAlSi3O8), 8 wt% Anorthit, 15 wt% Biotit (mit 1:1 Molarverhältnis von Mg/Fe) und insgesamt 1 wt% Spurenelementen. Die Spurenelementen wurden so gewählt, dass während der Analysen mit der Mikrosonde ihre Peaks einander nicht überlagern. Die Experimente wurden zwischen 35 und 45 Tage lang in cold-seal Autoklaven unter wassergesättigten Bedingungen durchgeführt. Die Sauerstoff-Fugazität entsprach in etwa dem Ni-NiO Puffer. Die Produkte der Experimente wurden mit der Elektronenmikrosonde analysiert. Außer Biotit enthielten die Produkte der Experimente andere Phasen, darunter Amphibol (Hornblende), Klinopyroxen, Plagioklas, Magnetit, Allanit und Glas. Die gemessenen Verteilungskoeffizienten zeigen, dass die meisten Alkalien, Erdalkalien und Übergangsmetalle im Biotit eingereichert wurden (z. B. DRb ~ 2.6, DCs ~0.6, DBa ~1.8, DSr ~0.6, DCo ~34, DNi ~84, DZn ~8.1, DV ~26, DCr ~15, and DTi ~10). Das Umgekehrte gilt jedoch für die REEs, mit D-Werten, die von 0,04 bis 0,6 variieren (z. B. DLa ~ 0.6, DGd ~0.04 und DLu ~0.4). Die Variation des Verteilungskoeffizienten der Spurenelemente in Abhängigkeit ihrer Ionenradien wurde beschrieben durch ein elastisches Verformungsmodell. Die Alkalien (Cs+, Rb+ und Na+) und Erdalkalien (Ba2+, Sr2+ und Ca2+) einschließlich Pb2+ folgen K+ in die Zwischenschichtgitterposition des biotite-Kristalls. Jede Gruppe hat eine eigene parabolische Kurve. Die meisten anderen Spurenelemente einschließlich den zweiwertigen (Ni, Co, Zn, Cu und Fe), dreiwertigen (V und Cr), vierwertigen (Ti und Zr), fünfwertigen (Nb und Ta) und sechswertigen Kationen (W und Mo) folgen Mg2+ in die M2-Position, in 6-facher Koordination, wobei jede Gruppe ihre eigene parabolische Kurve bildet. Die Seltenen Erden (REE) zeigen ein Verteilungsmuster, das nicht durch Die Substitution auf einer einzigen kristallographischen Position erklärt werden kann. Sie verteilen sich auf zwei kristallographischen Positionen des Biotites (d. h. K und M 1). Die LREEs und HREEs besetzen überwiegend die K- beziehungsweise M 1-Positionen. Die MREEs werden auf beiden Gitterpositionen eingebaut. Die gemessenen Verteilungskoeffizienten folgen daher zwei parabolischen Kurven. Das akzessorische Mineral Allanit wurde in den Produkten der Experimente gefunden, deren Ausgangsmischungen mit REEs dotiert waren. Die REEs sind sehr kompatibel mit Allanit mit ihrem Verteilungsverhalten, das möglicherweise durch die Temperatur beeinflusst wird (DCe ~390, DPr ~340, DNd ~290, DEr ~40, bei 800°C und DPr ~650, DNd ~630, DEr ~60, bei 775°C). Die Fit-Kurven auf der basis eines Brice-Modells fit-Kurven zeigen, dass alle REEs auf der Ca-Position des Allanit-Kristalls eingebaut werden. Biotit ist ein früh kristallisierendes Mineral in magmatischen Systemen, es tendiert dazu, einen größeren Anteil der kompatiblen seltenen Elemente aus der Schmelze zu fraktionieren und verhindert daher, dass diese Elemente zu Erzlagerstätten eingereichert werden. Andererseits werden inkompatible seltene Elemente allmählich in der Schmelze angereichert mit zunehmender Kristallisation und Fraktionierung des Biotits. Das Ergebnis ist, dass bei Wasser-Sättigung der Schmelze ein großer Teil dieser Elemente durch hydrothermale Fluide aus der Schmelze extrahiert wird, um später konzentriert und in Erzlagerstätten abgelagert zu werden. Der Verteilungskoeffizient der REEs zwischen Allanit und der Schmelze ist so hoch, dass eine sehr kleine Kristallisation und Fraktionierung von Allanit den REE-Gehalt der Schmelze schnell bis auf fast null verringern kann. 2. Speziation und Oxidationsstufe des Kupfers in Silikatschmelzen Der Oxydationszustand des Kupfers in Silikatschmelzen mit variabler Zusammensetzung wurde bei 1 bar und Temperaturen zwischen 1250 und 1400°C unter kontrollierter Sauerstoff-Fugazität untersucht. Aus Haplograniten, Tholeiit, Alkalibasalt und Andesit bestehend synthetische Silikatgläser (jedes dotiert mit 1 wt% Cu, in Form von CuO) wurden hergestellt aus entsprechenden Oxid-, Hydroxid- und Carbonat-Mischungen. Von den haplogranitischen Zusammensetzungen wurde eine Reihe von vier verschiedenen Gläsern hergestellt, in denen sich das Mol-Verhältnis von [Na2O+K2O]/Al2O3 (d. h. 0.6, 0.93, 1.42 und 1.75) veränderte, aber der SiO2-Inhalt und das Mol-Verhältnis Na2O/K2O ungefähr gleich blieb, um eine Reihe von peraluminischen, subaluminischen und peralkalischen Zusammensetzungen zu untersuchen. Die Experimente wurden mit einer Gasmisch-Technik durchgeführt, um den Effekt der Sauerstofffugazitäten auf den Redox-Zustand von Kupfer (Cu2+/Cu+) in Silikatschmelzen im Temperaturbereich von 1250 - 1400°C zu untersuchen. Die Sauerstoff-Fugazität in dem Ofen (1 bar Gesamtdruck) wurde eingestellt durch reines CO2 und eine Mischung verschiedener Anteilen von CO2 und H2. Ein Y-dotierter ZrO2 Sauerstoffsensor wurde im Ofen installiert, um die Sauerstofffugazität zu messen. Ein Bruker IFS 125 HR Fourier-Transform-Spektrometer (FTIR) wurde benutzt, um die Absorption durch die Kristallfeldbanden von Cu2+ in den abgeschreckten Gläsern zu messen. Der Cu+-Gehalt in den Gläsern wurde ermittelt als Differenz zwischen dem gesamten Cu, das gemessen wurde durch Elektronen-Mikrosonde, und dem Cu2+, das durch optische Spektroskopie bestimmt wurde. Standardgläser (die nur Cu2+ enthielten) wurden unter hohem Sauerstoffpartialdruck hergestellt, der durch den Zerfall von PtO2 in einer versiegelten Pt/Rh-Kapsel bei 1250°C erzeugt wurde. Die Extinktionskoeffizienten e (l/mol/cm) von den Standardgläsern wurden ermittelt als 12.8 für Alkalibasalt, 16.8 für Tholeiit, 11.6 für Andesit, 7.26 für Haplogranit mit (Na + K)/Al = 0.6, 33.2 für Haplogranit mit (Na + K)/Al = 0.93, 15.6 für Haplogranit mit (Na + K)/Al = 1.42 und 15.4 für Haplogranit mit (Na + K)/Al = 1.75. Das Glas von peraluminischem Haplogranit mit Mol-Verhältnis (Na+K)/Al = 0.60 enthielt nur Cu+-Ionen, die selbst unter den höchst oxidierenden Bedingungen mit PtO2 nicht in Cu2+-Ionen verwandelt werden konnten. Für eine gegebene Glaszusammensetzung unter unveränderter Gasatmosphäre steigen die Absorption (A), die Farbintensität und das Cu2+/Cu+-Verhältnis mit sinkenden Temperaturen im Experiment. Andererseits wachsen die Absorption, die Intensität der Glasfarbe und das Cu2+/Cu+-Verhältnis mit zunehmender Sauerstoff-Fugazität, wenn die Temperatur gleich bleibt und die Gasatmosphäre verändert wird. Im Allgemeinen lag das Maximum der von Cu2+-Ionen verursachten Absorptionsbande bei ~ 13000 cm-1 für Andesit-, Alkalibasalt- und Tholeiit-Gläser sowie bei ~ 12500 cm-1 für Haplogranit-Gläser. Für eine Silikatschmelze mit einer gegebenen Zusammensetzung zeigen die Diagramme von log (Cu2+/Cu+) im gegen log fo2 bei jeder Temperatur im Experiment eine Gerade, wobei die Geraden für verschiedene Temperaturen fast parallel zueinander sind mit Steigungen zwischen 0.239 und 0.256. Die Kurven für die niedrigsten und höchsten Temperaturen liegen am höchsten beziehungsweise am niedrigsten. Bei einer gegebenen Temperatur T zeigen die Diagramme von log (Cu2+/Cu+) gegen log fo2 für verschiedene Silikatschmelzen eine ähnliche Abfolge, wobei die Kurven für die granitischen-, dioritischen und basaltischen Schmelzen am höchsten, in der Mitte beziehungsweise unten liegen. ?H für die Oxidation von Cu+ zu Cu2+ wurde für Tholeiit auf -531.3, für Alkali-Basalt auf -392,8, für Andesit auf -386.9, für Haplogranit mit (Na + K)/Al = 0.93 auf -394.3, für Haplogranit mit (Na + K)/Al = 1.42 auf -473.9 und für Haplogranit mit (Na + K)/Al = 1.75 auf -521.9 kJ/mol geschätzt. Die Redox-Verhältnis von Cu2+/Cu+ für granitische und dioritische Magmen, die oft bei Temperaturen von 700 bis 800°C kristallisieren und unter Sauerstoff-Fugazitäten zwischen denen von QFM (Quartz-Fayalit-Magnetit), Ni-NiO und H-M (Hämatit-Magnetit) kristallisieren, wurden abgeschätzt. Die Ergebnisse zeigen ein Überwiegen von Cu2+-Ionen in granitischen und dioritischen Plutons, das heißt, das Verhältnis Cu2+/Cu+ ist immer größer als eins. Basaltische Schmelzen scheinen sich jedoch anders zu verhalten. Sie kristallisieren im Temperaturbereich zwischen 1100 und 1200°C unter Sauerstoff-Fugazitäten zwischen denen von QFM und Ni-NiO Puffern. Bei ihnen überwiegen Cu+- über Cu2+-Ionen in der Schmelze. 3. Löslichkeit von Kupfer in gesteinsbildenden Mineralien Eine Reihe von synthetischen Systemen wurde experimentell (in je zwei Reihen von Experimenten) bei gleich bleibenden Druck- und Temperaturbedingungen (2 kbar und 600-700°C) erforscht, um die Löslichkeit von Kupfer in einigen gewöhnlichen gesteinsbildenden Mineralien (Muskovit, Phlogopit, Orthoklas und Albit) zu untersuchen, die aus hydrothermalen Lösungen im Gleichgewicht mit überschüssigem metallischem Kupfer und Kupferoxid kristallisierten. Proben für die erste Reihe der Experimente wurden vorbereitet, indem Chemikalien entsprechend ~65 wt% Mineralien und ~ 35wt% Cu2O gemischt wurden, während die Proben für die zweite Reihen der Experimente aus Mischungen mit der Zusammensetzung von ~90 wt% Mineralien und ~ 10 wt% hypothetischem Cu-haltigem Mineral bestanden (z. B. für Muskovit: 90 wt% KAl2 [AlSi3O10] [OH]2 + 10 wt% Cu+Al2(AlSi3O10)(OH)2). Die Experimente wurden in cold-seal-Autoklaven bei 600 - 700°C über einen Zeitraum von 15 bis 20 Tagen in Kapseln aus reinem Kupfer durchgeführt. Abhängig von der Zusammensetzung der Ausgangsmischungen wurden verschiedene Kupferlöslichkeiten beobachtet, weil verschiedene Mischungen verschiedene Mineralansammlungen produzierten. Die Löslichkeit von Kupfer (als Gewicht % Cu2O) in Orthoklas zum Beispiel liegt zwischen 0.863 und 0.049 für die Produkte der ersten Reihe von Experimenten (Or1) beziehungsweise zwischen 0.089 und 0.049 für die Produkte der zweiten Reihe von Experimenten (Or2). In Albit, liegt CuAb zwischen 1.175 und 0.630 für Ab1 beziehungsweise bei 0.041 für Ab2. In Muskovit liegt CuMu zwischen 0.965 und 0.634 für Mu1 und bei 0.08 für Mu2. In Phlogopit liegt CuPhl zwischen 1.142 und 0.555 für Phl1. In Quartz liegt CuQtz zwischen 1.336 und 1.173 für Qtz1 beziehungsweise zwischen 0.054 und 0.049 für Qtz2. Die höchsten und niedrigsten Werte der Löslichkeit werden bei 600 beziehungsweise 700°C erreicht. Viele Phasen in den Produkten der beiden Reihen von Experimenten, sind noch nicht identifiziert, zum Teil sie nur in sehr geringern Mengen auftraten. Die Untersuchungen zu diesem Teilprojekt sind daher noch nicht abgeschlossen. Wenn die Proben vollständig charakterisiert sind, können im Prinzip die in diesen Experimenten erhaltenen Ergebnisse mit th

The effect of Tenofovir on renal function among Ugandan adults on long-term antiretroviral therapy: a cross-sectional enrolment analysis.

BACKGROUND: WHO recommends using Tenofovir containing first line antiretroviral therapy (ART), however, Tenofovir has been reported to be associated with renal impairment and dysfunction. We compared renal function among individuals on Tenofovir and those on non-Tenofovir containing ART. METHODS: In a cross-sectional study of HIV-Positive adults on ART, at enrolment into a prospective cohort to study the long-term complications of ART in Uganda, information on biophysical measurements, medical history, clinical examination and renal function tests (RFTs) was collected. Fractional Tubular phosphate reabsorption and estimated glomerular filtration rate (eGFR) were calculated. Mean values of RFTs and proportions with abnormal RFTs were compared between non-Tenofovir containing (Non-TDF) and Tenofovir containing (TDF-ART) ART regimen groups using a general linear regression model. Durations of TDF exposure were also compared. RESULTS: Between July 2013 and October 2014, we enrolled 953 individuals on ART for 6 or more months, median duration on ART was 9.3 years, 385 (40.4 %) were on non-TDF and 568 (59.6 %) on TDF-ART regimens. The proportion of participants with Proteinuria (>30 mg/dl) was higher among the TDF-ART group than the non-TDF ART group. However, in multivariable analysis, there were no significant differences in the adjusted mean differences of eGFR, serum urea, serum creatinine, fractional tubular reabsorption of phosphate and serum phosphates when patients on TDF-ART were compared with those on non-TDF containing ART. There were no differences in renal function even when different durations on Tenofovir were compared. CONCLUSIONS: We found no differences in renal function among patients on Tenofovir and non-Tenofovir containing ART for almost a decade. Tenofovir based first line ART can therefore safely be initiated even in settings without routine renal function monitoring

COHORT PROFILE: The Complications of Long-Term Antiretroviral Therapy study in Uganda (CoLTART), a prospective clinical cohort.

BACKGROUND: Antiretroviral therapy (ART) improves the survival and quality of life of HIV-positive individuals, but the effects of long-term ART use do eventually manifest. The Complications of Long-Term Antiretroviral Therapy cohort study in Uganda (CoLTART) was established to investigate the metabolic and renal complications of long-term ART use among Ugandan adults. We describe the CoLTART study set-up, aims, objectives, study methods, and also report some preliminary cross-sectional study enrolment metabolic and renal complications data analysis results. METHODS: HIV-positive ART naïve and experienced adults (18 years and above) in Uganda were enrolled. Data on demographic, dietary, medical, social economic and behaviour was obtained; and biophysical measurements and a clinical examination were undertaken. We measured: fasting glucose and lipid profiles, renal and liver function tests, full blood counts, immunology, virology and HIV drug resistance testing. Plasma samples were stored for future studies. RESULTS: Between July 2013 and October 2014, we enrolled 1095 individuals, of whom 964 (88.0%) were ART experienced (6 months or more), with a median of 9.4 years (IQR 7.0-9.9) on ART. Overall, 968 (88.4%) were aged 35 years and above, 711 (64.9%) were females, 608 (59.6%) were or had ever been on a Tenofovir ART regimen and 236 (23.1%) on a Protease Inhibitor (PI) regimen. There were no differences in renal dysfunction between patients on Tenofovir and Non-Tenofovir containing ART regimens. Patients on PI regimens had higher total cholesterol, lower high density lipoprotein, higher low density lipoprotein, higher triglycerides, and a high atherogenic index for plasma than the non-PI regimen, p = 0.001 or < 0.001. Patients on Non-PI regimens had higher mean diastolic hypertension than patients on PI regimens, p < 0.001. CONCLUSIONS: Our finding of no differences in renal dysfunction between patients on Tenofovir and those on Non-Tenofovir containing ART regimens means that Tenofovir based first line ART can safely be initiated even in settings without routine renal function monitoring. However, integration of cardiovascular risk assessment, preventive and curative measures against cardiovascular disease are required. The CoLTART cohort is a good platform to investigate the complications of long-term ART use in Uganda

Living-Related Kidney Graft Donors Sociodemographic Characteristics and Recipients Clinical Characteristics in Kenya: A Single Centre Experience Kenyatta National Hospital 2010-2015 Audit

This article provides summary of sociodemographic and clinical characteristics of the kidney transplant donors and recipients from 2010-2015 from Kenyatta national hospital, Nairobi, Kenya, East Africa. Only living-related organ donation is practiced in Kenya. Accelerated kidney transplantation activities picked up in Kenyatta national hospital from the 2010. The duration from 2010-2015 has seen more kidney transplantations undertaken in the hospital than the ones done in the same hospital from 1984 when first transplantation was performed in Kenya to 2009. The data were extracted from manual medical records. There were about 120 kidney transplantations performed during this period but only 113 complete records were traceable. There were 113 medical records for both kidney graft donors and recipients from 2010-2015. Demographic characteristics for donors and recipients captured included age, sex, and donor-recipient relationships. The mean donor age was 32.9

Does respiratory syncytial virus lower respiratory illness in early life cause recurrent wheeze of early childhood and asthma?:Critical review of the evidence and guidance for future studies from a World Health Organization-sponsored meeting

Respiratory syncytial virus (RSV) is a leading cause of lower respiratory tract infection (LRTI) and hospitalization in infants and children globally. Many observational studies have found an association between RSV LRTI in early life and subsequent respiratory morbidity, including recurrent wheeze of early childhood (RWEC) and asthma. Conversely, two randomized placebo-controlled trials of efficacious anti-RSV monoclonal antibodies (mAbs) in heterogenous infant populations found no difference in physician-diagnosed RWEC or asthma by treatment group. If a causal association exists and RSV vaccines and mAbs can prevent a substantial fraction of RWEC/asthma, the full public health value of these interventions would markedly increase. The primary alternative interpretation of the observational data is that RSV LRTI in early life is a marker of an underlying predisposition for the development of RWEC and asthma. If this is the case, RSV vaccines and mAbs would not necessarily be expected to impact these outcomes. To evaluate whether the available evidence supports a causal association between RSV LRTI and RWEC/asthma and to provide guidance for future studies, the World Health Organization convened a meeting of subject matter experts on February 12-13, 2019 in Geneva, Switzerland. After discussing relevant background information and reviewing the current epidemiologic evidence, the group determined that: (i) the evidence is inconclusive in establishing a causal association between RSV LRTI and RWEC/asthma, (ii) the evidence does not establish that RSV mAbs (and, by extension, future vaccines) will have a substantial effect on these outcomes and (iii) regardless of the association with long-term childhood respiratory morbidity, severe acute RSV disease in young children poses a substantial public health burden and should continue to be the primary consideration for policy-setting bodies deliberating on RSV vaccine and mAb recommendations. Nonetheless, the group recognized the public health importance of resolving this question and suggested good practice guidelines for future studies

Characteristics of HIV-1 Serodiscordant Couples Enrolled in a Clinical Trial of Antiretroviral Pre-Exposure Prophylaxis for HIV-1 Prevention

Stable heterosexual HIV-1 serodiscordant couples in Africa have high HIV-1 transmission rates and are a critical population for evaluation of new HIV-1 prevention strategies. The Partners PrEP Study is a randomized, double-blind, placebo-controlled trial of tenofovir and emtricitabine-tenofovir pre-exposure prophylaxis to decrease HIV-1 acquisition within heterosexual HIV-1 serodiscordant couples. We describe the trial design and characteristics of the study cohort.HIV-1 serodiscordant couples, in which the HIV-1 infected partner did not meet national guidelines for initiation of antiretroviral therapy, were enrolled at 9 research sites in Kenya and Uganda. The HIV-1 susceptible partner was randomized to daily oral tenofovir, emtricitabine-tenofovir, or matching placebo with monthly follow-up for 24-36 months.From July 2008 to November 2010, 7920 HIV-1 serodiscordant couples were screened and 4758 enrolled. For 62% (2966/4758) of enrolled couples, the HIV-1 susceptible partner was male. Median age was 33 years for HIV-1 susceptible and HIV-1 infected partners [IQR (28-40) and (26-39) respectively]. Most couples (98%) were married, with a median duration of partnership of 7.0 years (IQR 3.0-14.0) and recent knowledge of their serodiscordant status [median 0.4 years (IQR 0.1-2.0)]. During the month prior to enrollment, couples reported a median of 4 sex acts (IQR 2-8); 27% reported unprotected sex and 14% of male and 1% of female HIV-1 susceptible partners reported sex with outside partners. Among HIV-1 infected partners, the median plasma HIV-1 level was 3.94 log(10) copies/mL (IQR 3.31-4.53) and median CD4 count was 496 cells/µL (IQR 375-662); the majority (64%) had WHO stage 1 HIV-1 disease.Couples at high risk of HIV-1 transmission were rapidly recruited into the Partners PrEP Study, the largest efficacy trial of oral PrEP. (ClinicalTrials.gov NCT00557245)

Regional Differences in Prevalence of HIV-1 Discordance in Africa and Enrollment of HIV-1 Discordant Couples into an HIV-1 Prevention Trial

Background: Most HIV-1 transmission in Africa occurs among HIV-1-discordant couples (one partner HIV-1 infected and one uninfected) who are unaware of their discordant HIV-1 serostatus. Given the high HIV-1 incidence among HIV-1 discordant couples and to assess efficacy of interventions for reducing HIV-1 transmission, HIV-1 discordant couples represent a critical target population for HIV-1 prevention interventions and prevention trials. Substantial regional differences exist in HIV-1 prevalence in Africa, but regional differences in HIV-1 discordance among African couples, has not previously been reported. Methodology/Principal Findings: The Partners in Prevention HSV-2/HIV-1 Transmission Trial (“Partners HSV-2 Study”), the first large HIV-1 prevention trial in Africa involving HIV-1 discordant couples, completed enrollment in May 2007. Partners HSV-2 Study recruitment data from 12 sites from East and Southern Africa were used to assess HIV-1 discordance among couples accessing couples HIV-1 counseling and testing, and to correlate with enrollment of HIV-1 discordant couples. HIV-1 discordance at Partners HSV-2 Study sites ranged from 8–31% of couples tested from the community. Across all study sites and, among all couples with one HIV-1 infected partner, almost half (49%) of couples were HIV-1 discordant. Site-specific monthly enrollment of HIV-1 discordant couples into the clinical trial was not directly associated with prevalence of HIV-1 discordance, but was modestly correlated with national HIV-1 counseling and testing rates and access to palliative care/basic health care (r = 0.74, p = 0.09). Conclusions/Significance: HIV-1 discordant couples are a critical target for HIV-1 prevention in Africa. In addition to community prevalence of HIV-1 discordance, national infrastructure for HIV-1 testing and healthcare delivery and effective community outreach strategies impact recruitment of HIV-1 discordant couples into HIV-1 prevention trials

Antiretroviral Drugs Protect Against HIV-1 Infection in Heterosexuals

BackgroundAntiretroviral preexposure prophylaxis is a promising approach for preventing human immunodeficiency virus type 1 (HIV-1) infection in heterosexual populations.MethodsWe conducted a randomized trial of oral antiretroviral therapy for use as preexposure prophylaxis among HIV-1-serodiscordant heterosexual couples from Kenya and Uganda. The HIV-1-seronegative partner in each couple was randomly assigned to one of three study regimens--once-daily tenofovir (TDF), combination tenofovir-emtricitabine (TDF-FTC), or matching placebo--and followed monthly for up to 36 months. At enrollment, the HIV-1-seropositive partners were not eligible for antiretroviral therapy, according to national guidelines. All couples received standard HIV-1 treatment and prevention services.ResultsWe enrolled 4758 couples, of whom 4747 were followed: 1584 randomly assigned to TDF, 1579 to TDF-FTC, and 1584 to placebo. For 62% of the couples followed, the HIV-1-seronegative partner was male. Among HIV-1-seropositive participants, the median CD4 count was 495 cells per cubic millimeter (interquartile range, 375 to 662). A total of 82 HIV-1 infections occurred in seronegative participants during the study, 17 in the TDF group (incidence, 0.65 per 100 person-years), 13 in the TDF-FTC group (incidence, 0.50 per 100 person-years), and 52 in the placebo group (incidence, 1.99 per 100 person-years), indicating a relative reduction of 67% in the incidence of HIV-1 with TDF (95% confidence interval [CI], 44 to 81; P&lt;0.001) and of 75% with TDF-FTC (95% CI, 55 to 87; P&lt;0.001). Protective effects of TDF-FTC and TDF alone against HIV-1 were not significantly different (P=0.23), and both study medications significantly reduced the HIV-1 incidence among both men and women. The rate of serious adverse events was similar across the study groups. Eight participants receiving active treatment were found to have been infected with HIV-1 at baseline, and among these eight, antiretroviral resistance developed in two during the study.ConclusionsOral TDF and TDF-FTC both protect against HIV-1 infection in heterosexual men and women. (Funded by the Bill and Melinda Gates Foundation; Partners PrEP ClinicalTrials.gov number, NCT00557245.)