Uranium in granitic magmas: Part 1. Experimental determination of uranium solubility and fluid-melt partition coefficients in the uranium oxide-haplogranite-H2O-Na2CO3 system at 720–770°C,

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Geochimica et Cosmochimica Acta, Vol. 58, No. I I, pp. 2495-2507, 1994 Copyright 0 1994 Elsevier Science Ltd Printed in the USA. All rights reserved

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Uranium in granitic magmas: Part 1. Experimental determination of uranium solubility and fluid-melt partition coefficients in the uranium oxide-haplogranite-H,0-Na2C03

system at 720-77O”C, 2 kbar

CHANTAL PEIFFERT, MICHEL CUNEY, and CHINH NGUYEN-TRUNG

Centre de Recherche SW la Geologic des Mati&es Premibres MinCrales et Energktiques and GdR CNRS-CREGU 0077, BP 23, 54501 Vandoeuvre lb Nancy, Cedex, France

(Received March 17, 1993; accepted in revised form January 18, 1994)

Abstract-The solubility of uranium was investigated in both carbonated aqueous fluid and granitic melt in equilibrium in the system haplogranite-uranium oxide-H20-Na2C03 (OS-1 molal) at 720-770°C, 2 kbar, and fo, fixed by Ni-NiO, Fe304-Fe203, and CU~O-CuO buffers. As complete solid solution exists between UOz.,,, and UO2.25 (i.e., 75 mol% UOz + 25 mol% UOx), three distinct uranium oxides: UO~Z.Ol~O.Ol ), U0c2.10t~.~2), and W2.25+0.02) were, respectively, obtained at equilibrium, under the three fo, conditions cited above. Thus, the percentage of U( VI) in uranium oxide increased with increasing log f&. The thermal decomposition of Na2C03 to CO2 and Na20 led to the decrease of the sodium carbonate concentration from 0.5-l molal to - 10m2 molal in all aqueous fluids and to the dissolution of Na in the silicate melts. Crystal-free silicate glasses with four agpaitic coefficients, o( = (( Na + K)/ Al) = 1.1, 1.3, 1 S, and 1.7 were obtained.

The uranium solubility in 10m2 m aqueous carbonated fluid (( 8.1 + 0.1) I quench pH I (8.9 + 0.1)) was in the range 1- 17 ppm and increased linearly with increasing fo* according to the expression:

log (U) (ppm) = 0.09 - log fo, (bar) + 1.47.

This equation is valid for the temperature range 720-770°C and 2 kbar. U(lV) carbonate possibly were major species in aqueous solutions under reducing conditions (Ni-

NiO buffer) whereas U( VI) carbonate complexes dominated under higher oxidation conditions ( Fe304- Fe20s, Cu20-CuO buffers).

The uranium content in silicate glasses varied in a large range ( 102-2 X lo5 ppm) and log (U) (ppm) increases linearly with both fa and (Y in the range 1 . l- 1.5 according to the equation

log (U) (ppm) = 0.04 log fo, (bar) + 3.80a - 1.34.

This equation is valid for ( 1) fo ranging from Ni-NiO to Cu20-CuO, and (2) the temperature range 720-770°C at 2 kbar. The effect of fo, on the uranium solubility in silicate melt slightly decreased with increasing (Y from 1.1 to 1.5.

For (Y in the range 1.5-1.7, the effect of both fo and agpaicity index on the uranium solubility was considerably reduced.

The temperature variation in the range 720-77O’C had no significant effect on the uranium solubility in either aqueous fluid or silicate melt.

The partition coefficient ( D”uid’me’t ) of uranium was in the range 10-4~o-10-‘~5 and depended on both fo, and (Y according to the equation

log D fluid/me” = 0.05 log fo, (bar) - 3.78~~ + 2.84.

The validity conditions of this equation are similar to those of the preceding one. Results obtained in the present study could be used to predict the geochemical behaviour of uranium

during magma fractionation and to further understanding of the formation of uranium ore deposits related to partial melting or fractional crystallization of felsic magmas. The genesis of the Kvanefjeld (llimaussaq, Greenland) uranium deposit is discussed.

INTRODUCTION

PARTIAL MELTING AND crystal fractionation represent the most powerful processes leading to a steady enrichment of

anothorite ( CUNEY and FRIEDRICH, 1987), the most felsic members of granitic associations are generally enriched in uranium. Thus, measuring uranium solubility as a function of composition of silicate melt may allow us to predict ura-

lithophile elements such as uranium in the E&h’s lithosphere nium concentration trends in magmas as they differentiate. and more particularly in the upper part of the continental The determination of fluid-melt partition coefficients of ura- crust (ROGERS and ADAMS, 1969; TAYLOR and MCLENNAN, nium is fundamental for the prediction of uranium concen- 1985). Although uranium can be strongly partitioned in a tration in fluids coexisting with granitic magmas. The knowl- large variety of early crystallizing minerals in granitic magmas edge of uranium solubility and fluid-melt partition coefficients such as zircon, apatite, monazite, titanite, uraninite, and ur- is of major importance for the understanding of the distri-

2495

2496 C. Peiffert, M. Cuney, and C. Nguyen-Trung

bution of the major heat producing elements in the Earth and the genesis of uranium deposits resulting from magmatic processes. Several authors have carried out experimental studies using two approaches.

1985) is much higher than that of U(W). In the present study, the equilibrium was attained using three approaches:

1) normal experiments using U( IV) oxide as starting materials, 2) reversal experiments using dissolved or solid U(W) species as

In the first approach, experiments were conducted in water- free systems to study the mechanisms of uranium dissolution in synthetic silicate melts at very high temperature ( 1150- 16OO’C) and atmospheric pressure (CALAS, 1979; FARGES

et al., 1992; SCHREIBER, 1980, 1983; SCHREIBER and AN- DREW& 1980; SCHREIBER and BALAZS, 1982; SCHREI~ER et al., 1981, 1982; J~OMINE and VELDE, 1985). Results obtained from these works indicated that uranium dissolved in the melt under three valence states-IV, V, and VI-and that the propo~ions depend on the imposed Jo _ The effect of the agpaitic coefficient LY = (Na + K)/Al ofaluminosilicate melt and ,fo, on the uranium solubility in aluminosilicate melt was determined by DOMINO? and VELDE ( f 985). These authors have shown that the uranium solubility (4 1.8-67.5 wt’% U308) in aluminosilicate increased with increasing 1y and fo, at 1400°C, i bar.

starting materials, and 3) ex~~ments using a system under~turat~ with uranium.

At equilibrium, all the three a~v~-mentioned types of experiments having the same fluid-melt composition, under identical <, T, fo, conditions, should provide similar partition coefficient (Dflurdime”) of uranium. Moreover, both normal and reversal experiments should give the same results regarding ( I ) the uranium oxide composition, and (2) the uranium solubility in aqueous t&id and silicate melt.

Starting materials used in normal experiments were ( I ) stoichiometric sin&red spheres of U02.~xKI (2 100 pm in diameter}. UOz.ooo were obtained by reduction of natural UOz 120 by a Ti-Zr mixture in vacuum at 9OO*C during 36 h. &OS and UOz(OH)2*Hz0 were also used in reversal experiments: (2) Na2C03 solutions (0.5, 0.8. and 1 .O molal f (Analytical Reagent): (3) dehydrated synthetic gels with four compositions, indicated in Table 1, were made using the method of HAMILTON and HENDERSON ( 1968). Chemicals used were certified NaZC03, K2COX, A]( N03)3 - 9HzO. and (CzHs)$iO, (Analytical Reagents).

In the second approach, fluid-melt partition coefficients ( D"uid'me't) of uranium were determined between synthetic or natural silicate melt and aqueous solutions at 75O”C, 2 kbar, under a Ni-NiO buffer, close to geological conditions. In most cases, starting materials used were synthetic silicate melt and aqueous solutions with variable amounts of HCl ( KEPPLER and WYLLIE, 1990, 1991), HZ0 + CO*, HF (ZHARIKOV et al., 1987; KEPPLER and WYLLIE, 1990, 1991).

(Na, K)Cl, (Na, K)F, Ag&O, (ZHARIKOV et al., 1987; Yu- DINTSEV, 1990). Other experiments were done using natural topaz,-rhyolite melt and NaCl (WEBSTER et al., I989 ). Results obtained by WEBSTER et al. ( 1989) are difficult to consider because final glasses contain zircon which incorporates significant amounts of uranium in its structure. The effect of temperature in the range 750-1000°C and pressure From 2 to 4 kbar on the uranium solubility in haplogranite (0.78 I cy = (Na -i- K)/Al 5 1.08) containing Hz0 was measured by ZHAR~KOV et al. (1987). However, D"uid'me'~ values of uranium reported from above-mentioned studies must be used with caution because of lack of data on the equilib~um state of the system and, in some cases, on the modification of the composition of melt and aqueous fluid after a run, due to fluid-melt interactions.

For severai reversal experiments, three different starting materials were used: ( I ) Na2C03 solution oversaturated with umnyl (VI) and gel, (2) Na2C0, solution and gel doped with uranium as U,O, (OS-2 wt%), and (3) NazCOl solution, gel, and schoepite UOz( OH )> 1 H20.

For normal experiments, samples were prepared using a quadruple capsule technique. About 50 mg of stoichiometric UO,, and about 200 mg of gel were loaded into separate platinum capsules (3.6 mm ID. 4.0 mm OD, 8.0 mm long for UOz, and 25.0 mm long for gel). These two platinum capsules were only crimped. About 100 mg of one of the three assemblages ( Ni-NiO, Fe30a-FezOx, or Cu,O-CuO) and IO0 mg of HtO were loaded in the third platinum capsule (3.6 mm ID, 4.0 mm OD. 25.0 mm long). This capsule was welded shut.

The three platinum capsules con~ning UQ, gel, and oxygen buffer along with about 200 mg of Na2COX solution were loaded into a gold capsule (5.0 mm ID, 5.8 mm OD. 65.0 mm long). The gold capsule assembly was welded shut and loaded in a cold-seal pressure vessel. The end containing the UO-2 capsule was placed in the bottom, i.e., the warmest part of the vessel. The capsule with the gel was placed adjacent to the UOz capsule (Fig. 1). This technique has two major advantages: ( 1) UOz, loaded in excess, represents an inexhaustible source of uranium and thus saturates the system with this element: and (2 ) the separation of UO? and gel before the experiments prevents LJOz particles from entering the silicate melt and aqueous solution, thus preserving pure solid and aqueous phases after the run. Chemical reactions between UOz and silicate melt only occur through aqueous carbonated solutions.

This paper is the first of a series of contributions dealing with the systematic determination of the uranium solubility and the fluid-melt partition coefficient (Dfluid’““) of uranium between haplo~anite and aqueous solution as a function of ligands in aqueous solution, silicate melt composition, temperature, and ,fo, at equiIib~um. Preliminary results have been reported ( PEIFFERT et al., 1992), and the present study

reports comprehensive data concerning the system uranium oxide-haplogranite ( 1.1 _c; cy 1 1.7)-H20-Na2C03 in the temperature range 720-77O”C, 2 kbar, under fo2 conditions fixed by three buffers: Ni-NiO, Fe30,-Fe203 t and Cu,O-CuO.

For reversal experiments, the triple capsule technique was used to prepare samples. Two platinum capsules containing gel doped or not with U( VI) and oxygen buffer along with about 200 mg of Na2C03 solution free or oversaturated with uranium were loaded into a gold capsule. The dimensions of platinum and gold capsules are similar to those cited above.

Pre-run rupture tests of platinum and gold welded capsules were systematically done by placing them overnight in an oven at 120°C. Subsequent weighing checked for possible leaks.

Experimental Procedure

EXPERIMENTAL

Starting Materials and Preparation of Samples

Most experiments (80%) were conducted with a rapid-quench cold- seal pressure vessel similar in design to that used by FRANTZ and POPP ( 1979). All other runs were done in conventional cold-seal pressure vessels. The reaction vessel was externally heated in a hor- izontal electrical furnace. Experiments were done at 2.00 t 0.0 1 kbar and two temperatures: 720 t 15 and 770 C 15°C. A mixture ofwater and soluble oil was used as a pressure medium. Total pressure was measured using a Heist gauge and temperature with calibrated chro- mel-alumel thermocouple.

Earlier works have reported that the solubility of U( VI) in aqueous The temperature gradient in the vessel at 2 kbar in the temperature fluid ( RED’KIN et al., 1989) and silicate melt ( DOM~NB and VELDE, range 720-770°C was determined using two internal chrome&alumel

Partitioning of U between granite melt and aqueous fluids 2491

*” - Capsule

Pt

t

Capsules

C- _ NanCOrr SOLUTION

- GEL

OXYGEN BUFFER

FIG. 1. The quadruple capsule ( I Au, 3 Pt) used for the fluid-melt partitioning experiments.

thermocouples with their ends located 25 mm from each other. In order to duplicate the actual run conditions as closely as possible, the couple was successively inserted in ( I ) a Ni filler rod (80 mm long) which was drilled along its axis to allow the thermocouple to pass through and (2) a dummy charge gold capsule (30 mm long). The latter was placed at the tip of the thermocouple. Results obtained indicated a gradient of 2°C for each IO mm. The temperature gradient for a gold capsule 65 mm long was estimated to be 14°C across the charge.

Run durations were in the range 2-4 weeks. At the end of each run, the rapid-quench cold-seal pressure vessel was tipped and brought to a vertical position so that the capsule slid from the hot end to the cold end of the vessel under constant pressure (2 kbar). Estimated quenching time was 5 sec. This value was close to the quenching time (4 set) of a similar gold capsule (70 mm long) containing three empty small platinum capsules (20 mm long) heated to 770°C I bar, and plunged into Hz0 at ambient conditions. The conventional cold-seal pressurized vessel was disconnected from the pressure line and was withdrawn from the furnace. Pressurized air and water were used to quench the vessel. 3 minutes were necessary to bring back the vessel to room temperature and approximately 50 bar. Analysis of run products yielded similar results for both types of vessel.

Analysis of Run Products and Uncertainties Evaluation

After removal from the vessel, the gold capsule was opened. Aqueous solution was removed using polyethylene transfer pipets. Uranium oxide, silicate glass, and buffer assemblage were extracted from the three platinum capsules.

Analysis of aqueous fluids

Quench pH was rapidly measured (uncertainty f0. I pH unit) at room temperature using a microcombination glass pH probe (Mi- croelectrodes MI-4 IO). The aqueous sample was then rapidly and carefully filtered using an ultrafiltration membrane (Millipore PTGC, diameter I3 mm). The filtered solid consists of silicate glasses and trace amounts of uranium and aluminium. The filtration of aqueous solution was necessary to prevent all risks of accidental presence of uranium oxide particles from U-bearing capsule.

Trace amounts of dissolved uranium were determined by visible absorption spectrophotometry using Bromo-PADAP as chromogenic reagent with a relative uncertainty within 10%. The detection limit is 20 ng of uranium.

Several runs were made to determine whether dissolved uranium precipitated during the quenching. Two techniques were used.

The first technique employed the same starting materials and the loading system as in normal experiments. After each run, the gold capsule was punctured, the aqueous fluid was extracted and the platinum capsule containing uranium oxide was carefully removed. Then, the two platinum capsules containing silicate glasses and oxygen buffer and the gold capsule were boiled in I m HCI to dissolve possible uranium precipitates. The total uranium content determined in the filtered solid and in I m HCI obtained after boiling the capsules was always below 10% of the uranium content measured in the filtered solution. In some experiments, total uranium was also analysed in non filtered aqueous fluid mixed with the above cited I m HCI solvent. Results of this measurement agree fairly well with those obtained from filtered aqueous fluids. The difference between the two sets of results was below 10%.

In the second technique, an additional platinum capsule (3.6 mm ID, 4.0 mm OD, 20.0 mm long) perforated with many holes less than 0.2 mm diameter and loaded with purified quartz grains approximately IO pm size was placed in a gold capsule with three other reduced size platinum capsules containing UOZ, silicate glass, and buffer. On quenching, the aqueous fluid was trapped in interstices ofquartz grains inside the perforated platinum capsule. The perforated platinum capsule was extracted ffom the gold capsule and was rapidly weighed. The capsule was then dried in an oven at I 10°C overnight. This drying condition was adopted since experiments at temperature up to 200°C indicated that water extraction from quartz grains was total after 2 h at 110°C. After drying, the capsule was reweighed. The difference is the weight of the aqueous fluid. The platinum capsule was then carefully opened. Both quartz grains and the platinum cap sule were boiled in I m HNOx and the analysis of this acid solution provides the total uranium in the aqueous fluid. In the last technique, the amount of uranium is up to 10% higher than that determined in filtered solutions (Table 3). The uranium excess determined in this case is in the same order of magnitude as the measurement uncertainties. For this reason, the precipitation of uranium during quenching is considered negligible, and the amount of uranium measured at ambient conditions represents effectively the uranium solubility in aqueous fluid at high P, T conditions.

The molalities of Na, K, and Si were determined by atomic absorption spectrometry (relative uncertainty = 5%).

Trace amounts of aluminium were below the detection limit (30 ppb) of atomic absorption spectrometry.

Total aqueous carbonate was determined by ion chromatography (detection limit: 0. I ppm).

Analysis of oxygen buffers, uranium oxides, and silicate glasses

The buffers were checked by X-ray diffractometry to determine whether any of the phases had been exhausted during the run.

It is well known that a complete solid solution exists between U02,w and UOZ.zs (i.e., 75 mol% UOZ + 25 mol% U03). The composition of the solid solution UO ,Z+xj after each normal experiment was determined as follows: X-ray diffractometry was first employed to determine the unit cell parameter u, (A) from the position of the (620) band of cubic UO (2+x)(O I x 5 0.25). Values of a, (A) obtained were then used to calculate the fraction x of U03 in the solid solution UQ(?+*) based on the linear correlation between a, (A) and x (0.00 I x 5 0.25) (CATHELINEAU et al., 1982) according to the Eqn. I:

a, (A) = -0,116.x + 5.471. (1)

For reversal experiments, the amount of uranium oxide precipitation obtained after each run was not sufficient to be analysed with accuracy.

Careful observations of run products using polarizing microscope, electron microprobe, and scanning electron microscope did not reveal the presence of any additional solid compound containing uranium and silicate glass constituents (Al, Si, Na, K) after the run.

Five elements, Si, Al, Na, K, and U of silicate glasses were analysed by electron microprobe (Cameca SX 50). Low uranium concentra-


tions were calibrated against a NBS standard (46 1.5 ppm). The determination of four major elements was done at the acceleration voltage of 15 KeV, enlarged analytical spot (diameter = 20 pm), low beam current ( 10 nA), and a short integration period ( IO s) in order to minimize alkali loss. Uranium was analysed with a beam current in the range 30-60 nA and a relative long integration period (30-60 set). The detection limit for uranium was 120 ppm.

For glass samples containing uranium less than 1000 ppm, both electron microprobe and fission track methods were used to analyse the uranium content. The measurement technique for the latter is as follows: fission tracks of 23sU fragments, from irradiation by thermal neutrons, are recorded on a thin kapton film (thickness = 0.5 mm) placed upon the polished surface ofthe sample. Submicroscopic fission tracks on kapton are enlarged etching in a NaCI, NaClO solution. The uranium concentration is determined by comparison of the number of revealed fission tracks per surface-area unit of the kapton between the sample and NBS glass standards. Electron microprobe and fission track methods yielded similar results within 7% for low uranium content ( - 150 ppm) and 4% for uranium concentration in the range 340-540 ppm.

In order to check the homogeneity of the silicate glass and its uranium content, three glass chips were taken at about 5, 10, and 20 mm from the U-bearing capsule (see Fig. 1) and were systematically analysed. Spot analyses were done from one edge to the another through the center of each sample. Results indicated that, within a given glass sample, concentrations of Si, Al, Na, K, and U fluctuated within 3%, but this fluctuation appeared to be random. For uranium, a small concentration gradient up to 3% was observed between the sample located at 5 mm and two other samples at 10 and 20 mm from the U-bearing capsule. This concentration gradient, valid for the large a range 1. I - 1.7, was at most in the same order as measurements relative uncertainties for uranium (3-6% ) and was thus considered as negligible in the present work.

For four runs, Na and K contents in glass were determined by both electron microprobe on glass samples and global analysis of glass using atomic absorption spectrometry. The good agreement within 4% between results obtained from two methods (Table 2) attested the reliability and the accuracy of analysis by electron microprobe.

Total Hz0 content in silicate glass was estimated as the complement to 100 wt% of the electron microprobe analysis. For four runs, total Hz0 content was determined using the Karl Fischer method. The principle of the method is as follows: ( 1) water vapor from the heated glass sample ( 1250°C) is collected in a titration cell; (2) Hz0 is then titrated potentiometrically according to the redox reaction:

I2 + SO2 + 2HzO = 21- + 2H+ + HzS04. (2)

The agreement between these two methods was within 10%. Total dissolved COZ in silicate glass was determined using pulse

coulometry. Total CO* gas, extracted from a glass sample at 1100°C is transported by a neutral gas to a titration cell and reacts with Ba(ClO.,)z solution at pH = 9. The pH modification resulted from

- 30000

: _m z 20000

E & = 10000

0 IJ 10 20 30 40

0 Fe304Fe203

Duration (days)

FIG. 2. Kinetics of uranium dissolution in silicate glass in the system uranium oxide-haplogranite-HzO-NazCOj at 720-770°C and 2 kbar.

5 ,

o- (a)

-1 I 8 -20 -15 -10 -5 0

log f02 (bar)

FIG. 3. (a) Correlation between uranium solubility (U (ppm)) in carbonated fluid and log fo2 (bar). (b) Correlation between uranium solubility (U ( ppm)) in silicate granitic melt and log fs for agpaitic coefficient 01 = 1.1, 1.3, 1.5, 1.7. (square: Ni-NiO, circle: Fe,O,-Fe,O,; triangle: CuZO-CuO, +Reversal experiments).

the precipitation of BaCO, is determined by pulse coulometry. The detection limit is 50 ppm of CO*.

RESULTS

Table 2 shows analytical results obtained in silicate melt. Weight percent of metal oxides (metal = U, Na, K, Al, Si) displayed in Table 2 represent mean values of numerous electron microprobe measurements and its variation range.

The chemical composition of aqueous fluid after a run as well as the partition coefficient (Dfluid’me”) of uranium are reported in Table 3.

Equilibrium Conditions of the System

The dissolution kinetics of uranium in the silicate melt have been measured under three fo, conditions fixed in the experiments. Results obtained indicated that a minimum run duration of two weeks was necessary for the system to attain equilibrium (Fig. 2 ). Moreover, the present study took into account only experiments which fulfill the four following additional conditions:

1)

2)

3)

4)

Uranium solubility measurements in both aqueous fluid and silicate melt must be reproducible. All experiments have been repeated at least three times (Tables 2 and 3; Fig. 3). The distribution of dissolved uranium in silicate glasses must be homogeneous. This characteristic was controlled by the distribution of fission tracks for uranium concentrations below 1000 ppm and by similar analytical results obtained on various points of the same sample by electron microprobe for higher concentrations. Uranium solubility in both fluid and melt obtained from normal and reversal experiments must be similar or very close together (Tables 2 and 3; Fig. 3 ) . The uranium oxides obtained after the runs under the same redox condition must have the same composition.


These conditions are considered as four reliable experimental proofs indicating that the system is in equilibrium. Figures 3,5, and 6 display only values obtained at equilibrium (run duration r 15 days).

The Composition of Uranium Oxides

Results obtained from quantitative analysis of uranium solid phases using X-ray diffraction patterns indicated that only well-crystallized cubic uranium oxides in equilibrium with fluid and melt were formed after each run. The three values of cell parameters a, determined were: (5.470 f 0.02) (5.459 + 0.02), and (5.442 + 0.02) A corresponding, respectively, to the three fo, values fixed by the Ni-NiO, FesO.,- FeZ03 and CuzO-CuO buffers (Fig. 4). The plot of the values of a, (A) in the linear Eqn. 1 led to three compositions:

WZ.OM.OI ); WZJO~O.OZ~; and U0~~0.02). Figure 4 shows that two phases U02.01 and U02.10 obtained under reduced conditions ( Ni-NiO and Fes04-Fe209 ) agree fairly well with UO2.m and UO2.m + U409 predicted by calculation using thermodynamic data ( GRE~NVOLD et al., 1970; MAGLIC and HERAK, 1970; FUGER, 1971; MACLEOD, 1972; ROBIE et al., 1979). On the other hand, a discrepancy between experimental measurements and theoretical prediction was observed at the most oxidizing conditions. Under fs fixed by the Cu20-CuO buffer, cubic U02.25 is precipitated whereas calculations predicted the formation of orthorhombic U308.

The Composition of Aqueous Fluids

After the experiment, the sodium carbonate concentration decreased from 0.5-l molal to 10m2 molal in all aqueous fluids, resulting from the thermal decomposition of Na2COs :

Na2C03 (aqueous) = NazO (melt) + CO2 (gas). (3)

Na20 enters the silicate melt by affinity. The transformation of a major part of the carbonate to carbon dioxide decreased the pH of the solution from the initial value ( 12.1 + 0.1) to quench values in the range 8.1-8.9.

The potassium concentration was in the range 113-153 ppm. The solubility of aluminum could be estimated as lower than 30 ppb. Si02 concentrations, determined in some runs, were in the range 600- 1000 ppm. These low values resulted from precipitation, during quenching, of pure Si02 on the

0132 w-

x

091 -

0 Fe3OCFe203

w-l -20 -15 -10 -5 0

log f02 (bar)

FIG. 4. Correlation between x of uranium oxide (UOC2+,J and log fo, (bar).

Table 1 Composition of starting materials (aqueous solutions and gels)

gel compositions

wt%

SD2

A1203

K20

Na20

startmg s01ut10ns

-@ml/ kg H20)

Gl

82.5

13,l

4,4

O,O Sl

1 m

G2 G3 G4

78,4 80.0 76.9

12,5 12,a 12,3

4,2 4,3 4,l

4,9 3.0 659 52 S-3 S4

0.8 m 0.5 m 0.1 m

surface of silicate glass, revealed by scanning electron microscope. No U-Si solid compound was observed.

The uranium concentration in the carbonated aqueous fluid varied in the range I- 17 ppm. The logarithm of its concentration increased linearly with increasing log fo, (Table 3; Fig. 3a):

log (U) (ppm) = 0.09 -log fo, (bar) + 1.47. (4)

Variations of the silicate glass composition and the temperature in the range 720-770°C appear to have no significant effect on the uranium solubility in the carbonated aqueous fluid.

Characteristics and Composition of Silicate Glasses

Yellow color and strong UV fluorescence characterized glasses at equilibrium under Fe30.,-Fe203 and Cu20-CuO buffers. Under the Ni-NiO buffer, the glasses were colorless. Numerous two phase (aqueous carbonated solution, vapour) and some three phase (solid, aqueous carbonated solution, vapour) fluid inclusions, between 5 and 80 pm size, were trapped inside silicate glasses, probably during the quenching. The distribution density of the inclusions has been estimated from scanning electron microscope images. However, fluid inclusions represented only 0.2 wt% H20, whereas water content was up to 13 wt% of total composition of silicate glasses (see results below).

Silicate glasses with agpaitic coefficients (11 between 1.1 and 1.7 were obtained by varying the amount of Na20 in the starting gel and the concentration of Na2C03 in the starting solution (Tables 1 and 2). An increase of the sodium content in all silicate glasses compared to the starting gel compositions resulted from the incorporation in the melt of Na20 produced from the thermal decomposition of Na2C0, as discussed pre- viously. Relative concentrations of other major constituents (Si, Al, K) of glasses remain practically unchanged.

Hz0 contents in silicate glasses measured by the Karl Fischer method were found to be 10.15, 11.98, and 9.10 w-t% with relative uncertainty + 0.05 wt% in runs 2-5, 2-24, and 3- 18, respectively. These values are similar to the HZ0 contents estimated from the complement to 100 wt% ofthe electron microprobe analysis (respectively: 10.62, 11.92, 9.18 wt%; Table 2).

A concentration of 0.11 + 0.0 1 wt% CO2 was obtained for (Y = 1.5 (runs 2-5 and 2-24). This value appears to be in- dependant of fo,.

Uranium contents of silicate melts varied in a large range 1.43 X 102-3.37 X 10s ppm U. Increasing (Y from 1.1 to 1.5 and increasing fo2 values led to a linear increase of uranium solubility in the silicate melt of several orders of magnitude (Table 2; Fig. 3b). However, the effect of fo, on the uranium


Table 2 . Chemical composition of silicate glass after run.

RUIl

l-l CA.

days Nature F’

nb. G+S mg

15 G4+s2 180

T logfO2 Si02 Al203 KZO Na20 uo2 H20 K/(Na+K) (Na+K)/AI

(“C) (bar) WI % wt % wt % wt % wt % wt 9.

720 -15.6 62.4+0.2 10.2ztO.l 3.6fO.l 8.lf 0.1

1-2 R.Q. 15 idem 175 770 -15.0 62.5i0.3

1-3 R.Q. 21 idem 195 770 -15.0 62.5f0.2

l-4 R.Q. 15 idem 185 770 -103 61.9i0.4

1-5 CA. 15 idem 177 770 -103 61.4k0.3

1-6 R.Q. 21 idem 169 720 -10.9 62.3f03

1-7 R.Q. 15 idem 189 770 -4 .o 61.7k0.4

1-8 R.Q. 15 idem 199 770 -4.0 61.7fO.4

1-9 R.Q. 21 idem 156 770 -4.0 61.8+0.2

l-10 R.Q. us 15 idem 214 770 -15.0 a.1+0.3

10.ao.2

lO.OiO.2

lO.lf0.2

10.4iO.l

10.2kO.l

lO.lf0.2

10.2f0.2

10.2f0.2

1O.Om.l

3.7kO.l

3.5*0.1

3.5*0.1

3.RO.l

3.5fO.l

3.4iO.l

3.5fO.l

3.5t0.1

3.6?rO 1

8.liQ.l

8.OM.l

8.2fo.l

83tio.l

83iO.l

8.Otito.l

8.3kOo.l

8.3M.l

7.9ti.l

2.8 * 0.1

3.OM.2

3.liO.l

3.2i0.2

3.2iO.l

3.1HLl

3.3kO.l

3.4ro.l

3.4+0.1

0.45+O.Ob

12.92

12.62

12.85

13.09

12.97

12.62

13.53

13.02

12.81

9.97

0.23*0.01

0.23kO.01

0.22kO.01

0.22m.01

0.23jLO.01

0.22iO.01

0.22iO.01

0.22io.01

0.22ko.01

0.23f0.01

1.6H.05

1.7Mo.05

1.71M.05

1.71f0.05

1.7OiO.04

1.7Oio.05

1 h8kO.05

1.7BO.06

1.7010.06

1.7Oko.04

1.08ti.02

0.97M.06

1.04kO.04

0.92_mO4

0.97kOo.06

9.59 0.24t0.01 1.61iO.04

9.63 0.24iO.01 1.6ofo.04

936 0.25kO.01 1.46kO.03

9.58 0.24m.01 1.52#M4

10.62 0.24kO.01 1.5ao.03

0.98M.05

0.91m.05

0.95m.06

1.25kO.06 1.31 aoh

1.46kO.06

9.20 0.26i0.01 1.49io.04

13.39 0.25m.01 1.59m.04

12.95 0.25m.01 1.47m.04

11.12 0.23iO.01 1.63f0.04

12.25 0.23f0.01 1.5Oi0.03

9.12 0.24f0.01 1.52io.03

7.47m.06 8.84 0.24mto.01 1.52m.04

1.45+0.07 12.05 0.24f0.01 1.54f0.03

1.51mo.04 7.18 0.22LtO.01 1.57io.03

1.49f0.03 8.04 0.2YO.01 1.5OiO.025

1.50sl.02 8.75 0.23kO.01 1.51f0.03

7.33m.05 12.35 0.25m.01 1.4910.03

1 S6m.05 11.70 0.24m.01 I .52m.03

2.76f0.06 1135 0.25kO.01 1.55f0.04

2.4Otio.06 11.24 0.24+0.01 1.55io.05

2.10~0.06 11 .a 0.25iO.01 1.5ao.04

2.lYf13.07 12.07 0.25kO.01 1.56iO.04

2.19~.06 11.36 0.24f0.01 1 s4kO.04

2.23tiO.04 11.92 0.25+0.01 1.52ko.04

2.21kO.03 11.79 0.25iO.01 1.51+0.03

2.73m.04 12.16 0.2510.01 1.55m.04

2.18kO.04 10.92 0.24f0.01 1.51f0.03

2.Olm.04 11.45 0.23iO.01 1.48iO.03

2.41m.04 10.79 0.24m.oi 1.59m.04

0.45ffl.05 10.01 0.M0.01 1.59io.05

0.096ffl.01

0.11fo.01

0.12?0.01

9.97 0.32io.01 132io.034

10.55 0.3~0.01 131f0.03

10.70 0.31f0.01 1.29+0.03

0.12ffl.01

0.12?0.01

0.09m.01

0.7,3m.o1

0.16M.01

0.15+0.01

0.16iO.01

0 155m.01

0.16?0.01

0.14m.01

0. I 7m.01

033iO.02

10.03 0.31f0.01 132ko.033

10.24 0.31f0.01 13ofo.03

10.49 032m.01 1.32m.02

10.28 0.30m.01 1 .Z?rn.OZ

10.41 0.32zJLo.01 1.320.03

9.91 0.31*0.01 1.32io.03

9.77 0.30?0.01 131iO.02

9.91 0.32Tko.01 132ko.03

10.12 0.32io.01 132ko.03

10.11 0.3om.01 I .3om.o3

11.22 0.26m.01 3.35mo.03

7.74 0.3OLto.01 136iO.03

10.7fO.l

10.5iO.l

10.8fO.l

10.4m.2

10.3fO.l

10.6kO.l

1o.sm.f

77.0m.1

10.5?10.1

1o.n~o.1

10.3+0.1

70.5m.1

10.4fO.l

11 .lfO.l

10.9+_0.1

10.8kO.l

10.8M.I

ll.om.1

10.25?0.1

10.7~0.1

10.4f0.l

10.3fO.l

10.5*0.1

1O.O.M). 1 1o.Yko.1

10.6m.7

10.9LtO.l

ll.lfflo.l

10.8m.l

9.2fO.l

10.MO.l

10.5fO.l

10.4fO.l

10.65*0.1

10.7iO.l

i0.4m.05

70.7m.1

10.4kO.l

1 O.hfO.1

10.7kO.l

10.6fO.l

10.6fO.l

10.5m.2

i0.9m.l

10.9iO.l

3.7iO.l

3.7f0.01

3.6kO.l

3.6M.05

3.5to.05

(3.48)

3.7kO.04

3.8rn.7

.X8-m.7

3&O. I x4+0.1

3.5kO.05

(3.49)

3.5m.7

3.6kO.04

3.6tO.l

3.5M0.05

3.4MO.l

3.610.1

3.8m.l

3.7fO.l

3 7to.1

3.7fO 1

3.7m 1

3.55+0.1

.Mko I 3.8~01

3.7M.l

3.7fO.l

3.6m,i

3.8rn.l

3.2ko.05

4.lfO.l

4.OkO.l

3.Yko.05

(3.82)

4.MO.l

3.95kO.04

4.03mo.03

3.8m.7

4.ofO.l

4.ofO.l

3.eo.05

4.1ctO.l

4.1Lto.05

3.84M.03

3.5m.01

4.1kO.05

8.OM.l

7.8ffl.l

7.2M.l

7.3m.1

7.2LQ.l

(7.03)

7.lkO.l

7.6rn.l

74m7

8.OSfO.l

7.Mhl

7.2iO.l

(7.06)

7.45m.7

7.4IkO.l

8.3fi.l

7.6f0.05

7.6fo.l

7.4m.i

7.7M.l

7.2ti.l

7.hf0.1

7.2flo.l

7.7.5+0.1

7.5ro.l

7 2to.1

7.45kO 1

7.5m.07

7.6iOo.l

7.7m.1

8.Orn.l

7.6fo.l

5.8M.l

5.7kO.l

5.6fo.l

(5.58)

5.9fl.l

5.9kO.l

5.7M.l

5.8M.05

5.7M.l

5.Yko.05

5.Yrn.l

5.8M.l

5.81fO.l

5.8Orn.l

6.65rn.05

6.3kO.04

2-1 R.Q. 6 W+S3 163 720 -15.6 67.OiO.2

2-2 R.Q. 6 G4+s2 163 770 -15.0 67.4kO.2

2-3 R.Q. 15 G4+S3 182 770 -15.0 67.9f0.3

2-4 CA. R- 15 G4+S2 196 720 -15.6 68.2m.4

2-5 R.Q. 21 G4+S3 179 720 -15.6 67.4f0.2

2-6 R.Q.

2-7 R.Q. R*

2-8 R.Q. R”

2-9 R.Q.

2-10 R.Q.

2-11 R.Q.

30

15

15

6

G4+s2 196 720 -15.6 68.4f0.4

G4+S3 188 720 -15.6 63.910.4

G4+S3 177 720 -15.6 63.93.2

G3+S3 164 770 -10.3 65.5fO.3

C4+S2 199 720 -10.9 64.6kO.3

G4+S3 195 770 -10.3 68.4tO.2 15

2-12 C.A. R-

2-13 R.Q.

2-14 R.Q.

2-15 C.A.

2-16 R.Q.

2-17 R.Q. R’

2-18 R.Q. R”

2-19 R.Q.

2-20 R.Q.

2-21 R.Q.

2-22 CA.

2-23 R.Q.

2-24 R.Q.

2-25 CA.

2-26 R.Q. R-

2-27 R.Q.

2-28 R.Q. R*

2-29 R.Q. R”

2-30 R.Q. us

15

21

30

30

30

15

15

G4+s2 187 720 -10.9 68.2m.2

G4+S3 188 720 -10.9 65.OfO.3

G4+S3 168 770 -10.3 68.3f0.4

G4+S2 169 720 -10.9 68.5k0.3

G4+S3 153 720 -10.9 67.9fO.4

G4+53 187 720 -10.9 64.3mo.4

a+s3 156 720 -10.9 64.25m.3

G3+S3 174 770 -4.0 64.A0.3

G4+S2 199 720 -4.3 64.3co.3

G4+S3 194 720 -4.3 64.Ym.s

G4+S2 195 720 -4.3 643iro.2

G4+S3 197 720 -4.3 h5.2k0.2

G4+S3 183 770 -4.0 64.7?0.4

G4+S2 188 720 -4.3 63.9m.3

G4+s3 178 720 -4.3 63.9M.3

G4+s3 196 720 -4.3 64.1+0.3

G4+S3 199 720 -4.3 64.2M.3

G4+S3 197 720 -4.3 64.2m.3

idem 261 770 -4.0 69.520.3

6

15

15

21

30

30

30

37

15

15

15

31 R.Q. 15 G3+S3 155 770 -15.0 69.4f0.3

32 R.Q. 15 G3+s2 178 720 -15.6 69.1f0.3

33 R.Q. 21 W+S3 166 770 -15.0 69.4f0.4

34 R.Q. 30 Gl+Sl 156 770 -15.0 69.3i0.4

35 R.Q. 30 w+s2 142 720 -15.6 69.1k0.4

3-6 R.Q. R’ 15 G3+S3 123 770 -15.0 69.3m.5

3-7 R.Q. R- 15 G3+S2 145 770 -15.0 69.3_W.4

38 R.Q. 15 G3+S3 136 720 -10.9 69.3+0.3

39 C.A. 15 G3+S2 133 770 -10.3 69.45tO.3

310 R.Q. 21 G3+S3 122 770 -10.3 69.5m.3

311 R.Q. 30 Gl+Sl 133 770 -10.3 69.4k0.3

312 R.Q. 30 G3+s2 152 720 -10.9 69.3iO.2

3-13 R.Q. R* 15 c3+s3 123 770 -10.3 69.6mo.3

3-14 R.Q. R” 15 G3+S2 144 770 -10.3 67.5m.3

315 R.Q. 15 G3+S3 175 770 -4.0 70.6*03

316 CA. 15 G3+s2 164 720 -4.3 69.3f0.2 ll.lfO.l 3.3fO.l 6.9kO.04 0.35kO.02 9.08 0.24f0.01 135iO.03


Run

Table 2. (Continued)

days Nature gel T log fo2 SiO2 Al203 K20 Na20 uoz H20 K/Qlla+K) W+fO/AI

nb. G+S mg (‘cl (bar) wt% wt% wt% wt % wt % wt% (m&l) ( m&l )

3-17 R.Q. 21 G3+53 136

3-18 R.Q. 30 c1+s1 115

3-19 R.Q. 30 G3+S2 166

3-25 R.Q. R' 15 G3+s3 184

3-21 R.Q. R"' 15 G3+S2 1.59

4-l R.Q.

R.Q.

4-2 R.Q.

4-3 R.Q.

4-4 R.Q.

4-5 R.Q.

4-6 R.Q.

4-7 R.Q.

4-8 R.Q.

4-9 R.Q.

4-10 R.Q.

4-11 CA.

4-12 R.Q.

15 Gl+Sl 166

21 Gl+S1 186

21 G2+S4 1%

30 Gl+St 163

15 Gl+Sl 156

21 Gl+St 189

21 c2iS4 IS6

30 Gl+Sl 145

15 Gl+Sl 166

21 cl+% 159

21 G2+S4 158

30 G1+S1 175

770 -4.0

770 -4.0

720 -4.3

770 -4.0

770 -4.0

770 -15.0

770 -15.0

770 -15.0

770 -15.0

770 -10.3

770 -10.3

770 -10.3

770 -10.3

770 -4.0

770 -4.0

770 -4.0

770 -4.0

69.OzkO.2 lmto.l

70.2iO.2

68.6k0.4

68.MJ.2

63.7ia.2

1 D.MO.1

11.1+0.1

20.8_?0.2

ll.lM.7

71 .Oto.2

71.3io.3

72.cko.3

71.6M.4

72.4SLtO.S

72.4+0.3

71,1*03

72.3%x?

71.4*0.5

72.M0.5

71.7*0.3

72.320.3

11.4fO.l

11.3ztO.l

10.9M.l

10.95*0.1

10.8*0.1

10.8S.1

11.4fU.l

ll.W.1

ll.liO.1

10.5*0.1

10.9&0.1

10&O.?

3.6kO.l

(3.60)

3.45fO.l

4.ohO.l

3.4ztO.04

3.5M.03

4.4LtO.l

4.3ztO.05

4.3fo.l

4.lfO.l

4.2S.l

4 “310.04

4.4M.I

4.lW?4

4.20.03

4.2fiO.2

4.ei&O.l

4.1*il.o5

6.5x1.1

(6.47)

6.2?.&1

6.4M.I

6.3M.05

6.4.5ti.05

5.lfO.05

4.9ti.l

4SfOI

4.71ro.l

4.2zt0.0s

4.32L+zn.o5

4.75S.05

4.8ctO.05

4.6f0.M

4.EO.05

4..szto.o5

4.SSti.05

0.34M.M 9.53 0.27B.01 1 X&O.03

0.34kO.02

0335ItO.02

0.3.3B.02

0.36H.02

9.18

9.62

20.56

9.8s

0.27~0.01 1.32S.03

0.2~0.01 1.335~.03

0.26iO.01 1.3OLO.02

0.26iO.M 2.295iO.02

0.014M.001

lO.0133)

0.016~.~~

[0.01671

0.015Hl.001

[O.O167l

~).~14~.~1

10.01421

0.0.34?0.001

IO.03521

0.036fi1.001

JO.0346 I

0.034sxIO1

IO.03291

O.O~~.~~

f0.03151

0.057fO.001

10.05791

0.054M.001

10.05551

O.O~~.~l

iO.0526)

0.059m?O1

8.05 0.3&0.01 1.15fO.02

8.19 0.37~0.01 1 .tzifM2

8.24 0.39Sl.01 1 .llfO.M

8.69 0.37&0.01 1.11*0.03

8.35 0.39kO.01 1.06OkO.024

8.25

8.41

7.62

8.57

9.17

8.97

8.24

0.3%0.01 1 .o(Ho.o2

0.37*0.01 1 .li?iO.O2

035kO.m 1.11*0.02

0.37*0.01 1.09ko.02

0.4Ofo.01 I .09ko.02

0.37+0.01 1.07ti.M

0.37*0.01 l.mtO.02

IO.0574 1

G : initial gel ; S : initial aqueous solution. Compositions of gels and initial aqueous solutions are in table 1.

CA. : experiments using conven!ional autoclaves

R.O. : experiments using rapid quench cold-seal pressure vessels

gel (mg) : initial gel in milligrams

U.S. : experiments using granite gel undersalurated with uranium as U308 (0.45 %) and Na2C03 solutions.

R‘ : reversal experiments using granite and Na2C03 solufions oversaturated wiIh uranyl (VI)

R” : reversal experiments using granite gel doped with U308 (M-2.0 WI%) and Na2C03 sofutions.

R”’ : experiments using excess of U308 (or schoepife) inslead of excess of UOZ.

(f : wt % of Na20 and K20 determined by global analysis of silicate glass using atomic absorption specrrometry.

[] : wt % of U02 in silicate glass determined by fission tracks.

solubility in the silicate melt of several orders of magnitude (Table 2; Fig. 3b). However, the effect off& on the uranium solubility in the siticate melt progressively decreased with increasing a! from 1.1 to 1.5. in very peralkaline silicate glasses ( 1.5 < LY 5; 1.71, the role of both & and a on the u&Gum soiubility becomes negligible (Fig. 5). The limited temperature increase from 720 to 770°C did not appear to affect significantly the behaviour of uranium in silicate melts.

The uranium solubility curves as a function of log & and

buffers Ni-NiO, Fe304-Fe203, and CuzO-CuO, the uranium solubility can be expressed by Eqn. 6:

log (U) (ppm) = 0.04 log fs (bar) + 3.80~~ - 1.34. (61

Eqn. 6 is valid for 720 5 T I 770°C at 2 kbar. For cy in the range 1.5-1.7, the three uranium solubility curves for the three above cited oxygen buffers were obtained by interpo- lation of analytical data.

(Y were fitted using least square method with the Eqn. 5:

log(U) (ppm) = u1 log SS (bar) The Distribution of Potassium and !!hdium Between Carbonated Aqueous Fluid aud Silicate Melt

+ f&&Y f ff5 log j& (bar) a f ff4* (5)

Earlier works on the ~s~bution of potassium and sodium In all cases, the term a3 log & (bar) (Y was negligible. For o! between haplogmnite and chloride solution at 700-8OO”C, in the range 1.1-l .5 and for log fez values fixed by three 1.4-2.4 kbar have reported that potassium tends to concen-

2502

10

10

-2 8 cl g 10 3

10

q

4_

3_

2_

C. Peiffert. M. Cuney, and C. Nguyen-Trung

1.4

(Na+K)/AI

FIG. 5. Uranium solubility (ppm) in granitic silicate melt vs. agpaitic coefficient (Y = (Na + K)/AI under fo, fixed by Ni-NiO, Fe,O.,- Fe203, and CutO-CuO buffers. Comparison with Yudintsev’s data in granitic silicate melt in contact with Hz0 ( Ni-NiO buffer) ( 1990) (0).

trate in melt, whereas sodium prefers the aqueous fluid (GAMMON et al., 1969; HOLLAND, 1972; CARRON and LA-

CACHE, 1980). These authors also established a simple relation between two ratios [K/Na],,,, and [ K/Nalfluid (Eqn. 7):

(7)

In the present study, FK values determined from [K/Na] data (Tables 2 and 3) are in the range 2.5-6.2. These results are up to 3.6 times larger than those determined in a chloride system. Apparently, the carbonate l&and has a stronger affinity with sodium than with potassium and thus contributes to enhance considerably FK value.

DISCUSSION

The Behaviour of Uranium in the Aqueous Fluids

Earlier works ( ZHARIKOV et al., 1987; KEPPLER and WYL-

LIE, 1990, 199 1) have reported amounts ranging from 12 to 1100 ppm U in HCI, HF, Hz0 + CO*, and (Na, K)CI aqueous solutions in equilibrium with U-bearing haplogranite (0.78 5 (Y 5 1.08) at 750°C 2 kbar, under Ni-NiO or Fe304- FezOX buffers. The higher uranium content resulted from the acid pH and/or the large concentration of halides in the aqueous fluids, compared to the low uranium solubility ( I - 3 ppm) in carbonate solutions under similar fo, conditions in the present work.

RED’KIN et al. ( 1989) reported that the solubility of UOz in Hz0 at 1 kbar and under reducing conditions (Ni-NiO buffer) increased very slightly from 0.24 ppb U ( 10e9 mol) to 0.75 ppb U ( 1O-8.5 mol) for temperature increasing from 300 to 600°C. From this result and based on the fact that UOz does not undergo any phase transformation up to its melting point ( -2800°C) and 2 kbar, it is very probable that the solubility of U02 in reduced water up to 770°C 2 kbar

should be very low and in the range of ppb. In contrast, ZHARIKOV et al. (1987) and YUDINTSEV (1990) have reported that the uranium solubility in a mixture uranium oxide, HzO, and haplogranite at 750°C 2 kbar, and fo, condition fixed by Ni-NiO buffer increased from 1.5 to 14 ppm

U for CY increasing from 0.78 to 1.4. These values are three to four orders of magnitude higher than the ppb uranium

value extrapolated from solubility measurements by RED’KIN et al. ( 1989) and up to one order of magnitude higher than

those determined in carbonated solution ( 1-2 ppm) in this study. The high solubility of uranium obtained by ZHARIKOV

et al. ( 1987) and YUDINTSEV (1990) was probably due to the presence of small amounts of uranium solid or U-bearing

silicate glass in nonfiltered Hz0 after the runs. In the present study, the low uranium solubility ( 1-2 ppm)

obtained under reducing conditions ( Ni-NiO, Fe304-Fe203 buffers) was principally due to the low solubility of U( IV) complexes with OH- and CO:- ligands. The relatively high uranium solubihty ( 17 ppm) determined under oxidizing

conditions ( Cu20-CuO buffer) probably originated from two dependent factors: ( 1) the high solubility of U( VI) (25 mol%)

contained in UO~~.zs~uoz,, the solid phase in equilibrium with the aqueous fluid, and (2) the formation of more soluble U ( VI ) complexes with OH _ and mainly CO:- ligands in

aqueous fluid.

The Behaviour of Uranium in Silicate Melts

The behaviour of uranium in anhydrous silicate melts is different from that in aqueous solution. Three stable redox states of uranium-( VI), (V), and (IV)-characterized by yellow color, colorless, and green color, respectively, coexist in melts (CALAS, 1979; SCHREIBER, 1983; FARCES et al., 1992). The equilibrium distribution of U(VI), U(V), and U( IV) is dependent on the imposed fo, (CALAS, 1979; SCHREIBER, 1983; YUDINTSEV et al., 1990) and the alkalinity of the silicate melt ( CALAS, 1979; SCHREIBER, 1983 ). Recent works of FARCES et al. ( 1992) have indicated that ( 1) U( VI) occurs as linear uranyl, U “0 $‘, with four to five equatorial

bonds to oxygen, (2) U(V) exists in 6-coordinated sites under moderately reducing conditions (above the QFM buffer), and (3) U( IV) is present in 6-coordinated sites under reducing conditions (below the Ni-NiO buffer). U( VI), U(V), and U (IV) are likely to bond to nonbridging oxygen (NBO). Thus, the amount of NBO is considered as a factor controlling the uranium solubility in anhydrous silicate melt. The increase of peralkalinity greatly contributes to depolymerize the aluminosilicate network and thus increases the production of NBOs (MYSEN, 1988). Consequently, the solubility of uranium is enhanced by increasing peralkalinity of the silicate melt (FARGES et al., 1992).

In contrast, little is known about the behaviour of uranium in water-bearing silicate melt. This is due to the lack of reliable data on uranium speciation in hydrous melts and analytical difficulties. Earlier experimental works have established that the dissolution of water in silicate melt depolymerizes the aluminosilicate network. Numerous solubility mechanisms for water in silicate melt have been proposed ( BOWEN, 1928; BURNHAM, 1975; OXTOBY and HAMILTON, 1978; MANNING et al., 1980; MYSEN et al.. 1980; STOLPER, 1982; EPEL’BAUM,

P~itionin~ of U between granite melt and aqueous fluids 2503

1985). Based on above-mentioned models and recent Raman works of MYSEN and VIRGO ( 1986a,b), MYSEN ( 1988) sug- gested that water enters the aluminosilicate melts in the form of molecular Hz0 and OH-complexes bonded to both A13+ (non-tetrahedral) and Na+ , The formation of Si-OH and (Si, AI)-OH was not evidenced. For felsic liquids, with Al/ (Al + Si) < 0.2, essentially all the OH ligand is associated with alkali metals and Hz0 is dissolved in two principal forms: alkali-OH groups and molecular Hz0 ( MYSEN, 1988 ) . In the present study, as the ratio Al/(Al + Si) was in the range 0.13-0.16, molecular Hz0 as well as Na-OH and K-OH groups are three major forms of dissolved water (8- 13 wt%) in melts. Although the mechanisms of uranium solubility in hydrous silicate melt is not quite understood, the low uranium solubility ( 100-300 ppm) in low alkaline content hydrous melt (cy = 1. I ) indicates that the formation of stable complexes between various forms of dissolved water and uranium is improbable. The formation of stable U( IV), (V), and (VI) carbonate complexes was also improbable because the concentration of dissolved COz in silicate melt was low ( - 1100 ppm), constant, and independent of uranium concentration. Consequently, like the alkalinity, the only major effect of dissolved Hz0 in silicate melts on the uranium solubility is the production of the NBO due to the depolymerization of aluminosilicate network.

solubility is considerably reduced (Fig. 5 ) . The origin of the change of the behaviour of uranium is not yet understood.

The uranium solubility has been determined in a haplogranite melt, in contact with uranium oxide and H20, at similar P, T, and fez (Ni-NiO buffer) conditions ( ZHARIKOV et al., 1987; YUDINTSEV, 1990). These authors reported increasing uranium solubility from 3 X IO’ ppm to lo4 ppm with LY increasing from 0.78 to 1.60. For (Y = 1.1, a disagree- ment exists between data obtained by ZHARIKOV et al. ( 1987) (5.5X 103ppm)andbyYuDINTsEV(1990)(2X 103ppm). These results are one order of magnitude higher for a! = 1.1 and slightly lower for cy 2 1.5 than our results (Fig. 5). The higher uranium solubility, obtained from bulk analysis, may result from the heter~eneity (e.g., presence of small amounts of uranium solid) in silicate melts after the runs.

The Partitioning of Uranium Between Carbonated Aqueous Fluid and Silicate Melt

The redox conditions of the system also play an important role in the uranium solubility. Earlier works have established that increasing oxidation enhances uranium solubility in anhydrous silicate melts (CALAS, 1979; DOMINI& and VELDE, 1985; YUDINTSEV, 1990). In addition, uranium solubility measurements in sodium trisilicate glasses indicated that U(V) and U( VI) are four times more soluble than U(IV) (VEAL et al., 1987).

The partition coefficient ( Dn”id’Me”) of uranium between carbonated aqueous fluid and silicate melt increases linearly with increasing log fs from -15 to -4 by about 0.5 order of magnitude, for cx in the range 1. I- 1.5 (Fig. 6; I-III; Table 3). The D increase becomes slightly more important for n - 1.7. For a given f&, the decrease of (Y from 1.7 to 1.1 leads to an increase of log D of about two orders of magnitude. Raising the temperature from 720 to 77O’C does not significantly affect D. The variation curve of log D”uid’Me’t vs. log fo, and cy was fitted using the least square method with the Eqn. 5. Similarly, the term a3 log f& (bar) LY in Eqn. 5 was negligible. For cy in the range 1. l- 1.7, log D~uid/Me’t vs. log fo, and cy can be expressed by Eqn. 8:

Results obtained in the present study confirmed the positive effect of redox conditions (log fo,) and agpaicity (a) of the melt on the uranium solubility in a water-bearing haplogranite melt.

log Dnuid’Me’t = -3.78a + 0.05 log fo, (bar) + 2.84. (8)

Validity conditions of Eqn. 8 are similar to those of Eqn. 6.

Redox conditions

The low D values obtained in the present study clearly indicated that most of uranium is preferentially concentrated in the silicate melt, particularly in peralkaline melt under oxidizing conditions.

Under reducing conditions (Ni-NiO buffer), the low uranium content may result from the low solubility of U(IV) present with U(V) in colorless glasses. Under higher fo, conditions ( Fe304-Fe203, CuzO-CuO buffers), the higher uranium concentration originates from the higher solubility of uranium (V) and mainly uranium (VI) characterized by yellow glasses (Fig. 3 and 5).

Agpaicizy of silicate melts (al)

For a given log fo, value and an amount of dissolved water (8-l 3 wt%), the uranium solubility (log U) increases linearly up to two orders of magnitude with increasing (Y from 1.1 to 1.5 (Fig. 5). The additional production of NBOs, due to the increase of alkalinity or agpaicity ((Y = (Na + K)/Al), is likely to be responsible for the enhancement of the uranium solubility. The effect of agpaicity on uranium solubility is up to 25 times more important than that of fez_

Values of partition coefficient ( D~“id’Me’t) of uranium, determined between a haplogranitic melt and aqueous fluids containing variable amounts of HCl, HF ( ZHARIKOV et al., 1987; KEPPLER and WYLLIE, 1990, 199 1 ), H20, Hz0 + COz (ZHARIKOV et al., 1987; KEPPLER and WYLLIE, 1990, 1991; YUDINTSEV, 1990), or (Na, K)CI, or (Na, K)F ( ZHARIKOV et al., 1987; YUDINTSEV, 1990) at similar P, T, fo, ( Ni-NiO or Fe304-Fez03 ) conditions, were four orders of magnitude higher than those determined in the present study (Fig. 6). The discrepancy could originate from the differences in composition of the aqueous fluid (pH, ligand) and silicate melt. However, as the composition of the uranium solid phase, silicate glass, and aqueous solution after the run were not reported in most cases ( KEPPLER and WYLLIE, 1990, 1991; YUDINTSEV, 1990), a detailed discussion of these data is not possible.

GEOLOGICAL IMPLICATIONS

In highly peralkaline silicate melts ((Y = 1.7)) the effect of Results obtained in the present study provide greater un- both factors (redox conditions, agpaicity) on the uranium derstanding of the fractionation of uranium during magmatic


Table 3. Chemical composition of aqueous fluid after run

and partitioning of uranium between aqueous fluid and silicate melt

Nature aq.sol. T log102 pH Na

G+S mg (“C) (bar) PPm l-l C.A. F GQ+sz 120 720 -15.6

K x03 u K/(Na+K) Dfluid/melt

ppm Ppm PPm 4.2&E-05

l-2 R.Q. F idem 126 n0 -15.0 8.6

l-3 R.Q. F idem 129 770 -15.0 1125

14 R.Q. F idem 152 770 -10.3

l-5 CA. F idem 146 770 -10.3

l-6 R.Q. F idem 138 72.0 -10.9 8.9 983

l-7 R.Q. X idem 142 770 4.0

l-8 R.Q. F idem 147 i70 -1.0 x.7

1-9 R.Q. F idem 133 770 3 0

l-10 R.Q. us, x idem 131 77iJ -15.0 x

145

185

1.06

0.86

0.91 0.070

2.85

2.98

2.10 0.100

1302

12 87

12 6.5

0.12

3.248-05

3.33E-05

l.O2E-04

l.O5E-04

7.71E-05

4.38E-04

4.33&M

4.28E-04

3,OOE-OS

2-l R.Q. F G3ts3 254 720 -15.6 8.6 897

2-2 R.Q. F G&s2 105 770 -15.0 8.3

2-3 R.Q. F G4+S3 133 770 -15.0 8.7 1104

2-4 CA. R’L’ G4+s2 109 720 -15.6 8.8

2-S R.Q. F+ G4+S3 133 720 -15.6

2-6 R.Q. F G4+s2 102 720 -15.6 8.5

2-7 R.Q. R’ c%+s3 123 720 -75.6 7053

2-8 R.Q. R” cd+s3 124 720 -75.6

2-9 R.Q. X O+S3 256 770 -10.3

2-10 R.Q. SI G4+s2 166 720 -10.9

2-11 R.Q. F G4+S3 136 770 -10.3 8.7 Yb7

2-12 CA.

2-13 R.Q.

2-14 R.Q.

Z-15 CA.

2-16 R.Q.

2-17 R.Q.

2-18 R.Q.

2-19 R.Q.

2-20 R.Q.

2-21 R.Q.

2-22 CA.

2-23 R.Q.

2-24 R.Q.

2-25 C.A.

2-26 R.Q.

2-27 R.Q.

2-28 R.Q.

2-29 R.Q.

230 R.Q.

R”’

X

F+

F

SI

R’

R.’

F

F

F+

F

F+

X

F p**

SI

R’

R**

I.&X

G4+52

G4+S3

GM3

cx+s2

G4+S3

G&s3

c&s3

G3+S3

G4+s2

G&S3

G4+S2

G4+S3

G4+S3

G‘hsz

G4+S3

G4+S3

cws3

G4+s3

idem

3-l R.Q. F W+S3 lb3

3-2 R.Q. X G3+s2 122

3-3 R.Q. F G3+S3 150

34 R.Q. F GI+Sl 170

3-5 R.Q. X G3+s2 127

3-6 R.Q. R’ G3+s3 260

3-7 R.Q. R” c;+sz 122

3-8 R.Q. X G3+S3 123

3-9 CA. F w+s2 124

3-10 R.Q. X O+S3 I33

3-11 R.Q. F Gl tS1 123

3-12 R.Q. X u+s2 122

3-13 R.O. R’ c3+s3 112

113 720 .?0.9

145 720 -10.9

110 770 -10.3 8.4

106 720 -10.9

112 720 -10.9

14s 720 -10.9 8.3

185 720 -10.9

281 770 -4.0 1223

145 720 -4.3

123 7.20 -4.3 8.5

126 720 4.3

145 no 4.3

133 770 -4.0 8.6

122 720 -r1.3

114 720 -4.3 8.9 945

166 720 -4.3

133 720 4.3 8.1

123 720 -4.3

163 770 -4.0

i70 -15.0 8.7

720 -15.6

770 -15.0 8.5 898

770 -15.0 8.1

720 -15.6

770 -15.0

770 -7.5 0

720 -1O.Y

770 -10.3 8.9

i?O -10.3 1156

TO -10.3 8.7

720 -10.9

770 -10.3 8.8

113

153

794

132

125

124

113

215

4152

1276

7839

659

2432

2767

2400

0.88 0.069

0.91

0.075

1.05

0.92+0.01

9.25E-05

l.O6E-04

1.29804

1.08E-04

1.10

7 to 0.074

0 80

2..5?

2 59+0.02

0.074

1.2x-04

1.37G04 9.55E-05

2.3011-04

2.24E-@i

3.25

2.77

3.08+0.03

2.40

2.67+0.02

4.50

2.80

0.057

11.21

9 SO+0 0.5

10.43

12.6l +O.ll

11.92

12.10

10.31 0.072

12.61+0.09

13.26

8.75

1.60

2.#3E-04

2.17&04

2.31E-04

1.82E-04

2.01E-LM

3.84E-04

2.04F-04

5.30E-04

5.29~~04

5.4OE-04

6.53604

6.06E-04

6.208-M

5.49E-04

6.568-M

?.48E-04

4.llE-04

4,00E-@I

0.85 l.OOE-03

1.41 1.45E-03

1.75 0.069 1.60E-03

1.70 1.61E-03

1.62 1.53E-03

2.67 3.b?E-03

091 8.13E-04

4.70 3.39E-03

3.44 0.099 2.47E-(33

2.33 1.71E-(X3

3.33 2.36E-03

3 40 2.74E-03

P~itioning of U between granite melt and aqueous Buids 250.5

Run

Table 3. (Continued)

Nature aq.sol. T logfO2 pH Na K zco3 u K/(Na+K) Dfluid/melt

G+S me (“C) (bar) vvm vvm vvm vvm

3-14 R.Q. R” W+S2

3-B R.Q. X a+S3

3-16 CA. F G3+S2

3-17 R.Q. F G?J+S3

3-18 R.Q. X Cl+Sl

3-19 R.Q. F w+s2

3-20 R.Q. R’ w+s3

3-21 R.Q. R” W&2

4-1 R.Q. F Gl+Sl

R.Q.

4-2 R.Q. F+ Gl+Sl

43 R.Q. X G2+S4

44 R.Q. F Gl+Sl

45 R.Q. F Gl+Sl

4-6 R.Q. F+ Gl+S1

4-7 R.Q. X G2+S4

4-8 R.Q. X Cl+%

4-9 R.Q. F Gl+Sl

4-10 R.Q. X Gf+Sl

4-11 CA. F G2+S4

4-12 R.Q. F Gl+Sl

270

262

144

145

116

123

192

I10

163

156

125

134

123

143

112

133

134

112

123

146

770 -10.3

no -4.0 867

720 -4.3 8.5

no -4.0

T70 -4.0 8.4

720 -4.3

770 -4.0 8.7

770 -4.0

770 -15.0 1026

770 -15.0

i70 -15.0 8.3

770 -15.0

770 -10.3 945

770 -10.3

770 -10.3 8.2

770 -10.3

770 4.0 6.7

nil 4.0

no -4.0 942

770 4.0

2.92

206

15.87

1527

1.95E-03

0.123

5.14E-LB

5.14E-03

16.95 5.64E-03

14.52 4.921:-03

Jb.50 5.66C03

9.71 3.04E-03

185 1.32

0.9&0.01

0.096 l.O!iE-02

7.13E-03

1.21 9.21E-M

1.16 9.54E-M

2’12 3.33

3.as+o.o2

0.117 l.llE-02

9.5RE-a3

2.98 9.706-03

2.78 9.65E-03

13.21 2.63E-@

13.02

178 12.65

12.26

2.738-@2

0.100 2.6RE-02

2.36E-02

G : initial gel ; S : initial aqueous solution. Compositions of gels and initial aqueous solutions are in table 1.

CA. : experiments using conventional autoclaves

R.Q. : experiments using rapid quench cold-seal pressure vessels

aq. sol. (mg) : initial Na2C03 aqueous solution in milligrams

U.S. : experiments using granite gel undersaturated with U308 (0.45 %) and Na2C03 solutions.

R’ : reversal experiments using granite and Na2C03 solutions oversaturated with uranyl (VI)

Ff” : reversal experiments using granite gel doped with U308 (0.5-2.0 wP/o) and Na2C03 solutions,

R”’ : experiments using excess of U308 (or schoepite) instead of excess of U02.

X : solubility measurements of unfiltered aqueous solution

F : solubility measurements of filtered aqueous solution

F+ : amount of uranium of filtered aqueous solution and of filtered solid particles

SI : experiments using an additional Pt capsule containing purified qtlartz grains

differentiation, vapor oversaturation of the felsic magmas, will not present an early crystallization. These results ex- and the formation of magmatic uranium deposits. plains the strong incompatible behaviour of uranium

1) The experimental results show that uranium solubility is during magmatic processes as observed for example by

very high in peralkaline felsic melts ( lo* to 2-3 X lo4 NovAK~~~MAHooD(~~~~),VILLEMANT~~~~.(~~~O),

ppm U). Thus, peralkaline magmas represent extremely and VILLEMANT and PALLACIN (1987) in volcanic rock

efficient vectors for uranium transfer from the mantle to suites. the upper crust. The much lower uranium content mea- 2) The high uranium solubility in peralkaline silicate me&s sured in natural peralkaIine rhyolitic glasses (a few tens will lead to a steady enrichment of this element during of ppmf with agpaitic index values up to 1.9 (CHRIS- fractional crystallization. This behaviour may lead to the TIANSEN et al., 1983; KOVALENKO et al., 1989) indicates formation of large magmatic uranium deposits in asso- that these melts are strongly undersaturated with respect ciation with the most fractionated melts of the peralkaline to uraninite. Thus, during magma fractionation, uraninite igneous complexes. Such a mechanism is best illustrated


3)

”

-1 -

-2-

-3 -

-4-

1 d

d 2

3 4 4 5 f 6

7 0 6

i0 a= 1.1

13

15

a= 1.5

a= 1.7

-20 -15 4

-10 -5 0

log f02 (bar)

FIG. 6. Correlation between partition coefficient of uranium (log Dtluidlmeli) and log j& (bar) (square: Ni-NiO; circle: Fej04-Fe203; triangle: Cu20-CuO) for agpaitic coefficient (Y = 1.1, 1.3, 1.5, and 1.7. Comparison with data reported by(a)KE~~~~~andW~~~~~(l990):(l)HF4m,(2)HF3m,(3)HF2m,(5,6,8)HFlm;(4)2mHCl,(7)1.5 m HCI, (11) 0.5 m HCI, ( 12) 1 m HCl, (15) 0.5 m HCl, (16) 0.5 m HCl; (9) 2.5 m C02, (10) 5 m CO*, and (b) YUDINTSEV (1990) (a = (Na + K)/Al = 1.4): (17) 1 m CO,; (14) 0.1 m NarJ&F; (13) 1 m Na&&l, at 750°C 2 kbar, and fo2 fixed by Ni-NiO buffer.

by the mineralized iujavrites of the Kvanefjeld deposit in the Ilimaussaq peralkaline complex, Greenland, which represent the most highly fractionated melts of the complex with the highest agpaitic index. The highest uranium content is reached in the medium-coarse grained lujavrites with an average U content of 400 ppm for an agpaitic index of 1.5 (MRENSEN et al., 1974). Local enrichment up to 1550 ppm remains far below the saturation levels for such melts determined in the present work: ahout lo4 ppm for an agpaitic index of 1.5. Peralkaline granitic magma can dissolve uranium up to 1 O4 time more than an aqueous carbonated fluid at equilibrium. The amount of uranium in a H20-CO2 magmatic fluid coexisting with peralkaline magmas is very small ( l-15 ppm). Consequently, uranium fractionation in magmatic fluids during magma vapor oversaturation will not affect the uranium content of the original magma for peralkaline melt compositions and aqueous carbonated fluid (log D Ruid/Me’t = -4). The effect may hecome important during peraluminous magmas fluid oversatumtion in oxidizing conditions. According to the results of KEP- PLER and WYLLIE ( 199 1) and the occurrence of uranium- fluorite-rich veins spatially associated with peralkaline in- trusions such as Ilimaussaq ( WRENSEN et al., 1974)) this effect should be much more important for F- and/or Cl- rich fluids.

Acknowledgments-Most of the high-pressure and temperature experiments were done in the Experimental Laboratory of the Centre de Recherches Petrographiques et Gtochimiques (CRPG)-France. The authors thank A. Rouillier, M. Vemet, F. L’hote (CRPG), J. M. Claude (Univ. Nancy I), and M. Canals (CREGU) for their technical and analytical support. We acknowledge detailed and thoughtful reviews by GCA reviewers: Dr T. Latourette, Dr B. Mysen, Dr D. Shaw, and Dr B. Velde.

Editorial handling: D. M. Shaw

REFERENCES

B~HSE H., ROSE HANSEN J., WRENSEN H., STEENFELT A., I.&BORG L., and KUNZENDROF H. ( 1974) On the behaviour of uranium during crystallization of magmas with special emphasis on alkaline magmas. IAEA Proceeding Series; “Formation of uranium ore deposits”, Vienna, 49-60.

BOWEN N. L. ( 1928) The Evolution ofthe igneous Rocks. Princeton Univ. Press.

BURNHAM C. W. ( 1975 ) Thermodynamics of melting in experimental silicate-volatile systems. Geochim. Cosmochim. Acta 39, 1077- 1084.

CALAS G. ( 1979) Etude exp&mentale du comportement de l’uranium dans les magmas, &tats d’oxydation et de coordinance. Geo- chim. Cosmochim. Acta 43, 1521-1531.

CARRON J. P. and LAGACHE M. ( 1980) Etude exp&imentale du fractionnement des Bements Rb, Cs, Sr et Ba entre feldspaths al- calins, solutions hydrothermales et liquides silica& dam le systeme Q.Ab.0r.H20 a Zkbar entre 700 et 800°C. Bull. Minbral. 103, 571-578.


CATHELINEAU M., CUNEY M., LEROY J., L’HOTE F., NGUYEN TRUNG C., PAGEL M., and POTY B. ( 1982) Vein-type and similar uranium deposits in rocks younger than Proterozoic. IAEA-TC- 295/21,159-177.

CHRISTIANSEN E. H., BURT D. M., SHERIDAN M. F., and WILSON R. T. ( 1983) The Petrogenesis of Topaz Rhyolites from the Western United States. Contrib. Mineral. Petrol. 83, 16-30.

CUNEY M. and FRIEDRICH M. ( 1987) Physicochemical and crystal chemical controlson accessory mineral pamgenesis in granitoids: implications for uranium metallogenesis. Bull. Mineral. 110,235- 247.

DOMIN& F. and VELDE B. ( 1985) Preliminary investigation of the processes governing the solubility of uranium in siiicate melts. Bull. Min&al. 108, 755-765.

EPEL’BAUM M. B. ( 1985) The structure and properties of hydrous granitic melts. Geohgica Curpath~ca 36,491-498.

FARCES F.. PONADER C. W.. CALAS G.. and BROW G. E.. JR. ( 1992)

FRANTZ J. D. and POPP R. K. ( 1979) Mineral-Solution equilibria:

Structural environments of incompatible elements in silicate glass; melt systems: II. UIV, UV, and UVI. Geochim. Cosmochim. Acta 56,4205-4220.

I. An experimental study of complexing and thermodynamic properties of aqueous MgCI, in the system MgO-Siq-H20-HCl. Geochim. ~osmo~hi~. Acta 43, 1223-1239.

FLIGER J. ( 197 1) Thermod.vnamic Properties of Simple Actinide ~ampounds: MTP international Review of Science. Butterworth.

GAMMONS J. B., BORCSIK M., and HOLLAND H. D. ( 1969) Potas- sium-sodium ratios in aqueous solutions and coexisting silicate melts. Science 163, 179- 18 1.

GR@NVOLD F., KVESETH N. J., SVEEN A., and TICHY J. (1970) Thermodynamic of the UOlz+Xj phase. I. Heat capacity of U012.c17j and UO,, ,s1, from 300 to lOOOK and electronic contribution. J. \_.__ ., Chem. Thermodyn. 2,665-680.

HAMILTON D. L. and HENDERSON C. M. B. ( 1968) The preparation of silicate composition by a gelling method. Mineral. Magi 36, 832-838.

HOLLAND H. D. ( 1972) Granites, solutions and base Metal deposits. Ecoo. Geol. 67,28 l-30 I.

KEPPLER H. and WYLLIE P. J. ( 1990) Role of fluids in transport and fractionation of uranium and thorium in magmatic processes. Nature 48,53 l-533.

KEPPLER H. and WYLLIE P. J. ( 1991) Partitioning of Cu, Sn, MO, W, U, and Th between melt and aqueous fluid in the systems haplo~anite-H*O-Hal and haplogranite-H~O-HF. Contrib. ~inerui. Petrol. 109, 139- 150.

KOVALENKO V. I., HERVIG R. L., NAUMOV V. B., SOLOVOVA I. P., and SHERIDAN M. F. ( 1989) Using ion probe for analysis of rare elements and water in pantellerites of Pantelleria island, Italy. Geokhimia 9, 1307-l 320 (in Russian).

MACLEOD A. C. ( 1972) Enthalpy of U02.25 to 1600 K by drop cal- orimetry. J. Chem. Thermodyn. 4,699-708.

MAGLIC K. and HERAK R. ( 1970) Enthalpy and heat capacity of triuranium octaoxide between 273 and lOOOK. Rev. ht. Haute Temper. et Refract. 7, 247-25 1,

MANNING D. A. C., HAMILTON C. M. B., HENDERSON C. M. B., and DEMPSEY M. J. ( 1980) The probable occurrence of inter&&l Al in hydrous F-bearing and F-free ~uminosili~te melts. Contrib. Mineral. Petrol. 75257-262.

MYSEN B. 0. ( 1988) Structure and Properties of Sihcate Me&. El- sevier.

MYSEN B. 0. and VIRGO D. (1986a) Volatiles in silicate melts at high pressure and temperature. I. Interaction between OH groups and Si4’, A13+, Ca’+,-Na+ and H+. Chem. Geol. 57, 303-331..

MYSEN 3. 0. and VIRGO D. f 1986b) Volatiles in silicate melts at high pressure and temperature. 2. Water in melts along the join N&4102-Siq and a comparison of solubility mechanisms of water and fluorine. Chem. Geol. 57.333-358.

MYSEN B. O., VIRGO D., HARRISSON W. J., and ~CARFE C. M. ( 1980) Solubility mechanisms of Hz0 in silicate melts at high pressures and temperatures: A Raman spectroscopic study. Amer. Mineral. 65,900-9 14.

NOVAK S. W. and MAHOOD G. A. ( 1986) Rise and fall of a basalt-

trachyte-rhyolite magma system at the Kane Springs Wash Caldera, Nevada. Contrib. Mineral. Petrol. 94. 352-373.

OXTOBY S. and HAMILTON D. L. ( 1978) The discrete association of water with NazO and SiOz in Na Al silicate melts. J. Amer. Ceramic Sot. 42,4 13-423.

PEIFFERT C., NGUYEN-TRUNG C., and CLJNEY M. ( 1992) Experi- mental study of the solubiiity of uranium oxide in the system haplogranite-H@-Na,CO, at 7QO”C, 2 kbar. 29th In&l. Geol. Gong. (Kyoto, Japan) 3,763.

RED’KIN A. F. and OMEL’YANENKO B. I. ( 1987) The solubilities of uranium oxides in water at 773K and 100 MPa. Geokhimiya 8, 1200- 1206 (English translation).

RED’KIN A. F., SAVELYEVA N. I., SERGEYEVA E. I., OMEL’YANENKO B. I., IVANOV I. P., and KHODAKOVSKV 1. L. ( 1989) Investi~tion of uraninite ( U02( c)) solubility under hydrothe~al conditions. Sci. G&I. But. 42, 329-334.

ROGERS J. J. W. and ADAMS J. A. ( 1969) Uranium. In Handbook of Geochemistry (ed. K. H. WEDEPOHL), II-3,90. Springer-Verlag.

SCHREIBER H. D. ( 1980) Properties of redox ions in glasses: An inte~i~iplina~ perspective. J. Non-Cry% Solids 42, 175-184.

SCHREIBER H. D. ( 1983) The chemistry of uranium in glas~fo~ing alumin~silicate melts. J. mess-common Metal 91, 129-147.

SCHREIBER H. D. and ANDREWS S. M. ( 1980) The redox states of

ROBIE R. A., HEMINGWAY B. S., and FISHER J. R. ( 1979) Ther- modynamic properties of minerals and related substances at

uranium in s~theti~~~tic magmas. Lunar Planet. Sci. XI, lOOO-

298.15K and 1 bar ( 10’ Pascals) pressure and at higher temperatures. Geol. Surv. Bull. 1452.

1002. SCHREKBER H. D. and BAL~ZS G. B. ( 1982) The chemistry of uranium

in borosilicate glasses. Part 1. Simple base compositions relevant to the immobilisation of nuclear waste. Phys. Chem. Glasses 23, 139-146.

SCHREIBER H. D., BALAZS G. D., WILLIAMS B. J., and ANDREWS S. M. ( 198 1) Structural and redox properties of uranium in Ca- Mg-Al-Silicate glasses. In Scientific Basis,for Nuclear Waste Man- agement, Vol. 3 (ed. J. G. MOORE) pp. 109-l 14. Plenum,

SCHREIBER H. D., BALAZ~ G. D., and WILLIAMS B. J. ( 1982) Chem- istry of uranium in aluminophosphate glasses. J. Amer. Ceramic Sot. 65449-453.

SORENSEN H., ROSE-HANSEN J., NIELSEN B. L., LOVBORG L., !%- RENSEN E., and LUNDGAARD T. ( 1974) The uranium deposit at Kvanefield, the Illimaussaq intrusion, South Greenland. Geology reserves and beneficiation. Report Greenland Geol. Unders. 60.

STOLPER E. ( 1982) The speciation of water in silicate melts. Geochim. Cosmo~him. Acta 46,2609-2620,

TAYLOR S. R. and MCLENNAN ( 1985) The Continental Crust: Ifs Composition and Evolution. Blackwell.

VEAL B. W.. MUNDY J. N.. and LAM D. J. (1987) Actinides in silicate glasses. In Handbook on the Physics and Chemistry of the Actinides (ed. A. J. FREEMAN and G. H. LANDER), pp. 271-309. Elsevier.

VILIEMANT B. and PALLACIN P. ( 1987) Dil&enciation magmatique et mecanismes de ~on~ntmtion de l’uranium: l’exemple du vol- canisme du Latium (Italie centrale). Bull. Mineral. 110,3 19-333.

VILLEMANT B., JORON J. L., JAFFREZIC H., TREUIL M., MAURY R., and BROUSSE R. ( 1980) Cristallisation fmctionnee dun magma basaltique alcalin: la &ie de la cha?ne des Puys (Massif central, France), II: Geochimie. Bull. Mineral. 103.267-286.

WEBSTER~J. D., HOLLOWAY J. R., and HER&G R. L. ( 1989) Par- titioning of Lithophile Trace Elements between H& and H,O + CO, Fluids and Tonaz Rhvolite Melt. Econ. Geol. 84. 116-134.

YUDINT~EV S. V. ( 1990) The behaviour of uranium in an alkali granitic magma. Geokhimiya 4,538-544 (English translation).

YUDINTSEV S. V., OMEL’YANENKO B. I., and LYLJ~OMILOVA G. V. { 1990) Uranium valency state in granitic melts. Geokhimiya 9, 129 t - I297 (English translation).

ZHARIKHOV V. A., IVANOV I. P., OMEL’YANENKO B. I., RED’KIN A. F., and YUDINT~EV S. V. ( 1987) Experimental study of the solubility of uraninite in granitic melts and fluid solutions at high pressures and temperatures. Intl. Geof. Rev., pp. 997-1004 (English translation ) .

Documents

Uranium in granitic magmas: Part 1. Experimental determination of uranium solubility and fluid-melt partition coefficients in the uranium oxide-haplogranite-H2O-Na2CO3 system at 720–770°C,