American Mineralogist, Volume 77, pages 156-167, 1992

Synthetic fluid inclusions: Part XI. Notes on the application of synthetic fluidinclusions to high P-7 experimental aqueous geochemistry

S. Mrcrr,tnr- SrnnNnn*Department of Chemistry and Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720, U.S.A.

Ansrru,cr

A new modification to the procedure for trapping synthetic fluid inclusions effectivelyallows the experimenter to control the timing of the onset of inclusion formation. Themain advantage of the new procedure is that inclusion trapping may be postponed untilthe experimental pressure and temperature are stabilized and the fluid has equilibrated atP and T to a constant and uniform composition and density throughout the capsule. Thus,PVTX studies may be extended to higher temperatures in cases where premature fracturehealing previously resulted in volumetric and compositional heterogeneity among inclu-sions from a single sample.

The new method has been found to improve significantly the precision of volumetricdeterminations in the COr-HrO system at temperatures above 600'C. Additionally, thetechnique shows promise in the investigation of high-salinity brines and for mixed-gasaqueous systems where fluid compositions may evolve through time. The ability to samplethe fluid phase at P and 7 after equilibration at P and Z may prove invaluable in speciationstudies at high pressures and temperatures involving kinetically slow buffers or difusionalprocesses and in the experimental study of HrO-rock interactions.

INrnonucrroN

In early studies of synthetic fluid inclusions, Roedderand Kopp (1975) and Shelton and Orville (1980) dem-onstrated that the density of HrO trapped in syntheticinclusions was the same as the density of HrO at theexperimental conditions. Shaposhnikov and Ermakov(1978) reported the presence of daughter crystals of NaCland KCI in inclusions trapped from concentrated brinesand were able to detect CO, and HF in inclusions formedfrom solutions containing dissolved gases. Thus, it be-came apparent that synthetic inclusions represented a mi-croscopic sample of the fluid phase present at the time oftheir formation-at least to a first approximation. Theresults of these early studies were welcomed by geosci-entists because they validated the fundamental assump-tions in fluid inclusion geothermobarometry: that naturalinclusions contained fluids that were compositionally andvolumetrically representative of the fluid phase(s) presentat the time of their formation. Thus, pressure, tempera-ture, and the composition of fluids present during a geo-logic event can be constrained using microthermometricmeasurements of natural fluid inclusions together withappropriate phase diagrams.

These early studies had another important implication:with prior knowledge of fluid composition and pressureand temperature conditions of inclusion growth, it shouldbe possible to derive phase diagrams from appropriatemicrothermometric data. This was demonstrated bySterner and Bodnar (1984), who presented a detailed pro-

* Present address: Bayerisches Geoinstitut, Universitiit Bay-reuth, Postfach 101251, W-8580 Bayreuth, Germany.

0003-004x/92l0 l 02-0 l 56$02.00

cedure for routine synthesis of fluid inclusions and dem-onstrated the plausibility ofderiving phase equilibria andvolumetric properties for a number of geologically rele-vant fluid systems. Investigations by these and otherworkers have provided a wealth of information both aboutfluids at high pressures and temperatures (cf. Bethke etal., 1990; Bodnar and Sterner, 1985; Bodnar et al., 1985;Knlght and Bodnar, 1989; Kotelnikova and Kotelnikov,1988; Kotelnikov and Kotelnikova, 1990; Popp andFranlz,1990; Sterner and Bodnar, 1986, l99l; Sterner etal., 1984,1988; van den Kerkhof, 1988; Vanko et al.,19881, Zhang and Frantz, I 98 7, I 989) and about the prop-erties of fluid inclusions themselves (cf. Bodnar et al.,1989; Boullier et al., 1989; Davis et al., 1990; Haynes etal., 1988; Pecher and Boullier, I 984; Pecher, 198 l; Smithand Evans, 1984; Sterner and Bodnar, 1989).

An important advantage of the synthetic fluid inclusiontechnique over more conventional methods is the abilityto obtain a sample of the fluid(s) present at equilibriumat P and Z using relatively simple (and inexpensive)equipment. Major drawbacks of the technique have in-cluded somewhat reduced accuracy and difficulties in ob-taining homogeneous samples of certain fluid composi-tions. The latter point arises, in part, because all fluidcomponents, including gases, must normally be loadedinto the experimental capsules as condensed phases. (Ex-pandable gases require the use of solid or liquid com-pounds that decompose upon heating to yield the desiredspecies.) Furthermore, in multicomponent fluids there isa tendency to begin to form inclusions before the com-ponents mix completely (Bodnar and Sterner, 1987).

Important modifications to the "synthetic fluid inclu-

1 5 6

STERNER: SYNTHETIC FLUID INCLUSIONS r57

sion method" have evolved since the publication of thefirst paper in this series in 1984 and have significantlyextended the applicability of the method. The primaryobjective of this communication is to discuss these ad-vances in light of future applications of synthetic inclu-sions to geologic problems.

BlcxcnouNn

Quartz has been used in the majority of fluid inclusionsynthesis studies to date. The choice ofquartz as the hostmaterial is logical for several reasons. First, quartz pro-vides a direct analogue to natural systems; it is the mostcommonly studied mineral for fluid inclusions becauseofits widespread natural occurrence. Quartz has relative-ly low solubility in most aqueous fluid systems over muchof geologically important P-7 space so that its presencecan usually be expected to have an insignificant effect onthe fluid property being investigated; at the same time,the solubility of quartz in aqueous systems is high enoughto allow the formation of fluid inclusions using a disso-lution-reprecipitation mechanism. Quartz is stable overa wide range of pressures, temperatures, and fluid com-positions. Finally, quartz is a relatively "strong" mineralin that inclusions in quartz will withstand substantialamounts of internal over- or under-pressure withoutstretching or shrinking (Bodnar et al., 1989; Sterner andBodnar, 1989). Therefore, aside from the effects ofther-mal expansion and compressibility, which are easily takeninto account, inclusions in quartz represent isochoric sys-tems under normal experimental conditions.

While quartz remains the best candidate for generalinclusion synthesis, other minerals may be better suitedto some specific applications. Hydrocarbon-bearing fluidinclusions for microanalytical calibration have been syn-thesized in sylvite at low temperature by precipitating thesalt from saturated solutions (Pironon, 1990); the anom-alously high strength of olivine may provide an alterna-tive to quartz in high-pressure PW and PTX determi-nations, whereas the stretching and decrepitation behaviorof inclusions in softer minerals like calcite and barite couldbe best characterized using synthetic inclusions ofknownfluid composition so that internal pressures could be ac-curately calculated. The list of host minerals that havebeen used in synthetic fluid inclusion studies is extensive:forsterite, enstatite and diopside (Johnson 1990; Johnsonand Jenkins l99l); calcite, sphalerite, and pyrite (Parilovet al., 1990; Lefaucheux et al., 1972); sodium bariumplagioclase (Kotelnikov et al., 1990); fluorite (Loredo-Perez and Garcia-Iglesias, 1984); halite (Davis et al.,1990); and scapolite and wollastonite (Kotelnikova andKotelnikov, 1988; Kotelnikov and Kotelnikova, 1989).

Initial efforts in inclusion synthesis in quartz were di-rected toward the formation of primary inclusions innewly precipitated overgrowths on seed crystals. It soonbecame apparent that although it was indeed possible toform inclusions in overgrowths, from a practical stand-point it was preferable to form them as secondary inclu-sions along preexisting fractures as was done by Shelton

and Orville (1980). A single fracture plane parallel to themicroscope stage could contain dozens ofpancake-shapedsecondary fluid inclusions, each with its shortest axis per-pendicular to the stage-the orientation resulting in thebest possible optical resolution. Primary fluid inclusionson the other hand were sparse, randomly distributed, andusually did not occur in such advantageous geometries.

With the above considerations in mind, attempts weremade to minimize the effort involved in producing inclu-sions so that the emphasis could be placed on the goalsof the particular study. The procedure given in Sternerand Bodnar (1984) was found to satisl! this requirementby consistently producing large numbers of easily mea-surable fluid inclusions over a broad range of experimen-tal conditions. The significant feature ofthis procedure isthat it involves the use ofprefracturedquartz cores pro-duced by heating the quartz in an oven to 310'C (not350 'C as previously reported) and then rapidly quench-ing in cold distilled HrO. Fractures produced by this ther-mal fracturing technique (Fig. la) are superior in orien-tation and number to those resulting from mechanicalfracturing (Shelton and Orville, 1980), and the procedureis considerably simpler.

The fractured quartz cores are sealed with an arc weld-er into noble-metal capsules along with fluid of the de-sired composition. The capsules are then placed in a hy-drothermal pressure vessel at the desired P- 7 conditionsfor several days, allowing fluid inclusions to form alongthe fracture planes.

The above procedure is completely satisfactory for manysynthetic fluid inclusion applications such as the prepa-ration of low-salinity brine inclusions for use as calibra-tion standards (Haynes et al., 1988; Mernagh and Wilde,1989; Frantz et al., 1988) or in studies of properties ofthe inclusions themselves (Bodnar et al., 1989; Sternerand Bodnar, 1989). However, for the application ofsyn-thetic inclusions in phase equilibria or PW studies, themost accurate control possible of fluid composition, den-sity, temperature, and presswe is required. Toward thisend, several modifications to the 1984 procedure havebeen devised and are reviewed in the following discus-srons.

Compositional and volurnetric heterogeneity

Under some circumstances, the procedure described bySterner and Bodnar (1984) produces inclusions with vari-able compositions or densities within a single sample,even though the experimental P-T conditions are in theone-fluid phase field for the particular bulk composition.This situation arises when the inclusions begin to form(l) before the fluid components mix thoroughly in thecapsule or (2) before the experimental pressure and tem-perature have been stabilized or (3) both. The first sce-nario occurs with bulk compositions that are immiscibleat low temperatures (e.g., COr-HrO mixtures and high-salinity brines). These compositions will remain unmixedin the capsule until heating has begun at the start of anexperiment. Although mixing occurs as temperature in-

1 5 8 STERNER: SYNTHETIC FLUID INCLUSIONS

creases, inclusions may begin to form before the fluidscompletely homogenize, resulting in a compositionallyheterogeneous sample.

A clear statement of this problem is presented in Bod-nar and Sterner (1987). Compositionally homogeneouspopulations of inclusions may be prepared from under-saturated or moderately oversaturated brine solutions us-ing the 1984 procedure. However, the components fail tomix uniformly before the inclusions begin to form if thebulk salinity is above approximately 40 wto/o. Conse-quently, large ranges in composition result in inclusionswithin a single sample. This does not occur with under-saturated brines because they can be loaded as a singlephase or will mix in the capsule prior to heating. Theproblem can be minimized by using a low synthesis tem-perature, but this is often impractical because of the fluid

phase relations or because high-temperature fluid prop-erties are being sought.

A potential solution to the problem of premature frac-ture healing, presented by Bodnar and Sterner (1987),involves the use ofunfractured quartz cores. Capsules areloaded as described above except that unfractured quartzis used; the capsules are allowed to stand in the cold sealvessel at the experimental P and T for sufficient time(days) to allow the fluid to homogenize. At some point,the experimental vessel is removed from the furnace andair quenched a few hundred degrees. The quartz is frac-tured as it passes rapidly through the a-B transition, whichoccurs at 573 "C at I bar and 25 "C higher with eachsuccessive kilobar of pressure. The vessel is then imme-diately reinserted into the furnace, and the temperatureand pressure restablize in about 25 min. Inclusions aretrapped along the newly formed fractures from the ho-mogeneous fluid. This procedure effectively reduces thecompositional heterogeneity of the resulting inclusions toa point at which other experimental uncertainities be-come more important (i.e., thermal gradients in the heat-ing-freezing stage and thermocouple calibration). Unfor-tunately, the technique has several drawbacks. First, itapplies only to experimental conditions within the A quartzfield (the high-temperature side ofthe transition). Second,the fractures occur at 45' angles to the long axis of thequartz core (Fig. lb), which makes them less than idealfor later microscopy using ordinary sample preparationprocedures. Also, the large fractures penetrate most of theway through the qluartz, often resulting in disintegrationof the core during later sample preparation. Lastly, inclu-sions formed by this procedure are few and far between-one encounters lots of poorly healed fractures. Still, insome cases this approach may provide a viable solutionto problems of inclusion heterogeneity.

€-

Fig. 1. Photomicrographs of typical fracture patterns pro-duced in quartz by the different procedures described in the text.Each photograph is a side view of a 5-mm diameter quartz corewith its axis oriented horizontally (i.e., the short dimension ofeach photo is =5 mm). The fracture orientations are apparentlycontrolled only by the physical geometry ofthe quartz and areunrelated to its crystallographic orientation. (a) A tlpical frac-ture pattern resulting from thermal shock according to the 1984procedure. The numerous fracture planes oriented perpendicularto the long axis of the core (vertical in the photo) provide ideallocalities for inclusion synthesis and later microscopic observa-tion following sample preparation. The pattern of fractures shownin (b) is typical ofthose formed as the core passes rapidly throughthe a-B phase transition of quartz. Inclusions occurring alongfractures produced by this procedure are ill suited to routinemicrothermometric study owing to incomplete crack healing andproblems in sample preparation. Typical fractures resulting fromthe IFS procedure are shown in (c). Note the much gteater frac-ture density, smaller individual fractures, and apparent randomorientation compared with a and b. Such fractures rarely pene-trate the core deeper than 1.0-1.5 mm and therefore present nodifrculties during later sample preparation.

STERNER: SYNTHETIC FLUID INCLUSIONS 159

Sterner et al. (1988), using prefractured quartz cores,found that by cycling the pressure several kilobars duringthe first few hours of an experiment the fractures couldbe held opened long enough for very high salinity fluids(ca. 90 wto/o NaCl) to homogenize. This approach reducescompositional heterogeneity to a level comparable withother uncertainities while still yielding large numbers ofmeasurable inclusions. However, the procedure frequent-ly causes substantial volumetric heterogeneity; in exper-iments with high-salinity salt solutions, vapor bubble dis-appearance temperatures sometimes vary by as much as100 "C within a single sample.

Volumetric heterogeneity can also arise in the absenceof pressure cycling if, at sufficiently high temperatures(above ̂ "600 "C), inclusions start to form before the finalP-Z conditions are reached and. therefore. before thedensity is stabilized. Under these circumstances, a sub-stantial range in homogenization temperatures (fromwhich inclusion densities are calculated) is also recorded.One possible solution is to attain the desired experimen-tal conditions as rapidly as possible. This can be partiallyimplemented by preheating furnaces and using small odpressure vessels (smaller thermal mass), but these pro-cedures will not totally solve the problem. Also, the fasterthe desired experimental conditions are achieved, the lessapt initially heterogeneous fluids are to mix completelybefore inclusion formation.

ZhangandFrantz (1987) overcame the problem of vol-umetric heterogeneity by using a rapid-quench designpressure vessel (Wellman, 1970;Frantz and Popp, 1979).In this approach, the pressure vessel is sufficiently longso that the hot end can be placed in the furnace andpreheated to the desired temperature while the capsuleresides at the cold end outside the furnace at a temper-ature near 25 'C. After the temperature stabilizes, thevessel is rapidly pressurized with Ar, simultaneously forc-ing the capsule into the hot zone. The capsule reaches thedesired temperature "in just several minutes" accordingIo Zhang and Frantz.

The Zhang and Frantz (1987) procedure results in vol-umetrically homogeneous generations of inclusions fromfluids that are compositionally homogeneous at low tem-perature. However, the extremely rapid heating from lowtemperature would probably not allow suftcient time tohomogenize an initially heterogeneous bulk compositionsuch as a high-salinity brine. Adjustments could un-doubtedly be made to this procedure to enhance its ap-plicability to compositional heterogeneity problems. Spe-cifically, the capsule could be maintained at anintermediate temperature at high pressure for some timeand then the vessel tilted, allowing the capsule to slideinto the hot end.

The a-p transition fracturing procedure described pre-viously is applicable to problems of both compositionaland volumetric heterogeneity. However, because approx-imately 25 min are required to return to the experimentalconditions, the possibility ofvariable densities still existsalong with the poor quality of the inclusions.

It is apparent from the above discussions that althoughit is frequently possible to address either the problem ofcompositional or volumetric heterogeneity, the solutionto one problem can be the cause of another. The ultimateaim of the synthetic inclusion approach or any experi-mental procedure designed to study fluid properties athigh pressures and temperatures is to stabilize the systemat P and, Z, obtain a representative sample of the fluid,and then analyze the sample or preserve it for later anal-ysis. If the system is unstable or if the sample decaysbefore analysis, the procedure is unsatisfactory for thatapplication. During a recent synthetic fluid inclusion studyof the COr-HrO system (Sterner and Bodnar, l99l), amethod was devised whereby both compositional andvolumetric homogeneity could be routinely achieved inhigh-temperature (>600 "C) experiments from fluids thatare immiscible at low temperature (Sterner, 1990). Thisnew procedure involves fracturing the quartz inside thepressure vessel during the experiment and, therefore, willbe referred to as the in situ fracturing method (ISF). Thenew modifications to the inclusion synthesis procedureare outlined in the discussions that follow along with somepotential applications brought about by the improved ex-perimental design.

IN srru FRACTURTNG rnocnnunr (ISF)

The general procedure follows that described in Sternerand Bodnar (1984) and elaborated on in Bodnar andSterner (1987). Cylindrical cores 4.5 mm in diameter andabout I cm long are cut from inclusion-free Brazilianquartz. The unfractured cores are loaded into 5-mm di-ameter, l8-mm long noble-metal capsules along withsuitable starting materials to generate the desired fluidcomposition at the experimental conditions. The capsulesare sealed at each end by welding metal end caps in placeas described by Bodnar and Sterner (1987). A maximumof two such capsules is loaded into a cold-seal pressurevessel followed by a 7-cm length of filler rod (Fig. 2). (Theoverall length ofthe pressure vessel, excluding the closurenut, is 30 cm.)

The loaded pressure vessel is then installed on a spe-cially designed rack that includes a sliding furnace, high-pressure plumbing, and thermocouple assemblies forcontrolling and monitoring temperature. A schematic di-agram of the apparatus is presented in Figure 3. The im-portant feature of the design of this cold-seal rack is thatit allows complete rotation of the pressure vessel-furnaceassembly through nearly 180'(from vertical through hor-izontal to vertical) while the system is at pressure.

The pressure vessel is held in place by a rigid connec-tion to the high-pressure coupling, as shown in Figure 3,and supported initially by a removable metal strap. Atthe beginning of the experiment, the furnace is slid intoplace and locked, and the entire assembly is rotated to avertical position with the closure nut at the top (Fig. 2A).A few sharp raps on the closure nut with a metal rodinsure that the capsules and filler rod slide all the way tothe opposite end. While still in this vertical orientation,

r60

Gapsules

Fig. 2. Schematic illustration of the pressure-vessel, capsule,and filler-rod geometries used in the in situ fracturing procedurefor fluid inclusion synthesis.

the vessel is pressurized to approximately 500 bars andthe furnace is turned on. In experiments involving thegeneration of CO, from silver oxalate, the vertical ori-entation is maintained until the gas is liberated to insurethat the capsules are not forced toward the closure nut bythe explosive decomposition reaction.

Following the completion of any decomposition reac-tions required to generate desired fluid components, thepressure vessel-furnace assembly is rotated to the hori-zontal position and locked (Fig. 2B). During continuedheating, sufficient pressure is maintained in the vessel toprevent the capsule(s) from rupturing. Once the desiredtemperature is achieved, the pressure is set and the sys-tem is allowed to stabilize. There is no urgency at thispoint because inclusions have not yet begun to form. Af-ter the experiment has stood long enough to ensure com-plete thermal stability and fluid homogeneity, the quartzcores are fractured as described below, and inclusion syn-thesis ensues.

Regardless of the desired synthesis pressure, the exper-imental vessel is brought to a temporary pressure of 2kbar with the common line opened. The pressure vessel-furnace assembly is then unlocked and rotated to the ver-tical position-this time with the closure nut pointed down(Fig. 2C). The filler rod and capsules slide into the coldend of the vessel, and contact with the colder pressuremedium forced up around the filler rod fractures the quartzwithin the capsules (Fig. lc). Again, a few sharp raps onthe closure nut will jar loose a bound capsule. Immedi-ately after hearing the filler rod and capsules collide withthe closure nut, the pressure vessel-furnace assembly isrotated through horizontal to the vertical position withthe closure nut on top (Fig. 2A). The capsules can beheard to drop back into the hot end ofthe pressure vessel,and the entire apparatus is then returned to the horizontalposition (Fig. 28) and locked for the duration of the ex-periment. Finally, the pressure is returned to the desired

STERNER: SYNTHETIC FLUID INCLUSIONS

Fig. 3. Schematic illustration ofthe pressure vessel-furnaceassembly used in the in situ fracturing procedure for fluid inclu-sion synthesis. A, B, and C are the high-pressure, thermocouple,and furnace power leads, respectively. D is the sliding furnace,and E is the flexible (5-mm, high-P) pressure line. The rectan-gular-shaped rack supporting the furnace is capable of rotationthrough I 80" as indicated.

experimental value and the common line kept openeduntil the temperature again stabilizes (approximately 4min). The temperature should return to its exact prefrac-ture value with no further adjustment.

The experimental conditions are maintained for sev-eral days following the fracturing procedure during whichtime fluid inclusions form as imperfections along fractureplanes. At the end of the experiment, the furnace isswitched of and the vessel is allowed to cool slowlythrough the d-P transition until the pressure-temperatureconditions are within rhe a quartz field. The furnace maythen be slid offand the vessel cooled with room air, or aforced-air quench may be implemented. Rapid coolingthrough the a-B transition will cause further fracturing ofthe quartz core, and though this generally does not resultin the formation of new fluid inclusions, the unhealed a-0fractures will cause the core to disintegrate during latersample preparation. Following the quench, the capsulesare removed from the pressure vessel and opened, andthin sections are prepared according to the procedure de-scribed in Bodnar and Sterner (1987).

In the original procedure described by Sterner andBodnar (1984) a full-length filler rod was used (see Ker-rick and Boettcher, 1971). The purpose ofthe filler rodis to minimize thermal gradients within the hot zone ofthe pressure vessel. Although satisfactory results have beenobtained using a 7-cm filler rod in the procedure de-scribed above, it is possible that somewhat longer fillerrods (and commensurately longer pressure vessels) wouldmore effectively reduce the gradient. A further check onthe temperature control would be aforded by testing thechosen system geometry using an internal thermocouple.

STERNER: SYNTHETIC FLUID INCLUSIONS t 6 l

8 0 0 ' C

700 .c

600 .c

500 "c

Density determinations using the ISF method

The effectiveness ofthe above procedure in producinghomogeneous populations of inclusions under extremeexperimental conditions has been demonstrated in thePWX stttdy of the COr-HrO system by Sterner and Bod-nar (1991). Extensive fluid immiscibility exists in the COr-HrO binary at temperatures below 200-300.C. Thus, fora broad range of bulk compositions the fluid cannot ho-mogenize in a hydrothermal experiment until substantialheating has occurred. This posed no problem at moderateexperimental temperatures; densities of COr-HrO fluidswere successfully determined up to 600 "C using the 1984procedure. However, above 600 "C premature fracturehealing significantly reduced the accuracy ofdensity mea-surements made using this approach.

Molar volumes (MVs; l/molar density) of COr-H,Ofluids calculated from fluid inclusions formed at 700 .C

and 3 kbar using the synthesis procedures ofSterner andBodnar (1984) are shown as open circles in Figure 4. De-tails of the molar volume calculation are given in Sternerand Bodnar (1991). Each datum represents the averageof calculated MZs from several inclusions in a given sam-ple. The solid line corresponds to MVs derived assumingideal mixing of CO, and H,O at 700 'C and 3 kbar. Therelatively large uncertainties associated with each mea-surement and the erratic magnitudes of tlire MVs them-selves result from inclusions formation prior to equili-bration at the final P-Z conditions. The large range inMVs calculated from inclusions within a single sample(reflected in the uncertainties for these data shown on Fig.4) is indicative of inclusion trapping through time duringchanging P-?" conditions, whereas the consistently lowvalues ofthe calculated volumes result from trapping whileapproaching the final P-l'conditions from the Iow-MV(high-density) direction.

Uncertainties in MVs calculated from this set of ex-periments have been solely attributed to variation in fluiddensity resulting from trapping prior to attainment of thefinal P-?"conditions and, thus, are represented by verticalerror bars. However, the final errors could be due, in part,to compositional variation among individual inclusionsresulting from trapping prior to the attainment of cap-sule-wide fluid homogeneity and, as such, may be moreproperly represented by both vertical and horizontal er-ror bars. The extent of contribution from each of thesefactors is unknown-only that the combined effect resultsin substantial errors in the final calculated molar vol-umes.

Molar volumes of COr-HrO mixtures were redeter-mined at 3 kbar and 700 "tC using the ISF proceduredescribed above. The resulting volumes are shown as filledcircles in Figure 4. Note that both the overall scatter andthe individual uncertainty in calculated volumes for in-dividual samples are greatly improved. The new volumesare both internally consistent and of reasonable magni-tude (Sterner and Bodnar, l99l), implying both compo-sitional and volumetric homogeneity among the inclu-

1-'.i"-'-"""''""' E

60

50I

q)

a 300 .25 r . 0 0

Fig. 4. Comparison of molar volumes of COr-HrO mixturesat 700 'C and 3 kbar determined using the ISF method (filledcircles) and the 1984, prefractured quartz approach (open cir-cles). X.o, equals the mole fraction CO, relative to CO, + HrO.The solid line represents ideal mixing of the binary fluids at thesame pressure and temperature based on volumes of the pureend-members predicted by Haar et al. (1984) and Shmonov andShmulovich (1974). Dashed lines are ideal mixing volumes at500. 600. and 800 C.

sions within each sample and attesting to the effectivenessofthe new procedure.

A detailed error analysis of the volumetric study is pre-sented by Sterner and Bodnar (1991). The average un-certainty in experimentally derived molar volumes of COr-HrO mixtures is 0.80 volo/0. The average uncertainty inMV determinations at 400, 500, and 600 .C (1984 meth-od) is 0.82 volo/0, yet the average at 700 "C (ISF method)is only 0.74 volo/o. Although statistics for data at 700 "Crepresent only a modest improvement over those of thelower temperature data, they are significantly better thanthe results obtained by using the I 984 synthesis approachat 700'C (see Fig. 4).

Although the accuracy of PWX data derived from syn-thetic fluid inclusions varies from one system to another,it is instructive to identify the principal sources oferrorin a given study with the hope of improvement in futureapplications. The leading causes of error in volumetricdeterminations of COr-HrO mixtures, using either the1984 approach or the ISF procedure, are uncertainties inexperimental P and, T and ensuing variation in Th (CO)within a given sample. Assuming that the inclusions areindeed trapped from homogeneous, one-phase fluids, thevariation in CO, homogenization temperature betweeninclusions in a given sample probably reflects true bulkdensity variations and arises from fluctuations in tem-perature and pressure during the experiments. These aredifrcult problems to eliminate, but with proper electronicisolation and (ambient) temperature stability in the lab-oratory they can be further reduced.

Discussion

The ISF method has been found to produce large num-bers of compositionally and volumetrically homogeneous

0 .50 0 .7 5Xcoz

r62 STERNER: SYNTHETIC FLUID INCLUSIONS

fluid inclusions within a single sample. While the opticalclarity and abundance ofinclusions produced in this wayare somewhat less ideal than those synthesized using theI 984 method, a sufficient number of large inclusions willinvariably be found in each sample. the new procedurehas been found to work well at experimental tempera-tures of600, 700, and 800'C, although resulting fracturedensity and, thus, the number of inclusions formed israther low at 600'C. At temperatures below 600 "C, theformation rate of inclusions appears to be slow enoughthat the ISF procedure has been unnecessary thus far. Atexperimental temperatures above 700 oC, the fracturedensity can become so large that inclusions are literallystacked on top of each other. Under such circumstances,the inclusion density can be reduced by increasing thepressure above 2 kbar during the fracturing procedure. Al- or 2-kbar increase can significantly reduce the fracturedensity, although it will increase the risk of vessel failureso that additional safety precautions are advised.

In microthermometric studies of synthetic fluid inclu-sions, it is frequently observed that most inclusions alonga single fracture plane are of nearly identical compositionand bulk density. Early in the synthesis process, entirefracture planes are initially sealed offalong their outsideedges, thereby isolating their contents from the bulk cap-sule fluid. Subsequent dissolution and reprecipitation ofquartz within this large cavity causes necking and resultsin the formation of numerous smaller inclusions. Thecomposition of the smaller inclusions will reflect that ofthe fluid in the original fracture and may be different thanthe bulk fluid composition if large-scale heterogeneity ex-isted within the capsule at the time of initial isolation.The density of the smaller inclusions will depend on boththe fluid composition in the original fracture and the P-Iconditions of the system at the exact moment the fracturewas sealed off. Thus, the number of measurements fromindependent fracture planes is more important than thetotal number of inclusions measured for obtaining a rep-resentative set of microthermometric data. Use of the ISFmethod results in a relatively large number of small, ran-domly oriented, intersecting fractures (Fig. lc) along whicha small number of inclusions have formed. Although thetotal number of measurable inclusions present in a givenchip will generally be less than that produced using the1984 method, the number of measurable inclusions oc-curring on independent fractures is frequently greater.

During the ISF procedure, a rapid temperature deflec-tion of about 30 "C will be recorded on an externallymounted thermocouple. Obviously, the actual tempera-ture drop experienced by the samples is much larger than30'C-enough to result in thermal shock of the quartz-yet the temperalure will return to within one degree ofset point within approximately 4 min. This recovery timeis apparently instantaneous with respect to the time re-quired to begin to trap fluid inclusions. In our laboratory,the experimental temperature is monitored using an In-conel-sheathed, K-type thermocouple positioned in a welldrilled in the end of the pressure vessel. However, our

electrical configuration allows temperature controllingfrom either a pressure vessel-mounted thermocouple ora thermocouple located within the furnace. Although theprocedure appears to work equally well when controllingfrom either thermocouple, the temperature stabilizes atthe desired value somewhat sooner when the furnacethermocouple is used for temperature control'

The greater frequency ofcapsule failure using the ISFmethod compared with the 1984 approach is undoubt-edly due to the additional deformation experienced bythe metal during the fracturing procedure. Therefore, itis recommended that the capsule weights be recorded be-fore and after each experiment to detect any fluid leakage.

The ISF method has been found to work equally wellusing HrO, CHo, or Ar as the pressure medium. Thus,the procedure may be easily implemented on either gas-or HrO-pressure cold-seal stations. Because of the unlim-ited time available to reach chemical equilibrium prior

to inclusion formation, interesting possibilities presentthemselves regarding the use of mixed-gas buffering sys-tems.

A precursor to the experimental apparatus shown inFigure 3 was developed by S. M. Sterner and C. S. Oakes.A length of 5-mm diameter, high-pressure tubing wasformed into a flexible coil approximately 18 cm in di-ameter containing four complete revolutions. The coillinked the pressure vessel to the high-pressure couplingon a standard cold-seal rack. In situ fracturing ofthe quartzcores was accomplished by sliding the furnace off androtating the pressure vessel through the necessary orien-tations (Fig. 2) then replacing the furnace. Results similarto the ISF method described above were obtained usingthis technique except that the removal ofthe furnace re-sulted in considerable heat loss so that the experimentaltemperature required much longer to restabilize. If ex-perimental pressures are low ('2 kbar),2-mm diameterpressure line can be used to facilitate this procedure; how-ever, the ISF method described above is considerably saf-er, and the present (coil) method presents no apparentadvantages aside from simplicity.

A fundamentally different cold-seal apparatus, in prin-ciple, also capable of in situ fracturing, was designed byPhil Ihinger at the California Institute of Technology. Thepressure vessel-furnace assembly in this configuration re-mains stationary in the vertical position with the closurenut toward the bottom. The capsules are supported by a

thin rod that extends downward through the seal into

another inverted, cold-seal vessel. A small magnet is af-fixed to the lower end of the thin rod inside the lowerpressure vessel. The capsule-thin rod-inner magnet as-sembly is capable of several centimeters of vertical mo-tion while the entire apparatus is at pressure and the up-per vessel is at temperature. During operation, the lowervessel stays at room temperature and the capsule(s) aremoved in or out of the hot zone by adjusting the position

of the inner magnet using a larger circular magnet located

external to the lower vessel.

AonttloNll- CoNSIDERATToNS

Correction for the nonisochoric behavior ofquartzFluid inclusions are not strictly isochoric systems. At

high temperatures the solubility of the host mineral canbecome appreciable and the volumes of individual inclu-sions as well as the properties ofthe fluids can be affectedby dissolution of the inclusion wall. Silicate melt inclu-sions (Roedder, 1984) formed at temperatures near thesilicate liquidus are an extreme case where the proportionof dissolved silicate is greater than the amount of aqueousphase. Although host dissolution can often be neglectedfor quartz and other silicate host phases because oftheirlow solubilities even at relatively high temperatures, thevalidity of this assumption should always be assessed withregard to the particular system under investigation.

It is frequently necessary to account for the change inthe volume of an inclusion cavity between two sets ofP-Z conditions because of thermal expansion and com-pressibility of the host. For quartz, the maximum correc-tion is on the order of a few percent and can be accom-plished using information given in Figure 5 constructedfrom equations presented in Hosieni et al. (1985). Thevolume change factor is used to relate the volume of aninclusion at a new set of P-?"conditions to its volume atan initial pressure and temperature as follows:

/vr.,,\vP, , r , - vP, . r , l : : - l ( l )

\vx'''/where Wr\ and Wzr2 are the inclusion volumes (or spe-cific volumes) at the initial and final P-T conditions, re-spectively, and Vro,'r, and, Vlz,rz are the volume changefactors corresponding to each set of conditions. The com-putation is facilitated by a Fortran program available fromthe author that calculates l/Pz.rz using trar,rr, Pt, p2, Tband T, as initial input. The program uses the equationsof Hosieni et al. (1985) with corrections described inSterner and Bodnar (1991). Both the Fortran programand Figure 5 are amenable to use with natural samples,although it should be recalled that the specific equationsfrom which they are derived are applicable only to inclu-sions in quartz. Also, uncertainties in compositions ofnatural samples usually yield much larger errors than thoseresulting from the nonisochoric behavior ofthe host.

Liquid-vapor equilibria determinations

Synthetic fluid inclusions have been applied to liquid-vapor equilibrium determinations in several fluid sys-tems: NaCl-HrO (Bodnar et al., 1985; NaCl-KCl-HrO(Sterner and Bodnar, 1986); COr-HrO (Sterner and Bod-nar, l99l); CO,-H,O-NaCI (Sterner et al., 1984; Kotel-nikov and Kotelnikova, 1990; Popp and Frantz, 1990);COr-H,O-CaClr(Zhangand Frantz, 1989). Most of thesedeterminations employed the 1984 synthesis approach.

In studies of salt HrO systems (e.g., Bodnar et al., 1985),initial fluid compositions at or below room-temperaturesaturation are used to insure fluid homogeneity at the

STERNER: SYNTHETIC FLUID INCLUSIONS r63

0 2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0

Temperature ("C)

Fig. 5. Volume change factor (Z^) relating the volume of afluid inclusion at 20 t and I bar to its volume at high P and Z(see Eq. l). The light solid lines correspond to the 1 bar and,2,4, 6,8, and l0 kbar isobars of I/^. Alpha and F qnrtz regionsare separated by the heavy solid line. The diagram was con-structed using equations from Hosieni et al. (1985).

start of the experiment. The desired experimental tem-perature (Ztp) is achieved and stabilized before the fluidis allowed to unmix. The topologies of salt-HrO systemslend themselves to this approach because experimentscan be initially heated at high pressures well within theone-fluid phase field. The two phase field is then enteredby rapidly decreasing the pressure, and unmixing ensuesaL P and Z. The sudden pressure drop appears to causethe nucleation of a large number of small vapor bubblesthat become trapped more or less randomly throughoutthe fracture system, frequently resulting in the intimatecoexistence ofboth vapor- and liquid-rich inclusions alongthe same fractures. Available solubility and freezing-pointdepression data for the geologically common salts allowthe determination of compositions of the resultant inclu-sions using microthermometric measurement.

In addition to forming inclusions representing end-member (or near end-member) fluid compositions, theabove procedure also results in the formation of numer-ous inclusions that have trapped mixtures of the liquidand vapor phases present at equilibrium. Liquid-rich in-clusions from a given sample generally display a verynarrow range in composition, whereas a much broadercompositional range is frequently recorded for vapor-richinclusions. This is likely the result of trapping only theliquid in the liquid-rich inclusions and the concuffenttrapping of small but variable amounts of liquid in thevapor-rich inclusions. Thus, the determination of theequilibrium liquid composition is straightforward,whereas that for the composition of the coexisting vaporphase is somewhat arbitrary-generally taken to equal thelowest salinity measured. This phenomenon necessitatesthe salinity determination of a large number of vapor-rich inclusions. Since there is no guarantee offinding an

A 1 .05

v 1 .04

€ 1.03

fl 1.02

S 1.01

.E 1.oooo 0.99

= 0.e8

I o.e7

t64 STERNER: SYNTHETIC FLUID INCLUSIONS

inclusion that has trapped only the vapor, the procedureyields only a maximum salinity estimate for the compo-sition of the vapor end-member.

The observed range in composition of the vapor-richinclusions can be significantly reduced by entering thetwo-phase field slowly during isobaric heating at the finalexperimental pressure. The result is to segregate physi-cally the vapor and liquid, thereby reducing the oppor-tunity to form mixed inclusions. The separation can befurther enhanced by maintaining the capsules in a verticalposition during the experiment. However, problems mayarise using this approach if, at some point after initialphase separation, continued heating to T.*p results in in-creasing salinity of the equilibrium vapor or decreasingsalinity of the equilibrium liquid. Under such circum-stances, the physical separation of the two fluids mayprevent spontaneous remixing before inclusion begin toform (see Bodnar et al., 1985). For all pressures above500 bars in the system NaCl-HrO, neither branch of thesolvus begins to close below 1000'C (see Fig. l0 in Bod-nar et al., 1985). Whether this is true of other geologicallyrelevant brine systems is not known, so the consequencesof premature fracture healing must be considered.

Using an isobaric heating approach at high tempera-tures will undoubtedly result in the trapping of some in-clusions aIT < T. p. Provided the system is characterizedby divergence ofboth branches ofthe solvus with increas-ing temperature, the appropriate extreme compositionsmeasured for each type of inclusion should represent thebest experimental values.

In studies ofgas-bearing systems, a bracketing proce-dure is followed in the determination of liquid-vaporequilibria because the exact composition of such inclu-sions cannot be determined microthermometrically(Sterner et al., I 984; Kotelnikov and Kotelnikova, 1990;Zhang and Frantz, 1989). There is little choice of P-Ipaths in these systems because immiscibility occurs atlow temperatures at most pressures; thus, it is virtuallyimpossible to avoid the two-phase field. Fortunately,much geologically relevant information may be gleanedfrom these systems at low to moderate temperatures(=600 oC), where experience has shown that fluid equi-librium will be closely approached prior to the onset ofinclusion formation (Sterner and Bodnar, l99l).

It is not clear whether the ISF method would representany improvement over its precursor in the direct deter-mination of liquid-vapor equilibria. Advantages resultingfrom the relatively instantaneous stabilization of pressureand temperature would likely be offset by the formationof large numbers of mixed inclusions. However, the ISFmethod has been successfully employed in the indirectdetermination of liquid-vapor equilibria in the COr-HrOsystem (Sterner and Bodnar, l99l). In this procedure,inclusions are synthesized in the one-fluid phase field froma fluid of known composition. The ?" coordinate of apoint on the solvus is determined from the measuredinclusion total homogenization temperature (7h,",), andthe Pcoordinate is determined from an appropriate equa-

tion of state or a complete set of volumetric data. A se-rious drawback to this procedure compared with thebracketing approach is the inability to measure accurately2h,", when homogenization occurs in the vapor phase (seediscussion in Sterner and Bodnar, 1991).

Generation of rnulticomponent fluids at P a;nd T

Another important aspect of inclusion synthesis is ob-taining fluid(s) of desired composition at the experimen-tal P and Z. This is an important consideration-not onlyin PWX studies but also in the preparation of syntheticfluid inclusions to be used as microanalytical standards.The chemical reagents and procedures listed below havebeen successfully employed by a number of investigatorsto generate multicomponent fluids of known composi-tions in hydrothermal experiments.

Low-salinity brines (undersaturated at room tempera-ture) are the most straightforward and are generally load-ed into the capsule as premixed solutions using a syringe.More concentrated salt-HrO solutions are prepared byloading the anhydrous salts and independently weighingthe amount of each component. Salts that hydrate readi-ly, like CaCl, and NaOH, require special treatment toachieve known concentrations. Undersaturated CaClr-HrO solutions may be accurately prepared by gravimetrictitration of CaCO, with concentrated HCI until a neutralsolution is obtained, whereas the preparation of high-sa-linity CaClr-HrO brines may require the direct loading ofthe anhydrous salt in an inert atmosphere (i.e., using aglove box). Alkali-hydroxide solutions are best deter-mined by titration with a standard acid after preparation.

Expandable gases have been loaded in hydrothermalexperiments using solid compounds that break down athigh temperatures to yield stoichiometric amounts of thedesired components. Holloway and Reese (1974) rec-ommended several organic and inorganic reagents forgeneration of fluids in the C-O-H-N system. Additionalcompounds are discussed by Frantz et al. (1989), and tothe list one may also add silver azide (AgNJ, native sul-fur, and HCL"'. Two recent innovations in capsule load-ing protocol have been proposed for the direct introduc-tion of volatile components. The first, by Frantz et al.(1989), involves the cryogenic adsorption of knownquantities ofgases onto a solid substrate (gel) placed inthe bottom ofthe capsule. The substrate significantly re-duces the vapor pressure ofthe gas such that even N, canbe condensed at liquid N, temperatures. The second pro-cedure, by Boettcher et al. (1989), employs a special fix-ture that allows room-temperature loading of gases andgas mixtures at high pressures (up to 100 bars). Both pro-cedures show promise for generating geologically relevantfluids in synthetic fluid inclusion experiments.

Another technique for obtaining desired fluid compo-sitions at elevated P and T involves the use of buffersand semipermeable membranes to control fluid specia-tion once the experimental conditions have been realized(Chou, 1987; Gunter et al., 1987). Using this approach,some components are added directly to the capsule (e.g.,

STERNER: SYNTHETIC FLUID INCLUSIONS 1 6 5

some form of C, H2O, etc.); others are provided (or re-moved) by solid-fluid interaction (e.9., O, S, etc.) whileH is allowed to difihse in and out through the capsulewalls. The problem with these procedures in the contextof conventional fluid inclusion synthesis (i.e., the 1984method) is that the fluid phase requires time to equili-brate. The length of time is a complex function of diffu-sion rates, temperature, chemical potential gradients, bulkcomposition, system mass, reaction kinetics, and a mul-titude of other considerations. At almost all temperaturesthere is the imminent possibility (probability) that inclu-sions will begin to form before speciation in complex sys-tems has reached equilibrium. This includes virtually allcases where species directly loaded into the capsule, orthose that are the result of initial decomposition reactionsare out of chemical equilibrium at the prevailing experi-mental conditions. The new ISF method of inclusion syn-thesis could have significant impact in investigations ofsuch systems under these conditions by allowing bettercontrol of the timing of fluid sampling relative to the rateof fluid evolution.

Furunr AppLrcATroNS oF syNTHETrcFLUID INCLUSIONS

The ISF procedure is not a panacea for synthetic fluidinclusion research. However, having eliminated the com-plication of premature inclusion trapping in many appli-cations, the problems that remain (e.g., adequate controlof experimental pressure and temperature, difficulties ingenerating desired fluid compositions, etc.) appear muchmore manageable. Perhaps the most important contri-butions ofthe new procedure will be in the preparationof homogeneous populations of inclusions from chemi-cally complex fluids for the purposes of PW investiga-tions, studies of low-P- ?" phase equilibria, and standard-ization of microanalytical techniques. A number ofgeologically important fluid components that have thusfar eluded study because of problems associated with theirslow production or dispersion throughout the capsuleshould be accessible using the new procedure.

Because the ISF method allows the bulk fluid to equil-ibrate at P and T prior to inclusion formation, there isconsiderable potential for high-P- I fluid speciation stud-ies using buffers and H2 membranes to control .for, .f"r,4,, DH, etc. Kinetically sluggish equilibria could first beestablished at the desired experimental conditions, fol-lowed by trapping representative fluid samples as ho-mogeneous populations of inclusions. Chemical specia-tion, volumetric properties, and phase equilibria couldthen be investigated using microthermometric measure-ment of phase transitions coupled with chemical analysisby various methods such as laser Raman microprobeanalysis, bulk leaching, or crushing into a gas chromato-graph or mass spectrometer. The presence of large num-bers of inclusions having identical compositions withinan individual sample will insure ample quantities of ma-terial for most bulk analytical techniques. Additionally,the residual capsule fluid may be analyzed using chro-

matographic techniques like those described by Frantz eta l . (1989).

The new procedure will aid in solubility studies of bothsparingly and highly soluble species. In both cases in situfracturing should allow homogeneous distribution of dis-solved species throughout the capsule prior to inclusiontrapping. For those species that dissolve and precipitaterapidly, any precipitation during the fracturing procedurewould likely occur in the form of numerous small nucleithat would immediately redissolve during reheating. Therapid reestablishment of the original experimental P-Tconditions after fracturing should preclude any large-scalediffusion ofdissolved species that would result once againin bulk fluid heterogeneity. It is unlikely that kineticallysluggish species would precipitate in the short time avail-able between fracturing and return to the original pres-sure and temperature.

Finally, volumetric determinations of high-salinitybrines have presented difficulties in the past because tech-niques required to insure compositional homogeneity ofthe bulk fluid have often resulted in the production ofvolumetrically heterogeneous inclusion populations withina given sample (Sterner et al., 1988). Use of the newsynthesis procedure should provide both compositionaland volumetric homogeneity resulting in more accuratedeterminations of PW properties at high concentration.

AcxNowr-nocMENTs

Critical reviews of earlier versions of this manuscript by R.C. Burmss,I-Ming Chou, and W.T. Parry have significanrly improved the final draft.Funding for this pro-ject was provided by NSF grant EAR-8607356 toRobert J. Bodnar and by the Director, Ofrce of Energy Research, Officeof Basic Energy Sciences, Division of Engineering and Geosciences of theU.S. Department of Energy under contract DE-AC03-76SF00098. TheISF procedure was developed while tlte author was at the Virginia Poly-technical Institute and State University, Blacksburg, Virginia.

RrrnnrNcns ctrEDBethke, P.M., Lysne, P., Foley, N.K., Sweetkind, G.P., and landis, G.P.

(1990) In-situ fluid sampling by synthetic fluid inclusions, VC2B, VallesCaldera, NM (abs.). Eos,7l, 1683.

Bodnar, R.J., and Stemer, S.M. (1985) Synthetic fluid inclusions in nat-ural quartz. II. Application to PZI studies. Geochimica ot Cosmo-chimica Acta, 49, I 855-1 859.

- (1987) Synthetic fluid inclusions. In G.C. Ulmer and H.L. Barnes,Eds., Hydrothermal experimental techniques, p.423-456. Wiley, NewYork.

Bodnar, R.J., Binns P.R., and Hall, D.L. (1989) Synthetic fluid inclu-sions-Vl Quantitative evaluation of the decrepitation behavior offluid inclusions in quartz at one atmosphere confining pressure. Joumalof Metamorphic Geology, 7, 229-242.

Bodnar, R.J., Bumham, C.W., and Sterner S.M. (1985) Synthetic fluidinclusions in natural quartz. III. Determination of phase equilibriumproperties in the system HrO-NaCl to 1000 qc and 1500 bars. Geo-chimica et Cosmochimica Acta, 49, 186l-1873.

Boettcher, S.L., Guo, Q., and Montana, A. (19E9) A simple device forloading gases in high-pressure experiments. American Mineralogist, 74,I 383-1384.

Boullier, A.M., Michot, G., Pecher, A., and Barres, O. (1989) Diftrsionand/or plastic deformation around fluid inclusions in synthetic quartz.New investigations. NATO ASI Series, Ser. C, 281 Fluid movement-Element transport. Cornposition ofthe Deep Crust, 45-60.

Chou, I-Ming (1987) Oxygen buffer and hydrogen sensor techniques at

r66 STERNER: SYNTHETIC FLUID INCLUSIONS

elevated pressures and temperatures. In G.C. Ulmer and H.L. Bames,Eds., Hydrothermal experimental techniques, p. 61-99. Wiley, NewYork.

Davis, D.W., Irwenstein, T.K., and Spencer R.J. (1990) Melting behav-ior of fluid inclusions in laboratory-grown halite crystals in the systemssodiurn chloride-water, sodium chloride-potassium chloride-water,sodium chloride-magnesium chloride-water, and sodium chloride-calcium chloride-water. Geochimica et Cosmochimica Acta, 54, 591-601 .

Frantz, J.D., and Popp, R.K. (1979) Mineral-solution equilibria, I. Anexperimental study of complexing and thermodynamic properties ofaqueous MgCl, in the system MgO-SiOr-HrO-HCl. Geochimica et Cos-mochimica Acta. 43. 1223-1239.

Frantz, J.D., Mao, H.K., Zhang,Y.G., Wu, Y., Thompson, A.C., Under-wood, J.H., Giauque, R.D., Jones, K.W., and Rivers, M.L. (1988)Analysis of fluid inclusion by X-ray fluorescence using synchrotronradiation. Chemical Geology, 69, 235-244.

Frantz, J.D., Zhang, Y.G., Hickrnott, D.D., and Hoering, T.C. (1989)Hydrothermal reactions involving equilibrium between minerals andmixed volatiles l. Techniques for experimentally loading and analysinggases and their application to synthetic fluid inclusions. Chemical Ge-ology,76, 57-70.

Gunter, W.D., Myers, J., and Girsperger, S. (1987) Hydrogen: Metalmembranes. In G.C. Ulmer and H.L. Barnes, Eds., Hydrothermal ex-perimental techniques, p. 100-120. Wiley, New York.

Haar, L., Gallagher, J.S., and Kell, G.S. (1984) NBS/NRC stearn tables:Thermodynamic and transport properties and computer programs forvapor and liquid states of water in SI units, 320 p. Hemisphere, Wash-ington, DC.

Haynes, F.M., Sterner, S.M., and Bodnar, R.J. (1988) Synthetic fluid in-clusions in natural quartz. IV. Chemical analysis of fluid inclusions bySEM/EDA: Evaluation of method. Geochimica et Cosmochimica Acta,52, 969-977.

Holloway, J.R., and Reese, R.L. (1974) The generation of Nr-COr-HrOfluids for use in hydrothermal experimentation I. Experimental methodand equilibrium calculations in the C-O-H-N system. American Min-eralogist, 59, 587-597.

Hosieni, ICR., Howald, R.A., and Scanlon, M.W. (1985) Thermodynam-ics of the lambda transition and the equation of state of quartz. Amer-ican Mineralogist, 7 O, 7 8Z-7 93.

Johnson, E.L. (1990) Planar arrays ofsynthetic fluid inclusions in spon-taneously nucleated forsterite crystals gown at constant pressure andtemperature in a hydrostatic environment. Geochimica et Cosmochi-mica Acta, 54, I l9l-l194.

Johnson, E.L., and Jenkins, D.M. (1991) Synthetic water-carbon dioxidefluid inclusions in spontaneously nucleated forsterite, enstatite, and di-opside hosts: The method and applications. Geochimica et Cosmo-chimica Acta. 55. 1031-1040.

Kerrick, D.M., and Boencher, A.L. (1971) Temperature calibration incold-seal pressure vessels. In G.C. Ulmer Ed., Research techniques forhigh pressure and high temperature, p. 179-193. Springer-Verlag, NewYork-

Knight, C.L., and Bodnar, R.J. (1989) Synthetic fluid inclusions IX. Crit-ical PWX properties of NaCl-HrO solutions. Geochimica et Cosmo-chimica Acta. 53. 3-8.

Kotelnikov, A.R., and Kotelnikova,Z.A. (1989) Fluid inclusions in scap-olites synthesized at 600-800 'C, 200 MPa in saline aqueous carbonicacid solutions. Geokhimiya i Termobarometriya Endogennykh Flyui-dov, Kiev (in Russian; translated from Referativnyi Zhurnal, Geolo-giya 1989, abstract no. 4V265, 1988).

- (1990) Experimental study of phase state of the system HrO-COr-NaCl by method of synthetic fluid inclusions in quartz. Geokhimiya,1990, 526-537 (in Russian).

Kotelnikov, A.R., Romanenko, I.M., and Kotelnikova, Z.A. (1990) Ex-perimental study of barium partitioning between plagioclase of theNaAlSirOr-BaAlrSirO. series and aqueous saline fluid at 800 eC and 2kbar. Geokhimiya, 1990,346-355 (in Russian).

Kotelnikova, 2.A., and Kotelnikov, A.R. (1988) Experimental study offluid inclusions in minerals. Geokhimiya, 1988, 1075-1083 (in Rus-sian; translated in Geochemistry International, 1989, l-8).

kfaucheux, F., Touray, J.C., and Guilhaumou, N. (1972) Thermoopticalanalyses of primary fluid inclusions in the hydrorhermal synthesis ofcalcite. Bulletin of the Society of French Mineralogy and Crystallog-raphy,95, 620-622 (in French).

Loredo-Perez, J., and Garcia-Iglesias, J. (1984) Thermooptical analysis offluid inclusions obtained by hydrothermal synthesis. Revista de Minas,4,73-81 (in Spanish).

Mernagh, T.P., and Wilde, A.R. (1989) The use of the laser Raman mi-croprobe for the determination ofsalinity in fluid inclusions. Geochi-mica et Cosmochimica Acta. 53.765-77l.

Parilov, Y.S., Mikhaleva, V.A., and Eshkeeva, N.T. (1990) Experimentalverification of the reliability of thermometry based on fluid inclusionsas applied to sulfide ore deposits. Geologia Rudnykh Mestorozhdenii,32, 106-112 (in Russian).

Pecher, A. (198 l) Experimental descrepitation and reequilibration offluidinclusions in synthetic quartz. Tectonophysics, 78, 567-583.

Pecher, A., and Boullier, A.M. (1984) High pressure-high temperatureevolution offluid inclusions in synthetic quartz. Bulletin de Min6rolo-gie, 107, 139-153 (in French).

Pironon, J. (1990) Synthesis ofhydrocarbon fluid inclusion at low tem-perature. American Mineralogist, 7 5, 226-229.

Popp, R.K., and Frantz J.D. (1990) Fluid immiscibility in the systemHrO-NaCl-CO, as detemined from synthetic fluid inclusions. AnnualReport of the Director of the Geophysical Iaboratory, Carnegie Insti-tution. 1989-1990. 43-48.

Roedder, E. (1984) Fluid inclusions. In Mineralogical Society ofAmericaReviews in Mineralogy, 12,644 p.

Roedder, E., and Kopp, O.C. (1975) A check on the validity of the pres-sure correction in inclusion geothermometry, using hydrothemallygown quartz. Fortschritte der Mineralogie, 52, 431-446.

Shaposhnikov, A.A., and Ermakov, N.P. (1978) Fluid inclusions in syn-thetic quartz crystals (abs.). International Association on the Genesisof Ore Deposits Program and Abstracts, p. I 67. Fifth Symposia, Snow-bird, Alta, Utah, 197E.

Shelton, I(L., and Orville, P.M. (1980) Formation of synthetic fluid in-clusions in natural quartz. American Mineralogist, 65,1233-1236.

Shmonov, V.M., and Shmulovich, K.I. (1974) Molar volumes and theequation ofstate for CO, at 100-1000 eC and 2000-10,000 bar. Dok-lady Academy ofScience USSR, 216, 4,206-209.

Smith, D.L., and Evans, B. (1984) Diffusional crack healing in quartz.Journal ofGeophysical Research, 89 (86), 4125-4135.

Sterner, S.M. (1990) An in situ fractuing procedure for fluid inclusionsynthesis. Pan-American Conference on Research on Fluid Inclusions,3, 85.

Stemer, S.M., and Bodnar, R.J. (1984) Synthetic fluid inclusions in nat-ural quartz. I. Compositional types synthesized and applicarions toexperimental geochemistry. Geochirnica et Cosmochimica Acta, 48,26s9-2668.

- (1986) Experimental determination ofphase relations in the sys-tem NaCl-KCl-HrO at I kbar and 700 and 800 qC using synthetic fluidinclusions. Geological Society of America Abstracts with Programs, 18,763.

- (1989) Synthetic fluid inclusions-Vll. Re-equilibration of fluidinclusions in quartz during laborarory-simulated rnetamorphic burialand uplift. Journal of Metamorphic Geology, 7, 243-260.

- (1991) Synthetic fluid inclusions X: Experimental determinationof P-V-T-X properties in the COr-HrO system to 6 kbar and 700 qC.

American Journal of Scienc.e. 291, l-54.Stemer, S.M., Kerrick, D.M., and Bodnar, R.J. (1984) Experimental de-

termination of unmixing in H,O-CO'-NaCI fluids at 500 qC and I kbarusing synthetic fluid inclusions: Metamorphic implications. GeologicalSociety of America Abstracts with Programs, 16, 668.

Sterner, S.M., Hall, D.L., and Bodnar, R.J. (1988) Synthetic fluid inclu-sions. V. Solubility relations in the system NaCl-KCl-HrO under vaporsaturated conditions. Geochimica et Cosmochimica Acta, 52, 989-1005.

van den Kerkhof, A.M. (1988) The system CO,-CH.-N, in fluid inclu-sions: Theoretical modelling and geological applications, 206 p. FreeUniversity Press, Amsterdam.

Vanko, D.A., Bodnar, R.J., and Sterner, S.M. (1988) Synthetic fluid in-clusions: VIII. Vapor-saturated halite solutility in part of the systemNaCl-CaCl,-H,O, with application to fluid inclusions from oceanic hy-

STERNER: SYNTHETIC FLUID INCLUSIONS 167

drothermal systems. Geochimica et Cosmochimica Acta, 52, 2451-2456.

Wellman, T.R. (1970) The stability of sodalite in a synthetic syenite plusaqueous chloride fluid system. Journal ofPetrology, 11,49-:71.

Zhang,Y.G., and Frantz, J.D. (1987) Determination of the homogeni-zation temperatures and densities of supercritical fluids in the systemNaCl-KCl-CaClr-HrO using synthetic fluid inclusions. Chemical Ge-ology,64, 335-350.

- (1989) Experimental determination of the compositional limits ofimmiscibility in the system CaClt-HrO-CO, at high temperatures andpressures using synthetic fluid inclusions. Chemical geology, 7 4, 289-308-

MeNuscnrrr REcETvED JnNuenv 10, 1991MeNuscnrrr AcEErTED SrsrEvseR. 8, l99l