Graupner_T_2001_Microthermometric Laser Ramam Spectroscopic and Volatile Ion Chromatographic Analysis of Hydrothermal Fluids in the Pleozoic Muruntau

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IntroductionTHE MURUNTAU Au ore field is located in the Central KyzylKum Desert (Uzbekistan; inset, see Fig. 1). For the Murun-tau ore-bearing system, total contained Au is estimated at>4,300 metric tons (t) at grades of 2 to 3 g/t (Berger et al.,1994); 1,186 t of Au were mined from 1967 to 1995. In addi-tion, reserves were estimated for WO3 (65,000 t ore at an av-erage grade of 0.05% WO3). The Au ore field consists of, inaddition to the Muruntau deposit, the Myutenbai, Besapan-tau, Triada, Boilik, and Kosmanachi deposits.

Compared to other shear zone-related mesothermal Au-bearing quartz vein deposits, Muruntau is characterized by some special features. The main gold mineralization in Mu-runtau is of Paleozoic age (Kempe et al., 1996; Kostitsyn,1996) and is therefore significantly younger than most largemesothermal Au systems, which are of Archean age (Kerrich,1989). Furthermore, the wall rocks in Muruntau consist of schists, mudstones, sandstones, and minor limestones and notof greenstones or granitic rocks. A variety of contrasting opin-ions exist about the genesis of the Muruntau deposit; theserange from a sedimentary-epigenetic origin of the ore(Gar’kovets, 1973), to a magmatic-hydrothermal source of fluids (e.g., Kremenetsky et al., 1990; Kotov and Poritskaya,

Microthermometric, Laser Raman Spectroscopic, and Volatile-IonChromatographic Analysis of Hydrothermal Fluids in the

Paleozoic Muruntau Au-Bearing Quartz Vein Ore Field, Uzbekistan

TORSTEN GRAUPNER,† ULF KEMPE,

Institute of Mineralogy, Freiberg University of Mining and Technology, Brennhausgasse 14, 09596 Freiberg, Germany

EDWARD T.C. SPOONER, COLIN J. BRAY,

F. Gordon Smith Fluid Inclusion Laboratory, Department of Geology, University of Toronto, 22 Russell Street,Toronto, Ontario, Canada M5S 3B1

ALEXANDER A. KREMENETSKY,

IMGRE, ul. Veresaeva 15, Moscow 121357, Russia

AND GERT IRMER

Institute of Theoretical Physics, Freiberg University of Mining and Technology,Bernhard-von-Cotta-Strasse 4, 09596 Freiberg, Germany

Abstract

Fluid inclusions in quartz and scheelite from flat, steeply dipping central, and stockwork-type quartz veins within the Muruntau Au-bearing quartz vein ore field have been investigated in a reconnaissance study, usingfluid inclusion mapping, microthermometry, laser Raman spectroscopy, and integrated gas and ion chro-

matography for bulk volatile and cation-anion analysis. Muruntau central veins are dominated by inferred early CO2-bearing fluid inclusions. In contrast, flat quartz veins contain considerable numbers of low-density, pureaqueous inclusions on deformation- and recrystallization-related microstructures. Fluid phase separation is in-dicated for samples from the Muruntau central ore veins by fluid inclusion observational work, as well as by microthermometry and bulk fluid geochemistry (CO2 /CH4, CO2 /N2, and CO2 /C2-, and C3- hydrocarbon ratios;salinity data). However, in flat veins and all samples from the Myutenbai deposit no evidence for fluid immis-cibility could be found. Quartz microstructural results and fluid inclusion data suggest formation of the low-grade mineralized flat veins before the main stage of hydrothermal activity and considerable variation in thegeochemical conditions during fluid evolution in the Muruntau and Myutenbai deposits. Mixing of fluids fromdifferent sources in variable proportions may be inferred from halide geochemistry. Furthermore, fluid inclu-sion Br/Cl ratios differ significantly for samples from different vein types. Fluid phase separation is suggestedas a mechanism for the precipitation of Au from the hydrothermal fluid in the Muruntau high-grade Au min-eralized central veins.

E c o n o m i c G e o l o g yBULLETIN OF THE SOCIETY OF ECONOMIC GEOLOGISTS

V OL. 96 January–February 2001 NO. 1

Vol. 96, 2001, pp.1–23

† Corresponding author: e-mail, [email protected]



1992), to a metamorphic model of ore formation (cf. Kraftand Kampe, 1994).

To date, there is no research available on a comprehensivestudy of fluid inclusions in the deposit. Preliminary fluid in-clusion studies on the Muruntau system (Zairi and Kurbanov,1992; Alyoshin, 1994; Berger et al., 1994) present variable ho-

mogenization temperatures that suggest a fluid somewhathotter than fluids in other mesothermal Au deposits. Compo-sitions of fluids responsible for mineralization are describedto be low to moderate salinity and CO2 bearing, containinglesser amounts of N2 and CH4. The main problems involvedin previous publications are the inexact descriptions of thehost mineral, quartz, and the lack of a correlation of the fluiddata with the main vein types present in Muruntau. We sub-divided the main ore veins at Muruntau into three majortypes, similar to the classification of Drew et al. (1996) ac-cording to their geometry: flat veins, stockwork-type veins,and steeply dipping central veins (Graupner et al., 1999).Scheelite of two generations yielded additional criteria for a

differentiation of quartz formed in flat and steeply dippingcentral veins (cf. Uspenskiy and Aleshin, 1993; Kempe andOberthür, 1997).

Au mineralization at Myutenbai, located as a southeast con-tinuation of Muruntau (Fig. 2), shows some special features.Zairi and Kurbanov (1992) observed similar homogenizationtemperature (Th) values but variable volatile ratios for fluidinclusions in quartz from both deposits. Moreover, positiveEu anomalies, which are characteristic of minerals from theMyutenbai ore veins, are absent in Muruntau (Kempe andOberthür, 1997; Kempe et al., 1999).

In this study, sample selection was carried out to enablecomparison of fluids (1) trapped in minerals from different

vein types, (2) in minerals from similar veins from differentparts of the ore field (Muruntau, Myutenbai), and (3) in co-existing quartz and scheelite. Data are discussed based on re-sults from the microstructural analysis of the samples. Fluidinclusion microthermometry, laser Raman spectroscopy, andintegrated gas and ion chromatographic analysis of fluids

were applied, and all data produced by the different methods were tested regarding their consistency. Special attention wasfocused on H2O-CO2 immiscibility because, as in the case of Archean to Phanerozoic Au-bearing quartz vein systems, thisprocess may be a significant control on the precipitation of Au(e.g., Diamond, 1990; Bowers, 1991; Yardley et al., 1993;Channer and Spooner, 1994).

Geologic Setting and Mineralization

The Muruntau ore field is located in the southern part of the Tamdytau Mountains (Central Kyzyl Kum subzone of thesouthern Tien-Shan) near the intersection of the Dzhanbulakanticline and the Muruntau-Daughyztau fault (e.g., Kotov

and Poritskaya, 1992). It lies in a sequence of flyschlikegreenschist (Besapan suite) to amphibolite (Taskazgan suite)facies metamorphosed siltstones and shales, with interbeds of sandstone, of uncertain age (Fig. 1). The wall rocks of theMuruntau deposit are assigned to the “Colored” Besapansubsuite and form a lens-shaped block of more brittle rockscompared to the adjacent phyllitic schists (Drew et al., 1996).Intense hydrothermal alteration is widespread in wall rocks atMuruntau (Kotov and Poritskaya, 1992; Kol’tsov and Rusi-nova, 1997) and, within the ore contours, metasomaticlithologies contain economic Au ore concentrations.

The Muruntau deposit is related to the regional Tamdytau-Sangruntau shear zone system, which crosscuts the Muruntau

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Taskazganaskazgan

"Grey" Besapan

"Colored" Besapan

"Green" Besapan

Devonian

Carboniferous

Meso-Cenozoic

Quaternary

dikes

fault / main fault strike and dip45

Southern Fault

Structural Fault

FIG. 2

overthrusting open pit

UZBEKISTANZBEKISTAN

Aral Sea

SG 10

MURUNTAUURUNTAU

FIG. 1. Schematic geologic map of the Muruntau ore field (modified after P.A. Ivanov, pers. commun.).



anticline. The flanks of the anticlinal structure are broken by a system of high-angle faults striking east-northeast or north-east; the most important are the Structural and the Southernfaults (Fig. 1). The Southern fault represents a wide shearzone and separates the Myutenbai and Muruntau deposits(Fig. 2). Fault zones crosscutting the deposits are sometimesoutlined by strongly altered igneous dikes (e.g., the Dike faultbetween the first and second orebodies; Fig. 2). Dikes are theonly magmatic rocks exposed in the Muruntau deposit itself.Larger granite bodies occur in the vicinity of the deposit (e.g.,the Sardarin pluton exposed 7 km SE of Muruntau) andgranitic material has been observed in the superdeep drill

hole SG10, which is located just southeast of the Myutenbaideposit (Fig. 1); the so-called “Murun granite” occurs from4,005 m to the final depth of the drill hole (4,294 m;Shayakubov et al., 1999).

For Muruntau, five orebodies have been defined and onehas been defined in the Myutenbai deposit (Fig. 2). Accord-ing to our field observations, we suggest that the second andthird may represent a single orebody.

There are myriad, complex vein shapes and relationships atMuruntau. According to their geometry, Au-bearing quartz

veins may be subdivided into three major groups: flat veins,stockwork-type veins, and steeply dipping central veins. Allother types of veinlets in Muruntau (quartz-tourmaline-albite

sulfides; quartz-arsenopyrite Au; adularia-quartz Ag; calcite(-brookite?); Berger et al., 1994; Kostitsyn, 1996) are of minorimportance.

Flat quartz veins occur parallel to subparallel to the folia-tion of the metamorphosed host rocks, are frequently boudi-naged or folded, and do not extend for long distances. Thethickness of the veins ranges from a few millimeters to a few centimeters. Carbonates, microcline, chlorite, small amountsof sulfides, and colorless to pale yellow-brownish scheelite 1occur, in addition to quartz. Scheelite 1 is closely intergrown

with quartz. It can be inferred from relationships betweenscheelite 1 and quartz that precipitation of scheelite 1 cannot

be younger than the latest stage of deformation of the flat veins. Flat veins are generally low in Au (0.03–0.30 ppm;Khoklov, 1990; sometimes up to 2.0 ppm).

Au is highly enriched in stockwork-type and steeply dippingcentral quartz veins (see Fig. 2). The occurrence of mineral-ized megastockwork zones is characteristic of all orebodies inthe Muruntau and Myutenbai deposits. The thickness of thequartz veins ranges from a few millimeters to a few centime-ters in the stockwork zones.

High-grade Au mineralized central veins were formed inlarge east-west–striking tension fractures, which are relatedto the northeastern fault system. The maximum thickness of single veins of this type is ~14 m with a maximum length of

HYDROTHERMAL FLUIDS, MURUNTAU Au-BEARING QUARTZ VEIN ORE FIELD, UZBEKISTAN 3

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host rocks granitic dikes ore metasomatites

S O U T H

E R N F A U L T

D I K E

F A U L T

New orebody

First ore body

MT 3778

MT 3774

78-98-5

MT 7 (projected)

MT 4

MT 1T 1

MT 2

MT 3779

main faultsain faults

+ 78 m level

Myutenbai

MT 3423(projected)

"central" veins

MT 6

MT 5

Second / third orebody

Eastern ore body

MT 3

100 m

78-98-1

FIG. 2. Orebodies of the Muruntau and Myutenbai deposits. The first orebody is located east of the second-third orebody (outside this map area). The new orebody is not well developed at the +78-m level; however, it forms the northeastern con-tinuation of the second orebody in the open pit (Shayakubov et al., 1999). Samples MT3423 from Myutenbai and MT7 fromMuruntau are from the +220- and +410-m mining levels, respectively; however, their locations have been projected verti-cally to the +78-m level for illustration.



~160 m. The mineralogy of the veins is characterized by theoccurrence of milky quartz and low amounts of total sulfides(max 2–3%). Pyrite, arsenopyrite, and native gold are themajor ore minerals with associated calcite, apatite, light yel-low to dark brown scheelite 2, and bismuthinite (cf. Golo-

vanov et al., 1988). Scheelite 2 is commonly confined to theselvage zones of transverse quartz veins or to their exocon-

tacts and shows an association with Au mineralization intime and space (Uspenskiy and Aleshin, 1993; Kempe andOberthür, 1997). Scheelite 2 is sometimes brecciated andshows evidence of weak deformation. Its close spatial asso-ciation with quartz, pyrite, carbonate, and muscovite (so-called “beresite” mineral assemblage) and degree of defor-mation may suggest formation of the scheelitesimultaneously with the initial stages of quartz deposition.Typical of central veins is the frequent occurrence of xeno-liths and tectonic breccias at the contacts with the wallrocks. Steeply dipping main quartz veins similar to central

veins in morphology and appearance of quartz, but smallerin size, are exposed at a deeper mining level (+78 m) inMyutenbai.

Flat quartz veins are often crosscut by steeply dipping hy-drothermal veinlets and veins of milky quartz (see alsoZarembo, 1968). This observation and the higher degree of deformation of the flat veins supports a younger relative timeof formation for the steeply dipping vein structures comparedto the flat veins.

Based on Rb-Sr isotope investigations, Kostitsyn (1996)suggested an age of ~400 Ma for greenschist facies metamor-phism of the green Besapan and the gray Besapan schists,

which overlie and underlie the ore-hosting Colored Besapan.The age of the main ore-forming stage (including scheelite-bearing Au veins) has been independently defined at 270 to280 Ma (Lower Permian) from K-Ar, Rb-Sr, and Sm-Nd stud-

ies (Kostitsyn, 1991; Kempe et al., 1996). According toKempe et al. (1996), Sm-Nd isochrons for scheelite 1 fromflat veins and scheelite 2 from central veins indicate differentages of formation (scheelite 1: 351 ± 22 Ma; scheelite 2: 279± 18 Ma). However, these authors discuss that the isochronfor scheelite 1 may represent a mixing line, and therefore thedetermined age may be a minimum age.

Samples and Analytical Techniques

All data presented here for the Muruntau deposit comefrom 15 samples from two mining levels (+78 m; +410 m) of the second-third orebody and one sample from the eastern

orebody (+78 m level; Fig. 2). Altogether, four quartz samplesand one scheelite were taken from flat quartz veins and ninequartz and one scheelite from steeply dipping central veins.For each scheelite sample, one quartz sample was taken fromthe same piece. Flat veins were sampled within and outsidethe contours of the orebodies. In addition, one sample from a

wall-rock quartz nodule adjacent to a central ore vein (dis-tance <1 m) was analyzed.

For the Myutenbai deposit, six vein samples from two min-ing levels (+78 m; +220 m) were investigated. These fourquartz and two scheelite samples are from two large steeply dipping quartz veins and a veinlet in a stockwork zone nearthe Southern fault (Fig. 2).

In order to establish petrographic evidence for a fluid in-clusion chronology, samples from flat and steeply dipping

veins have been investigated using fluid inclusion mapping(e.g., Channer and Spooner, 1991; Boullier and Robert,1992). The fluid chemistry study included analysis of fluid in-clusions by microthermometry, laser Raman spectroscopy,and integrated volatile and cation-anion chromatographic

analysis.Fluid inclusions were examined using a Linkam THMS 600

heating-freezing stage. Two synthetic fluid inclusion stan-dards (SYN FLINC; pure H2O, mixed H2O-CO2) were usedto calibrate the equipment. The precision of the system was±2.0°C for homogenization temperatures (Th), and ±0.2°C inthe temperature range between –60° and +10°C.

The Raman microprobe used for the semiquantitativeanalysis of CO2, CH4, and N2 in the CO2-rich phases of fluid inclusions consists of a Jobin-Yvon triple monochro-mator T64000 equipped with a CCD multichannel detec-tion unit and an Olympus microscope (BH2-UMA). Themeasurements were carried out using the 488.0- and 514.5-nm radiations emitted from an Ar+ laser. The laser powerentering the sample was between 25 and 30 mW. Calibra-tion for response has been checked on standard samples(low-pressure CO2-N2 mixtures in glass vials, 25 and 67%N2) prepared by A. M. van den Kerkhof. The instrumentalcorrection factor for CO2 (van den Kerkhof and Kisch,1993) was calculated as 0.60 (488.0 nm; quantification fac-tor: 1.5) and 0.84 (514.5 nm; quantification factor: 2.1).Quantitative analyses are derived from the relative peak in-tensities and relative Raman cross sections (Pasteris et al.,1988; Dubessy et al., 1989).

Bulk volatile and ion compositions of fluids trapped in in-clusions were analyzed by combined gas and ion chromato-graphic analysis (Bray et al., 1991; Channer et al., 1999).

Analysis has been carried out on 12 quartz and four scheelitesamples in total from the two deposits (sample mass: ~1.2 g).In addition, 10 quartz samples were analyzed for their volatilecompositions only. In order to separate the N2(+) andC2H6(+) peaks, cryogenic gas chromatographic runs were car-ried out on six quartz samples and one scheelite at –70°C. Itshould be noted that volatile S species apart from COS can-not be analyzed by this technique at the present time becauseof adsorption problems.

Using the temperature of final ice melting (Tm(ice)), thetemperature of clathrate dissociation (Tm(clathrate)), the tem-perature of partial homogenization of the CO2-rich phase(Th(CO2)), the relative concentration ratios of electrolytes in

the aqueous solution (IC analysis), and the composition of the gas phase (laser Raman spectroscopic analysis), salinity data for the aqueous solutions in individual gas-bearingfluid inclusions were estimated. Salinity is calculated by using programs Density and Q2 from Bakker (1997), forTm(clathrate), values higher and lower, respectively, thanTh(CO2).

Phase separation pressures were estimated using the lowestrecorded Th for each fluid inclusion assemblage formed by phase separation (Brown and Hagemann, 1994) and densitiesof the CO2-rich phase and salinities of the H2O-rich phase formultiple inclusions, as calculated using the appropriate pro-grams from Bakker (1997).

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Microstructure of Quartz Vein Samples andFluid Inclusion Types

Quartz microstructure in flat and steeply dipping quartz veins

Flat quartz veins from Muruntau: Quartz from the multi-stage deformed flat veins occurring outside the second-third

orebody (close to the northern margin) is characterized by strong deformation features and shows a subgrain-dominatedmicrostructure. Typical fabrics of dynamic recrystallization inquartz appearing as domains of small, dynamically recrystal-lized grains, occur very frequently (Fig. 3A). Generally, mostof the quartz grains in these veins show indications of intenserecrystallization and areas of less strained quartz are scarce.The flat veins located inside the ore contours are also in-tensely recrystallized. Any primary fluids have probably beencompletely extinguished or early inclusions were overprintedby later fluids.

Muruntau and Myutenbai steeply dipping main quartz veins: No significant differences were found for quartz fromthe Muruntau central and Myutenbai main veins. Hydrother-mal quartz is intergrown with carbonate and minor amountsof scheelite 2.

In almost all samples, only one generation of quartz couldbe identified. The quartz was subdivided into two types dueto the variable degrees of deformation and recrystallization of aggregates. The first type shows a parquetlike undulose ex-tinction of the quartz grains (Fig. 3B) and an anastomosingsubgrain boundary network (medium degree of deformation;recrystallization of parts of grains starting from the grainboundaries). The second type occurs as aggregates of coarsergrained quartz, characterized by a limited number of oftenmore maturely developed subgrain boundaries (little or noevidence of recrystallization of the outermost parts of quartz

grains). Veinlets of late, fine-grained quartz were found inone sample, and recrystallization rims were observed in theadjacent quartz.

The wall-rock quartz nodule sample, taken adjacent to aMuruntau central vein (second-third orebody) is composed of hydrothermal, moderate to weakly deformed quartz, the lat-ter being less abundant. The presence of an additional quartztype was indicated by cathodoluminescence (Monecke,1996).

Description of fluid inclusion typesThe fluid inclusions are classified mainly according to their

distribution characteristics in quartz and scheelite; bulk com-positions at room temperature were also used (Fig. 4).

Type I: One- and two-phase, almost exclusively CO2-richfluid inclusions (Ia); H2O-rich inclusions (Ib) are rare; show isometric or regular forms; occur isolated in quartz. The oc-currence of inclusions of this type on growth zones of quartzcrystals may suggest a primary origin for this fluid inclusiontype (Graupner et al., 2000).

Type II: Two-phase, CO2-bearing inclusions with degree of fill mostly <0.30; CO2-rich (IIa) and H2O-rich (IIb) inclu-sions; show isometric, elongate or slightly irregular forms;occur as irregular clusters or as groups with no planar orien-tation. These inclusions could be pseudosecondary. Pureaqueous, two-phase fluid inclusions in scheelite were as-signed to a type I/II due to their distribution characteristics,

which are similar to those described above.Type III: Two-phase, CO2-bearing inclusions with degree of

fill mostly <0.35; CO2-rich (IIIa) and H2O-rich (IIIb) inclu-sions; show regular, elongate or irregular forms; occur in lin-eations cut by later microstructures. These inclusions couldalso be pseudosecondary.

Type IV: Mostly one-phase, vapor-rich (in samples fromsteeply dipping veins some of these fluid inclusions werefound to contain a CO2-rich phase), low-density fluid inclu-sions (leakage of fluid) associated with subgrain boundaries;

inclusions show many different forms.Type V: One-, two-, and more phase (daughter minerals are

scarce) aqueous, liquid-rich inclusions (traces of CO2); flat or


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B

500µm

FIG. 3. Microstructure of quartz from different types of quartz veins located inside the ore contours of the second-thirdorebody of the Muruntau deposit (mining level: +78 m). A. Small, recrystallized quartz grains with irregular grain bound-aries from a multistage deformed flat vein. B. Coarse-grained quartz with parquetlike undulose extinction from a steeply dip-ping central vein.

A



irregular shapes; inconsistent L/V ratios owing to fluid inclu-sion necking; occur in trails crosscutting types II and III in-clusion assemblages and grain boundaries; trails of CO2-richfluid inclusions showing many different forms occur re-stricted to quartz from flat veins.

Type VI: Very small, low-density fluid inclusions along high-angle grain boundaries between recrystallized quartz grains;show isometric to regular forms.

Types IV, V, and VI are dominant in flat vein quartz. CO2-bearing fluid inclusions occur less frequently in flat veins lo-cated outside the contours of the orebodies and more fre-quently in veins of this type found inside the orebodies. Type

I fluid inclusions could not be identified in flat vein quartz.Here, CO2-dominated fluid inclusions are mostly arranged intrails (type V). From the quartz microstructure and the tex-tural settings of the majority of the inclusions, it is suggestedthat CO2-bearing fluid inclusions in flat veins are secondary inorigin. However, a few CO2-dominated inclusions occur ingroups. Aqueous types II (or I) and V inclusions were foundto dominate in flat vein scheelite 1 only.

Central and main quartz vein samples and the wall-rockquartz nodule sample taken adjacent to a central quartz veinare dominated by CO2-bearing types II, III, and IV. Type Ifluid inclusions also occur but not very abundantly. Aqueoustype V fluid inclusions also occur. It is not possible to classify

fluid inclusions exactly in scheelite 2; most are assigned totypes I (or II), III (or II), and V (or III).

Distribution of fluid inclusions within mapped areas

Eight samples from the Muruntau and Myutenbai ore veinshave been investigated using fluid inclusion mapping. Micro-textures and textural settings of fluid inclusions in threemapped areas typical of the samples are shown in Figures 5,6, and 7.

A sketch of a quartz area in a sample from a Myutenbaimain quartz vein containing probable early CO2-rich fluid in-clusions is shown in Figure 5 (uppermost part of figure). Sub-grain boundaries outlined by low-density inclusions can be

seen at the left- and right-hand sides. One trail of type V aqueous fluid inclusions crosscuts all older microstructures.

In the area from a Muruntau central vein sample shown inFigure 6, weak to moderately deformed quartz occurs. Here,

we found clusters and short trails of types IIa (or IIIa?), uni-formly CO2-rich fluid inclusions which intersect with one trail

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I

IV

II

V

III

VI

FIG. 4. Main types of fluid inclusions observed in the Muruntau and Myutenbai Au-bearing quartz vein deposits.

FIG. 5. Microtextures and different textural settings of fluid inclusions insample MT2, area 2 (quartz). Types I, III, IV, and V fluid inclusions occur insubgrain dominated quartz.



formed by types IIb (or IIIb?), uniformly H2O-rich inclu-sions. The last mentioned trail is continuous, whereas some of the CO2-rich structures seem to be crosscut. At intersecting

points of CO2-rich structures with the H2O-rich trail, wefound CO2-rich fluid inclusions, which still show their proba-ble original composition. This observation supports the sug-gestion of a similar age for both types of inclusions. The mi-crostructures on which both types of inclusions are locatedare crosscut by later deformation-related structures and arecompletely extinguished in recrystallized parts of the quartzgrain.

A fluid inclusion assemblage with a very scattered degree of filling in a quartz sample from a central part of a Muruntaucentral vein is presented in Figure 7. The volume occupied by the carbonic phase ranges from ~10 to 95 percent of individ-ual inclusions. No leaking or necking down is suspected for

these inclusions. Analytical Data

Microthermometry results

General fluid inclusion characteristics: Microthermometricdata for Muruntau and Myutenbai are summarized in Table1. The Th values of CO2-bearing types I to V fluid inclusions

vary between vein types and sample locations. A predomi-nance of NaCl as the salt component in the gas-bearing fluidis indicated by the measured depression of the temperatureof first melting of ice (Tm(ice)) of such inclusions (e.g., Borisenko,1977). The melting process of ice or another highly soluble

phase (hydrohalite, antarcticite) was not observed within thetemperature range –35.0° to –56.6°C in types I to III fluid in-clusions. Measured temperatures of final melting of CO2

(Tm(CO2)) and Th(CO2) data in CO2-bearing inclusions (typesI–V) from Muruntau and Myutenbai are summarized in Fig-ures 8 and 9, respectively.

The latest fluid circulation event in the ore field is repre-sented by type V aqueous fluid inclusions. These inclusionsshow Th values predominantly between 100° and 250°C andmostly similar first melting temperature (Tfm) values, com-pared to the CO2-bearing inclusions. For such low-salinity pure aqueous fluid inclusions, we determined salinities of be-tween 0.0 and 10.7 wt percent NaCl equiv, with a mean of 3.2± 3.4 (1 σ ) wt percent NaCl equiv. A large number of type V brine inclusions with halite daughter crystals were found re-stricted to the sample taken from a veinlet in the vicinity of

the Southern fault (Myutenbai deposit). Fluid inclusionsshowing Tfm values below the sodium-dominated range(–37.8° to –48.0°C) occur in minor amounts in three samplesfrom flat and central main veins in both deposits. This obser-

vation may indicate higher amounts of Ca in the solution;however, fluid inclusions of this composition form <1 to 5 volpercent of the estimated total fluid inclusion volumes of therespective samples (Table 2).

Muruntau flat veins (quartz): Fluid inclusions in flat veinquartz are small. In addition, phase changes were difficult toidentify. Type IV inclusions located in deformation- and re-crystallization-related microstructures are frequent and al-most exclusively contain low-density fluids; phase changes


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FIG. 6. Microtextures and different textural settings of fluid inclusions insample MT7, area 6 (quartz), an assemblage of CO2-rich (type IIa) and H2O-rich (type IIb) fluid inclusions; for details see text.

FIG. 7. Assemblage of fluid inclusions showing a very variable degree of filling; quartz sample 98-A4 from the central part of a central ore vein.





indicating the occurrence of CO2 or other gases could not beobserved in this inclusion type. Type V CO2-dominated inclu-sions could be measured in slightly clearer areas of quartzfrom flat veins located outside the orebody (Table 1). Due todecrepitation of the inclusions before reaching Th, the Th val-

ues could not be determined for CO2-rich inclusions here. Inquartz from a flat vein found inside the ore contours, CO 2-bearing fluid inclusions from two assemblages were investi-gated. The high Th values of between 386° and 436°C for onetrail of type V inclusions are unusual (Table 1).


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FIG. 8. Tm(CO2) data for CO2-rich fluid inclusions from Muruntau and Myutenbai (flat quartz veins: type V inclusions;steeply dipping quartz veins: types I, II, and III inclusions). Note: different patterns used in histograms represent resultsfrom individual samples.

A. Myutenbai - main quartz veins (quartz)

B. Muruntau - flat quartz veins (quartz)

C. Muruntau - “central” quartz veins (scheelite)

D. Muruntau - “central” quartz veins (quartz)

E. Muruntau - quartz nodule in wall rock (quartz)

n = 21

n = 63

n = 12

n = 48

n = 51



Muruntau flat veins (scheelite 1): Types I and II aqueousfluid inclusions found in scheelite 1 are two phase, liquidrich and contain NaCl-dominated low-salinity solutions(Table 1). CO2 is not detected in these inclusions; however,the occurrence of related phase changes may not be visible

due to the small size and dark appearance of most fluidinclusions.

Muruntau central quartz veins and the wall-rock quartz nodule adjacent to a central vein (quartz): For types I to III CO2-bearing fluid inclusions, total homogenization predominantly

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FIG. 9. Th(CO2) data for CO2-rich fluid inclusions from Muruntau and Myutenbai (Th(CO2) homogenizing into the liquidonly; Th(CO2) homogenizing into the vapor is scarce). For fluid inclusion types see Figure 8. Note: different patterns used inhistograms represent results from individual samples.

n = 38

n = 44

n = 14

n = 67

n = 23

E. Muruntau - quartz nodule in wall rock (quartz)

D. Muruntau - “central” quartz veins (quartz)

C. Muruntau - “central” quartz veins (scheelite)

B. Muruntau - flat quartz veins (quartz)

A. Myutenbai - main quartz veins (quartz)



occurs into the vapor phase; however, inclusions homogeniz-ing into the liquid phase were also found. Decrepitation phe-nomena before reaching Th are frequent in fluid inclusion as-semblages found in this vein type. Th(CO2) mostly occurredinto the liquid phase. The Th values for types II and III in-clusions in one sample from the +410-m mining level arelower than for samples from the +78-m level (Table 1). Type

V fluid inclusions generally show low Th values; however, onetrail of type V (?) aqueous inclusions was characterized by Th

values as high as 225° to 344°C. For individual samples, themajority of types I to III inclusions, which had trapped a CO2-bearing fluid, are characterized by similar volatile composi-tions as indicated by similar T

m(CO2) values (Fig. 8D). How-

ever, extremely CO2 and H2O rich inclusions were frequently found to occur together in samples from central ore veins.The H2O-rich inclusions also contain aqueocarbonic fluids,although are more H2O rich than the majority of the types Ito III inclusions.

The sample from the +410-m level contains a somewhatmore gas-rich fluid in types II to III fluid inclusions com-pared to those fluids present in steeply dipping veins from the+78-m level. In this sample, the presence of small amounts of H2O in CO2-rich inclusions is confirmed by the occurrence of clathrates. Early type II, H2O-rich fluid inclusions are not fre-quent in the quartz sample from the +410-m level.

Muruntau central quartz veins and the wall-rock quartz nodule adjacent to a central vein (scheelite 2): One scheelitesample from a Muruntau central vein was measured (Table1). The occurrence of many dark, low-density fluid inclusionsis characteristic of this scheelite. CO2-bearing types I and/orII inclusions show highly variable degrees of fill. All types I orII fluid inclusions decrepitated between 280° and 335°C be-fore reaching Th.

Myutenbai main quartz veins: All types I to III inclusionshomogenized into the vapor phase (Table 1). Significantly lowered Tm(CO2) values indicate the presence of significantamounts of volatiles such as CH4 and N2 in the fluid (–59.8°to –63.6°C; triple point of CO

2: –56.6°C). T

h(CO2)occurred

mostly into the liquid and to a lesser extent into the vapor phase.In Table 2 the estimated relative amounts of all inclusions

of different types, but containing fluid of one of the two mainfluid types (CO2-bearing fluid, and H2O-NaCl fluid), aresummarized for each sample. Almost equal amounts of astrain-related, low-density H2O-dominated and a CO2-richfluid are estimated for flat veins. In contrast, inclusions con-taining the CO2-bearing fluid type predominate in samplesfrom steep quartz veins (70–>90 vol % of the total volume of all fluid inclusions in the studied samples) and occur as typesI to IV inclusions in different textural settings. Type V pureaqueous inclusions were found to occur in lesser amounts in


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TABLE 2. Estimated Amounts (vol % of the total volume of all fluid inclusions in the studied samples) of Different Fluid Types

Sample Fluid type Inclusion type Relative amount (vol %)

MyutenbaiMain quartz veins

MT1 (quartz) H2O-CO2(+)-NaCl1 I/II+III+IV 90–>95H2O-NaCl-(CaCl2?)2 V ~ 5

MT2 (quartz) H2O-CO2(+)-NaCl1 I+III+IV 80–85H2O-NaCl2-(CO2?) V 15–20

MuruntauFlat quartz veins

MT4/2 (quartz) Strain-related H2O-rich fluid IV 40–60H2O-CO2(+)-NaCl1 V+III? 30–40H2O-NaCl2 V 10

MT3774 (quartz) Strain-related H2O-rich fluid IV+VI 30–60H2O-CO2(+)-NaCl1 V+III? 25–40H2O-NaCl2 V 5–20(H2O-NaCl-(CaCl2?)2 V < 1)

MT3779 (quartz) Strain-related H2O-rich fluid IV+VI 30–60H2O-CO2(+)-NaCl1 V+III? 15–40H2O-NaCl2 V 15–25

MT3779 (scheelite 1) H2O-NaCl2 I+II/III 50–60H2O-NaCl2 V 20–40

Central quartz veins

MT5 (quartz) H2O-CO2(+)-NaCl1

II+III+IV 90H2O-NaCl2 V 10MT7 (quartz) H2O-CO2(+)-NaCl1 II+III+IV 85–>90

H2O-NaCl2 VI 5–15(H2O-NaCl-(CaCl2?)2 V < 3)

MT7 (scheelite 2) H2O-CO2(+)-NaCl1 I/II+III/II 65–90H2O-NaCl2 V+V/III 10–35

Quartz nodule in wall rockMT6 (quartz, group 2) H2O-CO2(+)-NaCl1 II+III 70–75

H2O-NaCl2-(CO2?) V 25–30MT6 (quartz, group 5) H2O-CO2(+)-NaCl1 I+II+IV 100

1 H2O-CO2(+)-NaCl = early fluid type H2O-CO2-CH4-N2-NaCl2 H2O-NaCl and H2O-NaCl-(CaCl2?) = H2O-rich fluid inclusions



quartz of both flat (5–25 vol %) and central and main veins(<5–20 vol %). Likewise, low but more variable amounts of the secondary aqueous fluid are present in quartz from thequartz nodule (~5–30 vol %) and probably also in scheelite(10–35 vol %).

Raman spectroscopy results

The laser Raman results for the CO2-rich subsystems of se-lected fluid inclusions in five quartz samples from Muruntauand Myutenbai are listed in Table 3; microthermometric dataare included for comparison. CO2 is the major non-H2O

volatile component in all inclusions. In addition, highly vari-able amounts of CH4 (2.0–39.5 mole %) and, to a lesser de-gree, variable amounts of N2 (<0.5 and 10.0 mole %) werefound. In three fluid inclusions, N2 was detected, but themeasured peak areas were too small for quantification. Thehighest CH4 values (16.4–39.5 mole %) were measured forthe Myutenbai main veins, being consistent with a significantdepression of the melting point of pure CO2 in all inclusionsfrom this location (–60.9° to –62.4°C; Table 3); the CO2 /CH4

ratios range from 1.4 to 4.8. Muruntau central veins and thequartz nodule (all from the same orebody) are characterizedby significantly lower CH4 concentrations (2.0–15.0 mole %;CO2 /CH4 ratios: 5.0–49.1). A good correlation of fluid inclu-sion volatile and microthermometric data is indicated by theless prominent lowering of the Tm(CO2) values for Muruntausamples (–56.9° to –58.5°C), compared to the Myutenbaisamples. In addition, differences in the fluid composition aresuggested for CO2- and H2O-rich fluid inclusions occurring inspatial association with each other, by their variable CO2 /CH4

ratios (Table 3); ratios of between 5.6 and 21.5 were calcu-lated for CO2-rich inclusions (three samples). For H2O-richinclusions, CO2 /CH4 ratios range from >20.0 to 49.1.

Results of combined gas and ion chromatographic analysisThe results of the gas and ion chromatographic analysis are

summarized in Tables 4 and 5. Gas analysis shows volatilecomponents in the following order of abundance: H2O > CO2

> CH4 > N2 > COS ≥ C2 and C3 hydrocarbons; in some analy-ses C2H6 was slightly higher than COS. Water is the predom-inant volatile with 76 to >99 mole percent for quartz, and 92to >99 mole percent for scheelite (% volatiles only). CO2

varies from 0.3 to 15.3 mole percent for quartz and from 0.4to 5.3 mole percent for scheelite. CH4 and N2 were measuredto be <0.1 to 8.4 mole percent for quartz and <0.1 to 1.8 molepercent for scheelite. C2- and C3- hydrocarbons lie mostly be-tween 0.2 and ~ 400 ppm (molar; quartz) and 0.2 and 940

ppm (scheelite).Cryogenic gas chromatographic experiments on quartz andscheelite samples show that the N2(+) peak consists of 98.4 to100.0 mole percent N2 and 0 to 1.6 mole percent CO. Ar andO2 were below detection limits. The C2H6 peak consists of 97.0 to 99.9 mole percent C2H6 and 0.1 to 2.9 mole percentC2H2.

Using ion chromatography on liquids of the same sample(Channer et al., 1999), Na+ and Cl- were determined to be theprincipal ions in all samples (Table 5). In addition, minoramounts of K+, Mg2+, Ca2+, Br-, and SO2–

4 are detected in mostleachates. All other ions are excluded because their respectiveblanks gave values with >25 percent of the sample leachate.

To test the accuracy of the crush-leach analyses charge bal-ances were calculated for all measured leachates (Table 5)and show a significant positive imbalance (Q+ /Q– = 1.22–5.46;ideally it should be 1). Most fluid inclusions in the samplescontain separate CO2-dominated phases. Hence, it is neces-sary to recalculate the charge balance to include dissolvedcarbonate species (Channer and Spooner, 1992). The recal-

culated values are better with a mean of 1.82 ± 1.08 (1 σ ) anda range of 0.16 to 3.66. The positive imbalances are probably caused by contamination of the quartz samples with submi-croscopic calcite inclusions. This is confirmed by petro-graphic investigations (Monecke, 1996). The ion chromato-graphic analytical methods used do not analyze CO2–

3

separately.

Comparison of the data resulting fromdifferent analytical methods

The determination of volatile and cation-anion composi-tions of fluid inclusions by gas and ion chromatography is abulk analytical method. On the other hand, the accuracy of quantitative gas analysis by Raman spectroscopy is influencedby the fluid pressure and optical parameters (Dubessy et al.,1989; van den Kerkhof and Kisch, 1993). Therefore, we haveto check if the data sets obtained by gas and ion chromato-graphic analysis, microthermometry, and laser Raman spec-troscopy are mutually consistent and can be used with equalconfidence in the interpretation of the data.

Major gas data: Bulk gas chromatographic vs. micro-Raman analysis: Taking into account the small number of fluid inclusions analyzed by laser Raman spectroscopy (Table6), the consistency of the data from gas chromatographic andmicro-Raman analysis for the Myutenbai sample and sampleMT5 from Muruntau is rather good. For the other two sam-ples (Table 6) the variability of the micro-Raman data is sig-

nificant. This reflects the heterogeneity of the fluid inclusionassemblages in the investigated areas of the samples with re-spect to their phase ratios and gas compositions. However,one of the objectives of this study was to investigate possiblephase separation processes in the hydrothermal fluid. There-fore, areas containing heterogeneously trapped fluids wereselected for laser Raman analysis. However, the majority of gas-bearing fluid inclusions in each sample usually shows asmaller variability in volatile composition (Fig. 8; Table 3).

Composition of the trapped aqueous phase: Laser Ramandata are restricted to individual gas-bearing fluid inclusionsfrom steeply dipping veins and the wall-rock quartz nodule.Therefore, salinities of gas-bearing fluid inclusions in quartz

and scheelite from flat veins were not calculated using pro-grams from Bakker (1997).The salinities of gas-bearing inclusions in four quartz sam-

ples from Muruntau and Myutenbai vary between 0.9 and15.2 wt percent NaCl equiv ( n = 24, Table 3). These values

were calculated assuming NaCl to be the principal salt com-ponent in the solution, which is supported by measured T fm

values. Low-temperature aqueous type V inclusions are almostexclusively NaCl dominated and of low salinity in central andmain quartz vein samples. The influence of these aqueousinclusions is assumed to be negligible for samples from this

vein type. This provides justification for comparing the bulksample salinities obtained by gas and ion chromatographic

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T A B L E 4 . S u m m a r y o f G a s C h r o m a t o g r a p h i c D a t a o f F l u i d I n c l u s i o n s i n t h e H o s t M i n e r a l s Q u a r t z a n d S c h e e l i t e f r o m t h e M u r u n t a u O r e F i e l d

N 2 ( + )

C H 4

C O 2

H 2 O

C 2 H 2

C 2 H 4

C 2 H 6

C 2 H 6 ( + )

C 3 H 6

C 3 H 8

C O S

V e i n t y p e

S a m p l e

M i n e r a l

( m o l % )

( m o l % )

( m o l % )

( m

o l % )

( p p m ) 1

( p p m )

( p p m ) 1

( p p m )

( p p m )

( p p m )

( p p m )

C O 2 / N 2 ( + ) C O 2 / C H 4

M y u t e n b a i

M a i n v e i n s

M T 1 - A

Q u a r t z

0 . 1 4

0 . 9 3

3 . 3 3

9 5 . 5 8

n . d .

1 . 7

n . d .

5 3 . 6

b . d .

2 . 4

3 1 . 4

2 3 . 3

3 . 6

M T 1

S c h e e l i t e 2

n . d .

1 . 8 2

2 . 0 6

9 5 . 7 8

n . d .

0 . 5

n . d .

2 6 8

b . d .

4 2 . 9

b . d .

n . d

1 . 1

M T 2 - B

Q u a r t z

0 . 4 9

3 . 4 5

1 0 . 0 9

8 5 . 9 1

1 . 9

1 1 . 8

4 4 5

4 4 7

b . d .

2 0 . 0

7 9 . 5

2 0 . 5

2 . 9

M T 2 - R

Q u a r t z

n . d .

3 . 0 8

6 . 6 0

8 9 . 2 9

1 . 8

2 . 9

4 2 3

4 2 5

0 . 6

2 6 . 7

1 5 0

n . d .

2 . 1

M T 3 4 2 3 - A

Q u a r t z

0 . 9 4

8 . 4 5

1 4 . 2 3

7 6 . 2 6

n . d .

3 3 . 1

n . d .

8 4 7

b . d .

5 7 . 3

2 3 6

1 5 . 2

1 . 7

M T 3 4 2 3

S c h e e l i t e 2

n . d .

0 . 9 7

3 . 3 4

9 5 . 2 2

n . d .

4 . 7

n . d .

9 5 7

0 . 2

2 6 4

b . d .

n . d .

3 . 4

S t o c k w o r k v e i n

M T 3

Q u a r t z

n . d .

1 . 0 8

4 . 5 9

9 3 . 5 6

n . d .

b . d .

n . d .

1 4 0

b . d .

b . d .

b . d .

n . d .

4 . 2

M u r u n t a u

F l a t v e i n s

M T 4

Q u a r t z

n . d .

0 . 2 4

0 . 3 2

9 9 . 2 0

n . d .

1 . 0

n . d .

2 3 . 3

0 . 4

1 . 2

9 . 6

n . d .

1 . 4

M T 3 7 7 4 - A

Q u a r t z

0 . 0 7

0 . 5 7

0 . 7 6

9 8 . 5 8

1 . 0

2 . 8

1 2 7

1 2 8

0 . 3

9 . 3

1 8 . 1

1 1 . 4

1 . 3

M T 3 7 7 8

Q u a r t z

n . d .

0 . 3 5

1 . 1 1

9 8 . 2 9

n . d .

b . d .

n . d .

3 8 . 5

b . d .

4 . 1

b . d .

n . d .

3 . 2

M T 3 7 7 8

S c h e e l i t e 1

0 . 0 3

0 . 1 4

0 . 3 7

9 9 . 4 5

n . d .

0 . 1

n . d .

3 3 . 7

b . d .

3 . 7

2 . 0

1 2 . 2

2 . 6

M T 3 7 7 9 - A

Q u a r t z

0 . 1 2

0 . 4 4

1 . 4 8

9 7 . 9 3

4 . 6

7 . 4

1 5 1

1 5 6

0 . 7

7 . 2

2 1 . 0

1 2 . 3

3 . 3

C e n t r a l v e i n s

M T 5 - A

Q u a r t z

0 . 7 4

0 . 9 4

8 . 6 2

8 9 . 6 7

3 . 4

6 . 2

1 4 8

1 5 2

b . d .

1 0 . 2

2 0 1

1 1 . 7

9 . 2

M T 5 - R 2

Q u a r t z

0 . 5 0

0 . 5 5

7 . 0 7

9 1 . 8 6

1 . 7

2 . 3

7 5 . 4

7 7 . 1

0 . 6

6 . 6

9 2 . 5

1 4 . 1

1 2 . 8

M T 7 - B

Q u a r t z

0 . 5 0

1 . 2 4

1 5 . 3 1

8 2 . 9 2

2 . 3

6 . 2

1 1 3

1 1 6

b . d .

3 . 5

1 2 3

3 0 . 8

1 2 . 3

M T 7 - A

Q u a r t z

0 . 2 7

0 . 7 8

8 . 4 7

9 0 . 4 7

1 . 1

2 . 0

5 3 . 3

5 4 . 4

0 . 3

2 . 3

8 7 . 2

3 1 . 4

1 0 . 9

M T 7 - R 1

Q u a r t z

n . d .

0 . 8 0

8 . 6 9

8 9 . 9 0

1 . 1

0 . 8

5 4 . 5

5 5 . 6

0 . 3

2 . 5

8 2 . 8

n . d .

1 0 . 9

M T 7

S c h e e l i t e 2

n . d .

1 . 3 0

5 . 2 6

9 2 . 4 3

0 . 2

0 . 8

2 0 2

2 0 2

0 . 5

2 2 . 7

b . d .

n . d .

4 . 1

7 8 - 9 8 - 1 B

Q u a r t z

0 . 1 7

0 . 7 1

7 . 2 9

9 1 . 7 9

n . d .

1 . 1

n . d .

2 1 4

0 . 2

2 0 . 2

1 8 1

4 2 . 1

1 0 . 3

7 8 - 9 8 - 5 - 3

Q u a r t z

0 . 1 1

0 . 7 7

2 . 8 4

9 6 . 2 5

n . d .

7 . 4

n . d .

1 6 5

b . d .

1 3 . 7

8 2 . 9

2 5 . 8

3 . 7

7 8 - 9 8 - 5 - 4

Q u a r t z

0 . 1 6

0 . 9 0

5 . 7 8

9 3 . 1 0

n . d .

6 . 5

n . d .

3 2 1

1 . 0

3 2 . 4

1 8 6

3 6 . 6

6 . 4

7 8 - 9 8 - 5 - 5

Q u a r t z

0 . 2 2

1 . 4 7

6 . 8 2

9 1 . 4 2

n . d .

6 . 1

n . d .

4 5 2

b . d .

4 1 . 0

2 4 2

3 0 . 9

4 . 7

Q u a r t z n o d u l e

M T 6 - R

Q u a r t z

0 . 4 9

0 . 3 8

4 . 2 5

9 4 . 8 8

1 . 5

3 . 5

6 0 . 4

6 1 . 9

0 . 8

3 . 1

6 0 . 3

8 . 7

1 1 . 3

M T 6 C - A

Q u a r t z

0 . 6 1

0 . 3 9

4 . 6 9

9 4 . 2 9

1 . 8

3 . 2

6 8 . 7

7 0 . 5

1 . 1

4 . 0

6 2 . 0

7 . 7

1 1 . 9

M T 6 B - A

Q u a r t z

0 . 4 6

0 . 2 7

3 . 5 0

9 5 . 7 6

1 . 4

3 . 6

5 3 . 4

5 4 . 8

0 . 7

2 . 9

6 4 . 3

7 . 5

1 3 . 2

A b b r e v i a t i o n s : b . d . = b e l o w d e t e c t i o n

l i m i t , n . d . = n o t d e t e r m i n e d ; N 2 ( + ) , C 2 H 6 ( + )

= N 2 ( ± C O , ± A r , ± O 2 ) a n d C 2 H 6 ( ± C 2 H 2 ) a r

e m a x i m u m c o n c e n t r a t i o n s

1 C O , C 2 H 2 , a n d C 2 H 6 w e r e c a l c u l a t e d

u s i n g r e s u l t s f r o m c r y o g e n i c g a s c h r o m a t o g r a p h y



analysis to the calculated values for types I to III CO2-bearingfluid inclusions (Table 6). The salinities of early CO2-bearingfluid inclusions are similar to the bulk data of the same sam-ple for three samples presented in this table; for one central

vein sample (MT5, quartz) the calculated salinities are somewhat lower compared to the bulk ion chromatographic data(Table 6).

Summary of fluid characteristics in Muruntau andMyutenbai central and main and flat veins(excluding low-temperature aqueous fluids)

In Muruntau flat veins, types I or II fluid inclusions werefound only in scheelite 1. The trapped early fluids are high

temperature, pure aqueous, NaCl dominated, and predomi-nantly low salinity. Type V, high-temperature, CO2-CH4-richinclusions occur in quartz in flat veins. These contain NaCl-dominated fluids. Nonaqueous volatiles are probably almostcompletely lacking in type IV and low-temperature aqueoustype V inclusions. This provides justification for using thebulk volatile gas chromatographic data as estimates for the

volatile composition of the CO2-rich fluid. The CO2 /CH4 ra-tios range from 1.3 to 3.3 (mean: 2.4 ± 1.0 (1 σ )), and theCO2 /N2 (+) ratios are between 11.4 and 12.3 (mean: 12.0 ±0.5 (1 σ )) for samples from flat veins.

The early fluid (types I–III inclusions) trapped in quartz andscheelite 2 from Muruntau central veins is high temperature,


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TABLE 5. Summary of All Volatile and Cation-Anion Data for Muruntau and Myutenbai SamplesObtained by Integrated Gas and Ion Chromatographic Analysis

CH4 CO2 H2O C2H4 C2H6 (+) COS C3H4 C3H6 C3H8 Cl– Br–

Vein type Sample Mineral mM/l mM/l mM/l µM/l mM/l mM/l µM/l µM/l mM/l mM/l mM/l

MyutenbaiMain veins MT1 Quartz 379 1,740 49800 b.d. 1.8 0.5 b.d. b.d. 0.1 1,350 0.4

MT1 Scheelite 2 1000 1,130 52600 28.3 14.7 b.d. b.d. b.d. 2.4 567 0.7MT2 Quartz 1360 2,750 48200 b.d. 15.3 5.1 b.d. b.d. 1.2 976 0.8MT2-R Quartz 1600 3,430 46400 149 22.1 7.8 19.5 32.5 1.4 1,310 2.3MT3423 Quartz 2370 4,080 45300 b.d. 19.2 7.5 b.d. b.d. 1.1 1,330 1.5MT3423 Scheelite 2 536 1,850 52700 258 53.0 b.d. b.d. 13.6 14.6 339 b.d.

Stockwork vein MT3 Quartz 479 2,030 41400 b.d. 6.2 b.d. b.d. b.d. b.d. 2,100 2.1

MuruntauFlat veins MT3774 Quartz 367 603 50500 104 9.3 b.d. b.d. 43.3 0.7 642 0.9

MT3778 Quartz 168 532 46900 b.d. 1.8 b.d. b.d. b.d. 0.2 433 1.3MT3778 Scheelite 1 75.4 198 53100 3.4 1.8 0.1 b.d. b.d. 0.2 111 0.4MT3779 Quartz 151 497 52200 43.8 2.2 0.5 b.d. 19.9 0.2 504 0.4

Central veins MT5 Quartz 326 1,940 43200 b.d. 3.2 b.d. b.d. b.d. b.d. 1,020 1.5MT7 Quartz 392 4,280 48000 b.d. 2.3 3.5 b.d. b.d. 0.1 1,180 0.7MT7-R Quartz 487 5,630 48700 49.6 3.1 4.9 14.9 10.1 0.1 1,420 1.9MT7-R1 Quartz 443 4,830 50000 47.0 3.1 4.6 11.7 15.7 0.1 1,210 1.5MT7 Scheelite 2 743 3,010 52900 45.2 11.6 b.d. b.d. 28.4 1.3 771 1.5

Quartz nodule MT6 Quartz 220 2,520 51100 63.9 3.0 2.8 b.d. b.d. 0.1 367 0.2

SO42– Na+ NH4

+ K+ Cs+ Mg2+1 Ca2+1 Sr2+1 Q Balance Corrected Vein type Sample Mineral mM/l mM/l mM/l mM/l mM/l mM/l mM/l mM/l (Q+ /Q–) Q Balance2

MyutenbaiMain veins MT1 Quartz o.bl. 1,130 b.d. 45.0 b.d. o.bl. 812 b.d. 2.07 1.27

MT1 Scheelite 2 o.bl. 679 b.d. 14.3 b.d. o.bl. o.s. o.s. 1.22 0.47MT2 Quartz o.bl. 896 b.d. o.bl. b.d. o.bl. 1,800 b.d. 4.60 2.50MT2-R Quartz o.bl. 1,230 o.bl. o.bl. b.d. 26.2 2,470 b.d. 4.73 2.95MT3423 Quartz o.bl. 916 o.bl. b.d. b.d. o.bl. 2,820 b.d. 4.92 3.12MT3423 Scheelite 2 o.bl. 561 o.bl. 138 b.d. o.bl. o.s. o.s. 2.07 0.57

Stockwork vein MT3 Quartz o.bl. 1,540 b.d. o.bl. b.d. o.bl. 4,370 b.d. 4.88 3.66

MuruntauFlat veins MT3774 Quartz o.bl. 657 b.d. o.bl. b.d. o.bl. 950 b.d. 3.98 1.70

MT3778 Quartz 652 946 o.bl. o.bl. b.d. o.bl. 1,450 b.d. 2.21 1.51MT3778 Scheelite 1 o.bl. 165 o.bl. o.bl. b.d. o.bl. o.s. o.s. 1.49 0.16MT3779 Quartz o.bl. 575 b.d. o.bl. b.d. o.bl. 246 4.0 2.13 0.77

Central veins MT5 Quartz 234 919 b.d. o.bl. 16.6 o.bl. 3,600 b.d. 5.46 3.66MT7 Quartz o.bl. 1,210 b.d. o.bl. b.d. o.bl. 1,830 b.d. 4.13 2.44MT7-R Quartz o.bl. 1,650 b.d. o.bl. b.d. 13.2 1,360 b.d. 3.08 1.95MT7-R1 Quartz o.bl. 1,210 26.1 o.bl. b.d. o.bl. 823 4.3 2.39 1.40MT7 Scheelite 2 o.bl. 1,920 112 o.bl. b.d. b.d. o.s. o.s. 2.63 1.22

Quartz nodule MT6 Quartz 37.0 567 b.d. o.bl. 4.4 o.bl. 774 b.d. 4.81 1.62

Abbreviations: b.d. = below detection limit, o.bl. = value excluded (blank is more than 25% of the leachate), o.s. = off scale, N2(+),C2H6(+) = N2 (±CO,±Ar, ±O2) and C2H6 (±C2H2) are maximum concentrations

1 Mg2+, Ca2+, and Sr2+ are minimum concentrations2 Refers to a charge balance corrected for CO2 dissolved in the aqueous phase; see Channer and Spooner (1992) for further details



NaCl dominated, low to intermediate salinity, and predomi-nantly CO2 rich. Bulk volatile gas chromatographic data forthese samples (Table 4) are dominated by the early fluid(Table 2) and can, therefore, be used to estimate its volatilecomposition. The CO2 /CH4 ratios range from 3.7 to 13.2(mean: 9.4 ± 3.4 (1 σ ); 4.1 for scheelite; 3.7–13.2 for quartz;Table 4), and CO2 /N2 (+) ratios range from 11.7 to 42.1(mean: 22.5 ± 12.8 (1 σ )).

In Myutenbai main veins, high-temperature types I to III

fluid inclusions are characterized by trapped CO2-CH4-dom-inated gas mixtures. In addition, variable amounts of NaCl-dominated solutions of low to mostly intermediate salinitiesare present. Bulk volatile gas chromatographic data can beused as good estimates for the volatile compositions of theearly fluids (types I–III inclusions) for these samples (see be-fore and Table 2). The CO2 /CH4 ratios are almost uniformand range from 1.1 to 3.6 (mean: 2.5 ± 1.0 (1 σ ); Table 4; Fig.10A) and the CO2 /N2 (+) ratios are between 15.2 and 23.3(mean: 19.7 ± 4.1 (1 σ )).

Discussion

H 2O-CO 2 fluid immiscibility: Evidence from petrography,

microthermometry, and volatile and ion geochemistryAreas showing fluid inclusions with variable volumetric ra-

tios of CO2-rich and aqueous fluids, and indicating trappingof more than one phase in the same inclusion (heterogeneoustrapping), were found in Muruntau central veins (Fig. 7) andin the quartz nodule sampled in the adjacent wall rock. Evi-dence for heterogeneous trapping of fluids could not befound in the Muruntau flat veins and all Myutenbai quartz

veins. To test if CO2- and H2O-rich inclusions shown in Fig-ures 6 and 7 were formed by fluid immiscibility, the criteriaderived by Ramboz et al. (1982) were used. Only if these con-straints are successfully tested, can immiscibility be suggested.

For the inclusion assemblage from sample MT7 shown inFigure 6 and Table 3, the results can be summarized as fol-lows: (1) types IIa/IIIa and IIb/IIIb inclusions homogenize

within a similar temperature range (225°–270° and 232°–286°C, respectively), (2) the CO2-rich inclusions homogenizeinto the vapor phase, whereas the H2O-rich inclusions ho-mogenize into the liquid phase, (3) the H2O-rich inclusionsare low but not free of volatiles, as indicated by the occur-rence of clathrates, and (4) the aqueous solutions in H2O-rich

inclusions are enriched in dissolved salts (Tm(clathrate):4.7°–6.5°C; salinity: 7.9–11.1 wt % NaCl equiv) compared tothe CO2-rich inclusions (Tm(clathrate): 7.0°–8.9°C, salinity: 4.5–7.5 wt % NaCl equiv).

Within a wall-rock quartz nodule sample, taken at a dis-tance of <1 m from a Muruntau central vein, we found a fluidinclusion assemblage similar to that shown in Figure 6. Here,the types Ia and Ib inclusions occur in adjacent areas, butthey are separated from each other by later inclusion trails.Types Ia and Ib inclusions show similar Th ranges(302°–320°C and 293°–358°C) and homogenize into the liq-uid and vapor phases, respectively.

For the assemblage from sample 98-A4 shown in Figure 7

and Table 3, the CO2- and H2O-rich inclusions are tested forthe criteria for immiscibility: (1) both inclusion typeshomogenize within similar temperature ranges (273°–328°and 285°– 324°C), (2) the CO2-rich inclusions homogenizeinto the vapor phase, whereas the H2O-rich inclusions ho-mogenize into the liquid phase, (3) the H2O-rich inclusionsare low but not free of volatiles, as indicated by the occur-rence of clathrates, and (4) the aqueous solutions in H2O-rich inclusions are probably enriched in dissolved salts(Tm(clathrate): 4.0°–4.4°C) compared to the CO2-rich inclusions(Tm(clathrate): 7.1°–8.5°C). However, Th(CO2) values could notbe measured for the H2O-rich inclusions and, therefore,salinities could not be calculated. (5) low and high CO2 /CH4

16 GRAUPNER ET AL.

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TABLE 6. Comparison of CO2 /CH4 Ratios and Salinity Data for Trapped Fluids in Individual Inclusions Determined by Laser Raman Spectroscopy and Microthermometry with Bulk Gas and Ion Chromatographic Data of the Respective Samples

Laser Raman data and Bulk gas and ioncalculated salinities (see text) chromatographic data

Salinity Salinity CO2 /CH4 (wt % NaCl) CO2 /CH4 (wt % NaCl)

Sample Range Mean Range Mean Range Mean Range Mean

Myutenbai

Main quartz vein; 1.4–4.8 3.5 3.3–15.2 9.9 4.6 7.9sample MT1 (quartz)

Muruntau

Central quartz vein; 5.0–13.3 10.5 (0.9)2.7–3.9 3.3 5.9–13.5 9.7 5.9sample MT5 (quartz)

Central quartz vein; 11.7–34.7 20.51 4.5–11.1 7.5 10.9–11.6 11.1 6.9–8.3 7.4sample MT7 (quartz)

Quartz nodule in wall rock; 5.6–38.3 20.51 1.5–3.3 2.5 11.2–11.4 11.3 2.1sample MT6 (quartz)

1 Mean of selected heterogeneously trapped inclusions; cannot be used as a mean for all inclusions of one sample




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C

D

0

5

10

15

20

0 0.5E+3 1.0E+3 1.5E+3 2.0E+3

0 1.0E+4 2.0E+4 3.0E+4 4.0E+4

0

5

10

15

20

6

C O 2 / C H 4

Muruntau

"central" quartz veins

flat quartz veins

wallrock quartz nodule

main quartz veins

Myutenbai

P h a s e

s e p a

r a t i o n

0

4

8

16

0 10 20 30 40 50 60

2

Mixing ?

12

III

Legend for Figs. A to D:

trend for Kirishima geothermalsystem (Sasada et al., 1992)

trend for Tanco granitic pegmatite(Thomas & Spooner, 1992)

I

II

10

14

18

0 400 800 1200 1600

0

15

Cl (mMol/l)–

Mixing ?

5

10

B A

single bond double bond triple bond

E Legend for Fig. E:

Tanco C 's

Tanco C 's

Muruntau C 's

Muruntau C 's

2

3

2

31.0

1.0E+2

1.0E+4

1.0E+6

C O 2 / C H

4

C O 2 / C H 4

C O 2 / C H 4

CO2 /C3H8

CO2 /C2H6+

CO2 /N2+

FIG. 10. Results from integrated gas and ion chromatographic analysis of trapped fluids in vein quartz and scheelite fromMuruntau and Myutenbai. A. Plot of CO2 /CH4 vs. CO2 /N2(+). The real data for the added trends for Kirishima and Tancosamples start at much higher values; the slopes are shown. B. Plot of CO2 /CH4 vs. Cl– (mmol/l) for samples from Muruntau.C.-D. Plots of CO2 /CH4 vs. CO2 /C2- and C3-hydrocarbons for samples from Muruntau. E. In this figure the partition coef-ficients during phase separation for each hydrocarbon species, ratioed to that for CH4, are compared to data from the Tancogranitic pegmatite (Thomas and Spooner, 1992).



ratios are characteristic of the CO2- and the H2O-rich inclu-sions, respectively. (6) fluid inclusions with intermediate de-grees of fill remained unhomogenized to ~350°C and arecharacterized by intermediate CO2 /CH4 ratios, compared tothe CO2- and the H2O-rich inclusions (Table 3). Summariz-ing all the data, there is good evidence that all the CO2- andthe H2O-rich fluid inclusions tested above formed by H2O-

CO2 fluid immiscibility.

Phase separation vs. fluid mixing

H2O-enriched fluid inclusions are usually the most abun-dant in samples containing phase-separated fluids (e.g.,Channer and Spooner, 1994). Starting from this observation,good indications of fluid immiscibility have resulted from gasand ion chromatographic bulk volatile compositional data. Inthe CO2 /CH4 vs. CO2 /N2(+) plot (Fig. 10A) most fluid inclu-sion data from the Muruntau central ore veins define an in-clined line consistent with phase separation (cf. Tanco peg-matite; Thomas and Spooner, 1992). Furthermore, theCO

2 /CH

4 vs. CO

2 /C

2and C

3hydrocarbons diagrams for Mu-

runtau samples presented in Figure 10C to D show, for allmeasured C2 and C3 hydrocarbons, a significant depletion rel-ative to CO2 from fluids with low to fluids with the highestCO2 /CH4 ratios. In these plots, central vein data define in-clined arrays. Thomas and Spooner (1992) reported for theTanco pegmatite that unsaturated hydrocarbons are parti-tioned into the CO2-rich phase more effectively than alkanesduring phase separation. For Muruntau a similar trend is ob-served (Fig. 10E), but the differences between the partitioncoefficients for single and double bond hydrocarbons aremore obvious than for double and triple bond hydrocarbons(these are very similar).

A definite identification of a parental fluid for types I to III

fluid inclusions, showing an intermediate composition be-tween exsolved liquid- and vapor-rich fluids, and giving finalevidence for fluid phase separation processes, was not possi-ble in our study. The situation is complicated by the existenceof many fluid inclusion assemblages with very scattered de-grees of filling, probably formed by heterogeneous trappingof unmixed fluids and, in addition, by a sometimes rather highdensity of microstructures resulting from late deformation of the host quartz (leakage phenomena in deformation-relatedfluid inclusion trails).

Quartz from marginal parts of central veins and from thequartz nodule sampled adjacent to a central vein are oftencharacterized by high CO2 /CH4 ratios and, in addition, an N2

enrichment relative to CO2, compared to other samples withhigh CO2 /CH4 ratios. If the trends presented in Figure 10Aand B for the data sets from the quartz nodule represent mix-ing of the phase-separated fluid with another fluid, then thelower CO2 /N2(+) ratios and the significantly lower salinity of the resulting fluid may be explained by an admixture of N2-enriched and low-salinity fluid from another, possibly wallrock-related source (e.g., Sasada et al., 1992). However, thesame effect on the bulk CO2 /N2(+) ratios and salinities wouldresult from a higher abundance of low-temperature inclu-sions with low salinity and possible N2 enrichment, whichcould indeed be found in some areas of the samples from the

vein margins.

Fluids trapped in coexisting quartz and scheelite

Compared to the coexisting quartz, scheelite 1 from Mu-runtau flat quartz veins is characterized by differences re-garding the microchemistry of the trapped fluids (see before;Tables 4 and 5). Indications for relative age relationships be-tween quartz and scheelite 1 in the Muruntau flat veins havebeen described in detail before. To explain the fluid inclusioncharacteristics, the following mechanism is suggested.

It is possible that quartz and scheelite behaved differently during vein deformation and high-temperature (>300°C)fluid circulation. From the characteristics of the mineral mi-crostructure found in our samples and the types of fluid in-clusions observed, it may be inferred that scheelite is moreresistant to recrystallization and alteration and/or extinctionof trapped early fluids, than coexisting quartz. Even in thecase that in intensely deformed quartz all early fluid inclu-sions were found to be influenced and/or extinguished by later recrystallization of the host mineral, at least some early inclusions were found in coexisting scheelite showing theiroriginal Th and phase composition. This inference is in agree-

ment with observations on quartz and scheelite in Hollinger-McIntyre, Ontario (Wood et al., 1986), the strongly deformedMittersill orebodies, Austria (Schenk, 1990), and the Bejse W occurrence (Modoto ore field, Mongolia; Dandar et al., 1993)and is important for interpretation of the fluid inclusion char-acteristics in the Muruntau flat veins.

Bulk CO2 /CH4 ratios for trapped volatiles are slightly vari-able in coexisting quartz and scheelite 2 from Myutenbaimain veins (Table 4). For the Muruntau Au-mineralizedcentral veins, the CO2 /CH4 ratio for scheelite 2 is at the low end of the range for quartz, showing values only slightly higher than the CO2 /CH4 ratios of flat vein samples. Mi-crothermometric data are consistent with the bulk gas chro-matographic data and show larger depressions of Tm(CO

2) val-

ues for inclusions in scheelite 2 compared to adjacent quartz(Fig. 8C and D).

Hydrothermal fluids in Muruntau flat and central veins

Evidence from geology (see above), quartz microstruc-tures, and fluid inclusion textural and compositional featuressupports formation of the flat quartz veins prior to the mainstage of hydrothermal activity, which includes central veinsand Au mineralized metasomatized wall rocks, as suggestedby the Sm-Nd isotope data for scheelites 1 and 2 (Kempe etal., 1996). These include the following:

1. Primary growth features (e.g., growth zoning) and re-lated early fluid inclusions were found in quartz from steeply dipping veins and are lacking in quartz from flat veins(Graupner et al., 2000). This observation is consistent withthe higher degree of deformation and secondary alteration(e.g., recrystallization) shown by flat vein quartz compared toquartz from the steeply dipping veins.

2. It may be suggested that primary fluids trapped in flatand central veins had significantly different compositions.Types I and II inclusions in scheelite 1, which are interpretedto be of about the same age as the coexisting quartz, are pureaqueous, liquid-rich inclusions. In addition, bulk nonaqueous

volatile concentrations in flat vein quartz and scheelite 1 are

18 GRAUPNER ET AL.

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similar; however, they are significantly different (Tables 4 and5) from those for samples from central veins. These observa-tions and the lack of types I to III inclusions in flat vein quartzindicate that the probable H2O-rich early inclusions in flat

vein quartz were removed during recrystallization.

Based on this interpretation, the similarity (i.e., phase com-

position and trapped volatiles) of the high-temperature, CO2-rich fluid inclusions found as types I to III inclusions in cen-tral veins and as type V inclusions in earlier flat veins issignificant. Summarizing the textural features of the CO2-richfluid inclusions found in flat vein quartz, an input of a sec-ondary CO2-dominated fluid trapped by flat vein materialafter recrystallization of quartz may be suggested. The CO2-bearing inclusions occur more frequently in quartz from a flat

vein found inside the orebody compared to flat vein quartzsamples from outside the orebody, and measured Th values of CO2-bearing fluid inclusions are higher in the flat vein sam-ple taken inside the orebody and are similar to the Th valuesfor early CO2-rich inclusions in central veins. The facts dis-cussed above support a relationship between central vein for-mation and entrapment of primary CO2-rich fluid and en-trapment of secondary CO2-rich fluid in flat veins.

Interpretation of fluid inclusion halide data

Unless evaporites are present, Cl and Br are relatively con-servative in solution and only weakly affected by fluid-rock in-teraction (Banks et al., 1991), because their concentrations innatural fluids are significantly higher than in most crustal

rocks. Hence, halide data are adequately well defined andmay be used as tracers for source analysis.

A plot of Br/Cl ratios versus chloride concentrations isgiven in Figure 11 for inclusion fluids from the Muruntau andMyutenbai quartz veins. The flat vein quartz samples haverelatively unfractionated Br/Cl values relative to “bulk earth”(Cl chondrite; Dreibus et al., 1977). In addition, all data from

this vein type are located close to the seawater point. Inter-estingly, flat vein fluids have Br/Cl ratios that are very similarto the Brusson postmetamorphic (Yardley et al., 1993) andthe Alleghany Au-bearing quartz veins (Böhlke and Irwin,1992). In contrast, both the Muruntau central and the Myuten-bai main vein samples show somewhat lower log(Br/Cl) val-ues, which partly overlap the range typical of volcanic fuma-role condensates (compilation of Böhlke and Irwin, 1992).The highest chloride values were measured in Myutenbai

vein samples.Yardley et al. (1993) have discussed deep-penetrating sur-

face, or connate, waters to be the source of the fluids involvedin the Brusson Au deposit; however, they suggested a fluid ori-gin by metamorphic devolatilization for this deposit. All Br/Clratios measured for the different vein types in the Muruntauore field are located between retrograde metamorphic quartz

veins crosscutting itabirites (Boiron et al., 1999) at high Br/Cl values, and the ranges typical of volcanic fumarole conden-sates and the St. Austell granites (compilation of Böhlke andIrwin, 1992). Flat veins show Br/Cl ratios closer to those typ-ical of metamorphic fluids; however, it may be suggested thatthere is an additional nonmetamorphic component present in


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Chloride vs. log (Br/Cl)

-4.0

-3.8

-3.6

-3.4

-3.2

-3.0

-2.8

-2.6

-2.4

-2.2-2.0

0 1500 3000 4500

Cl–(mMol/l)

l o g ( B r / C l )

1

2

3

MRMR

3

2

1

Legend:

"central" quartz veins

flat quartz veins

main and stockworkquartz veins

seawater"earth"/ Cl chondrites(Dreibus et al., 1977)log Br/Cl range forvolcanic fumarolecondensates, "magmaticrange" (compilation ofBöhlke and Irwin, 1992)Canadian Shield brines(Fritz and Frape, 1982)Brusson Au-quartz veins(Yardley et al., 1993) Alleghany Au-quartz veins(Böhlke and Irwin, 1992)Ouro Fino retrogrademetamorphic quartz veins(Boiron et al., 1999)St. Austell granites(Böhlke and Irwin, 1992)

Muruntau

Myutenbai

literature data

4

4

Muruntau flat quartz veins

Myutenbai quartz veins

Muruntau "central" quartz veins

FIG. 11. Plot of halide analyses for the Muruntau and Myutenbai fluid inclusions, with halide data from other ore depositsand crustal fluids for comparison. Br/Cl ratios and Cl– concentrations for Muruntau and Myutenbai samples are from com-bined gas and ion chromatographic analysis (method of Channer et al., 1999).



this vein type since the values are not identical. The bulkBr/Cl ratio for the flat veins clearly includes Br/Cl values fortwo fluids of different compositions in almost equal parts (asindicated by microthermometry), and an estimation of theireffects on the bulk cation-anion compositions of these sam-ples has many uncertainties. For Muruntau central andMyutenbai main veins the bulk Br/Cl signal is clearly domi-

nated by the early inclusions. Here, a stronger influence of amagmatic or other deep-seated source may be suggested inaddition to a possible metamorphic component.

Discussion of possible fluid evolution models for the Muruntau deposit

High-temperature, low- to intermediate-salinity CO2-richfluids were found to dominate in the Muruntau veins for themain stage of productive hydrothermal activity. Phase separa-tion temperatures for hydrothermal fluid trapped in quartzfrom central veins, which are thought to equal trapping tem-peratures, are between ~225° and ~320°C. For these veins

we obtained phase separation pressure estimates rangingfrom ~500 to ~800 bars. Some indications may be derivedfrom our data regarding possible evolutionary trends for thefluids of the main hydrothermal stage. In Figure 10A, all sam-ples from low-grade mineralized flat veins from inside andoutside the investigated orebodies in Muruntau with a gascomposition (excluding H2O) dominated by type V CO2-richfluid inclusions also fit the phase separation line suggested forthe Muruntau central veins. The volatile ratios for flat veinquartz are located at the low ends of the ranges for CO2 /CH4

and CO2 /N2(+) plotted in this figure. As shown before, a di-rect relationship between formation of early, CO2-rich inclu-sions in central veins and entrapment of CO2-rich fluids in flat

veins seems to be very likely. In flat veins, no indications of fluid immiscibility could be found from fluid inclusion pet-

rography. In contrast, the CO2-rich fluid trapped in central veins is modified by fluid unmixing. All facts mentioned be-fore and the volatile ratios (Fig. 10A) support the inferencethat the CO2-rich fluid in both vein types in Muruntau may have been formed from a similar original fluid. Starting fromsimilar initial volatile ratios (CO2 /CH4 ratio of ~2–3; CO2 /N2

ratio of ~10–15), the fluid trapped in the low-grade mineral-ized flat veins remained low-degree phase separated, whereasintense phase separation processes occurred in the hy-drothermal fluid in the high-grade mineralized central veinsof the investigated orebodies and, in addition, in the adjacent

wall-rock quartz nodule, which also contains Au (Monecke,1996). An admixture of an external fluid to the hydrothermal

system in the marginal parts of the ore veins is also suggestedby the data.

Comparison of the fluid characteristics observed for Muruntau and Myutenbai

In Myutenbai ore veins, CO2 /CH4 ratios of fluids (Table 4)are almost uniform and significantly lower than those for Mu-runtau central veins; Myutenbai main vein samples plot in thesame field for CO2 /CH4 versus CO2 /N2(+) (Fig. 10A) as theMuruntau flat vein samples. The Tm(CO2) (Fig. 8A-B) andTh(CO2) (Fig. 9A-B) values for CO2-rich inclusions from these

veins support the bulk analytical data. For the mineral pairs,quartz-scheelite 2, Myutenbai also differs from Muruntau. In

Myutenbai, characteristics of trapped volatiles and fluid in-clusion microthermometry data are similar for quartz andscheelite, whereas in Muruntau the variations between fluidinclusion data for the two minerals are significant (e.g., low CO2 /CH4 ratio in scheelite 2; often high CO2 /CH4 in quartz).Differences between the fluid characteristics of the two de-posits were also reported by Zairi and Kurbanov (1992). The

reason for these differences, which are also indicated by traceelement data for coexisting quartz and scheelite 2 (Kempe etal., 1999), are not yet clear. For example, positive Eu anom-alies only observed in quartz and scheelite from Myutenbaimay be interpreted to indicate a magmatic contribution to thehydrothermal fluid or additional changes in the fluid compo-sition. Summarizing, possible explanations for the fluid char-acteristics found in both deposits are (1) there are differentfluid systems at Muruntau and Myutenbai, (2) the two de-posits represent different levels of fluid migration in the hy-drothermal system, and (3) there are different scenarios of fluid evolution for the deposits. The first possibility abovemay be ruled out because the starting fluid characteristicsseem to be similar for both deposits (Fig. 10A); furthermore,the Sm/Nd isotope characteristics of scheelite 2 indicate auniform fluid source (Kempe et al., 1996). The fluid inclusiondata may suggest fluid unmixing in Muruntau and only a lim-ited degree of evolution of the fluid in Myutenbai.

Comparison to other mesothermal Au-bearing quartz vein systems

Despite many contrasting features (see Introduction), theMuruntau deposit shows a number of characteristics that aresimilar to mesozonal Archean Au-bearing quartz vein de-posits (e.g., Gebre-Mariam et al., 1995). These include themetamorphic grade of the ore-hosting sequence (greenschistfacies), the quartz vein geometric characteristics, and the P-T

conditions of mineralization. The hydrothermal fluid trappingtemperatures and salinity data for Muruntau central veinquartz and scheelite are variable and extend to quite low val-ues; however, they are similar (see Fig. 12) to those for themesozonal Au-bearing quartz vein deposits of, for example,Mount Charlotte, Kalgoorlie, Western Australia (Ho et al.,1992), Sigma (Robert and Kelly, 1987), and Hollinger-McIn-tyre, Abitibi, Canada (Wood et al., 1986; Spooner et al.,1987).

Mikucki (1998) considers fluid-rock interaction, and wall-rock sulfidation in particular, to be the most important type of precipitation mechanism in lode-gold systems. Drew et al.(1996) also discuss the effects of fluid-carbonaceous and fer-

rous-iron-bearing-rock interaction on metal precipitation forthe Muruntau system. However, there is good evidence forfluid phase separation in Muruntau (this study) as there is alsofor other mesozonal Au systems (e.g., Mount Charlotte,Sigma, and Hollinger-McIntyre mines; for references see be-fore). Chemical and physical consequences of fluid unmixingmay result in the deposition of gold depending on the initialfluid compositions and the relative rates of the variations inpH, mΣS, and ƒO2

(e.g., Drummond and Ohmoto, 1985;Spooner et al., 1987; Bowers, 1991; Mikucki, 1998). For theMuruntau ore field, the consistency of the theoretical consid-erations with observations made in our study is significant:low-degree evolved hydrothermal fluids and low Au contents

20 GRAUPNER ET AL.

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were found for Muruntau flat veins and Myutenbai quartz veins, and high-degree phase-separated fluids and high Aucontents have been found in the Muruntau central veins. Thismay indicate a close relationship between fluid unmixing and

Au deposition in Muruntau central quartz veins. Fluid un-mixing is also considered to be an important Au depositionmechanism in mesozonal Au-bearing quartz vein systems(e.g., Hollinger-McIntyre and Sigma deposits; compilation of de Ronde et al., 1997). However, Au mineralization in meta-somatized wall rocks, which is very significant in Muruntau,may reflect significant fluid-wall rock interaction.

Summary of Principal Conclusions

1. Geologic field observations, distribution characteristicsof fluid inclusions containing the main ore fluid (types I-IIIinclusions in central and type V in flat veins), and bulk volatilechemistry in Muruntau suggest formation of the flat veins be-

fore the main stage of hydrothermal activity, represented by the steeply dipping central ore veins.2. From both microthermometric and bulk microchemical

investigations, we have good evidence for H2O-CO2 phaseseparation processes in Muruntau central Au-bearing quartzore veins; however, in Muruntau flat veins and in Myutenbaiore veins no indications for unmixing were found. In marginalparts of Muruntau central veins, evidence for fluid mixing ispresent.

3. The consistency of highly phase separated ore fluidsand strong mineralization in Muruntau and the lack of evi-dence for phase separation in Myutenbai indicates differentprocesses and conditions for the two deposits.

4. Ore fluid temperatures and salinities measured for Mu-runtau high-grade mineralized central veins show significant

variability and range between ~225° and ~ 320°C and ~1 and>12 wt percent NaCl equiv, respectively. They are similar to

those for the Archean mesozonal Au-bearing quartz vein sys-tems of, for example, Mount Charlotte, Kalgoorlie (WesternAustralia), Sigma and Hollinger-McIntyre (Abitibi, Canada),and the Barberton greenstone belt (South Africa).

5. The phase separation trend discussed suggests an effec-tive mechanism for the precipitation of Au in veins from thehydrothermal fluid in the Muruntau Au deposit. In order tomake a more detailed statement regarding the relative im-portance of phase separation processes compared to, for ex-ample, wall-rock sulfidation (e.g., Au mineralized metasoma-tized lithologies) in Muruntau, further investigations areneeded.

Acknowledgments

The authors wish to express their gratitude to Navoi Min-ing and Metallurgical Complex, Zarafshan Central MineBoard, Uzbekistan, who allowed us to conduct investigationson their property. This work has been supported by a schol-arship from the Deutscher Akademischer Austauschdienst(DAAD), the Deutsche Forschungsgemeinschaft (DFG) (Wo489/15-1; Wolf and Irmer), the Natural Sciences and Engi-neering Research Council (NSERC), and the Department of Geology, University of Toronto. The authors are very gratefulto D. Wolf for his continuous help during organization of fieldand analytical work. We would also like to thank A. M. vanden Kerkhof for useful discussions. R. J. Bakker, J. Dubessy,


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FIG. 12. Microthermometric results (Th; salinity) for types I to III fluid inclusions from the Muruntau ore field; inclusion data for selected Archean andother Au-bearing quartz vein systems are added for comparison. Data sources for deposits are Goldfarb et al. (1989; Juneau Au belt, Alaska), Spooner et al.(1987; Hollinger-McIntyre deposit, Abitibi, Canada), Ho et al. (1992; Mount Charlotte, Kalgoorlie, Australia), Robert and Kelly (1987; Sigma deposit; Abitibi,Canada), and de Ronde et al. (1997; Barberton deposits, South Africa).

1

5

4

3

Muruntau "central" veins (quartz)

Muruntau flat veins (scheelite)

Myutenbai main veins (quartz)

Legend:

1 Juneau Au belt

2 Hollinger-McIntyre deposit

3 Mt. Charlottedeposit

4 Sigma deposit

5 Barbertondeposits

500

4

200 300 400

2

6

0 1000

12

10

8

16

14

Temperature ( °C)

a l i n i t y W t . % N a

l E q u i v .

2



and C. Heinrich are thanked for their reviews, which signifi-cantly improved the paper.

February 7, September 28, 2000

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Graupner_T_2001_Microthermometric Laser Ramam Spectroscopic and Volatile Ion Chromatographic Analysis of Hydrothermal Fluids in the Pleozoic Muruntau