Geochemistry of the magmatic–hydrothermal system of Kawah Ijen volcano, East Java, Indonesia

Journal of Volcanology and Geothermal Research 97 (2000) 31–53 www.elsevier.nl/locate/volgeores

Geochemistry of the magmatic–hydrothermal system of Kawah Ijen volcano, East Java, Indonesia P. Delmelle a,b,*, A. Bernard a, M. Kusakabe b, T.P. Fischer c, B. Takano d a

Laboratoire de Ge´ochimie, Universite´ Libre de Bruxelles, 160/02, Av. F. Roosevelt, 50, B-1050 Brussels, Belgium b Institute for Study of the Earth’s Interior, Okayama University, Misasa, 682-01 Tottori-ken, Japan c Department of Geology, Arizona State University, Tempe, AZ 85287-1404, USA d Department of Chemistry, College of Arts and Sciences, The University of Tokyo, Tokyo 153, Japan

Abstract Samples from Kawah Ijen crater lake, spring and fumarole discharges were collected between 1990 and 1996 for chemical and isotopic analysis. An extremely low pH (,0.3) lake contains SO4 –Cl waters produced during absorption of magmatic volatiles into shallow ground water. The acidic waters dissolve the rock isochemically to produce “immature” solutions. The strong D and 18O enrichment of the lake is mainly due to enhanced evaporation at elevated temperature, but involvement of a magmatic component with heavy isotopic ratios also modifies the lake D and 18O content. The large DSO4 –S0 (23.8–26.4‰) measured in the lake suggest that dissolved SO4 forms during disproportionation of magmatic SO2 in the hydrothermal conduit at temperatures of 250,2808C. The lake d 18OSO4 and d18 OH2 O values may reflect equilibration during subsurface circulation of the water at temperatures near 1508C. Significant variations in the lake’s bulk composition from 1990 to 1996 were not detected. However, we interpret a change in the distribution and concentration of polythionate species in 1996 as a result of increased SO2-rich gas input to the lake system. Thermal springs at Kawah Ijen consist of acidic SO4 –Cl waters on the lakeshore and neutral pH HCO3 –SO4 –Cl–Na waters in Blawan village, 17 km from the crater. The cation contents of these discharges are diluted compared to the crater lake but still do not represent equilibrium with the rock. The SO4/Cl ratios and water and sulfur isotopic compositions support the idea that these springs are mixtures of summit acidic SO4 –Cl water and ground water. The lakeshore fumarole discharges …T ˆ 170 , 2458C† have both a magmatic and a hydrothermal component and are supersaturated with respect to elemental sulfur. The apparent equilibrium temperature of the gas is ,2608C. The proportions of the oxidized, SO2-dominated magmatic vapor and of the reduced, H2S-dominated hydrothermal vapor in the fumaroles varied between 1979 and 1996. This may be the result of interaction of SO2-bearing magmatic vapors with the summit acidic hydrothermal reservoir. This idea is supported by the lower H2S/SO2 ratio deduced for the gas producing the SO4 –Cl reservoir feeding the lake compared with that observed in the subaerial gas discharges. The condensing gas may have equilibrated in a liquid–vapor zone at about 3508C. Elemental sulfur occurs in the crater lake environment as banded sediments exposed on the lakeshore and as a subaqueous molten body on the crater floor. The sediments were precipitated in the past during inorganic oxidation of H2S in the lake water. This process was not continuous, but was interrupted by periods of massive silica (poorly crystallized) precipitation, similar to the present-day lake conditions. We suggest that the factor controlling the type of deposition is related to whether H2S- or silicarich volcanic discharges enter the lake. This could depend on the efficiency with which the lake water circulates in the hydrothermal cell beneath the crater. Quenched liquid sulfur products show d 34S values similar to those found in the banded * Corresponding author. Present address. Unite´ des Sciences du Sol, Universite´ Catholique de Louvain, Place Croix-du-Sud 2/10, B-1348 Louvain-la-Neuve, Belgium. Tel.: 132-10473628; fax: 132-10474525. E-mail address: [email protected] (P. Delmelle). 0377-0273/00/$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. PII: S0377-027 3(99)00158-4

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deposits, suggesting that the subaqueous molten body simply consists of melted sediments previously accumulated at the lake bottom. q 2000 Elsevier Science B.V. All rights reserved. Keywords: Kawah Ijen volcano; geochemistry; magmatic–hydrothermal system; stable isotopes

1. Introduction

2. The hydrothermal system of Kawah Ijen

Acidic fluids produced during shallow interaction of magmatic volatiles with ground water can discharge and accumulate in summit volcanic craters to form lakes whose physico-chemical status depends on both atmospheric conditions and subsurface activity. Scientists have studied such crater lake systems and their products—including the liquid sulfur body that they often host—from geochemical, geophysical and hydrologic viewpoints using chemical and stable isotopic data, thermochemical models, underwater acoustic surveys and energy and mass balance calculations. Their results have helped (1) to understand water–rock and gas–water interactions in magma– hydrothermal systems (e.g. Giggenbach 1974; Casadevall et al., 1984; Christenson and Wood, 1993; Delmelle and Bernard, 1994; Pasternack and Varekamp, 1994; Delmelle et al., 1998; Taran et al., 1998); (2) to identify geochemical and geophysical precursors of volcanic activity (Brown et al., 1989; Takano and Watanuki, 1990; Rowe et al., 1992a; Ohsawa et al., 1993; Takano et al., 1994a); (3) to estimate long-term magma heat and volatile fluxes (Rowe et al., 1992b; Brantley et al., 1993; Ohba et al., 1994); (4) to describe the volcanic–hydrothermal ore-forming environments (Christenson and Wood, 1993; Arribas, 1995); and (5) to predict the composition and spectral properties of volcanogenic sulfur on Io, a moon of Jupiter (Oppenheimer, 1992; Kargel et al., 1999). In this paper we present the results of a chemical and isotopic study of gases, waters and elemental sulfur collected from a crater lake, fumaroles and springs at Kawah Ijen volcano from September 1990 to August 1996. We use these data to clarify the origin of the fumarole gas and thermal water discharges associated with the volcano–hydrothermal system by considering various geochemical and hydrological processes. The occurrence and formation of elemental sulfur in the crater lake system are also detailed.

Kawah Ijen (2386 m) is an active stratovolcano of basalt–andesitic to andesitic composition (Whitford et al. 1979; Delmelle and Bernard, 1994) located within the Ijen caldera on East Java (Fig. 1). The most recent magmatic eruption was in 1817, but frequent phreatic and geyser-like activity have reportedly occurred since that time (Newhall and Dzurisin, 1988), and the lake has lately shown signs of instability coupled with increased seismicity (Smithsonian Institution, 1993; 1994a,b; 1997a,b). The visible surface manifestations of the hydrothermal system associated with Kawah Ijen consist of a crater lake, arguably the largest natural reservoir of hot acidic waters on Earth (volume < 32 × 10 6 m 3, T . 358C; pH ,0.3; Delmelle and Bernard, 1994), crater fumaroles and few thermal discharges. One of the hot springs is in the crater and the others are found in Blawan village, located about 17 km below the volcano (see Delmelle and Bernard, 2000 – this volume; Fig. 1). There is also a cold spring discharge on the east flank at Paltuding. Delmelle and Bernard (1994) discussed the lake water chemistry and concluded that condensation and oxidation of volcanic gases containing SO2, H2S and HCl into ground water account for the high acidity and high anion concentrations, whereas isochemical dissolution of the rock builds up the cation contents (total dissolved solid concentration, TDS $ 100 g/kg) until silica, gypsum and barite precipitate. Evaporation further concentrates the lake water in dissolved elements. A local company mines elemental sulfur in the crater by channeling the fumarolic gas through metal pipes. Sulfur mats conveyed to the lake surface and pyroclastic sulfur ejecta produced during the July–August 1993 phreatic activity (Delmelle, 1995; C. Oppenheimer, pers. commun. 1993) indicate the likely occurrence of molten sulfur at the lake bottom. Elemental sulfur also occurs in partially eroded banded lake sediments (height ,40 m)

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Fig. 1. Map of the summit area of Kawah Ijen volcano showing the locations of fumarole, crater lake, crater spring and elemental sulfur deposits (modified from Delmelle and Bernard, 1994). Black circles indicate sampling points for lake water. Inset map shows Kawah Ijen on East Java. Symbols: CS ˆ crater hot spring.

exposed on the west lakeshore (Brouwer, 1925; Delmelle, 1995). Their presence attests to a relatively recent drop in the lake water level. The deposits consist of alternating fine- and coarse-grained laminations. The fine-grained laminations contain either elemental sulfur or poorly crystallized silica precipitates and vary in thickness from a few millimeters up to 3 m. The coarse laminations are made of rock fragments mixed with sediments. The deposits also record past explosions through the lake’s molten sulfur body, because pyroclastic sulfur similar to the 1993 ejecta occurs in a few coarse layers. The transition between one lamination to the next is not regular and is generally abrupt. In contrast to the sulfur-rich banded sediments of Tateyama volcano (Kusakabe and Hayashi, 1986), the Kawah Ijen deposits do not reveal

a seasonally controlled deposition pattern (Delmelle, 1995).

3. Field work and laboratory analyses We sampled the fumarole gases, the crater lake waters, the thermal spring and surface stream waters for chemical and D, 18O and 34S analysis according to procedures described elsewhere (Giggenbach and Goguel, 1989; Delmelle and Bernard 1994; Delmelle et al., 1998). We also collected various elemental sulfur materials in the crater, including floating spherules and slicks, pyroclastic ejecta, fumarole sublimates and cliff sediments for sulfur isotopic determination. Most sampling sites are shown in

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Fig. 2. Relative abundances (mg/kg) of Na, K, Mg and Ca of Kawah Ijen thermal discharges. Also shown is the composition of Kawah Ijen rocks (Delmelle and Bernard, 1994). The full equilibrium line represents the composition of waters in equilibrium with thermodynamically stable mineral assemblages of the rocks (Giggenbach, 1987). Symbols: CS ˆ crater hot spring; BL ˆ Blawan hot springs; PA ˆ Paltuding cold spring.

Fig. 1. 18O and D contents in the waters were determined according to Bigeleisen et al. (1952) and Epstein and Mayeda (1953). Elemental sulfur and sulfides were oxidized into SO4 by reaction with Br2 and HNO3, and the sulfur isotope ratio in dissolved SO4 was obtained using the method of Yanagisawa and Sakai (1983). The oxygen isotope ratio in SO4 was measured following Sakai and Krouse (1971). All SO4-containing solutions were purified with cation and anion exchange resins before conversion into BaSO4. Total sulfur in a powdered sample of a fresh basaltic andesite crater rock was prepared for isotopic analysis according to Sasaki et al. (1979). Isotopic results are expressed in the d notation relative to SMOW or CDT standards. The reproducibility of d values is ^1.5, ^0.05 and ^0.15‰ for D, O and S, respectively.

4. Chemical composition of waters 4.1. Crater lake waters Analyses of the crater lake waters and thermal spring waters are shown in Table 1. The dissolved cation and anion contents in the hot lake …T ˆ 33:8–43:28C† are constant with depth, indicating complete mixing. The lake composition did not vary significantly from 1990 through 1996 and is similar to that reported in 1941 (van Bemmelen, 1949). The relative Na, K, Mg and Ca contents in Kawah Ijen waters are shown in Fig. 2. All the lake compositions closely correspond to isochemical dissolution of the crater rocks, consistent with their high acidity. The lake molar S/Cl ratio ranges between 0.9 and 1.2 and is systematically lower than that of the fumarole gas (S/Cl ˆ 3.1–10.6, Table 2). If the latter is representative of the volcanic vapor being

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Fig. 3. Temporal variations of the Cl-normalized SO4, Mg, S4O6, S5O6, S6O6 and SSxO6 concentrations (mg/kg) in Kawah Ijen crater lake waters as measured in 1990–1996. Arrows indicate dates of phreatic eruptions. Note the increase in SSxO6 content and the concurrent increase in S4O6 concentration relative to the other polythionate species in 1996.

condensed in the lake’s hydrothermal system, this difference would account for the preferential partitioning of HCl over SO2 and H2S into the aqueous phase (Simonson and Palmer, 1993). It may also indicate that deposition of elemental sulfur occurs at depth, as discussed below. The lake waters contain significant polythionate (SxO6, x ˆ 4; 5 or 6) concentrations …SS x O6 ˆ 343–1095 mg=kg†; which attest to the discharge of SO2- and H2S-bearing volcanic gases into the lake–hydrothermal system (Takano, 1987; Takano and Watanuki, 1990). Some acidic crater lakes have shown conspicuous variations in their Cl-normalized SO4, Mg and SxO6 concentrations accompanying changes in the magma– hydrothermal activity (e.g. Giggenbach and Glover, 1975; Rowe et al., 1992a; Takano et al., 1994a). At Kawah Ijen, the Mg/Cl and SO4/Cl ratios did not vary significantly between 1990 and 1996 (Fig. 3). However, the SSxO6/Cl ratio increased from 0.017 in 1990 to 0.023 in 1993 and 0.048 in 1996. Furthermore, there was a change in 1996 from the order S5O6 . S4O6 . S6O6 to the order S5O6 < S4O6 . S6O6. The ratio increase may indicate an enhanced flux

of volcanic sulfur to the lake system, whereas the distribution change may reveal condensation of a gas enriched in SO2 (Takano et al., 1994a). 4.2. Crater, Paltuding and Blawan spring waters Although less concentrated (TDS ˆ 56 g/kg), the strongly acidic crater spring …T ˆ 618C; pH ˆ 0:6† is chemically similar to the lake, suggesting that it consists of lake seepage diluted with ground water. The thermal discharges …T , 608C† at Blawan are HCO3 –SO4 –Cl–Na waters with low TDS concentrations (,2 g/kg) and near-neutral pH values (pH . 6) Paltuding …T ˆ 138C† is a moderately acidic …pH ˆ 4:8† and slightly mineralized (TDS ˆ 0.3 g/kg) spring with a high SiO2 concentration (231 mg/kg). None of these spring discharges have reached equilibrium with the altered rock (Fig. 2), pointing to the “immature” nature of the Kawah Ijen acidic hydrothermal system. In Fig. 4, all thermal discharges are plotted for their SO4 and Cl contents. There is a clear linear trend defined by the springs and the average composition of the crater lake, which strongly suggests that the

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Table 1 Chemical composition of thermal waters from Kawah Ijen volcano (in mg/kg) (n.a.: not analyzed; n.m.: not measured) Label

T (8C)

pH

TDS Na (g/kg)

K

Mg

Ca

B

Al

SiO2

Fe

SO4

F

Cl

HCO3 S4O6

S5O6

S6O6

Crater lake IJ90-1 a 0 m IJ90-5 a 71 m IJ92-1 a 0 m VSI-1 0m VSI-2 0m VSI-3 0m VSI-4 0m VSI-5 0m IJ93-1 a 0 m VSI-6 0m IJ93-3 0 m IJ94-1 0 m IJ95-1 0 m IJ95-2 0 m IJ96-1 0 m IJ96-2 165 m IJ96-3 80 m IJ96-5 155 m IJ96-6 75 m IJ96-7 90 m

18/09/90 18/09/90 25/10/92 15/05/93 15/06/93 07/07/93 31/08/93 10/09/93 17/09/93 11/10/93 22/12/93 17/08/94 20/09/95 26/07/95 08/08/96 08/08/96 08/08/96 08/08/96 09/08/96 09/08/96

36.6 n.a. 33.8 36 40 40 42 44 43.2 42 41.6 n.m. n.m. 42.5 35.6 n.m. n.m. n.m. n.m. n.m.

0.20 0.18 0.19 n.m. n.m. n.m. n.m. n.m. 0.28 n.m. 0.09 0.30 0.25 0.39 0.29 n.m. n.m. n.m. n.m. n.m.

94.4 100.9 102.0 100.2 92.3 104.4 109.3 109.9 107.3 94.5 114.0 103.7 104.2 107.1 106.9 108.0 97.0 101.8 105.1 100.5

585 566 982 790 828 768 782 768 940 774 812 862 880 1260 1160 1140 1160 1160 1180 1140

1702 1732 1284 1364 1426 1326 1364 1368 1180 1382 1400 1289 1278 1360 1473 1469 1510 1490 1464 1462

688 686 714 688 666 677 679 690 569 682 751 561 509 767 630 639 658 681 702 657

1106 1092 1027 n.a. n.a. n.a. n.a. n.a. 911 n.a. 1262 n.a. 1329 873 968 856 1278 1036 824 1000

46 43 54 n.a. n.a. n.a. n.a. n.a. 54 n.a. 43 53 53 58 53 51 54 54 53 52

5490 5513 6078 4300 4394 4269 4437 4367 5530 4346 4865 5209 5365 6233 5413 5182 5349 5416 5408 5470

143 138 173 n.a. n.a. n.a. n.a. n.a. 175 n.a. 193 n.a. 190 150 161 150 148 150 116 120

1862 1855 1923 1953 2056 2040 2079 2096 1888 2052 2170 2004 2105 2370 2062 1929 2093 2074 2052 2074

59305 66552 63580 69551 62588 72397 76173 76943 74133 67944 77044 70542 70104 69899 71309 70692 64477 67352 69923 66795

1325 1128 1682 n.a. n.a. n.a. n.a. n.a. n.a. n.a. 1926 1015 998 1663 1045 1113 915 963 1001 986

22146 21517 24460 21528 20300 22933 23811 23670 21832 21218 23485 22138 21381 22385 22630 24780 19338 21357 22336 20720

n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a.

112 113 n.a. 127 134 139 124 147 215 166 n.a. n.a. n.a. n.a. 396 b n.a. n.a. n.a. n.a. n.a.

157 186 n.a. 208 263 264 253 266 290 270 n.a. n.a. n.a. n.a. 444 b n.a. n.a. n.a. n.a. n.a.

74 78 n.a. 76 108 124 86 90 133 102 n.a. n.a. n.a. n.a. 255 b n.a. n.a. n.a. n.a. n.a.

Springs BL2-90 BL1-92 BL1-93 BL2-93 BL1-96 BL2-96 CS-95 PA-92

20/09/90 26/10/92 24/12/93 24/12/93 13/08/96 13/08/96 26/07/95 26/10/92

51.2 47.1 48.2 50.2 31.3 46.7 61.0 13.1

6.58 6.41 6.20 6.32 6.43 6.45 0.58 4.75

1.9 0.8 1.8 1.9 1.4 1.2 56.4 0.3

97 200 126 130 90 176 663 11

1.6 1.6 1.6 1.4 n.a. n.a. 40 ,0.1

,0.5 0.1 0.5 0.3 1.54 0.3 3940 3.0

139 131 165 169 118 171 195 231

,1.0 302 n.a. 87 979 ,0.1 228 n.a. 82 n.a. 1.1 242 n.a. 80 842 1.0 291 n.a. 89 939 3.6 600 2 202 n.a. 3.1 505 1.5 85 n.a. 1110 36268 746 11161 n.a. ,0.1 58 n.a. 15 n.a.

n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a.

n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a.

n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a.

Blawan Blawan Blawan Blawan Blawan Blawan Crater Paltuding

67 110 46 74 45 99 48 115 32 89 50 77 856 510 5.5 3.8

109 87 150 128 250 102 887 12

From Delmelle and Bernard (1994). Averaged value of eight water samples collected at a depth of 0, 25, 75, 100, 125, 150 and 155 m, the SxO6 concentrations did not vary significantly with depth (B. Takano, unpublished data). b

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Date

a

Locality

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Table 2 Chemical composition of fumarole discharges from Kawah Ijen volcano (mmol/mol) (n.a., not analyzed; n.r., not reported) Label

Date

T (8C) H2O

CO2

SO2

H2S

HCl

HF

He

H2

Ar

O2

N2

CH4

CO

M40 a M57 a KIG-1 b KIG-2 KIG-3 KIG-4

??/07/79 ??/07/79 17/09/93 26/07/95 09/08/96 09/08/96

244 244 187 169 217 217

225616 146795 114000 94100 28000 30000

2289 2873 8600 2890 1280 1470

9133 7348 11500 15670 3110 3330

n.r. n.r. 1900 6080 560 460

n.r. n.r. n.a. 9 3 4

1.20 1.38 0.18 0.32 0.02 0.02

22.20 21.40 2.2 21.05 1.39 1.36

n.r. n.r. 1.52 1.40 0.03 0.03

n.r. n.r. 10.4 3.1 ,1.7 ,1.7

n.r. n.r. 386 476 24.3 25.7

1.40 0.80 0.1 0.19 ,0.57 ,0.59

33.5 20.3 n.a. ,0.02 0.05 ,0.05

a b

764000 843000 864000 880000 967000 964000

From Allard (1986). From J. Hirabayashi (pers. commun., 1993).

springs are related to a common SO4 –Cl reservoir. We conclude that the spring discharges represent various degrees of dilution with ground water of the SO4 –Cl waters formed in the summit acidic hydrothermal system. The high HCO3 content found in the Blawan springs probably resulted from the incorporation of surface ground waters that contained a CO2rich steam fraction boiled off the hydrothermal system (Ellis and Mahon, 1977).

5. Fumarolic gas chemistry The chemical compositions of fumarole discharges are reported in Table 2. The temperatures vary between 169 and 2448C. Water is the most abundant gas species, followed by CO2 and the sulfur species H2S and SO2. In terms of the inert, minor species N2, He and Ar, Kawah Ijen gases lie in the field of typical arc-type gases mixed with various amounts of air and

Fig. 4. Log SO4 vs. log Cl concentrations (mg/kg) in Kawah Ijen thermal discharges. Symbols are as in Fig. 2. The “average crater lake water” data point represents averaged analysis of all crater lake samples reported in Table 1.

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Fig. 5. Classification of Kawah Ijen fumarole gases in terms of relative Ar–N2 –He contents. Numbers correspond to sample labels in Table 2. The “arc-type” field corresponds to gases which are high in N2 and the “mantle-derived” field to gases enriched in He (Giggenbach, 1992a). Also shown are air and air-saturated water (asw).

air-saturated ground water, as observed at other subduction zone volcanoes (Giggenbach, 1992a; Fischer et al., 1998) (Fig. 5). The H2 –Ar geothermometer of Giggenbach and Goguel (1989) yields equilibrium temperatures of 260–2908C. Fig. 6 shows that all gas discharges are supersaturated with respect to liquid sulfur according to reaction: SO2 1 2H2 S , 3S0 1 2H2 O

…1†

The metal pipes through which the gases flow are coated on both sides with elemental sulfur, and liquid sulfur continuously “drains” from the outlet, consistent with its supersaturation at discharge temperatures. Removal of elemental sulfur from volcanic gases according to reaction (1) has been observed frequently on active volcanoes (e.g. Mizutani and Sugiura, 1966; Giggenbach, 1987). In SO2-dominated vapors, the deposition of elemental sulfur will consume 2 moles of H2S per mole of SO2 and lead to depletion of H2S in the gas discharge. By contrast, addition of a H2S-dominated hydrothermal vapor will also result in the deposition of elemental sulfur and will cause an increase in the H2S content of the discharged gas.

Fig. 6. Saturation of Kawah Ijen fumarole gases with respect to native sulfur. The theoretical lines are calculated according to reaction (1) (Mizutani and Sugiura, 1966; Giggenbach, 1987). Numbers correspond to sample labels in Table 2.

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Fig. 7. Relative contents of SO2, CO2 and H2S for Kawah Ijen fumarole gases. Numbers correspond to sample labels in Table 2. The gas collected in 1979 has a more magmatic signature, whereas the samples of 1990s are more hydrothermal in nature.

To determine the controlling elemental sulfur deposition process at Kawah Ijen, we have reported the relative abundance of CO2, SO2 and H2S and their changes throughout the sampling survey from 1979 to 1996 in Fig. 7. The gas composition changed from CO2-rich in 1979 to a more sulfur-rich gas in 1993, with the C/S ratio decreasing from ,20 to ,5. This was accompanied by a concurrent decrease in the H2S/SO2 ratio, indicating the addition of a relatively oxidized, SO2 rich component. During that time, the vapors added to the gas discharges were dominated by SO2, which led to the depletion of H2S as elemental sulfur was removed. From 1993 to 1995, the H2S/SO2 ratio increased significantly and the deposition of elemental sulfur most likely was the result of addition of a H2S-dominated, HCl-rich hydrothermal component. This idea is supported by a drop in the CO2/HCl ratios from 60 in 1993 to 15 in 1995. The situation was again reversed in 1996 as more SO2dominated magmatic vapors were supplied to the system. The crater lake may have also “chemically”

recorded this last episode, because the change observed in the distribution of its polythionates corresponds to a lower H2S/SO2 in the subaqueous fumaroles, as noted above. The addition of a low C/S, low CO2/H2S, reduced hydrothermal end member component with a relatively high HCl content to a more oxidized, high C/S magmatic component has been recognized at Vulcano by Chiodini et al. (1993). The chemical compositions of the gas discharges at Kawah Ijen are similarly affected. Fig. 8 represents the values of RH ˆ log…xH2 =xH2 O † plotted vs. outlet temperatures. In this diagram, the lines of the redox “gas” (H2S–SO2) and “hydrothermal” (FeO–FeO1.5 of the rock system) buffers correspond to the temperature dependence of the equilibrium constants (Giggenbach, 1987). The gas discharges have H2/H2O ratios apparently reflecting internal equilibration of the H2 –H2O–H2S–SO2 system close to the surface. Accepting this, the H2S/ SO2 equilibration temperatures can be evaluated

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Fig. 8. H2/H2O molal ratio of the Kawah Ijen fumarole gases vs. measured outlet temperatures. Numbers correspond to sample labels in Table 2. The altered rock buffer (FeO–FeO1.5) and the gas buffer (H2S–SO2) are from Giggenbach (1987).

according to: ts ˆ 10744=…Ls 1 3:66† 2 273:2

…2†

where Ls ˆ log…xH2 S x3H2 O =xSO2 x3H2 †:

represents conditions in the shallower parts of the system.

6. Isotopic composition of the waters and gas condensates 6.1. Crater lake waters

Therefore, ts ranges from 3308C in 1979 to 2258C in 1996, consistent with the H2 –Ar temperatures. The results suggest equilibration in more hydrothermal conditions in the 1990s and more magmatic conditions in 1979. The redox diagrams for Kawah Ijen gases in terms of RH ˆ log…xH2 =xH2 O †; RCH4 ˆ …xCH4 =xCO2 † and RCO ˆ …xCO =xCO2 † are shown in Fig. 9. The dashed lines correspond to equilibrium temperatures in a single liquid or single vapor phase. The solid lines represent equilibrium with the “hydrothermal” buffer (Giggenbach, 1987) in the vapor, liquid or two-phase system. For the H2 –H2O–CH4 –CO2 system (Fig. 9A), the gas discharges lie within the area indicating equilibrium in a single vapor phase between 120 and 2508C. In terms of CO, and using the detection limit for CO of the gas chromatograph, the equilibration occurs in the liquid–vapor coexistence field at temperatures of no more than 1608C (Fig. 9B). The 1979 samples have exceedingly high CO contents, which suggests equilibrium in a single liquid phase. Fig. 9A shows that CH4 is slow to equilibrate whereas CO equilibrates faster (Giggenbach, 1987) and

Hydrogen and oxygen isotope ratios of the Kawah Ijen waters and gas condensates reported in Table 3 are plotted in Fig. 10. The surface stream waters have d D and d 18O values plotting close to the meteoric water line. We assume that these compositions characterize local meteoric water (LMW) recharging the summit hydrothermal system, although seasonal variability may slightly change the isotopic signature of LMW. The lake waters exhibit D- and 18O-shifts of 44,48‰ and 16–17‰, respectively. There is always a haze above the surface of Kawah Ijen lake, which suggests that evaporation takes place continuously. This process variably concentrates the water in D and 18O depending on the lake surface temperature and on atmospheric conditions. In d D– d 18O space, cool water reservoirs generally fall on an evaporation line with a slope depending on the relative atmospheric humidity (Gonfiantini, 1986; Gat, 1996). However, hot lakes and geothermal pools show relatively “flat” isotopic evolution lines, because enhanced kinetic isotope fractionation of 18O relative

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Fig. 9. Redox diagrams for Kawah Ijen fumarole gases in terms of RH ˆ log…xH2 =xH2 O †; RCH4 ˆ log…xCO2 =xCH4 † and RCO ˆ log…xCO =xCO2 † (x is the mole fraction), according to Chiodini et al. (1993) and Taran et al. (1998). Numbers correspond to sample labels in Table 2. Hatched symbols show the detection limits of the gas chromatograph. Solid lines correspond to equilibria with the geothermal rock buffer in a vapor, liquid or two-phase system. Dashed lines correspond to equilibrium in a single vapor phase (upper isotherms) or liquid phase (lower isotherms). (A) in the RH –RCH4 system, data points show equilibrium in a single vapor phase. (B) CO was detectable only in the 1979 sample. For other samples, the detection limit places the fumarole gases within the two-phase region.

to D occurs at elevated water temperatures (Matsubaya and Sakai, 1978; Gonfiantini, 1986; Gat, 1996; Varekamp and Kreulen, 2000 – this volume). To investigate this process, we have represented the theoretical evaporation line for Kawah Ijen lake as calculated according to Gonfiantini (1986) and Varekamp and Kreulen (2000 – this volume) in Fig. 10.

Clearly, evaporation strongly influences the d D and d 18O of the lake water, but it cannot alone account for the observed values, since the data points plot off and to the right of the theoretical evaporation line. Deines (1979) argued that the d D of vapor evaporated from a 10 wt.% solution of HCl at 208C is 20‰ higher than that of vapor released from pure water. This effect

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Table 3 Isotopic composition (‰) of thermal and meteoric waters and fumarole condensates from Kawah Ijen volcano (n.a.: not analyzed) Label

Locality

Date

dD

d 18O

d 34S (SO4)

d 18O(SO4)

Crater lake IJ90-1 IJ92-1 IJ93-1 IJ93-2 IJ94-1 IJ95-1 IJ95-2 IJ96-1 IJ96-2 IJ96-3 IJ96-4 IJ96-5 IJ96-6 IJ96-7

0m 0m 0m 0m 0m 0m 0m 0m 165 m 80 m 0m 155 m 75 m 90 m

18/09/90 25/10/92 17/09/93 12/10/93 17/08/94 20/09/95 21/09/95 08/08/96 08/08/96 08/08/96 08/08/96 08/08/96 09/08/96 09/08/96

n.a. n.a. n.a. 1.2 21.1 21.9 22.8 0.8 20.8 0.6 20.7 0.9 23.1 20.5

n.a. n.a. n.a. 8.5 9.9 7.8 9.0 8.7 8.7 8.7 8.7 8.8 8.3 8.8

22.3 22.5 22.5 23.0 22.2 22.3 22.5 22.3 22.3 22.4 22.5 22.2 22.1 22.3

n.a. n.a. 21.5 n.a. 22.3 20.8 21.8 22.1 22.1 22.7 21.9 22.0 21.8 22.1

Springs BL1-93 BL1-93 BL2-93 BL1-96 BL2-96 BL3-96 CS-95 PA-95

Blawan Blawan Blawan Blawan Blawan Blawan Crater Paltuding

24/12/93 24/12/93 24/12/93 13/08/96 13/08/96 13/08/96 26/07/95 18/09/95

241.4 240.6 239.9 248.3 249.2 247.5 29.4 245.1

26.3 28.0 28.0 28.1 28.1 28.1 8.3 28.2

14.6 n.a. n.a. n.a. 18.2 n.a. n.a. n.a.

n.a. n.a. n.a. 9.8 16.8 n.a. n.a. n.a.

Meteoric Sodong Streamlet Streamlet Kalisat river

Flank Summit Summit Blawan

18/09/95 08/08/96 08/08/96 08/08/96

239.6 257.5 249.3 246.0

27.2 29.3 28.5 27.9

n.a. n.a. n.a. n.a.

n.a. n.a. n.a. n.a.

Fumaroles KIG-2 KIG-2b KIG-3

Lakeshore Lakeshore Lakeshore

26/07/95 18/09/95 08/08/96

223.9 221.2 214.0

3.2 4.1 4.7

– – –

– – –

could thus contribute to generate the low d D– d 18O slopes observed. However, we note that the Kawah Ijen water differs somewhat from Deines’ model by its composition (mixtures of H2SO4 and HCl), acidity (lower H 1 activity) and temperature (.208C). Strong isotopic enrichment has also been reported at other hot acidic crater lakes. For example, the offset from the theoretical evaporation line has been documented at Yugama Lake and Keli Mutu (Ohba et al., 2000 – this volume; Varekamp and Kreulen, 2000 – this volume). Rowe (1994) estimated the isotopic effect associated with water–rock interaction at high temperatures for Laguna Caliente on Poa´s. This

process may increase the d 18O values of the thermal waters feeding the lake but should not affect the hydrogen isotope ratios because the rocks typically contain little hydrogen compared to the amount of water involved (e.g. Taylor, 1974, 1986). Following the procedure described by Rowe (1994) and others (e.g. O’Neil and Taylor, 1967; Taylor, 1974), we estimated that the 18O enrichment in LMW during interaction of water with the basaltic–andesite rock …d18 Orock ˆ 17‰; Taylor, 1986) at high temperatures (.2508C) is at most ,10‰. The water/rock ratio of 28 (36 g rock/kg water) used here for the summit hydrothermal system of Kawah Ijen is evaluated

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43

Fig. 10. Oxygen and hydrogen isotopic composition of Kawah Ijen thermal discharges and fumarole gas condensates. Symbols are as in Fig. 2. The meteoric water line is from Craig (1961). Local meteoric water (LMW) represents the average of the surface water compositions reported in Table 3. “Volcanic arc gas” is from Kusakabe and Matsubaya (1986), Taran et al. (1989) and Giggenbach (1992b). The “theroretical evaporation curve” of Kawah Ijen lake is calculated according to Gonfiantini (1986) and Varekamp and Kreulen (2000 – this volume) with a lake temperature of 408C, an air temperature of 208C, air relative humidity of 80% and fractionation factors from Majoube (1971). Also shown is the observed “lake evaporation curve”. The difference between the two curves points to addition of a volcanic gas component with a heavy isotopic composition. The “single-step boiling curve” is calculated according to Giggenbach and Stewart (1982), where temperatures indicate temperature at which boiling occurs.

from the Na content in fresh rock (Delmelle and Bernard, 1994) and in the lake water by assuming complete dissolution of Na (Gislason and Eugster, 1987). This crude calculation suggests that the lake 18 O content may be influenced by water–rock interaction in the subsurface hydrothermal system. Aside from water–rock interaction, the contribution of an isotopically heavy volcanic component to the lake–hydrothermal system may play an important role in determining the final d D and d 18O values of Kawah Ijen waters, and would be similar to the situation found at other hot acidic crater lakes. For example, using time-series data on the Cl content and isotopic composition for Yugama Lake, KusatsuShirane, Ohba et al. (2000 – this volume) deduced that such a component accounts for 25,36% of the measured D- and 18O-enrichment in the lake. The volcanic endmember could be a mixture of meteoric water and magmatic vapor. Varekamp and Kreulen (2000 – this volume) argued convincingly

that the difference in the magnitude of the offsets from the calculated evaporation lines exhibited by the two lakes at Keli Mutu points to different volcanic gas inputs, i.e. larger inputs correlate with larger offsets. These results suggest that condensation of a volcanic component with d D and d 18O values typical of a volcanic arc-gas (Kusakabe and Matsubaya, 1986; Taran et al., 1989; Giggenbach, 1992b) is likely to occur at Kawah Ijen. This idea is also supported by our preliminary calculations of the lake’s Cl budget, which indicate that approximately 2 × 107 kg=day of volcanic vapor condense in the lake–hydrothermal system (Delmelle, 1995). 6.2. Crater, Paltuding and Blawan spring waters In Fig. 10, the crater hot spring plots slightly below the lake water compositions. Recalling that this discharge is fed by the crater lake, the difference may reflect the decreased fractionation of D with

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Table 4 Isotopic composition (‰) of elemental sulfur, fumarole sulfur and rock sulfur from Kawah Ijen volcano Sample description

Date

d 34S

Floating S 0 spherule Floating S 0 spherule Floating S 0 spherule Floating S 0 spherule Floating S 0 slick Floating S 0 slick Pyroclastic S 0 (erupted in July 1993) Pyroclastic S 0 (erupted in July 1993) Ancient pyroclastic S 0 (in S deposits) S 0 sediment layer 1 S 0 sediment layer 2 S 0 sediment layer 3 S 0 sediment layer 4 S 0 sediment layer 5 S 0 sediment layer 6 S 0 sediment layer 7 S 0 sediment layer 8 S 0 sediment layer 9 S 0 sediment layer 10 Fumarole S 0 Fumarole SO2 Fumarole H2P S Crater rock S

20/09/90 20/09/90 01/09/95 08/08/96 20/09/90 20/09/90 12/12/93

23.8 22.6 21.4 24.1 24.2 23.1 23.6

23/12/93

23.4

18/09/95

23.4

18/09/95 18/09/95 18/09/95 18/09/95 18/09/95 18/09/95 18/09/95 18/09/95 18/09/95 18/09/95 20/09/90 17/09/93 17/09/93 20/09/90

23.1 23.2 23.5 24.4 23.2 22.5 23.5 22.8 23.8 23.3 25.3 7.5 25.6 6.7

respect to 18O due to the higher temperature of the spring compared to the lake (Matsubaya and Sakai, 1978; Gonfiantini, 1986; Gat, 1996). The d D and d 18O values of the Blawan and Paltuding discharges are similar to LMW, supporting a meteoric-dominated origin.

6.3. Fumarolic gas condensates The d D and d 18O values of the fumarole condensates lie between the values of LMW and the crater lake (Fig. 10). Boiling of downward-seeping lake waters cannot yield these compositions, because the steam obtained from single-step boiling of a crater lake sample with an average isotopic composition …dDlake ˆ 20:7‰; d18 Olake ˆ 18:7‰† is notably enriched …dDsteam ˆ 26:4‰; d18 Osteam ˆ 17‰† compared to the heaviest fumarole condensate …dD ˆ 214‰; d18 O ˆ 14:7‰† (Fig. 10). We suggest that the fumarole isotopic values mainly reflect mixing of ground water with a volcanic arc vapor and summit acidic hydrothermal fluids, a situation also observed at the magmatic–hydrothermal systems of White-Island, Esan and Poa´s (Giggenbach, 1987; Hedenquist and Aoki, 1991; Rowe, 1994).

Fig. 11. Sulfur isotopic ratio of various sulfur-bearing materials from Kawah Ijen volcano.

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7. Isotopic composition of sulfur compounds 7.1. Crater lake sulfate 7.1.1. Sulfur isotopes Sulfur isotopic compositions from Kawah Ijen are reported in Tables 3 and 4, and Fig. 11. The 34S content of dissolved SO4 in the lake did not vary significantly (122.1–123.1‰) from September 1990 to August 1996 (Table 3), suggesting a stable source for SO4. It does not vary in the water column either. The observed d 34SSO4 values are among the most enriched ever reported for acidic SO4 –Cl thermal waters (Kiyosu and Kurahashi, 1983; Williams et al., 1990; Ohsawa et al., 1993; Sturchio et al., 1993; Rowe, 1994; Kusakabe et al., 2000 – this volume; Varekamp and Kreulen, 2000 – this volume). This indicates that inorganic oxidation of volcanic H2S (typically with a light isotopic signature) is not relevant in the lake SO4 formation process because of the lack of significant isotopic exchange associated with this reaction (Ohmoto and Rye, 1979). Instead, disproportionation (hydrolysis) of magmatic SO2 during condensation of volcanic gases in groundwater [Eqs. (3) and (4), Kusakabe et al., 2000 – this volume] and hydrolysis of elemental sulfur at elevated temperatures (100–3508C) [Eq. (5), Ellis and Giggenbach, 1971] are the potential mechanisms that can yield SO4 in the lake–hydrothermal system: 4SO2 1 4H2 O ) 3H2 SO4 1 H2 S

…3†

3SO2 1 3H2 O ) 2H2 SO4 1 H2 O 1 S0

…4†

4S0 1 4H2 O ) H2 SO4 1 3H2 S

…5†

During SO2 hydrolysis, reaction (4) is favored under relatively high redox potentials, low temperatures and high total sulfur concentrations (Kusakabe et al., 2000 – this volume). The sulfur isotope exchange in the SO4 –H2S and SO4 –S 0 systems that accompanies reactions (3) and (4) is almost similar, and its rate increases with acidity and temperature (Robinson, 1973; Ohmoto and Lasaga, 1982; Kusakabe et al., 2000 – this volume). Molten sulfur lying on the crater floor is associated with relatively elevated temperatures compatible with the elemental sulfur hydrolysis reaction. For example, the in situ temperatures recorded at several crater

45

lakes range from 120 to 1708C (Oppenheimer and Stevenson, 1989; Christenson, 1994; Takano et al., 1994b). At Kawah Ijen, the presence of pyrite in the sulfur spherules and pyroclastic ejecta (Delmelle and Bernard, 1994; Delmelle, 1995) suggests temperatures above 1508C, because marcasite instead of pyrite is the stable iron sulfide at lower temperatures (Murowchick and Barnes, 1986; Shoonen and Barnes, 1991; Takano et al., 1994b). The evaluation of the isotopic compositions of the sulfur species that would be produced during hydrolysis of elemental sulfur is complicated by the fact that the hydrothermal water involved in this reaction must already contain sulfur dissolved in some form. Thus, the isotopic mass balance calculations developed below will offer no more than a simplified view of the system. According to Eq. (5), the equilibrium d 34S values of the sulfur-bearing products are given by:

d34 SS0 ˆ 1=4d34 SSO4 1 3=4d34 SH2 S

…6†

The DSO4 –H2 S is 41.3 and 32.4‰ at liquid sulfur temperatures of 120 and 1708C, respectively (Ohmoto and Lasaga 1982). Substituting these values into Eq. (6) and assuming an initial dS0 ˆ 23:3‰ (average of the floating and pyroclastic sulfur isotopic compositions, Table 4), we obtain d 34SSO4 between 127.7 and 121.0‰ and d34 SH2 S between 213.6 and 211.4‰, respectively, for equilibrium in a closed system. We can reasonably assume that if H2S produced through reactions (3) or (5) enters the lake, it is quickly oxidized into elemental sulfur or SO4, because H2S could not be detected in the water column in 1990 nor in 1996. Obviously, if all H2S produced through reaction (5) is converted into SO4 during inorganic oxidation, the d 34SSO4 values observed in the lake would never be so high. Since isotopic fractionation in the H2S–S 0 system at the lake temperatures would slightly deplete elemental sulfur in 34S (Ohmoto and Rye, 1979), the d34 SH2 S values are also too low to account for the 34S-content of elemental sulfur. Therefore, hydrolysis of elemental sulfur cannot be the main source of SO4 in Kawah Ijen lake. Rowe (1994) reached the same conclusion in his study of Laguna Caliente and Poa´s. Alternatively, we believe that disproportionation of SO2 conveyed by high temperature vapors to the root

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of the crater lake generates SO4. Thermochemical modeling results have also demonstrated that condensation of SO2-, H2S-, HCl-containing volcanic gases into meteoric water can produce the range of SO4 and Cl contents observed in acidic crater lakes (Rowe et al., 1992a; Christenson and Wood, 1993; Delmelle and Bernard, 1994). The presence of polythionates in these systems further reveals input of volcanic SO2 and H2S (Takano, 1987). Finally, the SO2 disproportionation reaction is commonly evoked to explain the isotopic and chemical characteristics of acid SO4 – Cl thermal waters discharged at shallow magmatic– hydrothermal systems (e.g. Kiyosu and Kurahashi, 1983; Williams et al., 1990; Christenson and Wood, 1993; Ohsawa et al., 1993; Sturchio et al., 1993; Rowe, 1994; Kusakabe et al., 2000 – this volume). When we apply the equation from Kusakabe et al. (2000 – this volume), the isotopic fractionation measured between SO4 and S 0 …DSO4 –S0 ˆ 23:8 , 26:4‰† corresponds to an equilibrium temperature of 250,2808C. Large isotopic fractionations up to 21‰ also could result from initially sluggish reaction kinetics if disproportionation of SO2 occurs at temperatures below 1508C in the lake (Kusakabe et al., 2000 – this volume). Since temperatures above this value are likely to prevail in the bottom molten sulfur, we may safely conclude that the observed DSO4 –S0 values reflect equilibration in the high heat flow zone of the hydrothermal vent feeding the lake rather than a kinetic effect at the lake water temperature. In addition, low temperatures would diminish further isotopic exchange between SO4 and S 0, thus “freezing” the initial kinetic DSO4 –S0 at values a few per mils lower than those measured in the lake waters. The molar H2S/SO2 ratio, rs, of the condensing volcanic gas can be deduced from the sulfur isotope ratios of SO4 and S 0 if these compounds form according to the disproportionation of SO2. For the isotopic equilibrium, we can write (Taran et al., 1996; Kusakabe et al., 2000 – this volume):

d34 SSO4 ˆ d34 SSS 1 DSO4 –H2 S0 ‰rs =…1 1 r†Š 1 1=3DSO4 –S0 ‰1=…1 1 rs †Š

…7†

Assuming a DSO4 –H2 S value corresponding to the SO4 – S 0 sulfur isotopic equilibrium temperature deduced above and using the d 34S of total sulfur in a crater

rock (Table 4, d34 SSS ˆ 16:7‰†; we obtain r s ˆ 1:1 for the volcanic gas. This gas ratio is notably lower than that inferred from the distribution of the lake SxO6 (rs . 14 for S5O6 $ S4O6 . S6O6, Takano et al., 1994a). We may explain this difference if the latter forms from a volcanic vapor which had already reacted and lost some SO2 in the subsurface hydrothermal zone. The rs values (1.3–5.4) for the subaerial fumaroles are comparatively higher too, suggesting that the gas being injected into the lake–hydrothermal system corresponds to a more SO2-rich vapor. This supports the idea that magmatic gases interact with the hydrothermal cell underlying the crater to produce a reduced, H2S-rich gas and an oxidized, SO4-rich water which subsequently discharge in the fumaroles and in the crater lake, respectively. Using a given gas ratio value, one can further infer the temperature ts [Eq. (2)] at which sulfur species equilibrated in the gas phase being condensed at depth. For rs ˆ 1:1; and for a RH value of the vapors represented by the magmatic gases of 1979, ts is approximately 3508C. 7.1.2. Oxygen isotopes In Fig. 12, the d 18OSO4 and d 18 OH2 O values for the Kawah Ijen thermal waters (Table 3) are plotted together with isotherms showing the temperature dependence of DSO4 –H2 O (Lloyd 1968; Mizutani and Rafter, 1969). The 1993–1996 lake samples show equilibration temperatures in the narrow range 120– 1438C, well above the measured lake water temperatures. The rate of oxygen isotopic exchange in the pair SO4 –H2O increases with temperature (Lloyd, 1968; Chiba and Sakai, 1985). Therefore, the d 18OSO4 values could represent quenched equilibrium values if the lake waters circulate in the subaqueous hydrothermal conduit (Kusakabe et al., 2000 – this volume). There is a growing body of evidence that acidic crater lakes above magma–hydrothermal systems sustain subsurface recycling of their waters (Rowe et al., 1992b; Christenson and Wood, 1993; Ohba et al., 2000 – this volume). At Kawah Ijen, the heat and mass budget analysis also suggests that the lake water seeping through the crater floor is partly re-injected into the lake (Delmelle, 1995). However, the observed lake DSO4 –H2 O will reflect this process if we assume that the d18 OH2 O in the lake and in the underlying hydrothermal cell are identical. This condition is unlikely considering

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47

Fig. 12. Oxygen isotopic ratio in water and dissolved sulfate in Kawah Ijen thermal discharges. Symbols are as in Fig. 2. The theoretical grid is obtained using the equations of Lloyd (1968) and Mizutani and Rafter (1969).

that the isotopic composition of the former is strongly affected by evaporation and that its volume is likely to be smaller than that of the hydrothermal reservoir. Therefore, the DSO4 –H2 O measured in the lake may also represent non-equilibrium values. 7.2. Blawan hot spring sulfate 7.2.1. Sulfur isotopes The d 34SSO4 values of the Blawan thermal waters are lower than those in the crater lake (Table 3, Fig. 11) but are strongly enriched compared to SO4 produced by the inorganic oxidation of H2S. Considering that these springs are derived from the summit SO4 –Cl reservoir, the sulfur isotopic compositions may simply reflect mixing between 34S-enriched SO4 formed by disproportionation of SO2 and

34

S-depleted SO4 produced during oxidation of H2S distilled off the margin of the hydrothermal system.

7.2.2. Oxygen isotopes As shown in Fig. 12, the near-neutral pH thermal waters at Blawan have d 18OSO4 values corresponding to SO4 –H2O isotopic equilibrium temperatures in the range 48–948C. Since significant oxygen isotopic exchange between SO4 and H2O occurs only at low pHs and elevated temperatures (Lloyd, 1968; Chiba and Sakai, 1985), the results imply that the waters have resided at depth for exceedingly long periods of time. However, it is more likely that the 18Ocontent of the spring SO4 reflects non-equilibrium dilution of the isotopically heavy SO4 derived from the summit SO4 –Cl hydrothermal reservoir.

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7.3. Origin of sulfur sediment and molten sulfur in the crater lake The d 34S values of ten sulfur-rich layers representing the sediments on the lakeshore vary little (22.8 to 24.4‰, Table 4, Fig. 11), suggesting that the sulfur source did not change significantly through time. The occurrence of distinct elemental sulfur- and silica-rich laminations in the deposits implies that precipitation of elemental sulfur in the lake was not continuous. The sulfur grains in the sediment do not show the globular shape distinctive of bacteria-mediated precipitation (e.g. Krupp and Seward, 1987). This is consistent with the low pHs of the lake water which prevent biological activity. Three types of inorganic reactions can yield elemental sulfur in the lake: (1) disproportionation of SO2 [Eq. (4)]; (2) oxidation of H2S [Eqs. (8)–(12)], (e.g. Rowe, 1994); and (3) sulfitolysis of SxO6 [Eq. (13), Takano and Watanuki, 1990]: H2 SO4 1 3H2 S ) 4S0 1 4H2 O

…8†

H2 SO3 1 2H2 S ) 3S0 1 3H2 O

…9†

SO2 1 2H2 S ) 3S0 1 2H2 O

…10†

Fe31 1 H2 S ) S0 1 Fe21 1 2H1

…11†

O2 1 2H2 S ) 2S0 1 2H2 O

…12†

22 22 Sx O22 6 1 …3x 2 7†HSO3 ) …2x 2 3†SO4

1 …x 2 1†H1 1 …2x 2 4†S0 1 …x 2 3†H2 O

…13†

Sulfitolysis of SxO6 (Eq. (13)) can potentially give rise to significant amounts of elemental sulfur, but the sulfur isotopic effect associated with this reaction is not known. The destruction of the 1996 lake SxO6 content would produce ,10 7 kg of elemental sulfur in the lake, only a tenth of the estimated sulfur mass present in the lakeshore deposits (Brouwer, 1925). Reaction (4) cannot account for the formation of the sulfur sediments, because magmatic SO2 is believed to react at high temperatures in the subaqueous hydro-

thermal vent feeding the crater lake. Nevertheless, SO2 can disproportionate according to Eq. (3), releasing 34S-depleted H2S into the lake–hydrothermal vent system. This H2S may subsequently precipitate as elemental sulfur during oxidation. The final DSO4 –S0 will be close to the DSO4 –H2 S initially set by the SO2 disproportionation reaction if the oxidant is a nonsulfur bearing compound [reactions (11 and 12)]. Hydrogen sulfide also can be brought directly into the lake system by the volcanic vapor being injected from depth. Interestingly, neither the suspended solids nor the sediments sampled directly from the lake at depths of 20–40 m in 1990 and 1996 contained elemental sulfur (Delmelle and Bernard, 1994; B. Takano, unpublished data); instead, poorly crystallized silica was the dominant precipitate. These observations are evidence for the lack of elemental sulfur precipitation in the lake itself, which simply may link with the absence of H2S in the water. We propose that the factor controlling the type of deposition relates to the ability of either H2S- or silica-rich volcanic discharges to enter the lake. This could depend on the efficiency with which the lake water circulates in the hydrothermal cell beneath the crater. During subsurface seepage through this region, the lake waters may dissolve more silica as they become progressively heated. When re-entering the relatively cool lake, these hot waters would be supersaturated with respect to silica polymorphs, thus leading to massive precipitation. Meanwhile, the circulation of the relatively oxidized lake waters at shallow levels may prevent H2S-rich discharges from reaching the crater lake, because H2S will be converted into elemental sulfur or/and SO4 at depth. In contrast, enhanced elemental sulfur and depressed silica deposition could result from slow hydrothermal recycling of the lake water, leaving more H2S-bearing gas and less silica-rich water to be introduced into the lake. Hydrothermal circulation of the lake water could cease temporarily as a result of partial sealing of the crater floor due to mineral precipitation in the cracks and fractures and encrusting of molten sulfur. The spherules, slicks and pyroclastic material representing quenched molten sulfur products have d 34S values similar (except one sample in 1995) to those of the lakeshore sulfur sediments (Table 4, Fig. 11). This may simply indicate that previously

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49

Fig. 13. Conceptual cross-section of Kawah Ijen showing a model of the lake–hydrothermal system. See text for discussion. Symbols are as in Fig. 2.

deposited sulfur is remobilized at high temperature on the crater floor, likely in the hydrothermal vent. Consequently, the production of SO4 in the lake– hydrothermal system in 1990–1996 during disproportionation of magmatic SO2 preferentially occurred via reaction (3) instead of reaction (4). Again, this would agree with the generation of a H2S-rich hydrothermal vapor added to the lakeshore fumaroles.

7.4. Sulfur dioxide, hydrogen sulfide and sulfur sublimate in the fumarole discharges The DSO2 –H2 S measured in Kawah Ijen fumaroles is 13.1‰ (Table 4, Fig. 11), somewhat higher than the 10‰ fractionation determined experimentally by Grinenko and Thode (1970). These authors noted that sluggish reaction rates occur at temperatures below 3008C, possibly explaining our values and the resulting high apparent equilibrium temperature of ,3098C (Thode et al., 1971). The measured DH2 S–S0 is slightly negative (20.3‰), not consistent with the expected direction of the isotopic exchange. However, this value is small ( # 1‰) for the system H2S–S 0 at T , 3008C (Grinenko and Thode, 1970; Ueda et al.,

1979), suggesting conditions close to equilibrium in the Kawah Ijen gas discharges. The 34S content of total sulfur (d34 SSS ) in sample KIG-1 corresponds to:

d 34 SSS ˆ d 34 SH2 S xH2 S 1 d34 SSO2 xSO2

…14†

where xH2S and xSO2 are, respectively, the mole fractions of H2S and SO2 relative to total sulfur in the volcanic vapor. The calculated value of 0‰ does not match the isotopic composition reported for magmatic sulfur in the crater rock (16.7‰) nor that typical of island-arc lavas (15‰, Taylor, 1986). This probably reveals removal of 34S-rich SO2 from, and addition of 34S-poor H2S to, the rising high-temperature volcanic vapor during interaction with the summit hydrothermal system. Remobilization of elemental sulfur (Eq. (1)) coating the pipes through which the fumarolic gas flows also may affect the d 34SSS value in the fumaroles. 8. Summary and conclusions A schematic cross-section of the “immature” magma–hydrothermal system that can account for

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the chemical and isotopic characteristics of the thermal water and fumarole gas discharges at Kawah Ijen volcano is depicted in Fig. 13. Absorption of magmaderived high-temperature gases into shallow groundwater produces a two-phase vapor–liquid hydrothermal reservoir beneath the summit crater. The gases being condensed are relatively oxidized …H2 S=SO2 ˆ 1:1† and may have equilibrated in the liquid–vapor hydrothermal region at ,3508C. The liquid phase of the hydrothermal reservoir consists of SO4 –Cl waters which enter a convective cell through which the lake water circulates. The lake SO4 is highly enriched with respect to 34S, a characteristic which accounts for the disproportionation of magmatic SO2 at temperatures of 250–2808C. The summit SO4 –Cl liquid flows laterally and mixes with meteoric-dominated water to produce the spring discharges at Blawan and Paltuding. The crater spring originates in the same manner or simply corresponds to diluted lake water seepages. The lake exhibits strong D and 18O shifts which result to a large extent from a kinetic isotopic effect associated with evaporation at elevated lake water temperatures. Added to this is the likely contribution of the isotopically heavy magmatic vapor being condensed at depth. Water–rock interactions in the subsurface hydrothermal system also may influence the final d 18O values of the lake waters. The oxygen isotopic distance for the pair SO4 –H2O indicates quenched equilibrium temperatures close to 1508C that could reveal sublimnic recycling of the lake waters. The vapor phase in the hydrothermal reservoir consists of a reduced, H2S-rich component which mixes with the rising high-temperature volcanic gases to be subsequently discharged at the lakeshore fumaroles. Hydrogen sulfide comes from disproportionation of SO2 and from the condensing high temperature volcanic vapor. The gas in the fumaroles may have equilibrated at ,2608C. Time-series data show that there is an interplay between the oxidized, high-C/S magmatic gas and the hydrothermallyderived, reduced, low-C/S vapor through time which may depend on the activity of the volcano. The fumaroles in 1979 represented more magmatic conditions than in the 1990s. In 1996, however, the fumaroles exhibited a trend towards more SO2-rich compositions. Kawah Ijen lake produces two types of sulfur

material, one consisting of a precipitate accumulated in banded deposits exposed on the lakeshore and the second occurring as a molten body on the crater floor. The precipitate was formed in the lake during oxidation of H2S released from the subsurface hydrothermal reservoir. Deposition of elemental sulfur is not continuous, however, but may ultimately depend on the lake dynamics. Rapid subsurface circulation of the lake waters in the hot hydrothermal cell may cause relatively oxidized, H2S-poor, silica-supersaturated solutions to enter the lake, thus allowing massive precipitation of poorly crystallized silica. At the other extreme, elemental sulfur precipitates may dominate only if H2S-rich, relatively silica-poor discharges reach the crater floor owing to a limited recycling of the lake waters. The similar d 34S values in the sulfur lakeshore deposits and molten sulfur products indicate remobilization at high temperature of sulfur-rich sediments previously accumulated on the crater floor. The combination of chemical and isotopic data obtained at Kawah Ijen in 1990–1996 have provided constraints on the origin of the fumarole gases, thermal waters and elemental sulfur. The location and timing of polythionate formation and elemental sulfur deposition in the lake-hydrothermal system deserve further attention. Our results show that the geochemical dynamics of the magma–hydrothermal system may reveal changes in the volcanic activity.

Acknowledgements P.D. was supported by a doctoral fellowship from the Fonds pour la Recherche dans l’Industrie et l’Agriculture (FRIA) in Belgium and by a Visiting Research Scholarship from Mombusho in Japan. The Communaute´ Franc¸aise de Belgique, the Acade´mie Royale des Sciences and the Alice van Burren Foundation generously provided grants for fieldwork (PD). This research was a part of a Fonds National pour la Recherche Scientifique en Belgique (FNRS) program (AB). TPF acknowledges financial support from a NASA Earth System Science Fellowship. We thank S. de Brouwer for his fantastic assistance in the field and the sulfur miners of Kawah Ijen for their support and

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hospitality during all these years. The staff of the Volcanological Survey of Indonesia offered excellent logistic support during the 1993, 1995 and 1996 sampling campaigns. We are grateful to J. Hirabayashi (Kusatsu-Shirane Volcano Observatory) for providing us with the 1993 gas composition and SO2 and H2S gas samples, to S. Bottrell (University of Leeds) for helping with the isotopic analysis of the 1990 water and sulfur samples and to H. Maeda (Kyushu University) for the rock sulfur isotopic analysis. PD and AB analyzed the anions in waters at the Laboratory of Glaciology, Universite´ Libre de Bruxelles with the assistance of R. Lorrain. An earlier version of this paper benefited from discussions with D. Stevenson and G. Rowe. Comments from D.T. Gregory and an anonymous reviewer are acknowledged. J. Varekamp made several suggestions that greatly improved the interpretation of the lake isotopic compositions. We thank J. Stix for editing the English.

References Arribas, A., 1995. Characteristics of high-sulfidation epithermal deposits, and their relation to magmatic fluid. Thompson, J.F.H. (Ed.), Magmas, Fluids and Ore Deposits. Mineral. Assoc. Canada 23, 419–454. Bigeleisen, J., Perlman, M.L., Prosser, H.C., 1952. Conversion of hydrogenic materials to hydrogen for isotopic analysis. Anal. Chem. 24, 1356–1357. Brantley, S.L., Agustsdottir, A., Rowe, G.L., 1993. Crater lakes reveal heat and volatile fluxes. GSA Today 3, 176–178 see also p. 173. Brouwer, A.H., 1925. The Geology of the Netherlands East Indies. MacMillan, New York. Brown, G., Rymer, H., Dowden, J., Kapadia, P., Stevenson, D.S., Barquero, J., Morales, L.D., 1989. Energy budget analysis for Poa´s crater lake: implications for predicting volcanic activity. Nature 339, 370–373. Casadevall, T.J., De La Cruz-Reyna, S., Rose, W.I., Bagley, S., Finnegan, D.L., Zoller, W.H., 1984. Crater lake and post-eruption hydrothermal activity, El Chicho´n volcano, Mexico. J. Volcanol. Geotherm. Res. 23, 169–191. Chiba, H., Sakai, S., 1985. Oxygen isotope exchange rate between dissolved sulfate and water at hydrothermal temperatures. Geochim. Cosmochim. Acta 43, 993–1000. Chiodini, G., Cioni, R., Marini, L., 1993. Reactions governing the chemistry of crater fumaroles from Vulcano Island, Italy, and implications for volcanic surveillance. Appl. Geochem. 8, 357– 371. Christenson, B.W., 1994. Convection and stratification in Ruapehu

51

Crater Lake, New Zealand: implications for Lake Nyos-type gas release eruption. Geochem. J. 28, 185–197. Christenson, B.W., Wood, C.P., 1993. Evolution of a vent-hosted hydrothermal system beneath Ruapehu Crater Lake, New Zealand. Bull. Volcanol. 55, 547–565. Deines, P., 1979. A note on the hydrogen isotope fractionation involving acidic and basic solutions. Geochim. Cosmochim. Acta 43, 1575–1577. Delmelle, P., 1995. Geochemical, isotopic and heat budget study of two volcano-hosted hydrothermal systems: the acid crater lakes of Kawah Ijen, Indonesia, and Taal, Philippines, volcanoes. PhD Thesis, Univ. Libre de Bruxelles, Brussels, Belgium. Delmelle, P., Bernard, A., 1994. Geochemistry, mineralogy, and chemical modelling of the acid crater lake of Kawah Ijen volcano, Indonesia. Geochim. Cosmochim. Acta 58, 2445– 2460. Delmelle, P., Bernard, A., 2000. Downstream composition changes of acidic volcanic waters discharged into the Banyupahit stream, Ijen caldera, Indonesia. J. Volcanol. Geotherm. Res. 97 (1–4), 55–75. Delmelle, P., Kusakabe, M., Bernard, A., Fischer, T., del Mundo, E., de Brouwer, S., 1998. Geochemical and isotopic evidence for sea water contamination of the hydrothermal system of Taal volcano, Luzon, Philippines. Bull. Volcanol. 59, 562–576. Ellis, A.J., Giggenbach, W.F., 1971. Hydrogen sulphide ionization and sulphur hydrolysis in high temperature solution. Geochim. Cosmochim. Acta 35, 247–260. Ellis, A.J., Mahon, W.A., 1977. Geochemistry of Geothermal Systems. Academic Press, New York, 392 pp. Epstein, S., Mayeda, T., 1953. Variation of 18O content of waters from natural sources. Geochim. Cosmochim. Acta 4, 213–224. Fischer, T.P., Giggenbach, W.F., Sano, Y., Williams, S.N., 1998. Fluxes and sources of volatiles discharged from Kudryavy, a subduction zone volcano, Kurile Islands. Earth Planet. Sci. Lett. 160, 81–96. Gat, J.R., 1996. Oxygen and hydrogen isotopes in the hydrological cycle. Annu. Rev. Earth Planet. Sci. 24, 225–262. Giggenbach, W.F., 1974. The chemistry of crater lake, Mt. Ruapehu (New Zealand) during and after the 1971 active period. N. Z. J. Sci. 17, 33–45. Giggenbach, W.F., 1987. Redox processes governing the chemistry of fumarolic gas discharges from White Island, New Zealand. Appl. Geochem. 2, 143–161. Giggenbach, W.F., 1992a. The composition of gases in geothermal and volcanic systems as a function of tectonic setting. In: Kharaka, Y.K., Maest, A.S. (Eds.). Water–Rock Interaction, Balkema, Rotterdam, pp. 873–878. Giggenbach, W.F., 1992b. Isotopic shifts in waters from geothermal and volcanic systems along convergent plate boundaries and their origin. Earth Planet. Sci. Lett. 113, 495–510. Giggenbach, W.F., Glover, R.B., 1975. The use of chemical indicators in the surveillance of volcanic activity affecting the crater lake on Mt. Ruapehu, New Zealand. Bull. Volcanol. 39, 1–12. Giggenbach, W.F., Goguel, R.L., 1989. Collection and Analysis of Geothermal and Volcanic Water and Gas Discharges. Dept. Sci. Ind. Res. Report CD-2401, Petone, New Zealand. Giggenbach, W.F., Stewart, M.K., 1982. Processes controlling the

52

P. Delmelle et al. / Journal of Volcanology and Geothermal Research 97 (2000) 31–53

isotopic composition of steam and water discharges from steam vents and steam-heated pools in geothermal areas. Geothermics 11, 71–80. Gislason, S.R., Eugster, H.P., 1987. Meteoric–water–basalt interactions I: a field study in Northeast Iceland. Geochim. Cosmochim. Acta 51, 2827–2840. Gonfiantini, R., 1986. Environmental isotopes in lake studies. In: Frits, P., Fontes, J.C.H. (Eds.), Handbook of Environmental Isotope Geochemistry. Elsevier, Amsterdam, pp. 113–168. Grinenko, V.A., Thode, H.G., 1970. Sulfur isotope effects in volcanic gas mixtures. Can. J. Earth Sci. 7, 1402–1409. Hedenquist, J.W., Aoki, M., 1991. Meteoric interaction with magmatic discharges in Japan and the significance for mineralization. Geology 19, 1041–1044. Kargel, J.S., Delmelle, P., Nash, D., 1999. Volcanogenic sulfur on Earth and Io: composition and spectroscopy. Icarus 142, 249– 280. Kiyosu, Y., Kurahashi, M., 1983. Origin of sulfur species in acid sulfate–chloride thermal waters, northeastern Japan. Geochim. Cosmochim. Acta 47, 1237–1245. Krupp, R.E., Seward, T.M., 1987. The Rotokawa geothermal system, New Zealand: an active epithermal gold-depositing environment. Econ. Geol. 81, 1109–1129. Kusakabe, M., Hayashi, N., 1986. Genetic environments of the banded sulfur sediments at the Tateyama volcano, Japan. J. Geophys. Res. 91, 12159–12166. Kusakabe, M., Matsubaya, O., 1986. Volatiles in magmas, volcanic gases and thermal waters. Bull. Volcanol. Soc. Jpn. 30, 267–283 (in Japanese with English abstract). Kusakabe, M., Komoda, Y., Takano, B., Abiko, T., 2000. Sulfur isotopic effects in the disproportionation reaction of sulfur dioxide in hydrothermal fluids and the variation of d 34S values of dissolved bisulfate and elemental sulfur from some active crater lakes. J. Volcanol. Geotherm. Res. 97 (1–4), 287–307. Lloyd, R.M., 1968. Oxygen isotope behavior in the sulfate-water system. J. Geophys. Res. 73, 6099–6110. Majoube, M., 1971. Fractionnement en oxyge`ne 18 et en duete´rium entre l’eau et sa vapeur. J. Chim. Phys. 68, 1423–1436. Matsubaya, O., Sakai, H., 1978. D/H and 18O/ 16O fractionation factors in evaporation of water at 60 and 808C. Geochem. J. 12, 121–126. Mizutani, Y., Rafter, A.T., 1969. Oxygen isotopic fractionation in the bisulphate ion–water system. N. Z. J. Sci. 12, 54–59. Mizutani, Y., Sugiura, T., 1966. The chemical equilibrium of the 2H2S 1 SO2 ˆ 3S 1 2H2O reaction in solfataras of the Nasudake Volcano. Bull. Chem. Soc. Jpn. 39, 2411–2414. Murowchick, J.B., Barnes, H.L., 1986. Marcasite precipitation from hydrothermal solutions. Geochim. Cosmochim. Acta 50, 2615– 2629. Newhall, C.G., Dzurisin, D., 1988. Historical unrest at large calderas of the World. US Geol. Surv. Bull., 1855. Ohba, T., Hirabayashi, J., Nogami, K., 1994. Water, heat and chloride budgets of the crater lake Yugama, Kusatsu-Shirane volcano, Japan. Geochem. J. 28, 217–231. Ohba, T., Hirabayashi, J., Nogami, K., 2000. D/H and 18O/ 16O ratios of water in the crater lake at Kusatsu-Shirane volcano, Japan. J. Volcanol. Geotherm. Res. 97 (1–4), 329–346.

Ohmoto, H., Lasaga, A., 1982. Kinetics of reactions between aqueous sulfates and sulfides in hydrothermal systems. Geochim. Cosmochim. Acta 46, 1727–1745. Ohmoto, H., Rye, R.O., 1979. Isotopes of sulfur and carbon. In: Barnes, H.L. (Ed.), Geochemistry of Hydrothermal Ore Deposits. Wiley, New York, pp. 509–567. Ohsawa, S., Takano, B., Kusakabe, M., Watanuki, K., 1993. Variation in volcanic activity of Kusatsu-Shirane volcano as inferred from d 34S in sulfate from the Yugama crater lake. Bull. Volcanol. Soc. Jpn. 38, 95–99. O’Neil, J.R., Taylor Jr, H.P., 1967. The oxygen isotope and cation exchange chemistry of feldspars. Am. Mineral. 52, 1414–1437. Oppenheimer, C., 1992. Sulphur eruptions at volca´n Poa´s, Costa Rica. J. Volcanol. Geotherm. Res. 49, 1–21. Oppenheimer, C., Stevenson, D., 1989. Liquid sulfur lakes at Poa´s volcano. Nature 342, 790–793. Pasternack, G.B., Varekamp, J.C., 1994. The geochemistry of the Keli Mutu crater lakes, Flores, Indonesia. Geochem. J. 28, 243– 262. Robinson, B.W., 1973. Sulphur isotope equilibrium during sulphur hydrolysis at high temperatures. Earth Planet. Sci. Lett. 18, 443–450. Rowe, G.L., 1994. Oxygen, hydrogen, and sulfur isotope systematics of the crater lake system of Poa´s volcano, Costa Rica. Geochem. J. 28, 263–287. Rowe, G.L., Ohsawa, S., Takano, B., Brantley, S.L., Fernandez, J.F., Barquero, J., 1992a. Using crater lake chemistry to predict volcanic activity at Poa´s volcano, Costa Rica. Bull. Volcanol. 54, 494–503. Rowe, G.L., Brantley, S.L., Fernandez, M., Fernandez, J.F., Barquero, J., Borgia, A., 1992b. Fluid–volcano interaction in an active stratovolcano: the crater lake system of Poa´s volcano, Costa Rica. J. Volcanol. Geotherm. Res. 49, 23–51. Sakai, H., Krouse, H.R., 1971. Elimination of memory effects in 18 O/ 16O determinations in sulphates. Earth Planet. Sci. Lett. 11, 369–373. Sasaki, A., Arikawa, Y., Folinsbee, R.E., 1979. Kiba reagent method of sulfur extraction applied to isotopic work. Bull. Geol. Surv. Jpn. 30, 241–245. Shoonen, M.A.A., Barnes, H.L., 1991. Mechanisms of pyrite and marcasite formation from solutions: III. Hydrothermal processes. Geochim. Cosmochim. Acta 55, 3491–3504. Simonson, J.M., Palmer, D.A., 1993. Liquid–vapor partitioning of HCl (aq) to 3508C. Geochim. Cosmochim. Acta 57, 1–7. Smithsonian Institution, 1993. Kawah Ijen. Bull. Global Volcan. Network 18 (7), 7–8. Smithsonian Institution, 1994a. Kawah Ijen. Bull. Global Volcan. Network 19 (5), 3–4. Smithsonian Institution, 1994b. Kawah Ijen. Bull. Global Volcan. Network 19 (7), 15. Smithsonian Institution, 1997a. Kawah Ijen. Bull. Global Volcan. Network 22 (6), 8. Smithsonian Institution, 1997b. Kawah Ijen. Bull. Global Volcan. Network 22 (8), 2–3. Sturchio, N.C., Williams, S.N., Sano, Y., 1993. The hydrothermal system of Volcan Purace, Colombia. Bull. Volcanol. 55, 289– 296.

P. Delmelle et al. / Journal of Volcanology and Geothermal Research 97 (2000) 31–53 Takano, B., 1987. Correlation of volcanic activity with sulfur oxyanion speciation in crater lake. Science 235, 1542–1712. Takano, B., Watanuki, K., 1990. Monitoring of volcanic eruptions at Yugama crater lake by aqueous sulfur oxyanions. J. Volcanol. Geotherm. Res. 40, 71–87. Takano, B., Ohsawa, S., Glover, R.B., 1994a. Surveillance of Ruapehu crater lake, New Zealand, by aqueous polythionates. J. Volcanol. Geotherm. Res. 60, 29–49. Takano, B., Saitoh, H., Takano, E., 1994b. Geochemical implications of subaqueous molten sulfur at Yugama crater lake, Kusatsu-Shirane volcano, Japan. Geochem. J. 28, 199–216. Taran, Y.A., Pokrovsky, B.G., Dubik, Y.M., 1989. Isotopic composition and origin of water from andesitic magmas. Dokl. (Trans.) Ac. Ac. Sci. USSR 304, 440–443. Taran, Y.A., Znamenskiy, V.S., Yurova, L.M., 1996. Geochemical model of hydrothemal systems of Baranskiy volcano, Iturup, Kuril Islands. Volcanol. Seismol. 17, 471–496. Taran, Y., Fischer, T.P., Porovsky, B., Sano, Y., Armienta, M.A., Macias, J.L., 1998. Geochemistry of the volcano–hydrothermal system of El Chicho´n volcano, Chiapas, Mexico. Bull. Volcanol. 59, 436–449. Taylor Jr, H.P., 1974. The application of oxygen and hydrogen isotopic studies to problems of hydrothermal alteration and ore deposition. Econ. Geol. 69, 843–883. Taylor Jr, H.P., 1986. Igneous rocks II: isotopic case studies of circumpacific magmatism. In: Valley, J.W., Taylor Jr, H.P.,

53

O’Neil, J.R. (Eds.), Stable Isotopes in High Temperature Geological Processes. Mineral. Soc. Amer.: Rev. Mineral. 16, 273– 318. Thode, H.G., Cragg, C.B., Hulston, J.R., Rees, C.E., 1971. Sulphur isotope exchange between sulphur dioxide and hydrogen sulphide. Geochim. Cosmochim. Acta 35, 35–45. Ueda, A., Sakai, H., Sasaki, A., 1979. Isotopic composition of volcanic native sulfur from Japan. Geochem. J. 13, 269–275. van Bemmelen, R.W., 1949. The Geology of Indonesia. Government Printing Office, The Hague. Varekamp, J.C., Kreulen, R., 2000. The stable isotope geochemistry of volcanic lakes. J. Volcanol. Geotherm. Res. 97 (1–4), 309– 327. Whitford, D.J., Nicholls, I.A., Taylor, S.R., 1979. Spatial variations in the geochemistry of quaternary lavas across the Sunda Arc in Java and Bali. Contrib. Mineral. Petrol. 70, 341–356. Williams, S.N., Sturchio, N.C., Calvache, V.M.L., Mendez, R.F., London˜o, C.A., Garcia, N.P., 1990. Sulfur dioxide from Nevado del Ruiz volcano, Columbia: total flux and isotopic constraints on its origin. J. Volcanol. Geotherm. Res. 42, 53–68. Yanagisawa, F., Sakai, H., 1983. Thermal decomposition of bariumvanadium pentaoxide-silica glass mixtures for preparation of sulfur dioxide in sulfur isotope measurements. Anal. Chem. 55, 985–987.