Saskia Gevaert
Universit6 Libre de Bruxelles

Geochemistry Laboratory ‑ CPI 60/02
Av. F.D. Roosevelt, 50
1 050 Brussels

Belgium
Saskia.gevaert@ulb.ac,beA

j n9t 14 november ‑ 13 december 2000.

Institute for Study of the Earth's Interior, Okayama University,

Misasa, Japan.

The analyses done under the direction of the professor M. Kusakabe take part in a PhD
projeot whose aim is to understand the interactions between high temperature volcanic gases

and volcanio lakes superncial waters. The two major sites studied are the Kaba and theDempo volcanoes located in Sumatra (Indonesia). Both present at their summit one orseveral aetive crater lakes with extremely aoidic and mineralized waters. An ether feature ofthose lakes is their high contents in dissolved bisulfate but also the presence of elemental
sulfur in their waters that could be explained by the disproportionation reaetion of magmatic

S02‑
The work carried out consisted to leam and to apply the analyiical techniques used for sulfur
and oxygen isotopes determination. This in order to be able later to understand the processes
that could influence the crater takes chemistry.

Sulfur isotopic analysis were made on S02 9as coming from de thermal decomposition ofBaS04 precipitates mixed with V205 and Si021, following the method descrioed byYanigasawa and Sakai (1983)1. As for the oxygen isotopic analysis they were made on C02
resulting from the decomposition of BaS04 previously mixed with graphite, following theprocedure discribed by R fter (1967)2.

As a remark some tests were made on the BaS04 preparation:(1) some samples of water containing natural dissolved bisulfate were passed though cationand anion exchange columns before BaS04 precipitation by addition of BaC12, other werenot ;(2) most of the elemental sulfur samples were dissolved in hot aceton for sulfides separation(ex.pyrite, barite) before being oxidized with bromine and nitric acid to sulfuric acid andthen converted to BaS04, but measurments were made alsc on samples vvith no aceton
pretreatment.
All the isotopic value obtained for the different samples preparations felt vvithin the accuracyof :t 0.2 %o for 8e4S measurments. An example can be given for the sample K8 that has a6e4sHs04 Value of 1 8.969 %･ without columns treatment and 1 8.913 %o vvith columnstreatment.
All the data collected are listed in tables I and 2 (see following pages).

1 Yanagisawa. F. and Sakai, H., 1983. Thermal decomposition of barium sulfate‑vanadium pentaoxide‑silica glass mixtures for preparation of sulfur dioxide in sulfur isotope ratio measurements. Anal.

Chem., 5S: 985‑987.
2 Rafter, T.A., 1967. Oxygen isotopic composition of sulphates‑Part I . A method for the extraction ofoxygen and its quantitative conversion to carbon dioxide for isotope ratio measurments.
N.Z.J.Sci., IO: 493‑510.
‑ 47 .

Table1．Sugfurand

oxygenisotopicanalyses（inooo》ofdissolvedrr㍗

sulfates．

−、…霊』

κaba》0caη0ηdoηes

8

K3
K13
KO7
KO1524105／99

KabaLama

17．8

KabaBaru

9．9

26／05！99

KabaLama
KabaLama

4／07／00
5／07／00

13．9
13．1

一一一一ゴ

Deη書o》◎

K8
K10
K16
KO1
KO2
KO3
KO4
KO5
KO6

25105！9925105199

19．0

4／06／9919．1

3／07／00
3／07／OO

18．7
1815

3107／00

18．1

3／07／00

17．8
17．3
18．8

K4K5K12K18K19
KO8KO9KO1024105／99
24105／99

3／07／00

ldemK83／07／00

suspended eL sulfur
ye owel．sulfur
suspended eL sulfur
suspended el．suIfursuspended eL sulfur

25／05／99

4／06／99
4／06／99
4／07／00◎weL

sulfuトidem

greyeLsulfur

4／07／00

ye

K5

18．9
10．5
14．9

20．9
15．6
5．7
6．6

4／07100

grey

eL

sulfur』idem

K19

14．5
15．9
18．2
15．9

4／07／00

grey

eLsulfur』idem

K18

20．4

4107100

KO12KO13
KO14

4／07！00πdoηesye

4／07／00

KO11caηo

18．1

grey

owel，sulfur

el。sulfur−idem

K12

bluewate一曹

15．8
16．7
16．6
16．6
16．8
17．8
17．5
17．9
15．7

一一
一−
一一
一一一一
一
一aDl1

29／06／00

DL2

29／06／00

surfacewater
surfacewater

一48一

17．0
16．9

16．0
16．0

eτ

Saηfa

Aηavo4caηo

Savador

Ana1
Ana2
Ana3
V2
V3
V4
κe如fγ0σaπ〇一VbμV8

lake（一25m）

hotspringhotspring？！07／OO

lake

29／01／00

hotspring？108100

lake
lake

16．0
14．5
16．1

16．0
14．9
16．0
16．0

13．8
『聞一一一口∂

Kel3
Ke匿4
V6
AOわaγ029101／00
29／01／00？ノ011000∂η0〃，doηes｛竪．

J

29／01／00

V1

一ヨlakelakelake？ノ05／00

14107100？／？196

12．5
12．5
14．7

一一御La歯elake？ノ06／00

一49一

11．8

一＿

Table2．Sulfur

isotopic

alteratiOnmineraIS．

κaba》00召ηdoηesca

5
7
9

analyses（ininactivesulfur

pool

一5，2

2415／99

inactive

sulfurpool−4，8inactive

suifurpooレspherule−4，4

sulfurpool−K5−3，7

sulfurpool−K18

・4，5

active sulfur pool−K19
Iama Iake shore
Kaba lama lake shore−3，3

24／5／99

active6！04／99

active17禽

6／04／99
6／04／99
6／04／99
6／04／996104／99
6／04／99
6／04／99
7／04／00
7／04／00
7／04／00

20
21

22
23
24
25
ρeJ

pO》0

19without3

activesulfuractiveactivepooi−KOl−3，9
一4，0−3，6

−4，0

l

−4，1

sulfurpool−KO13

剛4，7

sulfurpool−KO14−4，4司」

pyroclastic−spherule

一8，028106100pyr◎clastic−spherule−8，1

28／06／00

2v両thoutsulfidesseparation
pyroclastic−paste−8，1

sediment
sediment

28／06／00

28／06／00

caηo・Vbu

8ddcc附ferμf》04caηoσηdoηes−8，2−7，4・8，0aκe陥ηu8fの」spherule
spherule

κe・4，3−4，2

sediment

28！06／00

45

sulfides separation
sediment
sediment？ノ09／98

2−，40baいoKabacaη0伽doπes

12sulfur

24！5／992415／99

191

elementalの16
17

18
19

o，oo》of

一9，7−10，1司」

alteration（anhydrite＋pyrite）

κμdりAavy

ab
Cvo

caηo

R∬ss司3？

alteration（anhydr旋e）5，4？

alteration（anhydrite）

8，2？

alteration（anhydrite）

7，4d？

alteration（anhydrite）

6，8e？

alteration（anhyd雨te）7，1？

alteration（anhydrite）

8，2

f

一50一and