Extreme alteration by hyperacidic brines at Kawah Ijen volcano, East

Transcription

Journal of Volcanology and Geothermal Research 196 (2010) 169–184
Contents lists available at ScienceDirect
Journal of Volcanology and Geothermal Research
j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / j vo l g e o r e s
Extreme alteration by hyperacidic brines at Kawah Ijen volcano,
East Java, Indonesia: II
Metasomatic imprint and element fluxes
Vincent van Hinsberg a,⁎, Kim Berlo b, Sri Sumarti c,d, Manfred van Bergen c, Anthony Williams-Jones a
a
Hydrothermal Geochemistry Laboratory, Department of Earth and Planetary Sciences, McGill University, Montréal, Québec, Canada
Volcanology Group, Department of Earth and Planetary Sciences, McGill University, Montréal, Québec, Canada
c
Petrology Group, Department of Earth Sciences, Utrecht University, The Netherlands
d
Center of Volcanology and Geological Hazard Mitigation, Yogyakarta Office, Java, Indonesia
b
a r t i c l e
i n f o
Article history:
Received 2 April 2010
Accepted 4 July 2010
Available online 1 August 2010
Keywords:
water–rock interaction
alteration
magmatic–hydrothermal system
Kawah Ijen
Banyu Pahit
a b s t r a c t
The hyperacidic brines of the Kawah Ijen crater lake and Banyu Pahit river, East Java, Indonesia, induce an
intense alteration on their magmatic host rock. This alteration is a proxy for water–rock interaction in
magmatic–hydrothermal systems and associated high-sulphidation mineralizing environments, as well as
for how these systems translate changes in the magmatic system to surface emissions, which are used in
volcanic hazard monitoring. Detailed bulk chemical study of altered and unaltered samples shows that
alteration is characterised by near-complete leaching of all major and trace elements, except for Pb, Sn and
Sb, which are progressively enriched (Pb up to 15-fold absolute enrichment). The resulting element release is
complementary to the observed changes in composition of the Banyu Pahit water downstream, when
corrected for dilution, indicating that alteration progressively increases the element load. The signature of
the change in water chemistry is best explained by complete alteration of fresh rock, rather than mature
alteration, which might be expected given the advanced altered state of the riverbed. Together with mass
balance considerations, this indicates that the dominant element source is material falling into the river from
the valley flanks. The chemical signature of the crater lake is inconsistent with the observed alteration in
samples from the hydrothermal system, and likewise is best explained by surface input of cations from rocks
falling in from the crater walls. This indicates that the lake water cation chemistry is not a direct reflection of
the underlying magmatic–hydrothermal system and that its cation content is therefore not an appropriate
monitor of changes in volcanic activity.
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
Crater lakes at active volcanoes develop through a complex and
dynamic interplay between element input from magmatic degassing,
water–rock interaction, rain and groundwater, and output by mineral
precipitation, evaporation and seepage. For crater lakes to persist and
reach a steady-state, these chemical fluxes, and the associated
thermal budget, have to be finely balanced (Oppenheimer, 1997;
Varekamp et al., 2000). Volcanic element input can be direct, or occur
via an intermediate magmatic–hydrothermal system developed
around the degassing magma, which itself is the result of interaction
between magmatic fluids, groundwater and the host rock. Such
magmatic–hydrothermal systems are of considerable geological
interest, because they represent important sites of mineralization,
driving the potential formation of high-sulphidation epithermal Cu–
⁎ Corresponding author.
E-mail address: [email protected] (V. van Hinsberg).
0377-0273/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jvolgeores.2010.07.004
Au deposits close to the magmatic centre, low-sulphidation Au–Ag
mineralisation in more distant geothermal areas and porphyry Cudominated deposits at depth (White and Hedenquist, 1990; Christenson and Wood, 1993; Hedenquist et al., 1993; Hedenquist and
Lowenstern, 1994; Robb, 2005). They furthermore represent the
interface between the degassing magmatic system at depth and its
surface expressions. Emissions from the magmatic–hydrothermal
system, in the form of vapour and/or liquid, therefore provide a
window into the magmatic system, and potentially a means to
monitor its activity. This is a prime avenue in hazard assessment at
many active volcanoes (e.g. Mt. Ruapehu—Christenson, 2000, Poás
volcano—Martínez et al., 2000, Kusatsu-Shirane volcano—Ohba et al.,
2008). The emissions themselves are commonly characterised by high
toxicity and reactivity, and they can therefore have a major impact on
their surrounding environment, including the destruction of vegetation and soils, and pollution of ground- and river water (Heikens et al.,
2005; Löhr et al., 2005; van Rotterdam-Los et al. 2008).
The key to understanding the above processes is evaluating the
water–rock interaction, because this controls, or strongly impacts
170
V. van Hinsberg et al. / Journal of Volcanology and Geothermal Research 196 (2010) 169–184
(depending on the water–rock ratio) the conditions of the hydrothermal system and the compositions of the associated liquid and
vapour. Unfortunately, our information on water–rock interaction in
magmatic–hydrothermal systems is commonly indirect and onesided, derived either from altered rocks in exposed, extinct hydrothermal systems, or from their liquid and vapour emissions on the
surface. Such studies reveal a discrepancy between element concentrations in volcanic emissions and observed enrichment in exposed
magmatic–hydrothermal mineralisations (e.g. Hedenquist and Lowenstern, 1994; Simmons and Brown, 2007), suggesting that either
water–rock interaction leads to strong preferential incorporation of
certain elements, or that alteration and mineralisation are decoupled
(cf. Hedenquist and Lowenstern, 1994).
Kawah Ijen volcano on the eastern tip of Java provides us with
the unique opportunity to study magmatic–hydrothermal water–
rock interaction directly and in-situ. At Kawah Ijen, hyperacidic
sulphate-chloride brines from the active crater lake and the Banyu
Pahit river interact with surface magmatic deposits, and this ongoing
interaction can be studied in-situ at several localities. This
interaction leads to the development of silicic and advanced argilic
alteration typical of high-sulphidation environments (cf. White and
Hedenquist, 1990; Giggenbach, 1997). In the preceding contribution
we discussed the mineralogical and textural impact of this water–
rock interaction in the various environments at Kawah Ijen. Here
we focus on its impact on bulk-rock chemistry to determine the
behaviour of a large suite of elements in a silicic alteration system
and to evaluate the resulting element fluxes between rock and
water.
2. Setting and geology
2.1. Kawah Ijen volcano
Kawah Ijen volcano is located on the south-east rim of the Ijen
caldera in East Java, Indonesia, and is part of the Sunda volcanic arc
(Fig. 1). The volcano is positioned on the flank of the Merapi rimvolcano and forms the easternmost member of the intra-caldera
volcano series. At Kawah Ijen, three styles of activity can be
differentiated. An initial episode of cone-building is characterised by
alternating strata of lava, scoria, lapilli and ash, varying in composition
from basalt to andesite (Kemmerling, 1921; Sitorus, 1990; this work).
On the outer slopes of the volcano, there is a series of large lava flows,
Fig. 1. Overview map of Kawah Ijen volcano and the upstream Banyu Pahit river showing the sample locations (insets show Kawah Ijen's location on the island of Java, and a detailed
map of the rapids sample site). The approximate positions of the large Kawah Ijen lava flows are also shown (after Sujanto et al., 1989). Topography based on the 1:20,000 scale map
by the topographical survey (1918), updated with our GPS measurements. Contour interval is 10 m, with thick lines for 100 m contours.
descending to the north on either side of Blau volcano, and towards
the east on the outside flank of the Ijen caldera (Fig. 1). These flows
are well exposed in river valleys, and marked by waterfalls at their
furthest extent. They are indistinguishable in composition, mineralogy and texture from those of the volcanic edifice and link up with the
higher levels of the volcanic cone where they can be traced back to the
volcano.
Hydrothermal, phreatic and phreato-magmatic deposits mark the
third style of activity. These deposits are exposed on the summit
where they discordantly overly the cone-building strata. They are
composed primarily of variably altered magmatic material, but locally
contain fragments of native sulphur, interspersed with charcoal-rich
soil layers and thin ash falls. Ballistics, ranging from dense magmatic
bombs characterised by large (up to 2 cm in length) plagioclase
phenocrysts, to strongly altered material, are present within and on
top of these deposits. Further phreato-magmatic deposits are exposed
in the river valley of the Banyu Pahit river, where they are
interspersed with lava flows, ash and scoria fall deposits, mud flows
and pyroclastic flows, all descending through this valley. The
thickness and competence of individual deposits vary strongly and
these are expressed directly in their lateral extent. Most end at the
Banyu Pahit rapids site where the valley opens up, although at least
one lava flow extends downstream to Watucapil (Fig. 1). The phreatomagmatic deposits are bimodal with variably altered grains and
pristine magmatic fragments consisting of (broken) phenocrysts
and angular, dark glass exhibiting varying degrees of vesiculation and
crystallization. The magmatic material is identical in texture and
mineralogy to the magmatic bombs sampled on the summit area (e.g.
sample KV08-501). The altered material varies strongly in the degree
of alteration among layers, although alteration intensity is reasonably
constant within layers. Altered lava, containing minor precipitates of
barite, dominates. Based on the exposures in the Banyu Pahit river
valley, the large lava flows are coeval with phreato-magmatic activity,
and this postdates development of the volcanic edifice as evidenced
by the complete lack of altered material in the cone-building deposits
and their unconformable relationships, where in contact. Interestingly, this change in activity does not coincide with a change in bulk-rock
composition.
2.2. Crater lake and Banyu Pahit river
The summit crater of Kawah Ijen volcano is occupied by a
lake of oxidized hyperacidic brine with a total dissolved solid load
of N100 g/kg. This fluid is extremely aggressive in its interaction
with rock due to its high acidity and F-content (Delmelle and Bernard,
1994, 2000; Sumarti, 1998; Takano et al., 2004; this work). The
crater lake brine seeps through the western flank of the volcano to
form the headwaters of the equally acidic Banyu Pahit river (Fig. 1).
Where it emerges, this water rapidly saturates in gypsum due to
evaporation, which has led to the development of a large gypsum
plateau, culminating in a gypsum covered terraced slope 50 m wide
and 100 m long. The Banyu Pahit subsequently flows down a steepsided valley in-between Kawah Ijen and Papak volcanoes (Fig. 1). It is
not continuous, however, twice disappearing into the riverbed (see
the preceding contribution). The discharge of the third set of springs
exceeds that of the previous springs and is maintained downstream
of this site to the waterfall at Watucapil. These springs are therefore
interpreted to be the main source of water in the Banyu Pahit river
and, considering their location, this water may not represent direct
seepage from the lake. Along its length, the Banyu Pahit passes
through a variety of deposits as described above, although it flows
mainly on top of an andesitic lava that is exposed at the rapids site
and Watucapil. The valley is broad where the riverbed is made up of
lava but narrows to a canyon where it flows through pyroclastic and
phreatic material.
171
3. Methods
Samples of fresh and altered magmatic material, and hyperacidic
lake and Banyu Pahit river water were collected at various localities at
Kawah Ijen volcano during fieldwork in 1999, 2007, 2008 and 2009
(Fig. 1). Unaltered material, representative of all major Kawah Ijen
lava flows as identified on the Ijen caldera geological map (Sujanto
et al., 1989), was sampled, as well as a subset of scoria deposits,
volcanic bombs and small lava flows. Altered material was sampled in
the riverbed of the Banyu Pahit river and from ballistics strewn on the
summit area of the volcano and present in phreatic deposits on its
outer flanks. These samples include two detailed in-situ transects of
progressively altered rock and their unaltered lava precursor. The first
of these suites consists of the concentric alteration layers developed
on a lava flow in the Banyu Pahit riverbed just below the dam (Fig. 3b
in the accompanying contribution). The second transect was sampled
at the Banyu Pahit rapids site (Fig. 1) and consists of a continuous
section of 14 samples from unaltered lava on either side of the river to
its altered equivalent below the water level. This setting is
characteristic of the riverbed for most of the Banyu Pahit river
between the third set of springs and Watucapil. Crater lake water was
sampled at the foot of the active dome and at the dam on the western
end of the lake. Water samples of the Banyu Pahit river were taken
from several of the uppermost springs below the dam, at the rapids
site and just before the waterfall at Watucapil (Fig. 1). Groundwater
was collected on the southern flank of Widadaren volcano, where it
emerges from a porous scoria deposit, and a sample of rainwater was
obtained on the southern flank of the Ijen caldera during the 2009
field season.
The bulk-rock composition was determined by XRF for 1999
samples and ICP-OES/MS for 2007 samples. XRF analyses were
conducted at the Faculty of Earth and Life Sciences, Free University,
Amsterdam. Samples were crushed in a tungsten-carbide jaw-crusher
before being powdered in an agate ball mill. In between samples,
quartz sand was milled to clean the equipment. Major element
concentrations were determined on fused beads prepared from
fired powder (fired at 1000 °C with LOI determined by weighing)
with Li-borate flux, whereas trace element concentrations were
determined on pressed pellets of non-fired rock powder. Both beads
and pellets were analysed with a Philips PW1404 sequential XRF
spectrometer. Duplicates and BCR1, GSP1 and BHVO1 standards were
analysed to determine precision and accuracy respectively. The ICPOES/MS analyses were carried out at the Geochemical Laboratory of
Utrecht University in the Netherlands. The samples were ground
manually in an agate mortar and dissolved by hot HClO4–HF–HNO3
acid digestion. Major element concentrations were analysed by ICPOES at a range of dilutions, and trace element concentrations by ICPMS. Duplicates and the ISE921 standard were digested and analysed
to determine the precision and accuracy of the full routine. In addition
to the bulk-rock samples, glass veins and skins of glass enclosing a
large (2 cm long) plagioclase phenocryst from a volcanic bomb
sampled on the summit (KV08-501), and a glass globule from the
active dome (KV08-702), were also analysed; the glass in both
samples represents a pristine, vesicular melt virtually devoid of
microlites. The composition of the glass was determined by electron
microprobe WDS on a JEOL 8900 microprobe at the Department of
Earth and Planetary Sciences, McGill University using a 15 kV
acceleration voltage, 4 nA beam current and 10 μm defocussed
beam, calibrating on a set of natural andesitic and rhyolitic glasses.
Water samples were filtered in the field using 0.45 μm nitrocellulose filters and stored in completely filled HDPE bottles. Rainwater
was collected using a funnel. Duplicates were taken at each sample
site. Ground- and rainwater were acidified using trace metal grade
nitric acid. This was not necessary for Banyu Pahit and crater lake
samples, because their pH was below 0.5 as determined at the sample
site in a 100 times dilution using a standard pH-electrode (see also
172
Table 1
Water properties and compositions of the Kawah Ijen crater lake and Banyu Pahit river. Ti obtained by ICP-MS in 2007 and 2009, Mg by ICP-MS in 2007, Co by ICP-OES in 2007 and
Mn by ICP-OES in 2009. n.a. not analysed, n.d. not detected, n.c. could not be calculated as major element or carbon content unknown.
Sample no.
KV99-857,858
KV99-840,841
KV99-845,846
KV99-838,839
KV99-836,837
KV07-IJN2
KV07-IJN5
KV07-BYPg
KV07-BYPc
Locality
Lake fumaroles
Lake dam
BP springs
BP rapids
BP Watucapil
Lake fumaroles
Lake dam
BP springs
BP springs
Coordinates
S 08°03′ 36″
E 114°14′ 39″
S 08°03′ 25″
E 114°14′ 15″
S 08°03′ 28″
E 114°14′ 06″
S 08°03′ 39″
E 114°12′ 39″
S 08°01′ 34″
E 114°10′ 56″
S 08°03′ 36″
E 114°14′ 39″
S 08°03′ 25″
E 114°14′ 15″
S 08°03′ 28″
E 114°14′ 10″
S 08°03′ 23″
E 114°14′ 01″
Field measurements
T air (°C)
21.0
T water (°C)
36.9
pH meas.
− 0.1
pH calc.
n.c.
21.3
37.1
− 0.1
0.45
20.4
33.9
0.0
0.52
19.7
17.6
0.3
1.14
26.7
21.4
0.6
1.13
n.a.
37.4
0.0
0.44
n.a.
36.7
0.0
0.42
n.a.
14.1
0.1
0.79
n.a.
22.1
0.4
0.38
ICP-OES (values
Si
Ti
Al
Fe
Mg
Ca
Na
K
P
B
54
7
5596
2069
682
769
1030
1147
n.a.
52
51
19
5262
1997
644
807
960
1093
n.a.
45
56
24
3191
1908
412
814
619
732
n.a.
24
54
24
3277
1829
387
774
579
672
n.a.
24
50
8
5740
2208
710
760
1125
1266
51
46
64
8
5737
2372
710
763
1280
1319
54
48
47
22
3462
1599
459
856
759
759
33
25
39
24
6438
2660
796
706
1240
1373
56
48
40
0.49
n.a.
0.35
5.1
n.a.
8.1
n.a.
n.a.
0.69
n.a.
3.8
n.a.
15.0
1.89
n.a.
n.d.
n.a.
0.06
0.30
0.03
n.a.
4.5
n.a.
1.624
n.a.
0.67
1.56
0.206
0.84
0.200
0.056
0.205
0.032
0.176
0.035
0.103
0.014
0.094
0.014
0.30
0.058
40
0.51
n.a.
0.40
4.9
n.a.
7.8
n.a.
n.a.
n.d.
n.a.
3.7
n.a.
15.0
1.81
n.a.
n.d.
n.a.
0.05
0.30
0.06
n.a.
4.4
n.a.
0.102
n.a.
0.63
1.54
0.208
0.85
0.193
0.057
0.199
0.033
0.174
0.037
0.104
0.015
0.097
0.015
0.29
0.058
22
0.30
n.a.
0.46
2.6
n.a.
6.2
n.a.
n.a.
0.39
n.a.
1.8
n.a.
9.3
0.63
n.a.
n.d.
n.a.
0.02
0.08
n.d.
n.a.
1.8
n.a.
0.172
n.a.
0.33
0.83
0.112
0.46
0.109
0.031
0.110
0.017
0.092
0.020
0.056
0.008
0.052
0.008
0.17
0.029
22
0.30
n.a.
0.45
2.6
n.a.
6.4
n.a.
n.a.
0.41
n.a.
1.8
n.a.
9.4
0.63
n.a.
n.d.
n.a.
0.02
0.08
n.d.
n.a.
1.7
n.a.
0.078
n.a.
0.34
0.83
0.111
0.46
0.108
0.030
0.106
0.017
0.091
0.019
0.055
0.008
0.049
0.008
0.17
0.028
42
0.52
0.23
0.41
4.9
1.03
10.2
0.27
0.59
0.81
0.109
3.6
0.063
15.3
1.98
0.046
0.002
0.004
0.06
0.38
0.04
0.8
4.3
n.a.
0.129
0.92
0.62
1.41
0.189
0.78
0.181
0.051
0.185
0.027
0.167
0.034
0.101
0.015
0.096
0.015
N 0.27
0.056
44
0.59
0.28
0.51
5.3
1.07
10.7
0.29
0.59
0.86
0.117
3.7
0.068
15.7
2.21
0.046
0.002
0.005
0.06
0.39
0.04
0.8
4.3
n.a.
0.142
0.94
0.67
1.49
0.187
0.76
0.177
0.049
0.184
0.027
0.162
0.032
0.098
0.014
0.093
0.014
N0.26
0.054
31
0.49
0.27
0.85
3.3
0.70
7.3
0.22
0.40
0.49
0.064
2.1
0.037
11.7
0.90
0.010
0.005
0.002
0.03
0.04
0.01
0.3
1.9
n.a.
0.055
0.62
0.44
0.96
0.124
0.51
0.118
0.034
0.120
0.017
0.104
0.021
0.061
0.009
0.057
0.009
N 0.12
0.026
49
0.65
0.29
0.63
5.6
1.17
11.4
0.31
0.71
0.81
0.118
4.0
0.057
17.0
2.22
0.043
0.005
0.005
0.06
0.34
0.09
0.7
3.9
n.a.
0.065
1.07
0.66
1.50
0.199
0.81
0.190
0.054
0.197
0.029
0.173
0.035
0.106
0.015
0.102
0.016
N 0.25
0.053
Collision cell ICP-MS (values in ppm)
As
2.0
1.6
Se
0.51
0.53
2.1
0.49
1.6
0.24
1.4
0.21
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
Ion chromatography (values in ppm)
Cl
n.a.
22,099
SO4
n.a.
66,855
F
n.a.
1258
19,985
61,035
1166
9161
29,069
511
8887
28,034
470
23,234
67,870
1473
23,685
69,293
1497
11,636
36,381
786
25,037
73,484
1582
in ppm)
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
ICP-MS (values in ppm)
Mn
44
Co
0.53
Ni
n.a.
Cu
0.39
Zn
5.6
Sc
n.a.
V
n.a.
Cr
n.a.
Ga
n.a.
Li
n.a.
Cs
n.a.
Rb
4.1
Be
n.a.
Sr
16.4
Zr
2.05
Hf
n.a.
Mo
n.d.
Ag
n.a.
Cd
0.06
Sn
0.34
Sb
0.03
Tl
n.a.
Pb
4.9
Bi
n.a.
Ba
0.500
Y
n.a.
La
0.73
Ce
1.70
Pr
0.225
Nd
0.92
Sm
0.213
Eu
0.061
Gd
0.217
Tb
0.035
Dy
0.184
Ho
0.038
Er
0.108
Tm
0.015
Yb
0.098
Lu
0.015
Th
0.31
U
0.062
173
Table 1
Water properties and compositions of the Kawah Ijen crater lake and Banyu Pahit river. Ti obtained by ICP-MS in 2007 and 2009, Mg by ICP-MS in 2007, Co by ICP-OES in 2007 and
Mn by ICP-OES in 2009. n.a. not analysed, n.d. not detected, n.c. could not be calculated as carbon content unknown.
KV07-BYPh
KV07-BYPi
SV09-IJN
SV09-AS1
KV09-506
SV09-RAP
SV09-WaCa
SV09-Pal
SV09-Rain
BP rapids
BP Watucapil
Lake fumaroles
BP springs
BP springs
BP rapids
BP Watucapil
Ground water
Rainwater
S 08°03′ 39″
E 114°12′ 39″
S 08°01′ 34″
E 114°10′ 56″
S 08°03′ 36″
E 114°14′ 39″
S 08°03′ 25″
E 114°14′ 03″
S 08°03′ 28″
E 114°14′ 08″
S 08°03′ 39″
E 114°12′ 39″
S 08°01′ 34″
E 114°10′ 56″
S 08°04′ 12″
E 114°13′ 43″
S 08°07′ 16″
E 114°15′ 12″
n.a.
18.4
0.4
0.86
n.a.
20.5
0.6
0.89
17.5
34.5
− 0.1
0.62
17.0
36.5
0.2
1.00
17.5
32.9
− 0.0
0.72
18.5
18.4
n.d.
1.09
21.0
20.5
n.d.
1.12
20.2
14.0
8.2
n.c.
15.0
n.a
n.a.
n.c.
46
24
3301
1697
389
705
678
809
32
23
53
26
3462
1745
392
723
696
826
32
24
n.a.
9
6217
2478
741
1040
1131
1377
55
n.a.
n.a.
24
5872
2519
714
971
1135
1261
54
n.a.
n.a.
26
6233
2617
756
1051
1130
1354
57
n.a.
n.a.
25
3516
1772
431
704
632
795
31
n.a.
n.a.
25
3586
1805
438
717
646
809
31
n.a.
n.a.
0.001
0.064
0.034
1.55
6.35
18.3
3.1
n.d.
n.a.
n.a.
0.000
0.016
0.089
0.03
0.11
15.3
n.d.
0.38
n.a.
28
0.37
0.16
0.70
3.2
0.69
7.1
0.17
0.46
0.43
0.063
2.1
0.032
11.3
0.78
0.007
0.003
0.002
0.03
0.10
0.00
0.4
1.8
n.a.
0.048
0.59
0.37
0.88
0.119
0.49
0.113
0.032
0.116
0.017
0.103
0.021
0.060
0.009
0.057
0.009
N 0.15
0.028
28
0.38
0.18
0.79
3.2
0.70
7.3
0.18
0.45
0.44
0.066
2.2
0.032
11.5
0.82
0.006
0.004
0.002
0.03
0.10
0.00
0.3
1.7
n.a.
0.078
0.60
0.38
0.90
0.120
0.49
0.113
0.033
0.115
0.017
0.100
0.020
0.058
0.008
0.055
0.008
N 0.14
0.026
50
0.56
0.23
0.23
6.2
1.26
12.8
0.34
1.23
1.21
0.110
4.1
0.096
17.1
2.18
0.047
0.004
n.a.
0.05
0.46
0.06
0.8
4.6
0.6
0.30
0.93
n.d.
1.52
0.204
0.87
0.194
0.055
0.183
0.028
0.197
0.036
0.107
0.016
0.100
0.015
0.29
0.063
45
0.61
0.24
0.28
5.9
1.80
12.4
n.d.
1.29
1.10
0.103
3.8
0.091
16.4
2.03
0.039
0.006
n.a.
0.04
0.32
0.06
0.7
3.9
0.6
n.d.
0.90
n.d.
1.41
0.193
0.80
0.185
0.053
0.176
0.027
0.171
0.035
0.103
0.015
0.097
0.015
0.27
0.059
51
0.61
0.24
0.20
6.2
1.41
13.4
0.44
1.22
1.20
0.11
4.2
0.095
18.0
2.195
0.04
0.01
n.a.
0.06
0.38
0.07
0.7
4.1
0.7
n.d.
0.97
n.d.
1.52
0.202
0.87
0.196
0.058
0.187
0.029
0.181
0.037
0.108
0.016
0.103
0.016
0.28
0.061
29
0.35
0.13
0.46
3.4
0.85
8.0
0.28
0.74
0.60
0.056
2.2
0.046
11.0
0.70
0.005
0.004
n.a.
0.03
0.09
0.0003
0.4
1.8
0.4
n.d.
0.54
n.d.
0.86
0.115
0.49
0.110
0.032
0.105
0.016
0.102
0.021
0.061
0.009
0.057
0.009
0.17
0.032
30
0.35
0.13
0.47
3.7
0.88
8.2
0.27
0.75
0.62
0.057
2.2
0.049
11.0
0.70
0.006
0.004
n.a.
0.03
0.09
0.0003
0.4
1.8
0.4
0.00
0.54
n.d.
0.87
0.117
0.49
0.112
0.033
0.107
0.016
0.101
0.021
0.062
0.009
0.058
0.009
0.17
0.033
b0.006
0.00003
0.0003
0.014
0.0080
b0.0002
0.010
0.0001
0.0000
0.0005
0.00005
0.0049
b0.00002
0.040
b0.0002
0.000004
0.00020
b0.00001
0.00001
0.00001
0.00001
0.000003
0.000003
0.0007
0.0059
0.00003
0.030
0.000071
0.000008
0.000032
0.000009
0.000003
0.000015
0.000003
n.d.
0.000005
0.000006
0.000001
0.000004
0.000003
0.000003
0.000013
b0.009
0.00002
0.0004
0.010
n.d.
0.0001
0.0001
0.0001
0.0000
0.0000
0.00001
0.0001
b0.00003
0.0007
b0.0003
b0.00001
0.00001
0.00001
0.00001
0.00003
0.00061
0.000003
0.000004
0.0023
0.0005
0.00001
0.039
0.000040
0.000005
0.000016
0.000002
0.000001
0.000012
0.000000
0.000004
0.000000
0.000001
0.000000
b0.000003
0.000000
b0.000003
0.000002
n.a.
n.a.
n.a.
n.a.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
0.0002
b0.0004
0.0036
b0.0006
11,235
32,803
687
11,096
33,794
710
20,989
60,718
1341
16,348
45,418
964
18,917
58,376
1242
9361
29,553
607
9203
29,895
622
1.80
25.4
0.38
n.a.
n.a.
n.a.
174
Table 2
Composition of unaltered and altered rocks at Kawah Ijen. KV99 samples and KV08-501a were analysed by XRF, and KV07 samples were analysed by ICP-OES/MS. Samples KV08-501b and 702 were analysed for the composition of their glasses,
which were determined by EMPA (average of 11, 2 and 10 analyses respectively).
Sample
no.
Sample
no.
Altered ballistics
KV99825
KV99826
KV99827
KV99844
KV99-8
44b
KV99883
KV99884
KV99017
KV99020
KV99030
KV99032
KV99035
KV99058
KV99075
KV07501
KV08501a
KV08501b
KV08501b
KV08702
KV99879
KV99880
KV99882
KV99854
KV07001
KV07609
KV07611
56.50
0.75
19.88
6.99
0.13
2.42
7.29
3.63
2.10
0.24
0.40
18
7
29
63
n.d.
144
n.d.
19
n.d.
n.d.
52
n.d.
499
144
4
6
n.d.
n.d.
n.d.
n.d.
n.d.
534
25
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
4
n.d.
2
n.d.
1
n.d.
8
7
2
50.69
1.10
19.77
10.47
0.16
3.79
9.37
3.10
1.18
0.31
1.00
28
4
13
31
n.d.
255
n.d.
12
n.d.
n.d.
17
n.d.
624
95
4
6
n.d.
n.d.
n.d.
n.d.
n.d.
464
63
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
4
n.d.
1
n.d.
bd.l.
n.d.
5
3
1
52.26
1.04
19.92
9.46
0.18
3.16
9.24
3.04
1.36
0.28
1.30
bd.l.
3.06
3.06
5.31
24.90
7.15
0.68
7.66
6.87
1.08
27.67
1.16
606.0
96.8
7.35
4.49
n.d.
0.29
0.60
0.07
0.43
998.4
44.61
21.49
42.33
5.93
25.55
5.92
1.95
6.75
1.05
6.38
1.40
3.85
0.53
3.42
0.50
6.4
3.68
0.82
51.60
1.10
19.85
9.69
0.17
3.20
9.48
3.23
1.34
0.29
0.60
25
8
167
87
n.d.
259
n.d.
20
n.d.
n.d.
22
n.d.
575
93
2
5
n.d.
n.d.
n.d.
n.d.
n.d.
437
28
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
4
n.d.
b d.l.
n.d.
2
n.d.
6
3
0
64.49
0.50
17.49
4.06
0.09
1.13
4.19
4.05
3.81
0.11
0.40
7.10
4.77
32.45
48.78
11.71
54.76
2.29
18.36
25.84
5.03
107.50
1.88
350.3
274.6
7.00
11.76
n.d.
0.07
1.93
0.24
0.70
802.2
31.13
27.56
55.56
6.62
25.33
5.22
1.20
5.04
0.80
4.92
1.04
3.09
0.47
2.98
0.50
17.5
12.68
3.45
56.87
0.76
17.88
7.79
0.14
3.57
7.16
3.25
2.35
0.17
0.30
2
16
75
67
n.d.
168
n.d.
18
n.d.
n.d.
63
n.d.
415
168
5
7
n.d.
n.d.
n.d.
n.d.
n.d.
521
27
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
2
n.d.
1
n.d.
1
n.d.
9
8
2
51.67
1.11
20.00
9.78
0.17
3.06
9.59
3.18
1.12
0.29
0.60
27
8
48
83
n.d.
277
n.d.
19
n.d.
n.d.
19
n.d.
586
92
3
5
n.d.
n.d.
n.d.
n.d.
n.d.
428
32
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
2
n.d.
1
n.d.
2
n.d.
6
3
1
57.51
0.86
17.52
8.06
0.15
2.95
6.37
3.58
2.74
0.19
0.00
22
7
48
72
n.d.
185
n.d.
18
n.d.
n.d.
75
n.d.
394
186
5
8
n.d.
n.d.
n.d.
n.d.
n.d.
611
30
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
2
n.d.
2
n.d.
1
n.d.
11
9
3
58.86
0.79
17.17
7.48
0.15
2.85
6.41
3.50
2.55
0.18
0.00
19
8
72
81
n.d.
151
n.d.
18
n.d.
n.d.
66
n.d.
412
173
4
8
n.d.
n.d.
n.d.
n.d.
n.d.
648
26
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
2
n.d.
b d.l.
n.d.
2
n.d.
9
8
2
50.38
1.02
18.75
10.98
0.19
4.51
9.72
3.06
1.14
0.22
0.00
33
13
112
85
n.d.
282
n.d.
20
n.d.
n.d.
24
n.d.
476
84
2
4
n.d.
n.d.
n.d.
n.d.
n.d.
353
22
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
3
n.d.
2
n.d.
2
n.d.
4
4
1
50.82
0.94
20.19
9.88
0.17
3.73
9.83
3.00
1.17
0.22
0.20
29
10
92
82
n.d.
254
n.d.
20
n.d.
n.d.
26
n.d.
518
88
3
4
n.d.
n.d.
n.d.
n.d.
n.d.
353
21
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
4
n.d.
2
n.d.
2
n.d.
7
4
1
50.67
0.95
20.30
9.86
0.18
3.66
9.99
2.95
1.18
0.21
0.10
29
10
120
82
n.d.
255
n.d.
20
n.d.
n.d.
26
n.d.
520
82
2
4
n.d.
n.d.
n.d.
n.d.
n.d.
346
21
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
4
n.d.
b d.l.
n.d.
1
n.d.
6
3
1
52.06
0.94
20.30
9.19
0.17
3.11
9.32
3.38
1.24
0.25
0.10
24
6
82
78
n.d.
208
n.d.
20
n.d.
n.d.
27
n.d.
533
90
3
4
n.d.
n.d.
n.d.
n.d.
n.d.
386
24
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
4
n.d.
b d.l.
n.d.
b d.l.
n.d.
6
3
1
50.58
0.96
18.77
11.11
0.19
5.01
9.01
2.86
1.21
0.25
0.10
32.05
20.63
136.20
83.12
28.43
255.38
11.82
19.73
8.08
1.08
26.19
1.08
513.0
91.2
2.20
4.07
n.d.
0.06
0.46
b d.l.
0.12
416.6
22.43
15.98
33.34
4.38
17.94
4.09
1.39
4.13
0.64
3.83
0.81
2.27
0.32
2.23
0.33
6.0
3.41
0.62
59.00
0.75
17.31
7.48
0.15
2.74
6.24
3.41
2.65
0.20
0.20
18.02
6.41
38.04
67.07
16.85
137.15
4.59
17.82
18.83
3.17
74.98
1.44
412.3
183.9
4.91
8.51
n.d.
0.05
1.28
0.08
0.39
574.6
26.13
20.69
42.66
5.29
20.86
4.57
1.28
4.26
0.69
4.18
0.89
2.54
0.38
2.65
0.42
11.1
8.41
1.70
51.20
1.01
19.54
11.18
0.18
4.44
9.64
3.02
1.10
0.21
n.d.
31.13
15.66
139.90
120.15
57.25
335.29
10.14
13.19
9.74
1.07
24.16
0.75
466.0
n.d.
n.d.
4.22
0.81
0.65
1.14
0.13
0.65
360.3
19.51
11.57
24.91
3.33
15.01
3.77
1.26
4.12
0.62
3.83
0.78
2.25
0.33
2.18
0.33
6.8
2.95
0.70
59.68
0.73
17.18
6.97
0.15
2.58
5.63
3.79
3.15
0.18
0.06
14
16
71
43
12
130
29
17
n.d.
n.d.
86
n.d.
355
221
n.d.
8
n.d.
n.d.
n.d.
n.d.
n.d.
625
29
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
10
10
3
67.50
0.67
14.81
4.29
0.08
0.72
2.19
3.96
5.23
0.18
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
13
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
70.53
0.53
14.62
3.23
0.06
0.35
1.17
4.06
5.77
0.09
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
15
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
71.17
0.58
14.35
3.16
0.06
0.38
1.28
3.80
6.00
0.09
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
15
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
58.70
0.64
15.57
5.09
0.04
1.57
4.46
3.65
3.19
0.09
6.80
9
6
46
26
n.d.
93
n.d.
16
n.d.
n.d.
88
n.d.
308
228
5
10
n.d.
n.d.
n.d.
n.d.
n.d.
653
25
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
5
n.d.
2
n.d.
3
n.d.
14
11
3
59.95
0.74
16.56
6.93
0.14
2.68
5.87
3.60
2.98
0.18
0.30
17
9
50
64
n.d.
136
n.d.
18
n.d.
n.d.
83
n.d.
375
212
6
10
n.d.
n.d.
n.d.
n.d.
n.d.
632
30
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
4
n.d.
4
n.d.
3
n.d.
13
10
4
60.57
1.51
24.94
5.77
0.00
0.03
0.23
0.91
5.38
0.56
29.20
36
5
59
20
n.d.
357
n.d.
31
n.d.
n.d.
19
n.d.
864
88
3
4
n.d.
n.d.
n.d.
n.d.
n.d.
662
2
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
b d.l.
n.d.
b d.l.
n.d.
b d.l.
n.d.
131
6
1
83.72
0.62
12.14
0.10
0.00
0.10
0.03
0.61
2.51
0.12
17.80
b d.l.
3
11
7
n.d.
78
n.d.
23
n.d.
n.d.
16
n.d.
297
407
10
18
n.d.
n.d.
n.d.
n.d.
n.d.
679
14
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
1
n.d.
4
n.d.
1
n.d.
76
13
4
n.d.
0.66
15.71
1.41
0.02
0.89
4.10
3.82
3.69
0.03
n.d.
b d.l.
13.81
127.99
104.99
57.18
310.36
9.17
12.35
9.03
0.99
22.56
0.74
437.3
n.d.
n.d.
3.84
0.64
0.73
0.97
0.08
0.58
338.6
18.15
10.47
22.71
3.04
13.74
3.50
1.15
3.73
0.57
3.48
0.71
2.01
0.30
1.95
0.30
5.8
2.58
0.60
n.d.
0.65
16.29
6.27
0.13
1.91
4.42
3.88
3.29
0.13
n.d.
12.13
3.94
11.82
85.65
25.53
129.81
3.99
15.59
21.00
2.52
85.33
1.27
355.6
n.d.
n.d.
11.23
0.92
0.22
1.53
0.28
0.31
729.4
17.97
19.85
35.93
4.03
15.53
3.49
1.18
3.65
0.56
3.52
0.71
2.12
0.33
2.22
0.34
17.3
7.90
1.46
n.d.
0.66
14.87
3.99
0.02
0.55
5.09
3.63
3.11
0.07
n.d.
5.22
2.30
21.30
45.25
17.13
92.21
2.69
14.61
13.69
2.13
80.53
1.19
320.8
n.d.
n.d.
11.29
0.62
0.19
2.16
0.37
0.72
710.7
13.77
20.23
36.43
4.11
15.65
3.12
1.06
3.11
0.45
2.73
0.55
1.61
0.23
1.50
0.23
18.4
4.61
1.13
Banyu Pait rapids alteration transect
KV99801
KV99802a
KV99802b
KV99803
KV99805
KV99806
KV99808
KV99811
KV07704
KV07705
KV07706
KV07708
KV07709
KV07710
Dam alteration transect
Altered samples from Banyu Pait dam area
KV07502
KV99850
KV07503
KV07504
KV99851
KV99852
KV99853r
KV99853w
KV07507
KV07508
SiO2
TiO2
Al2O3
Fe2O3
MnO
MgO
CaO
Na2O
K2O
P2O5
LOI%
Co
Ni
Cu
Zn
Sc
V
Cr
Ga
Li
Cs
Rb
Be
Sr
Zr
Hf
Nb
Ag
Cd
Sn
Sb
Tl
Ba
Y
La
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
Pb
Th
U
Unaltered Kawah Ijen magmatic deposits
KV99822
Table 2 (continued)
Sample
no.
Banyu Pait rapids alteration transect
Altered samples from Banyu Pait dam area
KV99802a
KV99802b
KV99803
KV99805
KV99806
KV99808
KV99811
KV07704
KV07705
KV07706
KV07708
KV07709
KV07710
KV07502
KV07503
KV07504
KV99850
KV99851
KV99852
KV99853r
KV99853w
KV07507
KV07508
69.06
0.97
11.58
4.75
0.05
0.84
7.39
2.46
2.77
0.07
6.50
12
14
145
97
n.d.
135
n.d.
22
n.d.
n.d.
75
n.d.
440
201
3
10
n.d.
n.d.
n.d.
n.d.
n.d.
660
6
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
9
n.d.
1
n.d.
6
n.d.
35
5
1
77.47
0.93
7.36
5.55
0.07
1.14
2.89
1.43
2.98
0.13
4.60
11
5
13
44
n.d.
116
n.d.
10
n.d.
n.d.
95
n.d.
266
242
6
11
n.d.
n.d.
n.d.
n.d.
n.d.
729
20
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
3
n.d.
4
n.d.
2
n.d.
96
12
2
91.04
1.16
2.32
3.15
0.03
0.42
0.25
0.28
1.26
0.02
4.90
8
4
16
21
n.d.
83
n.d.
4
n.d.
n.d.
23
n.d.
88
229
6
13
n.d.
n.d.
n.d.
n.d.
n.d.
746
2
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
1
n.d.
b d.l.
n.d.
b d.l.
n.d.
207
1
b d.l.
72.09
0.81
11.04
5.01
0.09
1.98
2.91
2.49
3.28
0.23
5.10
11
5
10
27
n.d.
50
n.d.
13
n.d.
n.d.
82
n.d.
249
248
6
10
n.d.
n.d.
n.d.
n.d.
n.d.
679
16
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
1
n.d.
3
n.d.
b d.l.
n.d.
39
11
2
85.02
0.60
6.04
1.74
0.05
1.17
1.03
1.18
2.94
0.14
5.40
4
4
3
13
n.d.
14
n.d.
7
n.d.
n.d.
83
n.d.
188
260
6
12
n.d.
n.d.
n.d.
n.d.
n.d.
769
15
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
1
n.d.
2
n.d.
1
n.d.
128
11
2
72.33
1.14
10.18
6.78
0.08
1.51
2.53
2.06
3.21
0.12
4.80
14
6
17
43
n.d.
145
n.d.
13
n.d.
n.d.
74
n.d.
288
210
5
10
n.d.
n.d.
n.d.
n.d.
n.d.
701
8
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
2
n.d.
3
n.d.
1
n.d.
27
8
1
61.15
0.80
16.05
7.78
0.15
2.59
5.32
3.25
2.69
0.16
0.60
17
7
31
70
n.d.
154
n.d.
18
n.d.
n.d.
75
n.d.
373
186
5
8
n.d.
n.d.
n.d.
n.d.
n.d.
598
23
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
bd.l.
n.d.
3
n.d.
1
n.d.
18
9
2
87.30
1.19
4.56
2.92
0.03
0.57
0.57
0.53
2.22
0.04
10.20
8
4
24
21
n.d.
114
n.d.
6
n.d.
n.d.
90
n.d.
174
218
5
13
n.d.
n.d.
n.d.
n.d.
n.d.
686
5
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
b d.l.
n.d.
1
n.d.
1
n.d.
264
6
b d.l.
n.d.
0.57
4.05
1.86
0.07
1.26
0.71
0.75
1.99
0.09
n.d.
bd.l.
2.18
8.16
39.98
13.20
24.99
2.22
9.22
4.10
1.25
54.38
0.28
146.2
n.d.
n.d.
12.43
1.10
0.62
19.04
1.41
0.41
734.9
12.09
13.40
19.80
2.09
8.10
2.01
0.28
2.08
0.35
2.24
0.48
1.48
0.24
1.65
0.26
214.1
N10.12
2.64
n.d.
0.53
4.02
1.73
0.06
1.19
0.69
0.72
2.05
0.21
n.d.
b d.l.
1.80
7.84
32.50
10.55
19.46
1.26
9.10
5.69
1.32
57.23
0.26
161.3
n.d.
n.d.
12.27
0.84
0.90
28.64
1.46
0.90
708.8
11.97
15.06
21.05
2.15
8.18
2.00
0.29
2.09
0.34
2.20
0.47
1.45
0.23
1.61
0.25
218.3
N 10.17
2.57
n.d.
0.43
12.90
3.64
0.10
1.96
5.49
2.90
2.58
0.08
n.d.
9.51
3.20
8.08
55.81
19.44
71.30
3.13
11.84
11.48
1.48
65.73
0.90
339.5
n.d.
n.d.
9.09
0.84
0.22
4.69
0.42
0.37
606.1
13.25
11.81
21.94
2.65
10.72
2.51
0.99
2.51
0.40
2.54
0.53
1.61
0.25
1.78
0.28
29.5
7.50
2.00
n.d.
0.71
15.34
6.55
0.14
2.39
6.23
3.29
2.70
0.17
n.d.
14.72
4.59
22.20
85.49
24.86
145.58
4.03
13.52
13.86
1.85
70.24
1.07
389.6
n.d.
n.d.
9.37
1.05
0.18
2.59
0.31
0.40
594.9
18.26
15.66
30.85
3.76
15.45
3.54
1.12
3.62
0.55
3.45
0.72
2.15
0.34
2.28
0.35
18.2
8.35
2.15
n.d.
0.65
10.89
3.53
0.09
1.87
2.79
2.47
2.98
0.20
n.d.
8.42
2.94
11.74
59.61
18.39
60.72
2.40
11.79
7.56
1.89
75.95
0.85
236.6
n.d.
n.d.
10.58
0.96
0.21
5.38
0.50
1.05
702.9
13.41
11.23
19.74
2.32
9.34
2.25
0.79
2.39
0.40
2.55
0.53
1.65
0.26
1.83
0.29
43.1
N8.84
2.37
n.d.
0.69
12.99
6.89
0.12
2.21
4.07
2.89
2.91
0.16
n.d.
12.02
4.07
276.61
67.91
25.72
119.92
3.93
14.10
11.24
1.70
68.21
0.94
318.2
n.d.
n.d.
9.14
0.95
0.19
3.59
0.38
2.18
607.1
14.30
12.69
22.79
2.66
10.38
2.48
0.94
2.58
0.42
2.66
0.56
1.72
0.28
1.88
0.30
55.0
N 9.15
2.06
n.d.
1.53
3.16
3.39
0.04
0.33
0.48
0.45
0.89
0.28
n.d.
6.34
2.48
129.62
41.72
11.16
109.11
3.91
8.45
2.96
1.11
23.57
0.29
127.5
n.d.
n.d.
7.12
0.80
0.27
8.00
1.00
0.95
539.9
3.53
5.93
8.72
0.84
2.99
0.65
0.19
0.71
0.11
0.65
0.14
0.44
0.07
0.50
0.08
42.0
2.87
0.80
n.d.
0.66
0.96
0.54
0.00
0.04
0.94
0.09
0.16
0.34
n.d.
bd.l.
1.31
12.47
25.93
14.49
21.20
1.38
5.42
1.19
0.97
11.51
0.15
64.6
n.d.
n.d.
5.06
0.91
0.71
22.42
4.25
1.67
450.0
1.55
3.71
5.00
0.49
1.90
0.37
0.06
0.35
0.05
0.30
0.07
0.21
0.03
0.23
0.04
42.4
1.65
0.60
n.d.
0.16
0.74
0.11
0.00
0.02
n.d.
0.08
0.13
0.05
n.d.
bd.l.
2.07
3.65
19.95
4.43
12.68
1.10
3.95
5.93
0.18
2.64
0.23
n.d.
n.d.
n.d.
1.71
0.63
0.23
7.06
1.79
0.31
403.7
1.90
4.47
11.82
1.70
7.37
1.37
0.30
0.92
0.11
0.56
0.10
0.26
0.03
0.18
0.03
37.5
0.62
0.20
84.41
0.92
2.36
1.38
0.01
0.14
9.38
0.26
0.62
0.46
9.40
11
4
3
12
n.d.
143
n.d.
4
n.d.
n.d.
29
n.d.
215
139
4
6
n.d.
n.d.
n.d.
n.d.
n.d.
543
4
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
3
n.d.
1
n.d.
1
n.d.
76
1
b d.l.
94.42
1.03
2.22
1.26
0.01
0.12
0.29
0.18
0.34
0.04
83.30
b d.l.
20
168
20
n.d.
54
n.d.
4
n.d.
n.d.
31
n.d.
45
282
5
19
n.d.
n.d.
n.d.
n.d.
n.d.
1141
17
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
b d.l.
n.d.
b d.l.
n.d.
18
n.d.
b d.l.
31
5
84.44
0.76
3.64
0.80
0.01
0.70
7.11
0.79
1.62
0.01
4.75
b d.l.
12
85
17
n.d.
72
n.d.
5
n.d.
n.d.
38
n.d.
229
304
6
17
n.d.
n.d.
n.d.
n.d.
n.d.
1160
24
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
2
n.d.
2
n.d.
10
n.d.
177
23
4
76.38
0.32
12.60
0.63
0.01
0.28
2.03
3.33
4.27
0.04
2.50
b d.l.
3
1
6
n.d.
5
n.d.
12
n.d.
n.d.
125
n.d.
215
320
8
11
n.d.
n.d.
n.d.
n.d.
n.d.
1006
11
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
3
n.d.
2
n.d.
1
n.d.
29
9
3
79.68
0.19
10.95
0.50
0.01
0.21
1.35
2.92
4.05
0.04
3.30
1
2
1
5
n.d.
4
n.d.
11
n.d.
n.d.
122
n.d.
203
305
7
12
n.d.
n.d.
n.d.
n.d.
n.d.
1030
10
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
2
n.d.
3
n.d.
1
n.d.
49
8
3
n.d.
0.24
5.25
0.60
0.02
0.23
5.91
1.25
1.88
0.02
n.d.
bd.l.
2.20
6.76
28.15
7.74
24.21
1.49
10.31
5.17
1.23
53.58
0.41
266.0
n.d.
n.d.
11.71
1.34
0.14
3.90
2.39
0.34
804.7
9.72
13.25
20.85
2.40
9.54
2.17
0.48
1.98
0.30
1.91
0.39
1.23
0.19
1.25
0.19
115.1
8.49
2.28
n.d.
0.42
10.96
1.45
0.03
0.59
7.69
2.73
3.13
0.09
n.d.
bd.l.
1.98
6.86
34.27
8.94
33.60
1.70
11.97
12.02
1.56
77.70
0.78
321.0
n.d.
n.d.
10.88
1.22
0.13
2.80
0.58
0.43
745.7
12.49
13.40
26.68
3.44
14.19
3.02
0.89
2.69
0.41
2.52
0.51
1.54
0.23
1.57
0.24
24.6
9.13
2.34
SiO2
TiO2
Al2O3
Fe2O3
MnO
MgO
CaO
Na2O
K2O
P2O5
LOI%
Co
Ni
Cu
Zn
Sc
V
Cr
Ga
Li
Cs
Rb
Be
Sr
Zr
Hf
Nb
Ag
Cd
Sn
Sb
Tl
Ba
Y
La
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
Pb
Th
U
Dam alteration transect
KV99801
KV99 and KV08-501a data from XRF, KV07 data from ICP-OES/MS, KV08-501b and 702 data from EMP.
KV08-501a = bulk, b = melt on plagioclase phenocryst.
175
176
Results section). Air and water temperatures were measured using a
type-K thermocouple. Discharge was estimated by measuring the
dimensions of the riverbed, and obtaining a flow rate by timing
bamboo floats passing a measured section of river. The time needed to
fill a fixed volume was used to estimate the discharge for smaller
springs. In 2009, we obtained more precise discharge measurements
using standard hydrological die-dilution and flow-meter techniques
(Palmer et al., submitted for publication). Water samples were
analysed at the Geochemical Laboratory of Utrecht University in
1999 and 2007, and Geoscience Laboratories of the Ontario Geological
Survey in 2009. Major element concentrations were determined by
ICP-OES and trace element concentrations by ICP-MS. A variety of
dilutions was used to cover the range of element concentrations in the
waters and to check for enhancement or suppression effects (none
were observed). Anions were analysed by ion chromatography in
1999 and 2009, and by ICP-OES in 2007. Arsenic and selenium were
analysed separately using a collision cell arrangement in the ICP-MS,
introducing 1 ml min− 1 He and 4 ml min− 1 H2 to remove Ar-dimer and
Ar–Cl mass interference.
4. Results
Table 1 lists the fluid composition, pH and temperature at the
various sample sites. pH values given were obtained by direct
measurement on 100 times diluted water (pH meas) and calculated
from water composition using the Pitzer model (pH calc). The latter
approach provides the best estimate of the activity of free H+ in
the solution (cf. Pitzer, 1973) and hence the true pH. However, this
value is a poor measure of the acidity, because a significant fraction of
the H+ is associated in these waters (mainly as HSO−
4 , calculated with
the Pitzer model using FactSage—Bale et al., 2002) and there is
therefore a large reservoir that supplies acid to the solution as free H+
is consumed during reactions with the host rocks. By diluting the
sample 100 times, this associated H+ is released and the measured pH
is therefore a more appropriate measure of the acidity of these fluids.
The fluid properties and compositions are similar to those reported by
Delmelle and Bernard (1994, 2000), Takano et al. (2004) and Löhr
et al. (2005), and the deviations are within the seasonal variability
observed by Sumarti (1998). The compositional differences observed
among years for the acid spring waters in our study are due to
different springs having been sampled every year. This is probably
also the reason for the differences with earlier works (cf. Delmelle and
Bernard, 1994, 2000; Takano et al., 2004). We have recognized 6 main
areas of discharge below the dam, as well as many smaller ones, and
these springs shift location and vary in discharge between years.
Despite this upstream variability, downstream compositions, as well
as lake water chemistry are remarkably similar among 1999, 2007 and
2009. Concentrations decrease from the crater lake downstream (with
the exception of Ti and Cu), whereas pH increases. Water temperature
closely follows air temperature except right at the spring outflow. The
precision of the results, as estimated from field and laboratory
duplicates is better than 5% for major elements and 10% for trace
elements, except for Be at 20% and Sb at 13%. Accuracy is better than
10% relative.
Bulk-rock compositions are reported in Table 2. The precision of
the XRF analyses as determined from laboratory duplicates is better
than 3% relative for the oxides and better than 6% for trace elements
above 5 ppm. Accuracy relative to BCR1, GSP1 and BHVO1 is better
than 5% relative for oxides and 10% for trace elements above 5 ppm.
For concentrations below 5 ppm, the combined accuracy and
precision is better than 80% relative. Precision for the 2007 analyses
is better than 10% relative, with the exception of Be, Sb and Li which
have an associated uncertainty of 20%, 13% and 12% respectively.
Accuracy is better than 10% relative as determined against ISE921. The
variability in glass compositions as determined from multiple
analyses is b15% relative for all cations except Mn at 50% and P at
25%. The Nb content of these glasses was estimated from the total
alkali—silica—Nb vector, which has an associated goodness-of-fit R2 of
better than 0.98 for all unaltered samples analysed.
5. The juvenile magmatic deposits at Kawah Ijen
The fresh magmatic deposits at Kawah Ijen are remarkably similar
in mineralogy and texture despite their large range in bulk
compositions, which extends from basalt to dacite, varying mainly
in the proportions of the constituent minerals. The phenocrysts are
concentrically zoned plagioclase and clino-pyroxene, titanomagnetite
with ülvospinel exsolution lamellae, and olivine in basaltic rocks.
These phenocrysts commonly cluster forming a glomero-porphyritic
texture. Ortho-pyroxene is also common, dominantly as a symplectitic intergrowth with magnetite after olivine. Olivine relicts are present
in andesite, but are invariably rimmed by ortho-pyroxene. A
phlogopite inclusion was found in one such olivine. The matrix
consists of glass with abundant microlites, aligned with a flow texture
around the phenocrysts. Apatite is abundant as an accessory phase in
the matrix and as inclusions.
The compositional variability of juvenile magmatic deposits is
shown in Fig. 2, in which Nb is used as a differentiation index. The
magmatic trend is remarkably regular, and extends from basalt to
rhyolite. The initial cone-building episodes of activity at Kawah Ijen
are restricted to basalt to andesite compositions, as are the large lava
flows, except for a dacite flow at the dam, whereas the compositions
of recent volcanic bombs and glasses (including those from the active
dome) extend to rhyolite. These trends are consistent with those
reported previously for the Ijen caldera complex as a whole (Sitorus,
1990; Handley et al., 2007), and reflect progressive fractionation of
olivine, clino-pyroxene, Ti-magnetite and plagioclase. Mingling
textures as well as the presence of glass veins in recent bombs,
however, also suggest an important role for mixing.
6. The effect of alteration on bulk-rock chemistry
Alteration at Kawah Ijen volcano is characterised by dissolution of
titanomagnetite and olivine, and replacement of glass, plagioclase,
and pyroxene by fine-grained silica devoid of other elements (see the
preceding contribution). This constitutes extreme chemical leaching
of these rocks, an observation that is borne out by the bulk-rock
chemistry of the altered samples, which display a strong decrease in
element concentrations relative to the unaltered magmatic precursors
(Fig. 2). In these diagrams, niobium is used as the alteration index
element as it displays the most conservative behaviour during
progressive alteration of Kawah Ijen magmatic deposits. It is expected
to reside dominantly in the ülvospinel based on its partitioning
behaviour (cf. GERM KD database—www.earthref.org), and this is
the most persistent phase during alteration (see the preceding contribution). It will also have an even stronger chemical affinity for
the Ti-oxide phase that develops upon alteration of the ülvospinel
(GERM KD database—www.earthref.org). The main alternative as an
alteration index would be Zr and the Zr:Nb ratio is indeed constant for
most of the altered samples. However, in the most intensely altered
samples the Zr:Nb ratio decreases, indicating removal of Zr from
the rock. Niobium is not conservative for all altered samples, as
is evident from the alteration transect collected at the dam. In
these samples, which represent the most strongly altered samples
identified at Kawah Ijen, the Ti-oxide lamellae also dissolve, thereby
releasing the Nb. No element showed conservative behaviour in these
samples.
The alteration trends display a marked divergence from the
magmatic evolution, with altered samples enriched in SiO2, TiO2, Zr,
Nb, Sn, Sb and Pb, and depleted in all other elements (Fig. 2).
Moreover, the changes in composition are consistent with progressive
alteration as evident in the in-situ Banyu Pahit transect sample suites.
177
Fig. 2. Compositional variability in unaltered (outlined by black ellipse) and altered samples at Kawah Ijen. Trends for two progressive alteration transects are marked with grey
arrows, and these generally show markedly different behaviour than the magmatic trend (e.g. Na2O). With the exception of Pb and Si, all elements are leached with progressive
alteration. Grey solid squares represent glass analyses, all other samples are bulk analyses. The uncertainty shown is the 1 standard deviation on the element and Nb as determined
from duplicate analyses.
Although only lava samples were measured, the other magmatic
deposits at Kawah Ijen, dominated by scoria, contain the same
minerals and textures as the lava samples. They also display identical
alteration textures and mineralogy, although the extent of alteration
is more pronounced due to porosity increasing the surface area, and
their commonly higher glass content. The chemical trends observed
for lava alteration should therefore apply equally to the other
magmatic deposits.
6.1. Alteration in the Banyu Pahit riverbed
The Banyu Pahit alteration transects provide the clearest picture of
the impact of alteration on bulk-rock chemistry. For both sample
suites, the composition of the fresh magmatic precursor has been
clearly established and predictably coincides with the intersection of
the alteration and magmatic trends (e.g. for Al2O3 and Na2O—Fig. 2b,
d). In the case of the dam suite, the precursor is a thin basalt flow
belonging to the cone-building stage of Kawah Ijen volcano, whereas
the andesite in the Banyu Pahit riverbed at the rapids represents a
large lava flow that descended through the valley. This flow is the
dominant bedrock in the Banyu Pahit river between the dam and
the waterfall at Watucapil and is further compositionally similar to
the majority of other unaltered material exposed in the river valley.
The alteration at the rapids is therefore taken to be representative of the
dominant alteration in the upstream part of the Banyu Pahit valley.
Additional altered rocks from the Banyu Pahit valley at the dam
show similar variations in bulk-rock chemistry to the sample suite at
the rapids, and extend the trend defined by the latter samples, in
agreement with textural observations that they are more altered. The
precursors of these samples are undefined as they represent loose
178
blocks in the river valley and the fresh magmatic deposits exposed on
the flanks and floor of the valley span almost the entire range of bulk
compositions from basalt to dacite. However, the strong chemical
affinity of sample KV99-850 (Nb = 6 ppm) to the alteration transect
at the dam indicates a common precursor, and a similar case can be
made for samples that plot on the trend defined by the rapids
alteration suite. The remaining samples define a trend that is mostly
parallel to the rapids alteration sequence, suggesting a more evolved
precursor.
Three trends are observed in the bulk-rock alteration of the rapids
suite (Fig. 2) corresponding to strong leaching, which is the dominant
process, enrichment, which is observed for SiO2, Sn, Sb and especially Pb
(from 10 to 260 ppm), and enrichment followed by depletion, which is
most obvious in K2O, Rb and Ba. For the most altered samples, leaching
even approaches completion for several elements (e.g. Al, Ca, Co and
Cu). This behaviour fits well with the textural and mineralogical
observations that indicate complete replacement of the rock by an
amorphous mass of silica. At the most advanced alteration stage,
dissolution of ülvospinel, and eventually the Ti-oxide that formed from
it, was also observed, and this is in agreement with the decrease in Ti and
Nb content found in the most intensely altered samples, including the
dam alteration suite. Precipitation of barite in these samples is reflected
in a higher Ba content compared to that of the general leaching trend.
6.2. Alteration of the ballistic samples
The altered ballistics exhibit a wide range of chemical behaviour in
agreement with strong variations in their texture, mineralogy and style
Fig. 3. Absolute changes in bulk-rock composition for the alteration transect at the Banyu Pahit rapids site anchored to the unaltered composition (solid square). With the exception
of Pb, Sn and Sb, all elements are progressively leached from the rock. A weighted least-squares best fit curve through these points is shown by the grey arrow. The error box
represents the 1 standard deviation uncertainty on the element and Nb normalization as determined from duplicates.
of alteration (see the preceding contribution). Samples containing Alsulphate precipitates are enriched in Al2O3 and the alkalis compared to
samples of equivalent alteration, and further show non-systematic
behaviour for many of the other elements. Loss of Nb also affected two
of the samples. The chemistry of these ballistics therefore does not
provide information on the alteration-induced changes in their bulk
composition.
The samples showing sulphidation of titanomagnetite during
alteration (see the accompanying contribution for more details) are
more consistent. For most elements, they plot within, or close to the
magmatic trend, suggesting only a limited modification of their bulk
chemistry during alteration. This is especially striking for Al2O3 and
Na2O (Fig. 2b,d), which are highly mobile in the other altered samples.
However, this limited chemical alteration of the rocks is in sharp
contrast to their mineralogy and textures, as they display intense
alteration of the matrix glass and phenocrysts, comparable to the
most altered samples in the rapids alteration suite. The absence of the
expected associated chemical leaching suggests that these samples
somehow retained their element load and were subjected to a
relatively closed-system alteration style. The inherited high Ti and Mn
content in pyrite after titanomagnetite (see the preceding contribution) supports such a limited chemical mobility scenario.
7. Element fluxes
7.1. Absolute changes in rock chemistry
The changes in bulk-rock chemistry as observed in the altered
rocks are (partially) controlled by residual enrichment effects as
progressively more elements are leached. To account for this residual
enrichment, we normalized the compositions of the rapids alteration
suite to its unaltered precursor using the respective Nb contents;
Cnormalised = Cmeasured ⋅
Nbprecursor
:
Nbsample
This procedure could not be applied to the other altered samples,
due to the absence of a conservative element (e.g. the dam alteration
suite) or uncertainty over the identity of their precursors.
Normalized compositions show that leaching completely dominates alteration and that the increasing concentrations of SiO2, TiO2,
K2O, Rb, Ba, Zr and Hf are, indeed, the result of residual enrichment
179
(Fig. 3). Only Pb, Sn and Sb show progressive absolute enrichment
during alteration, with Pb undergoing a 15-fold increase in concentration. In the case of Pb, this enrichment can be linked to the
precipitation of barite in the altered rock, which is saturated in the
river water as determined from thermodynamic calculations (Delmelle and Bernard, 2000; this work) and has been found to contain
up to 2.5 wt.% PbO (see Table 1 in the preceding paper). However, as
Ba is leached from the rock, the precipitation of barite must be limited
by another constituent, most likely Pb. The host phase accounting for
the elevated Sb and Sn content has not been identified.
The behaviour of the elements during progressive alteration varied
appreciably, with some being preferentially leached at an early stage
(e.g. Ca, Al2O3, Cu, Cs, Li, and REE), and others being retained up to the
final stages of alteration (K, Rb, TiO2, Zr, Hf, U, and Th). These
variations in the rate of alteration are linked to the dominant host
phase(s) in the original magmatic precursor. The incompatible
elements Li, Cs, Cu and the REE are enriched in the glass, which is
the first phase to be altered. An-rich plagioclase is altered subsequently, which explains the early, preferential release of Ca and Al.
The resistance of K and Rb is somewhat surprising, as these elements
are expected to reside preferentially in the glass. It is possible that the
alunite/jarosite precipitates that were observed in several of the
altered samples (Fig. 4d in the preceding paper) retain part of the K
and Rb content and this could explain the apparent resistance of these
elements to alteration. The late-stage leaching of Zr, Hf, U and Th
indicates that these elements are contained in a highly resistant
phase, most likely zircon, which was observed as an accessory phase
in the andesite. Similar behaviour is observed for TiO2, consistent with
the persistence of ülvospinel and Ti-oxide. The behaviour of P is
erratic, although it shows an overall gradual decrease with progressive alteration. This, together with textural observations, indicates
that apatite is not particularly resistant to alteration, but that its
breakdown, and associated P release, is mainly controlled by access of
the acid water to apatite inclusions.
The REE behave similarly during alteration with the exception of
Eu. Initial leaching of the REE is rapid, followed by a gradual decrease in
removal and retention of approximately 30% of the REE budget, due
probably to their residence in zircon, which resists alteration.
Europium, on the other hand, shows a continuous, nearly linear
decrease with progressive alteration. This produces a positive Eu
anomaly in the moderately altered samples and a strong negative Eu
anomaly in the most altered samples (Fig. 4a). The gradual release of
Fig. 4. Chondrite-normalized concentrations of the REE in the two alteration suites (a) and the resulting REE release from the initial to intermediate stages of alteration, the
intermediate to final stages of alteration and for complete alteration (b). Leaching of Eu initially lags behind, resulting in a small positive Eu anomaly in the moderately altered
material. Subsequent preferential leaching of Eu produces a strongly negative anomaly. The element input observed in the Banyu Pahit (solid black line in b) is most consistent with
complete alteration.
180
Eu in the early stages of alteration compared to the more rapid
leaching of the other REE is interpreted to be related to its more
compatible behaviour during crystallisation, by virtue of its preference
for a valence of two, and therefore a lower concentration of Eu in the
easily leached matrix glass.
7.2. Alteration element flux
To quantify the release of elements during progressive alteration,
the absolute concentration data were fit using a least-squares method,
weighted by the analytical uncertainty on individual values and
anchored to the composition of the precursor lava. This fit was then
used to calculate the composition of moderately and intensely altered
material (Nbi/Nb0 alteration index = 1.31 and 1.62 respectively). The
differences in composition between these two “end-members” and
the unaltered precursor allow us to calculate the absolute element
release or uptake associated with alteration from fresh rock to
moderately altered material (immature alteration), moderately to
intensely altered material (mature alteration) and the complete
alteration from fresh to intensely altered rock (Table 3). Fit values
were preferred over using actual samples, because of scatter relating
to heterogeneous preferred alteration along cracks, which could not
be excluded in bulk-rock analyses. It also allows an uncertainty to be
attributed to the element release/uptake reflecting the scatter around
the fit.
As discussed above, a reasonable assumption can be made about
the nature of the precursor of the majority of the altered samples in
the riverbed of the Banyu Pahit at the dam using their affinity to the
in-situ alteration suites. The resulting absolute element change
calculated for these samples is in excellent agreement with the fit
obtained on the rapids transect, indicating that the element release
and uptake values presented in Table 3 are representative of alteration
at Kawah Ijen. In contrast, the absolute change in composition
obtained for the sulphidised ballistics, assuming that they have a
similar precursor in terms of Nb content, is markedly different. The
limited change in Nb content suggests that alteration is immature,
which is in sharp contrast to the advanced alteration textures and
mineralogy of these samples. Furthermore, leaching is markedly less
pronounced for most elements compared to that observed in all other
samples, including for highly mobile elements such as Na and Al, and
no systematic host phase related behaviour is observed among
elements. This results in these samples mostly plotting within the
magmatic trend rather than showing alteration behaviour (Fig. 2). We
therefore conclude that these samples, which we propose are derived
from the hydrothermal system (see the preceding contribution), do
not reflect leaching masked by residual enrichment, but represent a
distinct style of alteration that is accompanied by insignificant
element release.
Table 3
Element release and uptake for immature, mature and complete alteration. Values in
ppm.
Si
Ti
Al
Fe
Mg
Ca
Na
K
P
Mn
Co
Ni
Cu
Zn
Sc
V
Cr
Ga
Li
Cs
Rb
Be
Sr
Zr
Hf
Sn
Sb
Ba
Y
La
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
Pb
Th
U
Full rock
Immature
Mature
Uncertainty
12,574
1608
83,961
40,117
15,561
44,314
24,396
16,193
894
1039
14.2
5.66
47.3
59.4
12.0
110.0
3.57
16.3
16.3
2.48
59.2
1.4
359.8
44.6
1.01
− 25.1
− 1.08
179.9
28.6
12.04
29.41
3.95
15.72
3.33
1.24
3.04
0.49
2.81
0.61
1.64
0.24
1.64
0.27
− 184.0
8.60
2.31
2711
962
56,868
28,686
10,106
31,918
15,466
2416
307
715
11.0
4.44
47.2
42.7
3.2
79.3
2.79
10.0
13.6
2.05
7.3
1.0
222.3
3.8
0.32
− 4.3
− 0.49
71.5
15.5
11.46
27.97
3.64
14.23
2.94
0.75
2.49
0.41
2.35
0.51
1.35
0.20
1.33
0.22
− 46.3
0.10
0.20
12,163
646
27,093
11,431
5455
12,396
8929
13,777
586
325
3.1
1.22
0.1
16.7
8.8
30.7
0.78
6.3
2.7
0.43
52.0
0.4
137.5
48.3
1.33
− 20.8
− 0.59
108.4
13.0
0.59
1.44
0.32
1.49
0.39
0.49
0.54
0.08
0.46
0.10
0.29
0.04
0.31
0.05
− 137.7
8.70
2.11
3414
903
4042
5925
1048
3749
1404
1270
130
68
1.7
0.78
5.7
8.4
1.3
23.1
0.23
0.9
0.7
0.15
8.2
0.1
18.9
7.7
0.25
1.5
0.06
19.4
2.4
0.90
2.16
0.28
1.22
0.25
0.05
0.25
0.04
0.21
0.04
0.12
0.02
0.11
0.02
14.0
0.87
0.32
To investigate whether changes in water chemistry are present
beyond those associated with dilution, we calculated the composition
of Banyu Pahit water at the rapids and Watucapil sample sites by
diluting upstream spring water with groundwater, using;
7.3. Changes in fluid chemistry
Downstream changes in the water chemistry of the Banyu Pahit
river from the lake to the waterfall at Watucapil are dominated by
dilution as is evident in the behaviour of the conservative components
Cl, F and SO4 (Table 1 and Delmelle and Bernard, 2000). The major
caveat in this assessment is that the river is not continuous from the
lake to Watucapil. Estimates of discharge show that seepage in the
area of the uppermost springs is significantly smaller than the
discharge at the third set of springs (2008 and 2009 observations).
It is therefore unclear whether the composition of the crater lake
water is representative of the principal source of waters in the Banyu
Pahit river. However, assuming that changes in water chemistry are
dominated by dilution and water–rock interaction, whether they
occur in the riverbed, or en-route to the surface, we can interpret the
water samples as one system.
Cpredicted = Cupstream ⋅
Asample −Agroundwater
Aupstream −Agroundwater
+ Cgroundwater ⋅ 1−
Asample −Agroundwater
Aupstream −Agroundwater
!
where A is the concentration of a conservative anion (F, Cl and SO4
were used as conservative anions and the mean Cpredicted was used in
further calculations. Values calculated from F, Cl and SO4 are highly
consistent). Calculations were performed for river water compositions obtained in 1999, 2007 and 2009, as well as a “preferred model”
that uses average compositions of spring and river water. Results for
different years are similar and for most elements within the
propagated compositional uncertainty. Subtracting the predicted
(i.e. dilution-corrected) composition from the measured composition
181
Fig. 5. Downstream changes in river water composition (black symbols) and predicted compositions from simple dilution (grey line). Concentrations decrease downstream, but
most elements are enriched in the river water compared to simple dilution (except for Pb, Sn and Sb) as a result of water–rock interaction.
reveals any additional changes in composition that would be the
result of water–rock interaction and mineral precipitation.
Results of these calculations show that there is a consistent
addition of elements to the river as it makes its way downstream,
most notably of aluminium, iron and the alkalis (Fig. 5). However,
lead, tin and antimony are significantly removed. This signature is
perfectly complementary to that observed for progressive alteration
of the rocks of the Banyu Pahit riverbed (Table 3), indicating that
water–rock interaction controls the dilution-corrected changes in
Banyu Pahit river water composition. The largest changes are
observed between the springs at the dam and the river at the rapids,
with only a minor change in composition being evident from the
rapids to the waterfall at Watucapil. This could reflect the drastic
change in river valley morphology at the rapids. Up to this point, the
Banyu Pahit descends rapidly through steep-sided valleys and
intersects a diversity of deposits ranging from lahars to scoria to
lava. In contrast, from the rapids to Watucapil, the river flows on top
of a lava flow in a broad valley with only a limited gradient, thereby
limiting its interaction with fresh material.
7.4. Water–rock interaction
Dilution-corrected changes in water chemistry show excellent,
complementary agreement in chemical signature with the signature
of element release during rock alteration, and this is consistent over
six orders of magnitude in concentration. Moreover, comparison of
the two signatures in a log–log plot (Fig. 6) yields the expected 1:1
relationship, within error, and this relationship has been maintained
for a period of at least ten years (i.e. from the initial fieldwork in 1999
to the most recent sampling in 2009). The agreement is observed both
for the elements leached from the rock, and, crucially, also for Pb, Sn
and Sb, which are added. Water–rock interaction therefore provides a
Fig. 6. Comparison of rock alteration element release versus the change in river water composition for the entire upstream Banyu Pahit (a), and the rapids to Watucapil sub-section
(b). Good agreement is observed for a wide range of elements and over 6 orders of magnitude in concentration. The best fit curve and its associated 1 standard deviation error
envelop are also shown.
182
better explanation for observed changes than simple rock dissolution,
because Sb, Sn and Pb would be released in the latter case. Good
agreement is also found for sub-sections of the river (e.g. the rapids to
Watucapil) although the small change in river water composition
leads to large uncertainty in the values (Fig. 6b). However, this part of
the river is important as it represents the best constrained section,
with the river flowing continuously on the same andesite lava flow
with no apparent major additional contributions of water. The
agreement in results for the various sections indicates that, aside
from dilution, alteration-related element release exerts the dominant
control on changes in the water chemistry.
A best fit is obtained between changes in water composition and
element release during total-rock alteration (R2 = 0.97), rather than
element release during immature or mature alteration. Furthermore,
the REE signature suggests against mature alteration as the dominant
contributor (Fig. 4b), whereas K deviates significantly for immature
element release. Given that the Banyu Pahit river flows over a riverbed
of highly altered material for its entire upstream length, this indicates
that fresh material must be added to the river continuously, as
otherwise a best fit with mature alteration would be expected. Such
continuous addition of material is, indeed, observed in the form of
common rock falls from the steep-sided canyons of the upstream
Banyu Pahit, as well as material washing into the river during rainfall.
The element that deviates most strongly from the trend in Fig. 6 is Ba.
This reflects saturation of the Banyu Pahit water in barite as discussed
above.
assumed that alteration products are continuously removed by
dissolution or erosion, 210 years of alteration would correspond to
1.1
approximately 2.5 +
− 0.8 m of valley incision downstream from the
4.5
rapids for a 3 m wide alteration zone, and 12.5 +
− 3.3 m in the upstream
section. Although such rapid incision could be true for the upstream
steep-sided sections of the river where it transects pyroclastic and
phreatic deposits, there is no evidence for incision on this scale into
the lava flows that make up most of the Banyu Pahit's riverbed. In fact,
historical photographs suggest that the river has not incised itself at
all into the andesite lava flow at the rapids in the last 100 years (e.g.
Kemmerling, 1921). For the downstream section, the river is confined
entirely to this lava flow and even a modest incision of 2.5 m is
incompatible with field observations. Furthermore, a mature alteration signature would be expected if a static or valley incision scenario
was to apply, because the riverbed would be primarily made up of
strongly altered material. In contrast, we find best agreement
between changes in rock and water chemistry for total-rock
alteration. We therefore conclude that most of the required rock
input is derived externally, from material falling and sliding into the
river from the valley slopes. There is abundant evidence that this is a
common process in the Banyu Pahit valley, with new slumps, slides
and rock falls observed every field season, some of which are tens of
metres wide. The predominance of steep valley walls in the river
section upstream of the rapids and the higher alteration rates in this
section of river also support this interpretation.
8. Lake water chemistry
7.5. Water–rock ratios and alteration rate
The slope in Fig. 6 defines the water–rock ratio of the alteration.
1119
Excluding Ba yields a rock- to water ratio of 2512 +
− 774 (median and
upper and lower inter-quartile range) for the Banyu Pahit river from
86
the rapids to Watucapil, and 234 +
− 63 for the full upstream section to
Watucapil when using the average water compositions for springs
and Banyu Pahit. Results for individual years are within error of these
values. These water–rock ratios are markedly different to those that
would be obtained for a model assuming simple dissolution of the
andesite (cf. Delmelle and Bernard, 1994). Using our most precise
measurement of Banyu Pahit discharge as determined at the rapids by
die-dilution and flow-meter measurements (46 ± 6 l/s—Palmer et al.,
submitted for publication), this translates to an alteration rate of 18 g
of fresh rock per second for the rapids to Watucapil, and 0.20 kg s− 1
for the full length of the upstream Banyu Pahit.
In the river section from the rapids to Watucapil, the Banyu
Pahit river flows continuously on a bedrock of andesite lava, and is
reasonably constant in its dimensions. The total length of the river
in this section is 6 km, and assuming a width of the altered riverbed
of 2 m and a thickness of the alteration zone in the bedrock of 10 cm
as observed in the field, the total volume of altered riverbed
equals 1208 m3, or 3.2 Gg when assuming an andesite density of
2660 kg m− 3 (Johnson and Olhoeft, 1984). This estimate of the altered
rock mass is a minimum value given that the riverbed contains
abundant boulders and rock fragments, which significantly increase
the surface area exposed to alteration. A similar assessment for the full
8.9 km of river from the dam to Watucapil, assuming a 2 m wide
alteration zone of 10 cm thickness, yields a total altered rock volume of
1772 m3, or 4.7 Gg. Based on this volume and the alteration rate
11
obtained above, we calculate that it would take just 6 +
− 4 years to
totally alter the riverbed of the Banyu Pahit to a depth of 10 cm from
3.5
the rapids to Watucapil and 0.8 +
− 0.5 years in the upstream section of
the river (uncertainties include the uncertainty on water–rock ratio
and a, generous, factor two uncertainty on altered rock mass in the
riverbed).
The above timescale does not agree with historical evidence,
which shows that this system has been stable for at least 210 years
(“Oudgast”, 1820; Hengeveld, 1920; Kemmerling, 1921). If it is
The composition of the Kawah Ijen crater lake is controlled by a
complex interplay between element input from volcanic gas, rock
alteration, rain- and groundwater, and output through mineral
precipitation, evaporation and seepage. Delmelle and Bernard
(1994) showed that the volcanic gas controls the anion input, and is
responsible for the singularly low pH in this system. On the other
hand, the cations are derived primarily from rock alteration, be it
directly or through an intermediate hydrothermal system. Groundwater and rain are important contributors of water. Their modelling of
the major element composition of lake water and Kawah Ijen andesite
suggests that approximately 60 g of rock are dissolved per kg of lake
water.
We have taken a similar approach to Delmelle and Bernard (1994),
but have included a much wider range of elements, and compared a
variety of Kawah Ijen lava compositions. Our results indicate that a
best fit is obtained for Kawah Ijen andesite lava (Fig. 7), with the
goodness-of-fit gradually decreasing towards more mafic compositions and rapidly towards more evolved material. Because the most
recent magmatic deposits of Kawah Ijen volcano, including the active
dome, progress towards rhyolite, this result indicates that the latter
material is not a major contributor to the chemistry of the lake water.
As discussed above, simple whole rock dissolution does not provide a
full description of water–rock interaction at Kawah Ijen. Given that
alteration of andesite best fits the lake chemistry, we can use the
alteration input derived from the Banyu Pahit riverbed and apply this
to the lake. A best fit is obtained for total-rock alteration, suggesting
that the addition of material to the lake is dominated by fresh rock.
Moreover, it is markedly inconsistent with an element input derived
from the alteration observed in the sulphide-bearing ballistics, in
particular in terms of Na and K the input of which is two orders of
magnitude lower than observed, and most of the trace elements that
are two to three orders of magnitude higher. We therefore conclude
that the dominant source of cations for the lake is alteration of its wall
rock, especially the material added to the lake in rock falls, which
occur daily. Based on this conclusion, the corresponding water–rock
ratio is 52.5 ± 2.3 g of fresh rock per kg of lake water, and this is highly
consistent for different parts of the lake, different years and over 6
orders of magnitude in concentration. Using this value, a conical shape
183
Fig. 7. Comparison of crater lake water chemistry with that of unaltered andesite lava
(sample KV99-75). There is excellent agreement over six order of magnitude in
concentration, between years (1999 and 2007), and between sample sites. The
elements depleted in the lake are incompletely released during alteration and mineral
precipitation, whereas the enriched elements are derived from the volcanic fluid input.
for the lake with 250 m average exposure from the lake level to the
cliff edge and a lower and upper diameter of 800 and 1000 m,
respectively, gives a slope erosion rate of 2.6 cm yr− 1. Although high,
such an erosion rate is not unreasonable for steep cliffs (Saunders and
Young, 1983; Hapke et al., 2007).
The use of the actual alteration element release removes the
depletion observed in Zr and Hf, because these are largely retained
during alteration. It does, however, produce an even stronger
deviation in Pb, Sn, and Sb, as these elements are sequestered during
alteration, but enriched in the lake water. As volcanic fluids are a
major contributor to the composition of the lake and account for its
high anion content, which cannot be derived from the rocks, they are a
likely source for these elements. Preliminary analyses of condensates
from the Kawah Ijen fumaroles collected in 2007 (van Hinsberg et al.,
in press) indicate that this source is indeed specifically enriched in Sb,
Pb and Sn. However, the relative concentrations of these elements do
not directly match their relative enrichment in the lake, and the
expected accompanying enrichment in Cu and Zn based on condensate data, is not observed. The remaining deviations in concentration
from the trend in Fig. 6 can be explained by mineral precipitation.
Cristobalite, anatase, barite and gypsum have been observed as
precipitates in lake sediment, and thermodynamic modelling suggests
additional saturation in covellite (Delmelle and Bernard, 1994, 2000;
our work).
These findings indicate that the lake water derives its cation
content principally from the material falling into the lake, rather than
from the hydrothermal system directly. This does not rule out a
contribution from the hydrothermal system, but simply shows that it
does not control the composition of the lake water. A cartoon of our
preferred model for the Kawah Ijen crater lake system is shown in
Fig. 8.
9. Conclusions and implications
Rock alteration at Kawah Ijen volcano by hyperacidic crater lake
and Banyu Pahit river waters is characterised by the near-complete
leaching of elements. The end-product of this alteration is a rock
dominated by silica, and developing porosity as silica itself is removed
during the final stages of alteration. These textural and chemical
features are typical of silicic alteration in high-sulphidation mineralizing environments. However, we do not observe the typical element
Fig. 8. Schematic model for Kawah Ijen crater lake system (subsurface modified after
Hedenquist and Lowenstern, 1994). Horizontal and vertical scales (in m) are correct for
surface topography, but the subsurface is schematic. The lake receives its water
dominantly from rain and groundwater, its anions from volatiles emitted by a magmatic
body at depth and its cations from rock falls. We assume a skewed hydrothermal system
due to dominant E to W groundwater flow from Merapi volcano.
association observed in high-sulphidation ores. There is indeed strong
preferential enrichment in Pb, Sn and Sb, but Cu, the characteristic
element in these ores, is leached. Water–rock interaction with highsulphidation hyperacidic fluids therefore does not appear to be able to
produce the associated ore deposits directly, despite producing the
characteristic alteration style. Instead, alteration and mineralization
appear to be decoupled, in agreement with results from ore element
fluxes in volcanic emissions (Hedenquist and Lowenstern, 1994).
Changes in river water composition are controlled by dilution with
neutral groundwater and water–rock interaction. The latter is
characterised by element addition, indicating that the Banyu Pahit
water is undersaturated with respect to most elements. Mass balance
calculations, as well as the lack of a mature alteration signature,
indicate that the majority of material being altered is derived from
fresh rocks falling into the river from the valley flanks, or being
washed in by rain. The same conclusion can be drawn for the crater
lake, which has a signature that is notably inconsistent with control on
cation chemistry by the hydrothermal system. This conclusion has
important implications in that it decouples the lake composition from
the magmatic–hydrothermal system beneath the lake in terms of
cations. This means that variations in the cation composition of the
lake cannot be used to monitor volcanic activity at Kawah Ijen.
Acknowledgments
This research was started as part of the Doctorandus degree of VvH
and KB at the Faculty of Earth Sciences, Utrecht University. We thank
Rudi Hadisantono, Guillaume Mauri, Stephanie Palmer, Nathalie
Vigouroux, and Glyn Williams-Jones for their help in the field and
184
discussions on the Ijen system, Paul Mason for insightful comments
and Pieter Vroon for help with XRF analyses. We further acknowledge
logistical support by the Volcanological Survey of Indonesia and
financial support from WOTRO, NWO, NSERC, and the Trajectum and
Amoco funds.
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Extreme alteration by hyperacidic brines at Kawah Ijen volcano, East

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