Hidrothermal Alteration Study of Tangkuban Perahu

Proceedings Indonesia International Geothermal Convention & Exhibition 2015

Jakarta Convention Center, Indonesia – August 19th – 21st, 2015

1

Hidrothermal Alteration Study of Tangkuban Perahu Craters, and Its Implication to

Geothermal Conceptual Model

Afy Syahidan ACHMAD 1, SURYANTINI

1,2, Arif SUSANTO

1, Astin NURDIANA

1

1 Geology Engineering Study Program, Faculty of Earth Science and Engineering, Institut Teknologi Bandung

2 Geothermal Engineering Study Program, Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung

[email protected], [email protected], [email protected], [email protected]

Keywords: alteration, advanced argillic, Tangkuban Perahu,

XRD, sulphur, crystobalite, tridimite, alunite, pyrite

ABSTRACT

Tangkuban Perahu is located in West Java, Indonesia. It is

active stratovolcano type which is still showing

hidrothermal activity. The main purpose of this study is to

determine the correlation between subsurface structure, and

the hidrothermal activity on the surface. Using topographic

map, SRTM images, and field observation, geological

condition and alteration area was mapped. Alteration

samples were analyzed trough petrographic analysis and X-

Ray Diffraction (XRD). Altered rocks in study area showing

white-yellowish white colour and texture changing variation

especially in hardness properties from softening to

hardening because of sillica and sulphur alteration.

According to mineral assemblages, alteration zone are

devided into two types, sulphur+crystobalite+tridimite±

pyrite zone and crystobalite+alunite zone. Whole mineral

assemblages generally indicate advanced argillic alteration

type with west-east alteration area orientation. Alteration

area distribution correlates with manifestations appearance

such as steam vents, fumarole, solfatar, steaming ground,

and warm to boiling pools. Most of the manifestations

appear in main crater; Ratu Crater and Upas Crater, and

parasitic craters; Domas Crater, Jurig Crater, Baru Crater,

and Jarian Crater. These manifestations indicate

permeability in subsurface which can be emerged trough

structural process from same orientation. Implication for

conceptual model is possibility that upflow distribution area

follow the west-east orientation trough geology structure

such as fault or joint created by magma vents. For further

study, geophysical method such as gravity and resistivity

can be required to find permeability zone pattern in

Tangkuban Perahu subsurface.

1. Introduction

Tangkuban Perahu is an active stratovolcano which is

located in West Java, Indonesia. Location is approximately

30 km northwards from Bandung City. Tangkuban Perahu

Volcano has high-entalphy, liquid-dominated geothermal

system (Ibrahim, et.al., 2015). This volcano has two main

craters in its summit that are Upas Crater and Ratu Crater.

Beside the main craters, there are one big parasitic crater;

Domas Crater, and three smaller parasitic craters; Jurig

Crater, Baru Crater and Jarian Crater.

Reconaissance study about Tangkuban Perahu Volcano

were carried out by Pertamina at 1970. During 2010-2011,

the Energy and Geoscience Institute “EGI”-USA, working

under a USTDA, awarded PT. Indonesia Power to took fluid

geochemical sampling, gas survey, and Magneto-Telluric

(MT) within range of 80 km2. Geothermal field development

of this area were divided into 3 exploration priority areas

that are P1, P2, and P3 (Ibrahim, et.al., 2015). This study

were carried out to support field data development,

particularly P3 area which is in the western part of the

volcano. Overall aim of this study is to support volcano

conceptual model development, and to determine the

suitable point for drilling exploration in P3 area (Figure 1).

2. Geological Setting

Tangkuban Perahu Volcano is a part of Sunda Volcanic

Arc. It was formed as a result of Indo-Australia plate and

Eurasia plate subduction that generated volcanic arcs

troughout Sumatra and Java. It is one of three great andesitic

Sunda Volcano body which caldera remnant can be observed

around Tangkuban Perahu Volcano. The present magmatic

activities are freatic – freatomagmatic eruption, whereas the

other two volcano bodies, Sunda and Burangrang, are not

showing any volcanic activities anymore (Nasution, et.al.,

2004).

Generally, Nasution, et.al., (2004) divided the

stratigraphy of Tangkuban Perahu Volcano into five major

units; Tertiary Sedimentary Basement, Pre-Sunda Volcanics,

Sunda Volcanics, Old Tangkuban Perahu Volcanics, and

Young Tangkuban Perahu Volcanics. Each unit had been

dated using 14C and arranged from older to younger.

Lithology of the research area generally consist of basaltic-

andesitic lava, tephra, and various grain size pyroclastics.

Two major linements can be observed in research area

and its surrounding (Figure 1). Approximately 22 km length

scarp slope were observed in the southern part of Tangkuban

Perahu Volcano with west-east orientation. It extending

from Gunung Palasari at the east to Cisarua at the west. It is

identified as Lembang Fault that formation related to

Pleistocene Sunda Volcano activities (van Bemmelen, 1949,

op.cit., Hendri, et.al., 2012). Other major fault was found in

the northeastern part of research area, specified in Ciater so

called Ciater Fault which was normal fault with northeast-

southwest orientation. It is featured with river valley

lineaments, abrupt slope lineament, and manifestations

spreading (Nasution et.al., 2004).

3. Methods

Research methods are began with literature study about

Tangkuban Perahu Volcano using prior publications, SRTM

images, and topographic maps. Furthermore, manifestations

and alteration zones in its volcanic area were mapped.

Mapping area consist of three big craters, those are Ratu

Crater, Upas Crater, and Domas Crater with some small

craters within. Some samples were taken and used for

laboratory analysis comprise of petrography and XRD

analysis. Analysis results were used to consider the

alteration zones as supporting data for mapping results.

mailto:[email protected]






2

4. Results

4.a. Manifestations

Manifestations that appeared in research area consist of

steam vents, fumarole, solfatar, steaming ground, warm to

boiling pools, and mud pools. Manifestations commonly

appear inside craters area despite some are found in the

outside (Figure 2). Generally, manifestation zones

distribution has west-east orientation. Rocks that surround

manifestation points are altered shown by changing of rocks

properties.

4.a.1. Ratu Crater, Upas Crater, and Baru Crater

Some manifestations are emerged as fumarole, solfatar,

and steaming ground in Ratu Crater and Upas Crater. Steam

and tephra colour changes into yellowish can be observed at

fumarole in Ratu Crater (Figure 2a). The fumarole

temperature ranging from 90 o – 100 o C (Saputra and

Suryantini, 2015). Some rocks colour were altered to white

because of steaming ground activity at southwestern of Upas

Crater (Figure 2b). There is fumarole manifestation remnant

that had been stopped steaming at the border area of Ratu

Crater and Upas Crater. There is also yellowish solfatar near

the border with non-altered in hardnes properties (Figure

2c). Active steaming ground was also appear at the border in

certain times and it was altered surrounding rocks into

blackish. This steaming ground emerge in the abrupt wall

about 6 m high that interpreted as fault between Ratu Crater

and Upas Crater (Figure 2d).

Steaming ground also appear at Baru Crater, parasitic

crater in the western wall of Upas Crate (Figure 2e).

Vegetation is absent, the steam is observable and sulphur-

smelling. Rocks from surrounding wall altered to white in

color properties.

4.a.2. Domas Crater and Jarian Crater

Fumarole, solfatar, steaming ground, warm to boiling

pools, and mud pools were found in the Domas Crater zone.

The highest manifestations intensity are emerged at the

western part of Domas Crater. Fumarole appear with solfatar

deposit around steam outgassing vent output. It has

temperature ranging between 70 o – 100 o C (Saputra and

Suryantini, 2015). The outgassing hole diameter is about 15

cm (Figure 2f). Rocks in the surrounding altered to

yellowish because of solfatara appearence. Steaming ground

emerge resemble a small hill that appear at the each end part

of minor fault in the crater (Figure 2g). Warm to boiling

pools and mud pools are emerged at the southwest area of

Domas Crater contiguously with diameter about 2,5 m

(Figure 2h). Boiling pools are in the temperature ranging

between 88o-92o C, whereas warm pools ranging between

54,8o - 68,1o C (Situmorang, 2012).

Jarian Crater is parasitic crater in the southeastern part of

Domas Crater. Fumarole, solfatar, and warm boiling pool

were found. Small warm pool outlet has diameter about 5

cm, and form small stream to eastern part of Jarian Crater

(Figure 2i). Warm boiling pools diameter are approximately

2 m.

4.a.3. Outside Area of Crater

Steaming ground emerged in southwestern part of Upas

Crater, particularly at post of the security and defense affair

department outside the crater. It is steaming but not showing

sulphur-smell, and still contain some vegetation at the

surface.

Figure 1. Tangkuban Perahu Map (Modified Saputra and Suryantini, 2015)



3

Figure 2. Tangkuban Perahu Manifestation and Alteration Map; and Photo



4

4.b. Alteration Zone

Alteration zone in the research are devided into two

types, sulphur+crystobalite+tridimite±pyrite zone and

crystobalite+alunite zone (Figure 2). Both of that zones are

distinguished according to its mineral assemblages. Whole

mineral assemblage indicate advanced argillic type common

alteration that featured by mineral assemblages as alunite,

crystobalite, and tridimite. That mineral assemblages are

obtained through field mapping, petrography analysis, and

XRD analysis comprehensively.

4.b.1. Sulphur+Crystobalite+Tridimite±Pyrite Alteration

Zone

This alteration zone are featured by secondary mineral

assemblages comprise of sulphur+crystobalite+tridimite±

pyrite. Sulphur, crystobalite, and tridimite are obtained

through XRD analysis (Figure 3), whereas pyrite is apparent

in the outcrop. Physical appearance of alteration rocks are

pale grey – yellowish grey, increasing of hardness,

increasing of the rock compactness, showing vuggy quartz

texture, and strong altered in the nearby manifestations area.

Alteration appeared in the Domas Crater area, ridge between

Ratu Crater and Upas Crater; Ratu Crater, Upas Crater, and

Baru Crater. This alteration zone spreading form relatively

west-east orientation which are interpreted as

manifestation’s activities effect.

The outcrops of andesite are altered and showing various

hardness changing from harder to softer in the northern part

of ridge between Upas Crater and Ratu Crater, KWU-01

observation point (Figure 4). Some part of the rocks are

showing yellowish grey, increasing of the hardness,

increasing of the rock compactness, and abit sulphur deposit.

The thin section indicate andesite with hipocrystalline

texture, strong altered, fenocryst (3%) consist of pyroxene,

plagioclase, 0,01 – 0,5 mm in size, entire plagioclase and

some pyroxene have been leached, groundmass (50%)

consist of volcanic glass, secondary mineral (17%) that

intensively leached (30%) and comprise of crystobalite,

anatase, and sulphur. Some volcanic glass are leached until

mineral trace on the parallel nicole is difficult to observed.

In the north part of ridge between Upas Crater and Ratu

Crater, KWR-11 observation point, there is volcanic breccia

that intensively altered. Breccia matrix comprise of fine –

coarse ash grain that color was changed become yellow,

whereas fragments were changed into grey. The rock

hardness and compactness are less (Figure 5). Volcanic

breccia, poorly sorting, open fabric, grains (30%) consist of

altered lithic fragment, 1 mm – 8 cm in size, angular –

subangular, lithic fragments are andesite and tuff, matrix

consist of volcanic glass, secondary minerals (70%) are

sulphur that change volcanic glass matrix, rocks are

intensively sulphur altered. Crystobalite is identified based

on XRD analysis result. From the intensive presence of

sulphur and altered grain by crystobalite, it can be

determined that the rocks are altered by high sulphur content

fluid and the grains previously had been altered by high

sillica content fluids.

This alteration zone was formed at the temperature

ranging between 20o – 50o C based on temperature plotting

table. Temperature range for each mineral are obtained

through reference from Morrison (1997). Alteration

temperature initial boundary determination is synchronized

with research area surface temperature, about 20o C. Last

boundary from temperature plotting is constrained by

tridimite at 50o C.

Figure 3. XRD analysis result

Figure 4. Photo and Petrography analysis

from KWU-01


from KWR-11



5

4.b.2. Crystobalite+Alunite Alteration Zone

This alteration zone are featured by the presence of

crystobalite and alunite. Altered rocks physical appearance

are white – grey, rock hardness variation from harder –

softer, increasing of the compactness, and showing vuggy

quartz texture. This alteration type appear in Domas Crater

area according to lithological description and field

observation.

Altered tephra color is grey – pale grey, rock hardness

and compactness are less observation point is JLD-11. There

are also grains that have texture resemble as clay minerals

(Figure 6). That lithological petrography analysis reveal

lithic ash tephra characteristics, clastic texture, well sorting,

close fabric, grains (7%) consist of pyroxene, plagioclase,

lithic fragment, crystal, 0,1 – 1,7 mm in size, angular –

subangular, almost entire grains were leached (77%).

Secondary minerals (16%) comprise of quartz, crystobalite,

anatase, alunite, and opaque minerals.

KWD-20 observation point is andesite outcrop that were

changed into white, the hardness and compactness are

unchanged (Figure 7). This alteration characteristic

differences are caused differences of lithology type that

altered. Andesite thin sections are featured by

hipocrystalline, hyalophyllitic, plagioclase and pyroxene

mineral traces, and trakhitic texture trace. Fenocryst

comprise of pyroxene, plagioclase, 0,04 – 1,4 mm in size,

were leached entirely, groundmass are entirely leached

plagioclase. Secondary minerals (15%) consist of quartz,

anatase, alunite, crystobalite, opaque minerals, that most of

were leached (85%). Predominantly leached fragments and

groundmass reveal that rocks were altered by high sillica

content fluid.

According to temperature plotting table, it can be

considered that the last alteration zone was formed at the

temperature ranging between 20o – 80o C (Figure 9).

Temperature range for each mineral are obtained through

reference from Morrison (1997). Alteration temperature

initial boundary is determined as research area room

temperature, and alteration temperature last boundary is

determined as the presence of secondary mineral,

crystobalite at 80o C.

4.b. Implication to Conceptual Model

Fumarole commonly emerged in upflow surface area

trough available permeability (Nicholson, 1993). It indicate

Ratu Crater, Upas Crater, and Domas Crater still included in

upflow zone because they have fumarole manifestation

inside. Crater, fumarole, and alteration zone which directed

to west – east indicate the presence of geological feature that

serve permeability with same orientation. The implication to

present conceptual model is upflow zone distribution that

may have same orientation with manifestation area

distribution (Figure 8).

The occurring of general alteration, advance argillic, can

support the formation of cap rock that have significance role

within geothermal system (Nicholson, 1993). Surface data

that show the absence of surface manifestation in the

western part of Tangkuban Perahu Volcano and fumarole

manifestations emergence in Baru Crater indicate that the

area likely have the heated fluid, yet cap rock layer have

been developed enough so steam could not reach the surface

in such like in the Domas Crater area, in the eastern side of

volcano. Warmer fluid which circulate subsurface may

located near the volcano because usually colder recharge

supply flew form caldera wall in high-entalphy system with

caldera (IGA, 2014).

5. Conclusions

Kesimpulan

Active surface manifestations in the research area

comprise of fumarole, solfatar, steaming ground, warm

to boiling pools, dan mud pools. That manifestations can

be found in the Upas Crater, Baru Crater, Domas Crater,

and Jarian Crater.


from JLD-11


from KWD-20



6

Hydrothermal alteration zone of the research area are

divided into 2 type according to mineral assemblages:

o Sulphur+crystobalite+tridimite±pyrite alteration

zone, alteration temperature ranging between 20o-

50o C

o Crystobalite+alunite alteration zone, alteration

temperature ranging between 0o-80o C.

Generally, hydrothermal alteration in the research area is

advance argillic that occur at low temperature and acid

pH.

There is geological feature subsurface which serve

permeability in Tangkuban Perahu Volcano with west-

east orientation, agree with manifestation and alteration

area distribution.

Acknowledgements

The first author would like to thank Institut Teknologi

Bandung, and Ms. Suryantini for the final project

scholarship support. This study also supported by ‘Program

Riset Desentralisasi Dikti 2014’.

References

Achmad, A.S., Geologi dan Studi Alterasi Hidrotermal

Gunungapi Tangkuban Perahu, Jawa Barat, Tugas Akhir

Program Sarjana Teknik Geologi, Fakultas Ilmu dan Teknik

Kebumian, Institut Teknologi Bandung (2015).

Hendri, R., Prabowo, B.S., Perdana, M., Korelasi Intensitas

Pola Kelurusan Tangkuban Perahu terhadap Keberadaan

Lokasi Manifestasi di Permukaan, Proceedings the 12th

Annual Indonesian Geothermal Association Meeting &

Conference, Bandung (2012).

Ibrahim, H.D., Artono, A.R.T., Triyono, S., Exploration

Dirlling on the TPGP Tangkuban Parahu Concession, West

Java, Indonesia, Proceedings World Geothermal Congress,

Melbourne, Australia (2015).

Morrison, K., Important Hydrothermal Minerals and Their

Significance, Geothermal and Mineral Services Division,

Kingston Morrison Limited (1997).

Nasution, A., Kartadinata, M. N., Kobayashi, T., Siregar, D.,

Sutaningsih, E., Hadisantono, R., Kadarstia, E.: Geology,

Age Dating and Geochemistry of the Tangkuban Perahu

Geothermal Area, West Java, Indonesia, J Geotherm. Res.

Soc. Japan, Vol. 26, No. 3 (2004), 285-303.

Nicholson, K.: Geothermal Fluid - Chemistry and

Exploration techniques, Springer-Verlag Berlin Heidelberg,

Berlin, ISBN 3-540-56017-3 (1993).

Saputra, M.P., Suryantini, A Correlation Study between

Volcanic Activities and Thermal Water Changes in

Tangkuban Perahu Hydrothermal Prospect, Jawa Barat,

Indonesia, Proceedings World Geothermal Congress,

Melbourne, Australia (2015).

Situmorang, J., Karakteristik Tanah Beruap di Kawah

Domas Tangkuban Perahu, Tesis Magister Teknik Panas

Bumi, Fakultas Teknik Pertambangan dan Perminyakan,

Institut Teknologi Bandung (2012).

Van Bemmellen, R. W.: The Geology of Indonesia. 2 edition

Martinus Nijhoff, Vol. 1 (1949).

Figure 8. Tangkuban Perahu Conceptual Model

Hidrothermal Alteration Study of Tangkuban Perahu

Documents

Transcript of Hidrothermal Alteration Study of Tangkuban Perahu