PDF 2003 Erwin Palimanan Jogja

8/6/2019 PDF 2003 Erwin Palimanan Jogja

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INTERNATIONAL CONFERENCE ON MINERAL AND ENERGY RESOURCES MANAGEMENT 2003

Yogyakarta, 2831 July 2003

NEW HYDROGEOLOGICAL DETERMINATION OF NORMAL AND

HOT SPRING COMPLEX AT CIWARINGIN G. KROMONG PESAWAHAN,

NORTH OF CIREMAI VOLCANO, WEST JAVA, INDONESIA

By

Deny Juanda P., Hendri Silaen, D. Erwin Irawan

[email protected];[email protected]; [email protected]

Laboratory of Hydrogeology, Department of Geology, Faculty of Earth Sciences and Mineral Technology

Institut Teknologi Bandung - Indonesia

Abstract

In North of Ciremai volcano (3078 meters) - West Java, Indonesia, many spring and hot springs arepresents at Ciwaringin - G. Kromong - Pesawahan Area. Base on field observation, there are 11 hot

springs at limestone aquifer, 2 hot springs at intrusive rocks aquifer, 8 normal springs at volcanic

aquifer, and 3 normal springs at intrusive rocks aquifer.

This study consists of 8 hydrochemical analysis (major elements) from 7 hot springs; 12

hydrochemical analysis from 12 normal springs; and 5 oxygen-isotope (18

O) analysis from 4 hot

springs and 1 normal spring. The methodology used are Piper Diagram, EC diagram,

geothermometric calculation, and isotopic method (Cl-vs

18O diagram).

The occurrence of normal and hot springs are controlled by different geological conditions.

Kromong spring zone is found in intrusive aquifer system and limestone aquifer system. Then

Ciremai spring zone exist in volcanic aquifer system. Normal springs are located at shallow

unconfined aquifer and discharge from fractured lava or porous media of weathering intrusive

rocks. Hot springs in PSB and PST are controlled by fault structure. While fractured intrusive rocks

control Bobos and Kedondong springs.

Water chemistry can be grouped in to 4 facies: Na-Cl/SO4, Na/Mg-HCO3, Ca-HCO3, and Na-

HCO3, consist of: Na-HCO3 and Ca-HCO3 facies (Normal springs), Na-Cl facies (hot springs:

PSB1, PSB2, PSB3 and PST1), Na-SO4 facies (hot springs: PST2), Na/Mg-HCO3 (hot springs:

Bobos and Kedondong).

Oxygen-18 isotope analyses indicates that the hot water is actually a mixing of meteoric water with

hot water. The influence of meteoric water is also shown by the decrease of hot spring flow rate in

dry season and the increase in rainy season.

The hot water is predicted from limestone aquifer of Cibulakan formation. The prediction is alsoproved by the result from geothermometry Na/K, which shows 200 m depth. The upward flow can

also drives oil droplets to surface as oil seeps.

Key words: hydrogeology, hot and normal spring, stable isotope18

O, oil seepage, structural and

stratigraphic controlled
mailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]


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1. BACKGROUND

The study of springs is still important to understand the complete hydrogeological settings of an

area. Normal temperature spring and hot springs can have a completely different hydrogeologicalcontrol. Nevertheless, they can present in short distance. In such condition, the hydrogeological

setting is always interesting to be detailed studied.

Fig 1. Location map of study area

2. GEOLOGICAL SETTINGS

Kromong area is Middle Miocene Parigi and Upper Cibulakan Limestone complex, which also

known as Kromong Limestone (Pringgoprawiro, et.al., 1977). These limestones are oil-bearing

formation and have been exploited at Jatibarang oil field. The maximum thickness of Kromong

Limestone does not exceed 200 m. Clay of Kaliwangu Formation (Cisubuh fm by Pringgoprawiro,

et.al., 1977) lies conformably on Parigi limestone. Limestone and clay sediment was intruded by

some Late Tertiary-Quaternary Andesitic and Dasitic intrusions (see fig 2). Southern part of area

study id dominated by volcanic product of Ciremai volcanoes, which consist of lava, volcanic

breccia, tuff, and laharic deposit. The area lies 9 to 22 km north of Mt. Ciremai (3078 m), West

Java.

Northeast and northwest trending faults and east-west axis fold is dominating the structure (Djuri,

1995). These structures are resulted from compressive tectonic and thrust faults system, which had

started since Pliocene. This thrust fault system has cut the oil bearing formation (Amril, et.al.,

1991).

Kromong Limestone is a karstic limestone; with some features of dissolution occur in the area. Hot

springs emerge from cavities as seen at PSB2 and PSB3 (as seen on fig. 3). The cavities are

probably caused by calcite or dolomite dissolution by hot water circulation. The cavities come asfracture or opening enlargement along bedding.

Palimanan

Majalengka

JavaSea

Arjawinangun

Kuningan

Waduk Darma

Cisanggarung River

Cilimus

CIREBONKromong

Cilutung River

Bongas

CiwaringinRiver

0 10 km

Ciremay3078


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The Kromong area has been developed as limestone source for cement industries up to now. At the

quarry locations some hot springs present. The hot springs have fluctuated discharge totally 2 l/sec

of groundwater (maximum), which also discharge traces of oil seeps in form of asphalt. Noticing

the condition, the hydrogeological setting is very interesting to be detailed observed.

Fig 2. Geological setting of study area (adapted from Djuri, 1995).


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Fig 3. Karstic feature is show at PSB 3 hot spring. Left photo took on March 2002. Right photo took on April

2002, after a short dry period.

3. PROBLEM

The most interesting problem is the genetic of hot springs, including:

Does the groundwater is part of meteoric water, formation water, or the mixing of the twotypes?

Where does the high temperature come from? How is the groundwater flow pattern in relation with the oil/gas seeps?All problems need a careful understand of the hydrogeological setting of the spring complex.

4. METHOD

The geological setting needs many approaches, from direct and indirect method (see fig 4). The

direct method consists of study previous research, which is in form of geologic and stratigraphic

data. Unfortunately, there are not many data in the study area. Authors have to refer to some data

outside the study area. The objective is to understand the macro geological settings, concerning

what is the aquifer and what is the impermeable layer. Another direct method is the potentiometric

surface mapping, based on springs data. The map will show the groundwater movement in the area.

The direct method is supported by indirect method, consisting of: hydrochemical test and isotopic

test. Hydrochemical test consists of the measurement of major element concentration (Ca2+

, Na+,

Mg2+

, K+, Cl

-, SO4

2-, HCO3

-). The isotopic test includes measurements of Oxygen-18 concentration.

The objective is to separate the genetic of groundwater, whether it is part of meteoric water,

formation water, or the mixing of the both types.

The laboratory results then plotted using the following diagram, plots, and equation: Piper diagram,

EC diagram, geothermometric equation, and standard isotopic plots. All of the analysis and the

interpretations are objected to find out:

The genetic of groundwater in the area: meteoric water, formation water, or the mixing of thetwo types.

The source of heat: from volcanic origin or formation origin. The groundwater flow pattern.


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Fig 4. Flowchart of the study. The study is divided in to 3 steps: pre-survey, field

survey, and post-survey

5. DATA

Based on field observation during September to Apr 2002, the author found 24 springs and 1 mud

pool. Springs are consisting of: 11 hot springs of limestone aquifer (temperature between 48 - 58oC), 2 hot springs of intrusive rocks aquifer (temp 31,5 - 36,5

oC), 8 normal temperature springs

(called normal spring later on) of volcanic aquifer (temp 21,4 - 23,3oC), and 3 normal springs at

intrusive rocks aquifer (temp 26,8 - 28,3oC) (see table 1).

Moreover, from spring discharge data, on the period of August 2001 - September 2001, there were

only 2 hot springs with low discharge (


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Table 1. The distribution of spring data and observation results

No. Name Location Date Altitude(m)

Temp(

oC)

Color Smell Media Litology

1 MaP-1.1Pabrik Semen

Barat (PSB) 110 Sept 2001 50 48 Colorless Odorless Fracture Limestone

2 MaP-1.2 PSB 2 10 Sept 2001 50 49 Whitish Odorless Fracture Limestone

3 MaP-1.3 PSB 3 29 Mar 2002 50 50 Colorless Odorless Fracture Limestone


5 MaP-1.5 PSB 5 29 Mar 2002 50 41,5 Colorless Odorless Fracture Limestone


7 MaP-1.7 PSB 7 5 Apr 2002 50 58 Colorless Odorless Fracture Limestone

8 MaP-1.8 PSB 8 19 Apr 2002 50 54 Colorless Odorless Fracture Limestone

9 MaP-2.1Pabrik Semen

Timur (PST) 1

10 Sept 2001 37,5 38,2 Blackish Sulfur Porous Limestone

10 MaP-2.2 PST 2 10 Sept 2001 37,5 37 Whitish Sulfur Porous Limestone

11 MaP-2.3 PST 3 10 Sept 2001 37,5 - Yellowish Sulfur Porous Limestone

12 Mud pool Cipanas 11 Sept 2001 100 31,5 Brown milk Oil - Limestone

13 MaP-3 Bobos 11 Sept 2001 150 36,5 Colorless Peroxide Fracture Intrusive rock

14 MaP-4 Kedondong 09 Oct 2001 150 36,5 Colorless Peroxide Fracture Intrusive rock

15 Ma-1 Telagaherang 26 Sept 2001 150 23,2 Colorless Odorless Fracture Lava

16 Ma-2 Bojong 26 Sept 2001 175 24 Colorless Odorless Fracture Lava

17 Ma-3 Telaga Remis 26 Sept 2001 225 21,4 Colorless Odorless Fracture Lava

18 Ma-4 Telaga Nilam 26 Sept 2001 187,5 23,3 Colorless Odorless Fracture Lava

19 Ma-5 Telaga Cicerem 03 Oct 2001 312,5 22 Colorless Odorless Fracture Lava

20 Ma-6 Telaga Pancar 03 Oct 2001 400 22,2 Colorless Odorless Fracture Lava

21 Ma-7 Cikejayaan 03 Oct 2001 400 21,8 Colorless Odorless Fracture Lava

22 Ma-8 Cibujangga 03 Oct 2001 437,5 23,2 Colorless Odorless Fracture Lava

23 Ma-9 Kedondong 1 09 Oct 2001 150 28,3 Colorless Odorless Porous Intrusive rock

24 Ma-10 Gunung Jaya 10 Oct 2001 250 26,8 Colorless Odorless Porous Intrusive rock

25 Ma-11 Kedondong 2 24 Mar 2002 125 27,5 Colorless Odorless Porous Intrusive rock

6. ANALYSES AND INTERPRETATION

6.1 Potentiometric mapping

There are two spring zones: Ciremai spring zone and Kromong spring zone. For Ciremai spring

zone, groundwater flows northward. This flow direction is follows the slope of Mt. Ciremai. Water

flows out trough fracture in andesitic - basaltic lava with high discharge, up to 170 l/sec at

Cibujangga springs (IWACO, 1990). Rainfall, which measured at 3 rain gauge stations, is ranging

from 1500 to 3000 mm/year (PWD, 2003). There is no data about relation between fluctuations of

springs discharge to fluctuation of rainfall. The flow is interpreted as regional flow from Mt.

Ciremai.

For Kromong spring zone, all normal springs occurs in weathering zone of andesitic - dasitic

intrusion. Water flows out with low discharge (


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and high discharge. The second (Kromong zone) is intrusive rocks aquifer characterized by local

flow and low discharge. Topographically low land area and impermeable strata of Kaliwangu

Formation separate both aquifer systems.

Table 2. The distribution of physical and chemical properties of water

No. Type Location Alt (m) DateTemperature

of air (oC)

Temperature

of water (oC)

pHDHL

(S)

Discharge

(L/sec)

1 Hot spring PSB 1 50 10 Sep 2001 31,6 35,5 8 - 0,1

2 Hot spring PSB 2 50 10 Sep 2001 29,4 33,8 8 9300 0,1

3. Hot spring PSB 1 50 29 Mar 2002 32 48 7 - 0,3

4. Hot spring PSB 2 50 29 Mar 2002 32 49 7 12350 0,2



7. Hot spring PSB 5 50 29 Mar 2002 32 41,5 7 - 0,15

8. Hot spring PSB 6 50 29 Mar 2002 32 49 7 8960 0,1

9. Hot spring PSB 7 50 5 Apr 2002 30,5 58 7 14100 0,3

10. Hot spring PSB 8 50 19 Apr 2002 29 54 7 - 0,2

11. Hot spring PST 1 37,5 10 Sep 2001 31,8 38,2 7 17130 0,05

12. Hot spring PST 2 37,5 10 Sep 2001 31,8 37 7 10730 0,05

13. Hot spring PST 3 37,5 10 Sep 2001 - - - - 0

14. Mud pool Cipanas 100 11 Sep 2001 30 31,5 2 7490 0

15. Hot spring Bobos 150 11 Sep 2001 28 36,5 6 835 0,35

16. Hot spring Kedondong 150 09 Oct 2001 29 37,2 6 1103 0,2

17. Hot spring Kedondong 150 5 Apr 2002 29 36,5 6 - 0,2

18. Normal spring Tlg Herang 150 26 Sep 2001 28,6 23,2 6 108 -

19. Normal spring Bojong 175 26 Sep 2001 29 24 6 118 -

20. Normal spring Tlg Remis 225 26 Sep 2001 30,8 21,4 6 133 -

21. Normal spring Tlg Nilam 187,5 26 Sep 2001 31,9 23,3 6 139 -

22. Normal spring Tlg Cicerem 312,5 03 Oct 2001 26,7 22 6 137 -

23. Normal spring Tlg Pancar 400 03 Oct 2001 32 22,2 6 159 -

24. Normal spring Cikejayaan 400 03 Oct 2001 26,3 21,8 6 146 -

25. Normal spring Cibujangga 437,5 03 Oct 2001 28,1 23,2 6 144 -

26. Normal spring Kedondong 1 150 09 Oct 2001 30,7 28,3 7 165 0,25

27. Normal spring Gunung Jaya 250 10 Oct 2001 29 26,8 6 136 0,2528. Normal spring Kedondong 2 125 24 Mar 2002 29 27,5 7 128 0,5

6.2 Temperature

The temperature of hot springs is ranging from 31,5 to 58oC (see table 2). Such temperature is

much higher compared to normal springs, which is ranging from 21,4 to 28,3oC.

From fig 5, analysis on 27 temperature data on 24 springs and 1 mud pool shows 13 hot springs (17

observations) in hyperthermal area (PSB1-8, PST1-3, Bobos springs, and Kedondong Springs), 6

springs in mesothermal, and 5 springs in hypothermal area. PST and PSB spring group of Kromong

zone are located at north of Kromong (50 masl-meter above sea level). Bobos spring and

Kedondong spring are located at southeast of Kromong (150 masl).


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facies: Na-Cl/SO4, Na/Mg-HCO3, Ca-HCO3, and Na-HCO3. Normal springs are included to Na-

HCO3 and Ca-HCO3 facies; while hot springs are included to Na-Cl facies (PSB1, PSB2, PSB3 and

PST1), Na-SO4 facies (PST2), Na/Mg-HCO3 (Bobos and Kedondong).

From Schoeller diagram (see fig 7) it can be seen that almost all of the hot water data contain

cation more than 10 meq/L. Sodium is the dominant cation with the amount more than 10 meq/L.

on the other hands, magnesium and calcium are dominate amount of cation in cold water from

volcanic aquifer. The occurrence of high sodium and potassium could be used to distinguish hot

spring in intrusive rock aquifer system and limestone aquifer system (Kromong zone) from

volcanic aquifer system.

High contents of HCO3 in normal springs caused by high influence of meteoric water and indicate a

short period of water flow. High contents of Ca in those springs are caused by reaction of water

with Ca-plagioclase mineral of andesitic to basaltic lava. While high contents of Na is due to

reaction between water with Na-plagioclase of andesitic to dasitic intrusive rocks.

Table 3. Chemical measurements

Ion Na K Ca Mg HCO3 Cl SO4

Location mg/l meq/l mg/l meq/l mg/l meq/l mg/l meq/l mg/l meq/l mg/l meq/l mg/l meq/l

Tlg. Herang 5,29 0,23 3,81 0,10 12,6 0,63 2,15 0,18 67,5 1,11 2,86 0,08 0 0

Bojong 5,82 0,25 3,99 0,10 11,1 0,55 4,33 0,36 67,7 1,11 4,8 0,14 0 0

Tlg. Remis 6,35 0,28 4,57 0,12 14,0 0,70 4,22 0,35 86,3 1,41 2,38 0,07 0,48 0,01

Tlg. Nilem 6,39 0,28 3,88 0,10 14,0 0,70 4,22 0,35 85,6 1,40 2,86 0,08 0,48 0,01

Tlg. Cicerem 5,82 0,25 4,68 0,12 13,3 0,66 3,85 0,32 82,8 1,36 2,38 0,07 2,99 0,06

Tlg. Pancar 6,70 0,29 4,45 0,11 14,8 0,74 5,93 0,49 98,0 1,61 2,38 0,07 0,48 0,01

Cikejayaan 6,17 0,27 4,67 0,12 14,0 0,70 6,37 0,52 85,8 1,41 1,90 0,05 4,02 0,08

Cibujangga 6,00 0,26 4,98 0,13 14,8 0,74 3,78 0,31 79,9 1,31 2,86 0,08 1,97 0,04Kedondong 1 22,76 0,99 3,10 0,08 10,40 0,52 3,91 0,32 110,0 1,80 4,80 0,14 2,48 0,05

Gn. Jaya 15,68 0,68 3,34 0,09 8,87 0,44 6,52 0,54 85,8 1,41 7,70 0,22 6,72 0,14

Kedondong 2 15,50 0,67 2,40 0,06 10,1 0,50 1,07 0,09 57,6 0,94 3,57 0,10 0 0

PSB 2 1800 78,3 121,8 3,11 29,6 1,48 33,02 2,72 1104 18,09 2438 68,77 57,99 1,21

PST 1 3900 169,9 230,4 5,89 29,6 1,48 24,5 2,02 1233 20,21 5095 144 35,97 0,75

PST 2 1992 86,65 143,0 3,66 59,15 2,95 40,6 3,34 1311 21,49 2897 81,7 4755 99,0

Bobos 86,72 3,77 7,01 0,18 44,4 2,22 18,9 1,55 452,3 7,41 10,6 0,30 0,48 0,01

Kedondong 70,60 3,07 5,55 0,14 78,4 3,91 60,8 5,00 845 13,34 5,76 0,16 0 0

Mud pool 1500 65,25 98,0 2,51 149 7,44 181 14,89 0 0 93,94 2,65 6128 128

PSB 2 2429 106 199 5,09 108 5,40 23,0 1,89 1266 20,75 2461 97,62 123 2,57

PSB 6 1639 71,29 142 3,63 81,2 4,05 69,1 5,68 1083 17,75 2548 71,87 140 2,91

PSB 7 2644 115 226 5,78 77,8 3,88 35,3 2,90 1405 23,03 4009 113 167 3,48

The abundant of travertine deposit that found in PSB area indicates occurrence of high CaCO 3 inhot water. This deposit is originated from limestone aquifer dissolution. Since the calcium

precipitate due to cooling process, sodium becomes the dominant ion in the hot water. Sodium is

only very minor in carbonate rocks, but in clay is the major component. It is possible if hot water

passes through shale layer of Upper Cibulakan Formation before enter the Parigi limestone. High

chloride in PSB and PST hot water indicates an intensive influence of evaporites, which occurs in

carbonate or shale aquifer. High chloride is also show that meteoric water near surface has

penetrated to significant depth.

The Bobos and Kedondong hot spring are classified as an HCO 3-type hot spring. High contents of

bicarbonate in these springs caused by high influence of meteoric water and also indicates a quite

short distance flows. Mud pool, which contain sulfuric-gas seep near Cipanas village classified asSO4-Cl-type water. High sulfur in this water caused by oxidation of gas seep by water in the pool.

Due to occurrence of Ciremai volcanism, Kromong intrusion, and hydrocarbon bearing layer, there

are two options to the source of this gas-seep: volcanic gas or hydrocarbon gas.


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Fig 7. Piper and Schoeller diagram

Schoeller Diagram (modified)

0.00

0.01

0.10

1.00

10.00

100.00

1000.00

Na K Ca Mg HCO3 Cl SO4

Cation - Anion

Concentratio

n(meq/L)

Tlg HerangBojongTlg Remis

Tlg NilemTlg CiceremTlg PancarCikejayaanCibujanggaKedondong 1Gn JayaKedondong 2PSB 2PST 1PST 2BobosKedondongMudPool KedPSB 2PSB 6PSB 7

Piper Diagram


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6.5 Concentration of O18

The range of18

O concentration of hot water is -7,42 to -3,18 (see table 4). The results are fairly

higher than the

18

O concentration from normal spring water (-7,96). This result can be theimportant clue to the hydrogeological setting.

Table 4. Ratio of chloride and oxygen-18 isotope

No. Location 18O (o/oo) Cl (meq/l)1 PSB 2 -4,7 97,62

2 PSB 6 -5,37 77,67

3 PSB 7 -3,18 113

4 Kedondong -7,42 0,3

5 Kedondong-2 -7,96 0,1

Fig 8 shows the plots between18

O

concentrations vs. chloride concentration. The plots show a goodcorrelation between the 2 parameters. This means that the enrichment of chloride have relationship

with enrichment of oxygen-18 isotope.

Fig 8. Chloride versus O-18 isotope diagram

Enrichment in18

O caused by isotope exchange with the aquifer rock. Waters from carbonate rocks

having originally 18

O between 20 - 30o/oo (Hoefs, 1987). High temperature and low water/rock

ratios causes shifting the oxygen concentration of water. Mixing of meteoric water with this kind of

water produce enrichment of18

O as occur at PSB 2, 6, and 7.

While in Kedondong hot spring, the oxygen shifting much smaller than in PSB springs. Smaller18

Oshifts accompany with hydrothermal alteration and high water/rock ratios in hydrothermal system

Relation of18

O isotope vs chloride

Kedondong

Kedondong2

PSB-6

PSB-2

PSB-7

0.0

0.1

1.0

10.0

100.0

1000.0

-10 -8 -6 -4 -2 0

18O isotope contents (

o/oo)

Chlorideconcentration(meq/L)

18O enrichment

Cl enrichment

Cl and 18Oenrichment


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(Hoefs, 1987). Evidence of alteration at intrusive rocks in this area is shown in the form of white

colored intrusive rocks and formation of secondary mineral.

6.6 Geothermometer calculation

Based on geothermic calculation of Na/K concentration, the temperature of heat source is varying

between 130220oC (see table 5). This temperature range indicated that the heat source occurred

from 50 up to 200 meters of depth.

Table 5. Geothermometric results

Calculation PSB-2 PST-1 PST-2 Bobos Kedondong PSB-2 PSB-6 PSB-7

Na + 1800 1992 3900 86,72 70,60 2429 1639 2644

K + 121,80 143,00 230,40 7,01 5,55 199,00 142,00 226,00

Ca2+ 29,60 59,15 29,60 44,40 78,40 108,20 81,20 77,80

SiO2 40,38 20,88 41,72 31,45 40,35 49,75 33,80 29,30T (SiO2,

oC) 94,143 70,396 95,404 84,767 94,114 102,355 87,421 82,197

T (Na/K; Fournier, oC) 185,641 190,124 175,665 199,398 197,186 200,469 204,988 203,889

T (Na/K; Truesdell, oC) 148,967 154,382 137,036 165,686 162,977 167,002 172,570 171,213

T (Na/K; Giggenbach,oC) 202,939 207,162 193,515 215,873 213,798 216,878 221,109 220,081

T (Na-K-Ca, oC) 43,765 35,139 54,151 -3,823 -13,842 31,712 31,346 39,732

Temperatures of heat source between 193 220oC Na/K are resulted from the geothermometry

calculation (Giggenbach method). Due to cooling process, silica geothermometry analysis produce

lower temperature than Na/K geothermometry result. By using the boiling point versus depth

curves for Na-Cl water, Na/K temperatures indicate the depth of hot water system is less than 200

meter under the surface. This system depth lowers chance of magmatic or volcanic activities as

heat source.

7. THE INPUT-OUTPUT SYSTEM OF GROUNDWATER IN NORTH KROMONG CASE

Based on the geological data, Kromong limestone takes part as the aquifer, while the hydrologic

boundary consist of Cisubuh clay, Cibulakan clay, and Kromong intrusive rocks (see fig. 9). The

Kromong limestone aquifer is consisting of two parts. The upper part is Parigi limestone, which is

overlain by Cisubuh clay and underlain by Cibulakan clay. The lower part is Cibulakan limestone,

which is overlain and underlain by Cibulakan clay. This stratigraphic form enables the occurrence

of a local recharge - discharge system.

As described above, the number and water discharge of hot springs in this area is decreasing as the

rainfall drops. Another facts, water temperature also rises in rainy season (from 35oC in dry season

to 58oC in rainy season). The increasing of volume of recharge-discharge water and reducing

travel time of water flows to the surface can raise the water temperature. These facts are interpreted

caused by the high dependency of the hot springs to rainfall. Based on the geothermometry

calculation, the depth of hot water system is 200 m below the surface. This depth is interpreted as

the other reason of fluctuation of hot water discharge. Percolate rainwater are not flows in long-

time and long path to reach the hot water system. The fluctuation also interpreted as result of karst

feature at some springs.

Oxygen-18 isotope analysis indicates mixing of meteoric water with water from limestone aquifer.

This process causes increasing concentration of bicarbonate in PSB and PST hot waters. And so,low sulfate in water indicates low influence of magmatic fluids. Hot water system suppose to takes

place in Kromong limestone, which is consist of Parigi and Cibulakan limestone layer. Chemical

analyses indicate the occurrence of hot water flow from Cibulakan limestone through Cibulakan


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clay to Parigi limestone. This process causes increasing of concentrations of chloride in hot water

of PSB and PST springs.

Fig 9. Sub surface cross section

There is no possibilities or indication of presence of regional flow to the hot water system. Heat

source is interpreted occurs at clay of Cibulakan formation due to the depth of the layer. Northward

and northwestward fault and also its subsidiary fractures are believed to be main conduit of hot

water to the surface. Subsequently for hot springs, O18

, Cl-, EC, and HCO3

-values increase, which

are accompanied by oil seepages from Parigi limestone formation. This condition is interpreted due

to groundwater flow in oil-bearing aquifer. The oil droplet probably resulted from action of hot

water or steam to this aquifer system, which is known at Jatibarang oil field as formation.

Parig

ifm.Ci

subu

hfm.

Cibu

lakan

fm.

PSB2

PSB6

PSB7Oilseep

Subsurface Cross SectionNorth Kromong Area

.

(no scale)

G. Picung254 m

++

++

+

+ ++

150 m

200 m

100 m

50 m

0 m

-50 m

-100 m

-150 m HEAT SOURCE

?


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8. CONCLUSIONS

1. The occurrence of normal and hot springs are controlled by different geological conditions.Kromong spring zone is found in intrusive aquifer system and limestone aquifer system. ThenCiremai spring zone exist in volcanic aquifer system. Normal springs are located at shallow

unconfined aquifer and discharge from fractured lava or porous media of weathering intrusive

rocks. Hot springs in PSB and PST are controlled by fault structure. While fractured intrusive

rocks control Bobos and Kedondong springs.

2. Water chemistry can be grouped in to 4 facies: Na-Cl/SO4, Na/Mg-HCO3, Ca-HCO3, and Na-HCO3, consist of: Na-HCO3 and Ca-HCO3 facies (Normal springs), Na-Cl facies (hot springs:

PSB1, PSB2, PSB3 and PST1), Na-SO4 facies (hot springs: PST2), Na/Mg-HCO3 (hot springs:

Bobos and Kedondong).

3. Oxygen-18 isotope analyses indicates that the hot water is actually a mixing of meteoric waterwith hot water. The influence of meteoric water is also shown by the decrease of hot spring

flow rate in dry season and the increase in rainy season.

4. The hot water is predicted from limestone aquifer of Cibulakan formation. The prediction isalso proved by the result from geothermometry Na/K, which shows 200 m depth. The upward

flow can also drives oil droplets to surface as oil seeps.

9. REFERENCES

Adnan A., Sukowitono, and Supriyanto, 1991 , Jatibarang Sub Basin A Half Graben Model in

The Onshore of Northwest Java, Proceedings Ind. Petr. Ass. 20th

, page 279297.

Bowen, R., 1989, Geothermal Resources, Elsevier Science Publisher, New York, page 117 182.

Djuri, 1995, Peta Geologi Lembar Arjawinangun Skala 1: 100.000, Geological Research andDevelopment Centre, Bandung, 1 sheet.

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