GeoL. Soc. MaLaYJia, BuLLetin 42, December 1998; pp. 119-128

Geophysical investigations of the hot spring occurrences in the Sungei Serai and Kampung Dusun Tua areas, Hulu Langat,

MOHD ANuAR MD. RAZALI

Jabatan Penyiasatan Kajibumi Peti Surat 1015 Jalan Sultan Azian Shah 30820 Ipoh, Perak

Abstract: At the request of the Director, Geological Survey Department of SelangorlW. Persekutuan, two geophysical surveys using regional gravity and transient electromagnetic (TEM) techniques were carried out at Hulu Langat area and Sg. Serai, Selangor. The objectives of the survey were to delineate major geological structures that may be associated with the occurrences of the hot springs in the area. The regional gravity survey detected two major faults along part of Sungai Langat and Sungai . These faults created a fractured zone. This fracture zone provided a conduit for the hot spring to seep through. The TEM results indicate the presence of two conductive zones which are attributed to fractures within the bedrock. Future physical development at the sites should be implemented away from these conductive zones to avoid potential interference to these structures which have been identified as the pathways of the hot springs. Abstrak: Atas permintaan Pengarah Kajibumi SelangorlW. Persekutuan, dua survei geofizik dengan menggunakan kaedah graviti rantau dan 'transient elektromagnetic (TEM)' telah dilaksanakan di sekitar kawasan Hulu Langat dan Sg. Serai, Selangor. Objektif survei ini ialah untuk memetakan struktur geologi yang berkaitan dengan pembentukan kolam air panas. Keputusan survei menunjukkan kaedah survei graviti rantau dapat mengesan dua struktur besar sesar di sepanjang Sungai Langat dan Sungai Semenyih. Sesar-sesar ini menghasilkan suatu zon rekahan. Zon-zon rekahan ini merupakan temp at pengeluaran air panas. Keputusan survei TEM menunjukkan terdapatnya dua zon konduktif yang disebabkan rekahan di batuan dasar. Segala pembangunan yang akan dilakukan dikawasan zon konduktifini patut dielakkan untuk tidak mengganggu struktur geologi yang merupakan laluan sumber air panas ini.

INTRODUCTION These structures should then be preserved whenever development takes place to avoid loosing the hot Two geophysical methods the gravity and the spring. transient electromagnetic (TEM) methods, were The geophysical investigations were undertaken used to investigate the occurrences of hot spring in at the request of the Geological Survey Department the Hulu Langat area, Selangor. There are four of SelangorlW. Persekutuan. known occurrences of hot springs within the survey area (Fig. 1). It is anticipated that there are major BASIC PRINCIPLE OF THE TEM subsurface geological structures (faults) that may TECHNIQUE be associated with the occurrences of these hot springs. A regional gravity survey was initiated to The transient-electromagnetic (TEM) technique identify and delineate these structures. involves passing a steady current through a wire A detailed investigation using the transient loop (usually square with fixed dimension) for a electromagnetic (TEM) method was then carried sufficiently long time, setting up a primary magnetic out at the Sungai Serai hot spring site (Fig. 1). A field. When the current (and thus the primary similar investigation was done by Abd. Rahim (1996) magnetic field) as abruptly terminated (in TEM at the Sungai Semenyih site. The two hot springs terminology this is referred to as the transmitter in nearby Dusun Tua have already been developed off-time), a circular sheet of current (termed 'smoke and were found to be unsuitable for detailed ring') immediately flows on the surface of the investigation. The primary objective of the TEM ground. As the smoke ring diffuses downwards technique is to map in detail geological structures and deeper into the ground, its radius increases. which are the source/pathway of the hot springs. The maximum value of the current density also 120 MOHO ANUAR MD. RAZALI

420000E 423000E 426000E 429000E 432000£ 435000E Z .---.------.------r------.------.------.------,~ o ~ LEGEND g b ~ 0 ~ 0 ~ z Road z ~ /" o 01 o Kg. Paya Lebar J~ o , Trock 8 , , " : I I 1 , -,, ", I~ \ I \~ o . River KEMAJUAN g~ K~... Dusu OJ / . I \ . TANAH J~ ~ ~ , 'fuo ~ MPANG S. TUNTONG I ~ .- (FElCRA) l§ Hot z ED Spring zl ("..J o .J'>. o o Gravity 1.0 ~ Station 1<') -, - I~ • ...... ~'_ ... . _.:.. ,I , .... IL \ z -~, I~ o \ o 'I o N ~~ ~ 0 rr) 1 HUTAN RlZA8 IZ z SUNGAl lAI..ANG o o o OJ I..... ; HULU SEMENYiH I") LADANG ::i ," ~i z SAM FOH ,',~~ r-_ .... o o CHERAS ''t' \ o I.D n rr) ~~z z '-'" o ~ o o f"-) I") l~ I") Z I~ ~ 0 0 0 . -0 I',)~~ ,-I__ -'- ______-'- ______-'- ______-'- ______-'- ______-'- ______---' ! "- 42DDOOE 423DOOE 426DOOE 429DODE 432DDOE 435DDOE

2500 5000 ! -t- (meters)

Figure 1. Distribution of gravity stations and location of TEM survey site.

Ceo L. Soc. J/!/a LaYJia, BuLLetin 42 GEOPHYSICAL INVESTIGATIONS OF THE HOT SPR IN G OCCURRENCES IN THE SUNGAI SERAI AND KAMPUNG DUSUN TUA AREAS 121 decreases. If conductors are present in the ground, A steady current is caused to flow ('on time') in the an electromagnetic force (emf) is induced. The transmitter loop for sufficiently long time before magnitude of this emf is proportional to the time being abruptly terminated ('off time') . TEM rate-of-change of the primary magnetic field at the measurements are made during the transmitter conductor. This emf also causes eddy currents to off-time, in the absence of the primary magnetic flow in the conductor with a characteristic decay field. During the off-time, the receiver coil measures ('transient decay') which is a function of conductivity the amplitude (often referred to as voltages) of the (the inverse of resistivity), size and shape of the transient decay over a series of time intervals known conductor. The decaying currents generate a as delay times. In fact, the measurement of the proportional (secondary) magnetic field, the time voltages are averaged over many cycles (known as rate-of-change of which is measured by a receiver stacking) of the transmitter pulses to enhance the coil. data. The width of these delay times (in milliseconds) is often referred to as 'windows', TEM MEASUREMENT 'channels' or 'gates'. The delay times dictate the depth of investigation; the later the delay time, the The current flowing through the transmitter deeper is the depth of investigation. A number of loop is in the form of 'pulses' (this technique is also delay time series is available to cater for different sometimes called Pulse EM) with on and off times. depths of investigation.

422 160E 422180E 422200E 422220E 422240E 422260E 422280E 422300E LEGEND z o co OJ N o r'l""" z ../ Sg. Serai Stream L5 / L4 D Building L2 Hot Spring pond !< [ill- - -- X X ",.,v"'''' Swamp o v"'''' 11 L9 LlO XXxx Fence

~ Dense bushes

LZ TEM line

TEM Station

422160E 422 180E 422200E 422220E 422240E 422260E 422280E 422300E

25 o (met ers) -f- Figure 2. Distribution ofTEM stations.

December 1998 122 MOHD ANUAR MD. RAZAU The TEM measurement can be made using The raw TEM data were automatically saved either the separate loop or the coincident loop. In in the equipment's solid state memory during field the separate loop configuration, two separate loops data acquisition. For processing, the raw data (a transmitter and a receiver loop) are required for were directly input into a portable computer using the data acquisition. The coincident loop the PC PLUS software. The inversion of the TEM configuration operates with only a single loop. The data to obtain resistivity depth profiles was done loop acts as a transmitter when the current is on using the TEMIXP software package. and as a receiver when it is off. RESULTS AND DISCUSSIONS TEM VOLTAGES AND APPARENT RESISTIVITY Regional gravity survey Although the TEM technique measures The bouguer anomaly map is shown in Figure amplitude (voltages) of the transient decay over a 3. A gradual increase in gravity values is observed number of delay times, it is possible and useful to towards the southwest of the survey area. This convert the TEM voltages to apparent resistivity. suggests the presence of a much denser rock type in This is done by applying a formula for the that direction. As this part of the survey area (L1) conversion. is underlain by the Formation, the higher When the TEM data are transformed to values are attributed to the metasediments apparent resistivities, the subsurface can be looked comprising of mainly schist with minor at as consisting of different layers (at the point of intercalations of limestone (marble) and phyllite. measurement), each with a distinct resistivity. This To the north-east of the survey area, the Jelebu is achieved by employing a technique known as I­ Schist (L2) is well defined by the gravity survey as n layered inversion (or simply 'inversion') which it appears as gravity highs on the bouguer anomaly calculates the true resistivity, thickness and depth map. The rest of the survey area is underlain by (from the surface) of each layer, thus producing a granite which exhibits much lower gravity values model of the subsurface. as it is less dense compare to the other rock types found within the survey area. Along Sg. Langat, the gravity contours are FIELD PROCEDURES significantly disturbed (F1) indicating the existence The geophysical surveys were carried out from of a major geological structure which is interpreted 3 to 17 July 1997, using the La Coste & Romberg as a fault. The interpreted fault appears as a series Model G-972 Gravity Meter for the regional gravity of gravity highs and lows (F1) trending northeast­ survey and the Sirotem MK3 equipment for the southwest on the residual anomaly map (Fig. 4). transient electromagnetic (TEM) technique. The Semenyih Fault (F2), although not clearly The regional gravity survey covered an area of observed on the bouguer anomaly map, appears as 450 km2 with a total of 96 gravity stations spaced a prominent lineament trending parallel to the Sg. at 1 km interval (Fig. 1). As the survey area is Langat Fault. All the known occurrences of hot generally inaccessible, the gravity survey was spring occur along either one ofthese faults. These confined to locations along the roads and tracks. are strong evidences suggesting that the hot spring For the TEM survey, readings at 128 stations, occurrences are fault controlled. at a 10-metre station interval were taken. The The residual anomaly map also indicates clearly stations were positioned along 14 lines, all aligned the granite/metasediment (L1) and granite/schist in a north-south direction (Fig. 2). The high (L2) contacts. The findings of the gravity survey resolution times series were used to obtain a better are summarised in Figure 5. resolution of the shallower layers. A lO-m coincident loop configuration was utilised for the survey. TEM survey The results of the survey at the Sg. Serai hot DATA REDUCTION AND PROCESSING spring site are presented as apparent resistivity maps (Figs. 6 and 7) and TEM voltage profiles All gravity data were reduced to the bouguer (Figs. 8, 9 and 10). anomaly using available software. A reduction density of 2.67 gm/cc was used for the bouguer Apparent resistivity map plate correction. The reduced data were further The apparent resistivity values of window 10 subjected to a regional/residual separation to (delay time of 0.113 ms) and window 15 (delay time discriminate between localised and regional features 0.341 ms) (Figs. 6 and 7 respectively) were gridded using the second derivative filters. to show lateral changes of the subsurface at different Ceol. Soc. MalaYJia, Bulletin 42 420000£ 42.3000£ 426000£ 429000£ 4.32000£ 4.35000£ 420000£ 42.3000£ 426000E 429000£ 4.32000E 4.35000£ z z ~-'~~--~~~~~~~~--~~~~--~~~~~~~~---'lN o LEGEND o (Jl LEGEND o o .p. o o 0 ..r ..r 0 I/) I/) 0 n n z Rood Road z z IN ~ o o VI o o a o a o o Track o Track II) o I/) o n z n z z GJ River z River o .p. o o Ol o o o o ro o Cl;) o ..r Hot ..r Hot n n 2 Spring Spring z z IN o o .p. o Fault o (11 o o o II) c<) o ..r , Semenyi ..r o n --, n z , fault z IN z o ~ o o N o o o Quartz o N N ..r 8 vein ..r n z / n z IN r:::l z '.,J Schist o <0 ~ o o8 o o Ol o Ol n o + ++ n + z +++ Granite +++ z GJ o IN o o} o o n Meta­ <0 o sedlmen n o LJ i n z I ~

- 14.00 - ;1 ~ --15.00.,.oo~ - 16 . 00 - 17. 00 - 18 . 00 - 20,00 _ 1 < - 22. 00 o 0 ~o I !0 o 0 mgals n - 0 '') L---1______....L ______L- ______-L ______L- ______-1. ______-.l Z 420000£ 423000£ 426000£ 429000£ 432000£ 435000£ 420000E 423000£ 426000E 429000E 432000£ 435000E

2500 0 2500 2500 5000 5000: I ...... -.--- (meters) (meters) Figure 3. Bouguer anomaly map and general geology of survey area. Figure 4. Residual anomaly map (second derivative filter). 124 MOHD ANUAR MD. RAZALI

420000E 423000E 426000E 429000E 432000E 435000E z ~ o (Jl LEGEND o .j>. o o o t1) t")"'" I~ Road z o ~--' ... ~ ~ o Kg. ~a Lebor o _ o ;. ~ __ _ ,.' f"'V J o " Track l[) rv a " t") z + , f"'V River \~~.~UAN . ~'lAH ~ TUNTONG ~ELCRA) Hot , Spring \ rv z , j! o o I Itn , ,-,o) , § , Fault n"'" 1z z o o + Schist o N + n"'" HUTAN RIZAB Granite z SUNGAI lALANG + ,'," o I , o 1 o I + + (J) Meta­ n HULU SEMENYlH t') sediment + I •1 I, J + , --,

420000E 423000E 426000E 429000E 432000E 435000E

2500 5000, (meters)

Figure 5. Gravity interpretation map.

Ceo!. Soc. MaLaYJia, BuLLetin 42 LEGEN D 422160E 422220E 422240E 422260E 422280E 422300E LEGEND zr=~~~~~~~~~~~~~~=7~~--.------.--~--.----.u o A 17 . 5;2 ~~ ~ o 16.32 3 ~~ . 4.07 N N ~::7 ~ V 13.86 * ... . r<) 15.2. 351'2 ':." . 3.J3 .. " .' 1 0.~.2 .' : u 2.9~ 7. 30> ~~~ ",~"" 2.41 ", . Ohm-m ~ ~~ . ~~~ ~~~ ~ ~ Ohm-m r<)L-~ ______~ ____~ ______~ ____~ ____~~ ____-J ______~ __~Z 42 21 60E 4221 80E 42 2200E 422220E 422240E 422260E 422280E 422300E 422160E 422180E 422200E 422220E 422240E 422260E 422280E 422300E

25 o 25 5 o 25 ( meters) (meters) -f- Figure 6. Apparent resistivity map of Windows 10 (0.0104 ms). Figure 7. Apparent resistivity map of Windows 15 (0.320 ms). 126 MOHO ANUAR MD. RAZALI

1000 -- Delay times (ms)

f---f---+---+------i----t---i . 0.C66 100 * 0.080 0.128 S' ,~ 0.224 2- 0.320 Ul Q) 10 0> . 0.464 ~ 0 0.656 > ..--'~ / * ,..- - -...... ~ / .. 0.848 -0.>. __ 1.232 --- ~--I- k ------:=== - " +- -+--"--1--- ":13 , 1 += -t---j------0.1 342040 342060 342080 342100 342120 342140 342160 342180 Northin m Figure 8. TEM voltages at selected delay times for Line 5.

ILlNE-6 I

1000

Delay times (ms) I Conductive Zone (LZ1)

100 • D.CE6 .. O.Cl!O - / . '- ./ '\ ~ 0.128 -- /'" :'-..., 1 / "- ~ ./ /" -- ',\ '. --, v 0.224 ~ ". ."" {' ;:.. ~ ./< -tJ ~ i/ , . ~ , I --- ~~\ ---'! 0.320 .' - , . - . 0.464 -. - - r- \ '\~ t- * 0.656 \ r-- ---" ....- .. 0.848 , 1.232

I

0.1 342040 342060 342080 342100 342120 342140 342160 342180 Northing (m) Figure 9. TEM voltages at selected delay times for Line 6.

Geo L. Soc. M alaYJia, BuLLetin 4] 1000 .ond ." ===±:- , Delay times (ms) hot spring pond (P2) :-r- - - --. - X-- - ~n- r- --I- . 0.032 /' f-:- 100 I--'--- - • O.ca; - - - .....::s ~ .-= = * 0 .(8) ,.- ~, ,, ~ ~r ~' - ~~ 0.128 >' -- . ~ ..... k--. .L/t -~ A., -L V l 2- ~ ~ . III ~ ::::::-< -- ~ , .il·· .....-: QI 10 ~~ - ~~~ "c-_ Ol "-<"- ~ ~ ' ~ ' 4l! '---T-~ -- 0 . 0.464 > .,...... J-- /' -...... , ~ ~~ .. /' / I *' 0.£56 ~ ' - . -" ~ . . . Q84B • , ----...... - - • I L l-· .- • 1232 t , .!, -- 1--- , '--1 0.1 I : 342040 342060 342080 342100 342120 342140 342160 342180 Northing (m)

Figure 10. TEM voltages at selected delay times for Line 7.

422160E 422180E 422200E 422220E 422240E 422260E 422280E 422300E LEGEND z / (.,J 0 -l>- 0Cl I j,/xx N N co .q- I x x 0 I") z Sg. 5erai I //x ./ z (.,J Stream 0 I '/f -l>- / lD t)x N N Ol .q- 11~/ 0 Building I") z D Z Iii /x x 0J 0 "x X .j>. Hot Spring .q- ,~ [ill]- - .. - pond N 11/ _ .j>. .q- 0 I") 1 x z ... .., Swamp z () (.,J ""'''' 0 x .j>. v"" N N ~ xxxx Fence N N .q- 0 I") z z "'. (.,J Dense bushes 0 -l>- ~ 0 bO N N " 0 Proposed .q- '" 0 S I") '" .. ... z Borehole z (.,J 0 " .j>. co ~ " '" N Conductive 0 0 N '" co Zone .q- '" 0 I") ~ " z Z IJ1 " (.,J 0 " 0 -l>- lD '" N 0 'Y 0 N ~~ Ol . 0 \V W ~ 0 .q- N 0 - 0 N .j>. .q- ~~~~~ 0 I") ~~~ z 422160E 422180E 422200E 422220E 422240E 422260E 422280E 422300E

5 0 25 (meters) -f- Figure 11. TEM interpretaiton map. 128 MOHD ANUAR MD. RAZAu 'levels' of depth. The later window (window 15) is spring ponds are located in conductive zone LZl. 'seeing' at a relatively greater depth. This indicates that the occurrences of the hot spring Both the apparent resistivity maps (Figs. 6 are associated with the fractures which allows the and 7) show almost similar features. Two conductive hot spring water to flow through to the surface. zones (LZI and LZ2) are observed on both the maps. The two existing hot spring ponds are located on CONCLUSIONS AND LZI. These conductive zones are due to fractures within the rock which acts as conduits for the hot RECOMMENDATIONS spring water to ascent to the surface. Fractures in The regional gravity survey delineated two the rocks will render the zone conductive as it major faults, Fl and F2 along Sungai Langat and allows water to flow through. The presence of the Sungai Semenyih respectively. All the hot spring fractures is further substantiated by the existence occurrences are located along these two faults. This of a major fault delineated by the gravity survey. strongly suggests that the occurrences of the hot Development of the fault would have induced springs are directly associated with the fault which fractures to occur in the rock. induced the development of fracture zones which The third conductive zone (LZ3) observed on provides a conduit for the hot spring to seep through the maps is not real and should be ignored. This is and ascent to the surface. due to the presence of water pipes and zincs close The TEM survey at Sungai Serai hot spring to the surface which affected the TEM site delineated two conductive zones which are measurements. attributed to fractures in the rock. These fractures TEM voltage profile have been identified as the main pathways of the hot springs. It is recommended that future Figures 8, 9 and 10 show the TEM voltages at development and construction on this site should selected delay times for lines 5, 6 and 7 respectively. be kept away from the known conductive zones so The liens crosses the conductive zone, LZI. The as to preserve these subsurface geological structures profiles indicate changes in conductivity, both and to avoid any potential impacts to the hot spring laterally and vertically. The delay times were flow. chosen to reflect different 'levels' of depth Boreholes are recommended to be drilled at penetration. The later delay times indicate a greater locations as shown in Figure 11 to confirm the depth of penetration. geophysical findings. The conductive zone appears as high voltages between stations 342100N to 342140N (Fig. 8), 342090N to 342140N (Fig. 9) and 342080N to REFERENCE 342130N (Fig. 10). In Line 5 (Fig. 8) the hot spring ABDUL RAHIM, H., 1996. Hot Spring Investigation Using pond (PI) occurs between 342116N to 342135N. Transient Electromagnetic Technique in Sg. Lalang,Hulu The second hot spring pond (P2) appears between Langat, Selangor. Report GF 06/96 (Unpubl.), /abatat! 342100N to 342110N in Line 7 (Fig. 10). All the hot...... Penyiasatan Kajibumi Malaysia. Mllnuscript received 2 November 1997

Geot. Soc. MataYJia, Bulletin 42