/,,,, +. 3 +, +,, +.,. +. 2 + Geochemistry of Fluids from Hot Springs, Mineral Springs, Wells and Fumarolic Area in the Shimabara Peninsula, Middle Western Kyushu, Japan Shinji OHSAWA +, Kohei KAZAHAYA, and Masaya YASUHARA, + Beppu Geothermal Research Laboratory, Kyoto University, Geological Survey of Japan, AIST Abstract Water and gas samples from hot springs, mineral springs, wells and fumarolic area in the Shimabara Peninsula, middle western Kyushu, were collected for chemical and isotopic analyses. Geochemical data analyses lead us to the following results. Hot spring water of acid SO. type in Unzen-Jigoku fumarolic area is derived from meteoric shallow groundwater heated up to +/ by secondary steam originated from deep hydrothermal water of about -. Thermal water of Cl type in Obama area, which is basically mixture of seawater and shallow groundwater of meteoric origin, interacts with reservoir rock at about,. The thermal water in the reservoir is heated by steam of about - containing magmatic He and CO,. Thermal waters of HCO - type in Shimabara and Harajo areas are slightly heated groundwater of meteoric origin. However, it is detected that magmatic CO, is dissolved in the thermal waters. Both thermal waters from Mizuho and Yue, which are classified chemically into Cl-HCO - mixed type and HCO - type, respectively, are likely to be non-volcanic formation waters. The accompanying methane gases with these waters have thermogenic and biogenic origins, respectively. Mineral water of Cl type from Karako may be mixture of seawater and meteoric groundwater, and is not a#ected by magmatic emanation. Mineral water of HCO - type from Karimizu in Obama area is originated from meteoric water, but the accompanying gas with strong H,S smell would be derived from the reservoir of the Obama thermal water 51
52 Key words : Shimabara Peninsula, Unzen Volcano, hot spring, mineral spring, hydrogeochemistry : + +,-/3 m +33 +33/ +,.20 m, Fig. + +, mm year +32/ / m 3 m, + m, +321 Fig + Sampling sites in the the Shimabara Peninsula. + : Shimabara-kanko Hotel (hot spring water [well]),, : Shimabara-onsen (hot spring water [well]), - : Motoike (hot spring water [well]),. : Shinyama-onsen (mineral spring water [well]), / : Shinyu (hot spring water), 0 : Kojigoku (hot spring water), 1 : Tanaka-so (boiling spring water and separated steam [well]), 2 : Karimizu (mineral spring water and bubble gas), 3 : Kunisaki-ryokan (hot spring water [well]), + : Karako-onsen center (mineral spring water [well]), ++ : Mizuho Sennen-no-yu (hot spring water and accompanying gas [well]), +, : Yugyoku-onsen (hot spring water and accompanying gas [well]), +- : Harajo-so (hot spring water [well]), +. : Harajo Masago (hot spring water [well]), +/ : Obama harbor (seawater), +0, +1 : Seishichi-jigoku (fumarolic gas). Numbers correspond to those in Tables + and /
/,,, 53 H,S +31- CO, CH., +31- ; +32. 1 m H,S H-SO. + m + m + Na-Cl CO, H,S + m 2 m HCO - - + m,. m +33 +33/ +31- ; +33-32 m +,// m / 0 Na-Cl-HCO -.0.1 m - Na-HCO -,, Na-Cl-HCO -,+ + m + m
54 - Na-HCO - - m - Ca, HCO - - - - + 1 +. Fig. + Table + ph No. 1 +303, Fig. + Table / KOH /M,+ KOH /M, -, -, + Na,K,Mg,,Ca, Cl,,SO. Al - ICP Fe HCO - BCG..2 DIC CO, aq IM-+B CE-,-/ D H +2 O +0 O V-SMOW dd d +2 O +.+ DIC +- C +, C Sr OH,. SrCO - CO, V-PDB d +- C.+ SO. HSO,. SO. +2 O +0 O BaCl, BaSO. +, CO, BaS Ag,S Cu,O 2 SO, SO. -. S -, S V-SMOW V-CDT d +2 O- SO. d -. S- SO..-.,
/,,, 55 -,, CO,,H,S, N,,CH., Ar, H,, He, O, +332 ;,+ H,O +332 C,H 0 Ar FID Polapac Q / m + ml / / / min +/, KOH CO, d +- C H,S -. S -, S H,O, KOH BaSO. SiO, V,O / SO, V-CDT d -. S., CH. +- C +, C / + ml +30 H,O CO, 3 Cu,O CH. CO, H,O 3 V-PDB d +- C., D H +2 O +0 O V-SMOW.. + Table + Cl-HCO --SO. Fig.,A No. ++ Cl-HCO - + No. +,,, -,. No. +-, +. No. +, No. 2 HCO - No. /, 0 SO. No. 1, 3 No. + Cl Table + H,S ph /.1 H,S HCO - Na-Cl Na-K- Giggenbach, +322 Fig.,B HCO - SO. No. + 0, 2, +-, +. No. 1, 3 No. + immature waters No. ++ No. +, Cl-HCO - HCO - SO. Na
56 Table + Chemical and isotope compositions of waters from wells5 hot springs and mineral springs in the Shimabara Peninsula No Area Name Temp ph Na mg l K mg l Mg, mg l Ca, mg l Al - mg l Fe mg l Cl mg l mg l dd d +2 O +, -. / 0 1 2 3 + ++ +, +- +. UZ UZ KK MH YH HJ HJ Shimabara-kanko Hotel w,.43 Shimabara-onsen w -41 Motoike w -4/ Shinyama-onsen Kami-no-yu w +04+ Shinyu h //41 Kojigoku h.14, Tanaka-so w + Karimizu m,.41 Kunisaki-ryokan w 014 Karako-onsen center w +-4, Mizuho Sennen-no-yu w.343 Yugyoku-onsen w -04, Harajo-so w,040 Harajo Masago w,042 +3 +./,21 +,4, 04+ 04/,52 +-41,5.3 +52+.5,0.-1,342 ++, 4/+ 4-1 3,4/ +240-24+ 241-41 -4/.53, 04,.5/ -53 /5+1 +,4/.41 ++43 SO., mg l HCO- 04. 14. 14, 041,4..4-24. /41 24 14/ 142 24. 24-141 --40,-4 -,4, -43,4-,4.,/0 24/,-. 324/ +04- +42 14, ++4,,/ 0-4- 334/ 34-,4.,4, +/1 +242 +/,.+ 142 +4. 34, 14, +13 //41 0,42,/40 141 042 +-1,.4, +.2,3- +24 /41 +24. +-4-,4-42 114 ++4- +.40 14-,.0 +,3,2. +24- -,/..+ n4d n4d n4d,43,50 223 +5., +-1,2 +1-,,, +.,51 +5+0 3,4. -3+.34..34..34/.14- /,4, /41-043.34/ -24+ -4,.+4- /141./4..240 14. 141, 1412 14.1 141, 14,..4.1 14.0.4// /4.3 /422 24-+ 14,1 14,0 +/ Seawater (Obama) +042 24-3522 -1. +5, -2 +250,5+. +/1 +4/ 4+0 Sampling date (in,) :Nos4+and +- on Feb4 2; Nos4.5 15 25 ++5 +, and +/ on Dec4 +-;Nos4+5,5-53and +0 on Dec4 +.;Nos4/50 and +. on Dec4 +/ @ : Shimabara5 UZ : Unzen5 : Obama5 KK : Karako5 MH : Mizuho5 YE : Yue5 HJ : Harajo w:well5 h : hot spring5 m : mineral spring ; n4 a4 : not analyzed5 n4d4 : not detected (detection limit of SO. ion 4+ mg/l) # : Water sample was collected from Shinyama-onsen Shimo-no-yu about + m away from Shinyama-onsen Kami-no-yu4 d +2 Oandd -. Sof SO. ( HSO. SO., )inno4/sample (Shinyu) are.4, and /41 5 respectively4
/,,, 57., Table + dd-d +2 O Fig. -A No. 1 Table +..0 ; dd d +2 O 00./ 3.3+ MWL d 1.,., d dd 2 d +2 O HCO - SO. No. + 0, 2, +-, +. No. +, No. + No. ++ No. +,, No. 1, 3 No. 1, 3, +, ++, +, Cl dd Cl Table + Fig. - B, dd No. 1, 3 dd-d +2 O Fig. -A No. 1, 3 Fig, Ternary plots used to classify waters based on the relative proportions of Cl, SO. and HCO - ions (A) and used to recognize equilibrated waters (B) for waters from wells, hot springs and mineral springs in the Shimabara Peninsula. Symbols with numbers correspond to those in Fig. +
58 +320 andesite-magmatic water dd, d +2 O 2 +, ; Giggenbach, +33,a Cl-dD Fig. -B No. +, No. ++ No. +/ dd-d +2 O Fig. - A Cl-dD Fig. -B Fig. -A, -B Fig - dd vs.d +2 O plot (A) and dd vs. Cl ion concentration plot (B) for waters from wells, hot springs and mineral springs in the Shimabara Peninsula. Cold spring and shallow groundwater data are referred from Kazahaya et al. (unpublished data). Symbols with numbers correspond. - to those in Fig. + No. 1 No. 3 No. ++ No. / -., Mg, Na-K-Ca Fournier and Potter, +313 H, O- SO. HSO,. SO. Mizutani and Rafter, +303 Table,, +32. +21,, +320 + 21 +,// m 0/, +/ SO. d -. S /.1 H,S..2..3
/,,, 59 Table, Estimations of underground fluid temperatures in the Shimabara Peninsula No Area @ Name Calculated Temp4( Geothermometer / 1 3 ++ UZ MH Shinyu Tanaka-so Kunisaki-ryokan Mizuho Sennen-no-yu +/+ +30,2 21 d +2 O H,O SO. A Mg-correction to the Na-K-Ca geothermometer[b] ditto ditto @ UZ : Unzen5 : Obama5 MH : Mizuho [A] Mizutani and Rafter (+303)5 [B] Fournier and Potter (+313) : SO. HSO,. SO. Table - Concentrations and isotope ratios of dissolved inorganic carbon (DIC) in waters from wells5 hot springs and mineral springs in the Shimabara Peninsula No Area Name DIC mg l d +- C DIC.. + Shimabara-kanko Hotel,51.4.. +, -. Shimabara-onsen Motoike Shinyama-onsen Kami-no-yu 00. +5+, +,. 1410 0411,4. 1 Tanaka-so,5-2 /40 2 Karimizu +53-40. HCO - 3 Kunisaki-ryokan +/ 240+ Cl Cl-HCO - + +, mg l HCO - HCO - + ++ +, +- +. +/ KK MH YE HJ HJ Karako-onsen center Mizuho Sennen-no-yu Yugyoku-onsen Harajo-so Harajo Masago Seawater (Obama)..41 +1. 1.4 +,,,1 2142 ++4/2 04.2 412 +,423 2421 +41 @ : Shimabara5 Yue5 HJ : Harajo : Obama5 KK : Karako5 MH : Mizuho5 YE : DIC CO,(aq HCO, - CO - collected values for CO, separation using chemical and isotopic compositions of steam phase5 and steam/water ratio (4.0) cited from Sakai and Matsuhisa (+330) DIC CO, aq HCO, - CO - d +- C,+ DIC d +- C Table - DIC No. 1 CO, DIC d +- C CO, d +- C Table /..0., No. 1, 3 DIC
60 Cl, DIC DIC No. + DIC nsw DIC smp DIC Cl sw Cl smp d +- C nsw d +- C smp d +- C swdic smp DIC nsw d +- C sw DIC nsw DIC DIC smp DIC DIC Cl sw DIC Cl Cl smp Cl d +- C nsw d +- C smp d +- C sw DIC No. 1 No. 3 No. + DIC DIC + +..+ DIC d +- C + DIC d +- C Fig.. No.. DIC No. +, d +- C DIC CO, +33/ ;,+ CO, DIC CO, d +- C / Fig.. No. + No. 2 d +- C CO, DIC CO, d +- C DIC, / Table - Table / ; Kita et al., +33- + DIC d +- C,, DIC CO, d +- C CO, Ohsawa et al.,,, d +- C CO, Fig. d +- C vs. reciprocal concentration plot of dissolved inorganic carbon (DIC) for waters from wells, hot springs and mineral springs in the Shimabara Peninsula. Symbols with numbers correspond to those in Fig. +. For soil water boxsee text.
/,,, 61 Table. Estimated carbon sources of dissolved inorganic carbon (DIC) in waters from wells5 hot springs and mineral springs in the Shimabara Peninsula No4 Area @ Name Contribution ( ) Magmatic CO, Soil CO, Seawater DIC +, -. 1 2 3 + +- +. KK HJ HJ Shimabara-kanko Hotel Shimabara-onsen Motoike Shinyama-onsen Kami-no-yu Tanaka-so Karimizu Kunisaki-ryokan Karako-onsen center Harajo-so Harajo Masago + 2/ 3 +. 3/ + 0+ 1 /0 13 +/ + 20.,/ /,..,+ + +..+ @ : Shimabara5 : Obama5 KK : Karako5 MH : Mizuho5 YE : Yue5 HJ : Harajo d +- C CO, No. + No. 2 - He. He Kita et al., +33- / d +- C CO, No. ++ No. +, CH. Table / DIC CO, d +- C CH. +, C CH. DIC d +- C CO, ;,+ DIC CO, CO, DIC DIC CO, CO, d +- C smp d +- C mgm X d +- C soil + X X CO, d +- C smp d +- C mgm d +- C soil DIC CO, CO, d +- C mgm d +- C soil /,- Ohsawa et al.,,, DIC Table. CO, DIC, +31- No. + DIC 1 CO, CO,
62. /.. CO, CO, CH. O, Table / CO,-He-Ar Giggenbach, +33,b Fig. / andesitic CO, AS andesitic subducted AT andesitic thermogenic basaltic CO, BM basaltic mantle BC basaltic contaminated ME meteoric endmember No. 1, 2, +0, +1 CO, Ar,./ + - +.3 +... +, / 0 CO, Fig / Relative CO,, He and Ar contents of sample gases listed in Table /, together with those of the potential endmember components : meteoric (ME), andestic (AS, AT) and basaltic (BM, BC) gases. Symbols with numbers correspond to those in Fig. +. For AS(andestic subducted), AT (andestic thermogenic), BM(basaltic mantle) and BC(basaltic contaminated) see text.
/,,, 63 Table / Chemical and isotope compositions of gases from fumaroles5 thermal water wells and mineral spring in the Shimabara Peninsula No4 Area @ Name Temp4 ( ) H,O (Vol4 ) Composition of gas exclusive of H,O (Vol4 ) d +- C( ) CO, H, S N, CH. O, Ar H, He C, H0 CO, CH. 1 2 ++ +, +0 +1 MH YE UZ UZ Tanaka-so w + Karimizu m,.41 Mizuho Sennen-no-yu w.343 Yugyoku-onsen w -04, Seishichi-jigoku f 314+ Seishichi-jigoku f +1 3142, n4a4 n4a4 n4a4 304.2 304-2 4// 4+. n4d4 n4d4,4.,4+ +43,40 04, ++4. +4 431 4/. +41 /+42 /342 40/ 42+ 4++ 4+2 41+ 4/1 43 4+, 4+0 421 4/ 4/ 4, 4, 4,2 4++ 4,2 4,3 n4a4 4.0 314 3/4-.+4,24 3/41 3/43 4-2 4-, 4-/ 4+- 4// 4/ 4/ 4+- 4/3 43. 4++ 4++ /4- /42 n4a4 n4a4.4,.4,,142,34, -/40 0242 n4a4,24, Sampling date (in,) :Nos41525++and +, on Dec4 +-; Nos4 +1and +2 on Dec4 +/ @ : Shimabara5 : Obama5 MH : Mizuho5 YE: Yue5 UZ : Unzen f : fumarole5 m : mineral spring5 w : thermal water well n4a4 : not analyzed5 n4d4 : not detected d -. SofH,S innos4+0and +1 samples collected from Seishichi-jigoku are.43 and.42 5 respectively4 dd andd +2 OofH,O inno41sample (Tanaka-so) are 004/ and 343+ 5 respectively4
64 No. ++, +, CH. CO, /.0 + - +.2 +, CO, CH. CH. CO, CH. +- C +, C CO, CO,.H, CH.,H, O Ono et al., +33- Fig. 0 Magmatic CO, CO, d +- C..+ ; Kita et al., +33- CO, CH. CO, Chemical isotopic equilibrium Figure 0 No. 1, 2, +1 CH. CO, - Giggenbach and Goguel, +323 Fig 0 d +- C values for CO, (open symbols) and CH. (closed symbols), and CH./CO, ratios of gases discharged from Unzen and Obama areas (Numbers correspond to those in Table /). The trend for both chemical and isotopic equilibrium between magmatic CO, with a values of..+ and CH. is shown as short dashed line, and the equilibrated temperatures are plotted along the top (Ono et al., +33-). No. ++ No. +, CH. Table / CH. d +- C CH. +333 CH. d +- C CH. C, H 0 Kiyosu et al., +33, CH. CH. d +- C CH. C, H 0 Fig. 1 No. ++ CH. Thermogenic No. +, CH. Biogenic CH. Table +
/,,, 65. 0 CO, Ar H, Ar Giggenbach and Goguel, +323 ; +332 ;, ;, Table /. / Fig. 2 No. +0, +1, Equilibrium liquid - Fig 1 d +- C values of CH. and CH./C, H 0 ratios of accompanying gases from Mizuho (Mizuho Sennen-no-yu : No. ++)and Yue (Yugyoku-onsen : No. +,). Thermogenic and biogenic boxes are referred from Sato et al. (+333). Ca-Al,-silicate K-feldspar CO, K-mica calcite. FeO +./. FeO O,. -. / CO, CH. No. 1 No. 2 No. ++ No. +, Equilibrium liquid CO, Ar Fig 2 Evaluation of H,-Ar, CO,-Ar equilibration conditions for gases from the Shimabara Peninsula. Symbols with numbers correspond to those in Fig. +.
66 Giggenbach and Goguel +323 CO,-Ar H,-Ar CO,-Ar,/,/,,. - / +333 H,-Ar +/ /. / - CO,-Ar,,/ H,-Ar, + +/ No. 2 +311 No.1, 0 + m, -, m / m +, m CO, Chiba +33+ / - +/ SO., - CO,
/,,, 67 Institute of Geological and Nuclear Sciences G. L. Lyon W. Gooley : ++ +- : :,+ : + +/2 +01 Chiba, H. (+33+) : Attainment of solution and gas equilibrium in Japanese geothermal system, Geochemical J.,,/, --/ -//. Fournier, R.O. and Potter, R.W. (+313) : Magnesiumcorrection to the Na-K-Ca chemical geothermometer, Geochim. Cosmochim. Acta,.-, +/.- +//. Giggenbach, W.F. (+322) : Geothermal solute equilibria. Derivation of Na-K-Mg-Ca geoindicators, Geochim. Cosmochim. Acta, /,,,1.3,10/. Giggenbach, W.F. and Goguel, R.L. (+323) : Collection and analysis of geothermal and volcanic water and gas discharges, Fourth Edition. Report CD,.+, Chemistry Division, DSIR, New Zealand, 2+p. Giggenbach, W.F. (+33, a) : Isotopic shifts in waters from geothermal and volcanic systems along convergent plate boundaries and their origin, Earth Planet. Sci. Lett., ++-,.3/ /+. Giggenbach, W.F. (+33, b) : The composition of gases in geothermal and volcanic systems as a function of tectonic setting, Proceedings of the Seventh International Symposium on Water-Rock Interaction, 21-212., :,,,-1,./ Kiyosu, Y., Asada, N. and Yoshida, Y. (+33,) : Origin of light hydrocarbon gases frommatsukawa geothermal area in Japan, Chem. Geol., 3., -,+ -,3. +333 : +,.,./,2+, : / 20 3- Kita, I., Nagao, K., Taguchi, S., Nitta, K. and Hasegawa, H. (+33-) Emission of magmatic He with di#erenct - He/. He ratios fromthe Unzen volcanic area, Japan, Geochemical J.,,1,,/+,/3. Mizutani, Y. and Rafter, T.A. (+303) : Oxygen isotopic composition of sulfates, -. Oxygen
68 isotopic fractionation in the bisulfate ion-water system, N.Z. J. Sci., +,, /. /3. +33/ : +,- +.0 +332 :,,23,3,, : /+ +3,2,+ : /,,+,0, :.3 +/+ +0+ Ohsawa, S., Kazahaya, K., Yasuhara, M., Kono, T., Kitaoka, K., Yusa, Y. and Yamaguchi, K. (,,) : Escape of volcanic gas into shallow groundwater systems at Unzen volcano (Japan) : Evidence from chemical and stable isotope compositions of dissolved inorganic carbon, Limnology, (in press) +31- : 2 + -- +311 : II +31.. +31/ 1 ++ +-,/ +32. : 32p +321 : -- 1+ 2/ Ono, A., Sano, Y., Wakita, H. and Giggenbach, W.F. (+33-) : Carbon isotopes of methane and carbon dioxide in hydrothermal gases of Japan, Geochemical J.,,1,,21,3/. +330 : +.-,,, +333 :..,13,2- +32/ :, -2 + +, +33- : /./p +303 : +31,- +320 : -1, -+