Geochemical Journal, Vol. 27, pp. 147 tO 154, 1993
B o ro n is oto pic co m p o sitio n s o f S him o g a m o h ot sp rin gs, Izu ,
Jap an
TAKAO OI, JUNKO O GAW A and T OMOKO O SSAKA
Department of C hemistry, Sophia U niversity, 7-1 Kioicho, Chiyodaku, Tokyo 102, Japan
(R eceived Septem ber24, 1992; A ccepted M ay 19, 1993)
H ot spring waters in Shim ogam o, Izu Peninsula, Japan, were analyzed for the stable isotopes of
boron as well as for chemical com positions. The boron isotopicratios,11B/lOB, ofthe w aters range
from 4.190to 4.216,corresponding to the variation in 611B from + 36.2 to + 42.6 perm il. These values
are very high com pared to thoseof hotspring watersin otherareason theJapaneseislands and closeto
that ofsea w ater. The results oftheisotopic andchem icalanalysesindicate thatthe Shim ogam o hot spring waters are m ixtures of surface w ater and a deep geotherm al brine directly derived from sea water
through the interaction with heated silicate rocks.
the T ohoku (northeast Japan) district have high
boron isotopic ratios, IIB lIOB, (> 4.070), w hile
hotspringsin other areas of the Japaneseislands
show low llB / roB values (< 4.07). T his regional
variation in boron isotopic com pisotions might
indicate involvem ent of sea w ater boron into the
Tohoku hydrotherm al system s to som e extent
through any pathw ays.
Sea w ater is considered to infl uence hot spring w aters in various kinds of processes. The
above m entioned influence is a large-scale but indirect one. A different and m ore directinfi uence
m ay be observed for hot springs in special circum stances, for instance, forthose close to seas.
The Shim ogam o hot springs in the lzu Peninsula, Japan, although not very close to sea (the
Pacifi c O cean), is expected to provide a good
chance of observing infl uence of sea w ater on
hot springs. H ydrogen and oxygen isotopic
study (M izutani and H am asuna, 1972; M izutani
et al., 1975) indicated that the Shim ogam o hot
spring w aters are of sea w ater origin. If this indication is correct, the llB lroB values of the
Shim ogam o hotspring w aters should be high.In
any case,the boronisotopic data will provide inform ation on the existence and the extent of the
infi uence of sea w ater on the hotspring w atersin
INTRODUCTION
The abundance ratio of the tw o stable
isotopes of boron, 10B and 11B, varies relatively
large in nature. D ue to this large natural variation, boron isotopic com positions have various
applications in geo- and cosm ochem ical studies.
T hey can be used as a geochem ical tracer to investigate genesis of ore deposits (Swihart et al.,
1986;P alm er and Slack,1989; Slack etal., 1989;
Oi et al., 1989), genesis of coals (N om ura et al.,
l990), interaction of m agm as with sea w ater
(N om ura et al., 1982; Palm er, 1991), sedim entary cycle of boron (Spivack et al., 1987),
hydrotherm al and
geotherm al processes
(Spivack and E dm ond, 1987; Palm er and Sturchio, 1990), and evolution of brines(V engosh et
al., 1991).
The boron isotopic com position is also
utlizableto exam inetheinfl uence ofsea w ater on
hotspr_ing w aters.In previous papers(K akihana
etal., 1987;M usashietal.,1988; M usashi, 1989;
Oi et al., 199lb; Oi and K akihana, 1993), w e
reported the m easurem ents of boron isotopic
com positions of hot spring w aters in Japan. W e
foundthat,very roughlyspeaking,hotspringsin
the eastern C hubu (centralJapan) district and in
147
148
T. Oi et al.
the area and possibly on the process of the infiuence. W ith this expectation, w e collected
w ater sam ples ofthe Shim ogam o hotspring and
m easured their boron isotopic com positions. In
this paper, w e reportthe results of the m easurem ents and discuss the infi uence of sea w ater on
the Shim ogam o hot spring w aters.
E XPERIMENTAL
Shim ogam o hot springs and sam ple collection
Shim ogam o islocated in the southern part of
the lzu Peninsula, Japan, about 4 km inland
from the southernm ost edge of the Peninsula
(Fig. 1). H ot springs are distributed in a relatively sm all area along the A ono and M inam ino
rivers. A s of February, 1989, there w ere 105
w ater outlets including pum ping w ells, out of
w hich 95 areusable and 62 are currently in operation (Shizuoka Prefecture, 1989). A ccording to
Sam ejim a et al. (1969), the strata of the
Shim ogam o area,consisting of dacitic and pyroxene-andesitic rocks, belong to the Shiraham a
group w hich is com m on to m ost areas in thelzu
Peninsula.
U
O n June 12 and 13, 1991, w e collected eleven
hot spring w ater sam ples at different w ater
outlets, tw o river w ater sam ples (A ono and
M inam ino rivers), as representative Shim ogam o
surface w aters not contam inated by hot spring
w aters, at the points w here no m ixing of hot spring waters w as expected, and one sea w ater sam ple from the shore of O se, about 3 km southsoutheast of the Shim ogam o area, avoiding an
apparent m ixing of river w aters. T he volum e of
each-sam pled w ater w as I.O dm 3. Sam pling locations are show n in Fig. I; num ber I in the figure
is the sam pling location of sea w ater, num bers
2-12 those of hotspring w aters, and num bers 13
and 14 those of river w aters.
C hem ical analysis
T he contents of the m ajor dissolved com ponents are determ ined by the following
m ethods. N a+ and K + concentrations w ere determined by fiam e photom etry, Ca2+, M g2+, A13+
Si and B (N om ura et al., 1984) by inductively
coupled plasm a-atomic emission spectrom etry
(IC P-A ES), Fe2+ and Fe3+ by colorim etry with
the use of 2,2'-bipyridine, M n by atom ic absorp-
r
:
>
･ 14
lzu peninsula
)
<
4:
6
.9
23
' 4
J
Aono
river
'5
8'
l2
¥(
i3
)(
lO
'
shimogamo
/
1
V
)f >
Minamino
river
O
!
500m
Fig. 1. Sam pling locations. 1. Ose shore, 2. M orim enoyu; 3. Sakaeyu; 4. G ojyoonsen, 5. Shirasakayu; 6.
Yasum iishiyu, 7. Izuyu! 8. Tomidaiyongo! 9. K urabuyu! 10. A zum ayu; 11. Kinokuniyayu; 12. Fukujinyu, 13.
M inam ino river, 14. A ono river.
B isotopes of hot springs
tion spectroscopy, and Cl- and SO - by ion
chrom atography (Oi et al., 199la).
M easurem ent of boron isotopic ratios
A fter the determ ination ofthe boron concentration by IC P-A E S, an aliquot containing
about 300 pg boron of a w ater sam ple w as
treated forthe boron isotopicratio m easurem ent
(For a sam ple w hose total boron w as less than
300 pg,an aliquotofabout900 cm 3w astreated.).
T he aliquot w as first passed through a
chrom atographic colum n packed with a strongly
acidic cation exchange resin (M urom ac 50W 12X , H +_form , 100-200 m esh) to rem ove cationic species. T he boron contained in the
efiluent w as extracted by the m ethyl borate
distillation (K anzaki et al., 1978). T he boron
isotopic ratio, 11B lIOB, of the extracted boron
w as m easured with the surface ionization technique on a Varian M A T C H -5 m ass spectrom eter (N om ura et al., 1973). T he ion collector used w as a Faraday cup.In a few cases w here
the ion beam intensities of the N a2BO t species
were not suffi ciently high for the m easurem ent
with the Faraday cup, a secondary electron
m ultiplier (SE M ) w as used as collector. T he
11B /10B values determ ined with the SE M , (llB /
10B)SEM, w ere converted to the values with the
Faraday cup, (11B /ro B)F*,.d.y, by the equation,
(1IB / roB)F.,.d.y= I.0054(1IB/10B)SEM
(N om ura,
1990). O ur 11B/ roB value of the N B S SR M 951
boric acid standard with the Faraday cup (Oi et
al., 1989) is in good agreem ent with the certified
value of 4.0436 (C atanzaro et al., 1970). The
950/0 confi dence lim it in the present w ork w as
typically :!:0.20/0(Oietal., 1989;N om ura,1990).
R ESULTS
A nalytical results aresum m arized in T able I.
T he pH valuesof the hotspring w aters are betw een 7.45 and 8.67 (very w eakly basic), and the
w ater tem peratures range from 43.1 to 100'C
with the arithm etic m ean of66.7"C. The concentrations of m ajor dissolved com ponents differ
from w ater to w ater;the M orim aenoyu hot spring w ater is in general richest in various com -
149
ponents and the Fukujinyu w ater is poorest.
Each w ater contains N a+ and Cl- atthe highest
concentrationsascationic and anionicspecies,respectively. C om pared to the hot spring w aters,
the river w aters exam ined are very poor in
dissolved chem ical species. T he chem ical com position of the sea w ater sam ple is within the
range of com positions reported for surface sea
w aters by other researchers (Tsunogai, 1989).
T he boron contents of the hot spring w aters
vary from 0.02 to 2.01 m g/dm 3 and the average
is 0.87 m g/dm 3. This value is m uch sm aller than
the value of 9.I m g/dm 3 reported as average of
boron contents of 199 hot spring w aters collected throughout the Japanese island arcs
(M usashi, 1989). N o boron is found in the river
w ater sam ples within experim ental errors. The
sea w ater sam ple contains boron at 4.44
m g/dm 3, w hich is within the range of previously
reported values (N om ura, 1990).
T he boron isotopic com positions of the
w ater sam ples are given in tw o expressions in
Table I. O neisthe boronisotopic ratio,11B /roB,
and the other is 611B in perm il defi ned as
61IB =:[(1IB / ro B)sample/(1IB / ro B)standard II'1000,
w here (11B /10B)st..d*,d is the isotopic ratio of the
N BS SR M 951 boric acid (= 4.0436) and
(11B /ro B)sa*pte is that of the sam ple. T he boron
isotopic ratios ofthe hot spring w aters exam ined
range from 4.190 to 4.216 w hich correspond to
the variation in 611B from + 36.2 to + 42.6 perm il. C om pared to the previously reported values
for other hot spring w aters on the Japanese
island arcs (K akihana et al., 1987; M usashi et
al., 1988; M usashi, 1989; Oiet al.,199lb; O i and
K akihana, 1993), the present values are exceptionally high. Figure 2 shows the range of 611B
values previously reported for hot spring w aters
(consisting ofabout 140 data points) with [] and
that ofthe present data with I .T he fi gure clearly show s how the present 611B values are high as
those ofhotspring w aters.T he data on sea w ater
are also show n in Fig. 2. The boron isotopic
ratio of our sea w atersam ple( I ) w as within the
range of the variation in boron isotopic ratio
reported forsea w aters by other researchers (c])
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151
B isotopes of hotsprings
Sea water
Hot spring water
11B/10B
4.0
811B -20
C:L i
4.1
o
4.2
*20
*40
Fig. 2. Previous and present results for hot spring
waters on the Japanese islands and sea water. I , this
work; [], previousresults.
o
1:f
¥hFo 4000
(a)
+'e
+
Go;
Na+
I
2000
Ca2+
s 42-
(Schw arcz et al., 1969; N om ura et a/., 1984;
Spivack and E dm ond, 1987).
K+
10000
tcl ]/mgdm
O
DISCUSSION
C orrelation am ong the concentrations of dissolved com ponents of the hot spring waters
In Figs. 3a and 3b, w e plotted the contents of
the m ajor dissolved com ponents against the
chloride ion content for all the hot spring w aters
exam ined. All the com ponents show good linear
relations to the chloride content. T he leastsquares fit (L SF) calculations in the form of [A ]
= a[Cl-] + b yield:
[N a+] = 0.383[Cl-] + 61.3
[K +] = 0.0274[CI-] + 0.454
[M g2+]= _ 0.0000630[Cl-I + 6.29
[C a2+] = 0.233[C1-]- 38.9
[Si]= 0.00418[Cl-] + 18.5
[B] = 0.000173[CI-I + 0.0349
and
is:'
ho 60
F:
*'e
,foFi,::40
8
(b)
o
sj
o
o
o
20 o o
I
o
M gB+
B
10000
[cl]/mgdTne
Fig. 3(a). 3(b). C orrelations between concentrations
of m ajor dissolved components and that of chloride
ion forthe hotspring watersexam ined. Thesolidlines
are the least-squares fi tted lines in the form of
[species]= a[Cl ] + b.
o
[SO -1= 0.0146[Cl-] + 13.6,
w here concentrations are given in m g/dm 3. T he
solid lines in the fi gures are draw n by using these
relations. The relations strongly support the
speculation by Fukutom i (1936) and Sugisaki
(1962) that there is a deep geotherm al brine
under the Shim ogam o area, and that w hile flowing upw ards through its underground channels,
itis diluted by a surface w ater and com es outto
the surface as hotspring w aters at different w ater
outlets, with the degree of dilution diff ering
from outlet to outlet.
From the study on 6D and 3180 values and
chem ical com positions of hot spring w aters in
the Shim ogam o area, M izutani and H am asuna
(1972) estim ated the chem ical com position of the
Shim ogam o deep geotherm al brine and suggested that the brine is of m arine origin, being
derived from sea w ater. Based on their estim ation of the chloride ion content ofthe brine and
using the relations given above, w e estim ated the
contents of the m ajor dissolved com ponents of
the brine and tabulated the results in T able 2,
together with those of M izutani and H am asuna
(1972) and, for com parison, our results on sea
w ater. E xcept for m agnesium , our estim ate is
vef y similar to that of M izutani and H am asuna
(1972). T he large discrepancy in the m agnesium chloride relation betw een the tw o estim ates is
T. Oi et al.
152
Table 2. Estim ated chemical com position of the
Shim ogam o deep geotherm al brine
This work
Na+/ mgdm 3
K+
Mg2+
Ca2+
ClSO B
9220
654
7.80
5530
23900
363
4.17
M izutaniand
Hamasuna
(1972)
9270
618
1.34
5150
23900
298
Sea
water
(Ose)
10200
404
1240
404
18700
2680
4.44
probably due to the large data scattering around
the straightlinein the low m agnesium concentration region. T he enrichm ent of potassium ,
calcium and chloride ion contents and depletion
of sodium , m agnesium and salfate ion contents
in the geotherm al brine relative to those in sea
w ater suggest that the brine is a consequent of
the interaction ofsea w ater and hot silicate rocks
occurring underground (M atsubaya, 1991). T hat
is, the brine is directly derived from sea w ater as
has been suggested by M izutani and H am asuna
(1972).
Boron isotopic com positions
A s m entioned earlier, the boron isotopic
ratios (11B /10B) of the Shim ogam o hot spring
w aters are very close to that ofsea w ater, ranging from 4.190 to 4.216. T his result is concordant with the conclusions of the previous
geochem ical studiesthatthe Shim ogam o geotherm al brine is directly derived from sea w ater and
the Shim ogam o hot spring w aters are m ixtures
ofthe brine and a surface w ater with little boron
content. If the hot spring w aters contain not
only boron with m arine origin but bo ron with
nonm arine origin, the boron isotopic ratios of
the hot spring w aters should be low er than that
ofsea w ater (M usashi,1989; Oiet a/., 199lb; O i
and K akihana, 1993).
A nother im portant feature is that the boron
isotopic ratios ofthe hot spring w aters are close
to but as a w hole seem slightlylow erthan those
of sea w aters (See Fig. 2).
It has been experim entally observed and
theoretically explained that w hen boron is
distributed betw een liquid (w ater) and solid
phases in nature, the lighter isotope, IoB, is
preferentially distributed into the solid phase,
and thus the boron isotopic ratio of the w ater
phase becom es higher than that of the solid
phase (Shergina and K am inskaya, 1967;
Schw arcz et a/., 1969; P alm er et al., 1987;
Spivack and E dm ond, 1987; M usashi et al.,
199la). If a part of boron in sea w ater is adsorbed onto hot silicate rocks, the rem aining hot
brine m ust have a higher 11B l10B ratio than that
ofthe original sea w ater. Since the 11B /10B ratios
observed for the Shim ogam o hot spring w aters
are not higher than that of the O se sea w ater, a
sim ple m echanism of boron adsorption could
not be responsible for the low ering of the
11B l10B ratios of the heated sea w ater. Since the
boron content ofthe hot brine is low er than that
of sea w ater, a sim ple dissolution of llB-poor
boron from the rocks into the brine also m ay not
have taken place.
Alternative is that the 11B /ro B ratio of the
original sea w ater m ay have been low ered by
isotope exchange with llB-poor rocks.
K aw aguchi (1958) reported that volcanic rocks
in Japan containes boron at 7.5 ppm on an
average. Isozaki et al. (1973) estim ated that
value at 14 ppm . As for the boron isotopic com positions of volcanic rocks in Japan, w e in a
previous paper (M usashi et al., 199lb) reported
thatthe 11B l10B values ofthe G SJ rock reference
sam ples, JR-1(rhyolite), JR-2 (rhyolite) and JB2 (basalt),published by the G eological Survey of
Japan are 4.047 (611B = + 0.8), 4.044 (+ 0.1) and
4.047 (+ 0.8), respectively, all m uch low er than
that of sea w ater. Provided that the llB /10B
ratios of rocks surrounding the reservoirs and
uprising channels of hot brines are sim ilar to
those of the G SJ rock reference sam ples, boron
exchange betw een sea w ater/brine and these
rocks m ight low er the boron isotopic ratios of
the Shim ogam o hot spring w aters, although the
m agnitude of the boron isotopic exchange accom panying such boron exchange depends on
tem perature, pH of w ater, boron concentration
ratio betw een rock and w ater and so forth.
In Fig. 4, we plotted the llB /ro B (and 611B)
153
B isotopes of hot springs
4.22
, ,
*4 2
4.21
a)
o
+40
,
4.20
e,e
4.1 9 e e O
200
Depth/m
e
a)
*38 D
+36
400
Fig. 4. R elation of the boron isotopic ratio with the
depth of wells in the Shim ogam o area.
values against the depth of the w ells in the
Shim ogam o area. In spite oflarge errors on individual 11BlloB values, deeper w ells in general
seem to have higher llB /lOB ratios, with a couple
of exceptions. This tendency m ay supportthe existence of boron isotope exchange betw een the
brine and its surrounding rocks w hile flowing upw ards from its reservoir; a shorter path, i.e., a
deeper w ell, provides a lesser degree of boron
isotope exchange and hence gives a heavier
boron isotopic com position, although a deeper
w ell m ay not necessarily correspond to a shorter
path, w hich m ay cause the exceptions in the
11B /ro B-depth plot (M izutani, private com m unication, 1 993).
C ONCLUSIONS
T he m ajor fi ndings of the pre ent w ork on
boron isotopic com positions of the Shim ogam o
hot springs are sum m arized as follows.
1) T he boron isotopic ratios ofthe Shim ogam o
hot spring w aters range from 4.190 to 4.216,
w hich corresponds to the variation in 311B from
+ 36.2 to 42.6 perm il. T hese values are very high
com pared to those of hot springs in other areas
ofthe Japanese islands and are close to the value
of sea w ater.
2) T he chem icalcom positions ofthe w aters suggest that hot spring w aters are m ixtures of a deep
geotherm al brine and surface w ater with variable
m ixing ratios.
3) The estim ated chem ical com position of the
brine and the boron isotopic ratios ofthe hotspr-
ing w atersindicatethat the brine is form ed by a
direct interaction of sea w ater with hot
underground rocks.
Acknowledgm ents- W e gratefully acknowledge M r.
S. W atanabe of the H ot Spring Association of
M inamiizu for his help in collecting hot spring water
sam ples, Professor M . O kam oto of Tokyo Institute of
Technology For putting a Varian M A T C H-5 m ass
spectrometer at our disposal and Dr, M . N om ura,
T.1.T., for his assistance in the m ass spectrom etric
m easurementsof boronisotopic ratios. This work was
supported by the Salt Science Research Foundation
(Contract N o. 9112).
R EFERENCES
Catanzaro, E. S., C ham poin, C. E., Garner, E. L.,
M arinenko, G., Sapenfield, K. M . and Shields, W .
R.(1970) N B S Spec. P ubl. (US) N o. 260-17.
Fukutomi, T.(1936) Physical andchemicalproperties
of the Sim ogam o, Rendaizi and Sim okawazu therm al springsin southern lzu Peninsula. I.B ull. Earthq. R es. Inst. 14, 259-270.
Isozaki, A., Yoshida, M ., Utsumi, S. and lw asaki, I.
(1973) The boron content of volcanic rocks in
Japan.Nihon Kagakukai Shi(J. Chem. Soc. Jpn.),
1896-1904 (Japanese).
Kakihana, H ., Ossaka, T., Oi, T., M usashi, M .,
Okam oto, M . and N om ura, M . (1987) Boron
isotopic ratios of som e hot spring w aters in the
Kusatsu-shirane area, Japan. G eochem. J. 21, 133137.
Kanzaki, T., Nom ura, M ., Ozawa, T. and Kakihana,
H. (1978) Separation of boron from fum arolic condensates by the m ethyl borate distillation m ethod
for the isotopic analysis. B unseki Kagaku (A na/.
Chem.) 27,481-485 (Japanese).
Kaw aguchi, H. (1958) Boron in volcanic rocks in
Japan. Nihon K agaku Zasshi (J. Chem. Soc. Jpn.),
478-484 (Japanese).
M atsubaya, O. (1991) N essui no C hikyukagaku
(Geochemistry of geotherm al fluids). Shokabo,
Tokyo (Japanese).
M izutani, Y. and H am asuna, T. (1972) Origin ofthe
Shim ogam o geotherm al brine, Izu. K azan 2 (B ull.
Volcanol. Soc. Jpn. 2) 17, 123-134 (Japanese).
M izutani, Y., Asai, H. and H am asuna, T. (1975)
Origin of neutral chloride therm al w aters from the
south-eastern part oflzu Peninsula, Japan. K azan
2 (B ull. Volcanol. Soc. Jpn. 2) 19, 139-150
(Japanese).
M usashi, M ., N om ura, M .,O kam oto M ., Ossaka, T.,
Oi, T. and K akihana, H. (1988) Regional variation
l54
T. Oi et al.
in the boron isotopic com position of hot spring
waters from central Japan. Geochem . J. 22, 205214.
M usashi, M . (1989) Boron isotopic com positions in
nature. D octoral thesis, Sophia U niversity, Tokyo
(Japanese).
M usashi, M ., Oi, T., Ossaka, T. and Kakihana, H.
(199la) N atural boron isotope fractionation between hot spring water and rock in direct contact.
Isotopenpraxis 27, 163-166.
M usashi, M ., Oi, T., Ossaka, T. and Kakihana, H.
(199lb) Extraction of boron from GSJ rock
reference sam ples and determination of their
isotopicratios, A nal. C him. A cta 231, 147-150.
N om ura, M ., Okam oto, M . and Kakihana, H. (1973)
Determination of boronisotope ratio by the surface
ionization m ethod. Shitsuryo B unseki (M ass Spectrom etry) 21, 277-281 (Japanese).
N om ura, M ., Kanzaki, T., Ozaw a, T., Okam oto, M .
and K akihana, H. (1982) Boron isotopic com position of fum arolic condensates from som e volcanoes
in Japaneseisland arcs. Geochim. Cosm ochim. A cta 46, 2403-2406.
Nom ura, M ., O kam oto, M . and K akihana, H.(1984)
D etermination ofboron content and boron isotopic
ratio of seawater sam ples. N ihon K aisuigakkai Shi
(B ull. Soc. Sea W ater Sci.. Jpn.) 38, 14-19
(Japanese).
N om ura, M . (1990) M easurem ent of boron isotopic
ratios and its application in geochem istry. D octoral
thesis, Sophia U niversity, Tokyo (Japanese).
N om ura, M ., Fujii,Y. and O kam oto, M . (1990) The
isotopicratios of boron in coals. Shitsuryo B unseki
(M ass Spectrom etry) 38, 95-100 (Japanese).
Oi, T., N om ura, M ., M usashi, M ., Ossaka, T.,
O kam oto, M . and K akihana, H. (1989) Boron
isotopic com positions of som e boron minerals.
G eochim . Cosm ochim. A cta 53, 3189-3195.
Oi, T., Ossaka, T., Hiratsuka, Y., Y am azaki, T.,
K akihana, H. and Ossaka, J. (199la) Infiuence of
acidic waste waters from the Shirane sulfur mine
upon river waters of the Osozaw a river w ater
system . Nihon Kagakukai Shi (J. Chem. Soc. Jpn.)
1991, 478-483 (Japanese).
Oi, T., M usashi, M ., Nom ura, M ., Ossaka, T.,
O kam oto, M . and Kakihana, H . (199lb) Influence
of sea w ater on boron isotopic ratios of hot spring
watersin Japan.N ihon KaisuigakkaiShi(Bull. Soc.
Sea W ater Sci.. Jpn.) 45, 29-34(Japanese).
Oi, T.and Kakihana, H.(1993)Influence of seaw ater
on boron isotopic com positions of hot spring
w aters in Japan. 7th Symp. on Salt I, 159-164.
Palm er, M . R., Spivack, A. J. and Edm ond, J. M .
(1987) Tem perature and pH controls over isotopic
fractionation during adsorption of boron on m ari-
ne clay. Geochim. Cosm ochim. A cta 51, 23192323.
Palmer, M . R. and Slack, J. F.(1989) Boron isotopic
com position of tourm aline from m assive sulfide
deposits and tourm alinites. C ontrib. M ineral.
Petrol. 103, 434-451.
Palm er, M . R. and Sturchio, N. C.(1990) The boron
isotope system atics of the Yellowstone N ational
Park (W yoming) hydrotherm al system: A reconnaissance. Geochim. Cosm ochim. A cta 54, 28112815.
Palm er, M . R. (1991) Boron-isotope system atics of
H alm ahera arc (Indonesia) Iavas: Evidence for involvem ent of the subducted slab. Geology 19, 215217.
Sam ejim a, T., Iwahashi, T. and Kuroda, N. (1968) A
basic investigation on the geotherm al developm ent
in the lzu Peninsula. Shizuoka Prefecture
(Japanese).
Schwarcz, H. P., Agyei, E. K. and M cM ullen, C. C.
(1969) Boron isotopic fractionation during clay adsorption from sea-water.Earth Planet. Sci. Lett. 6,
l-5.
Shergina, Y u. P. and Kaminskaya, A. B. (1967) Experim ental sim ulation of the natural separation of
boron isotopes. G eokhim iya 10, 1111-1115.
Shizuoka Prefecture (1989) Survey of hot springsin
Shizuoka Prefecture, pp. 16-17 (Japanese).
Slack, F. L., Palm er, M . R. and Stevens, B. P. J.
(1989) Boron isotope evidence for theinvolvem ent
of non-m arine evaporites in the origin of the
Broken Hill ore deposits. N ature 342, 913-916.
Spivack, A . J. and Edm ond, J. M . (1987) Boron
isotope exchange between sea-water and the
oceanic crust. Geochim. C osm ochim. A cta 51,
1033-I043.
Spivack, A. J., Palmer, M . R. and Edm ond, J. M .
(1987) The sedim entary cycleofthe boron isotopes.
Geochim. Cosm ochim. A cta 51, 1939-1949.
Sugisaki, R. (1962) Geochemical study of ground
w ater. J. Earth Sci. N agoya Univ. 10, 1-33.
Swihart, G. H., M oore, P.B.and Callis,E. L.(1986)
Boron isotopic com position of m arine and nonm arine evaporite borates. G eochim. Cosm ochim.
A cta 50,1297-1301.
Tsunogai, S.(1989) Chikyuhyoso niokeru busshitsujunkan (M aterial cycles in the earth's surface) in
C hikyukagaku (Geochemistry) ed. by S. M atsuo,
K odansha, Tokyo pp. 107-128 (Japanese).
Vengosh,A.,Starinsky,A.,Kolodny, Y.and Chivas,
A. (1991) Boron isotope geo-chem istry as a tracer
oftheevolution ofbrinesand associated hotsprings
from the Dead Sea,Israel. Geochim. Cosm ochim.
A cta 55,1689-1695.