-
t077
Canadian MineralogistVol. 30, pp. 1077-1092 (1992)
CI.BEARING AMPHIBOLE IN THE SALTON SEA GEOTHERMAL
SYSTEM.CALIFORNIA
MASAKI ENAMI-, JTIHN G. LIOU nTvn DENNIS K. BIRDDeparttnent of
Geology, Stanford University, Stanford, Califumia 94305, U.S.A.
ABsrRAcr
Calcic amphiboles with up to 2.7 wt.fo Cl occur in
metasandstones, metabasites and veins at depths berween 3, 100 to
3,180 mand temperatures in excess of 350'C in the State 2-14 well
of the Salton Sea geothermal system (California). These
amphiboleswere formed by reactions involving high-salinity
geothermal fluids, with 15.4 to 19.7 wt.Vo total dissolved Cl.
Coexisting phasesinclude quartz, plagioclase, K-feldspar, epidote,
clinopyroxene, apafite, and titanite. The Cl-bearing amphiboles
range incomposition from hastingsitic (Cl > 1 wt.Vo) to
actinolitic (Cl < 0.5 wt.7o). Texturally complex intergrowths of
actinolitic andhastingsitic amphiboles occur at depths greaterthan
3,140 m, suggesting a miscibility gap benveen the two amphiboles.
Measuredcompositional variations suggest a crystal-chemical control
on the Cl content in the calcic amphiboles: (1) the chlorine
content ofamphiboles increases with increasing edenite substitution
{tAl1Na6;t+lAltr-lSi-t}; (2) the maximum observed Cl content of
anamphibole increases with increasing X(Fez*) value. Comparison of
Cl content in amphiboles from the Salton Sea geothermalsystem,
submarine metabasites, skams, high-grade metamorphic rocks and
igneous rocks implies that a main factor in controllingCl-for-OH
substitution in amphibole is different in low- and high-chlorinity
environments. In low-chlorinity environments, the Clcontent of an
amphibole increases with increasing chlorinity of the coexisting
fluid, and is defined by partitioning of Cl betweenthe two phases,
as well as the crystal-chemical constraints imposed by (Na+K), Fe,
and Al substitution. On the other hand,amphiboles coexisting with
the Salton Sea and more saline fluids are enriched in Cl; Cl
content strongly depends on X(Fez+) andthe edenite content of the
amphiboles. They may achieve a maximum Cl content, and the extent
of Cl-for-OH substitution iscrystal-chemically controlled.
Keywords: Cl-bearing amphibole, crystal chemistry, salinity,
geothermal system, Salton Sea Califomia.
SoruMarnE,
Nous trouvons des amphiboles caJciques ayant des teneum en Cl
jusqu'h 2.7Vo (poids) dans des grbs mdtamorphis6s, desm6tabasites,
et des veines d profondeul entre 3 I 00 et 3 I 80 m, et h des
tempdratures au dessus de 350"C dans le puits State 2-l 4du systbme
g6othermique de la mer de Salton (Califomie). Ces amphiboles ont
6td form6es par rdaction impliquant des saumuresgdothermiques, I
salinit6 entre 15.4 et l9.7Vo en Cl dissout. Sont aussi prdsents
quartz, plagioclase, feldspath potassique, 6pidote,clinopyroxbne,
apatite et titanite. Les amphiboles chlorifdres ont une composition
hastingsitique (>lVo en poids de Cl) dactinolitique (< 0.57o
de Cl). Une intercroissance complexe des deux amphiboles,
rencontr6es b une profondeur au deli de 3,140m, t6moignerait de
I'imporrance d'une lacune de miscibilit6 entre les deux amphiboles.
l.es variations mesur6es en teneur en Clseraient r6gies par des
contraintes. cristallochimiques: ( I ) Ia teneur des amphiboles en
chlore augmente avec I'impoftance d'unesubsti tut
ionverslep6le6deniteI l^l(Na,K)t4lAltrtsi r ]
,et(2)lateneurmaximumobserv6eenCl
augmenteavecX(Fez+).Unecomparaison de la teneur en Cl des
amphiboles provenant du systdme g6othermique de la mer Salton, des
m6tabasites, des skams,des roches m6tamorphis6es h un facies 6lev6,
et des roches magmatiques indique qu'un facteur diffdrent rdgit la
substitution duCl dans des milieux i chlorinitd faible et 6lev6e.
Dans un milieu l faible chlorinitd, la teneur d'une amphibole en Cl
augmenteavec la chorinit6 de la phase fluide coexistante, et ddpend
de la r6partition du Cl entre les deux phases, et des
contraintescristallochimiques dues d I'incorporation de (Na+K),Fe
et al. D'autre part, les amphiboles qui coexistent avec les
saumures de lamer Salton et des saumures encore plus salines sont
enrichies en Cl; leur teneur en Cl ddpend de X(Fez+) et de la
teneur en 6denite.Elles peuvent aueindre la saturation en Cl, et la
port6e de la substirurion du Cl au OH esi ici rdgie par des
contraintescristallochimiques.
(Traduit par la R6daction)
Mots-clds: amphibole chlorifore, chimie cristalline, salinitd,
systdme g6othermique, mer de Salton, Califomie.
"Present address: Department of Earth and Planetary Sciences,
School of Science, Nagoya Univenity, Nagoya 46zt-0 l, Japan.
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1078 THE CANADIAN MINERALOCIST
INTRODUcnoN
High concentrations of Cl in calcic amphiboles havebeen reported
from various rock-types: submarinemetabasite, skarn, amphibolite,
granulite, granitic andgabbroic rocks, but the conditions necessary
for theformation of Cl-rich amphiboles are notwell understood(see
review by Suwa et al. 1987). Determination of Clpartitioning
between calcic amphibole and a coexistingfluid is important for
evaluating the geological cycling,amount and distribution Cl in the
Earth's crust.
Relationships between Cl content and the major-element chemistry
of amphiboles on one hand, and Clcontent of the coexisting fluid
have been discussed bymany authors. Volfinger et al. (1985) and
Kamineni( 1986) emphasized that Cl content of a calcic
amphiboleincreases with increasing of Fe2*. Ito &
Anderson(1983) studied calcic amphibole in metamorphosedgabbros
from the Mid-Cayman Rise and consideredthat A1 substitution at
tetrahedral sites allows increas-ing substitution of Clfor OH.These
authors emphasizeda crystal-chemical control of Cl content in
amphibole.On the other hand, Vanko (1986) concluded that theCl
content of amphibole from the Mathematician Ridgevaries as a
function of the Cl activity of coexistinghydrothermal fluid, and
pointed out that Cl does notsimply replace OH wherever Fe is
available in thefluid phase. Vanko (1986) also showed that some
am-phiboles in greenschists from the Mathematician Ridgeare more
Cl-rich than those in amphibolites. Theseobservations and
occurrences of Cl-rich amphibole inigneous rocks (e.9., Kamineni
1986) and high-grademetamorphic rocks (e.g., Sharma 1981) suggest
that Clsubstitution for OH in calcic amphiboles can occur overwide
range ofpressure, temperature, and fluid composition.
The Salton Sea Scientific Drilling Project success-fully drilled
Colorado River sediments within the SaltonSea geothermal system to
a depth of 3,220 m, wheretemperatures exceed 350oC. Hydrothermal
solutions ofthe Salton Sea geothermal system a.re NaCl-rich
brineswith Cl contents of approximately 15 wt.7o (White1968). Fluid
inclusions within anhydrite contain up to507o crystals of halite,
sylvite and carbonates in aNa{a-K{l brine (e.9., White 1968,
McKibbenet al.1987). During the course ofour study
ofamphibolite-fa-cies mineral assemblages within core and chip
samplesof the State 2-14 well, we identified and analyzed grainsof
Cl-rich (up to 2.7 wt.Vo) calcic amphibole in hy-drothermally
altered metasandstones, metabasites andveins at depths greater than
3,140 m. To our knowledge,this is the first description of Cl-rich
amphibole from anactive geothermal system. In this paper, we report
thechemical characteristics of the Cl-bearing amphibolefrom the
Stats 2-14 well, and discuss the crystal-lographic constraints of
Cl substitution in calcic amphi-bole in geothermal, metamorphic,
and igneous environ-mems.
GEoLocICAL SEI'ING
AND PETROGRAPIilC DESCRTP,NON
The Salton Sea geothermal system lies near thesoutheastern end
of the Salton Sea" within the SaltonTrough of southern Californi4
which is the landwardextension of the Gulf of California Rift
system (Whiteet al. 1963, Helgeson 1968). The
high+emperature(>350'C) and high-salinity brine (> 15 wt.Vo
totaldissolved solids) is responsible for crystallization
ofsilicate, sulfide, and oxide minerals throughout thegeothermal
system. Muffler & White (1969) andMcDowell & Elders (1980)
described greenschist-faciesmetamolphism occurring at temperature
above 300oC at2-3 km depth. On the basis of mineral parageneses
inmetasandstones from the Elmore I well (cl Fig. 1), threemineral
zones were identified with increasing tempera-ture, and are
referred to as the chlorite, biotite, and garnetzones (McDowell
& Elders 1980). These studies haveshown dramatic mineralogical
modifications of Colo-rado Riverdelta sediments within and nearthe
numerousthermal anomalies at the Salton Trough. In
particular,systematic changes in mineralogy of authigenic
layersilicates (McDowell & Elders 1980) and alkali
feldspar(McDowell 1986) with increasing temperature suggestan
approach to chemical equilibration between theauthigenic minerals
and the coexisting fluid phase in thegeothermal system.
The State 2-14 well is located near the northeasternflank of the
Salton Sea geothermal system Gtg. 1).Grsenschist- and
amphibolite-facies metamorphism ac-companying hydrothermal
metasomatism observed inmetasandstone and metashale core samples
have beenreported by Cho et al. (1988) and Shearer et al.
(1988).Parageneses of secondary minerals along veins andfractures
have been extensively investigated (e.9.,Caruso et al. 1988,
McKibben & Elders 1985, McKib-ben & Eldridge 1989).
On the basis ofdegree ofhydrothermal alteration ofmetasandstone"
three zones have been described withincreasing depth and
metamorphic temperature: chlo-rire--calcite (6lG-2,480 m), biotire
(2,480-3,000 m) andclinopyroxene (3,00V3,220 m) zones.
Characteristicassemblages of minerals of metasandstone, in
additionto epidote, quartz, albite, apatite and titanite, are:
chlorite+ K-feldspar + phengitic mica + calcite for the
chlorite-calcite zone, biotite + chlorite + K-feldsparfor the
biotitezone, and diopside + actinolite (or actinolitic horn-blende)
+ K-feldspar + oligoclase for the clinopyroxenezone(Cho et a/.
1988, Enami et al.,inprep.). tow-gradeamphibolite-facies
assemblages of minerals, includinghastingsitic amphibole and
andesine or more calcicplagioclase, occur in metasandstone,
metabasite andveins at depths greater than 3,140 m in the
clinopyroxenezone. A chain silicate with composition
intermediatebetween actinolite and diopside (Ca-bearing
pyribole)was reported in a sample from the lowest-grade part ofthe
clinopyroxene zone (Cho et al. 1988). Agarnet-bear-
-
l fullEt lsland 11f35'f,
Salton Sea
Geothermal wel I
Quaternaryrhyol ite dome
o o
'o'GlCIor;-il
oo--J o
ing assemblage reported from the Elmore I well(McDowell &
Elders 1980) was not found in the samplesstudied.
SAMPLE DESCRIPTONAND ANALYT'ICAL PROCEDLRES
The workreportedherewas done on ten sampJes fromdepths of 3,100
to 3,180 m in the Stile 2-14 well (Fig.2), where the measured
temperature exceeds 350"C(Sass er a/. 1988). Excluding core sample
9907b, all thesamples were drilling chips less than 0.5 cmin
maximumdimension. The chips include mixtures of metashale
andmetasandstone with subordinate metabasite and aggre-gates of
vein minerals. These samples were pulverizedto 0.1-0.35 mm with a
disk crusher. Amphibole-bearingfractions were concentrated with an
isodynamic separa-tor, impregnated with epoxy resin and polished
forpetrographic observation and electron-probe microana-lysis.
Chlorine-bearing amphibole was identified using aKEVEX
energy-dispersion spectrometer. Quantitativechemical analyses were
done on automated JEOLelectron-probe microanalyzers JCXA-733 at
StanfordUniversity and Nagoya University. Accelerating volt-age,
specimen current and beam diameter were 15 kV,12 nA and 3 pm,
respectively. Well-characterizedminerals and synthetic phases,
including sodalite andCl-rich hastingsite (for Cl), were used as
standards.
tw9
Precision (1o level) of Cl microanalysis is 0.1 wt.%io incount
statistics on Cl-rich amphibole. Fluorine contentfor all analyzed
grains is below the detection limit of0. Iwt.Vo. Fe3+ contents were
estimated using the methodsof Papike et al. (1974).
AMPHTBOLES AND COEXISTING MTNSRALS
Mineral assemblages associated with Cl-bearing am-phibole are
given in Table l. Owing to the small size ofthe chips, it was not
always possible to determinewhether the protolith is sandstone,
basaltic material, orvein material. In such cases, quartz-bearing
chips areconsidered to be metasandstone. Among undifferenti-ated
quartz-free chips, monomineralic or K-feldspar-bearing chips are
considered to be vein material, andwhere amphibole and plagioclase
are dominant phases,the chip is considered to be metabasite.
The amphibole-bearing metasandstone chips ana-lyzed ue composed
mainly of quartz, plagioclase,amphibole, epidote and K-feldspar;
clinopyroxene, apa-tite, biotite, titanite, pyrite and zircon also
occur as minorphases. The metabasite chips consist of
amphibole,plagioclase and epidote, with minor amounts of
clinopy-roxene, quartz, apatite, and pyrite. The major phases ofthe
veins are amphibole, epidote, and plagioclase;clinopyroxene,
K-feldspar, quafiz, apatite, titanite, andpyrite occur in some vein
chips. Most grains of plagio-clase in the metasandstone have An
contents less than
CI-BEARING AMPHIBOLE IN THE SALTON SEA GEOTI{ERMAL SYSTEM
Ftc. l. Location map of the State 2-14 well, together with sites
of previous drilling in the
Salton Sea seothermal field.
-
TTIE CANADIAN MINERALOGISTr080
F,{l?F_.?t! I[:]rri,N::l II IG -
-II
@
r-n4trsil
ilnlL-,
| | lletasandstone
! uetauasiteffi vein
5 t 0 1 5Alz0r (wt%)
2(wt%)
0 tc l
3,tw/
$Tr*
_ ) /f L f
l+0510
Alz0r (rt%)
Major-element chemistry of amphiboles
More than 200 chemical analyses of calcic amphi-boles were
carried out; representative compositions aregiven in Table 2.
Al-poor actinolitic amphibole occursin all the samples studied
(Fig. 2). Only five samples(10300, 10330, 10360" 10390, and 10430)
from depthsbetween 3,140 and 3,180 m contain coexisting
Al-richhastingsitic and Al-poor actinolitic amphiboles (Fig.
3a).There is a dramatic increase in the Cl and Al contents
ofamphibole between 3,130 m (sample 10260) and 3,140m (sample
10300). This also corresponds to an increasein the abundance of
metabasite sills and dykes in the
t]FE- '
l1tll l -
0 1Cl (rt%)
Frc. 2. Variations ofthe Cl and Al2O3 contents (wr.7o) ofcalcic
amphiboles in metasandstone, metabasite and vein chips from
theSahon Sea State 2-14 well, with depths of chip samples. Some of
the data on Al2O3 for samples 10160 and 10230 are fromCho etal.
(1988).
50 mol%o; some plagioclase in metabasite and veinchips are as
calcic as Ane6. The albite content of theK-feldspar coexisting with
plagioclase is about7-8 molVo, suggesting equilibrium temperatures
of350-400'C using the two-feldspar geothermometerproposed by Green
& Usdansky (1986) and Fuhrman &Lindsley (1988). The Al2O.,
CaO contents, and X(Fe2*)[= Fe2*(Fez* + Mg)] value of clinopyroxene
are < 0.5wt.%o, 23.5-24 wt.%o, and 0.3-0.5, respectively.
Phaserelations, parageneses and chemical compositions ofother
minerals in the clinopyroxene zone of the State2-14 well will be
presented in a subsequent communi-cation.
-
CI-BEARING AMPHIBOLE IN THE SALTON SEA CEOTI{ERMAL SYSTEM
TABLE 1. MINERALASSEMBTAGES OF ANALYZED CHIPS
l08 l
Cam Pt Ep Qa Kfs Cpx Samples
6 , 71 , 6J
4 , 82 , 3 , 71 , 525 , 6< 1
2
Mstasandstone tAp,fitsTit
r Ap, Ti! ZrnrTit, Pyt Ap, Titt Ap, fit Zrn,Py,Bt
+ + + + ++ + . f . t+ + ++ + + + ++ + + . t+ + ++ + ++ + + ++ +
++ +
4 , 83 , 4 , 6 , 744 , 654 ,s4
+ r P y!AP
+
Metabasite f + +f + f+ ++ t+ + ++ ++
c P y! P y
t
4 , 7
)4 , 6
2 , 4 , 5 , 6 ,7 ,8
+ + ++ + ++ ++ + ++ f ++ . t ++ +
tAp,Tit
s P yr P y
Note: Abbrwiations are: Cam, calcic amphibole; Pl plagioclase;
Ep, epidote; Qtz, quare;Kfs, K-feldspac Cpx, clinopyroxeneaAp,
apatitei Tit, titanite; Zm' zircon; Py, pynte; Bt' biotile;t, 101
60; 2,- 1D50i 3, lO?KOi 4, 103CXi, 5; 10330; 6, 10360; 7, 10390; 8,
I 0430.
chips recovered. The maximum Cl and Al contents ofamphibole
at3,140 m are essentially the same as thoseobserved at the bottom
of the drill hole (3, I 80 m).
Most of the compositions corespond to actinoliticand
hastingsitic amphiboles (Fig. a). Some of theintermediate
compositions may refer to mixtures of twoor more amphiboles that
could not be resolved with theanalytical techniques used.
Hastingsitic amphibole isdark bluish green and occurs as prismatic
subhedralcrystals 0.02-0.1 mm in size. Chemical variations
fromferro-homblende, through ferro-pargasitic hornblendeand
hastingsitic hornblende, to hastingsite (Fig. )reflect both
chemical variations among different drillchips and zonation within
single grains. Some grainsshow complex zoning represented by patchy
inter-gowths of hastingsite with either hastingsitic horn-blende or
ferro-pargasitic hornblende (Fig. 3b). Thehastingsitic amphibole in
metabasites and veins has avalue ofX(Fe2+) between 0.5 and 0.85; in
metasandstonechips, values are between 0.45 and 0.65. The
atalyzedhastingsitic amphibole contains 034.7 vtt.Vo TiO2,similar
to Cl-rich amphibole from submarinemetabasites and skarns
(e.g.,0.3V1.14 wt.7o, Jacobson1975). The total alkali content
(Na+K) is between 0.5and 0.8 pfu (per formula unit for O=23), and K
contentincreases from 0.3 to 0.6 pfu with increasing total
alkalicontent. Sodium is fairly constant at 0.27 t 0.03 pfu.
Theactinolitic amphibole is colorless or pale green andoccurs
mostly as acicular subhedral crystals (less than
0.1 mm long). Some grains of actinolitic amphibole areintergrown
with hastingsitic amphibole (Fig. 3a).
Two lines of evidence suggest that both hastingsiticand
actinolitic amphiboles are formed in the present-daygeothermal
system: (l) they show a prismatic andsubhedral habit, and occur as
pore fillings in somemetasandstones, and (2) Al, Na and K contents
ofamphibole increase with increasing depth and tempera-ture (Fig.
2).
The coexisting actinolitic and hastingsitic amphibolessuggest a
miscibility gap in the calcic amphibole series(Cooper &
Lovering 1970, Tagiri l9ll,Marayama etal. 1983, Ishizuka 1985). In
coexisting amphiboles,average contents of tetrahedrally coordinated
aluminum,t4lAl, andA-site alkali contents, h1154+K), are
0.224.54and 0.02-0.13 pfu, respectively, for actinolitic
amphi-bole, and 1.42-1.79 and 0.474.73 ptu for
hastingsiticamphibole (Fig. 5). The compositional range of
themiscibility gap in terms of Tschermak substitution {=f4lAl -
fAl(Na+K)] is from 0.22 to 1.06 for a Mg-poorpair (Mg is 2.3 pfu in
actinolitic amphibole and 0.9 ptuin hastingsitic amphibole), and
from 0.41 to 0.98 ptu fora Mg-rich pair (3.1 ptu in actinolitic
amphibole and 2.0ptu in hastingsitic amphibole). The miscibility
gapbecomes narrower with increasing Mg content.
Cl content of amphibole
Relationships between Cl content of calcic amphi-
-
1082 TTIE CANADIAN MINERALOGIST
TABI,E Z REPRESENTATIVE ANALYSES OF CI-BEARJNG CArcIC
AMPHIBOLES
Sample
Chip
103m 1(D60 10250 10160
01b 01b 01b 05v 05v 05v 14s 01s 04s 09v 06b 08s Lzv 11b 16v 06s
10s 01s
53.6 52.6 52.90.07 0.15 0.113.80 3.20 2.89n.d. n.d. n.d.
16.0 18.0 13.0o.23 0.37 0.L7
L2.2 LL.8 15.6t2.5 L2.3 L2.60.37 0.31 0.230.07 0.16 0.180.04
0.13 0.M
42.8 52.90.51 0.039.89 3.380.00 0.10
18.2 10.6034 0.229.62 16.9
L2.1 12.6L.O1 0.281.52 0.081.(B 0.05
39.O 42.t 5r.8 52.2o.32 0.33 0.16 0.03
10.9 9.86 4.08 1.69n.d. n.d. n.d. n.d.
26.4 23.5 t3.7 25.7o.28 0.29 0.32 0.69s.37 7.44 L4.4 6.88
Lt.I tz.O L2.4 rl.go.75 0.87 0.31 0.182.39 L.4L 0.14 0.04LA O.93
0.08
-
CI-BEARING AMPHIBOLE IN THE SALTON SEA GEOTHERMAL SYSTEM
6.5
1083
6.0
8.0
tA l (Na + K) 0.5 , t6 lA l>Fe3+
Fr-EdcHbl
Fr-PrgcHblo%' Fr-Prg
Fn PrgcHbl Fn Prgo
Edc Hbl
Prgc Hbl Prg
6.5 6.0Si (pfu. )
tAl(Na + K) 80.5, t6 lAl< Fe3+
Fr-EdcHbl o (
o o
Hsc Hbl
t;dHs
[|gn HsTsF'
o
HblI'lgnHsc
Edc HblHgs-Hsc
Hbl Hgs-Hs
6.5Si (p fu . )
00
Frc. 4. Chemical characteristics of calcic amphiboles from the
Salton Sea S@te2-14 well as a function of X@e2+) [= Fe2*/(Fe2*+
Mg)l , numbers of atoms of Si and (Na+K) in theA-site {lAl(Na+K)}
performula unit (pfu). The nomenclature of amphibolesfollows l.eake
(1978). Abbreviations are: Act actinolite, Actc actonolitic, Edc
edenitic, Frferro, Fn ferroan, Hs hastingsite,Hsc hastingsitic, Hbl
hornblende, Mgn magnesian, Mgs magnesio, Prg pargasite, hgc
pargasitic, Tr tremolite, Trc tremolitic,Tsc tschermakitic.
Tsc Hbl(wt%)
o ct
-
1084 THE CANADIAN MINERALOGIST
0 . 6
tAr1tr16 + 1) 1ptu.)
j 1 . 5
e.=r 1 . 0
Frc. 5. Variations in proportion of Cl (wt.%o\ as a function of
the number of atoms of Al inthe tetrahedral site 1f+iat, -6
tallNa+Kl in amphiboles from the Salton Sea State2-14well. Five
pairs of coexisting amphiboles are shown by tie lines thal
represent averagecompositions of coexisting actinolitic and
hastingsitic amphiboles.
bole,lithology anddepth in thedrill hole are summarizedin Figure
2. Actinolite at depths less than 3,125 m(samples 10160, 10250,
10260) contains usually lessthan 0.2 wt.Vo Cl. The coexisting
amphiboles at depthsgreater than 3,140 m (samples 10300, 10330,
10360,10390, and 10430) have Cl contents in the range0.0-2.7wt.7o.
Amphiboles in metabasites and veins have similarranges in Cl
content, but at any given depth, amphibolegrains in metasandstones
have lower Cl content (usuallyless than I wt.Vo). The Cl-rich
amphibole in themetabasites and veins also has higher X(Fe2+)
andta(gatK) contents than the amphibole in metasand-stones at
similar depths. This relationship suggests thatthe variations in
extent of Cl-for-OH substitution in theamphibole structure are
largely controlled by crystal-chemical constraints rather than
differences in tempera-ture or Cl-content of the coexisting fluid
phase.
On the basis of a variety of drill hole and fluid-inclu-sion
experiments, measured temperatures, pressures andfluid
compositions, Helgeson (1968) and McKibben etal. (1987, 1988) have
identified large gradients insalinity within the Salton Sea
geothermal system. Ahigh-salinity geothermal brine is overlain by a
lower-sa-linity fluid; steep gradients in salinity and
perhapsdensity occur at depths between 1,000 and 1,500 m atthe
center of the geothermal system. Near the centralgeothermal anomaly
(at depths > 1,900 m), the measuredCl content of the geothermal
brine is fairly constant at15.4-19.7 wt.7o (Michels 1986, Thompson
& Fournier1988). In addition, apatite in the Cl-rich and
Cl-pooramphibole-bearing samples have similar Cl contents(0.37 t
0.16 wt.Vo Cl in samples 10360 and 10390, 0.34+ 0.08 wt.7o in
samples 10250 and 10260). The near-
constant chlorinities predicted for the deep geothermalfluid and
for apatite suggest that both the Cl-rich andCl-poor amphiboles in
the samples studied were formedunder similar chlorinities of the
fluid. We conclude thatvariation in Cl content of amphiboles (Fig.
2) is not aconsequence of amphibole formation in fluids of
widelyvarying chlorinity, but rather of crystal-chemical
con-straints among the calcic amphiboles, as discussedbelow.
Crystal-chemical control of Cl content in amphibole
Several authors have noted that the Cl content ofcalcic
amphibole is crystal-chemically controlled. Ito &Anderson ( I
983) noted that Al substitution at tetrahedralsites coupled with
Fe3* substitution at octahedral sites or(Na+K) substitution at the
A site allow increasingreplacement of OH by Cl. Vielzeuf (1982)
showed apositive correlation between Cl and K contents ofamphiboles
in chamockite from Sakeix, French Py-ren6es. Volfinger et al.
(1985) and Kamineni (1986)emphasized that substitution of Cl for OH
is accompa-nied by Fe2* substitution at octahedral sites. All
thesesubstitutions increase the unit-cell volume and may
alsoenlarge size of the cavity normally occupied by OH, sothat Cl,
with an ionic radius of 1.81 A, can be accommo-dated. The unit-cell
volume of Cl-rich hastingsite is 3-47o larger than that of Cl-poor
or Cl-free hastingsite(Suwa et al. 1987).
In the Salton Sea geothermal system, Cl is preferen-tially
incorporated in hastingsitic amphibole relative tocoexisting
actinolitic amphibole (Table 2). Grains of thehastingsitic
amphibole are compositionally heterogene-
-
)- o/oDn/
ous, and the Cl-rich domains are rich in Fe2+, t4lAl
andh]1|r{a+K) (Fig. 3b, Table 2). Variations of Cl content
inamphibole (Fig.6) as functions of tAl(Na+K) andX(Fe2*)suggest a
crystal-chemical control on Cl content. Twocharacteristic features
are apparcnt: (l) Cl content ofamphibole increases with increasing
tAl(Na+K), and (2)the maximum Cl content of amphibole increases
withincreasing X(Fe2*). Amphibole compositions with Cl inexcess of
0.5 tt'rt.%o plot along an edenite{t4115416;ta14ltr-rsi-r}
substitution vector (Fig. 5).This fact indicates that the extent of
tschermakitesubstitution {t4lAlt6lAlsi-r(Mg, Fe2*)-r } in cl-rich
am-phibole is relatively constant {0.9 < I41Al - tallNa+K)
<1.0). The chemical characteristics shown in Figure 6thus
indicate that (1) Cl variation of the Salton Seaamphibole is
controlled primarily by variations in theedenite component; (2)
X(Fe2\ value of the amphiboleshows little correlation with Cl and
edenite contents, butis correlated with the maximum Cl content of
amohibole.Increasing trlg166;tal41n-,Si-, and FeMg-, iubsritu-tions
favor incorporation of Cl in the amphibole struc-rure. Both
hl15n+19lal41n ,Si_, (Ito & Anderson 1983)and FeMg-1 (e.9.,
Volfinger et al. 1985) substitutionsseem essential but not
sufficient for Cl enrichment.Where coupled, the two substitutions
seem to increasethe content of Cl incorporation in amphibole.
Thisscheme is consistent with the fact that examples ofCl-rich
calcic amphibole (> 3 wt.Vo Cl) reported in
1085
literature are mostly ferro-hastingsite with X(Fe2*) >0.75,
(Na+K) > 0.9 pfu, and I4lAl between 1.8 and 2.3pfu (total Fe as
FeO and O = 23; Suwa et al. 1987).
Figure 7 shows the relationships among Cl,tatgla+K), X(Fe4), and
t4lAl contents of the Salton Seaamphiboles. The data indicate that
(l) on Figure 7a"
Dn",/dnlAllNa+K) - 0.6 for t4lAl < 1.6 anddn./dntAl(Na+K) =
1.q for t4lAl >1.6,
and (2) on Figure 7b,dn"y'EX(Fe2*) = 0.3 for talQr{a+K) <
0.55 andEn6/dX(Fe2*) = 0.8 for tel(\arK) 2 0.55,
where n is the number of atoms of the subscriptedelements.
Yolfinger etal. (1985) demonstrated the fundamentalrole of the
local structure of the anion site in exchangeof anions in silicate
minerals. In the case of amphibole,the closer the symmetry of the
ring of six tetrahedra inthe double chain to ideal hexagonal
symmetry, the largerthe sizes of anionic and alkali sites. The
adaptation ofthe tetrahedral chains to the octahedral strips is
control-led particularly by their iron content. This schemeexplains
the positive correlation between Cl andtatlya+K) and that between
Cl and X(Fe2+) in calcicamphiboles. Figure 7, however, shows that
(1) the extentof Cl substitution for OH as a function of
edenitesubstitution at tAl(Na+K) > 0.55 is twice that for
anamphibole with ntlNa+K) < 0.55, and (2) the Cl content
CI-BEARING AMPHIBOLE IN TI{E SALTON SEA GEOTHERMAL SYSTEM
Salton Sea
:s3
5
Detect i on (26 ls'ral)0.01-
0 0 . 5 1 . 0r^t( i la + K) (pfu.)
FIc. 6. Variations in proportion of Cl (wt.7o) as a function o1
tAllNa+K) and X(Fe2+) inamohiboles from the Salton Sea State 2-14
well.
-
1086 THE CANADIAN MINERALOGIST
0 . 8
^ 0 . 6;
50.4
U , Z
- ' - ' t l r
a - tN1p6 + K )0.55
o o . z 0 . 4 - .
0 . 6 0 . 8 1 . 0
XFe'-
FIc. 7. Variations in the,proponion of C\ (wt.Va) as a function
of (a) tAl(Na+K) and t4lAl,
and (b) X(Fe'*) and tor(Na+K), in amphiboles from the Salton Sea
State 2-14 well. Solidand broken lines indicate the regression
lines for amphiboles with t4lAl < 1.6 and > 1.6in (a), and
those *it5 FllNa+K) < 0.55 and > 0.55 in (b),
respectively.
(a)
E_,,ril;ll l
-*-tanr>r.o I E /
a
o
a o la
E t r
E nE'
. c D l ".e q56'btrt - t ' o o
" EpF- .{tl
/ t r 8
6 t t r
o
E
t r 6ru:tr
_ t r & 6u _ . ' e" - d " F wd.E' ^q,
r " En E r - -
. t - '
d-
^ 0 . 6
0 . 4
ata
o1 ta1(Na+K)-rich amphibole is higher than that oftAl(Na+K)-poor
amphibole for a fixed X(Fe2+). Totalexpansion of unit-cell volume
with increasing edenitecomponent may also make the increased
substitution ofCl-for-OH possible.
Cl panitioning between amphibole andfluid
Figure 8 summarizes the relationships among Cl,X(Fe}), -4
tal(Na+K) in calcic amphibole composi-
tions reported in the literature. The data pertain toamphibole
formed under various geological environ-ments: submarine
metabasites @g. 8a), skarns (Fig. 8b)"high-grade metamorphic rocks
(Fig. 8c), and igneousrocks @g. 8d). Available data on fluid
composition andP-T conditions of the representative examples
aresummarized in Table 3. Although the Cl-bearing amphi-boles shown
in Figure 8 were mostly formed underhigher P-T conditions (0.4-10
kbar, 450-850'C) thanthose in the Salton Sea samples (0.3 kbar,
350'C), most
-
(a) Submarine netabasites [96
CI-BEARING AMPHIBOLE IN THE SALTON SEA GEOTT{ERMAL SYSTEM
1087
(d) lgnoous rocks 11361
0.0130.5 1 .0
r^11,1, * K) (ptr.)
wt.7o) amphibole can form at lower temperatures thancoexisting
Cl-poor (less than 1.0 wt.Vo) amphibole.
Some amphiboles in granodioritic charnockite(Karineni et a/.
1982) and anorthosite-gabbro complex(Kamineni 1986) have Cl-rich
compositions exceedingthe maximum Cl-for-OH substitution of the
Salton Seaamphiboles @gs. 8c, d). This material has a
highercalculated Fe2O3 content (5.+-7.9 wt.Vo) than the
othersamples (Fe2O, = 3.8 + 2.2 wt.7o). Increasing Fe3*Al-,
r';i,
o
*E
-o -
&to o
o o o o
o
, @
oo
O xr."5.aO 0.4sxFo&
-
1088 TTIE CANADIAN MINERALOGIST
TABIE 3. MODB OF OCCURRENCE OF SOME CI-BEARING CAI,CXC
AMPHIBOLES
Cl-content Cl-content EouiliMumofanphibole offluid cbndition
References
Submarine t 6.03-6.5L wt.Vom€tabasite .0.024.6wtVa
t O.OL-4.O2'ttt.Vo' 0.01-3.fi) wt7a
amphibolite Jacobson (1975)550-75fC Io and Anderson
(1983)amphibolitef, Vanko(1986)greenschistf. Vanko(1986)
> sw(?)> sw(?). sw(?)> $*,(?)
Skam t 7.24,ttt.fot 0.L3-2.68,tttTo
n.d. pyroxeneh(?) Krutov(l93Qn.d. pyroxenehf(?)
Gutyaevaaal.(l98Q
High-glade t 4.LSrxtVamamorphic I O.O4.65,*t.Vo
rock
grmulile lGmineni et at. (1982)8m-85(fc Matsubara and
&10 kbar Motoyoshi (1985)
n.d.nd.
Igneousrock' O.O7-2.44' t t tVo. [email protected] q't.7a
' 0.024.78,ttt,Vo
n.d. ? Czamanskeetal,(L9l)nd. 4O0-60fC lGmineni (1986)
1-2 kbar46wt.Vo ir 500-75fC Bird et al. (1986)naximum(?)
0.4-0.7kbar
Geothermal t 0.0-2.7 wt.Vometamorphic
rock
L5-19.7'xtVo 350-40trC Thisstudv0.3 kbar
No!e: Abbreviations arc: n.d., not determined; sw, seawater;
amphibolite f., amphibolitc facies;greenschist f., greenschist
facies; pyroxene hf, pyroxene homfels facies.
substitution expands the entire chain ofthe amphibole(Ito &
Anderson 1983) and thus may facilitare substiru-tion of Cl for
OH.
Variable Cl contents in amphibole have been corre-lated with
water-rock interaction and Cl fixation duringmetamorphism and
hydrothermal alteration of oceaniccrust. In submarine metabasite
and skarn. chlorinecontents of some amphiboles attain7.2 wt.7o
(Figs. 8a,b), which is distinctly higher than that of the Salton
Seaamphiboles (up to 2.7 wt.Va). Many authors haveconsidered that
Cl-rich amphibole grew from extremelychlorine-rich fluid (e.g., Ito
& Anderson 1983, Vanko1986). Such fluids may exist in oceanic
hydrothermalsystems and during skarn formation (e.g.,Tan &
Kwak1979, Vanko 1988). However, cases of Cl-rich amphi-bole with
more than 3 wt.Vo Cl have greater tAI(Na+K)than the Sallon Sea
amphiboles. Therefore, the high Clcontent of amphiboles is
considered also to be due toincreasing volume-expansion. The
similarity in themaximum extent of Cl-for-OH substitution with
fixedtAl(NarK) among the Salton Se4 submarine metabasite,and skarn
amphiboles implies that the extent of Cl-for-OH substitution in
these amphiboles is not sensitive tovariations in fluid
chlorinity.
Amphiboles in high-grade metamorphic rocks andigneous rocks
contain less Cl than the maximum extentof Cl-for-OH substitution
found in the Salton Seasamples. These amphiboles were formed
underconditions of lower chlorinity than those in the SaltonSea
geothermal system. Nabelek ( 1989) showed that theCl content of
calcic amphibole in mafic hornfelsesaround the Laramie anorthosite
complex, Wyoming,
increases systematically from 0.03 to 0.37 wt.Vo wilhdecreasing
proportion (vo1.7o) of amphibole; heinterpreted this finding in
terms of progressive lossof water and preferential concentration of
Cl in amphi-bole during contact metamorphism. These observa-tions
imply that the Cl content of amphiboles coexistingwith a
low-chlorinity fluid is sensitive to variationsin fluid chlorinity
and is controlled by Cl partition-ing between the two phases as
well as the crystal-chemi-cal constraints imposed by (Na+K), Fe and
Al substitu-tions.
Figure 9 illustrates Cl partitioning between coexistingamphibole
and fluid, inferred from the chemical data ofthe Salton Sea
geothermal system (this study) andMathematician Ridge (Stakes &
Vanko 1986, Vanko1986, 1988, Suwa & Enami, unpubl. data). In
low-chlorinity environments, the Cl content of amphibole isdefined
by partitioning of Cl between amphibole andfluid, and increases
with increasing Cl content in fluid,tAl(Na+K), and X(Fe2+) of the
amphibole. The estimatedratio of 3(X6)a'p to E(Xcr)nuid is
approximately 3 at 0.4< Ietgla+K) < 0.6 and 0.4 < X(Fez+)
< 0.7, andapproximately 4 or 5 at 9.6 < Ial(Na+K) < 0.8
and 0.4 <X(Fe2) < 0.7. An amphibole *i6 tal(Na+K) > 0.4
andX(Fe}) > 0.4 seems to preferentially concentrate Clrelative
to the coexisting fluid in low-chlorinity environ-ments. On the
other hand, amphiboles coexisting withthe Salton Sea brine or with
more saline fluids havenearly constant Cl content for fixed X(Fe2+)
andtAl(Na+K) contents, and seem independent of variationof
chlorinity in the coexisting fluid.
-
CI.BEARINC AMPHIBOLE IN THE SALTON SEA GEOTHERMAL SYSTEM
XFe2*l lilfl
* o.ssc^loa 0.6stl t
-
r090 T}IE CANADIAN MINERALOGIST
of this research is gratefully acknowledged. Criticalreviews by
Philip A. Candela David A. Vanko, Craig E.Manning, Moonsup Cho,
Robert F. Martin, NoriyukiNakasuka and two anonymous referees
improved thismanuscript.
REFERENCEs
Berza, R. & VANKo, D.A. (1985): Petrologic evolution
oflargefailedrifts in the Eastem Pacific: petrology ofvolcanicand
plutonic rocks from the Mathematician Ridge area andGuadalupe
Trough. J. Petrol.26, 56+602.
Brann, J.S. & Dev, H.W. ( 1986): Origin of gabbro
pegmatitein the Smartville intrusive complex, nonhem Siena Neva-da,
Califomia. Am. Mineral. Tl, 1085-1099.
Bno, D.K., RocERs, R.D. & MaNNrNc, C.E. (1986): Mineralized
fracture systems of the Skaergaard intrusion, EastGreenland. Medd.
Grqnland, Geosci. 16.
BLooMFTELD, A.L. & Ancur-us, R.J. (1989): Magma mixing inthe
San Francisco volcanic freld, AZ. Petrogenesis of theO'Leary Peak
and Strawberry Crater volcanics. Contrib.M ine ral. P etrol, 102,
429 453.
BoRLEy, G.D. (1962): Amphiboles from the Younger Graniresof
Nigeria. I. Chemical classification. Mineral. Mag. 33,358-376.
BuoorNcroN, A.F. & LsoNanl, B.F. (1953): Chemical petro-logy
and mineralogy of hornblendes in northwest Adiron-dack granitic
rocks. Atn. M ine ral. 38, 89 I -902.
Cenuso, L.J., Brno, D.K., Cso, MooNsup & Lrou, J.G.
(1988):Epidote-bearing veins in the State 2-14 drill hole:
implica-tions for hydrothermal fluid composition. J. Geophys.
Res.93" 13123-13133.
Cstvas, A.R. (1981): Geochemical evidence for magmaticfluids in
porphyry copper mineralization. I. Mafic silicatesfrom the Koloula
igneous complex. Contrib. Mineral.Petrol. 78,389-403.
CHo, MooNsup, Lrou, J.G. & Bno, D.K. (1988): Progradephase
relations in the State 2-14 well metasandstones,Salton Sea
geothermal field, Califomia. J. Geophys. Res.93 .1308t -13103.
Courrou, R.R. (l 958): Significance of amphibole paragenesisin
the Bidwell Bar region, California. Am- Mineral. 43,890-907.
- ( 1989): Mineral paragenesis of altered basalts from
holeCooPER, A.F. & LovsnrNc, J.F. (1970): Greenschist amphi-
5048, ODP LEG I I I, Proc. Ocean Drilling Program, Sci.
boles from Ha2st River, New Zealand. Contrib. Mineral.
Resultslll,6l-76.Petrol. 27. 1l-24.
Iro, E. & ANnrnsoN, A.T., JR. (1983): Submarine
metamor-phism of gabbros from the Mid-Cayman Rise: petrographicand
mineralogic constrains on hydrothermal processes atslow-spreading
idges. Contrib. Mineral. PetroL 4,371-388.
gy and petrology of the intrusive complex of the Plinyrange, New
Hampshire. An. J. Sci. tl7, 1U3-1123.
DAMMAN, A.H. (1989): Mn-silicate skams from the GAsbomarea, West
Bergslagen, central Sweden. Mineral. Mag.53,613-626.
DICK, L.A. & RosINsoN, G.W. (1979): Chlorine-bearing
poras-sian hastingsite from a sphalerite skam in southem Yukon.Can.
Mineral. L7, 25-26.
DRUrrr, T.H. & Becou, C.R. (1989): Petrology of the
zonedcalcalkaline magma chamber of Mount Mazama, CraterLake,
Oregon. C ont rib. M ine ral. P et rol. I0l, 245 -259.
Erent, M., ZANG, QrrrA & YrN, Yu:ull (1993):
High-pressureeclogites in northem Jiangsu - southem Shandong
pro-vince, east China. J. Metamorph. Geol.11,399-414.
FuHnraeN, M.L. & Llr.rosr-ev, D.H. (1988):
Ternary-feldsparmodeling and thermometry. Arz.r. M ineral. 73, 201
-215.
Goro, A. & BaNNo, S. (1990): Hydration of basic granulite
togarnet-+pidote amphibolite in the Sanbagawa metamorphicbelt,
central Shikoku, Iapan. Chem. Geo|.85,247-263.
GREEN, N.L. & UsoeNsrv, S.I. (1986): Ternary-feldsparmixing
relations and thermobarometry. Am. Mineral. Tl,I 100-l 108.
Gulvaeva, T.YA., GoRELrKova, N.V. & Kenesrsov, A.A.(1986):
High potassium-+hlorine-bearing hastingsites inskams from himorye,
Far East U.S.S.R. Mineral. Mag. 50,724-728.
HELcEsoN, H.C. (1968): Geologic and thermodynamic
charac-teristics of the Salton Sea geothermal system. Am. J.
Sci.zffi. 129-t66.
HoNNonrz, J. & KrRsr, P. (1975): Petrology ofrodingites
fromthe Equalorial Mid-Atlantic fracture zones and their
geotec-tonic signifi canc e. C ont r i b. M ine ral. P et ro l. 49,
233-257 .
-, MEVEL, C. & MoNrraNv, R. (1984): Geotectonicsignificance
of gneissic amphibolites from the Vema frac-ture zone Equatorial
Mid-Atlantic Ridge. J. Geophys. Res.89 .11379-1 t400.
Isutzure, H. (1985): Prograde metamorphism of the
Homkanaiophiolite in the Kamuikotan zone, Hokkaido, Japan.
J.Petrol.26,39l-417.
CZAMANSKE, G.K., ISHTHARA, S. & Arrn, S.A. (1981):
Che-mistry of rock-forming minerals of the Cretaceous*Paleo-cene
batholith in southwest Japan and implications formagma genesis. "/.
Geophys. Res. 86, 1043 I - 10469.
-, WoNEs, D.R. & EtcmmERcER, J.C. (1977): Mineralo-
JAcoBsoN, S.S. (1975): Dashkesanite: high-chlorine amphibole
-
from St. Paul's rocks, equatorial Atlantic, and Transcauca-sia"
U.S.S.R. ̂Srzithsonian Contrib. Earth Sci. L4, l'7-2O.
KAMINENT, D. C. (1986): A petrochemical study of
calcicamphiboles from the East Bull l,ake anonhosite-gabbroIayered
complex, District of Algoma, Ontario. Contrib.M ineral. Petrol. 93.
47 1 -481.
-, Bonenol, M. & RAo, A.T. (1982): Halogen-bearingminerals
from Airport Hill, Visakhapatnam, India. Anr.Mineral.67,
1001-10M.
KoLKER, A. & LImslrv, D.H. (1989): Geochemical evolutionof
the Maloin Ranch pluton, l,aramie anorthosite complex,Wyoming:
petrology and mixing relations. Am. Mineral.74,3M-324.
KRtrov, G.A. (1936): Dashkessanite - a new chlorine amphi-bole
ofthe hastingsite group. Bzl/. Acad. Sci. URSS, C/. Sci.M at. Nat.
Se r. G e oL, 341 -37 4 fM ine ral. Ab st r. 6, 4381.
- & VtNocRADovA, R.A. (1966): Chlorohastingsite fromthe
Odinochnoye magnetite deposit, eastern Sayan. Dokl.Acad. Sci. USSR,
Eanh Sci. Sect.169,1 l6-l 19.
LEAKE, B.E. (1978): Nomenclature of amphiboles. Can. Mine-ral.
16.501-520.
LEELANANDAM, C. (1970): Chemical mineralogy of horn-blendes and
biotites from the chamockitic rocks of Konda-palli, India. J.
Petrol ll,475-505.
MARUvAMA, S., SuzuKI, K. & Ltou, J.G. (1983):
Greenschist-amphibolite transition equilibria at low pressures. J.
Patrol.u,583-6M.
MarsuBene, S. & MoroYosHt, Y. (1985): Potassium
pargasitefrom Einstiidingen, Ltitzow - Holm Bay, East Antarctica.M
ine ral. M ag. 49, 7 03-7 07.
Marsuuoto, Y. (1968): Fenohastingsite from the Kinbu mine,Nagano
prefecture, Japan. Bull. Fac. Liber. Arts, NagasakilJniv., Nat.
lci.8,39-46 (in Japanese with English abstr.).
- (1969): Fenohastingsite from the Moji mine, Fukuokaprefecture,
Japan. Sci. Rep. Fac. Sci., Kyushu Univ., Geol.9, l-7 (in Japanese
with English abstr.).
- & MrArilsA, M. (1960): Fenohastingsite from theObira Mine,
Oita prefecture, Japan. J. Mineral. Soc. Japan4" 372-383 (in
Japanese with English abstr.).
McDowE[, S.D. (1986): Composition and structural state
ofcoexisting feldspan, Salton Sea geothermal freld.
Mineral.Maq.50,75-84.
- & ELDERs, W.A. (1980): Authigenic layer silicateminerals
in borehole Elmore 1, Salton Sea geothermal field,Califomia, U.S.A
. Contrib. Mineral. Petrol, 74,293-310.
MCKTBBEN, M.A. & EI-DERS, W.A. (1985):
Fe-Zn{u-Pbmineralization in the Salton Sea geothermal system,
Impe-rial Valley, Califomia. Econ. Geol. 80, 539-559.
l09r
- & Elontoce, C.S. (1989): Sulfer isotopic variationsamong
minerals and aqueous species in the Salton Seageothennal system: a
SHRIMP ion microprobe and conven-tional study of active ore genesis
in a sediment-hostedenvironment, Arn. J. Sci. 289, 661-707.
-, WInnvs, A.8., ELDERs, W.A. & Emnlocr, C.S.(1987): Saline
brines and metallogenesis in a modemsediment-filled rift: the
Salton Sea geothermal system,California U.S.A. Appl. Geochem' 2,
563-578.
& Oruso, S. (1988): Metamorphosed Plio-Pleistocene
evaporites and the origins ofhypersaline brinesin the Salton Sea
geothermal system, Californi4 fluidinclusion evidence. Geochim.
Cosmochim. Acta 52, 1047'1056.
MIcHEt-s, D.E. (1986): SSSDP fluid compositions at first
flowtest of State 2-14. Trans. Geothermal Resources
Council10,461-465.
Murn-en, L.J.P. & WHrrs, D.E. (1969): Active metamorphismof
Upper Cenozoic sediments in the Salton Sea geothermalfield and the
Salton Trough, southeastern Califomia. Geol.Soc. Am. Bull. 80, 157
-182.
NennEr, C.R. (1989): lsochemical contact metamorphism ofmafic
schisl, Laramie anorthosite complex, Wyoming:amphibole compositions
and reactions. Am. Mineral.74,530-548.
Nesu, W.P. (1976): Fluorine, chlorine, and OH-bearing mine-rals
in the Skaergaard intrusion. Anu. J. Sci. T16,54G556.
Pnprrr. J.J.. CavrnoN, K.L. & BALDWN, K. (1974): Amphi-boles
and pyroxenes: characterization of other fian quadri-lateral
components and estimates of ferric iron frommicroprobe data. Geol.
Soc. Am.' Abstr. Programs 6,l0s3-1054.
RooEN. M.K., Henr, R.S., Fnsv,F.A. &MprsoN,W.G. (1984):Sr,
Nd and Pb isotopic and REE geochemistry of St. Paul'sRocks: the
metamorphic and metasomatic development ofan alkali basalt mantle
source. Cortib. Mineral. Petrol.85,376-390.
Sess, J.H., Pzussr, S.S., DUDA, L.E., CARsoN, C.C.,
HENDRICKS'J.D. & RostsoN, L.C. (1988): Thermal regime of the
State2-14 well, Salton Sea Scientific Drilling Project. "/. Gao-phy
s. Re s. 93, 12995 - 13004.
Ssenua, R.S. (1981): Mineralogy ofa scapolite-bearing rockfrom
Rajasthan, northwest peninsula, lndra. Lithos 14'165-172.
Snpensn, C.K., PAPIKE, J.J., SlMoN, S.B., DAvls, B.L.
&LauLJ. C. (1988): Mineral reactions in altered sediments
fromthe Califomia State 2-14 well: variations in the
modalmineralogy, mineral chemistry and bulk composition of
theSalton Sea Scientific Drilling hoject core. J. Geophys. Res.93,
t3tM-13122.
Spren, J.A. (1987): Evolution of magmatic AFM mineralassemblages
in granitoid rocks: the hornblende + melt =
CI.BEARING AMPHIBOLE IN THE SALTON SEA GEOTI{ERMAL SYSTEM
-
1092 TI{E CANADIAN MINERALOGIST
biotite reaction in the Libety Hill pluton, south Carolina.Am. M
ine ral. 72, 863-87 8.
Srarns, D. & VANKo, D. A. (1986): Multistage
hydrothermalalteration of gabbroic rocks from the failed
MathematicianRidge. Eanh Planet Sci. ktt.79,75-92.
SuwA, K., Ereur, M. & Homucur, T. (1987):
Chlorine-richpotassium hastingsite from West Ongul Island, Ltitzow
-Holm Bay, East Antarctica. Mineral. Mag.51,709-714.
TAcIRI, M. (1977): Fe-Mg partition and miscibility gap be-tween
coexisfing calcic amphiboles from the southernAbukuma Plateau,
Japan. Contrib. Mineral. Petrol. 62,27 l-281.
TAN, T.H. & Kwar, T.A.P. (1979): The measurement ofthermal
history around the Grassy granodiorite, KingIsland, Tasmania by use
of fluid inclusion data. "/. Geol. 87 ,43-54.
THoMpsoN, J.M. & FounNrER, R.O. (1988): Chemistry
andgeothermometry of brine produced from the Salton SeaScientific
Drill Hole, Imperial valley, Califomia. J. Geo-phys. Res. 93,
13165-13173.
VANKo, D.A. (1986): High-chlorine amphiboles from oceanicrocks:
product of highly-saline hydrothermal fluid? Am.Mineral.
Tl,5l-59.
- (1988): Temperature, pressure, and composition ofhydrothermal
fluids, with their bearing on the magnitude of
tectonic uplift at mid-ocean ridges, inferred from
fluidinclusions in oceanic layer 3 rocks. J. Geophys. Res.
93,45954611.
VIEIzEUF, D. (1982): The retrogressive breakdown
oforthopy-roxene in an intermediate chamockite from Sakeix
(FrenchPyr€n6es). Bull. M indral. 105, 68 1-690.
Vor-prNcsn, M., RoBERT, J.L., VlErznw, D. & NHVA;
A.M.R.(1985): Structural control of the chlorine content of
OH-bearing silicates (micas and amphiboles). Geochim. Cosmo-chim.
Acta 49,37-48.
WHALEN, J.B. & CH,cppsr-L, B.W. (1988): Opaque mineralogyand
mafic mineral chemistry ofl- and S-type granites ofthel,achlan fold
belt, southeast Australia. Am" Mineral. 73,281-296.
WHI'rE, D.E. (1968): Environments of generafion of
somebase-metal ore deposits. Econ. Geol.63, 301-335.
-, ANosnsoN, E.T. & GRUBBS, D.K. (1963): Geothermalbrine
well: Mile deep hole may trap ore-bearing magmaticwater and rocks
undergoing metamorphism. Science L39,9t9-922.
YAMAGUCHT, Y. (1989): F and Cl contents ofhomblende-acti-nolite
from metagabbros in Ashidachi area of the Sangunbelt, southwest
Japan. Geol. Soc. Japan, Mem. 33,81-88.
Received August 7, 1991, revised mnnuscipt acceptedJanuary 30,
1992.