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Chapter
9
CHARACTERTSTICS
F
HIGH.SULFIDATION
EPITHERMAL
DEPOSITS,
AND THEIR
RELATTON
TO
MAGMATIC
FLUID
Antonio Arribas Jr .
Mineral Resources
Department,
Geological
Survey
of Japan,
l-l-3 Higashi,
Tsukuba
305,
Japan
[NTRODUCTIoN
A consequence
f the increased
xploration or
gold
deposits
dur ing
the Iate 1970s
and
early
1980swas
tlre revision
of the
classification
of
epithermaldeposits
n
order to account
or the
variations bservedn stylesof mineralization nd
inferred
genetic
environments.
Among
th e
numerous
lassifications
hat followed,
one
group
of deposits
clearly
showed a
common set
of
features,
his deposit
ype is
characterized y
th e
presence
of
minerals
diagnostic
of
high-
sulfidation
tates
e.g.,
enargiteand luzonite)
an d
acidic hydrothermal
conditions
(e.g.,
alunite,
kaolinite,
pyrophyll i te).
The
terms enargite-gold
(Ashley
1982),
Goldfield-type
Bethke
1984,after
Ransome 1909),
high-sulfur
(Bonham
1984,
1986), quartz-alunite u (Berger 1986), acid-
sulfate
Heald
et
crl. 1987),and alunite-kaolinite
(Berger
Henley 198 9) were appl ied
o th is
group
n reference
o someof its mineralogica l
r
inferred
geoclremical
attributes.The
term high-
sulf idat ion
HS) (Hedenquist
987) s now
widely
used; he term was
proposed
riginally o refer
o
a fundamental genetic
aspect,
the relatively
oxidized state
of sulfur contained
in the
hydrothermal
ystem
i.e.,
nitial ly
SO2-rich). his
aspect s
significantbecause
t links HS deposits
with
one of the two
main types of terrestrial
magma-related ydrothermal
ystems
Henley
El l is 1983), those
associatedwith
andesit ic
volcanoes
whose
surface manifestation ncludes
high-temperature
umaroles and
acid sulfate-
chloridehot
springsand
crater
akes.
By contrast,
Iow-sulfidation
deposits orm from
neutral-pH,
reduced
H2S-rich)
hydrothermal
luids similar o
thoseencountered
n geothermal
ystems
Henley
Ellis
1983),
with
surface manifestation
including
i l ica
sinter-deposit ing
ot
springs
nd
steam-heated
cid-sulfate
lteration.
The main
objective
of this
review
is
to
summarize
he characteristics
f HS
minerali-
zation
formed primarily
within
the
epithermal
environment,
lrough ecognizing
he
potential
or
HS conditions o occur at greaterdepths.Earlier
studies
have
argued for
a magmatic
fluid
component
n
HS deposits
e.g.,
Si l l i toe
1983,
1989,
1991a;Hayba
et
al. 1985;
Henley
t99t
White
1991;Rye
1993;
Hedenquist
t al.
1994a),
and the identif ication
nd characterization
f HS
deposits as
contributed
o a re-evaluation
f the
role
of magmatic
fluids
in
other
types
of
hydrothermal
ystems
Hedenquist
Lowenstern
1994;
Simmons
this volume;
de Ronde
this
volume). In
this
context, particular
aftention
s
given to the characteristicshat are helpful in
determining
he
nature
of the
magmatic
contri-
bution to the
hydrothermal
ystem
hrough
time
and
space. his
review
considers
eatures
f many
of
the
deposits
isted in
Table l,
with
locations
shown n Figure
1,
but is based
on a
selection
f
fourteen
eposits or
which
the results
of
detailed
geological
and
geochemical
tudies
are available
(Tables
2,
and 3). For
simpl i f icat ion,
bibl io-
graphic
references
re
not
given
in the
text for
general
deposit eatures;
hese references
may
be
found in
Table 1. For
regional
studiesof HS
deposits, articularly
with respect
o
other ypes
of
magmatic-hydrothermal
ase-
and
precious-metal
deposits,
he reader is
referred
to reviews
by
Heald
et ul .
(1987),
Bonham
(1989),
Si l l i toe
(1989,
99la),
Berger Bonham 1990),
Camus
(1990),
White
Hedenquisr
1990),
Mitchel l
Leach
(1991),
Mitchell
(1992),
and
White
et al.
(
I
99s).
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H gh-sulfidation
Epithermal
Depos ts
Figure
l. Worldwide
distr ibution
f
high-sulfidation
eposits
nd
principal
documented
rospects.
he
main high-
suifidation
metallogenic
rovinces
re
ndicated.
ee
Table
for deposit
ames
nd selected
eferences.
OPSNTNC
EMARKS
ONGENETIC
ENVIRONMENT
Based
on
detailed
esearch
f
the
Summiwille
Au-Cu-Ag
deposit,
Stoffregen
(1987)
demon-
strated
that
a
nearly
ubiquitous
feature
of
HS
deposits,
fracture-controlled
uggy
sil ica
rock
(intensely leached volcanic rock consisting
dominantly
of
quartz;
Fig.
2)
is
the
product
of
very
acidic
conditions
pH
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A. Arribas, Jr.
Table
2. Main
geological
haracteristics f
l4
selected
igh-sulfidation
pithermal
deposits
Deposit /disrict .
Ag e
locat ion
{Ma)
Metals.
( t onnes )
Local volcanic
sett ing
Principal host
roc Ks
Genetically
rclated rtxks
Time
betwecnhost
rock
& deposit Dcposit l i)rm
Motomboto.
Indonesia
Na lesb i t i n .
Phi i ppincs
Lcpanto.
Ph ippincs
Chi
nkuash ih .
k iwu
Z i i i n s h a n .
Ch ina
Nansatsu,
Japiur
Sunrnr in l lc .
Color:rdo
Goldl ic ld.
Ncvadir
Central-vcnt
volcanir
Small cenral-
vent volcano
Diatreme
complex
Dome
complex
Domc
akrng
caldcra m:trgin'l
Snrall volcanos
in
a c:rldrra'i
Dome
along
preexrst lnS
c:ildera margin
Dac
donr, zrnds/dac/rhy
l-1ows.
yr
and volx
Ands
pyr
+ l lows
Ands/dac vol.
Mioccnc +
older
volx
+ metavol
Dac volc
Mioccnc
se d
Jurassic
granite.
Cretaceousdac
porpyhry
+pyr
Ands
pyr.
l lows +
vo lx
Qtz-lat ite
porphyry
Miocene
andesitc
Diorit ic.
qtz-
diorit ic stocks
None
observed
Qtz{iorite
porphyry
Dacite
domes
md l lows
Not reported
Horblende
:rrds
(Middlc
Volcs)
< 1 . 0n r . y .
N/A
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H gh-sulfidalion
Epithermal
Deposits
Table
2
(continued)
Dcposit /district
locat lon
Control
on mineralizat ion
Vertical ext-
ent of epiri .
ore
(m)2
Relat ion to
porphyry
systen)
Relerences
Motomhoto.
lndurcsia
Nalcshitan.
Ph ippi
ne s
Lcpanto.
Ph
i
ppi
nc s
Ch in luash
h,
Taiw;rrr
Z i i i nshan.
Ch ina
Nansatsu.
Japiut
S u n r m r t v i l l e .
Colorado
Goldlrcld.
Nevalir
Paradisc cak.
Nev:da
P uch loV ie . jo .
Don) in i can
Rcp.
Ju lcan i .
Pcru
El
lnd io .
Ch i le
La
Me.j ic:na &
Ne -
vadosdcl
Fantat ina
AJScntlna
Rrxllr i t1uiIar.
Spai t r
Contact
bctwcendome and
volcmic Krk. steep
ault
Stecp
strike-sl ip ault
Major
steep+ minor faults.
diatrcn)e
ontact.unc0mlor
mrty,
permeable
ayers
Stecp
normal laults
+
thcir intcrscct ions,
bedding
plancs
Steep srike-sl ip
fault
zones
+
contact 0f
volcztntc ent
Stecp ractures
+
permeable
pyroclast ic
ayers
Steep
ldial fracturcs
+
dtxnc contact
Modcratcly
+
shallow
dipping
faults & f issures
Stccp
Iaults
ant l
permeable
pyroclast ic
ayers
Diatreme
rinq fault +
permcable
ayers
Steep
iactures
Stccp normal faults
LOcal aults
Caldera
ring faults
+
nornral local faults
Porphyry Cu-Au
prospects
earby.
ag e
wi thin 1.0 m.y .
hoposcd,
none lo)owr)
Above +
adjaccnt
samc age
porynyry
Cu-Au
dcposit
Nonc k-nown
None
known
None known
Inrusion-ccncred
scricit ic, ow
grade
stk mineralizat ion
Nonc
lnown
Sericit ic.
stk Au
minerahzation
East
Zone)
Ntne l*rown
None klown
Porphyry Cu-Mo
mineralizat ion
nearby
HS
ore il
Nevado del
Famatina s a
pirt
of a
porphyry
Cu
prospect
Nrne Lrown
Pcrcll6
(
I 994)
Sil l i toe ?r a/.
(
I 990)
Garcia
(
99l
),
Anihas et a/.
(
I 995b)
Huang 1955) ,
Tan et al.
(1993)
Rcn er a/ .
(
1992) ,
Zhang et ul.
(1994)
Izawa & Cunningham
(
I 9f l9).
Hedentluist et al.
\1991a)
Steven
& Rat t i
(1960) .
Menhc r l
et al.
(19'7
).
Stoffregen
I
987
.
Rye
(199, j )G ray
& Coo lbaugh
(
1994)
Ransomc
1909) ,
A sh ley
1974) .
Ashlcy & S i l berman
1976) .
V ikc
(1989.
wr i t ten
conrmun.
I 995)
John?/ a/ .
(
1991
.
S i l l i toe &
Lorson
(1994)
Russel l
&
K es le r 1991
.
Muntean et a1. I990)
Petersen
I
al.
(19'11\.
Noh le & S i lberman
198,+) .
Dccn
(
I
990)
Siddcley
&
Araneda 1986).
Jannasel a1.
1990)
Losurda-Calder(xr
McPhail
(
I 994). Losada-Caldcr6n l a/.
{
994)
Anibas
e/
d/.
(
I
995a)
25 0
15 0
500
800
60()(')
< 1 5 0
250
400
< 1 5 0
4UX
)
600
>l(x)
< 1 5 0
principal
geologic environments
Bethke
1984;
Rye el
al.
1992):
l
)
by
the
disproportionation
f
magmatic SOz to
H2SO4 and
HzS
following
absorption
by
groundwater
(magmatic-
hydrothermal),
2)
by atmospheric
xidation
of
H2S
in the
vadose
zone over
the
water
table,
associated
with
fumarolic
discharge
of vapor
released
y deeper
boiling
fluids
(steam-heated),
and
(3)
by atmospheric
oxidation
of sulfides
during
weathering
(supergene). Magmatic-
hydrothermal
lunite
occurs
with
mir-rerals
uch
as
d iaspore,
y rophy l l i te ,
ao l in i te ,
d ick i te ,
and
zunyite,
which are
ypical of
hypogene
T
:
200-
350
C)
acidic
condit ions
(advanced
argi l l ic
assemblage;
eyer
& Hemley
1961).
This type of
alunite
s characterist ic
f
HS deposits,
ut it may
alsoappear
n areas
f advanced
rgillic
alteration
void of
ore
mineralization
e.g.,
wao 1962;
Flall
1978).
Alunite
in steam-heated
nvironments
forms
with kaolinite
and
interlayered
illite-
smectite
t about
100 o
160
C
where
umarolic
vapor
condenses
above
the boiling
zone of
neutral-pH,
H2S-rich
luid,
typical of
geothermal
s y s t e m s
h a t
f o r m l o w - s u l f i d a t i o n
e p o s i t s .
423
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A. Arribcts,,Ir.
Propylitic
Argillic
+
Adv.
argillic
rock
rock
rock
Because
of the
relatively shallow
and
dynamic
environment
of
mineral izat ion,
overprint ing
among
the three
types of
acid-sulfate
lteration
(including
sLrpergene)
s
possible; owever,
he
spatial
relation
of each
ype of
alunite
o ore is
different,
and correct
identif ication
s important
for exploration
(Rye
et al.
1992:. White
.
Hedenquis t
995) .
DISTRIBUTION,
GEAND
ECONOI\{IC
StcNInrcaNcB
In common
with other
magmatic-
lrydrothermal
deposits
(e.g., porphyry copper
deposits),
HS deposits
oincide
worldwide
with
plutonic-volcanic
rcs.
This associat ion
s
best
observed
n the Cenozoic
deposits
f
the Circurn-
Pacific
and he
Balkanbelt
of
southeastern
urope
(F-ig
I
) .
These deposits
occur
in two main
settings:
n islandarcs
and at continental
margins.
The tectonic
regime during
formation of
the
deposits
seems
to be dominantly
extensional
(Si l l i toe 1993). Some deposits e.g., Goldf ield,
Rodalquilar,
Summitville)
formed
in
intra-
continental
egionsduring
periods
of
extensiot l
that
followed
regional compression
and sub-
ductiorr
y
several
m.y.
Tertiary
HS deposits
redominate, nd only
a
few deposits
are
Mesozoic
(e.g.,
Pueblo Viejo,
Zijinshan),
Paleozoic
e.g.,
Temora
and others
n
southeastern
ustralia), r
PreCambrian
the
early
Quartz
alunite
Mineralized
uggy
quartz
rocl(
ProterozoicEnAsenAu deposit located in the
Balt ic shield
of central Sweden;Fig. I
).
The
youngest
eposits re Pleistocene
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H
g
h-s
ulfi dat
on Ep
he
ma Dep
os s
Figure
3. K2Oversus
SiO,
variation
diagram
for rocks
hought
o be
genetically
elated
o
high-sulfidation
eposits.
he
samples
ro m
12 deposits
or districts
r
:
140)
define
a
small
compositional
ield,
which
contrasts
sharply
with
the large
field
defined
by
volcanic rocks associated rvith low-
sulfidation
or intrusion-related
u
deposits
(>
100 samples
rom
l6
distr icts;
Si l l i toe
1991b,
1993;Mri l ler
&
Groves 1993).
The
degree
f alteration
f the
rock
samples
nd
precision
of the
analytical
data
are Iargely
unknown; however,
according
to
the
individual
datasources,
most
of the samples
are unaltered
r very weakly
altered.
Circles
indicate
average
values
for each
high-
sulfidation
deposit or
district:
Ch
Chinkuashih,Cq
=
Choquel impie,
Go
-
Goldf ie ld, n
:
El Indio.Ju
:
Julcani . a
Laurani ,
Le
:
Lepanto,
Mo
-
Motomboto,
Na
-
Nansatsu, P Paradise
eak,Ro
:
Rodalquilar,
u
-
Summitville.
Compositional
ields
afrerKeith
et al.
(
199 ).
See
Appendix
br referencesnd nformation
n data
plotted.
50
60 70
SiO2 wt / )
simi lar
o that of mineral izat ion.
hereabundant
radiometric
gesare available, he ageof
the
host
rocksand the age of mineral izat ion
re within
analyt ical
precision: where
a di f ference is
indicated,t is
typical ly ess han
1.0
m.y.
Table
2). A comrnon
spatialassociation xists
between
the
deposits
and shal low. ypical ly
porphyri t ic
intrusions. hese ntrusions re interpretedo be
the
roots
of volcanic domes
or
the feeders
of
central-ventvolcanoes or maar-diatrerne
com-
plexes,
he t hree rnain volcanic
settings or HS
deposits
1'able
2). Some
depositsare hosted
entirely
within a
singledome
(Summitvi l le),
r
within a
dornecomplex
Julcani).
n most
cases
tfre
mineralization
extends rorn the
subvolcanic
intrusion nto
country ro cks, such as
the Main
Vein Cu-ALr-Agdepositand associated
reccia
depositsn the Penshan
reaof the Chinkuashih
distr ict.Somedeposits, owever, o not showany
(known)
spatial associat ionwith
subvolcanic
intrusions hought to
be
genetical ly
elated
o
mineral izat ion
e.g.,
Nalesbitan. ansatsu).
n the
Rodalqui lar Au deposit , dykes
and small
intrusions of hornblendeandesitewhich
are
interpreted to be temporally related
to the
mineral izat ion eprcsent
nly a fract ion of the
altered and mineralized
area exposed
at
the
present
epth
of erosion; larger ntrusive
ody
s
tlrought o
exist at depth
(Arrrbas
et al. 1995a).
The main
controlon location
f mineral izat ion
t
Rodalquilar
s the
structural nargin
of two nested,
resurgent
calderas. With
the
exception
of
Rodalquilar,
he role
of calderas n
the formation
of HS
deposits eems o
be l i rni ted
o faci l i tat ing
the emplacement
f late
intrusive
magrna
along
preexistingcaldera ing-fractures Rytuba cl rzl.
1990) .
The
magmas
hought o be
genetically
elated
to
HS deposits
have a remarkably
limited
compositional ariation.
The ranges
f
wt.%
K2O
and SiO2 or
twelve deposits
verlapgreatly
and
show a
dominance f
calc-alkal ine
ndesit ic
nd
dacit ic
composit ions, i th
subordinate
hyol i te
(Fig.
3). Intermediate
alcic volcanic
rocks
are
limited
to
porphyritic
intrusions
n
the Lepanto
and Motomboto
Cu-Au-Ag
districts,
and
intermediate-to-felsicalkali-calcic rocks ar e
characterist ic f the
Summitvi l le
and Laurani
distr icts
Fig.
3). Interest ingly,
o
deposits ave
been
discoveredn associat ion
ith
alkal ineor
mafic magmas,
ven hough
hesemagmas
an be
genetical ly
related
to low-sulf idat ion
and
intrusion-related
u
deposits
(Si l l i toe
1991b,
1993; Mii l ler
&.
Groves 1993; Richards
this
volume).
The data
shown in Figure
3 suggest
a
relation
exists between nagma
cornposition
an d
/
\
ca\c.,^
t
3\Katt
*t '
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A Arribas,
Jr .
Table 3. Main
alteration and mineraliza tioncharacteristics
f 14 selected
igh-sutfidation
epithermal
deposits
Dcposit
Lateral
alteration
oning
(outward
rom nrinem-
lizcd
xxlies)
Vertical
altcration
zonin-9
(shallow
() dccp) Pnncial renrinerals
(
)re
mineralization
rn: Ag/Au
Silica
corc
Vcry
Io* As
N/A
Si l i cu ore
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A.
Arribus,
r.
is diff icult,
but
useful
for discussion
of the
differences
among
deposits
and
design
of
exploration
strategies.
n this
context,
White
(1991)
dist inguished
hree
end-member
tyles
of
HS deposits,
amed
after
deposits
f
the Circum-
Pacific:Temora,El Indio,andNansatsu.rregular
bodies
f disseminated,
i l ic i f ied
res
dominate
n
the
Temora-style.
Cavity-filling
veins
with
sericitic
and
clay-rich
haloes
are
characteristic
f
El
Indio-style
ALr
deposits.
A
large
group of
deposits
al ls
into
White's
1991)
Nansatsu-style,
which
is
characterized
by
wallrock-alteratiort
zoning
similar
o
that
shown
n Figure
2, and
by
the occurrence
f
enargite-bearing
res
within
a
si l ica
core
consist ing
f
vuggy
or
massive
i l ica
rock
(Table
3).
Mineralization
n this
style
of
deposit orms irregular
stratabound
odies
(e.g.,
Nansatsu,
Lepanto)
or
subvertical
vein-like
masses
r
ledges
(e.g.,Chinkuashih,
oldf ield,
Lepanto,
Rodalqui lar,
Summitvi l le).
These
deposits
ontain
breccia
bodies,
eins,
stockworks
of small
veins.
and
disseminated
res
hat
replace
or
irnpregnate
ntensely
altered
country
rock'
Ericksen
Cunningham
1993)dist inguished
wo
styles
of
HS deposits
n the
Andean
province:
Ag -
and
Au-rich
polymetallic
base-metal
eins'
and
low-grade
uggy
silica
and
breccias;
he wo
types
are
broadly
comparable
with
El
Indio-
and
Nansatsu-styles,
esPectivelY.
l,ocal
subvertical
aults
and
fractures
re
the
dominant
control
on
HS
mineralization
nd they
are
present n
rnost
deposits
(Table
2).
Other
examples
f
structural
ontrols
observed
n some
districts
arnong
the
foufteen
selected
nclude:
rnoderately
o shallow-dipping
aults
(Goldfield)'
caldera
ing
and
radial
faults
(Rodalquilar),
he
di lat ional
og
of
a
str ike-sl ip
ault
(Nalesbitan),
diatreme
ing-faults
Lepanto,Pueblo
Viejo),
th e
contact
between
a dome
or
volcanic
conduit
and
country rock (Motomboto, the Missionary
orebody
at
Summitvi l le),
and
a
l i thologic
unconfbrmity
PuebloViejo,
Lepanto).
n three
of
the
fburteen
deposits,
he
principal
control
is
l i thological
maar
sediments
t
Pueblo
Viejo,
and
interbedded
yroclastic
ayers
at
Paradise
Peak
and
Nansatsu;
able
2).
A
unique
cornbination
of
the
structural
an d
lithological
controls
characteristic
f
HS deposits
is
exhibi ted
by
the
Lepanto
Cu-Au-Ag
deposit .
The deposit
s
3
km
long and
consists f a
tnain
zone of
breccia
and
replacement
mineralization
along
he
Lepanto
ault
Fig.
4A).
Mult iple
veins
associated
with smaller
diagonal
faults branch
from
the rnain
zone and
extend
into both
the
hangingwall and foot'ivall
(Garcia
l99l).
The
characteristic
mushroom-shaped
ross-section
f
many of
the orebodies
t
Lepanto
s related o
th e
intersection
f
the steeply
dipping
Lepanto
ault
and
branch
veins
with the
unconfonnity
at
th e
base
of Imbangui la
acite
Fig.
aB). Li thologic
variations
in the
host
rocks
also
played
an
important
ole
in the
fonnation
of the
deposit.
as
shown
by
lensesof
stratiform
enargite-luzotrite
ore
which
resulted
rom
replacernent
f detrital
layers
within
volcaniclastic
and
sedirne
tary
basement
nits
Garcia
99l
) .
AITEN.ITION
MINERALOGY
ND
ZONING
As mentioned
above,
the
lateral
alteration
zoning
that
is characteristic
of
HS
deposits
reflects
he
reaction
and
neutralization
f
high-
temperature
acidic
fluids
with
wallrock.
The
innermost
zone
of
vuggy or
tnassive
si l ica
alteration
ommonly
has sharp
boundaries
ith a
zone
that
may
contaitr
quartz, alurrite,
kaolinite,
dicki te,
pyrophyl l i te,
iaspore,
nd
zunvite'.
'his
advanced rgillic assemblagerades nto a second
envelope
of argi l l ic
al terat ion,
composed
of
minerals
uch
as
quartz, aol ini te,
l l i te,
serici te,
and smectite,
nd
an outermost
alo of
propylitic
al terat ion,
with
chlori te.
i l l i te,
smecti te.
and
carbonate
Fig. 2,
Table 3).
The width
o1'eacl.t
zone
varies
widely;
or example,
uggy
si l ica
and
advanced
argillically
altered
rock
fonn
narrow
(
-
8/9/2019 Epythermal Arribas 1995 MinAssocCanada23
10/33
@
NW
High-sulfidation
Epithermal
Deposits
Figure
4. Longitudinal
A)
and ransverse
B)
cross-sections
f the Lepanto-FSE
Cu-Au-Ag
deposits
phitippines),
showing
tructural nd lithologic
controls
on formation
of the high-sulfidati on
nd
porphyry-type
res
(simplif ied
fromGarcia 99l
).
Potassium-argon
ating
of country ocks
andalteration
minerals
ssociated
ith
the
porphyry
an d
high-sulfidation
epositsndicates
hat hydrothermal
u-Au
mineralization
ook
place
n
the middle
of a
pliocene
to
Pleistocene vent of dacitic-andes itic
agmatism
Arribas
et al. 1995b).
Note
the overall
spatial
overlap
of the
magmatic
nd hydrothermal
plumbing
systems
i.e.,
volcanic
ventsof Pliocene
acite,
quartz
diorite
ntrusions.
porphyry
eposit, nd
deeper
arts
of epithermal
mineralization).
The zones
of alterationwith
increasing
epth
typically
grade
from
a shallow
silicic zone
through
advanced
argi l l ic, argi l l ic,
argi l l ic/
serici t ic, nto a serici t ic or phyl l ic zone with
quartz,
sericite, and
pyrite.
This
alteration
sequence
occurs over a
vertical interval
that
ranges rom
a
few
hundredmeters
o more
than
1000
m, and has
been best documented
y deep
dri l lholesn the
deposits f smal ler
ize, n which
the vertical
span of rnineralization
s
less than
about300 m
(e.9.,
Rodalqui lar,
ummitvi l le; ig.
5B). At Lepanto,
sericiticalteration
at depths
of
400 o
500
m
below he
epithermal eposit
ives
way, laterally
towards the
south, to K-sil icate
alterationof the FSE porphyry Cu-Au deposit.
Porphyry-type
stockwork mineralization
at
Paradise eak s
containedwithin the
sericiticores
of the East Zone
deposit which,
according
o
Sillitoe & Lorson
(1994),
ormed
underneath
he
main HS ore bodies rr
the area.A
quartz-sericite-
pyrite
zonewith trace
amounts f chalcopyrite
nd
molybdenite
urrounds n intrusion
f monzonite
porphyry
>300
m below
the HS deposit
at
Summitvi l le
Grav
& Coolbaush
994\.
The
lateral
and vertical
alteration
zones
described
above
correspond
o a
generalized
model.
They
are useful
in exploration
because
they help in understandinghe geneticenviron-
ment of
a deposit
and
provide
spatial
markers
within
the
extinct
hydrothermal
system.
Experimental
data on
the relative
stability
of
rninerals
uch as
alunite, kaolinite, pyropliyllite,
and diaspore
Hemley
et al. 1969,
1980),
oupled
with
the
temperature
angesnoted
for
these
an d
other related
acid
minerals
in active
systems
(Reyes
1990; Reyes
et al. 1993),
also
provide
information
hat
contributes
o definition
of the
paleoconduits
n extinct
systems.
If studied n detailed,severalsuperimposed
and
crosscutting
tagesof
pervasive
as well
as
fracture
(conduit)-related
mineralization
may
be
recognized
n the majority
of deposits.
hese
ar e
the expected
esult
ofvariations,
during
he course
of mineralization,
n
temperature, ressure,
nd
composition
of the hydrothermal
luid
and
the
degree
f wallrock
interaction.
Detailed
ield
an d
petrographic
tudiesat the
Monte
Negro
orebody
in the
Pueblo
Vieio deposit
have
resulted
n
-
8/9/2019 Epythermal Arribas 1995 MinAssocCanada23
11/33
A. Arribas,
.Jr.
Vuggysilica
Advanced
rgillic
Argillic
S€ricitic
Propylitic
Inlense upergene
cij-sulfate
vsrprint
-100
I K M
Au-(Cu-Te-Sn)
htgh-
sulfidation
deposits
particular
eatures
f the
deposits
isted n Table
3.
Pyrite
and enargite
and
its low-temperature
dimorph
uzonite)
re
he
dominant
sulfides
n
HS
deposits;pyrite is abundantbut the amount of
enargite
and
luzonite
is
variable.
Common
ore
minerals,
isted by
decreasing
abundance
rom
variable
to
very
minor,
include
tennantite-
tetrahedrite,
ovellite,
native
gold and argentian
gold
(electrum),
marcasite,
chalcopyrite,
spha-
lerite,
and
galena.
Famatinite
s
locally abundant
in some
deposits
Goldfield,La Mejicana).
Sparse
ore
minerals
nclude
bornite,
cassiterite,
tnnabar,
molybdenite,
orpiment,
realgar,
stibnite,
an d
wolframite
the
last
locally
important
at
Julcani).
Other minerals
present in
minor amounts
in
several
eposits
nclude
Pb-,
Ag-Pb,
Bi- and
Sn -
bearing
ulfbsalts
Table
3).
Fine-grained
uartz s the
dominant
gangue n
HS
deposits.
Other
comrnon
but
minor
gangue
minerals
include
bari te,
kaol ini te,
alunite,
pyrophyllite,
iaspore,
nd Ca-,Sr-,
Pb- and
REE-
bearing
phosphate-sulfate
mineral(s)
such
as
svanbergite-woodhouseite
r crandall i te
(Stoff-
regen
&
Alpers
1987).
For example,
igh-grade
Elsvat ion
m)
|
5 0 0 m
I
I
ffi
l ^
^
a
f - ' - ^ l
tl
m
@
Figure
5. Generalized
urface
lteration
map
(A)
and
cross-section
B)
of
the Rodalquilar
HS deposit
n the
Rodalquilar
nd
Lomilla
calderas,
outheastern
pain
fiom Arribase/
at.
1995a).
he
boundaries
hown
between
alteration
ones
are
rregular
and
gradational.
identification
of
two
stages
of
mineralization,
interpreted
o
correspond
o
two
distinct
magmatic
pulses
(Muntean et al.
1990).
During
the
first
stage (responsible or -600/oof the Au in the
deposit),
hallow
kaolinite-quartz-pyrite
nd deep
alunite-quartz-pyrite-quartz
zones
were
de-
veloped,
with
gold mineral izat ion
n associat ion
with
disseminated
yrite
in the
wallrock;
during
the
second
tage
responsible
or about
40 ofthe
Au),
an extensive
oneof
silicification
with
pyrite
+
sphalerite
+
errargite
eins
formed
at
shallow
levels.
above
a
zone of
pyrophyll i te-diaspore
alteration
Munteanet
al.
1990).
Ono aNu GANGUEMINERAL0GY' ND
TIMING
OF
MINERALIZATION
White
et
ul .
(1995)
and
White
&
Hedenquist
(1995)
presented
etai led
iscussions
n
various
aspects
f
epithermal
gold mineralization
n the
basis
of
observations
rom
a
large
number
of
deposits
round
he
Pacif ic;
heir
conclusions
ith
respect
to
ore
and
gangue
mineralogy
in HS
deposits
are
included
here,
in addition
to the
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8/9/2019 Epythermal Arribas 1995 MinAssocCanada23
12/33
veinspecimens
rom Chinkuashih,
Goldfield,
and
La
Mejicana
have
spectacular
ntergrowths
f ore
minerals
with kaolinite,
alunite,
or
pyrophyll i te.
This
observation
implies that
ore
formation
occurred
under
moderately
acidic to
acidic
conditions, hich are inconsistent ith transport
of
Au as
a bisulfide
complex
(Seward
1973).
Recent
studies
of
Au solubi l i ty
in high-
temperature
cid sulfide
solutions
ave
esulted
n
identif ication
f
AuHS" a s one
of
the
principal
gold
complexes
n HS
mineral izat ion
Bening
&
Seward
1994),
he other
possibilitybeing
AuCl2
(e.g.,
Hedenquist
/ al.
1994a).
The
number
and order
of
mineralizing
vents
providecritical
information
or reconstruction
f
the
hydrothermal
system
that
results
in HS
mineral izat ion.
minimum
of
two stages
of
alteration/mineralization
as been
recognized
n
most
deposits
on
the
basis of
crosscutting
relations
Table
3).
The most
common
evolution
is from
an early
leaching
nd
alteration
tage
o a
laterore-forming
stage.
Vuggy
sil ica
ock and
he
advanced
argillic
assemblage
ith disseminated
pyrite orm
typically
early-stage
cidic
alteration,
and are
followed
by Cu
+
Au
+
Ag
deposition.
Detai led
tudies
n some
distr icts
e.g.,
El
Indio,
Lepanto),
owever,
have
resulted
n identif ication
of two
metal
stages,
an
early
Cu-rich,
Au-poor
stage,dominatedby enargite-luzonite,nd a late
Au-rich,
Cu-poor
stage,
associated
with
intermediate-sulfidation-state
ulfides
such
as
tennantite-tetrahedrite
nd
chalcopyrite,
and
tellurides.
The
transition
from
quartz-alunite-
pyrite
alteration
o enargite-pyrite
nd
finally
to
tennantite-tetrahedrite,
he
last typically
without
sulfate
(alunite)
but
with
quartz-sericite
angue
and
wallrock
alteration,
indicates
a fluid
progressively
more
reduced
and
less
acid.
At
Summitvi l le
and
Chinkuashih
also
Tambo
and
Furtei-Serrenti; able l), a late stageof barite-
gold
has
been
documented.
CsaRactnRISTICS
ANDSoURCES
F
HvuRorsnRMAL
FI-utos
Results
f
recent
detai led
luid-inclusion
nd
stable-isotopic
studies
reveal
much about
th e
composition,
temperature
and
sources
of
hydrothermal
luids n
HS deposits" ombination
H gh-suffidation pithermalDeposts
of these
data with
geological
and mineralogical
observations
mentionedabove
allows the nature
of the
altering and ore-forming
fluids to be
determined.
The framework
for the interpretation
has benefited
from information on
the compo-
sitionand luxesof volcanicdischargesnd active
magmatic-hydrothermal
ystems
Hedenquist
&
Lowenstern
1994; Giggenbach
this volume;
Hedenquist
his volume).
F uid-in
c usion
Ev dence
Suitable
hosts
or fluid-inclusionstudies
are
scarce
n HS deposits,
s the
ganguemineralsare
typically
fine-grainedand
even mill imeter-size
hydrothermal
uartz
crystals
re usually
ate
stage
and vug-filling.
Satisfactory
esults
are obtained
on secondary
luid-inclusions
n igneous
quartz
phenocrysts rom
altered
wallrocks; although
lacking
temporal
information,
these inclusions
seem o
provide a representativeross-section
f
the fluids
involved.
The most
reliabledataon the
ore-forming
luids are obtained hrough
infrared
microscopy
directly on
ore minerals, such
as
enargite
(Deen
1990;
Mancano & Campbell
1ee5).
The temperatures
nd salinitiesestimated
or
HS deposits e fine
a
wide range,
rom 90o o
48 0
oC
and
300
"C )
fluids
of
variable
salinity,
which have
been
documented
n several
eposits
nd are
generally
431
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8/9/2019 Epythermal Arribas 1995 MinAssocCanada23
13/33
A. Arribas,
Jr .
Table 4.
Summary of
fluid-inclusionmicrothermometric
data
for high-sulfidation
deposits
Deposit
Host-mineral
studicd
Tcmpcrature
Salinity
Asstriatcd
( C) t (cquivwt .%NaCl )
al tcrat ion
Mrxoniboto, Indoncsia
Nalcsbi tan,Phi l ippines
Lcpanto,
Phi l ippines
Chinkuashih, a iwan
Zi . l inshan.
hina
Nansatsu,
apan
Akaiwa,
Japan
Mitsumori-Nukeishi,
Japan
Sunimi tv i l le ,Colorado
Coldlielcl,
Nevada
Pradise Peak,
Nevada
Julclni,
Peru
Ccarhuaraso,
Peru
Colqui.j irca,Peru
Can-Can
(La
Coipa),
Chi lc
El Indio, Chile
La Mejicana
LM)
an d
Ncvados Famatina
NF),
Argentina
Rrxlalquilar,Spain
Furtei-Serrenti, taly
Barite
Quartz
Enargitc
Quartz,
baritc.
a luni te
Qu:rtz
(no
dctails
rcfx)rtcd)
Quartz
DiasJnre
Quartz.
ba-ritc,
quanz
pnen(x
Quartz
phcnoc
Baritc
Quartz-
phenoc
Quartz,
baritc
Quartz,
barite
Quartz
Quartz
phenrr
Quartz
phenoc
Wol, ena,
quartz
Sidcritc
Quartz
phenoc
Qufiz
phcnoc
Sphalcritc. quartz
hiibnerite
Quartz
phenoc
N/A
Quartz
quartz
phcnm
Quartz,
arite,
quartz
hentr
3(n)
2(XI'+60
l6(i-340
230-480
17F300
22(}.450
I 9(),320
9(I 140
(390-5m)
o .2 - t2
a 1 a
3 , 9
0-5
(3-2(
)
< l
up
o
30
0.5-
1. 1
2 - 1 8
(up o 9)
5 1 8
0.2-8
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8/9/2019 Epythermal Arribas 1995 MinAssocCanada23
14/33
H
gh-sulfdation
Epithermal
Deposits
Table 4.
(continued)
Dcposit Commcnls
Rcl'crcnccs
M() tornboto,ndoncs ia
n*alcsbi lan. h i l ippincs
Lcpanto,
Phi l ipprncs
Chinkuashih.
a iwan
Zi . j inshan, h ina
Nansatsu,
lpan
Akaiwa,Japan
Mi tsumor i
Nuke: ishi ,
apan
Su
nmi tv i l c . Colorat io
Coltl l iekI,
Ncvatla
Piiraclise
Pcrk, Ncvatla
Julcani ,Pcru
Ccrrhuaraso,
Pcru
Colc lu i l i r ca,
c ru
Can-Can
La
Coipa) .
Ch i l e
El Indiu, Chi lc
La Mc.jicana
LM)
an d
Ncvacirs Famatina
NF),
Argcnt ina
Rrxlalquilu,
Spain
Furtci-Scrrcnti, taly
Rcconnaisancc
rudy n latc-stagc
arite
Reconnaissancc
tudyi
iquid
CO2 observcd
Samplcd intcrval
3
knl long
by 0.5 kn hieh
t
ctnling tluit ls
awav fionr subjaccntporphyry Cu-Au degrsit, whcrc
Th >.150'C
& salinity up to 5.1eq wt.rl NaCl
Prx r r ly -documented
amples
longa'15( lnr
ver t i cal
ntc rval :
the highcr Ths in
sanples lt
-7,50
m
dcpth: CO2 ohserved
Asstrciatcdwith
main stagc
Cu
Dorrp
altcrationzonc
(>6(X)
nr
depth)
Associatcdwith late.
shallow sil ica-Au
Assrriated
with
carly sil ica and
quartz-dickite
Late, vug-li l ling quirtz
Qtz
in
brcccia. salrne iquid and krw-salimty vapor
cmxist
Vein quartz
-4(X)
m
helow Kasugadeposit
Coarsc-grainedclilsgrre
Not
(known)
Au
or Cu
mincralization,
but high salinity
l lu ids
Lic lui t l - r ich:
a l in i ty>6
eq
wl .7 NaCl
only
in vuggy
si l ica
associatedwith
Cu
mineralization:
CO2
obscrvcd
Lrquid- and vapor-rich nclusions: alsopolyphase nclusions
Latc
barite-Au
assemblagc
Truc T5 is interpreted
o be 25(1290 C
Hydrostatic
and ncar-l ithostatic
rcssures
uggested
Latc, vug-li l l ing
crystals n hydrothermal
brcccia:
Frorn
stockwork Au East Zonc
dcoosit: COr observed
Quaru-alunitetpyrite
Pro-ore
ourmalinc
brcccia dykes, ithostatic
pressures
ikely.
Main-stagc
orc
fluicls,
also nner veins, iquid-rich inclusions
Latc-stage
ore fluids,
also
n
outcr
vcinsl P
correction applied
Quartz-alunitctpyrite
Quartz-al
u
ni
etpyrite
Two
generations
dcntil lcdl
both
may
be
very
salinc. Evidcncc
firr P abovc hydrostatic
and
higher
salinit iesat
dcplh
Coppcr and gold stages
Late stage
Interprctcd
as carly,
with vapor-rich
nclusions,
CO2 observetl
LM
& NF. includes iquid-,
vapxrr-rich
nd
potyphasc
nclusions
NF:
complctc transiLion iom
porphyry-type
fluids in K-
sil icatc stage
30(),6(X)+ C,
up to 67 eq wtq, NaCl)
through sercit ic
o epithcrmal
f ' luids n HS
(AA)
stage;
vapor-rich nclusions
ypically
less
saline
Vcrtical
temperature
and salinity
gradient:
high-lcmperature
brines coexist with low
-;Llinity
vapor
inclusions:
hydrostatic
and
near-lithostatic
pressures
suggested
Includes
hi-eh+ low-salinity f luids
(22-23,
-
8/9/2019 Epythermal Arribas 1995 MinAssocCanada23
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A. Arribas,
r.
and Julcani
Deen
1990)
are broadly
similar, but
their sal ini t iesare
dist inct ly di f ferent
(0.2-4.5
equiv.wt.% NaCl versus
-18equiv.wt.%
NaCl,
respectively),
roviding
constraints
n the role
of
a sal ine magmatic l iquid
(versus
Iow-sal ini ty
vapor) n the
generation
f HS deposits.
Group 3. Lower temperature
e.g.,
90-180
C),
dilute
(typically
600-m
vertical
interval
extending
00
m below he ore zone;Fig.
6) shows a
gradient
which
correlates
with the
change n dominant alteration, rom silicic an d
advanced rgi l l ic
Q
:
170-300
C,
sal ini ty
2-15
equiv.
wt.% NaCl at
the
elevation f the orebody)
to
serici t ic
T:
220-450
C,
sal ini ty
2-45
equiv.
wt.% NaCl)assemblages.
The transition
rom
advanced
argillic alteration,
through
quartz-sericite-pyrite,
to
K-silicate
alteration and typical
porphyry-type
high-
temperature
600+
C)
and
high-salinity
up
to 67
equiv.
wt.% NaCl) f luids of magmatic r igin
is
displayed,among he examples
eviewed,
at
th e
Lepanto-FSE and La Mejicana-Nevadosdel
Famatina epithermal-porphyry opper systems.
The
cooler and less sal ine
inclusion f luids
documented
n the ore zoneof the HS deposits
re
interpreted o reflect mixing
of magmatic and
meteoric
luids
in an environment hallower
han
that
of
porphyry
mineralization.
urthermore,n
common
with
porphyry-type deposits, high-
temperature,
vapor-r ich.
low-sal ini ty f luid
inclusionscoexist
with high-temperature,iquid-
434
Temperature C)
200
300
400
Figure
6. Elevation versus temperature
diagram
showing the range
(horizontal
line)
and average
(vertical
l ine)
of fluid-inclus ion homogenization
temperatures easuredn
the RodalquilarAu deposit,
Spain.Also shownare he temperatures
alculated, n
the basisof
63aS
urfide-surrare
or four
coexisting alunite-
pyrite
samples
large
il led
circles),
eference
oil ing-
point
curves,and vertical spansof the alterationzones
mentioned n
the text. Estimatedsalinit iesof f luid
inclusionsn the
shallowadvanced rgillic/silicic one
and deepsericit iczone rangebetween2 to 30
equiv.
wt.% NaCl and2 to 45 equiv.wt.% NaCl, respectively
(modified
from
Arribas et al. 1995a).
r ich hypersal inenclusions
i.e.,
with
Groups 1
and4, above).These luids may be the resultof
boiling of
a high-temperatureiquid,
or they may
reflect immiscible
vapor
and hypersaline
iquid
derived directly
from shallow-emplaced
magma
(Rye
1993;
Hedenquist & Lowenstern
1994
Shinohara
994;Hedenquisthis
volume).
Sulfur-is otope
Ev den ce
The abundance
of coexisting hydrothermal
sulfidesand
sulfates,
n addition o the
possibility
o
0)
q)
dno
6
'
( g
o
(s
3
q)
Ann ;
- '
o
a,
E
q)
o
H 2 O + 5 w f / . N a C l
-
8/9/2019 Epythermal Arribas 1995 MinAssocCanada23
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2-6
4
5
Lepanto
Chinkuashih
Nansatsu
Summitvi l le
Goldfield
PuebloViejo
Julcani
El Indio
Rodalquilar
of measuring
oS/"S
in host rock and
genetically
related
gneous ock
(Sasaki
et al.
1919),allows
sulfur-isotope
tudies
o
provide
information
on
the composition, emperature, nd sulfur sources
of
the hydrothermal luids. The resultsof
detailed
studies
n nine HS districts show a
remarkable
consistency
(Fig.
7). In
agreement
with
the
observations in active
volcanic-hydrothermal
systems
e.g.,
Kiyosu
&
Kurahashi 983), ul f ide
and sulfate
minerals
are
mainly in isotopic
equil ibrium,
and, therefore, heir overall
'oS/1'S
depends.on
he temperature
f mineralization
nd
the
'"S/"S
of
total sulfur in the
hydrothermal
system. Only
the data
for alunite from the
Campana ein in El Indio (Fig. 7) are different. f
the
measuredEl
Indio alunites are
not
steam-
heated
r supergene
unlikely
as hey contain ine-
grained
pyrite;
Jannas t al. 1990),
he most ikely
explanation
s a
"magmatic-steam"
(Rye
et al.
1992)origin,
n which
he 63aS
f alunite
s close
to the compositionof total sulfur
in the system
(e.g.,
Alunite Ridge n Marysvale;
Cunningham
l
al.
1984: Rve
el al. 1992\
. Combined
with the
p0
-
420
20
-270
200
-
240
200
390
200
350
180
26 0
210 270
220
330
'(minerat
pairs)
63aS
alues
of
pyrite
and enargite rom the same
vein, these values indicate
drastic changes n
H2S/SO4during the
course of mineralization
(similar to those for the Red Mountain alunite
deposit;Bove
et
al. 1990;Rye 1993).
The main
conclusionsof the sulfur-isotope
studies n HS deposits are:
(
I
)
sulfur in
the
deposits s magmatic,
but
the magmatic
sulfur is
overallheavier han mantlevalues
from
63aS
2
+2olooat
ummi fv i l l e ,
o 9
+2o/noat
Rodalqu i la r ;
Fig. 7). This is not surprising
given
the most
common
geological
setting of
the
deposits;
isotopicallyheavy igneoussulfur is co mmon in
volcanic arc
environments
e.g.,
Ueda & Sakai
1984). (2) A simple mass-balancealculat ion
done
n
severaldeposits sing
the
3oS/"S
values
of the igneous rocks and the average
oS/"S
values of sulfides and sulfates indicates
that
H2S/SO4n the hydrothermalluids was
generally
about
4
*
2
(Fig.
7; Rye
et
al. 1992;Hedenquist
l
ctl.
1994a; Arribas
et al.
1995a).
This is a
minimum value for ore-forming luids
because t
applies
mainly to the early stageof hydrothermal
-Sultides
-
*
Sulfates
^
V& V=
634515
r V
--F
I
'1-
- t v
I
v
- l i
r s z
--.--*
r J
Y
l v
-
I
- ;
o
r Y l
t - ' l
t l
l r f f i
t l
I
@
I
I
I
ry
I
I
@"f"
I
H gh-sulfidation
Epithermal
Depos
ts
aSSHzs-sor
Temp.
"C)'
H2S/
SO 4
10 20
6345
%",
CDT)
-igure
7.
Range of 63o5
per
mil) values
or
sulf ides
and
sulfates rom nine high-
sulfidation eposits.
lso shownare he values
alculatedor
5'oS
or
total sulfur n the
hydrothermal system
(triangles),
H2S/SO4. nd the
range
of temperatures
determined
from sulfide-sulfate
mineral
pairs.
Solid triangles ndicatedeposits n which
6toS*
was
calculatedon
the basis of
isotopic analysesof samples
of unalteredwhole rock
genetically
related o mineralization.
See Appendix for references
and information
on
data
plotted.
43s
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.4. 4rrihns.
/r .
al terat ion.
hich s characterizedv
a sulfate-r ich
alunite-pyri te
ssemblage
3)
lsotopic equi l ib-
rium between
sulfide and
sr-rlfate n the
hydrothermalolut ions
esults,n a nrajori ty f
the
deposits.
n rel iable emperatures
alculatedn
he
basis on A3aSrr:s-so+Fig 7). Pyri te-alunite
rnineral
pairs
were used
most commonly,
and
rvhere ampling
vith depth
s available,hev shorv
a
thermal
radient:
.g.,220
o 330
oC
over200-m
clevation
at Rodalqui lar
Arribas
et al . 1995a).
200 to 390
C
over
.--900
m at S'.tmmitvil le
R1'e
1993)1
20 to 420
'C
over 500
m at l -epanto
(Hedenquist
nd
Carcia
1990:J
\\r. Hedenquist.
unpr-rb. ata).
Other
mineral
prirs
used
with
consistent
results
include
p1'rite-barite
Vikre
1989:
Deen
1990), phaleri te-bari te
Venncmann
et al . 1993), ndplr i te-g1'psurnVikre 1989). he
rangeof
isotopic
emperalures
s consistent
vi th
temperatures
stimated
rom
fluid inerlusionsnd
alteration
mineralogy
e.g.,
Flemley'
t ul. 1980;
Reyes
1990;
Rey'es t ul.
1993).
-he range s also
consistent
with
formation
of
altrnite at
temperatures
elorv
400
C,
rvhenSO2
gas
starts
to dispropottionate
n the
h1'drothermal
olution
(Sakai
&
Matsubaya
911;,
ethke
1984).
Oxygen-
and
Hydrogen-isotope
Evidence
In terms
of oxygett
and
hydrogen
isotopic
composition,
he
fluids that
form
HS deposits
re
arguably
some
of the better
documented
an d
understood
n ore-deposit
tudies.
his si tuation
contrasts
sharply
witli t hat of a
decade
ago, at
which time
no data
were available
o corroborate
the
affinity
suggested
etween
luids
in active
volcanic-hydrothermal
ystems
and
HS deposits
(e.g.,
Heald
et al .
1987;Hedenquist
987).Stable-
isotope
studies
of
HS deposits
are
particularly
i l luminating
because
f :
( l )
the abundance
nd
variety
of oxygen-
and
hydrogen-bearing
inerals
(e.g., lunite, l l i te,kaol ini te),2) thedevelopment
of
analytical
procedures
or complete
stable-
isotope
nalysis
f alunite,
ncluding l8oroo
and
6' tOu'
that help
o dist inguish
he various
ypes
of alunite
and
associated
cid-sulfate
alteration
(Rye
et al.
1992;
Wasserman
t
ctl.
1992),
(3)
fewer limitations
on
the
interpretation
of the
isotopicdata
because
f the
relatively
young
age
of mineralization
f
most
HS deposits
nd
general
lack
of
post-deposit ional
f fects hat disturb he
stable-isotopeystematics.
nd
4)
the avai labi l i ty
of detai led information
on
the
isotopic
composit ion f
f luids in act ive
geothermal
nd
volcanic-hvdrothermal
ystems. which
al lows
fluids estimated n HS deposits o be compared
with
hose
n thei ract ive quivalents.
Some
limitat ionssti l l exist.
fhese
rnay be
rndependentf obvious actors uchas sampling
or
mineral-preparation
rocedures
fundamental
for
achieving
epresentat ivcnd
rel iable
esults).
analyt ical mprecision. nd
naturalvariat ions, s
observed
n active ystems
c.g.,
Aoki 1991,1992,
Rowe
1994). mpo rtant imitat ions hat rnustbe
taken
nto accourrtor optimum useof the stable-
isotope data
are related to
(
l
)
the choice of
temperature f mineral
formatiott br
calculation
of
the l luid isotop ic ompos it ion.
2)
thc lack
of
mineral-water
lractionation
factors for
some
minerals
(e.g
pyrophyl l i te),
and
(3)
the
disagreement among
fractionation constants
proposed
br evencommon
minerals uchas l l i te
(see
Dil les er a/.
1992, for a discussion) nd
kaol ini te. For examole.
at 200
oC
there is a
difference
of
-20
no
between
tlte D/lI fiac-
tionationconstants
or kaolinite
water
as
given
by Marumo et al.
(1980)
on the basisof samples
of
minerals nd rvater
rom activesystems, nd
by
t, iu & Epstein 1984) n the basis f experimental
results.
For these reasons.discussion
of the
sourcesof
water during acidic
alteratiorr
n
the
deposits onsidered
ere
s
basedon
the average
of
the data
collected for alunite,
for which
fractionation
actors are
well-known
(Stoffregen
et al.
1994).
The magmatic-hydrothermal
lunite
typical
of HS deposits
ives good resultsbecause
it is relatively
coarse-grained
post-mineral
D- H
exchange
s not a
problem;
Stoffregen t al.
1994)
and commonly
s closely
associated
ith
ore,
hus
recording qui l ibr iurn ondit ions f a f- luid loser
in composit ion
o
the ascending
mirreral iz ing
solution
than the
kaolinite
or illite
from outer
alteration
ones.
Oxygen
and
hydrogen
sotopic
compositions
of
water n HS deposits
re
clearly
consistent
it h
mixing
between a
high-temperature
magmatic
f lu idof
6180:9
+
1o/nond6D:
-30
+
20 /oond
meteoric
groundwaters
Fig.
8).
In
part
because f
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H gh-su(idation
Epithermal
Depos
ts
-1
00
- t z v
-1
40
6180
% ,
Mow)
Figure 8. Summary
diagramshowingvariation
n
oxygen-and
hydrogen-isotope
omposit ionof hydrothermal
fluids in high-sulfidation eposits.
The average sotopiccomposition
or
the main stagesof acidic alteration
(squares)
nd ore-mineralizat ion
circles)
luids are shown.Where
possible,
nly alunitedata were used
or the
alteration
tage
6D
and
6r8O5eo);'tOo,
is not
usedbecause
ydroxyloxygen equilibrates ith the hydrothermal
fluid during
cooling
(Rye
et al. 1992),
Tie-lines
befween
data
points
connectsamples rom the same
deposit. nset
shows
he isotopic compositionof
fields defined by waters rom active
geothermal
systemsand high-temperature
fumarolecondensates
n
subduction-related
ndesit ic
olcanoes
from
Giggenbach 992b).Go:
Goldfield,Ju :
Julcani,
Le-
Lepanto,
Nansatsu
istrict:
Ka
-
Kasuga, w
:
Iwato, NF
:
Nevados
del Famatina,PV
:
Pueblo
Veijo, Ro
:
Rodalquilar,RM
:
Red Mountain,
Lake City , Colorado, Su
:
Summitville. The
approximate
compositions
of
groundwaters
suggested
or severaldepositsare
indicatedby the intials
parallel
to the meteoric
water
ine. SeeAppendix for references nd
nformationon data
plotted.
the
very
light isotopic composition of local
relations are identical to those
of
volcanic-
meteoric
water,
this meteoric-magmatic water-
hydrothermal and
geothermal
systems associated
mixing
trend
is displayed
particularly
well by
the with subduction-rel ated
volcanism
(Giggenbach
three
stages
of alterationlmi neralization at
Julcani 1992b;
Fig.
8,
inset). The
similarity is even closer
(Deen
1990;
Rye
1993): from
a
magmatic-water- between
he composition of aci dic
alteration
fluids
dominated
early
stage of
(alunite)
acid-sulfate
(large
shaded
field, Fig.
8) and the
vapor
alteration
(Ju,
Fig. 8),
through main ore-stage condensates
rom high-temperature fumaroles of
fluid-inclusion
waters
(Ju1
and Ju2), o meteoric-
andesitic volcanoes
(dark
shaded field, Fig. 8 ,
water-dominated
late ore-stage
fluid-inclusion
inset), such as Nevado del Ruiz,
Satsuma
-40
3
>
-ou
a
d
t9
-eo
o
ta
waters
Ju3).
n
addition
o Julcani,
he
ore
fluids
at Summitville
(Rye
et
al. 1990:'Rye
1993) and
Rodalquilar
Arribas
et al.
1995a) lsohave
ower
6180
values
han thoseof
acidic alteration
luids,
indicating
greater
dilution
by
groundwater
Fig.
8).
The extent of an O-shift
in the
groundwater
component
due to
water-rock
interaction,
as
typically
seen in some
neutral-pH
geothermal
systems,
s not known, but
such
a shift
is not
indicated
y
the Julcanidata.
The overall oxygen-
and hydrogen-isotope
Iwojima, or White Island, he last documentedo
have
a
geochemical
nvironment imilar o that of
HS mineralization
Hedenquist
et al. 1993).
The
origin
of the D-enrichedmagmatic
end-
member) luid of HS deposits asbeen nterpreted
in two ways. Most workers conclude that the
acidic fluid in HS dep osits
is
derived from
absorptionof magmatic vapors outgassing rom
arc volcanoes r
felsic magmas n
crustalsettings
(e.g.,
Hedenquist Aoki
1991;
Matsuhisa 992;
Giggenbach
1992q' Vennemann et
al. 1993;
n
Alunite
lterationtg.
Q
Ore
mineralization
tg.
O
Alteration/
. ^?y,
Subduction-related
volcanrc apor
437
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A. Arribas, Jr.
ALTERATION
Figure 9. Model showing he two main stages f evolutionof HS deposits. : Early stageof advanced rgil l ic
alteration
dominated
by
magmaticvapor.
B, and
Bt: Two
genetic
hypotheses
roposed
or the
stageof ore
formation.
B,
-
absorption
f high-pressure
aporby entrainment
n meteoric
water cell at depth o explain ow-
salinity,
mixed
magmatic-meteoric
re
fluid
(Hedenquist
his volume).B,
-
ascending
metal-bearing
agmatic
brine
with shallow
cooler
meteoricwaters
o explain
high-salinity,mixed magmatic-meteoric re
fluid
(White
I 99
;
Rye
I 993;
Hedenquist t al.
1994a).
metals
strongly
partit ioned nto the
high-density
l iquid
(Hemley
et al .
1992; Hedenquist
his
vo lume) .
At this
early ntrusive
stage, everal
modes
of
magma
degassing
may occur
which wi l l lead o
different styles of magmatic-hydrothermal
systems
with or
without associated
ineralization
(Giggenbach
1992a).
To
form the styles
of
alteration
and he spatial
distribution
of alteration
zones characteristic
of
HS deposits,
degassing
must be
very efficient,
with oxidized
high-
temperature
magmatic
vapor
reaching shallow
depths
with little
reaction
with rock or
dilution by
groundwaters t
greater
epths
Fig.
9A).
Dilution
with
groundwater s s unlikely
because
he high
temperatures
surrounding
the
cooling
magma
causemeteoricwater cells to be displaced rom
the
magma core
(Fig.
9A). In
addition to
the
relat ively
ow
pressure
t
the depth
of intrusion,
effective
degassing
will be
favored by
the
structural
actors
characteristic
f
HS deposits,
such
as fractured
volcanic
domes
or roots of
domes,
aldera
or diatreme
aults,
volcanic
vent
contacts.
and active
faults
with a dilational
comporrent.
As thc
high-temperature
nagmatic
vapor
440
reaches hallowdepths
of less han a kilometer, t
may be absorbedby
groundwater
f it does not
discliarge
as a
fumarole. The
acidity of
this
groundwater-absorbed
apor condensate
ncreases
as the
liquid cools, first a t temperatur es elow
-400
C
by disproportionation f SO2 to form
H2SO4 nd H2S
(Day
&
Allen 1925; Sakai &
Matsubaya
1971), then by
progressive
disso-
ciation
of H2SOa nd
HCI at lowe r temperatur es
(
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8/9/2019 Epythermal Arribas 1995 MinAssocCanada23
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consti tut ing relat ivelv mal l
part
of
the
rnixturc-
(gcneral ly
-
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A. Arrihas,
r.
vapor is required
for transport
of sufficient
amounts of metals
(Hedenquist
his
volume;
Si l l i toe this volume).
These
condit ions are
consistent ith the low
salinityof the Lepanto
nd
El Indio
f luid-inclusion
ata.
Mineral
deposit ion
in this casemay be caused y mixing with cooler
groundwater
r by boiling,
possibly
esulting
ro m
the
abrupt
pressure
reduction
associatedwith
hydrothermal
recciation.
In the
hypersaline
liquid transporl
hypothesis
Fig.
9B2), ol lowing waning
of the
rnagmatic
vapor
plume
responsible
or early
alteration, he l i thostatic-pressured
ystem frac-
tures and the metal-bearing
hypersaline iquid
ascendsnto the
porous
eached
one
Deen
1990;
White l99l; Rye 1993;Hedenquist
/ al . 1994a).
The dominantore-forming
mechanismn this
case
is
rnixingof the metal-bearingypersal ine
iquid
with
cooler
groundwaters
t the site
of deposition,
not
at depth
n
the meteoricwater onvection
el l .
This hypothesis as
been
proposed
o explain
he
high
sal ini t ies
ecorded
by inclusion
luids in
several eposits
e.g.,
ulcani).
A
part
of the ore-fbrming
componentsmay
originate frorn leaching
of
wallrock,
but both
hypothesesagree on a dominantly
magmatic
source br metals,with an increasen
the meteoric
water
component with t ime. The
principal
differencebetween he two hypothesess in th e
nature of the magmatic
phase
responsible
or
transporting the metals into
the epithermal
environment.and in the site of meteoric water
dilution. A
potential
contributor o ore fbrmation
in
HS deposits
nvolves
remobi l izat ion f the
metals by a meteoric-wat er-dominate dydro-
thermal
system
fiom
a subjacent K-silicate
assemblage nd
porphyry-typeprotore,
such as
that
which may have
ormedclose o the intrusion
(e.g. ,
Brimhal l 1980).This mechanism, owever,
has not beensuggested s the main ore-fbrming
process
n
any of the deposits
eviewed n
this
study.
The three models or formation of HS ores.
assimilated here from the l iterature, are not
mutually exclusive;
on
the contrary, they may
occur
in the same HS
deposit
as the magmatic-
hydrothermalsystem evolves,with complexities
arising from multiple intrusions, variations in
depth
of emplacement, nd
changes n
the
local
442
tectonic
and hydrodynami c
nvironment.
one
of
the hree nodels
atisfies
he
overall
evidence.
or
example, f
metalswere
supplied
only by
a dense,
high-salinity
iquid,
a relation
would
be
expected
among
estimated
salinities,
metal
associations,
and ore gradeor metalabundancesf the various
deposits.
uchseems rot
o
be he case.
Similarly,
if alteration
and mineralization
were
solely
th e
result
of interaction
between groundwater
an d
low-
and high-pressure
apor,
respectively.
ig h
salinities
houldnot be as
comtnon
as hey
unlesshey
areexplained
y local
boi l ing
of di lute
to
moderately
saline meteoric
or seawater-
dominatedluids.
SYNTHESIS
Gold, Cu, and
Ag
(and
in
a few
exceptional
cases
also Hg, W, Bi,
Pb, and
Zn) are produced
from
HS deposits. s
a source
f Au,
and because
their mode
of occurrence
and the potential
to
overlie
porphyry-type
nineralization
have
been
widely recognized
nly within
the past
10
to l5
years,
HS deposits
represent
a
valuable
exploration
arget that
has
been overlooked
n
some egions.
Most known
HS deposits
re
young
in age, Tertiary
and
even
Quaternary.
High-
sulfldation
deposits fbrm
dominantly
in
subduction-related plutonic-volcanic arcs,
commonly
duringcrustal
xtension.
fhe
deposits
form
at a depth ntermediate
etween
he
surface
and shallow
few
kilometersdepth)
ntermediate-
composit ionntrusions.
The nt imate elat ionship
mong
HS deposits,
volcanic
host rocks,and
oxidized magrnatic
luid
derived rom
a degassingntrusion
s supported
y
the ol lowing
observations:
l)
the
volcanic ocks
hosting
HS depositswere
erupted immediately
prior
to mineralization,
(2)
the
ore-fbrming
hydrotherma l ystem ommonly ollows the same
plumbing
as that
of t he magmatic
system
i.e.,
rnineralization
patiallyassociated ith
domes
or
volcanic
onduits),
3)
he sotopic
omposit ion
f
hypogene
ulfides
e.g.,
enargite
and
pyrite)
and
sulfates
e.g.,
lunite
nd.bari te)
ommonly
anbe
model led rom
the
'oS/ S
of sul l ' ur n rg neous
rocks thought
to be
genetically
related,
by
equilibrium ractionation
etweenH2S
and
SOa
n
solutionat
T
-200-400
oC,
and
(4)
on the
basisof
-
8/9/2019 Epythermal Arribas 1995 MinAssocCanada23
22/33
oxygen
and
hydrogen
sotopic
ratios, he
waters
involved
n formation
of HS
deposits re
dentical
to
waters
in active
volcanic-hydrothermal
ys -
tems,
in
which the
same
HS
geochemical
environment
asbeendocumented.
Ore formation in some HS depositsmay
accompany
cidic
alteration,
nd
recentstudies
f
the
hydrothermal
geochemistryof
Au
provide
preliminary evidence
hat
this
element
may be
transported
n HS
and low-sulfidati on
ystems
s
different
hydrosulfide
complexes
(AuHS
and
Au(HS)2,
respectively;
ening& Seward
1994;
Seward
1913).On
the other
hand, he
presence f
moderate
o high sal ini t ies
n many
HS deposits.
the
intimate
association
with
porphyry copper-
type
deposits,
and the
assumptions
f
the most
recentgeneticmodels transport f Au and Cu
by
either
hypersaline
iquid or
high-pressure
apor)
indicate
that
chloride
complexes
must also
be
considered
or
metal ransport.
Most
HS deposits
volve
rom an early
period
of
acidic
wallrock alteration
o a
late
period
of
precious-and
base-metal
nineralization.
cidic
alteration
s characterized
y
advanced
argillic
assemblages
nd
porous
(leached)
ock, and
th e
hydrothermal
luid
responsible
or this
alteration
is dominated
y
high-temperature
agmatic
apor
containing
SO2,
H2S,
and
HCl. Less
reactiveand
oxidized
fluids
are typically
responsible
or
or e
mineralization.
actors uch
as
multiple
ntrusions
and
opening
or closing
of
fractures
conduits)
result
in variations
n the
temperature,
ressure,
and composit ion
of
the
ascending
solut ions.
Combined
with
the shal low
environment
of
mineralization,
hese
conditions
ead o
a variety
of deposit
styles
(mainly
replacements,
reccias,
and
veins)
that
usually
occupy
a
limited
vertical
span
of
800
m at the
giant Chinkuashih
deposit).
The
geological,
mineralogical, and geochemical evidence,
particularly he
association
etween
he orebodies
and the
lateral
and
vertical
zones of
alteration,
illustrates
the basic
genetic condition
of
HS
deposits,
hat
a magmatic
luid
interacts
xtensive
ly
with
country
rock and
groundwaters
n
it s
relatively
short
path o the
earth's
urface.
High-sulfidation pithermalDeposts
ACKNOWLEDGMENTS
Valuable
nsighton variousaspects elated o
this excitingore-forming
environmentwas
gained
throughdiscussions
nd ield work
with
M. Aoki,
A. ArribasSr.,C. G.
Cunningham, . Hedenquist.
W.C.
Kelly, R. O. Rye, J. J.
Rytuba,andT. A.
Steven.
Earlier versions of
this manuscript
benefited
from constructive
reviews by Phil
Bethke,
Andrew Campbell,
Anne Thompson,
ohn
Thompson,
Peter Vikre, Noe l White, and Jeff
Hedenquist,
who also
provided
abundant
documentation
n HS deposits
worldwide.
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