Hydrothermal Controls on Metal Distribution in Porphyry Cu (-Mo-Au) Systems

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573
Chapter 22
Hydrothermal Controls on Metal Distribution in Porphyry Cu (-Mo-Au) Systems
KALIN KOUZMANOV1,† AND GLEB S. POKROVSKI2
1 Earth and Environmental Sciences, Department of Mineralogy, University of Geneva,
rue des Maraîchers 13, CH-1205 Geneva, Switzerland
2 Géosciences Environnement Toulouse, GET (ex-LMTG), Université de Toulouse,
CNRS-IRD-OMP, 14 Av. E. Belin, F-31400 Toulouse, France
Abstract
Extensive research during the 20th century on porphyry Cu (-Mo-Au) deposits has revealed the following
major geodynamic, petrological, mineralogical, and geochemical features that characterize these deposits: (1) these
systems commonly occur in continental and oceanic magmatic arcs or in collisional orogenic belts; (2) they have
spatial and genetic relationships to basaltic-to-felsic magmas emplaced in the upper 10 km of the crust; (3) lat-
eral and vertical alteration-mineralization zoning consists of a Cu (± Mo ± Au) ore shell in the shallow portion
of a potassic alteration zone, produced by magmatic fluids; this can be overprinted by phyllic alteration, also
largely magmatic in signature, that in turn may be overprinted by argillic alteration, with a dominantly mete-
oric signature; (4) associated deposits such as skarns, Cordilleran vein, and high and intermediate sulfidation
epithermal deposits may occur above or adjacent to porphyry orebodies; (5) porphyry systems form from
S- and metal-rich, single-phase aqueous fluid of moderate salinity (2–10 wt % NaCl equiv) exsolved from mag-
mas; during its ascent toward the surface this fluid undergoes a variety of processes that can cause metal pre-
cipitation, including decompression, phase separation, cooling, interaction with host rocks, and mixing.
In the last 20 years, novel microanalytical techniques for in situ characterization of individual fluid inclusions
have provided direct evidence for the chemical and phase composition plus metal content of ore-forming flu-
ids in porphyry systems. In this contribution, we compile a large dataset of published fluid inclusion composi-
tions from more than 30 deposits of the porphyry-skarn-epithermal suite. Four main types of fluid inclusions
are identified, based on their origin and phase composition at the time of entrapment: (1) single-phase, inter-
mediate-density inclusions, regarded as equivalent to the primary single-phase fluid exsolved from the magma,
(2) vapor-rich and (3) hypersaline liquid inclusions, both resulting from phase separation of the single-phase
fluid, and (4) low to intermediate salinity aqueous liquid inclusions. The first three fluid types are characteris-
tic of porphyry and skarn environments at elevated temperatures and depths, whereas the last is present dur-
ing the retrograde stage, both in skarn and porphyry deposits as well as in the shallow epithermal environment.
Absolute concentrations of ore-related metals in the pristine single-phase magmatic fluids are typically one
to three orders of magnitude higher than their average crustal abundances, demonstrating the ability of mag-
matic-hydrothermal fluid to concentrate and transport metals. Decompression-induced phase separation of
this magmatic fluid upon ascent and intersection of the two-phase vapor-liquid boundary of the water-salt sys-
tem results in metal fractionation, as evidenced by coexisting vapor and hypersaline liquid inclusions. The hy-
persaline liquid is largely enriched in metals such as Zn, Pb, Fe, Mn, and Ag, whereas Au, As, S and, to a lesser
and uncertain extent, Mo may partition into the vapor phase. Copper is likely to have a partitioning behavior
intermediate between these groups of elements; however, its true vapor-liquid distribution may be obscured
by post-entrapment diffusion processes which lead to an apparent enrichment in Cu in natural S-rich vapor
and single-phase fluid inclusions. These metal fractionation trends are quantitatively explained by recent
experimental data on vapor-liquid partitioning that show a preferential affinity of Au (and partly Cu) for re-
duced sulfur and that of other metals for chloride, and by physical-chemical models involving the fluid density.
Single-phase, vapor-rich, and hypersaline liquid inclusions from giant porphyry deposits at Bingham, El
Teniente, Bajo de la Alumbrera, Questa, and Butte present a characteristic Zn/Pb ratio, ranging from 1 to 6 in
the order of the listed deposits, which is constant for a given deposit and is not affected by phase separation of
the input magmatic fluid or Cu-Au-Mo precipitation in the porphyry environment, thus implying differences
in the Zn/Pb ratio of the parental magmas.
Recent experimental studies on metal speciation and ore mineral solubilities under hydrothermal conditions
coupled with thermodynamic modeling allow the reported metal contents in natural inclusion fluids to be
interpreted. Modeling shows that cooling of a magmatic fluid, accompanied by water-rock interaction, is likely
to be the major cause of most metal deposition, as well as the cause of spatial separation between Cu-Mo and
Zn-Pb-Ag mineralization in porphyry systems. Changes in sulfur speciation on cooling lead to SO2dispropor-
tionation; this is likely to control the observed fractionation of Au from Cu and other base metals during fluid
evolution in the transition from the porphyry to epithermal environment. Fluid neutralization by wall-rock
reaction appears to be the main driving force for Zn, Pb, Ag, and partially Au deposition in more distal portions
of the porphyry system. Fluid immiscibility in the porphyry regime mostly affects Au and to a lesser extent Cu
† Corresponding author: e-mail, kalin.kouzmanov@unige.ch
© 2012 Society of Economic Geologists, Inc.
Special Publication 16, pp. 573–618
Kouzmanov_Pokrovski_Layout 1 3/19/13 8:50 AM Page 573

Introduction
RESEARCH on porphyry Cu (-Mo-Au) systems and associated
base and precious metal deposits has been conducted for over
a century, and our present understanding of their genesis is
based primarily on geologic observations, complemented by
petrological, geochemical, mineralogical, structural, geo -
chronological, and geophysical data. This ensemble of data
has allowed the genetic link between porphyry Cu deposits
and magmatic-hydrothermal processes to be established and
has contributed to field observations on the geology to build
genetic models successfully used in mineral exploration.
However, knowledge of the hydrothermal fluid itself has re-
mained limited. Ore-forming fluids in these deposits have
been mainly characterized by conventional fluid inclusion mi-
crothermometry, providing a constraint on their PVTX (pres-
sure-volume-temperature-composition) parameters. Their
origin and isotopic composition have been inferred by using
indirect data from mineral assemblages and isotopic signa-
tures of minerals. Prior to the turn of the century, the metal
content of inclusion fluids was studied by bulk crush-leach
methods, analyzing a large number of inclusions that were
commonly related to different inclusion populations, each as-
sociated with a different hydrothermal event.
In the last 15 years, major advances in microanalytical tech-
niques, particularly for individual fluid inclusion characteriza-
tion, such as laser ablation-inductively coupled plasma- mass
spectrometry (LA-ICP-MS), proton-induced X-ray emission
spectroscopy (PIXE), synchrotron radiation X-ray fluores-
cence (SR-XRF), infrared, Raman, and fluorescence spec-
troscopy, have provided direct data for the chemical and phase
composition and metal content of ore-forming fluids. These
data have better constrained metal sources and budgets in
porphyry systems. In addition, recent progress in experimen-
tal approaches and physical-chemical modeling of hydrother-
mal fluids has provided far more accurate information on the
identity and stability of dissolved metal-bearing species, and
improved predictions of ore-mineral solubilities, metal vapor-
liquid partitioning, and depositional mechanisms.
The principal aim of this contribution is to provide an
overview of the current knowledge of hydrothermal fluid com-
positions and the chemical speciation of ore metals (Cu, Au,
Ag, Mo) and accompanying elements (S, Fe, Zn, Pb) in vari-
ous types of fluids under the conditions relevant to porphyry
Cu (-Mo-Au) formation. We have compiled recently published
metal concentrations from direct analyses of fluid inclusions,
with corresponding temperature and salinity measurements,
from more than 30 deposits of porphyry Cu, Cu-Au, Mo, and
Cu-Mo systems, Sn-W–mineralized granites, and various por-
phyry-related skarn, vein, and epithermal deposits. This data
set is compared to thermodynamically predicted metal con-
tents of hydrothermal fluids, based on the calculated solubil-
ity of the major metal-bearing ore minerals as a function of
key intensive parameters (temperature, pressure, Cl content,
acidity, redox potential, and sulfur fugacity). The major
hydrothermal processes leading to the redistribution and de-
position of metals in porphyry systems are discussed in an at-
tempt to illustrate the complexity of factors controlling ore
formation in the deep (porphyry and skarn) and shallow (epi-
thermal) parts of these systems. The paper concludes with a
summary of near-future analytical, experimental, and theoret-
ical challenges for research on fluid processes in porphyry
systems.
Porphyry Systems
Definition and significance
The economic importance of porphyry deposits grew con-
stantly over the last 50 years and now they supply a majority
of the world’s Cu, Mo, and Re and a substantial amount of Au,
together with some Ag, Pd, Te, Se, Bi, Zn, and Pb (Sillitoe,
2010). They are probably the best studied of all hydrothermal
ore deposits and their salient features have been discussed in
a number of special volumes and review articles published
over the past half century (summarized by Hedenquist and
Richards, 1998). Several recent papers offer exhaustive
overviews of the geologic and geotectonic setting, architec-
ture, associated magmatism, metal and mineral alteration
zoning, and space-time relationships of porphyry systems
(e.g., Tosdal and Richards, 2001; Richards, 2003, 2011; Cooke
et al., 2005; Seedorff et al., 2005; Sillitoe, 2010).
Porphyry deposits are composite magmatic-hydrothermal
systems that involve large volumes (~10–100 km3) of altered
rocks resulting from extensive circulation of hydrothermal flu-
ids at shallow crustal levels (Kirkham, 1971; Beane and Titley,
1981; Titley, 1982, 1993; Beane and Bodnar, 1995; Seedorff et
al., 2005; Sillitoe, 2010). Porphyry systems typically occur in
continental and oceanic arcs, 100s to 1,000s of kilometers
long and mainly of Tertiary age, or in collisional orogenic belts
(Cooke et al., 2005; Richards, 2011). A diagnostic feature of
these deposits is the development of low-grade stockwork Cu,
Au, and/or Mo mineralization within and around porphyritic
intrusive stocks and associated dike swarms, some of which
intrude the base of intermediate to felsic volcanoes; others
574 KOUZMANOV AND POKROVSKI
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and Mo behavior by enabling a significant fraction of these metals to be transported by the vapor phase. Mix-
ing with external waters is uncommon and not directly involved in ore formation in the porphyry environment.
These predicted tendencies agree with the commonly observed metal zoning pattern in porphyry systems, and
may provide useful clues for specific metal prospecting if the major fluid evolution events can be identified
from fluid inclusion, mineralogical, or stable isotope analyses.
Comparison between mineral solubility calculations and metal contents in natural fluids shows that for some
metals, such as Cu, Ag, Fe, Zn, and Pb, there is a good consistency. In contrast, thermodynamic predictions for
Au and, particularly, Mo commonly underestimate their contents compared to natural fluid compositions. This
requires reassessment of existing speciation models for these metals and consideration of recently discovered
sulfur species that could potentially be important as metal transporting agents. Further development of
microanalytical and in situ experimental approaches in hydrothermal geochemistry may provide new predic-
tive tools in mineral exploration; coupled with physical hydrology models, this will allow the generation of
integrated reactive transport models of fluid evolution and three-dimensional ore distribution in magmatic-
hydrothermal systems, thus contributing to better exploration strategies.
Kouzmanov_Pokrovski_Layout 1 3/19/13 8:50 AM Page 574

are emplaced in sedimentary and crystalline rocks (Gustafson
and Hunt, 1975; Seedorff et al., 2005). It is generally ac-
cepted that porphyry systems are initiated by injection of
oxidized magma, saturated with S- and metal-rich aqueous
fluids, from cupolas of large underlying parental dioritic-to-
granitic composite plutons emplaced in the upper 10 km of
the crust (Emmons, 1927; Burnham, 1979; Cline and Bodnar,
1991, 1994; Dilles and Einaudi, 1992; Hedenquist and
Lowenstern, 1994; Bodnar, 1995; Richards, 2003, 2011; Hal-
ter et al., 2005). Multiple overprinting stages of alteration and
mineralization result from aqueous hydrothermal fluid cool-
ing from >700° to <200°C, in parallel with the solidification
of the underlying volatile-saturated magma reservoir; subse-
quent cooling results in the downward propagation of the
lithostatic-hydrostatic pressure transition zone (Burnham,
1979; Fournier, 1999; Proffett, 2009; Sillitoe, 2010).
The following section summarizes the typical features of
porphyry systems—their characteristic hydrothermal alter-
ation, mineralization, and metal zonation, resulting from de-
pressurization and cooling of the magmatic-hydrothermal flu-
ids, and their reaction with wall rocks.
Architecture of porphyry systems
Porphyry systems, sensu largo (Fig. 1; Sillitoe, 2010), host
various ore deposit types that formed at distinct but partly
overlapping depths and temperature and pressure ranges.
These include porphyry deposits, sensu stricto, associated
proximal and distal skarns, subepithermal, carbonate-re-
placement, high and intermediate sulfidation polymetallic ±
Au ± Ag vein deposits, disseminated high-sulfidation Au-Cu-
Ag deposits in the shallow epithermal environment, and sed-
iment-hosted disseminated Au ± As ± Sb ± Hg deposits in
more distal positions. Mineralization associated with all these
deposit types has diagnostic wall-rock alteration assemblages
that can be used as a defining feature of the environment of
ore formation.
Alteration and mineralization zoning: No matter their age,
tectonic setting, and size, porphyry systems around the world
share common alteration and mineralization styles with
broadly similar spatial distribution patterns (Meyer and Hem-
ley, 1967; Lowell and Guilbert, 1970; Rose, 1970; Beane,
1982). Broad-scale alteration zoning comprises sodic-calcic,
potassic, chlorite-sericite, sericitic, and advanced argillic as-
semblages, from the base upward and outward to propylitic
alteration (Fig. 2; see details about definition, characteristics,
mineral composition, occurrences, and processes of forma-
tion for different alteration types in Seedorff et al., 2005, and
Sillitoe, 2010). The temporal evolution observed in porphyry
systems starts with early biotite ± K-feldspar ± magnetite as-
semblages (potassic alteration, also called K-silicate by some,
e.g., Meyer and Hemley, 1967) formed at high temperature,
continues with lower temperature muscovite ± chlorite as-
semblages (chlorite-sericite and sericitic alteration), and ends
with low-temperature, clay-bearing assemblages (intermedi-
ate argillic); shallow advanced argillic alteration begins to form
during the deep potassic stage, but can continue to form later
in the life of a system. Later assemblages commonly overprint
earlier formed alteration, as summarized by Seedorff et al.
(2005) and Sillitoe (2010). Such evolution of alteration as-
semblages is consistent with the progressive cooling and
acidification of magmatic fluids during their ascent toward
the surface, with an increase in the fluid/rock ratio with time,
and prior to their neutralization by wall-rock reactions, as dis-
cussed below.
Geologic observations, stable isotopic compositions of min-
erals and fluids, and fluid inclusion analyses provide evidence
that magmatic fluids generally dominate the high-tempera-
ture potassic alteration and are still dominant in sericitic al-
teration; nonmagmatic fluids dominate much deep sodic-cal-
cic and propylitic alteration, whereas advanced argillic—
related to condensates of magmatic vapor— and intermediate
argillic alteration are influenced by meteoric waters (Seedorff
et al., 2005; Sillitoe, 2010, and references therein).
Precipitation of Cu-Fe-sulfide ore minerals (mainly chal-
copyrite and bornite), locally associated with molybdenite
and/or gold in quartz stockwork veins and disseminations, is
governed by the same factors that control wall-rock alteration.
In porphyry deposits, detailed field and microscale observa-
tion of crosscutting relationships between veins with different
mineralogy and alteration provides the most reliable criteria
for establishing relative timing of hydrothermal events.
Cathodoluminescence imaging of hydrothermal quartz im-
proves the textural interpretation of crosscutting relationships
in porphyry stockwork veining and the timing of sulfide pre-
cipitation (e.g., Rusk and Reed, 2002; Redmond et al., 2004;
Landtwing et al., 2005, 2010; Vry et al., 2010). These studies
revealed complex growth histories of sulfide-quartz veins in
porphyry Cu (-Mo-Au) deposits; early Cu-bearing quartz
veins are usually associated with the high-temperature potas-
sic alteration and cut by molybdenite-quartz veins, which in
turn are cut by pyrite-dominated veins with sericitic alter-
ation envelopes (e.g., Meyer and Hemley, 1967; Gustafson
and Hunt, 1975; Beane and Titley, 1981; Titley, 1982; Red-
mond and Einaudi, 2010). This paragenetic scheme is widely
generalized; in each individual deposit varied relationships
between different vein types occur due to the cyclic behavior
of porphyry systems—repetitive emplacement of multiple
porphyry stocks and associated hydraulic fracturing that led
to complex textural relationships between veins, alteration as-
semblages, and intrusions (Seedorff et al., 2005, 2008; Silli-
toe, 2010). In some deposits, late veins, which contain Cu ±
Zn, Pb, Ag, and Au within sericitic, intermediate argillic, and
advanced argillic alteration envelopes, cut the early Cu- and
Mo-bearing veins (e.g., Meyer et al., 1968; Gustafson and
Hunt, 1975; Ossandón et al., 2001; Proffett, 2003; Masterman
et al., 2005; Rusk et al., 2008a; Catchpole et al., in review).
Such late veins may overprint the deep potassic alteration
where telescoping occurs (Sillitoe, 1994).
Epithermal deposits commonly form above or adjacent to
porphyry orebodies (Fig. 1). Ore and gangue minerals typi-
cally occupy open space in veins, breccia zones, or volumes
of secondary porosity (Hayba et al., 1985; Sillitoe and Heden-
quist, 2003; Simmons et al., 2005); replacement textures are
common in carbonate-replacement analogues of epithermal
deposits. Mineralization can be associated with sericitic,
chloritic, intermediate argillic, and advanced argillic alter-
ation. Where carbonate-rich sedimentary rocks host porphyry
systems, calcic or magnesian endo- and exoskarns develop
(Einaudi, 1982). Prograde garnet-pyroxene assemblages in
calcic skarns form contemporaneously with early potassic
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576 KOUZMANOV AND POKROVSKI
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High-sulfidation epithermal
disseminated Au ± Ag ± Cu
High-sulfidation
lode Cu-Au ± Ag
Carbonate-replacement
Zn-Pb-Ag ± Au (or Cu)
Distal Au/Zn-Pb
skarn
Proximal
Cu-Au skarn
Porphyry
Cu ± Au ± Mo
Base of
lithocap
1km
1km
Subepithermal
vein Zn-Cu-Pb-
Ag ± Au
Sediment-
hosted distal-
disseminated
Au-As ± Sb ± Hg
Late-mineral porphyry
PORPHYRY
STOCK
PRECURSOR
PLUTON
HOST
ROCKS
Intermineral magmatic-hydrothermal breccia
Intermineral porphyry
Early porphyry
Equigranular intrusive rock
Dacite dome
Felsic tuff unit
Andesitic volcanic unit
Subvolcanic basement / carbonate horizon
V
V
V
V
V
V
V
V
V
V
Phreatic breccia
Dacite porphyry plug-dome
Lacustrine sediment
Late phreatomagmatic breccia
Early phreatomagmatic breccia
Late-mineral porphyry
LITHOCAP
MAA R -
DIATREME
COMPLEX
High-density vapor (60-90% V)
Polyphase hypersaline liquid
Single-phase intermediate density
Low- to intermediate-salinity aqueous
Hypersaline liquid
Low-density vapor (>90% V)
Fluid flow pathways and characteristics:
Single-phase magmatic fluid
Saline, non-magmatic brines
Meteoric water
Low-density acidic vapor
Low-to-moderate density vapor
Hypersaline liquid
Fluid inclusion types in different environments:
Intermediate-
sulfidation
epithermal Au-Ag
g
p
Auddisseminate
High-sulfidation epithermal
p
Au-Ag
l
epitherma
nosulfidati
Intermediate-
Cu
±
± Cu
g A±
High-sulfidation epithermal
lithocap
Base of
lithocap
Base of
skarn
Au/Zn-PblDista
Zn-Pb-A
Carbonate-replacement
ulode Cu-A
High-sulfidati
on
lhosted dista
-
tSedimen
Au/Zn-Pb
Au (or Cu)±gZn-Pb-A
Carbonate-replacement
gA±
n
o
High-sulfidati
mk1
mk1
Ag ±
vein Zn-Cu-Pb-
Subepithermal
Au ± Mo±Cu
Porphy
ry
uAAg ±
vein Zn-Cu-Pb-
Subepithermal
Au ± Mo
y
r
Porphy
Cu-Au ska
Proximal
Au-As ± Sb ± Hg
disseminated
-lhosted dista
nrCu-Au ska
Proximal
ONTULP
ROSRPRECU
KCSTO
RYYPORPH
ry
Equigranular intrusive rock
yrEarly porphy
y
r
Intermineral porphy
Intermineral magmatic-hydrothermal brecc
Late-mineral porphyry
Equigranular intrusive rock
aiIntermineral magmatic-hydrothermal brecc
Fluid flow pathways and characteristics:
Hypersaline liquid
Low-to-moderate density vapor
Low-density acidic vapor
Meteoric water
Fluid flow pathways and characteristics:
Low-to-moderate density vapor
Fluid flow pathways and characteristics:
SKROC
STOH
-RAAM
APCOHLIT
ff un
Subvolcanic basement / carbonate horizon
Andesitic volcanic unit
ti
f un
f
Felsic tu
Dacite dome
V
V
V
V
V
V
V
V
V
V
Lacustrine sediment
Dacite porphyry plug-dome
aiPhreatic brecc
Subvolcanic basement / carbonate horizon
Dacite porphyry plug-dome
Fluid inclusion types in dif
Single-phase intermediate density
Polyphase hypersaline liquid
apor (60-90% V)High-density v
onments:ent envir
fer
d inclusion types in dif
ffer
Saline, non-magmatic brines
Single-phase magmatic fluid
apor (>90% V)Low-density v
Single-phase intermediate density
onments:
XELPMOC
MEERTAID
yrLate-mineral porphy
Early phreatomagmatic brecc
Late phreatomagmatic brecc
aiEarly phreatomagmatic brecc
aiLate phreatomagmatic brecc
Hypersaline liquid
aqueousLow- to intermediate-salinity
Polyphase hypersaline liquid
aqueous
FIG. 1. Schematic cross section through a typical porphyry Cu system showing spatial relationships of the porphyry Cu-
Au deposit, centered on a porphyry stock, with peripheral proximal and distal skarns, carbonate-replacement and distal sed-
iment-hosted disseminated deposits, subepithermal veins in noncarbonate rocks, and overlying lithocaps plus high and in-
termediate sulfidation epithermal deposits (from Sillitoe, 2010; with fluid flow pathways and spatial distribution of the main
fluid inclusion types commonly found in different environments added). Figure used with permission of R.H. Sillitoe.
Kouzmanov_Pokrovski_Layout 1 3/19/13 8:50 AM Page 576

alteration in aluminosilicate rocks at lithostatic pressures,
whereas later hydrated, retrograde skarn assemblages (acti-
nolite, epidote, chlorite, smectite, magnetite, carbonate) as-
sociated with sulfides form under hydrostatic conditions,
analogous to sericitic alteration in porphyry deposits (Meinert
et al., 2003, 2005).
Metal zoning of porphyry systems: A characteristic feature
of many porphyry systems is the regular pattern of zonal
metal distribution—both vertically from deep levels proximal
to the composite porphyry stocks, and laterally from centrally
located potassic alteration to marginal propylitic zones (Fig.
2). In porphyry-centered districts like Butte, Montana
(Meyer et al., 1968; Rusk et al., 2008a, b), Bingham Canyon,
Utah (John, 1978; Babcock et al., 1995), or Morococha, Peru
(Catchpole et al., 2011, in review), Cu ± Mo ± Au character-
ize the central, deep parts of the systems, forming an ore shell
in the upper parts of the potassic alteration zones. Vertical Cu
± Au ± Ag zones may be present in the upflow conduits above
the centers of the systems, as high-sulfidation Cu-Au-Ag
lodes and high-sulfidation disseminated epithermal Au-Ag
deposits (Fig. 1). However, due to erosion, these zones are
commonly absent in porphyry-centered districts; in such
cases, a Cu ± Mo ± Au core ringed by successive Cu-Zn, Zn-
Pb-Ag, Pb-Ag (± Mn), and As-Sb-Au-Hg zones is observed in
plan view (Fig. 2). Metal zoning both upward and outward
from the core is a primary function of mineral solubility,
transport, and depositional mechanisms of base and precious
metals, controlled by intensive parameters of the fluids, as
discussed below.
Lifespan and multiphase character of magmatic-hydrother-
mal processes: Most porphyry deposits are centered on com-
posite stocks formed during prolonged magmatic evolution,
commonly consisting of pre-, syn-, and postmineral intru-
sions. Recent studies on the geochronology of porphyry sys-
tems, combining different geochronometers (most frequently
U-Pb, Re-Os, and Ar/Ar), indicate a protracted magmatic and
hydrothermal lifespan for some giant porphyry deposits, as
long as 4 to 5 m.y. (e.g., Ballard et al., 2001; Maksaev et al.,
2004; Valencia et al., 2005; Harris et al., 2008; Sillitoe and
Mortensen, 2010; Barra, 2011; Deckart et al., 2012). Else-
where, magmatic-hydrothermal activity was shorter, ≤1 m.y.
(e.g., 0.08 m.y. at Batu Hijau, Indonesia: Garwin, 2002; 0.09
m.y. at Bajo de la Alumbrera, Argentina: von Quadt et al.,
2011; 0.10 m.y. at Lepanto-Far Southeast, Philippines: Ar-
ribas et al., 1995; 0.32 m.y. at Bingham Canyon: von Quadt et
al., 2011; 0.80 m.y. at Grasberg, Indonesia: Pollard et al.,
2005; and ~1 m.y. at Elatsite, Bulgaria: von Quadt et al., 2002).
The multiphase character of magmatism and the resulting
prolonged magmatic-hydrothermal activity in porphyry sys-
tems cause a superposition of multiple events that reflect the
cyclic evolution of these systems. Such superposition can
significantly complicate the interpretation of the alteration,
mineralization, and metal zonation of the early events, which
can be (partially) destroyed by the younger magmatic and/or
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Cu-Zn
Zn-Pb-Ag
Ag-Pb
As-Sb
-Hg-Au
basinal
recirculated
magmatic
Igneous rocks:
Hydrothermal alteration:
Porphyry 2
Porphyry 1
Granite cupola
Chlorite-sericite to sericitic
Sodic-calcic
Propylitic
Potassic
Fluid paths
Cu ± Au
Au ± Ag ± Cu
surface
derived
Advanced argillic
C
u
±
A
u
±
M
o
0
1
1 km
Approximate
scale
Au ± Ag ± Cu
rface
surfa
Au ± Ag ± Cu
As-Sb
u
u
C
u
Au ± Ag ± Cu
C
d
d
C
C
C
u
C
u
derived
Z
Zn
n
g
g
o
o
n
Ag
g
o
Z
u
C
Zn
g
Ag-Pb
Zn-Pb-Ag
Cu ± Au
Cu-Zn
o
M
Au ± Ag ± Cu
Cu ± Au
M
M
M
o
M
o
±
u
A
±
-Hg-Au
As-Sb
Granite cupola
Porphyry 1
Porphyry 2
Hydrother
Igneous rocks:
Advanced ar
Granite cupola
Porphyry 1
Porphyry 2
mal alteration:
rmal alteration:
Igneous rocks:
gillicAdvanced ar
e
ci
r
r
ec
ir
culated
ecir
r
r
basinal
magmatic
basinal
Fluid paths
Potassic
opyliticPr
Sodic-calcic
Chlorite-sericite to sericitic
Advanced ar
scale
oximateAppr
1 km
1
0
Fluid paths
Potassic
opylitic
Sodic-calcic
Chlorite-sericite to sericitic
gillicAdvanced ar
FIG. 2. Generalized scheme of metal zoning, alteration patterns, and fluid paths in a porphyry-centered system. Ore shell
of Cu ± Au ± Mo is centered on the porphyry stock and extends to the wall rocks. Outward base-metal zoning, commonly
observed in porphyry-centered districts, includes in order of increasing distance from the porphyry: Cu-Zn, Zn-Pb-Ag, Pb-
Ag, and As-Sb-Hg-Au zones (see Fig. 1 for the different associated deposit styles). Note that this zonation of metals reflects
changes in fluid compositions, as well as metal transport and precipitation mechanisms. High sulfidation Cu ± Au mineral-
ization may develop in the upflow zone over the center of the system; however, due to erosion this part of the system is com-
monly missing in well-zoned porphyry-centered base-metal districts (e.g., Butte, Morococha). Juvenile magmatic fluids, hav-
ing potential sources in composite porphyry stocks and/or deeper granitic cupolas, may mix at depth with saline fluids of
nonmagmatic origin (e.g., formation waters) or recycled magmatic fluids (e.g., earlier stage residual hypersaline porphyry liq-
uids), as well as surface-derived meteoric waters at later stages of hydrothermal evolution. Adapted from Emmons (1927),
Meyer et al. (1968), Corbett and Leach (1998), Dilles et al. (2000), Seedorff et al. (2005, 2008), and Sillitoe (2010).
Kouzmanov_Pokrovski_Layout 1 3/19/13 8:50 AM Page 577

hydrothermal events (e.g., Proffett, 2003). Redistribution of
metals by later fluid circulation can also occur, resulting in
more complex deposit- to district-scale metal zonation than in
the ideal case of a single mineralizing intrusion (Fig. 2).
Overprinting of multiple magmatic and hydrothermal
events can also complicate the interpretation of PVTX prop-
erties of hydrothermal fluids from fluid inclusion analysis,
due to possible postentrapment modification and re-equili-
bration of the fluid inclusions. Thus, extreme care is needed
in acquisition and interpretation of fluid inclusion data in por-
phyry systems. We next summarize the potential fluid
sources, as well as the main physical properties, evolution,
and spatial distribution of the principal fluid inclusion types in
porphyry systems, as these inclusions are our principle source
of information on metal concentrations.
Origin and evolution of fluids in porphyry systems
Fluid sources in porphyry systems: When intermediate-to-
felsic magmas ascend in the crust and crystallize in response
to pressure decrease and cooling, the residual silicate melt
becomes saturated with a volatile phase, generating an aque-
ous magmatic fluid (Burnham, 1979). The exsolved fluid
phase is dominantly aqueous, but contains significant quanti-
ties of CO2and lesser amounts of SO2 (± H2S) and other
minor gases (H2, N2); in addition, HCl, NaCl, KCl, and metal
chlorides are present in variable proportions as a function of
the depth of exsolution and parental magma composition
(Candela, 1989; Giggenbach, 1992, 1997; Heden quist, 1995;
Einaudi et al., 2003). The salinity of the single-phase mag-
matic fluid at high pressures, above the two-phase surface in
the H2O-NaCl system (Fig. 3), is typically in the range of 2 to
10 wt % NaCl equiv (Shinohara and Hedenquist, 1997;
Hedenquist and Richards, 1998; Audétat and Pettke, 2003;
Redmond et al., 2004; Rusk et al., 2004, 2008b; Audétat et al.,
2008; Table 1). This magmatic fluid initially has a near-neutral
pH because most of acid-like volatiles (HCl, SO2) are fully as-
sociated at high temperatures, but it becomes acidic on cool-
ing, if not sufficiently buffered by aluminosilicate rocks, due
to dissociation of acidic components and disproportiation of
SO2 to H2S and sulfuric acid (Giggenbach, 1997; see below).
578 KOUZMANOV AND POKROVSKI
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0
250
500
750
1000
1250
1500
0102030405060708090100
P (bar)
wt. % NaCl
700°
650°
600°
550°
500°
450°
400°
350°
300°
Single-phase
magmatic
input fluid
V + L
L + V + H
2
4
3
1
4
Porphyry
Epithermal
Critical curve
3
1
2
4
deep single-phase magmatic fluid exsolution
single-phase fluid intersects V-L solvus
single-phase fluid never intersects V-L solvus
shallow magmatic fluid exsolution
4
0
250
500
750
1000
1250
1500
0 100 200 300 400 500 600 700 800
T (°C)
P (bar)
Low- to moderate
salinity aqueous
solutions
2
V + H
V + L
V/L + H
1
1
34
Single-phase
magmatic
input fluid
Coexisting low-salinity
vapor and hypersaline
liquid
10 wt% NaCl
5 wt% NaCl
Porphyry
4
Epithermal b
a
FIG. 3. Pressure-composition (a) and pressure-temperature (b) cross sections of the NaCl-H2O phase diagram (adapted
from Richards, 2011, based on data from Sourirajan and Kennedy, 1962; Driesner, 2007, and Driesner and Heinrich, 2007),
illustrating principal evolution pathways of a magmatic-hydrothermal fluid exsolved from a crystallizing magma with an ini-
tial bulk salinity of ~10 wt % NaCl (gray area in a). L, V, and H refer respectively to liquid, vapor and halite, which are the
three phases in the H2O-NaCl system. When the single-phase magmatic fluid expands on ascent, its pressure and tempera-
ture (P-T) evolution path may or may not intersect the two-phase vapor-liquid domain of the NaCl-H2O system (V-L solvus).
Because of the curvature of the critical curve (i.e., the curve connecting the summits of the V-L solvus at each given tem-
perature in the T-P section) to lower salinities at temperature ~450°C, fluids that intersect the V-L solvus at higher temper-
atures will be moderate-density vapors and will condensate a small amount of dense hypersaline liquid, while fluids that in-
tersect the solvus at lower temperatures will be liquid and will boil and form a low-density aqueous vapor. Path 1 illustrates
deep single-phase magmatic fluid exsolution and path 2 shows fluid exsolution from shallowly emplaced magma. Path 3 refers
to the single-phase magmatic fluid contraction to an aqueous low to moderate salinity liquid phase without entering the V-L
two phase domain (Hedenquist et al., 1998), and path 4 refers to a fluid evolution with intersection of the V-L solvus, allow-
ing initial condensation of hypersaline liquid and subsequent contraction of the ascending vapor phase to a low-salinity aque-
ous liquid in the epithermal environment (Heinrich et al., 2004). In both cases, subsequent near-surface boiling of this low
salinity liquid may optimize metal deposition in the low P-T epithermal environment, mainly due to loss of H2S from the liq-
uid. Major fluid inclusion types generated by different P-T fluid evolution paths in porphyry and epithermal environments
(Table 1) are shown by the same symbols as in Figure 1 (see text for details). Fluid paths are according to Richards (2011).
Kouzmanov_Pokrovski_Layout 1 3/19/13 8:50 AM Page 578

Magmas are the main source of fluids that transport metals,
salts, and sulfur to the porphyry environment (e.g., Roedder,
1971; Nash, 1976; Eastoe, 1978; Cline and Bodnar, 1991,
1994; Dilles et al., 1992; Hedenquist and Lowenstern, 1994;
Hedenquist and Richards, 1998; Halter et al., 2005; Harris et
al., 2005; Heinrich et al., 2005). Despite the overall magmatic
signature of fluids involved in porphyry systems, in a few
cases external fluids (basinal brines, seawater or meteoric
water; Fig. 2) may affect alteration zoning patterns, as re-
vealed by stable and radiogenic isotope signatures of hydro-
thermal minerals (e.g., Sheppard et al., 1971; Chivas et al.,
1984; Dilles et al., 1995). In contrast, in the shallow epither-
mal environment, meteoric water interacts with the ascend-
ing magmatic fluids, causing dilution and cooling of the latter;
meteoric water also acts as the condenser of magmatic vapor
that leads to acidification and creation of epithermal lithocaps
above the porphyry centers (e.g., Rye, 1993; Arribas, 1995;
Hedenquist et al., 1998; Deyell et al., 2005a, b; Fifarek and
Rye, 2005).
Fluid inclusion types: Terminology, physical properties,
and spatial distribution: Fluid inclusions trapped in gangue
and ore minerals from porphyry systems are direct mi-
crosamples of paleomagmatic-hydrothermal fluids responsi-
ble for hydrothermal alteration and mineral precipitation
(Roedder, 1967). Fluid inclusion data provide direct informa-
tion on the pressure, temperature, and composition of the flu-
ids at the time of their entrapment; combined with thermo-
dynamic calculations of mineral stabilities, such data can be
used to constrain intensive parameters of ore formation.
There are few general review papers on fluid inclusions re-
lated to ore formation in porphyry systems sensu largo (Bod-
nar, 1995; Hedenquist and Richards, 1998, on porphyry de-
posits; Bodnar et al., 1985, on epithermal deposits; Kwak,
1986, on skarns), compared to the large number of papers
that discuss the characteristics of mineralizing fluids based on
physical chemistry or indirect mineral alteration patterns of
these deposits. Various aspects of fluid inclusion research on
porphyry systems can also be found in several reviews on fluid
inclusions in ore deposits and shallow intrusions (e.g., Spooner,
1981; Weisbrod, 1981; Roedder, 1984; Lattanzi, 1991, 1994;
Roedder and Bodnar, 1997; Wilkinson, 2001).
There is much variability in the terms used in the fluid in-
clusion literature on ore deposits (Table 2); this can create
confusion, especially when fluid inclusions with similar char-
acteristics have different, contradictory names. A summary of
terms used to describe fluid types and processes in magmatic-
hydrothermal systems and a discussion of their use, misuse,
and interpretation can be found in Liebscher and Heinrich
(2007) and references therein.
Although the commonly used classifications account accu-
rately for most fluid inclusion aspects at room temperature,
they provide little direct information about the fluid charac-
teristics at the pressure and temperature of entrapment. In
the present study, we use a genetic classification of fluid in-
clusions typically observed in porphyry deposits, based on
the properties of the fluid at the time of entrapment. Four
major types of fluid inclusions are defined; their main char-
acteristics, including phase proportions at room tempera-
ture, temperature of homogenization, salinity, density, and
metal content are summarized in Table 1. In the following
sections we refer to these four types of fluid inclusions and
their properties:
1. Single-phase, intermediate-density, aqueous inclusions,
containing liquid phase and vapor in equal proportions (L ≈
V) at room temperature; commonly a small opaque daughter
crystal is also present. These fluid inclusions are trapped at
high temperature and pressure in the single-phase domain,
above the two-phase vapor-liquid boundary of the H2O-NaCl
system (Fig. 3). This fluid inclusion type is typically CO2-rich
(e.g., Roedder, 1971; Nash, 1976; Klemm et al., 2008, Rusk et
al., 2008b), with CO2content reaching ~12 mol % (Rusk et
al., 2008c; 2011). These fluid inclusions have densities be-
tween ~0.50 and 0.75 g/cm3and are considered as represen-
tative of the original single-phase fluid exsolved from magma
during crystallization.
2. Vapor-rich fluid inclusions dominated by a vapor phase
(>60–65 vol %) at room temperature. They are inferred to
have trapped a volatile fluid phase that was produced by
magma degassing and/or vapor-liquid separation over a wide
temperature range (800°–~300°C). The density of such fluids
is less than the critical density for a given fluid composition,
typically <0.3 to 0.5 g/cm3.
3. Hypersaline liquid inclusions trapped a high-salinity
(26–80 wt % NaCl equiv) liquid phase containing a high con-
centrations of dissolved salts, typically NaCl>KCl>FeCl2.
Fluid density is greater than the critical density for a given
fluid composition and can reach >1.3 g/cm3. At room tem-
perature, these inclusions contain a vapor bubble, liquid
phase, and one or more daughter crystals in addition to a
halite crystal; the presence of opaque daughters and/or red
hematite plates is common. In porphyry deposits, such fluids
are typically produced by fluid phase separation under mag-
matic or hydrothermal conditions (Fig. 3).
4. Aqueous, low-to-intermediate salinity inclusions are
dominated by liquid water and have a small vapor bubble,
typically 20 to 40 vol% at room temperature. Fluid density is
generally low – 0.1 to 0.6 g/cm3; temperature and pressure of
entrapment are much lower than those of single-phase fluids.
These inclusions are free of daughter phases; however, in
some cases, they may contain accidentally trapped crystals.
Each fluid inclusion type has a particular spatial distribu-
tion in porphyry systems (Table 1): single-phase fluids are typ-
ical of the deep central and peripheral zones; hypersaline liq-
uid and coexisting vapor inclusions mark the level where
phase separation takes place in the porphyry environment,
and low-density buoyant vapor ascends toward the surface;
low-salinity aqueous fluids dominate the shallow parts of the
systems (Fig. 1). Although potassic alteration in the core of
systems (Fig. 2) can be produced by a single-phase magmatic
fluid (Redmond et al., 2004; Rusk et al., 2008b; Redmond and
Einaudi, 2010), it may also form in the domain of coexisting
vapor + hypersaline liquid cooling together from ~700°C to
~350°C, as evidenced by stable isotope analyses of hydro-
thermal minerals and fluid inclusion microthermometry (e.g.,
Hedenquist et al., 1998; Redmond et al., 2004). In proximal
and distal skarns, the fluid associated with the early prograde
skarn formation is dominantly high temperature (tempera-
tures exceeding 350°–400°C), single-phase and/or hypersaline
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liquid, whereas during the retrograde stage low-to-moderate
salinity aqueous fluids are dominant (e.g., Meinert et al.,
2003, 2005; Baker et al., 2004; Vallance et al., 2009; Williams-
Jones et al., 2010). In contrast, in the shallow, low-pressure
and temperature, high-sulfidation epithermal environment,
ore-precipitating fluids are aqueous solutions of low-to-mod-
erate salinity, 0.2 to 8 wt% NaCl equiv (e.g., Mancano and
Campbell, 1995; Ruggieri et al., 1997; Jannas et al., 1999;
Wang et al., 1999; Kouzmanov et al., 2002; Molnár et al.,
2008; Moritz and Benkhelfa, 2009; Fig. 1). However, these
low salinity fluids are still dominantly of magmatic origin, as
evidenced by stable isotope analyses of alteration minerals
(e.g., Vennemann et al., 1993; Hedenquist et al., 1998; Catch-
pole et al., in review).
The formation and properties of the four main fluid types
are largely controlled by the PVTX properties of a water-salt-
volatile system, which may be reasonably approximated by
the well-known H2O-NaCl system (Fig. 3).
PVTX evolution of single-phase magmatic fluid on ascent:
Figure 3, based on the H2O-NaCl model system (Sourirajan
and Kennedy, 1962; Driesner, 2007; Driesner and Heinrich,
2007), schematically illustrates possible evolutionary path-
ways of an intermediate-density aqueous fluid exsolved from
a hydrous magma at depth, on its ascent through porphyry
and epithermal environments toward the surface, projected
onto pressure-composition and pressure-temperature space
(according to Heinrich, 2007, and Richards, 2011). The fluid
paths are strongly controlled by the initial density, and salt
and volatile composition of the exsolved magmatic fluid and
the nature of its pressure-temperature evolution, which can
vary from deposit to deposit. According to Richards (2011)
such paths are summarized as follows (Fig. 3): (1) path 1 il-
lustrates the generation and deep exsolution of a single-phase
magmatic fluid with initial salinity of 2 to 10 wt % NaCl equiv,
at magmatic temperature and pressure exceeding 1 kbar; (2)
path 2 illustrates magmatic fluid exsolution from shallowly
580 KOUZMANOV AND POKROVSKI
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TABLE 1. Various Types of Fluid Inclusions Commonly Found in Porphyry and Epithermal Environments with Their
Nomenclature based on Temperature Salinity
Fluid inclusion types genetic aspects (see text) Environment of hom. (°C) (wt % NaCl equiv)
Single-phase inclusions are intermediate- Deep barren and deep 300–650 2–16
density aqueous inclusions containing equal central and peripheral
proportions of liquid and vapor; many contain Cu-Au (Mo) ore zones
small opaque daughter crystals (arrow) of in PCD; porphyry-
constant relative size associated skarns
Vapor-rich inclusions can be high- (60-90% Stockwork mineraliza- 260–650, vapor:
vapor) or low-density (>90% vapor) and tion at moderate to rarely up 0.2–20
commonly contain small opaque daughter shallow depth in central to 800
crystals (arrow); hypersaline liquid inclusions parts of Cu-Au (Mo) ore
always contain a vapor bubble, a saline zones and upper parts hypersaline
aqueous liquid and halite (H); additionally, of Cu-rich periphery; liquid: 26–75
polyphase inclusions contain a few other porphyry-associated
transparent and opaque daughter phases; skarns
in many cases vapor-rich and hypersaline
liquid inclusions form boiling assemblages
Aqueous low- to intermediate-salinity Late-stage porphyry 150–450 vapor: <0.5
inclusions with predominantly liquid water veining (quartz-sericite-
and smaller vapor bubbles ranging from pyrite); base and pre- liquid: 0–20
20 to 40 vol % may occur together or not cious metal mineral-
with low-density vapor-rich inclusions ization in skarns,
(>90 % vapor); aqueous inclusions are usually carbonate-replacement
free of daughter crystals; however, some may and epithermal
contain accidentally trapped sericite crystals; orebodies
coexistence of aqueous and low-density vapor
inclusions is indicative of fluid boiling at low
pressure
Kouzmanov_Pokrovski_Layout 1 3/19/13 8:50 AM Page 580

emplaced magma; and (3) paths 3 and 4 refer to single-phase
magmatic fluid evolution through the porphyry to the shallow
epithermal environment without and with intersection of
the two-phase vapor-liquid domain of the NaCl-H2O system,
respectively.
During decompression, the ascending magmatic fluid of
relatively low salinity will intersect the two-phase liquid +
vapor surface (V-L solvus) on the vapor-rich side of the criti-
cal curve, leading to condensation of small amounts of hyper-
saline liquid from the intermediate-density juvenile fluid
(path 4; Fig. 3a). This results from the physical-chemical
properties of the H2O-NaCl ± CO2system that allow for a
large domain of coexistence of the vapor and hypersaline liq-
uid, extending over a temperature range from 700° to ~200°C
and with pressures below ~1.5 kbar (Sourirajan and Kennedy,
1962; Takenouchi and Kennedy, 1965; Henley and McNabb,
1978; Fig. 3). This fluid unmixing results in the generation of
two phases, a vapor and a liquid, with contrasting density,
salinity, and volatile and metal content (Table 1); this process
has important implications for ore-forming processes both in
the porphyry and epithermal environments. Henley and
McNabb (1978) suggested that the hypersaline liquid phase,
because of its high density and viscosity that restrict its up-
ward migration, would accumulate at depth close to the site
of phase separation, and then progressively drain under grav-
ity and divert toward the margins of the system. In contrast,
the more voluminous and lower-density vapor phase, rich in
volatile components, would dominate the center of the sys-
tem and form a magmatic vapor plume over the top of the
porphyry intrusion due to its low-density, buoyant nature
(Henley and McNabb, 1978; Fournier, 1999). Toward the pe-
riphery of the system, mixing with groundwater would even-
tually cause dilution and decrease of the magmatic compo-
nent of the fluids.
If hydrous magma is emplaced at shallow depth, under low
pressure within the two-phase V+L field (path 2; Fig. 3), its
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Typical Ranges of Temperature, Salinity, Pressure, Density, Metal, and Sulfur Concentrations (range and average)1
Pressure Density
(bar) (g/cm3) Cu (ppm) Mo (ppm) Au (ppm) Ag (ppm) As (ppm) Sb (ppm) Zn (ppm) Pb (ppm) S (ppm)
300– >2000 0.4–0.7 20–20000 2–300 <1–20 <1–300 20–2000 <1–30 20–6500 10–4500 2600–23000
————— ——— ——— ——— ———— ——— ———— ———— —————–
2660 70 1.6 30 250 9 600 330 9400
90–1300 vapor: <1–33000 1–70 0.05–11 <1–600 2 –1200 1–150 <1–6800 <1–4000 960–26000
0.01–0.4 ————— ——— ——— ——— ———— ——— ———— ———— —————–
4300 25 1.9 45 175 35 660 340 6300
hypersaline 3–30000 1–2000 0.03–22 2–3400 6–6600 1–1200 90 –40000 5 –60000 220–25000
liquid: ————— ——— ——— ——— ———— ——— ———— ———— —————–
0.8–>1 4770 180 1.5 95 230 95 4620 3790 7600
<100 vapor: <0.02 No data available for metals
liquid: <1–5500 2–160 0.08–26 <1–100 <1–3200 <1–950 <1–22000 <1 –4000 810–11280
0.1–0.6 ————— ——— ——— ——— ———— ——— ———— ———— —————–
325 30 2.9 10 415 85 715 165 2700
1 Data sources: Allan et al. (2011), Anderson et al. (1989), Audétat et al. (2000a, b), Audétat and Pettke (2003), Audétat et al. (2008), Baker et al. (2004),
Beuchat et al. (2004), Catchpole et al. (2011, in review), Cline and Vanko (1995), Gysi and Herbort (2006), Harris et al. (2003), Heinrich et al. (1992, 1999),
Kamenetsky et al. (2002, 2004), Kehayov et al. (2003), Klemm et al. (2007, 2008), Kostova et al. (2004), Kotzeva et al. (2011), Kouzmanov et al. (2010), Kuro-
sawa et al. (2003, 2010), Landtwing et al. (2005, 2010), LeFort et al. (2011), Müller et al. (2001), Pettke (2008), Pettke et al. (2001, 2012), Pudack et al. (2009),
Rusk et al. (2004, 2008b, c), Seo et al. (2009, 2011, 2012), Ulrich et al. (1999, 2001), Vanko et al. (2001), Wallier et al. (2006), Williams-Jones and Heinrich
(2005), Williams-Jones et al. (2010), Wolfe and Cooke (2011). Abbreviations: hom = homogenization, PCD = porphyry copper deposits
Kouzmanov_Pokrovski_Layout 1 3/19/13 8:50 AM Page 581

crystallization leads to expulsion of high-temperature, low-
density vapor with minor segregation of hypersaline brine,
the salinity of which normally exceeds 60 wt % NaCl equiv.
The vapor, enriched in acidic volatiles (SO2, HCl), condenses
into groundwater on ascent toward the surface, producing an
acidic solution; this leads to leaching (residual quartz, typi-
cally with a vuggy texture) and pervasive advanced argillic al-
teration, in the upper parts of magmatic-hydrothermal systems
(Fig. 1; Hedenquist and Aoki, 1991; Rye, 1993; Hedenquist et
al., 1998; Sillitoe, 2010; Chang et al., 2011). High sulfidation
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TABLE 2. Comparative Terminology of the Main Fluid Inclusion Types in Porphyry Systems
Fluid inclusion Terminology used in the literature for
types (this study), petrographically similar fluid inclusion types References
Single-phase B60 Rusk et al. (2004, 2008b, c, 2011)
Critical Baker et al. (2004)
Deep supercritical magmatic fluid Richards (2011)
High-temperature magmatic fluid Hedenquist and Richards (1998)
Intermediate-density Catchpole et al. (in review), Klemm et al. (2007, 2008),
Pudack et al. (2009), Seo et al. (2012)
Liquid-rich low salinity Cline and Bodnar (1994)
Liquid-rich with V>50% Beane and Bodnar (1995), Bodnar and Beane (1980)
Liquid-vapor aqueous (liquid fraction 0.3-0.7), Allan et al. (2011)
Moderate salinity inclusions Nash (1976)
Single-phase Audétat et al. (2000a, 2008)
Supercritical fluid Audétat and Pettke (2003)
Two-phase Kurosawa et al. (2003)
Vapor-rich low salinity Cline and Bodnar (1994)
Vapor-rich B85 Rusk et al. (2004, 2008c)
Gas rich Nash (1976)
Liquid-vapor aqueous (liquid fraction <0.3), Allan et al. (2011)
Steam Roedder (1971)
Vapor Audétat and Pettke (2003), Audétatet al. (1998, 2000a, 2000b, 2008),
Baker et al. (2004), Catchploe et al. (2011, 2012), Heinrich et al. (1992,
1999), Klemm et al. (2007, 2008), Landtwing et al. (2005, 2010),
Pudack et al. (2009), Richards (2011), Seo et al. (2009, 2011, 2012),
Ulrich et al. (1999, 2001)
Vapor-phase Cauzid et al. (2007)
Vapor rich Beane and Bodnar (1995), Cline and Bodnar (1994), Harris et al. (2003),
Hedenquist and Richards (1998), Kamenetsky et al. (2002),
Kouzmanov et al. (2010), Wolfe and Cooke (2011)
Hypersaline liquid Aqueous inclusions with solid daugther phases Allan et al. (2011)
B15H Rusk et al. (2004, 2008c)
Brine Audétat and Pettke (2003), Audétatet al. (1998, 2000a, 2000b, 2008),
Baker et al. (2004), Catchpole et al. (2012), Guillong et al. (2008),
Harris et al. (2003), Heinrich et al. (1992 (1999), Kamenetsky et al. (2002),
Klemm et al. (2007, 2008), Landtwing et al. (2005, 2010),
Pudack et al. (2009), Richards (2011), Seo et al. (2009, 2011, 2012),
Ulrich et al. (1999, 2001), Wolfe and Cooke (2011)
Halite-bearing Nash (1976), Eastoe (1978), Beane and Bodnar (1995)
Hypersaline liquid Redmond et al. (2004)
Hypersaline liquid-rich Hedenquist and Richards (1998)
Liquid-phase Cauzid et al. (2007)
Liquid rich Cline and Bodnar (1994)
Liquid-vapor-halite / LVH Kouzmanov et al. (2010), Williams-Jones et al. (2010)
Multiphase Bodnar and Beane (1980), Kamenetsky et al. (2004), Roedder (1971)
NaCl-saturated liquid rich Hedenquist et al. (1998)
Polyphase Kurosawa et al. (2003)
Polyphase hypersaline Harris et al. (2003)
Low-salinity aqueous Aqueous Audétat et al. (2000), Klemm et al. (2007, 2008), Landtwing et al. (2005,
2010), Pudack et al. (2009), Seo et al. (2012)
B20 Rusk et al. (2004, 2008c)
NaCl-undersaturated liquid rich Hedenquist et al. (1998)
Liquid rich Baker et al. (2004), Catchpole et al. (2011, in review),
Wolfe and Cooke (2011)
Liquid rich low-salinity Cline and Bodnar (1994)
Liquid rich with V<50% Beane and Bodnar (1995), Bodnar and Beane (1980)
Liquid-vapor / LV Kouzmanov et al. (2010), Williams-Jones et al. (2010)
Moderately saline liquid Richards (2011)
Liquid-vapor aqueous (liquid fraction >0.7), Allan et al. (2011)
Two-phase LeFort et al. (2011), Roedder (1971)
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epithermal Au deposits can subsequently form in this envi-
ronment, where the residual quartz provides the permeable
host for metal deposition, introduced by later aqueous fluids
that are also magmatic in origin (e.g., Deen et al., 1994;
Hedenquist et al., 1994b, 1998; Arribas, 1995; Bethke et al.,
2005; Deyell et al., 2005a, b; Baumgartner et al., 2008).
Richards (2011) summarized two scenarios to explain how a
single-phase intermediate-density magmatic fluid can evolve
into an epithermal aqueous ore-forming solution without sig-
nificant loss of metals due to sulfide precipitation: (1) cooling
at sufficient pressure, prohibiting the single-phase fluid from
intersecting the two-phase V-L surface before reaching epi-
thermal pressure and temperature conditions (path 3; Fig. 3),
as suggested by Hedenquist et al. (1998); (2) brief intersec-
tion of the V-L solvus at high pressure and temperature (path
4; Fig. 3a), resulting in partitioning of salts and chloride-com-
plexed metals (e.g., Fe, Pb, Zn) into a small portion of hyper-
saline liquid, whereas Au ± Cu partition into the vapor phase,
which eventually cools and contracts to a low-salinity aqueous
liquid, as proposed as an alternative by Heinrich et al. (2004)
and Heinrich (2005, 2007). In both cases, the resulting epi-
thermal fluid will lie on the liquid side of the solvus, because
of the curvature of the critical curve to lower salinities at low
temperatures (Fig. 3a). Subsequent near-surface boiling of
this low-salinity aqueous solution and loss of H2S will cause
metal deposition at the low pressures and temperatures of the
epithermal environment (see below for details).
Temperature-salinity characteristics of fluids: The two
main parameters of fluid inclusions routinely obtained from
microthermometric experiments are the temperature of ho-
mogenization and salinity. Homogenization temperature (Th)
is the temperature at which a fluid inclusion transforms from
a multiphase (heterogeneous) to one-phase (homogeneous)
state (Diamond, 2003). In general, Th provides an estimate of
the minimum temperature of entrapment. For coexisting liq-
uid and vapor inclusions, a unique estimate of temperature
and pressure of entrapment is possible using the well-known
PVTX properties of the H2O-NaCl (-CO2) system (e.g., Roed-
der and Bodnar, 1980; Sterner and Bodnar, 1985; Sterner et
al., 1988); in all other cases a correction is required. This cor-
rection concerns the temperature of formation, which may be
independently estimated using different geothermometers
(e.g., trace element- or stable isotope-based geothermome-
ters). In porphyry systems, such a correction usually does not
exceed 50° to 100°C for low-salinity aqueous fluids; however,
for single-phase fluids, it may reach 200° to 250°C (Rusk et
al., 2008b), implying that entrapment temperatures may be
much higher than the measured Th. Being unable to deter-
mine or predict the true temperature of entrapment in many
cases for the published fluid inclusion data, we use Th as the
best proxy available for temperature of formation in the fol-
lowing text when discussing variations of physical parameters
or element concentrations of fluid inclusions as a function of
temperature. The second parameter, salinity, corresponds to
the amount of solutes in aqueous solution, including elec-
trolytes (e.g., NaCl, KCl) and nonelectrolytes (e.g., CO2), and
can be estimated based on temperature of final dissolution of
solids (ice, hydrohalite, clathrate, or halite) and experimental
phase equilibria in the NaCl-H2O (-CO2) model system (Bod-
nar and Vityk, 1994; Diamond, 1994).
Data base for this study: In this paper we compiled a large
dataset of published fluid compositions, temperatures of ho-
mogenization, and salinity measurements, which includes 801
fluid inclusion assemblages1(with 2–17 inclusions per assem-
blage) and 469 single fluid inclusions from more than 30 de-
posits in porphyry Cu, Cu-Au, Mo, and Cu-Mo systems, Sn-
W–mineralized granites, and various porphyry-related vein
and epithermal deposits. Data are classified into the four
main fluid inclusion types as follows: single-phase, 109 as-
semblages and 84 single inclusions; hypersaline liquid, 352 as-
semblages and 112 single inclusions; vapor-rich, 153 assem-
blages and 7 single inclusions; and low to intermediate salinity
aqueous inclusions, 187 assemblages and 266 single inclu-
sions (data sources in Table 1).
Figure 4 illustrates the homogenization temperatures and
salinities of the four types of fluid inclusions in porphyry sys-
tems discussed in this paper. The largest amount of mi-
crothermometric data exists on hypersaline liquid inclusions,
but their abundance is due mostly to the relative ease of ob-
taining microthermometric data compared to vapor-rich or
single-phase inclusions. Values of Th for hypersaline liquid in-
clusions vary from ~250° to >700°C; their salinities (limited
by the NaCl saturation curve in Fig. 4) range from 26 to >65
wt % NaCl equiv. The few data points that lie above the NaCl
curve may result from (1) heterogeneous entrapment of a
NaCl-saturated fluid, or (2) postentrapment modification of
the fluid inclusions (Becker et al., 2008). Due to similarities
in their properties (Table 1), single-phase, vapor-rich, and low
to moderatesalinity aqueous inclusions partially overlap in the
ranges of 350° to 420°C and 0 to 10 wt % NaCl equiv; this can
create confusion regarding the definitions given by different
authors to these inclusions (Table 2). However, single-phase,
intermediate density inclusions, regarded as analogues of the
parental magmatic fluid (Redmond et al., 2004; Audétat et al.,
2008; Rusk et al., 2008; Landtwing et al., 2010), have, on av-
erage, higher salinities than vapor-rich inclusions, usually be-
tween 5 and 10 wt % NaCl equiv for identical Th intervals,
between 350° and ~650°C (Fig. 4).
At temperatures of <320°C, corresponding to formation of
retrograde assemblages in skarns, porphyry-related veins and
replacement bodies, and epithermal deposits, the dominant
inclusions are the low-to-intermediate salinity aqueous type.
Hypersaline liquid inclusions at these temperatures are un-
common, but they may be produced in some cases by boiling
of a low-salinity aqueous fluid at low pressure and tempera-
ture (e.g., Simmons and Browne, 1997). Low density, vapor-
rich inclusions also result from boiling of a moderate-salinity
aqueous liquid; however they are not shown on the tempera-
ture-salinity plot in Figure 4, because of difficulties in obtain-
ing the corresponding microthermometric data.
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1The term “fluid inclusion assemblage” (FIA) was introduced by Gold-
stein and Reynolds (1994) for simultaneously trapped (cogenetic) fluid in-
clusions occupying an individual petrographic feature (e.g., crystal-growth
zone, healed fracture). Working with FIAs rather than individual fluid inclu-
sions allows the identification of a fluid inclusion population that is repre-
sentative of a given hydrothermal event; the standard deviation of various
physical parameters and composition of the fluids can also be determined.
The geologic meaning of the data acquired can be better evaluated and data
scatter can be attributed to natural variations or to various fluid processes.
Kouzmanov_Pokrovski_Layout 1 3/19/13 8:51 AM Page 583

Composition of Ore Fluids in Porphyry
Cu-Mo-Au Systems
Metal concentrations in ore fluids:
Iinsights from fluid inclusion analyses
In the 1990s, LA-ICP-MS, PIXE, and SR-XRF analytical
techniques were successfully applied to measure metal con-
centrations in individual fluid inclusions from magmatic-
hydrothermal systems (e.g., Anderson et al., 1989; Ryan et al.,
1991; Heinrich et al., 1992; Rankin et al., 1992; Wilkinson et
al., 1994; Audétat et al., 1998; Günther et al., 1998). As a re-
sult, a large amount of data on metal concentrations in ore-
bearing fluids from a variety of porphyry and associated
deposits was generated. The first compilation of the data was
reported by Williams-Jones and Heinrich (2005) in their review
of vapor transport of metals; they compared the concentra-
tions of metals in vapor discharged from volcanic fumaroles
with data from fluid inclusions in magmatic-hydrothermal
systems and concluded that the metal-transporting capacity
of aqueous fluids and vapors at depth is much higher than
that of low-pressure and hence low-density volcanic vapors.
Later, Audétat et al. (2008) discussed the composition and
metal content of fluids from 17 mineralized and barren mag-
matic-hydrothermal systems; they demonstrated that the metal
content of magmatic aqueous fluids correlates positively with
the type and amount of mineralization in the associated
intrusions. Wilkinson et al. (2008) compared LA-ICP-MS
analyses of single-phase and hypersaline liquid inclusions
from the Chuquicamata and El Teniente, Chile, and Butte
porphyry Cu deposits and suggested that both fluid types may
be equally capable of transporting Cu, and that their relative
mass proportion in the system will influence Cu mobility and
spatial distribution. Recently, Rusk et al. (2011) reported
analyses of single-phase, parental magmatic fluid from ten of
the largest porphyry Cu, Cu-Mo, Mo, and Cu-Au deposits,
pointing out that this fluid was trapped at near-magmatic
temperatures and pressures (~600°C and 1.5–2.5 kbar), and
was dominated by Na, K, and Cu, with subordinate Fe; Na/K
ratios range between 1 and 4, and most of the Na/Cu ratios
range from 1 to 200.
Our compilation of the concentrations of metals (Mn, Fe,
Cu, Zn, As, Mo, Ag, Sb, Au, Pb) and major alkalis (Na, K) in
the four fluid types in porphyry systems defined in this study
is summarized in Table 1 and presented for selected metals in
Figure 5. The general features of metal concentration pat-
terns are discussed below.
For each fluid inclusion type, large variations in metal con-
tent have been observed, up to two orders of magnitude for
most metals in the single-phase type and up to four orders of
magnitude in the other three fluid types. For single-phase flu-
ids trapped at near magmatic temperatures and having the
most pristine magmatic signatures (i.e., prior to modification
by cooling, fluid unmixing, wall-rock reaction, and mineral
precipitation), these variations should reflect variability in
584 KOUZMANOV AND POKROVSKI
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single-phase
hypersaline liquid
vapor-rich
low-salinity aqueous
NaCl saturation curve
0
10
20
30
40
50
60
70
80
100 200 300 400 500 600 700 800
Th (°C)
Salinity (wt% NaCl eq.)
FIG. 4. Plot of salinity vs. temperature of homogenization for the four main fluid inclusion types in porphyry systems sum-
marized in Table 1: single-phase: intermediate-density aqueous inclusions (with liquid/vapor ≈1 at room temperature), rep-
resenting the single-phase magmatic fluid; hypersaline liquid: high-salinity liquid inclusions, usually containing saline aque-
ous liquid, vapor bubble, and halite, sometimes also other transparent and/or opaque daughter phases at room temperature;
vapor-rich: high- and low-density vapor-rich inclusions containing >60% vapor at room temperature; low-salinity aqueous:
liquid-rich low to intermediate salinity inclusions (<40% vapor at room temperature), free of daughter crystals. Almost all
data points correspond to average values for fluid inclusion assemblages (FIAs), where several inclusions were measured (see
Table 1 for data sources).
Kouzmanov_Pokrovski_Layout 1 3/19/13 8:51 AM Page 584

chemical and physical parameters of the parental magma, in-
cluding composition, depth and pressure, and redox state
(Audétat and Simon, 2012). The larger variations for hyper-
saline liquid, vapor-rich, and low-salinity aqueous inclusions
can be explained by metal fractionation upon unmixing and
cooling plus mineral precipitation.
Copper exhibits the largest concentration range amongst
the metals, varying more than three orders of magnitude. Its
concentrations span from 10s to 10,000s ppm, with a maxi-
mum value of ~20,000 ppm in single-phase fluid inclusions, ,
from a few ppm to ~30,000 ppm in vapor-rich and hyper-
saline liquid inclusions, , and from ≤1 ppm to 5,500 ppm in
low salinity aqueous inclusions (Fig. 5). Such variations likely
reflect a combination of factors, such as magma characteris-
tics, silicate melt-fluid partitioning, fluid unmixing, mineral
precipitation, and, as recently demonstrated, very likely sig-
nificant postentrapment modifications, particularly in the
vapor-rich inclusions (as discussed below). Molybdenum
shows similar concentrations in single-phase and vapor-rich
fluids (10s ppm on average), whereas in hypersaline liquid in-
clusions Mo attains several 100s ppm, with a maximum of
2,000 ppm. This was attributed to Mo enrichment in the
hypersaline liquid as a result of fluid unmixing in the por-
phyry regime (e.g., Klemm et al., 2008) prior to molybdenite
precipitation. Gold tenors in the different fluid types are
highly variable—from 0.0 nto nppm, uncommonly up to 20
ppm; in most cases, gold concentrations are below the limit
of detection (LOD), and in the present compilation only sig-
nificant values (>LOD) for Au are taken in account. Gold
mean concentrations in single-phase, hypersaline liquid, and
vapor-rich inclusions are similar, 1.6, 1.4, and 1.9 ppm, re-
spectively. Low salinity aqueous fluids show the highest av-
erage content of Au, 3.0 ppm, as well as the highest Au con-
centration reported, 26 ppm (Table 1; Fig. 5). Silver has an
average content of 10s ppm in all fluid types; however, in hy-
persaline liquid inclusions, Ag can attain several 1,000s ppm,
with a maximum of 3,400 ppm. Lead and zinc have very sim-
ilar behavior—their average concentration in single-phase,
vapor-rich, and low salinity aqueous fluids is on the order of
100s ppm, and attains several 1,000s ppm in hypersaline
liquids, with a maxima of 40,000 and 60,000 ppm for Zn and
Pb, respectively. This is due to transport of these metals
dominantly as highly soluble chloride complexes (discussed
below).
HYDROTHERMAL CONTROLS ON DISTRIBUTION IN PORPHYRY Cu (-Mo-Au) SYSTEMS 585
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0.01
0.1
1
10
102
103
104
105
106
Na K Mn Fe Cu Zn As Mo Ag Sb Au Pb
Vapor-rich
concentration (ppm)
Na K Mn Fe Cu Zn As Mo Ag Sb Au Pb
concentration (ppm)
Low-salinity aqueous
0.01
0.1
1
10
102
103
104
105
106
Na K Mn Fe Cu Zn As Mo Ag Sb Au Pb
Hypersaline liquid
concentration (ppm)
0.01
0.1
1
10
102
103
104
105
106
Na K Mn Fe Cu Zn As Mo Ag Sb Au Pb
Single-phase
concentration (ppm)
0.01
0.1
1
10
102
103
104
105
106
FIG. 5. Alkali (Na and K) and metal (Mn, Fe, Cu, Zn, As, Mo, Ag, Sb, Au, Pb) concentrations (in ppm) in single-phase,
hypersaline liquid, vapor-rich and low salinity aqueous inclusions in porphyry systems. Average concentrations are shown by
gray diamonds; vertical bars reflect data scatter. Elements are arranged on the horizontal axis by mass (see Table 1 for data
sources).
Kouzmanov_Pokrovski_Layout 1 3/19/13 8:51 AM Page 585

Based on the mean concentrations calculated for different
elements, the following relative abundance trends for the
four fluid inclusion types can be established:
1. Single-phase inclusions: Na>K>Fe>Cu>Mn>Zn>Pb ≈
As>Mo>Ag>Sb>Au;
2. Hypersaline liquid inclusions: Na>K>Fe>Mn>Cu ≈Zn
≈Pb>As ≈Mo>Ag ≈Sb>Au;
3. Vapor-rich inclusions: Na>K ≈Fe>Cu>Mn>Zn ≈
Pb>Ag ≈Sb ≈Mo>Au;
4. Low salinity aqueous inclusions: Na>K ≈Fe>Mn ≈
Zn>Cu ≈Pb>Sb ≈As>Mo>Ag>Au.
Some of these trends may be explained by the relative solu-
bility of different metal-controlling solid phases, coupled with
the abundance of complexing ligands (Cl, S) in the different
fluid types (see below). In addition, a positive correlation ex-
ists between the average concentration of metals in the pris-
tine single-phase magmatic fluids and their average abun-
dance in the crust (Fig. 6; Rudnick and Gao, 2003). Except
for Fe and Mn, which are abundant elements in the Earth’s
crust, the absolute concentrations of all other ore-relevant
metals in single-phase inclusion fluids are systematically one
to three orders of magnitude higher than their average Clarke
values in crustal rocks and magmas (Fig. 6). This agrees with
aqueous fluid/silicate melt partitioning coefficients of 10 to
1,000 for most metals, as shown by experimental studies (e.g.,
Candela, 1989; Simon et al., 2008; Zajacz et al., 2008), sup-
porting the magmatic origin of the single-phase fluid type.
Metal concentrations as a function of fluid temperature
and salinity
The compiled data are plotted versus Th and salinity in Fig-
ures 7 and 8 for Cu, Au, and accompanying metals (Mo, Ag,
Zn, Pb, Fe, Mn). There is no clearly defined correlation be-
tween Th and metal content of the different fluid types. This
may be due to: (1) potentially large differences between the
Th values and the true entrapment temperature (particularly
for single-phase and low salinity aqueous inclusions, as dis-
cussed above), and (2) the variability of factors other than
temperature, which may strongly affect the solubilities of
metals (e.g., fluid acidity, H2S content; see below). However,
several tendencies may be identified.
First, fluids of high-temperature inclusion types (single-
phase, hypersaline liquid, and vapor-rich) exhibit comparable
concentrations at Th >400°C for each element in the group
Cu, Au, Mo, and Ag, within data scatter of ±1 order of mag-
nitude; in contrast, Zn, Pb, Fe, and Mn in the hypersaline liq-
uid inclusions systematically show one order of magnitude
higher concentrations than the single-phase and vapor-rich
inclusions. Second, local changes in temperature trends may
be seen at Th ~400°C for some metals. Thus, at Th >400°C,
Cu contents normally vary between 100 and 10,000 ppm; at
400° ± 25°C, Cu reaches a well-defined maximum of ~30,000
ppm in some hypersaline liquid and vapor-rich fluid inclusion
assemblages (except for a few data points with Th values of
~600°–650°C; Fig. 7a); this behavior is not noted for the
other metals. At Th <400°C, Cu, Zn, Pb, and Mn concentra-
tions show a pronounced decrease with decreasing tempera-
ture; this tendency is most obvious for aqueous fluid inclu-
sions, which exhibit more than 3 orders of magnitude
decrease in Cu, Zn, Pb, and Mn between 400° and 200°C
(from >1,000 ppm to a few ppm; Fig. 7). Third, in contrast to
Cu, Zn, Pb, and Mn, the low salinity aqueous fluids with Th
of 350° to 250°C show the highest gold concentrations, reach-
ing 20 ppm in some inclusions. As mentioned above, this fluid
type also shows the highest average Au concentration of ~3
ppm. In addition to the potential formation of highly soluble
aqueous Au complexes with sulfur ligands (discussed below),
such high concentrations might also reflect heterogeneous
entrapment of gold nanoparticles from the fluid at tempera-
tures of <350°C, as suggested by Wallier et al. (2006), Pudack
et al. (2009), and Kouzmanov et al. (2010) for some interme-
diate and high sulfidation epithermal systems; gold transport
and deposition as nanoparticles has also been proposed for
some low sulfidation bonanza-grade epithermal veins (e.g.,
Saunders, 1990; Saunders and Schoenly, 1995).
Hypersaline liquid inclusions (salinity >26 wt % NaCl
equiv) plot in distinct fields on the salinity versus metal con-
centration diagrams (Fig. 8), with Zn, Pb, Mn, Fe, and Ag
typically an order of magnitude higher than in single-phase,
vapor, or low-salinity aqueous inclusions. This is explained by
the increasing stability of chloride species of the above-men-
tioned elements in salt-rich fluids (see below). Molybdenum,
Cu, and Au show a more variable pattern. Some hypersaline
liquid inclusions have Mo contents identical to single-phase
and vapor inclusions (1–100 ppm), but a large number of hy-
persaline liquid inclusions have higher concentrations (100–
2,000 ppm; Fig. 8). Gold does not show any dependence on
586 KOUZMANOV AND POKROVSKI
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1:1
1:10
1:100
1:1000
average crust (ppm)
average metal concentration in single-phase fluids (ppm)
0.1
1
10
100
1000
104
105
0.001 0.01 0.1 1 10 100 1000 104105
Fe
Mn
Cu
Zn
Pb
As
Sb
Au
Mo
Ag
FIG. 6. Average metal concentrations (in ppm) in single-phase magmatic
fluids from porphyry systems compared to their average crustal abundance
(Clarke values; data from Rudnick and Gao, 2003). Vertical bars correspond
to data scatter. Most metals, except Fe and Mn which are major elements in
the crust, show one to three orders of magnitude higher concentrations in the
juvenile magmatic single-phase fluid than their Clarke values (see text for
discussion).
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Th (°C)
Th (°C)
Th (°C)
Th (°C)
Th (°C)
Th (°C)
Th (°C)
Th (°C)
0.1
1
10
100
1000
10000
100000
100 200 300 400 500 600 700 800
Zn (ppm)
0.1
1
10
100
1000
10000
100 200 300 400 500 600 700 800
Mo (ppm)
1
10
100
1000
10000
100000
1000000
100 200 300 400 500 600 700 800
Fe (ppm)
0.1
1
10
100
1000
10000
100000
100 200 300 400 500 600 700 800
Mn (ppm)
0.1
1
10
100
1000
10000
100000
100 200 300 400 500 600 700 800
Pb (ppm)
0.1
1
10
100
1000
10000
100 200 300 400 500 600 700 800
Ag (ppm)
0.01
0.1
1
10
100
100 200 300 400 500 600 700 800
Au (ppm)
0.1
1
10
100
1000
10000
100000
100 200 300 400 500 600 700 800
Cu (ppm)
single-phase
hypersaline liquid
vapor-rich
low-salinity aqueous
FIG. 7. Concentrations of metals (in ppm) in single-phase, hypersaline liquid, vapor-rich and low-salinity aqueous inclu-
sions in porphyry systems as a function of temperature of homogenization (°C)( see Table 1 and Figure 4 for fluid types and
data sources).
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Sali nity (wt. % NaCl e q.)
Sali nity (wt. % NaCl e q.)
Sali nity (wt. % NaCl e q.)
Sali nity (wt. % NaCl e q.)
Sali nity (wt. % NaCl e q.)
Sali nity (wt % NaCl eq.)
Sali nity (wt. % NaCl e q.)
Sali nity (wt. % NaCl e q.)
0.1
1
10
100
1000
10000
100000
010 20 30 40 50 60 70 80
Cu (ppm)
0.1
1
10
100
1000
10000
100000
01020304050607080
Zn (ppm)
0.1
1
10
100
1000
10000
010 20 30 40 50 60 70 80
Mo (ppm)
0.1
1
10
100
1000
10000
01020304050607080
Ag (ppm)
0.01
0.1
1
10
100
01020304050607080
Au (ppm)
0.1
1
10
100
1000
10000
100000
01020304050607080
Pb (ppm)
0.1
1
10
100
1000
10000
100000
01020304050607080
Mn (ppm)
1
10
100
1000
10000
100000
1000000
01020304050607080
Fe (ppm)
single-phase
hypersaline liquid
vapor-rich
low-salinity aqueous
FIG. 8. Plots of metal concentrations (in ppm) in single-phase, hypersaline liquid, vapor-rich and low-salinity aqueous in-
clusions in porphyry systems as a function of apparent salinity (wt % NaCl equiv)(see Table 1 and Fig. 4 for fluid types and
data sources).
Kouzmanov_Pokrovski_Layout 1 3/19/13 8:51 AM Page 588

salinity, consistent with the dominant presence of Au-sulfide
complexes in most S-rich hydrothermal fluids (see below).
Single-phase and vapor inclusions systematically show
higher Cu contents than those in aqueous fluids of the same
salinity but lower temperature; this can be explained by de-
crease of the solubility of Cu sulfide minerals with cooling.
However, recent studies suggest that the high Cu contents in
vapor-rich and single-phase inclusions (up to 33,000 ppm;
Table 1) are likely due to postentrapment modifications.
Lerch baumer and Audétat (2012) conducted laboratory ex-
periments on synthetic and natural coexisting vapor-rich and
hypersaline liquid inclusions, subjected to re-equilibration
with external fluids of different compositions. Their findings
suggest that the Cu enrichment in the high-temperature
vapor-like inclusions, reported in many studies, may be a re-
sult of postentrapment Cu diffusion from the cooling external
fluid into the S-rich inclusion fluid, previously trapped at
higher temperature. Although the quantitative interpretation
of this phenomenon both in natural and synthetic inclusions
requires accurate knowledge of fluid composition, sulfur and
copper aqueous speciation, and solution pH and their evolu-
tion over time and with temperature and pressure, the funda-
mental driving force of the diffusion is likely to be the low sol-
ubility of Cu-bearing sulfides, like chalcopyrite, in S-rich
fluids with decreasing temperature (see below). The precipi-
tation of Cu-bearing sulfides in the inclusion on cooling low-
ers the aqueous Cu+concentration in the inclusion. This cre-
ates a diffusion gradient between Cu+concentrations inside
the S-rich inclusion and in the external fluid, which has lost
most of its sulfur on cooling. This concentration gradient,
coupled with elevated Cu+diffusion coefficients along the
crystallographic c-axis of quartz (Lerchbaumer and Audétat,
2012, references therein), leads to Cu diffusion from the ex-
ternal fluid and its accumulation in the S-rich inclusion in the
form of chalcopyrite or another Cu-bearing sulfide. The elec-
trical charge balance in this diffusion process is likely to be
maintained by H+and/or Na+diffusing out of the inclusion
(Lerchbaumer and Audétat, 2012). Precipitation of copper
sulfides from a saline H2S-bearing fluid also creates addi-
tional acidity (see reactions 1a, b below), which further favors
outward diffusion of H+.
Because the solubility of Cu-S solids is far greater in S-poor
salt-rich liquid phase than in the vapor (see below), S-rich
vapor inclusions can accomodate more Cu than the coexisting
hypersaline liquid inclusions. Thus, the elevated Cu contents
in vapor-like inclusions from porphyry deposits may be due to
post-entrapment modifications in many cases, depending on
the thermal history of the host quartz and the chemical evo-
lution of the surrounding fluid. Unfortunately, it is difficult to
accurately estimate the degree of diffusion to determine the
original Cu concentration in natural inclusions of fluid upon
trapping. Gold and base metals, such as Zn, Fe, or Pb, are un-
likely to be affected by such diffusion processes, because of
the larger ionic radius and charge of their cations, yielding
much lower diffusion coefficients than that of Cu+(Lerch-
baumer and Audétat, 2012).
Sulfur content of ore fluids
In addition to metals, Guillong et al. (2008) and Seo et al.
(2009) recently quantified by LA-ICP-MS the S contents of
individual fluid inclusions from porphyry systems. Since then,
Seo et al. (2011, 2012) produced a data set, including analy-
ses of S and metals for a large number of single-phase, hy-
persaline liquid, and vapor-rich inclusion assemblages from
the Bingham Canyon porphyry Cu-Au(-Mo) deposit. Using
the same technique, Catchpole et al. (2011, in review) ana-
lyzed low to intermediate salinity aqueous inclusion assem-
blages from the polymetallic vein system at Morococha. The
Bingham Canyon data show that the S content of most single-
phase, vapor-rich, and hypersaline liquid inclusions ranges
from 1,000 to 10,000 ppm, with a few inclusions attaining
30,000 ppm. At Morococha, low-salinity aqueous fluids usu-
ally have an order of magnitude lower S concentration, of
1,000s to 100s ppm. Catchpole et al. (2011) noted that in the
case of Morococha, the low-to-intermediate salinity aqueous
fluids have sufficient reduced S in solution to precipitate all
available base metals in the fluid as sulfide minerals.
The S content of the four fluid inclusion types in porphyry
systems is summarized in Table 1 and plotted in Figure 9. On
average, the single-phase fluids exhibit the highest S concen-
trations (9,400 ppm), compared to hypersaline liquid (7,600
ppm), vapor-rich (6,300 ppm), and low salinity aqueous
(2,700 ppm) inclusions (Table 1). This is in agreement with
the elevated solubility of metal sulfides at high temperatures
and its progressive decrease with cooling of the magmatic
fluid (see below). In most cases the limit of detection is high
(≥1,000 ppm); rarely concentrations below 1,000 ppm have
been determined (Fig. 9). There is no clear correlation be-
tween Th, fluid salinity, and S content of the different fluid in-
clusion types (Fig. 9a, b); there is also no apparent correlation
between S and Fe, Mo, and Au of the four main fluid inclu-
sion types (Fig. 9d-f). In contrast to these metals, the Cu con-
tent correlates positively with S content for many high-tem-
perature and Cu- and S-rich inclusions, which plot along the
1:1 Cu/S line (Fig. 9c); the rest of the data shows an excess of
S over Cu.
Interestingly, the 1:1 Cu/S plot on a ppm scale (Fig. 9c) cor-
responds to the 1:2 Cu/S molal ratio in the inclusion. Seo et
al. (2009) initially interpreted this observation by the forma-
tion of stable volatile complexes of copper with a 1:2 Cu/S sto-
ichiometry, which carry the major part of Cu and S in the
vapor phase. However, this stoichiometry is also in agreement
with that in chalcopyrite (CuFeS2), which is the most likely
solid phase observed in such inclusions (Sawkins and
Scherkenbach, 1981; opaque mineral, Table 1). This Cu/S
ratio suggests that all Cu in the inclusion is in the form of
chalcopyrite, and points again to a diffusion of Cu into the in-
clusion driven by the precipitation of CuFeS2during posten-
trapment cooling of the system. The fact that the Cu/S molal
ratio never exceeds 2, within the existing data scatter (Fig.
9c), strongly suggests that the formation of chalcopyrite is the
limiting factor of postentrapment Cu enrichment. The lower
Cu/S ratios (Fig. 9c) may be explained by an incomplete Cu
diffusion depending on the fluid inclusion thermal history
and external fluid composition and evolution. The absence of
Fe-S correlation (Fig. 9d) is also consistent with the fact that
Fe concentrations are typically a factor of 5 to 10 higher that
those of Cu, so that the chalcopyrite formation has a minor ef-
fect on the total Fe content, most of which remains in solu-
tion in the inclusion fluid.
HYDROTHERMAL CONTROLS ON DISTRIBUTION IN PORPHYRY Cu (-Mo-Au) SYSTEMS 589
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Vapor-liquid partitioning of sulfur and metals
Vapor-rich and hypersaline liquid inclusions commonly co-
exist in quartz and quartz-sulfide stockwork veins in porphyry
deposits (Roedder, 1984, and references therein), forming
trails of inclusions which homogenize at similar temperatures.
Such fluid inclusion assemblages result from unmixing of ho-
mogeneous single-phase magmatic fluid (Fig. 3a; Henley and
McNabb, 1978), and are formed by simultaneous entrapment
of single vapor or hypersaline liquid inclusions along healed
fractures (Roedder, 1971; Nash, 1976). Whereas the large
metal transporting capacities of the hypersaline liquids have
long been appreciated, the solubility of metals in low-density,
salt-poor vapor was long overlooked due to the lack of robust
analytical data on natural samples and experimental measure-
ments. Results of PIXE, LA-ICP-MS, and, recently, SR-XRF
analyses of vapor-liquid fluid inclusion assemblages demon-
strate the following: (1) significant element fractionation be-
tween hypersaline liquid and vapor is widespread in mag-
matic-hydrothermal systems, regardless of pressure and
temperature, and (2) the vapor phase has the ability to trans-
port high concentrations of some metals at high pressure
(Heinrich et al., 1992, 1999; Audétat et al., 1998; Cauzid et
al., 2007; Seo et al., 2009).
590 KOUZMANOV AND POKROVSKI
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100
1000
10000
100000
1000000
100 1000 10000 100000
S (pp m)
Fe (ppm)
0.1
1
10
100
1000
100 1000 10000 100000
S (pp m)
Mo (ppm)
0.01
0.1
1
10
100
100 1000 10000 100000
S (pp m)
Au (ppm)
100
1000
10000
100000
020406080
Sali nity (wt% NaCl eq .)
S (ppm)
100
1000
10000
100000
100 1000 10000 100000
S (pp m)
Cu (ppm)
1:1
single-phase
hypersaline liquid
vapor-rich
low-salinity aqueous
100
1000
10000
100000
100 200 300 400 500 600 700 800
Th (°C)
S (ppm)
ab
cd
ef
FIG. 9. Plots of sulfur concentration (in ppm) in single-phase, hypersaline liquid, vapor-rich and low salinity aqueous in-
clusions in porphyry systems as a function of temperature of homogenization (a), fluid salinity (b), Cu (c), Fe (d), Mo (e),
and Au (f) content. Data from Guillong et al. (2008), Seo et al. (2009, 2011, 2012), and Catchpole et al. (2011, in review).
Kouzmanov_Pokrovski_Layout 1 3/19/13 8:51 AM Page 590

Figure 10 summarizes recently published data on coexist-
ing hypersaline liquid and vapor-rich inclusions formed in
porphyry and skarn environments. The data are reported as
distribution coefficients, Kmetal = Cvap/Cliq, where C refers to
the concentration (in ppm) of the metal in each of the two
phases, vapor (vap) or liquid (liq). Sulfur, Cu, and As have av-
erage partitioning coefficients around 1 but the overall mag-
nitude of this partitioning varies strongly between different
datasets, especially for Cu (e.g., KCuranges from ~0.1 to 100).
Gold, where detectable, shows a clear preference for the
vapor phase. Note that absolute concentrations in the vapor
phase attain values of >10,000 and ≥10 ppm, respectively, for
Cu and Au (Table 1), which is about two to four orders of
magnitude higher than their average crustal abundances.
Metals such as Mo, Bi, and Ag have K values between 0.1 and
1, with a few exceptions where they are enriched in the vapor
phase. Metals such as Fe, Zn, and Pb, together with Na (and
K, not shown), are clearly concentrated in the Cl-rich hyper-
saline liquid, with typical partitioning coefficients between
0.01 and 0.1. These trends are confirmed by experimental
measurements and physical-chemical models (e.g., Pokrovski
et al., 2005a; see below).
On the basis of their recent experiments under conditions
where postentrapment Cu diffusion in quartz-hosted fluid in-
clusions was limited or may be accurately evaluated, Lerch-
baumer and Audétat (2012) estimated KCu values of 0.11 to
0.15 for typical vapor-liquid immiscibility conditions in por-
phyry systems. Such Cu vapor/liquid partition coefficients
imply that hypersaline liquids likely carry more Cu than coex-
isting vapors. These values, together with other experimen-
tally measured KCu values <1 in the majority of previous stud-
ies (see below), allow reconstruction of vapor/hypersaline
liquid mass ratios in porphyry systems, which are estimated to
be between ~4 and 9 (Lerchbaumer and Audétat, 2012).
These results support the early models suggesting that the
major transporting medium of Cu at porphyry depths is hy-
persaline liquid generated by phase separation (e.g., Henley
and McNabb, 1978; Bodnar, 1995; Beane and Bodnar, 1995).
Zn/Pb ratio in porphyry fluids as a potential tracer of
fluid sources and fluid-melt partitioning
The whole dataset for Cu, Zn, and Pb compiled in Figures
7 and 8 shows large scatter of Cu/Zn and Cu/Pb ratios in all
types of fluid inclusions, likely because of Cu precipitation,
vapor-liquid partitioning, and/or postentrapment diffusion.
The only consistency in the dataset concerns the Zn/Pb ratio
that varies over a narrow range, from 1 to 6 in high-tempera-
ture fluids (single-phase, hypersaline liquid, and vapor) from
different deposits. It can be seen in Cu-Zn-Pb ternary dia-
grams (Fig. 11) that single-phase, hypersaline liquid, and
vapor-rich inclusions form well-defined linear trends, corre-
sponding to a constant Zn/Pb ratio of the mineralizing fluids
for each of the deposits considered. These trends do not cor-
respond to Cu precipitation trends; rather, they reflect differ-
ences in Cu, Zn, and Pb concentrations between the three
major types of high-temperature fluids in porphyry systems.
Single-phase fluids plot together with the vapor-rich inclu-
sions toward the Cu-rich side of the trends, whereas hyper-
saline liquid inclusions show systematically lower Cu concen-
trations, as discussed above. Note that for two of the deposits,
data provided by different analytical techniques are used, SX-
XRF (Cline and Vanko, 1995) and LA-ICP-MS (Klemm et al.,
2008) for Questa, New Mexico, and PIXE (Harris et al., 2003)
and LA-ICP-MS (Ulrich et al., 2001) for Bajo de la Alumbr-
era, Argentina. For Butte, El Teniente, Chile, and Bingham
Canyon, only published LA-ICP-MS data are used.
The Zn/Pb ratios in fluids from the five selected porphyry
deposits are as follows: 6.0 ± 0.25, Butte; 4.0 ± 0.2, Questa;
3.0 ± 0.2, Bajo de la Alumbrera; 2.0 ± 0.1, El Teniente; and
1.1 ± 0.2, Bingham Canyon. The linear trend of data for each
individual deposit in Figure 11 for the pristine single-phase
magmatic fluid, and hypersaline liquid and vapor-rich inclu-
sions produced by phase separation of the former fluid, con-
firms that phase unmixing and Cu-Au-Mo ore precipitation in
the porphyry environment do not affect the initial Zn/Pb ratio
of the fluid, which thus should reflect the original Zn/Pb ratio
of the source magma.
Interestingly, Mo-rich deposits (Questa and Butte) display
higher Zn/Pb ratios than Cu and Cu-Au deposits (El Teniente,
Bingham Canyon, and Bajo de la Alumbrera). This observa-
tion does not correlate, however, with the magma chemistry
and the expected magmatic fluid signatures. In fact, porphyry
Mo deposits are broadly associated with evolved felsic mag-
mas, commonly of rhyolitic composition, whereas porphyry
Cu and Cu-Au deposits show spatial associations with inter-
mediate-composition intrusions, commonly including interac-
tions with mafic melts (Seedorff et al., 2005, and references
therein). Large geochemical databases (e.g., http://earthref.
org/GERM/ and http://georoc.mpch-mainz.gwdg.de/georoc)
provide compilations of whole-rock data of various intrusion
types from different tectonic settings. Thus, by comparing
fractionated (dacitic to rhyolitic) with intermediate (andesitic)
HYDROTHERMAL CONTROLS ON DISTRIBUTION IN PORPHYRY Cu (-Mo-Au) SYSTEMS 591
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0.001
0.01
0.1
1
10
100
NaSFeCuZnAsMo AgAuPbBi
in vaporin hypersaline liquid
Cvapor / Cliquid
FIG. 10. Sulfur and metal concentration ratios (equivalent to vapor-liquid
distribution coefficient) measured in coexisting vapor and hypersaline liquid
inclusions from “boiling assemblages” in quartz from porphyry and related
deposits. Data from Heinrich et al. (1999), Ulrich et al. (1999, 2001), Pettke
et al. (2001), Audétat and Pettke (2003), Kehayov et al. (2003), Baker et al.
(2004), Williams-Jones and Heinrich (2005), Klemm et al. (2007, 2008), and
Seo et al. (2009).
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592 KOUZMANOV AND POKROVSKI
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Questa
Zn P b
Cu
El Teniente
Zn P b
Cu
Zn P b
Cu
A
Bn
ET
Q
Bt
Butte
Zn P b
Cu
Zn : Pb = 1
Bingham
Zn P b
Cu
single-phase
hypersaline liquid
vapor-rich
Bajo de la
Alumbrera
Zn P b
Cu
FIG. 11. Cu-Zn-Pb triangular plots of fluid compositions from selected porphyry Mo, Cu-Mo-Au, and Cu-Au deposits.
Only compositions of high-temperature single-phase, hypersaline liquid, and vapor-rich inclusions are used. Linear trends
marked by straight orange lines correspond to constant Zn/Pb ratio, at variable Cu/Zn and Cu/Pb for the different systems.
The panel in the lower right corner summarizes the different Zn/Pb signatures of mineralizing fluids in the deposits, likely
reflecting different Zn/Pb ratios in the source magmas (see text for discussion). Data used: Butte (Rusk et al., 2004); Questa
(Cline and Vanko, 1995; Klemm et al., 2008); El Teniente (Klemm et al., 2007); Bingham (Landtwing et al., 2005, 2010; Seo
et al., 2012); Bajo de la Alumbrera (Ulrich et al., 2001; Harris et al., 2003). Abbreviations: A = Alumbrera, Bn = Bingham,
Bt = Butte, ET = El Teniente, Q = Questa.
Kouzmanov_Pokrovski_Layout 1 3/19/13 8:51 AM Page 592

magmas, it can be established that fractionated magmas are
normally characterized by low Zn/Pb ratios (commonly 0.5–3)
and intermediate magmas by higher and more variable Zn/Pb
ratios (4–15). The few available fluid/melt partition coeffi-
cients, which are higher by a factor of 3 for Zn compared to
Pb (Zajacz et al., 2008), could indeed explain the observed
Zn/Pb ratios of ~3 in the fluids from Bajo de la Alumbrera, if
the concentrations of the two elements in the silicate melt are
similar. However, a large dataset on whole rocks and melt in-
clusion compositions from the Farallón Negro magmatic
complex, host to the porphyry Cu-Au deposit at Bajo de la
Alumbrera, indicates a Zn/Pb ratio between 2 and 5 in the sil-
icate melt (Halter et al., 2004a, b). These Zn and Pb abun-
dances in the melt would require a fluid/melt partition coef-
ficient of Pb to be equal to or higher than that of Zn, to match
the Zn/Pb ratio of 3 at Bajo de la Alumbrera (Fig. 11). Al-
though we do not have a quantitative explanation of the ori-
gin of the Zn/Pb variations in the different deposits shown in
Figure 11, more data on Pb and Zn speciation and partition-
ing in fluid-melt systems with different compositions are re-
quired to resolve this issue.
Metal Transport by Liquid and Vapor Phases
in Porphyry Systems
Metal speciation, mineral solubility, and effect of
major ligands in aqueous liquid and vapor
Past-century situation: Understanding metal transport and
ore deposition mechanisms requires knowledge of the identity
and stability of aqueous species as well as the solubility of min-
erals. Such data are acquired via laboratory experiments cou-
pled with thermodynamic modeling. Numerous studies carried
out from the 1960s to 1990s have provided a dataset on key
metal complexes in aqueous solutions (reviews by Brimhall
and Crerar, 1987; Barnes, 1997; Wood and Samson, 1998, and
references therein). These data were integrated into thermo-
dynamic equations, such as the Helgeson-Kirkham-Flowers
(HKF) equation of state (Tanger and Helgeson, 1988; Shock
et al., 1997; Sverjensky et al., 1997), the density model (An-
derson et al., 1991), or the electrostatic model (Ryzhenko,
1981), enabling predictions of thermodynamic properties of
aqueous metal complexes and solubility of minerals over a
range of temperature and pressure (typically to 600°C and 5
kbar for fluid of densities above 0.4–0.5 g/cm3), and salinities
up to ~10 mol of NaCl equiv per kg of fluid (~50–60 wt %)
(Helgeson et al., 1981; Oelkers et al., 2009). The resulting
thermodynamic databases (e.g., SUPCRT; Johnson et al.,
1992), coupled with user-friendly computer codes, allowed
equilibrium calculations of mineral solubility, phase relation-
ships, and chemical speciation in fluid-mineral systems (Oelk-
ers et al., 2009, and references therein for a recent review).
Despite the different chemical properties of metals and di-
versity of ligands capable of binding them in aqueous solu-
tion, four main parameters have been shown to control min-
eral solubility: temperature, acidity, salinity, and S content of
the fluid. The effect of pressure itself on the solubility in liq-
uid and dense supercritical2fluid is rather small, at least
within the range of depths relevant to the formation of por-
phyry deposits (<10 km). This is due to the low compressibil-
ity of liquid and supercritical water at densities of >0.4 to 0.5
g/cm3, as recognized by the thermodynamic models cited
above. However, the pressure effect is strong for the low-den-
sity vapor phase.
These achievements allow the major types of aqueous
metal complexes to be identified (Table 3). Thus, in a typical
hydrothermal fluid containing alkali chloride salts and S as
sulfide and/or sulfate, metalloids such as As, Sb, Si, and B
form uncharged hydroxide species. Molybdenum and W are
likely to exist as oxyhydroxide anions and ion pairs with Na
and K. The speciation of base and associated metals such as
Cu, Fe, Zn, Pb, Cd, and Ag is largely dominated by chloride
complexes (probably with the rare exception of some concen-
trated sulfate brines and low-temperature H2S-rich liquids, in
which these metals may also form sulfate and sulfide com-
plexes, respectively). Gold and Pt form predominantly sulfide
and/or chloride complexes depending on temperature, pH,
and Cl and S contents. This relatively simple picture, consis-
tent with the fundamental soft-hard classification of metals
and ligands, allows a first-order estimation of metal solubility
trends and ore precipitation mechanisms (Crerar et al., 1985).
However, the exact composition (i.e., the number of ligands
around the metal in the complex and its electric charge) and
stability (i.e., thermodynamic formation constant) of the dom-
inant complexes for many metals remained uncertain or were
studied over small pressure and temperature ranges, pro-
hibiting quantitative predictions. In addition, metal transport
by a low-density vapor phase was almost unknown, owing to
the lack of experimental data.
Major recent advances: In the past decade, there have been
significant improvements in the knowledge of metal trans-
port, particularly for porphyry-relevant metals such as Cu, Au,
As, Sb, Mo, and Ag due to the following: (1) new systematic
solubility studies using hydrothermal-reactor and synthetic-
fluid inclusion techniques in model aqueous solutions (e.g.,
Stefánsson and Seward, 2003, 2004; Zotov et al., 2003; Tagirov
et al., 2005, Ulrich and Mavrogenes, 2008; Zhang et al., 2012)
and vapor-brine systems (Pokrovski et al., 2005a, 2008a), and
(2) the development and application of spectroscopic meth-
ods (in particular, UV-visible and X-ray absorption spec-
troscopy) for in situ measurement of molecular structure of
dissolved metal species, their solubility, and partitioning coef-
ficients in model chemical systems relevant to porphyry de-
posits (e.g., Mavrogenes et al., 2002; Pokrovski et al., 2002a,
2006, 2008b, 2009a, b; Brugger et al., 2007; Testemale et al.,
2009, 2011; Bazarkina et al., 2010; Etschmann et al., 2010;
Minubayeva and Seward, 2010). The new data improved the
accuracy of stability constants for major metal-bearing species
in aqueous solution, better constrained their stoichiometry,
and extended the data to a much larger temperature and
pressure range. The current state of knowledge of speciation
and solubility in hydrothermal liquid and vapor phases of the
major groups of chemical elements typical for porphyry de-
posit environments is briefly summarized below.
HYDROTHERMAL CONTROLS ON DISTRIBUTION IN PORPHYRY Cu (-Mo-Au) SYSTEMS 593
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2In this section, we use the term supercritical fluid for an aqueous phase
above the critical point of pure water. The properties of this phase are fur-
ther distinguished by its density as “dense supercritical fluid” (density > 0.4-
0.5 g/cm3) and “low-density supercritical fluid” (or “vapor” with density < 0.4-
0.5 g/cm3). This division is mostly imposed by the limitations of the available
thermodynamic equations of state, as discussed in the text.
Kouzmanov_Pokrovski_Layout 1 3/19/13 8:51 AM Page 593

Aqueous liquid and dense supercritical fluid: The aqueous
speciation of metalloids (Si, B, Ge, As, Sb) is now well con-
strained. Among them, As and Sb are ubiquitous in porphyry
systems and commonly accompany Au and Cu. Both As and
Sb form soluble hydroxide species for which a robust dataset
is available (Table 3). The stability of major chloride com-
plexes of base and associated metals (Cu, Zn, Pb, Ag, Fe) is
also known with reasonable accuracy, despite some disagree-
ment about the exact stoichiometry of some metals (e.g., Fe,
Zn, Ag; see Bazarkina et al., 2010; Saunier et al., 2011;
Pokrovski et al., 2013, for details). Hydrogen sulfide and chlo-
ride complexes of Au are also well known from a number of
recent experimental studies and thermodynamic compilations
(Table 3), but there may be a significant contribution from
species with other reduced sulfur forms in S-rich fluids (e.g.,
polysulfides; Pokrovski et al., 2009a; Pokrovski and Dubrovin-
sky, 2011). The current understanding of the speciation of Mo
appears to be the poorest among the porphyry-relevant met-
als, owing to the lack of consistent data for oxyhydroxide
species and its alkali metal ion pairs and suspected contribu-
tions of S- (e.g., Zhang et al., 2012) and Cl- (e.g., Ulrich and
Mavrogenes, 2008) complexes.
Independent of information on aqueous speciation, ther-
modynamic properties of the metal-bearing minerals are also
required to estimate their solubility. Whereas robust data are
now available for the major sulfide minerals of base and asso-
ciated metals (Fe, Cu, Ag, Mo, Zn, Pb, Cd), there is a lack of
data for As- and Sb-bearing sulfide minerals forming in por-
phyry and epithermal environments, such as enargite, arsen-
ian pyrite, and complex Sb sulfosalts. The resulting overall
uncertainty in solubility predictions for each metal is reported
in Table 3; it increases with increasing temperature (for all el-
ements) and salt content in the fluid (for metals that form
chloride complexes). For liquid phases and dense single-
phase fluids (density >0.4 g/cm3), the reported thermody-
namic uncertainty for most metals (except Mo) is probably
≤1 order of magnitude in terms of metal concentration in
equilibrium with its major mineral phase for moderate Cl and
S contents in the fluid (<~30 wt % NaCl equiv, <1–2 wt %
total dissolved S). Such uncertainty is relatively small com-
pared to those associated with the natural variations of tem-
perature, acidity, salinity, sulfur fugacity, and redox potential
during porphyry and epithermal deposit formation. This al-
lows at present semiquantitative thermodynamic modeling of
594 KOUZMANOV AND POKROVSKI
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TABLE 3 Speciation of Metals in Aqueous Fluids and Hypersaline Liquids at Conditions Relevant to Porphyry Deposit Formation, as Inferred from
Recent Experimental and Thermodynamic Studies
Major aqueous species in saline aqueous Mean uncertainty in
fluid (200°-600°C, density >0.3-0.4 g/cm3), predicted metal
Metal Major solid phases at conditions of porphyry deposits 1concentration (log10Cmetal)2Key references3
As Arsenopyrite, enargite, As(OH)3>1.0 Pokrovski et al. (1996, 2002a, b)
arsenian pyrite
Sb Cu-Fe-Sn sulfosalts Sb(OH)3>1.0 Zotov et al. (2003)
[±Sb(OH)2Cl, Sb(OH)3Cl–] Pokrovski et al. (2006)
Zn Sphalerite ZnCl2, ZnCl3–, ZnCl4
2– 1.0 Sverjenky et al. (1997)
[±Zn(HS)2, Zn(HS)3–] Wood and Samson, 1998)
Tagirov and Seward, 2010)
Pb Galena PbCl2, PbCl3–, PbCl4
2– 1.0 Sverjenky et al. (1997)
[±Pb(HS)2, Pb(HS)3–] Wood and Samson, 1998)
Fe pyrite, magnetite, FeCl20.5 Sverjenky et al. (1997)
hematite, pyrrhotite [±FeCl4
2–] (1.0) Wood and Samson (1998)
Testemale et al. (2009)
Saunier et al. (2011)
Cu Chalcopyrite, CuCl2–0.5 Akinfiev and Zotov (2001)
bornite, enargite [±CuCl3
2–, Cu(HS)2–] Brugger et al. (2007)
Akinfiev and Zotov (2010)
Ag Argentite, sulfosalts AgCl2–0.5 Akinfiev and Zotov (2001)
[±AgCl3
2–] Pokrovski et al. (2013)
Au Native gold AuHS, Au(HS)2–, AuCl2–0.5 Akinfiev and Zotov (2010)
Au(HS)H2S (1.0) Pokrovski et al. (2009a, b)
(± polysulfide/sulfite)
Mo Molybdenite H2MoO4, HMoO4–, MoO4
2– > 2.0 Zotov et al. (1995)
NaHMoO4, KHMoO4Shock et al. (1997)
(± sulfide/chloride) (> 3.0) Ulrich and Mavrogenes (2008)
Minubayeva and Seward (2010)
Zhang et al. (2012)
1 Species shown in brackets are subordinate or uncertain (see text)
2 Estimated in terms of the variation of metal dissolved concentration in equilibrium with its major solid phase for typical porphyry fluid compositions at
a given T, P, pH, and sulfur and oxygen fugacity, and using the range of published stability constants for the corresponding aqueous species from different
studies; values in brackets are for the case where uncertain species are included in the calculations
3 Major recent experimental or theoretical studies reporting thermodynamic data for aqueous complexes that were used in this study for calculating min-
erals solubility (numerous older references can be found therein)
Kouzmanov_Pokrovski_Layout 1 3/19/13 8:51 AM Page 594

ore-depositional mechanisms for moderate-temperature
(<~500°C), moderate salinity (<30–40 wt % NaCl) aqueous
solutions (e.g., Heinrich, 2005), and better constraints on
some of these variables, which are difficult to obtain from nat-
ural samples (see below).
Vapor and low-density, single-phase fluids: In contrast to
liquid and single-phase fluids, metal transport by low-density
vapors is less well understood. Although the first direct ex-
perimental data on liquid-vapor partitioning coefficients for
some porphyry ore-relevant metals (As, Sb, Cu, Zn, Pb, Fe,
Cd, Au) have become available in the last decade (see below),
the exact nature of vapor species and their molecular compo-
sitions, particularly in S-bearing systems, are still unknown.
Scarce data are available about how total partitioning coeffi-
cients vary as a function of salt content other than NaCl (e.g.,
KCl, CaCl2, FeCl2), S content and speciation, and fluid acid-
ity. The fundamental difference between the vapor phase and
the liquid/single-phase fluids discussed above is the high
compressibility of the former, resulting in large density varia-
tions with small pressure changes. Such changes are not ac-
counted for by the widely used thermodynamic models, like
the HKF equation-of-state, which are accurate for the dense
aqueous phase, but not applicable to the vapor domain (i.e.,
density <0.3–0.4 g/cm3; Plyasunov and Shock, 2001). Among
the approaches currently used to describe the low-density,
vapor-phase solubility of minerals and liquid-vapor partition-
ing are density (e.g., Pokrovski et al., 2005a, and references
therein) and hydration models (e.g., Williams-Jones and
Heinrich, 2005); however, they still remain largely empirical
(see below). New models are currently under development
that attempt unified descriptions of the liquid-vapor region
(e.g., Akinfiev and Diamond, 2003), but they lack experimen-
tal data. In the last decade, molecular approaches based on
quantum chemistry and molecular dynamics began to provide
new insights into atomic structure and hydration energy of
ore metal complexes (e.g., Au, Cu), helping to interpret spec-
troscopic signatures and solubility data and to allow a choice
of the right speciation models to describe experimental re-
sults (e.g., Sherman, 2010; Pokrovski et al., 2013). Such ap-
proaches, albeit in their infancy, are expected to provide a di-
rect link between the molecular properties of the dissolved
species and their stability and solubility. Before discussing in
detail the solubility and transport of porphyry ore metals in
liquid and vapor phases, two issues intimately connected to
hydrothermal fluid properties and metal distribution in por-
phyry systems are considered, the effect of CO2and the solu-
bility of quartz.
Effect of CO2:Carbon dioxide is a common volatile con-
stituent in fluids associated with porphyry deposits, as shown
by analyses of single-phase fluid inclusions from the deep
high-temperature cores of Climax and Henderson, Colorado,
Butte, Bingham Canyon, and El Salvador (Rusk et al., 2008c,
2011). These data indicate that CO2can be present at average
concentrations of 10 wt % (~5 mol %), locally attaining 20 wt
% (~10 mol %). However, the quantification of CO2contents
in fluid inclusions from these systems is not routine, and re-
quires detailed microthermometric measurements (e.g., Rusk
et al., 2008b), and/or in situ spectroscopic methods such as
Fourier transform infrared or Raman spectroscopy and in-
volved calibration procedures (e.g., Wopenka and Pasteris,
1986; Dubessy et al., 1989; Burke et al., 2001; Frezzotti et al.,
2012, and references therein). This explains, at least partly,
the paucity of quantitative data for CO2in fluid inclusions
from porphyry systems. Much more is known about CO2in
magmatic rocks and silicate melts; Lowenstern (2001) pro-
vides a detailed review of CO2sources, contents, and behav-
ior in magmas.
There are two key properties of CO2in magmatic systems
that distinguish this compound from other volatiles such as
water, Cl, and S: (1) low solubility of CO2in most types of sil-
icate melts, and (2) absence of major mineral phases capable
of retaining CO2in magmatic rocks. These properties are re-
sponsible for early degassing of CO2from magmas compared
to water, Cl, and S (Lowenstern, 2001), and are likely to be
the reason for the relatively modest CO2concentrations re-
ported in fluids from porphyry systems compared to other
types of Au deposits such as orogenic, Carlin-type, and intru-
sion-related gold, as well as mafic pegmatite-related Cu and
PGE deposits, where CO2may attain >50 wt % of the fluid
phase (e.g., Phillips and Evans, 2004; Hanley and Gladney,
2011). Under hydrothermal conditions characterized by
water-salt-sulfur fluid systems, which are the subject of this
paper, CO2may affect metal behavior in different ways, both
direct and indirect.
First, the presence of CO2affects vapor-liquid equilibrium
relationships as compared to a CO2-free system. The PVTX
properties of the H2O-NaCl-CO2system are now reasonably
well constrained, and physical-chemical models are available
for predicting the densities of the vapor and liquid phases in
this system (e.g., Bowers and Helgeson, 1983; Duan et al.,
1995; Bakker, 2009). Phase separation conditions and exact
phase compositions are, however, not sufficiently known to
allow accurate modeling of the evolution of the CO2-NaCl-
H2O system, in contrast to the volatile-free NaCl-H2O system
(Fig. 3; e.g., Driesner and Heinrich, 2007). Nevertheless,
available data indicate that moderate quantities of CO2may
significantly extend the vapor-liquid immiscibility domain and
increase the pressure of phase separation. For example, the
presence of 10 wt % CO2in a single-phase fluid containing 10
wt % NaCl at 400°C will raise the pressure of phase unmixing
(i.e., the pressure below which two phases, an aqueous vapor
and a saline liquid, exist) from 270 bar (in CO2-free, 10 wt %
NaCl-H2O system) to ~500 bar (in the presence of CO2;
Bakker et al., 2009). This difference corresponds to >2 km
depth at hydrostatic pressure or to ~1 km depth in a lithosta-
tic regime. In the evolution path of the cooling and ascending
magmatic fluid, this will allow earlier (i.e., greater depth) sep-
aration of the vapor phase and corresponding metal fraction-
ation. Another effect of this phase separation is an increase in
pH of the liquid phase due to preferential partitioning of acidic
volatile components (CO2and also HCl, H2S, and SO2) into
the vapor. As a numerical example illustrating this phenome-
non, boiling of a 10 wt % NaCl + 5 wt % CO2aqueous solu-
tion from 350° to 320°C results in removal of 90% of CO2into
the vapor phase, which will increase the pH of the liquid by
over half an order of magnitude (from 5.0 in the initial solution
to 5.5 after boiling). This may eventually lead to precipitation
of some base metals remaining in the liquid phase (see below),
depending on the efficiency of pH buffering via fluid-rock in-
teraction. At the low-to-moderate temperatures (≤350°C) of
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epithermal environments this effect may be important, where
water-silicate rock reactions are slow and vapor/liquid parti-
tion coefficients of CO2are high. In contrast, in higher-tem-
perature (>400°C), salt-rich fluids of porphyry environments,
the pH change of the liquid phase induced by removal of CO2
is likely to be compensated for by rapid fluid equilibration
with silicate rocks and an increase in salt content of the liquid
phase, both favorable for sulfide mineral solubility (see
below).
Second, CO2and particularly its anionic counterparts, bi-
carbonate (HCO3–) and carbonate (CO3
2–) ions, may poten-
tially act as ligands for so called hard metals such as rare earth
elements (REE), Sn, Zr, U, Nb, and probably Fe (e.g., Se-
ward and Barnes, 1997; Wood and Samson, 1998; Pokrovski,
2010, and references therein). Base metals, Ag, and Au are
expected to be less affected by carbonate complexing, both
because of their low chemical affinity with the hard carbonate
ligand (e.g., Seward and Barnes, 1997) and the low abun-
dance of carbonate ions in weakly acidic-to-neutral pH fluids
in porphyry environments. For example, the concentration of
bicarbonate and carbonate ions in an aqueous fluid of 10 wt
% NaCl plus 5 wt % CO2at 400°C and 500 bars is <10 ppm
at pH ~5, typical of that buffered by equilibrium with granitic
or andesitic rocks. This concentration is negligible compared
to the 100s to 1,000s ppm of Cu, Fe, or Sn in most fluids from
magmatic-hydrothermal systems (see above).
Third, CO2(in large fractions) may lower the activity of
H2O in the fluid and thus affect solvation phenomena. Be-
cause most metal chloride and hydroxide complexes are
strongly hydrated by water molecules, both in vapor and liq-
uid phase (see below), lowering H2O activity (~mole fraction)
in the presence of CO2decreases the complex stability and
thus metal solubility. Experimental studies on a few oxide and
chloride solids in H2O-CO2mixtures attest to this behavior
over a wide range of T-P-XCO2 conditions. For example,
quartz solubility in a 20 wt % (10 mol %) CO2-H2O fluid at
600°C and 2 kbars is approximately two times lower than in
pure water at the same pressure and temperature (Walther
and Orville, 1983). A larger effect is observed for ionic com-
pounds, AgCl for example, for which the solubility is lowered
by a factor of three in the same CO2-H2O fluid compared to
pure H2O at 400°C and 1 kbar (Fig. 12; Akinfiev and Zotov,
1999). In contrast, for some nonpolar metal sulfide species
(e.g., AuHS, Au(HS)H2S), the presence of CO2might have
the opposite effect due their preferential solvation in a CO2-
bearing solvent of low polarity and dielectric constant
(Pokrovski et al., 2008a, 2009a). This hypothesis, however,
awaits direct experimental confirmation. The solvation effect
operates at large CO2fractions that change significantly the
properties of the aqueous solvent. At the CO2contents of por-
phyry systems (typically ≤10 mol %; Rusk et al., 2008c), this
effect on mineral solubility and the transport capacities of a
fluid is expected to be minor compared to other factors (see
below).
Solubility of quartz: Quartz is the ubiquitous gangue min-
eral associated with sulfide ore minerals in most porphyry
deposits. In contrast to those minerals (see below), the sim-
plicity and constancy of aqueous Si speciation over a wide
pressure-temperature-composition range makes quartz solu-
bility relatively insensitive to changes in acidity, salinity, redox
potential, and S content. In aqueous fluids, the dominant sol-
ubility reaction for quartz is SiO2(s) + 2 H2O = Si(OH)4,
which is a function of temperature and pressure; this solubil-
ity is known over a wide pressure and temperature range,
from subduction zone fluids to the vapor phase, as a result of
numerous studies (summarized by Walther and Helgeson,
1977; Manning, 1994; Newton and Manning, 2000, 2009, and
references therein). The presence of CO2lowers the water
activity, but has relatively little effect on SiO2solubility at CO2
concentrations typical of porphyry fluids (less than a factor of
2). The presence of salt has a more complex effect due to a
combination of changes in water activity and activity coeffi-
cients of aqueous silica. For example, at temperatures above
400°C and pressures below 1 to 2 kbars, moderate salt con-
centrations (up to 20 wt %) increase SiO2solubility by a fac-
tor of two to three compared to pure water and eliminates the
retrograde solubility; by contrast, further salt addition leads to
a solubility decrease (e.g., Fournier, 1999; Newton and Man-
ning, 2000, and references therein). The effects of both CO2
and salt are thus rather minor compared to the pressure and
temperature effects themselves, which lead to orders of mag-
nitude variations in quartz solubility.
Figure 13a shows quartz solubility in pure water as a func-
tion of temperature and pressure. An important property of
quartz that affects rock permeability and fluid flow in por-
phyry deposits is its retrograde solubility in the temperature
range of ~370° to 470°C at pressures below ~800 bars (Fig.
13a). This phenomenon is due to the change of the fluid den-
sity in this pressure and temperature range; water density at
these conditions exhibits a pronounced drop (Fig. 13b), cor-
responding to the change from a liquid-like to vapor-like
fluid, and the quartz solubility pattern closely matches the
density curve. The fluid density is thus the major variable
controlling the solubility of quartz, which is reflected in SiO2
solubility equations over a wide range of pressure and
596 KOUZMANOV AND POKROVSKI
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00.20.40.60.81
0.001
0.01
0.1
1
Quartz, 800°C, 10 kbar
(Newton and Manning, 2009)
Quartz, 600°C, 2 kbar
(Walther and Orville, 1983)
AgCl, 400°C, 0.6 kbar
(Akinfiev and Zotov, 1999)
CO2 mole fraction
dissolved Ag or Si (mol/kg H2O)
FIG. 12. Solubility of quartz and silver chloride in a H2O-CO2fluid at indi-
cated temperatures and pressures, as a function of the CO2mole fraction, ac-
cording to published experimental data. Symbols stand for experimental data
points from indicated references; straight lines show a linear fit to each dataset.
Note the significant decrease of solubility with increasing CO2content.
Kouzmanov_Pokrovski_Layout 1 3/19/13 8:51 AM Page 596

temperature (e.g., Manning et al., 1994). Note that the solu-
bility pattern shown in Figure 13 is not unique for quartz; it
has also been observed for other oxides, such as GeO2
(Pokrovski et al., 2005b). Similar pressure and temperature
(~density) dependencies are expected to hold for silicate min-
erals (e.g., Dolejs and Manning, 2010). From a physical-
chemical point of view, such patterns are a combination of
solvation (which is a direct function of the solvent density)
and thermal disorder (which is a function of temperature)
(see Pokrovski et al., 2005b, for details).
In contrast, experimental data for sulfide minerals are insuf-
ficient at present to establish predictive equations over such a
wide range of densities as that available for quartz. In addi-
tion, dissolution and precipitation reactions of sulfides are
much more complex than that of quartz; they involve volatile
components (H2S) and are acidity and redox dependent.
Quantitative prediction of all these effects on sulfide mineral
solubility is possible at present only for fluids with liquid-like
densities (typically, >0.5 g/cm3), corresponding to the pres-
sure and temperature domain of prograde quartz solubility
(Fig. 13). These effects are discussed in the following section.
Solubility-controlling reactions of ore metals in
aqueous solution
In this section, we discuss the main solubility-controlling
reactions for Cu, Au and accompanying metals (Ag, Zn, Pb,
Fe, Mo) in aqueous solution and dense supercritical fluid.
Figure 14 shows the solubility of major ore minerals as a func-
tion of four key parameters—temperature, acidity, salinity,
and S content—calculated using the available thermody-
namic data for minerals and aqueous species cited in Table 3.
Compared to these parameters, pressure has a minor effect
on mineral solubility in the liquid-phase and dense supercrit-
ical-fluid domain, as discussed above, but it was included in
the calculations to be consistent with the evolution of cooling
and ascending magmatic fluids in porphyry systems. Two fun-
damental factors that control metal transport by the fluid
phase are (1) the nature of the dissolved species (chloride vs
sulfide vs oxyhydroxide), and (2) the chemical composition
and stability of the major mineral phases. In most cases, chal-
copyrite, pyrite, molybdenite, sphalerite, galena, argentite/
acanthite, and native gold are the major mineral phases of Cu,
Fe, Mo, Zn, Pb, Ag, and Au, respectively, allowing them be
used as model minerals for identifying the major trends in
metal behavior during fluid-rock interactions in porphyry sys-
tems. The amplitudes and trends in solubility are quite dif-
ferent among the metals considered (Fig. 14). For conditions
typical of porphyry deposits, these trends are governed by the
following reactions:
CuCl2–+ FeCl2
0+ 2H2S =
CuFeS2(s) + 3H++ 0.5H2+ 4Cl–(1a)
CuCl2–+ FeS2(s) + 0.5H2=
CuFeS2(s) + H++ 2Cl–(1b)
FeCl2
0+ 2H2S = FeS2(s) + 2H++ 0.5H2+ 2Cl–(2)
ZnCln
2–n + H2S = ZnS(s) + 2H++ nCl–, n = 2, 3, 4 (3)
PbCln
2–n + H2S = PbS(s) + 2H++ nCl–, n = 2, 3, 4 (4)
AgCl2–+ 0.5H2S = 0.5Ag2S(s) + H++ 2Cl–(5)
Au(HS)2–+ 0.5H2+ H+= Au(s) + H2S,
in near-neutral and alkaline fluids (6a)
AuHS0+ 0.5H2= Au(s) + H2S, in acidic fluids (6b)
Au(HS)H2S0+ 0.5H2= Au(s) + 2H2S,
in acidic S-rich fluids and possibly vapors (6c)
AuCl2–+ 0.5H2= Au(s) + H++ 2Cl–,
above 500°C in acidic saline fluids (6d)
HMoO4–+ H++ 2H2S + H2= MoS2(s) + 4H2O (7a)
NaHMoO4
0+ H++ 2H2S + H2=
MoS2(s) + 4H2O + Na+(7b)
KHMoO4
0+ H++ 2H2S + H2=
MoS2(s) + 4H2O + K+(7c)
HYDROTHERMAL CONTROLS ON DISTRIBUTION IN PORPHYRY Cu (-Mo-Au) SYSTEMS 597
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0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
50150250350450550650
Tem pe ratu re (°C)
density (g/cm3)
b
1
10
100
1000
10000
50150250350450550650
Tem pe ratu re (°C)
Si (ppm)
300 bar
400 bar
600 bar
1000 bar
2000 bar
a
FIG. 13. Quartz solubility (silicon concentration) in pure water as a function of temperature (a) at different pressures cal-
culated using the density equation of Manning (1994). Note the zone of retrograde solubility between ~370° and 470°C, at
pressures below 800 bars. This pattern matches well the change of the fluid density from liquid-like to vapor-like in this do-
main (b), demonstrating that fluid density has a primary control on quartz solubility.
Kouzmanov_Pokrovski_Layout 1 3/19/13 8:51 AM Page 597

598 KOUZMANOV AND POKROVSKI
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400°C, 500 bar, pH = 5, sulfur (0.017m H2S), redox = Py-Mt-Hm
metal (ppm)
Salinity (wt. % NaCl eq.)
0.01
0.1
1
10
100
1000
10000
100000
1000000
0.1 1 10 100
CuFeS2 + FeS2
MoS2
ZnS
Au
Ag2S
FeS2
b
d
400°C, 500 bar, pH = 5,
redox = Mt-Hm
metal (ppm)
H2S (mol/kg)
1000000
0.01
0.1
1
10
100
1000
10000
100000
0.0001 0.001 0.01 0.1 1
CuFeS2 + FeS2
MoS2
ZnS
Au
Ag2S
FeS2
CuFeS2 (no pyrite)
c
400°C, 500 bar, 10 wt. % NaCl eq., sulfur (0.017m H2S),
redox = Py-Mt-Hm
metal (ppm)
pH
1000000
0.01
0.1
1
10
100
1000
10000
100000
3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8
CuFeS2 + FeS2
MoS2
ZnS
Au
Ag2S
FeS2
300-1000 bar, 10 wt. % NaCl eq., pH = 5,
sulfur and O2 buffered by Py-Mt-Hm
metal (ppm)
Temperature (°C)
0.0001
0.001
0.01
0.1
1
10
100
1000
10000
100000
150 200 250 300 350 400 450 500 550
CuFeS2
MoS2
ZnS
Au
Ag2S
FeS2
a
FIG. 14. Solubility of chalcopyrite, pyrite, sphalerite (± galena), molybdenite, argentite, and native gold (a), expressed as elemental metal concentrations, a) as a func-
tion of temperature in fluids with salinity of 10 wt % NaCl equiv at pH 5 in equilibrium with the pyrite-magnetite-hematite (py-mt-hm) buffer at pressure progressively
decreasing from 1,000 bar at 500°C to 300 bars below 300°C; b) as a function of salinity at 400°C, 500 bars in equilibrium with pyrite-magnetite-hematite (py-mt-hm);
c) as a function of pH at 400°C, 500 bars, 10 wt % NaCl, and in the py-mt-hm stability field; and d) as a function of H2S concentration at 400°C, 500 bar, 10 wt % NaCl,
and redox of the magnetite-hematite univariant. Calculations were performed using the HCh computer code (Shvarov, 2008). Thermodynamic properties of the miner-
als are taken from SUPCRT (Johnson et al., 1992); those of major fluid constituents and activity coefficient models are detailed in Pokrovski et al. (2009a, b). Stability
constants of metals complexes are from references in Table 3.
Kouzmanov_Pokrovski_Layout 1 3/19/13 8:51 AM Page 598

The differences in aqueous speciation between base metals
plus Ag (chlorides), Au (predominantly sulfides), and Mo
(oxyhydroxides) yield contrasting solubility trends versus pH,
H2S, and salinity for these three groups of metals (Fig. 14).
The only feature common to all metals is an increase in solu-
bility with temperature, at least for Fe sulfide, Fe oxide, and
silicate-buffered systems, which are a reasonable proxy for
sulfur fugacity, redox, and pH, respectively, in rock-domi-
nated porphyry environments (e.g., Giggenbach, 1997). How-
ever, the absolute dissolved concentrations of Cu, Fe, Zn, and
Pb in equilibrium with relevant sulfide minerals are much
higher than for Au and Mo, and the effect of temperature is
most pronounced for Cu and Mo, yielding steeper solubility
curves as a function of temperature (Fig. 14a).
For all metals except Au, solubility increases significantly
with salinity (Fig. 14b), the largest increase being for Zn (and
Pb, not shown), which are likely to form tri- and tetrachloride
species (Table 3). Fluid acidity (pH) exerts a strong effect on
ZnS and FeS2(and PbS, not shown) solubility. For example,
with all other parameters being equal, a pH change from 4 to
5 yields a 100-fold decrease in solubility at a given tempera-
ture and salinity (Fig. 14c). This is likely the major factor
leading to ZnS, PbS, and FeS2precipitation (see below). Cop-
per and Ag also have elevated solubilities in acidic fluids, but
are less affected by pH changes. In contrast to other metals,
Mo solubility is very low under acidic conditions and in-
creases with increasing pH. The effect of reduced sulfur is
also fundamentally different for base metals and Mo in con-
trast with Au (Fig. 14d); high H2S concentrations are not fa-
vorable for Zn, Fe, Ag, and Mo solubility, but are likely to be
the major cause of efficient Au transport. Copper concentra-
tions in equilibrium with the pyrite-chalcopyrite assemblage,
ubiquitous in porphyry systems, is independent of H2S con-
tent (as H2S is not involved in reaction 1b), whereas in a
pyrite-free system, the stoichiometric solubility of CuFeS2
decreases with increasing H2S (Fig. 14d). These different sol-
ubility trends provide a foundation for interpreting metal dis-
tribution in porphyry systems (see below).
Experimental insights into vapor-phase transport of
metals in porphyry systems
One of the major advances in understanding porphyry Cu
(-Mo-Au) systems over the past decade is the recognition that
the vapor phase can transport significant quantities of metals
(Figs. 5, 7, 8). This fact has motivated experimental and the-
oretical research that allows the physical and chemical factors
affecting the metal vapor-phase transport and vapor-liquid
partitioning to be constrained, as discussed in the following
subsections.
Lessons from volcanic gases: Extensive work on volcanic
gases sampled from fumarolic discharges since the mid-20th
century suggests selective vapor transport of some metals in
some places, particularly in ash-laden vapor plumes related to
quiescently erupting volcanoes (summary by Hedenquist,
1995). However, the majority of vapor samples from atmos-
pheric-pressured fumaroles of passively degassing volcanoes
show low metal concentrations, typically less than a few ppm
for base metals (Zn, Pb, Cu, Sn, Mo), Ag, and As, and less than
a few ppb for Au (e.g., Hedenquist et al., 1994a; Hedenquist,
1995; Williams-Jones and Heinrich, 2005; and references
therein). Such measured concentrations are in agreement
with gas-sublimate equilibria in water-free systems, involving
chloride, sulfide, oxide, or native metal gaseous species whose
thermodynamic properties are available in large databases
(e.g., JANAF; Chase, 1998; Ivtanthermo, 1983). The metal
contents of the vapor from volcanic fumaroles associated with
passively degassing volcanoes are, however, 2 to 5 orders of
magnitude lower than those measured in vapor inclusions
from porphyry deposits (Figs. 7, 8; Table 1). The main differ-
ence between the surficial volcanic vapors and hydrothermal
vapors trapped at high pressure is the density, which increases
by a factor of ~100 from the surface (dvapor~0.001 g/cm3at
<10 bars) to a few kilometers depth (dvapor~0.01-0.4 g/cm3at
100–1,000 bars). Density appears to be the major parameter
affecting mineral solubility in the vapor phase.
Hydration control on solid-phase solubility in vapor: Re-
cent solubility studies of Au, Cu, Sn, Mo, and Ag oxides and
chlorides in unsaturated water vapor (i.e., at pressures below
the vapor-liquid saturation curve of water or H2O-salt solu-
tion) confirm that the dominant control of metal solubility is
water pressure, which is directly proportional to density
(Archibald et al., 2001, 2002; Williams-Jones and Heinrich,
2005; Rempel et al., 2006; and references therein). They
show that at water pressures of a few hundred bars, the solu-
bility of a metal-bearing solid phase, such as oxide, chloride or
native metal, is many orders of magnitude higher compared
to the volatility of this solid in a dry H2O-free system. This en-
hanced solubilization in the presence of water may be ex-
plained by solid-gas reactions:
CuCl(s) + nH2O(gas) = CuClⴢnH2O(gas) (8a)
MoO3(s) + nH2O(gas) = MoO3ⴢnH2O(gas) (8b)
Au(s) + HCl(gas) + nH2O(gas) =
AuClⴢnH2O(gas) + 0.5 H2(gas) (8c)
where nis the apparent hydration number, which varies be-
tween ~1 and ~20, depending on the species, temperature,
and pressure; in most cases, it increases systematically with
pressure. These studies reveal three fundamental controls on
vapor-phase transport of metals: (1) in the hydrothermal
vapor phase, metals form complexes with the same ligands as
in aqueous solution (chloride, sulfide, or hydroxide); (2) in
contrast to the aqueous solution or hypersaline liquid, the
major vapor species are uncharged (at least in unsaturated
vapor below the water critical point), in agreement with the
low dielectric constant of the vapor favoring ion association;
and (3) as in aqueous solution, the metal complexes are sol-
vated by water molecules; the higher the pressure the more
metal that can be dissolved in the vapor phase in equilibrium
with a metal-bearing solid or melt. The main limitation of this
hydration approach is the relatively narrow temperature and
pressure range of measurements (most were conducted at
250°–350°C at <200 bars), and large changes in apparent hy-
dration numbers with pressure (e.g., AuClⴢnH2O, n= 3-5;
MoO3ⴢnH2O, n = 2–4 in that small range; Archibald et al.,
2001; Rempel et al., 2006); this makes practical application of
these results difficult to conditions of porphyry deposits. An
alternative to the hydration models discussed above may be
an approach that relates solubility to vapor-phase density,
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which is shown to be extremely efficient in the case of quartz
solubility (see above) and of vapor-liquid fractionation of var-
ious metals, as shown below.
Fluid density control on vapor-liquid partitioning in S-free
systems: Further insights into vapor-phase transport have
been provided by direct measurements of vapor-liquid parti-
tion coefficients of metals in model salt-water systems analo-
gous to hypersaline liquid and vapor inclusions from porphyry
deposits (Pokrovski et al., 2005a, 2008a, b; Pokrovski, 2010,
and references therein). These works demonstrate that vapor-
liquid distribution of elements obeys simple relationships in-
volving the densities of the coexisting vapor and liquid phases.
Figure 15 shows that the partition coefficient of each metal
(K, which is the ratio of metal mass concentrations in the co-
existing phases, Cvapor/Cliquid) is linearly proportional on a log-
arithmic scale to the ratio between the vapor and liquid den-
sities, which are well known in the H2O-NaCl system (e.g.,
Driesner and Heinrich, 2007). All lines tend to converge to
the critical point, where the concentrations are identical in
both phases and the partition coefficient is, by definition, equal
to one. Such ray diagrams have long been known for salts and
acids dissolved in water (e.g., Styrikovich et al., 1955; Alvarez
et al., 1994; Palmer et al., 2004); they stem from classical
thermodynamics and statistical mechanics that demonstrate
that the hydration energy of the solute evolves linearly with
the solvent density (Mesmer et al., 1988; Palmer et al., 2004).
These relationships (Fig. 15) confirm the validity of this
model for a variety of metals and metalloids over a wide tem-
perature range; they support the findings in unsaturated
vapor systems and demonstrate that water-solute interaction
(or hydration) is a key factor controlling metal vapor-phase
solubility and vapor-liquid partitioning. In S-free water-salt
systems, where the speciation of metals and metalloids is
dominated either by hydroxide or chloride complexes (Table
3), any significant deviation from a linear trend with an origin
at the critical point should be regarded as an experimental or
analytical artifact (Pokrovski, 2010). With the exception of ar-
senous, boric, and, probably, molybdic (not shown) acids,
whose K values cluster around unity in liquid-vapor systems
at >400°C, all other elements, from silica to rare earths being
transported in the fluid or liquid phase in the form of chloride
or hydroxide species, have no chance to enrich the vapor
phase relative to the coexisting liquid (Fig. 15). All are con-
centrated in the liquid by a factor of 10 to 1,000 at conditions
typical of vapor-hypersaline liquid separation in porphyry sys-
tems at temperatures between 300° and 500°C.
At magmatic temperatures (600°–800°C), limited experi-
mental data from synthetic fluid inclusions for Au, Cu, Zn,
and Ag in S-free systems involving Na, K, and Fe chloride
saline liquids, silicate melts, and H2O-HCl vapor phases, in-
dicate density relationships similar to those established for
lower temperature hydrothermal conditions (Fig. 15), al-
though with absolute vapor-hypersaline liquid partition coef-
ficients somewhat higher than 500°C for similar vapor/liquid
density ratios (Fig. 16a). The difference, however, rarely ex-
ceeds an order of magnitude and may be explained by the in-
creasing fraction of neutral, and thus more volatile, chloride
species in the hypersaline liquid with increasing temperature
(e.g., Pokrovski et al., 2008a) and/or possible formation of
oxychloride or hydrogen-chloride species in the magmatic
vapor phase (e.g., Simon et al., 2005). Both phenomena are
due to the reinforcement of electrostatic interactions in aque-
ous complexes with increasing temperature and decreasing
dielectric constant of the solvent. This enhances the stability
of uncharged species and strengthens chemical bonds with
hard ligands (e.g., O/OH versus Cl). Even at temperatures as
high as 800°C, all principal porphyry-deposit metals (Au, Cu,
Fe) are enriched in the liquid phase compared to the vapor
(Fig. 16a). Note that both vapor and liquid densities change
in regular and predictable fashion that may be reasonably ap-
proximated by the H2O-NaCl system (Driesner and Heinrich,
2007) for natural vapor and hypersaline liquid compositions
dominated by Na, K, and Fe chlorides. Consequently, these
simple density trends provide an efficient and practical way of
predicting vapor-liquid fractionation over the range of mag-
matic-hydrothermal conditions, with an uncertainty within an
order of magnitude.
The presence of CO2, which has a weak capacity for direct
binding to most base and chalcophile metals, will affect the
fluid properties mainly by enlarging the degree of immiscibil-
ity between the vapor and liquid, thus further enhancing the
density contrast between these two phases. This effect is ex-
pected to lead to a larger contrast in the vapor-liquid parti-
tioning for most metals and their further enrichment in the
600 KOUZMANOV AND POKROVSKI
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-1.5 -1 -0.5 0
-6
-5
-4
-3
-2
-1
0
1
2
Zn
Ag
Au
Na,Fe,Cu
Sb
Si
As
B
La
Lu
-1.5 -1 -0.5 0
-6
-5
-4
-3
-2
-1
0
1
2
Zn
Ag
Au
Na,Fe,Cu
Sb
Si
As
B
La
Lu
into the vaporinto the liquid
log (K vapor / liquid)
log (density vapor / density liquid)
critical
point
FIG. 15. Vapor-liquid partition coefficients (log Kvapor/liquid = log [mvapor/
mliquid] where mis the number of moles of the element per 1 kg of fluid in
the corresponding phase) of different metals and metalloids at two-phase
equilibrium in the system H2O + NaCl ± KCl ± HCl; at ~200° to 600°C as a
function of the vapor-to-liquid density ratio. Symbols stand for experimental
data from the following sources: B = Styrikovich et al. (1960), Kukuljan et al.
(1999), Liebscher et al. (2005), Foustoukos and Seyfried (2007); AsIII, Si, Na,
Zn, FeII, CuI, AgIand AuI= Pokrovski et al. (2005a); SbIII = Pokrovski et al.
(2005a, 2008b); Lu and La = Shmulovich et al. (2002). Limited data for MoVI
(Rempel et al., 2009) and Pb (Pokrovski et al., 2008b) plot close to As/B and
Zn/Fe/Cu, respectively (omitted for clarity). Lines represent the regression
through origin (i.e., critical point) of the experimental data for each element
using the equation log K = n ×log (dvapor/dliquid), where nis an empirical co-
efficient for each metal (Pokrovski et al., 2005a).
Kouzmanov_Pokrovski_Layout 1 3/19/13 8:51 AM Page 600

dense liquid phase. The effect of S, which may selectively
bind some metals, appears to be different.
Effect of sulfur on vapor-liquid partitioning in porphyry
systems: Experimental data for S-free systems agree with ob-
servations on natural coexisting liquid and vapor inclusions
for all metals and metalloids, except Au and Cu (Fig. 10). The
most plausible explanation for Au and Cu enrichment in the
vapor phase is the formation of volatile species with S, the
second most important ligand after chloride; this effect has
recently been demonstrated experimentally. With the addi-
tion of 1 to 2 wt % of S to the water-salt system at acidic-to-
neutral pH and temperatures of 350° to 500°C, Cu and Au
partition coefficients (Kvapor/liquid) at equilibrium increase by
one to two orders of magnitude (Fig. 16b), attaining values in
favor of the vapor for Au (KAu > 1), whereas the volatility of
Ag, Zn, Fe, and Pb is almost unaffected (Pokrovski et al.,
2008a). Platinum exhibits partitioning similar to that for Au,
largely in favor of the vapor phase (K~10; however no exper-
imental data in S-free systems are available for comparison).
Synthetic fluid inclusion studies at higher temperatures
(600°-800°C) also demonstrate an increase of Kvalues for Cu
in the presence of S, but exhibit large discrepancies. For ex-
ample, Lerchbaumer and Audétat (2012) reported KCu values
two orders of magnitude lower than those of Nagaseki and
Hayashi (2008) in the same H2O-NaCl-S system, with H2S
concentrations up to 5 to 10 wt % in the vapor phase (KCu
~0.1 vs. 10; Fig. 16b). Other experimental studies, both at
hydrothermal (Pokrovski et al., 2008a) and magmatic (Simon
et al., 2006; Frank et al., 2011) temperatures, reported
vapor/liquid partitioning coefficients for Cu between 0.1 and
0.5 at dissolved S contents of 1 to 2 wt %, typical for porphyry
systems (Seo et al., 2009). Although these K values are sys-
tematically less than one (with the exception of the study by
Nagaseki and Hayashi, 2008), they are up to an order of mag-
nitude higher than in S-free systems for the same conditions
and data source (Fig. 16a).
Although the exact nature and stoichiometry of Au, Pt, and
Cu complexes in the vapor phase remain unconstrained, it is
likely that these metals form neutral hydrogen sulfide com-
plexes. Such species might behave as regular gases, which en-
rich the vapor phase with a decrease in the vapor/liquid den-
sity ratio. The higher volatility of Au and Pt compared to Cu
HYDROTHERMAL CONTROLS ON DISTRIBUTION IN PORPHYRY Cu (-Mo-Au) SYSTEMS 601
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-1.5 -1 -0.5 0
-6
-5
-4
-3
-2
-1
0
1
2
Ag
Au
Fe,Cu
Zn
-Au, 350-500°C, P08
-Au, 800°C, F11
-Cu,350-500°C,P08
-Cu, 500-650°C, NH08
-Cu, 800°C,S06, F 11
-Cu, 800°C,LA12
-Pt, 450-500°C,P08
log (K vapor / liquid)
log (density vapor / density liquid)
critical
point
b
Ag
Au
Fe,Cu
Zn
-Au, 800°C, S05, F11
-Cu,500-650°C,NH08
-Cu,800°C,F11
-Cu,800°C,S06
-Fe, 800°C, S04
-Zn,500-650°C,NH08
-Ag,800°C,S08
critical
point
-1.5 -1 -0.5 0
-6
-5
-4
-3
-2
-1
0
1
2
log (K vapor / liquid)
log (density vapor / density liquid)
a
FIG. 16. (a) Vapor-liquid partition coefficients (log Kvap or/liquid = log [mvapor /mliquid] of Au, Cu, Fe, Zn, and Ag in the two-
phase model system H2O + NaCl ± KCl ± HCl at magmatic temperatures (500°–800°C) as a function of the vapor-to-liq-
uid density ratio. Symbols stand for experimental data from the following sources: NH08 = Nagaseki and Hayachi (2008),
S04 = Simon et al. (2004), S05 = Simon et al. (2005), S06 = Simon et al. (2006), S08 = Simon et al. (2008), F11 = Frank et
al. (2011). The straight lines through the critical point for the indicated elements represent the density-model predictions
in the S-free system based on data below 500°C (Pokrovski et al., 2005a, 2008a). With the exception of a few nonsystem-
atic outliers, most high-temperature data follow, within errors, a roughly linear log K vs log (dvap /dliq) dependence with an
origin at the critical point, similar to that established at hydrothermal temperatures; the somewhat higher K values likely
reflect the increasing fraction of neutral, and thus more volatile, metal chloride species with increasing temperature and/or
possible formation of new oxy-chloride and hydrogen-chloride species in magmatic vapor phase. (b) The effect of sulfur on
vapor-liquid partition coefficients (log Kvapor/liquid = log [mvapor/mliqui d] of Au, Cu and Pt in model two-phase salt-water sul-
fur-rich systems (H2O-NaCl-KCl-HCl-FeCl2-S-pyrrhotite-bornite) at acidic-to-neutral pH, 350° to 800°C, and 1 to 10 wt
% sulfur in the vapor. Symbols stand for experimental data from the following sources: P08 = Pokrovski et al. (2008a), NH08
= Nagaseki and Hayachi (2008), S06 = Simon et al. (2006), F11 = Frank et al. (2011), LA12 = Lerchbaumer and Audétat
(2012). Partitioning of Zn, Fe, and Ag is not affected within errors by the presence of sulfur (symbols are omitted for clar-
ity). The straight lines for the indicated elements represent the density-model predictions in the S-free system (from
Pokrovski et al., 2005a; see Fig. 16a).
Kouzmanov_Pokrovski_Layout 1 3/19/13 8:51 AM Page 601

is consistent with the far greater stability of Au hydrogen sul-
fide species in aqueous solution, as discussed above. The low
volatility of Zn, Fe, and Ag is a direct consequence of the
larger stability of their chloride versus sulfide complexes in
aqueous solution (Table 3).
Another important factor controlling the vapor-liquid dis-
tribution of these metals in S-rich systems is the fluid acidity
(pH). Because neutral sulfide species have a far greater
volatility than their charged counterparts (Pokrovski et al.,
2002a, 2008a), Au (and Cu) are expected to be more volatile
at acidic conditions under which AuHS0and probably
AuHSH2S0are more abundant in the liquid phase (reactions
6b, c). At pH >5, where Au(HS)2–(reaction 6a) and Cu(HS)2–
form in the solution, K values for Au and Cu are systemati-
cally <1 (Pokrovski et al., 2008a). Phase separation of such a
fluid will thus not favor Au and Cu fractionation into the
vapor phase.
The effect of CO2on vapor-liquid partitioning of S-bound
metals remains experimentally unconstrained. The scarce
data for CO2-free systems (Fig. 16b) suggest that partitioning
of volatile Au- and Pt-bearing sulfide complexes into the
vapor phase might be enhanced in the presence of CO2, both
due to an increase in the density contrast between liquid and
vapor and specific solvation of neutral nonpolar molecules,
such as Au-H2S complexes, by nonpolar CO2(Pokrovski et al.,
2008a). The selective solvation capacities of supercritical CO2
are used in chemical engineering for synthesis and purifica-
tion of organometallic and organic compounds at moderate
temperatures (e.g., Erkey, 2000). However, this hypothesis
awaits experimental confirmation for conditions applicable to
porphyry systems.
Experimental data for the S-bearing systems discussed
above explain vapor-liquid distributions of Au, Ag, and base
metals observed in fluid inclusions from porphyry Cu (-Mo-
Au) deposits; however, they still fail to reproduce the strong
enrichment of Cu measured in vapor-like inclusions (KCu as
high as 10–100; Fig. 10). Recent experiments on natural and
synthetic fluid inclusions in quartz re-equilibrated with dif-
ferent fluid and melt compositions revealed rapid diffusion of
Cu+through the quartz host, leading to large postentrapment
changes in Cu concentrations in the inclusion fluid (Li et al.,
2009; Zajacz et al., 2009; Lerchbaumer and Audétat, 2012).
These studies may thus explain the observed Cu enrichment
in natural S-rich vapor inclusions through preferential diffu-
sion of Cu+from the surrounding fluid into previously formed
S-rich inclusion fluids (see above).
Discussion: Ore Deposition and Metal Distribution
in Porphyry Cu (-Mo-Au) Systems
Ore formation and metal distribution in porphyry systems
result from a combination of processes, ultimately leading to
decreases in the solubility of metals in the hydrothermal fluid
and their precipitation. In this section, we apply thermody-
namic modeling to interpret the metal contents of natural
fluid inclusions from porphyry systems, discuss the major
processes controlling metal precipitation, and identify factors
that cause the observed metal zoning in porphyry-centered
districts.
Comparison of metal concentrations measured in
ore fluids with thermodynamic predictions
The majority of previous studies devoted to thermody-
namic modeling of porphyry deposits focused on the major-
element composition of fluid inclusions by considering the
PVTX properties of NaCl-KCl-CO2-H2O systems (e.g., Bod-
nar and Sterner, 1984; Sterner et al., 1988; Bodnar and Vityk,
1994; Heinrich, 2007), mineral assemblages, alteration se-
quences, and sulfidation state (e.g., Reed, 1997; Einaudi et
al., 2003), as well as Au, plus Fe, Cu, Zn, and Pb sulfide solu-
bility and metal precipitation in model aqueous fluids (e.g.,
Hemley and Hunt, 1992; Hezarkhani et al., 1999; Heinrich et
al., 2004; Heinrich, 2005). These studies provided constraints
on fluid properties and major element composition, tempera-
ture, and pressure of deposition, minerals that control the
redox and sulfur state of the fluid, and general trends in the
behavior of some metals during fluid evolution. The large
dataset of metal concentrations in natural fluid inclusions
compiled in this study, together with an improved knowledge
of aqueous metal speciation and dissolved species stability, al-
lows more detailed and direct comparisons of natural metal
contents with thermodynamic predictions. This approach pro-
vides new insights into depositional mechanisms and metal
fractionation in the porphyry and epithermal environments.
Figure 17 shows the calculated solubility of major metal-
bearing ore minerals as a function of temperature and salinity
under redox and acidity conditions typical of porphyry sys-
tems, as inferred from mineral associations and wall-rock al-
teration patterns. The assemblage pyrite-magnetite-hematite
was chosen as a proxy for the redox state and H2S fugacity
(Einaudi et al., 2003) and the pH was constrained between 4
and 5 assuming buffering by aluminosilicate assemblages
common in porphyry deposits over a wide temperature range
(Meyer and Hemley, 1967; Reed, 1997). Significant devia-
tions from these conditions will be directly reflected in dif-
ferences between calculated and measured metal concentra-
tions. The main trends for the principal metals in porphyry
deposits are highlighted below.
Zinc, lead, and silver: Calculations show that for Zn, Pb,
and Ag at 400°C, the great majority of single-phase fluids
and hypersaline liquids are undersaturated with respect to
ZnS, PbS, and Ag2S minerals at pH ≤5 (Fig. 17a-c). These re-
sults accord well with the observed paucity of Zn, Pb, and Ag
602 KOUZMANOV AND POKROVSKI
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FIG. 17. Comparison of the calculated Zn, Pb, Ag, Mo, Cu, and Au dissolved concentrations in the fluid in equilibrium
with the corresponding major ore minerals, sphalerite (a), galena (b), argentite (c), molybdenite (d), chalcopyrite (e and f)
and native gold (g and h) as a function of temperature (all metals) and salinity (for Cu and Au); metal concentrations ana-
lyzed in the four types of fluid inclusions are shown in Figures 7 and 8. The data points of the different inclusion types are
shown as contours of different color for simplicity. The calculations were performed at NaCl concentrations of 3, 10, and 40
wt % at pH 5 and buffered by the pyrite-magnetite-hematite assemblage (unless indicated in the legend). Arrows illustrate
the effect of pH (and redox for Mo) change on the calculated solubilities (see text for discussion). Abbreviations: MH = mag-
netite-hematite; NNO = nickel-nickel oxide.
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HYDROTHERMAL CONTROLS ON DISTRIBUTION IN PORPHYRY Cu (-Mo-Au) SYSTEMS 603
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0.1
1
10
100
1000
10000
100000
100 200 300 400 500 600 700 800
single-phase
hypersaline
liquid
vapor-rich
low-salinity
aqueous
3 wt% NaCl
10 wt% NaCl
40 wt% NaCl
Zn (ppm)
Th (°C)
pH change
from 5 to 4
0.1
1
10
100
1000
10000
100000
100 200 300 400 500 600 700 800
3 wt% NaCl
10 wt% NaCl
40 wt% NaCl
Pb (ppm)
Th (°C)
pH change
from 5 to 4
0.1
1
10
100
1000
10000
100000
100 200 300 400 500 600 700 800
3 wt% NaCl
10 wt% NaCl
40 wt% NaCl
Cu (ppm)
Th (°C)
pH change
from 5 to 4
0.1
1
10
100
1000
10000
100000
Cu (ppm)
Salinity (wt% NaCl eq.)
110100
0.1
pH change
from 5 to 4
pH 5; 400°C
pH 5; 300°C
0.1
100 200 300 400 500 600 700 800
3 wt% NaCl
10 wt% NaCl
40 wt% NaCl
Ag (ppm)
Th (°C)
pH change
from 5 to 4
1
10
100
1000
10000
0.1
100 200 300 400 500 600 700 800
Mo (ppm)
Th (°C)
pH change
from 5 to 4
1
10
100
1000
10000
fO2 change
from MH to NNO
set-1: 3 wt% NaCl
set-1: 10 wt% NaCl
set-1: 40 wt% NaCl
set-2: 3 wt% NaCl
set-2: 10 wt% NaCl
set-2: 40 wt% NaCl
100 200 300 400 500 600 700 800
3 wt% NaCl
10 wt% NaCl
40 wt% NaCl
Au (ppm)
Th (°C)
pH change
from 5 to 4
0.01
0.1
1
10
100
pH change
from 5 to 4
Au (ppm)
0.01
0.1
1
10
100
Salinity (wt% NaCl eq.)
110100
0.1
pH 5; 400°C
pH 4; 400°C
pH 5; 300°C
pH 5; 400°C; 1 wt% H2S
ab
cd
ef
gh
hypersaline liquid
vapor-rich
low-salinity
aqueous
hypersaline liquid
vapor-rich
low-salinity
aqueous
hypersaline liquid
vapor-rich
low-salinity
aqueous
hypersaline
liquid
vapor-rich
low-salinity
aqueous
hypersaline
liquid
vapor-rich
low-salinity
aqueous
hypersaline liquid
vapor-rich
low-salinity
aqueous
hypersaline liquid
vapor-rich
low-salinity
aqueous
single-phase
single-phase
single-phase
single-phase
single-phase
single-phase
single-phase
Kouzmanov_Pokrovski_Layout 1 3/19/13 8:51 AM Page 603

mineralization in typical porphyry deposits, and explain the
constancy of the Zn/Pb ratios in the evolving magmatic-
hydrothermal fluid (Fig. 11). Fluid saturation with these min-
erals occurs at lower salinities (<10 wt % NaCl equiv) and
temperatures (<350°C) typical for low-to-intermediate salin-
ity aqueous fluids. These observations are consistent with the
occurrence of Pb-, Zn-, and Ag-bearing minerals in more dis-
tal, marginal to epithermal, settings. The most efficient mech-
anism for the precipitation of Zn and Pb, at both high and low
temperatures, is the neutralization of an acidic fluid (pH ~3-
5); this may occur, for example, by interaction with carbonate
or other sedimentary rocks. This effect leads to a pH increase
of 2 to 3 units (e.g., pH ~6–7 of an evolved fluid in equilib-
rium with calcite), yielding a 10,000-fold decrease of both
ZnS and PbS solubility (Fig. 17a, b; reactions 3, 4). This solu-
bility decrease explains the abundance of Pb and Zn mineral-
ization in skarns and carbonate-replacement deposits (Fig. 1),
very likely caused by pH increase resulting from reaction with
carbonate rocks.
Copper: Calculated chalcopyrite solubility (in the presence
of pyrite) between pH values of 4 and 5 agrees relatively well
above 450° to 500°C with data for metals in single-phase and
hypersaline fluids (Fig. 17e). This observation explains the
ubiquitous presence of CuFeS2over the wide temperature
range of porphyry systems, and accounts for the large de-
crease of Cu/Zn and Cu/Pb ratios during the evolution of
magmatic fluids (Fig. 11); in contrast to Cu, both Zn and Pb
remain in the hypersaline liquid and vapor phase. At 350° ±
50°C, the calculated Cu solubility is an order of magnitude
lower on average than Cu contents measured in single-phase
and hypersaline liquid inclusions (Fig. 17e, f). This discrep-
ancy may, however, be reconciled if the true entrapment tem-
peratures were ~50°C higher than homogenization tempera-
tures and/or if there was postentrapment Cu enrichment of
some inclusions due to preferential Cu+diffusion, as dis-
cussed above. The solubility of CuFeS2in moderate-salinity
solutions below 300°C is 100 to 1,000 times lower than the Cu
concentrations found in aqueous fluid inclusions from por-
phyry-related vein and epithermal deposits (Fig. 17f). To effi-
ciently transport Cu to the epithermal environment, such
fluids should be acidic (pH ~3) and probably somewhat re-
duced. These properties may be consistent with fluid origin
from condensation of an HCl- and H2S-bearing vapor pro-
duced from phase separation of a magmatic fluid (Heinrich et
al., 2004; Heinrich, 2005). They are also consistent with a sin-
gle-phase H2S/SO2-bearing fluid that cools above the solvus
(Fig. 3; Hedenquist et al., 1998) and becomes acidic as a re-
sult of SO2disproportionation to sulfuric acid and H2S with
decreasing temperature (see below). In the latter case, to
maintain the high acidity favorable for Cu solubility, such a
fluid should either flow through previously leached rocks
characterized by residual vuggy quartz without neutralization
potential or be focused in fractures to limit its interaction
with Na- and K-bearing silicates, as the latter would cause
neutralization of acidic components.
Gold: In most high-temperature (>400°C), single-phase
fluids and hypersaline liquids in which Au is predominantly
transported as AuCl2–(reaction 6d), the calculated Au solubil-
ity over a wide salinity range matches the average concentra-
tion found in the majority of inclusions of the corresponding
types (Fig. 17g, h). Below 400°C, by contrast, the predicted
total Au concentrations in equilibrium with pyrite are two to
three orders of magnitude lower than those measured in low-
salinity aqueous fluids (typically 1–10 ppm; Fig. 17g). In
order to be able to transport such high Au contents, this type
of fluid would require 10 to 50 times more H2S than that al-
lowed by equilibrium with an excess of pyrite and hematite/
magnetite. Such H2S concentrations may originate from a
condensed Fe-deficient, but S- and Au-rich vapor phase, pro-
duced by intersection of the V-L solvus by the single-phase
fluid on ascent, at high pressure and temperature (Heinrich,
2005; fluid path 4 in Fig. 3, as discussed above). However,
such an H2S-rich aqueous solution would not be able to trans-
port Cu as well as Fe, Ag, Pb, and Zn (CuFeS2stoichiometric
solubility at 300°C would indicate <1 ppm Cu and 1 ppm Fe
in an aqueous solution of 5 wt % NaCl and 1 wt % H2S at
pH~4). The inability of such a H2S-rich fluid to transport base
metals disagrees with the high concentrations of these ele-
ments measured in low to intermediate salinity aqueous
fluid inclusions (Figs. 5, 7, 8). Knowledge of the exact chem-
ical speciation and amount of S is likely to be the key to re-
solving these discrepancies. For example, the recent discov-
ery of polysulfide forms, such as S3–, in S-rich acidic fluids
might account both for enhanced Au transport as direct com-
plexes with S3–and increased solubility of other metal sulfide
minerals in such solutions due to the consumption of H2S to
form S3–(Pokrovski and Dubrovinsky, 2011; Pokrovski and
Dubessy, 2012).
Molybdenum: Calculated molybdenite solubility is consis-
tent between two independent datasets within better than
one order of magnitude; one study used thermodynamic data
for molybdic acid, its anions, and ion pairs with alkali metals
(reactions 7a-c; Zotov et al., 1995; Shock et al., 1997) and the
other was based on extrapolations to lower temperatures of
direct MoS2solubility measurements at 600° to 800°C, inter-
preted in terms of thiomolybdate-sodium species (Zhang et
al., 2012). However, at conditions applicable to porphyry de-
posits, both datasets predict MoS2solubilities up to 3 to 4 or-
ders of magnitude lower than Mo contents in natural fluid in-
clusions at Th<450°C (Fig. 17d). Neither acidic (pH < 3-4)
nor reduced and H2S-rich fluids (arrows, Fig. 17d) are able to
transport Mo; corrections of Thto true temperature of en-
trapment are also insufficient to account for this discrepancy.
A possible explanation may be the existence of other impor-
tant Mo complexes (e.g., oxychlorides, sulfides, or polysul-
fides), which have not been included in experiments con-
ducted on simple model systems; another cause may be an
overestimation of H2S contents resulting from omission of
other S species, which may form at the expense of H2S (e.g.,
S3–). Both factors will tend to increase MoS2solubility (reac-
tions 7a-c).
Major hydrothermal controls on ore formation in
porphyry systems
During their evolution in porphyry systems, magmatic-
hydrothermal fluids undergo five major processes that cause
metal redistribution and deposition: decompression, phase
separation (or boiling), cooling, interaction with rocks, and
mixing with external waters. These processes are intercon-
nected and one may overprint or act in parallel with another.
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The improved knowledge of both natural metal concentra-
tions and their chemical speciation in the liquid and vapor
phases may help to better estimate the effect of each of these
processes on the different metals, and potentially lead to an
improvement in exploration strategies. Below we discuss
major consequences of each of these processes on metal
transport and deposition.
Decompression: All ascending fluids, magmatic and other-
wise, undergo pressure decrease. Although the most direct
result of decompression is phase separation (see next subsec-
tion) and temperature decline, pressure decrease in a single-
phase fluid may also affect mineral solubility. However, the
quantification of this effect on solubilities of sulfide minerals
is difficult because of lack of experimental data, particularly in
low-density vapor and supercritical fluid. Robust data are only
available for quartz, which shows a sharp decrease in solubil-
ity with decreasing pressure at a given temperature (Fig. 13;
Fournier, 1999). This property, together with retrograde sol-
ubility of quartz in the temperature range ~370° to 470°C at
pressures below ~800 bars, affects the formation of veins and
fluid flow by changing permeability due to quartz dissolution
or precipitation. For example, at Bingham Canyon, Cu depo-
sition occurred by cooling and decompression in a narrow
temperature and pressure interval (425°–350°C, 200–140
bars) coupled with the retrograde quartz solubility, which
generated secondary vein permeability by quartz dissolution
with temperature decrease (Landtwing et al., 2005).
Pressure is also suggested to have a major influence on
Cu/Au ratios in many porphyry deposits, likely because its
evolution is easier to trace than those of other parameters.
For example, Murakami et al. (2010) compiled Cu/Au ratios
for 50 porphyry-style Cu-Au ± Mo deposits and noted that
there is a large variation in the values, from 103to 106, and
these appear to correlate with the depth and pressure of ore
deposition. According to the authors, deep-seated porphyry
Cu ± Mo deposits are expected to be deficient in Au and to
have Cu/Au ratios higher than that of their primary mag-
matic-hydrothermal input fluid. This may be explained by
earlier precipitation of chalcopyrite relative to gold from a
cooling moderate-salinity fluid, consistent with the solubility
trends discussed above. Landtwing et al. (2010) proposed that
deposit-scale variation of Cu/Au ratios in the Bingham
Canyon ore is due to different fluid paths, under slightly dif-
ferent pressure regimes, of a common input fluid in the cen-
tral part and periphery of the stock, leading to the inverted-
cup morphology of the orebody. According to their model, in
the central zone of the orebody, characterized by denser frac-
turing and higher permeability (Gruen et al., 2010), the mag-
matic fluid expanded due to the transition from lithostatic to
hydrostatic pressure, and ore deposition occurred at lower
pressure than on the periphery, dominantly from a vapor-like
fluid that was enriched in S, Au, and Cu compared to the sin-
gle-phase magmatic fluid, and to a lesser degree from minor
condensing brine. In the deeper peripheral zones, by con-
trast, this same magmatic fluid cooled at higher pressure and
thus underwent less phase separation. An analogous mecha-
nism might explain the similar Cu/Au zonation observed in
other porphyry Cu-Au deposits (e.g., Batu Hijau, Indonesia;
Arif and Baker, 2004). However, because the pressure and
temperature decrease and associated changes occur together,
it is challenging to identify the contribution of pressure itself
on metal distribution. Furthermore, robust thermodynamic
modeling of the pressure effect in complex vapor-liquid sys-
tems is difficult (see above).
Phase separation: The second key process is phase immis-
cibility, which is caused by pressure decrease as the fluid as-
cends toward the surface (Fig. 3); this is recorded in various
parts of magmatic-hydrothermal systems by coexisting liquid-
and vapor-rich fluid inclusions (Fig. 1; Table 1). In the deep
porphyry environment, phase separation results in condensa-
tion of a minor amount of hypersaline liquid from the domi-
nant low-salinity vapor phase (Fig. 3, path 4), whereas in the
epithermal environment, phase separation occurs by boiling
of the dominant aqueous liquid via generation of vapor bub-
bles. The effect of phase separation on metal transport and
deposition in these two cases is different.
As shown above, phase separation in porphyry deposits at
high temperature and pressure results in a contrasting frac-
tionation of ore-forming elements, with As, S, Au (and partly
Cu) enriched in the vapor phase compared to Fe, Zn, Pb, and
Ag (Figs. 10, 15, 16). This enrichment was believed to be a
prerequisite for the generation of fluids that could form epi-
thermal Au-Cu deposits (Heinrich, 2005), with contraction of
the supercritical phase to an acidic S-bearing liquid capable
of transporting Cu and Au at relatively low temperatures.
Such conditions may be met in high-sulfidation Cu-Au de-
posits (Hedenquist et al., 1993, 1998; Heinrich et al., 2004),
which are spatially associated with magmatic intrusions and
underlying porphyry deposits. Sulfur is likely to play an im-
portant role in the distribution of the Cu and Au between liq-
uid and vapor phases, particularly considering the fact that
the mass of the vapor produced during magmatic fluid sepa-
ration exceeds that of the hypersaline liquid (typical vapor/hy-
persaline liquid mass ratios are 4–9; e.g., Hedenquist et al.,
1998; Pudack et al., 2009; Landtwing et al., 2010; Lerch-
baumer and Audétat, 2012).
The effect of phase separation in the porphyry environment
on the behavior of Mo is less clear. For some porphyry Mo
deposits it has been suggested that vapor-liquid separation
may cause pre-enrichment of Mo in the hypersaline liquid,
prior to molybdenite deposition by cooling (Klemm et al.,
2008). However, limited fluid-inclusion analyses (Fig. 10; Seo
et al., 2009, 2012) and laboratory experiments in S-free sys-
tems (Rempel et al., 2009) suggest that a significant portion
of the Mo may also partition into the vapor phase. In contrast
to Cu and Au, however, a S-rich vapor phase is expected to
precipitate all Mo when it cools and condenses, because of
predicted extremely low MoS2solubility at temperatures
below 400°C (Figs. 14a, 17d), whereas Au and Cu will remain
in the fluid. However, in both high and low sulfidation epi-
thermal systems, Mo can be locally abundant (up to >0.1 wt
%), thus implying existence of other, not studied yet, Mo
complexes, capable of transporting Mo at conditions relevant
to epithermal environment.
In the low-temperature and pressure (<~100 bar) epither-
mal environment, the density of the vapor phase is too low for
significant metal partitioning into the vapor phase (Fig. 15).
The main effect of boiling of a liquid under such conditions is
the removal of H2S and CO2from the liquid phase. This process
leads to the breakdown of Au hydrogen-sulfide complexes and
HYDROTHERMAL CONTROLS ON DISTRIBUTION IN PORPHYRY Cu (-Mo-Au) SYSTEMS 605
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causes gold precipitation in veins, such as gold-rich, bonanza-
grade veins, corresponding to the depth at which boiling oc-
curred below the paleowater table (e.g., Saunders and
Schoenly, 1995; Simmons et al., 2005). In addition, boiling re-
sults in the pH of the liquid increasing due to the loss of CO2,
which, in turn, may lead to precipitation of base metal and Ag
sulfides such as galena, sphalerite, chalcopyrite, pyrite, and
argentite (see above).
Cooling: Temperature is likely the most direct factor that
influences mineral solubility and, thus, metal transport and
precipitation, as indicated by a number of porphyry deposit
case studies. Landtwing et al. (2005) used fluid inclusion
studies to demonstrate that cooling of a magmatic-hydrother-
mal fluid over a small temperature interval (425°–350°C) was
the main cause of Cu ± Au deposition at Bingham Canyon
(Fig. 18a); similar conclusions were reached for other por-
phyry Cu-Au and Cu-Mo systems, such as Bajo de la Alum-
brera (Ulrich et al., 2001) and Butte (Rusk et al., 2004). Re-
cently, Catchpole et al. (2011, in review) reported similar
findings for porphyry Cu-related base metal veins at Moro-
cocha, where the magmatic fluid evolved to an aqueous liquid
that formed polymetallic mineralization in the epithermal en-
vironment at temperatures of 380° to 250°C (Fig. 18b). They
observed that Cu concentrations decreased by more than
three orders of magnitude where the temperature decreased
by 150°C. This observation agrees well with thermodynamic
calculations of chalcopyrite solubility in a low-salinity (<5 wt
% NaCl), S-rich (1,000–5,000 ppm S), and acidic (pH ~3)
fluid characteristic of that at Morococha. Similar tempera-
ture-dependent trends were also established for Zn, Pb, Ag,
and Mn (Catchpole et al., in review). These two examples
(Fig. 18) demonstrate that both in deep porphyry and shal-
lower epithermal environments, cooling below 400°C of a sin-
gle-phase fluid initially containing ~10,000 ppm (1 wt %) Cu
is an efficient mechanism of ore formation. These observa-
tions from ore deposits are consistent with the general tem-
perature dependences of sulfide mineral solubility (Fig. 14a).
Cooling of a magmatic fluid is also accompanied by large
changes in sulfur speciation, which in turn affect H2S con-
centration and acidity, according to the following reaction:
4 SO2+ 4 H2O = H2S + 3 HSO4–+ 3 H+(9)
This reaction does not lead to significant redox changes since
it is independent of oxygen fugacity, whereas it is strongly pH-
dependent, and its extent will depend on the degree of fluid
interaction with surrounding silicate rocks. Where pH is
buffered by silicate rocks (albite, K-feldspar, and muscovite;
pH ~5) during fluid flow and cooling, reaction (9) shifts to the
right with decreasing temperature due to consumption of H+
by the rock, and SO2breakdown proceeds to 99% completion
at temperatures below 400°C.
The behavior of metals in two extreme cases of rock equili-
bration is quite different; a model magmatic fluid containing
10 wt % NaCl equiv, 1 wt % H2S, 1 wt % SO2, 10,000 ppm Fe,
5,000 ppm Cu, 300 ppm Mo and an excess of metallic Au
(Fig. 19) was cooled numerically in or out of equilibrium with
606 KOUZMANOV AND POKROVSKI
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B2 - syn-sulfide
precipitation
B1 - pre/syn sulfide
precipitation
Hypersaline liquid assemblages:
10
102
103
104
105
Input ore fluids
Spent ore fluids
T (°C)
Cu (ppm)
1
Bingham
aSingle-phase
intermediate-density
Vapor-rich
Hypersaline liquid
FLUID
SATURA-
TION IN
MAGMA
CHAM-
BER
water saturated solidus
100 200 300 400 500 600 700 800
44 wt% NaCl
10 wt% NaCl
boiling
100 200 300 400 500 600
10
102
103
104
105
1
700
Input ore fluid ?
T (°C)
single-phase
hypersaline liquid
low-salinity aqueous
in porphyry
veins
in Cordilleran
polymetallic veins Morococha
b
3.6 wt% NaCl; pH 3
3.6 wt% NaCl; pH 4
Low-salinity aqueous
Single-phase
intermediate-density
Hypersaline liquid
Cu (ppm)
FIG. 18. Concentrations of Cu measured in fluid inclusions as a function of homogenization temperature in (a) the Bing-
ham porphyry Cu-Mo-Au deposit and (b) the porphyry copper-related base metal vein system in Morococha, central Peru.
Modified from Heinrich et al. (2005), Landtwing et al. (2005), and Catchpole et al. (in review). Each point represents a fluid
inclusion assemblage, with 1σerror bars. Gray arrows correspond to fluid evolution paths. In both systems, the magmatic
input fluid of intermediate density has initial concentration of ~10,000 ppm Cu (1 wt %). At Bingham, phase separation is
associated with massive Cu precipitation in the porphyry environment at temperatures of 420° to 350°C, whereas at Moro-
cocha, a temperature decrease from 400° to 250°C caused a three orders of magnitude decrease in Cu concentration in the
low-to-intermediate salinity aqueous fluids that formed polymetallic veins which overprinted the porphyry Cu-Mo system.
Chalcopyrite solubility curves (this study) are reported for comparison as follows: in Bingham, for fluids with salinity of 10
and 40 wt % NaCl equiv at pH 5, in equilibrium with the pyrite-magnetite-hematite assemblage; and in Morococha, for flu-
ids with salinity of 3.6 wt % NaCl equiv, 0.1 m H2S, pH 3 and 4, and oxygen fugacity of hematite-magnetite assemblage.
Acidic fluids (pH <3), likely produced by condensation of a vapor phase, are necessary to account for the observed Cu con-
centrations in low salinity aqueous inclusions.
Kouzmanov_Pokrovski_Layout 1 3/19/13 8:51 AM Page 606

an assemblage of quartz+muscovite/andalusite+K-feldspar.
The initial fluid composition corresponds to typical salt, S,
and metal contents found in single-phase fluid inclusions
from major porphyry deposits (see above), and is similar to
that adopted in previous modeling studies (e.g., Heinrich,
2005). In the absence of fluid neutralization by silicate rocks
(Fig. 19a), reaction (9) causes acidification of the cooling
fluid, which is very favorable for Cu and Fe mobility (Fig. 14).
Thus, large metal concentrations (in the form of chloride
complexes) may be carried without significant loss by such a
fluid to temperatures as low as 200°C (Fig. 19c). In contrast,
where pH of the fluid is neutralized by interaction with alu-
minosilicate rocks, >90% of the initial Cu and Fe will precip-
itate from the solution between 600° and 400°C in the form
of magnetite (at 500–600°C) and pyrite + chalcopyrite (at
<500°C). This agrees with observed Cu-Fe mineralization in
high-temperature porphyry stages (potassic alteration). De-
pending on the fluid-rock ratio and fluid flow paths and
HYDROTHERMAL CONTROLS ON DISTRIBUTION IN PORPHYRY Cu (-Mo-Au) SYSTEMS 607
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10-4
10-3
10-2
10-1
1
200 250 300 350 400 450 500 550 600 650
Stot
H2S
SO2
SO4tot
Sulfur species, no buffering
Concentration (mol/kg)
Temperature(°C)
a
pH=2 pH=3 pH=4-5pH=1
10-7
10-6
10-5
10-4
10-3
10-2
10-1
1
Fe
Cu
Au
Mo
Fe, Cu, Au, Mo, no buffering
Concentration (mol/kg)
Temperature (°C)
c
200 250 300 350 400 450 500 550 600 650
Sulfur species, silicate buffering, pH ~5
Temperature (°C)
b
Concentration (mol/kg)
200 250 300 350 400 450 500 550 600 650
10-4
10-3
10-2
10-1
1
Stot
H2S
SO2
SO4tot
Fe, Cu, Au, Mo, silicate buffering, pH ~5
Temperature (°C)
d
Concentration (mol/kg)
10-7
10-6
10-5
10-4
10-3
10-2
10-1
1
200 250 300 350 400 450 500 550 600 650
Fe
Cu
Au
Mo
FIG. 19. Concentrations of principal sulfur forms (a, b) and Fe, Cu, Mo and Au (c, d) as a function of temperature in a
model magmatic fluid initially containing 10 wt % NaCl equiv, 1 wt % H2S, 1 wt % SO2, 10,000 ppm Fe, 5,000 ppm Cu, 300
ppm Mo and an excess of metallic Au. Thermodynamic properties for S-species were taken from the SUPCRT database
(Johnson et al., 1992; Sverjensky et al., 1997), whereas those of metal species are from references in Table 3. Panels (a) and
(c) show the situation where the fluid cools in a closed system and is not allowed to react with alkali silicate minerals. Note
the acidification of such a fluid on cooling; this is shown by pH values close to the temperature axis on panel (a), due to gen-
eration of sulfuric acid from the SO2disproportionation reaction (reaction 9). These acidic pH values favor Fe, Cu and Au
transport as chloride complexes to temperatures as low as 300°–250°C; below these temperatures a significant portion of the
Fe and Cu, Au and S precipitates as pyrite, chalcopyrite, covellite, native Au, and native S. Significant Mo transport by such
a fluid is limited to >550°C. Panels (b) and (d) show the same fluid, cooling in contact with an excess of the quartz-mus-
covite/andalusite–K-feldspar assemblage that buffers the solution pH between 4.5 and 5.0 over the complete investigated
temperature range. Note a sharp decrease of SO2concentrations below ~400°C, and high H2S contents persisting down to
200°C. These contents, coupled with near-neutral pH, are unfavorable for Cu and Fe solubility below 400°–350°C, but are
favorable for significant Au transport in the range from 600° to 200°C, to conditions of formation of Au epithermal deposits;
by contrast, Mo mobility in the fluid phase is significant only above 450° to 500°C. These two contrasting scenarios are likely
to encompass the range of conditions that natural fluids undergo (see text for details).
Kouzmanov_Pokrovski_Layout 1 3/19/13 8:51 AM Page 607

velocities, neutralization of this acidic fluid may be delayed
until further ascent and cooling. For this reason, in many por-
phyry deposits the bulk of the Cu mineralization (mainly as
chalcopyrite and bornite) precipitates at temperatures close
to 400°C, where reaction (9) moves strongly to the right, and
at lower temperatures than the initial quartz veining that ac-
companies the potassic alteration (e.g., Landtwing et al.,
2005). However, such a neutralized fluid will be unable to
carry significant amounts of Cu and Fe (and Pb, Zn, Ag) to
the low-temperature epithermal environment. The effective
transport of these metals to such settings by S-rich fluids is
thus only possible if the pH of the acidic fluid does not
change as it ascends through the rock, which requires the
buffering capacity of the rock to already have been altered by
an earlier acidic fluid. Such an early acidic fluid prepares a fa-
vorable conduit for one or more subsequent pulses of fluid
rich in metals, both by consuming the neutralization capacity
of the rock and creating additional permeability due to partial
mineral dissolution. This effect allows Cu and Fe to be trans-
ported further and deposited later in pyrite-chalcopyrite
veins associated with a phyllic overprint of potassic alteration
(e.g., Hedenquist et al., 1998; Pudack et al., 2009). In addi-
tion, a portion of the Cu initially precipitated during the
potassic stage may be redissolved by a subsequent acidic fluid
and redeposited in the upper and cooler levels of the system,
e.g., within the phyllic zone or shallower advanced argillic
lithocap overlying the porphyry environment (Brimhall, 1977;
Sillitoe, 2010; Fig. 1).
The behavior of Au upon the disproportionation of SO2is
more complex, because of the change of dominant Au species
from chloride (reaction 6d) to sulfide (reactions 6a-c) with a
decrease in the temperature and an increase in the progress
of reaction (9) to the right. With an excess of S over metals, a
magmatic fluid will be able to carry Au at concentrations of
>10 ppm to low temperatures (~250°C), buffered or not with
rocks and without reaching saturation with the metal (Fig.
19); this is despite the large differences in Au speciation and
solubility-controlling factors between acidic and neutral flu-
ids. The interplay between the initial fluid redox, S, Cl, and
major metal concentrations may have different effects on Au
behavior in different deposits (e.g., Heinrich, 2005). This un-
certainty is superimposed on another major unknown of Au
aqueous chemistry; the existence or not of dissolved S-bear-
ing complexes other than H2S, such as SO2or polysulfides
(Pokrovski et al., 2008a, 2009a).
In contrast to all other metals, the capacity for Mo transport
will be decreased sharply upon SO2disproportionation, be-
cause an increase in the H2S content and acidity both de-
crease MoS2solubility (Figs. 14c, d, 17d, 19d). Fluid neutral-
ization by reaction with aluminosilicate rocks may help
maintain significant Mo concentrations (>~10s ppm) in the
fluid down to ~500°C (Fig. 19d). This effect might explain
the higher temperature of molybdenite formation compared
to that of Cu and Au (~400°C) in some Mo-dominated por-
phyry deposits (e.g., Henderson; Seedorff and Einaudi, 2004).
However, in typical porphyry Cu-Au deposits, Mo generally
postdates the main stage of Cu-Fe sulfide precipitation and/or
can be more distal from the intrusion than Cu (e.g., Sillitoe,
1979, 2010; Seedorff et al., 2005; Rusk et al., 2008b; Seo et
al., 2012). A quantitative physical-chemical interpretation of
this distribution pattern is not obvious. Seo et al. (2012) sug-
gested that small differences in redox potential and acid/base
balance of the magmatic source might lead to the temporal
and spatial separation of Mo from Cu in porphyry Cu-Au de-
posits such as Bingham Canyon (Porter et al., 2012). How-
ever, the available thermodynamic data on Mo species (see
above), coupled with a realistic range of redox and acidity pa-
rameters for porphyry systems and associated magmatic
rocks, underestimate by many orders of magnitude (e.g., Fig.
19a, b) the Mo concentrations measured in natural fluid in-
clusions (100s ppm; Figs. 5, 7, 8). Either variations in source-
magma chemistry, fluid-magma interaction, and metal and S
contents are much larger than those inferred from available
geologic observations and analyses, or as yet unknown Mo-
bearing species control the transport of this metal, both in liq-
uid and vapor phases. The latter issue is expected to be re-
solved by future experimental work.
Fluid-rock interaction: The fourth major process accompa-
nying the evolution of a magmatic-hydrothermal fluid is its in-
teraction with surrounding rocks, leading to changes of pH,
redox state, and sulfide content, and thus mineral alteration
and metal precipitation. In porphyry and related settings,
fluid-rock interaction is expressed as alteration zonation cen-
tered on the fluid source and propagating into the surround-
ing rocks (Figs. 1, 2). As highlighted above, the stronger the
neutralizing capacity of the rock, the more efficient will be
the metal precipitation. A particularly good example is pro-
vided by the skarn environment with its commonly observed
metal zonation from proximal Cu ± Au to distal Zn-Pb zones,
resulting from a combination of temperature decrease and
neutralization of the fluid by the carbonate wall rocks. Car-
bonate sediment-hosted Au deposits may form in the distal
portions of porphyry systems (e.g., the Bingham Canyon dis-
trict; Cunningham et al., 2004; Fig. 1), likely due to rock de-
carbonitization and the resulting pH increase.
The redox state of the fluid may also change during alter-
ation processes. For example, intermediate-composition calc-
alkaline magmatic rocks typically contain a significant fraction
of iron as FeO, which tends to reduce SO2to H2S in the mag-
matic fluid during temperature decrease (Giggenbach, 1992;
Einaudi et al., 2003). Although the typical redox changes in
porphyry systems have a relatively modest effect on Fe, Cu,
and Au mineral solubility (e.g., an fO2change by an order of
magnitude will change FeS2, CuFeS2, and Au solubility by
only a factor of 2–3), the interaction with an Fe(II)-bearing
rock may act as a sink for hydrogen sulfide by precipitation of
pyrite ± pyrrhotite, and lower the sulfidation state of the fluid
when temperature decreases to <300°C (Einaudi et al.,
2003). This H2S consumption will shift reactions (6a-c) to the
right, leading to precipitation. This explains the common
presence of chalcopyrite in biotite sites in porphyry deposits,
and high porphyry Cu and Au grades in deposits associated
with mafic rocks, such as Oyu Tolgoi, Mongolia, and Resolu-
tion, Arizona (Sillitoe, 2010).
Fluid mixing: The fifth major phenomenon is mixing of two
fluids with distinct temperature, salinity, acidity, and/or redox
properties. This process may contribute to ore formation in
some near-surface crustal settings such as seafloor hydrother-
mal systems and Mississippi Valley-type deposits (Franklin et
al., 2005; Leach et al., 2005). However, in porphyry deposits
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there is little evidence for incursion of external waters into the
deep porphyry orebody, either before or during Cu and Au
precipitation. It is widely accepted, based on stable isotope
(e.g., Hedenquist et al., 1998; Watanabe and Hedenquist, 2001;
Harris and Golding, 2002) and fluid inclusion (e.g., Ulrich et
al., 2001; Pudack et al., 2009) studies that fluids that cause
potassic alteration cores and large phyllic alteration over-
prints have a dominantly magmatic fluid component (Heden-
quist et al., 1998; Seedorff and Einaudi, 2004; Rusk et al.,
2008b). As emphasized by Seedorff et al. (2008), field evi-
dence and hydrological modeling suggest that dense brines
such as saline formation waters or re-circulated magmatic hy-
persaline liquid (Fig. 2) may access the deep, central, and pe-
ripheral high-temperature parts of the hydrothermal systems,
causing deep sodic-calcic alteration during heating. However,
the influence of such potential fluid mixing on Cu and Au
precipitation in porphyry orebodies has not been evaluated.
In summary, cooling of a magmatic fluid during ascent and
depressurization, accompanied by water-rock interaction, is
likely to be the major cause of most metal deposition in por-
phyry systems. Fluid immiscibility is a major process that may
occur at different levels in magmatic-hydrothermal systems
and strongly affect sulfur, and precious and base-metal be-
havior. Large-scale mixing with meteoric and sedimentary-
basin fluids is a relatively uncommon phenomenon during
metal precipitation, and is not expected to be a major cause
of ore formation in the porphyry environment. These general
tendencies determine the metal zoning in magmatic-hydro-
thermal systems and may provide clues for prospecting, if the
major events in fluid evolution are identified from geologic as
well as fluid inclusion, mineralogic or stable isotope studies.
Conclusions
This paper compiles recent data on fluid compositions from
porphyry Cu (-Mo-Au) and associated deposits as recorded by
fluid inclusions, quantitatively analyzed by new microanalyti-
cal techniques such as LA-ICP-MS, PIXE, and SR-XRF. The
resulting data, together with the known properties of the
H2O-NaCl system, reveal four major genetic types of inclu-
sions in the porphyry environment that reflect the tempera-
ture and pressure evolution of a magmatic metal-bearing fluid:
(1) single-phase fluid of moderate salinity containing metals
and volatiles (CO2, H2S, SO2) exsolved from the magma, (2)
aqueous low-density vapor and (3) hypersaline high-density
liquid, both produced by unmixing of the single-phase fluid on
cooling and decompression when it crosses the two-phase
vapor-liquid boundary of the salt-water system in porphyry and
skarn environments, and (4) low-salinity aqueous fluids gen-
erated by condensation of the single-phase or vapor-type flu-
ids and their eventual mixing with meteoric waters in the epi-
thermal environment—the shallow parts of porphyry systems.
The metal contents of the single-phase magmatic fluid at
the base of the porphyry environment show patterns con-
trolled by metal abundances in crustal silicate magmas, cou-
pled with elevated fluid/melt metal partitioning coefficients;
this results in the single-phase fluid having the following gen-
eral composition: Fe (~10,000 ppm) > Cu (~4,000 ppm) ≈
Mn (~2,000 ppm) > Zn (~700 ppm) ≈Pb (~300 ppm) > Mo
(~80 ppm) > Ag (~30 ppm) > Au (~1 ppm), with typical vari-
ations within about an order of magnitude around these mean
values. For the metals of economic interest in porphyry Cu-
Au and related deposits (Cu, Au, Mo ± Zn, Pb), these con-
centrations are one to three orders of magnitude higher than
their average crustal abundances, resulting in a high potential
of magmatic-hydrothermal fluids to form porphyry and re-
lated deposits.
Metal concentrations in the aqueous vapor and hypersaline
liquid inclusions are controlled by vapor-liquid partitioning
coefficients, which depend on the vapor and liquid densities
and chemical metal speciation. Thus, Fe, Mn, Zn, Pb, and Ag,
which form chloride complexes in both phases, are generally
enriched in the saline chloride liquid, whereas Au, which
preferentially forms hydrogen sulfide complexes, is systemat-
ically enriched in the vapor phase. Metalloids, like As and Sb,
and Mo show, on average, similar concentrations in the liquid
and vapor phase, consistent with the volatile properties of
their oxyhydroxide species revealed by experiments in model
systems. Copper contents exhibit the largest variation relative
to the other metals, with vapor-liquid distribution coefficients
from 0.01 to 100. This is likely to be due in part to posten-
trapment modification of the primary single-phase and vapor-
rich fluid inclusions caused by diffusion of Cu through quartz
to the inclusion fluid from the evolving hydrothermal fluid, as
shown by recent laboratory measurements. These data, com-
bined with other recent experiments on vapor-liquid parti-
tioning, strongly suggest that the true vapor-liquid distribu-
tion of Cu during phase separation is intermediate between
that of base metals and metalloids, with Cu contents on aver-
age an order of magnitude higher in the hypersaline liquid
phase than in the vapor in porphyry systems.
Metal concentrations in the low-salinity aqueous fluids are
generally one to two orders of magnitude lower than those in
the high-temperature single-phase, vapor-rich, and hyper-
saline liquid inclusions, and decrease with decreasing tem-
perature. This reflects the decrease of sulfide mineral solu-
bility with fluid cooling and mixing with external waters in the
epithermal environment. The only exception among these
metals is Au, whose concentrations in low-salinity aqueous
fluids are similar to those in higher temperature porphyry flu-
ids (~1–10 ppm). This observation may be explained by the
selective transport of Au by the vapor phase, which condenses
into an H2S-rich aqueous solution on cooling and carries large
amounts of Au as S-bearing complexes.
The metal contents measured in natural fluid inclusions may
be interpreted in light of the present-day knowledge of the sol-
ubility of ore minerals and the speciation of metals in hydro-
thermal solutions under the conditions typical of porphyry
systems. The available thermodynamic data on the stability of
sulfide minerals and the main aqueous chloride, sulfide, and
hydroxide species of metals allow predictions of mineral solu-
bilities in the liquid and dense supercritical fluids as a function
of key parameters such as temperature, pressure, salinity (Cl
content), acidity (pH), S concentration, and redox potential.
When these parameters are constrained to the typical range of
porphyry systems, based on temperatures and pressures and
major fluid components recorded in fluid inclusions and al-
teration mineral patterns, calculations of mineral solubilities
generally reproduce well the Cu, Ag, Fe, Zn, and Pb concen-
trations measured in the different types of fluid inclusions. In
contrast, thermodynamic predictions for Au in epithermal
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fluids, and, more particularly, Mo in both epithermal and por-
phyry fluids underestimate the contents of these metals com-
pared to natural compositions. This situation points to gaps in
existing speciation models of both metals and S, likely due to
neglecting some important species.
This comparison of natural data and physical chemistry
provides useful constraints on the mechanisms and processes
controlling metal transport and deposition in the porphyry
and epithermal environments. Modeling shows that cooling
of a magmatic fluid, accompanied by water-rock interaction,
is likely to be the major cause of most metal deposition in por-
phyry systems, resulting in the formation of Cu ± Au ± Mo
ore shells, centered on the porphyry stock. Outward base-
metal zoning consists of Cu-Zn, Zn-Pb-Ag, Pb-Ag, and As-Sb-
Hg-Au zones, in order of increasing distance from the por-
phyry center; this matches well the observed metal zonation
in many porphyry districts around the world. Changes in S
speciation on cooling, caused by SO2disproportionation, are
likely to control the fractionation of Au from Cu during fluid
evolution on ascent. Efficient neutralization through water-
rock interaction is also a major driving force for Zn, Pb, and,
in part, Au and Ag deposition in more distal portions of por-
phyry systems. Fluid immiscibility is a major process that may
occur at different levels in magmatic-hydrothermal systems
and strongly affects the behavior of S and Au versus other
metals by contrasting fractionation between the resulting
vapor and liquid phases. Large-scale mixing with meteoric
and sedimentary-basin fluids is a relatively uncommon phe-
nomenon and is not expected to be a major cause of ore for-
mation in the porphyry environment.
Challenges
Despite significant progress in understanding the composi-
tion and properties of ore-forming fluids in porphyry systems,
much remains to be done. The necessary work spans analyti-
cal, experimental, and theoretical fields of research whose
major near-future challenges are briefly outlined below.
Analytical challenges
A number of analytical challenges regarding fluid inclu-
sions, which are the only direct samples of ore-forming fluids,
remain to be addressed. Among the elements in ore fluids, S
is one of the most poorly understood and quantified compo-
nents. Because the S concentration and redox state of the
fluid phase commonly control the metal supply, mineraliza-
tion efficiency, and ore grade in porphyry and associated epi-
thermal systems, systematic S analyses of fluid inclusions are
needed. Although this is now analytically possible, only a few
studies have actually analyzed S contents in individual fluid
inclusions using LA-ICP-MS techniques (Guillong et al., 2008;
Seo et al., 2009, 2011, 2012; Catchpole et al., 2011, in review).
Such total S analyses should be coupled with in situ spectro-
scopic determination of the speciation of S, using in situ micro-
Raman spectroscopy (e.g., Giuliani et al., 2003), and potentially
X-ray absorption spectroscopy (e.g., Métrich et al., 2009).
Further in situ measurement of Cl/Br, 87Sr/86Sr and Pb-iso-
tope ratios via LA-ICP-MS analyses of individual fluid inclu-
sions can improve our understanding of component sources
in porphyry systems as well as the chronology of ore for-
mation (Pettke et al., 2010, 2011, 2012; Seo et al., 2011). An
interesting finding of the present study is the potential to use
Zn/Pb ratios in high-temperature fluids from porphyry sys-
tems for tracing magmatic processes and magma-host rock in-
teraction involved in ore fluid generation. A better apprecia-
tion of possible fluid-inclusion postentrapment modifications,
such as selective metal diffusion (e.g., Lerchbaumer and Au-
détat, 2012), is also essential for robust interpretation of ore
fluid compositions. Many elements may be powerful geo-
chemical tracers, such as REE, but are not yet routinely ana-
lyzed in fluid inclusions, even if they are present at concen-
trations easily detectable by in situ techniques such as
LA-ICP-MS.
In contrast to porphyry-style deposits, for which a large
fluid-composition data set is available, the information on
ore-forming fluid compositions in low pressure and tempera-
ture environments dominated by aqueous-type fluids, such as
epithermal and Carlin-type Au deposits, is still fragmentary.
In such settings, a recently developed method, combining
near-infrared microscopy with LA-ICP-MS (Kouzmanov et
al., 2010), allows direct analyses of the actual metal-precipi-
tating fluids in inclusions hosted by opaque ore minerals, such
as enargite, wolframite, stibnite, sphalerite, tetrahedrite, and
pyrite. This opens up new potential for fluid inclusion re-
search in ore deposits, enabling direct determination of PTX
characteristics of the fluids that precipitated ore minerals, in
addition to information provided by the commonly used opti-
cally transparent gangue minerals; this will allow verification
of the broadly accepted assumption that gangue and associ-
ated ore minerals are cogenetic. For example, Simmons et al.
(1988) reported microthermomic data of sphalerite-, pyrar-
gyrite-, quartz-, and calcite-hosted fluid inclusions from the
Santo Niño intermediate-sulfidation epithermal vein at Fres-
nillo, Mexico, and demonstrated that ore minerals in this sys-
tem precipitated from chemically distinct fluid compared to
those that precipitated the gangue minerals (“brine fluids”
with salinity of 8.5–12 wt % NaCl equiv vs. dilute fluids with
salinity of ~2 wt % NaCl equiv, respectively), suggesting
episodicity of ore-forming pulses in the hydrothermal system.
Experimental challenges
The novel analytical directions outlined above should be
coupled with speciation and solubility experiments in geolog-
ically relevant model systems under controlled laboratory
conditions that nature does not offer to geologists. One of the
major remaining gaps in this field is S speciation in high-tem-
perature fluids (aqueous and silicate melts). The recent dis-
covery of a new polysulfide sulfur form in S-rich fluids, the
trisulfur ion S3–, which is stable in aqueous fluids over a wide
temperature and pressure range (Pokrovski and Dubrovinsky,
2011; Pokrovski et al., 2011; Jacquemet et al., 2012; Pokrovski
and Dubessy, 2012), might affect our interpretation of S
transport in porphyry systems, its isotopic fractionation, and S
control on metal mobility. In situ spectroscopy approaches
(Raman, XAS) are necessary to better constrain the stability
field of S3–and other intermediate S forms (e.g., SO2) and
quantify their effect on Au, Cu, and Mo mineral solubility and
metal transport via direct complexing.
Another essential experimental need is to improve our knowl-
edge of the speciation and solubility of certain porphyry-
related metals, such as Mo, for which large discrepancies
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persist. Better knowledge of aqueous speciation and mode of
occurrence in host sulfide phases of trace elements, such as
Pt, Bi, Se, and Te that commonly accompany the major ore
metals, is also required. Another experimental challenge will
be to better understand the effect of CO2, a major volatile in
magmatic-hydrothermal systems, on metal transport. Recent
studies (e.g., Pokrovski et al., 2008a; Hanley and Gladney,
2011) point to enhanced transport of Cu, Au, Pd, and Ni by
such CO2-rich fluids, but there is no sound physical-chemical
interpretation of this potentially important phenomenon,
since experimental data on metal sulfide solubility in CO2-
rich fluids are lacking. Finally, a recent direction in hydro-
thermal research related to porphyry deposits is the use of
nontraditional stable isotopes of metals (Cu, Fe, Mo) in an at-
tempt to trace metal and fluid sources and evolution (e.g.,
Graham et al., 2007; Hannah et al., 2007; Mathur et al., 2009,
2010). However, interpretation of these new analytical data
requires knowledge of equilibrium and kinetic isotope frac-
tionation factors among different minerals and between min-
erals and fluids, which can only be acquired via experimental
measurements. For example, such data may provide better
constraints on timing and conditions of iron sulfide mineral
formation under hydrothermal conditions (e.g., Saunier et al.,
2011, and references therein).
Theoretical challenges
A major challenge in ore-deposit research continues to be
interpretation of pertinent experimental data for mineral sol-
ubility and metal speciation in the framework of physical-
chemical equations of state and development of theoretical
approaches enabling predictions over a wide range of condi-
tions relevant to porphyry deposits, from the single-phase
fluid to hypersaline liquid or low-density vapor phase. These
equations should be integrated in user-friendly databases and
computer codes (e.g., Oelkers et al., 2009). These data, cou-
pled with physical hydrology models based on heat and fluid
flow plus rock permeability, will allow integrated reactive
transport models of fluid paths and three-dimensional ore
distribution (Driesner and Geiger, 2007; Ingebritsen et al.,
2010; Ingebritsen and Appold, 2012), which can contribute to
better exploration and extraction strategies.
Acknowledgments
This work was supported by the Swiss National Science
Foundation (grant 20021-127123 to K.K.) and l’Agence Na-
tionale de la Recherche (grant SOUMET-ANR 2011 Blanc
SIMI 5-6/009-01 to G.S.P). We thank J.W. Hedenquist for
inviting us to write this contribution, his patience while wait-
ing for both initial and revised manuscript, and his invaluable
comments and suggestions. R.H. Sillitoe is acknowledged for
permission to use one of his published figures and for his de-
tailed comments on the manuscript, T. Driesner for sharing
numerical data on the NaCl-H2O system, and J.P. Richards
and B. Rusk for thoughtful reviews that greatly improved the
clarity of the paper.
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