copper-gold ore from west papua, indonesia

www.elsevier.com/locate/oregeorev

Ore Geology Reviews 2

A Re–Os isotope study of sedimentary rocks and copper–gold ores

from the Ertsberg District, West Papua, Indonesia

Ryan Mathura,b,T, Spencer Titleya, Joaquin Ruiza, Stacie Gibbinsa, Kurt Friehauf c

aDepartment of Geosciences, University of Arizona, Tucson, AZ 85721, USAbDepartment of Geology, Juniata College, Huntingdon, PA, 16652, USA

cDepartment of Physical Sciences, Kutztown University, Kutztown, PA 19530, USA

Received 1 November 2003; accepted 21 July 2004

Available online 17 March 2005

Abstract

The ores of the Ertsberg district consist of both porphyry stockwork and contact controlled mineralization related to the

Grasberg and Ertsberg intrusion centers. High-grade copper mineralization with gold occurs in skarns on the periphery of each

of the intrusion centers. The periphery mineralization includes the Kucing Liar skarn-related ores, the massive sulfide lenses on

the borders of the Grasberg Intrusive Complex, and the giant skarn bodies of the Deep and Intermediate Ore Zones, together

with the ores of the Dom complex on the margin of the Ertsberg diorite. The Ertsberg orebody, the basis of discovery of the

district, is a copper–gold, roof-pendant of sedimentary strata in the diorite. In order to clarify genetic and geochronologic links

between the peripheral sediment-hosted ore bodies and the intrusion-hosted ore bodies, Re–Os isotopes of the ores and

subjacent Precambrian and Phanerozoic crust were analyzed. Re–Os geochronology of molybdenites was used to resolve the

age relationships of the ore bodies. The Grasberg and Kucing Liar molybdenites have older molybdenite mineralization ages of

2.88F0.02 Ma, and 3.01F0.02 Ma, respectively, whereas the Ertsberg molybdenite has a younger age of 2.54F0.02 Ma.

These data agree with Ar chronologies of the alteration associated with mineralization (Pollard and Taylor, 2000 [Pollard, P.J.,

Taylor, R., 2000. Geochronology of intrusive rocks and Cu–Au mineralization in the Ertsberg District. In: Proceedings of

Freeport-Institut Teknologi Bandung (ITB) Geological Symposium, Bandung, Java, pp. 17–19.]), and also indicate that the

Grasberg and Kucing Liar molybdenites are closely similar in age, and older than the Ertsberg Intrusive System.

Re–Os data from pyrite, chalcopyrite, magnetite, gold, and the surrounding sedimentary rocks from the district define a

mixing relationship between samples from the initial stockwork mineralization and peripheral ores of each intrusion center.

Sulfide and oxide minerals from primary stockwork mineralization are isotopically homogeneous and define trends on isochron

diagrams with distinct Os initial ratios, whereas sulfides and oxides taken from peripheral ores are isotopically heterogeneous

and define trends on mixing diagrams. One possible end member for the mixing is sedimentary rock surrounding the

porphyries. The measured Os ratios of the sedimentary rocks range from 0.52 to 2.21, and overlap the Os initial ratios of the

0169-1368/$ - s

doi:10.1016/j.or

T Correspondi

3687.

E-mail addr

6 (2005) 207–226

ee front matter D 2005 Elsevier B.V. All rights reserved.

egeorev.2004.07.001

ng author. Department of Geology, Juniata College, Huntingdon, PA 16652, USA. Tel.: +1 814 641 3725; fax: +1 814 641

ess: [email protected] (R. Mathur).

R. Mathur et al. / Ore Geology Reviews 26 (2005) 207–226208

sulfides and oxides sampled from both stockwork and contact mineralization. The data suggest a model in which the continental

crust supplied some of the Os (and by inference other metals) during magma genesis in the lower crust and the remainder came

from sedimentary rocks near the intrusion centers.

D 2005 Elsevier B.V. All rights reserved.

Keywords: Re–Os; Porphyry copper deposit; Gold; Ertsberg

1. Introduction

The origin of gold in various types of epigenetic

mineral deposits remains enigmatic; consequently,

their origin has been a major question in economic

geology and in mass balance considerations con-

cerning the role of the crust and mantle as metal

sources in ore genesis. Two possible sources have

been suggested for metals in most ore deposits.

The most commonly suggested possibility is that

metals are derived directly from the magma.

Possible sources for metals in magmas include an

enriched mantle wedge, the subducted slab, and

assimilation of continental crust (Burnham, 1959;

Krauskopf, 1967; Noble, 1970; Sillitoe, 1972;

Zartman, 1974; Titley, 1991; Goldfarb et al.,

2001). In the simplest case, such as porphyry-

related deposits, the metals are thought to be

concentrated in a fluid exsolved from a cooling

magma and deposited in metal-rich minerals. A

second possible source for metals is wall rocks

surrounding the magma and ore deposit. In this

case, as the intrusion cools, exsolved fluid leaches

metals from the surrounding crust. Few studies

have provided evidence for the source of Au and

other metals in ores (McInnes et al., 1999; Mathur

et al., 2000; Kesler et al., 2002; Kirk et al., 2002).

In this study, we consider both the magma and the

surrounding crust as a source for metals by use of

Re and Os isotopic compositions of sulfide ore

minerals and wallrocks in the Ertsberg district.

Mathur et al. (2000) presented the first Re–Os

evidence demonstrating that both sources might be

important in the Ertsberg district. This study examined

two distinctly different kinds of mineralization asso-

ciated with the porphyry stock, typical primary

stockwork porphyry copper mineralization and mas-

sive sulfide ores that border the deposit. The Os

isotopic composition of the sulfide minerals suggested

two distinct crustal sources of Cu–Au for the two

types of ore:

1. Os in stockwork mineralization, which is isotopi-

cally homogeneous, was interpreted to come from

magmas generated from both mantle and crust and

mixed at depth.

2. Os in massive sulfide mineralization, which is

isotopically complex and heterogeneous, was

interpreted to have been scavenged from adjacent

wall rocks by circulating hydrothermal fluids.

The results and ideas presented in this earlier study

have been tested further here by examination of

different parts of the ore-forming system and analyses

of samples from other parts of the Ertsberg district.

Our new results reveal clear isotopic signatures typical

of a crustal source in ore minerals of the district.

Consequently, we propose that consideration be given

to the continental crust as a source for Os in this and

other ore systems.

1.1. Rationale and objectives

Re–Os isotope analyses are carried out on ore

minerals and therefore provide data that are more

directly related to the source of ore metals than other

isotopic analyses carried out on alteration minerals

(Luck and Allegre, 1980; Shirey and Walker, 1998).187Os is derived from the decay of 187Re that has a

half-life of 41.6 billion years. Because Re is orders of

magnitude more incompatible than Os in the rocks

and minerals of the mantle (Walker et al., 1989,

Righter and Hauri, 1998, Burton et al., 2002, Brenan

et al., 2003), any crustal material derived from the

mantle has a greater Re/Os ratio than the mantle and

will evolve greater 187Os/188Os ratios than the mantle.

For the purposes of this study, the presence of187Os/188Os initial ratios significantly greater (N0.15)

Fig. 1. Location map of the Ertsberg area (after Rubin and

Kyle, 1997).

R. Mathur et al. / Ore Geology Reviews 26 (2005) 207–226 209

than the mantle (~0.13, Meisel et al., 2001) indicates a

crustal source for Os. The mantle from which the

magmas that are responsible for mineralization in the

Ertsberg district came may have a slightly greater187Os/188Os (perhaps 0.15) because the exact187Os/188Os of the mantle wedge in subduction zone

environments is most likely not constant. There is

some evidence that the mantle wedge in arc environ-

ments does have 187Os/188Os values greater than

~0.13. For instance, McInnes et al. (1999) and Widom

et al. (2003) suggested that metasomatized portions of

the mantle have measured 187Os/188Os of up to 0.17,

although Chesley et al. (2004) demonstrated through

the used of chemical mixing diagrams that the187Os/188Os value of metasomatized mantle is no

greater than 0.15.

Questions remain regarding the utility of Re and

Os as a geochemical tracer for the source of base

metals. Goldschmidt originally defined Re and Os as

chalcophile and siderophile elements, thus their

general behavior during magma generation and ascent

to the surface is similar to the behavior of other base

metals. Roy-Barman et al. (1998) confirmed this

relationship by finding that the sulfide blebs in

MORB contained more Re and Os than the surround-

ing matrix. Experimental studies by Sattari et al.

(2002), Peach and Mathez (1996), and Barnes et al.

(1985) further demonstrate that Re and Os readily

partition into immiscible sulfur-rich melts in mafic

magmas. No information is available on the partition-

ing of rhenium and osmium between magmas and

coexisting hydrothermal solutions, but Xiong and

Wood (2000, 2001) have demonstrated that Os can be

transported in hydrothermal solutions associated with

porphyry copper deposits. Their experiments were run

at a pH of 5 and temperatures between 400 and 500

8C. Their results suggest that Os is transported and/or

present as a chloride complex and that fluids

associated with porphyry copper deposits are capable

of transporting enough PGE to produce a mid-sized

PGE deposit, and they identified several deposits that

contained the predicted amount of PGE. However,

they recognized that Re and Os in mantle sulfides may

not be completely soluble in the magma thus explain-

ing some of the variations in PGE concentrations

measured in porphyry copper deposits. Xiong and

Wood (1999) also found that Re is highly soluble in

Cl-rich fluids and can be transported in solutions

similar to those associated with porphyry copper

deposits. They noted that the behavior of Re would

most likely change with the addition of sulfur causing

most of the Re and Os to be associated with the sulfur

rich fluid. Suzuki et al. (2000) noted that both

elements can be leached from molybdenite and they

suggested low temperature, saline fluids could also

transport Re and Os. These observations show that the

behavior of Re and Os in magmatic and hydrothermal

systems is sufficiently similar to that of base and

precious metals for it to be used as a tracer for these

elements in efforts to define metal sources.

Molybdenite contains orders of magnitude more

Re than the common sulfides and effectively no initial

radiogenic 187Os (Luck and Allegre, 1983). Therefore,

it can be used as a precise geochronometer (e.g.,

McCandless and Ruiz, 1993; Stein et al., 1998; Selby

et al., 2002).

2. The Ertsberg/Grasberg system

Ore deposits of the Ertsberg district (Figs. 1 and 2)

compose one of the largest and richest porphyry and

skarn copper–gold systems on earth (Van Nort et al.,

1991; Freeport McMoRan, 1997, 1998; Meinert et al.,

1997) and formed due to a series of complex tectonic

events. New Guinea resulted from the collision,

during Oligocene time, between the northward mov-

ing Australian continental plate and an island arc

within the southward moving Pacific-Indo Plate (e.g.,

Dewey and Bird, 1970; Van Nort et al., 1991;

MacDonald et al., 1995). Accretion of this island arc


created a suture zone that attached slices of ophiolite

and oceanic sedimentary units from the Pacific Plate

to the northeastern margin of the Australian continent

(Hamilton, 1979). Compressional stress continued and

rapid uplift ensued (Weiland and Cloos, 1996),

creating the Papuan Fold and Thrust Belt (Central

Mobile Fold and Thrust Belt), south of the suture. The

over-thickened crust contributed to the formation of

partial melts, probably through anatexis (MacDonald

et al., 1995; Housh and McMahon, 2000), which

resulted in substantial calc-alkaline to alkaline igneous

activity along the Lagaip Fault Zone during the

Pliocene (e.g., McMahon, 1994; Rubin and Kyle,

1997). Both the Grasberg Intrusive Center and the

Ertsberg Intrusive System are products of this activity.

The magmas associated with mineralization

intruded highly deformed Paleozoic and Mesozoic

sedimentary rocks. Housh and McMahon (2000)

used U–Pb and Sm–Nd geochemistry to determine

that Proterozoic to Archean crust were significant

contributors to the source of magmas related to

mineralization.

Styles of mineralization in the two centers contrast

in significant ways. The Grasberg Intrusive Center

comprises three distinct stages of intrusions, from

monzodioritic to monzonitic in composition. The

oldest and largest intrusive mass of the Grasberg

Intrusive Center is the Dalam Fragmental, a funnel-

shaped body in the sedimentary host rocks. The

Dalam Fragmental unit is a clast-supported breccia

unit with dioritic matrix and clasts. The center of the

Dalam Fragmental is cut by the Main Grasberg

Intrusion, a monzonite (MacDonald and Arnold,

1994). The Kali dike swarm is the youngest intrusive

event in the Grasberg Intrusive Center. Ore reserves

and resources in the Grasberg Intrusive Center are

approximately 2000 Mt @ 1% Cu and 1.2 g/t Au.

Both the porphyry and surrounding breccia masses

host stockwork mineralization. This mineralization is

characterized by chalcopyrite in an assemblage with a

high chalcopyrite: pyrite ratio (N5) with iron occur-

ring mostly in magnetite. The dominant silicate

alteration phase found in the system is orthoclase.

Adjacent to the Grasberg Intrusive Center is the

Kucing Liar ore body, located between the southern

contact of the Grasberg Intrusive Center and the

Idenberg No.1 fault, approximately 1000 to 1500 m

below the present surface. Kucing Liar is an Mg-skarn

hosted in the Cretaceous Kembelangan Ekmai lime-

stone, and limestones/dolomites of the Tertiary New

Guinea Group Carbonates, and has a resource and

reserve of 320 Mt @ 1.4% Cu and 1.4 g/t Au.

Although the Kucing Liar is not in direct contact with

the Grasberg Intrusive Center unit, its proximity

(~200 m) to the Grasberg Intrusive Center is a

compelling argument for a genetic relationship.

The Ertsberg Intrusive System, in contrast, is a mass

of holocrystalline pyroxene-diorite with wall rocks

containing forsterite–monticellite–diopside skarns

with copper and gold (Rubin and Kyle, 1998). The

original Ertsberg Orebody, which was rooted in the

Ertsberg Intrusive System, consists of the Ertsberg

diorite, an equigranular, phaneritic intrusion that

constitutes most of the Ertsberg Intrusive System, and

a series of 1108 trending porphyritic dikes of diorite to

monzodiorite composition that parallel its northeastern

boundary (Friehauf et al., 2000). Within the diorite

mass, stockwork fractures are mineralized mostly by

bornite and magnetite in magnetite–chlorite altered

rocks. The Ertsberg stockwork zone is proximal to the

series of porphyry dikes, and has reserves and

resources of 100Mt@ 1%Cu and 1 g/t Au. Proximally

associated with the Ertsberg Intrusive System are calcic

and magnesium skarns, occurring as either roof

pendants or at the wall rock-intrusion contact. Exam-

ples of these skarns are the Gunung Bijih, Dom, West

Hanging Valley, and massive skarns along its north-

eastern contact (Fig. 2). The Dom is located on the

southern periphery of the Ertsberg Intrusive System.

The Dom ore body is a monticellite–forsterite–garnet

skarn, with retrograde alteration of specular hematite–

calcite–anhydrite–chalcopyrite. Dom is a 31 Mt

resource and reserve with 1.67% Cu and 0.47g/t Au

(Freeport Mining Report, 1998).

2.1. Mineralogical setting of Au and Cu

In the Grasberg Complex, copper mineralogy is

dominated by chalcopyrite whereas in the Ertsberg

Complex, copper is mostly in bornite. In the district,

gold is most frequently observed as inclusions in or on

the rims of chalcopyrite, bornite, and to a lesser extent

pyrite (Rubin and Kyle, 1997). Gold occurs with

bornite and chalcopyrite in the Ertsberg skarns. In the

Grasberg ore body, some Au occurs in veins and

fillings. Our petrographic observations of the samples

Fig. 2. Geologic map of the Ertsberg area. Numbers on the map indicate sample locations. Dark black line represents location where the drill

core samples for the study by Mathur et al. (2000) were taken.


analyzed in this study confirm that most of the Au is

included in or associated with sulfide phases. In order

to further understand the Os signature in gold, we

analyzed a pure gold separate. The gold sample

consisted of very fine-grained fragments that were

separated from fine-grained copper rich ores by

gravitational and centrifugal methods.

3. Sampling and analytical techniques

All ore samples were taken from drill core or hand

specimens collected underground and in the active pit.

Fig. 2 and Tables 1 and 2 provide sample location and

mineral/rock descriptions. There are both high and

low concentrations of Re and Os in the mineral suites

analyzed.

Molybdenite is not a common phase in this district

and its relative scarcity limited this study to only three

samples. The ages obtained from these molybdenite

samples will be compared with crystallization and

alteration ages taken from the literature to further

understand the timing of mineralization and alteration.

A debate surrounds ways to determine whether the

Re–Os isotope system in molybdenite has been altered

since it was deposited. This is an important point

when looking at complex hydrothermal systems (such

as porphyry copper deposits) where multiple miner-

alization and alteration events overprint one another.

McCandless et al. (1993) suggested several ways to

detect alteration of the Re–Os system in molybdenite.

McCandless et al. (1993) also argued that samples

with Re rich clay overgrowths produced geologically

unreasonable ages. Suzuki et al. (2000) investigated

the suggestions of McCandless et al. (1993) by

conducting laboratory experiments using low temper-

ature, saline fluids to alter molybdenites. Their results

did not indicate that changes in crystallography

accompanied the alteration of the Re–Os system in

molybdenite. Therefore, they strongly suggested that

Table 1

Description of analyzed ore and sedimentary rocks samples, from a suite of 25, collected along the GBMA Road, West Papua, Indonesia

Sample names Description

MGI Grasberg cpy Main Grasberg Intrusion cpy: Irregular 1–2 cm wide chalcopyrite lens within quartz vein.

Host rock is quartz–biotite-altered Main Grasberg Intrusive rock.

Erts cpy 1 Underground sample of cpy–py–mo mineralization from a quartz vein in the Ertsberg Diorite.

Vein selvage is principally quartz–sericite and wall rock is K-altered Diorite.

Erts cpy 2 Ore sample (10 cm�10 cm) of high-grade skarn ore from the original Ertsberg

orebody-provided by Frank Nelson. The sample is that of a magnetite–chalcopyrite

pseudo-breccia or an original mass of replaced magnetite. Mineralization associated with

marginal bands of forsterite and magnetite.

Erts cpy 3 Sample of mineralization from the Ertsberg orebody-provided by Frank Nelson. The sample

represents skarn associated chalcopyrite blebs in a mass of magnetite. The host was within the

sedimentary strata of the Kembalagan Group.

Erts cpy 4 Underground sample of quartz–vein mass of chalcopyrite and bornite from the stockwork zone

of the Ertsberg Diorite Wallrock alteration of the diorite appears feldspar-stable.

KL 36-7 332 Massive magnetite replacement of probable carbonate beds in Tertiary strata bordering lenses

of serpentinized carbonate and clay-altered sandstone. NQ Drill core.

KL 36-7 302 Chalcopyrite and pyrite (replacement) in magnetite–serpentine-altered Tertiary strata. NQ Drill core

KL 36-7 300 Mixed lenses or veins of pyrite and chalcopyrite in massive magnetite rock within serpentine-altered

sedimentary strata, below KL36-7 300 NQ Drill core.

DOM Massive sulfide replacement of tertiary clastic in contact with magnetite lens. Alternating layers

of mixed pyrite and chalcopyrite.

GBMA-1 Kariem Formation, A Member (Proterozoic–Cambrian). Thinly-laminated grey to black mudstone

(Phyllite) ~20 m above basal contact with Awatagon Formation.

GBMA-7 Kariem Formation, B Member. (Proterozoic–Cambrian). Compact to thinly-laminated black

mudstone from 20 m thick layer between fine-grained sandstone units. Near center of mapped

unit, ~1000 m above base.

GBMA-10 Tuaba Formation. Possibly Ordovician, mapped by Quarles van Ufford as Proterozoic–Cambrian.

Sample is medium-grained cross-bedded sandstone from lower third of section.

GBMA-12 Modio Formation. (Devonian–Silurian). Sample is from Quarles van Ufford’s A member, a black weathering,

white, algal dolostone. Collected at Tunnel entrance.

GBMA-20 Tipuma Formation. (Triassic–Jurassic). Sample is massive red, green-mottled siltstone, collected

from ~200 m below the top of the 2400 m thick formation.

GBMA-21 Kopai Formation (Basal Formation of the Kembalangen Group) Cretaceous to Jurassic age. Sample

is weakly calcareous, black mudstone.

GBMA-22 Kopai Formation. Sample is black mudstone to shale. Collected ~100 m up-section from GBMA-22.

GBMA-23 Kopai Formation. Sample is calcareous black shale 1000 m above GBMA-22, 23.

Analytical data are shown in Tables 2 and 3 and locations in Fig. 4. Nomenclature and ages of the sedimentary strata are extracted from and

adapted from Quarles van Ufford (1996). cpy=chalcopyrite.


repeat analyses of molybdenite samples are necessary

to indicate that samples have not experienced alter-

ation of the Re–Os system.

Stein et al. (2001, 2003) and others pointed out that

Re and Os can be decoupled and indicate that all

molybdenite samples that are ground to become

homogenized produce the most geologically reason-

able ages. They suggest multiple analyses of the

sample to ensure reliable age determinations. Further

discussion of this topic can be found in McCandless et

al. (1993), Stein et al. (1998, 2001), Xiong and Wood

(1999), Suzuki et al. (2000), Selby and Creaser

(2001), and Barra et al. (2003).

Rock and ore samples for this study were

wrapped in paper, crushed, and handpicked to

obtain a pure sample of molybdenite. Pure molyb-

denite samples were powdered for analysis. Microp-

robe analyses of the samples did not reveal any Re

rich clay overgrowths, and the samples have the 2H

crystal structure. Replicate samples were run for the

Kucing Liar sample to demonstrate reproducibility

of the technique and homogeneity of the sample.

Table 2

Sample descriptions and Re–Os data

Sample name Location Phase Re (ppt) Os (ppt) 187Re/188Os 187Os/188Os 187Os/188Osi Au (ppb) 187Os/188Osi age

MGI Grasberg

cpy

Fig. 1 #1 cpy 74 60 6.64F1 0.872F0.008 0.87

Grasberg Au Composite

Au sample

Au 578 873 3.65F0.13 1.237F0.003 1.23

Erts cpy 1 Fig. 2 #2 cpy 2206 4 7955F1500 0.68F0.15 0.26F0.13

Erts 2 mg+cpy Fig. 2 #3 mg 3384 6 2781F255 0.48F0.03 0.36

Erts 2 mg+cpy Fig. 2 #3 cpy 11,308 5 10,893F950 0.66F0.04 0.22

Erts 3 cpy+mg-2 Fig. 2 #3 mg 1516 8 945F71 0.41F0.02 0.37

Erts 3 cpy+mg-2 Fig. 2 #3 cpy 1038 8 676F51 0.46F0.02 0.44

Erts 4 cpy-1 Fig. 2 #3 cpy 11,185 9 7662F590 0.69F0.04 0.26F0.13

Erts 4 cpy-1 Fig. 2 #3 cpy 8802 8 5492F412 0.56F0.03 0.26F0.13

KL 36-7 332 Fig. 2 #4 mg 1657 33 254F5 0.59F0.01 0.58F0.01

KL 36-7 302 Fig. 2 #4 cpy+py 16,905 183 492F2 0.945F0.005 0.922F0.005

KL 36-7 300 Fig. 2 #4 cpy+py 18,011 65 1474F15 0.88F0.01 0.81F0.01

KL 36-7 332 Fig. 2 #4 cpy 2119 40 275F5 0.71F0.01 0.77F0.01

KL 36-7 332 Fig. 2 #4 mg 2619 51 264F4 0.59F0.01 0.58F0.01

DOM Fig. 2 #5 mg 28,167 341 424.4F0.9 0.627F0.002 0.606F0.002

BS Karim-1 Fig. 4 mdst 20 18 7.2F1 1.56F0.1 1.63 5

BS Karim-7 Fig. 4 mdst 7 1.44F0.21 58

BS Kem-22 Fig. 4 bs 173 263 3.38F0.1 0.528F0.001 5

BS Kem-22-2 Fig. 4 bs 201 0.532F0.002 5

BS Kem-23-2 Fig. 4 bs 468 0.831F0.001

BS Kem-23-1 Fig. 4 bs 399 0.804F0.002

Arkose Tri 20-1 Fig. 4 ark 10 2.21F0.18 5

Dev LS 12 Fig. 4 ls 5 3.79F0.71

BS 20-1 Fig. 4 bs 30 1.58F0.04 12

Error treatment is discussed in the article. Gold analyses were completed by Skyline Labs, Tucson AZ. Abbreviations: cpy=chalcopyrite,

mg=magnetite, py=pyrite, mdst=mudstone, bs=black shale, ark=arkose, ls=limestone, mly=molybdenite. Column labeled 187Os/188Osi=Os

initial ratio calculated from isochron plots, 187Os/188Osi age=Os initial ratio calculated for the Ertsberg skarn ores using the molybdenite age of

2.54 Ma.


We used the carius tube method (Shirey andWalker,

1995) for sample digestion, and distillation for extrac-

tion of Re and Os from all ores and sedimentary rocks

(Frei et al., 1998; Mathur, 2001). Concentrations were

determined by isotope dilution, and we used two non-

3.63.43.23.02.82.62.42.2

GrasberKucing Liar

Age

(M

a)

Fig. 3. Comparison of KAr, 40Ar39Ar, and Re–Os geochronologic informati

5 =Average age of 40Ar–39Ar analyses from Pollard and Taylor (2001); x

mixed spikes, 185Re enriched spike (161.58 ppm) and190Os enriched spike (99.84 ppb) for molybdenite

separates and 185Re enriched spike (6.72 ppb) and190Os enriched spike (1.11 ppb) for lower concen-

tration samples. Samples were measured on a Negative

g Ertsberg

on. o =Average age of K–Ar analyses from McDowell et al. (1996);

=molybdenite ages from this contribution.

0 5

kilometers

2Km

4

pCkt

TnTnTnTnTn

A A'

A

A'

Rock Types:

Ds Pa JtiaKk

PintpCka pCkb

pCka- Kariem Fm. A Member

pCkb- Kariem Fm. B Member

pCt- Tuaba Fm.

Ds- Modio Fm.

Pa- Aiduna Fm.

Jtia- Tipuma Fm. Kk- Kopia Fm. Pint- Grasberg Igneous Intr.

Tn- Tertiary Ls.

137° 00' E 137° 02' E

137° 04' E 137° 06' E 137° 08' E 137° 10' E

137° 04' E

4° 04' S

4° 10' S

4° 12' S

4° 08' S

4° 10' S

4° 12' S

4° 14' S

4° 16' S

Kopai Fm. (Jur.-Cret.) Tipuma Fm. (Tr.Jur.)Aiduna Fm. (Perm)Modio Fm, B member (Sil.-Dev.)Modio Fm, A member(Sil.-Dev.)Tuaba Fm.(Precamb.-early Palazoic)Kariem Fm, B member(Precamb.-early Palazoic)Kariem Fm, A member(Precamb.-early Palazoic)

KJkoJTtPaDSmb

DSma

pCt

pCkb

pCka

Kembalangan (J-K)and New GuineaLimestone (Tert.)Groups, Undivided

Enlarged area

GBMA 23

GBMA 22

GBMA 21

GBMA 20

GBMA 7

GBMA 1

GBMA 10

GBMA 12

35

KJko

JTt

JTt

Pa

DSmb

DSmapCt

pCkb

pCka

Fig. 4. Sketch map showing generalized geologic section and location of sedimentary rocks that were collected. Enlarged area of the map is

shown in detail in Fig. 2.



Thermal Ionization Mass Spectrometer, using loading

and instrument procedures that are described in Creaser

et al. (1991).

Molybdenite ages are calculated by assuming no

initial 187Os (these are reported in Table 3; Fig. 3),

similar to McCandless and Ruiz (1993). Fig. 3

summarizes the different types of geochronologic

information taken from all the deposits in the district.

The plot compares molybdenite ages to 40Ar/39Ar and

K–Ar ages from silicate alteration minerals from the

respective deposits. The decay constant we used for187Re is 1.666�10�11 yr�1 F1% (Smoliar et al.,

1996). Errors are calculated based on the calibration

of the spike (0.22–0.4%), and the uncertainty of the

decay constant of Re. Replicate analyses indicate an

error on analysis of F0.5% for each element.

We analyzed materials with lower Re and Os

concentrations than the molybdenites, including sedi-

mentary rocks, pyrite, gold, magnetite, and chalcopyr-

ite. Sedimentary rocks were collected on the Gunung

BijihMine Access Road (GBMA; Fig. 4) a mining road

leading to the ore deposit. The road bisects the limb of a

syncline that exposes a relatively complete section of

the northward-dipping, late Precambrian through Cen-

ozoic sedimentary rocks. The down-dip projection of

this section lies beneath the mining district and was

crossed by magmas that formed the porphyry copper

deposits. We sampled shales, arkoses, limestones, and

mudstones across this thick succession of sedimentary

strata (Fig. 4). The pure Au sample was provided by

Freeport McMoRan Inc. (labeled Grasberg Au in Table

2) and is a composite metallurgical concentrate of many

ores from the Ertsberg district. According to esti-

mates based on proportions of ores taken from the

district, probably 95% of the Au in this concentrate

originated from the Grasberg Intrusive Center. The

other sulfide and oxide samples were collected

underground from drill core, or taken directly from

the operating pit.

Table 3

Molybdenite ages

Sample name Location 187Re (ppm) 187Os (pp

Grasberg Fig. 2 #6 1405.5 (4) 67.55 (3)

Kucing Liar Fig. 2 #4 98.91 (4) 4.981 (2)

Kucing Liar Fig. 2 #4 98.41 (4) 4.991 (2)

Ertsberg Fig. 2 #3 121.16 (6) 5.245 (2)

Sample preparation for all of the low-concentration

samples required crushing of the material. The

crushed sedimentary rocks were powdered and

directly loaded into the carius tubes. The sulfide

samples were handpicked after the initial crushing,

and powdered for analysis. Some of the sulfide

samples contained magnetite, which was separated

magnetically.

Internal reproducibility for the measurements of the

isotopic ratios is always better than F0.2% (2j).However this value is an underestimate of the error for

the whole procedure because the concentration of the

Os blank varies. Procedural chemical blanks during

this study varied from 1 to 2 pg for Os and 20 to 40 pg

for Re. Because the greatest source of error in the

analysis is the variation in the concentration of the Os

blank, errors for the magnetite, sulfide, and sedimen-

tary rock samples are calculated by varying the blank

concentration between 1 and 2 pg. Thus, the ratios

reported assume a concentration of the Os blank of 1.5

pg and the errors record the variation of the ratio with

the change in Os blank concentration. The 187Os/188Os

of the blank remained constant (0.175F0.008)

throughout this study.

4. Results

Concentrations of Re and Os for the molybdenites

vary between 156 and 2235 (ppm) and between 4 and

66 (ppb), respectively (Tables 2 and 3). The ages

calculated assuming no initial 187Os for the molyb-

denites sampled are: 2.88 MaF0.02 for the Grasberg,

3.01F0.02 Ma (and 3.03F0.02 Ma for a repeat

analysis) for the Kucing Liar, and 2.54F0.01 Ma for

the Ertsberg sample.

For the sedimentary rocks, the concentration of Os

varies from 5 to 468 ppt, and the measured 187Os/188Os

ratios range from 0.54 to 3.8. Skyline Actlab in Tucson,

b) Age Associated minerals

2.88F0.02 Quartz–sericite vein with cpy

3.01F0.02 Covellite–pyrite in ls host

3.03F0.02 Covellite–pyrite in limestone host

2.54F0.02 Quartz–sericite vein with cpy


AZ measured gold concentrations for the sedimentary

rocks. The Au values reported in Table 2 are averages

for 3 different measurements on each sample.

Samples from Ertsberg stockwork mineralization

have Re and Os concentrations and ratios similar to

those found in Grasberg stockwork mineralization.

The concentration of Os varies from 4 to 9 ppt and

Re from 1 to 11 ppb in the sulfides and oxides.

The 187Os/188Os measured ratios range from 0.41 to

0.68, and the 187Re/188Os measured ratios range

from 676 to 10893. Splits of two samples from the

stockwork mineralization of the Ertsberg (Erts-1

and Erts-3 and replicate) form a two sample, 3-

point isochron (MSWD=0.61) with an age of 3.3F1.2

Ma and Os initial value equal to 0.26F0.13 (Fig. 5).

If the samples from the skarn mineralization are

plotted along with the stockwork samples of the

Ertsberg, the isochron statistics yield an imprecise

age (MSWD=6.2) of 1.62F0.72 Ma, 187Os/188Os=

0.42F0.07. Because Erts-2 and Erts-3 are genet-

ically different and yield a less precise isochron, we

also solve for the 187Os/188Os initial ratio using the

molybdenite age (2.54 Ma; Table 2) for time (t) in

the age equation:

ð187Os=188OsÞm ¼ ð187Os=188OsÞI

þ ð187Re=188OsÞmekt � 1 ð1Þ

where (187Os/188Os)m=measured ratio, =(187Os/188O-

s)I=initial Os ratio, (187Re/188Os)m=measured ratio,

and k=decay constant of Re (1.666�10�11). Age

and initial 187Os/188Os ratios for the isochron

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0 1000 2000 3000 4000187Re/

187 O

s/18

8 Os

Age = 3.3 ±Initial 187Os/188O

MSWD =

Fig. 5. Isochron plot of the low concentration

calculations were calculated with the computer

program developed by Ludwig (2001).

It is important to note that we analyzed the

molybdenite and chalcopyrite (Erts-1) from the same

hand-sized sample in which both sulfide phases are

intergrown. There has been debate surrounding the

use of Os initial ratios from low concentration sulfide

minerals calculated by the isochron method. For

example, Stein et al. (2003) stated that bRe–Osanalysis of sulfides in contact or direct association

with molybdenite is highly inadvisable, and can lead

to ages that are too old and, in the case of Re–Os

isochrons, can provide initial 187Os/188Os ratios that

are too high, leading to errant geologic inter-

pretationsQ. It is relevant to note that the Erts-1

chalcopyrite has an Os initial ratio less than all of

the observed Os initial ratios calculated for the sulfide

minerals and sedimentary rocks in this data set. This

observation holds true regardless of how the Os initial

ratio is calculated; by the isochron method or by

substituting age information to derive Os initial ratios.

Therefore, for the samples analyzed in this study,

migration (diffusion) of either element after the

precipitation of these two phases and the calculated

Os initial ratios does not appear to have caused binitial187Os/188Os ratios that are too high. . .Q Perhaps a

plausible explanation for these results is that the

diffusion rate of Os is too slow to have predicted the

migration of Os atoms across these minerals interface,

therefore when considering that Os isotopic ratios can

be disturbed, a time frame for the diffusion should be

considered.

5000 6000 7000 8000 9000188Os

1.2 Ma

s =0.26 ± 0.13 0.61

samples from the Ertsberg stockwork.

A.)

Au ppm Cu %

Length of drill core (m)

1

2

3

100 200 300 400 500 700

AuCu

Os ppt

10

50

100

Os

1

6

3

187Os/188Os = 0.56

187Os/188Os initial > 0.56

B.)

1/Os (ppt)

187 O

s/18

8 Os

initi

al

0 0.01 0.02 0.03 0.04 0.05

0.5

1

1.5

0

Grasberg Stockwork

Grasberg Massive sulfide

C.)

0 2000 4000 6000 8000 10000 12000 140000

0.5

1.0

1.5

2.0

187 O

s/18

8 Os

Initial187Os/188Os = 0.56+/-0.02

Age= 2.9+/-0.3Ma

187Re/188Os

Fig. 6. (A) Isochron diagram of the stockwork ores taken from the Grasberg, isochron statistics calculated by a program developed by Clark, if

the data are reduced using Ludwig (2001), the age=2.8F0.5 Ma, MSWD=4.5, the initial 187Os/188Os=0.56F0.05. (B) Distribution of metals

along drill core segment (dark black line in Fig. 2), note that the Os concentration along with Cu, Au, and Os initial ratio increases in the

massive sulfide. (C) Mixing diagram with the stockwork mineralization (n) and massive sulfide (.) minerals of the Grasberg (use of symbols

remains constant through next three figures).



Concentrations of Re and Os in the contact ores

from the Kucing Liar and Dom are much greater than

the stockwork mineralization, and range from 2 to 28

ppb and 40 to 341 ppt, respectively. The 187Os/188Os

measured ratios range from 0.59 to 0.94 and the187Re/188Os measured ratios range from 254 to1474.

None of the data from the peripheral ore deposits

(Kucing Liar and Dom) lie on the isochrons devel-

oped for the Grasberg or Ertsberg stockwork miner-

alization. Instead, data from the Kucing Liar are

isotopically heterogeneous. The Os initial ratios

presented for these samples are calculated by using

Eq. (1). By assuming a mineralization age of 3Ma for

the Kucing Liar samples and 2.5Ma for the Dom

sample, the calculated Os initial ratios range from

0.58 to 0.92. The samples from the Kucing Liar lie on

the mixing trend between the Grasberg intrusion

sulfides and the massive sulfide mineralization

peripheral to the Grasberg ore deposit (Mathur et al.,

2000). Figs. 6 and 7 illustrate this relationship. The

Dom sample, spatially associated with the Ertsberg

mineralization, does not lie on this trend or the

errorchron plot of the Ertsberg stockwork samples.

The composite gold sample has 578 ppt Re and

873 Os, and has measured 187Os/188Os of 1.23 and187Re/188Os of 3.6. This datum point does not plot on

isochron diagrams. The calculated Os is 1.23 if a

mineralization age of 2.9Ma is assumed. The Os

initial ratio for this sample lies near the apex of the

187 O

s/18

8 Os

initi

al

0 0.01 0.02

0.5

1

1.5

0

*

Kucing Liar

Au concentrate

1/Os (

Fig. 7. Mixing diagram of samples from the Grasberg ore body, data from M

composite gold sample. Note the general trend exists and suggests a geneti

mixing trend demonstrated for the Grasberg peripheral

ores (Fig. 7).

5. Discussion

5.1. Geochronology of the district

In order to examine the relationship between the

Ertsberg and the Grasberg systems, we analyzed both

sulfides with low concentrations of Re–Os (pyrite,

chalcopyrite) and molybdenites with high Re concen-

trations. The two low concentration/conventional

isochron plots of stockwork mineralization from the

Ertsberg (isochron in Fig. 5; with an age of 3.3F1.2

Ma), and the Grasberg (isochron; 2.9F0.3 Ma;

Mathur et al., 2000) yield ages that are the same

within the error of the analysis.

In order to develop a more accurate and precise

chronology for the area, we analyzed molybdenite

samples from each of the deposits. Each of the

molybdenite samples from different parts of the

district yields a different age. We interpret the

molybdenite ages to represent mineralization ages.

Therefore, these molybdenite ages reveal that there

have been at least three distinct mineralization events

in the Ertsberg district.

Fig. 3 compares K–Ar, 40Ar/39Ar, and our new Re–

Os molybdenite ages for the district. The K–Ar and

0.03 0.04 0.05

Grasberg Stockwork

Massive Sulfide

ppt)

athur et al. (2000) and the present study. o=Kucing Liar, and *=thec link between the Kucing Liar ore body and the Grasberg ore body.


40Ar/39Ar ages come from two sources. McDowell et

al. (1996) illustrated that the K–Ar alteration and

intrusion ages for the Ertsberg are slightly younger

than those present in the Grasberg. Pollard and Taylor

(2000) continued exploring the geochronologic rela-

tionships of the area by examining the 40Ar/39Ar

systematics of biotite, muscovite, and phlogopite from

each of the alteration sequences in the Kucing Liar ore

body, Kali intrusion (Grasberg Intrusive Complex),

and the Ertsberg diorite. They also found that the

Grasberg and Kucing Liar alteration/cooling ages are

older than the Ertsberg.

The Re–Os molybdenite ages (Fig. 3) are in accord

with the K–Ar and Ar–Ar ages defined by Pollard and

Taylor (2000) and McDowell et al. (1996). The

Kucing Liar and Grasberg molybdenites are distinctly

older than the Ertsberg molybdenite (according to the

statistical analysis derived by Dalrymple and Lan-

phere (1969) errors of the molybdenite ages are small

enough to indicate different events). Further geologic

evidence that supports the notion that the Grasberg

Intrusive Center is older than the Ertsberg Intrusive

System comes from paragenetic crosscutting relation-

ships defined by the following studies (Katchan,

1982; Meinert et al., 1997; Predenergast et al., 2001).

5.2. Deposit scale geochronology

5.2.1. Re–Os evidence for links between the massive

sulfide, Kucing Liar, and the Grasberg stockwork

mineralizations

Mathur et al. (2000) examined two mineralization

events in the Grasberg. Re–Os results from sulfide

stockwork related to porphyry copper gold mineral-

ization in the Grasberg Intrusive Center were

sampled from different silicate alteration assemblages

and host rocks and plotted on an isochron with an

initial 187Os/188Os of 0.56F0.02 (Fig. 6A). The

initial 187Os/188Os of this isochron is highly radio-

genic compared to the present mantle 187Os/188Os of

0.1296 (Meisel et al., 2001). This indicates that the

source of Os and, by inference, the associated metals

have a significant crustal component. A younger

mineralization event, characterized by massive pyr-

ite, crosscuts the typical stockwork mineralization

and borders the intrusive complex. The samples do

not plot on the isochron developed for the stockwork

mineralization of the Grasberg, thus the Os initial

ratios calculated for these samples were determined

by substituting in a mineralization of 2.9 Ma. These

samples have evolved heterogeneous initial Os

isotopic ratios that are greater than the stockwork

mineralization (labeled N0.5 on Fig. 6B), ranging

from 0.61 to 1.23. The samples with the highest and

most radiogenic signatures (Os isotope ratios) also

have higher Au concentration than stockwork min-

eralization of the Grasberg system.

The mixing diagram in Fig. 6C illustrates a

relationship between massive sulfide and the stock-

work mineralization. The data suggest that the stock-

work mineralization event began as isotopically

homogeneous, and as the hydrothermal system

evolved, it became isotopically heterogeneous as the

fluids mixed with a highly radiogenic source that is

mirrored in the minerals of the massive sulfide

orebody. A reasonable end member for this mixing

trend is black shale, and evidence linking the ores to

sedimentary rocks is presented below.

In order to test the relationship between the

Kucing Liar skarn and the Grasberg stockwork

orebody mineralization, we analyzed five samples

from drill core that sampled skarn and stockwork.

Magnetite, chalcopyrite, and pyrite samples from this

skarn do not define a trend on an isochron diagram

with age significance. They plot on the mixing trend

developed along with samples from massive sulfide

and stockwork mineralization of the Grasberg ore-

body (Fig. 7). Included in the graph is the composite

gold separate from the Ertsberg district. The approx-

imate trend of the data suggests that there is a

relationship between these three ore bodies. The

addition of the Kucing Liar data further demonstrates

the isotopically heterogeneous nature of the fluids

that precipitated the peripheral Kucing Liar and the

massive sulfide ore bodies and that some Os was

acquired from the surrounding crust. The data

support a model in which the primary, isotopically

homogenous, copper–gold rich fluid had its source

presumably associated with the igneous intrusion and

while this intrusion cooled by convection; the

hydrothermal fluids leached metals from the sur-

rounding host sedimentary rocks and deposited them

in the mineralization center.

In the Ertsberg district, there is widespread

evidence of fluid and thermal activity extending for

at least 2 km beyond the intrusive centers. Gammons


and Williams-Jones (1997) proposed a mechanism in

which cool solutions in the periphery of such systems

could derive gold through leaching in an environment

of high H2S activity. We suggest that heating of these

fluids during the convective process would reduce

gold solubility and precipitate the metal in the

mineralization center.

5.2.2. Comparison of Os initial ratios of stockwork

and skarn minerals in the Ertsberg and Grasberg

systems

These two intrusion-centered ore bodies occur

within a 6 km radius of each other. The similarities

or differences among the Re–Os isotope systematics

seen within the ores can be used to interpret possible

genetic relationships among the ore stockwork type

mineralization present in each ore body and the

surrounding wall-rock mineralization. In other words,

the isotopic signatures present in the ores can be used

to link the complex, crosscutting mineralization

events present in this intensely fractured portion of

crust.

The Os initial ratios calculated for the stockwork

mineralization from these two intrusion centers are

different. As stated above, the Re–Os data from

stockwork mineralization from the Grasberg con-

strain an Os initial ratio of 0.54F0.02 (Fig. 6A). In

contrast, chalcopyrite and magnetite from the stock-

work mineralization of the Ertsberg form a 3 point

isochron that has an initial 187Os/188Os of 0.26F0.13

(MSWD=0.61; Fig. 5). The two analyses from skarn

sulfide mineralization taken from within the mine

also plot on the isochron diagram and yield an age

of 1.62F0.72 Ma (MSWD=6.3). Because these

skarn samples are paragenetically different from

the stockwork samples and they reduce the stat-

istical significance of the Ertsberg stockwork min-

eralization isochron plot, we also used the age

calculated by the molybdenite from the Ertsberg

(2.54 Ma) and solved for the Os initial ratio (Table

2). Both the isochron plot method and solution for

the Os initial ratios by substituting the molybdenite

ages indicate that the ranges of initial Os values for

the Ertsberg samples are different than those

calculated for the Grasberg stockwork samples.

Importantly, Os initial values calculated by both

methods constrain Os initial values that are greater

than the mantle. Nonetheless, the concentrations of

Re and Os for both of the Grasberg and Ertsberg

stockwork samples are roughly similar. The single

sample from the Dom (peripheral skarn of the

Ertsberg) does not plot on the isochron trends. This

sample has elevated Re and Os concentrations in

comparison to the stockwork mineralization from

both intrusions.

Figs. 7 and 8 are mixing diagrams with data from

the district. The Grasberg and Kucing Liar mixing

relationship lies to the left of the diagram on Fig.

8A. The distinctly different Os initial ratio of the

Ertsberg Intrusive System stockwork mineralization

does not plot on the mixing trend seen in the

Grasberg and Kucing Liar deposits. The diagram

demonstrates that there is no district scale genetic

correlation among the Os isotopic signatures for the

ores and could be indicating several possible

scenarios. For instance, the magmas responsible for

stockwork mineralization could be related to a

dparentT batholith at great depths (N5 km) and as

these dapotheosesT intruded, they assimilated differ-

ent amounts of crust or these magmas have no

relationship at depth. Most importantly, the Os data

indicate that the stockwork of the Grasberg and

Ertsberg ore bodies are relics of two unique hydro-

thermal systems that developed independently and

are not related to the same stock.

Interestingly, the Dom and Ertsberg skarn samples

can be related to the Ertsberg stockwork in a fashion

similar to that suggested for the relationship of the

massive sulfide and Kucing Liar samples, to those of

the Grasberg stockwork. The Dom sample has higher

concentrations of Os and more radiogenic Os initial

ratios, which are comparable to those seen in the

surrounding continental crust. Thus, the Os present in

the Dom skarn could also originate from the

surrounding crust via a process of crustal leaching

similar to that discussed above for the Kucing Liar

and massive sulfide of the Grasberg.

5.3. Genetic link to the sedimentary rocks and the ores

present throughout the Ertsberg district

Os evidence from the ores presented above

suggests that there are two distinct crustal sources

for Os. To develop more insight into where the crustal

metals could have originated and how much of the

metals were derived from sedimentary sources, we

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 0.05 0.1 0.15 0.2 0.25

1/Os (ppt)

187 O

s/18

8 Os

initi

al

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 0.05 0.1 0.15 0.2 0.25

1/Os (ppt)

187 O

s/18

8 Os

initi

al

A.)

B.)

Grasberg/ K

ucing Liar

Ertsberg/DOM

Stockwork Grasberg

Stockwork Ertsberg

Sedimentary Rocks Analyzed

Fig. 8. (A) Mixing diagram plot of the all the data from the sulfide ore samples. x=Kucing Liar and massive sulfides; .=Ertsberg skarns;

E=Dom. Dashed line is the mixing line among the massive sulfide, Kucing Liar, and the Grasberg stockwork, and the solid line is the mixing

line for the Ertsberg stockwork, skarns, and Dom. (B) The outlined area represents measured Os ratios and concentrations of the sedimentary

rocks analyzed in this study. The open squares in this figure are sedimentary rock analyses (some sedimentary rocks do not fit in the plotted area,

therefore the arrows indicate that there are higher Os ratios measured within the cross hatched area). Note the overlap of the crust field with the

peripheral ore bodies (e.g., Kucing Liar, massive sulfide, and Dom) and stockwork mineralization of the Grasberg.


analyzed the Os isotopic composition and concen-

tration of gold in selected sedimentary rocks. Figs. 4

and 8B illustrate the variation of Os isotope ratios and

concentrations present in the selected samples from

the stratigraphic section. We measured Os ratios and

concentrations to use for comparison on mixing

diagrams because the 187Re/188Os ratios for these

sediments are low (e.g., GBMA1, 22-1) and ore

formation occurred recently in the geologic past

(correction for 2 Ma would insignificantly shift the

measured ratios).

Interpretation of the mixing diagrams proposed as

evidence for crustal leaching in the Grasberg system

by Mathur et al. (2000) invoked shale as a possible

end member. This study presents Re–Os results from

Mesozoic shale units that the hydrothermal system

could have interacted. These rocks have higher

concentrations of Os (between 200 and 400 ppt) and


radiogenic ratios roughly similar to or slightly greater

(0.52 to 0.89) than the stockwork mineralization of

the Grasberg and Ertsberg ores (0.56 and 0.26,

respectively). In comparison, the limestone, arkose,

and mudstone have considerably less Os (5 to 25 ppt)

and radiogenic 187Os/188Os ratios greater (between 1.4

to 3.7) than the stockwork mineralization. These

differences in concentrations are in accord with

previous observations showing that, on the average,

black shales contain relatively larger concentrations of

Os and Re than do other sedimentary lithologies

(Ravizza and Turekian, 1992; Esser and Turekian,

1993; Horan et al., 1994; Singh et al., 1999). The187Os/188Os measured in the sedimentary rocks of this

study is reasonable because the measured 187Os/188Os

of the shale units is identical to the Os isotopic

signature of fluvial systems draining from the

mountains of Irian Jaya found by Martin et al. (2000).

The fundamental purpose of this study has been to

examine and if possible quantify the role of con-

tinental crust and igneous intrusions as sources of

some metals of the ores of the Ertsberg district. We

believe that the Re and Os data demonstrate a link

between the ores and the sedimentary rocks of the

surrounding crust. Of the several sedimentary rock

samples analyzed here, none provide the exact Os

characteristics for doneT stratigraphic unit-source to

account for the observed mixing trend. However, a

mixture of the Os concentrations and isotopic

compositions from these sedimentary sources could

easily account for the mixing trends present at the

district scale of the Ertsberg and Grasberg intrusive

complexes. Fig. 8B demonstrates this point by high-

lighting the concentrations and measured ratios of the

sedimentary rocks on the mixing diagram plot. Since

the hydrothermal aureole affects all of the surrounding

Cenozoic and Mesozoic strata, leaching of a specific

stratigraphic unit probably did not occur. Rather, the

hydrothermal system’s acquisition of metals included

a mixture of Os from all of the sedimentary units and

the resulting product of this process is illustrated in

the isotopic heterogeneity of the massive sulfide,

Kucing Liar, and the Dom.

These data provide an explanation for aspects of

metallization in peripheral skarns, but do not explain

the extent to which, nor the means by which, initial

magmas were enriched in copper and gold before the

mixing process took place in the upper crust. Conven-

tional views would propose that sources of possible

magma (and radiogenic) components of the igneous/

hydrothermal system evolve at depths where the

progenitors could be each, or combinations of, the

lower crust, the subducted slab, or metasomatized

mantle. The data and interpretations of magma and

possible metal sources interpreted here are consistent

with the model of crustal assimilation and fractional

crystallization proposed for Neogene magmatism in

New Guinea by Housh and McMahon (2000) and for

some porphyry related intrusions in North American

by Anthony and Titley (1988) and Lang and Titley

(1998). A two-end member geochemical mixing

calculation that assumes the average lower continental

crust of Australia (187Os/188Os=0.85, Os=50 ppt; Saal

et al., 1998) and a mantle (187Os/188Os=0.1296, Os=2

ppb; Meisel et al., 2001) indicates that about 40% of

the lower crust may have been assimilated to generate

an Os initial ratio of 0.56 present in the Grasberg

stockwork ores. If the Kariem Os datum from this

study is used, then the percentage of dKariem-likeTlower crust necessary to generate the Grasberg stock-

work Os (initial value of 0.56) reduces slightly to

30%. If the Ertsberg Os initial ratio of 0.26 is

considered, the amount of continental crust (either

from Saal et al. (1998) or the Kariem crust of this

study) is reduced to approximately 15 to 20%.

Although sample quality precluded the collection

of dunalteredT samples (sedimentary rocks near the

intrusion that did not display low grade hydrothermal

metamorphic mineralization) in the district, we under-

score the possibility of hydrothermal interaction with

strata of the Cretaceous and Tertiary sections that

compose the wall rock at the deposit level of the

Ertsberg and Grasberg systems. The geologic evi-

dence of widespread development of marble, a broad

(km-scale) aureole of weak metamorphism, and

scattered exposures of altered strata are indicators, at

mineralization levels, of the effects of intrusion and

wall rock interaction during the intrusion and miner-

alizing process.

Several studies have explored this concept. Brim-

hall (1979, 1980) has addressed deep hypogene

leaching of plutonic hosts and porphyries to develop

ore grade assemblages at Butte Montana. Norton

(1982) has modeled the nature of fluid flow around

cooling plutons of the North American craton and has

shown the nature and habits of source regions and


pathlines for fluids involved in the process. Kendrick

et al. (2001) have identified the provenance of ore

fluids in this same North American province; Gerlach

et al. (1975) and Norton (1979) report the results of

studies of chemical mass transfer between plutons and

wall rocks. In the studies of concern here, we see

many of the same physical properties of altered

fractures and intrusion and carbonate hosts present

in the Grasberg and Ertsberg intrusive systems. These

observations allow us to consider hydrothermal

leaching as a possible mechanism to explain the

chemical mixing relationships seen throughout the

deposits.

We have demonstrated that the continental crust

has a profound influence on the source of Os in the

ore minerals from the Erstberg district. Given that

the Os data from the selected units in the surround-

ing crust reveal a direct genetic relationship, the Os

signatures in the stockwork mineralization quite

likely represent the result of a mixing process that

involved igneous and hydrothermal interaction with

multiple crustal sources during the igneous and

hydrothermal processes. Further evidence from the

concentration of gold in the sedimentary rocks

adjacent to the hydrothermal system provides support

that there are sources of radiogenic elements and

gold within the crust that the mineralizing processes

interacted.

6. Conclusions

A combination of the molybdenite chronology of

the area, and the Os initial ratio data from the ores

points to a model in which two adjacent intrusions

and hydrothermal systems evolved independently in

the epicrustal environment. The highly radiogenic

and concentrated Os values from the surrounding

rocks demonstrate that the continental crust is a

likely source for Os, whether by leaching and/or

assimilation. The radiogenic initial Os initial values

from stockwork ores present in both systems indicate

that the metals originated from a crustal source. The

contribution of at least some Os (and by inference

other metals) from the continental crust was further

amplified during the cooling process, when the fluids

responsible for precipitating the periphery ores

apparently mixed with and acquired Os (and by

inference other metals) from the surrounding con-

tinental crust. The relevance of these observations is

that there are two distinct crustal sources present in

the ores, one related to lower crustal magmatic origin

and another found in the middle to upper crust of

these deposits that reside in the thick Australian

continental crust.

Acknowledgements

We wish to thank Freeport McMoRan, Cu and Au

Inc., and P.T. Freeport Indonesia for their support of

the geological studies, during the several field

seasons on which this report is based and for

permission to publish this work. Analytical work

was supported by the National Science Foundation

Grants EAR 9708361, and EAR 9628150, and an

instrumentation grant from the W. M. Keck Founda-

tion. We also thank Brian New for providing the

molybdenite sample from the Kucing Liar deposit.

Dave Potter and Steve Van Nort encouraged this

work in the district. Keith Parris and George

MacDonald sustained liaison. Chuck Brannon, Al

Edwards, Wahyu Sunyoto. Sugeng Widodo, Norris

Beluz, Lasito Soebari, Larry Segerstrom, together

with numerous Freeport geologists were instrumental

in facilitating field support and providing access to

pit and underground sample sites, and core. We

acknowledge with thanks the productive discussions

of precious metal geology with Imants Kavalieris

and Jay Pennington. Frank Nelson provided samples

of Ertsberg orebody mineralization. Paul Warren’s

help and knowledge of regional stratigraphy were

crucial to those aspects of the field study. Finally, we

would like to thank two anonymous reviewers and

Associate Editor Stephen Kesler for their insightful

comments to improve this presentation.

References

Anthony, E.Y., Titley, S.R., 1988. Progressive mixing of isotopic

reservoirs during magma genesis at the Sierrita porphyry copper

deposit, Arizona: inverse solutions. Geochimica et Cosmochi-

mica Acta 52, 2235–2249.

Barnes, S.-J., Naldrett, A., Gorden, M., 1985. The origin of the

fractionation of platinum group elements in terrestrial magmas.

Chemical Geology 53, 303–323.


Barra, F., Ruiz, J., Mathur, R., Titley, S., Schmitz, C., 2003. A Re–

Os study of sulfides from the Bagdad porphyry Cu–Mo deposit,

northern Arizona, USA. Mineralium Deposita 35, 585–596.

Brenan, J., McDonough, W., Daple, C., 2003. Experimental

constraints on the partitioning of rhenium and some platinum

group elements between olivine and silicate melts. Earth and

Planetary Science Letters 198, 135–150.

Brimhall, G.H., 1979. Lithologic determination of mass transfer

mechanisms of multiple-stage porphyry copper mineralization at

Butte, Montana; vein formation by hypogene leaching and

enrichment of potassium–silicate protore. Economic Geology

79, 556–589.

Brimhall, G.H, 1980. Deep hypogene oxidation of porphyry copper

potassium–silicate protore at Butte, Montana, a theoretical

evaluation of the copper remobilization hypothesis. Economic

Geology 75, 384–409.

Burnham, C.W., 1959. Metallogenic provinces of the Southwestern

United States and Northern Mexico. New Mexico State Bureau

of Mines and Mineral Resources Bulletin 65 (76 pp.).

Burton, K.W., Gannoun, A., Birck, J.-L., Allegre, C.J., Schiano, P.,

Clocchiatti, R., Alard, O., 2002. The compatibility of rhenium

and osmium in natural olivine and their behavior during mantle

melting and basalt genesis. Earth and Planetary Science Letters

198, 63–76.

Chesley, J., Righter, K., Ruiz, J., 2004. Large-scale mantle

metasomatism: a Re–Os perspective. Earth and Planetary

Science Letters 219, 49–60.

Creaser, R.A., Papanastassiou, D.A., Wasserburg, G.J., 1991.

Negative thermal ion mass spectrometer of Os, Re and Ir.

Geochimica et Cosmochimica Acta 55, 397–401.

Dalrymple, R.A., Lanphere, M.A., 1969. Potassium Argon Dating.

Freeman Publishing. 258 pp.

Dewey, J.F., Bird, J.M., 1970. Mountain belts and the new global

tectonics. Journal of Geophysical Research 75, 2625–2647.

Esser, B.K., Turekian, K.K., 1993. The osmium isotopic composi-

tion of the continental crust. Geochimica et Cosmochimica Acta

57, 3093–3104.

Freeport Mining, 1997. Annual company report. Freeport

McMoran.

Freeport Mining, 1998. Annual company report. Freeport

McMoran.

Frei, R., Nagler, T., Schonberg, R., Kramers, J., 1998. Re–Os, Sm–

Nd, U–Pb and stepwise lead leaching isotope systematics in

shear zone hosted gold mineralization: genetic tracing and age

constraints of crustal hydrothermal activity. Geochimica et

Cosmochimica Acta 62, 1925–1936.

Friehauf, K., Soebari, L., Titley, S., 2000. Porphyry-style mineral-

ization in the Ertsberg diorite, Gunung Bijih (Ertsberg/Grasberg)

District Irian Jaya, Indonesia. Proceedings of Freeport-Institut

Teknologi Bandung (ITB) Geological Symposium, Bandung,

Java, pp. 26–31.

Gammons, C., Williams-Jones, A., 1997. Chemical mobility of gold

in the porphyry-epithermal environment. Economic Geology 92,

45–59.

Gerlach, T., Norton, D., Knight, J.E., 1975. Porphyry pluton

environments; computed mass transfer for reactions between

hydrothermal fluids and sedimentary host rocks. Annual Meet-

ing, Abstracts with Programs, vol. 7. Geological Society of

America, p. 1085.

Goldfarb, R.J., Groves, D.I., Gardoll, S., 2001. Orogenic gold

and geologic time: a global synthesis. Ore Geology Reviews

18, 1–75.

Hamilton, W., 1979. Plate motions in western Melanesia and

eastern Indonesia. General assembly, Canberra, Australia,

vol. 17. International Union of Geodesy and Geophysics,

p. 52.

Horan, M., Morgan, J.W., Coveney, R., Murowchick, J., Hulbert, L.,

1994. Rhenium and osmium isotopes in black shales and Ni–

Mo–PGE-rich sulfide layers, Yukon Territory, Canada, and

Hunan and Guizhou provinces, China. Geochimica et Cosmo-

chimica Acta 58, 257–265.

Housh, T., McMahon, T., 2000. Ancient isotopic characteristics of

Neogene potassic magmatism in western New Guinea (Irian

Jaya, Indonesia). Lithos 50, 217–239.

Katchan, G. 1982. Mineralogy and geochemistry of the Ertsberg and

Ertsberg East skarns, Irian Jaya, Indonesia and the OK Tedi

skarns, Papua New Guinea. Unpublished PhD thesis, University

of Sydney, Australia, 498 p.

Kendrick, M.A., Burgess, R., Patrick, R.A.D., Turner, G., 2001.

Fluid inclusion noble gas and halogen evidence on the origin of

Cu–porphyry mineralizing fluids. Geochimica et Cosmochimica

Acta 65, 2651–2668.

Kesler, S.E., Chryssoulis, S.L., Simon, G., 2002. Gold in porphyry

copper deposits: its abundance and fate. Ore Geology Reviews

21, 103–124.

Kirk, J., Ruiz, J., Chesley, J., Walshe, J., England, G., 2002. A

major Archean, gold- and crust-forming event in the Kaapvaal

Craton, South Africa. Science 297, 1856–1858.

Krauskopf, K.B., 1967. Source rocks for metal bearing fluids. In:

Barnes, H.L. (Ed.), Geochemistry of Hydrothermal Ore Depos-

its. Holt, Rinehart and Winston, Inc, pp. 1–33.

Lang, J.R., Titley, SR., 1998. Isotopic and geochemical character-

istics of Laramide magmatic systems in Arizona and implica-

tions for the genesis of porphyry copper deposits. Economic

Geology 93, 138–170.

Luck, J., Allegre, C., 1980. Osmium isotopes as petrogenetic

tracers. Earth and Planetary Science Letters 48, 148–154.

Luck, J.M., Allegre, C.J., 1983. The study of molybdenites through

the 187Re–187Os chronometer. Earth and Planetary Science

Letters 61, 291–296.

Ludwig, K.R., 2001. Computer program isoplot/Ex version 2.49, a

geochronological toolkit for Microsoft Excel: Berkeley Geo-

chronological Center Special Publication 1a.

MacDonald, G.D., Arnold, L.C., 1994. Geological and geochemical

zoning of the Grasberg igneous complex, Irian Jaya, Indonesia.

Journal of Geochemical Exploration 50, 143–178.

MacDonald, D., Arnold, L.C., Kyle, R.J., 1995. Factors responsible

for extreme concentration of Cu and Au in the Grasberg deposit.

In: Clark, A.H. (Ed.), Giant Ore Deposits II, Kingston Ontario,

pp. 101–113.

Martin, C.E., Peucker-Ehrenbrink, B., Brunskill, G., Szymczak, R.,

2000. Sources and sinks of unradiogenic osmium runoff from

Papua New Guinea. Earth and Planetary Science Letters 183,

261–274.


Mathur, R. 2001. Re–Os isotopes of base metal porphyry deposits,

Unpublished PhD thesis, University of Arizona. 156 pp.

Mathur, R., Ruiz, J., Titley, S., Gibbins, S., Martogomo, W., 2000.

Different crustal sources for Au-rich and Au-poor ores of the

Grasberg Cu–Au porphyry deposit. Earth and Planetary Science

Letters 183, 7–14.

McCandless, T.E., Ruiz, J., 1993. Rhenium–osmium evidence for

regionally-timed mineralization events in southwestern North

America. Science 261, 1282–1286.

McCandless, T.E., Ruiz, J., Campbell, A.R., 1993. Rhenium

behavior in molybdenite in hypogene and near-surface environ-

ments: implications for Re–Os geochronology. Geochimica et


McDowell, F.W., McMahon, T.P., Warren, P.Q., Cloos, M., 1996.

Pliocene Cu–Au-bearing igneous intrusions of the Gunung Bijih

(Ertsberg) District, Irian Jaya, Indonesia—K–Ar geochronology.

Journal of Geology 104, 327–340.

McInnes, B.I., McBride, J.S., Evan, N.T., Lambert, D.D., Andrew,

A.S., 1999. Osmium isotope and noble metal recycling in

subduction zones: implication for metallogenesis of porphyry-

epithermal Cu–Au deposits. Science 286, 512–516.

McMahon, T.P., 1994. Pliocene intrusions in the Gunung Bijih

(Ertsberg) mining district, Irian Jaya, Indonesia; major- and

trace-element chemistry. International Geology Review 36,

925–946.

Meinert, L.D., Hefton, K.K., Mayes, D., Tasiran, I., 1997. Geology,

zonation, and fluid evolution of the Big Gossan Cu–Au skarn

deposit, Ertsberg District, Irian Jaya. Economic Geology 92,

509–534.

Meisel, T., Walker, R.J., Irving, A.J., Lorand, J.P., 2001. Osmium

isotopic compositions of mantle xenoliths: a global perspective.

Geochimica et Cosmochimica Acta 65, 1311–1323.

Noble, J.A., 1970. Metal provinces of the western United States.

Geological Society of America Bulletin 81, 1607–1624.

Norton, D., 1979. Transport phenomena in hydrothermal systems;

the redistribution of chemical components around cooling

magmas. Bulletin de Mineralogique 102, 471–486.

Norton, D., 1982. Fluid and heat transport phenomena typical of

copper-bearing pluton environments. In: Titley, S.R. (Ed.),

Advances in Geology of the Porphyry Copper Deposits.

University of Arizona Press, Southwestern North America,

Tucson, pp. 59–72.

Peach, C., Mathez, E., 1996. Constraints on the formation of

platinum group element deposits in igneous rocks. Economic

Geology 91, 439–450.

Predenergast, K., Taylor, R.G., Clarke, G.W., Pollard, P.J., 2001.

Metal zonation and the timing of gold mineralization associated

with the Big Gossan Cu–Au deposit, Ertsberg District, Irian

Jaya. in Abstracts with programs. Geological Society of

America Program with Abstracts 33, 358.

Pollard, P.J., Taylor, R., 2000. Geochronology of intrusive rocks and

Cu–Au mineralization in the Ertsberg District. Proceedings of

Freeport-Institut Teknologi Bandung (ITB) Geological Sympo-

sium, Bandung, Java, pp. 17–19.

Pollard, P., Taylor, R., 2001. Geochronology of intrusive rocks and

Cu–Au mineralization in the Ertsberg mining district, Irian Jaya,

Indonesia 2001–A hydrothermal Odyssey. ERGU, 167–168.

Quarles van Ufford, A.I., 1996. Stratigraphy, structural geology, and

tectonics of a young forearc-continent collision, western Central

Range, Irian Jaya (western New Guinea), Indonesia. Unpub-

lished PhD thesis, University of Texas, Austin.

Ravizza, G.E., Turekian, K.K., 1992. The osmium isotopic

composition of organic rich marine sediments. Earth and


Righter, K., Hauri, E.H., 1998. Compatibility of rhenium in garnet

during mantle melting and magma genesis. Science 280,

1737–1741.

Roy-Barman, M., Wasserburg, G., Papanastassiou, D., Chaussidon,

M., 1998. Osmium isotopic compositions and Re–Os concen-

trations in sulfide globules from basaltic glasses. Earth and


Rubin, J.N., Kyle, J.R., 1997. Precious metal mineralogy in

porphyry-, skarn-, and replacement-type ore deposits of the

Ertsberg (Gunung Bijih) District, Irian Jaya, Indonesia. Eco-

nomic Geology 92, 535–550.

Rubin, J.N., Kyle, J.R., 1998. The Gunung Bijih Timur (Ertrsberg

East) skarn complex, Irian Jaya, Indonesia: geology and genesis

of a large magnesian, Cu–Au skarn. In: Lentz, D.R. (Ed.),

Mineralized Intrusion-Related Skarn Systems: Mineralogical

Association of Canada, Short Course, vol. 26, pp. 245–288.

Saal, A.E., Rudnick, R.L., Ravizza, G.E., Hart, S.R., 1998. Re–Os

isotope evidence for the composition, formation, and age of the

lower continental crust. Nature 393, 58–61.

Sattari, P., Brenan, J., Horn, I., McDonough, W., 2002. Exper-

imental constraints on the sulfide and chromite–silicate melt

partitioning behavior of rhenium and platinum group elements.

Economic Geology 97, 385–398.

Selby, D., Creaser, R.A., 2001. Re–Os geochronology and system-

atics in molybdenite from the endako porphyry molybdenum

deposit, British Columbia, Canada. Economic Geology 96,

197–204.

Selby, D., Creaser, R.A., Hart, C.J.R., Rombach, C.S., Thompson,

J.F.H., Smith, M.T., Bakke, A.A., Goldfarb, R.J., 2002.

Absolute timing of sulfide and gold mineralization: a compar-

ison of Re–Os molybdenite and Ar–Ar mica methods from the

Tintina Gold Belt, Alaska. Geology 30, 791–794.

Shirey, S., Walker, R., 1995. Carius tube digestion for low-

blank rhenium–osmium analysis. Analytical Chemistry 67,

2136–2141.

Shirey, S., Walker, R., 1998. The Re–Os isotope system in

cosmochemistry and high temperature geochemistry. Annual

Review of Earth and Planetary Sciences 26, 423–500.

Sillitoe, R.H., 1972. Relation of metal provinces in western America

to subduction of oceanic lithosphere. Geological Society of

America Bulletin 83, 813–818.

Singh, S., Trivedi, J., Krishumsumji, S., 1999. The Re–Os isotope

systematics in black shales from the Lesser Himalaya; their

chronology and role in the 187Os/188Os of seawater. Geochimica

et Cosmochimica Acta 63, 2381–2392.

Smoliar, M.I., Walker, R.J., Morgan, J.W., 1996. Re–Os ages of

group IIA, IIIA, IVA and IVB iron meteorites. Science 271,

1099–1102.

Stein, H.J., Sundblad, K., Markey, R., Morgan, J.W., Motuza, G.,

1998. Re–Os ages for Archean molybdenite and pyrite, Kuittila–


Kiviso, Finland and Proterozoic molybdenite, Kabeliai, Lith-

uania: testing the chronometer in a metamorphic and metaso-

matic setting. Mineralium Deposita 33, 329–345.

Stein, H., Morgan, J., Schersten, A., 2001. The remarkable Re–Os

chronometer in molybdenite: how and why it works. Terra Nova

13, 479–486.

Stein, H., Schersten, A., Hannah, J., Markey, R., 2003. Subgrain-

scale decoupling of Re and 187Os and assessment of laser

ablation ICP-MS spot dating in molybdenite. Geochimica et


Suzuki, K., Kagi, H., Nara, M., Takano, B., Nozaki, Y., 2000.

Experimental alteration of molybdenite: evaluation of the Re–

Os system, infrared spectroscopic profile and polytype. Geo-

chimica et Cosmochimica Acta 64, 223–232.

Titley, S.R., 1991. Phanerozoic ocean cycles and sedimentary-rock

hosted gold ores. Geology 19, 645–648.

Van Nort, S.D., Atwood, G.W., Collinson, T.B., Flint, D.C., Potter,

D.R., 1991. Geology and mineralization of the Grasberg

porphyry copper–gold deposit, Irian Jaya, Indonesia. Mining

Engineering 43, 300–303.

Walker, R.J., Carlson, R.W., Shirey, S.B., Boyd, F.R., 1989. Os,

Sr, Nd, and Pb isotope systematics of Southern Africa

peridotite xenoliths: implications for the chemical evolution

of subcontinental mantle. Geochimica et Cosmochimica Acta

64, 223–232.

Weiland, R.J., Cloos, M., 1996. Pliocene–Pleistocene asymmetric

unroofing of the Irian fold belt, Irian Jaya, Indonesia; apatite

fission-track thermochronology. Geological Society of America

Bulletin 108, 1438–1449.

Widom, E., Kepezhinskas, P., Defant, M., 2003. The nature of

metasomatism in the sub arc mantle wedge: evidence from Re–

Os isotopes in Kanchatka peridotite xenoliths. Chemical

Geology 196, 283–306.

Xiong, Y., Wood, S.A., 1999. Experimental determination of the

solubility of ReO2 and the dominant oxidation state of

rhenium in hydrothermal solutions. Chemical Geology 158,

245–256.

Xiong, Y., Wood, S.A., 2000. Experimental quantification of

hydrothermal solubility of platinum-group elements with special

reference to porphyry copper environments. Mineralogy and

Petrology 68, 1–28.

Xiong, Y., Wood, S.A., 2001. Hydrothermal transport and deposi-

tion of rhenium under subcritical conditions (up to 200 degrees

C) in light of experimental studies. Economic Geology 96,

1429–1444.

Zartman, R.E., 1974. Lead isotopic provinces in the cordillera of the

western United States and their geologic significance. Economic

Geology 69, 792–805.

copper-gold ore from west papua, indonesia

Documents

ertsberg district

periphery mineralization

mineralization pollard

ertsberg molybdenite

ertsberg diorite

ertsberg intrusion centers

peripheral ores

cuau mineralization