©2013 Society of Economic Geologists, Inc.Economic Geology, v. 108, pp. 1879–1888

The Erbutu Ni-Cu Deposit in the Central Asian Orogenic Belt: A Permian Magmatic Sulfide Deposit Related to Boninitic Magmatism in An Arc Setting

Runmin Peng,1,† Yusheng Zhai,1 Chusi Li,2 and edwaRd m. RiPLeY2

1 State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China2 Department of Geological Sciences, Indiana University, Bloomington, Indiana 47405

AbstractThe Erbutu Ni-Cu sulfide deposit is hosted in a small ultramafic intrusion located at the southern margin

of the Central Asian orogenic belt, Inner Mongolia. This deposit is the first case of a magmatic sulfide deposit related to boninitic magmatism in an arc setting. The host intrusion is composed of orthopyroxenite and olivine orthopyroxenite. More than three quarters of the intrusion contains economic, disseminated sulfide mineraliza-tion. SHRIMP U-Pb dating of zircons from the intrusion gives a crystallization age of 294.2 ± 2.7 Ma, similar to the age of the Permian Tarim plume in northwest China. Olivine orthopyroxenite is characterized by olivine crystals with relatively high Fo contents (85−88 mol %) and extremely low Ca contents (<250 ppm). Coexisting orthopyroxene crystals have clinoenstatite composition with enstatite from 86 to 88 mol %. Whole-rock data show characteristic enrichments of light REE relative to heavy REE, pronounced negative Nb-Ta anomalies, and moderately positive Hf anomaly. The d34S values of sulfide separates are 4 to 5‰, significantly higher than the typical mantle value (0 ± 2‰). The eHf values of zircons are from –4 to –9. These data indicate that the parental magma was a boninite. Crustal contamination was involved during magma evolution and ore formation.

IntroductionThe mosT important magmatic sulfide deposits in the world are associated with komatiites and mafic-ultramafic intrusions formed by picritic to basaltic magmas in intraplate settings (see summary in Naldrett, 2011); only a few of less importance are associated with Ural-Alaska–type mafic-ultramafic com-plexes (Thakurta et al., 2008) and calc-alkaline intrusions in arc settings (see summary in Tomkins et al., 2012). Magmatic sulfide deposits associated with mafic-ultramafic intrusions formed by boninitic magma in a convergent plate tectonic setting have never been reported before. Some researchers argued that one of the magmas (U-type magma or siliceous high Mg basalt) involved in the formation of the PGE ore-bearing Bushveld Complex in South Africa was an analog of boninite (Hamlyn and Keays, 1986). Other researchers believed that it was a contaminated komatiite (Barnes, 1989; Maier et al., 2000). The first possibility has been dismissed by many researchers (see summary in Arndt et al., 2005) due to a lack of evidence of subduction at the time of the Bushveld event and the trace element and isotopic compositions of the Bushveld rocks which are inconsistent with boninite (Kruger, 1994; Maier et al., 2000). In this communication we describe the first known magmatic sulfide deposit related to boninitic magmatism in an arc setting in the Central Asian orogenic belt. The Erbutu deposit is a small Ni-Cu sulfide deposit con-taining ~1 million metric tons (Mt) of nickel. However, it is significant in the study of ore genesis owing to its unique geo-logical context.

Geologic BackgroundThe Erbutu Ni-Cu sulfide deposit is hosted in a small

ultramafic intrusion which occurs in the southern part of the Central Asian orogenic belt where several important mag-matic Ni-Cu sulfide deposits such as the Kalatongke (Li et al., 2012b) and Huangshandong (Sun et al., 2013) occur (Fig.

1). The Ni-Cu deposits in the Central Asian orogenic belt are all hosted in small mafic-ultramafic intrusions with a surface exposure <10 km2. The majority of these intrusions have a Permian age, broadly contemporaneous with the eruption of alkaline basalts in the Tarim craton, or the Tarim plume. A younger Ni-Cu sulfide deposit hosted in the Honqiling 7 intrusion occurs in the southeastern part of the Central Asian orogenic belt (Wei et al., 2013).

The Erbutu region is dominated by E-W–trending arc terranes (Fig. 1b) that were accreted to the northern mar-gin of the North China craton from the late Paleozoic to the Early Triassic (Xiao et al., 2003; Jian et al., 2010). The most prominent tectonic units in this part of the Central Asian orogenic belt are the Solonker suture zone and the Ondor Sum subduction-accretion terrane (Fig. 1b). The Ondor Sum subduction-accretion terrane is mainly composed of Paleozoic arc complexes. The Solonker suture zone contains ophiolites and olistostrome (Xiao et al., 2003). Zircons separated from the gabbroic unit of the ophiolite complex give ages from 292 to 299 Ma (Jian et al., 2010). The Solonker suture zone is thought to be a Permian intraoceanic arc-trench system (Jian et al., 2010) or the remnant of the Paleo-Asian Ocean which was closed in Early Triassic (Xiao et al., 2003).

Early Permian andesitic volcanic rocks are abundant within the Central Asian orogenic belt but rare in the North China craton. Coeval granodioritic intrusive rocks occur across the boundary between the North China craton and the Central Asian orogenic belt. Early Permian mafic-ultramafic intru-sions are also present in the region but volumetrically insig-nificant in comparison with the coeval granodioritic plutons (see summary in Zhang, X. et al., 2011).

Geology and PetrographyThe host intrusion of the Erbutu magmatic sulfide deposit is

a small ultramafic body with a surface exposure <200 m across (Fig. 2a). It has a bowl shape with a downward extension up to ~200 m (Fig. 2c). The country rocks of the intrusion are the

0361-0128/13/4169/1879-10 1879

† Corresponding author: e-mail, cprm@cugb.edu.cn

1880 PENG ET AL.

metamorphosed volcano-sedimentary rocks of the Baoyintu Group (Fig. 2a). Fault contacts with country rocks character-ize much of the western part of the intrusion. In the eastern part of the intrusion, a chilled margin (fine-grained dolerite) with a thickness up to 30 cm and a hornfels zone up to 0.5 m thick occur in places on both sides of the contacts.

The Erbutu intrusion consists of an olivine orthopyroxenite zone at the base and an orthopyroxenite zone at the top (Fig. 2c). The transition between these two zones is gradational. Up to ~50 m of the orthopyroxenite cap is oxidized and weath-ered. Sulfide mineralization with Ni grades varying from 0.3 to 2 wt % occurs in the lower part of the orthopyroxenite zone and throughout much of the olivine orthopyroxenite zone. Net-textured sulfide mineralization with a Ni grade up to 2 wt % most commonly occurs in the lower part of the intru-sion. A thin sulfide-poor marginal zone (Ni <0.2 wt %) with thickness varying from ~1.5 m (Fig. 2c, ZK101) to ~4 m (Fig. 2c, ZK102) wraps around the intrusion. The total Ni and Cu reserves of the Erbutu deposit have never been given to the public but the deposit has been mined by a small open pit (Fig. 2b) since 2006. The host intrusion of the Erbutu deposit is slightly smaller than that of the Eagle Ni-Cu deposit in the Midcontinent rift rystem, United States. The Eagle deposit is one of the smallest magmatic sulfide deposits in the world. It contains ~4 Mt of sulfide ores with average grades of 3.6 wt % Ni and 2.9 wt % Cu (Ding et al., 2012). These data indicate that the Erbutu deposit is smaller than the Eagle deposit.

The samples used in this study were collected below the oxidized zone in an open pit (Fig. 2b). The locations of some of our samples are shown in a photo of the open pit (Fig. 2b). The samples used in this study all contain disseminated sul-fides. A representative sample is shown in Figure 3a. The sul-fide assemblage is composed of pyrrhotite, pentlandite, and chalcopyrite. The host rocks are medium grained (1−5 mm across a crystal in thin section) and commonly exhibit an inter-granular texture in which both olivine and orthopyroxene crystal are randomly oriented (Fig. 3b). Olivine crystals are partially altered to serpentine plus secondary magnetite in the cleavages and microfractures. Coexisting orthopyroxene crys-tals commonly do not show visible alteration (Fig. 3b). In addition to predominant olivine and orthopyroxene, minor clinopyroxene, hornblende, and phlogopite are also present in the rocks. Locally the content of phlogopite in the rocks can reach ~10 vol %. In the phlogopite-rich samples, orthopyrox-ene occurs as elongated crystals, forming a framework by ran-dom orientation, and as smaller, rounded inclusions within phlogopite crystals (Fig. 3c).

Analytical MethodsMineral compositions were determined by EMPA in the

Department of Geological Sciences, Indiana University. The analytical conditions were a 15-kV, 20-nA beam current, 1-mm beam size, and peak counting time of 20 s for major elements. Calcium and Ni in olivine were analyzed using a beam current

~295Ma

277Ma

271Ma

252-281Ma

278-282Ma

283-291Ma

277-291Ma

Sonidzuoqi

JiningHohhot

Solonker

Bayan Obo

Eren Hot

42oN

44oN

North China Craton

Mongolia

China

Zircon U-Pb age

114oE110oE106oE

42oN

Khan Bogd pluton

b

Fig. 2a

100 km

Erbutu

Late

Kazakhstan

140oE

50oN

Centr al

AsiaOrogenic

Belt

80oE

Tar im Cr aton

Transbaikal ia

Proter ozoi c

Qinl ing-Dabie Orogenic Bel t

Y

Tibet

angtze Craton

South China

30oN

50oN

40oN

100oE 120oE

100oE

30oN

a

TarimCraton

North ChinaCraton

Alkalinebasalts

Huangshandong~274Ma Fig.1b

Kalatongke~287Ma

Hongqiling~216Ma

RussiaSiberian Craton

East

Gob

i Fau

lt

276Ma

Bainiaomiao arc terrane

Solonker suture zone

Ondor Sum

subduction-accretion terrane

Early Paleozoic intrusive rocks

Carboniferous intrusive rocks

Lower Permian volcano-sedimentary strata

Permian intrusive rocks

Ophiolite

CA

OB

~280Ma

Fig. 1. (a). Tectonic units of Asia (modified from Jahn, 2004). (b). Simplified geology of the studied region (modified from Zhang et al., 2010). Sources of U-Pb zircon ages: Tarim alkaline basalts: Tian et al. (2010); Kalatongke and Huangshandong: Han et al. (2004); Hongqiling: Wu et al. (2004).

ERBUTU Ni-Cu DEPOSIT, CENTRAL ASIAN OROGENIC BELT 1881

of 100 nA and a peak counting time of 100 s. The detection lim-its for Ca and Ni under these conditions are ~40 and ~80 ppm, respectively.

Sulfi des for S isotope analyses were collected by microdrill-ing from rock chips. The sulfi de samples were analyzed in the Department of Geological Sciences, Indiana University, following the procedures described in Studley et al. (2002). Whole-rock major element compositions were determined by XRF, and whole-rock trace element abundances were deter-mined by acid digestion in steel-jacketed Tefl on “bombs” fol-lowed by analysis by ICP-MS, both at the Institute of Uranium Deposits Geology, Beijing, China. U-Th-Pb zircon analyses were performed by SHRIMP II in the Institute of Geology, Chinese Academy of Geological Sciences, Beijing, following the procedures described in Jian et al. (2010). Lu-Hf isotopes

of zircons were determined using laser ablation-multiple col-lectors-inductively coupled plasma-mass spectrometry (LA-MC-ICP-MS) in the State Key Laboratory of Continental Dynamics, Northwest University, Xi’an, China, following the procedures described in Yuan et al. (2008).

Results

U-Pb zircon age

The U-Pb isotope compositions of zircons determined by SHRIMP are given in the Appendix (Table A1). The zircon crystals were separated from a single, large orthopyroxenite sample from the Erbutu intrusion. The euhedral, transparent crystals with oscillatory zoning were selected for SHRIMP analysis. These gave concordant and overlapping data with a

Erbutu 100 m

EB1

EB11EB14

EB3

EB8

EB2

Caterpillarexcavatoras scale

Erbutuultramaficintrusion

A

AB

B

Quaternary AmphibolitePaleozoicgranite

Fault

Meso-ProterozoicBaoyingtu GroupPaleo-ProterozoicBaoyingtu Group

b

c

a

294 MaC

C

D

D

ZK101

ZK102 ZK102TC107

Oxidized zone

Oxidized zone

Orthopyroxenite

Olivineorthopyroxenite

ZK1010 0.2 0.4 0.6 0.8 1 1.2

Ni (wt. %)

Ni (wt. %)

Disseminated

Net-textured

0 0.2 0.4 0.6 0.8

50 m

50 m

105o40’56’’ 105o40’68’

41o 27

’17’

41o 27

’11’

Fig. 2. (a) Plan view. (b) Photo of open pit. (c) Cross section with drill core data of the Erbutu sulfi de-bearing ultramafi c intrusion.

1882 PENG ET AL.

weighted mean age of 294 ± 2.7 Ma (2σ, MSWD = 1.5) (Fig. 4). The zircon U-Pb age for the Erbutu intrusion is within the range of some mafic intrusions and granodiorite plutons in the region (Fig. 1b).

Mineral chemistry

The average compositions of olivine and orthopyroxene crystals from the Erbutu intrusion are listed in Table 1. The Fo contents in the olivine vary between 85 and 87.5 mol %. The Erbutu olivine crystals exhibit a negative Fo-Ni correla-tion (Fig. 5) due to Fe-Ni exchange between olivine and sul-fide liquid (e.g., Li and Naldrett, 1999). The contents of Mn in the olivine vary significantly between 700 and 1,400 ppm but have no correlation between Fo contents (Fig. 5). The con-tent of Ca in the Erbutu olivine is <300 ppm (Fig. 5). Orthopy-roxene in the Erbutu intrusion has clinoenstatite composition, containing 86 to 88 mol % enstatite (Table 1).

Major and trace elements in whole rocks

Whole-rock major and trace element compositions of the Erbutu intrusion are given in the Appendix (Table A2). Whole-rock MgO and TiO2 contents vary from 25 to 33 and 0.2 to 0.5 wt %, respectively. The chondrite-normalized REE and primitive mantle-normalized alteration-resistant trace element patterns are illustrated in Figure 6. Orthopyroxenites tend to have higher trace element abundances than olivine orthopyroxenites. However, they are all characterized by sig-nificant enrichments in heavy light REE relative to heavy REE, negative Eu anomaly (Fig. 6a), pronounced negative Nb-Ta anomalies, and moderately positive Hf anomaly (Fig. 6b). In the diagram of Th/Yb versus Nb/Yb, the Erbutu sam-ples plot above the Cenozoic boninite lavas from the Izu-Bonin-Mariana system (Pearce et al., 1992; Reagan et al., 2010) and Cape Vogel, Papua New Guinea (König et al.,

ABa

Sulf

AB cb

Phl

Opx

Opx

Opx

Sulf

Ol

1 cm

Olivine orthopyroxenite

Fig. 3. Photograph of a hand specimen with disseminated sulfides (a) and microphotographs of olivine orthopyroxenite (b) and orthopyroxenite (c). Olivine orthopyroxene is characterized by an intergranular texture (b). Orthopyroxene occurs as elongated crystals forming a framework by random orientation and as small inclusion in phlogopite (c). Ol = olivine, Opx = orthopyroxene, Phl = phlogopite, Sulf = sulfides.

ERBUTU Ni-Cu DEPOSIT, CENTRAL ASIAN OROGENIC BELT 1883

270

280

290

300

310

0.042

0.044

0.046

0.048

0.050

0.052

0.30 0.32 0.34 0.36

207Pb / 235U

206 P

b/

238 U

2008EB1

Mean = 294.2 ± 2.7 Ma14 spots

MSWD = 1.5

Fig. 4. Concordia plot of U-Pb isotope data for zircon crystals from the Erbutu sulfide-bearing ultramafic intrusion.

TabLe 1. Average Olivine and Orthopyroxene Compositions, Erbutu Sulfide-Bearing Ultramafic Intrusion

Sample Rock type n SiO2 MgO FeO MnO CaO NiO Total Fo Ni (ppm)

Olivine08EB8 Ol orthopyroxenite 9 40.41 46.85 12.69 0.15 0.02 0.24 100.35 86.7 1,89508EB9 Ol orthopyroxenite 12 40.33 46.44 13.52 0.14 0.01 0.28 100.72 85.8 2,16508EB11 Ol orthopyroxenite 6 40.35 47.04 12.52 0.13 0.01 0.24 100.30 86.8 1,88508EB14 Ol orthopyroxenite 12 40.44 46.94 12.65 0.13 0.01 0.23 100.41 86.8 1,837

Sample Rock type n SiO2 Al2O3 MgO FeO MnO Cr2O3 TiO2 CaO Total En

Orthopyroxene08EB5 Orthopyroxenite 7 56.97 1.43 33.43 7.23 0.12 0.56 0.12 0.89 100.77 87.008EB6 Orthopyroxenite 6 56.38 1.77 33.00 7.57 0.15 0.61 0.18 0.78 100.46 86.308EB7 Orthopyroxenite 5 56.87 1.46 33.11 7.31 0.14 0.57 0.13 0.97 100.58 86.308EB10 Orthopyroxenite 10 57.06 1.44 33.31 7.35 0.13 0.53 0.10 0.76 100.69 86.908EB9 Ol orthopyroxenite 6 56.99 1.42 33.51 6.89 0.11 0.53 0.12 0.93 100.52 87.908EB14 Ol orthopyroxenite 5 56.76 1.44 33.62 6.83 0.13 0.53 0.12 0.95 100.41 88.1

Notes: n = number of grains analyzed

0

400

800

1200

1600

2000

2400

2800

3200

85 85.5 86 86.5 87 87.5 88

Oli

vine

Ni,

Mn

and

Ca

cont

ents

(ppm

)

Olivine Fo content (mole %)

Ni

Mn

Ca

Fig. 5. Plot of Ni, Mn, and Ca contents vs. Fo content in olivine from the Erbutu sulfide-bearing ultramafic intrusion.

1

10

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Sa

mp

le/C

ho

nd

rite

orthopyroxenite

olivine orthopyroxenite

0.3

1

10

Th Nb Ta La Ce Pr Nd Zr Hf Sm Ti Dy Y Ho Yb

Sa

mp

le/P

rim

itive

ma

ntle

Lu

40 40a b

Fig. 6. Chondrite-normalized REE patterns and primitive mantle-nor-malized alteration-resistant trace element patterns of rock samples from the Erbutu sulfide-bearing ultramafic intrusion. The chondrite values and the primitive mantle values are from Anders and Grevesse (1989) and Sun and McDonough (1989), respectively.

1

10

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Sa

mp

le/C

ho

nd

rite

orthopyroxenite

olivine orthopyroxenite

0.3

1

10

Th Nb Ta La Ce Pr Nd Zr Hf Sm Ti Dy Y Ho Yb

Sa

mp

le/P

rim

itive

ma

ntle

Lu

40 40a b

1884 PENG ET AL.

2010), overlapping the field of Cenozoic arc basalts in the world (data from http://www. petdb.org).

Sulfur isotopes

Sulfur isotope data for the Erbutu deposit are listed in Table 2. One sample is from the orthopyroxenite zone; the rest are from the olivine orthopyroxenite zone. The d34S val-ues vary between 4 and 5‰, which are significantly higher than typical mantle values (0 ± 2‰; see summary in Ripley and Li, 2013).

Zircon Hf isotopes

Zurcon Hf isotope data for the Erbutu intrusion are listed in Table 3. The 176Yb/177Hf ratios are <0.11. The eHf (t = 294 Ma) values range from −4.2 to −8.5, which are significantly lower than that of detrital zircons with similar crystallization ages from the region (Fig. 7).

DiscussionThe modal compositions of the Erbutu intrusion are

remarkably similar to that of typical arc cumulates derived from boninitic magma such as those from Howqua, Victoria, Australia (Crawford, 1980). Olivine and orthopyroxene in the Erbutu intrusion are slightly less primitive than those in the Howqua ultramafic rocks but this can be explained by frac-tional crystallization. Low Ca in olivine from the Erbutu intru-sion provides another line of evidence for its close affinity with

arc cumulates formed by boninitic magma. The Ca contents of olivine from the Erbutu intrusion are significantly lower than the values of olivine from komatiites, midocean ridge basalts, ocean island basalts, and continental flood basalts (see summary in Li et al., 2012a) but similar to that of olivine from some low Ca boninites (e.g., Kamenetsky et al., 2006). Higher Th/Yb ratios of the Erbutu intrusion than that of Cenozoic boninite lavas (Fig. 8), higher d34S values of sulfides from the intrusion than the typical mantle values, and negative eHf(t) values of zircons from the intrusion (Fig. 7) are also consistent with a boninitic parental magma plus crustal contamination.

As shown in Figure 1a, several small Ni-Cu sulfide depos-its hosted in some Permian mafic-ultramafic intrusions such as Kalatongke (Li et al., 2012b), Huangshanxi (Zhang, M. et al., 2011), and Huangshandong (Gao et al., 2013; Sun et al., 2013) are present in the southern part of the Central Asian orogenic belt, northern Xinjiang, northwestern China. The zircon U-Pb ages of these intrusions are similar to those of the

TabLe 3. Hf Isotope Data of Zircons from the Erbutu Sulfide-Bearing Ultramafic Intrusion, Inner Mongolia

Grain/spot 176Yb/177Hf 2σ 176Lu/177Hf 2σ 176Hf/177Hf 2σ (176Hf/177Hf)i eHf TDM (Ma)

2008EB1-1.1 0.105438 0.000457 0.003310 0.000012 0.282463 0.000024 0.282444 −4.8 1188 2008EB1-2.1 0.024511 0.000966 0.000913 0.000034 0.282372 0.000017 0.282367 −7.7 1240 2008EB1-3.1 0.107827 0.000278 0.003649 0.000006 0.282442 0.000022 0.282422 −5.7 1231 2008EB1-4.1 0.051524 0.000743 0.001818 0.000023 0.282462 0.000017 0.282451 −4.8 1142 2008EB1-5.1 0.091624 0.000198 0.002895 0.000007 0.282482 0.000022 0.282466 −4.2 1146 2008EB1-6.1 0.101540 0.000539 0.002999 0.000021 0.282367 0.000016 0.282351 −8.5 1319 2008EB1-7.1 0.071307 0.000748 0.002356 0.000028 0.282428 0.000017 0.282416 −6.3 1207 2008EB1-8.1 0.044799 0.000660 0.001553 0.000021 0.282412 0.000016 0.282403 −6.4 1205 2008EB1-9.1 0.072526 0.000353 0.002440 0.000011 0.282441 0.000018 0.282428 −5.7 1191 2008EB1-10.1 0.062102 0.000154 0.001911 0.000009 0.282452 0.000019 0.282442 −5.2 1158 2008EB1-11.1 0.038122 0.000423 0.001132 0.000012 0.282463 0.000016 0.282457 −4.7 1119 2008EB1-12.1 0.077527 0.000595 0.002569 0.000012 0.282456 0.000022 0.282442 −5.4 1174 2008EB1-13.1 0.105782 0.000423 0.003270 0.000010 0.282371 0.000024 0.282353 −8.5 1324 2008EB1-14.1 0.028086 0.001085 0.000925 0.000037 0.282374 0.000013 0.282369 −7.8 1237 2008EB1-15.1 0.072370 0.000717 0.002441 0.000022 0.282442 0.000018 0.282429 −5.9 1190

Notes: eHf calculated using the method of Blichert and Albarede (1997), 176Lu decay constant λ = 1.865 × 10−11/yr (Soderlund et al., 2004), TDM = depleted mantle age, t = 294 Ma

TabLe 2. Sulfur Isotopes of the Erbutu Ni-Cu Sulfide Deposit

Sample Rock type Mineralization d34S

08EB6 Orthopyroxenite Disseminated sulfides 3.9908EB8 Ol orthopyroxenite Disseminated sulfides 4.7708EB9 Ol orthopyroxenite Disseminated sulfides 5.0708EB11 Ol orthopyroxenite Disseminated sulfides 4.1711EB1 Ol orthopyroxenite Disseminated sulfides 4.2811EB2 Ol orthopyroxenite Disseminated sulfides 4.36

Notes: Sulfur isotope data are reported relative to V-CDT in standard d notation

De ple te d ma ntl e

1.1Ga

1.6Ga

0.5Ga

Chondrite

10

20

0

-10

-20

-300 250 500 750 1000 1250

Age (Ma)

ε Hf

2.5Ga

Hegenshan detrital zircons(Li et al., 2011)Erbutu igneous zircons(this study)

Crustalcontamination

Fig. 7. Plot of eHf(t) values vs. U -Pb age of zircons from the Erbutu sul-fide-bearing ultramafic intrusion. A comparison with detrital zircons of simi-lar ages from the region (Li et al., 2011) reveals that in the Erbutu magma was contaminated with crustal materials.

ERBUTU Ni-Cu DEPOSIT, CENTRAL ASIAN OROGENIC BELT 1885

Tarim plume. The temporal correlation has let some research-ers to suggest that the Permian mafic-ultramafic intrusions in the Central Asian orogenic belt are parts of the Tarim plume (e.g., Zhang et al., 2010; Qin et al., 2011). The discovery of a Permian age for the Erbutu ultramafic intrusion, which occurs in an arc setting, highlights the limitation of using age correlation alone to establish the sizes of the Tarim plume and the associated metallogenic province.

ConclusionsImportant conclusions from this study are summarized

below.

1. The Erbutu intrusion formed in th Early Permian as a result of subduction-related magmatism instead of mantle plume activity.

2. Modal compositions, mineral chemistry, and trace ele-ment compositions indicate a boninitic parental magma for the intrusion.

3. Sulfur isotopes of sulfide separates and zircon Hf iso-topes indicate that crustal contamination was involved in magma evolution and ore formation.

AcknowledgmentsThis study was financially supported by the Chinese National

Key Technologies R and D Program (2006BAB01A09), the Chinese National Basic Research 973 Program (2012 CB416604 and 2006CB403503), and a research grant from the China Geological Survey (1212011220923). Inputs from the guest editors as well as thoughtful comments from an anonymous reviewer and Xie-Yan Song are appreciated.

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Kamenetsky, V.S., Elburg, M., Arculus, R., and Thomas, R., 2006, Magmatic origin of low-Ca olivine in subduction-related magmas: Co-existence of contrasting magmas: Chemical Geology, v. 233, p. 346–357.

König, S., Münker, C., Schuth, S., Luguet, A., Hoffmann, J.E., and Kuduon, J., 2010, Boninites as windows into trace element mobility in subduction zones: Geochimica et Cosmochica Acta, v. 74, p. 684–704.

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0.1

1

10

20

0.1 1 10 100

Th/

Yb

Nb/Yb

UC

OIB

E-MORB

N-MORB

MORB-OIB

array

Cenozo

ic arc

basalts

Erbutu intrusionBoninite, Izu�Bonin�MarianaBoninite, Papua New Guinea

Fig. 8. Plot of Th/Yb vs. Nb/Yb. Sources of data: the upper crust (UC) is from Rudnick and Gao (2003); OIB, N-MORB, and E-MORB are from Sun and McDonough (1989); the global volcanic arc basalts are from an online public database (http://www.petdb.org); the Izu-Bonin-Mariana boninites are from Pearce et al. (1992) and Reagan et al. (2010), the Papua New Guinea (Cape Vogel) boninites are from König et al. (2010).

1886 PENG ET AL.

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ERBUTU Ni-Cu DEPOSIT, CENTRAL ASIAN OROGENIC BELT 1887

Tab

Le

A1.

SH

RIM

P Zi

rcon

U-P

b Is

otop

e D

ata

of th

e E

rbut

u Su

lfide

-Bea

ring

Ultr

amafi

c In

trus

ion,

Inn

er M

ongo

lia

(1)

(2)

(3)

(1)

(1)

U

T

h 23

2 Th/

20

6 Pb/

238 U

20

6 Pb/

238 U

20

6 Pb/

238 U

20

7 Pb/

206 P

b

208 P

b/23

2 Th

%

Dis

- To

tal

To

tal

Gra

in/s

pot

(ppm

) (p

pm)

238 U

ag

e ag

e ag

e ag

e ag

e co

rdan

t 23

8 U/20

6 Pb

(±%

) 20

7 Pb/

206 P

b (±

%)

2008

EB

1-1.

1

4744

31

24

0.68

30

8.9

± 5.

3 30

8.8

± 5.

3 31

1.2

± 5.

9 32

1 ±

13

288.

2 ±

5.2

4

20.3

7 1.

8 0.

0528

6 0

.54

2008

EB

1-2.

1

9019

33

50

0.38

30

1.5

± 5.

0 30

1.5

± 5.

1 30

1.9

± 5.

4 3

07 ±

9.0

2

95 ±

11

2

20.8

9 1.

7 0.

0524

1 0

.39

2008

EB

1-3.

1

5060

18

90

0.39

30

2.9

± 5.

1 30

3.0

± 5.

1 30

3.4

± 5.

4 29

2 ±

12

295.

9 ±

5.3

−4

20.7

8 1.

7 0.

0521

3 0

.53

2008

EB

1-4.

1

3231

13

03

0.42

29

8.7

± 5.

0 29

8.6

± 5.

1 29

9.2

± 5.

4 31

0 ±

21

291.

2 ±

5.6

4

21.0

8 1.

7 0.

0526

2 0

.68

2008

EB

1-5.

1

4213

23

59

0.58

30

0.4

± 5.

0 30

0.5

± 5.

1 30

0.5

± 5.

5 28

3 ±

16

299.

1 ±

5.5

−6

20.9

5 1.

7 0.

0525

0 0

.60

2008

EB

1-6.

1

6170

33

24

0.56

29

0.1

± 4.

9 29

0.0

± 4.

9 29

1.4

± 5.

4 30

0 ±

12

274.

8 ±

6.5

3

21.7

3 1.

7 0.

0521

5 0

.49

2008

EB

1-7.

1

4853

14

64

0.31

28

8.6

± 4.

9 28

8.6

± 4.

9 28

9.1

± 5.

1 29

3 ±

16

277.

7 ±

5.3

2

21.8

3 1.

7 0.

0525

1 0

.58

2008

EB

1-8.

1

2241

8

65

0.40

30

1.8

± 5.

1 30

1.8

± 5.

1 30

1.8

± 5.

4 30

1 ±

20

302.

7 ±

5.9

0

20.8

6 1.

7 0.

0523

9 0

.80

2008

EB

1-9.

1

2093

9

31

0.46

29

6.9

± 5.

1 29

6.8

± 5.

1 29

7.1

± 5.

5 31

5 ±

21

294.

6 ±

5.7

6

21.2

1 1.

8 0.

0527

9 0

.82

2008

EB

1-10

.1

3536

23

18

0.68

29

3.7

± 4.

9 29

3.7

± 5.

0 29

5.4

± 5.

5 30

1 ±

18

278.

5 ±

5.2

2

21.4

5 1.

7 0.

0524

6 0

.77

2008

EB

1-11

.1

4338

14

49

0.35

29

3.2

± 4.

9 29

3.2

± 5.

0 29

3.9

± 5.

2 29

8 ±

15

280.

8 ±

5.3

1

21.4

8 1.

7 0.

0524

6 0

.58

2008

EB

1-12

.1

4014

28

43

0.73

28

7.0

± 4.

8 28

6.8

± 4.

9 28

9.3

± 5.

5 31

7 ±

14

268.

0 ±

4.8

9

21.9

6 1.

7 0.

0528

1 0

.60

2008

EB

1-13

.1

3669

20

80

0.59

28

8.1

± 4.

9 28

8.1

± 4.

9 28

9.3

± 5.

3 28

9 ±

16

275.

6 ±

5.3

0

21.8

7 1.

7 0.

0521

5 0

.66

2008

EB

1-14

.1

876

1

69

0.20

29

4.2

± 5.

1 29

4.2

± 5.

1 29

3.5

± 5.

2 29

7 ±

32

319.

5 ±

8.0

1

21.4

3 1.

8 0.

0514

0 1.

4 20

08E

B1-

15.1

40

15

1681

0.

43

284.

7 ±

4.8

284.

7 ±

4.8

285.

0 ±

5.1

282

± 15

28

0.5

± 5.

6 −1

22

.14

1.7

0.05

205

0.6

1

Gra

in/s

pot

(1)

(1

)

(1)

(1

)

(3)

(3

)

(3)

(3

)

238 U

/206 P

b*

(±%

) 20

7 Pb*

/206 P

b*

(±%

) 20

7 Pb*

/235 U

(±

%)

206 P

b*/23

8 U

(±%

) 23

8 U/20

6 Pb*

(±

%)

207 P

b*/20

6 Pb*

(±

%)

207 P

b*/23

5 U

(±%

) 20

6 Pb*

/238 U

(±

%)

2008

EB

1-1.

1

20.3

7 1.

8 0.

0528

2 0

.57

0.35

75

1.8

0.04

909

1.8

20.2

2 1.

8 0.

0589

9 0

.50

0.40

23

1.8

0.04

946

1.8

2008

EB

1-2.

1

20.8

8 1.

7 0.

0525

0 0

.39

0.34

66

1.8

0.04

788

1.7

20.8

6 1.

7 0.

0535

5 0

.38

0.35

40

1.8

0.04

795

1.7

2008

EB

1-3.

1

20.7

8 1.

7 0.

0521

5 0

.53

0.34

60

1.8

0.04

812

1.7

20.7

5 1.

7 0.

0533

1 0

.52

0.35

42

1.8

0.04

818

1.7

2008

EB

1-4.

1

21.0

8 1.

7 0.

0525

6 0

.91

0.34

38

1.9

0.04

743

1.7

21.0

5 1.

7 0.

0539

4 0

.66

0.35

34

1.8

0.04

751

1.7

2008

EB

1-5.

1

20.9

6 1.

7 0.

0519

5 0

.70

0.34

17

1.9

0.04

770

1.7

20.9

5 1.

7 0.

0522

9 0

.61

0.34

41

1.8

0.04

772

1.7

2008

EB

1-6.

1

21.7

3 1.

7 0.

0523

2 0

.53

0.33

20

1.8

0.04

602

1.7

21.6

2 1.

7 0.

0562

4 0

.46

0.35

86

1.8

0.04

625

1.7

2008

EB

1-7.

1

21.8

4 1.

7 0.

0521

8 0

.70

0.32

94

1.9

0.04

578

1.7

21.8

0 1.

7 0.

0536

9 0

.57

0.33

96

1.8

0.04

587

1.7

2008

EB

1-8.

1

20.8

6 1.

7 0.

0523

7 0

.86

0.34

61

1.9

0.04

793

1.7

20.8

7 1.

7 0.

0522

1 0

.80

0.34

50

1.9

0.04

792

1.7

2008

EB

1-9.

1

21.2

1 1.

8 0.

0526

8 0

.91

0.34

24

2.0

0.04

714

1.8

21.2

0 1.

8 0.

0531

6 0

.82

0.34

57

1.9

0.04

717

1.8

2008

EB

1-10

.1

21.4

5 1.

7 0.

0523

6 0

.78

0.33

66

1.9

0.04

662

1.7

21.3

2 1.

7 0.

0571

4 0

.71

0.36

94

1.9

0.04

689

1.7

2008

EB

1-11

.1

21.4

9 1.

7 0.

0522

8 0

.65

0.33

55

1.8

0.04

654

1.7

21.4

4 1.

7 0.

0541

8 0

.56

0.34

85

1.8

0.04

665

1.7

2008

EB

1-12

.1

21.9

6 1.

7 0.

0527

2 0

.60

0.33

09

1.8

0.04

553

1.7

21.7

8 1.

7 0.

0593

6 0

.55

0.37

57

1.8

0.04

590

1.7

2008

EB

1-13

.1

21.8

8 1.

7 0.

0520

7 0

.70

0.32

82

1.9

0.04

571

1.7

21.7

8 1.

7 0.

0554

8 0

.62

0.35

11

1.8

0.04

591

1.7

2008

EB

1-14

.1

21.4

1 1.

8 0.

0522

6 1.

4

0.33

65

2.3

0.04

670

1.8

21.4

7 1.

8 0.

0500

9 1.

5

0.32

17

2.3

0.04

658

1.8

2008

EB

1-15

.1

22.1

5 1.

7 0.

0519

3 0

.64

0.32

33

1.8

0.04

515

1.7

22.1

3 1.

7 0.

0527

6 0

.60

0.32

88

1.8

0.04

520

1.7

Not

es: E

rror

s ar

e 1σ

; Pb c

and

Pb*

indi

cate

the

com

mon

and

rad

ioge

nic

port

ions

, res

pect

ivel

y; e

rror

in s

tand

ard

calib

ratio

n w

as 0

.77%

(not

incl

uded

in a

bove

err

ors

but r

equi

red

whe

n co

mpa

ring

da

ta fr

om d

iffer

ent m

ount

s);

(1) C

omm

on P

b co

rrec

ted

usin

g m

easu

red

204 P

b(2

) Com

mon

Pb

corr

ecte

d by

ass

umin

g 20

6 Pb/

238 U

-207

Pb/23

5 U a

ge c

onco

rdan

ce(3

) Com

mon

Pb

corr

ecte

d by

ass

umin

g 20

6 Pb/

238 U

-208

Pb/23

2 Th

age

conc

orda

nce

1888 PENG ET AL.

TabLe A2. Major and Trace Element Compositions of the Erbutu Sulfide-Bearing Ultramafic Intrusion, Inner Mongolia

Sample 08EB1 08EB2 08EB3 08EB5 08EB6 08EB7 08EB8 08EB9 08EB10 08EB11 08EB14 11EB1 11EB2

SiO2 50.50 43.39 50.24 52.32 50.90 51.09 37.94 45.65 50.13 37.36 45.38 50.04 43.19TiO2 0.31 0.29 0.32 0.34 0.51 0.32 0.20 0.27 0.26 0.22 0.27 0.29 0.28Al2O3 3.13 2.23 3.17 3.20 4.05 3.71 2.13 2.33 2.75 1.95 2.35 3.01 2.21FeOT 11.67 14.11 13.34 11.39 12.38 11.55 17.05 14.44 13.98 17.42 14.05 11.44 14.13MnO 0.15 0.13 0.15 0.18 0.17 0.18 0.14 0.18 0.18 0.15 0.18 0.12 0.13MgO 25.85 29.87 23.99 27.13 25.11 26.93 33.17 30.19 26.95 33.41 30.40 25.95 29.75CaO 1.86 1.26 1.58 1.36 1.80 1.52 0.68 1.44 1.15 0.75 1.53 1.64 1.28Na2O 0.22 0.08 0.20 0.53 0.64 0.61 0.28 0.37 0.46 0.29 0.39 0.30 0.08K2O 0.38 0.28 0.45 0.31 0.46 0.26 0.20 0.15 0.24 0.19 0.15 0.41 0.27P2O5 0.04 0.03 0.03 0.03 0.02 0.03 0.02 0.02 0.02 0.02 0.02 0.03 0.04LOI 3.70 5.98 3.56 1.54 2.16 2.08 5.90 3.03 1.96 5.73 3.68 3.76 6.24Total 98.38 98.58 97.66 98.33 98.21 98.28 97.71 98.06 98.08 97.49 98.39 96.98 98.40Ba 87 89 118 68 125 53 47 44 58 54 49 93 99Rb 13 13 26 15 29 15 10 6 14 11 7 8 12Sr 39 34 29 40 63 43 31 25 36 35 28 228 40Y 3.45 3.43 4.44 3.49 6.35 4.26 2.55 3.49 3.04 2.64 3.98 3.54 3.49Zr 35 36 28 38 43 41 30 23 31 29 23 25 38Nb 1.24 1.28 1.45 1.28 2.35 1.64 1.07 0.82 1.11 1.07 0.91 1.06 1.27Th 1.16 1.11 1.87 1.11 2.02 1.24 0.99 0.70 1.08 0.90 0.81 0.58 1.00Pb 4.57 7.32 18.90 6.51 24.30 10.10 6.36 3.60 7.15 5.29 3.42 6.27 7.12Ga 4.99 3.89 5.89 4.66 6.72 5.18 3.23 4.27 4.56 3.15 4.31 8.01 3.80Zn 71 83 82 62 64 57 72 68 60 67 77 153 89Cu 157 117 733 169 991 234 1249 457 213 906 336 119 141Ni 2253 1753 4962 2105 4931 2807 9291 4047 1652 10071 3556 626 1864Co 74 114 141 79 155 99 253 150 136 265 150 147 125V 113 72 160 122 155 114 60 78 128 65 84 89 74Cr 3519 1275 3220 3162 3441 2802 1342 1412 3405 1343 1523 987 1432Hf 1.00 1.06 0.93 0.96 1.34 1.22 0.79 0.71 0.90 0.74 0.78 0.64 1.13Cs 2.67 2.55 3.64 1.77 3.45 2.03 1.67 1.15 2.15 1.89 1.08 0.61 2.53Sc 13.9 9.5 16.9 14.7 19.3 14.6 8.5 14.1 13.8 8.5 14.6 15.8 9.9Ta 0.10 0.11 0.19 0.10 0.17 0.12 0.09 0.26 0.09 0.08 0.08 0.32 0.12Li 12.3 7.1 14.5 8.2 11.5 11.1 6.3 4.8 7.7 6.3 6.3 4.7 6.1U 0.28 0.24 0.31 0.31 0.38 0.29 0.27 0.16 0.22 0.22 0.19 0.19 0.22W 0.16 0.20 0.27 0.20 0.39 0.22 0.34 0.27 0.28 0.25 0.29 0.27 1.92Mo 0.44 0.29 1.17 0.34 0.89 0.38 1.20 0.56 2.32 1.76 0.44 0.76 0.34Cd 0.13 0.17 0.28 0.13 0.26 0.16 0.17 0.09 0.13 0.14 0.25 0.16 0.20Bi 0.86 0.65 1.46 0.55 2.35 0.66 3.54 1.17 0.48 2.66 1.12 0.15 2.05La 3.83 3.76 5.90 3.58 6.33 4.74 3.29 2.49 3.50 2.96 2.96 3.28 3.46Ce 7.4 7.6 11.4 7.5 13.3 10.3 6.6 5.1 6.9 6.1 6.0 7.3 7.7Pr 0.85 0.89 1.29 0.96 1.73 1.35 0.81 0.66 0.86 0.74 0.76 0.92 0.91Nd 3.21 3.41 4.72 3.65 6.99 5.23 3.00 2.59 3.31 2.96 3.09 3.99 3.76Sm 0.66 0.72 1.00 0.80 1.65 0.99 0.63 0.63 0.70 0.66 0.72 0.72 0.74Eu 0.16 0.18 0.18 0.21 0.34 0.26 0.17 0.15 0.18 0.16 0.19 0.32 0.21Gd 0.66 0.72 0.92 0.73 1.44 0.93 0.55 0.60 0.64 0.59 0.74 0.78 0.78Tb 0.11 0.11 0.15 0.12 0.23 0.14 0.09 0.10 0.09 0.09 0.13 0.13 0.12Dy 0.61 0.65 0.84 0.72 1.35 0.85 0.51 0.69 0.59 0.54 0.80 0.81 0.70Ho 0.13 0.13 0.17 0.13 0.25 0.17 0.10 0.14 0.11 0.11 0.15 0.14 0.14Er 0.40 0.37 0.49 0.43 0.74 0.50 0.29 0.45 0.35 0.31 0.49 0.36 0.43Tm 0.07 0.06 0.08 0.06 0.11 0.08 0.05 0.07 0.06 0.05 0.08 0.06 0.07Yb 0.42 0.37 0.48 0.46 0.70 0.57 0.31 0.49 0.38 0.34 0.54 0.41 0.45Lu 0.07 0.07 0.09 0.06 0.11 0.08 0.05 0.07 0.06 0.05 0.08 0.07 0.08

Notes: 08EB3 and 08EB6 are orthopyroxenite, the rest are olivine orthopyroxenite; all samples are sulfide mineralized; major oxides in wt %, trace ele-ments in ppm, total iron reported as FeOtotal, LOI = loss in ignition