ARTICLE

A modified genetic model for the Huangshandong magmaticsulfide deposit in the Central Asian Orogenic Belt, Xinjiang,western China

Ya-Jing Mao & Ke-Zhang Qin & Chusi Li & Dong-Mei Tang

Received: 22 January 2014 /Accepted: 11 April 2014# Springer-Verlag Berlin Heidelberg 2014

Abstract The Huangshandong Ni–Cu deposit is the largestmagmatic sulfide deposit discovered to date in the CentralAsian Orogenic Belt in northern Xinjiang, western China. Thehost intrusion is a 274-Ma composite mafic–ultramafic intru-sion consisting of four separate intrusive units: a large layeredgabbroic sequence (phase I), a sheet-like ultramafic body(phase II), a dyke-like gabbronorite body (phase III), and anirregular ultramafic unit (phase IV). Important sulfide miner-alization is present in the last three intrusive units, predomi-nantly as disseminated and net-textured sulfides (pyrrhotite,pentlandite, and chalcopyrite). The Huangshandong mafic–ultramafic intrusive rocks are characterized by arc-like geo-chemical signatures such as low Ca content in olivine andnegative Nb–Ta anomalies in whole rocks. This, together witha post-subduction setting for the East Tianshan in the Permian,suggests that the source mantle was modified previously by

slab-derived fluids in the Carboniferous. The mantle-derivedmagma was ponded in a staging chamber in the lower part ofthe newly formed arc crust. The first batch of magma to arriveat Huangshandong was most fractionated and depleted in Ni,crystallizing Fe-rich and Ni-depleted olivine (Fo67, <300 ppmNi). The second batch of magma was more primitive, crystal-lizing more primitive olivine (Fo81–84). The third batch ofmagma was also highly fractionated and depleted in Ni,crystallizing Fe-rich and Ni-depleted olivine (Fo72,~600 ppm Ni). The final batch of magma became moreprimitive again, crystallizing the most primitive olivine(Fo81–86). The occurrence of rounded sulfide inclusions inolivine primocrysts in the Huangshandong ultramafic rocksindicates that immiscible sulfide liquid droplets were presentduring olivine crystallization. The Ni tenors of disseminatedsulfide ores in the gabbronorite dyke vary mainly between 5and 8 wt%, which are too high to have been produced by theparental magma of the dyke. The Ni, Cu, and platinum-groupelements (PGE) tenors of disseminated sulfide ores in thedyke (phase III) and the ultramafic sheet (phase II) are re-markably similar. These observations, together with the se-quence of magma emplacement, suggest that the sulfide liq-uids entrapped in the magma of the dyke formed at depth by aprevious pulse of more primitive magma. The estimated pa-rental magma for the most primitive lherzolites in theHuangshandong intrusion contains 10 wt% MgO. Modelingshows that sulfide saturation in the parental magma of theHuangshandong lherzolites could have resulted from fraction-al crystallization. Significant PGE depletions relative to Niand Cu in the disseminated sulfide ores of the Huangshandongdeposit may be due to sulfide retention in the source mantle.

Keywords Magmatic sulfide deposit . Nickel . Copper .

Platinum group elements .Mafic–ultramafic rocks .

Huangshandong . Central Asian Orogenic Belt . China

Editorial handling: B. Lehmann

Electronic supplementary material The online version of this article(doi:10.1007/s00126-014-0524-5) contains supplementary material,which is available to authorized users.

Y.<J. MaoXinjiang Research Center for Mineral Resources, Xinjiang Instituteof Ecology and Geography, Chinese Academy of Sciences,Urumqi 830011, China

Y.<J. MaoUniversity of Chinese Academy of Sciences, Beijing 100049, China

Y.<J. Mao :K.<Z. Qin (*) :D.<M. TangKey Laboratory of Mineral Resources, Institute of Geology andGeophysics, Chinese Academy of Sciences, Beijing 100029, Chinae-mail: kzq@mail.iggcas.ac.cn

C. LiDepartment of Geological Sciences, Indiana University,Bloomington, IN 47405, USA

Miner DepositaDOI 10.1007/s00126-014-0524-5

Introduction

Several important clusters of Ni–Cu sulfide deposits associat-ed with Permian mafic–ultramafic intrusions are present in thesouthern part of the Central Asian Orogenic Belt (CAOB) innorthern Xinjiang, western China. The origin of the hostintrusions is highly debated. Some researchers suggested thatthey are Alaskan-type zoned complexes in an arc setting (Xiaoet al. 2004; Han et al. 2010, 2013). Other researchers proposedthat they formed in a post-subduction environment, eitherrelated to the Tarim mantle plume (Su et al. 2011a,c) orindependent basaltic magmatism associated with lithospheredelamination and asthenosphere upwelling (Tang et al. 2011;Li et al. 2012a; Song et al. 2013; Sun et al. 2013a). In thisdebate, the petrological and geochemical data from theHuangshandong mafic–ultramafic intrusion are important be-cause this intrusion (274 Ma, Han et al. 2004) is broadlycontemporaneous with the Tarim mantle plume (275–291 Ma, Tian et al. 2010). The intrusion also hosts the largestknown magmatic sulfide deposit in the Tianshan region.Hence, it offers an ideal opportunity to study the fundamentalcontrols on sulfide mineralization in this type of intrusions inthe region. Many studies on the ore genesis in theHuangshandong intrusion have been carried out recently(Gao et al. 2013; Gao and Zhou 2013; Sun et al. 2013a;Deng et al. 2014). These studies have greatly improved ourunderstanding of sulfide ore formation in the Huangshandongmagmatic system, but some uncertainties still remain. Theseinclude (1) whether sulfide saturation in the system resultedfrom fractional crystallization or crustal contamination, (2)how the immiscible sulfide liquids were concentrated, and(3) whether PGE depletion relative to Ni and Cu in the sulfideores was due to sulfide retention in the source mantle orprevious sulfide segregation during magma ascent. In thispaper, we use new and existing mineralogical, petrological,and geochemical data to address these important questions.Based on the new observations, we present a modified geneticmodel for the Huangshandong Ni–Cu deposit, focusing on thegenetic relationship between the different batches of magmainvolved in the development of the host intrusion, the timingof sulfide saturation during magma evolution, and the mech-anisms of sulfide concentration.

Geological background

The CAOB is the largest Paleozoic juvenile orogenic belt inthe world (Jahn 2004; Xiao et al. 2009). It extends for~7,000 km from west to east and for >1,500 km from theSiberian Craton in the north to the Tarim and North ChinaCratons in the south (Fig. 1). Several clusters of economicallyvaluable magmatic Ni–Cu sulfide deposits occur within thesouthern part of the CAOB in China. The most important ones

are the Kalatongke (Song and Li 2009; Zhang et al. 2009; Liet al. 2012a) and East Tianshan clusters (see summary in Sunet al. 2013b) in northern Xinjiang, western China, and theHongqiling cluster (Wei et al. 2013) in NE China. TheKalatongke and East Tianshan clusters formed in the earlyPermian (Han et al. 2004; Qin et al. 2011), whereas theHongqiling cluster formed in the Triassic (Wu et al. 2004).In both cases, the ages of the magmatic sulfide deposits are20–40 Ma younger than subduction in the regions (EastTianshan: Qin et al. 2011; Song et al. 2013; Hongqiling: Wuet al. 2004).

The Tianshan Orogenic Belt is a collage of Paleozoic arcterrains and microcontinents (Xiao et al. 2009), as indicatedby multiple E-W trending ophiolite belts in the region (Fig. 2).The Tianshan is divided into East Tianshan andWest Tianshan(Xiao et al. 2009). From south to north, the East Tianshan isfurther divided into Central Tianshan and North Tianshan,separated by a prominent regional fault (Fig. 2). To the south,the Central Tianshan is bounded by the Beishan fold belt,which belongs to the Tarim Craton (Song et al. 2011; Xiaet al. 2013; Yang et al. 2014). Ophiolites with ages varyingfrom 516 to 377Ma are present along the suture between thesetwo tectonic units (Fig. 2). Carboniferous granodiorite plutonsare widespread in Beishan and East Tianshan, whereas Perm-ian A-type granitoids are present in the North Tianshan(Fig. 2). Early Permian bimodal volcanic rocks (basalt-rhyolite) are found in the Bogda mountain north of the Tuhabasin (Chen et al. 2011).

Early-Permian mafic–ultramafic intrusions with significantsulfide mineralization are present in the Beishan, CentralTianshan, and North Tianshan. They occur as two clusters,one in the western part of the Beishan fold belt and the other inthe Huangshan–Tianyu region (Fig. 2). The temporal andspatial distributions of this type of intrusion in the Huangshanarea are shown in Fig. 3. In this area, the ages of the intrusionsvary from 274 to 283Ma (Han et al. 2004; Qin et al. 2011; Sunet al. 2013b). Two sulfide ore-bearing mafic–ultramafic intru-sions occur east of the Huangshan cluster, Hulu and Tulaergen(Fig. 3). The ages of these two intrusions are 282 and 301 Ma,respectively (San et al. 2010; Han et al. 2013).

Geology of the Huangshandong deposit

The Huangshandong deposit contains >50 Mt of sulfide oreswith 0.52 wt% Ni and 0.27 wt% Cu (Wang et al. 1987).Sulfide mineralization occurs in an elongated mafic–ultramaf-ic intrusion, which was emplaced into the Carboniferousschists and slates. On the surface, it measures ~3.5 km inlength and ~1.2 km in width (Fig. 4a). The downward exten-sion of the intrusion exceeds 1,000 m in the central part(Fig. 4b). The long axis of the intrusion is slightly oblique tothe general orientation of prominent foliations in the country

Miner Deposita

rocks (Fig. 4a), indicating that magma emplacement tookplace during regional dextral shearing (Branquet et al. 2012).

Mapping and drill core data show that the Huangshandongintrusion is a composite intrusion consisting of four separateintrusive units (Wang et al. 1987). In the order of magmaemplacement, these are a relatively voluminous layered gab-broic sequence (phase I), a sheet-like ultramafic body (phaseII), a dyke-like gabbronorite body (phase III), and an irregularultramafic unit (phase IV). The gabbroic body occurs at thecenter. It represents >80 % of the intrusion on the surface(Fig. 4a). Modal layering and mineral lineation are visible inthe outcrops of this unit. Major rock types in this unit areolivine gabbro, gabbro, hornblende gabbro, gabbrodiorite,and diorite. The zircon U–Pb age of olivine gabbro is274 Ma (Han et al. 2004). The sheet-like ultramafic body(phase II) shows an upward concave shape in the cross-section (Fig. 4c). It is composed of olivine websterite andlherzolite. No visible modal layering or mineral lineation ispresent in this unit. Disseminated and net-textured sulfides arepresent at the basal portion of this unit. In several places, thebasal sulfide mineralization in phase II extends downward intothe underlying olivine gabbro of phase I (Fig. 4c). The spatialrelationship indicates that the sulfide mineralization in theolivine gabbro formed by downward percolation of sulfideliquids from the overlying ultramafic unit. This type of sulfide

mineralization is thus referred to as exotic sulfide hereafter.Except the exotic sulfide, no economically valuable sulfidemineralization is present in phase I. The dyke-likegabbronorite body (phase III) occurs in the west. The thick-ness of this injected dike-like body is up to ~200 m (Fig. 4a).In the cross-section, it forms a keel for the intrusion (Fig. 4b).The ratio of plagioclase to pyroxenes in the dyke is highlyvariable, but no regular modal layering is observed. Sulfidemineralization occurs mainly as small lenses in the center ofthe dyke (Fig. 4b). Small massive sulfide veins and semi-massive sulfide patches are also present. The last ultramaficintrusive phase (phase IV) cut the lower part of the layeredgabbroic sequence (phase I) and the dyke-like gabbronoritebody (phase III). Lherzolite is predominant but olivinewebsterite is also present in this unit. No visible modallayering or mineral lineation is observed in this unit. Dissem-inated and net-textured sulfides are present in various parts ofthis unit (Fig. 4b).

Sample descriptions

The samples used in this study were collected from outcrops,drill cores ZK12-12 and ZK36-3, and mining tunnels at 650-and 700-m elevations in the western part of the intrusion and

Omolon

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Fig. 1 Simplified geological mapof the Central Asian OrogenicBelt (modified from Jahn 2004)and the distribution of importantmagmatic Ni–Cu deposits in theregion. Sources of U–Pb zirconages: Emeishan flood basalts (Fanet al. 2008), Siberia flood basalts(Kamo et al. 2003), Tarim floodbasalts (Tian et al. 2010), ErbutuNi–Cu deposit (Peng et al. 2013),Hongqiling Ni–Cu deposit (Wuet al. 2004), and Kalatongke Ni–Cu deposit (Han et al. 2004)

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Kawabulak

Huoshishan Niujuanzi

Poshi

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Carboniferous granodiorite

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Junggar basin Santanghu

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Hongliuhe 516 Ma

Tianyu 280 MaBaishiquan 284 Ma

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Fig. 3

Xiadong 313 Ma

Heishan 356 Ma

KumishiPermian granitoids

Beishan

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Central Tianshan

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Fig. 2 Simplified geological map of East Tianshan (modified from Xiaoet al. 2004). Zircon U–Pb ages of ophiolites: Hongliuhe (Zhang and Guo2008), Huoshishan, and Niujuanzi (Tian et al. 2014), Kangguertage (Liet al. 2008), Kawabulak (Xiao et al. 2008), and Kumushi (Yang et al.2011). Zircon U–Pb ages for Baiyanggou basalts, Cheguluquan andQijiaojing rhyolites are from Chen et al. (2011). Zircon U–Pb ages for

mafic–ultramafic intrusions: Baishiquan, Poyi, Poshi, and Tianyu (Qinet al. 2011 and references therein), Heishan (Xie et al. 2012), and Xiadong(Su et al. 2013). Zircon U–Pb ages of granite plutons: the DJSP, BTB, andDLGP (Yuan et al. 2010), Shaerhu (Mao et al. 2014), Kumishi (Ma et al.2013), and others in the Jueluotage terrane (Zhou et al. 2010)

96 00′

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Middle Carboniferous sedimentary rocksLower Carboniferous sedimentary rocksMiddle Devonian volcanic rocks

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Biotite granite

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Huangshan-Jingerquan fualt

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283 Ma

282 Ma282 Ma

301 Ma301 Ma

274 Ma 274 Ma80 Ma80 Ma

280 Ma280 Ma

252 Ma

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Huangshanxi 2Xiangshan

Huangshandong

Fig. 3 The distribution of Early Permian mafic–ultramafic intrusions inthe Jueluotage terrane. Zircon U–Pb ages of mafic–ultramafic intrusions:Erhongwa (Sun et al. 2013b), Huangshandong (Han et al. 2004),

Huangshanxi and Xiangshan (Qin et al. 2011), Hulu (Han et al. 2013),and Tulaergen (San et al. 2010)

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at 610-, 710-, 810-, and 910-m elevations in the central part ofthe intrusion. The sample locations and their projections to theselected cross sections are shown in Fig. 4a–c. Our samplecollection includes all major ore types and important rocktypes. Below are brief descriptions of the samples.

Olivine gabbro is the most primitive rock type in thelayered sequence (phase I). It contains 5–20 % olivine, 30–40 % clinopyroxene, and 30–50 % plagioclase. Olivine crys-tals commonly occur as anhedral grains with diameters vary-ing from 1 to 5 mm (Fig. 5a). Clinopyroxene and plagioclaseoccur as intergrowth surrounding relatively large olivine crys-tals. Minor amounts of hornblende, biotite, and Fe–Ti oxidesoccur in the interstitial spaces.

Gabbronorite of phase III is fine-grained and has a granulartexture (Fig. 5b). It contains 20–35 % clinopyroxene, 10–30 % orthopyroxene, and 15–40 % plagioclase, plus minoramounts of olivine and hornblende. Orthopyroxene occurs asintergrowth with other silicate minerals, not as overgrowth onthe rim of olivine (Fig. 5b).

The ultramafic rocks (olivine websterite, lherzolite) ofphases II and IV commonly show a poikilitic texture

characterized by the occurrence of multiple small roundedolivine inclusions within a large clinopyroxene crystal(Fig. 5c, d). Olivine websterite contains 20–40 % olivine,20–40 % clinopyroxene, and 10–20 % orthopyroxene, plusminor amounts of plagioclase, phlogopite, and Cr-spinel. Cr-spinel occurs as small inclusions within olivine and pyroxenecrystals, whereas plagioclase and phlogopite occur as intersti-tial assemblages. Texturally, lherzolite and olivine websteritein the ultramafic units of the Huangshandong intrusion areremarkably similar, but lherzolite contains higher amounts ofolivine (>40 %). Small, rounded sulfide inclusions within theolivine primocrysts are present in both types of rocks (Fig. 5e).The sulfide inclusions are commonly composed of pyrrhotite,pentlandite, and chalcopyrite.

The most common sulfide ores in the Huangshandongdeposit are disseminated and net-textured ores. Semi-massive sulfide ores and massive sulfide veins are also presentbut volumetrically insignificant. Figure 5f shows a typical net-textured sulfide ore sample from the gabbronorite unit (phaseIII). The primary sulfide assemblage is composed of pyrrho-tite, pentlandite, and chalcopyrite. Secondary pyrite is present

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GabbronoriteUltramafic rocks Ultramafic rocks

Cu-Ni sulfide orebody Infered lithofacies boundary

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Sample locationOrientation of cleavage

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Fig. 4 Plan view (a) and cross-sections (b, c) of the Huangshandong intrusion (modified from Wang et al. 1987)

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in highly altered samples in which olivine, orthopyroxene,clinopyroxene, and plagioclase are replaced by serpentine,talc, tremolite, and epidote, respectively.

Analytical methods

Mineral compositions were determined by wavelength-dispersive analysis using a JEOL JXA8100 electron probe atthe Institute of Geology and Geophysics, Chinese Academy ofSciences, Beijing. The operating conditions were 15 kV ac-celerating voltage, 12 nA beam current, 5 μm beam size, and30 s peak counting time. The compositions of olivine from thephase IV ultramafic rocks were determined by wavelengthdispersive analysis using a CAMECA SX50 electron micro-probe at Indiana University. The operation conditions were15 kV accelerating voltage, 1 μm beam size, 20 s peak

counting time, and beam currents of 20 and 100 nA for majorelements and Ni, respectively. The detection limit for Ni underthese conditions was <100 ppm.

The concentrations of major elements in whole rocks wereanalyzed on fused glass discs using a Shimadzu XRF-1500instrument at the Institute of Geology and Geophysics, Chi-nese Academy of Sciences, Beijing. The loss-on-ignition(LOI) was determined by the weight loss of a powderedsample after 1 h heating at 1,000 °C. The sample powders,1.2 g for each sample, were fused with 6 g lithium tetraborate(Li2B4O7) at 1,050 °C for 20 min. The precision for majorelements was better than 2 %. The accuracy and reproducibil-ity were monitored by the Chinese national standard GSR3.The standard deviation of the standard was better than 1 %.

The abundances of trace elements in whole rocks weredetermined using a Finnigan MAT inductively coupled plas-ma mass spectrometer (ICP-MS) at the Institute of Geology

Fig. 5 Photomicrographs ofimportant rock types and sulfidemineralization in theHuangshandong mafic–ultramafic intrusion. Mineralabbreviations: Cpxclinopyroxene, Cpy chalcopyrite,Hb hornblende, Ol olivine, Opxorthopyroxene, Pl plagioclase, Pnpentlandite, Po pyrrhotite, Sulfsulfide

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and Geophysics, Chinese Academy of Sciences, Beijing. For-ty milligrams of powder from each sample was dissolved in1 ml HF mixed with 0.5 ml HNO3 in a Teflon screw-capcapsules at 170 °C for 10 days. The sample solutions werethen dried and dissolved again in 2 ml HNO3 in the capsules.Finally, the solutions were diluted with 1%HNO3 to 50ml fortrace element analysis. The Chinese national standard GSR3was used to monitor the accuracy and reproducibility. Thestandard deviation of the standard was better than 3 %. Theprecision was better than 5 %.

The contents of Ni, Cu, and Co in sulfide-poor sampleswere analyzed by ICP-MS at the Institute of Geology andGeophysics, Chinese Academy of Sciences, Beijing. Powders(0.1 g) from each sample were mixed with 1.1 g sodiumperoxide and then fused at 700 °C. After cooling, the sampleswere dissolved in 30 % hydrochloric acid for ICP-MS analy-sis. The concentrations of sulfur in sulfide-poor rocks weredetermined using a LECO carbon–sulfur analyzer in the ALSChemex laboratory, Guangzhou, China. The concentrations ofS, Ni, Cu, and Co in sulfide-bearing samples were analyzed byX-ray fluorescence in the same laboratory.

The concentrations of PGE in sulfide-bearing samples weredetermined by the combination of NiS-bead pre-concentration, Te co-precipitation, and ICP-MS analysis inthe National Research Center for Geo-Analysis, Beijing. Theconcentrations of PGE in sulfide-poor samples were deter-mined by the Carius tube digestion and isotope dilution ICP-MS technique of Qi et al. (2007) at the Institute ofGeochemistry, Chinese Academy of Sciences in Guiyang.The detailed analytical procedures, blank concentrations, anddetection limits are given in Qi et al. (2007).

Analytical results

Cr-spinel and olivine compositions

The compositions of Cr-spinel from the Huangshandong ul-tramafic rocks (phases II and IV) are given in the data repos-itory (electronic supplementary material, ESM Table 1). Interms of major element compositions, Cr-spinels from theHuangshandong intrusion are more similar to those fromisland arc basalts than those from Alaskan-type complexesand mafic–ultramafic intrusions associated with continentalflood basalts worldwide (Fig. 6a, b). Specifically, theHuangshandong Cr-spinels tend to have higher Al contentsand Fe2+/(Fe2++Mg) ratios than Cr-spinels from island arcbasalts worldwide. Regionally, the compositions of Cr-spinels from the Huangshandong intrusion are similar to thecompositions of those from the contemporaneous (~284 Ma)Poshi ultramafic intrusion in the Beishan region (Su et al.2011b) but are significantly different from the compositionsof those from the older (~313 Ma) Xiadong Alaskan-type

intrusion in Central Tianshan (Sun et al. 2009; Su et al.2012). Using the empirical equation from Maurel andMaurel (1982), (Al2O3)spinel=0.035×(Al2O3)liquid

2.42, theAl2O3 content in the parental magma of the most primitiveCr-spinel with the highest Cr/(Cr+Al) ratio is estimated to be13.5 wt%.

The compositions of olivine from the Huangshandongmafic–ultramafic intrusion are given in ESM Table 2. It isimportant to note that olivine crystals from theHuangshandong intrusion are all depleted in Ca, containing<1,000 ppm Ca (ESM Table 2). Ca-depleted olivine crystals(i.e., containing <1,000 ppm Ca) are common in arc basaltsand associated mafic–ultramafic intrusions, but rare in mid-ocean ridge basalts, ocean island basalts, continental floodbasalts, and associated layered intrusions (see summary in Liet al. 2012b). In the Tianshan–Beishan region, in addition tothe Huangshandong intrusion, some contemporaneous mafic–ultramafic intrusions such as Erhongwa (Sun et al. 2013b) andPoyi (Xia et al. 2013) also contain Ca-depleted olivine. Theolder, subduction-related mafic–ultramafic intrusions in theregion such as the 356 Ma Heishan intrusion (Xie et al.2012, 2014) and the 313 Ma Xiadong intrusion (Su et al.2012) all contain Ca-depleted olivine.

The variation of Mn versus Fo in olivine from theHuangshandong mafic–ultramafic intrusion is illustrated inFig. 7a. Olivine crystals from the ultramafic rocks have higherFo and lower Mn contents than those from the coexistingmafic rocks. There is a compositional gap for olivine betweenthe mafic and ultramafic host rocks. The variation of Ni versusFo in olivine from the different types of rocks in theHuangshandong intrusion is illustrated in Fig. 7b. Olivinecrystals from the gabbroic layered sequence (phase I) are mostfractionated, containing Fo<69 mol%. Within this unit, oliv-ine in sulfide-barren samples is highly depleted in Ni(<250 ppm), whereas olivine in sulfide-bearing samples issignificantly enriched in Ni (>1,300 ppm). Olivine crystalsfrom the gabbronorite unit (phase III) are also highly fraction-ated, containing Fo <77 mol%. Similar to the relationshipobserved in phase I, olivine in sulfide-barren samples fromthe gabbronorite unit is significantly depleted in Ni(<600 ppm), whereas olivine in sulfide-bearing samples fromthe same unit is relatively enriched in Ni (>1,600 ppm). Thedramatic change in Ni contents between sulfide-barren andsulfide-bearing samples, which characterizes the mafic unitsof the Huangshandong intrusion, is not observed in the ultra-mafic units of the intrusion (see ESM Table 2). For clarity, thecompositions of olivine in sulfide-bearing samples from theultramafic units are not shown in Fig. 7b. The Fo contents ofolivine crystals from the ultramafic units overlap, but thosefrom phase IV tend to be higher, varying between 81 and85 mol% (Fig. 7b). The Fo contents of olivine crystals fromphase II are between 81 and 84 mol%, and the grains showwide Ni variation. In both units, olivine crystals from sulfide-

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barren samples show a rapid decrease in Ni content with smalldecrease in Fo content (Fig. 7b). The significance of thisrelationship will be discussed below based on modelingresults.

Whole rock major and trace element compositions

The concentrations of major and trace elements in theHuangshandong mafic–ultramafic intrusive rocks analyzedby us are given in ESM Table 3. Some of the samples containup to 0.5 wt% S. A compositional comparison of whole rockswith important minerals is illustrated in Fig. 8. In the compar-ison, the whole-rock compositions are normalized to 100 %free of LOI and sulfides. The total amount of sulfide in asulfide-bearing sample was estimated using the compositionof FeS (pyrrhotite) to represent bulk sulfide composition, i.e.,total sulfide=2.75×S. From the total Fe in the sample, the Fecontent in the bulk sulfide was then subtracted. The error forthe estimated amount of total sulfide in a sample is negligiblebecause the total metal/S weight ratios of other importantsulfide minerals such as pentlandite and chalcopyrite are alsoclose to 2.75. The error of estimated Fe in the bulk sulfidewithout considering Ni and Cu contents in the sulfide is alsonegligible because the contents of Ni and Cu in the sulfide arecommonly one order of magnitude lower than Fe. As shownin Fig. 8, the mafic and ultramafic rocks plot in two separateclusters. The major element compositions of the ultramaficrocks are mainly controlled by the abundances of olivine,pyroxenes, and hornblende. In contrast, the major elementcompositions of the mafic rocks are mainly controlled by theabundances of plagioclase, pyroxenes and hornblende.

The concentrations of trace elements in the Huangshandongmafic–ultramafic intrusive rocks are given in ESMTable 3. Thechondrite-normalized rare-earth element (REE) and primitivemantle-normalized immobile trace element patterns for theHuangshandong intrusion are shown in Fig. 9a–d. The averagecompositions of Permian basalts from the Tarim and Tuha

a bFe3+

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Dunite, Xiadong intrusion

Subvolcanic intrusions related to flood basaltsAlaskan-type zoned ultramafic complexesIsland arc basalts

Fig. 6 Compositionalcomparison of Cr-spinels fromthe Huangshandong ultramaficrocks and elsewhere in the world.Data sources: Huangshandongultramafic rocks (this study), Poyiultramafic intrusion (Su et al.2011b), Xiadong Alaskan-typeintrusion (Sun et al. 2009), andother types of rocks (Barnes andRoeder 2001)

Fo (mole %)657075808590

Ni (

ppm

)

0

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1000

1500

2000

2500Fo (mole %)

657075808590

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(ppm

)

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Ultramafic rocks

Ol gabbroGabbronorite

Data from Gao and Zhou (2013)

Data from Sun et al. (2013)

Sulfide-bearing ol gabbro

Sulf : Ol= 1 : 80

Sulf : Ol= 1 : 100

Olivine fractionation

a

b

Ol gabbro Phase I

Phase IV

Phase IIIPhase IIUltramafic

rocks

Sulfide-bearing gabbronorite

Phase IISulfide-bearing ultramafic rocks

Ni gainfrom

sulfide Ni gainfrom

sulfide

Fig. 7 Compositional variations of olivine from the Huangshandongmafic–ultramafic intrusion. See text for modeling results

Miner Deposita

basins are included for comparison. All of the Huangshandongintrusive rocks show slight enrichments in light REE relative toheavy REE (Fig. 9a, b). Most of the mafic rocks are character-ized by positive Eu anomalies (Fig. 9a). Strikingly differentfrom the Tarim basalts but remarkably similar to the Tuhabasalts, all of the Huangshandong intrusive rocks show pro-nounced negative Nb–Ta anomalies relative to Th and La(Fig. 9c, d).

In the plot of Th/Yb versus Nb/Yb (Fig. 10), all of thesamples from the Huangshandong intrusion plot within thefield of modern volcanic arc basalts worldwide, which issimilar to the result for the Tuba basalts but clearly differentfrom that for the Tarim basalts.

Chalcophile elements

The concentrations of PGE, Ni, Cu, and S in the sulfide-mineralized samples from the Huangshandong intrusion aregiven in ESM Table 4. Good positive correlations between Niand S are observed in the whole-rock samples containing>0.3 wt% S (Fig. 11a). The ultramafic rocks containing<0.3 wt% S plot significantly above the Ni–S correlation trenddue to significant Ni contribution from olivine in the samples.Copper also shows a good positive correlation with S except a

few semi-massive and massive sulfide ores containing>20 wt% S (Fig. 11b). The decoupling between Ni and Cuin these samples indicates fractionation between pentlanditeand chalcopyrite at the sample scale. The sulfide-mineralizedsamples (>0.3 wt% S) show good positive correlations be-tween PGE and S contents (Fig. 11c, d).

The concentrations of chalcophile elements in therecalculated 100 % sulfide are referred to as metal tenorsbelow. Using the equation of Barnes and Lightfoot (2005),which is based on the assumption that the magmatic sulfideassemblage is composed of pyrrhotite, pentlandite, and chal-copyrite (Naldrett and Duke 1980; Li et al. 2001), we havecalculated the metal tenors for the Huangshandong sulfide-mineralized samples containing >0.3 wt% S. These values areused in the discussion below. Except several samples, Ru andIr are positively correlated with Rh in the Huangshandongdeposit (Fig. 12a, b). In contrast, no correlations are presentbetween Pd and Rh (Fig. 12c), and between Pt and Rh(Fig. 12d).

The primitive mantle-normalized patterns of metal tenorsin the samples are shown in Fig. 13a–d. Regardless of hostlithology, the bulk sulfide ores are all depleted in PGE relativeto Ni and Cu and show PPGE (Pt, Pd) enrichments relative toIPGE (Os, Ir, Ru, and Rh). Platinum anomalies relative to Rh

0

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MgO (wt%) MgO (wt%)

MgO (wt%) MgO (wt%)

Mafic rocks, Phase IGabbronorite, Phase III

Ultramafic rocksMafic rocks, Phase IGabbronorite, Phase IIIUtramafic rocks, Phase II and Phase IV

Data from Gao and Zhou (2013),Sun et al. (2013a) and Deng et al. (2014)

This study

Fig. 8 Comparison of majoroxide contents in whole rocks.Also shown are the compositionsof constituent minerals in therocks, Huangshandong mafic–ultramafic intrusion. Mineralabbreviations: Cr-sp Cr-spinel;others are the same as in Fig. 5

Miner Deposita

are common for the exotic sulfide mineralization in olivinegabbros (phase I) containing >7 wt% S (Fig. 13a). NegativePd anomalies relative to Rh are common in the sulfide

mineralization within the gabbronorite unit (phase III), espe-cially in the samples containing >7 wt% S (Fig. 12c). Nosignificant Pt–Pd anomalies are present in the sulfide oreshosted in the ultramafic units (phases II and IV) (Fig. 13b, d).

Modeling and discussion

Controls on PGE tenors

Positive correlations between Rh, Ir, and Rh in theHuangshandong deposit (Fig. 12a, b) are expected becausethese elements behave similarly during immiscible sulfidesegregation from magma and fractional crystallization ofmonosulfide solid solution (MSS) from sulfide liquid (seeexperimental data compiled by Naldrett 2011). Lack of corre-lation between Rh and Pd or Pt in the Huangshandong deposit(Fig. 12c, d) is also expected because these elements behavedifferently during MSS fractional crystallization (seesummary in Naldrett 2011). The PGE data reveal that the bulksulfide compositions of the Huangshandong deposit are main-ly controlled by variations in parental magma compositionand R-factor (magma/sulfide mass ratio, Campbell andNaldrett 1979) during sulfide–liquid segregation, and by sub-sequent MSS fractional crystallization.

Pronounced negative and positive Pt anomalies relative Rhand Pd that are present in some of the samples from theHuanshandong deposit (Fig. 13a) could be due to crystalliza-tion of Pt minerals from magmatic sulfide liquid or Pt redis-tribution during post-magmatic hydrothermal alteration. The

Ultramafic rocks, Phase IIUltramafic rocks, Phase IV

Ultramafic rocksData from previous studiesMafic rocks, Phase I

Gabbronorite, Phase III

Data from previous studes

Data from this study Data from this study

Gabbronorite, Phase III Ol gabbro and gabbro, Phase I Hb gabbro, Phase I

Tarim basaltTuha basalt

Tarim basaltTuha basalt

sam

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itive

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Th Nb Ta La Ce Pr Nd Zr HfSmGdDyHo Er Y Yb Lu Th Nb Ta La Ce Pr Nd Zr HfSmGdDyHo Er Y Yb Lu

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

sam

ple

/ cho

ndrit

e

10-1

100

101

102

103

a b

c d

Fig. 9 Chondrite-normalizedREE patterns (a, b) and primitivemantle-normalized incompatibleelement patterns (c, d) for theHuangshandong mafic–ultramafic intrusive rocks. Datasources: Huangshandong (thisstudy; Zhou et al. 2004; Gao andZhou 2013; Sun et al. 2013a;Deng et al. 2014), Tuha basalts(Zhou et al. 2006), Tarim basalts(Zhou et al. 2009), chondrite(Anders and Grevesse 1989), andprimitive mantle (Sun andMcDonough 1989)

VAB

Tarim basalt

Tuha basalt

PM

LC

MC

UC

OIB

E-MORB

MORB-OIB Arra

y

N-MORB

Nb / Yb10-1 100 101

Th

/ Yb

10-2

10-1

100

101

Thisstudy Gabbronorite, Phase III

Ultramafic rocksUltramafic rocks, Phase II

Ultramafic rocks, Phase IV

Ol gabbro, Phase I Previous studies

Fig. 10 Th/Yb versus Nb/Yb plots for the Huangshandong mafic–ultra-mafic intrusion. Data sources: Huangshandong (this study; Gao and Zhou2013; Sun et al. 2013a), Tarim basalts (Zhou et al. 2009), Tuha basalts(Zhou et al. 2006), the upper, middle, and lower crusts (UC,MC, and LC)(Rudnick and Gao 2003), primitive mantle (PM), OIB, N-MORB and E-MORB are (Sun andMcDonough 1989), MORB-OIB array (Pearce et al.1992), and modern global volcanic arc basalts (VAB) (http://www.petdb.org)

Miner Deposita

former is thought to have taken place in the Jinchuan deposit,China (Prichard et al. 2013), whereas the latter is believed tohave occurred in the Lac des Iles Pd deposit, Canada(Boudreau et al. 2014).

The classification of the olivine gabbro-hosted sulfide min-eralization (phase I) beneath the basal sulfide mineralizationof the overlying ultramafic unit (phase II) as exotic sulfide (seeFig. 4c) is supported by similar metal tenors between thesetwo types of sulfide mineralization (Fig. 14). Specifically, theNi tenors of the exotic sulfide ores are too high to havesegregated from the parental magma of the gabbro. As shownin Fig. 7b, olivine crystals from sulfide-barren gabbros ofphase I contain ~67 mol% Fo and <300 ppm Ni. Using anassumed olivine/magma DNi=20, which is similar to the av-erage experimental value for such highly fractionated olivine(see summary in Li and Ripley 2010), the Ni content in theparental magma is estimated to be <15 ppm. The partitioncoefficient of Ni between immiscible sulfide liquid and basal-tic magma is ~500 (see experimental data compiled byNaldrett 2011). Applying this value, the Ni content in thesulfide liquid segregating from the parental magma is estimat-ed to be <0.75 wt%, which is about one order of magnitudelower than the Ni tenors in the exotic sulfide ores (Fig. 14a).

Similarly, the Ni tenors of the sulfide ores in thegabbronorite dyke (phase III) are too high to have segregatedfrom the parental magma of the dyke. Olivine in sulfide-barren samples from this dyke contains ~72 mol% Fo and<600 ppm Ni (Fig. 7b). Using reasonable olivine/magmaDNi=18 for such olivine (see summary in Li and Ripley2010) and sulfide/magma DNi=500 (see summary inNaldrett 2011) for modeling, the Ni content in the sulfideliquid to segregate from the parental magma of this dyke isestimated to be <1.7 wt%, which is two to four times less thanthe Ni tenors in the sulfide ores in the dyke (Fig. 14a). Thisobservation, together with the fact that the sulfide ores in thegabbronorite dyke (phase III) and the early ultramafic intru-sive unit (phase II) have similar metal tenors (Fig. 14a, b),supports a new interpretation that the sulfides in thegabbronorite dyke were cannibalized. It is deduced that thecannibalized sulfides originally segregated from the parentalmagma of the ultramafic unit (phase II) in the conduit andwere subsequently picked up by the parental magma of thegabbronorite dyke (phase III), which used the same conduit.

The forgoing analysis shows that the sulfide ores in theHuangshandong composite intrusion all originated from theparental magmas of two ultramafic intrusive units (phases II

S wt%

10-2 10-1 100 101 102

Ni p

pm

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Gabbronorite, Phase III Exotic sulfide in Ol gabbro, Phase I

Ultramafic rocksGabbronorite, Phase III Ultramafic rocks, Phase II

Exotic sulfide in Ol gabbro, Phase I

Ultramafic rocks, Phase IV

Previous studiesThis study

Fig. 11 Plots of metals versus Scontents in whole-rock samplesfrom the Huangshandong Ni–Cudeposit. Data are from this study,Gao et al. (2013), Sun et al.(2013a), and Deng et al. (2014)

Miner Deposita

and IV). We have used the equation of Campbell and Naldrett(1979) to estimate the initial contents of Pd and Rh in the

magmas and R-factors based on the samples containing 0.3–12 wt% S and >0.2 wt% Ni in whole rocks. Samples

Exotic sulfide in Ol gabbro, Phase IThis study Previous study

Ultramafic rocksGabbronorite, Phase IIIExotic sulfide in Ol gabbro, Phase I

Gabbronorite, Phase IIIUltramafic rocks, Phase IIUltramafic rocks, Phase IV

a b

c d

Rh ppb10-1 100 101

Ru

ppb

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Ir p

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103

Rh ppb10-1 100 101

Pt p

pb

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102

103

Fig. 12 Plots of Rh versus Ru(a), Ir (b), Pd (c), and Pt (d)contents in recalculated 100 %sulfide for the samples containing>0.3 wt% S from theHuangshandong Ni–Cu deposit.Data sources: this study, Gao et al.(2013), Sun et al. (2013a), andDeng et al. (2014)

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Ni Os Ir Ru Rh Pt Pd Cu

Ni Os Ir Ru Rh Pt Pd CuNi Os Ir Ru Rh Pt Pd Cu

Ni Os Ir Ru Rh Pt Pd Cu10-2

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Phase II Ultramafic unitExotic sulfide in Ol gabbro of Phase I ba

d

0.3 < S < 7 wt%Previous studiesThis study

0.3 < S < 7 wt%S > 7 wt% S > 7 wt%

0.3 < S < 7 wt%Previous studies

This study0.3 < S < 7 wt%S > 7 wt%

S > 7 wt%

0.3 < S < 7 wt%Previous studiesThis study

0.3 < S < 7 wt%S > 7 wt%

This study0.3 < S < 7 wt%

Gabbronoritic dyke Ultramafic unit

Fig. 13 Primitive mantle-normalized patterns of metaltenors in the Huangshandong Ni–Cu deposit. Data for the depositare from this study, Gao et al.(2013), Sun et al. (2013a), andDeng et al. (2014). The primitivemantle values are from Barnesand Maier (1999)

Miner Deposita

containing <0.2 wt% Ni are excluded to avoid large errors forthe estimated metal tenors due to significant Ni contributionfrom olivine. Samples containing >12 wt% S are also exclud-ed because these samples are more likely to have experiencedsulfide liquid fractionation at the sample scales. As shown inFig. 14b, the samples containing 0.3–7 wt% S all plot close tothe model line of sulfide liquid segregation from magmacontaining 0.01 ppb Rh and 0.2 ppb Pd. The modeled R-factors vary between 100 and 1,000. Some of the samples,especially those with higher S contents (7–12 wt%), aredisplaced from the model line due to MSS fractional crystal-lization. The samples containing more cumulus MSS fallfarther below the model line, whereas those containing morefractionated sulfide liquid plot farther above the model line.Based on the compositions of sulfide ores from Sudbury,Naldrett et al. (1994) pointed out that sulfide liquid fraction-ation tends to occur in samples with high S contents (>6 wt%)because residual sulfide liquids formed by MSS fractionalcrystallization are more likely to escape from the samples.The data from the Huangshandong deposit are consistent withthis observation.

Our modeling results show that the parental magmas of theHuangshandongmagmatic sulfide deposit are depleted in bothIPGE (represented by Rh) and PPGE (represented by Pd). Theestimated initial contents of these elements in the parental

magmas for the Huangshandong deposit are about two ordersof magnitude lower than the abundances of these elements inPGE undepletedmantle-derivedmagmas such as some picriticbasalts from Siberia (Lightfoot and Keays 2005) andEmeishan, western China (Li et al. 2012c).

Magma compositions

No chilled margins that may represent the compositions ofparental magmas for the different units of the Huangshandongintrusion have been found. As shown in Fig. 5d, somelherzolite samples from the phase IV ultramafic unit are char-acterized by orthocumulus texture. A method to estimate theliquid composition for this type of samples based on whole-rock and olivine compositions is given in Li and Ripley(2011). We have used this method to estimate the parentalmagma composition for the samples. In our calculations weused the average composition of two sulfide-barren lherzolitesamples containing the most primitive olivine (Fo86) withinthis unit (sample HSD19 and HSD21-2), the olivine–liquidexchange coefficient (FeO/MgO)Ol/(FeO/MgO)Liq of 0.3 byRoeder and Emslie (1970) and an assumed FeO/(FeO+Fe2O3) ratio of 0.9 for the liquid. The results are listed inTable 1. The Al2O3 content in the estimated parental magmafor the Huangshandong ultramafic rocks is 13.8 wt%, similar

Previous studies

Previous studies

This study

This studyThis study

7<S<12 wt.% 0.3<S<7wt.%0.3<S<7wt.%

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Gabbronorite, Phase III Exotic sulfide in olivine gabbro of Phase I

This study

a b

R100

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10

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Fig. 14 Variations of metaltenors in the samples containing0.3–12 wt% S and >0.2 wt% Nifrom the Huangshandong Ni–Cudeposit. Data sources: this study,Gao et al. (2013), Sun et al.(2013a), and Deng et al. (2014).See text for modeling results

Table 1 Estimated magma compositions for the Huangshandong lherzolite (in wt%)

Magma Reference SiO2 TiO2 Al2O3 Fe2O3 FeO MnO MgO CaO Na2O K2O P2O5 Total

Parental magma Sun et al. 2013a 51.92 0.76 18.82 8.36a 0.15 7.38 8.56 3.32 0.53 0.2 100

Parental magma This study 53.59 0.86 13.79 1.01 9.38 0.15 10.03 8.26 1.88 0.90 0.15 100

Primary magma This study 52.04 0.75 12.15 0.89 9.61 0.14 14.56 7.28 1.66 0.79 0.13 100

a Total Fe reported as FeO

Miner Deposita

to the value (13.5 wt%) estimated based on the composition ofthe most primitive Cr-spinel in the rocks. The MgO content inthe estimated parental magma is 10 wt%, which is ~2.5 wt%higher than the value estimated previously by Sun et al.(2013a). The difference mainly reflects different olivine com-positions in the samples used in the calculations. The Focontent of olivine in the lherzolite samples chosen by Sunet al. (2013a) is 83 mol%, which is 3 mol% lower than in thesamples used in this study.

We have also estimated the compositions of primarymagma for the Huangshandong intrusion by adding theaverage composition of olivine with Fo contents varyingfrom 86 to 90 mol% to the parental magma for the mostprimitive lherzolite in the intrusion until the magma is inequilibrium with mantle olivine (i.e., Fo90). The totalamount of added olivine is ~12 wt%. A primary magmais an original mantle-derived magma before undergoingany differentiation during ascent and ponding in the crust.Our estimates are listed in Table 1. The MgO content inthe estimated primary magma is 14.6 wt%. The modelingresults of mantle partial melting by Naldrett (2011) showthat a primary magma containing <16 wt% MgO will bedepleted in PGE because such magma cannot dissolve allof the sulfides in the mantle during partial melting.Therefore, we conclude that the PGE depletion in theparental magmas of the Huangshandong deposit is dueto sulfide retention in the mantle, though we cannotcompletely rule out the possibility of another sulfidesegregation event after the magma had left the sourcemantle but before the sulfide segregation event thatproduced the sulfide liquids for the Huangshandongdeposit.

Olivine fractional crystallization and sulfide segregation

We have used theMELTS program of Ghiorso and Sack (1995)and Asimow and Ghiorso (1998) to simulate the fractionalcrystallization of the parental magma for the most primitivelherzolite in the Huangshandong intrusion at 1 kb total pressureand a constant oxidation state equal to that of a half logarithmunit below the fayalite–magnetite–quartz buffer. The initialcontent of H2O in the magma was set at 1.0 wt%. This choiceis based on the ubiquitous occurrence of minor magmatichornblende in the ultramafic rocks of the intrusion. Under theseconditions the crystallization sequence for the first 30 wt%crystallization is olivine, orthopyroxene, clinopyroxene, andplagioclase plus clinopyroxene, which is generally consistentwith the textural observations described above.

The variations of olivine Fo and Ni contents with thedegree of fractional crystallization can be obtained fromthe MELTS simulation and numerical modeling using theRayleigh fractionation equation for trace elements, respec-tively (see summary in Li et al. 2007). We have used

these methods to model the observed compositionalvariations of olivine from the Huangshandong intrusion.In our calculations, the partition coefficients of Ni betweenolivine and magma and between sulfide liquid and magmawere assumed to be 13 and 500, respectively. The formeris within the range estimated based on liquid compositionand temperature using the equation of Li and Ripley(2010); the latter is within the experimental values forbasaltic magma (see data compiled by Naldrett 2011).The modeling results are shown in Fig. 7b. The observedNi–Fo variations of olivine from the sulfide-barren ultra-mafic rocks can be explained by olivine fractional crystal-lization coupled with immiscible sulfide liquid segregationfrom the magma. The occurrence of small, rounded sulfideinclusions in olivine crystals enclosed in clinopyroxeneoikocrysts in the ultramafic units (e.g., Fig. 5e) is consis-tent with the modeling results.

Cause of sulfide saturation

Magma mixing, fractional crystallization and crustal contam-ination are important processes to induce sulfide saturation inmantle-derived mafic magma (see summary in Ripley and Li2013). These processes may be all involved in a single mag-matic system. If this does occur, it is difficult to know whichprocess is critical in triggering sulfide saturation in themagma.

As described above, the parental magmas of theHuangshandong magmatic sulfide deposit are moderatelyfractionated. Thus, it is useful to investigate if olivinefractional crystallization alone can cause sulfide saturationin the magmas. At 30 kb (~90 km), the sulfur content atsulfide saturation (SCSS) in the primary magma is esti-mated to be 1,300 ppm using the equation of Li andRipley (2009). The temperature of the primary magma at30 kb is estimated by extrapolation from the temperaturesfor 10–20 kb calculated using pMELTS (Ghiorso et al.2002). At 1 kb, the SCSS in the primary magma isestimated to be 1,900 ppm, which is 600 ppm higher thanthe content of S in the primary magma (Fig. 15). After~8 wt% olivine fractional crystallization, the fractionatedmagma will become saturated with sulfide again due todecreasing SCSS and increasing S content in the magma(S enrichment, Fig. 15). The modeling results show that itis possible that sulfide saturation in the Huangshandongmagmatic system was induced by olivine fractionalcrystallization.

A modified ore genetic model

The arc-like geochemical characteristics for the PermianHuangshandong intrusion in a post-subduction environmentcan be explained by modification of the source mantle by slab

Miner Deposita

fluids associated with the Pre-Permian subduction event. Par-tial melting in the fluid-modified mantle is thought to haveresulted from heating by a mantle plume (e.g., Qin et al. 2011;Su et al. 2011a) or asthenosphere upwelling associated withlithosphere delamination (e.g., Zhang et al. 2011; Song et al.2013).

The ore formation in the Huangshandong magmaplumbing system is illustrated in Fig. 16. The first batchof magma to arrive at Huangshandong was most fraction-ated. It formed the ore-barren gabbroic layered sequence.This was followed by a more primitive magma, whichcarried small amounts of immiscible sulfide droplets andolivine crystals from depth. After arrival, the sulfidedroplets settled down to form the basal sulfide minerali-zation in this unit. Some of the sulfide liquids percolatedfurther down into the underlying gabbroic rocks. Thesulfide ores in the gabbronorite dyke formed by cannibal-ized sulfide liquids that were transported from depth.These sulfide liquids were produced by an early batch ofmagma (phase II) in the conduit. They were picked up by

a new surge of magma (phase III) ascending through thesame conduit. The sulfide liquids became concentratedtoward to center of the dyke, possibly due to flow differ-entiation in the rapidly ascending magma. The last batchof magma going through the Huangshandong plumbingsystem formed another sulfide-mineralized ultramafic unit(phase IV).

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S enrichment

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ma

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Fig. 15 Variation of sulfur contents at sulfide saturation in theHuangshandong magma during ascent and fractional crystallization.Mineral abbreviations are the same as in Fig. 5. See text for modelingand explanations

a

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sulfide downward percolation

Phase I

Phase I

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�Fig. 16 A multistage magma plumbing model for the Huangshandongmagmatic sulfide deposit. The first pulse magma to arrive atHuangshandong was most fractionated. It crystallized to form the sulfideore-barren gabbroic layered sequence (phase I) (a). This was followed by amore primitive magma containing immiscible sulfide droplets. Uponemplacement, the sulfide liquids settled down to form the basalmineralization in this unit (phase II). Some of the sulfide liquidspercolated downward into the underlying gabbros (a). A new surge ofmore fractionated magma (phase III) ascended through the same conduit,picked up the sulfide liquids left in the conduit by the second pulse magma(phase II) and deposited them at Huangshandong as the magma continuedto ascend to higher levels (b). The last pulse magma ascending through theHuangshandong plumbing system formed another sulfide-mineralizedultramafic unit (phase IV) (c)

Miner Deposita

Conclusions

The Huangshandong sulfide-ore bearing mafic–ultramafic in-trusion is the product of basaltic magmatism in a post-subduction setting. The Huangshandong intrusive rocks arecharacterized by arc-like geochemical signatures because thesource mantle was modified previously by slab-derived fluids.The PGE tenors in the Huangshandong deposit are extremelylow, possibly because the primary magma was depleted inPGE due to sulfide retention in the source mantle. Sulfidesaturation in the Huangshandong magma was most likelyinduced by moderate degree of olivine crystallization in astaging chamber and/or during magma ascent. The resultantimmiscible sulfide liquids were transported by several batchesof ascending magma and deposited upon their arrival atHuangshandong.

Acknowledgments We thank Guan-Liang Ren, Jun-Hui Xie, and Xue-Jun Yan for logistic support in field work; Sheng-Chao Xue, Hong-YeFeng, and Ye Tian for assistance in sampling; Liang Qi, Ya-Li Sun, Yue-HongWang, and Ding-Shuai Xue for guidance in chemical analyses; andWen-Jiao Xiao and Ke-Fa Zhou for useful discussion. Constructivereviews by Alan Boudreau and Wolfgang Maier are appreciated. Thisstudy was financially supported by the NSF of China (41030424), theCAS/SAFEA International Partnership Program for Creative ResearchTeams (KZZD-EW-TZ-20), and the Xinjiang NonferrousMetals IndustryGroup Ltd.

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