Lithos 212–215 (2015) 128–144

Contents lists available at ScienceDirect

Lithos

j ourna l homepage: www.e lsev ie r .com/ locate / l i thos

Mineral inclusions and SHRIMP U–Pb dating of zircons from the Alamasnephrite and granodiorite: Implications for the genesis of a magnesianskarn deposit

Yan Liu a,⁎, Rongqing Zhang b, Zhiyu Zhang a, Guanghai Shi c, Qichao Zhang d,Maituohuti Abuduwayiti e, Jianhui Liu f

a Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, PR Chinab State Key Laboratory for Mineral Deposits Research (Nanjing University), School of Earth Sciences and Engineering, Nanjing University, Nanjing 210093, PR Chinac State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, PR Chinad Chinese Academy of Geological Sciences, Beijing 100037, PR Chinae Hetian Bureau of Quality and Technical Supervision, Hetian, 848000 Xinjiang, PR Chinaf Beijing SHRIMP Center, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, PR China

⁎ Corresponding author.E-mail address: ly@cugb.edu.cn (Y. Liu).

http://dx.doi.org/10.1016/j.lithos.2014.11.0020024-4937/© 2014 Elsevier B.V. All rights reserved.

a b s t r a c t

a r t i c l e i n f o

Article history:Received 20 April 2014Accepted 3 November 2014Available online 14 November 2014

Keywords:Zircon U–Pb datingMg-skarn depositAlamas nephrite depositHetianXinjiangNW China

Extending approximately 1300 km and located in theWestern KunlunMountains, the Hetian nephrite belt is thelargest nephrite belt in theworld and contains approximately 11major deposits andmore than 20 orebodies in-cluding the Alamas deposit. Hetian nephrite deposits can be classified as Mg-skarn deposits with Precambriandolomitic marble host rock and green, green–white and white nephrite zones are distributed gradually in thezone of a granodiorite pluton. The green nephrite ismainly predominately composed of tremolite with generallyminor to trace constituents of diopside, grossularitic garnet, actinolite and other minerals. Also green nephritehas higher content of TFe2O3, than green–white and white nephrites have. We subdivided the zircons from thegreen nephrites into four types, depending on their internal textures, mineral inclusions, and SHRIMP U–Pbages. Type I zircons are round instead of idiomorphic in shape and lack obvious zoning. Type II and IV zirconshave broad, clear oscillatory zoning and are hypidiomorphic or idiomorphic in shape; they contain inclusionsof diopside, tremolite, chlorite and calcite. Most Type III zircons are narrow rims (b10 μm) surrounding Type IIand Type I zirconswith highly luminous brightness and no zoning. Both Type I and Type II zircons have individualages of 411 to 445 Ma and Type IV zircons have younger ages (388 to 406 Ma). Among the concordant ages,425.7 ± 5.8 Ma and 420.0 ± 9.9 Ma for the QYZr1 and QYZr2 are consistent within error, with the 418.5 ±2.8 Ma of the Alamas granodiorite formation age and themaximum age of the Alamas nephrite deposit. The par-tially recrystallization of zircons during skarn formation possibly lead to some younger individual ages (406.5 to308Ma). In theWestern KunlunMountain, both Buya granite and Alamas grandiorite are high Ba–Sr granites andcrystallized in Western Kunlun Orogen. The Buya granite formed at about 430 Ma in a post-orogenic tectonicenvironment. Considering Alamas granodiorite formed at about 12 Ma younger than that of Buya granite andit is convincible that Alamas granodiorite also formed at a post-orogenic tectonic environment. Together withthe evolution ofWestern KunlunMountain, it is also possible that high Ba–Sr Alamas granodiorite and the neph-rite deposit formed in the post-orogenic stage. Most zircons in the Alamas granodiorite and green nephrite havehigh Th/U ratios (N0.1), similar REE and trace element patterns, a Ce anomaly (Ce/Ce* N 5), and ΣREE contents of454 to 922 ppm and 102 to 3182 ppm with averages of 627 ppm and 855 ppm, respectively. The similar geo-chemical signatures, morphologies, and ages indicate that most zircons (or fragments of zircon) in the nephritecame from the granodiorite and some experience partially recrystallized during skarnization. This is consistentwith the field observation that original granodiorite–dolomitic marble boundary is now represented within anephrite sequence, with the green nephrite close to the granodiorite and the white/white–green nephritesadjoining the dolomitic marble. Typical skarn deposits experience prograde and retrograde metasomatismstages. According to the field observations and petrographic studies, both prograde metasomatism and theearly retrograde altered stages are two main stages for the formation of Alamas nephrite deposits. The replace-ments of coarse-grained tremolite by fine-grained tremolite (nephrite) lead to the formation of nephrite.

129Y. Liu et al. / Lithos 212–215 (2015) 128–144

Based onpetrographic studies, themain formation processes of thenephrite are 1) diopside←dolomite; 2) trem-olite (nephrite)← diopside; and 3) chlorite← tremolite (nephrite). Thus, the timing of the formation of nephriteis later than that of Mg-skarn.

© 2014 Elsevier B.V. All rights reserved.

1. Introduction

Nephrite has both metasomatic and metamorphic origins (Harlowand Sorensen, 2000, 2005; Leaming, 1978). For Hetian nephrite de-posits, they are formed in igneous contact zone and have the metaso-matic origin (Y. Liu et al., 2010, 2011a). Still some other nephritedeposits have the metamorphic origin in various places. As a world-class nephrite deposit worthy of broad scientific interest, the Hetiannephrite belt is imperfectly understood in particular aspects of its for-mation age and tectonic background. The intrusion of the granodioritesand granites would have been the main driving force behind theformation of the nephrite, especially in the Hetian nephrite belt,

Fig. 1. Tectonic division of XinjFrom Xu et al. (2008).

which extends for about 1300 km along the Western Kunlun Moun-tains. Themechanism of nephrite formation in Hetian should reveal im-portant clues on the migration of elements during the metasomaticprocesses involved in the formation of skarn. Theoretically, the age ofthe nephrite should provide an accurate and necessary timing con-straint on regional tectonics. An understanding of the Alamas granodio-rite and nephrite deposits will, in turn, partly provide us with anunderstanding of the geological and tectonic evolution inWestern Kun-lun Mountains.

Nephrite is an almost monomineralic rock, consisting mainly oftremolite (Ca2Mg5Si8O22(OH)2) together with minor apatite, diopside,actinolite, chlorite, calcite, and other minerals. It is valuable for its

iang and its adjacent area.

130 Y. Liu et al. / Lithos 212–215 (2015) 128–144

potential to be turned into ornamental carvings, and polished pieces arehighly prized.Major nephrite deposits occur in theKunlunMountains ofXinjiang, China, the East Sayan Mountains of Siberia, Russia (Prokhor,

Fig. 2. A. Geological sketch map showing three main primary nephrite deposit belts alongthe Kunlun Mountains in the Hetian nephrite deposit: Shache–Yecheng, Hetian–Yutian,and Qiemo–Ruoqiang. “▲” represents nephrite orebodies. Liushen Village is shown as oand the Alamas nephrite orebody as▲, in the rectangle. Two secondary nephrite depositson the Yurungkash River (White Jade River) and the Karakash River (Black Jade River) arealso found in the Hetian nephrite deposit, Xinjiang, China (modified after Tang et al.,1994). B. Y11-1 and Y11-2, the twomain nephrite veins in Alamas. Samples are from crosssection A–A′ (modifiedafter Jiang, 1986). C. The cross section shown asA–A′ in Fig. 1Bwithlocations of wallrocks and nephrite samples (modified after Tang et al., 1994). Abbrevia-tions: DM = dolomitic marble; DI = diorite; GN = granodiorite; QD = quartz diorite;SN= syenite; KAD= K (potassium) altered diorite.

1991), Chuncheon in South Korea (Yui and Kwon, 2002), South West-land in the South Island of New Zealand (Wilkins et al., 2003), and Cow-ell in South Australia (Flint andDubowski, 1990). Among these nephritedeposits, the giant Hetian belt stands out as the largest nephrite belt inthe world.

The petrogenesis of nephrite has been interpreted to be eithermeta-morphic or metasomatic (Harlow and Sorensen, 2000, 2005; Leaming,1978), and a fewnephrite deposits have been documented petrological-ly, geochemically, and isotopically (Coleman, 1966; Cooper, 1995;Leaming, 1978; Prokhor, 1991; Wenner, 1979; Yui and Kwon, 2002).On the basis of detailed petrographic observations and geochemicaldata, Harlow and Sorensen (2000), Yui and Kwon (2002), and Y. Liuet al. (2010, 2011a,b) suggested that nephrite deposits associated withdolomite were formed as a result of metasomatism. In this study, wetry to determine whether these dolomite-related nephrite deposits arespecial kinds of skarn deposit or typical skarn deposits that underwentparticular kinds of geological process. Until now, no ages for the neph-rites have been obtained anywhere along the Hetian belt, and thismakes it difficult to constrain the petrogenesis of the nephrites andtheir relationship to the granodiorite. In recent years, zircon U–Pb agesfrom various rocks have been used to constrain geological processes,especially in some uncommon rocks such as jadeitite (Shi et al., 2008;Yui et al., 2010, 2013). Nevertheless, although it is relatively easy tofind zircons in different rocks, and to date them, it is not always easyto understand their origin and geological significance.

Nearly allmain primary nephrite deposits are located in theWesternKunlun Orogen (WKO), a 1000 km long early Paleozoic mountain beltlocated along the northern periphery of the Tibetan plateau, connectedwith the Pamir syntaxis to the west and the Altyn–East Kunlun Orogento the east (Fig. 1). This area is of considerable importance in under-standing the reconstruction of paleo-Asia because it occupies a key tec-tonic position between the Tarim block to the north and the Tethyandomain to the south (Ye et al., 2008, 2013).

Thus, in this paper, we present new zircon SHRIMP U–Pb datingresults for nephrite granodiorite samples at Alamas. Based on new geo-chronological and petrological evidence, we also discuss the age andorigin of the nephrites and their relationships to tectonism.

2. Geological setting

Geologically, Xinjiang can be subdivided into northern Xinjiangand southern Xinjiang, separated by the Tianshan Mountains (Fig. 1).Northern Xinjiang is famous for its metal mineral deposits as an impor-tant ore belt in China. In contrast, Southern Xinjiang is world famous forits nonmetal deposits (Mao et al., 2005), such as nephrite and asbestosin the Kunlun Mountains.

The Kunlun Mountains are divided by longitude 81°E into theWestern and Eastern Kunlun mountains. Some deposits such as theQiemo and Ruoqiang nephrite deposits are distributed in the AltunMountains, part of the Eastern Kunlun Mountains (Fig. 2A), but mostof the nephrite deposits were found in the Western Kunlun Orogen(WKO) (Fig. 2A), a 1000-km-long early Paleozoic orogenic belt locatedalong the northern periphery of the Tibetan Plateau, and connectedwith the Pamir to the west and the Altyn–East Kunlun Orogen to theeast (Fig. 1). The WKO is of considerable importance in understanding

131Y. Liu et al. / Lithos 212–215 (2015) 128–144

the reconstruction of paleo-Asia Block, because it occupies a key tecton-ic position between the Tarim Block to the north and the Tethyandomain to the south (Deng et al., 2013, 2014; Gao and Reiner, 2000;Wang et al., 2001; Xiao et al., 2001, 2005; Yang et al., 2007). The Buyahigh Ba–Sr granite, which seems to be responsible for the Buya neph-rite deposits, was studied to elucidate the evolution of the WKO. Incombination with previous investigations, the new results indicatedthat the Buya high Ba–Sr pluton represents as sequence of tectonicthickening at the end of an early Paleozoic crust thickening eventthat followed terrane accretion on the southern Tarim craton, and thebeginning of a phase of post-orogenic collapse in the Paleozoic WKO(Ye et al., 2008).

The giant Hetian nephrite belt is located in the southern part of theWKO in Xinjiang, China. The belt includes three main primary nephriteore locations at Shache–Yecheng, Hetian–Yutian, and Qiemo–Ruoqiang(Fig. 2A). All the nephrite deposits occur in similar geological settings,andmost are located at the contact zone between Precambriandolomit-ic marbles and intermediate–acidic igneous rocks that were emplacedduring the HercynianOrogeny under low-pressure conditions butwith-out specific ages or dating data. Secondary alluvial nephrite deposits arefoundwithin the terraces of the Yurungkash (White Jade) and Karakash(Black Jade) rivers in theHetian area (Fig. 2A). The primary nephrite orebodies in the KunlunMountains are thought to have a dolomite-relatedorigin, based on the occurrence of dolomitic marble in the Tarim Basinand have elevations of up to ~5000m (Fig. 2B) (Jiang, 1986). Accordingto the geological setting for most primary nephrite in Hetian, the typicalmineral zonings such as diopside, tremolite, nephrite and other mineralzonings are distributed in the contact zone (Liu et al., 2011b).

Among the primary nephrite deposits of the Hetian belt, the Alamasdeposit (Fig. 2B) is situated 65 km southeast of Liushen village in YutianCounty (N36°12′, E81°55′) and about 4500 m above sea level. Theorebody is highly valued, not only for its “mutton-fat” luster and variedcolors (white, green–white, and green), but also for its 250-year historyof usage. More than 100 tons of nephrite has been mined from this de-posit since 1957 (Tang et al., 1994). Granite and granodiorite are morewidely distributed than diorite and quartz diorite around the nephriteorebodies in No. 11 nephrite vein of Alamas nephrite deposit (Fig. 2B).Granites near the deposit record three main periods of emplacement

Fig. 3. Photographs of green nephrite and nephrite. A. Green nephrite sample QYZr1. B. Green nE. Diopside (Di) crystals occur as idiomorphic porphyroblasts with diameters up to 800 μm (crG. Zircon fragments with tremolite largely replaced by chlorite (BSE). H. Zircon fragments in tr

(Jiang, 1986): Caledonian, middle Variscan and late Variscan. The lateVariscan granites and granodiorites form stocks and have been thoughtto be closely associated with the formation of nephrite (Tang et al.,1994). However, these periods were not precisely constrained by de-tailed age data. Thewallrock for the Alamas nephrite deposit is Precam-brian dolomitic marble. Mineral zonings, with diopside (400 °C–600 °C)close to the granodiorite, and tremolite and serpentine (330 °C–420 °C)(Y. Liu et al., 2010, 2011a) close to the dolomitic marble, indicate adecreasing temperature gradient from granodiorite to marble (Fig. 2Band C) (Y. Liu et al., 2010, 2011a). About 11 nephrite veins, up to 20 mlong (10 m on average) and about 0.1–0.5 m wide, have been found inAlamas (Fig. 2B). Most of the veins are distributed along faults and frac-tureswithin the dolomiticmarble, possibly as a result ofmetasomatism.

The variously colored varieties of nephrite, from white to white–green and green, caused by differences in iron content, also occur inzones (Fig. 2C), but locally white and white–green nephrite can befound in one sample with sharp boundaries.

The widths of the white, white–green, and green zones of nephritevary from 30 to 50 cm (Fig. 2C), with the white nephrite zone at30 cm wide the narrowest. Green nephrite samples (QYZr1, QYZr2,QYZr3, and QYZr4) from one cross section were selected for zirconseparations and petrographic studies (Figs. 3 and 4), as shown inFig. 2B (A–A′) in the Y11-2 nephrite vein, one of the two main veins ofthe Alamas deposit.

3. Methods

Microscope observation, backscattered electron (BSE) images andchemical compositions of amphiboles were acquired at the Instituteof Geology and Geophysics, Chinese Academy of Sciences, using aJXA-8100 Electron Microprobe Analyzer (EMPA) with a voltage of15 kV, a beam current of 10 nA, and a spot size less than 10 μm. EMPAstandards include the followingminerals: andradite for Si and Ca, rutilefor Ti, corundum for Al, hematite for Fe, eskolaite for Cr, rhodonite forMn, bunsenite for Ni, periclase for Mg, albite for Na, and K-feldspar forK (Shi et al., 2012). All mineral formulae were recalculated using thesoftware MINPET 2.0. Amphibole formulae were calculated by choosinga method based on “15 NK”.

ephrite sample QYZr2. C. Green nephrite sample QYZr3. D. Green nephrite sample QYZr4.ossed nicols). F. Diopside cut across by tremolite (Tr) along the cleavage (crossed nicols).emolite that occurs as isolated grains due to its replacement by chlorite (BSE).

Fig. 4. Backscattered electron (BSE) images of nephrites. A. Diopside crystals occur as idiomorphic porphyroblasts and are cut across by Tr-I along cleavages. B. Tr-I replacing diopside andchlorite replacing Tr-I along its boundary. C. Tr-II replacing diopside along a fissure. D. Chlorite replacing Tr-I along its boundary. E. Tr-II replacing diopside along its cleavages, with thediopside left as isolated grains. F. Tr-II with large aspect ratios replacing Tr-I so that the Tr-I occurs only as isolated grains.

132 Y. Liu et al. / Lithos 212–215 (2015) 128–144

All samples were ground to c. 200 mesh size in an agate mortar.Major oxides were determined by X-ray fluorescence spectroscopy(XRF) using a Phillips PW2400 system (Phillips, Amsterdam, TheNetherlands) at the Institute of Geology and Geophysics, Chinese Acad-emy of Sciences (IGGCAS), Beijing, China. Fused glass disks were used,and the analytical precision is better than 5%, as estimated from repeatanalyses of GSR-3 (basalt, Chinese standard reference materials; seeShi et al., 2008). In addition, TFe2O3 was analyzed by XRF at IGGCAS.

Trace element abundances were obtained by inductively-coupledplasma mass spectrometry (ICP-MS) using a VG-PQII system, which isalso located at the IGGCAS. All samples were ground in an agate mortarto−200 mesh. Samples were then dissolved in distilled HF+ HNO3 in15 ml Savillex Teflon screw-cap beakers at 120 °C for 6 days, dried andthen diluted to 50 ml for analysis. A blank solution was prepared, andthe total procedural blank was b50 ng for all trace elements. Analyticalaccuracy is ca. ±5% for trace elements with abundances ≧20 ppm andca. ±10% for trace elements ≦ 20 ppm, as determined by analyses ofthe GSR-3 standard (Deng et al., 2009; Zheng et al., 2012).

Zircon separation, cathodoluminescence (CL) imaging and U–Th–Pbisotope measurements were all carried out at the Beijing SHRIMPCenter, Chinese Academy of Geological Sciences (CAGS). Zircon grainswere extracted from rock samples using the conventional proceduresincluding rock crushing, sieving, elutriating, drying, dressing bymagneticseparation, electromagnetic selection, heavy liquid separation and hand

picking under a binocular microscope. Zircon grains were then mountedonto a double-sided adhesive tape and enclosed in an epoxy resin diskwith a diameter of 2.5 cm, along with TEMORA 1 reference zircon(206Pb/238U age = 416.8 ± 1.3 Ma) and M257 (U = 840 ppm) (Blacket al., 2003; Nasdala et al., 2008). The morphology was examined inboth transmitted and reflected light, and the images were retrieved byan optical microprobe. CL image reflects the difference in the abun-dances of some trace elements (such as U, Y, Dy, and Tb) and/or the de-fects in the crystal lattice of zircon. A negative correlation has beenobserved between the CL intensity and the trace element content (Wuand Zheng, 2004). The CL images were separately retrieved using aHITACHI S3000-N Scanning Electron Microscope (SEM) equipped witha ROBINSON backscatter probe and GATAN Chroma CL probe prior toU–Th–Pb isotope measurements. All the zircon U–Th–Pb analyseswere determined on SHRIMP II at CAGS. Inter-element fractionationduring zircon ion emission was used to monitor analytical conditionsrelative to the TEMORA 1 reference zircon (Black et al., 2003), withthis reference sample being measured once every three unknowns tomonitor the stability of the instrument and to guarantee the productionof reliable results. Instrumental conditions and measurement proce-dures were similar to those reported previously (Black et al., 2003;Compston et al., 1992; Stern, 1998) or in recent publications includingmeasurements from the same lab (Deng et al., 2010a,b,c; Sun et al.,2010; Zhang et al., 2008; Zheng et al., 2012). The primary O2− ion

Fig. 5.Microphotograph images and BSE of nephrite. A. Group of chlorite grains in nephrite from Alamas under crossed nicols. B. Groups of grossular grains in nephrite from the Karakashriver deposits, under crossed nicols. C. BSE image of a group of chlorite grains in nephrite from Alamas. D. BSE image of a group of grossular grains in nephrite from the Karakash riverdeposits.

133Y. Liu et al. / Lithos 212–215 (2015) 128–144

beam at the required intensity measures between 5 and 7 nA, and wasused to impinge the zircon target and spot sizes ranging between 25and 30 μm during SHRIMP analysis. Each spot was rastered for be-tween 3 and 4 min prior to analysis to remove surficial common Pbor contamination. Five scans of nine mass station, including 196Zr2O,204Pb, background, 206Pb, 207Pb, 208Pb, 238U, 248ThO and 254UO, were ac-quired for the standards. Reference zircon M257 was analyzed for ele-mental abundance calibration. TEMORA1 was analyzed for calibrationof 206Pb/238U after every 3–4 analyses on unknowns. Common Pb cor-rectionwas referred to themeasured 204Pb abundances. The data reduc-tion was performed using SQUID 1.0 (Ludwig, 2001) and ISOPLOT/Exsoftware (Ludwing, 2003). Errors in individual analyses are based onthe counting statistics and are quoted at the 1σ (one standard devia-tion) level, whereas those for the pooled analyses are quoted at the2σ confidence level. Because of small amounts of 207Pb formed inyoung (i.e. b800 Ma) zircons, which results in low count rates and

Fig. 6. A. Chondrite-normalized REE patterns of the Alamas nephrites. B. Primitive mantle-normand McDonough (1989).

high analytical uncertainties, the determination of the ages for youngzircons has to be based primary on their 206Pb/238U ratio.

Measurements of U–Pb isotopes were performed using a CamecaSIMS 1280 ion microprobe at the Institute of Geology and Geophysics,Chinese Academy of Sciences, with analytical procedures described byLi et al. (2011). The O2− primary ion beam with an intensity of ca.15 nA was used to produce even sputtering over the entire analyzedarea of about 20 × 30 μm. The Pb/U ratios were calibrated with apower law relationship between Pb/U and UO2/U relative to the R10rutile standard dated at 1095Ma (Luvizotto et al., 2009) andmonitoredby the 99 JHQ-1 rutile dated at 218 Ma by ID-TIMS (Li et al., 2003). Thestandard deviation of Pb/U values of the reference curve was propagat-ed together with errors from the unknowns to give an overall error forthe Pb/U ratio of each analysis (Li et al., 2010, 2011). U concentrationswere calculated by U + ion yield which is estimated from the R10standard with 30 ppm U (Luvizotto et al., 2009). The 208Pb-based

alized trace element diagrams for the Alamas nephrites. Normalizing values are after Sun

Fig. 8. Ternary plots of diopside in nephrite and diopside as mineral inclusions in zircons.Jo = johannsenite, Di = diopside, and Hd = hedenbergite.

134 Y. Liu et al. / Lithos 212–215 (2015) 128–144

common Pb correction was used during dating (Clark et al., 2000; Liet al., 2011; Luvizotto et al., 2009). Uncertainties on individual analysesin data tables are reported at 1 level; mean ages for poled U/Pb (andPb/Pb) analyses are quoted with 95% confidence interval. Data reduc-tion was carried out using the Isoplot/Ex v.2.49 Program (Ludwig,2001). Analyses (Suppl. Table 6) were obtained from zircon grains orfragments, and all these data fail to form a tight cluster and concordantage (Fig. 11D). Trace element analyses of zircon were conductedsynchronously by LA-ICP-MS at the State Key Laboratory of GeologicalProcesses and Mineral Resources, China University of Geosciences,Wuhan. Detailed operating conditions for the laser ablation systemand the ICP-MS instrument and data reduction are the same as the de-scription by Liu et al. (2008, 2010a,b). Laser sampling was performedusing a GeoLas 2005. An Agilent 7500a ICP-MS instrument was usedto acquire ion-signal intensities. A “wire” signal smoothing device is in-cluded in this laser ablation system, by which smooth signals areproduced even at very low laser repetition rates down to 1 Hz (Huet al., 2012). Helium was applied as a carrier gas. Argon was usedas the make-up gas and mixed with the carrier gas via a T-connectorbefore entering the ICP. Nitrogen was added into the central gas flow(Ar+He) of the Ar plasma to decrease the detection limit and improve

Fig. 7. Backscattered electron (BSE) images of zircons from green nephrites and mineralinclusions in the zircons. A. Diopside (Di) grain in zircon as a mineral inclusion. B. Chloritegrain as a mineral inclusion in zircon. C. Calcite (Cc) grain as a mineral inclusion in zirconwith diopside at the boundary. D. Chlorite (Chl) and diopside grains occurring together asmineral inclusions in zircon. E. Tremolite (Tr) grain appearing as amineral inclusion in zir-con with tremolite veins cutting across the zircon. F. Chlorite grain showing as a mineralinclusion in zircon with small chlorite veins cutting across the zircon. G. Baddeleyite(Bad) and chlorite grains in zircon with chlorite veins cutting across the zircon. H. Apatite(Ap), biotite (Bi), baddeleyite, and thorite (Thr) grains occurring together in the zircons.

Fig. 9. A, B, C and D cathodoluminescence images of zircon grains from the granodiorite atAlamas; E. 207Pb–corrected 206Pb/238U ages correspond to those in Suppl. Table 4.

Fig. 10. Group types and 207Pb–corrected 206Pb/238U ages correspond to those in Suppl. Table 5.

135Y. Liu et al. / Lithos 212–215 (2015) 128–144

precision (Hu et al., 2008; Liu et al., 2010b). Each analysis incorporated abackground acquisition of approximately 20–30 s (gas blank) followedby 50 s of data acquisition from the sample. The Agilent Chemstationwas utilized for the acquisition of each individual analysis. Off-lineselection and integration of background and analyte signals, andtime-drift correction and quantitative calibration for trace elementanalyses and U–Pb dating were performed by ICPMSDataCal (Liuet al., 2008, 2010a).

4. Results

4.1. Petrography

All four green nephrite samples consist predominately of tremolite,with subordinate diopside and chlorite. Apatite, zircon, phlogopite,and titanite can also be found in the green nephrite.

In some cases, diopside crystals are obvious and occur as idiomor-phic porphyroblasts up to 800 μm in diameter (Figs. 3A, 4A, and E). Inthe green nephrite, diopsides are partially replaced by tremolite alongtheir cleavages (Figs. 3A, 4A, and E) with their grain boundaries(Figs. 3B and 4B) or cracks (Fig. 4C). In someplaces, isolated grains of di-opside are found as relics due to the replacement by tremolite (Fig. 4E).

Green nephrite is composed predominantly of tremolite, withminor minerals such as zircon, barite, and actinolite and the greennephrite samples have higher content of TFe2O3 (1.03–1.96 wt.%) thanwhite/green–white nephrite samples which have (0.41–0.96 wt.%) (Liuet al., 2011a). The tremolite crystals are either coarse-grained (Tr-I),

deformed (Fig. 3B) or undeformedfine-grained (Tr-II) (Fig. 4F). Tr-I crys-tals are very rare and occur as idiomorphic porphyroblasts about 200 μmlong and 100 μmwide (Fig. 4F). These Tr-I crystals have commonly beenreplaced by Tr-II, and Tr-I crystals also occur as isolated residual crystals(Fig. 4F). In nephrite with high quality, most fine-grained (Tr-II) crystalsare undeformed.

Tr-II crystals characteristically form aggregates of micro- to crypto-crystalline tremolite. In the green nephrite samples, Tr-II commonlyreplaces diopside along cleavages, cracks, or grain boundaries, and itmay then be replaced by chlorite (Fig. 3B). These tremolite crystalscommonly have large aspect ratios, some even occurring as long fibrils,similar to those observed by Dorling and Zussman (1985), Germine andPuffer (1989), and O'Hanley (1996). In some domains, a preferredcrystallographic orientation is obvious, indicative of recrystallizationdriven by ductile deformation (Fig. 4E and F). But in the ore veins, brittledeformation rather than ductile deformation can be found. That is,fracture, faulting, and cracks occur, suggesting that nephrites havebeen subjected to late stage brittle deformed. Thus, ductile deformationfails to contribute to the nephrite ore veins very much.

Chlorite commonly replaces tremolite along cracks or grain bound-aries (Figs. 3B and 4D). Thus, chlorite usually occurs as fine-grainedaggregates (Fig. 3B), lumps (Fig. 4B and D), or small veins. Some chlo-rites have large aspect ratios, similar to the Tr-II crystals. In somecases, the chlorite forms small balls with diameters less than 100 μm(Fig. 5A and C), and these balls have configurations and sizes that aresimilar to the grossular crystals in black placer nephrite from KarakashRiver (Fig. 5B andD). It is therefore very likely that these balls of chlorite

Fig. 11. SHRIMP U–Pb diagrams for nephrite samples. A. QYZr1 nephrite sample. B. QYZr2 nephrite sample. C. SHRIMP U–Pb diagram for zircons from the QYZr3 nephrite samples. D. SIMSU–Pb diagram for zircons from several green nephrite samples. Figure 11C and D from Yang (2013).

136 Y. Liu et al. / Lithos 212–215 (2015) 128–144

represent grossular that was completely replaced by chlorite. Most ofthe micro- to cryptocrystalline aggregates of chlorite exhibit foliationtextures.

Apatite, zircon, phlogopite, and titanite are distributed sporadicallyin the green nephrite.

4.2. Mineral chemistry

Pyroxene in the green nephrite has a nearly constant chemicalcomposition. Their SiO2 contents range from 53.79 to 56.14 wt.%, MgOcontents from 16.30 to 17.60 wt.%, and CaO contents from 24.87 to25.45 wt.%, and the concentration of FeO is low (0.54 to 1.07 wt.%).The pyroxene has the following chemical characteristics: 1.98 to 2.03a.p.f.u. of Si on the T site and 0.89 to 0.95 a.p.f.u of Mg (M1) with 0.98to 0.99 a.p.f.u of Ca (M2) (Suppl. Table 1), which can be classified asdiopside.

According to the amphibole nomenclature of Leake et al. (1997),green nephrite is predominantly composed of tremolite in the calcicgroup. They are characterized by 8.06 to 8.19 a.p.f.u. of Si and 1.79to 1.92 a.p.f.u of Ca on the B site, with Mg/(Mg + Fe2+) being 0.96to 0.98. The tremolites have no Na and K on the A site (less than 0.01a.p.f.u. Na + K), whereas the FeO content ranges from 0.90 to 2.16%(Suppl. Table 2).

The chemistry of the chlorites varies in a narrow range with SiO2

and Al2O3 contents of 31.14 to 33.91 wt.% and 15.49 to 18.48 wt.%, re-spectively. The MgO contents vary from 29.36 to 30.99 wt.%, and FeO

contents from 2.34 to 4.98 wt.%. The chlorites have Al(IV) of 1.35 to1.94 a.p.f.u. and Al(VI) of 2.08 to 2.38 a.p.f.u. (Suppl. Table 3).

4.3. Chemical characteristics of the green nephrites

The green nephrite samples are similar to the tremolites in chemicalcompositions (Table 1). Their compositions vary in a limited range.Compared with QYZr2-1, QYZr3-4, and QYzr4-3, sample QYZr1-1 islower in SiO2 (49.72 wt.%) and CaO (8.26 wt.%), and higher in Al2O3

(5.78 wt.%), MgO (26.92 wt.%), H2O+ (4.99 wt.%), and LOI (7.15 wt.%).According to petrographic observations, the amounts of chlorite leadto the compositional distinction. All the nephrite samples have pro-nounced negative Eu anomalies (δEu = 0.08–0.17), and they are de-pleted in LREE and flat HREE in chondrite-normalized patterns(Fig. 6A). They contain very low REE abundances ranging from 8.28to 52.07 ppm (averaging 21.76 ppm, approximately 1–5 times morethan in chondrites) (Table 1). In the primitive mantle (Sun andMcDonough, 1989) normalized spidergram, the nephrite samples arestrongly enriched in Rb and U, and depleted in Ba, Nb, and Ti (Fig. 6B).All these REE patterns and trace element characteristics are similar tothose of the Alamas nephrite reported by Liu et al. (2011a).

4.4. Mineral inclusions and internal textures of the analyzed zircons

According toBSE images (Fig. 7) andEMPAanalytical results (Table 2),twomain types of mineral inclusionswere observed in the zircons from

Table 1Bulk-rock chemical compositions of nephrites from Alamas, Xinjiang, China.

Samples QYZr1-1 QYZr2-1 QYZr3-4 QYZr4-3

SiO2 49.72 54.41 57.82 58.05TiO2 0.01 0.04 0.02 0.03Al2O3 5.78 2.59 0.44 0.61Fe2O3 0.11 0.06 0.03 0.05FeO 1.92 3.07 2.71 1.60MnO 0.08 0.09 0.07 0.08MgO 26.92 24.14 23.09 23.23CaO 8.26 10.65 12.37 12.57Na2O 0.15 0.15 0.12 0.17K2O 0.05 0.04 0.04 0.08P2O5 0.01 0.01 0.01 0.03H2O+ 4.99 2.26 0.50 0.84CO2 0.82 0.30 0.30 0.81LOI 7.15 4.65 3.01 3.41La 1.67 2.57 1.97 10.3Ce 3.37 5.37 4.01 20.2Pr 0.38 0.67 0.52 2.40Nd 1.34 2.93 2.30 9.20Sm 0.30 0.69 0.52 1.80Eu b0.05 0.06 0.06 0.33Gd 0.37 0.74 0.58 2.01Tb 0.06 0.14 0.09 0.37Dy 0.30 0.79 0.52 2.07Ho 0.07 0.17 0.11 0.44Er 0.23 0.52 0.33 1.33Tm b0.05 0.07 b0.05 0.18Yb 0.20 0.49 0.34 1.25Lu b0.05 0.07 0.06 0.19Y 2.18 5.21 3.02 12.5Cr 8.11 4.27 3.08 9.13Ni 11.9 13.1 14.3 18.0Rb 2.76 1.74 1.82 4.51Sr 4.64 4.54 3.91 10.9Ba 9.32 15.2 4.24 10.9Th 0.19 0.07 0.11 1.97U 0.54 0.28 0.18 2.08Pb 0.91 2.68 17.0 2.40Nb 0.29 2.98 0.44 1.01Ta b0.05 0.14 b0.05 0.14Zr 1.92 4.03 2.23 29.5Hf 0.06 0.13 b0.05 0.88Be 2.86 3.91 2.53 6.18Sc 1.55 1.40 0.77 2.71V 12.1 7.38 5.00 6.53Cu 1.97 35.0 8.81 13.0Zn 62.4 84.0 31.0 58.4Ga 10.2 5.34 1.26 1.13Mo 0.11 0.05 0.12 0.16Cd b0.05 b0.05 b0.05 b0.05In b0.05 b0.05 b0.05 b0.05Cs 1.70 0.71 0.25 0.97W 0.15 0.18 0.44 0.39Tl b0.05 b0.05 b0.05 b0.05Bi 0.11 b0.05 0.14 b0.05Eu* – 0.08 0.11 0.17Gd/Yb 1.49 1.21 1.37 1.29La/Sm 3.41 2.28 2.32 3.51La/Yb 5.51 3.46 3.83 5.44La/Nd 2.35 1.66 1.62 2.11

137Y. Liu et al. / Lithos 212–215 (2015) 128–144

the green nephrites: (1) single idiomorphic crystals or veins of diopside,chlorite or calcite (Fig. 7A–D); and (2) single idiomorphic apatite, bio-tite, and titanite (Fig. 7G and H). Baddeleyite is abundant in zirconsfrom the green nephrites, presumably reflecting either relatively lowactivities of Si or pronounced fluid flow that replaced Si during the for-mation of the nephrite. Also, mineral crystals such as tremolite or chlo-rite crosscut the zircons (Fig. 7E and F), indicating that zircon occurredearlier than theseminerals. Because nominerals such as tremolite, chlo-rite or diopside crystallized in granodiorite and these minerals formedin skarnization, it is also very possible that these minerals entered zir-cons through fissures during skarnization. The chemical compositionsof the mineral inclusions of diopside, tremolite, chlorite, amphibole,

biotite, apatite, titanite, and calcite were determined by EMPA, andthe results are listed in Table 2. The compositions are similar to thoseof the same minerals in the nephrite, where they do not occur as inclu-sions (Y. Liu et al., 2010, 2011a,b), but there are slight differences, asshown by the diopsides (Fig. 8), indicating that fluid activity haschanged their compositions with time. The primary solid inclusionsand intergrowths are for the most part unrelated to transgranularfractures, and accordingly they are considered to have grown coevallywith the other minerals in the contact zone.

We attempted to separate zircons for analysis from the white andwhite–green nephrite samples, and also from the dolomitic marbles,but no zircon grains were found. Zircons were separated using conven-tional heavy liquid and magnetic techniques. Representative zircongrains were handpicked under a binocular microscope, mounted inepoxy resin disks, then polished and gold-coated. Totals of 500, 300,85, and 2 zircon grains were collected from the green nephrite sam-ples QYZr1, QYZr2, QYZr3, and QYZr4, respectively. Zircons and zir-con fragments from the samples occur closely together withtremolite and chlorite, and show signs of brittle deformation; theyare irregularly shaped with lengths of 30–250 μm and width of30–100 μm (Figs. 3C–D, 7 and 10). Zircons separated from theAlamas granodiorite are dominantly idiomorphic, prismatic, and col-orless with width of 50–100 μm and length of 100–300 μm (Fig. 9),and they have typical oscillatory zoning with inclusions of smallgrains of albite, biotite and feldspar.

Zircons separated from the green nephrites of the Alamas depositcan be subdivided into four types on the basis of their growth patterns,relative locations, morphologies, CL brightness, SHRIMP analyses, andmineral inclusions. Type I zircons are considered to have been inheritedbecause of their round shapes and obscure zoning (Fig. 10A–D). Type IIzircons have broad and relatively obvious oscillatory zoning, and thecrystals are hypidiomorphic or idiomorphic. Wedge-shaped zones canbe observed in CL images, which suggest different growth ratios onspecific crystal faces of the zircons (Vavra et al., 1996). Diopside is themain type of mineral inclusion in Type II zircons (Fig. 10E–H). MostType III zircons form narrow rims around the edges of Type II zircons,and we assume that they are related to the activity of fluids due to thehomogeneous texture without zones, brightness under CL images andirregular shape (Fig. 10D, G, and H). However, because of the narrow-ness of the rims, this type of zircon is not easy to analyze. Type IV zirconsare mostly idiomorphic, with low luminescence under CL, and they ex-hibit narrow growth zones (Fig. 10I–L). Inclusions of tremolite, chlorite,and calcite are very common in this type of zircon. Those of Types I, II,and IV appear to have been derived from the granodiorite but experi-enced recrystallization during the nephrite formation, based on theirmorphologies and mineral inclusions. On the other hand, Type III zir-cons are probably coeval with the nephrite; the ore-forming fluidsthat contributed to the formation of nephrite would have facilitatedthe formation of these zircons.

4.5. Zircon SHRIMP U–Pb dating

Fourteen analyses of 16 zircons in Alamas granodiorite were ob-tained, and the SHRIMP U–Pb data for these zircons are summarizedin Suppl. Table 4. Thirteen of the analyses yield excellent concordantresultswith aweightedmean 206Pb/238U age of 418.5±2.8Ma (n=13,MSWD= 0.16; Fig. 9E). This age is interpreted to be the crystallizationage of the granodiorite at Alamas.

SHRIMP U–Pb dating of zircons from the Alamas green nephritesyielded weighted mean 206Pb/238U ages of 425.7 ± 5.8 Ma (n = 4,MSWD = 0.17; Fig. 11A) and 406.5 ± 5.5 Ma (n = 4, MSWD = 0.5;Fig. 11A) for QYZr1, 407.9 ± 4.4 Ma (n = 8, MSWD = 0.95; Fig. 11B)and several individual ages of 399.2 ± 5.9 Ma, 443.9 ± 8.4 Ma,380.8 ± 5.6 Ma, and 445.2 ± 6.8 Ma for QYZr2, and 420.0 ± 9.9 Ma(n = 5, MSWD = 1.5; Fig. 11C) for QYZr3 with two individual ages of412.9 ± 6.2 Ma and 414.4 ± 6.1 Ma. Both Type I and Type II zircons

Table 2Representative chemical compositions of mineral inclusions in zircons from green nephrite, Alamas, Xinjiang.

Samples Na2O MgO Al2O3 K2O CaO SiO2 FeO TiO2 P2O5 Cr2O3 MnO NiO Total Mineral name

QYZr1-7 0.03 24.75 0.11 0.03 13.08 57.50 1.31 0.00 0.00 0.00 0.03 0.00 96.84 TrQYZr1-9 0.06 24.55 0.18 0.03 12.89 58.55 1.56 0.00 0.03 0.05 0.09 0.00 97.97 TrQYZr1-10 0.06 25.02 0.29 0.02 13.39 58.46 1.54 0.00 0.00 0.00 0.09 0.00 98.85 TrQYZr1-11 0.06 24.58 0.32 0.02 13.27 59.19 1.67 0.15 0.01 0.00 0.15 0.03 99.44 TrQYZr1-1 0.01 33.90 17.50 0.02 0.00 31.92 3.17 0.08 0.02 0.02 0.10 0.04 86.78 ChlQYZr1-2 0.00 33.30 17.02 0.02 0.00 31.84 2.82 0.00 0.00 0.00 0.07 0.00 85.07 ChlQYZr1-3 0.01 34.62 18.14 0.00 0.01 32.86 3.26 0.03 0.00 0.00 0.06 0.01 88.99 ChlQYZr2-2 0.00 31.81 18.12 0.00 0.01 30.62 4.94 0.00 0.00 0.00 0.10 0.01 85.61 ChlQYZr2-3 0.00 31.15 18.85 0.00 0.01 30.08 5.07 0.00 0.01 0.00 0.07 0.02 85.27 ChlQYZr3-8 0.01 31.43 18.53 0.02 0.00 30.26 4.67 0.00 0.02 0.00 0.07 0.00 85.00 ChlQYZr3-9 0.02 32.74 18.39 0.00 0.00 31.31 4.70 0.00 0.01 0.00 0.08 0.02 87.27 ChlQYZr3-10 0.01 32.39 20.00 0.00 0.01 29.52 4.64 0.00 0.01 0.00 0.06 0.00 86.64 ChlQYZr1-5 0.01 0.31 0.00 0.00 58.54 0.14 0.15 0.00 0.01 0.00 0.17 0.00 59.33 CcQYZr1-6 0.01 0.15 0.08 0.00 58.86 0.07 0.01 0.04 0.00 0.00 0.13 0.00 59.36 CcQYZr1-4 0.02 0.18 0.00 0.00 58.58 0.12 0.02 0.00 0.05 0.00 0.13 0.03 59.12 CcQY-1 0.00 33.33 16.75 0.06 0.05 32.47 2.43 0.04 0.00 0.02 0.06 0.00 85.21 ChlQY-2 1.91 18.21 16.45 1.52 12.74 43.10 3.50 0.71 0.02 0.02 0.03 0.04 98.24 AmpQY-3 0.04 28.15 15.97 4.67 0.01 36.01 1.99 0.24 0.02 0.00 0.03 0.03 87.18 BiQY-4 0.00 1.20 7.38 0.26 27.40 32.10 0.35 28.56 0.00 0.00 0.00 0.00 97.24 Sph

Abbreviation: diopside (Di), tremolite (Tr), chlorite (Chl), calcite (Cc), amphibole (Amp), biotite (Bi), sphene (Sph).

138 Y. Liu et al. / Lithos 212–215 (2015) 128–144

have individual ages of 411 to 445Ma and Type IV zircons have relative-ly younger ages of 388 to 406 Ma. Type III zircons have no ages due tonarrow rims (b10 μm).

SHRIMPU–Pb dating onmagmatic zircons from the Alamas granodi-orite yielded aweightedmean 206Pb/238U age of 418.5±2.8Ma. Amongthe zircon ages found in the nephrites, 425.7 ± 5.8 Ma from QYZr1 and420.0± 9.9Ma fromQYZr3 are relatively close to the zircon date for thegranodiorite. The ages of 443.9 ± 8.4 Ma and 445.2 ± 6.8 Ma for QYZr2are somewhat older thanmost ages, but consistentwith several individ-ual ages of zircons obtained from the granodiorite; these older zirconsmay therefore have been acquired during the ascent of the younger418.5 ± 2.8 Ma granodiorite magma. In these zircons from nephrite, Uconcentrations range from 105 to 4122 ppm and Th concentrationsfrom 7 to 747 ppm. The Th/U ratios are relatively high with a rangefrom 0.06 to 0.55. In magmatic zircons from the granodiorite, U andTh contents range from 459 to 1700 ppm and 244 to 560 ppm, respec-tively, and the Th/U ratios are correspondingly high at 0.25–0.60.

4.6. Trace element compositions of the zircons

Zircons separated from the granodiorite have distinct positive Ceanomalies and negative Eu anomalies (Ce/Ce* = 3–859), and high∑REE contents (454–922 ppm) (Table 3) with HREE enrichment(Fig. 12A). Zircons from the green nephrites also exhibit high Th/U ra-tios in the range 0.05–0.55 (Suppl. Table 5), large Ce positive anomalies(Ce/Ce*=6–456) and negative Eu anomalies, and high∑REE contents(103–3183 ppm) (Table 3) with HREE enrichment (Fig. 12B). All thesefeatures indicate that zircons from the green nephrites and the granodi-orite have similar REE patterns (Fig. 13); the only exceptions arefive zir-con grains from the granodiorite that havehigher REE contents, possiblydue to the ablation of REE-richmineral inclusions in zircons such as ap-atite and monazite. The close similarities of the geochemical signaturesand morphologies of Type I, Type II, and Type IV zircons from the greennephrites, and magmatic zircons from the granodiorite, indicate thatthey share the same origin (Figs. 12 and 13).

5. Discussion

5.1. Genesis of zircons in green nephrites

As both zircons and fragments of zircons in the green nephrites andgranodiorite have the similar textural characteristics indicated by theirCL and BSE images, all these zirconsmight be derived from the granodi-orite; this notion is also supported by their geochemical signatures. The

most obvious differences among Type I, II, and IV zircons are theirmineral inclusions and morphologies, they variously contain diopside,tremolite, and chlorite inclusions, which are consistent with those inthe contact zone. There are no fissures in Type I zircons, but many inType II and IV zircons; the fissures contain minerals such as tremoliteand chlorite, indicating that the Type II and IV zircons underwentleaching from ore-forming fluids. In addition, different degrees of recrys-tallizationmay have resulted in obscure images of these zircons. The ore-forming fluids would have allowed the movement of Zr, probably facili-tating the growth of Type III zircons but the whole amount is very low.

Two types of mineral inclusions were found in Type II zircons. Onetype of inclusion contained apatite, biotite and thorite, which aremainlyrock-formingminerals or associatedminerals in granodiorite present inminor amounts; the other type of inclusion included tremolite, diopside,and chlorite, which are the main mineral inclusions in zircons (Fig. 7)and are part of the green nephritemineral assemblages producedmainlyin skarn. Minerals associated with skarn closely also occurred as isolatedgrains in zircons (Fig. 7A, B, D and H) or veins cut zircons (Fig. 7E and F),indicating that zircons crystallized earlier than or at least at the sametime with these minerals and the green nephrite (Fig. 7C and D). Allthese characteristics suggest that Type II zircons might be derived fromthe granodiorite.

The Type III zircons commonly show rounded crystal edges, corro-sion, and skeletal structures along the edges of various growth stages.These domains have highly luminous brightness and no obvious zoningand they are mainly rims surrounding the earlier zircon cores. Theorigin of Type III zircons cannot be proved by examination results dueto the limited grain size.

Type IV and II zircons have similar textural characteristics but differin their mineral inclusions. Chlorite and tremolite inclusions fill fissuresin Type II zircons, indicating that these zircons were affected by ore-forming fluids (Fig. 10E, F, and H). This also has been demonstrated bythe fact that green nephrite formed as a result of metasomatism in thecontact zone between the granodiorite and dolomitic marble (Y. Liuet al., 2010, 2011a).

5.2. Interpretation of zircon U–Pb ages from the nephrite and granodiorite

According to the formation process of nephrite, four types of zirconsin the nephrite can be recognized: two types of zircons (Types I, II)inherited from the protoliths since the green nephrite is close togranodiorite and formed through metasomatism between granodio-rite and dolomitic marble; zircons that possibly grew contemporane-ously with nephrite formation (Type III), and zircons that were

Table 3Rare earth element analyses (ppm) of zircon from Alamas granodiorite and nephrite samples, Xinjiang, China.

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Ce/Ce* Eu/Eu* (Sm/La)N (Yb/Gd)N REE

GranodioriteAHG01 6.8 51 1.8 8.9 4.1 0.8 14 4.7 58 22 107 24 265 47 3.0 0.3 1.0 23 644AHG02 2.3 36 0.6 3.4 3.0 0.9 16 5.8 76 29 151 35 379 70 7.0 0.4 2.1 29 846AHG03 0.0 27 0.0 0.6 1.6 0.5 10 3.7 47 19 99 23 268 49 356 0.4 357 33 1295AHG04 0.0 31 0.0 0.7 2.1 0.5 12 4.2 52 20 101 23 251 46 – 0.3 – 25 569AHG05 1.0 47 0.3 2.3 4.3 1.0 19 6.2 72 25 124 27 284 50 19 0.4 6.9 19 708AHG06 0.1 32 0.0 0.9 1.9 0.7 13 4.1 53 21 104 24 271 50 113 0.4 30 26 745AHG07 0.0 38 0.0 1.5 3.3 0.8 18 5.5 69 26 131 29 316 58 532 0.3 763 22 2013AHG08 0.1 37 0.1 1.3 3.0 0.7 14 4.8 61 22 109 24 265 48 95 0.3 41 23 748AHG09 0.2 32 0.1 1.4 2.6 0.6 14 4.6 57 21 102 23 247 44 52 0.3 18 22 641AHG10 0.0 25 0.1 0.7 1.8 0.5 12 4.7 67 29 164 40 484 94 125 0.4 71 51 1169AHG11 4.3 39 1.3 6.3 2.7 0.6 12 3.5 45 17 89 21 243 45 4.0 0.3 1.0 25 561AHG12 0.0 36 0.1 1.1 2.6 0.7 14 4.6 58 22 108 24 262 47 517 0.4 822 24 1943AHG13 4.8 44 1.3 6.5 3.1 0.6 13 4.3 53 20 99 23 259 46 4.0 0.3 1.0 24 607AHG14 0.0 34 0.1 1.4 3.3 0.8 18 5.7 68 26 123 27 300 52 218 0.3 281 21 1181AHG15 0.0 37 0.1 1.3 3.0 0.7 18 5.6 70 27 131 29 324 57 354 0.3 470 23 1551AHG16 0.0 33 0.0 1.1 2.5 0.7 14 4.8 58 22 108 23 264 46 – 0.4 – 23 601AHG17 4.6 78 1.2 6.8 5.6 1.0 25 7.7 96 35 167 37 386 68 8.0 0.3 2.0 19 948AHG18 0.3 39 0.1 1.1 2.5 0.7 15 4.8 59 22 110 24 261 46 50 0.3 12 21 668AHG19 0.0 31 0.0 0.6 2.0 0.5 12 3.8 49 18 91 21 232 43 859 0.3 1397 24 2784AHG20 0.3 30 0.1 1.1 2.4 0.7 12 3.7 45 17 83 18 205 36 43 0.4 14 22 533AHG21 1.9 39 0.5 3.2 2.7 0.7 14 4.3 55 20 106 24 268 48 10 0.4 2.3 23 624AHG22 0.0 40 0.1 1.4 3.1 0.8 16 5.3 65 24 116 26 282 47 553 0.3 1110 21 2311AHG23 0.0 39 0.1 1.4 3.1 0.7 17 5.4 66 24 119 26 299 49 153 0.3 127 22 952AHG24 0.0 36 0.1 1.2 2.9 0.7 14 4.8 59 21 103 24 261 43 219 0.3 208 23 1020

Green nephriteQYZr1-01 0.0 9.5 0.1 0.9 2.9 1.2 22 9.9 145 61 317 82 922 141 47 0.5 121 53 1934QYZr1-02 0.0 29.7 0.0 1.2 6.4 2.0 50 21 291 121 618 148 1644 250 313 0.3 700 40 4236QYZr1-03 0.0 2.5 0.0 0.2 0.2 0.3 2.0 0.9 12 6.0 32 9.0 113 21 18 1.5 7.0 68 292QYZr1-04 0.2 13 0.1 1.2 2.1 0.6 12 4.2 55 24 129 33 421 80 23 0.4 21 43 864QYZr1-05 0.1 22 0.2 1.6 3.7 1.5 30 12 183 77 403 107 1260 215 37 0.4 50 52 2456QYZr1-06 0.0 5.6 0.0 0.2 1.0 0.3 4.8 2.0 28 13 71 19 230 46 121 0.5 245 60 847QYZr1-07 0.0 17 0.0 0.7 4.0 1.3 35 15 228 99 542 133 1515 257 325 0.3 1313 53 4539QYZr1-08 0.0 2.9 0.0 0.0 0.4 0.2 5.3 2.6 43 20 114 32 392 66 78 0.5 73 91 920QYZr1-09 0.0 9.3 0.0 0.6 3.4 1.5 25 11 165 70 357 94 1073 157 194 0.5 881 53 3094QYZr1-10 0.0 4.7 0.0 0.5 1.4 0.7 11 5.3 78 35 201 56 715 140 72 0.5 218 78 1616QYZr1-11 0.1 24 0.2 2.3 4.7 1.8 33 13 191 79 417 104 1235 220 38 0.4 59 46 2469QYZr1-12 0.0 0.6 0.0 0.1 0.2 0.1 0.5 0.3 5.0 2.6 16 5.0 61 12 15 0.5 12 160 290QYZr1-13 0.0 2.8 0.0 0.1 0.3 0.2 2.2 1.1 15 6.6 38 11 144 29 44 0.7 66 80 442QYZr1-14 0.0 23 0.0 0.9 3.2 1.0 20 7.7 100 41 219 59 738 124 310 0.4 594 45 2287QYZr2-01 5.5 0.0 0.2 1.3 0.4 9.5 3.9 59 26 148 40 499 92 – 0.3 – 65 950QYZr2-02 6.3 0.0 0.2 0.7 0.5 7.3 3.4 50 23 132 37 478 96 – 0.7 – 81 917QYZr2-03 0.0 2.9 0.0 0.1 0.3 0.1 2.6 1.4 21 10 60 17 224 44 116 0.2 222 105 826QYZr2-04 0.0 4.9 0.0 0.3 1.3 0.4 9.9 3.9 59 26 145 40 500 90 456 0.4 968 62 2367QYZr2-05 3.8 0.0 0.2 0.6 0.2 5.8 2.3 35 16 88 25 312 55 – 0.3 – 67 611QYZr2-06 4.6 0.0 0.2 0.9 0.3 6.9 3.0 47 21 117 33 417 76 – 0.4 – 75 802QYZr2-07 0.0 2.4 0.0 0.2 0.1 1.8 0.6 12 5.2 31 9.0 115 20 83 0.5 81 77 440QYZr2-08 0.0 4.2 0.0 0.1 0.6 0.3 4.5 2.2 33 15 83 23 294 53 119 0.5 65 81 777QYZr2-09 0.5 6.9 0.1 0.9 0.9 0.5 6.3 3.1 45 19 111 29 363 70 6.0 0.7 3.0 71 736QYZr2-10 5.5 0.0 0.4 1.1 0.5 8.8 3.2 47 21 116 31 383 73 – 0.5 – 54 744QYZr2-11 0.0 2.4 0.0 0.2 0.4 0.1 2.3 1.2 18 8.0 47 12 150 28 41 0.4 15 82 409QYZr2-12 0.1 7.4 0.0 0.4 1.1 0.5 7.2 3.0 43 20 115 32 414 84 29 0.5 25 71 853QYZr2-13 7.6 0.0 0.3 0.9 0.4 7.8 3.2 48 19 107 28 352 61 – 0.5 – 56 692QYZr2-14 0.1 3.3 0.1 0.4 0.6 0.2 4.7 2.2 36 19 116 35 462 93 10 0.4 9.0 122 915QYZr2-15 3.7 0.0 0.2 0.5 0.1 3.0 1.3 18 8.0 45 12 148 29 – 0.3 – 62 330QYZr2-16 0.0 1.6 0.0 0.2 0.2 0.1 1.3 0.5 8.0 3.3 20 5.0 68 14 11 0.4 10 63 207QYZr3-01 0.0 12 0.0 0.9 1.6 0.6 7.2 2.5 36 15 80 21 246 41 234 0.5 636 42 1375QYZr3-02 2.8 0.0 0.1 0.3 0.1 2.9 1.0 15 6.9 40 13 191 40 – 0.5 – 81 394QYZr3-03 0.1 9.9 0.1 1.0 1.3 0.6 8.5 2.8 37 15 82 21 244 43 26 0.5 21 35 548QYZr3-04 0.0 8.7 0.1 0.9 1.4 0.6 9.0 3.1 41 17 90 25 307 56 54 0.5 100 42 756QYZr3-05 0.0 7.6 0.0 0.5 0.7 0.3 3.9 1.2 17 7.1 38 10 125 22 119 0.5 184 39 576QYZr3-06 0.0 8.4 0.0 0.2 1.1 0.2 7.1 3.2 47 20 111 31 380 61 214 0.3 141 66 1091QYZr3-07 0.0 3.8 0.0 0.2 0.6 0.2 4.1 1.8 29 13 76 21 265 51 62 0.4 95 80 703

139Y. Liu et al. / Lithos 212–215 (2015) 128–144

recrystallized (Type IV). Accordingly, the U–Pb dating of such zirconsshould theoretically yield either the nephrite age, the igneousprotolith age or younger. Problems to take into account include theoccasional lack of clear-cut criteria to discriminate igneous zirconsfrom hydrothermal/metamorphic zircons, as noted by Harley et al.(2007) and Bulle et al. (2010). The geological significance of the U–Pbdating results for zircons from nephrite should be explained with care,

even with information on internal texture, mineral/fluid inclusions,Th/U ratios, and trace element characteristics.

Phlogopite in the nephrite deposits could also be used for dating.Three samples from the Alamas nephrite deposit were selected for40Ar/39Ar step-heating experiments at the Institute of Geology andGeophysics, Chinese Academy of Sciences. However, no reliable resultswere produced because of the limited K content.

Fig. 12. Discrimination plots for magmatic and hydrothermal zircon (from Hoskin, 2005).(A) chondrite-normalized Sm/La ratio vs. La (ppm) and (B) Ce anomaly (Ce/Ce*) vs.(Sm/La)N.

Fig. 13. Chondrite (Sun and McDonough, 1989) normalized REE patterns of (A) Alamasgranodiorite and (B) green nephrite samples.

140 Y. Liu et al. / Lithos 212–215 (2015) 128–144

As the intrusion of granodiorite or granite was the driving force be-hind the formation of the skarn and nephrite deposits, the emplacementage of the Alamas granodiorite constrains the upper limit for the forma-tion age of the nephrite. The concordant age of 418.5 ± 2.8 Ma for theAlamas granodiorite is interpreted to be its emplacement age, which isnear the upper age limit (420 Ma) for nephrite formation. Among theconcordant ages for zircons from the nephrite, the 425.7 ± 5.8 Ma and420.0 ± 9.9 Ma ages are consistent with the 418.5 ± 2.8 Ma age of thegranodiorite, within the analytical errors inherent in the SHRIMP U–Pbmethods. As these zircons are primarily magmatic zircons, as discussedabove, and are therefore from granodiorite, their ages suggest the for-mation of granodiorite, the beginning of the metasomatism stage, andthe formation of skarn or nephrite deposits.

Both Type I and Type II zircons have individual ages of 411 to 445Maand Type IV zircons have relatively younger individual ages of 380 to406 Ma (Fig. 10). Type III zircons have no ages due to narrow rims(b10 μm). Concordant ages such as 425.7 ± 5.8 Ma, 420.0 ± 9.9 Ma,406.5 ± 5.5 Ma and 407.9 ± 4.4 Ma for zircons for QYZr1 and QYZr2samples, or individual ages of 380 Ma to 406 Ma for Type IV zircons,are also within the individual age range of 395 to 477 Ma provided bySIMS on 37 grains from 447 zircon grains or fragments selected fromseven green nephrite samples (Fig. 11 D) (Yang, 2013).

The Alamas deposit is not the only major nephrite deposit along theHetian belt. The zircon U–Pb age of 418 Ma for the Alamas granodioriteis close to the 430Ma age for the Buya appinite–granite (SHRIMP U–Pbmethod), whichmay also constrain the age of the Buya nephrite depos-it. These nephrite deposits and granites occurred in the northern part ofthe West Kunlun orogenic belt along the northwestern margin of theTibetan Plateau, indicating that nephrite formation in the West Kunlunorogenic belt formed after 430 Ma (Ye et al., 2008).

5.3. The metasomatism process in nephrite

Recently, the REE patterns and isotopic compositions of nephritesfrom various zones in the Alamas have been successfully applied to de-termine the metasomatic origin of dolomite-related nephrite deposits(Liu et al., 2011a). On the basis of petrography, the geochemical analy-ses of green nephrite samples, and previous studies (Y. Liu et al., 2010,2011a), we newly propose the following processes for the formationof nephrite in the Alamas:

(1) The dolomite marble was replaced by diopside, which in turnwas replaced by tremolite. That is, the reaction proceeds by thesequence of dolomite→ diopside→ tremolite.

(2) During the later part of this process, tremolite (Tr-II; nephrite)with more fine-grained crystals began to replace the earliertremolite (Tr-I). In the green nephrite, diopside was relativelythoroughly replaced by tremolite, which explains why intact di-opside is rare.

(3) Subsequently, chlorite began to replace the tremolite during alater stage of hydrothermal activity, destroying the structuralhomogeneity and mineral composition and thus the quality ofthe nephrite.

On the basis of petrographic studies of the nephrites and mineralassemblages in the contact zone, Jiang (1986) determined the se-quence of mineral formation in the contact zone of the Hetian belt(Fig. 11), and summarized the major mineral assemblage. Generally,skarns can be grouped into Ca-, Mg-, and Mn-skarns, which are de-fined by mineralogy (Meinert et al., 2005). When compared withmagnesian skarn deposit bearing typical minerals such as olivine,spinel, garnet, diopside and tremolite, Ca-bearing minerals such asgarnet, hedenbergite, scapolite and idocrase are very common.Johannsenite, rhodonite, pyroxmangite, and bustamite are rich inMn-skarn.

Fig. 14. Sequence of formation and stages of mineral development in the metasomatic contact zones that include the primary nephrite deposits of the Hetian belt.

141Y. Liu et al. / Lithos 212–215 (2015) 128–144

Of other dolomite-related and Mg-skarn nephrite depositsaround the world, the nephrite deposit in Chuncheon, Korea, for ex-ample, has a calcic mineral assemblage including grossular, diopside,tremolite, chondrodite, quartz, and calcite (Kim et al., 1986; Jin et al.,1993; Noh et al., 1993). Thus, it is concluded that the nephritedeposits in Hetian are Mg-skarn deposits in which diopside, tremo-lite, chlorite and calcite mineral inclusions are found in both zirconsof the green nephrites and may have crystallized at the same time asthe minerals in the skarn.

5.4. Possible mechanism for the formation of nephrite in Mg-skarn

There should be some specific geologic explanation as to why morethan 30 primary nephrite deposits and orebodies exist in the Hetianbelt, all with similar geologic settings. The chemical reactions and min-eral assemblage in skarn usually depend on the characteristics of the in-trusion and the wallrock, the compositions of metasomatic fluids, andthe overall P–T conditions (Guilbert and Lowell, 1974; Titley, 1973).The mineral assemblages and microstructures of the rocks provideclear evidence of the metamorphism and metasomatism, and severalmetamorphism andmetasomatism facies provide evidence for the evo-lution of the skarn deposit in the production of nephrite. Temporally,the deposit successively experiences a contact thermal metamorphicstage, a prograde metasomatic stage and a retrograde metasomatic

stage, which is corresponds to the occurrences of different mineralassemblages in the contact zone. In general, the difference of chemicalcharacteristics and temperature for granodiorite and dolomite marbleare the main control factors for the mineral zones including nephrite(Y. Liu et al., 2010, 2011a).

For a typical skarn deposit, the prograde stages specifically include acontact metamorphism stage and a prograde metasomatism stage, andthe retrograde stage includes early and late substages (Meinert et al.,2003; Zhang et al., 2013). Several metasomatic facies also provideevidence for the evolution of the nephrite in the primary nephritedeposits as they experienced the change from high-temperature tolow-temperature conditions. Based on their occurrence andmineral as-semblages along with petrographic studies (Fig. 14), the two mainstages of nephrite formation are the prograde metasomatic stage andthe early retrograde stage.

In most primary nephrite deposits in Hetian, skarn between granite/granodiorite and dolomitic marble shows clear zonation. That is, themineral assemblages in the nephrite-bearingMg-skarn deposits varyaccording to their distances from the intrusive body, and the majorelement contents of particular mineral phases, such as diopside,tremolite, green nephrite or white nephrite are also variable (Fig. 3C).Thus, the spatial zoning features can be postulated according to theobtained horizontal and vertical zoning patterns in nephrite or skarndeposits.

142 Y. Liu et al. / Lithos 212–215 (2015) 128–144

5.5. The prograde and retrograde stages

The contact metamorphic stage was coeval with the initial emplace-ment of granodioritic magma. The progrademetasomatic stage probablycommenced at the onset ofmagma consolidation and crystallization. Theprograde metamorphic and metasomatic stages occur at relatively hightemperatures; then, as temperature decreases, magmatic fluids evolve,phases separate, and a late-stage retrograde alteration takes place(Meinert et al., 2003). In the nephrite-bearingMg-skarn,which is relatedto the granodiorite intrusion, the early-stage retrograde alteration wasgenerally superposed on anhydrous silicate minerals (diopside and gar-net) that formed during the early prograde stage. That is, as magma con-tinued to crystallize, the temperature decreased, and magmatic fluidsrich in Si, Fe or other elements replaced the high-temperature phases,forming tremolite and chlorite. O–H isotopic studies (Liu et al., 2011a)have indicated meteoric water gradually increased in the ore-formingfluids during the retrograde stage. In the contact zone, more tremolite,and chlorite formed due to the lower temperatures and the presence ofmeteoric water. At this stage, nephrite began to form (Fig. 14).

Then the following retrograde substage is important for the formationof nephrite. At this stage, brittle deformationoccurred and coarse-grainedtremolite was replaced by fine-grained tremolite (nephrite). However,ductile deformation commonly causes fissures in nephrite, which facili-tate the occurrence of replacement of nephrite by chlorite, tremolite orotherminerals (Fig. 3B). But only in some domains can this ductile defor-mation can be found. Thus, the timing of the formation of nephrite is laterthan the timing of Mg-skarn.

Spatial zonings in the skarn reflect the distribution of elements influids, the compositions of the wall rocks, variations in temperature,the state of reduction or oxidation, and the depth of formation, andthey provide an essential guide when prospecting for economicminerals (Meinert et al., 2005). In the Alamas nephrite deposit, green,green–white and white nephrite zones are distributed between grano-diorite and dolomitic marble. The chemical characteristics of nephritesamples and tremolite in these nephrite samples indicate that thecolor saturation in nephrite samples increases with the concentrationsof FeO,MnO and Cr2O3, which are themajor coloring elements of neph-rite (Y. Liu et al., 2010, 2011a).Moreover, themetasomatic process playsan important role in the occurrence of the zonal structures. Becausethere are no other fluidic activities or rock types, granodiorite wouldbe the supplier of iron in nephrite through thermal fluids. Accordingto the chemical compositions, the content of iron in dolomitic marbleis lower than that in white nephrite (Y. Liu et al., 2010, 2011a). Thus,some iron in nephrite may have come from granodiorite. For nephriticzones in the Alamas, green–white and white nephrite occurs closer toor in dolomitic marble and farther away from granodiorite; thus lacksthe “coloring elements”. This accounts for the color differences in thezonal structure, indicating that the nephrite zonal structure resultsfrom the enrichment in coloring elements in nephrite zones producedby metasomatism between granodiorite and dolomitic marble. Thischaracteristic is also consistentwith the fact that zircons and fluid inclu-sions can be found in green nephrite rather than in white and green–white nephrite (Liu et al., 2011a,b).

5.6. Tectonic implications

According to the chemical composition of granodiorite in Alamas,the granodiorite is a kind of high Ba–Sr granodiorite with high contentof Ba (523–676 ppm) and Sr (1560–2134 ppm) (Yang, 2013) and wascrystallized at ca. 418 Ma. In the same northern WKO belt along thenorthwestern margin of the Tibetan Plateau, another high Ba–Sr Buyagranites are also found (Suppl. Fig. 1) and were crystallized at ca.430 Ma (Ye et al., 2008). Thus, as both granodiorite and granite are lo-cated in the same northern WKO and chemical characteristics, ages ofboth Alamas granodiorite and Buya granite may provide some cluesfor the evolution of WKO.

Experiencing a series of complex tectonic evolution,WKOwas formedby progressive stages of terrane accretions along the southwestern mar-gin of the Tarim craton (Dewey et al., 1988; Pan and Wang, 1994; Xiaoet al., 1999, 2002, 2005; Zhang et al., 2007) (Fig. 1), such as northern Kun-lun Terrane (NKT), the southern Kunlun Terrane (SKT), and theKarakorum–Tianshuihai Terrane accreted in sequence (Xiao et al., 1999,2002, 2005) (Fig. 2A).

The metamorphic age spectrum of paragneisses in the SKT exhibitsmaxima at ca. 500 Ma, ca. 450 Ma, 430 Ma and 400 Ma (Fig. 11, Yeet al., 2008). As the early Paleozoic ophiolites in the NKT of the WKOwere dated at 502–526 Ma (Table 5 in Ye et al., 2008), ocean ridgeextension was occurring until ca 500 Ma (Ye et al., 2008). The subduc-tion of oceanic crust continued to at least ca. 470 Ma (the age of thevolcanic-arc Yierba grandiorite pluton; Yuan et al., 2002). The ca.450 Ma 39Ar/40Ar hornblende age from the Kudi shearing zone makesit plausible that the NKT and the SKT amalgamated at this time anddextral east–west shearing deformation developed along the Kudi su-ture zone (Xiao et al., 2005; Zhou et al., 2000). In combination withtheir alkaline affinities and the ca. 450 Ma amalgamations betweenthe NKT and the SKT, the Buya granites were most likely formed in apost-tectonic environment (Ye et al., 2008). Considering Alamas grano-diorite formed about twelve million years earlier than the Buya graniteand both are Ba-Sr rich and crystallized in WKO, it is very convinciblethat they have the similar geological background. Thus, it is convinciblethat Alamas granodiorite also formed in a post-orogenic tectonicenvironment.

6. Conclusions

1. Four types of zircons in green nephrites have been classified on thebasis of CL images and mineral inclusions, and the geochemicalsignatures and most zircons are ultimately derived from thegranodiorite. The absence of zircon in the white and green–white nephrites suggests that they were derived by metasoma-tism of the zircon-free dolomite-marble protolith, whereas thegreen nephrite was derived from the granodiorite. The geochem-istry of zircons from the granodiorite is not compatible with ametasomatic/hydrothermal origin of zircon in the green nephrite.The age of 418.5 ± 2.8 Ma for the Alamas granodiorite providesthe upper age-limit for the formation of the Alamas nephritedeposit. Concordant ages of 425.7 ± 5.8 Ma, 420.0 ± 9.9 Ma,406.5 ± 5.5 Ma and 407.9 ± 4.4 Ma and younger ages rangingfrom 414 Ma to 380 Ma for zircons in nephrite were found. Theseages possibly correspond to the zircons from granodiorite or therecrystallization during nephrite formation.

2. Several pieces of evidence show that the nephrites at the Alamaswere produced during metasomatism in the contact zone betweengranodiorite intrusions and dolomitic marble. Petrographic observa-tions and chemical analyses of theminerals reveal themain process-es of nephrite formation to be as follows: diopside ← dolomite,tremolite ← diopside, and chlorite← tremolite.

3. The green nephrite formed as a result of metasomatism in the con-tact zone between granodiorite and a dolomiticmarble. It is also pos-sible, that Alamas granodiorite and the nephrite deposit occurred inthe post-orogenic environment.

4. The prograde metasomatism stage and the early retrograde alteredstage are the two main stages of nephrite formation. However,tectonic activity is also necessary, which led to both ductile and brit-tle deformations. Brittle deformation made it possible for fine-grained tremolite (nephrite) to occur, however, ductile deformationcommonly causes fissures and makes the uneven structure, thusdestroying the quality of the nephrite. Moreover, the metasomaticprocess plays an important role in the occurrence of the zonal struc-tures of green, green–white and white nephrite zones and the factthat zircons were found in green nephrite rather than white andgreen–white nephrite.

143Y. Liu et al. / Lithos 212–215 (2015) 128–144

Supplementary data to this article can be found online at http://dx.doi.org/10.1016/j.lithos.2014.11.002.

Acknowledgments

Thoughtful comments and reviews by Dr. Alan F. Cooper, N. AlexZirakparvar, Dr. Li X.H. and Yui. T.F. are gratefully appreciated. We aregrateful to both Dr. Li X.H. and Dr. Li Q.L. (IGGCAS) for their help inobtaining SIMS U–Pb data. Mr. Duan L.F., Liang W., and Mrs. Li Q.Y.(CAGS) also helped us obtain the SHRIMP II data. This study wasfunded by the Major State Basic Research Program of China(2015CB452600, 2011CB403100), the Natural Science Foundationof China (Grant 41102039), and the IGCP/SIDA (600) project.

References

Black, L.P., Kamo, S.L., Allen, C.M., Aleinikoff, J.N., Davis, D.W., Korsch, R.J., Foudoulis, C.,2003. Temorai: a new zircon standard for Phanerozoic U–Pb geochemistry. ChemicalGeology 200, 155–170.

Bulle, F., Bröcker, M., Gärtner, C., Keasling, A., 2010. Geochemistry and geochronology ofHP mélanges from Tinos and Andros, cycladic blueschist belt, Greece. Lithos 117,68–81.

Clark, D.J., Hensen, B.J., Kinny, P.D., 2000. Geochronological constraints for a two-stagehistory of the Albany–Fraser Orogen, Western Australia. Precambrian Research 102,155–183.

Coleman, R.G., 1966. New Zealand serpentinite and associated metasomatic rocks. Bulle-tin, New Zealand Geological Survey 76, 102.

Compston, W., Williams, I.S., Kirschvink, J.L., Zichau, Zhang, Guogan, Ma, 1992. ZirconU–Pb ages for the Early Cambrian time-scale. Journal of Geological Society, London149, 171–184.

Cooper, A.F., 1995. Nephrite and metagabbro in the Haast Schist at Muddy Creek,Northwest Otago, New Zealand. New Zealand Journal of Geology and Geophysics38, 325–332.

Deng, J., Yang, L.Q., Gao, B.F., Sun, Z.S., Guo, C.Y., Wang, Q.F., Wang, Q.F., 2009. Fluid evo-lution and metallogenic dynamics during tectonic regime transition: example fromthe Jiapigou Gold Belt in Northeast China. Resource Geology 59, 140–152.

Deng, J., Wang, Q.F., Yang, S.J., Liu, X.F., Zhang, Q.Z., Yang, L.Q., Yang, Y.H., 2010a. Geneticrelationship between the Emeishan plume and the bauxite deposits in WesternGuangxi, China: constraints from U–Pb and Lu–Hf isotopes of the detrital zircons inbauxite ores. Journal of Asian Earth Sciences 37, 412–424.

Deng, J., Wang, Q.F., Yang, L.Q., Wang, Y.R., Gong, Q.J., Liu, H., 2010b. Delineation and ex-ploration of geochemical anomalies using fractal models in the Heqing area, YunnanProvince, China. Journal of Geochemical Exploration 105, 95–105.

Deng, J., Xiao, C.H., Zhou, X.Z., Yang, L.Q., Zhang, J., Zhao, Y., 2010c. The influence of theChuxiong Yaoan earthquake on the mineralization of hot springs: an case studyfrom Tengchong geothermal area, Southwestern China. Acta Geologica Sinica(English Edition) 84, 1391–1400.

Deng, J., Wang, Q.F., Li, G.J., Li, C.S., Wang, C.M., 2013. Tethys tectonic evolution and itsbearing on the distribution of important mineral deposits in the Sanjiang region,SW China. Gondwana Research http://dx.doi.org/10.1016/j.gr.2013.08.002.

Deng, J., Wang, Q.F., Li, G.J., Santosh, M., 2014. Cenozoic tectono-magmatic andmetallogenic processes in the Sanjiang region, southwestern China. Earth ScienceReviews http://dx.doi.org/10.1016/j.earscirev.2014.05.015.

Dewey, J.F., Shackleton, R., Chang, C.F., 1988. The tectonic evolution of the Tibetan Plateau.Philosophical Transactions of the Royal Society of London, Series A: Mathematicaland Physical Sciences 327, 379–413.

Dorling, M., Zussman, J., 1985. An investigation of nephrite jade by electron microscopy.Mineralogical Magazine 49, 31–36.

Flint, D.J., Dubowski, E.A., 1990. Cowell nephrite jade deposits. In: Hughes, F.E. (Ed.),Geology of the Mineral Deposits of Australia and Papua New Guinea vols. 2 & 14. In-stitute of Mineralogy and Metallurgy, Melbourne, Australia, pp. 1059–1062.

Gao, J., Reiner, K., 2000. Eclogite occurrences in the southern Tianshan high pressure belt,Xinjiang, Western China. Gondwana Research 3, 33–38.

Germine, M., Puffer, J.H., 1989. Origin and development of flexibility in asbestiform fibres.Mineralogical Magazine 53, 327–335.

Guilbert, J.M., Lowell, J.D., 1974. Variations in zoning patterns in porphyry copperdeposits. Canadian Institute of Mining and Metallurgy Bulletin 67, 99–109.

Harley, S.L., Kelly, N.M., Möller, A., 2007. Zircon behaviour and thermal histories of moun-tain chains. Elements 3, 25–30.

Harlow, G.E., Sorensen, S.S., 2000. Jade: occurrence and metasomatic origin. 31st Interna-tional Geologic Congress, Rio de Janeiro, Brazil, August 6–17, 2000, Congress Program,Abstracts, p. 72.

Harlow, G.E., Sorensen, S.S., 2005. Jade (nephrite and jadeitite) and serpentinite:metasomatic connections. International Geology Review 47, 113–146.

Hoskin, P.W.O., 2005. Trace-element composition of hydrothermal zircon and the alter-ation of Hadean zircon from the Jack Hills, Australia. Geochimica et CosmochimicaActa 69, 637–648.

Hu, Z.C., Gao, S., Liu, Y.S., Hu, S.H., Chen, H.H., Yuan, H.L., 2008. Signal enhancement inlaser ablation ICP-MS by addition of nitrogen in the central channel gas. Journal ofAnalytical Atomic Spectrometry 23, 1093–1101.

Hu, Z., Liu, Y., Gao, S., Xiao, S., Zhao, L., Günther, D., Li, M., Zhang, W., Zong, K., 2012.A “wire” signal smoothing device for laser ablation inductively coupled plasmamass spectrometry analysis. Spectrochimica Acta Part B: Atomic Spectroscopy78, 50–57.

Jiang, R.H., 1986. Preliminary study on genetic type, minerogenetic model and the law ofdistribution of Hotan nephrite. Xinjiang Geology 4, 1–12 (in Chinese).

Jin, M.S., Shin, S.C., Kim, S.J., Choo, S.H., 1993. Geochronology and thermal history of theChuncheon granite in the Gyeonggi massif, South Korea. Journal of PetrologicalSociety of Korea 2, 122–129 (in Korean).

Kim, S.J., Lee, D.J., Chang, S., 1986. A mineralogical and gemological characterization of theKorean jade from Chuncheon, Korea. Journal of Geological Society of Korea 22,278–288 (in Korean).

Leake, B.E., Woolley, A.R., Arpes, C.E.S., 1997. Nomenclature of amphiboles. report of the.Subcommittee on amphiboles of the International Mineralogical Association,Commission on New Minerals and Mineral Names. American Mineralogist 82,1019–1037.

Leaming, S.F., 1978. Jade in Canada. Geological Survey of Canada, papers 78–19 , pp. 1–59.Li, Q.L., Li, S.G., Zheng, Y.F., Li, H.M., Massonne, H.J., Wang, Q.C., 2003. A high precision

U–Pb age of metamorphic rutile in coesite–bearingeclogite from the DabieMountainsin central China: a new constraint on the cooling history. Chemical Geology 200,255–265.

Li, Q.L., Lin, W., Su, W., Li, X.H., Shi, Y.H., Liu, Y., Tang, G.Q., 2011. SIMS U–Pb rutile age oflow-temperature eclogites from southwestern Chinese Tianshan, NW China. Lithos122, 76–86.

Li, X.H., Long, W.G., Li, Q.L., Liu, Y., Zheng, Y.F., Yang, Y.H., Chamberlain, K.R., Wan, D.F.,Guo, C.H., Wang, X.C., Tao, H., 2010. Penglai zircon megacryst: a potential new work-ing reference for microbeam analysis of Hf-O isotopes and U-Pb age. Geostandardsand Geoanalytical Research 34, 117–134.

Liu, Y.S., Hu, Z.C., Gao, S., Günther, D., Xu, J., Gao, C.G., Chen, H.H., 2008. In situ analysis ofmajor and trace elements of anhydrous minerals by LA-ICP-MS without applying aninternal standard. Chemical Geology 257 (1–2), 34–43.

Liu, Y., Deng, J., Shi, G., Lu, T.J., He, H.Y., Ng, Yi-Nok, Yang, L.Q., Wang, Q.F., 2010. Chemicalzone of nephrite in Alamas, Xinjiang, China. Resource Geology 60, 249–259.

Liu, Y.S., Gao, S., Hu, Z.C., Gao, C.G., Zong, K.Q., Wang, D.B., 2010a. Continental and oceaniccrust recycling-induced melt–peridotite interactions in the Trans-north ChinaOrogen: U–Pb dating, Hf isotopes and trace elements in zircons of mantle xenoliths.Journal of Petrology 51, 537–571.

Liu, Y.S., Hu, Z.C., Zong, K.Q., Gao, C.G., Gao, S., Xu, J., Chen, H.H., 2010b. Reappraisementand refinement of zircon U–Pb isotope and trace element analyses by LA-ICP-MS.Chinese Science Bulletin 55, 1535–1546.

Liu, Y., Deng, J., Shi, G., Yui, T.F., Zhang, G., Maituohuti, A., Yang, L., Sun, X., Wang, Q., 2011a.Geochemistry and petrology of nephrite from Alamas, Xinjiang, NW China. Journal ofAsian Earth Sciences 42, 440–451.

Liu, Y., Deng, J., Shi, G., Ng, Yi-Nok, Yang, L., Wang, Q., 2011b. Geochemistry and petrogen-esis of placer nephrite in Hetian, Xinjiang, Northwest China. Ore Geology Reviews 41,122–132.

Ludwig, K.R., 2001. Squid 1.02: a user's manual. Berkeley Geochronology Center SpecialPublication No. 2, pp. 1–21.

Ludwig, K.R., 2003. User's Manual for Isoplot 3.00: A Geochronological Toolkit forMicrosoft Excel. Berkeley Geochronology Center Special Publication, Berkeley.

Luvizotto, G.L., Zack, T., Meyer, H.P., Ludwig, T., Triebold, S., Kronz, A., Münker, C., Stockli,D.F., Prowatke, S., Klemme, S., Jacob, D.E., vonEynatten, H., 2009. Rutile crystals aspotential trace element and isotope mineral standards for microanalysis. ChemicalGeology 261, 346–369.

Mao, J.W., Goldfarb, Richard J., Wang, Y.T., Hart, Craig J., Yang, J.M., Wang, Z.L., 2005. LatePaleozoic base and preciousmetal deposits, East Tianshan, Xinjiang, China: character-istics and geodynamic setting. Episodes 28, 23–36.

Meinert, L.D., Hedenquist, J.W., Satoh, H., Matsuhisa, Y., 2003. Formation of anhydrous andhydrous skarn in Cu–Au ore deposits by magmatic fluids. Economic Geology 98,147–156.

Meinert, L.D., Dipple, G.M., Nicolescu, S., 2005. World skarn deposits. Economic Geology100, 299–336.

Nasdala, L., Hofmeister, W., Norberg, N., Mattinson, J.M., Corfu, F., Dor, W., Kamo, S.L.,Kennedy, A.K., Kronz, A., Reiners, P.W., Frei, D., Kosler, J., Wan, Y.S., Goze, J., Hoer, T.,Kröner, A., Valley, J.W., 2008. Zircon M257— a homogeneous natural referencemate-rial for the ion microprobe U–Pb analysis of zircon. Geostandards and GeoanalyticalResearch 32, 247–265.

Noh, J.H., Yu, J.-Y., Choi, J.B., 1993. Genesis of nephrite and associated calc-silicate mineralsin Chuncheon area. Journal of Geological Society of Korea 29, 199–224 (in Korean).

O'Hanley, D.S., 1996. Serpentinites, recorders of tectonic and petrological history. OxfordMonographs in Geology and Geophysics 34, 256.

Pan, Y.S., Wang, Y., 1994. Tectonic evolution along the geotraverse from Yecheng toShiquanhe (in Chinese). Acta Geologica Sinica 68, 295–307.

Prokhor, S.A., 1991. The genesis of nephrite and emplacement of the nephrite-bearingultramafic complexes of East Sayan. International Geology Review 33, 290–300.

Shi, G.H., Cui, W.Y., Cao, S.M., Jiang, N., Jian, P., Liu, D.Y., Miao, L.H., Chu, B.B., 2008. Ionmicroprobe zircon U–Pb age and geochemistry of the Myanmar jadeitite. Journal ofGeological Society, London 165, 221–234.

Shi, G.H., Li, X.H., Li, Q.L., Chen, Z.Y., Deng, J., Liu, Y.X., Kang, Z.J., Pang, E.C., Xu, Y.J., Jia, X.M.,2012. Ion microprobe U–Pb age and Zr-in-rutile thermometry of rutiles from theDaixian rutile deposit in the Hengshan Mountains, Shanxi Province, China. EconomicGeology 107, 525–535.

Stern, R.A., 1998. High-resolution SIMS determination of radiogenic tracer–isotope ratiosin minerals. In: Cabri, L.J., Vaughan, D.J. (Eds.), Modern Approaches to Ore and Envi-ronmental Mineralogy. Mineralogical Association of Canada, Short Course Series 27,pp. 241–268.

144 Y. Liu et al. / Lithos 212–215 (2015) 128–144

Sun, S.S., McDonough, W.F., 1989. Chemical and isotopic systematics of oceanic basalts.Implications for mantle composition and processes. In: Saunders, A.D., Norry, M.J.(Eds.), Magmatism in the Ocean Basins. Geological Society, London, Special Publica-tion 42, pp. 313–345.

Sun, X., Deng, J., Zhao, Z.Y., Zhao, Z.H., Wang, Q.F., Yang, L.Q., Gong, Q.J., Wang, C.M., 2010.Geochronology, petrogenesis and tectonic implications of granites from the Fuxinarea, Western Liaoning, NE China. Gondwana Research 17, 642–652.

Tang, Y.L., Chen, B.Z., Jiang, R.H., 1994. Chinese Hetian Nephrite. Xinjiang People's Publish-ing House, Xinjiang, pp. 103–206 (in Chinese with English abstract).

Titley, S.R., 1973. Pyrometasomatism—an alteration type. Economic Geology 68, 1326–1328.Vavra, G., Gebauer, D., Schmid, R., 1996. Multiple zircon growth and recrystallization dur-

ing polyphase Late Carboniferous to Triassic metamorphism in granulites of the IvreaZone (Southern Alps): an ion microprobe (SHRIMP) study. Contributions to Mineral-ogy and Petrology 122, 337–358.

Wang, Z.Q., Jiang, C.F., Yan, Q.R., Yan, Z., 2001. Accretion and collision orogeneses in theWest Kunlun Mountains, China. Gondwana Research 4, 843–844.

Wenner, D.B., 1979. Hydrogen, oxygen and carbon isotopic evidence for the origin ofrodingites in serpentinized ultramafic rocks. Geochimica et Cosmochimica Acta 43,603–614.

Wilkins, C.J., Tennant, W.C., Williamson, B.E., Mccammon, C.A., 2003. Spectroscopic andrelated evidence on the coloring and constitution of New Zealand jade. AmericanMineralogist 88, 1336–1344.

Wu, Y.B., Zheng, Y.F., 2004. Genesis of zircon and its constraints on interpretation of U–Pbage. Chinese Science Bulletin 49 (15), 1554–1569.

Xiao, W.J., Hou, Q.L., Li, J.L., 1999. Tectonic facies and the archipelagoaccretion process ofthe West Kunlun, China. Science in China (D-Series) 43, 135–143 (supp.).

Xiao, W.J., Windley, B.F., Fang, A.M., Yuan, C., Wang, Z.H., Hao, J., Hou, Q.L., 2001.Palaeozoic–Early Mesozoic accretionary tectonics of the Western Kunlun Range,NW China. Gondwana Research 4, 826–827.

Xiao, W.J., Windley, B.F., Hao, J., 2002. Arc-ophiolite obduction in the western Kunlunrange (China): implications for the Palaeozoic evolution of central Asia. Journal ofGeological Society, London 159, 517–528.

Xiao, W.J., Windley, B.F., Liu, D.Y., Jian, P., Liu, C.Z., Yuan, C., Sun, M., 2005. Accretionarytectonics of the Western Kunlun Orogen, China: a Paleozoic–Early Mesozoic, long-lived active continental margin with implications for the growth of Southern Eurasia.Journal of Geology 113, 687–705.

Xu, Z.G., Chen, Y.C., Wang, D.H., Chen, Z.H., Li, H.M., 2008. The Scheme of the Classificationof the Minerogenetic Units in China. geological publ. House, Beijing (in Chinese).

Yang, X.D., 2013. Mineralization of Nephrite Metallogenic Belt in HeTian, Xin Jiang.(Unpublished Ph.D. dissertation), China University of Geosciences, Beijing (in Chinesewith English abstract).

Yang, S., Li, Z.L., Chen, H.L., Santosh, M., Dong, C.W., Yu, X., 2007. Permian bimodal dykeof Tarim Basin; NW China: geochemical characteristics and tectonic implications.Gondwana Research 12, 113–120.

Ye, H.M., Li, X.H., Li, Z.X., Zhang, C.L., 2008. Age and origin of high Ba–Sr appinite–granitesat the northwestern margin of the Tibet Plateau: implications for early Paleozoic tec-tonic evolution of the Western Kunlun orogenic belt. Gondwana Research 13,126–138.

Ye, H.M., Li, X.H., Lan, Z.W., 2013. Geochemical and Sr–Nd–Hf–O–C isotopic constraints onthe origin of the Neoproterozoic Qieganbulake ultramafic–carbonatite complex fromthe Tarim Block, Northwest China. Lithos 182–183, 150–164.

Yin, J., Bian, Q., 1995. Geologic Map of the Karakorum–Western Kunlunand Adjacent Re-gions (1:2M). Science Press, Beijing (in Chinese).

Yuan, C., Sun, M., Zhou, M.F., Zhou, H., Xiao, W.J., Li, J.L., 2002. Tectonic evolution of theWestern Kunlun: geochronologic and geochemical constraints from Kudi granites.International Geology Review 44, 653–669.

Yui, T.F., Kwon, S.T., 2002. Origin of a dolomite-related jade deposit at Chuncheon, Korea.Economic Geology 97, 593–601.

Yui, T.F., Maki, K., Usuki, T., Lan, C.Y., Marten, U., Wu, C.M., Wu, T.W., Liou, J.G., 2010. Gen-esis of Guatemala jadeitite and related fluid characteristics: insight from zircon.Chemical Geology 270, 45–55.

Yui, T.F., Fukoyama,M., Lizuka, Y.,Wu, C.M., Tsai-WayWu, T.W., Liou, J.G., Grove, M., 2013.Is Myanmar jadeitite of Jurassic age? A result from incompletely recrystallizedinherited zircon. Lithos 160–161, 268–282.

Zhang, C.L., Lu, S.N., Yu, H.F., Ye, H.M., 2007. Tectonic evolution of theWest KunlunOrogenin north of Qinghai–Tibet Plateau: evidences from zircon SHRIMP and LA-ICP-MSU–Pb ages. Science in China (D-Series) 50, 825–835.

Zhang, G.B., Song, S.G., Zhang, L.F., Niu, Y.L., 2008. The subducted oceanic crust within con-tinental type UHP metamorphic belt in the North Qaidam, NW China: evidence frompetrology, geochemistry and geochronology. Lithos 104, 99–118.

Zhang, Z.Y., Du, Y.S., Zhang, J., 2013. Alteration, mineralization, and genesis of the zonedTongshan skarn-type copper deposit, Anhui, China. Ore Geology Reviews 53,489–503.

Zheng, Y.C., Hou, Z.Q., Li, Q.Y., Sun, Q.Z., Liang,W., Fu, Q., Li,W., Huang, K.X., 2012. Origin oflate Oligocene adakitic intrusives in the southeastern Lhasa terrane: evidence from insitu zircon U–Pb dating, Hf–O isotopes, and whole-rock geochemistry. Lithos 148,296–311.

Zhou, H., Chu, Z.Y., Li, J.L., Hou, Q.L., Wang, Z.H., Fang, A.M., 2000. 40Ar/39Ar dating of duc-tile shear zone in Kuda, West Kunlun, Xinjiang. Chinese Journal Geology 35, 233–239(in Chinese with English abstract).