The Himalayan Mianning–Dechang REE belt associated with carbonatite–alkaline complexes

25 Pages·2009·4.7 MB·English

OreGeologyReviews36(2009)65–89
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Ore Geology Reviews
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The Himalayan Mianning–Dechang REE belt associated with carbonatite–alkaline
complexes, eastern Indo-Asian collision zone, SW China
Zengqian Houa,b,g,⁎, Shihong Tianc, Yuling Xied, Zhusen Yangc, Zhongxin Yuanc, Shuping Yinb,
Longsheng Yid, Hongcai Feie, Tianren Zouc, Ge Baic, Xiaoyu Lif
aEastChinaInstituteofTechnology,Fuzhou344000JiangxiProvince,PRChina
bInstituteofGeology,ChineseAcademyofGeologicalSciences,Beijing100037,PRChina
cInstituteofMineralResources,ChineseAcademyofGeologicalSciences,Beijing100037,PRChina
dCivil&EnvironmentalEngineeringSchool,BeijingUniversityofScienceandTechnology,Beijing100083,PRChina
eChineseAcademyofGeologicalSciences,Beijing100037,PRChina
f109TeamofGeology,SichuanBureauofGeologyandMineralResources,Chengdu610100,SichuanProvince,PRChina
gSchoolofEarthandGeographicalSciences,UniversityofWesternAustralia,Australia
a r t i c l e i n f o a b s t r a c t
Articlehistory: TheHimalayanMianning–DechangREEbelt,westernSichuan,SWChina,isapproximately270kmlongand
Received11February2008 15 kmwide, and contains total reserves of N3 Mt of LREE, including one giant (Maoniuping), one large
Receivedinrevisedform27February2009 (Dalucao)andanumberofsmall-mediumREEdeposits(Muluozhai,Lizhuang)andoccurrences.Thebeltis
Accepted3March2009
tectonically located within a continental collision zone, i.e., the eastern Indo-Asian collision zone. REE
Availableonline16March2009 mineralizationisassociatedwithHimalayancarbonatite–alkalinecomplexes,whichconsistofcarbonatitic
sillsordykesandassociatedalkalinesyenitestocks.AvailabledatingdatadefineaHimalayanmetallogenic
Keywords:
Carbonatite epoch(40–10Ma).Themagmatic–hydrothermalREEsystemswerecontrolledbyCenozoiclarge-scalestrike-
Syenite slipfaultingandtheresultanttensionalfissurezones,developedinatransformphasefromatranspressional
REEdeposit toatranstensionalregime.
Indo-Asiancollisionzone Alterationischaracterizedbyfenitization,whichformedfenitehalosenvelopingtheREEorebodies.Associated
SWChina REEmineralizationoccursascomplexveinsystemsconsistingofvariousveinlets,stringerandstockwork
Maoniuping zones,andbreccia-pipesystems.TheREEorebodiesshowvariousshapesfromplate-like,lenticulartopipe-like
Dalucao
indifferentdistricts.Oretypesaredominatedbypegmatitic,carbonatitic,breccia,andstringer(stockwork),
Muluozhai
and disseminated ores, mainlycomposed of barite + fluorite + aegirine-augite + calcite + bastnaesite
Lizhuang
assemblages. Bastnaesite precipitation (275–325 °C) appears in three assemblages: earlyclastics-bearing
barite+arfvedsonite+calcite+bastnaesite;intermediatequartz+fluorite+barite+bastnaesite;andlate
fluorite+barite+bastnaesiteassemblages.Thesewerefollowedbylow-temperaturepyrite+galena+
sphaleriteassemblages.Fluidinclusionstudiesindicatethatganguequartzandfluoritehostsnumerousmelt/
fluidinclusionswithalargeproportionofsulfate(i.e.,BaSO ,K SO ,andCaSO ),inadditiontoCaCO andCaF ,
4 2 4 4 3 2
yieldingabnormallyhigh(upto750°C)butwide-ranginghomogenizationtemperatures(750–125°C).The
similarityofSr–Ndisotopiccompositionsforganguemineralswiththoseofthehostcarbonatite–syenite
suggeststhatore-formingfluids,especiallytheF−,HCO2−,SO2−components,werederivedfromcarbonatite–
3 4
syenitemagmas.TheO–D–Cisotopicdatafromganguecalcite,fluoriteandquartzindicatethatthefluidswere
oforthomagmaticorigin,butalsoinvolvedmixingwithanexternalfluid.
Onthebasisofoursynthesis,weproposeapossiblegeneticmodelforREEmineralization,inwhich the
hydrothermalsystemtemporallyunderwentacomplicatedevolutionfromseparationofhigh-Tsulfate-bearing
NaCl–KClbrineresultingineffectiveprecipitationofREE-fluorocarbonateandsulfate,tosubsequentmixing
withlow-temperaturemeteoricwaterprecipitatingminorsulfideassemblages.Spatially,thissequenceof
events generated a three-tier REE mineralized architecture, in which pipe-like breccia orebodies grade
downwardsfromshallowtodeepstructurallevelsintolargeveinletoresystems,andveinlet-disseminated
orebodies.
©2009PublishedbyElsevierB.V.
1.Introduction
Inthelastfewdecades,awidely-acceptedconceptualmodelforthe
⁎ Correspondingauthor.InstituteofGeology,CAGS,Beijing100037,PRChina. genesis of primary REE deposits has been developed. In this model,
E-mailaddress:[email protected](Z.Hou). primary REE deposits are mainlyassociated with carbonatite–alkaline
0169-1368/$–seefrontmatter©2009PublishedbyElsevierB.V.
doi:10.1016/j.oregeorev.2009.03.001
66 Z.Houetal./OreGeologyReviews36(2009)65–89
Fig.1.SimplifiedtectonicmapoftheHimalayan–TibetanOrogen(modifiedafterYinandHarrison,2000;Houetal.,2003).
complexesandoccurincontinentalriftzones.Thisfacthasbeenverified StudiesintheREEbeltduringthepasttwodecadeshavefocused
bystudiesonnumerousREEdeposits,widelydevelopedinriftzones, mainly on individual deposits (e.g., Maoniuping, and Dalucao) (Niu
such as the East African Rift (Mitchell and Garson, 1981) or the andLin,1994;Yuanetal.,1995;Niuetal.,1996;Yangetal.,1998,2000,
Proterozoic Langshan–Baiyan Obo Rift of North China (Wang and Li, 2001;Pu,2001;Xuetal.,2002,2004;Tianetal.,2003,2005;Li,2005).
1992).However,notallREEdepositsoccurincontinentalriftenviron- However,therelationshipsbetweenREEmetallogenyandHimalayan
ments;theycanalsobedevelopedincontinentalcollisionzones.The collisionorogenyandthegeneticlinksamongtheseREEdepositsin
Himalayan Mianning–Dechang (MD) REE belt, western Sichuan, SW thebeltarelesswellconstrained.Thispaperdescribesthegeologyand
China,isthefirsttypicalexampleofsuchatype.Here,REEdepositsare mineralizationfeaturesofdepositswithinthebelt.Basedonthelatest
associated with Cenozoic carbonatite–alkaline complexes that occur observationsandasynthesisoftheentireEIACZ,REEmetallogensis
tectonicallyintheeasternIndo-Asiancollisionzone(EIACZ),aregionof andthegeodynamicsettingoftheMDREEbeltarediscussed.
hightopographicreliefboundedbyaseriesofCenozoicstrike-slipfaults
(Fig.1;YinandHarrison,2000;Houetal.,2003,2006a,HouandCook, 2.Geologicaltectonicsetting
2009-thisissue).Ingeneral,REEdepositsincollisionalenvironmentsare
lesswellunderstoodthanthoseinanorogenicriftenvironments. TheHimalayanMDREEbeltislocatedonthewesternmarginof
TheMDREEbeltisoneofthemosteconomicallysignificantbeltsin the Yangtze craton (Fig. 1), a Cenozoic EIACZ. Available age date
China.Itisupto270kminlengthand15kminwidth,andhostsone defines a Himalayan metallogenic epoch (40–10 Ma) for REE
giantdeposit(Maoniuping),onelargedeposit(Dalucao),twomedium- mineralization associated with Cenozoic carbonatite–alkaline com-
sizeddeposits(MuluozhaiandLizhuang),andnumerousotherminer- plexes (cf. Hou et al., 2006a). The basement of the Yangtze craton
alizedcarbonatite–alkalinecomplexes(Table1;Fig.2).TheREEbeltis consists of Archaean high-grade metamorphic rocks, Proterozoic
locatedwithinthePanxiRift,aPermianpaleo-riftzone(Zhangetal., meta-sedimentary rocks and overlying Phanerozoic clastic and
1988;Cong,1988),butavailableagedataforthehostrocksandgangue carbonatesequences (Cong,1988; Luo et al.,1998). The Proterozoic
mineralsshowtheybelongtotheHimalayanmetallogenicepoch(40– Kangdinggranitoidbatholiths(Xuetal.,1995),~150kmnorthofthe
10Ma;Yuanetal.,1995,1998;Pu,2001;Tianetal.,2008a,b),suggesting REEbelt, were associatedwith contemporaneous arcvolcanic rocks
formation in a collisional orogenic environment rather than a within the western mobile belt of the Yangtze craton, suggesting
continentalrift.ThisledWang,D.-H.etal.(2001)tosimplyregardthe subduction of the Pro-Tethyan oceanic plate beneath the Yangtze
Maoniupingdepositasaspecial“orogenic-type”REEdeposit. craton during the Proterozoic (Xu et al., 1995; Luo et al., 1998). A
Table1
SummaryofgeologicalcharacteristicsofthemaindepositsintheMDREEbelt,westernSichuan,SWChina.
Deposit Structure Wallrock Hostrock Mineralassemblage Alteration Gradeandtonnage Orebodyform Oretype Orestructure Ref.
Maoniuping Hahastrike-slip Granite, Nordmarkite Microcline,quartz,biotite,aegirine,aegirine-augite, Fenitization; About1.2Mt Semi-layered, Pegmatitic,carbonatitic, Massive,Mottle, Yuanetal.,
fault basalt, arfvedonite,chevkinite;calcite+fluorite+barite+ carbonatization; ofREO;gradingon banded, breccia,andstringer ribbon-banded, 1995;Yang Z.
rhyolite, celestine+bastnaesite;fluorite+barite+quartz+ aegirineor averageof irregular (stockwork) banded etal.,2000; Ho
nordmarkite, bastnaesite;Fe–Mnoxidesandcalcite;cerussite+ aegirine–augite 2.89%REO lensand Tian,2005 ue
carbonatite witherite+strontianite+wulfenite alteration pocket ta
l.
/
O
re
G
Dalucao sDluiplcfaaoulSttrike- qnuoardrtmsadrikoirtiete,, Nordmarkite aMrfivcreodcolinniete,,qcuhaervtzk,inbiitoet;itcea,laceitgeir+inefl,uaoergiitrein+e-abuargiittee,+ Fcaernbitoinzaattiioznat;ion AofbRouEOt0;.76Mt Laenndtipciuplea-rlike Bbaresctnciaaesoirtee;obraersi;tece+lesfltuinoeri+te+ Bmraescsciivaes,,block, S19h9i6a;ndYaLni,g eology
carbonatite celestine+bastnaesite;fluorite+barite+quartz+ gradingon withminor fluorite+bastnaesite;stringer banded, etal.,1998; Re
bastnaesite;Fe–Mnoxidesandcalcite;cerussite+ averageof vein-like ore;massive,block-like disseminated Tian,2005 vie
witherite+strontianite+wulfenite 5.0%REO disseminatedore andstringer ws
Lizhuang Intersectionsof Granite, Nordmarkite ThemineralassociationsatLizhuangare Fenitization 1.05–6.69% Semi-layered, Browndisseminatedore; Massive, Tian,2005 36
NE-strikingwith nordmarkite, relativelysimple REO banded, Yellowbandedore;Stockwork banded (2
0
NW-striking carbonatite irregularlens ore;Blackpowder-likeore 0
9
strike-slip )
6
faults 5–
Muluozhai Yalongjiang Granite, Nordmarkite ThemineralassociationsatMuluozhaiare Fenitization; About0.45Mt Semi-layered, Massivefluorite–bastnaesite, Massive, Tian,2005 89
strike-slipfault nordmarkite, relativesimple carbonatization; ofREO, banded, impregnated,abandedores banded
carbonatite aegirineor gradingon irregularlens
aegirine-augite averageof andveinlets
alteration 3.97%REO
6
7
68 Z.Houetal./OreGeologyReviews36(2009)65–89
Fig.2.(A).CenozoictectonicmapofeasternTibet(Wang,J.-H.etal.,2001),showingthedistributionoftheHimalayanpotassicrockbelt(Chungetal.,1998;ZhangandXie,1997),
shoshoniticlamprophyredistrict(Guoetal.,2005),andcarbonatite–alkaliccomplexbelt(Yuanetal.,1995),whichformaCenozoicsemi-discontinuousigneousprovinceinthe
easternIndo-Asiancollisionzone.(B).SketchtectonicmapshowingdistributionoftheHimalayancarbonatite–alkaliccomplexescontrolledbyreactivatedfaultsinwesternSichuan
(modifiedfromYuanetal.,1995).
sequenceofmid-Permianfloodbasaltswithminorpicriteandpicritic shuiheandXiaojiangfaultsintheYangtzecraton(Fig.2A).Associated
basaltscoversthewesternpartoftheYangtzecraton,anearlyPermian Cenozoicdeformation ischiefly manifestedbyPaleocene–Oligocene
passive continental margin (Hou et al., 2006b), forming a large (55–32Ma)transpression,early–middleMiocene(26–17Ma)trans-
igneousprovince(LIP)withanareaof~500,000km2(Lu,1996;Xu, tension,andalateNeogene–QuaternaryE–WextensionintheEIACZ
Y.-G. etal.,2001). LIP development hasbeenwidelyconsideredto (Wang,J.-H.etal.,2001).
relatetotheEmeishanmantleplume(ChungandJahn,1995;Lu,1996; Himalayan magmatic activity in the EIACZ forms a semi-contin-
Xu,Y.-G.etal.,2001;Houetal.,2006b).ThisPermianmantleplumealso uous potassic igneous province in SW China (Guo et al., 2005). It
resultedinformationofthePanxipaleo-riftzone(Cong,1988),bounded includes fromwest to east: (1) a 1000-km-long potassic rock belt,
by NS-striking faults along thewestern margin of the Yangtze craton associated with a series of early-middle Cenozoic pull-apart basins
(Zhangetal.,1988). anddevelopedalonganarrowbeltfollowingtheNanqianthrust,the
Indo-Asiancollisionat65–50MaintheHimalayanorogen(Yinand Batang–Lijiangfault,andtheRedRivershearzone(RRSZ)(Zhangand
Harrison,2000; Zhongetal., 2001; Moet al., 2003) resultedin the Xie,1997;Wang,J.-H.etal.,2001;Houetal.,2003);(2)a50,000km2
western margin of the Yangtze craton, forming a collision orogenic shoshonitic(calc-alkaline)lamprophyredistricteastoftheRRSZ(Luo
belt, i.e., the NS-striking Jinpingshan Orogen in the EIACZ (Fig. 2A) and Yu, 2001; Guo et al., 2005); and (3) a 270 km-long belt of
(Luoetal.,1998).AseriesofCenozoicstrike-slipfaults(Fig.2B)were carbonatite–alkalinecomplexesinwesternSichuan,boundedbythe
subsequently developed in the EIACZ to accommodate stress and NS-strikingYalongjiangandAnninghefaultswhichwerereactivated
strainproducedbythecollision.Thesestrike-slipfaultsinclude,from duringtheperiodofIndo-Asiancollision(Fig.2B).Alltheseigneous
west to east, the Jiali and Gaoligong faults around the eastern activities took place over a relatively short duration of 40–24 Ma,
Himalayansyntaxis;theBatang–Lijiangfault(northernsegment)and peakingat35Ma(ZhangandXie,1997;Wang,J.-H.etal.,2001;Chung
the Ailaoshan–Red River fault (southern segment); and the Xian- et al.,1998; Hou et al., 2003; Guo et al., 2005). The monzogranite
Z.Houetal./OreGeologyReviews36(2009)65–89 69
Fig.3.Simplifiedgeologicalmapshowingthedistributionofcarbonatite–alkaliccomplexesandassociatedREEorebodiesatMaoniuping(modifiedfromYuanetal.,1995).
stocks in the potassic felsic rock belt were associated with Cu syenite (Luoand Yu, 2001)and 31.7 Ma forcarbonatite (Pu,2001).
mineralization,whichformtheHimalayanYulongporphyryCubelt SyenitefromtheMuluozhaicomplexyieldeda40Ar/39Arageof31.2Ma
in eastern Tibet (Hou et al., 2003), whereas carbonatite–alkaline (Tianetal.,2006),whereasthatfromtheLizhuangcomplexgavea
complexes were associated with REE mineralization (Tian, 2005), younger40Ar/39Arageof21.7Ma(Tian,2005).Inthesoutherndistrict,
whichproducedtheMDREEbeltinwesternSichuan(Fig.1). thecarbonatite–alkalinecomplexiscontrolledbytheDalucaostrike-
slip fault (Fig. 2B), and intruded both a Proterozoic quartz diorite
3.Geologyandgeochemistryofthecomplexes plutonwithaSHRIMPU-Pbzirconageof764Ma(Tianetal.,2008a)
andaTriassic–Jurassicsedimentarysequence,suggestingarelatively
3.1.Spatial–temporaldistribution shallowdepthforthecomplex.Thecomplexconsistsofsyenitestocks,
carbonatite sills, and REE-bearing breccia-pipes (Fig. 6, Yang et al.,
The carbonatite–alkaline complexes in western Sichuan are 1998).SHRIMPU-Pbzircondatingforcarbonatiteandnordmarkiteare
located in the eastern part of the Cenozoic igneous province 12.99±0.94Ma,and14.53±0.31Ma,respectively(Tianetal.,2008a).
(Fig.2A).TheymainlyintrudeProterozoiccrystallinebasementand
anoverlyingPaleozoic–Mesozoicvolcano-sedimentarysequence,and 3.2.Geochemistry
constituteanarrow,NS-tendingREE-bearingbelt.Thebeltisbordered
by NS-striking strike-slip faults (Figs.1 and 2), whereas individual Thedominantlithologiesofcarbonatitesfromthesecomplexesare
complexes with irregular shapes were controlled by second-order pinkcoarse-grainedandwhitefine-medium-grainedcalcitecarbona-
strike-slipfaultsortranstensionalfaults(Fig.2B). tites, with 80–90% modal calcite and subordinate aegirine, aegirine-
Atleasttwodistrictsofcarbonatite–alkalinecomplexeshavebeen augite,riebeckite,arfvedsonite,biotite,microcline,andquartz.Allrocks
recognized.Thenortherndistrictincludesthreecomplexes:Maoniup- arelowSiO (b10.22%),FeO(b1.20%)andMgO(b0.73%),butwitha
2
ing(Fig.3);Lizhuang(Fig.4);andMuluozhai(Fig.5),whichgenerally rangeofCaOcontents(40.65–55.40%)(Liuetal.,2004;Tian,2005;Hou
strike in an almost N–S direction (Fig. 2B). These complexes are etal.,2006c),distinguishingthemfromprimary,calcitecarbonatites.
dominatedbybodiesofsyenite,withminorcarbonaticsillsanddykes Themainphaseintheassociatedsyeniticrocksisnordmarkite,with
(Figs.3–5).Availableagedatedefinesamagmaticdurationof27.1to minor aegirine-augite syenite and porphyritic syenite, with high
40.8 Ma for these complexes. Bulk-rock and arfvedsonite separated Al O (N13.3%) and alkali contents (K O + Na O N9.1%) and awide
2 3 2 2
from the Maoniuping complex yielded a K–Ar age of 40.8 Ma for rangeofK Ocontents(3.63–5.94%)andK O/Na Oratios(0.41–1.45),
2 2 2
70 Z.Houetal./OreGeologyReviews36(2009)65–89
Fig.4.Schematicmapshowingthefeaturesofcarbonatite–syenitecomplexandassociatedREEorebodiesatLizhang.
thusdistinguishingthemfrompre-Cenozoicgranitoidplutonsbytheir suggestingametasomatizedmantlesource(Tatsumietal.,1986;Foley
lowSiO (b71.5%)andmodalquartzcontents(b20%)(Yuanetal.,1995). andWheller,1990).AssociatedsyenitesarerelativelyenrichedinLILE
2
ThecarbonatitesareenrichedinLREEandlarge-ionincompatible andHFSE,showingsimilartraceelementpatternsandREEpatterns,
elements (LILE: Sr: 1002–56,300 ppm; Ba: 378–125,750 ppm), and butwithLREEenrichment(Houetal.,2006c).
thus similar to carbonatites that host REE-Nb–Fe orebodies in Carbonatites from these complexes yield a range of δ18O values
anorogenic environments (Liu et al., 2004; Tian, 2005; Hou et al., varyingfrom6.4to10.5‰andδ13Cvaluesbetween−3.9and−8.5‰
2006c).Theyarerelativelydepletedinhigh-fieldstrengthelements (Yangetal.,1998;Xuetal.,2002;Niuetal.,2003;Tian,2005;Houetal.,
(HFSE),andshownegativeanomaliesinNb,Ta,P,Zr,Hf,andTiina 2006c),whichgenerallyfallinthefieldoftheprimary,mantle-derived
mantle-normalizedtraceelementpatterndiagram(Houetal.,2006c), carbonatitesonaδ18Ovs.δ13Cdiagram(Fig.7;Tayloretal.,1967).Bulk-
Fig.5.SketchgeologicalmapoftheMuluozhaioredistrict(modifiedfromTian,2005).
Z.Houetal./OreGeologyReviews36(2009)65–89 71
Fig.6.Sketchgeologicalmapshowingthefeaturesofcarbonatite–syenitecomplexandassociatedREEorebodiesatDalucao(modifiedfromHouetal.,2006a).
rockδ18Ovaluesoftheassociatedsyenitesare3.5–7.9‰(Tian,2005) etal.,2001b;Xuetal.,2002,2004;Huangetal.,2003;Tianetal.,2003).
and~1–2.5‰,whicharesimilarorslightlylightlylighterthanthoseof Geologyandmineralizationfeaturesarebrieflydescribedhere.
calcitesfromcarbonatites(Xuetal.,2002;Tian,2005).TheNdandSr
isotopiccompositionsofthecarbonatitesarecharacterizedbyanegative 4.1.1.Geology
ε of −3.2 to −6.4 and relative high (87Sr/86Sr) of 0.706020– Fourmainlithologicunitsarerecognizedinthedistrict(Fig.3):(1)
Nd(t) i
0.707922 (Hou et al., 2006c). They are thus distinct from most a90km-long,6to14km-wide,NS-strikinggraniticplutonunitwitha
carbonatites with positive ε and negative ε , generated by
Nd(t) Sr(t)
anorogenicprocesses(BellandBlenkinsop,1987)andfromthePakistan
collision zone carbonatites with negative ε but low ε (Tilton
Nd(t) Sr(t)
etal.,1998)(Fig.8).Associatedsyenitesshowasimilarε butwider
Nd(t)
rangeof(87Sr/86Sr),comparedwiththecarbonatites(Yuanetal.,1995;
i
Liuetal.,2004;Tian,2005;Houetal.,2006c).
Insummary,theclosespatialandtemporalassociationofcarbonatites
withsyenitesinwesternSichuansuggestsageneticlink.TheirSr–Ndand
C–Oisotopesignaturesindicatethattheyarederivedfrompartialmelting
ofametasomatized,enrichedmantlesource(Houetal.,2006c).
4.Mineralization
The Himalayan MD REE belt was discovered in the 1990s, and
related REE deposits were subsequently explored by 109 Team of
Geology, Sichuan Bureau of Geology and Mineral Resources. Pre-
liminaryevaluation indicates that the REE belt contains reserves of
over 3 Mt REO, including one giant (Maoniuping), one large
(Dalucao), one intermediate (Muluozhai) and a number of small
REEdeposits(e.g., Lizhuang)andoccurrences. Mostdepositsin the
REEbelthavebeenminedbydomesticminingcompanies,andhave
met most of the demand for REE metals in China. Geological and
mineralization features of the deposits are summarized in Table 1.
SignificantREEdepositsaredescribedinthefollowingsections.
4.1.Maoniupingdeposit
TheMaoniupingdepositisaworld-classdeposit,followingonlythe
BayanOboREE-Nb–Fe(China)andMountainPass(USA)REEdepositsin Fig. 7. Carbon and oxygen isotope compositions of calcites from carbonatites and
associatedREEorebodies(gangueminerals)intheMDREEbelt.Thefieldofprimary,
termsofsize.Maoniupingcontainsca.1.2MtREO,gradinganaverage
mantle-derived carbonatites is shown. Arrows schematically indicate the main
2.89%REO.Thedeposithasbeenstudiedbymanyresearchers(Niuand processesresponsibleforchangeintheC–Oisotopiccomposition(Tayloretal.,1967;
Lin,1994;Yuanetal.,1995;Niuetal.,1996;Yangetal.,2000,2001;Wang Rayetal.,1999,2000).
72 Z.Houetal./OreGeologyReviews36(2009)65–89
Fig.8.Nd–Srisotopecorrelationdiagramforcarbonatite–syeniteandassociatedREEorebodiesintheMDREEbelt.Comparativedatafromyoung(b200Ma)carbonatitesfrom
aroundtheworldareincluded.EACL:EastAfricanCarbonatiteLine(BellandBlenkinsop,1987),EA:EastAfricanriftcarbonatites(BellandBlenkinsop,1987);AD:AmbaDongar
carbonatites(60Ma)(SimonettiandBell,1995);PC:Pakistancollision-zonecarbonatites(30Ma)(Tiltonetal.,1998).PG—FluoritefromtheGalwaydeposit,Ireland(Menugeetal.,
1997),FAD—FluoritefromtheSierradelGuadarramadeposit,Spain(Galindoetal.,1994);FSP—FluoritefromtheSierrasPampeansdepositinArgentina(cf.Houetal.,2008),
andFSG—FluoritefromtheAmbaDongarcarbonatiteinIndia(SimonettiandBell,1995).DM,EMI,EMIIandHIMUareend-membercomponentsfromZindlerandHart(1986).
M-Maoniuping,ML-Muluozhai,D-Dalucao,L-Lizhuang.
zirconU–Pbageof146Ma(Zhangetal.,1988),whichintrudes;(2)a TheMaoniupingcomplexiscontrolledbytheHahastrike-slipfault
1100 m-thick metamorphosed sequence consisting of Devonian– and intrudes a Mesozoic granitic pluton and nearby rhyolitic
Permian clastic rocks, limestones and flood basalts; and (3) an succession (Fig. 3). It is a multiphase complex with a length of ca.
overlying,700m-thickcoal-bearingTriassicsedimentarysequence,as 1400mandwidthof260to350m,andmainlyconsistsofsyenitic
wellas;(4)arhyoliticsuccession,theageofwhichremainsunknown. stocks,carbonatitesills,andassociatedporphyriticgranitedykesand
Fig.9.Geologicalcross-sectionsalongexplorationlines31(A)and47(B)intheMaoniupingREEdeposit(modifiedfromYuanetal.,1995).
Z.Houetal./OreGeologyReviews36(2009)65–89 73
Fig.10.OreveinsystemoftheMaoniupingREEdeposit(modifiedfromYangetal.,2000).
numerous alkaline pegmatite dyke swarms with complex composi- replacement of K-feldspar and quartz by aegirine and/or aerigine-
tions (Fig. 3; Yuan et al.,1995; Yang et al., 2000). Steeply-dipping augite, and albite, mainly developed in the carbonatite–alkaline
carbonatite dykes or sills grade downwards into a 90 m-wide complex itself. The intensity of this zone increases toward the
medium- and coarse-grained calcite carbonatite body (Yang et al., pegmatitic vein swarms. A biotite–arfvedonite zone overprints the
2000). Aegirine-augite-bearing granitic dykes locally cut these aegirinezoneaspatches,andismainlydevelopedintheinteriorofthe
carbonatite sills and pegmatitic swarm, suggesting they represent carbonatiteandassociatedpegmatiticsill.
thefinalphaseofthecomplex. Although minor bastnaesite occurs as a dissemination in the
fenitization halo, the main REE mineralization is related to intense
4.1.2.Alteration late-stage alteration, dominated by carbonatization and aegirine or
Widespreadfenitizationcharacterizesalterationinthedistrict,and aegirine-augitealteration(Yuanetal.,1995).Bothstylesofalteration
forms a 1800 m-long, 100 to 600 m-wide fenitization halo, that overprinttheearly-formedfenitizationhalo,andwereassociatedwith
envelopes almost all orebodies at Maoniuping. This alteration is ore vein assemblages of calcite + fluorite + barite + celestine +
characterized by replacement of plagioclase and quartz by alkalic aegirine-augite+bastnaesite.
feldspar and the formation of secondary aegirine, aegirine-augite,
arfvedoniteandassociatedMg-enrichedbiotite.Alateralzonationin 4.1.3.Mineralizationstyle
the halo, ranging from an inner biotite–arfvedonite zone outwards TheMaoniupingdepositisaveinsystemconsistingofmineralized
throughanaegirinezonetoanouteralbitezone,hasbeenrecognized veinlets,stringersandstockworkzones(Fig.3).Themineralizedvein
(Yang et al., 2000). The albite zone is characterized by fine REE- systemextendstotheNNEfor2.65km,andexhibitsan“S”shapein
bearingalbiteveinsandstockworksthatoccurintheMesozoicgranite planeview(Fig.3),indicatingconstraintsfromthestrike-slipfaultingon
plutonandrhyoliticsuccession.Anaegirinezoneischaracterizedby theveinsystem.Theoreveinletsareusuallymorethan30cmthick,and
74 Z.Houetal./OreGeologyReviews36(2009)65–89
Fig.11.PhotographsshowingkeyoretypesintheMaoniupingandDalucaodeposits.(A)pegmatiticbarite+fluorite+aegirine-augite+bastnaesiteore.(B)pegmatiticorthoclase+
aegirine-augite+fluorite+bastnaesiteore.(C)Brecciatedoresgradinglaterallyintostringeroreanddownwardsintoparallelzonesofveining.(D.Brecciaedoreinthebrecciaspipe,in
whichclastsconsistpredominatelyofmagmaticdetritusandorefragmentshostedwithinacalcite-richmatrixwithsubordinatequartzandREEminerals.(E).Taxiticoreinthebrecciaspipe.
mainly occur as swarms in the centre of the complex (Fig. 9). The morphologiesvaryfromsemi-layeredandbandedtoirregularlenses
mineralized stringers have a various thicknesses (1–30 cm), and andpocket-shaped(Fig.9).
commonly constitute parallel vein zones that enveloped the central
ore veinlets. Stockwork zone generally occurs at the margins of the 4.1.5.Oretypeandzonation
veinlets and vein zones, and mainly consists of various fine-vein Fourmainoretypeshavebeenrecognized:pegmatitic;carbonatitic;
assemblagesofbastnaesite-bearingbarite+aegirine-augite,fluorite+ brecciated; and stringer (stockwork) ores. The pegmatitic ore occurs
orthoclase,andcalcite+fluorite.Ingeneral,thickoreveinletswarms mainly as thick ore veinlets or pockets, clustering in the northern
aremainlydistributedinthenorthernsegmentofthedeposit,locally segment(Figs.9Aand10),andcanbedividedintopegmatiticbarite+
formingveinletnetworks(Fig.9;Yangetal.,2000),inwhichabundant fluorite + aegirine-augite + bastnaesite and orthoclase + aegirine-
bastnaesite occurs as mega-crystals (50×15 cm) and shows mineral augite+fluorite+bastnaesiteores(Fig.11A,B).Therearetwozonation
zonationvaryingfromacentralfluorite–quartz–barite–bastnaesitezone modesforpegmatiticbarite+aegirine-augite+bastnaesiteore.When
toanouterbarite–aegirine-augitezone(Yangetal.,2000).Brecciated bastnaesiteoccursasbandsinbothsidesoftheoreveinlets,zonationcan
mineralizationoccurslocallyinthecentreoftheveinletnetwork,andis bedescribedasaninnerzoneofaegirine-augite,atransitionalzoneof
associatedwithpegmatiticmineralization(Fig.10). barite and aegirine-augite, and an outer zone of alternating barite–
aegirine-augiteandbastnaesite–fluoritebands.Ifthebastnaesitebands
4.1.4.Orebodyshape concentrateinthecentreoftheoreveinlets,mineralzonationisinthe
About71orebodieshavebeenoutlinedbydrillingandchemical oppositesense(Yangetal.,2000).Pegmatiticorthoclase+aegirine-
analysis. They have a length varying from 10 to 1168 m, thickness augite+fluorite+bastnaesiteoresarecharacterizedbytheappearance
varyingfrom1.2to32m,andgradeonaveragefrom1.04to9.05%REO ofquartzandmicrocline,andshowalateralzonationvaryingfroma
(Yuanetal.,1995).TheseorebodiesdipsteeplytowardsNWat65–80° quartzcorethroughamicroclineorbarite–microcline–aegirine-augite–
and show an S-shaped layers in plane view (Fig. 3). Orebody bastnaesitetransitionalzonetoanaegirine-augiteouterzone.