mesoproterozoic carbonatitic magmatism in the bayan obo ...mesoproterozoic carbonatitic magmatism in...
TRANSCRIPT
Mesoproterozoic carbonatitic magmatism in the Bayan Obo deposit, Inner Mongolia,North China: Constraints for the mechanism of super accumulation of rare earthelements
Kui-Feng Yang a, Hong-Rui Fan a,⁎, M. Santosh b, Fang-Fang Hu a, Kai-Yi Wang a
a Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, PR China 100029b Division of Interdisciplinary Science, Faculty of Science, Kochi University, Kochi 780-8520, Japan
a b s t r a c ta r t i c l e i n f o
Article history:Received 24 March 2010Received in revised form 21 May 2011Accepted 21 May 2011Available online 6 June 2011
Keywords:CarbonatiteREE depositPetrologyGeochemistryMesoproterozoicBayan OboChina
The Bayan Obo mine in North China contains the largest rare-earth element (REE) resources in the world. Themechanism of giant REE enrichment in such a restricted region has been the focus of several studies.Carbonatites are known to contain high concentrations of REE. Three types of carbonatite dykes occur aroundthe Bayan Obo deposit, including dolomite, calcite and calcite-dolomite carbonatite varieties. The contactrelations show that the intrusion of calcite carbonatite dykes post-date the dolomite dykes during the processof evolution of the carbonatite magma. The geochemical data show that the content of Sr and light (L) REE inthese dykes gradually increases from dolomite [(La/Yb)N values range from 1.6 to 3.8], through calcite-dolomite [(La/Yb)N ranging from 51 to 57], to calcite type [(La/Yb)N ranging from 85 to 4617]. Thisevolutionary trend suggests the crystal fractionation of the carbonatite magma, which might have played acritical role for the giant REE accumulation in the Bayan Obo region. The εNd(t) values of the carbonatitic dykesshow a tight cluster between −0.47 and 0.65, whereas the initial Sr isotope values show a broad range from0.703167 to 0.708871. The massive ore-hosting dolomite marbles show comparable element content and Ndisotope composition, and a Sm–Nd isochron age similar to that of the carbonatite dykes, implying a closerelationship during their magmatic origin. This interpretation is also supported by the intrusive contactbetween the ore-hosting dolomite marble and Mesoproterozoic Bayan Obo group, as well as the presence ofwall-rock xenoliths in the dolomite marble.
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
The Giant Bayan Obo ore deposit in the Inner Mongolia region ofNorth China is one of the best known rare-earth element (REE)deposits in the world. Since the discovery of the main orebody in1927, several studies have been carried out over the last 80 years onthe mineral constituents, chronology and geochemistry of thisdeposit. However, the genesis of this giant orebody, including itspotential resources, particularly with regard to the mechanism of REEenrichment, still remains debated.
The main arguments have focused on the genesis of the ore-hosting dolomite marble. Chao et al. (1992, 1997) proposed that thedolomite marble is a sedimentary formation and the REE minerali-zation formed from fluids associated with granitic magmatism andmetamorphism during the Paleozoic. Wang et al. (1992), Yuan et al.(1991) and Bai et al. (1996) suggested that the ore-hosting dolomitemarble is a volcano-sedimentary formation and that the REE mine-
ralization was derived from a mantle fluid. However, Drew et al.(1990), Le Bas et al. (1992, 1997, 2007), Yang et al. (2003) and Yangand Le Bas (2004) argued that the ore-hosting dolomite marble is acarbonatite intrusion and that the REE mineralization was derivedfrom a Mesoproterozoic carbonatitic magma.
Recent studies (Ionov and Harmer, 2002; Xu et al., 2008, 2010)appear to favor the model of carbonatite magma for the REE mine-ralization. Carbonatite magmas are usually characterized by highliquid–vapor component (e.g., H2O, CO2 and Cl-, Fan et al., 2001), lowviscosity (from 1.5×102 to 5.0×103 Pa·s), low density (2.2 g/mm3),and high fluidity (Dobson et al., 1996), thereby possessing thecapability of transporting large-ion-lithophile and high-field-strengthelements at high temperatures (Fan et al., 2001; Yang et al., 1998).
Many carbonatite dykes occur around the Bayan Obo deposit (Taoet al., 1998) (Fig. 1a). Le Bas et al. (1992), Tao et al. (1998) and Wanget al. (2002) reported the mineralogical compositions and geochemicalcharacteristics of the carbonatite dykes in detail, and provided evidencefor a magmatic origin. Wang et al. (2002) classified these carbonatitedykes into three types: dolomite type, calcite-dolomite type, and calcitetype based on their mineralogical composition. The calcite carbonatitedykes show consistently higher REE content as compared to the other
Ore Geology Reviews 40 (2011) 122–131
⁎ Corresponding author. Tel.: +86 13621298068; fax: +86 10 62010846.E-mail address: [email protected] (H.-R. Fan).
0169-1368/$ – see front matter © 2011 Elsevier B.V. All rights reserved.doi:10.1016/j.oregeorev.2011.05.008
Contents lists available at ScienceDirect
Ore Geology Reviews
j ourna l homepage: www.e lsev ie r.com/ locate /oregeorev
two types. Yang et al. (2003) noted that some of the calcite carbonatitedykes have more than 10% total REE content. The extremely high REEcontent in the carbonatite dykes led to the speculation that a carbonatitemagma might have played the critical role in the REE mineralization.The relationship between carbonatite and REE mineralization at BayanObo is therefore an important aspect. Furthermore, Wang et al. (2002)suggested that the three types of carbonatite dykesmight correspond todifferent evolutionary stages of themajor carbonatitemagmatism in theBayan Obo region. Nevertheless, there is no clear evidence for thesequence of formation of these dykes as yet, and no detailed reports onthe evolution of the carbonatitic magma and the progressive change inthe magma composition.
Our recent field work revealed an outcrop that exposes the sharpcontact between dolomite type and calcite type carbonatite dykes atthe Jianshan region to the north of the East Orebody (E 109°59′10.2″, N41°49′02.9″). In this outcrop, a dolomite carbonatite dyke is cut across
by a calcite carbonatite dyke (Fig. 1b), indicating a younger age for theintrusion of the calcite carbonatite dyke. This cross-cutting relation-ship also provides a valuable opportunity to study the evolutionaryhistory of the carbonatite magma in the Bayan Obo region.
In this paper, we employ detailed data from the different types ofcarbonatite dykes occurring in a larger area around the Bayan Obo REEdeposit, as well as from the massive ore-hosting dolomite marble, tounderstand the mineralogical and geochemical composition of thecarbonatitic magmas and their evolutionary process. Based on theresults, we address the relationship between carbonatitic magmatismand the giant REE accumulation in the Bayan Obo deposit.
2. Geological setting
The Bayan Obo district is located at the northern margin of theNorth China Craton (NCC), bordering the Central Asian Orogenic Belt
Fig. 1. Geological map of the Bayan Obo REE deposit (a). Intrusive contact between dolomite and calcite carbonatite dykes (b). Xenoliths of K-rich slate and diorite in fine-grainedore-hosting dolomite marble with extensive fenitization and flow structure around them (c).
123K.-F. Yang et al. / Ore Geology Reviews 40 (2011) 122–131
to the north (Xiao et al., 2003, 2010) (Fig. 1a). Gentle fold structures,composed mostly of low grade metasedimentary units of theMesoproterozoic Bayan Obo Group, are distributed from south tonorth in the region (Fig. 1a). The famous Bayan Obo giant REE deposit,hosted in the Bayan Obo Group massive dolomite marble, occurs inone of the syncline cores. To the north of the ore body, a completesequence of Bayan Obo Group is exposed in the Kuangou anticline,which is developed on the Paleoproterozoic basement rocks with adistinct angular unconformity. The ore-hosting dolomite marble,covered by K-rich slate (H9 term), was generally considered as acomponent of Bayan Obo Group and called H8 term. The low gradeclastic sequences of the Bayan Obo Group represent the sedimentaryunits deposited within the Bayan Obo marginal rift, which correlateswith the Mesoproterozoic continental breakup event of the NCC (Houet al., 2008a, b; Li et al., 2006; Wang et al., 1992; Yang et al., 2011;Zhai, 2004; Zhai and Santosh, 2011; Zhao et al., 2004). The Bayan OboREE deposit, which accounts for more than 70% REE resources of theworld within a restricted area of 48 km2, is located in the Bayan Obocontinental margin rift in the north of the NCC.
The REEdeposit is composed of three ore bodies:MainOrebody, EastOrebody, and West Orebody (Fig. 1a). The Main Orebody and EastOrebody are distributed in between the boundary of ore-hostingdolomite marble and Bayan Obo group K-rich slate. The West Orebody,includingmany small ore bodies, occursmainly in themassive dolomitemarble. The Main Orebody and East Orebody occur as large lenses(Fig. 2). Fenitization between the dolomite marble and wallrock K-richslates is common. Fluorite appears in the fenitized dolomitemarble, andriebeckite and phlogopite are observed in the K-rich slate. The ores aredistributed along a west-east striking belt (Fig. 2). From south to north,they define four groups, namely the riebeckite type, aegirine type,massive type, and banded type.
3. Sampling and field relation
3.1. Carbonatite dykes
Abundant carbonatite dykes occur adjacent to the Bayan Obo giantREE deposit and particularly within the Kuangou anticline. These dykesintrude the Bayan Obo Group of low grade metasediments (Fig. 1a), aswell as the basement rocks, with fenitization of the wall rocks. Inaddition, two small carbonatite stocks occur towards the northerndomain of the Main and East Orebody. Le Bas et al. (2007) consideredthese stocks as the coarse-grained carbonatites that survived from theextensive mineralization event in the Mesoproterozoic.
The carbonatite dykes, steeply cutting the strata, are usually 0.5 to2.0 m wide and 10 to 200 m long, and show a northeast or northweststrike. The dykes can be divided into dolomite, calcite-dolomite, andcalcite types based on their mineralogical compositions. In this study,
the different types of carbonatite dykes were collected for analyses(Fig. 1a).
The dolomite carbonatite dykes (samples M-12-2 and 05B157a) aredistributed mainly in the Kuangou anticline. The rocks show marooncolor in weathered surface and are grayish white in fresh section. Theyare mainly composed of dolomite and calcite, together with accessoryminerals such as magnetite and monazite. They commonly show acoarse-grained texture, with clearly defined triple junction betweendolomite and calcite.
The calcite-dolomite carbonatite dykes (samples M-3-2 and06B119) are mainly found to the south of the East and West Orebody.They appear brownish yellow in weathered surface and milky white infresh section, and mainly comprise dolomite and calcite, together withaccessoryminerals such as apatite,magnetite, monazite, and bastnäsite.The rock is generally medium-fine-grained, with fine-grained calcitesurrounding coarse-grained dolomite (Wang et al., 2002).
The calcite carbonatite dykes (samples M-3-1, 05B123, M-12-1 and05B006) are distributed around the ore body, and appear brownishyellow in weathered surface and green yellow in fresh section. They aremainly composed of dolomite and calcite, together with accessoryminerals such as apatite, magnetite, monazite, bastnäsite, fluorite,and minor quartz. They show medium-fine-grained microporphyritictexture, with granular aggregates consisting of fine-grained REE mi-nerals in the matrix and in the interstices of calcite. These REE mineralsare likely to be primary minerals that crystallized directly from thecarbonatitic magma (Yang et al., 1998).
3.2. Ore-hosting dolomite marble
The massive ore-hosting dolomite marble at Bayan Obo showscoarse-grained and fine-grained facies. The fine-grained dolomitemarble constitutes the wall rocks of REE ores, and is considered as anorebody because of its abundant REE content. The coarse-graineddolomite marble, occurring as little stocks, is seen only outside the fine-grained variety. Chao et al. (1992) suggested that the fine-graineddolomite marble formed by the recrystallization of coarse-graineddolomite marble of sedimentary origin, which underwent multipleregional metamorphism and tectonic deformation. However, based onthe intrusive relationship between the coarse-grained dolomite andBayan Obo groups, Le Bas et al. (1997, 2007) and Yang et al. (1998)argued that thefine-grained dolomitemarble is a variantwith extensiveREE mineralization of the coarse-grained Mesoproterozoic dolomitepluton.
Outcrops to the north of the Main Orebody indicate that the coarse-grained dolomite marble is in fact a small carbonatite stock. A smallapophysis, emanating from the coarse-grained dolomite stock, appar-ently intruded into Bayan Obo group quartz sandstone (E109°57′39.0″,N41°48′29.4″). Xenoliths of H9 K-rich slate (E110°01′04.0″, N41°48′
Fig. 2. Structural map of the Main and East Orebody. (Modified after Institute of Geology and Guiyang Geochemistry Chinese Academy of Sciences, 1974).
124 K.-F. Yang et al. / Ore Geology Reviews 40 (2011) 122–131
32.1″) and diorite (E110°01′06.4″, N41°48′30.1″) were also found in thefine-grained dolomite from eastern Boluotou district (Fig. 1c), withsurrounding extensive fenitization and flow structure. This findingprovides additional new evidence for themagmatic origin of the coarse-grainedandfined-graineddolomitemarbles. For this study, both coarse-grained dolomite marble (samples 06B283 and 05B130) and fine-grained dolomite marble (samples 05B162, 05B184, 05B185, 06B098,06B099, 06B100 and 06B103)were collected fromnear the ore body forgeochronology. The sedimentary dolomite marble (sample 06B282) atDahua and limestone (sample 06B272) at Saiwusuwere also sampled todetermine the contrast (Fig. 1a).
4. Analytical methods
Sample wafers, with a diameter of 2.5 cm, were prepared by TR-1000S Automatic Bead Fusion Furnace, for major element analysesusing XRF-1500 Sequential X-Ray Fluorescence Spectrometer housedat the Laboratory for Elements Analysis, Institute of Geology andGeophysics, Chinese Academy of Sciences (IGGCAS). FeO content inthe samples was measured using the solution Potassium Permanga-nate Titration method, under protection of CO2 gas, after dissolvingwith HF-H2SO4. Content of SrO was calculated from the results of thetrace elements analyses.
Trace element and REE abundanceswere determined by solution inFinnigan MAT ELEMENT Inductively Coupled Plasma-Mass Spectrom-eter (ICP-MS) at the Laboratory for Elements Analysis, IGGCAS. Precise40 mg of whole rock powder of the samples was dissolved in HF-HNO3-HClO4 mixture, evaporated to incipient dryness, and subse-quently evaporated twice at 150–200 °C with 0.2 ml of HClO4 todissolvefluorides. The dry samplewas then dissolved for analysis in 1%HNO3. Composite synthetic pure solutions were used as externalstandards. Element Inwas added to both sample and external standardsolutions as internal standards. The China National Standard GSR-1was used for analytical quality control. The precision of concentrationsis better than 8%.
Whole rock powders (100 mg) for Sr and Nd isotopic analyses weredissolved in Teflon bombs after being spikedwith 87Rb, 84Sr, 149Sm and150Nd tracers prior to HF+HNO3+HClO4 dissolution. Rb, Sr, Sm andNdwere separated using conventional ion exchange procedures andmeasured using a Finnigan MAT262 multi-collector mass spectrometerat IGGCAS. Detailed descriptions of the analytical techniques have beendocumented in Chu et al. (2009). The total procedural blanks for Rb-Srand Sm–Nd were less than 100 pg and 50 pg, respectively. Precision ofthe concentrations is within 0.5% of the quoted values (2σ). Average87Sr/86Sr values of NBS987 standard were 0.710232±12 (2σ, n=10,relative to 86Sr/88Sr=0.1194), and average 143Nd/144Nd values of Amesstandard were 0.512125±8 (2σ, n=12, relative to 146Nd/144Nd=0.7219) in this study. Data regression of isochron age calculation wereperformed with the ISOPLOT ver. 3.0 software (Ludwig, 2003), em-ploying analytical errors. Detailed analytical procedures and isotoperatio measurements followed those given in Chen et al. (2000).
5. Analytical results
5.1. Major elements
The major elements data of carbonatite dykes, ore-hosting dolo-mite marble, and sedimentary carbonate rocks in the Bayan Obodistrict are presented in Table 1. All the samples are classified in termsof CaO-MgO-(FeO+Fe2O3+MnO) (Fig. 3). The samples from fine-grained dolomite marble and the dolomite carbonatite dykes fallwithin the region overlapping magnesio-carbonatite and ferro-carbonatite. The coarse-grained dolomitemarble and calcite-dolomitecarbonatite dyke samples mostly fall within themagnesio-carbonatitefield. All of the calcite type carbonatite dyke samples fall within thecalcio-carbonatite region. However, the sedimentary carbonate rock
samples, apparently lacking in FeO+Fe2O3+MnO component, fallalong the MgO-CaO line. These results are consistent with those re-ported in Yang and Le Bas (2004), who also showed that the sedi-mentary carbonate rocks have higher CaO and MgO, and lower FeO,MnO, and SrO (less than 0.1 wt.%) contents as compared with the ore-hosting dolomite marble.
The data from the carbonatite dykes, the ore-hosting dolomitemarble, and the sedimentary carbonate rocks are evaluated on a SrOversus FeO diagram (Fig. 4). It is notable that all the data except thosefrom the sedimentary carbonate rocks, showadecreasing trend from thefine-grained dolomite marble and dolomite carbonatite dyke samples,through the coarse-grained dolomite marble and calcite-dolomitecarbonatite dyke samples, to the calcite carbonatite dyke samples. Asmentioned in theprevious sections, thedolomite carbonatite dykeswereemplaced earlier than the calcite dykes based on their field relationship.Therefore, the decreasing trend in Fig. 4might indicate the change in themajor element composition of the carbonatitic magma during itsevolution. The SrO and FeO variations are similar to those of SrO andMnO from coarse-grained sövite to fine-grained alvikite controlled bycrystal fractionation of carbonatite magma (Clarke et al., 1994; Le Bas,1989).
5.2. Trace element and REE
5.2.1. Carbonatite dykesThe trace element and REE data on the carbonatite dyke samples
from the Bayan Obo district are presented in Table 1. On the primitivemantle-normalized trace element abundance pattern (Fig. 5a), all thecarbonatite dyke samples show relative enrichment of Ba and Th, anddepletion of Rb, Ta, Zr, and Hf, with no negative Eu anomaly. The Srcontent gradually increases from dolomite to calcite carbonatite dykewith a remarkable variation. Thus, the samples from dolomite andcalcite-dolomite type dykes show positive Sr anomaly, whereas thesamples from the calcite type dykes shownegative Sr anomaly (Fig. 5a).Similar to the observations in the dolomite carbonatite dykes from theBayan Obo district, Ionov and Harmer (2002) concluded that relativelylow REE abundances and high Sr are common in primary mantle-derived carbonate liquids based on trace element data of carbonatitesfrom South Africa. Under the complex crystal fractionationmechanism,however, the content of incompatible elements (e.g., LREE and Sr) in-creases gradually as the carbonatiticmagma evolves (Clarke et al., 1994;Le Bas, 1989). Furthermore, compared with Sr, LREE are preferentiallyenriched in the residual calcite carbonatitic melt. This accounts for thedifference in the Sr anomalywith respect to the LREE content in the earlydolomite and later calcite carbonatite dykes. Although the Sr content ishigh in the residual melt, a negative anomaly is displayed in contrast tothe extremely enriched LREE in the later calcite carbonatite dykes.
The REE composition of samples from the three types of carbonatitedykes shows markedly different characteristics. The dolomite carbo-natite dyke samples have low REE abundance and nearly flatchondrite-normalized distribution pattern (Fig. 6a), with no enrich-ment in LREE [(La/Yb)N values range from 1.6 to 3.8]. In comparison,the calcite carbonatite dyke samples have extremely high REE abun-dance and are strongly enriched in the light over heavy REE [(La/Yb)Nvalues range from 85 to 4617]. The calcite-dolomite carbonatite dykesamples havemediumREE abundance and LREE enrichment [(La/Yb)Nvalues range from 51 to 57], compared to samples from the other twotypes of dykes. The overall REE content in carbonatite dykes, especiallythe LREE, apparently increases with the component of calcite fromdolomite type through the calcite-dolomite type to the calcite typecarbonatite dykes.
5.2.2. Ore-hosting dolomite marbleThe coarse-grained and fine-grained dolomite marbles have
markedly different trace element and REE contents. The samples ofcoarse-grained dolomite marble are comparable with those of the
125K.-F. Yang et al. / Ore Geology Reviews 40 (2011) 122–131
Table1
Conten
tsof
major
(wt.%
),RE
Ean
dtrace(p
pm)elem
ents
ofcarbon
atitedy
kes,ore-ho
stingdo
lomitemarblean
dsedimen
tary
carbon
aterock
sfrom
Baya
nObo
district.
Rock
type
Fine
-grained
dolomite
Coarse-grained
dolomite
Dolom
ite
carbon
atitedy
keCa
lcite-do
lomite
carbon
atitedy
keCa
lcitecarbon
atitedy
keSe
dimen
tary
dolomite
Limestone
SampleNo.
06B1
0006
B103
05B1
8405
B185
06B0
9806
B099
05B1
6206
B283
05B1
30M-12-2
05B1
57a
M-3-2
06B1
19M-3-1
05B1
23M-12-1
05B0
0606
B282
06B2
72
SiO2
0.07
3.40
10.50
7.44
0.02
2.40
0.31
0.00
0.84
3.26
4.52
0.14
0.60
2.30
12.43
7.22
3.45
3.05
2.13
TiO2
0.00
0.00
0.03
0.02
0.01
0.04
0.01
0.00
0.01
0.02
0.02
0.01
0.01
0.00
0.29
0.02
0.00
0.01
0.03
Al 2O3
0.00
0.01
0.20
0.35
0.00
0.61
0.22
0.16
0.03
0.23
0.24
0.01
0.02
0.30
1.53
0.27
0.06
0.42
0.43
TFe 2O3
12.38
7.88
19.75
20.07
12.62
7.48
8.45
6.06
4.64
10.54
10.19
4.26
6.07
0.54
5.62
0.86
0.41
0.88
0.19
FeO
5.70
4.93
8.16
9.67
6.72
5.83
2.88
2.27
3.20
7.41
6.71
3.09
2.97
0.44
2.52
0.34
0.34
0.40
0.20
MnO
1.26
1.16
1.65
1.72
3.00
0.94
0.90
0.67
0.52
1.95
1.96
0.51
0.40
0.55
0.35
0.14
0.33
0.03
0.02
MgO
14.50
13.41
13.40
13.65
11.04
15.41
16.68
16.18
17.34
12.04
12.99
18.53
17.35
1.23
8.34
0.17
0.25
19.66
0.36
CaO
22.76
25.16
18.65
19.38
25.11
23.18
25.64
29.14
29.53
27.97
28.20
28.64
29.61
46.51
36.22
28.26
25.77
28.11
53.85
Na 2O
0.00
0.13
0.28
0.19
0.06
0.03
0.00
0.00
0.05
0.05
0.06
0.03
0.04
0.38
0.10
0.00
0.05
0.00
0.01
K2O
0.02
0.09
0.71
0.67
0.02
0.48
0.04
0.01
0.04
0.23
0.23
0.04
0.02
0.05
2.27
0.24
0.07
0.06
0.09
P 2O5
0.10
0.81
0.53
0.39
1.19
1.60
0.69
1.60
1.16
0.01
0.02
0.14
0.03
0.09
1.29
0.06
0.33
0.01
0.03
LOI
38.13
34.85
29.75
31.62
38.92
38.46
41.41
41.55
43.07
41.57
41.33
45.00
44.24
41.08
25.03
32.05
29.49
45.22
42.51
Total
89.22
86.90
95.45
95.50
91.99
90.63
94.35
95.37
97.23
97.87
99.76
97.31
98.39
93.03
93.47
69.29
60.21
97.45
99.65
Rb0.52
1.90
11.5
16.7
0.37
16.9
2.13
0.57
0.73
3.87
5.84
0.91
1.01
1.06
67.3
6.64
2.89
2.55
3.64
Ba18
,493
16,487
2127
2268
221
2537
1170
741
122
135
536
598
98.2
8794
2039
1573
42,954
17.5
129
Th69
.771
.491
.610
228
.642
.836
.71.40
1.25
1.71
1.02
8.18
1.06
1.43
145
1669
884
0.57
0.98
U0.56
0.04
0.56
0.52
0.51
1.37
0.07
7.02
0.13
0.30
0.21
0.12
0.20
0.09
1.35
4.02
2.61
0.37
1.48
Nb
435
9.45
641
526
190
651
23.7
384
1.80
17.20
1.92
1.39
3.76
1.38
120
16.6
5.70
1.02
1.08
Ta1.11
0.12
0.41
0.29
0.12
0.19
0.09
18.5
0.09
0.21
0.09
0.10
0.21
0.10
1.80
0.21
0.14
0.15
0.23
La92
2810
,456
2913
2943
6637
16,885
7114
176
72.5
10.9
11.9
332
53.8
1409
955
55,937
54,622
2.66
8.43
Ce16
,928
20,198
6952
7108
14,136
22,337
10,473
346
179
25.3
32.8
657
113
2455
2411
95,227
70,300
4.73
13.2
Pr16
2420
9288
790
416
1117
8910
5640
.823
.13.95
5.41
75.1
13.2
269
308
10,362
5840
0.51
2.09
Sr11
2723
7819
8419
2781
521
2623
1362
2656
2737
7738
8247
4760
2114
,324
2930
5046
7234
25.3
162
Nd
4248
6032
2870
2908
5278
4440
2934
136
82.2
18.6
25.9
268
46.3
776
1063
27,425
12,243
1.78
8.13
Zr1.91
20.8
15.1
7.32
6.13
9.43
3.37
6.11
2.38
1.77
1.46
1.64
3.01
5.33
197
2.32
2.01
4.18
7.59
Hf
0.31
0.97
0.76
0.43
0.65
0.70
0.30
0.42
0.17
0.07
0.04
0.09
0.12
0.20
9.56
0.66
0.29
0.22
0.27
Sm29
944
823
921
945
927
727
519
.913
.86.00
7.75
59.5
6.57
85.9
122
3255
1004
0.33
1.70
Eu64
.679
.538
.734
.481
.854
.258
.95.76
3.48
2.39
2.72
15.2
1.84
18.5
27.5
669
193
0.07
0.41
Gd
198
228
109
106
216
231
146
13.7
9.59
6.38
7.73
39.6
4.69
48.5
80.2
1557
589
0.33
1.97
Tb20
.920
.88.29
7.52
18.6
17.0
11.5
1.42
1.11
1.15
1.20
4.42
0.54
5.36
11.3
125
46.3
0.05
0.32
Dy
63.3
55.1
18.0
16.0
48.7
47.0
26.9
5.28
4.63
6.79
6.46
18.2
2.33
22.2
54.7
261
107
0.29
1.96
Y13
510
728
.824
.187
.094
.044
.216
.716
.037
.029
.866
.58.88
79.0
260
506
281
2.85
19.0
Ho
7.44
6.03
1.55
1.29
5.04
5.29
2.48
0.75
0.70
1.43
1.18
2.90
0.37
3.33
8.83
21.7
10.8
0.06
0.43
Er12
.210
.42.67
2.26
8.11
7.66
3.76
1.50
1.47
3.99
2.79
6.47
0.90
7.74
17.9
27.8
13.2
0.18
1.30
Tm1.02
0.82
0.25
0.22
0.69
0.55
0.34
0.16
0.18
0.65
0.37
0.75
0.12
0.84
1.72
2.60
1.35
0.03
0.20
Yb3.86
3.13
1.51
1.34
3.33
2.25
1.57
0.80
0.95
4.81
2.27
4.16
0.75
4.24
8.03
16.8
8.49
0.14
1.32
Lu0.43
0.33
0.19
0.17
0.36
0.25
0.17
0.09
0.12
0.78
0.32
0.56
0.11
0.50
0.95
2.06
1.19
0.02
0.21
Eu/Eu*
0.81
0.76
0.73
0.69
0.64
0.65
0.90
1.07
0.93
1.18
1.07
0.95
1.01
0.88
0.85
0.91
0.77
0.69
0.68
(La/Yb
) N17
1323
9413
8515
7714
2953
7632
5915
955
.01.63
3.75
57.2
51.5
238
85.3
2391
4617
13.8
4.57
126 K.-F. Yang et al. / Ore Geology Reviews 40 (2011) 122–131
calcite-dolomite carbonatite dykes. The coarse-grained dolomite mar-bles show enrichment in Ba and Th, and positive Sr anomaly (Fig. 5a, b).They show medium REE abundance and LREE enrichment [(La/Yb)Nvalues range from 55 to 159], similar to the data from the calcite-dolomite carbonatite dykes [(La/Yb)N values range from 51 to 57].
In contrast to the coarse-grained dolomite marbles, the samples offine-grained dolomite marbles show consistent REE and trace elementscharacteristics with the calcite carbonatite dykes. The fine-graineddolomite marbles show enrichment in Ba and Th, and negative Sr ano-maly (Fig. 5a, b). They are characterized by extremely high REE abun-dance and LREE enrichment [(La/Yb)N values range from 1385 to 2394],comparable to the data of calcite carbonatite dykes [(La/Yb)N valuesrange from 85 to 4617]. Similarities in the element concentrationsindicate their close genetic relationship.
5.2.3. Sedimentary carbonate rocksTrace elements and REE contents of the sedimentary carbonate
rocks are clearly different from those of the ore-hosting dolomitemarble and carbonatite dykes (Fig. 5b and Fig. 6b). The limestonefrom Saiwusu (sample 06B272) and the sedimentary dolomite marblefrom Dahua (sample 06B282) possess not only lower REE abundance,but also display negative Eu, and positive U and Y anomalies, featuresthat are comparable with the Neoproterozoic carbonates of the Edia-caran system in South China (e.g., Jiang et al., 2011; Zhao et al., 2009b;Zhao and Zheng, 2010), although markedly different from the ore-hosting dolomite marble of the Bayan Obo deposit.
5.3. Sr–Nd isotope and Sm–Nd isochron age
5.3.1. Sr–Nd isotopeThe Sr and Nd isotope data of samples from the carbonatite dykes
and the ore-hosting dolomite are given in Table 2 and illustrated inFig. 7. The εNd(t) values of the carbonatite dyke samples show a tightcluster between −0.47 and 0.65, but the initial Sr isotope ratios showa broad range from 0.703167 to 0.708871, which is quite differentfrom the Sr isotopic compositions of the carbonatites from East Africa(Bell and Blenkinsop, 1987, 1989; Bell and Tilton, 2001), Brazil (Rodenet al., 1985) and India (Simonetti et al., 1995; Veena et al., 1998). Forhigh Sr–Nd content, the isotopic characteristics of carbonatite magmasare not easily affectedby crustmaterial duringascent and emplacement.Considering a continental margin rift setting, the carbonatite in theBayan Obo district might have originated from a heterogeneous mantlesource. The northern margin of the NCC is considered as a vast Paleo-proterozoic accretionary orogen (e.g., 1.9-2.0 Ga, Li et al., 2006; Santoshet al., 2007a, b; Santosh, 2010). Zhai et al. (2003) also suggested an
Fig. 3. CaO-MgO-(FeO+Fe2O3+MnO) classification diagram (Woolley and Kempe,1989) for the carbonatite dykes, ore-hosting dolomite marble and sedimentarycarbonate rocks from Bayan Obo district.
Fig. 4. Plot of SrO (wt.%) versus FeO (wt.%) of the carbonatite dykes, ore-hostingdolomite marble and sedimentary carbonate rocks from Bayan Obo district.
Fig. 5. Primitive mantle-normalized trace element abundance pattern for carbonatitedykes, ore-hosting dolomite marble and sedimentary carbonate rocks from Bayan Obodistrict. Primitive mantle values are from Sun and McDonough (1989).
127K.-F. Yang et al. / Ore Geology Reviews 40 (2011) 122–131
enriched lithospheric mantle under the NCC during the late Paleopro-terozoic, and therefore the upper mantle beneath Bayan Obo regionprobably possessed a heterogeneous Sr isotope composition due toreconstitution by subducted oceanic sediments. During the subsequent
break up of the NCC from its assembly within the Columbia superc-ontinent (e.g., 1.20-1.78 Ga, Hou et al., 2008a, 2008b; Peng et al., 2007;Zhang et al., 2009; Zhao et al., 2006) and related continental rifting, theearly dolomite carbonatite and the later calcite carbonatite magmaswere generated within the Bayan Obo continental margin rift. Thistectonic setting probably contributed to the geochemical heteroge-neity as displayed in the varying Sr isotope compositions. The ore-hosted dolomitemarblesmight have originated from the Sr-depleteddomain and the carbonatite dykes from the Sr-enriched domainof the heterogeneous mantle lithosphere. Compared with Sr, the Smand Nd contents are very low in oceanic sediments and wouldtherefore barely affect the Nd isotopic composition of the mantlelithosphere of the NCC.
The εNd(t) values of the ore-hosting dolomite marble (from 0.39 to1.87), and the initial 87Sr /86Sr (from 0.703180 to 0.704302) show alimited range and the values are close to the Bayan Obo dolomitecarbonatite dykes, as well as to the carbonatites from East Africa andBrazil (Fig. 7). In contrast to the results from the carbonatite dykes, theconsistent isotope compositions of the ore-hosting dolomite marblessuggest a relatively homogeneous magmatic evolutionary stage.
5.3.2. Sm–Nd isochron ageThe eight carbonatite dyke samples analyzed in this study that
includes all the three types of dykes yield a whole rock Sm–Nd iso-chron age of 1354±59 Ma (Fig. 8), which is comparable with thezircon TIMS U–Pb age of 1416±77 Ma obtained from the Wu car-bonatite dyke at Bayan Obo within error (Fan et al., 2006). In addition,nine ore-hosting dolomite marble samples from the two facies yield awhole rock Sm–Nd isochron age of 1341±160 Ma (Fig. 9), which isconsistent with the age of 1290±96 Ma obtained by Zhang et al.(1994). Although the carbonatitic magma originated from a homoge-neous Sm and Nd isotopic source, the different types of carbonatites inthe Bayan Obo area were emplaced sequentially, which probablyaccounts for the relatively high MSWD and error values.
6. Discussion
The origin of the ore-hosting dolomite marbles in the Bayan Obodeposit has been addressed in various models, ranging from a sedi-mentary carbonate model (Chao et al., 1992) to volcano-sedimentary(Wang et al., 1992), and igneous carbonatites (Le Bas et al., 1997,2007; Yang et al., 2003; Yang and Le Bas, 2004). The coarse-grainedand fine-grained facies of the dolomite marbles occurring in thisregion introduced additional complexities in the interpretation oftheir genesis.
Fig. 6. Chondrite-normalized REE abundance diagram for carbonatite dykes, ore-hosting dolomite marble and sedimentary carbonate rocks from Bayan Obo district.Chondrite values are from Taylor and McLennan (1985).
Table 2Sr and Nd isotope composition of ore-hosting dolomite marble and carbonatite dykes from Bayan Obo district. The Rb/Sr ratios were from isotopic dilution analysis.
Rock type Sample No. 87Rb/86Sr 87Sr/86Sr ±2σ 147Sm/144Nd 143Nd/144Nd ±2σ ISr(t) εNd(t) TDM 1 (Ga)
Fine-grained dolomite marble 06B100 0.0005 0.703557 0.000012 0.0466 0.511346 0.000013 0.703547 0.83 1.64506B103 0.0008 0.703180 0.000013 0.0478 0.511378 0.000010 0.703164 1.25 1.62705B184 0.0147 0.703509 0.000013 0.0513 0.511365 0.000012 0.703223 0.39 1.67405B185 0.0223 0.703512 0.000011 0.0472 0.511352 0.000011 0.703079 0.87 1.64406B098 0.0001 0.704154 0.000014 0.0551 0.511417 0.000013 0.704152 0.76 1.66406B099 0.0211 0.704302 0.000012 0.0401 0.511299 0.000011 0.703893 1.04 1.62405B162 0.0011 0.704125 0.000013 0.0537 0.511462 0.000012 0.704103 1.87 1.607
Coarse-grained dolomite marble 06B283 0.0001 0.702984 0.000011 0.0841 0.511662 0.000014 0.702983 0.50 1.74805B130 0.0001 0.702866 0.000013 0.0965 0.511807 0.000012 0.702866 1.18 1.745
Dolomite carbonatite dyke M-12-2 0.0020 0.704784 0.000011 0.1914 0.512624 0.000017 0.704745 0.65 3.59605B157a 0.0019 0.705456 0.000013 0.1870 0.512530 0.000014 0.705419 −0.43 3.542
Calcite-dolomite carbonatite dyke 06B119 0.0001 0.703168 0.000012 0.0842 0.511630 0.000012 0.703167 −0.15 1.788M-3-2 0.0005 0.708153 0.000010 0.1266 0.512023 0.000011 0.708143 0.16 1.971
Calcite carbonatite dyke M-3-1 0.0001 0.706373 0.000009 0.0590 0.511433 0.000015 0.706371 0.38 1.69005B123 0.0563 0.708139 0.000013 0.0695 0.511525 0.000012 0.707047 0.35 1.71705B006 0.0005 0.708556 0.000013 0.0444 0.511259 0.000011 0.708546 −0.47 1.700M-12-1 0.0021 0.708911 0.000013 0.0639 0.511488 0.000012 0.708871 0.61 1.689
128 K.-F. Yang et al. / Ore Geology Reviews 40 (2011) 122–131
Le Bas et al. (2007) proposed that the coarse-grained dolomitemarble represents a Mesoproterozoic carbonatite pluton and the fine-grained dolomite marble resulted from the extensive REE minerali-zation and modification of the coarse-grained variety. Our fieldobservations in the northern part of the Main Orebody revealed thatthe coarse-grained dolomite marble intrudes into the Bayan Obogroup quartz sandstone as apophyses. However, the geochemicalcharacteristics of the coarse-grained dolomite marble are notconsistent with those of the fine-grained ones. The major and traceelement contents of the coarse-grained dolomite marble are very
similar to the calcite-dolomite carbonatite dykes in the Bayan Obodistrict. Data from these samples overlap within the magnesio-carbonatite region on the CaO-MgO-(FeO+Fe2O3+MnO) classifica-tion diagram (Fig. 3), and show similar REE content and distributionpatterns on the chondrite-normalized abundance diagram (Fig. 6).The similar geochemical characteristics of coarse-grained dolomitemarble and calcite-dolomite carbonatite dykes, and the intrusivecontact between the coarse-grained dolomite and wallrocks, indicatethat the coarse-grained dolomite marble is likely an earlier phase ofcalcite-dolomite carbonatite stock, which did not witness the sub-sequent mineralization event from the residual carbonatitic melt,probably because it is located far from the main mineralized zone.
The fine-grained dolomite marble from the Main, East and WestOrebody differs from the coarse-grained dolomite marble in theirmajor, trace element and REE characteristics. The fine-grained dolo-mite shows major element compositions comparable to that of thedolomite carbonatite dykes. All the samples fall in the field of dolomitecarbonatite dykes on the CaO-MgO-(FeO+Fe2O3+MnO) classifica-tion diagram (Fig. 3). The REE content and distribution patterns of thefine-grained dolomite samples, however, are similar to those of thecalcite carbonatite dykes (Fig. 6). Therefore, the fine-grained dolomitecannot be compared with any specific type of carbonatite dykes in theBayan Obo region.
As mentioned above, the REE content in the dolomite carbonatitedykes is relatively low, as compared to the extreme accumulation inthe calcite carbonatite dykes. Chao et al. (1992) noted that the REEminerals in the fine-grained dolomite marble occur as ribbon oraggregates. Wang et al. (2010) also found that the REE minerals aredistributed around dolomite phenocryst in the fine-grained dolomitemarble. Therefore, the REE minerals formed later than the formationof the dolomite phenocryst. These observations lead us to believe thatthe fine-grained dolomitemarble represents an early stage large-scaledolomite carbonatite pluton, and the superposed REE mineralizationwas derived from the later calcite carbonatite magma. The presence ofxenoliths of diorite and H9 K-rich slate that is surrounded by extensivefenitization and flow structure in the fine-grained dolomite marble,also support its magmatic origin.
Petrological observation and experimental studies show that a lowdegree of partial melting of carbonated mantle peridotite can producecarbonatite magma (Wyllie and Lee, 1998), which is the favorablecarrier for incompatible elements. Fractional crystallization would
Fig. 8. Sm–Nd isochron diagram for the whole rock samples of dolomite, calcite-dolomite and calcite carbonatite dykes from Bayan Obo district. MSWD stands for meansquare of weighted deviates.
Fig. 9. Sm–Nd isochron diagram for the whole rock samples of coarse-grained and fine-grained ore-hosting dolomite marble from Bayan Obo district. MSWD stands for meansquare of weighted deviates.
Fig. 7. εNd(t) versus (87Sr/86Sr)i diagram for the carbonatite dykes and ore-hostingdolomite marble, compared with the global carbonatites from India (Simonetti et al.,1995; Veena et al., 1998) and Brazil (Roden et al., 1985). EACL stands for East Africacarbonatite line (Bell and Tilton, 2001). DMM, EMI, EMII, PREMA and HIMU are themantle end-member components (Zindler and Hart, 1986). Values for lines labeled B.E.(bulk Earth) and CHUR (chondritic uniform reservoir) are those for 1354 Ma, assumingpresent-day values of 87Sr/86SrBE=0.7045 and 87Rb/86SrBE=0.083 (λ=1.42×10−11
per year) and 143Nd/144NdCHUR=0.512638 and 147Sm/144NdCHUR=0.1967(λ=6.54×10−12 per year).
129K.-F. Yang et al. / Ore Geology Reviews 40 (2011) 122–131
lead to the enrichment of incompatible elements in the residualmagma (Ionov and Harmer, 2002; Xu et al., 2010; Yang and Le Bas,2004). The intrusive contact and filed relations documented in thepresent study provides robust evidence to infer that the formation ofthe dolomite carbonatite dykes occurred relatively earlier than thecalcite carbonatite. Consequently, the evolution of the carbonatitemagma in the Bayan Obo district is characterized by a trend fromdolomite through the calcite-dolomite variety to the calcite types. Themineralization in the dolomite consumed considerable amount ofsiderophile elements (e.g., Fe and Mg), leading to a marked accu-mulation of calcite minerals and incompatible elements (e.g., Sr, Ba,Th, Nb and LREE) in the residual carbonatite magma (Le Bas, 1981;Wyllie et al., 1996). A prolonged differentiation of the carbonatiticmagma might therefore explain the mechanism of REE accumulationin the Bayan Obo district.
The Bayan Obo deposit is located in the north margin of the NCC,which experienced a major rifting event (the Langshan-Bayan Oborift) in the Mesoproterozoic (Wang et al., 1992). The large Langshan-Bayan Obo continental rift, together with Yan-Liao rift in the east andXiong'er rift in the south of NCC, marked by swarm of mafic dykesbetween 1.75 and 1.79 Ga (Hou et al., 2008a; Li et al., 2007; Peng et al.,2007; Santosh et al., 2010; Zhao et al., 2009a), correlate with thefragmentation of the Columbia supercontinent (Li et al., 2006; Rogersand Santosh, 2002, 2009; Santosh et al., 2009; Zhai, 2004; Zhao et al.,2004). The Bayan Obo deposit was likely associated in space and timewith large-scale carbonatitic magmatic activity (1354±59 Ma) inresponse to the long-term rifting and magma evolution in the northmargin of NCC. The depleted mantle model age (TDM) from the Ndisotope data on carbonatite dyke and ore-hosting dolomite marblesamples range from 1.61 to 1.79 Ga (Table 2), which coincide with theinitiation of the Bayan Obo rift (ca. 1.75 Ga, Li et al., 2007). Along withthe prolonged and slow extension of the Bayan Obo rift, the mantlelithosphere underwent low degree of partial melting leading to theproduction of carbonatite magma at the final stage of break up thesupercontinent Columbia (ca. 1.2–1.4 Ga, Hou et al., 2008b; Zhao et al.,2006). Through continuous evolution (crystal fractionation), abun-dant LREE accumulation occurred in the terminal calcite carbonatitemagma, which was then superposed on the early dolomite carbona-tite pluton, thus resulting in the formation of the giant Bayan Obo REEdeposit.
7. Conclusions
The carbonatite dykes in the Bayan Obo region can be divided intothree types based on their mineralogical compositions: dolomite,calcite, and calcite-dolomite types. The sharp intrusive contact showsthat the formation of the calcite carbonatite dykes post-dated theformation of the dolomite ones. The geochemical data show that Srand LREE contents in these dykes gradually increase from dolomitetype, through calcite-dolomite type, to calcite type. This trend re-sulted from the crystal fractionation of a carbonatite magma, poten-tially generating the giant REE accumulation in the Bayan Obo region.
The BayanObomassive ore-hostingdolomitemarble contains afine-grained facies and a coarse-grained facies. The whole rock Sm–Ndisochron age of the ore-hosting dolomite is consistent with the agesobtained from the carbonatite dykes. The coarse-grained dolomitemarble has very similar element contents as to those of the calcite-dolomite carbonatite dykes. Considering its intrusive contact, thecoarse-grained dolomitemarble is likely an early small calcite-dolomitecarbonatite stock. The fine-grained dolomite marble shows majorelement content comparable to those of the dolomite carbonatite dykes,and trace element and REE contents similar to those of the calcitecarbonatite dykes. The crystallization of REEminerals subsequent to thedolomite phenocryst, as well as the presence of wall-rock xenoliths,support thenotion that thefine-grained dolomitemarble represents the
early dolomite carbonatite pluton, which was superposed by the REEmineralization from the residual calcite carbonatitic magma.
Acknowledgements
The constructive reviews of two anonymous referees and com-ments by Associate Editor Prof Y.F. Zheng and Editor-in-Chief Prof N.J.Cook improved this contribution and are gratefully acknowledged.We are also thankful to Chuang Xuan and Stephanie Mills for theircareful English editorial work and suggestions. This work wasfinancially supported by the National Natural Science Foundation ofChina (grant Nos. 40902028 and 40625010), and the State Key BasicResearch Development Program of China (grant No. 2006CB403503).
References
Bai, G., Yuan, Z.X., Wu, C.Y., Zhang, Z.Q., Zheng, L.Y., 1996. Geological features andgenesis of Bayan Obo Ore deposit. Geological Publishing House, Beijing, pp. 99–104(in Chinese).
Bell, K., Blenkinsop, J., 1987. Nd and Sr isotopic compositions of East Africancarbonatites: implications for mantle heterogeneity. Geology 15, 99–102.
Bell, K., Blenkinsop, J., 1989. Neodymium and strontium isotope geochemistry ofcarbonatites. In: Bell, K. (Ed.), Carbonatites: Genesis and Evolution. Unwin Hyman,London, pp. 278–300.
Bell, K., Tilton, G.R., 2001. Nd, Pb and Sr isotopic compositions of East Africa car-bonatites: evidence for mantle mixing and plume in homogeneity. Journal ofPetrology 42, 1927–1945.
Chao, E.C.T., Back, J.M., Minkin, J.A., Ren, Y., 1992. Host-rock controlled epigenetic,hydrothermal metasomatic origin of the Bayan obo REE-Fe-Nb ore deposit, InnerMongolia, PRC. Applied Geochemistry 7, 443–458.
Chao, E.C.T., Back, J.M., Minkin, J.A., Tatsumoto, M., Wang, J., Conrad, J.E., Makee, E.H.,Hou, Z., Meng, Q., Huang, S., 1997. The sedimentary carbonate-hosted giant BayanObo REE-Fe-Nb ore deposit of Inner Mongolia, China: a cornerstone example forgiant polymetallic ore deposits of hydrothermal original. USGS Bulletin 2143, 1–65.
Chen, F., Hegner, E., Todt, W., 2000. Zircon ages, Nd isotopic and chemical compositionsof orthogneisses from the Black Forest, Germany–evidence for a Cambrianmagmatic arc. International Journal of Earth Sciences 88, 791–802.
Chu, Z.Y.,Wu, F.Y.,Walker, R.J., Rudnick, R.L., Pitcher, L., Puchtel, I.S., Yang, Y.H.,Wilde, S.A.,2009. Temporal evolution of the lithosphericmantle beneath the eastern North ChinaCraton. Journal of Petrology 50, 1857–1898.
Clarke, L.B., Le Bas, M.J., Spiro, B., 1994. Rare earth, trace element and stable isotopefractionationof carbonatites atKruidfontein, Transvaal, SouthAfrica. In:Meyer,H.O.A.,Leonardos, O.H. (Eds.), Kimberlites, Related Rocks and Mantle Xenoliths, Proceedingsof the 5th International Kimberlite Conference, Brazil, 1, pp. 236–251.
Dobson, D.P., Jones, A.P., Rabe, R., Sekine, T., Kurita, K., Taniguchi, T., Kondo, T., Kato, T.,Shimomura, O., Urakawe, S., 1996. In-situ measurement of viscosity and density ofcarbonatemelts at high pressure. Earth and Planetary Science Letters 143, 207–215.
Drew, L.J., Meng, Q., Sun, W., 1990. The Bayan Obo iron-rare earth-niobium deposit,Inner Mongolia, China. Lithos 26, 46–65.
Fan, H.R., Xie, Y.H., Wang, K.Y., Yang, X.M., 2001. Carbonatitic fluids and REEmineralization. Earth Science Frontiers 8, 289–295 (in Chinese with Englishabstract).
Fan, H.R., Hu, F.F., Yang, K.F., Wang, K.Y., 2006. Intrusive age of No.1 carbonatite dykefrom Bayan Obo REE-Nb-Fe deposit, Inner Mongolia: with answers to comment ofDr. Le Bas. Acta Petrologica Sinica 22, 519–520 (in Chinese with English abstract).
Hou, G., Santosh, M., Qian, X., Lister, G.S., Li, J., 2008a. Configuration of the latePaleoproterozoic supercontinent Columbia: Insights from radiating mafic dykeswarms. Gondwana Research 14, 395–409.
Hou, G., Santosh, M., Qian, X., Lister, G.S., Li, J.H., 2008b. Tectonic constraint on the 1.3–1.2Ga final breakup of Columbia supercontinent from a giant radiating dyke swarm.Gondwana Research 14, 561–566.
Institute of Geology and Guiyang Geochemistry Chinese Academy of Sciences, 1974.The geochemical composition and mineralization regularity of Bayan Obo deposit,Inner Mongolia, pp. 8–18 (in Chinese).
Ionov, D., Harmer, R.E., 2002. Trace element distribution in calcite–dolomitecarbonatites from Spitskop: inferences for differentiation of carbonatite magmasand the origin of carbonates in mantle xenoliths. Earth and Planetary ScienceLetters 198, 495–510.
Jiang, G., Shi, X., Zhang, S., Wang, Y., Xiao, S., 2011. Stratigraphy and paleogeography ofthe Ediacaran Doushantuo Formation (ca. 635–551Ma) in South China. GondwanaResearch 19, 831–849.
Le Bas, M.J., 1981. Carbonatite magmas. Mineralogical Magazine 44, 133–140.Le Bas, M.J., 1989. Diversification of carbonatite. In: Bell, K. (Ed.), Carbonatites: Genesis
and Evolution. Unwin Hyman, London, pp. 428–447.Le Bas, M.J., Keller, J., Tao, K., Wall, F., William, C.T., Zhang, P.S., 1992. Carbonatite dykes
at Bayan Obo, Inner Mongolia. China Mineralogy and Petrology 46, 195–228.Le Bas, M.J., Spiro, B., Yang, X.M., 1997. Oxygen carbon and strontium isotope study of
the carbonatitic dolomite host of the Bayan Obo Fe-Nb-REE deposit, InnerMongolia. N. China. Mineralogical Magazine 61, 531–541.
Le Bas, M.J., Yang, X.M., Taylor, R.N., Spiro, B., Milton, J.A., Peishan, Z., 2007. Newevidence from a calcite-dolomite carbonatite dyke for the magmatic origin of the
130 K.-F. Yang et al. / Ore Geology Reviews 40 (2011) 122–131
massive Bayan Obo ore-bearing dolomite marble, Inner Mongolia, China.Mineralogy and Petrology 91, 281–307.
Li, J.H., Niu, X.L., Cheng, S.H., Qian, X.L., 2006. The early Precambrian tectonic evolutionof continental craton: a case study from north China. Earth Science-Journal of ChinaUniversity of Geosciences 31, 285–293 (in Chinese with English abstract).
Li, Q.L., Chen, F.K., Guo, J.H., Li, X.H., Yang, Y.H., Siebel, W., 2007. Zircon ages and Nd–Hfisotopic composition of the Zhaertai Group (Inner Mongolia): evidence for earlyProterozoic evolution of the northern North China Craton. Journal of Asian EarthSciences 30, 573–590.
Ludwig, K.R., 2003. User's manual for Isoplot 3.00, a geochronological Toolkit forMicrosoft Excel. Berkeley: Berkeley Geochronlogical Center Special Publication 4,25–32.
Peng, P., Zhai, M.G., Guo, J.H., Kusky, T., Zhao, T.P., 2007. Nature of mantle sourcecontributions and crystal differentiation in the petrogenesis of the 1.78 Ga maficdykes in the central North China craton. Gondwana Research 12, 29–46.
Roden, M.F., Murthy, V.R., Gaspar, J.C., 1985. Sr and Nd isotopic compositions of theJacupiranga carbonatite. Journal of Geology 93, 212–220.
Rogers, J.J.W., Santosh, M., 2002. Configuration of Columbia, a Mesoproterozoicsupercontinent. Gondwana Research 5, 5–22.
Rogers, J.J.W., Santosh, M., 2009. Tectonics and surface effects of the supercontinentColumbia. Gondwana Research 15, 373–380.
Santosh, M., 2010. Assembling North China Craton within the Columbia superconti-nent: the role of double-sided subduction. Precambrian Research 178, 149–167.
Santosh, M., Tsunogae, T., Li, J.H., Liu, S.J., 2007a. Discovery of sapphirine-bearing Mg-Algranulites in the North China Craton: implications for Paleoproterozoic ultrahightemperature metamorphism. Gondwana Research 11, 263–285.
Santosh, M., Wilde, S.A., Li, J.H., 2007b. Timing of Paleoproterozoic ultrahigh-temperature metamorphism in the North China Craton: evidence from SHRIMPU–Pb zircon geochronology. Precambrian Research 159, 178–196.
Santosh, M., Maruyama, S., Sato, K., 2009. The making and breaking of supercontinents:some speculations based on superplume, super downwelling and the role oftectosphere. Gondwana Research 15, 324–341.
Santosh, M., Zhao, D., Kusky, T., 2010. Mantle dynamics of the Paleoproterozoic NorthChina Craton: a perspective based on tomography. Journal of Geodynamics 49,39–53.
Simonetti, A., Bell, K., Viladkar, S.G., 1995. Isotopic data from the Amba Donga carbonatitecomplex, west-central India: evidence for an enriched mantle source. ChemicalGeology 122, 185–198.
Sun, S.S., McDonough, W.F., 1989. Chemical and isotopic systematics of oceanic basalt:implications for mantle compositions and processes. In: Saunders, A.D., Norry, M.J.(Eds.), Magmatism in the Ocean Basins: The Geological Society Special Publication,42, pp. 313–345.
Tao, K.J., Yang, Z.M., Zhang, P.S., Wang, W.Z., 1998. Systematic geological investigationon carbonatite dykes in Bayan Obo, InnerMongolia, China. Scientia Geologica Sinica33, 73–83 (in Chinese with English abstract).
Taylor, S.R., McLennan, S.M., 1985. The continental crust: its composition and evolution.Blackwell, Oxford. 312 pp.
Veena, K., Pandey, B.K., Krishnamurthy, P., Gupta, J.N., 1998. Pb, Sr and Nd isotopicsystematics of the carbonatites of Sung Valley, Meghalaya, northeast India:implications for contemporary plume-related mantle sources characteristic.Journal of Petrology 39, 1875–1884.
Wang, J., Li, S.Q., Wang, S.B., Li, J.J., 1992. Langshan-Bayan Obo rift. Peking University.132 pp. (in Chinese).
Wang, K.Y., Fan, H.R., Xie, Y.H., 2002. Geochemistry of REE and other trace elements ofthe carbonatite dykes at Bayan Obo: implication for its formation. Acta PetrologicaSinica 18, 340–348 (in Chinese with English abstract).
Wang, K.Y., Fan, H.R., Yang, K.F., Hu, F.F., Ma, Y.G., 2010. The Bayan Obo carbonatites: apolyphase intrusive and extrusive carbonatites-based on their texture evidence.Acta Geologica Sinica 84, 1365–1376.
Woolley, A.R., Kempe, D.R.C., 1989. Carbonatites: nomenclature, average chemicalcompositions, and element distribution. In: Bell, K. (Ed.), Carbonatites: Genesis andEvolution. Unwin Hyman, London, pp. 1–14.
Wyllie, P.J., Lee, W.J., 1998. Model system controls on conditions for formation ofmagnesiocarbonatite and calciocarbonatite magmas from the mantle. Journal ofPetrology 39, 1885–1893.
Wyllie, P.J., Jones, A.P., Deng, J., 1996. Rare earth elements in carbonate-rich melts frommantle to crust. In: Jones, A.P., Wall, F., Williams, C.T. (Eds.), Rare Earth Minerals:Chemistry, Origin and Ore Deposits. Chapman & Hall, London, pp. 77–104.
Xiao, W.J., Windley, B.F., Hao, J., Zhai, M.G., 2003. Accretion leading to collision and thePermian Solonker suture, Inner Mongolia, China: termination of the Central AsianOrogenic Belt. Tectonics 22, 1–20.
Xiao,W., Hunag, B., Han, C., Sun, S., Li, J., 2010. A reviewof thewestern part of the Altaids: akey to understanding the architecture of accretionary orogens. Gondwana Research18, 253–273.
Xu, C., Campbell, I.H., Allen, C.M., Chen, Y.J., Huang, Z.L., Qi, L., Zhang, G.S., Yan, Z.F., 2008.U–Pb zircon age, geochemical and isotopic characteristics of carbonatite andsyenite complexes from the Shaxiongdong, China. Lithos 105, 118–128.
Xu, C., Kynicky, J., Chakhmouradian, A.R., Campbell, I.H., Allen, C.M., 2010. Trace-element modeling of the magmatic evolution of rare-earth-rich carbonatite fromthe Miaoya deposit, Central China. Lithos 118, 145–155.
Yang, X.M., Le Bas, M.J., 2004. Chemical compositions of carbonate minerals from BayanObo, Inner Mongolia, China: implications for petrogenesis. Lithos 72, 97–116.
Yang, X.M., Yang, X.Y., Le Bas, M.J., 1998. Geological and geochemical characteristics ofcarbonatites and their implication for tectonic settings. Advance in Earth Sciences13, 457–466 (in Chinese with English abstract).
Yang, X.M., Yang, X.Y., Zheng, Y.F., Le Bas, M.J., 2003. A rare earth element-richcarbonatite dyke at Bayan Obo, Inner Mongolia, North China. Mineralogy andPetrology 78, 93–110.
Yang, K.F., Fan, H.R., Santosh, M., Hu, F.F., Wang, K.Y., 2011. Mesoproterozoic mafic andcarbonatitic dykes from the northern margin of the North China Craton:implications for the final breakup of Columbia supercontinent. Tectonophysics498, 1–10.
Yuan, Z.X., Bai, G., Wu, C.Y., 1991. Genesis and metallogenic age of Bayan Obo Ni, REEand Fe ore deposit Inner Mongolia. Mineral Deposit Geology 10, 59–70 (in Chinesewith English abstract).
Zhai, M.G., 2004. 2.1–1.7 Ga geological event group and its geotectonic significance.Acta Petrologica Sinica 20, 1343–1354 (in Chinese with English abstract).
Zhai, M.G., Santosh, M., 2011. The Early Precambrian odyssey of the North China Craton:a synoptic overview. Gondwana Research 20, 6–25. doi:10.1016/j.gr.2011.02.005.
Zhai, M.G., Guo, J.H., Li, Y.G., Liu, W.J., Peng, P., Shi, X., 2003. Two linear granite belts inthe central-western North China Craton and their implication for late Neoarch-aean-Paleoproterozoic continental evolution. Precambrian Research 127, 267–283.
Zhang, Z., Tang, S., Wang, J., Yuan, Z., Bai, G., Zhang, Z., Tang, S., Wang, J., Yuan, Z., Bai, G.,1994. New data for ore-forming age of the Bayan Obo REE ore deposit. ActaGeoscientia Sinica 85–94 (in Chinese with English abstract).
Zhang, S.H., Zhao, Y., Yang, Z.Y., He, Z.F., Wu, H., 2009. The 1.35 Ga diabase sills from thenorthern North China Craton: Implications for breakup of the Columbia (Nuna)supercontinent. Earth and Planetary Science Letters 288, 588–600.
Zhao, Y.Y., Zheng, Y.F., 2010. Stable isotope evidence for involvement of deglacial meltwater in Ediacaran carbonates in South China. Chemical Geology 271, 86–100.
Zhao, G.C., Sun, M., Wilde, S.A., Li, S.Z., 2004. A Paleo-Mesoproterozoic supercontinent:assembly, growth and breakup. Earth-Science Reviews 67, 91–123.
Zhao, G.C., Sun, M., Wilde, S.A., Li, S.Z., Zhang, J., 2006. Some key issues inreconstructions of Proterozoic supercontinents. Journal of Asian Earth Sciences28, 3–19.
Zhao, G., He, Y., Sun, M., 2009a. The Xiong'er volcanic belt at the southern margin of theNorth China Craton: Petrographic and geochemical evidence for its outboardposition in the Paleo-Mesoproterozoic Columbia Supercontinent. GondwanaResearch 16, 170–181.
Zhao, Y.Y., Zheng, Y.F., Chen, F., 2009b. Trace element and strontium isotope constraintson sedimentary environment of Ediacaran carbonates in southern Anhui, SouthChina. Chemical Geology 265, 345–362.
Zindler, A., Hart, S., 1986. Chemical geodynamics. Annual Review of Earth and PlanetarySciences 14, 493–571.
131K.-F. Yang et al. / Ore Geology Reviews 40 (2011) 122–131