http://www.paper.edu.cn

Dec. 2002 Journal of University of Mining & Technology Vol. 12 No. 2

Geochemical Characteristics of REE in of Yan’an Formation from Dongsheng Coalf ield

ZHAO Feng2hua (赵峰华) , CONG Zhi2yuan (丛志远) , PENG S u2ping (彭苏萍) , TANG Tue2gang (唐跃刚) , REN De2yi (任德贻) ( The Key Laboratory of Coal Resource , Education Ministryof China, CUMT, Beijing 100083 ,China)

Abstract : Concentrations of rare earth elements (REE) in J urassic coal of YanAn Formation from Dongsheng coalfield located in the northeast of Ordos basin were determined by instrumental neutron activation analysis ( INAA) . Curves of distribution patternof REE were drawn , and many geochemical parameters were calculat2 ed. The result shows that 1) The contentsof REEinJurassic coal with low ash and sulfur are lower than those of and coal from the Basin of North China; 2) Inside the Dongsheng coalfield , coal from the north has higher contentsof REE than that form the south because the north is near the area of source rock which is the main supplier of REE, while the south is far away from the area of source rocks; 3) Al2 though J urassic coal in Dongsheng is the low2ash coal with less than 10 %, the contentsof REEare stillpropor2

tional to ash yield of ash and SiO2 contents. 4) Although the J urassic coal in Dongsheng were deposited in ox2 idative continental environment of river2lake , Eu depletion of REE in coal commonly exists, and positive ab2 normity of Ce dose not exist. This reflects the REE distribution pattern of REE in source rock of continental area ; and 5) Compared with other rocks, coal shows extremely complexity of distribution pattern of REE, which is the result of continuous alteration and redistribution of matter in coal occurred in open basin system. Key words : rare earth elements; geochemistry ; J urassic coal , Dongsheng coalfield

CLC number : P594 Document code : A Article ID : 100621266 (2002) 0220138205

1 Introduction were determined using instrumental neutron activa2 Rare earth elements (REE) are extensively ap2 tion analysis ( INAA) , and geochemical characteris2 plied owing to its special role as geochemical tracer. ticsof REE were analyzed on the basis of these data They can provide much geological and geochemical for REE contents. information such as character of source rock , coal2 2 Geologic Setting and Samples forming environment , and origin of rock. Rare earth elements are common elements in coal , and Dongsheng coalfield located in the northeast of many scholars have ever determined them[125 ] . Ordos basin , Autonomous Region. However , most of these studies focused on REE in YanAn Formation of middle2lower J urassic is the the Carboniferous2Permian , only a few on main coal2bearing strata , which is coal measure of a Jurassic coals. Hence , this paper concentrates on large2scale continental basin. Fig. 1 shows the stra2 J urassic coal samples from YanAn Formation in ta and sedimentary environment. The coal seams in Dongsheng coalfield located in the northeast of Or2 the north of this coalfield were formed in the fluvial dos basin. The contents of REE in these samples environment , the coal seams in the south were de2 posited in delta of lake. Received date : 2002 05 26 Foundation item : National Natural Science Foundation of China ( 49902013) and Special Funds for Major State Basic Research Projects ( G1999022212201) . Biography : ZHAO Feng2hua(1969 - ) , male , from Shanxi Province , associate professor , doctor on philosophy , engaged in the research on coal geochemistry and environment geochemistry. 转载 中国科技论文在线 http://www.paper.edu.cn

ZHAO Feng2huan et al. Geochemical Characteristics of REE in J urassic Coal of Yan’an ⋯ 931

tration of light rare earth elements (LREE) is 2. 01 - 57. 55μg/ g , geometric mean is 10. 84μg/ g , ap2 proximatelyfive timesof that of chondrite. And that of heavy rare earth elements ( HREE) is 0. 56 - 10. 04μg/ g , geometric mean is 1.67μg/ g , approxi2 mately equal to that of chondrite. The ratio of LREE to HREEis3.28- 11.71,geometric mean of which is 6.48. The above data show that the LREE is richer than HREE. δEuis0.23- 1.25, with ge2 ometric mean of 0. 65 , showing a negative abnor2 mality of Eu in most coal samples. δCeis0.59- 0. 98 , with geometric mean of 0. 80 , indicating that

the abnormality of Ce is not obvious. (La/ Yb) N is 2.98- 13.74, with geometric mean of 7.34. Fig. 1 Integrated histogram of Yan’an Formation ∑REE in most of Dongsheng’s J urassic coal in Dongsheng coalfield samples is far lower than 46. 3μg/ g , the average The samples were collected from the north and value of ∑REE in coal of the whole world calculated the south of Dongsheng coalfield , respectively. The [7 ] by Valkovic , also obviously lower than that of northern samples of coalfield were from No. 4 coal Carboniferous2Permian coals calculated by Zhao[3 ] seam in Nalingou Mine, Hantaichuan Mine and and Huang[5 ] . As a whole , ∑REE in coal samples Changhangou Mine. The samples from the south of from the south mines is apparently lower than that coalfield were collected in No. 3 coal seam in Majia2 from the north mines. MJT21 and MJ T22 coal sam2 ta Mine and Yumin Mine, No. 2 coal seam in Bu2 ple is near the roof of coal seam , so they have high lianta Mine. For No. 3 coal seam of Majiata Mine contents of ∑REE. and Yumin Mine , ply samples were collected from Correlation analysis shows that ∑REE concen2 top to bottom. The reminders are the whole seamor trations are still proportional to ash yield ( Fig. 2) , lithotype samples. We also sampled mudstone sam2 with a correlation coefficient ( R) of 0.8006 at the ples of the coal measures. level of 0. 001 , although most coal samples have a Instrument neutron activation analysis ( INAA) lower ash yieldof less than 10 %, lower than that of was used to determine concentrations of eight ele2 Carboniferous2Permian coal[3 , 5 ] . Hence , the con2 ments (La, Ce, Nd, Sm, Eu, Tb, Yb andLu) . tentsof REE in Jurassic coal mainly depend on ash The contents of Pr, Gd, Dy, Ho, Er and Tm in yield of coal. In addition, REE contents are also coal samples were obtained by interpolation calcula2 proportional to SiO2 yield , with a correlation coeffi2 tion based on distribution pattern of REE normalized cient ( R) of 0.7794 at the level of 0.001( Fig. 2) . by chondrite. The standard concentrations of REE 3. 2 Distribution pattern of REE in chondrite are the average value of 22 chondrite The curves of distribution pattern of REE in [6 ] samples . Table 1 is the concentrations of REE in Dongsheng coals were drawn based on geometric these samples. mean of REE contents ( Fig. 3) . The curves show 3 Results that the distribution patterns of REE in different coal samples are very similar , with the trend of de2 3. 1 Abundance of REE crease for normalization value of REE from La to From Table 1 , the range of total concentrations Lu, LREE is obviously rich, and the curve of of REE( ∑REE) in coal samples is 2. 62263. 94μg/ HREE is flat , the coal samples from the north of g , geometric mean is 12.58μg/ g , which is approxi2 coalfield have higher REE contents than that of oth2 mately four timesof that of chondrite. The concen2 er coal samples. Although Dongsheng ’s J urassic 中国科技论文在线 http://www.paper.edu.cn

041 Journal of China University of Mining & Technology Vol. 12 No. 2

coals were deposited in oxidative continental envi2 normity of Ce dose not exist . The above characteris2 ronment of river2lake , Eu depletion of rare earth ele2 tics reflect distribution pattern of REE in source ments in coal commonly exist (especiallyfor the coal rock of continental area. sample from Hantaichuan Mine) , and positive ab2

Fig. 2 The correlatographof REEin Dongsheng’s coals with ash yield and SiO2 contents

- 6 Table 1 The analytical results on rare earth elements in Jurassic coal of Dongsheng coalf ield w B/ 10

Mine Sample La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu MJ T21 8. 77 17. 60 2. 43 9. 73 1. 79 0. 32 2. 08 0. 33 1. 88 0. 41 1. 10 0. 12 0. 75 0. 11 MJ T22 12. 60 20. 20 1. 72 6. 88 1. 42 0. 15 1. 59 0. 25 1. 44 0. 32 0. 85 0. 11 0. 69 0. 10 MJ T23 3. 02 4. 46 0. 55 2. 21 0. 33 0. 06 0. 40 0. 06 0. 39 0. 09 0. 25 0. 03 0. 14 0. 02 MJ T24 1. 97 2. 19 0. 21 0. 82 0. 16 0. 05 0. 24 0. 04 0. 25 0. 06 0. 17 0. 02 0. 11 0. 02 Majiata MJ T25 3. 46 3. 22 0. 38 1. 51 0. 24 0. 06 0. 35 0. 06 0. 34 0. 08 0. 23 0. 04 0. 23 0. 04 mine MJ T26 1. 59 3. 85 0. 45 1. 79 0. 24 0. 06 0. 21 0. 03 0. 22 0. 05 0. 16 0. 03 0. 15 0. 02 MJ T27 1. 97 2. 07 0. 21 0. 84 0. 18 0. 02 0. 20 0. 03 0. 21 0. 05 0. 15 0. 02 0. 14 0. 02 MJ T28 1. 09 2. 47 0. 36 1. 45 0. 20 0. 04 0. 20 0. 03 0. 21 0. 05 0. 15 0. 03 0. 17 0. 02 MJ T29 1. 59 1. 90 0. 14 0. 54 0. 15 0. 06 0. 21 0. 03 0. 22 0. 05 0. 16 0. 02 0. 10 0. 02 MJ T210 1. 34 2. 10 0. 19 0. 74 0. 19 0. 06 0. 22 0. 04 0. 23 0. 06 0. 16 0. 02 0. 11 0. 01 Bulianta Mine BL T 3. 68 5. 90 0. 55 2. 19 0. 31 0. 07 0. 35 0. 06 0. 35 0. 08 0. 23 0. 03 0. 16 0. 03 YM21 0. 87 1. 51 0. 17 0. 68 0. 16 0. 04 0. 13 0. 02 0. 15 0. 04 0. 12 0. 02 0. 08 0. 01 Yumin YM22 0. 78 1. 81 0. 20 0. 79 0. 17 0. 04 0. 15 0. 03 0. 17 0. 04 0. 13 0. 02 0. 10 0. 01 mine YM23 0. 58 0. 75 0. 11 0. 44 0. 11 0. 03 0. 13 0. 02 0. 15 0. 04 0. 12 0. 02 0. 12 0. 02 YM24 2. 09 3. 78 0. 42 1. 69 0. 19 0. 04 0. 16 0. 03 0. 17 0. 04 0. 13 0. 02 0. 13 0. 02 Changhangou CHG21 4. 77 8. 83 1. 19 4. 76 0. 75 0. 15 0. 73 0. 12 0. 68 0. 15 0. 42 0. 04 0. 21 0. 03 mine CHG22 7. 77 16. 10 1. 70 6. 81 2. 29 0. 64 3. 01 0. 47 2. 70 0. 58 1. 56 0. 21 1. 30 0. 20 NL G21 7. 83 10. 50 0. 90 3. 59 0. 99 0. 16 1. 43 0. 23 1. 30 0. 29 0. 77 0. 07 0. 43 0. 08 Nalingou NL G22 66. 60 104. 00 13. 43 53. 70 7. 76 0. 98 5. 27 0. 83 4. 71 1. 01 2. 70 0. 39 2. 47 0. 39 mine NL G23 12. 70 28. 20 2. 83 11. 30 2. 07 0. 45 1. 86 0. 29 1. 68 0. 37 0. 99 0. 15 0. 93 0. 12 Hantaichuan HTC21 3. 83 7. 29 0. 96 3. 84 1. 05 0. 06 0. 85 0. 13 0. 79 0. 18 0. 48 . 09 0. 53 0. 07 mine HTC22 6. 30 11. 50 1. 66 6. 65 1. 38 0. 11 1. 22 0. 19 1. 12 0. 25 0. 67 0. 12 0. 74 0. 11

Note :NL22: mudstone sample of coal formation; BLT,NLG21 and NL G23 : whole seam sample ; CHG21 ,CHG22 , HTC21 and HTC22 : coal lithotype sample The similar REE distribution patterns show that coal samples have similar origin of REE to mudstone sample , although the concentration of REE in mudstone sample is 5- 10 timesof that in coal samples.

Fig. 3 The distribution pattern of REE Fig. 4 The distribution pattern of REE in coal of in Dongsheng’coals Nalingou Mine and mudstone sample of coal measure 中国科技论文在线 http://www.paper.edu.cn

ZHAO Feng2huan et al. Geochemical Characteristics of REE in J urassic Coal of Yan’an ⋯ 141

Table 2 Geochemical parameters for rare earth elements in coal

- 6 w B/% w B/ 10 Ratio Mine Sample Ad SiO2 ∑REE LREE HREE L/H δEu δCe (La/ Yb) N MJ T21 5. 58 2. 20 47. 44 40. 65 6. 79 5. 98 0. 57 0. 79 6. 91 MJ T22 7. 79 3. 87 48. 32 42. 97 5. 35 8. 04 0. 35 0. 90 10. 84 MJ T23 2. 70 1. 02 12. 02 10. 63 1. 39 7. 67 0. 59 0. 72 12. 45 MJ T24 2. 76 0. 98 6. 31 5. 40 0. 91 5. 94 0. 84 0. 72 10. 54 MJ T25 3. 32 2. 11 10. 24 8. 87 1. 37 6. 49 0. 76 0. 59 9. 01 Majiata mine MJ T26 3. 36 2. 06 8. 85 7. 98 0. 87 9. 16 1. 00 0. 95 6. 17 MJ T27 4. 50 3. 94 6. 11 5. 29 0. 82 6. 45 0. 40 0. 67 8. 60 MJ T28 4. 47 3. 96 6. 47 5. 61 0. 86 6. 54 0. 66 0. 82 3. 85 MJ T29 7. 88 5. 21 5. 17 4. 38 0. 79 5. 52 1. 25 0. 85 9. 86 MJ T210 2. 81 1. 52 5. 44 4. 61 0. 84 5. 50 0. 94 0. 88 7. 44 Bulianta BL T 7. 57 7. 21 13. 99 12. 70 1. 29 9. 86 0. 75 0. 87 13. 74 mine YM21 3. 0 2. 00 3. 98 3. 42 0. 56 6. 14 0. 87 0. 82 6. 45 Yumin YM22 4. 14 3. 84 4. 44 3. 78 0. 65 5. 80 0. 89 0. 96 4. 72 Mine YM23 2. 87 1. 87 2. 62 2. 01 0. 61 3. 28 0. 87 0. 62 2. 98 YM24 4. 0 2. 73 8. 92 8. 22 0. 70 11. 71 0. 76 0. 84 9. 85 Changhangou CHG21 8. 0 6. 00 22. 84 20. 45 2. 38 8. 58 0. 69 0. 77 13. 68 mine CHG22 9. 28 8. 21 45. 35 35. 31 10. 04 3. 52 0. 83 0. 92 3. 55 Nalingou NL G21 17. 78 16. 03 28. 54 23. 96 4. 58 5. 23 0. 45 0. 83 10. 91 mine NL G23 10. 11 9. 13 63. 94 57. 55 6. 40 9. 00 0. 78 0. 98 8. 10 Hantaichuan HTC21 7. 24 6. 21 20. 14 17. 03 3. 11 5. 48 0. 23 0. 79 4. 30 mine HTC22 15. 0 12. 40 32. 02 27. 60 4. 42 6. 24 0. 28 0. 74 5. 03

Note: LREE=La+Ce+Pr+Nd+Sm+ Eu; HREE= Gd+ Tb+Ho+ Er+ Tm+ Yb+Lu; ∑REE=LREE+ HREE; L/ H 1/ 2 =LREE/ HREE; (La/ Yb) N is the ratio of element content normalized by chondrite;δEu = EuN/ (SmN × GdN) ; EuN ,SmN , GdN 1/ 2 is the contents of these elements normalized by chondrite;δCe = CeN/ (LaN × PrN ) ; CeN ,LaN , PrN is the contents of these ele2 ments normalized by chondrite.

Fig. 4 is the curves of REE distribution pat2 Eu. Nalingou Mine of Dongsheng coalfield is near terns of upper coal sample (NL21) , lower coal sam2 the source rock area , thereby leading to similar dis2 ple (NL23) in Nalingou Mine and interbedded mud2 tribution patternsof REE in coal samples and in in2 stone sample (NL22) between coal seams. terbedded mudstone sample of coal measures ( Fig. 4) . Namely , REE in coal and inerbedded mudstone 4 Discussion sample has the same origin. Although coal2forming plant can provide a part The north of Dongsheng coalfield is near the of REEfor , it is not the main sourceof REEin coal source rock area , thereby it has abundant continen2 owing to low REE concentration in these plants[3 ] . tal debris. The coal2forming environment in the Continental debris provides most of REE for coal , north of Dongsheng coalfield is fluvial and upper therefore , abundance of REE in coal mainly depend deltaic plain environment , and far away from lacus2 on the extent of supply of continental debris. The trine environment. By contraries, the south of supply extent of continental debris can be represent2 Dongsheng coalfield is far away from source rock ed by ash yield of coal. High ash yield reflects abun2 area , with less supply of continental debris. The dant supply of continental debris , thereby leading to coal2forming environment of the south of Dongsheng high contents of REE in coal. coalfield belonged to lower deltaic plain and shore of During sedimentary process of YanAn Forma2 lake. The coal2forming swamp was influenced fre2 tion, source rocks distribute along transmeridional quently by lake process , which led to the loss of direction in the north of Ordos basin. Source rocks REEfrom swamp. Therefore , all of the above fac2 mainly consist of Presinian granite gneiss , gneiss of tors eventually resulted in obviously higher concen2 biotite2hornblende , epimetamorphic rock , and gran2 trations of REE in coal samples from the north of ite. These source rocks have negative abnormality of Dongsheng coalfield than that from the south of 中国科技论文在线 http://www.paper.edu.cn

241 Journal of China University of Mining & Technology Vol. 12 No. 2

Dongsheng coalfield. 5 Conclusions Among 10 ply coal samples , MJ T21 and MJ T22 1 ) The Jurassic coal with low ash yield sample have a higher REE concentration. This is ( < 10 %) and sulfur content ( 1 %) has low REE because these two samples are near the roof of coal concentration, and commonly lower than that of seam , hence having higher ash yield. When the roof Carboniferous2Permian coal from Basin of North of coal seam deposited , coal2accumulating process China ; was terminated and abundant continental debris pro2 2) The REE in Jurassic coal mainly originate vide much more REE for coal seam. In addition, from continental debris of source area. The north of REE in pore solution continuously penetrate into Dongsheng coalfield is nearer source rock than the coal seam near roof. The above two factors led to south of coalfield. Therefore , coal samples from the rapid increase of REE in coal near roof of coal seam. north have higher REE contents than that from the The Eu depletion is common in most of coal south. The REE contents are proportional to ash samples under control of Eu depletion of source yield and SiO2 content ; rock. The geometric mean of δEu is 0. 65 for coal 3) The distribution pattern of REE in Jurassic samples. However , MJ T28 sample is positive abnor2 coal samples depends on that of source rocks. The mality of Eu (δEu = 1. 25) . δEu of MJ T26 sample is depletion of Eu is common in most of coal samples 1. 00. Real reason is unclear for these phenomena. except for two coal samples. There is no positive ab2 It may be related to stable coal2forming environment normality of Ce. TheδCe of coal samples is similar of oxidation under which Eu3 + could not be reduced to that of shale of the North American (0. 94) and to Eu2 + , thereby not be lost . Russia platform (0. 79) . The Coal2forming swamp δCe of coal samples is between 0.70 and 0.90 , environment did not cause much Ce depletion or en2 with a geometric mean of 0.80. It is similar to that richment . ; of shale of the North American (0. 94) and Russia 4) Compared with other rocks, distribution platform ( 0. 79 ) . This shows that coal2forming patterns of REE in coal show extremely complexity , swamp environment did not cause big Ce depletion which is the result of continuous alteration and re2 or enrichment. distribution of matter in coal occurred in open basin system.

References

[1 ] 王运泉 ,任德贻 ,雷加锦 ,等. 煤中微量元素分布特征初步研究[J]. 地质科学 ,1997 ,32 (1) :65273. [2 ] 邵靖邦 ,曾凡桂 ,王宇林 ,等. 平庄煤田煤中稀土元素地球化学特征[J]. 煤田地质与勘探 ,1997 ,25 (4) :13215. [3 ] 赵志根 ,冯仕安 ,唐修义. 微山湖地区石炭 - 二叠纪煤的系统运行沉积地球化学[J]. 地质地球科学 ,1998 ,26 (4) :622 67. [ 4 ] Ren D Y ,Zhao F H ,Wang Y G,et al.Distributions of minor and trace elements in Chinese coals[J ]. International Journal of Coal Geology ,1999 ,40(223) :1092118. [5 ] 黄文辉 ,杨起 ,汤达祯 ,等. 华北晚古生代煤的稀土元素地球化学特征[J]. 地质学报 ,1999 ,73 (4) :3602369. [6 ] Herrmann A G. Yttrium and Lanthanides[A] ,In:Wedepohl K H. Handbook of Geochemistry (Vol. II/ 2 ,39 ,572712C) [C]. Berlin2Heidelberg :Spring2Verlag ,1970. 1210. [7 ] Valkovic V. Trace Elements in Coal (Vol. ⅠⅡ) [M].Boca Raton ,Florida:CRC Press Inc ,1983.1522156.