A new type of rare earth elements deposit in weathering crust of Permian basalt in western Guizhou, NW China

JOURNAL OF RARE EARTHS, Vol. 26, No. 5, Oct. 2008, p. 753

A new type of rare earth elements deposit in weathering crust of Permian basalt in western Guizhou, NW China YANG Ruidong()1, WANG Wei( )1, ZHANG Xiaodong ()1, LIU Ling ( )1, WEI Huairui ( )1, BAO Miao ( )1, WANG Jingxin ()2 (1. Guizhou University, Guiyang 550025, China; 2. Research Institute of Science and Technology Information, General Research Institute for Non-ferrous Metals, Beijing 100088, China) Received 21 December 2007; revised 11 April 2008

Abstract: A new type of rare earth elements (REEs) deposit was discovered from the gaolinite mudstone in the weathering crust of Permian basalt, Bijie region, western Guizhou, China. It contained ΣRE2O3 0.065%–1.086%. This type of REEs deposit was widely distributed with steady horizon and thickness of 3–4 m. The ore-bearing weathering crust (kaolinite) of the three discovered REEs deposits belonged to the third episode of the Emeishan basalt eruption. The new type of REEs deposit was suggested that basalt (tuff) weathering could lead to the enrichment of the rare earth elements. Therefore, it is of important economic significance to explore REEs deposits in the weathering crust of basalt (tuffs) in Yunnan, Guizhou, and Sichuan Provinces. Keywords: rare earth elements deposits; weathering crust; basalt (tuffs); upper Permian; Guizhou Province

Rare earth elements are widely used in the metallurgical, petroleum, glass, electrical, and chemical industries as an important mineral resource. In nature, 60 kinds of minerals have high rare earth elements content, however, 10 kinds of minerals, such as monazite, bastnaesite, yttrocerite, ytterbite have be used to extract industrially rare earth elements. The ion-adsorbed type rare earth deposit is generally of low grade, but it is extracted easily. Therefore, it becomes an important REEs resource in Jiangxi Province, China. Rare earth elements resource is rich in China. However, until now, only a few rare earth deposits, such as Baotou deposit, Jiangxi ion-adsorbed type deposits have been developed. As more and more rare earth resource is consumed with the progress of the metallurgical, petroleum, glass, electrical, and chemical industries, the exploration of rare earth elements resources is becoming an important geological task. Permian Emeishan basalt (tuffs), considered as a product of a Permian mantle plume, is widely distributed in western China[1–6]. Recent studies suggest that basalt (tuffs) is closely related to gold, cupper, antimony, pyrite, manganese, Pb-Zn, and bauxite deposits[7–23]. Previous data indicate that the basalt (tuffs) is rich in rare earth elements (REEs) up to 106×10–6[24]. The rare earth deposits with very high rare earth element contents commonly occur in the weathering crust (kaolinite) of basalt (tuffs) similar to Jiangxi

ion-adsorbed type rare earth deposits. More and more geologists have attempted to find a new type of rare earth deposit in the weathering crust (kaolinite) of the Emeishan basalt (tuffs) in southwest China. In 1995, rare earth elements deposits and bauxite in the weathering crust of the basalt (tuffs) in western Guizhou Province were first reported[25,26]. In recent years, bauxite and laterite gold deposit were discovered in Cenozoic basalt-weathering crust in Hebei, north China and Hainan, China[27,28]. These progresses hint that ion-adsorbed type rare earth deposits will be possibly discovered in the weathering crust of the Emeishan basalt (tuffs). In 2005, our team started the study on the weathering crust of the basalt (tuffs) at Yuwanchong, Bijie County and Shiyakou, Hezhang County, western Guizhou Province. The analysis results of the weathering crust (kaolinite) samples of the two localities show high content of rare earth element, ΣRE2O3 is generally 0.065%–0.70%, and ΣRE2O3 is highest up to 1.086% in a few samples. Expiration extracted by soaping of (NH4)S2O4 and NaCl shows that the rare earth elements occur mostly in the fine-grade rare earth mineral in weathering crust (kaolinite) sample; 10% rare earth element is extracted by soaping of (NH4)S2O4 and NaCl, and precipitating of oxalic acid in weathering crust (kaolinite) sample; the result shows that ion-adsorbed rare earth is about 10% of the total rare earth

Foundation item: Project supported by the Major State Basic Research Development Program of China (2006CB403202), the Doctoral Discipline Foundation of Guizhou University Corresponding author: YANG Ruidong (E-mail: [email protected]; Tel.: +86-851-3620551)

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content in the rare earth deposits of the weathering crust (kaolinite). The grade of the rare earth deposits mentioned above is over the industry grade (ΣRE2O3 0.05%), over 1 m in thickness, and its content of rare earth is higher than that of Lower Cambrian phosphorite in Zhijin County, Guizhou Province[29]. The new type of REEs deposits are characterized by wide distribution, large thickness, and low grade. It is of importance to find large REEs deposits in the weathering crust (kaolinite) of the basalt (buffs) in Yunnan, Guizhou, and Sichuan Provinces.

1 Distribution and horizon of the REEs deposits in the weathering crust (kaolinite) of Emeishan basalt Late Permian Emeishan basalt is widely distributed with 400–600 m thickness. The thickest Permian basalt is 1249 m in Shejule, Weining County, Guizhou Province. Mao et al. (1992) suggested that the Emeishan basalt eruption is comprised of three episodes, and up to 24 sub-pulses[24]. The first episode was dominated by basalt, volcanic clastic rock; the second episode by basalt; and the third episode by volcanic clastic rock, basalt, and tuffs[23]. The third episode mostly consists of basalt and tuffs in Weining County, Hezhang County, and Bijie County of Guizhou Province. The study area is located at Yuwanchong, Bijie County,

JOURNAL OF RARE EARTHS, Vol. 26, No. 5, Oct. 2008

Lufang, Weining County, and Shiyakou, Hezhang County in western Guizhou. The rare earth deposits in the weathering crust (kaolinite) are products of the weathering and dripping of the third episode of basalt (Fig.1). The three REEs deposits are of high grade (>0.02%) and with thickness more than 1 m. Horizons of ore beds are located in the middle of kaolinite mudstone in the weathering crust (kaolinite) of basalt and buffs, and the ore beds are under mudstone bearing plant fossil of the Longtan Formation over the basalt (Fig.2).

2 Characteristics of REEs deposits in weathering crust (kaolinite) of basalt and buffs White-grey kaolinite mudstone under Upper Permian Longtan Formation in Yuwanchong, Bijie County is a large kaolinite deposit. The dip angle of the kaolinite mineral bed is small. The outcrop of the ore bed is 300–500 m in length and 3–4 m in thickness with prospective reserves of the kaolinite deposit up to 1000×104 T. We systematically analyzed the REEs contents of the kaolinite deposit, and the result of analysis shows that the content of ΣRE2O3 ranges from 0.065% to 0.231%, and most of the contents are over the content of ΣRE2O3 (0.1%) of Cambrian phosphorite, in Zhijin County, Guizhou Province[29]. According to the composition, features, and color of the ore, the ore bed was divided into 5 sub-beds (Fig.2), with an ascending order: (1) brown-grey kaolinite mudstone, 2 m in

Fig.1 Map showing the distribution of Emeishan basalt and the localities of weathering crust REEs deposits at Bijie County, Guizhou Province 1-Basalt outcrop; 2-Localities of section

YANG R D et al., A new type of rare earth elements deposit in weathering crust of permian basalt in western…

thickness, ΣRE2O3 content ranging from 0.154% to 0.231%. (2) grey-white kaolinite mudstone, 1.5 m in thickness, ΣRE2O3 content of 0.139%. (3) vein white kaolinite mudstone, 0.5 m in thickness, ΣRE2O3 content up to 0.204%. (4) grey-white kaolinite mudstone, 0.6 in thickness, ΣRE2O3 content low to 0.065%. (5) brown-grey thin bedded mudstone, 2.0 m in thickness, ΣRE2O3 content of 0.132%. The composition of rare earth in the REEs deposit showed richness in LREE (Ce, Nd, La, Pr, Sm, Eu), and the percent of LREE was up to 91.72% in the total REEs. The REEs minerals are dominated by micron grade grain in clay mineral. 10% REEs was extracted by soaping of (NH4)S2O4 and NaCl, and it showed that the rare earth content of 10% was ion-type exist in the rare earth deposit. The REEs deposits in Lufang, Weining County of Guizhou Province consisted of Lower and Upper ore beds (Fig.2); this rare earth deposit was discovered by Huang Xunhua in 1997. The content of ΣRE2O3 mainly ranges between 0.1%–0.7% with some up to 1.086%[25]. These are rich in LREEs, and LREEs was about 83.87% in the total content of ΣREE. The ore-bearing bed was –13.5 m in thickness and the ore bed with high grade0.25%–0.7%was 4.2 m in thickness. REES minerals and ion were preserved in grey-white kaolinite mudstone with micro-clay feature and a little limonite mineralization. The ore body presented as bed-shape in morphology, and was parallel with the strata. The outcrop of the ore body was 4000–5000 m in length, and about 3 m in thickness. Interval mudstone presented in

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ore beds. The REEs minerals are yttroalumite, ytterbite, monazite, and bastnaesite according to X-ray diffraction and electric microprobe analyses[25]. Additionally, REEs deposits in the weathering crust (kaolinite) were also reported at Liangshuijing, Yangjie, and Chahe, Weining district, Guizhou Province, which indicates that this type of REEs deposit is widespread in Weining County, western Guizhou Province. The REEs deposits at Shiyakou, Hezhang County were under the silty mudstone of Longtan Formation (Fig.2), over the Emeishan basalt (Fig.3(a)). The total thickness of the ore bodies was about 15 m. ΣRE2O3 was 0.037%–0.222% (Table 1). According to the composition, feature, and color of ore, ore beds can be divided into 6 sub-beds, in an ascending order: (1) brown kaolinite mudstone interlayed with limonite and basalt pebble (Fig.3(b)), 2 m in thickness, ΣRE2O3 0.037%–0.077%. (2) grey-white kaolinite mudstone, 0.5 m in thickness, ΣRE2O3 0.089%. (3) brown beans kaolinite mudstone (Fig.3(c)), 0.5 m in thickness, ΣRE2O3 0.026%. (4) grey-white kaolinite mudstone (Fig.3(d)), 1.2 m in thickness, ΣRE2O3 –0.222%. (5) grey vein kaolinite mudstone (Fig. 3e), 5.3 m in thickness, ΣRE2O3 0.027%–0.0682%. (6) grey bedded kaolinite mudstone, 5.0 m in thickness, ΣRE2O3 0.087%–0.092%. Fig.4 shows the comparison between the REE contents of Emeishan basalt (average value of 19 samples from Mao et al.1992)[24] and that of kaolinite mudstone in the weathering crust of basalt (tuffs). It was noticed that the basalt has low

Fig.2 Map showing rare earth content and horizon in Yuwanchong, Bijie County, Lufang, Weining County, and Shiyakou, Hezhang County, Guizhou (data show contents of ΣRE2O3×10–2, the data of Lufang section, Weining County from Huang Xunhua, 1997) 1. Thin bedded kaolinite mudstone; 2. Middle bedded kaolinite mudstone; 3. Thick bedded kaolinite mudstone; 4. Thick bedded kaolinite mudstone bearing Fe; 5. Veined kaolinite mudstone; 6. Silty mudstone; 7. Basalt

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JOURNAL OF RARE EARTHS, Vol. 26, No. 5, Oct. 2008

total REEs; nevertheless, the kaolinite mudstone in the weathering crust of basalt (tuffs) contains considerably higher total REEs (Fig.4). The content variations of individual elements of the REE in the kaolinite mudstone are

very similar to those of Emeishan basalt, which maintain that the REEs deposits were formed by the weathering process of basalt or tuffs.

Fig.3 Structure and feature of the rare earth deposit at Shiyakou, Hezhang County, Guizhou (a) Boundary between basalt and bearing-RE (rare earth) kaolinite mudstone; (b) Base bearing-RE kaolinite mudstone with limonite interval; (c) Brown beans kaolinite mudstone; (d) Grey-white bearing-RE kaolinite mudstone; (e) Brown pebble kaolinite mudstone Table 1 Content of rare earth elements and major elements from the weathering crust of the basalt at Shiyakou, Hezhang County, and Yuwanchong, Bijie County, Guizhou Province* Sample No.

SiO2/

Al2O3/

Fe2O3/

-2

-2

-2

10

10

10

FeO/ 10

-2

CaO/ 10

-2

MgO/ 10

-2

K2O/ 10

-2

Na2O/

TiO2/

P2O5/

MnO/

-2

-2

-2

-2

10

10

10

10

Loss/ 10

-2

ΣRE2O3/ 10-6

E-1

54.07

11.85

13.81

7.92

0.450

1.69

0.182

0.132

3.87

0.432

0.078

4.50

372

E-3

44.46

21.00

14.36

1.56

0.101

0.140

0.139

0.061

7.03

0.522

0.189

10.06

767

E-4

42.96

20.28

14.99

0.774

0.028

0.564

0.619

0.235

7.70

0.652

0.038

9.56

223

E-6

52.82

17.29

12.19

1.98

0.220

0.745

1.45

0.198

5.51

0.475

0.039

6.66

626

E-8

47.46

20.76

13.26

0.847

0.118

0.708

1.66

0.226

6.56

0.086

0.032

7.98

712

E-9

48.38

24.27

7.77

0.424

0.127

0.475

2.18

0.439

7.83

0.096

0.008

7.75

894

E-10

29.60

24.16

23.62

1.43

0.081

0.481

0.918

0.497

7.36

0.059

0.018

11.42

256

E-11

35.52

26.70

15.21

0.847

0.149

0.410

1.20

0.632

7.94

0.220

0.015

10.86

966

E-12

30.36

25.74

20.54

1.11

0.082

0.476

0.623

0.372

8.10

0.329

0.019

11.93

2220

E-13

33.18

25.36

20.02

0.759

0.063

0.354

0.809

0.620

7.22

0.070

0.010

11.26

270

E-14

59.40

24.36

1.84

0.117

0.099

0.538

2.71

0.704

3.83

0.097

0.018

6.06

679

E-15

46.73

33.11

0.750

0.117

0.157

0.278

1.57

1.84

5.86

0.193

0.002

9.19

873

E-16

46.48

33.44

0.570

0.263

0.151

0.276

1.49

1.82

5.91

0.199

0.001

9.16

922

Sample No.

Y-1

Y-2

Y-3

Y-4

Y-5

Y-6

Y-7

Y-8

ΣRE2O3×10-6

0.016

0.154

0.231

0.139

0.204

0.065

0.151

0.095

* Data analyzed by ICP-AES in the Lab. of Yichang Institute of Geology and Mineral Resources

YANG R D et al., A new type of rare earth elements deposit in weathering crust of permian basalt in western…

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Table 2 Composition of rare earth elements from the weathering crust of the basalt at Shiyakou, Hezhang County, Guizhou Province* Sample No.

La

Ce

Pr

Nd

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

Yb

Lu

Y

E-1

57.5

101

13.3

59.6

11.8

4.59

12.1

1.70

10.3

1.84

5.28

0.60

3.50

0.41

27.5

E-3

156

219

29.7

124

22.9

5.80

15.2

2.33

12.1

2.21

5.13

0.72

3.99

0.44

41.4

E-4

23.4

49.8

6.49

28.4

7.11

3.08

8.40

1.42

9.15

1.70

4.53

0.62

3.59

0.42

37.3

E-6

108

203

21.8

101

17.0

4.43

11.1

1.82

9.99

1.65

4.11

0.45

2.85

0.29

34.9

E-8

111

191

29.6

155

26.9

5.86

14.8

1.92

11.1

2.22

5.11

0.72

4.01

0.52

36.8

E-9

101

122

32.0

144

29.4

7.23

30.6

5.59

37.8

8.31

23.9

3.01

19.8

2.29

178

E-10

34.6

69.0

6.98

22.2

7.13

3.59

13.2

2.14

10.9

1.68

3.48

0.45

2.75

0.41

34.4

E-11

156

296

35.4

176

38.2

12.3

28.0

3.90

16.7

2.58

4.96

0.62

3.09

0.34

34.2

E-12

269

734

92.9

498

99.9

23.4

50.3

6.97

29.2

4.05

6.30

0.77

3.39

0.33

43.1

E-13

55.6

83.1

9.25

36.0

5.80

1.36

4.70

0.80

4.76

0.71

2.45

0.34

2.13

0.26

17.9

E-14

116

209

22.0

77.5

14.3

2.69

12.7

2.16

16.2

3.02

9.02

1.31

8.16

0.98

69.5

E-15

142

256

30.0

137

27.6

6.02

19.3

3.12

20.3

3.47

10.1

1.30

7.49

0.96

63.7

E-16

149

268

31.0

137

26.6

6.26

20.8

3.32

21.4

3.74

10.3

1.40

8.22

0.94

80.1

Basalt

40.46

84.66

6.56

38.08

7.55

2.27

5.08

1.60

2.10

1.56

1.30

0.55

2.47

0.42

28.52

* Data analyzed by ICP-MS in the Lab. of Yichang Institute of Geology and Mineral Resources. Basalt data from Mao et al.[24]

Fig.4 Map showing the relationship between the composition of rare earth elements from the weathering crust of basalt and the basalt at Shiyakou, Hezhang County (Basalt data from Mao et al.[24])

3 Geological significance of the new type of RE deposit in weathering crust of basalt (tuffs) REEs deposits are closely related to the weathering crust of basalt. In the course of weathering, REEs gradually gather in kaolinite mudstone during the basalt weathering. Lateritic process leads to rare earth elements removing and precipitating, and latest, rare earth elements were adsorbed and gathered in clay minerals. As kaolinite mineral grain is difficult to adsorb HREE complex compound, kaolinite mudstone in the weathering crust is depleted in HREE. On the contrary, LREE complex compound is affinitive to be adsorbed in mineral grain. Thus, the weathering crust kaolinite is rich in LREE, especially, in elements such as Ce, La, Nd, Pr, Sm, and Eu. The REEs deposits were formed by the weathering, removing, precipitating, and adsorbing processes [30~35]. Therefore, the weathering crust of basalt (tuffs) is the main horizon of the high content of REE, and the

weathering crust of basalt (tuffs) controls the distribution of the new type of REEs deposits. The outcrop of Emeishan basalt is widespread in northeast Yunnan, Southern Sichuan, and western Guizhou. Owing to the large scale up lift after the eruption of basalt in Large Igneous Province, the basalt was weathered and seeped for a long time. The weathering crust of basalt (tuffs) is widely distributed in northeast Yunnan, Southern Sichuan, and western Guizhou. This study shows that the weathering crust REE deposit is well preserved in Bijie, Weining, and Hezhang districts, western Guizhou Province, and we suggest that the outcrop region of Emeishan basalt is a perspective area for a new type of REEs deposit in the weathering crust of basalt. Acknowledgement: The authors express thanks to Prof. Zhang Chuanlin and Zeng Minguo for their help to this work.

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