ree geochemistry of marine oil shale from the changshe mountain area， northern tibet， china

1、REE geochemistry of marine oil shale from the Changshe Mountain area, northern Tibet, ChinaXiugen Fu a,?, Jian Wang a, Yuhong Zeng b, Fuwen Tan a, Xinglei Feng aa Chengdu Institute of Geology and Mineral Resources, Cheng

2、du 610081, China b College of Chemistry, Sichuan University, Chengdu 610065, Chinaa b s t r a c t a r t i c l e i n f oArticle history:Received 29 October 2009Received in revised form 7 December 2009Accepted 13 December

3、2009Available online 22 December 2009Keywords:Marine oil shaleRare earth elementsQiangtang basinChinaThe Shengli River–Changshe Mountain oil shale zone, located in the North Qiangtang depression, northernTibet plateau, r

4、epresents a potentially large marine oil shale resource in China. The contents and distributionpatterns of rare earth elements (REEs) in selected oil shale and micritic limestone samples from theChangshe Mountain area we

5、re studied by inductively-coupled plasma mass spectrometer (ICP-MS).Analyzed oil shale samples from the Changshe Mountain area are characterized by high total organic carbon(TOC) contents (7.02–16.32%) and ash yields (53

6、.22–82.12%) with shale oil contents from 3.85% to 11.76%.The total rare earth element (∑REE) contents in oil shale samples are 68.19 μg/g, close to those of US coals,and higher than those of micritic limestone samples (3

7、7.69 μg/g) from the Changshe Mountain area, butlower than those of world-wide black shales, common Chinese coals, and North American Shale Composite.There are two types, A and B, of distribution patterns of REEs in the C

8、hangshe Mountain oil shale samples.Type A shows negligible Ce anomalies (0.97–1.01), with slightly higher ∑REE concentrations (36.87–118.38 μg/g) and LREE/HREE (6.79–10.74) and (La/Yb)n (6.68–8.36) ratios, whereas type B

9、 exhibits a slightlynegative Ce anomaly (0.84–0.88), with slightly lower ∑REE concentrations (13.73–15.31 μg/g) and LREE/HREE (5.54–6.34) and (La/Yb)n (5.03–6.65) ratios. Both types A and B oil shales are characterized b

10、ydistinctly sloping LREE trends (Lan/Smn=3.60–5.44) accompanied by flat HREE trends, with distinct Eunegative anomalies (0.51–0.69). The vertical variations of ∑REE contents are similar to those of ash, Si, Al, K,Na, Ti

11、and Fe, and show a negative correlation with organic sulfur and organic carbon, indicating that the REEcontents in oil shale seams are mainly controlled by land-derived detritus.© 2009 Elsevier B.V. All rights reser

12、ved.1. IntroductionIn China, with rapid increases in consumption of energy andchemicals, oil supply and demand imbalances are intensifying. It ispossible that oil will become a restraining factor for China'seconomic

13、growth. In 2007, China had to import about 163 million -tonnes of crude oil and approximately 179 million tonnes in 2008.The lack of appreciable oil reserves and the increase in oil pricesurge the search for alternative

14、energy sources. Oil shale, as analternative resource awaiting exploitation, has received muchattention for large reserves.Chinese oil shales were formed mainly in lacustrine environments,such as Tertiary oil shale in the

15、 Huadian (Liu et al., 2009) and Fushunareas (Qian and Wang, 2003), and Cretaceous oil shale in the Songliaobasin (Wang et al., 1996). Recently, a new marine oil shale zone wasdiscovered in the Changshe Mountain area, nor

16、thern Tibet, China(Fu et al., 2009a). This zone, combined with the oil shale zone found inthe Shengli River area (Fu et al., 2008, 2009b), represents a largemarine oil shale resource in China. Therefore, studies of the S

17、hengliRiver and Changshe Mountain oil shale zones are important forassessing petroleum prospects in the Qiangtang basin and the overallsignificance of marine oil shale researches in China.In recent years, rare earth elem

18、ents (REEs) in coal and shalehave received much attention (Rantitsch et al., 2003; Wang et al.,2008) owning to their stable geochemistry characteristics andpotential economic value. Therefore, many researchers studied RE

19、Egeochemistry of different coals and shales (Condie, 1991; Rantitschet al., 2003; Qi et al., 2007; Dai et al., 2008; Wang et al., 2008; Ketrisand Yudovich, 2009). However, little work has been done so far onthe distribut

20、ion of REEs in oil shale, especially in marine oil shale.With the aim of better understanding geochemistry of marineoil shale, this paper investigates the concentrations, modes ofoccurrence, and vertical variations of RE

21、Es in the Cretaceous marineoil shale from the Changshe Mountain area.International Journal of Coal Geology 81 (2010) 191–199? Corresponding author. Tel.: +86 28 83231651.E-mail address: fuxiugen@126.com (X. Fu).0166-5162

22、/$ – see front matter © 2009 Elsevier B.V. All rights reserved.doi:10.1016/j.coal.2009.12.006Contents lists available at ScienceDirectInternational Journal of Coal Geologyjournal homepage: www.elsevier.com/locate/ij

23、coalgeo3. Samples and analytical methodsThe studied section is located in the Changshe Mountain area, thenorthern part of the Shengli River–Changshe Mountain oil shale zone(Fig. 1b). A total of 18 samples were collected

24、from this section.Thirteen of them were collected from oil shale seams with a verticalsampling interval of 30 cm on average, and the other five sampleswere collected from micritic limestone layers. All samples werecollec

25、ted and stored in plastic bags to ensure as little contaminationand oxidation as possible.The samples for geochemical analysis were all crushed and groundto less than 200 mesh. Major element data were collected using X-r

26、ayfluorescence (XRF) on fused glass beads using a Rigaku ZSX100espectrometer in the Analytical Center, Chengdu Institute of Geologyand Mineral Resources. The analytical procedures are similar to thosedescribed by Kimura

27、(1998). The analytical uncertainty is usually<5%. REE concentrations were determined by a Perkin Elmer SciexElan 6000 inductively-coupled plasma mass spectrometer (ICP-MS)at the Guangzhou Institute of Geochemistry, Ch

28、inese Academy ofSciences, following the method of Li (1997) and Qi et al. (2007). Theanalytical precision is generally within 5%. Ash yield, shale oil and thecontent of total sulfur were conducted at the Coal Field Geolo

29、gicalBureau of Heilongjiang Province, following the Chinese standardmethods GB/T212-2001, SH/T0508-1992 and GB/T214-1996, respec-tively. Organic sulfur and total organic carbon (TOC) were determinedin the Geological Labo

30、ratory of Exploration and Development ResearchInstitute of PetroChina Southwest Oil and Gas Field Company, using achemical method according to Chinese standards GB/T215-2003 andGB/T19145-2003.4. Results and discussion4.1

31、. Oil shale characterizationThe TOC contents of thirteen oil shale samples from the ChangsheMountain area vary from 7.02% to 16.32%, whereas micritic limestonesamples contain 0.32% to 1.23% TOC (Table 1). The organic sul

32、fur (So,d)contents of oil shale and micritic limestone samples from theChangshe Mountain area varies between 0.31–0.53% and 0.24–0.27%, respectively.As shown in Table 1, the analyses confirm that the ChangsheMountain oil

33、 shale samples exhibit a high ash yield (53.22–82.12%)with low total sulfur (St,d) contents (0.67–1.52%) and intermediateshale oil contents (3.85–11.76%, air dried basis).4.2. Major element geochemistryMajor element data

34、 in conjunction with mineralogical data may beused to establish the element–mineral associations for oil shales.Although the element associations may vary from one oil shale toanother, a correlation analysis would demons

35、trate the general trends.Results of major element analysis of oil shale and micritic limestonesamples are listed in Table 1 and it shows that Si, Al, Fe and Ca are themain elements present. In the Changshe Mountain oil s

36、hale, mostmajor elements show positive correlation with ash yield at 95% con-fidence level; they are SiO2 (r=0.98), Al2O3 (r=0.97), K2O (r=0.98),Na2O (r=0.81), TiO2 (r=0.98), and Fe (r=0.73), indicating thatthese element

37、s are mainly associated with minerals.The elements Si, Al, Ti, and K are mainly associated with quartz andclay minerals. The significantly positive correlations among all theseelements (Fig. 2) demonstrate that Si, Al, K

38、 and Ti mainly originatefrom a mixed clay assemblage, which is consistent with theoccurrence of kaolinite, illite, and illite/smectite mixed layersidentified by the X-ray diffraction (XRD) analysis. The Al/Si ratio ofoil

39、 shale and micritic limestone samples is low (0.31–0.47), suggest-ing that SiO2 has another source in addition to clay minerals. Theabundant quartz identified by the XRD analysis suggests that the extraSiO2 is present in

40、 the form of quartz.Na2O contents of thirteen oil shale samples from the ChangsheMountain area vary from 0.05% and 0.35%, whereas micritic limestonesamples contain 0.033% to 0.071% Na2O (Table 1). Na2O values havehighly

41、significant correlations with values of Al2O3 (r=0.85), SiO2 (r=0.84) and K2O (r=0.85), indicating that Na mainly occurs in clayminerals rather than in porewater, which is generally regarded as asource of Na.Fe is usuall

42、y associated with pyrite in high sulfur coals, and apositive correlation between Fe and sulfur is commonly observed inmost coal measures (Shao et al., 2003). This correlation has also beenobserved in the Changshe Mountai

43、n oil shale. A high correlation(r=0.91) between Fe2O3 and total sulfur contents indicates that theproportion of Fe2O3 arising from sulfide oxidation is high and theorganic sulfur prevails low pyrite sulfur. A low correla

44、tion (r=0.34)between Fe2O3 and organic sulfur contents further supports the aboverecognition. Additionally, the results of this study also show that thereis a significant correlation between Fe2O3 and SiO2 (r=0.83), Al2O

45、3 (r=0.86), and K2O (r=0.81), indicating that iron is also present inthe clay minerals.The concentration of CaO correlates negatively (r=?0.89) withash content and shows a negligibly negative correlation with organicTabl

46、e 1Concentrations of ash, shale oil, total sulfur, organic sulfur, organic carbon and major elements in samples from the Changshe Mountain oil shale (unit in %).Sample nos. Lithology Organic carbon Shale oil Ad St,d So,d

47、 SiO2 Fe2O3 Al2O3 CaO MgO K2O Na2O TiO2 P2O5 MnOCP1–3 Micritic limestone 0.33 nd 65.67 0.66 0.26 13.52 1.64 4.15 41.93 1.21 1.03 0.048 0.2 0.049 0.017CP2–1 Oil shale 10.85 7.22 66.33 1.11 0.46 19.85 3.34 7.12 31.21 2.11

48、1.3 0.076 0.26 0.73 0.034CP2-2 Oil shale 9.11 6.34 54.63 0.67 0.35 2.39 0.88 0.67 47.22 0.75 0.14 0.11 0.03 0.56 0.029CP2-3 Oil shale 11.78 5.62 53.22 0.88 0.53 2.54 1.75 0.87 44.71 0.97 0.17 0.16 0.035 0.8 0.042CP2-4 Oi

49、l shale 9.77 4.99 55.08 0.82 0.47 2.11 1.75 0.72 45.88 0.89 0.14 0.07 0.031 0.75 0.058CP3-1 Micritic limestone 1.23 nd 56.22 0.68 0.27 5.42 1.74 1.66 43.95 1.7 0.35 0.033 0.072 0.61 0.043CP3-2 Micritic limestone 0.45 nd

50、63.10 0.47 0.24 8.24 0.77 2.24 46.58 1.1 0.52 0.035 0.1 0.032 0.019CP4-1 Oil shale 15.78 11.23 60.55 1.1 0.46 17.25 2.98 5.37 28.88 3.42 1.08 0.046 0.23 0.3 0.039CP4-2 Oil shale 16.32 11.45 63.42 1.3 0.43 19.36 2.75 6.31

51、 27.13 3.57 1.31 0.055 0.27 0.49 0.048CP4-3 Oil shale 15.89 11.76 56.33 1.52 0.49 9.55 4.04 3.98 33.34 1.33 0.51 0.05 0.13 0.8 0.071CP5-1 Micritic limestone 0.32 nd 62.44 0.51 0.26 8.75 0.96 2.88 46.36 1.05 0.66 0.037 0.

52、11 0.033 0.023CP6-1 Micritic limestone 0.45 nd 66.13 0.62 0.25 15.87 1.66 5.15 39.73 1.35 1.27 0.071 0.26 0.15 0.037CP7-1 Oil shale 10.02 6.4 82.12 1.5 0.42 44.51 5.56 15.92 9.1 1.42 3.54 0.33 0.79 0.54 0.033CP7-2 Oil sh

53、ale 7.02 3.85 80.54 1.44 0.36 40.8 3.4 14.04 15.5 1.27 3.05 0.34 0.7 0.17 0.027CP7-3 Oil shale 8.79 4.4 81.24 1.19 0.34 43.78 4.07 14.8 11.94 1.27 3.33 0.35 0.73 0.24 0.026CP7-4 Oil shale 9.82 5.52 81.09 1.26 0.33 43.57

54、4.49 15.29 11.23 1.25 3.56 0.2 0.76 0.27 0.028CP7-5 Oil shale 8.12 4.9 79.45 1.24 0.35 38.24 4.01 13.21 16.61 1.14 3.14 0.26 0.66 0.35 0.034CP7-6 Oil shale 7.88 4.76 77.54 1.12 0.31 34.8 3.86 11.92 20.02 1.08 2.75 0.23 0