Geochemical characteristics of the Late Permian

Arab J Geosci (2017) 10:98 DOI 10.1007/s12517-017-2916-1

ORIGINAL PAPER

Geochemical characteristics of the Late Permian coals from the Yueliangtian Coalfield, western Guizhou, southwestern China Panpan Xie 1,2 & Siyu Zhang 1,2 & Zhen Wang 1,2 & Lei Wang 1,2 & Yaguang Xu 1,2

Received: 17 October 2016 / Accepted: 15 February 2017 # Saudi Society for Geosciences 2017

Abstract This paper investigated geochemical characteristics of the Late Permian No. 6 upper (YLT6U) and No. 6 lower (YLT6L) coals from the Yueliangtian Coalfield, Guizhou, southwestern (SW) China, using x-ray fluorescence spectrometry, inductively coupled plasma mass spectrometry, field emissionscanning electron microscopy plus an energy-dispersive x-ray spectrometry, and optical microscopy. The YLT6U coal is slightly enriched in Se and W. The YLT6L coal is enriched in elements Hg, As, Tl, Co, Cu, Se, Mo, and Cd. Different with other Late Permian coals from SW China, the Yueliangtian coals are depleted in Sc, V, Cr, Ni, and Zn. The enrichment patterns of rare earth elements and yttrium (REY, or REE if Y is not included) in the benches of the Yueliangtian coal are characterized by heavy-REY enrichment and, to a lesser extent, light- and medium-enrichment types. Germanium in the YLT6U coal is mainly organic-associated and relatively enriched in the middle portion of the coal seam. It is due to Ge adsorption by organic matter during the input of Ge-rich solution into peat swamp of the YLT6U coal. Boron in the Yueliangtian coal mainly occurs in clay minerals and is derived from terrigenous materials rather than marine influence. Owing to the parting leaching by circulated hydrothermal solutions, the Nb/Ta, U/Th, Yb/La, and Zr/ Hf ratios are higher in the coal benches relative to their corresponding overlying partings. The parent rocks of the sedimentsource region for the Yueliangtian coal are not only the mafic

* Panpan Xie [email protected]

1

State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology, Beijing, China

2

College of Geoscience and Surveying Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China

basalts but also the felsic-intermediate rocks in the upper portion of the Kangdian Upland. Keywords Coal geochemistry . Sediment-source region . Hydrothermal solutions . Seawater influence . Late Permian coal . Southwestern China

Introduction Trace elements in coal have significant impacts on practical application, environment issues, and human health (Dai et al. 2012a; Saha et al. 2016; Misch et al. 2016). Some elements in coal deposits, e.g., rare earth elements and yttrium (REY) (Seredin and Dai 2012; Hower and Dai 2016), Nb(Ta)– Zr(Hf) (Dai et al. 2010, 2011, 2017), Ga, Al (Dai et al. 2012b), Ge (Dai et al. 2014a, 2015a), U (Seredin and Finkelman 2008; Hower et al. 2016a), Se, and V (Dai et al. 2017, 2015b), as well as Au and platinum group elements (Seredin and Finkelman 2008; Seredin and Dai 2014) could be highly enriched and thus could be served as valuable byproducts. The emission of toxic elements from coal combustion could also cause environment hazards and endemic diseases, such as the endemic arsenosis (Ding et al. 2001) and fluorosis in Guizhou of China (Dai et al. 2004, 2007), lung cancer in Yunnan of China (Dai et al. 2008; Tian 2005; Tian et al. 2008), and Balkan endemic nephropathy in Bosnia (Finkelman et al. 2002). Apart from these, contents, distribution, modes of occurrence, and origins of trace elements can serve as useful indicators for understanding the depositional environment of the coal deposit and regional geological evolution (Dai et al. 2012a). Hence, it is important to investigate trace elements in the coal both practically and academically. Geochemical and mineralogical characteristics of the Late Permian coals in SW China have attracted much attention (Dai

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Arab J Geosci (2017) 10:98

et al. 2005a; Li et al. 2014b; Luo and Zheng 2016; Wang 2016; Wang et al. 2012, 2015, 2016; Xie et al. 2016; Zhuang et al. 2000, 2003, 2012; Zhou and Ren 1992; Zhou et al. 1994; Zou et al. 2016; Zhao et al. 2016b). Previous studies (Dai et al. 2005a; Xie et al. 2016; Wang et al. 2012, 2015; Wang et al. 2016) have shown that the Kangdian Upland is the dominant sediment-source region for the coals in SW China, and the relevant coals are enriched in transition elements (e.g., V, Cr, Co, Ni) which are enriched in the basalts in the upland. The Late Permian coals in the Yueliangtian Coalfield, Guizhou, have been reported to have the same sediment-source region (Xie et al. 2016; Wang et al. 2016) as those of other Late Permian coals in SW China, and thus they would be expected to be enriched in these elements; however, coals from the Yueliangtian Coalfield are depleted in transition elements as revealed in this study. The mineralogical compositions’ characteristics of the Yueliangtian coals have been described by some studies (Xie et al. 2016; Wang et al. 2016), but the geochemistry of these coals have rarely been investigated. This paper investigated the factors responsible for these unique geochemical anomalies.

has been reported to provide terrigenous materials during coal deposition in the Late Permian period (Fig. 1a) (Coal Geology Bureau of China 1996; Zhuang et al. 2000; Zhao et al. 2016b). The sedimentary sequences in the Yueliangtian Coalfield include Late Permian Emeishan Basalt Formation, Late Permian Longtan Formation, and Early Triassic Feixianguan Formation (Fig. 1b). The upper and lower portions of the Emeishan Basalt Formation (300 m on average in thickness) mainly comprise tuffs and basalts, respectively (Xie et al. 2016). The Early Triassic Feixianguan Formation, dominated by silty sandstone and mudstone, varies from 558 to 578 m in thickness. The Longtan Formation (234.66 m on average) is the major coal-bearing sequence in the Yueliangtian Coalfield, and it consists mainly of siltstone, fine sandstone, mudstone, and 30 coal seams, along with minor fossils, siderite layers, and bauxite (Fig. 1b). The Late Permian No. 6 upper (YLT6U) and lower (YLT6L) coal seams, separated by siltstone and siderite layers, are located in the upper portion of the Longtan Formation (Fig. 1b) (Xie et al. 2016).

Geological setting

Samples and analysis methods

The Yueliangtian Coalfield is located in Guizhou Province, SW China (Fig. 1a). Guizhou is situated in the west margin of Yangzi platform (Ding et al. 2001), which changed from a continental terrain period in the Early Permian to epicontinental sea basin in the Late Permian due to the Dongwu stage (Coal Geology Bureau of China 1996; Zhuang et al. 2000). The Kangdian Upland in western Yangzi platform

A series of 19 bituminous coal and non-coal samples of the YLT6U and YLT6L coals were collected from the working face of the Yueliangtian Coalfield (Fig. 1c) (Xie et al. 2016). Each coal bench sample was cut over a volume of 10-cm wide, 10-cm deep, and 7.5–30-cm high. The floor of the YLT6U coal and the roof of YLT6L coal could not be accessed due to the complex sampling condition.

Fig. 1 Paleogeographical map (a) (Dai et al. 2015b), sedimentary sequences (b), and coal-seam sections (c) of the Yueliangtian Coalfield


Mineralogy of samples was determined in coal briquette by optical microscopy and field emission-scanning electron microscopy (FE-SEM) plus energy-dispersive x-ray spectrometry (EDAX) (Dai et al. 2017). X-ray fluorescence spectrometry (XRF) was used to determine the major-element oxide for each sample ash. Prior to the XRF analysis, each raw sample was ashed in the muffle furnace (815 °C, 4 h). As outlined by Dai et al. (2011, 2015d), inductively coupled plasma mass spectrometry (ICP-MS) was used to determine the trace element contents in raw coal and non-coal samples, except for Hg and F. Prior to ICP-MS analysis, the prepared samples were digested using an UltraClave Microwave High Pressure Reactor. In order to avoid disturbance of polyatomic ions, arsenic and Se were determined by ICP-MS plus collision cell technology (ICP-CCT-MS) (Li et al. 2014a). An additional 0.5 ml H3PO4 was used in the digestion process for B determination (Dai et al. 2014b). A DMA-80 Hg analyzer was used to determine Hg content in each ~0.1-g sample. Fluorine was determined by pyrohydrolysis in conjunction with an ion-selective electrode (ASTM Standard D5987-96 2002).

Results Major-element oxides Compared with the average values for Chinese coals (Dai et al. 2012a), oxides including MgO, SiO2, CaO, and MnO are enriched in the YLT6U coal (Table 1); oxides Fe2O3, SiO 2, CaO, and MnO are enriched in the YLT6L coal (Table 2). The remaining major-element oxides, including Na2O, Al2O3, P2O5, K2O, and TiO2, are at lower concentrations compared with average values for Chinese coals. Except for sample YLT6U-2p, the host rocks (roof and floor strata) and partings within the Yueliangtian coal are enriched in TiO2, Fe2O3, and Al2O3, but depleted in Na2O, as compared with the average values for world clays (Tables 1 and 2) (Grigoriev 2009). As listed in Table 1, percentages of major-element oxides in the partings are significantly higher than those of the YLT6U coals, with the exceptions of MnO and CaO, which are lower in the parting samples. In the YLT6L coal (Table 2), the assemblage coupled with Fe2O3 is also lower in the partings. The relatively lower CaO in the partings is attributable to the exiguity of calcite contents [calcite contents of average for parting sample (Pa) and weighted average for bench sample (Wa)—YLT6U-Pa, 3.1%; YLT6U-Wa, 34.2%; YLT6L-Pa, 1.2%; YLT6L-Wa, 10.8%; data are given by Xie et al. 2016). The respective weighted average values for SiO2/Al2O3 in the YLT6U (2.89) and YLT6L (6.83) coals are much higher than those of the ubiquitous Chinese coal (1.42) (Dai et al. 2012a), consistent with the high quartz (Fig. 2a) percentages

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in the coal (Xie et al. 2016). The TiO2 is positively correlated to ash yield, SiO2, Al2O3, and K2O (YLT6U—rTiO2-ash = 0.74, r TiO2-SiO2 = 0.67, r TiO2-Al2O3 = 0.70, r TiO2-K2O = 0.77; YLT6L—r Ti O 2 - a s h = 0.96, r Ti O 2 - S i O 2 = 0.83, r Ti O 2 Al2O3 = 0.99, rTiO2-K2O = 0.98), suggesting that TiO2 mainly occurs in the anatase (Fig. 2b) and clay minerals, particularly kaolinite (Fig. 2b). The highly elevated Fe2O3 in the YLT6L coal mainly occurs in the pyrite (Fig. 2c) and, to a lesser extent, chlorite (Fig. 2d). Trace elements The concentrations of trace element in the Yueliangtian coal samples, in comparison with average values for world hard coal (Ketris and Yudovich 2009), are listed in Tables 1 and 2, and Fig. 3. The YLT6U and YLT6L coals present different trace element abundances. Compared to average values for world hard coal (Ketris and Yudovich 2009) and based on the enrichment classification of trace elements in coal by Dai et al. (2015b), elements Se and W are slightly enriched in the YLT6U coal (CC, the ratio of trace element concentration in coal samples investigated versus average values for world hard coals; 2 < CC < 5); many other elements, e.g., F, B, Cr, Zn, As, Rb, Mo, Cd, Sb, Cs, Ba, Hg, Tl, and Bi, are depleted (CC < 0.5). The remaining elements are close to the average values for world hard coals (0.5 < CC < 2). Mercury in the YLT6L coal is significantly enriched (10 < CC < 100); elements As and Tl are enriched (5 < CC < 10); elements Co, Cu, Se, Mo, and Cd are slightly enriched (2 < CC < 5); and other remaining elements are either close to or depleted compared to the world hard coals. Except for elements As, Se, Mo, Hg, and Tl in the YLT6L coals, the remaining element contents in the partings are either higher or close to those of the coal samples (Tables 1 and 2, Fig. 3). Germanium in coal is ubiquitously associated with organic matter (Finkelman 1982; Dai et al. 2012c, 2015a; Zhuang et al. 2006; Du et al. 2004, 2009), although traces of scheelite (CaWO4) were detected in coal (Zhuang et al. 2006). The inverse vertical variations between Ge and ash yield (Fig. 4) as well as the correlation coefficient of Ge-Ash yield (0.12) in the YLT6U coal suggest that Ge is mainly organic associated. As shown in the vertical distribution variation (Fig. 4a), the Ge is relatively enriched in the middle portion of the YLT6U coal seam, which deviates significantly from the BZilbermints Law^ (Yudovich 2003) with the Ge concentrated near the roof, floor, and partings of the coal seam. Thus, the above data may indicate that the organic matters adsorbed germanium in the Ge-rich solutions during the period of peatification in the YLT6U coal. The vertical distribution of Ge and thickness (Fig. 4a) also suggest that the thinner a coal bench is, the higher its Ge content (Yudovich 2003). The germanium in the YLT6L coal, however, presents inconspicuous vertical variation.

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Table 1 Concentration of trace elements (μg/g), percentages of major-element oxides (%), loss on ignition (LOI, %), and thickness (cm) in the YLT6U coal from the Yueliangtian Coalfield (on a whole coal basis) Sample

YLT6U-r

YLT6U-1

YLT6U-2p

YLT6U-3u

YLT6U-3 l

YLT6U-4u

YLT6U-4 l

YLT6U-5u

Thickness SiO2 TiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O P2O5 LOI SiO2/Al2O3 Al2O3/TiO2 Li Be F B Sc V Cr Co Ni Cu Zn Ga Ge As Se Rb Sr Y Zr Nb Mo Cd In Sn Sb Cs Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta W Hgc Tl Pb

44.03 3.85 18.06 12.96 0.265 2.39 1.97 0.22 2.41 0.307 13.4 2.44 4.69 15.29 3.02 551.69 13.29 27.8 339.72 126.28 44.01 106.2 188.12 145.26 32.71 1.37 1.24 1.7 73.26 300.07 53.57 544.75 54.93 1.03 0.79 0.12 3.79 0.24 2.11 385.85 77.18 171.36 19.38 75.57 14 3.66 14.15 2.04 11.54 2.23 6.03 0.77 5.02 0.73 13.93 3.14 10.38 15.48 0.13 9.62

20 20.6 0.13 4.19 4.19 0.138 0.85 5.77 0.01 0.08 0.025 63.58 4.91 32.75 6.35 0.82 57.14 1.67 3.56 45.81 5.05 8.25 35.81 12.66 12.58 5.98 0.95 4.91 4.32 2.79 171.13 13.51 80.39 2.9 0.61 0.12 0.04 1.91 0.16 0.55 50.64 31.89 53.19 5.47 20.99 3.87 0.69 3.45 0.45 2.53 0.47 1.49 0.21 1.51 0.21 2.19 0.15 1.46 47.55 0.04 14.45

42.9 0.25 27.88 1.52 0.018 0.67 2.74 0.14 1.51 0.016 22.25 1.54 112.42 39.17 4.18 194.05 13.97 5.73 4.74 11.2 3.13 19.95 7.34 10.96 37.92 2.81 1.42 13.8 21.77 142.34 24.92 180.62 25.24 1.71 0.25 0.15 11.19 0.44 1.18 230.55 23.61 39.03 5.23 19.31 4.2 0.57 4.83 0.85 5.49 1.11 3.2 0.47 3.25 0.47 9.63 2.05 2.21 20.18 0.06 64.96

12.5 25.62 0.21 11.57 1.66 0.009 0.5 1.57 0.08 0.34 0.026 58.25 2.21 54.24 10.69 1.89 75.07 6.5 3.55 13.33 5.19 6.14 37.76 7.8 9.06 12.61 1.72 0.28 9.49 7.18 110.35 22.4 159.01 13.14 1.27 0.21 0.07 3.98 0.47 0.46 110.05 54.95 127.39 12.48 46.75 9.1 0.99 8.5 1 4.9 0.83 2.45 0.36 2.47 0.35 3.42 0.56 8.27 10.81 0.01 36.19

12.5 11.74 0.1 3.14 1.34 0.022 0.31 1.54 0.02 0.05 0.006 81.42 3.74 30.94 10.44 1.42 16.87 1.77 2.24 11.24 6.1 12.07 22.87 11.83 2.19 4.33 2.07 bdl 2.93 1.2 52.9 11.18 28.83 1.89 0.41 0.04 0.02 0.78 0.6 0.07 25.56 4.95 12.28 1.46 5.98 1.37 0.23 1.5 0.26 1.68 0.35 1.13 0.16 1.13 0.16 0.74 0.17 0.55 7.42 0 5.38

7.5 25.97 0.16 5.44 1.23 0.005 0.3 0.46 0.04 0.12 0.018 66.16 4.78 33.16 20.61 1.23 20.39 3.23 3.82 16.15 8.98 7.07 31.66 7 2.97 5.66 1.41 bdl 5.62 2.71 40.03 19.74 106.24 10.74 0.35 0.13 0.03 1.77 0.39 0.18 50.32 39.74 88.22 9.53 36.88 7.78 0.87 7.08 0.88 4.28 0.75 2.22 0.32 2.32 0.32 1.89 0.46 22.57 4.86 0.01 16.35

7.5 6.85 0.11 2.51 0.48 0.007 0.13 0.52 0.02 0.04 0.006 89.14 2.73 22.83 9.99 1.13 8.48 0.71 2.14 15.67 7.36 11.88 16.31 18.43 1.91 3.48 3.43 bdl 2.71 1.24 25.84 6.11 30.27 1.71 0.57 0.05 0.02 0.84 0.42 0.07 20.15 2.02 4.58 0.5 2.04 0.58 0.13 0.75 0.14 0.96 0.2 0.62 0.09 0.58 0.09 0.79 0.11 0.46 12.44 0 3.68

9 6.59 0.12 2.5 0.43 0.067 0.13 5.53 0.02 0.04 0.009 84.11 2.63 20.45 6.99 0.85 41.05 0.74 2.56 21.14 7.42 9.64 10.36 18.98 6.8 2.53 2.79 bdl 3.53 1.22 137.95 9.13 21.79 1.53 0.58 0.07 0.02 0.77 0.25 0.07 27.9 3 6.15 0.66 2.77 0.78 0.18 1.2 0.23 1.46 0.27 0.83 0.11 0.76 0.1 0.62 0.13 0.42 13.08 0.01 4


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Table 1 (continued) Sample

YLT6U-r

YLT6U-1

YLT6U-2p

YLT6U-3u

YLT6U-3 l

YLT6U-4u

YLT6U-4 l

YLT6U-5u

Bi Th U δCe δEu ∑REY ∑REOd

0.23 15.45 3.11 1.01 1.19 457.23 635.03

0.37 6.32 1.27 0.91 0.87 139.94 461.71

1.07 54.91 5.66 0.8 0.57 136.56 211.25

0.66 15.56 6.51 1.11 0.52 294.92 849.55

0.2 2.28 0.68 1.03 0.73 43.85 285.39

0.29 5.97 4.22 1.03 0.54 220.94 784.5

0.15 1.87 0.63 1.04 0.87 19.4 216.5

0.33 1.36 0.63 0.99 0.83 27.64 210.93

Sample

YLT6U-5 l

YLT6U-6

YLT6U-7

YLT6U-8

YLT6U-9p

YLT6U-Pa

YLT6U-Wa

Thickness

9

19

19

24

SiO2 TiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O P2O5 LOI SiO2/Al2O3 Al2O3/TiO2 Li Be F B Sc

2.76 0.05 1.64 0.6 0.057 0.16 4.63 0.01 0.01 0.009 89.49 1.68 36.2 3.08 0.87 23.33 2.94 0.94

4.45 0.05 2 0.63 0.138 0.2 10.7 0.01 0.04 0.027 81.05 2.23 37.44 4.37 0.73 30 1.16 0.98

6.85 0.1 4.49 2.07 0.102 0.4 9.25 0.01 0.04 0.012 73.28 1.53 45.39 9.74 0.76 22.23 2.27 4.55

4.94 0.07 1.92 0.36 0.016 0.07 1.74 0.02 0.03 0.005 90.01 2.57 28.56 5.03 1.46 9.86 0.89 1.59

42.84 6.56 27.48 2.83 0.003 1.35 0.52 0.15 1.64 0.097 16.46 1.56 4.19 40.11 3.32 209.98 18.11 30.55

42.87 3.41 27.68 2.18 0.01 1.01 1.63 0.15 1.58 0.06 19.36 1.55 58.31 39.64 3.75 202.02 16.04 18.14

V Cr Co Ni Cu Zn Ga Ge As Se Rb Sr Y Zr Nb Mo Cd In Sn

13.61 3.29 9.71 13.09 13.37 2.52 3.8 3.73 bdl 2.57 0.29 111.33 3.91 10.21 0.94 0.93 0.03 0.01 0.57

17.6 4.27 8.72 11.51 12.75 2.95 2.38 1.72 bdl 2.09 1 292.34 5.94 15.3 0.88 0.51 0.05 0.01 0.39

141.49 11.45 5.64 11.14 34.36 5.65 3.86 1.41 3.74 3.27 1.4 268.31 7.61 35.75 1.97 1.16 0.11 0.02 0.71

84.31 6.24 10.66 13.32 33.87 1.77 2.5 1.27 0.38 2.87 1.42 58.15 9.14 14.51 0.58 2 0.09 0.03 0.34

564.96 159.77 13.2 30.29 300.04 134.22 50.95 4.38 0.98 1.35 27.84 352.49 73.38 926.12 109.79 0.74 1.24 0.2 6.82

284.85 85.49 8.17 25.12 153.69 72.59 44.44 3.60 1.20 7.58 24.81 247.42 49.15 553.37 67.52 1.23 0.75 0.18 9.01

48.72 6.5 8.84 19.96 19.2 5.13 4.54 1.8 1.26 3.78 2.02 144.63 10.56 47.04 3.07 0.95 0.09 0.03 1.13

Sb Cs

0.32 0.02

0.17 0.08

0.17 0.13

0.18 0.09

0.14 2.12

0.29 1.65

0.27 0.19

11.02 0.1 3.81 1.45 0.066 0.33 4.81 0.02 0.07 0.015 77.41 2.89 36.66 7.86 1.1 30.83 2.04 2.59

Worldb

8.47a 0.33a 5.98a 4.85a 0.015a 0.22a 1.23a 0.16a 0.19a 0.092a nd 1.42a 18.12a 14 2 82 47 3.7 28 17 6 17 16 28 6 2.4 9 1.6 18 100 8.2 36 4 2.1 0.2 0.04 1.4 1 1.1

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Table 1 (continued) Sample

YLT6U-5 l

YLT6U-6

YLT6U-7

Ba La Ce

17.2 0.78 1.71

31.73 11.12 20.96

38.52 4.72 14.25

Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta W Hgc

0.19 0.93 0.36 0.09 0.54 0.1 0.64 0.13 0.38 0.05 0.37 0.05 0.32 0.03 0.18

2.11 7.65 1.13 0.2 1.24 0.16 0.87 0.17 0.51 0.07 0.49 0.07 0.44 0.02 10.47

Tl Pb

7.55 0 1.86

Bi Th U δCe δEu ∑REY ∑REOd

0.13 0.58 0.37 1.01 0.89 10.23 118.12

YLT6U-8

YLT6U-Wa

Worldb

YLT6U-9p

YLT6U-Pa

26.71 2.81 7.04

358.66 78.34 232.59

294.61 50.98 135.81

40.13 15.02 31.53

150 11 23

1.27 5.39 1.53 0.37 1.73 0.26 1.43 0.25 0.68 0.09 0.59 0.08 0.96 0.1 0.55

0.9 3.66 0.97 0.29 1.17 0.25 1.44 0.33 0.95 0.17 0.89 0.15 0.45 0.07 0.39

20.89 83.17 15.83 5.92 15.94 3.09 11.96 3.05 7.73 0.99 6.21 0.86 23.04 3.09 4.57

13.06 51.24 10.02 3.25 10.39 1.97 8.73 2.08 5.47 0.73 4.73 0.67 16.34 2.57 3.39

3.23 12.43 2.54 0.41 2.52 0.35 1.92 0.36 1.09 0.16 1.06 0.15 1.16 0.16 3.83

3.4 12 2.2 0.43 2.7 0.31 2.1 0.57 1 0.3 1 0.2 1.2 0.3 0.99

7.56 0 2.08

128.48 0.21 3.68

23 0.05 0.85

54.75 0.23 6.7

37.47 0.15 35.83

33.08 0.05 8.15

100 0.584 9

0.08 1.28 0.29 0.98 0.75 52.7 334.88

0.1 1.95 0.9 1.33 1.05 40.24 181.84

0.24 2.95 0.38 1 1.22 30.15 365.28

0.2 23.27 5.27 1.31 1.71 559.95 808.56

0.64 39.09 5.47 1.06 1.14 348.26 509.91

0.25 3.98 1.37 1.05 0.89 83.33 374.82

1.1 3.2 1.9

δCe = CeN/[0.5 × (LaN + PrN)]; δEu = EuN/[0.5 × (SmN + GdN)]. CeN is the ratio of Ce concentration in the investigated sample versus the Ce value in the upper continental crust (UCC; Taylor and McLennan 1985). Ditto that for LaN, PrN, EuN, SmN, and GdN (Dai et al. 2016a). LOI loss on ignition, nd no data, bdl below the detection limit, Pa average for parting sample, Wa weighted average for bench sample (weighted by thickness of sample interval), thickness data from Xie et al. (2016) a

Major-element oxides in Chinese coals, data from Dai et al. (2012a)

b

World coal data from Ketris and Yudovich (2009)

c

The unit for Hg is nanograms per gram

d

On ash basis

The elevated concentration of Boron in coal can be ascribed to marine influence (Goodarzi and Swaine 1994). It was also derived from hydrothermal fluids (Lyons et al. 1989; Dai et al. 2012c, 2015a); the B from Ge-rich and lowGe coals from Shengli Coalfield in northern China, for instance, was caused by acid waters (Dai et al. 2012c, 2015a). The enrichment of B in coal was also caused by volcanic activity (Bouška and Pešek 1983; Karayigit et al. 2000) and climate change (Bouška and Pešek 1983). Although the YLT6L coal rather than the YLT6U coal was invaded by seawater (Xie et al. 2016), the weighted average for the B content in the former (0.87 μg/g) is lower than the latter (2.04 μg/g).

The marine influence, thus, had little impact on the B contents in the Yueliangtian coal. Previous studies (Dai et al. 2015b; Finkelman 1982) have suggested that B derived from sediment-source region in the coal may occur in clay minerals (e.g., illite, mixed-layer illite/ smectite). The respective correlation coefficient of B-Ash yield for the YLT6U and YLT6L coals are 0.95 and 0.93. Except for samples YLT6U-5u, 5l, and 6, the vertical distribution in the studied coals of B content bears a strong resemblance to that of ash yield (Fig. 4), suggesting that element B mainly occurs in inorganics. In addition, the relations of B to ash yield, B to K2O, and B to MgO for the YLT6U and


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Table 2 Concentration of trace elements (μg/g), percentages of major-element oxides (%), loss on ignition (LOI, %), and thickness (cm) in the YLT6L coal from the Yueliangtian Coalfield (on a whole coal basis) Sample

YLT6L-1

YLT6L-2

YLT6L-3p

YLT6L-4p

YLT6L-5

YLT6L-f

YLT6L-Pa

YLT6L-Wa

Worldb

Thickness SiO2 TiO2 Al2O3

20 7.74 0.48 4.22

21 9.43 0.04 1.13

33.88 1.49 9.56

39.58 6.22 23.12

30 24.9 0.06 1.77

44.02 5.91 21.47

36.73 3.855 16.34

15.49 0.17 2.27

8.47a 0.33a 5.98a

Fe2O3 MnO MgO CaO Na2O K2O P2O5 LOI SiO2/Al2O3 Al2O3/TiO2 Li Be F B Sc V Cr Co

26.61 0.021 0.25 0.47 0.01 0.12 0.059 59.76 1.83 8.79 5.57 0.5 70.55 0.18 3.88 65.27 21.08 19.25

12.33 0.035 0.1 2.57 0.02 0.02 0.006 72.52 8.37 32.16 3.98 0.83 5.5 2 7.33 32.62 6.25 20.1

11.75 0.008 1.03 0.64 0.11 0.5 0.034 40.6 3.54 6.44 10.2 1.25 52.89 3.47 13.46 162.42 65.39 42

8.77 0.018 1.69 0.63 0.3 1.71 0.174 17.63 1.71 3.72 31.18 3.43 371.05 15.31 37.13 554.51 196.12 77.08

5.74 0.026 0.25 2.22 0.01 0.06 0.008 63.79 14.09 31.63 3.99 1.26 14.45 0.53 2.24 30.83 6.42 7.88

6.78 0.079 1.92 3.25 0.31 2.23 0.516 13.21 2.05 3.63 20.66 2.8 122.26 14.6 30.22 438.5 294.36 49.28

10.26 0.013 1.36 0.635 0.205 1.105 0.104 29.115 2.625 5.08 20.69 2.34 211.97 9.39 25.295 358.465 130.755 59.54

13.57 0.027 0.21 1.83 0.01 0.07 0.022 65.24 6.83 13.4 4.43 0.92 27.6 0.87 4.21 41.06 10.5 14.7

4.85a 0.015a 0.22a 1.23a 0.16a 0.19a 0.092a nd 1.42a 18.12a 14 2 82 47 3.7 28 17 6

Ni Cu Zn Ga Ge As Se Rb Sr Y Zr Nb Mo Cd In Sn Sb Cs Ba

26.49 76.37 46.15 5.38 2.9 129.82 11.09 4.76 42.6 10.04 76.41 7.56 29.69 1.42 0.04 1.12 0.81 0.27 122.77

19.36 16.83 8.57 2.45 1.23 4.56 6.67 1.73 137.6 12.59 8.11 0.48 3.95 0.21 0.01 0.34 0.18 0.12 327.62

80.03 143.88 45.36 13.24 1.96 5.64 4.95 13.13 125.37 24.84 199.7 17.53 1.76 0.36 0.06 1.51 0.32 0.76 277.71

194.28 316.74 277.44 42.51 2.25 4.26 2.21 52.6 374.63 60.81 765.71 80.29 6.09 1.28 0.21 5.81 0.36 2.23 358.38

17.76 16.78 5.44 2.66 0.83 33.36 5.02 2.69 72.45 14.85 16.55 4.76 2.04 0.1 0.01 0.46 0.81 0.78 97.52

80.68 220.09 249.91 37.36 1.68 1.82 1.34 70.77 422.34 48.84 565.9 66.33 1.84 0.92 0.17 4.58 0.17 2.2 597.1

137.155 230.31 161.4 27.875 2.105 4.95 3.58 32.865 250 42.825 482.705 48.91 3.925 0.82 0.135 3.66 0.34 1.495 318.045

20.69 33.58 17.83 3.36 1.53 52.01 7.22 2.99 83.31 12.82 30.92 4.28 10.39 0.51 0.02 0.61 0.62 0.44 172.69

17 16 28 6 2.4 9 1.6 18 100 8.2 36 4 2.1 0.2 0.04 1.4 1 1.1 150

La Ce Pr Nd Sm Eu Gd

18.07 40.33 4.68 20.27 4.16 1.11 4.28

6.23 14.49 1.72 7.11 1.67 0.47 1.87

68.84 168.53 20.01 85.13 16.69 4.34 14.53

101.72 257.19 35.05 141.8 25.99 6.8 26.11

11.62 25.27 2.9 11.8 2.62 0.46 2.88

70.16 152.96 19.11 79.61 16.69 4.87 16.65

85.28 212.86 27.53 113.465 21.34 5.57 20.32

11.84 26.32 3.05 12.8 2.77 0.64 2.98

11 23 3.4 12 2.2 0.43 2.7

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Table 2 (continued) Sample Tb Dy Ho Er Tm Yb Lu Hf Ta W Hgc Tl Pb Bi Th U δCe δEu ∑REY ∑REOd

YLT6L-1 0.5 2.32 0.37 0.99 0.13 0.82 0.12 2.01 0.54 1.83 4589.29 8.81 3.4 0.12 2.83 4.49 1 1.2 108.2 322.7

YLT6L-2 0.31 1.95 0.38 1.15 0.17 1.08 0.15 0.25 0.07 bdl 1580.17 2 1.2 0.07 1.5 0.51 1.01 1.2 51.34 225.85

YLT6L-3p

YLT6L-4p

1.53 6.53 1.11

2.27 17.77 2.37

2.76 0.35 2.33 0.33 4.86 1.02 3.18 627.29 0.4 8.87 0.04 6.27 1.95 1.03 1.28 417.86 843.54

6.29 0.8 5.13 0.73 19.41 4.6 3.76 232.97 0.29 18.52 0.08 16.52 4.6 0.97 1.2 690.82 1006.25

YLT6L-5 0.43 2.44 0.46 1.44 0.21 1.45 0.21 0.55 0.48 bdl 407.64 0.36 10.89 0.07 1.74 0.58 0.99 0.76 79.03 263.16

YLT6L-f

YLT6L-Pa

2.21 11.22 2.03

1.9 12.15 1.74

5.26 0.67 4.24 0.61 14.48 3.76 2.14 17.48 0.14 16.34 0.02 14.63 3.33 0.95 1.34 435.14 601.98

4.525 0.575 3.73 0.53 12.135 2.81 3.47 430.13 0.345 13.695 0.06 11.395 3.275 1 1.24 554.34 924.895

YLT6L-Wa 0.41 2.26 0.41 1.23 0.18 1.16 0.17 0.87 0.37 0.52 1932.38 3.23 5.92 0.08 1.97 1.66 1 1.02 79.06 268.89

Worldb 0.31 2.1 0.57 1 0.3 1 0.2 1.2 0.3 0.99 100 0.584 9 1.1 3.2 1.9

δCe = CeN/[0.5 × (LaN + PrN)]; δEu = EuN/[0.5 × (SmN + GdN)]. CeN is the ratio of Ce concentration in the investigated sample versus the Ce value in the upper continental crust (UCC; Taylor and McLennan 1985). Ditto that for LaN, PrN, EuN, SmN, and GdN (Dai et al. 2016a) LOI loss on ignition, nd no data, bdl below the detection limit, Pa average for parting sample, Wa weighted average for bench sample (weighted by thickness of sample interval), thickness data from Xie et al. (2016) a

Major-element oxides in Chinese coals, data from Dai et al. (2012a)

b

World coal data from Ketris and Yudovich (2009)

c

The unit for Hg is nanograms per gram

d

On ash basis

YLT6L coals are listed in Fig. 5. The B in the Yueliangtian coal is positively correlated with ash yield, K2O, and MgO, suggesting that the B in the Yueliangtian coal mainly occurs in illite and mixed-layer illite/smectite. Thus, the low concentrations of B in the Yueliangtian coal are thought to be derived from terrigenous materials.

Rare earth elements and yttrium (REY) The nomenclature of rare earth elements and Y used in the present study is based on the Seredin-Dai’s classification, which divides REY into light (L-REY—La, Ce, Pr, Nd, and Sm), medium (M-REY—Eu, Gd, Tb, Dy, and Y), and heavy (H-REY—Ho, Er, Tm, Yb, and Lu) groups (Seredin and Dai 2012).The REY are normalized to upper continental crust (UCC; Taylor and McLennan 1985) to show REY enrichment types, including light REY (L), medium REY (M), and heavy REY (H) types (Seredin and Dai 2012), as well as anomalies for Ce, Eu, and Y (Dai et al. 2016a).

As listed in Tables 1 and 2, the weighted average REY contents for the YLT6U and YLT6L coals are 83.33 and 79.06 μg/g, respectively, slightly higher than that for world hard coals (68.6 μg/g) (Ketris and Yudovich 2009). Samples YLT6U-9p, YLT6L-3p, YLT6L-4p, and YLT6U-3u contain REY oxides (∑REO) above 800 μg/g (ash basis). Florencite was observed in sample YLT6U-9p by scanning electron microscopy plus energy-dispersive x-ray spectrometry (SEMEDS) (Fig. 2b) and is ascribed to the high REY contents. Relative to the UCC (Taylor and McLennan 1985), the REY in the Yueliangtian coal benches are mainly characterized by an H-type enrichment (Fig. 6) and, to a lesser extent, L-type and L- and M-type enrichments (Fig. 6). Samples YLT6U-3u and YLT6U-4u are characterized by distinctly negative Eu and positive Ce anomalies (Fig. 6a). The partings within the Yueliangtian coals exhibit similar M-REY distribution patterns and strong positive Eu anomalies, except for parting YLT6U-2p that is characterized by an H-REY enrichment type and slightly negative Eu anomalies (Fig. 6e). The host rocks in the Yueliangtian coals are characterized by L-


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Fig. 2 Optical photomicrographs and SEM back-scattered images of quartz, anatase, pyrite, chamosite, florencite, and kaolinite in the Yueliangtian coal. a Quartz in sample YLT6L-5, reflected light; b anatase, florencite, and Ti-bearing kaolinite in sample YLT6U-9p; c pyrite in sample YLT6L-1; d pyrite and chamosite in sample YLT6L-4p. Qua quartz, Kao kaolinite, Ana anatase, Py pyrite, Chamo chamosite

and M-REY enrichment type and maximum Eu anomalies, resembling those in low- and high-Ti basalts (Xiao et al. 2004). In addition, Y in host rocks displays slightly negative anomalies (Fig. 6f).

Discussion Sediment-source region The parent rocks in the sediment-source region for the Yueliangtian coals are not only the mafic basalts in the Kangdian Upland but also the felsic-intermediate rocks located in the upper portion of the upland. Owing to their stable geochemical characteristics, REY often serve as provenance indicators both for coal-forming environment and for post-geological process of coal deposit (Seredin and Dai 2012; Dai et al. 2016a; Hower et al. 2016b; Zou et al. 2014; Zhao et al. 2016a, 2017). The mafic basalt input as terrigenous materials of the Yueliangtian coal is indicated by the REY distribution patterns. For example, most of the YLT6L coal benches, partings (YLT6U-9p, YLT6L-3p, YLT6L-4p), and host rocks are characterized by strong

positive Eu anomalies; all the samples in the Yueliangtian coals have no or weak Ce anomalies (Fig. 4). Mafic basalts in the sediment source region (Kangdian Upland) show strong positive Eu anomalies and weak or no Ce anomalies (Dai et al. 2014c, 2016a). The positive Eu anomalies in samples YLT6U-9p and YLT6L-4p suggest that the terrigenous materials in the two partings were largely derived from basaltdominated sediment source region, although as reported by Xie et al. (2016) a small proportion of the inorganic materials were derived from felsic volcanic ash. The similar REY distribution patterns between host rocks and basalts (Fig. 6f) indicate that the host rocks of Yueliangtian coals have similar magma origin to the basalt from the Kangdian Upland. Because of its similar value in sedimentary materials to that of their parent rocks, the Al2O3/TiO2 ratio is a useful provenance indicator for sedimentary rocks (Hayashi et al. 1997), for volcanic ash-associated partings within the coal (Burger et al. 2002), and for coal itself (Hower et al. 2015; Johnston et al. 2015; Dai et al. 2015c). Mafic, intermediate, and felsic igneous rocks have an Al2O3/TiO2 ratio of 3:8, 8:21, and 21:70, respectively (Hayashi et al. 1997). Except for samples YLT6U-r, -9p, YLT6L-1, -3p, -4p, and -f, the Al2O3/TiO2 ratios of the remaining samples in the present study are mostly

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Fig. 3 Concentration coefficients (CC), average for parting samples versus weighted average for coal sample of trace elements in the coals from the Yueliangtian Coalfield. CC the ratio of trace element

concentration in studied coals versus averages for world hard coals. Data of world hard coals are given by Ketris and Yudovich (2009)

higher than 21, suggesting that parent rocks are composed of felsic-intermediate rocks. Similar to the Late Permian coals with felsic or felsic-intermediate rocks input in the Guxu Coalfield (Sichuan, China) (Dai et al. 2016b) and the Mahe Coalfield (Yunnan, China) (Wang et al. 2015), most of the YLT6U coal benches display distinctly negative Eu anomalies (Fig. 6). The low concentrations of Sc, V, Cr, Ni, and Zn in these present samples also support that the sediment-source region is composed of felsic and intermediate rocks.

Hydrothermal solutions Previous studies (Ren et al. 1999; Dai et al. 2005a, b; Xie et al. 2016; Wang et al. 2016; Zhuang et al. 2000; Zhou and Ren 1992) show that hydrothermal overprinting plays an important role on the trace-element and mineral anomalies in the Late Permian coals in Guizhou, SW China, as well as coals from other areas (e.g., Seredin and Finkelman 2008; Seredin et al. 2013; Eskenazy et al. 2013; Wang et al. 2011, 2012).


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Fig. 4 Vertical variations of selected ratios of trace-element pairs, B, Ge, and ash yield (Aad) in the YLT6U and YLT6L coals. a YLT6U coal, b YLT6L coal

Hydrothermal activities also have impacts on the geochemical and mineralogical compositions of the Yueliangtian coals, partings, and host rocks. The Nb/Ta, U/Th, Yb/La, and Zr/Hf ratios are higher in the coal benches relative to the overlying partings in the coal (Fig. 4) because relative to the second elements in the above element pairs, the first elements (Nb, U, Yb, and Zr) are easily leached from the overlying partings and then deposited in the coal benches. Such re-distribution led to higher element ratios in most of the Yueliangtian coal benches than those of world

hard coals (Nb/Ta = 7.86, U/Th = 0.31, Yb/La = 0.09, and Zr/ Hf = 38) (Ketris and Yudovich 2009). The re-distribution of HFSEs (high field strength element) in the YLT6L coal (Fig. 4b) is weaker than that in the YLT6U coal (Fig. 4a), suggesting a lesser circulated hydrothermal fluid influence of this kind in the YLT6L coal than the YLT6U coal. Similar geochemical distributions, particularly for rare earth elements in the coal benches and their overlying partings, have been observed in other coals (e.g., Crowley et al. 1989; Dai et al. 2006, 2013; Hower et al. 1999).

Fig. 5 Relation of B to ash yield (a), B to K2O (b), and B to MgO (c) in the coals from the Yueliangtian Coalfield

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Fig. 6 REY distribution patterns in the coal benches, partings, and host rocks of the Yueliangtian Coalfield. REY are normalized to the Upper Continental Crust (UCC) (Taylor and McLennan 1985). LT low-Ti basalt, HT high-Ti basalt; basalt data are given by Xiao et al. (2004)

Samples in the upper portion of the YLT6U coal (from sample YLT6U-r to YLT6U-4u) have REY distribution patterns characterized by L-REY-type enrichment (Fig. 6), probably due to the LREE leached from the roof by circulated hydrothermal fluids. The florencite was considered as a mineral of hydrothermal solution origin (Dai et al. 2016b). Secondary florencite (Fig. 2b) was also observed in the sample YLT6U-9p. Sample YLT6U-9p is characterized by MREY enrichment pattern (Fig. 6e); Ti substitutes Al within the lattice of kaolinite as observed in sample YLT6U-9p (Fig. 2b), which may be caused by acid circulated hydrothermal solutions, such as the high pCO2 waters within coal basins (Dai et al. 2016b; Shand et al. 2005). Aluminum substituted by Ti is not uncommon in coal and coal partings (e.g., Ward 2002, 2016; Ward et al. 1999) as well as in other non-coal related rocks (e.g., Shoval et al. 2008; Dolcater et al. 1970). The Yueliangtian Coalfield is located near the Carlin-type Au deposits in SW Guizhou (Dai et al. 2015b; Tan et al. 2015), and thus the Hg, As, Se, Cd, and Tl with concentrations 2–20 times higher than world hard coals (Fig. 3b) in the YLT6L coal are suspected to be caused by circulated syngenetic hydrothermal solutions during peat accumulation. Seawater influence The total sulfur contents of the YLT6U coals (0.48% on average) are much lower than those of the YLT6L coals (7.94% on average). Neither pyrite nor other sulfide minerals were observed in the YLT6U coal except for samples YLT6U-8 and YLT6U-9p (data of total sulfur and pyrite from Xie et al. 2016). The correlation coefficients between total sulfur and Fe2O3 for YLT6L coal is 0.91, suggesting that sulfur in the YLT6L coal mainly occurs in sulfide, consistent with the high

syngenetic pyrite (Fig. 2c) contents observed by optical microscope and XRD (Xie et al. 2016). The relevant data suggest that the YLT6L coal rather than the YLT6U coal was subjected to seawater during peat accumulation and early stage of diagenetic process.

Conclusions Three factors including the sediment-source region (the Kangdian Upland), the activity of circulated hydrothermal solutions, and seawater had significantly influenced the geochemical compositions of the Yueliangtian coal. The parent rocks in the sediment-source region (the Kangdian Upland) for the Yueliangtian coal are both mafic basalts and, to a lesser extent, felsic-intermediate rocks. The parent rocks with mafic basalt compositions can be indicated by the similar REY distribution patterns between the host rocks and the low- and high-Ti basalts; the strong positive Eu anomalies in host rocks, partings (YLT6U-9p, YLT6L3p, YLT6L-4p), and most of the YLT6L coal benches; and weak or no Ce anomalies in all the samples of the Yueliangtian coal. The sediment-source region composed of felsic or felsicintermediate rock compositions is indicated by the Al2O3/ TiO2 ratios higher than 21 in most of the present samples, the distinctly negative Eu anomalies in most of the YLT6U coal benches, and the depletion of transition elements. The Yueliangtian coal is also significantly influenced by circulated hydrothermal solutions: the Nb/Ta, U/Th, Yb/La, and Zr/Hf ratios are higher in the coal benches relative to the overlying partings; sample YLT6U-9p is characterized by MREY enrichment pattern, and Ti substitutes Al within the lattice of kaolinite in it; some epithermal-associated elements in


the YLT6L coal, such as Hg, Se, As, Tl, and Cd, show high contents. Acknowledgements This research was supported by the National Key Basic Research Program of China (no. 2014CB238902), the 111 Project (no. B17042), and the Program for Innovative Research Team in University (IRT13099). The authors wish to thank two anonymous reviewers for their detailed suggestions, which greatly improved the quality of the paper.

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